JP7777508B2 - Engine EGR system - Google Patents

Description

The technology disclosed in this specification relates to an EGR system that is installed in an engine and has an EGR valve with a poppet valve structure in which the valve body moves perpendicularly from the seat portion of the valve seat.

An example of this type of technology is the "EGR valve" described in Patent Document 1 below. This EGR valve comprises a housing having a flow passage, a valve seat provided in the flow passage, a valve element capable of seating on the valve seat, a valve stem provided with the valve element, the valve stem having one end and the other end, the valve element fixed to one end and a male thread provided to the other end, a step motor for reciprocating the valve stem in its axial direction, the step motor including a rotor having a female thread that is threaded onto the male thread, the flow passage being divided into a near side and a far side of the rotor by the valve seat, and the valve element being positioned in the near side of the flow passage so that it can seat on the valve seat, disclosing the structure of a so-called inward-opening two-way poppet valve. In this EGR valve, the male screw has a male thread that continues helically in the axial direction of the valve stem and includes a first male thread surface facing the valve seat and a second male thread surface located opposite the first male thread surface, and the female screw has a female thread that continues helically in the axial direction of the valve stem and includes a first female thread surface facing the valve seat and a second female thread surface located opposite the first female thread surface. A predetermined backlash is provided between the male and female threads in the axial direction of the valve stem, and a valve element spring is provided to urge the valve element together with the valve stem in a direction away from the valve seat, i.e., in the direction to open the valve.

JP 2022-3237 A

In the EGR valve described in Patent Document 1, when fully closed, a full-close abutment control is performed in which a step motor strokes the valve stem against the biasing force of the valve spring to abut the valve disc against the valve seat. In this case, there is a risk of the step motor losing synchronization. If the step motor loses synchronization, the valve disc may open slightly away from the valve seat, even when fully closed and abutted, which could result in EGR gas leakage.

This disclosed technology was developed in light of the above circumstances, and its purpose is to provide an engine EGR system that suppresses step-out of the step motor caused by the repulsive force of the abutment during full-close abutment control of the EGR valve, thereby making it possible to suppress minute opening of the valve body.

In order to achieve the above object, the technology described in claim 1 is an engine EGR system configured to control an EGR valve provided in an EGR passage of the engine by a control means in accordance with an operating state of the engine, the EGR valve comprising: a housing having a flow path; a valve seat provided in the flow path; a valve element provided so as to be able to seat on the valve seat; a valve stem provided with the valve element; the valve stem having one end and the other end, the valve element being fixed to the one end and a driven screw being provided to the other end; a step motor for reciprocating the valve stem in its axial direction; the flow path is divided into a side closer to the rotor and a side farther from the rotor by the valve seat, and the valve element is arranged in the flow path on the near side so as to be able to seat on the valve seat; the driven thread has a driven thread continuing helically in the axial direction of the valve stem, the driven thread including a first driven thread surface facing towards the valve seat and a second driven thread surface located on the opposite side of the first driven thread surface; the drive screw has a drive thread continuing helically in the axial direction of the valve stem, the drive thread having a first drive thread surface facing towards the valve seat and a second driven thread surface located on the opposite side of the first drive thread surface a valve element spring for urging the valve element together with the valve stem in a direction away from the valve seat, and wherein, when the valve element is fully closed, the control means performs a full-closed contact control in which the valve element is brought into contact with the valve seat by stroking the valve stem with the step motor against the urging force of the valve element spring; and The purpose of this invention is to move the step motor to close the valve to a position close to the fully closed position where the valve disc abuts against the valve seat, and then drive the step motor at a drive frequency lower than the normal drive frequency to close the valve disc and abut the valve disc against the valve seat, the valve seat having a seat portion that can abut against the valve disc, and at least one of the valve seat and the valve disc is provided with a sealing member that seals the gap between the valve disc and the valve seat in an area other than where the valve disc abuts the seat portion when the valve disc is fully closed, and after performing the fully closed abutment control, the control means performs a small opening valve opening control that drives the step motor so that the valve disc opens at a small opening .

According to the configuration of the above technology, when executing the fully closed butting control, the control means drives the step motor at a normal drive frequency to close the valve to a position close to the fully closed position where the valve disc abuts against the valve seat, and then drives the step motor at a drive frequency lower than the normal drive frequency to close the valve disc and abut the valve disc against the valve seat. Therefore, when the valve disc abuts against the valve seat, the step motor is driven at a low drive frequency, which causes the valve disc to abut against the valve seat more gently than when driven at a normal drive frequency, thereby weakening the repulsive force the valve receives from the valve disc spring during the abutment. Furthermore, even if the step motor loses synchronization during the fully closed butting control, causing the valve disc to be positioned in a region other than the seat portion, creating a gap between the valve disc and the valve seat, the gap is sealed by the seal member. Furthermore, after executing the fully closed butting control, the valve disc is reliably opened at a small opening by the small opening valve control, ensuring a gap between the valve disc and the valve seat.

In order to achieve the above object, the technology described in claim 2 is an engine EGR system configured to control an EGR valve provided in an EGR passage of the engine by a control means in accordance with the operating state of the engine, the EGR valve comprising: a housing having a flow path; a valve seat provided in the flow path; a valve element provided so as to be able to seat on the valve seat; a valve stem provided with the valve element; the valve stem having one end and the other end, the valve element being fixed to the one end and a driven screw being provided to the other end; a step motor for reciprocating the valve stem in its axial direction; the flow path is divided into a side closer to the rotor and a side farther from the rotor by the valve seat, and the valve element is arranged in the flow path on the near side so as to be able to seat on the valve seat; the driven thread has a driven thread continuing helically in the axial direction of the valve stem, the driven thread including a first driven thread surface facing towards the valve seat and a second driven thread surface located opposite to the first driven thread surface; the drive screw has a drive thread continuing helically in the axial direction of the valve stem, the drive thread having a first drive thread surface facing towards the valve seat and a second driven thread surface located opposite to the first drive thread surface In an EGR system for an engine configured to include a second drive screw thread surface located on the opposite side, a predetermined backlash being provided between the driven screw and the drive screw in the axial direction of the valve stem, and a valve element spring for urging the valve element together with the valve stem in a direction away from the valve seat, the control means performing a full-closed abutment control in which, when the valve element is fully closed, the valve stem is caused to stroke by a step motor against the urging force of the valve element spring to abut the valve element against the valve seat, the control means, when performing the full-closed abutment control, drives the step motor at a normal drive frequency. The valve is driven at a frequency of 1/2 wave number to close the valve until it is fully closed and the valve disc abuts against the valve seat , and then the fully closed abutment control is continued at a drive frequency lower than the normal drive frequency to abut the valve disc against the valve seat, the valve seat has a seat portion that can abut against the valve disc, and at least one of the valve seat and the valve disc is provided with a sealing member that seals the gap between the valve disc and the valve seat in an area other than where the valve disc abuts the seat portion when the valve disc is fully closed, and the control means, after executing the fully closed abutment control, executes a small opening valve opening control that drives the step motor so that the valve disc opens at a small opening .

According to the configuration of the above technology, when executing the fully closed butting control, the control means drives the step motor at a normal drive frequency to close the valve until the valve disc abuts against the valve seat, and then continues the fully closed butting control at a drive frequency lower than the normal drive frequency to abut the valve disc against the valve seat. Therefore, during the fully closed butting control, the step motor is driven at the normal drive frequency to close the EGR valve, and when the valve disc abuts against the valve seat, the valve disc is subjected to the repulsive force of the valve disc spring, causing it to step out. However, when the step motor is subsequently driven again at the low drive frequency to close the EGR valve and the valve disc abuts against the valve seat again, the repulsive force of the valve disc spring at the time of the abutment weakens. Furthermore, even if the step motor steps out of step during the fully closed butting control, causing the valve disc to be positioned in a region other than the seat portion, creating a gap between the valve disc and the valve seat, the gap is sealed by a seal member. Furthermore, after executing the fully closed butting control, the valve disc is reliably opened by a small opening degree using the small opening degree valve opening control, ensuring a gap between the valve disc and the valve seat.

In order to achieve the above object, the technology described in claim 3 is the technology described in claim 1 or 2, in which the valve body is configured to open to a predetermined degree by the biasing force of the valve body spring when the step motor is not driven.

With the configuration of the above technology, in addition to the effects of the technology described in claims 1 and 2, when the step motor is not driven, the valve disc opens to a predetermined degree due to the biasing force of the valve disc spring, so water does not remain between the valve disc and the valve seat even when the engine is stopped in a low-temperature environment.

In order to achieve the above object, the technology described in claim 4 is the technology described in claim 3 , in which the control means executes full-closed butting control after a request to start the engine is received, and then starts the engine.

According to the configuration of the above technology, in addition to the function of the technology of claim 3 , after a request to start the engine is made, the control means executes the fully closed butting control and then starts the engine. Therefore, when the engine is started, the valve body is in a fully closed state without a slight valve opening.

In order to achieve the above object, the technology described in claim 5 is the technology described in claim 3 , in which the control means executes full-closed butting control for a predetermined time after a request to stop the engine is made.

According to the configuration of the above technology, in addition to the effect of the technology described in claim 3 , the control means executes the fully closed butting control for a predetermined time after a request to stop the engine is made. Therefore, even after a request to stop the engine is made and the engine has stopped, the fully closed butting control is executed for the predetermined time, so that the EGR valve is kept in a fully closed state during that time, and the EGR gas remaining in the EGR passage is diffused over time and its concentration decreases.

In order to achieve the above object, the technology described in claim 6 is the technology described in claim 1 or 2, in which the control means executes full-closed butting control for a predetermined time after a request to stop the engine is received, and then opens the valve body to a predetermined opening degree.

With the configuration of the above technology, in addition to the effects of the technology described in claim 1 or 2, the control means executes full-closed abutment control for a predetermined period of time after a request to stop the engine is received, and then opens the valve disc to a predetermined degree. Therefore, even if the engine stops in a low-temperature environment, water will not remain between the valve disc and the valve seat.

In order to achieve the above object, the technology described in claim 7 is the technology described in claim 1 or claim 2 , wherein the control means is configured to execute small opening valve control, which drives the step motor so that the valve body opens at a small opening, and the control means is intended to execute one of the fully closed butting control and the small opening valve control before executing the other when the valve body is in a closed state when the engine is stopped and the EGR valve is driven in a predetermined low temperature environment.

According to the configuration of the above technology, in addition to the function of the technology of claim 1 or 2 , when the valve disc is in the closed state when the engine is stopped and the EGR valve is driven in a predetermined low-temperature environment, the control means first executes one of the fully closed butting control and the small opening valve control and then executes the other. Therefore, when the engine is started in a low-temperature environment, the valve disc is opened and closed relative to the valve seat.

According to the technology described in claim 1, the amount of step-out of the step motor due to the repulsive force of the abutment during full-close abutment control of the EGR valve can be suppressed, and minute valve opening of the valve body can be suppressed. As a result, leakage of EGR gas between the valve body and the valve seat can be suppressed. Furthermore, even if the valve body opens minutely due to step-out of the step motor, leakage of EGR gas between the valve body and the valve seat can be prevented. Furthermore, even if the EGR valve vibrates due to the influence of engine vibration, etc., vibration wear between the valve body and the valve seat can be suppressed.

According to the technology described in claim 2, the amount of step-out of the step motor due to the repulsive force of the abutment during full-close abutment control of the EGR valve can be suppressed, and minute valve opening of the valve body can be suppressed. As a result, leakage of EGR gas from between the valve body and the valve seat can be suppressed. Furthermore, even if the valve body opens minutely due to step-out of the step motor, leakage of EGR gas between the valve body and the valve seat can be prevented. Furthermore, even if the EGR valve vibrates due to the influence of engine vibration, etc., vibration wear between the valve body and the valve seat can be suppressed.

According to the technology described in claim 3 , in addition to the effect of the technology described in claim 1 or 2, it is possible to prevent the valve body and the valve seat from freezing and becoming stuck when the engine is stopped.

According to the technology described in claim 4 , in addition to the effect of the technology described in claim 3 , it is possible to prevent EGR gas from leaking from the EGR passage to the intake passage at the same time as the engine starts, thereby preventing engine misfires and stalls.

According to the technology described in claim 5 , in addition to the effect of the technology described in claim 3 , even if the EGR valve opens after the engine is stopped and EGR gas enters the intake passage from the EGR passage, the entering EGR gas is at a low concentration, so it is possible to prevent the engine from restarting poorly.

According to the technology of claim 6 , in addition to the effect of the technology of claim 1 or 2, it is possible to prevent the valve body and the valve seat from freezing and becoming stuck when the engine is stopped.

According to the technology described in claim 7 , in addition to the effects of the technology described in claim 1 or claim 2 , even if the valve body or valve seat and the sealing member are frozen together when starting the engine in a low-temperature environment, the frozen adhesion can be released, and the opening of the valve body can be guaranteed.

1 is a schematic configuration diagram showing an engine system according to a first embodiment; FIG. 3 is a cross-sectional view showing a fully closed butting state of the EGR valve in the first embodiment. FIG. 4 is a cross-sectional view illustrating a state in which the step motor is out of step when the EGR valve is fully closed in the first embodiment. FIG. 3 is a cross-sectional view showing a fully open state of the EGR valve in the first embodiment. FIG. 4 is an enlarged cross-sectional view showing a part of the step motor in a fully closed butted state for the EGR valve in the first embodiment. FIG. 6 is an enlarged cross-sectional view showing a part of the state in which the male thread and the female thread in FIG. 5 are screwed together in the first embodiment. FIG. 3 is an enlarged cross-sectional view showing a part of the step motor in a fully open state of the EGR valve in the first embodiment. FIG. 8 is an enlarged cross-sectional view showing a part of the state in which the male thread and the female thread in FIG. 7 are screwed together in the first embodiment. 4 is a flowchart showing the contents of a first EGR valve control according to the first embodiment. 4 is a flowchart showing the contents of a first EGR valve control according to the first embodiment. 10 is a flowchart showing the contents of second EGR valve control according to the second embodiment. 10 is a flowchart showing the contents of second EGR valve control according to the second embodiment. 10 is a flowchart showing the content of a third EGR valve control according to the third embodiment. 10 is a flowchart showing the contents of a fourth EGR valve control according to the fourth embodiment. 10 is a flowchart showing the content of a fifth EGR valve control according to the fifth embodiment. 13 is a flowchart showing the content of a sixth EGR valve control according to the sixth embodiment. 13 is a flowchart showing the contents of engine start control according to the seventh embodiment. FIG. 13 is a cross-sectional view showing a fully closed butting state of the EGR valve according to the eighth embodiment. FIG. 13 is a cross-sectional view illustrating a state in which the step motor is out of step when the EGR valve is fully closed in the eighth embodiment. FIG. 13 is a cross-sectional view showing a fully open state of the EGR valve according to the eighth embodiment.

Below, we will explain several embodiments in which an engine EGR system is implemented in a gasoline engine system.

First Embodiment
First, the first embodiment will be described in detail with reference to the drawings.

[About the engine system]
FIG. 1 is a schematic diagram showing a gasoline engine system (hereinafter simply referred to as the "engine system") according to this embodiment. The engine system mounted on an automobile includes an engine 1 having multiple cylinders. The engine 1 is a four-cylinder, four-stroke reciprocating engine, and includes well-known components such as pistons and a crankshaft. The engine 1 is provided with an intake passage 2 for introducing intake air into each cylinder, and an exhaust passage 3 for discharging exhaust gas from each cylinder of the engine 1. An air cleaner 9, a throttle device 4, and an intake manifold 5 are provided in the intake passage 2, from its upstream side.

The throttle device 4 is located in the intake passage 2 upstream of the intake manifold 5 and adjusts the amount of intake air flowing through the intake passage 2 by opening and closing a butterfly-type throttle valve 4a to a variable degree in response to the driver's accelerator pedal operation. The intake manifold 5 is primarily made of resin and is located in the intake passage 2 immediately upstream of the engine 1. It includes a surge tank 5a into which intake air is introduced, and multiple (four) branch pipes 5b branching off from the surge tank 5a to distribute the intake air introduced into the surge tank 5a to each cylinder of the engine 1. The exhaust passage 3 is provided with an exhaust manifold 6 and a catalyst 7, arranged in this order from upstream to downstream. The catalyst 7 may contain, for example, a three-way catalyst to purify the exhaust gas.

Engine 1 is provided with a fuel injection device (not shown) for injecting fuel into each cylinder. The fuel injection device is configured to inject fuel supplied from a fuel supply device (not shown) into each cylinder of engine 1. In each cylinder, a combustible mixture is formed by the fuel injected from the fuel injection device and the intake air introduced through the intake manifold 5.

Engine 1 is provided with an ignition device (not shown) corresponding to each cylinder. The ignition device is configured to ignite a combustible mixture in each cylinder. The combustible mixture in each cylinder explodes and burns when ignited by the ignition device, and the exhaust gas after combustion is discharged from each cylinder to the outside via exhaust manifold 6 and catalyst 7. At this time, pistons (not shown) in each cylinder move up and down, causing the crankshaft (not shown) to rotate, generating power for engine 1.

[About the EGR system]
The EGR system of this embodiment includes an exhaust gas recirculation device (EGR device) 11 of a high-pressure loop type and an electronic control unit (ECU) 80 (described later). The EGR device 11 includes an exhaust gas recirculation passage (EGR passage) 12 for causing a portion of the exhaust gas discharged from each cylinder of the engine 1 into the exhaust passage 3 to flow as exhaust gas recirculation gas (EGR gas) into the intake passage 2, an exhaust gas recirculation cooler (EGR cooler) 13 for cooling the EGR gas flowing through the EGR passage 12, an exhaust gas recirculation valve (EGR valve) 14 provided downstream of the EGR cooler 13 for adjusting the flow rate of the EGR gas flowing through the EGR passage 12, and a resin exhaust gas recirculation gas distributor (EGR gas distributor) 15 for distributing the EGR gas flowing through the EGR passage 12 to each branch pipe 5b of the intake manifold 5 in order to distribute the EGR gas flowing through the EGR passage 12 to each cylinder of the engine 1. The EGR gas distributor 15 is provided in the EGR passage 12 downstream of the EGR cooler 13 and the EGR valve 14. The EGR passage 12 includes an inlet 12a and an outlet 12b. The inlet 12a of the EGR passage 12 is connected to the exhaust passage 3 downstream of the catalyst 7, and the outlet 12b of the EGR passage 12 is connected to the EGR gas distributor 15. In this embodiment, the EGR gas distributor 15 constitutes the final stage of the EGR passage 12. In the EGR passage 12, the EGR valve 14 is provided adjacent to the EGR cooler 13 downstream of the EGR cooler 13. As will be described in detail later, the EGR valve 14 is configured to drive a valve body 25 using a step motor 27 as a drive source. Engine cooling water is configured to flow through the EGR cooler 13. The EGR cooler 13 is configured to perform heat exchange between the EGR gas and the cooling water of the engine 1 in order to cool the EGR gas flowing through the EGR passage 12. Here, a detailed description of the configuration of the EGR cooler 13 will be omitted.

In this EGR device 11, when the EGR valve 14 opens, a portion of the exhaust gas flowing through the exhaust passage 3 flows through the EGR passage 12 as EGR gas, and is distributed to each branch pipe 5b of the intake manifold 5 via the EGR cooler 13, EGR valve 14, and EGR gas distributor 15, and is further distributed and recirculated to each cylinder of the engine 1.

In this embodiment, the EGR cooler 13 is provided with a bypass passage 16. The bypass passage 16 is a passage in the EGR passage 12 that allows a portion of the EGR gas flowing to the EGR cooler 13 to detour. The bypass passage 16 is provided with a bypass valve 17 for opening and closing the passage 16.

The EGR gas distributor 15 is primarily made of resin and has an elongated shape overall. As shown in FIG. 1, it is positioned so that its longitudinal direction (left-right direction in FIG. 1) crosses multiple branch pipes 5b of the intake manifold 5. In this embodiment, the EGR gas distributor 15 includes one gas chamber 15a where EGR gas introduced from the outlet 12b of the EGR passage 12 collects, and multiple (four) gas distribution passages 15b that branch off from the gas chamber 15a and distribute the EGR gas from the gas chamber 15a to each branch pipe 5b.

[Electrical configuration of the engine system]
Next, an example of the electrical configuration of an engine system will be described. In FIG. 1 , various sensors 69 to 78 provided in this engine system constitute an operating condition detection means for detecting the operating conditions of the automobile and engine 1. A vehicle speed sensor 69 provided in the automobile detects the automobile's speed SPD and outputs an electrical signal corresponding to the detected value. An ignition switch (IG switch) 70 provided in the driver's seat is turned on and off by the driver to start or stop the engine 1 and outputs an electrical signal corresponding to the operation. A water temperature sensor 71 provided in the engine 1 detects the temperature (coolant temperature) THW of the coolant flowing inside the engine 1 and outputs an electrical signal corresponding to the detected value. A rotation speed sensor 72 provided in the engine 1 detects the rotation angle (crank angle) of the crankshaft of the engine 1 and detects changes in the crank angle (crank angular velocity) as the rotation speed (engine speed) NE of the engine 1 and outputs an electrical signal corresponding to the detected value. An air flow meter 73 provided near the air cleaner 9 detects the amount of intake air Ga flowing through the air cleaner 9 and outputs an electrical signal corresponding to the detected value. An intake pressure sensor 74 provided in the surge tank 5a detects the intake pressure PM in the intake passage 2 (surge tank 5a) downstream of the throttle device 4 and outputs an electrical signal corresponding to the detected value. A throttle sensor 75 provided in the throttle device 4 detects the opening degree (throttle opening degree) TA of the throttle valve 4a and outputs an electrical signal corresponding to the detected value. An oxygen sensor 76 provided in the exhaust passage 3 upstream of the catalyst 7 detects the oxygen concentration Ox in the exhaust and outputs an electrical signal corresponding to the detected value. An intake air temperature sensor 77 provided at the inlet of the air cleaner 9 detects the temperature (intake air temperature) THA of the outside air taken into the air cleaner 9 and outputs an electrical signal corresponding to the detected value. An accelerator sensor 78 provided on the accelerator pedal 10 at the driver's seat detects the amount of depression of the accelerator pedal 10 by the driver as an accelerator opening ACC, and outputs an electric signal corresponding to the detected value.

This engine system also includes an electronic control unit (ECU) 80 that controls the system. Various sensors 69-78 are connected to the ECU 80. In addition to the EGR valve 14, an injector (not shown) and an ignition coil (not shown) are also connected to the ECU 80. The ECU 80 is an example of a "control means" in the disclosed technology. As is well known, the ECU 80 includes a central processing unit (CPU), various memories, external input circuits, and external output circuits. The memory stores predetermined control programs related to various controls. The CPU executes fuel injection control, ignition timing control, EGR control, and other controls based on predetermined control programs, in response to detection signals from the various sensors 69-78 input via the input circuits.

In this embodiment, the ECU 80 controls the EGR valve 14 (and its step motor 27) in EGR control according to the operating state of the engine 1. Specifically, the ECU 80 controls the EGR valve 14 to be fully closed when the engine 1 is stopped, idling, or decelerating. During other operating conditions, the ECU 80 calculates a target EGR opening according to the operating state and controls the EGR valve 14 to the target EGR opening. When the EGR valve 14 is opened, exhaust gas is discharged from the engine 1 into the exhaust passage 3. A portion of the exhaust gas flows as EGR gas through the EGR passage 12, EGR cooler 13, EGR valve 14, EGR gas distributor 15, etc. into the intake passage 2 (intake manifold 5), where it is distributed and recirculated to each cylinder of the engine 1. In this embodiment, when the engine 1 is started, the ECU 80 opens the EGR valve 14 and starts EGR when the coolant temperature THW detected by the water temperature sensor 71 reaches 40°C or higher and the EGR operation conditions are met.

[Configuration of EGR valve]
FIG. 2 is a cross-sectional view of the EGR valve 14 of this embodiment, showing a fully closed state in which the valve element 25 is abutted against the valve seat 24 to fully close the valve. FIG. 3 is a cross-sectional view of the EGR valve 14, showing a state in which the step motor 27 loses step when the valve is fully closed. FIG. 4 is a cross-sectional view of the EGR valve 14, showing a fully open state. As shown in FIGS. 2 to 4 , the EGR valve 14 of this embodiment includes a housing 23 having a flow passage 22, a valve seat 24 provided in the flow passage 22, a valve element 25 provided so as to be able to seat on the valve seat 24, a valve stem 26 provided with the valve element 25, and a step motor 27 for reciprocating (stroking) the valve stem 26 in its axial direction. The valve seat 24 has a seat portion 24a that can abut against the valve element 25. The EGR valve 14 of this embodiment is configured as a two-way valve having a poppet valve structure in which one valve element 25 moves perpendicularly from a seat portion 24 a of a valve seat 24 .

The valve shaft 26 is disposed vertically through the housing 23. The valve shaft 26 includes one end 26a (the lower end in Figures 2 to 4) and the other end 26b (the upper end in Figures 2 to 4). The valve element 25 is fixed to the one end 26a, and the other end 26b is provided with a male thread 30. A flange-shaped spring retainer 31 is provided on the valve shaft 26 below and adjacent to the male thread 30. Below the spring retainer 31 on the valve shaft 26, a two-flat portion 26c having a generally oval cross section is provided. In this embodiment, the male thread 30 corresponds to an example of a "driven screw" in the disclosed technology.

The flow path 22 includes an inlet 32 and an outlet 33. The flow path 22 is divided by the valve seat 24 into a first flow path section 22A closer to the step motor 27 and a second flow path section 22B farther from the step motor 27. A valve element 25 is positioned in the first flow path section 22A so that it can be seated on the valve seat 24. The valve seat 24 has a valve hole 24b that constitutes the flow path 22.

The valve disc 25 is disc-shaped and has a flat sealing surface 25a on its periphery, which is capable of seating against the flat seat portion 24a of the valve seat 24. In this embodiment, as shown in Figures 2 to 4, the seat portion 24a of the valve seat 24 is circular and conforms to the valve hole 24b. A rubber sheet 28 is provided on the outer side of the seat portion 24a, protruding above the seat portion 24a and capable of contacting the sealing surface 25a of the valve disc 25. The rubber sheet 28 is annular and fits into a circumferential groove 24c formed in the seat portion 24a. This rubber sheet 28 corresponds to an example of a sealing member of the disclosed technology. The rubber sheet 28 provided on the valve seat 24 is configured to seal the gap between the valve disc 25 and the valve seat 24 when the valve disc 25 is fully closed, except in the area where the valve disc 25 contacts the seat portion 24a.

In the fully closed butted state shown in Figure 2, the sealing surface 25a of the valve element 25 abuts against the seat portion 24a of the valve seat 24, and the upper end of the rubber sheet 28 is pressed against the sealing surface 25a, fully closing the valve element 25. It is desirable that the elastic force of the rubber sheet 28 in this fully closed butted state be as small as possible. In the out-of-step state shown in Figure 3, the valve element 25 moves slightly upward from the seat portion 24a of the valve seat 24, and the sealing surface 25a is separated from the seat portion 24a. However, the upper end of the rubber sheet 28 contacts the sealing surface 25a, creating a seal between the valve element 25 and the valve seat 24. The rubber sheet 28 is required to have sufficient elasticity to follow the movement of the valve element 25 during this out-of-step state. Meanwhile, in the fully open state shown in Figure 4, the valve element 25 is separated from the valve seat 24 to the maximum extent, resulting in a maximum opening.

Two thrust bearings 39, 40 are provided in the housing 23 to support the valve shaft 26 so that it can perform stroke movement in the axial direction. The inner periphery of the thrust bearing 39 has a generally oval cross section and forms a rotation restricting portion 39a that can engage with the two-sided width portion 26c of the valve shaft 26. Engagement of the two-sided width portion 26c with the rotation restricting portion 39a guides the stroke movement of the valve shaft 26 and restricts its rotation.

The step motor 27 includes a stator 42 with two coils 41, one above the other, and a magnet rotor 43 mounted inside the stator 42. These components 41 to 43 are molded and covered in a resin casing 44. A connector 45 protruding laterally is formed on the casing 44. The connector 45 is provided with terminals 46 extending from the coils 41.

The magnet rotor 43 includes a rotor body 47 and a cylindrical magnet 48 integrally provided on the outside of the rotor body 47. A first radial bearing 49 is provided on the outer periphery of the upper end of the rotor body 47, between it and the casing 44. A second radial bearing 50 is provided on the inner periphery of the lower end of the magnet 48, between it and the thrust bearing 39. These first and second radial bearings 49, 50 rotatably support the magnet rotor 43 inside the stator 42. A female thread 51 is provided in the center of the rotor body 47, which is threaded onto the male thread 30 of the valve shaft 26. In this embodiment, the female thread 51 corresponds to an example of a "drive gear" in this disclosed technology.

Figure 5 shows an enlarged cross-sectional view of a portion of the step motor 27 for the EGR valve 14 in a fully closed butted state. Figure 6 shows an enlarged cross-sectional view of a portion of the engagement between the male thread 30 and female thread 51 in Figure 5. Figure 7 shows an enlarged cross-sectional view of a portion of the step motor 27 for the EGR valve 14 in a fully open state. Figure 8 shows an enlarged cross-sectional view of a portion of the engagement between the male thread 30 and female thread 51 in Figure 7. As shown in Figures 5 to 8, the male thread 30 has a male thread 30a that continues helically in the axial direction of the valve stem 26. This male thread 30a includes a first male thread surface 30aa that faces toward the valve seat 24 (downward) and a second male thread surface 30ab located on the opposite side (upper side) of the first male thread surface 30aa. The female thread 51 also has a female thread 51a that continues helically in the axial direction of the valve stem 26. The female thread 51a includes a first female thread surface 51aa facing downward toward the valve seat 24, and a second female thread surface 51ab located on the opposite side (upper side) of the first female thread surface 51aa. As shown in Figures 6 and 8, a predetermined backlash 55 (play) is provided between the male thread 30 and the female thread 51 in the axial direction of the valve shaft 26.

A valve element spring 52 is provided between the spring retainer 31 of the valve shaft 26 and the lower second radial bearing 50, i.e., between the spring retainer 31 and the housing 23, to urge the valve element 25 together with the valve shaft 26 in a direction away from the valve seat 24 (upward in Figures 2 to 8). Furthermore, a rotor spring 53 is provided between the magnet rotor 43 (magnet 48) and the second radial bearing 50 to urge the magnet rotor 43 in a direction away from the valve seat 24.

A generally cylindrical lip seal 57 is provided adjacent to the thrust bearing 40 between the housing 23 and the valve shaft 26 to seal the gap between the housing 23 and the valve shaft 26. A generally cylindrical deposit guard plug 58 is also provided adjacent to the lip seal 57 to protect the gap between the housing 23 and the valve shaft 26 from deposits.

In this embodiment, the EGR valve 14 configured as described above executes full-close control, in which the step motor 27 strokes the valve stem 26 against the biasing force of the valve spring 52 to cause the valve element 25 to abut against the valve seat 24 when the valve is fully closed. However, in this EGR valve 14, depending on tolerance variations in the rubber seat 28, if the repulsive force of the seat 28 (the elastic force acting in a direction to open the valve element 25) becomes strong, the step motor 27 may step out when full-close control is executed. In this case, the valve element 25 is subjected to the sum of the biasing force of the valve spring 52 and the repulsive force of the rubber seat 28, and there is a concern that the number of steps out of step of the step motor 27 may reach a maximum of four or more. If the number of steps out of step exceeds four, the valve element 25 may separate from the rubber seat 28, potentially resulting in EGR gas leakage between the valve seat 24 and the valve element 25. Therefore, in this embodiment, in order to keep the maximum number of out-of-step steps to less than "4 steps" when full-closed butting control is being executed, the following "first EGR valve control" is executed.

[Regarding the first EGR valve control]
9 and 10 are flowcharts showing the contents of the "first EGR valve control." When the process proceeds to the routine of this flowchart, the ECU 80 determines in step 100 whether the ignition (IG) is on, i.e., whether the IG switch 70 has been turned on. If the result of this determination is positive, the ECU 80 proceeds to step 110 because the ECU 80 has started and the engine 1 has started. If the result of this determination is negative, the ECU 80 has not started and the engine 1 has not started, so the process proceeds to step 270.

In step 110, the ECU 80 determines whether the initial setting completion flag XISC, which indicates that the initial setting of this control has been completed, is "1." If the result of this determination is positive, the ECU 80 determines that the initial setting has been completed and proceeds to step 120. If the result of this determination is negative, the ECU 80 determines that the initial setting has not been completed and proceeds to step 190.

In step 120, the ECU 80 determines whether there is a request to fully close the EGR valve 14, i.e., whether the engine 1 should cut off EGR. The ECU 80 makes this determination based on the operating state of the engine 1 obtained from detection signals from various sensors 71-78. If the result of this determination is positive, the ECU 80 proceeds to step 130; if the result of this determination is negative, the ECU 80 proceeds to step 230.

In step 130, the ECU 80 determines whether the full-close control completion flag XCL, which indicates that the EGR valve 14 has reached the full-close state at a lower-than-normal drive frequency (e.g., 125 pps), is "0." If the result of this determination is positive, the ECU 80 determines that the full-close control is not yet complete and proceeds to step 140. If the result of this determination is negative, the ECU 80 determines that the full-close control is in progress and proceeds to step 180.

In step 140, the ECU 80 controls the EGR valve 14 (step motor 27) to close by 100 steps at a normal drive frequency (e.g., 250 pps).

Next, in step 150, the ECU 80 executes full-close control. That is, the ECU 80 controls the EGR valve 14 (step motor 27) to close by an additional 10 steps at a low drive frequency, completing the full-close control.

Next, in step 160, after the fully closed position is reached, the ECU 80 controls the EGR valve 14 (step motor 27) to open by three steps.

Next, in step 170, the ECU 80 sets the full-closure control completion flag XCL to "1."

Then, in step 180, the ECU 80 holds the current control position of the EGR valve 14 (step motor 27), i.e., the control position of the valve body 25. Then, the ECU 80 returns the process to step 100.

Continuing from step 110, in step 190, the ECU 80 executes fully closed valve contact control. That is, the ECU 80 controls the EGR valve 14 (step motor 27) to close by 110 steps at a low drive frequency, completing the fully closed valve contact. Here, the maximum number of steps of the step motor 27 related to the component tolerances between the fully closed valve contact, in which the valve element 25 mechanically contacts the valve seat 24 when fully closed, and the fully open valve contact, in which the male thread 30 mechanically contacts the female thread 51 when fully open, is set to, for example, 100 steps. In this case, if the EGR valve 14 is controlled to close by 110 steps toward the fully closed position, the valve element 25 can be fully closed and contacted against the valve seat 24 regardless of its initial position. Furthermore, opening the valve element 25 by 110 steps from the fully closed valve contact state ensures the fully open valve contact.

Next, in step 200, after the fully closed position is reached, the ECU 80 controls the EGR valve 14 (step motor 27) to open by three steps.

Next, in step 210, the ECU 80 sets the initial setting completion flag XISC to "1."

Next, in step 220, the ECU 80 sets the full-closure control completion flag XCL to "1" and proceeds to step 180.

On the other hand, moving from step 120 to step 230, the ECU 80 determines whether there is a request to fully open the EGR valve 14. If the result of this determination is positive, the ECU 80 proceeds to step 240, and if the result of this determination is negative, the ECU 80 proceeds to step 180.

In step 240, the ECU 80 controls the EGR valve 14 (step motor 27) to open 97 steps at the normal drive frequency.

Next, in step 250, the ECU 80 executes full-open limiting control. That is, the ECU 80 controls the EGR valve 14 (step motor 27) to open an additional 10 steps at a low drive frequency, completing full-open limiting.

Next, in step 260, the ECU 80 sets the full-closure control completion flag XCL to "0" and proceeds to step 180.

On the other hand, moving from step 100 to step 270, the ECU 80 determines whether the full-close control completion flag XCL is "0." If the result of this determination is positive, the ECU 80 determines that the state is other than full-close control and proceeds to step 280. If the result of this determination is negative, the ECU 80 determines that the state is full-close control and proceeds to step 330.

In step 280, the ECU 80 controls the EGR valve 14 (step motor 27) to close by 100 steps at the normal drive frequency.

Next, in step 290, the ECU 80 executes full-close control. That is, the ECU 80 controls the EGR valve 14 (step motor 27) to close by an additional 10 steps at a low drive frequency, completing full-close control.

Next, in step 300, after the fully closed position is reached, the ECU 80 controls the EGR valve 14 (step motor 27) to open by three steps.

Next, in step 310, the ECU 80 sets the initial setting completion flag XISC to "0."

Then, in step 320, ECU 80 shuts down the ECU and terminates subsequent processing.

On the other hand, moving from step 270 to step 330, the ECU 80 sets the full-closure control completion flag XCL to "0" and proceeds to step 310.

According to the above-described "first EGR valve control," when executing the fully closed contact control, the ECU 80 drives the step motor 27 at the normal drive frequency (step 140 or step 280) to close the valve to near the fully closed position where the valve element 25 contacts the valve seat 24, and then drives the step motor 27 at a low drive frequency lower than the normal drive frequency (step 150 or step 290) to close the valve element 25 and contact it with the valve seat 24. In other words, when executing the fully closed contact control, the ECU 80 controls the step motor 27 at a low drive frequency instead of the normal drive frequency to slow the closing speed of the valve element 25, thereby reliably keeping step-out of the step motor 27 to "4 steps" or less.

According to the above-described "first EGR valve control," after executing the fully closed butting control (step 150 or step 290), the ECU 80 drives the step motor 27 so that the valve element 25 opens by a small amount, i.e., performs "small opening valve control" (step 160 or step 300) to control the EGR valve 14 (step motor 27) to open by "three steps."

[EGR valve operation]
This EGR valve 14 is designed to adjust the position of the valve element 25 relative to the valve seat 24 by driving the step motor 27 to rotate the magnet rotor 43, and converting the rotational motion into a stroke motion of the valve shaft 26 and the valve element 25 via the female thread 51 and male thread 30.

In other words, this EGR valve 14 rotates the magnet rotor 43 in one direction, causing the valve stem 26 and the valve element 25 to stroke against the biasing force of the valve element spring 52. This causes the valve element 25 to move away from the step motor 27, resulting in the fully closed state shown in Figure 2. At this time, by controlling the step motor 27 to fully close so that the valve element 25 abuts against the valve seat 24, the sealing surface 25a of the valve element 25 abuts against the seat portion 24a of the valve seat 24, and the tip of the rubber sheet 28 presses against and deforms against the sealing surface 25a. In this abutting state, the valve seat 24 functions as a valve-closing stopper for the valve element 25, restricting the rotation of the rotor body 47 and the stroke movement of the valve stem 26 and valve element 25. The position of the valve stem 26 at this time can be defined as the initial position.

If the step motor 27 loses synchronization during full-close contact control, the biasing force of the valve spring 52 causes the valve element 25 to move slightly toward the step motor 27, as shown in Figure 3, causing the valve element 25 to open slightly. However, because the rubber sheet 28 is provided on the valve seat 24, even if the valve element 25 opens slightly, the tip of the rubber sheet 28 elastically contacts the sealing surface 25a of the valve element 25, allowing the rubber sheet 28 to seal the gap between the valve seat 24 and the valve element 25.

At this time, the biasing force of the valve disc spring 52 causes the first female thread surface 51aa of the female thread 51 to engage with the second male thread surface 30ab of the male thread 30, as shown in FIG. 6 . In this engaged state, the valve stem 26 is biased toward the step motor 27 (upward in FIG. 6 ) by the biasing force F1 (indicated by the black arrow) of the valve disc spring 52, so the male thread 30a abuts the female thread 51a without backlash 55, preventing the valve stem 26 from moving upward. Therefore, even if the pressure of the EGR gas acts to pull or push the valve disc 25 toward the step motor 27, the valve disc 25 is prevented from moving. As a result, the valve disc 25 can be maintained in a fully closed state without requiring the step motor 27 to be particularly powerful or large.

Meanwhile, from this fully closed state, rotating the magnet rotor 43 in the opposite direction causes the valve shaft 26 and valve element 25 to perform a stroke motion in cooperation with the biasing force of the valve element spring 52, moving the valve element 25 toward the step motor 27 and achieving the fully open state shown in Figure 4. At this time, if the step motor 27 loses synchronization due to the fully open abutment control, as shown in Figures 7 and 8, the biasing force F1 of the valve element spring 52 biases the valve shaft 26 and valve element 25 toward the step motor 27, causing the second male thread surface 30ab to abut against the first female thread surface 51aa, thereby maintaining the fully open state.

[Operation and Effects of Engine EGR System]
According to the configuration of the EGR system of this embodiment described above, when the ECU 80 executes the fully closed butting control, it drives the step motor 27 at the normal drive frequency to close the valve until the valve element 25 abuts against the valve seat 24. Then, it drives the step motor 27 at a low drive frequency lower than the normal drive frequency to close the valve, causing the valve element 25 to abut against the valve seat 24. Therefore, when the valve element 25 abuts against the valve seat 24, the step motor 27 is driven at the low drive frequency, causing the valve element 25 to abut against the valve seat 24 more gently than when driven at the normal drive frequency. This weakens the repulsive force that the valve element 25 receives from the valve element spring 52 and the rubber sheet 28 during the abutment. This reduces the amount of step-out of the step motor 27 due to the abutment repulsive force during the fully closed butting control of the EGR valve 14, thereby suppressing the slight opening of the valve element 25. As a result, it is possible to suppress EGR gas leakage between the valve element 25 and the valve seat 24.

In this embodiment, after executing the fully closed butting control, the ECU 80 executes minute opening valve control, which drives the step motor 27 three steps so that the valve element 25 opens at a minute opening. Therefore, after executing the fully closed butting control, the minute opening valve control ensures that the valve element 25 opens at a minute opening, ensuring a gap between the valve element 25 and the valve seat 24. Therefore, even if the EGR valve 14 vibrates due to the influence of engine 1 vibrations, etc., vibration wear between the valve element 25 and the valve seat 24 can be suppressed.

According to the configuration of this embodiment, assuming that the step motor 27 will lose synchronism due to full-closed contact control, after full-closed contact, the open valve position of the step motor 27, for example, three steps, becomes the full-closed control position. This reduces contact wear between the valve disc 25 and the valve seat 24. If the step motor 27 loses synchronism at its minimum value of one step, the gap between the valve disc 25 and the valve seat 24 will be less than 0.05 mm, raising concerns about contact wear between the valve disc 25 and the valve seat 24 due to engine 1 vibration. In this embodiment, by ensuring a gap of 0.15 mm (equivalent to "0 + 3 steps") to 0.35 mm (equivalent to "4 + 3 steps") between the valve disc 25 and the valve seat 24 after full-closed contact, the vibration wear between the valve disc 25 and the valve seat 24 can be reduced.

In this embodiment, step-out of the step motor 27 occurs due to full-close butting control that is not affected by temperature, etc., so the step-out position of the step motor 27 is stable and the reference full-close position of the valve element 25 can be set within a narrow range of "0 to 4 steps." Therefore, by executing small-opening valve opening control that drives the step motor 27 by "3 steps," the full-close position of the valve element 25 can be controlled to "3 to 7 steps." Therefore, for example, by configuring the rubber sheet 28 to come into contact with the valve element 25 at "10 steps," it is possible to simultaneously suppress vibration wear between the valve element 25 and the valve seat 24 and suppress seal leakage of EGR gas.

According to the configuration of this embodiment, even if, during full-close butting control, the step motor 27 loses synchronization and the valve element 25 is positioned in an area other than where it contacts the seat portion 24a, creating a gap between the valve element 25 and the valve seat 24, the gap is sealed by the rubber sheet (sealing member). Therefore, even if the valve element 25 opens slightly due to loss of synchronization of the step motor 27, leakage of EGR gas between the valve element 25 and the valve seat 24 can be prevented.

Second Embodiment
Next, a second embodiment will be described in detail with reference to the drawings. In the following description, the same components as those in the first embodiment will be denoted by the same reference numerals, and differences will be mainly described.

[Regarding the second EGR valve control]
This embodiment differs from the first embodiment in the content of the "second EGR valve control." Here, the fully closed position determined by the fully closed butting control cannot be accurately determined. In the "first EGR valve control" of the first embodiment, the closing speed of the valve disc 25 is slowed at a low drive frequency before the valve disc 25 hits the valve seat 24 during the fully closed butting control. However, considering product tolerances, the closing speed of the valve disc 25 needs to be slowed approximately 10 steps before the fully closed butting. However, slowing the closing speed raises concerns about a delay in the fully closed response. Therefore, in this embodiment, the following "second EGR valve control" is executed to prevent a delay in the fully closed response and limit the step-out of the step motor 27 to a maximum of four steps.

Figures 11 and 12 show the "second EGR valve control" of this embodiment in the form of a flowchart. As shown in Figures 11 and 12, this flowchart differs from the flowcharts of Figures 9 and 10 in that steps 140, 240, 260, 280, and 310 have been omitted. Also, as shown in Figures 11 and 12, this flowchart differs from the flowcharts of Figures 9 and 10 in that step 400 is provided between step 130 and step 150, step 410 is provided between step 110 and step 190, step 420 and step 430 are provided between step 410 and "return", step 440 is provided between step 230 and step 250, step 450 is provided between step 250 and "return", step 460 and step 470 are provided between step 400 and "return", step 480 is provided between step 270 and step 290, step 490 and step 500 are provided between step 480 and "return", and step 510 is provided between step 300 and step 320.

When processing transitions to the routine of the flowcharts in Figures 11 and 12, the ECU 80 executes steps 100 to 130. If the determination result in step 130 is positive, the ECU 80 determines in step 400 whether the full-close control completion flag Xcl, which indicates that the EGR valve 14 is in a full-close control state at the normal drive frequency, is "1." If the determination result is positive, the ECU 80 determines that the full-close control of the EGR valve 14 at the normal drive frequency has been completed, and transitions to step 150. If the determination result is negative, the ECU 80 determines that the EGR valve 14 is in a state other than full-close control, and transitions to step 460.

In step 460, the ECU 80 controls the EGR valve 14 (step motor 27) to close by 110 steps at the normal drive frequency.

Next, in step 470, the ECU 80 sets the full-open control flag Xop, which indicates that the EGR valve 14 is in a full-open control state at the normal drive frequency, to "0," and sets the full-close control completion flag Xcl, which indicates that the EGR valve 14 is in a full-open control state at the normal drive frequency, to "1," and then returns the process to step 100.

On the other hand, moving from step 110 to step 410, the ECU 80 determines whether the full-close control completion flag Xcl at the normal drive frequency is "1." If the result of this determination is positive, the ECU 80 determines that the full-close control state is in effect and proceeds to step 190. If the result of this determination is negative, the ECU 80 determines that the state is not full-close control and proceeds to step 420.

In step 420, the ECU 80 controls the EGR valve 14 (step motor 27) to close by 110 steps at the normal drive frequency.

Next, in step 430, the ECU 80 sets the full-open control flag Xop at the normal drive frequency to "0" and the full-close control completion flag Xcl at the normal drive frequency to "1", and then returns the process to step 100.

On the other hand, if the determination result in step 230 is positive, ECU 80 determines in step 440 whether the full-open control flag Xop at the normal drive frequency is "1." If the determination result is positive, ECU 80 proceeds to step 250, and if the determination result is negative, ECU 80 proceeds to step 180.

After executing step 250, ECU 80 sets the low drive frequency full-close control completion flag XCL to "0" in step 450, and then proceeds to step 180.

On the other hand, if the determination result in step 270 is positive, ECU 80 determines in step 480 whether the full-close control completion flag Xcl at the normal drive frequency is "1." If the determination result is positive, ECU 80 proceeds to step 290, executes steps 290 and 300, and then proceeds to step 510.

Then, in step 510, the ECU 80 sets the initial setting completion flag XISC to "0", and the full-open control flag Xop and the full-close control completion flag Xcl at the normal drive frequency to "0", and then proceeds to step 320.

According to the above-described "second EGR valve control," when executing the fully closed contact control, the ECU 80 drives the step motor 27 at the normal drive frequency (step 420, step 460, or step 490) to close the valve until the valve element 25 contacts the valve seat 24 (fully closed), and then continues the fully closed contact control at a low drive frequency lower than the normal drive frequency (step 190, step 150, or step 290) to contact the valve element 25 against the valve seat 24.

According to the above-described "second EGR valve control," after executing the fully closed butting control (step 190, step 150, or step 290), the ECU 80 executes the small opening valve opening control (step 200, step 160, or step 300) to drive the step motor 27 so that the valve element 25 opens by a small opening.

[Operation and Effects of Engine EGR System]
According to the configuration of the EGR system of this embodiment described above, when the ECU 80 executes the fully closed contact control, it drives the step motor 27 at the normal drive frequency to close the valve until the valve element 25 abuts against the valve seat 24, and then continues the fully closed contact control at a low drive frequency lower than the normal drive frequency to abut the valve element 25 against the valve seat 24. Therefore, in the fully closed contact control, the step motor 27 is driven at the normal drive frequency once to close the EGR valve 14, and when the valve element 25 abuts against the valve seat 24, the valve element 25 receives the repulsive forces of the valve element spring 52 and the rubber sheet 28 and loses step-out. However, when the step motor 27 is then driven again at the low drive frequency to close the EGR valve 14 and the valve element 25 abuts against the valve seat 24 again, the repulsive forces of the valve element spring 52 and the rubber sheet 28 at the time of the abutment are weakened. Therefore, it is possible to suppress the amount of step-out of the step motor 27 due to the repulsive force of the abutment during the full-close butting control of the EGR valve 14, and to suppress slight opening of the valve element 25. As a result, it is possible to suppress leakage of EGR gas between the valve element 25 and the valve seat 24. Furthermore, in this embodiment, when the full-close butting control is executed, the step motor 27 is driven at the normal drive frequency to abut the valve element 25 against the valve seat 24, and then the valve element 25 is abutted against the valve seat 24 again at the low drive frequency to fully close the EGR valve 14. Therefore, compared to the first embodiment, it is possible to suppress the amount of step-out of the step motor 27 without causing a full-close response delay.

According to the configuration of this embodiment, after executing the fully closed butting control, the ECU 80 executes minute opening valve control, which drives the step motor 27 so that the valve element 25 opens at a minute opening. Therefore, after executing the fully closed butting control, the minute opening valve control reliably opens the valve element 25 at a minute opening, ensuring a gap between the valve element 25 and the valve seat 24. Therefore, even if the EGR valve 14 vibrates due to the influence of engine 1 vibrations, etc., vibration wear between the valve element 25 and the valve seat 24 can be suppressed.

According to the configuration of this embodiment, even if, during full-close butting control, the step motor 27 loses synchronization and the valve element 25 is positioned in an area other than where it contacts the seat portion 24a, creating a gap between the valve element 25 and the valve seat 24, the gap is sealed by the rubber sheet (sealing member). Therefore, even if the valve element 25 opens slightly due to loss of synchronization of the step motor 27, leakage of EGR gas between the valve element 25 and the valve seat 24 can be prevented.

In this embodiment, the actions and effects obtained by the same configuration as in the first embodiment are the same as those in the first embodiment.

Third Embodiment
Next, a third embodiment will be described in detail with reference to the drawings.

[Regarding the third EGR valve control]
This embodiment differs from the previous embodiments in the content of the "third EGR valve control." Assuming that stepping out of step motor 27 occurs due to full-close butting control, if stepping out is minimized to "one step," the gap between valve element 25 and valve seat 24 will be "0.05 mm." If vibration of engine 1 causes vibration of EGR valve 14, there is a concern that contact wear will occur between valve element 25 and valve seat 24. Therefore, in this embodiment, the following "third EGR valve control" is executed.

Figure 13 shows the details of this "third EGR valve control" in the form of a flowchart. As shown in Figure 13, this flowchart differs from the flowcharts of Figures 9 and 10 in that steps 110, 140, 150, 190 to 220, 240, 250, 280, 290, and 310 have been deleted. Also, as shown in Figure 13, this flowchart differs from the flowcharts of Figures 9 and 10 in that step 600 is provided between step 130 and step 160, step 610 is provided between step 230 and step 260, and step 620 is provided between step 270 and step 300.

When processing transitions to the routine of the flowchart of this embodiment, the ECU 80 executes the processes of steps 100, 120, and 130. If the determination result of step 130 is positive, the ECU 80 executes full-closed stopping control in step 600. That is, the ECU 80 controls the EGR valve 14 (step motor 27) to close for 110 steps at the normal drive frequency, completing full-close stopping.

Next, in step 160, the ECU 80 controls the EGR valve 14 (step motor 27) to open three steps after the fully closed position is reached. The processing of step 160 after step 600 is characteristic of this embodiment.

Then, the ECU 80 executes steps 170 and 180, and then returns to step 100.

On the other hand, if the determination result in step 230 is affirmative after step 120, the ECU 80 executes full-open limiting control in step 610. That is, the ECU 80 controls the EGR valve 14 (step motor 27) to open by 110 steps at the normal drive frequency, completing full-open limiting.

Then, the ECU 80 executes steps 260 and 180, and then returns to step 100.

On the other hand, if the determination result in step 270 is affirmative after step 100, the ECU 80 executes full-close control in step 620. That is, the ECU 80 controls the EGR valve 14 (step motor 27) to close by 110 steps at the normal drive frequency, completing full-close control.

Next, in step 300, after the fully closed position is reached, the ECU 80 controls the EGR valve 14 (step motor 27) to open by three steps.

The ECU 80 then executes step 320 and terminates subsequent processing.

According to the above-mentioned "third EGR valve control," after executing the fully closed butting control (step 600 or step 620), the ECU 80 drives the step motor 27 so that the valve element 25 opens by a small amount, i.e., executes "small opening valve control" that controls the EGR valve 14 to open by "three steps" (step 160 or step 300).

[Operation and Effects of Engine EGR System]
According to the configuration of this embodiment, after executing the fully closed butting control, the ECU 80 executes the minute opening valve opening control, which drives the step motor 27 so that the valve element 25 opens at a minute opening. Therefore, after executing the fully closed butting control, the minute opening valve opening control reliably opens the valve element 25 at a minute opening, thereby ensuring a gap between the valve element 25 and the valve seat 24. Therefore, even if the EGR valve 14 vibrates due to the influence of vibrations of the engine 1, etc., vibration wear between the valve element 25 and the valve seat 24 can be suppressed.

Fourth Embodiment
Next, a fourth embodiment will be described in detail with reference to the drawings.

[Regarding EGR valve control]
This embodiment differs from the previous embodiments in the content of the "fourth EGR valve control." In an extremely low-temperature environment, there is a risk of contact freezing of the rubber sheet 28. Therefore, in this embodiment, the following "fourth EGR valve control" is executed.

Figure 14 shows the details of this "fourth EGR valve control" in the form of a flowchart. As shown in Figure 14, this flowchart differs from the flowchart in Figure 13 in that steps 120, 130, 600, 160-180, 230, 610, and 260 have been omitted. Also, as shown in Figure 14, this flowchart differs from the flowchart in Figure 13 in that steps 630-710 are performed when the determination result in step 100 is positive, and steps 720 and 730 are added between steps 300 and 320.

When processing transitions to the routine of this flowchart, if the determination result in step 100 is positive, the ECU 80 transitions processing to step 630. Then, in step 630, the ECU 80 acquires the intake air temperature THA based on the detection value of the intake air temperature sensor 77.

Next, in step 640, the ECU 80 determines whether the intake air temperature THA is lower than 5°C. If the result of this determination is positive, the ECU 80 proceeds to step 650; if the result of this determination is negative, the ECU 80 proceeds to step 710.

In step 650, the ECU 80 determines whether the defrost control completion flag XCOCL, which indicates that defrost control of the EGR valve 14 has been completed, is "0." If the result of this determination is positive, the ECU 80 determines that defrost control is not yet complete and proceeds to step 660. If the result of this determination is negative, the ECU 80 determines that defrost control has been completed and proceeds to step 710.

In step 660, the ECU 80 executes full-close control. That is, the ECU 80 controls the EGR valve 14 (step motor 27) to close by 110 steps at the normal drive frequency, completing full-close control.

Next, in step 670, after the fully closed position is reached, the ECU 80 controls the EGR valve 14 (step motor 27) to open by 10 steps.

Next, in step 680, ECU 80 increments the number of defrosting control operations COCLN(i) by "1".

Next, in step 690, ECU 80 determines whether the number of defrosting control cycles COCLN(i) is equal to or greater than a predetermined value A1. This predetermined value A1 can be set to, for example, a number between 2 and 5. If the result of this determination is positive, ECU 80 determines that the predetermined number of cycles has been completed and proceeds to step 700. If the result of this determination is negative, ECU 80 determines that the predetermined number of cycles has not been completed and returns to step 660.

In step 700, ECU 80 sets the defrosting control completion flag XCOCL to "1" and returns processing to step 100.

On the other hand, moving from step 640 or step 650 to step 710, the ECU 80 executes normal opening and closing control of the EGR valve 14, and then returns the process to step 100.

When proceeding from step 100 to step 270, the ECU 80 executes the processing of step 300 or step 310, and then sets the defrosting control completion flag XCOCL to "0" in step 720.

Next, in step 730, the ECU 80 resets the number of defrosting control operations COCLN(i) to "0" and then proceeds to step 320.

According to the above-described "fourth EGR valve control," the ECU 80 is configured to execute "small opening valve control" (step 670), which drives the step motor 27 of the EGR valve 14 in "10 steps" so that the valve element 25 opens at a small opening. Furthermore, when the valve element 25 is in a closed state while the engine 1 is stopped and the ECU 80 drives the EGR valve 14 in a predetermined low-temperature environment where the intake air temperature THA is lower than 5°C (steps 640 and 650), the ECU 80 executes one of the "fully closed butting control" (step 660) and the "small opening valve control" (step 670) before executing the other. In this embodiment, the ECU 80 alternates between the "fully closed butting control" and the "small opening valve control."

[Operation and Effects of Engine EGR System]
According to the configuration of the EGR system of this embodiment described above, when the valve element is in a closed state when the engine 1 is stopped and the ECU 80 drives the EGR valve 14 in a predetermined low-temperature environment, the ECU 80 first executes one of the "fully closed butting control" and the "small opening valve control" before executing the other. Therefore, when the engine 1 is started in a low-temperature environment, the valve element 25 opens and closes relative to the valve seat 24, causing the rubber sheet 28 to deform. Therefore, even if the valve element 25 and the rubber sheet 28 are frozen together when the engine 1 is started in a low-temperature environment, the frozen state can be released, ensuring that the valve element 25 opens. Furthermore, by repeatedly opening and closing the valve element 25 relative to the valve seat 24, cracks or breaks can be generated in the frozen state, thereby reliably releasing the frozen state.

In the first embodiment, the ECU 80 is configured to execute only the "first EGR valve control," and in the second embodiment, the ECU 80 is configured to execute only the "second EGR valve control." In contrast, in the first embodiment, the ECU 80 may be configured to execute a combination of the "first EGR valve control" and the "fourth EGR valve control," or in the second embodiment, the ECU 80 may be configured to execute a combination of the "second EGR valve control" and the "fourth EGR valve control."

Fifth Embodiment
Next, the fifth embodiment will be described in detail with reference to the drawings.

[Configuration of EGR valve]
In each of the above-described embodiments, when the "fully closed butting control" is executed, the valve element 25 is opened by a predetermined small opening degree by the biasing force of the valve element spring 52 due to the step motor 27 stepping out. In contrast, in this embodiment, in addition to the above-described configuration, the EGR valve 14 is configured such that the valve element 25 is opened by a predetermined small opening degree by the biasing force of the valve element spring 52 when the step motor 27 is not driven.

[Regarding the fifth EGR valve control]
This embodiment differs from the previous embodiments in the content of the "fifth EGR valve control." If the EGR valve 14 is immediately opened from a closed state after the engine 1 is stopped, high-concentration exhaust gas remaining in the exhaust passage 3 may enter the intake passage 2, causing a misfire or stall when the engine 1 is restarted. Therefore, in this embodiment, the following "fifth EGR valve control" is executed.

Figure 15 shows the details of the "fifth EGR valve control" in the form of a flowchart. As shown in Figure 15, this flowchart differs from the flowchart in Figure 13 in that step 300 is omitted and steps 740 and 750 are added between steps 620 and 310.

When processing transitions to the routine of this flowchart, if the determination result of step 100 is negative, the ECU 80 transitions processing to step 270. If the determination result of step 270 is positive, the ECU 80 executes processing of step 620.

Then, in step 740, the ECU 80 acquires the elapsed time Toff after the IG switch 70 is turned off. The ECU 80 measures this elapsed time Toff after the IG switch 70 is turned off.

Then, in step 750, moving from step 740 or step 270, ECU 80 determines whether the elapsed time Toff is equal to or greater than the predetermined time B1. If the result of this determination is positive, ECU 80 proceeds to step 300; if the result of this determination is negative, ECU 80 proceeds to step 180.

According to the "fifth EGR valve control" described above, after a request to stop the engine 1 is made, the ECU 80 executes "full-closed stop control" (step 620) of the EGR valve 14 for a predetermined time B1 (steps 100, 270, 620, 740, and 750).

[Operation and Effects of Engine EGR System]
According to the configuration of the EGR system of this embodiment described above, the ECU 80 executes the "full-closed butting control" for a predetermined time B1 after a request to stop the engine 1 is made. Therefore, even after a request to stop the engine 1 is made and the engine 1 is stopped, the "full-closed butting control" is executed for the predetermined time B1. During this time, the EGR valve 14 is maintained in a fully closed state, and the EGR gas remaining in the EGR passage 12 diffuses and decreases in concentration over time. Therefore, even if the EGR valve 14 opens after the engine 1 is stopped and EGR gas enters the intake passage 2 from the EGR passage 12, the entering EGR gas has a low concentration, which prevents the engine 1 from failing to restart.

With the configuration of this embodiment, when the step motor 27 is not driven, the valve element 25 opens to a predetermined degree due to the biasing force of the valve element spring 52. Therefore, even when the engine 1 is stopped in a low-temperature environment, water does not remain between the valve element 25 and the valve seat 24. This prevents the valve element 25 and the valve seat 24 from freezing and becoming stuck together when the engine 1 is stopped.

In the first embodiment, the ECU 80 is configured to execute only the "first EGR valve control," and in the second embodiment, the ECU 80 is configured to execute only the "second EGR valve control." In contrast, in the first embodiment, the ECU 80 may be configured to execute a combination of the "first EGR valve control" and the "fifth EGR valve control," or in the second embodiment, the ECU 80 may be configured to execute a combination of the "second EGR valve control" and the "fifth EGR valve control."

Sixth Embodiment
Next, a sixth embodiment will be described in detail with reference to the drawings.

[Regarding the sixth EGR valve control]
This embodiment differs from the previous embodiments in the content of the "sixth EGR valve control." If the EGR valve 14 is left closed after the engine 1 is stopped, there is a concern that the valve body 25 and the rubber sheet 28 may freeze in extremely cold weather. Therefore, in this embodiment, the following "sixth EGR valve control" is executed.

Figure 16 shows the details of the "sixth EGR valve control" in the form of a flowchart. As shown in Figure 16, this flowchart differs from the flowchart in Figure 13 in that steps 740 to 760 are provided between steps 300 and 310.

When processing transitions to the routine of this flowchart, if the determination result of step 100 is negative, the ECU 80 transitions processing to step 270. If the determination result of step 270 is positive, the ECU 80 executes the processing of steps 620 and 300.

Then, in step 740, the ECU 80 acquires the elapsed time Toff after the IG switch 70 is turned off. The ECU 80 measures this elapsed time Toff after the IG switch 70 is turned off.

Then, in step 750, moving from step 740 or step 270, the ECU 80 determines whether the elapsed time Toff is equal to or greater than the predetermined time B1. If the result of this determination is positive, the ECU 80 proceeds to step 760; if the result of this determination is negative, the ECU 80 proceeds to step 180.

Then, in step 760, the ECU 80 controls the EGR valve 14 (step motor 27) to open by 20 steps, and then transitions to step 310.

According to the "sixth EGR valve control" described above, after a request to stop the engine 1 is made, the ECU 80 executes "fully closed stop control" for a predetermined time B1 (steps 100, 270, 620, 740, and 750), and then opens the valve element 25 by a predetermined amount of opening equivalent to "20 steps" using the step motor 27 (step 760).

[Operation and Effects of Engine EGR System]
According to the configuration of the EGR system of this embodiment described above, after a request to stop the engine 1 is made, the ECU 80 executes the "fully closed butting control" for a predetermined time B1 and then opens the valve element 25 by a predetermined opening amount equivalent to "20 steps" using the step motor 27. Therefore, even if the engine 1 is stopped in a low-temperature environment, water will not remain between the valve element 25 and the valve seat 24. This makes it possible to prevent the valve element 25 and the valve seat 24 from freezing and becoming stuck together when the engine 1 is stopped.

In the first embodiment, the ECU 80 is configured to execute only the "first EGR valve control," and in the second embodiment, the ECU 80 is configured to execute only the "second EGR valve control." In contrast, in the first embodiment, the ECU 80 may be configured to execute a combination of the "first EGR valve control" and the "sixth EGR valve control," or in the second embodiment, the ECU 80 may be configured to execute a combination of the "second EGR valve control" and the "sixth EGR valve control."

Seventh Embodiment
Next, the seventh embodiment will be described in detail with reference to the drawings.

[Configuration of EGR valve]
In this embodiment, as in the fifth embodiment, the EGR valve 14 is configured so that the valve element 25 opens by a predetermined small amount due to the biasing force of the valve element spring 52 when the step motor 27 is not driven.

[Engine start control]
This embodiment differs from the first or second embodiment in that the ECU 80 also executes "engine start control." If the engine 1 is started with the EGR valve 14 open after the engine 1 has been stopped, a large amount of EGR gas may flow into the intake passage 2, potentially causing misfire or stalling of the engine 1. By reducing the inclination angles of the threads 30 a, 51 a of the male and female threads 30, 51 of the EGR valve 14, movement of the valve stem 26 can be restricted when the coil 41 is de-energized, preventing the EGR valve 14 from opening. However, reducing the inclination angles of the threads 30 a, 51 a can degrade the motion response of the valve stem 26 or require the installation of new parts. Therefore, this embodiment executes the following "engine start control."

Figure 17 shows the details of this "engine start control" in a flowchart. When processing transitions to the routine of this flowchart, the ECU 80 determines whether the ignition (IG) is on, i.e., whether the ECU 80 has started and the IG switch 70 has been turned on. If the result of this determination is positive, the ECU 80 transitions processing to step 810, since the engine 1 has started. If the result of this determination is negative, the engine 1 has not started, so the ECU 80 transitions processing to step 860.

In step 810, the ECU 80 determines whether the initial engine start flag XEO is "0". This flag XEO indicates that the initial start of the engine 1 has been completed. If the result of this determination is positive, the ECU 80 determines that the initial engine start is incomplete and proceeds to step 820. If the result of this determination is negative, the ECU 80 determines that the initial engine start has been completed and proceeds to step 850.

In step 820, ECU 80 determines whether the initial setting completion flag XISC is "1." If the result of this determination is positive, ECU 80 determines that the initial setting is complete and proceeds to step 830. If the result of this determination is negative, ECU 80 determines that the initial setting is not complete and returns to step 800.

In step 830, the ECU 80 starts the engine 1. That is, the ECU 80 begins executing various control programs for starting and operating the engine 1.

Next, in step 840, the ECU 80 sets the initial engine start flag XEO to "1" and returns processing to step 800.

On the other hand, moving from step 810 to step 850, the ECU 80 executes normal engine operation control and returns processing to step 800.

On the other hand, moving from step 800 to step 860, the ECU 80 resets the initial setting completion flag XISC and the initial engine start flag XEO to "0".

Next, in step 870, ECU 80 shuts down and terminates subsequent processing.

According to the above-described "engine start control," the ECU 80 executes "fully closed butting control" after a request to start the engine 1 is received, and then starts the engine 1. That is, in the first or second embodiment, in steps 100, 110, 190, 200, and 210 of the flowcharts in FIGS. 9, 10, 11, and 12, when a request to start the engine 1 is received, if the initial setting completion flag XISC is "0," the ECU 80 executes "fully closed butting control" and then sets the initial setting completion flag XISC to "1." In the flowchart in FIG. 17, in steps 800 to 830, the ECU 80 executes engine start only if the initial setting completion flag XISC is "1" when a request to start the engine 1 is received.

[Operation and Effects of Engine EGR System]
According to the configuration of the EGR system of this embodiment described above, after a request to start the engine 1 is made, the ECU 80 executes the "fully closed butting control" and then starts the engine 1. Therefore, when the engine 1 is started, the valve element 25 is in a fully closed state without any slight opening. Therefore, leakage of EGR gas from the EGR passage 12 to the intake passage 2 can be prevented simultaneously with the start of the engine 1, and misfires and stalls of the engine 1 can be prevented.

Eighth Embodiment
Next, the eighth embodiment will be described in detail with reference to the drawings.

[Configuration of EGR valve]
This embodiment differs from the previous embodiments in the configuration of the valve seat 24 and the seal member of the EGR valve 14. FIG. 18 is a cross-sectional view of the EGR valve 14 of this embodiment, showing a fully closed state in which the valve element 25 abuts against the valve seat 24 to fully close the valve. FIG. 19 is a cross-sectional view of the EGR valve 14, showing a state in which the step motor 27 loses step when the valve is fully closed. FIG. 20 is a cross-sectional view of the EGR valve 14, showing a fully open state. As shown in FIGS. 18 to 20 , in this embodiment, the valve seat 24 has an annular ridge shape that protrudes upward along the valve hole 24b, and its upper end surface forms a seat portion 24a. A seal surface 25a on the lower peripheral edge of the valve element 25 can abut against this seat portion 24a (to close the valve). In this embodiment, the valve seat 24 does not have a rubber sheet 28. Instead, an annular rubber lip seal 29 is provided along the outer periphery of the valve element 25. The lip seal 29 has a lip portion 29a on its outer periphery that slopes downward and inward. The lower end of the lip portion 29a is capable of elastically contacting the vicinity of the outer periphery of the valve seat 24. The lip seal 29 corresponds to an example of a sealing member of the disclosed technology. The lip seal 29 provided on the valve element 25 is configured to seal the gap between the valve element 25 and the valve seat 24 in an area other than where the valve element 25 contacts the seat portion 24a when the valve element 25 is fully closed.

In the fully closed butted state shown in Figure 18, the seal surface 25a of the valve disc 25 abuts against the seat portion 24a of the valve seat 24, and the lower end of the lip portion 29a of the lip seal 29 is pressed against the wall surface near the outer periphery of the valve seat 24, fully closing the valve disc 25. It is desirable that the elastic force of the lip portion 29a in this fully closed butted state be as small as possible. In the out-of-step state shown in Figure 19, the valve disc 25 moves slightly upward from the seat portion 24a of the valve seat 24, and the seal surface 25a is separated from the seat portion 24a. However, the lower end of the lip seal 29 contacts the wall surface near the outer periphery of the valve seat 24, thereby sealing the gap between the valve disc 25 and the valve seat 24. The lip seal 29 is required to have sufficient elasticity to follow the movement of the valve disc 25 during this out-of-step state. On the other hand, in the fully open state shown in Figure 20, the valve disc 25 is farthest away from the valve seat 24, achieving the maximum opening.

[Operation and Effects of Engine EGR System]
The configuration of the EGR system of this embodiment described above differs from the previous embodiments in the configuration of the valve seat 24 and the lip seal 29 (sealing member) of the EGR valve 14, but provides the same functions and effects as the previous embodiments. In particular, the lip seal 29 also suppresses vibration of the valve element 25 during full-close contact or step-out, thereby suppressing full-close wear between the valve element 25 and the valve seat 24 and wear of the thrust bearings 39, 40.

<Another embodiment>
The disclosed technology is not limited to the above-described embodiments, and can be implemented by appropriately modifying part of the configuration within the scope of the disclosed technology.

(1) In the above embodiments, the driven screw provided on the valve shaft 26 is configured as a male screw 30, and the drive screw provided on the rotor body 47 is configured as a female screw 51. However, the driven screw may also be configured as a female screw, and the drive screw may be configured as a male screw that is threaded into the female screw.

(2) In the first to seventh embodiments, the rubber sheet 28 is provided on the valve seat 24 side, but the rubber sheet may also be provided on the valve body side.

(3) In the eighth embodiment, the lip seal 29 is provided on the valve body 25 side, but the lip seal may also be provided on the valve seat side.

(4) In the third embodiment, the ECU 80 was configured to execute the small-opening valve control after executing the fully closed-off butting control. However, the ECU can also be configured to execute only the small-opening valve control without executing the fully closed-off butting control.

This disclosed technology can be used in automotive gasoline engine systems.

REFERENCE SIGNS LIST 1 engine 12 EGR passage 14 EGR valve 22 flow path 23 housing 24 valve seat 24a seat portion 25 valve body 26 valve stem 26a one end 26b other end 27 step motor 28 rubber sheet (sealing member)
29 Lip seal (sealing member)
30 Male thread (driven thread)
30a male thread (driven thread)
30aa: First male thread surface (first driven thread surface)
30ab: Second male thread surface (second driven thread surface)
43 Magnet rotor (rotor)
51 Female thread (drive screw)
51a Female thread (drive thread)
51aa: First female thread surface (first driving thread surface)
51ab second female thread surface (second driving thread surface)
52 Valve body spring 55 Backlash 80 ECU (control means)

Claims (7)

An EGR system for an engine configured to control an EGR valve provided in an EGR passage of the engine by a control means in accordance with an operating state of the engine,
The EGR valve is
a housing having a flow path;
a valve seat provided in the flow path;
a valve body that is capable of being seated on the valve seat;
a valve stem provided with the valve body;
the valve shaft includes one end and another end, the valve body is fixed to the one end, and a driven screw is provided to the other end;
a step motor for reciprocating the valve stem in its axial direction;
the stepper motor includes a rotor having a drive screw threadedly engaged with the driven screw;
the flow path is divided into a side closer to the rotor and a side farther from the rotor with the valve seat as a boundary, and the valve element is arranged in the flow path on the near side so as to be able to seat on the valve seat;
the driven screw has a driven thread that continues helically in the axial direction of the valve stem, and the driven thread includes a first driven thread surface facing toward the valve seat and a second driven thread surface located on the opposite side of the first driven thread surface;
the drive screw has a drive thread that continues helically in the axial direction of the valve stem, the drive thread including a first drive thread surface facing toward the valve seat and a second drive thread surface located opposite the first drive thread surface;
a predetermined backlash is provided between the driven screw and the drive screw in the axial direction of the valve stem;
a valve body spring for biasing the valve body together with the valve stem in a direction away from the valve seat,
In the EGR system of the engine, the control means executes a full-close abutment control in which, when the valve element is fully closed, the step motor causes the valve stem to perform a stroke motion against the biasing force of the valve element spring so that the valve element abuts against the valve seat,
When executing the fully closed abutment control, the control means drives the step motor at a normal drive frequency to close the valve to a position close to the fully closed position where the valve element abuts against the valve seat, and then drives the step motor at a drive frequency lower than the normal drive frequency to close the valve element and abut against the valve seat ,
the valve seat has a seat portion that can come into contact with the valve disc, and at least one of the valve seat and the valve disc is provided with a seal member that seals a gap between the valve disc and the valve seat in an area other than the area where the valve disc comes into contact with the seat portion when the valve disc is fully closed,
After executing the full-closed abutting control, the control means executes a small opening valve opening control for driving the step motor so that the valve element opens at a small opening.
An EGR system for an engine. An EGR system for an engine configured to control an EGR valve provided in an EGR passage of the engine by a control means in accordance with an operating state of the engine,
The EGR valve is
a housing having a flow path;
a valve seat provided in the flow path;
a valve body that is capable of being seated on the valve seat;
a valve stem provided with the valve body;
the valve shaft includes one end and another end, the valve body is fixed to the one end, and a driven screw is provided to the other end;
a step motor for reciprocating the valve stem in its axial direction;
the stepper motor includes a rotor having a drive screw threadedly engaged with the driven screw;
the flow path is divided into a side closer to the rotor and a side farther from the rotor with the valve seat as a boundary, and the valve element is arranged in the flow path on the near side so as to be able to seat on the valve seat;
the driven screw has a driven thread that continues helically in the axial direction of the valve stem, and the driven thread includes a first driven thread surface facing toward the valve seat and a second driven thread surface located on the opposite side of the first driven thread surface;
the drive screw has a drive thread that continues helically in the axial direction of the valve stem, the drive thread including a first drive thread surface facing toward the valve seat and a second drive thread surface located opposite the first drive thread surface;
a predetermined backlash is provided between the driven screw and the drive screw in the axial direction of the valve stem;
a valve body spring for biasing the valve body together with the valve stem in a direction away from the valve seat,
In the EGR system of the engine, the control means executes a full-close abutment control in which, when the valve element is fully closed, the step motor causes the valve stem to perform a stroke motion against the biasing force of the valve element spring so that the valve element abuts against the valve seat,
When executing the full-closed contact control, the control means drives the step motor at a normal drive frequency to close the valve until the valve element contacts the valve seat, and then continues the full-closed contact control at a drive frequency lower than the normal drive frequency to contact the valve element against the valve seat,
the valve seat has a seat portion that can come into contact with the valve disc, and at least one of the valve seat and the valve disc is provided with a seal member that seals a gap between the valve disc and the valve seat in an area other than the area where the valve disc comes into contact with the seat portion when the valve disc is fully closed,
After executing the full-closed abutting control, the control means executes a small opening valve opening control for driving the step motor so that the valve element opens at a small opening.
An EGR system for an engine. 3. The EGR system for an engine according to claim 1,
10. An EGR system for an engine, wherein the valve element is opened to a predetermined degree by the biasing force of the valve element spring when the step motor is not driven. 4. The engine EGR system according to claim 3 ,
The EGR system for an engine, wherein the control means, after a request to start the engine, executes the fully closed butting control and then starts the engine. 4. The engine EGR system according to claim 3 ,
The EGR system of an engine, wherein the control means executes the full-closed butting control for a predetermined time after a request to stop the engine is received. 3. The EGR system for an engine according to claim 1,
The EGR system for an engine, wherein the control means executes the fully closed butting control for a predetermined time after a request to stop the engine is received, and then opens the valve body to a predetermined opening degree. 3. The engine EGR system according to claim 1 ,
the control means is configured to execute a small opening valve control for driving the step motor so that the valve element opens at a small opening,
The EGR system of the engine is characterized in that when the valve body is in a closed state when the engine is stopped and the EGR valve is driven in a predetermined low-temperature environment, the control means first executes one of the fully closed butting control and the small opening valve opening control before executing the other.