JP7345971B2 - Internal combustion engine control device - Google Patents

Description

The present invention relates to a control device that controls the operation of an internal combustion engine installed in a vehicle or the like.

High-temperature combustion gas flows into the exhaust system of an internal combustion engine, and the members that make up the exhaust system are exposed to high heat. If the temperature of the constituent members of the exhaust system rises excessively, there is a risk that the members may no longer exhibit the necessary and sufficient performance or may be damaged. For example, a three-way catalyst for purifying exhaust gas is installed in the exhaust passage of an internal combustion engine, but if this catalyst overheats, its efficiency in purifying harmful substances will actually decrease.

Conventionally, the temperature of the exhaust system components is estimated or actually measured, and if the temperature exceeds the allowable temperature, the amount of fuel injection is increased to reduce the temperature of the target component using the latent heat (heat of vaporization) of the fuel. A correction control (“Over Temperature Protection Increase”) is implemented to prompt the user (see Patent Document 1 above).

Japanese Patent Application Publication No. 2013-249792

In the conventional correction control, the increment of the fuel injection amount was set according to the current operating range of the internal combustion engine [engine speed, engine load factor]. For this reason, it is necessary to perform adaptation work in which the increment of the fuel injection amount is determined in advance for each rotation speed and each load factor, which increases the number of development steps.

Moreover, the above-mentioned adaptation work must be performed every time the permissible temperature of the constituent members of the exhaust system is changed. In reality, even if some or all of the components are the same, the allowable temperature often changes depending on the vehicle type or model or during the development process. Alternatively, it may be assumed that the allowable temperature of the constituent members changes due to aging or the like.

An objective of the present invention is to make it possible to more easily determine an increment in fuel injection amount when the temperature of a component of an exhaust system exceeds an allowable temperature.

In order to solve the above-mentioned problems, in the present invention, when the temperature of a member constituting the exhaust system of an internal combustion engine exceeds an allowable temperature, the amount of fuel injection is increased compared to the case where this is not the case, so as to reduce the temperature drop of the member. The system stores in memory map data that defines the relationship between the difference between the current temperature of the member and the allowable temperature and the target air-fuel ratio when implementing the correction control. , a control device for an internal combustion engine is configured that searches the map using the current temperature of the member as a key, learns the target air-fuel ratio when implementing the correction control, and determines the fuel injection amount. The current temperature of the member may be estimated or measured. If the current temperature of the member is to be estimated, map data that defines the relationship between the operating range of the internal combustion engine and the current estimated temperature of the member is stored in memory, and the current operating range of the internal combustion engine is estimated. Search the map using as a key to obtain the current estimated temperature of the member, and also obtain map data that defines the relationship between the ignition timing in the cylinder of the internal combustion engine and the correction amount to be added to the current estimated temperature of the member. It is possible to store the map in memory, search the map using the current ignition timing as a key, learn the correction amount to be added to the current estimated temperature of the component, and correct the current estimated temperature of the component. preferable.

According to the present invention, it becomes possible to more easily determine the increment of the fuel injection amount when the temperature of the constituent members of the exhaust system of the internal combustion engine exceeds the permissible temperature.

1 is a diagram showing a schematic configuration of an internal combustion engine and a control device in an embodiment of the present invention. FIG. 3 is a flowchart showing an example of a procedure of processing executed by the control device for an internal combustion engine according to the embodiment according to a program. FIG. 3 is a diagram illustrating map data that defines the relationship between the operating range of the internal combustion engine and the estimated temperature of the constituent members of the exhaust system. FIG. 3 is a diagram illustrating map data that defines a relationship between ignition timing in a cylinder of an internal combustion engine and a correction amount added to an estimated temperature of a component of an exhaust system. FIG. 3 is a diagram illustrating map data that defines the relationship between the estimated temperature of the exhaust system component and the target air-fuel ratio of the air-fuel mixture in correction control. 2 is a graph experimentally obtained to show how the temperature of a component changes from the temperature under the normal target air-fuel ratio by changing the air-fuel ratio of the air-fuel mixture from the normal target air-fuel ratio.

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an overview of a vehicle internal combustion engine in this embodiment. The internal combustion engine in this embodiment is a spark ignition four-stroke gasoline engine, and includes a plurality of cylinders 1 (for example, four cylinders, one of which is shown in FIG. 1). Upstream of the intake valve of each cylinder 1 and near the intake port connected to each cylinder 1, an injector 11 is provided that injects fuel toward the intake port. Further, a spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The spark plug 12 causes a spark discharge between a center electrode and a ground electrode upon application of an induced voltage generated in an ignition coil. The ignition coil is integrally built into the coil case together with the igniter, which is a semiconductor switching element.

The intake passage 3 for supplying intake air takes in air from the outside and guides it to the intake port of each cylinder 1. On the intake passage 3, an air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from upstream.

The exhaust passage 4 for discharging exhaust gas guides exhaust gas generated by burning fuel in the cylinders 1 from the exhaust port of each cylinder 1 to the outside. An exhaust manifold 42 and a three-way catalyst 41 for exhaust purification are arranged on the exhaust passage 4.

Upstream and downstream of the catalyst 41 in the exhaust passage 4, air-fuel ratio sensors 43 and 44 are installed to detect the air-fuel ratio of gas flowing through the exhaust passage 4. The air-fuel ratio sensors 43 and 44 may each be a linear A/F sensor that has output characteristics proportional to the air-fuel ratio of exhaust gas, or may be an O ₂ sensor that has output characteristics that are non-linear with respect to the air-fuel ratio of exhaust gas. There may be.

The exhaust gas recirculation device 2 realizes so-called high-pressure loop EGR, and is an external EGR device that communicates the upstream side of the catalyst 41 in the exhaust passage 4 with the downstream side of the throttle valve 32 in the intake passage 3. The components include a passage 21, an EGR cooler 22 provided on the EGR passage 21, and an EGR valve 23 that opens and closes the EGR passage 21 and controls the flow rate of EGR gas flowing through the EGR passage 21. The entrance of the EGR passage 21 is connected to the exhaust manifold 42 in the exhaust passage 4 or a predetermined location downstream thereof. The outlet of the EGR passage 21 is connected to a predetermined location downstream of the throttle valve 32 in the intake passage 3, specifically, to a surge tank 33.

The variable valve timing mechanism 5 can variably control the opening/closing timing of at least the intake valve of each cylinder 1. The intake VVT mechanism 5 may be, for example, a vane type that changes the rotational phase of the intake camshaft relative to the crankshaft that drives the intake valves of each cylinder 1 using hydraulic pressure (lubricating oil pressure), or an electric type that changes the rotational phase using an electric motor. (Motor drive VVT). In addition, the internal combustion engine may be equipped with an exhaust VVT mechanism that can variably control the opening and closing timing of the exhaust valves of each cylinder 1.

An ECU (Electronic Control Unit) 0, which is a control device for an internal combustion engine in this embodiment, is a microcomputer system including a processor, a memory, an input interface, an output interface, and the like. The ECU0 may include a plurality of ECUs or controllers connected to each other so as to be communicable via a telecommunication line such as a CAN (Controller Area Network).

The input interface of the ECU0 includes a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed, a crank angle signal b output from a crank angle sensor that detects the rotation angle of the crankshaft and the engine rotation speed, and an accelerator pedal. The accelerator opening signal c output from a sensor that detects the amount of depression or the opening of the throttle valve 32 as the accelerator opening (so to speak, the required engine load factor or engine torque), the accelerator opening signal c in the surge tank 33 of the intake passage 3 Intake temperature/intake pressure signal d output from a temperature/pressure sensor that detects intake air temperature and intake pressure, master cylinder pressure that is the pressure of brake hydraulic fluid discharged from a sensor that detects the amount of depression of the brake pedal or the master cylinder A brake depression amount signal e output from a sensor that detects the temperature of the internal combustion engine, a cooling water temperature signal f output from a water temperature sensor that detects the cooling water temperature that indicates the temperature of the internal combustion engine, and multiple cam angles of the intake camshaft or exhaust camshaft. a cam angle signal g output from a cam angle sensor; a tilt angle (or acceleration) signal h output from a tilt angle sensor (or acceleration sensor) that detects the slope of the road surface on which the vehicle is located; and a catalyst 41. An air-fuel ratio signal p output from an air-fuel ratio sensor 43 that detects the air-fuel ratio of exhaust gas on the upstream side of the catalyst 41, and an air-fuel ratio signal output from the air-fuel ratio sensor 44 that detects the air-fuel ratio of exhaust gas on the downstream side of the catalyst 41. q etc. are input.

From the output interface, an ignition signal i is sent to the igniter of the spark plug 12, a fuel injection signal j is sent to the injector 11, an opening operation signal k is sent to the throttle valve 32, and an opening operation signal l is sent to the EGR valve 23. , outputs a control signal m etc. for the opening/closing timing of the intake valve to the VVT mechanism 5.

The processor of ECU0 interprets and executes programs stored in memory, calculates operating parameters, and controls the operation of the internal combustion engine. ECU0 acquires various information a, b, c, d, e, f, g, h, p, and q necessary for operational control of the internal combustion engine through an input interface, and adjusts the amount of air taken into cylinder 1. The required fuel injection amount (and can realize the target air-fuel ratio), fuel injection timing (including the number of fuel injections for one combustion), fuel injection pressure, ignition timing, and required EGR amount (or EGR determine operating parameters such as engine speed), intake valve timing, etc. ECU0 applies various control signals i, j, k, l, m corresponding to operating parameters via an output interface.

As shown in FIG. 2, the ECU 0 of this embodiment estimates the current temperature of the constituent members of the exhaust system of the internal combustion engine, particularly the catalyst 41 (step S1), and if the temperature exceeds a predetermined allowable temperature (step S2). ), a correction control is performed to increase the fuel injection amount compared to the case where this is not the case (step S3).

In step S1, the target component is selected based on the current operating range of the internal combustion engine [engine speed, engine load factor (or engine torque, intake air amount, intake pressure inside the surge tank 33, fuel injection amount, etc.)]. 41 temperature estimation is performed. As shown in FIG. 3, the memory of ECU0 stores a map that defines the relationship between parameters related to the operating range of the internal combustion engine [engine speed, engine load factor, etc.] and the estimated temperature T _ij of the target component 41. Data is stored. The ECU0 searches the map using the current operating range as a key, and learns the estimated temperature T _ij of the component 41.

Further, in step S1, the estimated temperature T _ij of the component 41 may be corrected based on the current timing of spark ignition of the air-fuel mixture in the cylinder 1 of the internal combustion engine and other factors. For example, the more the ignition timing is retarded from the MBT (Minimum advance for Best Torque), the lower the thermomechanical conversion efficiency is, the higher the temperature of the exhaust gas discharged from the cylinder 1 to the exhaust passage 4, and the more the configuration changes. It is considered that the temperature of the member 41 increases. As shown in FIG. 4, the memory of the ECU 0 stores map data that defines the relationship between the ignition timing, etc. in the cylinder 1 of the internal combustion engine and the correction amount t _k added to the estimated temperature T _ij of the target component 41. Stored. The ECU 0 searches the map using the current ignition timing as a key, and learns the correction amount t _k to be added to the estimated temperature T _ij .

Therefore, the ECU 0 compares the estimated temperature (T _ij +t _k ) of the target component 41 with the allowable temperature in step S2, and if the former exceeds the latter, it corrects the increase in the fuel injection amount in step S3. It will be executed.

In step S3, based on the difference ΔT obtained by subtracting the allowable temperature from the estimated temperature of the component 41, a target air-fuel ratio of the air-fuel mixture is determined when performing an increase correction of the fuel injection amount. As shown in FIG. 5, the memory of the ECU 0 stores map data that defines the relationship between the difference ΔT between the estimated temperature of the component 41 and the allowable temperature and the target air-fuel ratio when performing increase correction of the fuel injection amount. is stored. The ECU0 searches the map using the current temperature difference ΔT as a key, and learns the target air-fuel ratio of the air-fuel mixture. Then, a fuel injection amount that achieves this target air-fuel ratio is calculated from the current intake air amount, and fuel is injected from the injector 11 into the cylinder 1.

A supplementary note regarding the target air-fuel ratio of the air-fuel mixture in step S3. The difference ΔT obtained by subtracting the allowable temperature from the current estimated temperature of the component 41 means the width by which the temperature of the component 41 should be lowered by the latent heat of the increased amount of injected fuel. In fact, the relationship between this temperature drop width ΔT and the target air-fuel ratio when executing the fuel injection amount increase correction is greatly influenced by the current operating range of the internal combustion engine (engine speed, engine load factor, etc.). do not have.

FIG. 6 shows that by changing the air-fuel ratio of the air-fuel mixture filled into the cylinder 1 from the normal target air-fuel ratio that does not involve an increase correction of the fuel injection amount, the temperature of the component 41 becomes lower than the normal target air-fuel ratio. This is an experimental finding of how it changes with temperature. The horizontal axis in FIG. 6 is the air-fuel ratio of the air-fuel mixture, and the vertical axis is the amount of change in temperature of the component 41. The amount of change in the temperature of the component 41 when the air-fuel ratio of the air-fuel mixture matches the normal target value is zero. The normal target air-fuel ratio is the stoichiometric air-fuel ratio or a value close to it, and is approximately 14.6 for a gasoline engine.

In FIG. 6, the solid line represents the amount of change in the temperature of the component 41 in the operating range where the engine speed is close to the lowest, and the broken line represents the amount of change in the temperature of the component 41 in the operating range where the engine speed is somewhat higher than that. The one-dot chain line represents the amount of change in the temperature of the component 41 in the operating range where the engine speed is high, and the two-dot chain line represents the amount of change in the temperature of the component 41 in the operating range where the engine speed is close to the maximum. It represents the amount of change. The deviation between the solid line and the two-dot chain line along the vertical axis direction is only about 10° C. to 20° C. at most. This suggests that the relationship between the difference ΔT and the target air-fuel ratio can be uniformly applied to a wide range of operating regions. In other words, by creating map data as exemplified in FIG. 5 through adaptation, it is possible to determine the increment of the fuel injection amount when the temperature of the component 41 exceeds the allowable temperature.

Moreover, the map data illustrated in FIG. 5 can be used as is even if the allowable temperature of the component 41 is changed. As a result of changing the allowable temperature, the difference ΔT expands or contracts, and the target air-fuel ratio corresponding to the difference ΔT changes. As a result, the fuel injection amount in step S3 increases or decreases.

In this embodiment, when the temperature of a member 41 constituting the exhaust system of an internal combustion engine exceeds an allowable temperature, correction control is performed to increase the fuel injection amount and encourage a decrease in the temperature of the member 41 compared to a case where this is not the case. A control device 0 for an internal combustion engine is configured to determine a target air-fuel ratio when performing the correction control based on the difference ΔT between the current temperature of the member 41 and the allowable temperature.

According to this embodiment, the increment in the fuel injection amount during correction control can be more easily determined, which can contribute to reducing the number of development steps. Furthermore, even if the allowable temperature of the component 41 fluctuates due to aging deterioration or the like, the control device 0 can cope with it.

Note that the present invention is not limited to the embodiments detailed above. In particular, the component to be protected is not limited to the exhaust purification catalyst 41. The target components may include the manifold 42 and other exhaust pipes through which exhaust gas flows, which are upstream or downstream of the catalyst 41, the air-fuel ratio sensors 43 and 44, and the like.

Further, in the embodiment described above, the current temperature of the target component 41 is estimated based on the current operating range of the internal combustion engine, etc. However, this does not prevent the current temperature of the component 41 from being directly detected and measured via the sensor.

In addition, the specific configuration of each part can be variously modified without departing from the spirit of the present invention.

INDUSTRIAL APPLICATION This invention is applicable to the control of the internal combustion engine mounted in a vehicle etc.

0...Control unit (ECU)
1...Cylinder 11...Injector 12...Spark plug 4...Exhaust passage 41...Exhaust system component (catalyst)
b...Crank angle signal c...Accelerator opening signal i...Ignition signal j...Fuel injection signal

Claims (2)

When the temperature of a member constituting the exhaust system of an internal combustion engine exceeds a permissible temperature, a correction control is performed to increase the amount of fuel injection and promote a temperature drop of the member compared to a case where this is not the case.
map data defining a relationship between a difference between the current temperature of the member and an allowable temperature and a target air-fuel ratio when performing the correction control is stored in a memory;
A control device for an internal combustion engine that searches the map using the current temperature of the member as a key, learns a target air-fuel ratio when implementing the correction control, and determines a fuel injection amount. map data defining a relationship between an operating range of the internal combustion engine and a current estimated temperature of the member is stored in the memory;
Searching the map using the current operating range of the internal combustion engine as a key and obtaining the current estimated temperature of the member,
map data defining a relationship between ignition timing in a cylinder of the internal combustion engine and a correction amount to be added to the current estimated temperature of the member is stored in the memory;
Control of an internal combustion engine according to claim 1, wherein the map is searched using the current ignition timing as a key, and a correction amount to be added to the current estimated temperature of the member is acquired to correct the current estimated temperature of the member. Device.

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