JP4019969B2 - Fuel system control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel system control device for an internal combustion engine.
[0002]
[Prior art]
An in-cylinder direct injection internal combustion engine includes a fuel pressure accumulation chamber that stores high-pressure fuel from a high-pressure fuel pump, and a fuel injection valve that injects high-pressure fuel guided from the fuel pressure accumulation chamber into the engine. The discharge amount of the high-pressure fuel pump is controlled so that the target fuel pressure is set according to the engine operating conditions (rotation speed and load).
[0003]
On the other hand, in current internal combustion engines, as one of the controls aimed at improving fuel efficiency, generally, fuel cut control during deceleration that performs fuel cut when the vehicle decelerates from a high speed is adopted. In an internal combustion engine that performs control, the target fuel pressure at the start of fuel cut (at the time of fuel cut-in) may be different from the target fuel pressure at the time of fuel cut recovery.
[0004]
However, in a system that controls the high-pressure fuel pressure by controlling the discharge amount of the high-pressure fuel pump and the flow rate balance with the fuel injection amount, the fuel injection amount becomes zero during fuel cut, so the operation of the high-pressure fuel pump Even if the operation is stopped, the fuel pressure does not decrease, and the fuel pressure at the time of fuel cut-in is maintained.
[0005]
For this reason, immediately after the fuel cut is recovered, a deviation of the actual fuel pressure occurs with respect to the target fuel pressure.If this deviation is large, the time until the actual fuel pressure reaches the target fuel pressure becomes longer. It deteriorates and exhaust and drivability deteriorate.
[0006]
For this reason, in Patent Document 1, after the fuel cut requirement condition is satisfied, the start of fuel cut is delayed until the fuel pressure in the fuel pressure accumulation chamber reaches the target fuel pressure at the time of fuel cut recovery by fuel injection.
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-18067
[Problems to be solved by the invention]
However, if the start of fuel cut is delayed, the fuel efficiency improvement effect cannot be obtained accordingly.
[0009]
In addition, if the fuel pressure is reduced in advance until the target fuel pressure at the time of fuel cut recovery is reached, the driver depresses the accelerator during the fuel cut delay time to cancel the fuel cut or immediately after the fuel cut starts. When the accelerator is depressed to enter the recovery control, the fuel pressure has become too low, resulting in a deviation from the target fuel pressure.
[0010]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fuel system control device capable of quickly performing fuel pressure control during fuel cut recovery without affecting fuel cut control during deceleration.
[0011]
[Means for Solving the Problems]
For this reason, the present invention provides a capacity variable means capable of changing the capacity of the fuel pressure accumulating chamber, and according to the determination result of the means for determining whether or not the fuel cut recovery request condition is satisfied after the fuel cut starts, the fuel cut recovery request When the condition is satisfied, the capacity of the fuel pressure accumulation chamber is reduced before the fuel cut recovery and before the fuel cut recovery .
[0012]
【The invention's effect】
According to the present invention, even when a deviation between the target fuel pressure and the actual fuel pressure occurs at the time of fuel cut recovery, the response speed of the fuel pressure feedback control can be increased because the capacity of the fuel accumulator chamber is reduced, and the combustion Stability can be improved.
In addition, by reducing the capacity of the fuel pressure storage chamber prior to fuel cut recovery, the volume of the fuel pressure storage chamber can be reliably reduced by the time of fuel cut recovery, and the responsiveness of fuel pressure feedback control is ensured immediately after fuel cut recovery. Can be improved.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows the configuration of a fuel system of a direct injection type internal combustion engine as an embodiment of the present invention.
[0014]
An electric low-pressure fuel pump 2 that pumps the fuel in the fuel tank 1 into the fuel tank 1, a fuel filter 3 that filters the fuel on its discharge side, and a discharge-side pressure that returns surplus fuel to the fuel tank 1. And a low pressure regulator 4 for adjusting the pressure to a constant pressure (usually about 0.3 to 0.5 MPa).
[0015]
The fuel pumped by the low pressure fuel pump 2 is supplied to the high pressure fuel pump 6 through the low pressure fuel passage (low pressure pipe) 5.
The high-pressure fuel pump 6 includes a plunger pump 7, an electromagnetic control valve 8 provided on the suction side thereof, and a check valve 9 provided on the discharge side.
[0016]
The plunger pump 7 performs a suction / discharge operation by a reciprocating motion of a plunger driven by a pump drive cam connected to an engine cam shaft.
The electromagnetic control valve 8 is controlled by an engine control unit (ECU) 20 so that it opens during the intake stroke of the plunger pump 7 and closes during the discharge stroke. The discharge amount of the fuel pump 6 (plunger pump 7) can be controlled.
[0017]
Therefore, in the high-pressure fuel pump 6, fuel is sucked in via the suction-side electromagnetic control valve 8 when the plunger is lowered, and when the plunger is raised, the fuel is drawn via the discharge-side check valve 9 after the electromagnetic control valve 8 is closed. Is discharged.
[0018]
The discharge side (check valve 9 side) of the high-pressure fuel pump 6 is connected to a fuel accumulator chamber (high-pressure pipe) 10.
The fuel pressure accumulating chamber 10 is connected to the fuel injection valves 12 corresponding to the number of cylinders via the branch pipes 11 branched from now on, and these fuel injection valves 12 face the combustion chambers of the respective cylinders of the engine (not shown).
[0019]
In addition, a fuel pressure sensor 13 for detecting the fuel pressure in the pressure accumulation chamber 10 is attached to the fuel pressure accumulation chamber 10, and a signal thereof is input to the ECU 20.
Furthermore, a relief valve 14 is mounted at the end of the fuel pressure accumulating chamber 10, and is connected to a return pipe 15 to the fuel tank 1 via the relief valve 14. The relief valve 14 is opened to release the pressure when the fuel pressure in the fuel pressure accumulation chamber 10 increases excessively.
[0020]
Here, in order to control the fuel pressure injected from the fuel injection valve 11, the fuel pressure in the fuel pressure accumulation chamber 10 is controlled. This fuel pressure controls the closing timing of the electromagnetic control valve 8 by a signal from the ECU 20. By controlling the discharge amount of the high-pressure fuel pump 6, feedback control is performed to an arbitrary target fuel pressure (usually about 3 to 15 MPa).
[0021]
The target fuel pressure is set, for example, as shown in FIG. 2 according to the operating conditions (engine speed and load).
The fuel pressure is controlled by variably adjusting the discharge amount of the high-pressure fuel pump with respect to the actual fuel injection amount calculated from the target fuel pressure and the required injection pulse width. When the high-pressure fuel pump discharge amount and the fuel injection amount are 1: 1, the flow rate balance is balanced and the fuel pressure is kept constant. When increasing the fuel pressure, the discharge amount is controlled so as to temporarily increase the discharge amount of the high-pressure fuel pump and return the flow rate balance to 1: 1 when the target fuel pressure is reached. The opposite is true when lowering fuel pressure.
[0022]
That is, in this fuel system, since the fuel pressure is controlled by the flow rate balance between the high pressure fuel pump discharge amount and the fuel injection amount, the control factor of the fuel pressure control is the high pressure fuel pump discharge amount. If the actual fuel pressure (fuel pressure sensor output) is lower than the target fuel pressure, increase the discharge amount of the high-pressure fuel pump to increase the fuel pressure until it reaches the target fuel pressure, and vice versa if the actual fuel pressure is higher than the target fuel pressure. Become.
[0023]
Therefore, the ECU 20 calculates the high-pressure fuel pump discharge amount from the target fuel pressure and the fuel injection amount based on the target fuel pressure set according to the operating conditions, and based on this, the valve closing timing of the electromagnetic control valve 8 is set. The control is performed with reference to the crank angle sensor signal (engine speed) and the cylinder discrimination sensor signal (pump drive cam phase angle).
[0024]
By the way, in the current engine, as one of the controls aimed at improving the fuel efficiency, the fuel cut control at the time of deceleration is generally adopted in which the fuel is cut when the vehicle is decelerated from the high speed.
[0025]
In this case, as shown in FIG. 2, in the engine in which the target fuel pressure is set according to the operating condition, the target fuel pressure at the start of fuel cut (at the time of fuel cut-in) is different from the target fuel pressure at the time of fuel cut recovery. There is a case.
[0026]
However, in a system that controls the high-pressure fuel pressure by variably controlling the discharge amount of the high-pressure fuel pump 6 in accordance with the fuel injection amount of the fuel injection valve 11, the fuel injection amount becomes 0 during fuel cut. Even if the operation of the high-pressure fuel pump 6 is stopped by holding the electromagnetic control valve 8 in the open state, the fuel pressure in the fuel accumulator chamber (high-pressure pipe) 10 does not drop, but remains at the fuel pressure at the time of fuel cut-in. Retained.
[0027]
Therefore, as shown in FIG. 3, the actual fuel pressure may deviate from the target fuel pressure immediately after the fuel cut recovery.
Further, in this system, in order to reduce the variation in the fuel injection amount, it is generally necessary to suppress the fuel pressure pulsation by increasing the capacity of the fuel accumulator chamber 10 or the like, but if this capacity is increased, the fuel pressure feedback is reversed. There was a problem that the response speed of the control was reduced. This is because the amount of fuel required to change the fuel pressure in the fuel pressure accumulation chamber 10 by an arbitrary fuel pressure width increases, and a larger pump discharge amount (at the time of pressure increase) and fuel injection amount (at the time of pressure reduction) are required. It is.
[0028]
In particular, when the actual fuel pressure greatly deviates from the target fuel pressure, just after the fuel cut recovery described above, the time until the actual fuel pressure reaches the target fuel pressure becomes longer. And the drivability deteriorates.
[0029]
Accordingly, in the present invention, a capacity variable means capable of changing the capacity of the fuel pressure storage chamber (high pressure pipe) 10 is provided, and the capacity of the fuel pressure storage chamber 10 is temporarily reduced at the time of fuel cut recovery.
[0030]
Specifically, as shown in FIG. 1, the fuel accumulator chamber (high-pressure pipe) 10 is divided into a chamber 10a on the fuel injection valve 11 side and a chamber 10b on the end portion side. An open solenoid valve 16 is provided so that communication and shut-off can be controlled. The electromagnetic valve 16 is opened and closed by the ECU 20.
[0031]
Specific control is shown in the flowchart of FIG.
In S1, the engine operating state is monitored, and it is determined whether or not the fuel cut request condition during deceleration is satisfied. If satisfied, the process proceeds to S2. The deceleration fuel cut requirement condition is satisfied when, for example, the engine speed is equal to or higher than a predetermined fuel cut speed and the accelerator opening is zero.
[0032]
In S2, in order to cut fuel during deceleration, the fuel injection is stopped, and at the same time, the high-pressure fuel pump operation is stopped (the electromagnetic control valve 8 is kept open) and the fuel pressure feedback control is stopped. As a result, the fuel pressure in the fuel pressure storage chamber (high pressure pipe) is held at the fuel pressure at the start of fuel cut.
[0033]
In S3, the current fuel pressure P is read based on the output of the fuel pressure sensor 13, and the actual fuel pressure Pin = P at the start of fuel cut is stored in the ECU.
In S4, the engine operating state is monitored, and it is determined whether or not the fuel cut recovery request condition is satisfied. If satisfied, the process proceeds to S5. The fuel cut recovery requirement condition is satisfied after the fuel cut is started, for example, when the engine speed falls below a predetermined fuel cut recovery speed or when the accelerator is depressed.
[0034]
In S5, the target fuel pressure TP is read from the current operating conditions (engine speed and load) with reference to the map of FIG. 2, and the value is stored in the ECU as target fuel pressure TPout = TP at the time of fuel cut recovery.
[0035]
In S6, it is determined whether or not the difference (| Pin−TPout |) between the fuel pressure Pin at the start of fuel cut and the target fuel pressure TPout at the time of fuel cut recovery exceeds a predetermined fuel pressure deviation Pw1. Pw1 is a ROM value determined in advance based on the limit value of the fuel pressure deviation that does not deteriorate the combustion stability even when the capacity control of the fuel pressure accumulation chamber is not performed.
[0036]
When | Pin−TPout | ≦ Pw1, it is determined that the difference between the target fuel pressure and the actual fuel pressure is small, and there is no problem with the response of the fuel pressure feedback control. ), The process proceeds to S12, the fuel injection start is resumed for fuel cut recovery, and simultaneously the high pressure fuel pump operation and the fuel pressure feedback control are resumed, and the process is terminated.
[0037]
When | Pin−TPout |> Pw1, it is determined that the difference between the target fuel pressure and the actual fuel pressure is large, and the process proceeds to S7.
In S7, in order to improve the responsiveness of the fuel pressure feedback control, the solenoid valve 16 is turned on and closed to reduce the capacity of the fuel pressure accumulation chamber 10. That is, the fuel pressure accumulating chamber 10 connected to the high-pressure fuel pump 6 and the fuel injection valve 12 is only the 10a portion, and the responsiveness of the fuel pressure feedback control is improved by blocking the 10b portion.
[0038]
Thereafter, in S8, for fuel cut recovery, the fuel injection is resumed, and at the same time, the high-pressure fuel pump operation and the fuel pressure feedback control are resumed.
In S9, the current fuel pressure P is read based on the output of the fuel pressure sensor 13, and the target fuel pressure TP is read from the current operating conditions (engine speed and load) with reference to the map of FIG. It is determined whether or not the deviation (| P−TP |) between P and the target fuel pressure TP is smaller than a predetermined fuel pressure deviation Pw2. Pw2 is a predetermined ROM value for determining whether the actual fuel pressure is stabilized by feedback control.
[0039]
If | P-TP | <Tw2, the capacity reduction control of the fuel pressure accumulation chamber by the solenoid valve 16 is terminated. If the solenoid valve 16 is immediately turned OFF (fully opened), the fuel pressure at the time of fuel cut-in remains. Since the chamber 10b that is not on the fuel injection valve 11 side that has been held is opened, the inside of the high-pressure piping before and after the solenoid valve 16 is averaged at once, a fuel pressure step is generated, and the actual fuel pressure is compared with the target fuel pressure. Deviation occurs. Also in this case, as described above, the time until the actual fuel pressure reaches the target fuel pressure becomes longer, and the combustion stability may be deteriorated to deteriorate the exhaust and the drivability.
[0040]
In order to alleviate this change in fuel pressure as much as possible, first, in S10, the electromagnetic valve 16 is intermittently opened and closed for a predetermined time. That is, OFF → ON → OFF → ON... The number of cycles and the cycle are determined in advance by experiments or the like so that the fuel pressure gradually decreases.
[0041]
Thereafter, in S11, the solenoid valve 16 is turned off (fully opened), and all the processes are terminated.
As described above, according to the present embodiment, the variable capacity means (solenoid valve 16) that can change the capacity of the fuel pressure storage chamber (high pressure pipe) 10 is provided, and the fuel pressure storage chamber is temporarily used during fuel cut recovery. By reducing the capacity of 10, even when a deviation between the target fuel pressure and the actual fuel pressure occurs at the time of fuel cut recovery, the capacity of the fuel accumulator chamber 10 is reduced, so that the response speed of the fuel pressure feedback control is increased. Combustion stability can be improved (see FIG. 5).
[0042]
Further, according to the present embodiment, when the difference between the fuel pressure at the start of fuel cut and the target fuel pressure at the time of fuel cut recovery is equal to or greater than a predetermined value, capacity reduction control is not required by reducing the capacity of the fuel accumulator chamber. Since control is not performed under certain conditions, the durability of the system is improved.
[0043]
Further, according to the present embodiment, by reducing the capacity of the fuel pressure accumulating chamber prior to the fuel cut recovery, the volume of the fuel pressure accumulating chamber can be reliably reduced until the fuel cut recovering, and the fuel pressure feedback immediately after the fuel cut recovering. Control responsiveness can be reliably improved. In this case, in order to further improve the certainty, during the fuel cut, for example, immediately after the start of the fuel cut, as shown by the dotted line in FIG. 5, the solenoid valve 16 is turned on to reduce the capacity of the fuel accumulator chamber. It may be. However, if there is no problem with the operation delay of the capacity reduction control, the capacity of the fuel pressure accumulation chamber may be reduced immediately after the start of fuel cut.
[0044]
Further, according to the present embodiment, by using the electromagnetic valve 16 capable of shutting off a part of the fuel accumulating chamber 10 as the capacity varying means, it can be realized with a relatively simple configuration.
Further, according to the present embodiment, when the capacity is restored after the capacity of the fuel accumulator is reduced, the fuel pressure before and after the solenoid valve 16 is averaged stepwise by opening and closing the solenoid valve 16 intermittently. Thus, the occurrence of a fuel pressure step can be suppressed, and deterioration of combustion stability due to the fuel pressure step can be prevented (see FIG. 5).
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a fuel system of a direct injection type internal combustion engine showing an embodiment of the present invention. FIG. 2 is a diagram showing a target fuel pressure setting map. FIG. 3 is a fuel pressure during fuel cut-in to fuel cut recovery. Behavior diagram [Fig. 4] Control flow chart [Fig. 5] Control time chart [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fuel tank 2 Low pressure fuel pump 6 High pressure fuel pump 10, 10a, 10b Fuel pressure storage chamber (high pressure piping)
12 Fuel Injection Valve 13 Fuel Pressure Sensor 14 Relief Valve 16 Solenoid Valve 20 ECU

Claims (4)

A fuel pressure accumulation chamber that stores high-pressure fuel from the high-pressure fuel pump, a fuel injection valve that injects high-pressure fuel guided from the fuel pressure accumulation chamber into the engine, and the fuel pressure in the fuel pressure accumulation chamber are detected and set according to engine operating conditions A fuel pressure feedback control means for controlling the discharge amount of the high-pressure fuel pump so as to achieve a target fuel pressure,
In a fuel system control device for an internal combustion engine comprising a fuel cut means at the time of deceleration, which performs fuel cut by stopping fuel injection of the fuel injection valve at the time of engine deceleration,
A capacity variable means capable of changing the capacity of the fuel accumulator chamber is provided,
According to the determination result of the means for determining whether or not the fuel cut recovery requirement condition is satisfied after the fuel cut is started, the fuel is recovered before the fuel cut recovery and before the fuel cut recovery when the fuel cut recovery requirement condition is satisfied. A fuel system control device for an internal combustion engine, wherein the capacity of the pressure accumulating chamber is reduced. When the fuel cut recovery requirement condition is satisfied , if the difference between the fuel pressure at the start of fuel cut and the target fuel pressure at the time of fuel cut recovery is a predetermined value or more, the capacity of the fuel pressure accumulation chamber is reduced. The fuel system control device for an internal combustion engine according to claim 1. 3. The fuel system control device for an internal combustion engine according to claim 1 , wherein the capacity varying means is an electromagnetic valve capable of shutting off a part of the fuel accumulator chamber. 4. The fuel system control device for an internal combustion engine according to claim 3 , wherein when the capacity is restored after the capacity of the fuel accumulator is reduced, the solenoid valve is intermittently opened and closed.

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