JP2004251193A - Fuel system controlling equipment of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the compliance of actual fuel pressure for a target fuel pressure at the time of fuel cut recovery in controlling the discharging amount of a high-pressure fuel pump 6 so as to obtain the target fuel pressure set up in accordance with an operating condition by detecting the fuel pressure inside the fuel accumulator 10, in a fuel control system provided with a fuel accumulator (high-pressure piping) 10 for storing high-pressure fuel from the high-pressure fuel pump 6 and a fuel injection valve 12 in which the high-pressure fuel in the fuel accumulator 10 is led. <P>SOLUTION: Part (10b) of the fuel accumulator 10 is blocked, and a solenoid valve 16 capable of reducing the volume of the fuel accumulator 10 (10a) is provided. At the time of the fuel cut recovery, the volume of the fuel accumulator room 10 (10a) is reduced by temporarily closing the electric valve 16. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel system control device for an internal combustion engine.
[0002]
[Prior art]
The in-cylinder direct injection type internal combustion engine includes a fuel accumulator 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 accumulator 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 (the number of revolutions and the load).
[0003]
On the other hand, in the current internal combustion engine, as one of the controls for improving the fuel efficiency, generally, a deceleration fuel cut control for performing a fuel cut when the vehicle is decelerated from a high rotation speed is adopted. In an internal combustion engine that performs control to the target fuel pressure, 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 in which the discharge amount of the high-pressure fuel pump is controlled and the fuel pressure of the high-pressure system is controlled based on the flow balance with the fuel injection amount, the fuel injection amount becomes zero during the fuel cut. Is stopped, the fuel pressure does not decrease and is maintained at the fuel pressure at the time of fuel cut-in.
[0005]
Therefore, immediately after the fuel cut recovery, there is a deviation of the actual fuel pressure from the target fuel pressure. If the deviation is large, the time until the actual fuel pressure reaches the target fuel pressure becomes longer, and during that time, the combustion stability is reduced. It worsens and exhaust and driving performance deteriorate.
[0006]
For this reason, in Patent Document 1, after the fuel cut request condition is satisfied, the start of the fuel cut is delayed until the fuel pressure in the fuel accumulator reaches the target fuel pressure at the time of fuel cut recovery by fuel injection.
[0007]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2000-18067
[Problems to be solved by the invention]
However, if the start of the fuel cut is delayed, the fuel efficiency improvement effect cannot be obtained.
[0009]
In addition, if the fuel pressure is reduced until the fuel pressure reaches the target fuel pressure at the time of fuel cut recovery, the driver may depress the accelerator during the fuel cut delay time to cancel the fuel cut, or the driver may immediately cancel the fuel cut. When the recovery control is started by depressing the accelerator, the fuel pressure has become too low, and a deviation from the target fuel pressure also occurs.
[0010]
The present invention has been made in view of the above circumstances, and has as its object to provide a fuel system control device that can quickly perform fuel pressure control during fuel cut recovery without affecting fuel deceleration control during deceleration.
[0011]
[Means for Solving the Problems]
For this reason, the present invention has a configuration in which a capacity variable means capable of changing the capacity of the fuel accumulator is provided, and the capacity of the fuel accumulator is temporarily reduced during fuel cut recovery.
[0012]
【The invention's effect】
According to the present invention, even when a difference 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 is small, and the combustion can be improved. Stability can be improved.
[0013]
BEST MODE FOR CARRYING OUT 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 an in-cylinder direct injection internal combustion engine as one embodiment of the present invention.
[0014]
An electric low-pressure fuel pump 2 for pumping the fuel in the fuel tank 1 into the fuel tank 1, a fuel filter 3 for filtering the fuel on the discharge side thereof, and a discharge side pressure by returning excess 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 a high-pressure fuel pump 6 through a 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 a suction side thereof, and a check valve 9 provided on a discharge side.
[0016]
The plunger pump 7 performs a suction / discharge operation by reciprocating a plunger driven by a pump driving cam connected to an engine camshaft.
The electromagnetic control valve 8 is controlled by an engine control unit (ECU) 20 so as to open during the suction stroke of the plunger pump 7 and close 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, when the plunger is lowered, fuel is sucked through the electromagnetic control valve 8 on the suction side, and when the plunger is raised, the fuel is sucked through the check valve 9 on the discharge side after the electromagnetic control valve 8 is closed. Is discharged.
[0018]
The discharge side (the check valve 9 side) of the high-pressure fuel pump 6 is connected to a fuel accumulator (high-pressure pipe) 10.
The fuel pressure accumulating chamber 10 is connected with fuel injection valves 12 for the number of cylinders via branch pipes 11 branching therefrom, and these fuel injection valves 12 face the combustion chambers of the respective cylinders of the engine (not shown).
[0019]
Further, a fuel pressure sensor 13 for detecting the fuel pressure in the pressure accumulating chamber 10 is attached to the fuel accumulating chamber 10, and its signal is input to the ECU 20.
Further, a relief valve 14 is attached to an end of the fuel accumulator 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 accumulator 10 rises excessively.
[0020]
Here, in order to control the fuel pressure injected from the fuel injection valve 11, the fuel pressure in the fuel storage chamber 10 is controlled. The fuel pressure controls the closing timing of the electromagnetic control valve 8 based on 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 according to operating conditions (engine speed and load), for example, as shown in FIG.
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 balance is balanced, and the fuel pressure is kept constant. When increasing the fuel pressure, the discharge amount of the high-pressure fuel pump is temporarily increased, and the discharge amount is controlled so that the flow balance returns to 1: 1 when the target fuel pressure is reached. The opposite is true when lowering the fuel pressure.
[0022]
That is, in the present fuel system, since the fuel pressure is controlled by the flow 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. When the actual fuel pressure (fuel pressure sensor output) is lower than the target fuel pressure, the discharge amount of the high-pressure fuel pump is increased and the fuel pressure is guided until the target fuel pressure is reached, and when the actual fuel pressure is higher than the target fuel pressure, the reverse is true. Become.
[0023]
Accordingly, the ECU 20 calculates the discharge amount of the high-pressure fuel pump from the target fuel pressure and the fuel injection amount based on the target fuel pressure set according to the operating conditions, and determines the closing timing of the electromagnetic control valve 8 based on this. The control is performed with reference to a crank angle sensor signal (engine speed) and a cylinder discrimination sensor signal (pump drive cam phase angle).
[0024]
By the way, in the current engine, as one of the controls for improving the fuel economy, generally, a deceleration fuel cut control for performing a fuel cut when the vehicle is decelerated from a high speed is adopted.
[0025]
In this case, as shown in FIG. 2, in the engine in which the target fuel pressure is set according to the operating conditions, 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 are cases.
[0026]
However, in a system in which the discharge amount of the high-pressure fuel pump 6 is variably controlled in accordance with the fuel injection amount of the fuel injection valve 11 to control the fuel pressure of the high-pressure system, the fuel injection amount becomes zero during fuel cut. By keeping the electromagnetic control valve 8 in the open state, even if the operation of the high-pressure fuel pump 6 is stopped, the fuel pressure in the fuel accumulator (high-pressure pipe) 10 does not decrease, and remains at the fuel pressure at the time of fuel cut-in. Will be retained.
[0027]
Therefore, as shown in FIG. 3, immediately after the fuel cut recovery, a deviation of the actual fuel pressure from the target fuel pressure may occur.
In addition, in the present system, in order to reduce the fuel injection amount variation, it is generally necessary to suppress the fuel pressure pulsation by increasing the capacity of the fuel accumulator 10 or the like. There is a problem that the response speed of control is reduced. This is because the amount of fuel required to change the fuel pressure in the fuel accumulator 10 by an arbitrary fuel pressure width increases, and a larger pump discharge amount (during pressure increase) and a fuel injection amount (during pressure reduction) are required. It is.
[0028]
In particular, when the actual fuel pressure greatly deviates from the target fuel pressure, such as immediately after the fuel cut recovery described above, the time required for the actual fuel pressure to reach the target fuel pressure becomes longer, and during that time, the combustion stability deteriorates and the exhaust And driving performance is deteriorated.
[0029]
Therefore, in the present invention, a capacity variable means capable of changing the capacity of the fuel accumulator (high-pressure pipe) 10 is provided, and the capacity of the fuel accumulator 10 is temporarily reduced during fuel cut recovery.
[0030]
Specifically, as shown in FIG. 1, the fuel pressure accumulating chamber (high-pressure pipe) 10 is divided into a chamber 10a on the side of the fuel injection valve 11 and a chamber 10b on the end side, and the fuel accumulating chamber (the high-pressure pipe) is always located between the two. An open solenoid valve 16 is provided so that communication and cutoff can be controlled. The opening and closing of the solenoid valve 16 is performed by the ECU 20.
[0031]
Specific control is shown in the flowchart of FIG.
In S1, the engine operation state is monitored, and it is determined whether or not the deceleration-time fuel cut request condition is satisfied. If the condition is satisfied, the process proceeds to S2. The deceleration-time fuel cut request condition is satisfied, for example, when the engine speed is equal to or higher than a predetermined fuel cut speed and the accelerator opening becomes zero.
[0032]
In S2, the fuel injection is stopped for the fuel cut during deceleration, and at the same time, the operation of the high-pressure fuel pump is stopped (the electromagnetic control valve 8 is kept open) and the fuel pressure feedback control is stopped. Thus, the fuel pressure in the fuel accumulator (high-pressure pipe) is maintained at the fuel pressure at the start of the 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 the fuel cut is stored in the ECU.
In S4, the engine operation state is monitored, and it is determined whether or not the fuel cut recovery request condition is satisfied. If the condition is satisfied, the process proceeds to S5. It is assumed that the fuel cut recovery requirement condition is satisfied after the start of the fuel cut, for example, when the engine speed falls below a predetermined fuel cut recover 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 in FIG. 2, and the target fuel pressure TPout = TPout at the time of fuel cut recovery is stored in the ECU.
[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 that is 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 storage 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 the responsiveness of the fuel pressure feedback control is not a problem. ), Proceeding to S12, restarting the fuel injection for fuel cut recovery, and at the same time, restarting the operation of the high pressure fuel pump and the fuel pressure feedback control and ending the processing.
[0037]
If | Pin-TPout |> Pw1, it is determined that the difference between the target fuel pressure and the actual fuel pressure is large, and the routine proceeds to S7.
In S7, in order to improve the responsiveness of the fuel pressure feedback control, the solenoid valve 16 is turned on to close the valve, and the capacity of the fuel accumulator 10 is reduced. That is, the responsiveness of the fuel pressure feedback control is improved by setting the fuel pressure accumulating chamber 10 connected to the high-pressure fuel pump 6 and the fuel injection valve 12 to only the portion 10a and cutting off the portion 10b.
[0038]
Thereafter, in S8, the fuel injection is restarted and the high-pressure fuel pump operation and the fuel pressure feedback control are restarted at the same time for fuel cut recovery.
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 in FIG. It is determined whether the deviation (| P-TP |) between P and the target fuel pressure TP has become smaller than a predetermined fuel pressure deviation Pw2. Pw2 is a ROM value determined in advance for determining whether the actual fuel pressure has been stabilized by feedback control.
[0039]
If | P−TP | <Tw2, the control for reducing the capacity of the fuel accumulator by the solenoid valve 16 is terminated. However, if the solenoid valve 16 is immediately turned OFF (fully opened), the fuel pressure at the time of fuel cut-in is maintained. Since the held chamber 10b on the side other than the fuel injection valve 11 side is opened, the inside of the high-pressure pipe before and after the solenoid valve 16 is averaged at a stretch, and a fuel pressure step is generated, and the actual fuel pressure becomes lower than the target fuel pressure. Misalignment 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, and the exhaust and drivability may be deteriorated.
[0040]
Then, in order to reduce this fuel pressure change as much as possible, first, at S10, the electromagnetic valve 16 is opened and closed intermittently for a predetermined time. That is, the sequence is repeated from 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 electromagnetic valve 16 is turned off (fully opened), and all the processes are terminated.
As described above, according to the present embodiment, the capacity variable means (electromagnetic valve 16) capable of changing the capacity of the fuel pressure accumulating chamber (high-pressure pipe) 10 is provided, and the fuel pressure accumulating chamber is temporarily The response speed of the fuel pressure feedback control is increased by reducing the capacity of the fuel pressure feedback control by reducing the capacity of the fuel pressure storage chamber 10 even when a difference between the target fuel pressure and the actual fuel pressure occurs during the fuel cut recovery. And the 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, the capacity of the fuel pressure accumulating chamber is reduced, thereby eliminating the capacity reduction control. Since no control is performed under such conditions, the durability of the system is improved.
[0043]
Further, according to the present embodiment, by reducing the capacity of the fuel accumulator chamber prior to the fuel cut recovery, the volume of the fuel accumulator chamber can be reliably reduced before the fuel cut recovery, and the fuel pressure feedback can be performed immediately after the fuel cut recovery. Control responsiveness can be reliably improved. In this case, in order to further improve the certainty, the solenoid valve 16 is turned on during the fuel cut, for example, immediately after the start of the fuel cut as shown by a dotted line in FIG. 5 to reduce the capacity of the fuel accumulator. It may be. However, if there is no problem in the operation delay of the capacity reduction control, the capacity of the fuel accumulator may be reduced immediately after the start of the fuel cut.
[0044]
Further, according to the present embodiment, by using the electromagnetic valve 16 capable of shutting off a part of the fuel pressure accumulating chamber 10 as the variable capacity means, it is possible to realize the comparatively simple configuration. Further, according to the present embodiment, when the capacity of the fuel accumulator is reduced and then restored, the solenoid valve 16 is opened and closed intermittently to average the fuel pressure before and after the solenoid valve 16 stepwise. Thus, the occurrence of the fuel pressure step can be suppressed, and the 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 map for setting a target fuel pressure. FIG. 3 is a fuel pressure during fuel cut-in to fuel cut recovery. Behavior explanatory diagram [Fig. 4] Control flowchart [Fig. 5] Control time chart [Explanation of symbols]
Reference Signs List 1 fuel tank 2 low-pressure fuel pump 6 high-pressure fuel pump 10, 10a, 10b fuel accumulator (high-pressure pipe)
12 fuel injection valve 13 fuel pressure sensor 14 relief valve 16 solenoid valve 20 ECU

Claims (5)

A fuel accumulator for storing high-pressure fuel from a high-pressure fuel pump, a fuel injection valve for injecting high-pressure fuel guided from the fuel accumulator into the engine, and a fuel pressure in the fuel accumulator which are set according to engine operating conditions. Fuel pressure feedback control means for controlling the discharge amount of the high pressure fuel pump so that the target fuel pressure is
In a fuel system control device for an internal combustion engine including deceleration-time fuel cut means for stopping fuel injection of a fuel injection valve at the time of engine deceleration and performing fuel cut,
A fuel system control device for an internal combustion engine, characterized in that a capacity variable means capable of changing the capacity of the fuel accumulator is provided, and the capacity of the fuel accumulator is temporarily reduced during fuel cut recovery. 2. The fuel system control for an internal combustion engine according to claim 1, wherein 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 more than a predetermined value, the capacity of the fuel accumulator is reduced. apparatus. 3. The fuel system control device for an internal combustion engine according to claim 1, wherein the capacity of the fuel pressure accumulating chamber is reduced prior to the fuel cut recovery. The fuel system control device for an internal combustion engine according to any one of claims 1 to 3, wherein the capacity variable means is an electromagnetic valve capable of shutting off a part of the fuel pressure accumulation chamber. 5. The fuel system control device for an internal combustion engine according to claim 4, wherein when the capacity of the fuel accumulator is reduced after the capacity is reduced, the solenoid valve is opened and closed intermittently.

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