JP2001003784A - Common rail type fuel injection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform injection of fuel in a target fuel injection amount by a method wherein a common rail pressure exceeding a target common rail pressure is reduced to a target common rail pressure before fuel injection. SOLUTION: This device is operated such that when, during interruption t1 after completion of a period in which fuel is discharged from a fuel supply pump, an actual common rail pressure Praint exceeds a target common rail pressure Prtint, a controller generates a trigger signal Tr to calculate a drive amount of a pressure leak means, such as a pressure leak valve, disposed on a common rail and calculates the command value Pwl of a command pulse signal Cleak to the pressure leak mean. By a command pulse signal Cleak outputted at a time t3, a common rail pressure Pr is reduced to a target value Prtint until it comes to the fall starting period t5 of a common rail pressure Pr accompanied by fuel injection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a common rail type fuel injection device which stores fuel supplied from a fuel supply pump under pressure in a common rail and injects fuel supplied from the common rail from an injector into a combustion chamber.

[0002]

2. Description of the Related Art Conventionally, for example, regarding a fuel injection control of an engine, a method of increasing an injection pressure and optimally controlling injection conditions such as a fuel injection timing and an injection amount in accordance with an operation state of the engine is known. A common rail fuel injection system is known. The common rail type fuel injection system stores a working fluid for fuel injection control pressurized to a predetermined pressure by a pump in a common rail in a pressure accumulated state, and operates injectors respectively arranged in each cylinder using the working fluid pressure. This is a system in which fuel is injected from an injector into a corresponding combustion chamber. The controller controls a control valve provided in each injector so that fuel is injected from each injector under optimal injection conditions for the operating state of the engine.

[0003] In the case of a fuel pressure operated common rail type fuel injection system using a working fluid as fuel, a fuel flow path from the common rail to an injection hole formed at the tip of each injector through a fuel supply pipe is always injected. A fuel pressure equivalent to the pressure is applied, and each injector includes a control valve for performing control to pass or shut off fuel supplied through a fuel supply pipe, and an actuator for driving the control valve. . The controller controls the pressure of the common rail and the operation of the actuator provided in each injector so that the pressurized fuel is injected in each injector under the optimum injection condition for the operating state of the engine. In addition, a common rail fuel injection system of a type that stores engine oil as a working fluid in a common rail and increases the pressure of a fuel supplied to a pressure increasing chamber in the injector to a predetermined pressure by an oil pressure supplied from the common rail to a pressure chamber of the injector. Has also been proposed.

A conventional fuel pressure operated type common rail fuel injection system will be described with reference to FIG. The fuel sucked from the fuel tank 7 by the feed pump 6 is sent to the fuel supply pump 1 through the filter 4. The fuel supply pump 1 is a plunger-type variable displacement high-pressure pump driven by an engine, and supplies high-pressure fuel to the common rail 2 through a fuel discharge path 14. In this example, the fuel supply pump 1 is a suction amount control type pump that controls the discharge amount by the suction amount. The amount of fuel suctioned from the feed pump 6 to the fuel supply pump 1 is controlled by a flow control valve 15 which is an electromagnetic valve disposed in the fuel suction passage 13. The flow rate sent through the flow control valve 15 is controlled by, for example, driving the actuator 16 to adjust the valve opening degree during the valve opening period or the pulse duty ratio. When the fuel pressure (feed pressure) in the fuel intake passage 13 exceeds the upper limit pressure limited by the relief valve 18, the relief valve 18 opens, and excess fuel is supplied to the fuel tank 7 through the return pipe 19.
Is returned to.

The fuel supply pump 1 includes a pump driving cam 10 driven by the output of the engine, and a plunger 11 which reciprocates in contact with the pump driving cam 10. The top surface of the plunger 11 is a pump chamber. Twelve wall surfaces are formed. Fuel suction passage 13 and pump chamber 12
A suction check valve 26, which is opened by the negative pressure of the pump chamber 12 and closed during the discharge stroke of the plunger 11, is provided at the connection portion with the suction valve. A discharge valve 17 that opens at a predetermined discharge pressure of the fuel supply pump 1 is provided in a fuel discharge path 14 that is connected from the fuel supply pump 1 to the common rail 2. The fuel supply pump 1 may be a pump having a single plunger as shown, but may be a rotary pump or a row pump having a plurality of plungers according to the type of engine. Further, the fuel supply pump 1 may be a pre-stroke control type pump that returns a part of the intake fuel amount to the intake side as the intake amount control type, in addition to the above-described type of pump, A pump of a discharge amount control type that returns a part of the discharge amount to the tank instead of the expression may be used.

The fuel stored in the common rail 2 in a pressure-accumulated state is supplied through a fuel supply pipe 23 constituting a part of a fuel flow path to injectors 3 provided for each cylinder in accordance with the type of engine. 3 is injected into the corresponding combustion chamber. The common rail 2 is opened when the common rail pressure becomes higher than a predetermined set pressure in order to prevent the common rail pressure from abnormally rising due to a system abnormality or the like, and the fuel in the common rail 2 is discharged to the fuel tank 7 through the discharge passage 21. A normally closed relief valve 20 for reducing the common rail pressure is provided. Further, the common rail pressure Pr detected by the pressure sensor 22 provided on the common rail 2 is determined by an electronic control module (EC
M).

The controller 8 has a common rail pressure P
In addition to r, detection signals are input from various sensors 9 as detection means such as an engine speed sensor for detecting the engine speed Ne and an accelerator pedal depression amount sensor for detecting the accelerator pedal depression amount Ac. In addition, signals from various sensors for detecting the operating state of the engine, such as a cooling water temperature sensor, an engine cylinder discrimination sensor, a top dead center detection sensor, an atmospheric temperature sensor, an atmospheric pressure sensor, and an intake pipe pressure sensor, are input to the controller 8. Is done.

[0008] The injector 3 is hermetically attached to a hole provided in a base (not shown) such as a cylinder head by a seal member. The injector 3 is provided with a needle valve 31 that can be lifted in the injector body. The injector body is formed at the tip of the nozzle and opens when the needle valve 31 is lifted to open the combustion chamber (not shown). ) And a balance chamber 3 described later.
0 is formed. The balance chamber 30 is formed by the inner wall surface of the hollow hole of the injector 3 and the top surface 33 of the needle valve 31. The high-pressure fuel in the common rail 2 branches off from the fuel supply pipe 23, and the first orifice 39 is provided. It is supplied to the balance chamber 30 through the supply path 38. The fuel supplied from the fuel passage 34 connected to the fuel supply pipe 23 fills a gap around the fuel supply reservoir 35 and the needle valve 31. A second orifice 41 is provided in a discharge path 40 connected to the balance chamber 30, and a second orifice 41 is provided.
The orifice 41 is set to be larger than the effective passage sectional area of the first orifice 39.

The lift of the needle valve 31 includes a lift force based on the fuel pressure acting on the first tapered surface 36 of the needle valve 31 facing the fuel reservoir 35, a depressing force based on the pressure action of the fuel in the balance chamber 30, and a return. It is controlled by the balance of the return force of the spring 47. Controller 8
When the electromagnetic solenoid 45 as an actuator is operated by the drive current from the controller to open the on-off valve 44 provided in the discharge passage 40, fuel is discharged through the discharge passage 40, but the first orifice 39 is in the second orifice 39. Orifice 4
Since the flow of fuel is more strongly restricted than one, the fuel pressure in the balance chamber 30 is reduced. The lift force acting on the needle valve 31 exceeds the combined force of the pressing force based on the fuel pressure in the balance chamber 30 and the return force of the return spring 47, the needle valve 31 lifts, and the fuel flows from the opened injection hole 32. It is injected into a combustion chamber (not shown). Fuel that has not been consumed for injection and has flowed out of the balance chamber 30 through the discharge path 40 is collected in the fuel tank 7 through the fuel return pipe 46. When the electromagnetic solenoid 45 is deactivated, the fuel pressure in the balance chamber 30 recovers, and the resultant force with the return force of the return spring 47 exceeds the lift force acting on the needle valve 31 and is formed at the tip of the needle valve 31. The second tapered surface 37 is seated on the tapered valve seat of the injector body, communication between the fuel reservoir 35 and the passage formed around the needle valve 31 and the injection hole 32 is closed, and the needle valve 31 is closed. .

The controller 8 controls the fuel injection based on the target fuel injection timing, fuel injection amount, and the like so that the engine output becomes an optimum output corresponding to the operating state of the engine detected by the detection signals from the various sensors 9. The condition is set, and the lift of the needle valve 31 is controlled by opening and closing the on-off valve 44 according to the fuel injection condition. The fuel injection timing and fuel injection amount from the injector 3 are determined by the injection pressure and the lift of the needle valve 31 (lift amount, lift period).
The drive current sent to the electromagnetic solenoid 45 to control the opening and closing of the on-off valve 44 is determined based on the command pulse output by the controller 8.

Since the injection pressure of the fuel injected from the injector 3 is substantially equal to the pressure of the fuel stored in the common rail 2, the required injection pressure obtained from the operating state of the engine can be obtained by controlling the common rail pressure. Can be When the injector 3 injects fuel and consumes the fuel in the common rail 2, the common rail pressure decreases. Therefore, it is necessary to restore the common rail pressure to a predetermined pressure for each injection. In addition, if the operating state of the engine is constant, a common rail is maintained so as to maintain a constant pressure corresponding to the state, and if the operating state of the engine is changed, the common rail is optimized according to the change. It is necessary to control the pressure in the increasing or decreasing direction. The controller 8 controls the common rail pressure by controlling the discharge flow rate (pressure feed amount) of the fuel supply pump 1. Therefore, in order to improve the performance of the entire common rail fuel injection system, it is necessary that the common rail pressure is accurately controlled.

A constant relationship between the target fuel injection amount and the engine rotation speed Ne is given in advance as a basic injection amount characteristic map using the accelerator pedal depression amount Ac as a parameter. It is obtained by calculation from the basic injection amount characteristic map according to the operating state. The target fuel injection amount is determined according to the operating state of the engine, the target common rail pressure is determined according to the target fuel injection amount and the engine speed, and the common rail pressure is controlled by the target common rail pressure and the pressure sensor 22. This is performed by performing feedback control of the pumping amount of the fuel supply pump 1 so as to eliminate a deviation from the detected actual common rail pressure, that is, to make the actual common rail pressure coincide with the target common rail pressure. The relationship between the fuel injection amount of the injector 3 and the pulse width of the command pulse output by the controller 8 is determined by a map using the common rail pressure Pr (fuel pressure in the common rail 2) as a parameter. Since fuel injection is started or stopped with a certain time delay from the falling time and rising time of the command pulse, it is possible to control the injection timing by controlling when the command pulse is turned on or off. It is. In the illustrated example, only one injector 3 is shown, but the engine is a multi-cylinder engine such as a four-cylinder or six-cylinder engine, and a controller 8 is provided for each injector 3 arranged corresponding to each cylinder. Perform fuel injection control.

By the way, even if the amount of pressure supplied by the fuel supply pump is adjusted so that the common rail pressure coincides with the target common rail pressure, the temperature of the fuel supply pump and the common rail pressure at that time change. It is extremely difficult to control the amount precisely. In addition, the common rail pressure is constantly fluctuating due to fuel injection from the injector and fuel pumping from the pump.The common rail pressure is detected in a time synchronization which is conventionally performed, and the fuel supply pump is controlled based on the detected common rail pressure. In the control for generating a feedback signal of the pumping amount and the drive current to the actuator provided in the injector, it is not possible to reduce the variation from the pump discharge each time to the fuel injection of the injector. In the case of the common rail type fuel injection system, no matter how precisely the control of the fuel injection amount from the injector or the fuel pumping amount from the fuel supply pump is performed,
Unless the variation of the common rail pressure is eliminated, the fuel injection amount cannot be made uniform. For example, as shown in FIG. 2B, the actual common rail pressure Plant at the end of the pump discharge period of the fuel supply pump 1 is equal to the target common rail pressure. It may exceed Prtint. In particular, in an operation state in which the engine rotates at a low speed such as idling, the variation in injection among the cylinders appears as variation in combustion, which causes uncomfortable vibration and noise.

When the common rail pressure is detected and the actual common rail pressure exceeds the target common rail pressure and the target fuel injection amount is zero, the deviation from the target common rail pressure is determined by utilizing the fuel leak during the non-injection period of the injector. Japanese Patent Application Laid-Open No. H11-50899 discloses a fuel injection control device for a pressure-accumulation engine in which the common rail pressure is reduced to make the common rail pressure equal to a target common rail pressure. That is, since the target fuel injection amount is zero, the needle valve is not lifted, so that fuel is not injected into the combustion chamber from the injection hole of the injector.
The common rail pressure is reduced by a fuel leak during a non-injection period caused by a dynamic leak from the balance chamber into which a part of the high-pressure fuel is introduced.

Further, in the fuel cut state, when the actual common rail pressure exceeds the target common rail pressure, the control valve driving means causes the time width shorter than the delay time until the start of fuel injection at the fuel injection valve, that is, If driving is continued further, the control valve is driven within the time interval until fuel injection starts, and high-pressure fuel in the accumulator pipe is continuously discharged to the low-pressure side of the injector fuel system, and a part of the fuel is discharged. Japanese Patent No. 2,636,39 discloses a fuel injection device that reduces high-pressure fuel in a pressure accumulation pipe by introducing the fuel into a low-pressure side of a system.
No. 4 discloses this. According to this fuel injection device, the control valve is driven with a time width shorter than the delay time leading to the start of fuel injection, so that the fuel is actually injected during the rapid deceleration operation without performing the fuel injection without stepping on the accelerator. Instead, the fuel pressure decreases due to fuel leakage during the non-injection period.

[0016]

SUMMARY OF THE INVENTION Japanese Patent Application Laid-Open No. H11-5089
No. 9 and Japanese Patent No. 2636394 discloses a fuel injection device for a pressure-accumulation engine, in which the target fuel injection amount is zero under the condition that fuel injection is not performed.
That is, the injector is driven within a shorter time period than the period during which fuel injection starts when the drive is continued, and the common rail pressure is reduced by dynamic leakage from a balance chamber provided in the injector.

As the actual operating state of the engine, the state with fuel injection occupies most of the engine operating state. Therefore, in the common rail type fuel injection device, when the common rail pressure constantly fluctuates and the common rail pressure exceeds the target common rail pressure, not only when the fuel injection amount is zero but also when the fuel injection is actually performed, the common rail pressure is not limited. Is reduced to the target common rail pressure, and the fuel injection is started. This solves the problem that the fuel injection can be performed at a predetermined common rail pressure according to the operating state of the engine, and the deterioration of fuel efficiency can be prevented. There are issues to be addressed.

[0018]

SUMMARY OF THE INVENTION An object of the present invention is to prevent a situation where the common rail pressure exceeds a predetermined target pressure determined from the operating state of the engine due to mechanical variations in the injectors or changes in the operating state of the engine. If this occurs, the common rail pressure is reduced to the target common rail pressure by leaking fuel from the fuel flow path where high-pressure fuel from the common rail to the injector is stored, and the target fuel from the injector according to the operating condition of the engine is reduced. An object of the present invention is to provide a common rail type fuel injection device that performs fuel injection at a predetermined common rail pressure so as not to inject more fuel than the injection amount and does not consume more fuel than necessary.

According to the present invention, there is provided a fuel supply pump for pumping fuel, a common rail for storing the fuel pumped by the fuel supply pump in an accumulated state, and a fuel provided for each cylinder of the engine and supplied from the common rail. Injector, a detecting means for detecting the operating state of the engine, a pressure sensor for detecting the pressure of the common rail, and a fuel injection condition to be injected from the injector and a target common rail pressure based on a detection signal from the detecting means. And feedback control of fuel pumping by the fuel supply pump so that the pressure of the common rail matches the target common rail pressure.Fuel injection from the injector is performed so that fuel is injected under the fuel injection condition. A controller for controlling the The roller responds to the fact that the pressure of the common rail after the end of the fuel pressure feeding by the fuel supply pump detected by the pressure sensor exceeds the target common rail pressure, and in response to the fuel flow from the common rail to the injector. The present invention relates to a common rail type fuel injection device which leaks stored high-pressure fuel through a pressure leak means to reduce the pressure of the common rail to the target common rail pressure before the start of fuel injection from the injector.

According to the common rail fuel injection device of the present invention, if the force of the common rail after the completion of the fuel supply from the fuel supply pump detected by the pressure sensor exceeds the target common rail pressure for each injector, the controller determines The high-pressure fuel stored in the fuel passage from the common rail to the injector leaks through the pressure leak means. Due to this fuel leak, the common rail pressure is reduced to the target common rail pressure before the fuel injection from the injector starts, that is, at the non-injection timing before the common rail pressure starts to decrease due to the fuel injection from the injector. . Therefore,
The fuel injection from the injector is performed in a state where the common rail pressure is reduced to the target common rail pressure, and the fuel injection amount from the injector does not exceed the target fuel injection amount according to the operating state of the engine.

The pressure leak means may be the fuel pressure operated injector described above. In this case, the injector is provided with an injector body formed with an injection hole for injecting fuel and a balance chamber for supplying and discharging a part of the high-pressure fuel from the common rail, and the injector body is liftably accommodated in the injector body. A needle valve that opens and closes the injection hole based on the pressure action of the fuel pressure in the balance chamber, and an actuator that controls supply and discharge of fuel to and from the balance chamber to control fuel pressure in the balance chamber. It is a fuel pressure operated injector provided. The controller operates the actuator to discharge fuel from the balance chamber, thereby leaking high-pressure fuel stored in the fuel flow path.

The pressure leak means is a pressure leak valve disposed on the common rail, and the controller operates the pressure leak valve to leak high-pressure fuel stored in the fuel flow path. The fuel stored in the common rail in a state of pressure accumulation is discharged.

In response to the completion of the fuel supply from the fuel supply pump to the common rail, the controller responds to the control of the fuel injection from the injector by controlling the pressure of the common rail detected by the pressure sensor. Interrupt processing for comparing with the target common rail pressure is performed. It is considered that the common rail pressure becomes the highest at the end of the fuel supply from the fuel supply pump to the common rail. At this time, the controller compares whether or not the common rail pressure detected by the pressure sensor exceeds the target common rail pressure with respect to the main processing for executing the fuel injection such as determining the output timing and the pulse width of the command pulse. Interrupt processing.

The controller calculates a fuel leak amount to be leaked from the fuel fuel flow path based on a pressure difference between the pressure of the common rail and the target common rail pressure after the end of the fuel supply by the fuel supply pump. . As one means of calculating the fuel leak amount,
The controller calculates the fuel leak amount based on the pressure deviation from a map created and stored in advance by an experiment. Further, as another means, when the controller sets the volume of the fuel flow path to V, the bulk modulus of the fuel to E, and the pressure deviation to ΔPrint,
The fuel leak amount Qleak is calculated by the following equation. Qleak = V / E × ΔPrint

Fuel temperature is an important factor in changing the value of fuel viscosity. Therefore, in the calculation of the fuel leak amount, the controller performs a fuel temperature correction that increases the fuel leak amount as the fuel temperature increases. Further, in the calculation of the operation period for operating the pressure leak unit, the controller performs a fuel temperature correction to shorten the operation period as the fuel temperature increases.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a common rail fuel injection device according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a common rail fuel injection system to which an embodiment of a common rail fuel injection device according to the present invention is applied. FIG. 2 is an injector and a pressure leak valve in the common rail fuel injection device shown in FIG. 6 is a time chart showing a change over time in a command signal for and with respect to a common rail pressure. The system shown in FIG. 8 can be adopted as the common rail fuel injection system to which the common rail fuel injection device is applied. Therefore, a repeated description of the common rail fuel injection system to which the common rail fuel injection device according to the present invention is applied will be omitted.

In the common rail fuel injection system shown in FIG. 1, the pressure leak means is a pressure leak valve 24 provided on the common rail 2 instead of the pressure relief valve 20 in the common rail fuel injection system shown in FIG.
It is. The pressure leak valve 24 includes an actuator 25. The actuator 25 is actuated by a control signal from the controller 8 so that the pressure leak valve 24
Is controlled, the amount of fuel leaking high-pressure fuel from the common rail 2 is controlled in accordance with the period during which the valve is open or the degree of opening, and the common rail pressure is reduced in accordance with the amount of fuel leak. The fuel leaked from the pressure leak valve 24 is slightly returned to the fuel tank 7 through the discharge passage 21.

According to the timing chart shown in FIG.
At time t ₀ , fuel discharge from the fuel supply pump 1 is started, and the common rail pressure Pr starts to increase. At time t ₁ during the fuel discharge period from the fuel supply pump 1, the actual common rail pressure Pra exceeds the target common rail pressure Pr calculated from the operating state of the engine at time t ₂ , which is the timing after the end of the subsequent fuel discharge period. , And the actual common rail pressure Pra is maintained at that pressure. At the timing (time t ₂ ) after the end of fuel discharge from the fuel supply pump 1, a trigger signal Tr is generated inside the CPU, and an interrupt is made to a main process (to be described later) which is always performed. The actual common rail pressure at the time of the interruption is Praint, and the target common rail pressure is Prtint.

As shown in FIG. 2, the actual common rail pressure P
When the train exceeds the target common rail pressure Print, the pressure reduction control of the common rail pressure Pr is performed. The controller 8 instantaneously calculates the command value to the pressure leak valve 24, that is, the pulse width Pwl required to reduce the pressure deviation ΔPrint between the actual common rail pressure Prain and the target common rail pressure Prtint. to operate, and outputs the command pulse Cleak having a pulse width Pwl at time t _3.
Since high-pressure fuel is leaked from the common rail 2 through the pressure leak valve 24 in an open state, a command pulse to the injector 3 is preferably supplied during a non-injection period until the common rail pressure Pr decreases with actual fuel injection. C
by the time t ₄ when inj is output, the common rail pressure Pr is reduced to a target common rail pressure Prtint. The output timing (time t ₄ ) and the pulse width Pwi of the command pulse Cinj to the injector 3 are set according to the operating state of the engine, and the common rail pressure Pr
Starts decreases with the time t ₄ to the fuel consumption by injection at time t ₅ of time delay. Therefore, the execution of the fuel injection is started at the common rail pressure Pr reduced to the target common rail pressure Prtint.

FIG. 3 is a flowchart showing the main processing of the fuel injection from the injector and the common rail pressure control in the common rail type fuel injection system according to the present invention. FIG. 4 is a flowchart showing the main processing shown in FIG. It is a flowchart which shows a lowering process. The main process of controlling the common rail pressure and the fuel pumping amount in the common rail fuel injection device will be described with reference to the flowchart shown in FIG. In the main process, first, an engine rotation speed Ne is calculated as one of the operating states of the engine based on a detection signal from a sensor that detects a pulse signal generated with rotation of the crankshaft, for example (step 1). . Based on a detection signal from a sensor disposed on the accelerator pedal, an accelerator operation amount Ac such as an accelerator pedal depression amount representing an engine load as one of the operating states of the engine is calculated (step 2). Basic fuel injection amount Qib to be injected from injector 3 and fuel injection timing (injection start timing and injection period) in accordance with the detected operating state of the engine
Is calculated (steps 3 and 4). An actual common rail pressure Pra of the common rail 2 is calculated based on a detection signal from the pressure sensor 22 disposed on the common rail (Step 5). A target common rail pressure Prt required to inject the basic fuel injection amount Qib obtained in Step 3 in the fuel injection period obtained in Step 4 is calculated (Step 6). The common rail pressure Pr is controlled by controlling the amount of fuel discharged from the fuel supply pump 1 so that the actual common rail pressure Pra calculated in step 5 matches the target common rail pressure Prt calculated in step 6. (Step 7).

After the fuel discharge from the fuel supply pump 1 is completed, the controller 8 issues a command pulse to the injector 3 in order to execute the fuel injection from the injector 3 which comes in a predetermined order according to the order of the fuel injection. The interrupt processing for the main processing is executed at the timing until the output is performed, for example, in synchronization with the rotation of a predetermined crank angle. The interrupt process is executed in a predetermined order for each cylinder. However, since the content of each interrupt control is the same, one cylinder will be described below with reference to the flowchart of the interrupt process shown in FIG. If an interrupt occurs in the main processing, steps 5 and 6
The actual common rail pressure Pra and the target common rail pressure Prt calculated respectively are read (steps 11 and 12). Actual common rail pressure Plant and target common rail pressure Prtin at the time of interruption
Pressure deviation ΔPrint from t (= Print−Prt)
int) is calculated (step 13). Pressure deviation ΔP
print is a positive value, that is, the actual common rail pressure Prai
It is determined whether or not nt is a value higher than the target common rail pressure Prtint (step 14). Actual common rail pressure Prt is the target common rail pressure Prt
When it is equal to int, there is no need to control the common rail pressure Pr. When the actual common rail pressure Prain is lower than the target common rail pressure Prtint, the control according to the present invention cannot be performed, and the interruption process ends.

When the actual common rail pressure Prain is higher than the target common rail pressure Prtint, the following processing is continued to reduce the actual common rail pressure Prain. The actual common rail pressure Prai
When nt exceeds a predetermined threshold value than the target common rail pressure Prtint, the pressure reduction control of the common rail pressure Pr may be started. Pressure deviation ΔPrint
In order to reduce the common rail pressure Pr to the target common rail pressure Prtint from the magnitude of the value, the fuel leak amount Qleak that causes fuel to leak from the common rail 2
Is calculated (step 15). Fuel leak Qlea
k is the actual common rail pressure Prain
t, the fuel temperature Tf, and the pressure deviation ΔPrint, and can be obtained from a map stored in the controller 8.

An example of a map for obtaining the fuel leak amount Qleak is shown in the graph of FIG. The graph in FIG.
The horizontal axis is the leaked fuel amount Qleak, and the vertical axis is the pressure deviation Δ
Print, and the fuel temperature Tf is used as a parameter. If the fuel temperature is constant, as the pressure deviation ΔPrint increases, the fuel leak amount Qleak increases substantially in proportion, and the fuel temperature Tf increases as the pressure deviation ΔPrint increases. It can be seen that the fuel leak amount Qleak tends to increase.

Further, the fuel leak amount Qleak required to eliminate ΔPrint may be obtained by calculating the following physical equation. Qleak = V / E × ΔPrint Here, V is the high pressure part volume, and E is the bulk modulus of the fuel. The bulk modulus E is a parameter that depends on the fuel pressure (common rail pressure Pr) and the fuel temperature Tf, and data obtained by experiments in advance is prepared by mapping as shown in Table 1.

[Table 1]

The pressure leak valve 24 is opened from the function f using the leaked fuel amount Qleak to be released from the fuel flow path calculated in step 15 and the fuel pressure (common rail pressure Pr) as a variable or a map obtained from an experiment. A command value (pulse width) Pwi that determines the period is obtained (step 1).
6). By driving the pressure leak valve 24 with the obtained command value Pwi, the common rail pressure Pr decreases (step 17). FIG. 6 shows an example of the relationship between the fuel leak amount Qleak and the command value Pwi to the pressure leak valve 24.
It is a graph which shows common rail pressure Pr which is fuel pressure as a parameter. As is commonly understood, the command value Pwi required to obtain the fuel leak amount Qleak is:
The longer the fuel leak amount Qleak is, the longer the tendency is. Also, the higher the common rail pressure Pr,
Command value Pwi for obtaining the same fuel leak amount Qleak
Is short.

In the above embodiment, the pressure leak valve 24 disposed on the common rail 2 is shown as the pressure leak means, but the injector 3 can be used as the pressure leak means. That is, the injector 3 is for injecting fuel from the injection hole 32 into the combustion chamber. In the fuel injection control of the injector 3, the fuel is leaked to the low pressure side through the balance chamber 30. Fuel in the fuel passage from the common rail 2 to the injector 3 can be leaked. In this case, since it is necessary to cause the fuel to leak without accompanying fuel injection, the period during which the actuator such as the electromagnetic solenoid 45 is excited to open the on-off valve 44 is set to a short period during which no fuel injection is performed. . Also, in practice, even during such a short leak period, the common rail pressure Pr is reduced to the target common rail pressure Pr at the fuel injection start timing that comes later due to the fuel leak through the balance chamber 30.
It can be reduced to tint. Fuel leak amount Qlea for reducing pressure deviation ΔPrint
k and the command value Pwi for determining the fuel leak amount Qleak (in the case of this embodiment, the period for energizing the actuator such as the electromagnetic solenoid 45) is described with reference to the pressure leak valve 24. Since it is the same as the case obtained, the description will not be repeated.

If the command value Pwi is set longer, the command value at which fuel injection is started and the fuel leak amount at that time are obtained in advance as the maximum idling command value Pwim and the maximum fuel leak amount Qleakm ( In FIG. 6, the common rail pressure Pr is shown for 100 MPa). Although the fuel is not actually injected from the injection hole, the maximum idling command value Pw is set to reduce the common rail pressure Pr.
In the idling region equal to or less than im, a command value Pvia for the fuel leak amount Qleaka is obtained.

FIG. 7 is a map for obtaining a correction coefficient Kth for correcting the command value Pwi based on the fuel temperature Tf. When calculating the fuel leak amount Qleak from FIG.
f, the fuel temperature Tf depends on the fuel leak amount Qle.
Since it is related to the common rail pressure Pr other than ak,
When determining the command value Pwi according to FIG. 6, the fuel temperature Tf is considered again. From FIG. 7, it can be seen from FIG. 7 that the higher the fuel temperature Tf is, the lower the viscosity of the fuel is. Therefore, the same effect as the common rail pressure Pr is obtained is obtained for the fuel leakage.
The correction coefficient Kth is determined so that the command value Pwi is shortened for the same fuel leak amount Qleak.

[0039]

According to the common rail fuel injection system of the present invention, a situation occurs in which the common rail pressure exceeds the target pressure determined from the operating state of the engine due to mechanical variations in the injectors and changes in the operating state of the engine. In some cases, the common rail pressure is reduced to the target common rail pressure by leaking fuel from the fuel flow path where high-pressure fuel from the common rail to the injector is stored, and fuel is injected at the reduced target common rail pressure. Therefore, the injector does not inject more fuel than the target fuel injection amount according to the operating state of the engine, and does not consume more fuel than necessary. Moreover, according to the common rail fuel injection device of the present invention, not only in the area where the fuel injection amount is zero, but also in the state where there is actually fuel injection occupying most of the engine operating state, and even when the common rail pressure fluctuates every moment. Thus, the excessively raised common rail pressure can be reduced to the target common rail pressure. Further, since the variation in the fuel injection amount injected from each injector can be eliminated, the variation in fuel in each cylinder can be eliminated, and the generation of unpleasant vibration and noise can also be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a common rail fuel injection system to which an embodiment of a common rail fuel injection device according to the present invention is applied.

FIG. 2 is a command signal relating to an injector and a pressure leak valve in the common rail type fuel injection device shown in FIG. 1;
5 is a time chart showing a time change with respect to a common rail pressure.

FIG. 3 is a flowchart showing main processing of fuel injection from an injector and common rail pressure control in a common rail fuel injection device according to the present invention.

FIG. 4 is a flowchart showing a common rail pressure determination and reduction process interrupting the main process shown in FIG. 3;

FIG. 5 is a diagram showing an example of a map for obtaining a fuel leak amount Qleak.

FIG. 6 is a diagram illustrating an example of a relationship between a fuel leak amount Qleak and a command value Pwi to a pressure leak unit, using a common rail pressure Pr as a fuel pressure as a parameter.

FIG. 7 shows a command value Pwi to the pressure leak means as a fuel temperature T
FIG. 9 is a diagram illustrating an example of a map for obtaining a correction coefficient Kth to be corrected by f.

FIG. 8 is a schematic view showing an example of a conventional common rail type fuel injection device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Fuel supply pump 2 Common rail 3 Injector 8 Controller 9 Sensor 12 Pump room 15 Flow control valve 21 Discharge pipe 22 Pressure sensor 24 Pressure leak valve 25 Actuator 30 Balance chamber 31 Needle valve 32 Injection hole 34 Fuel passage 38 Supply path 44 Open / close valve Pr Common rail pressure Prain Actual common rail pressure at interrupt Prtint Target common rail pressure at interrupt ΔPrint Pressure deviation Pwi Command value of command pulse to injector (pulse width) Pwl Command value of command pulse to pressure leak means (pulse width) Qleak Fuel leak Volume V Volume of fuel supply system E Bulk modulus Tf Fuel temperature Kth Correction coefficient

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) MA18 NC02 ND01 PB01Z PB08A PB08Z PE01Z PF03Z

Claims (9)

[Claims] 1. A fuel supply pump for pumping fuel, a common rail for storing the fuel pumped by the fuel supply pump in an accumulating state, and a fuel supply pump provided for each cylinder of the engine and supplied from the common rail. Injector, detecting means for detecting the operating state of the engine, a pressure sensor for detecting the pressure of the common rail,
And obtaining a fuel injection condition to be injected from the injector and a target common rail pressure based on a detection signal from the detection means, and performing fuel pumping by the fuel supply pump such that the common rail pressure matches the target common rail pressure. A controller that performs feedback control and controls fuel injection from the injector so that fuel is injected under the fuel injection condition, wherein the controller terminates fuel pumping by the fuel supply pump detected by the pressure sensor. In response to the later pressure of the common rail exceeding the target common rail pressure, the high-pressure fuel stored in the fuel flow path from the common rail to the injector is leaked through a pressure leak means, so that the injector Fuel injection from Common rail fuel injection system comprising a pressure in the common rail from lowering to the target common rail pressure before. 2. The pressure leak means is the injector, wherein the injector is formed with an injection hole for injecting fuel and a balance chamber for supplying and discharging a part of high-pressure fuel from the common rail. A main body, a needle valve housed in the injector main body so as to be liftable, for opening and closing the injection hole based on the pressure action of the fuel pressure in the balance chamber, and to the balance chamber for controlling the fuel pressure in the balance chamber. An actuator for controlling the supply and discharge of the fuel, and the controller operates the actuator to discharge the fuel from the balance chamber to leak the high-pressure fuel stored in the fuel flow path. The common rail fuel injection device according to claim 1, comprising: 3. The pressure leak means is a pressure leak valve disposed on the common rail, and the controller operates the pressure leak valve to leak high-pressure fuel stored in the fuel flow path. 2. The common rail fuel injection device according to claim 1, further comprising discharging the fuel stored in the common rail in a pressure accumulated state. 4. The controller, in response to the completion of the fuel supply from the fuel supply pump to the common rail, controlling the fuel injection from the injector to the common rail detected by the pressure sensor. The common rail fuel injection device according to any one of claims 1 to 3, further comprising performing an interruption process for comparing a pressure with the target common rail pressure. 5. The controller according to claim 1, wherein the controller determines a fuel leak amount to be leaked from the fuel fuel passage based on a pressure difference between the pressure of the common rail and the target common rail pressure after the end of the fuel supply by the fuel supply pump. The common rail fuel injection device according to any one of claims 1 to 4, comprising calculating. 6. The common rail fuel injection device according to claim 5, wherein the controller calculates the fuel leak amount based on the pressure deviation from a map created and stored in advance by an experiment. 7. The controller according to claim 1, wherein the volume of the fuel flow path is V, the bulk modulus of the fuel is E, and the pressure deviation is Δ.
6. The common rail fuel injection device according to claim 5, wherein when Print is used, the fuel leak amount Qleak is calculated by the following equation. Qleak = V / E × ΔPrint 8. The controller according to claim 5, wherein the controller calculates a fuel leak amount by performing a fuel temperature correction to increase the fuel leak amount as the fuel temperature increases.
8. The common rail fuel injection device according to any one of items 7 to 7. 9. The controller according to claim 1, wherein, in calculating an operation period for operating the pressure leak unit, the controller performs a fuel temperature correction that shortens the operation period as the fuel temperature increases. Item 8. The common rail fuel injection device according to item 1.