JP2021014842A - Control device of fuel supply system - Google Patents

Abstract

To provide a control device of a fuel supply system capable of reducing generation of spike fuel pressure at a low pressure portion when opening a relief valve.SOLUTION: A fuel supply system 10 includes a high pressure pump 20 for pressurizing and discharging a low pressure fuel supplied from a fuel tank 11, a rail 16 as an accumulator vessel for storing the high pressure fuel discharged from the high pressure pump 20, a fuel injection valve 52 for directly injecting the high pressure fuel in the accumulator vessel into a cylinder of an engine 50, and a relief valve 15 disposed on a high pressure portion at a downstream side with respect to the high pressure pump 20 and opened when the fuel pressure of the high pressure portion is higher than the valve opening pressure. An ECU 60 includes a fuel pressure control portion executing valve opening suppression control to suppress the opening of the relief valve 15 during an injection stop period by executing a control to lower the fuel pressure of the high pressure portion at least just before the injection stop period of the fuel injection valve 52 or during the injection stop period.SELECTED DRAWING: Figure 1

Description

The present invention relates to a control device for a fuel supply system.

The fuel supply system of the internal combustion engine is equipped with a high-pressure pump that raises the pressure of the low-pressure fuel pumped from the fuel tank and a pressure-accumulation container (rail) that stores the high-pressure fuel pumped from the high-pressure pump. An in-cylinder injection type fuel supply system is known in which fuel is directly injected into the cylinder of an internal combustion engine from a fuel injection valve. Further, in such a fuel supply system, the pressure inside the pressure accumulator container is reduced by opening the relief valve when the pressure inside the pressure accumulator is abnormal (see, for example, Patent Document 1). The fuel supply system of Patent Document 1 is configured to return the high-pressure fuel to the low-pressure portion on the upstream side of the high-pressure pump by opening the relief valve when the high pressure in the accumulator container is abnormal.

Japanese Unexamined Patent Publication No. 2009-91963

In the fuel supply system that returns the fuel in the high-pressure section to the low-pressure section by opening the relief valve, the high-pressure fuel flows into the low-pressure section at once when the relief valve is opened, causing spike fuel pressure that temporarily raises the pressure in the low-pressure section. May occur. The peak value of the spike fuel pressure becomes a value larger than the fuel pressure pulsation that occurs during normal use, and there is a risk of damaging the components of the low pressure portion. Therefore, it is necessary to reduce the occurrence of spike fuel pressure as much as possible.

The relief valve usually operates when the pressure in the high pressure section becomes excessively high (for example, when a full discharge abnormality of the high pressure pump occurs). However, depending on the operating condition of the engine, the fuel temperature of the high-pressure part may rise, and the high-pressure part may unintentionally increase the pressure. In this case, there is a concern that the relief valve opens even though the high pressure portion has not failed, and the high pressure fuel flows into the low pressure portion at once, causing spike fuel pressure in the low pressure portion.

The present invention has been made in view of the above problems, and in a fuel supply system for returning the fuel in the high pressure portion to the low pressure portion by opening the relief valve, it is possible to reduce the occurrence of spike fuel pressure in the low pressure portion due to the opening of the relief valve. The main purpose is to provide a control device for a fuel supply system that can be used.

The present invention includes a high-pressure pump (20) that increases the pressure of the low-pressure fuel supplied from the fuel container (11) and discharges it, a pressure accumulator container (16) that stores the high-pressure fuel discharged from the high-pressure pump, and the inside of the accumulator container. The fuel injection valve (52) that directly injects the high-pressure fuel into the cylinder of the internal combustion engine (50) and the high-pressure portions (14, 16) on the downstream side of the high-pressure pump are provided, and the fuel pressure of the high-pressure portion is increased. It is applied to a fuel supply system including a relief valve (15) that opens when the valve opening pressure is higher than a predetermined valve opening pressure. According to the first aspect of the present invention, control for lowering the fuel pressure in the high pressure portion is performed immediately before the injection stop period for stopping the injection of fuel from the fuel injection valve and at least during the injection stop period. The fuel pressure control unit is provided to perform valve opening suppression control for suppressing the opening of the relief valve during the injection stop period.

During the injection stop period in which fuel injection from the in-cylinder injection type fuel injection valve is stopped, the fuel circulation is stagnant in the fuel path of the high-pressure pump, accumulator, and fuel injection valve, so that the temperature of the fuel tends to rise. The pressure in the high-pressure part may rise due to the heat received after the injection is stopped. In this case, the relief valve opens even though the high-pressure portion has not failed, and the high-pressure fuel flows into the low-pressure portion at once, which may cause spike fuel pressure in the low-pressure portion during the injection stop period.

In this regard, according to the above configuration, the relief valve is opened during the injection stop period by controlling the fuel pressure in the high pressure portion to be lowered immediately before the injection stop period or at least during the injection stop period. Since the valve opening suppression control is carried out, it is possible to prevent the fuel pressure in the high-pressure portion from reaching the valve opening pressure during the injection stop period. As a result, the relief valve can be prevented from opening during the injection stop period, and as a result, it is possible to reduce the occurrence of spike fuel pressure in the low pressure portion.

Schematic configuration of the engine fuel supply system. A time chart illustrating an embodiment when stop delay control is not performed. A time chart illustrating an embodiment when stop delay control is not performed. A time chart for explaining a specific mode when the stop delay control is performed. A time chart for explaining a specific mode when the stop delay control is performed. The flowchart explaining the processing procedure of stop delay control. A time chart for explaining an embodiment in which injection start control is not performed. A time chart for explaining a specific mode when the injection start control is performed. The flowchart explaining the processing procedure of injection start control. A time chart illustrating a specific embodiment of injection start control of another embodiment. A time chart illustrating a specific embodiment of injection start control of another embodiment. The figure which shows the relationship between the temperature rise rate and the pressure change rate. The figure which shows the relationship between a rail volume and a rail fuel pressure boosting speed.

(First Embodiment)
Hereinafter, the fuel supply system according to the first embodiment will be described with reference to the drawings. The fuel supply system 10 shown in FIG. 1 is mounted on a vehicle and supplies fuel into a cylinder of an engine 50 as an internal combustion engine.

The fuel supply system 10 includes a fuel tank 11 for storing fuel, an electromagnetically driven low-pressure pump 12, a high-pressure pump 20 for increasing the pressure of fuel, and a rail 16 which is an accumulator container. The low-pressure pump 12 pumps up the fuel in the fuel tank 11 and pressurizes it to a feed pressure Pf (for example, about 0.3 MPa), and supplies the pressurized low-pressure fuel to the high-pressure pump 20 through the low-pressure pipe 13.

The high-pressure pump 20 increases the pressure of the fuel supplied from the low-pressure pipe 13 and discharges the fuel to the high-pressure pipe 14. A low pressure chamber 22 and a pressure chamber 23 are formed in the cylinder body 21 of the high pressure pump 20. The low pressure chamber 22 communicates with the low pressure pipe 13 and stores the fuel supplied through the low pressure pipe 13. A metering valve 24 is provided in the passage where the low pressure chamber 22 and the pressurizing chamber 23 communicate with each other. The metering valve 24 controls the amount of fuel supplied from the low pressure chamber 22 to the pressurizing chamber 23.

The pressurizing chamber 23 is provided with a plunger 25 that changes the pressure in the pressurizing chamber 23 by a reciprocating operation. In the plunger 25, the end opposite to the pressurizing chamber 23 is connected to the cam 26. The cam 26 is connected to the crankshaft 51 of the engine 50. As the cam 26 rotates with the rotation of the crankshaft 51, the plunger 25 reciprocates between the top dead center and the bottom dead center.

The pressurizing chamber 23 is provided with a discharge valve 27 for discharging the fuel pressurized in the pressurizing chamber 23. The discharge port of the discharge valve 27 communicates with a high-pressure pipe 14 connected to the rail 16. The discharge valve 27 is a check valve that allows fuel to flow from the pressurizing chamber 23 to the high-pressure pipe 14. The discharge valve 27 is opened when the fuel pressure in the pressurizing chamber 23 exceeds a predetermined discharge pressure.

When the metering valve 24 is opened and the plunger 25 moves from the top dead center to the bottom dead center, the fuel in the low pressure chamber 22 is sucked into the pressurizing chamber 23. When the plunger 25 moves from the bottom dead center to the top dead center with the metering valve 24 opened, the fuel in the pressurizing chamber 23 is returned to the low pressure chamber 22 via the metering valve 24. When the metering valve 24 is closed while the plunger 25 is moving from the bottom dead center to the top dead center, the fuel in the pressurizing chamber 23 is pressurized. After that, when the pressure in the pressurizing chamber 23 becomes equal to or higher than the discharge pressure, the fuel is discharged from the discharge valve 27. The high-pressure fuel discharged from the discharge valve 27 is supplied to the rail 16 through the high-pressure pipe 14.

The rail 16 stores the fuel discharged from the high-pressure pump 20 in a high-pressure state. The rail 16 is connected to a fuel injection valve 52 provided in each cylinder of the engine 50. The fuel injection valve 52 is an in-cylinder injection type fuel injection valve that injects fuel directly into the cylinder. A spark plug is attached to the cylinder head of the engine 50 for each cylinder. The spark plug ignites the air-fuel mixture in the cylinder by spark discharge. As a result, the air-fuel mixture in the cylinder is used for combustion.

The high-pressure pipe 14 and the low-pressure chamber 22 are communicated with each other through a return pipe 17, and a relief valve 15 is provided in the return pipe 17. The inlet side of the relief valve 15 communicates with the high pressure pipe 14, and the outlet side communicates with the low pressure chamber 22. The relief valve 15 is an on-off valve that opens and closes according to the difference between the upstream pressure and the downstream pressure of the relief valve 15.

Specifically, the fuel pressure of the high-pressure pipe 14 rises to the valve opening pressure Po, and the differential pressure between the upstream side and the downstream side of the relief valve 15 becomes larger than the predetermined pressure, so that the relief valve 15 opens. .. As a result, the fuel in the high-pressure pipe 14 is returned to the low-pressure chamber 22 through the relief valve 15. Further, when the fuel pressure of the high-pressure pipe 14 drops to a predetermined valve closing pressure Pc after the relief valve 15 is opened and the differential pressure between the upstream side and the downstream side of the relief valve 15 becomes smaller than the predetermined value, the relief valve 15 is relieved. The valve 15 closes. Therefore, when a high-pressure abnormality (for example, a full discharge abnormality of the high-pressure pump 20) occurs in the high-pressure portion, the relief valve 15 is opened to return the high-pressure fuel in the high-pressure portion to the low-pressure portion. In this way, when a high-voltage abnormality occurs in the high-voltage portion, fail-safe is implemented so that the abnormal state does not continue.

Here, the valve opening pressure Po is set to a value on the higher pressure side than the system fuel pressure Px by a predetermined pressure α (for example, 15 MPa) or more in anticipation of pressure pulsation and fuel pressure variation (Po ≧ Px + α). The system fuel pressure Px is the maximum controlled fuel pressure of the rail fuel pressure, and is set to a value of 30 MPa or more, preferably 35 MPa or more in this embodiment. The valve closing pressure Pc is set to a lower pressure side than the valve opening pressure Po.

The low pressure portion is composed of a return pipe 17, a low pressure chamber 22, a low pressure pipe 13, and a fuel tank 11 on the upstream side of the high pressure pump 20. The return pipe 17 may be connected to the low pressure pipe 13 and return fuel to the low pressure pipe 13. Further, the high pressure portion is formed on the downstream side of the high pressure pump 20, specifically, the high pressure pipe 14 and the rail 16.

The rail 16 is provided with a rail pressure sensor 31 that detects the rail fuel pressure (actual rail pressure Pr), which is the fuel pressure in the rail 16. Further, the low pressure pipe 13 is provided with a feed pressure sensor 32 that detects the feed pressure Pf. The fuel tank 11 is provided with a fuel temperature sensor 33 that detects the fuel temperature Tf.

The fuel supply system 10 and the engine 50 are controlled by the ECU 60. The ECU 60 is a microcomputer provided with a CPU, ROM, RAM, drive circuit, input / output interface, and the like. The detection values of the sensors 31 to 33 and the operation signals of the key switches 34 are input to the ECU 60. When the key switch 34 is operated from off to on by the driver, operating power is supplied to each actuator from a battery (not shown) to start the engine 50, and the key switch 34 is switched from on to off to switch the battery. The supply of operating power to each actuator is stopped and the engine 50 is stopped. Further, the ECU 60 feedback-controls the discharge amount of the high-pressure pump 20 based on the deviation between the target fuel pressure R *, which is the target value of the rail fuel pressure, and the actual rail pressure Pr detected by the rail pressure sensor 31. As a result, the rail fuel pressure is controlled by the target fuel pressure R *.

In the fuel supply system 10, the high-pressure fuel pressurized by the high-pressure pump 20 may flow into the low-pressure pipe 13 at once as the relief valve 15 opens at the time of a high-pressure abnormality in the rail 16. In this case, spike-shaped surge fuel pressure (hereinafter referred to as “spike fuel pressure”) may be generated in the low-pressure pipe 13. The peak value of the spike fuel pressure is larger than the fuel pressure pulsation that occurs during normal use, and there is a risk of damaging the low-pressure portion such as the low-pressure pipe 13. Therefore, it is desirable to minimize spike fuel pressure.

Here, it is assumed that the relief valve 15 operates when some failure occurs on the high pressure side of the high pressure pump 20 or the high pressure pump 20, such as when the high pressure pump 20 has a full discharge abnormality. .. However, after the operation of the engine 50 is stopped, in the state where the engine 50 is stopped (soak state), the fuel injection from the fuel injection valve 52 is stopped, and the fuel of the high pressure pump 20, the rail 16 and the fuel injection valve 52 is stopped. Fuel circulation is stagnant on the route. Therefore, the fuel in the high-pressure portion may rise in temperature after the engine is stopped, and the pressure in the high-pressure portion may rise. In such a case, the relief valve 15 opens even though the high-pressure portion has not failed, and the high-pressure fuel flows into the low-pressure pipe 13 at once, which may cause spike fuel pressure during the engine stop period. .. In addition, there is a concern that the frequency of spike fuel pressure will increase and damage to low-pressure components will increase.

Therefore, in the present embodiment, the relief is performed immediately before the injection stop period of the fuel injection valve 52, more specifically, immediately before the operation of the engine 50 is stopped in response to the operation stop request of the engine 50, and during the subsequent engine stop period. It is decided to carry out valve opening suppression control for suppressing the valve opening of the valve 15. In particular, in the present embodiment, as valve opening suppression control, control for lowering the fuel pressure in the high-pressure portion by delaying the execution of the operation stop of the engine 50 in response to the operation stop request (hereinafter referred to as "stop delay control"). ) Is carried out. The stop delay control will be described in detail below.

In the stop delay control, when there is a request to stop the operation of the engine 50, specifically, when there is a switching operation to turn off the key switch 34, the operation of the engine 50 is immediately performed in response to the request to stop the operation. The control is such that the fuel pressure in the high-pressure portion is sufficiently lowered immediately before the operation of the engine 50 is stopped without stopping, and then the operation of the engine 50 is stopped. First, a case where the stop delay control is not performed will be described with reference to FIGS. 2 and 3. FIG. 2 shows a case where the driver switches the key switch 34 from on to off after the vehicle has stopped, and FIG. 3 shows a case where the driver switches the key switch 34 from on to off while the vehicle is running. ing.

In FIG. 2, the vehicle decelerates as the accelerator operation is released at time t11 while the vehicle is running. At this time, the target fuel pressure R * is gradually changed to the low pressure side by releasing the accelerator operation. When the vehicle speed becomes zero and the vehicle stops, the engine 50 is held in the idle operation state until the key switch 34 is switched off (time t12 to t13). After that, when the key switch 34 is switched off at time t13, a fuel cut is performed immediately after that, and the operation of the engine 50 is stopped (time t13).

During the shutdown period of the engine 50, when the rail fuel pressure rises due to heat reception and reaches the valve opening pressure Po, the differential pressure before and after the relief valve 15 becomes sufficiently large, and the relief valve 15 opens at time t14. Further, when the relief valve 15 is opened, the high-pressure fuel in the rail 16 is returned to the low-pressure portion at once through the return pipe 17. As a result, the rail fuel pressure drops rapidly, and spike fuel pressure Sp is generated in the low-pressure pipe 13 (time t14).

Next, consider the case where the driver switches the key switch 34 off while the vehicle is traveling (in the case of FIG. 5). In FIG. 5, when the key switch 34 is switched off at the time t21 while the vehicle is running, the fuel cut is immediately performed with the switching of the key switch 34. As a result, the vehicle speed decreases and the vehicle stops (time t22). When the fuel in the rail 16 rises due to the heat received after the vehicle is stopped and the rail fuel pressure rises to reach the valve opening pressure Po, the relief valve 15 opens at that time t23. Further, when the relief valve 15 is opened, the high-pressure fuel in the rail 16 is returned to the low-pressure portion at once through the return pipe 17, and a spike fuel pressure Sp is generated in the low-pressure pipe 13 (time t23).

The stop delay control for suppressing the occurrence of such spike fuel pressure Sp will be described with reference to FIGS. 4 and 5. FIG. 4 shows a case where the driver switches the key switch 34 from on to off after the vehicle is stopped, and FIG. 5 shows a case where the driver switches the key switch 34 from on to off while the vehicle is running.

In FIG. 4, consider a case where the vehicle decelerates due to the release of the accelerator operation at the time t31 while the vehicle is running, and then the vehicle stops at the time t32. In this case, the engine 50 is held in the idle operation state during the period from when the vehicle is stopped until the key switch 34 is turned off (time t32 to t33). After that, when the key switch 34 is switched off at time t33, the operation of the engine 50 is not stopped immediately after the key switch 34 is turned off (that is, after the request to stop the operation of the engine 50), and the operation of the engine 50 remains as it is. continue. Here, the idle operation state of the engine 50 is continued. As a result, the actual rail pressure Pr is further lowered from the rail pressure P1 when the key switch 34 is off (time t33 to t34).

After that, when it is determined at time t34 that the actual rail pressure Pr becomes equal to or less than the decrease determination value Ps, fuel cut is performed and the operation of the engine 50 is stopped (time t34). After the time t34, the actual rail pressure Pr increases by the boost amount ΔP due to the heat received when the engine is stopped. However, in this case, the rail fuel pressure when the engine is stopped (that is, the rail fuel pressure at time t34) is sufficiently reduced by implementing the stop delay control. Therefore, the fuel in the rail 16 rises due to the heat received when the engine is stopped, and even if the rail fuel pressure rises, the valve opening pressure Po does not reach, and the valve closed state of the relief valve 15 is maintained. As a result, the generation of spike fuel pressure Sp is suppressed during the shutdown period of the engine 50.

After the time t31 when the accelerator operation is released, the target fuel pressure R * is gradually set to be smaller toward the lowering judgment value Ps or the predetermined value Ph on the lower pressure side than that, and is eventually held constant at the predetermined value Ph. To.

Here, the decrease determination value Ps is a value set in advance based on the step-up amount ΔP in which the rail pressure rises due to heat reception after the engine is stopped and the valve opening pressure Po of the relief valve 15. Specifically, the decrease determination value Ps is set so as to satisfy the relationship of the following equation (1).
Ps ≦ Po−ΔP… (1)
The boosting amount ΔP is a value set based on the temperature rising amount ΔT of the fuel in the high pressure portion after the engine is stopped and the fuel physical characteristic value, and is specifically calculated by the following equation (2).
ΔP = K · (ρ (T0 + ΔT) −ρ (T0)) / ρ (T0)… (2)
(In equation (2), K is the volume elastic modulus, ρ is the fuel density, t0 is the fuel temperature when the engine is stopped, and ΔT is the amount of temperature rise of the fuel due to heat reception after the engine is stopped.)
For the decrease determination value Ps, a predetermined maximum value is used as the temperature rise amount ΔT in consideration of the layout of the engine 50, the boost amount ΔP is calculated according to the above equation (2), and the value satisfies the above equation (1). The calculated value is set.

Similarly, when the driver switches the key switch 34 from on to off while the vehicle is running, the operation of the engine 50 is not stopped immediately after the key switch 34 is switched off, and the idle operation state is maintained as it is. (Times t41 to t42 in FIG. 5). When the actual rail pressure Pr is lowered to the decrease determination value Ps or less by continuing the operation of the engine 50, the fuel cut is performed at that timing (time t42), and the operation of the engine 50 is stopped. With such control, after the engine operation is stopped, even if the rail fuel pressure rises due to the heat received after the engine is stopped, the rail fuel pressure does not reach the valve opening pressure Po, and the relief valve 15 is maintained in a closed state.

Next, the processing procedure of the stop delay control will be described with reference to the flowchart of FIG. After the key switch 34 is turned on, this process is repeatedly executed by the ECU 60 in a predetermined control cycle.

In FIG. 6, in step S100, it is determined whether or not the key switch 34 is switched off. Here, the determination is made based on whether or not the off operation signal of the key switch 34 is input. If the off operation signal is not input from the key switch 34, this routine is terminated as it is, and if the off operation signal is input, the process proceeds to step S101. In step S101, it is determined whether or not the engine 50 is in operation, and if affirmative determination is made, the process proceeds to step S102.

In step S102, it is determined whether or not the rail fuel pressure (actual rail pressure Pr) detected by the rail pressure sensor 31 is equal to or less than the decrease determination value Ps. If the actual rail pressure Pr is higher than the decrease determination value Ps, the process proceeds to step S103, and fuel cut is prohibited. In this case, the operating state of the engine 50 (for example, the idle operating state) is continued as it is.

On the other hand, when the actual rail pressure Pr is equal to or less than the decrease determination value Ps, an affirmative determination is made in step S102, the process proceeds to step S104, and fuel cut is performed. As a result, the operation of the engine 50 is stopped. After that, this routine ends.

According to the present embodiment described in detail above, the following excellent effects can be obtained.

Valve opening suppression that suppresses the opening of the relief valve 15 during the subsequent engine stop period by performing control to reduce the fuel pressure in the high-pressure section immediately before stopping the operation of the engine 50 in response to the engine stop request. It was configured to carry out control. During the period when the fuel injection from the fuel injection valve 52 is stopped, the fuel circulation may be stagnant in the fuel path of the high pressure pump 20 to the rail 16 to the fuel injection valve 52, and the pressure in the high pressure part may rise due to heat reception. .. In this regard, according to the configuration in which the valve opening suppression control is implemented, the relief valve 15 can be prevented from opening during the engine stop period, and as a result, spike fuel pressure can be prevented from being generated in the low pressure portion. it can.

In particular, after the key switch 34 is turned off, the vehicle remains stopped, and heat tends to be trapped around the high-voltage portion. In this respect, according to the above system that implements the stop delay control, since the pressure in the high pressure portion is sufficiently lowered before the engine is stopped, it is suitable for suppressing the spike fuel pressure in the low pressure portion.

After the engine stop request is made, the operation of the engine 50 is continued until it is determined that the actual rail pressure Pr detected by the rail pressure sensor 31 becomes equal to or less than the decrease determination value Ps, and then the actual rail pressure Pr is changed. The operation of the engine 50 is stopped when it is determined that the reduction determination value is Ps or less. According to this configuration, it is possible to directly grasp from the actual rail pressure Pr that the rail fuel pressure has sufficiently decreased to a pressure that can suppress the opening of the relief valve 15 after the engine stop request, and the determination accuracy is improved. be able to. As a result, the spike fuel pressure in the low pressure portion can be suppressed as much as possible.

(Second Embodiment)
Next, the second embodiment will be described focusing on the differences from the first embodiment. In the first embodiment, as valve opening suppression control, when there is a request to stop the operation of the engine 50, the fuel pressure in the high pressure portion is lowered immediately before the operation of the engine 50 is stopped, and then the engine is stopped. Was carried out. On the other hand, in the present embodiment, as the valve opening suppression control, injection start control for lowering the fuel pressure in the high pressure portion during the operation stop period after the operation of the engine 50 is stopped is performed. Hereinafter, injection start control will be described in detail.

In the present embodiment, the ECU 60 implements automatic stop / restart control of the engine 50. Specifically, the ECU 60 stops fuel injection to automatically stop the engine 50 when a predetermined automatic stop condition is satisfied, and restarts fuel injection when a predetermined restart condition is satisfied after the automatic stop of the engine 50. Then, the engine 50 is restarted. The automatic stop conditions are that the vehicle speed has dropped below the permitted stop speed (the vehicle speed has become zero in this embodiment), the brake pedal has been depressed, and the engine cooling water temperature is within the predetermined temperature range. The engine 50 is automatically stopped when all of these conditions are satisfied, including that there is no abnormality in the charging system and that the battery state is good.

The injection start control restarts fuel injection by the fuel injection valve 52 when the fuel pressure in the high-pressure portion becomes higher than the predetermined rise determination value Pw during the automatic stop period of the engine 50, and suppresses the rise in fuel pressure. It is a control to do. First, a case where the injection start control is not performed will be described with reference to FIG. 7.

In FIG. 7, consider a case where the accelerator operation is released at time t51 while the vehicle is running, and then the automatic stop condition of the engine 50 is satisfied at time t53. In this case, at time t53, the fuel injection by the fuel injection valve 52 is stopped, and the engine 50 is automatically stopped. During the engine stop period, the rail fuel pressure rises due to the heat received after the engine is stopped and reaches the valve opening pressure Po, so that the relief valve 15 opens at time t54. Further, when the relief valve 15 is opened, the high-pressure fuel in the rail 16 is returned to the low-pressure portion at once through the return pipe 17. As a result, although the rail fuel pressure drops rapidly, spike fuel pressure Sp is generated in the low-pressure pipe 13 (time t54).

Next, a case where the injection start control is performed during the engine stop period will be described with reference to FIG. In FIG. 8, at time t63 during engine operation, the engine 50 is automatically stopped when the automatic stop condition of the engine 50 is satisfied. After that, the fuel in the rail 16 rises due to the automatic engine stop, so that the actual rail pressure Pr rises. Then, when the actual rail pressure Pr reaches the rise determination value Pw, the fuel injection by the fuel injection valve 52 is restarted at that time t64, and the engine 50 is restarted. Therefore, even if the rail fuel pressure rises due to heat reception after the engine is stopped, the rail fuel pressure does not reach the valve opening pressure Po, and the valve closed state of the relief valve 15 is maintained. As a result, the generation of spike fuel pressure is suppressed during the shutdown period of the engine 50. The rise determination value Pw is set to a value that is lower than the valve opening pressure Po of the relief valve 15 and is equal to or less than the maximum fuel pressure at which fuel can be injected from the fuel injection valve 52.

Next, the processing procedure of the injection start control executed during the engine stop period will be described with reference to the flowchart of FIG. This process is repeatedly executed by the ECU 60 at a predetermined control cycle.

In FIG. 9, in step S201, it is determined whether or not the engine is in the automatic engine stop period. If an affirmative judgment is made in step S201, the process proceeds to step S202, and it is determined whether or not the rail fuel pressure (actual rail pressure Pr) detected by the rail pressure sensor 31 is equal to or higher than the rise determination value Pw. If the actual rail pressure Pr is lower than the rise determination value Pw, the process proceeds to step S203, the fuel injection is kept stopped, and the automatic engine stop is continued. On the other hand, when the actual rail pressure Pr becomes equal to or higher than the rise determination value Pw, the process proceeds to step S204, fuel injection is restarted, and the engine 50 is restarted. After that, this routine ends.

According to the present embodiment described in detail above, the following excellent effects can be obtained.

When the fuel pressure in the high-pressure portion becomes higher than the rise determination value Pw during the engine stop period, the injection start control for injecting fuel from the fuel injection valve 52 is performed. During the engine stop period, the fuel circulation may be stagnant in the fuel paths of the high-pressure pump 20 to the rail 16 to the fuel injection valve 52, and the pressure in the high-pressure portion may increase due to heat reception. In this regard, according to the configuration in which the injection start control is performed, the relief valve 15 can be prevented from opening during the engine stop period, and as a result, spike fuel pressure can be prevented from being generated in the low pressure portion. ..

(Other embodiments)
The present invention is not limited to the above embodiment, and may be implemented as follows, for example.

-The present invention may be applied to a vehicle including an engine 50 and a generator (motor) as a vehicle drive source. In this case, the injection start control is performed by the fuel injection valve 52 when the fuel pressure in the high pressure portion becomes higher than the rise determination value Pw during the operation stop period of the engine 50 after switching from the engine running to the motor running. Fuel injection is restarted and control is performed to suppress the rise in fuel pressure. The injection start control of this embodiment will be described with reference to FIG. In FIG. 10, the solid line shows the case where the valve opening suppression control is executed during the engine stop period, and the alternate long and short dash line shows the case where the valve opening suppression control is not executed.

In FIG. 10, when there is a request to switch the vehicle drive source from the engine 50 to the motor, first, the motor is turned on at time t71, the motor output is gradually increased, and the output of the engine 50 is gradually decreased. Will be done. Then, at time t72, the engine 50 is automatically stopped. When the actual rail pressure Pr rises due to the heat received due to the automatic stop of the engine and the actual rail pressure Pr eventually reaches the rise determination value Pw, the fuel injection by the fuel injection valve 52 is restarted at that time t73, and the engine 50 is restarted. Rail. The engine output generated when the engine is restarted is consumed for power generation, for example. By such an engine restart, even if the pressure in the rail 16 rises due to the heat received due to the engine stop, the rail fuel pressure does not reach the valve opening pressure Po, and the valve closed state of the relief valve 15 is maintained. Therefore, as shown by the solid line in FIG. 10, the generation of spike fuel pressure is suppressed during the engine stop period (time t74). In a vehicle provided with an engine 50 and a motor as a vehicle drive source, stop delay control may be performed together with or instead of injection start control as valve opening suppression control.

The present invention may be applied to a fuel supply system including a first injection valve which is an in-cylinder injection type fuel injection valve 52 and a second injection valve which is a port injection type fuel injection valve as a fuel injection valve. .. Specifically, the injection start control is a period after the injection mode of the fuel supplied into the cylinder of the engine 50 is switched from the direct injection mode by the first injection valve to the port injection mode by the second injection valve (that is,). When the fuel pressure in the high-pressure part becomes higher than the rise determination value Pw during the fuel injection stop period from the first injection valve), the fuel injection by the fuel injection valve 52 is restarted, and the fuel pressure further rises. Control to suppress. The injection start control of this embodiment will be described with reference to FIG. In FIG. 11, the solid line indicates the case where the valve opening suppression control is executed during the fuel injection stop period from the first injection valve, and the alternate long and short dash line indicates the case where the valve opening suppression control is not executed.

In FIG. 11, when there is a switching request for switching the injection mode to the port injection mode during the period when the engine 50 is being operated in the direct injection mode, the time t81 to t82, which is the timing of the switching request, The required injection amount of the first injection valve (direct injection required injection amount) is gradually reduced, and the required injection amount of the second injection valve (port injection required injection amount) is gradually increased. Further, at time t82, fuel injection from the first injection valve is stopped. After that, the actual rail pressure Pr rises due to heat reception due to the stagnation of the fuel cycle, and when the actual rail pressure Pr eventually reaches the rise determination value Pw, fuel injection by the first injection valve is restarted at that time t83. As a result, even if the pressure inside the rail 16 rises due to the heat received by switching from the direct injection mode to the port injection mode, the rail fuel pressure does not reach the valve opening pressure Po, and the relief valve 15 is closed. Is retained. As a result, as shown by the solid line in FIG. 11, the generation of spike fuel pressure Sp is suppressed (time t84). In a fuel supply system including a first injection valve and a second injection valve as fuel injection valves, stop delay control may be performed together with or instead of injection start control as valve opening suppression control.

-In the first embodiment, stop delay control is performed as valve opening suppression control, and in the second embodiment, injection start control is performed as valve opening suppression control. However, stop delay control and injection start control are performed. It may be a system that implements good performance.

-The boost amount ΔP tends to increase as the fuel temperature decreases. In consideration of this point, the stop delay control may be performed on the condition that the fuel temperature of the high pressure portion at the time of requesting the engine stop is equal to or lower than the determination value. This is because when the fuel temperature in the high-pressure portion is high, the boosting amount ΔP does not increase so much, and the relief valve 15 does not open so much due to the heat received during the engine stop period. If the fuel temperature in the high-pressure section is high and the risk of the relief valve 15 opening unintentionally is small, the rail fuel pressure after the engine is stopped is maintained on the high-pressure side so that the engine will be started the next time the engine is started. The startability of 50 can be ensured. Here, it may be determined whether or not the fuel temperature is equal to or lower than the determination value by providing a temperature sensor in the high pressure portion and using a value directly detected by the temperature sensor. Alternatively, the outside air temperature detected by the outside air temperature sensor may be used to determine whether or not the detected value of the outside air temperature is equal to or less than the determination value.

-In the above embodiment, when it is determined that the actual rail pressure Pr detected by the rail pressure sensor 31 is lower than the decrease determination value Ps, a fuel cut is performed to stop the operation of the engine 50. The stop delay control is not limited to the configuration in which the fuel cut is performed based on the comparison result between the actual rail pressure Pr and the decrease determination value Ps. For example, when there is a request to stop the operation of the engine 50 (in the above embodiment, when there is an operation to switch off the key switch 34), from the time when the request to stop the engine is made until a predetermined time T elapses. During the period of, the operating state of the engine 50 (for example, the idle operating state) is kept continuous, and then the operation of the engine 50 is stopped. In this case as well, the operation of the engine 50 can be stopped after the fuel pressure in the high pressure portion is sufficiently lowered immediately before the operation of the engine 50 is stopped. The predetermined time T may be set according to the target decompression amount for lowering the fuel pressure in the high pressure portion after the operation stop request timing and the fuel injection amount per injection by the fuel injection valve 52.

-In the stop delay control, it is determined that the actual rail pressure Pr detected by the rail pressure sensor 31 after the operation stop request of the engine 50 has decreased from the rail fuel pressure (P1 in FIG. 4) at the time of the operation stop request. If this happens, the operation of the engine 50 may be stopped.

-In the above embodiment, the decrease determination value Ps may be variably set based on the fuel temperature of the high pressure portion. When the key switch 34 is turned on immediately after the key switch 34 is switched off to start the engine 50, the higher the fuel temperature, the more the startability is required at the next engine start. Further, the boost amount ΔP tends to increase as the fuel temperature decreases. In view of these points, the higher the fuel temperature, the higher the decrease determination value Ps is set. As a result, it is possible to suppress the opening of the relief valve 15 due to the automatic stop of the engine while sufficiently ensuring the engine restartability when the fuel temperature is relatively high.

The volume of the rail 16 so that the boosting speed Va of the rail fuel pressure during the engine stop period is equal to or less than the limit flow rate Qp that can maintain the rail fuel pressure at the valve opening pressure Po of the relief valve 15 without fully opening the relief valve 15. By setting, the generation of spike fuel pressure during the engine stop period is suppressed (see FIG. 12). That is, the boosting speed Va of the rail fuel pressure when the rail fuel pressure reaches the valve opening pressure Po and the fuel flow rate (decompression speed Vp) flowing out to the low pressure side by the minute valve opening of the relief valve 15 match or are boosted. If the velocity Va is lower than the decompression velocity Vp, the valve opening pressure Po can be maintained while maintaining the minute valve opening. On the other hand, when the boosting speed Va becomes large and the minute valve opening of the relief valve 15 is not maintained, the relief valve 15 is fully opened and the high-pressure fuel flows into the low-pressure side at once, causing spikes in the low-pressure part such as the low-pressure pipe 13. Fuel pressure will be generated. Therefore, in the present embodiment, the volume of the rail 16 is set so as to satisfy the relationship of "limit flow rate Qp (volume flow rate / hour) ≥ boost speed Va (volume increase amount / hour)". As a result, when the rail fuel pressure becomes close to the valve opening pressure Po during the engine stop period, the relief valve 15 is made to open minutely, and the generation of spike fuel pressure is suppressed.

If the rail fuel pressure boosting speed Va at the time of soaking is defined as the rail fuel pressure boosting speed Vspeed and the rail fuel pressure boosting speed Vspeed is defined by the volume increase amount per hour (volume increase amount / hour), the rail fuel pressure boosting speed Vspeed is expressed by the following equation ( It can be represented by 3).
Vspeed = dP / dt * Vrail * K ... (3)
(In equation (3), dP / dt represents the pressure change rate, Vrail represents the rail volume, and K represents the bulk modulus of the fuel.)

Here, the pressure change rate dP / dt is determined according to the rate of temperature rise and the physical characteristics of the fuel. Specifically, the faster the temperature rising rate, the faster the pressure change rate dP / dt. In addition, the pressure change rate dP / dt at the same temperature rise rate is smaller for gasoline fuel than for ethanol fuel, and the pressure change rate dP / dt at the same temperature rise rate is higher at high temperature than at low temperature. Small (see FIG. 13). Therefore, if the pressure change rate dP / dt increases, the rail fuel pressure boosting speed Vspeed also increases, but the rail fuel pressure boosting speed Vspeed changes according to the temperature rise rate and the fuel physical characteristics, and is difficult to control. Therefore, in the present embodiment, the rail fuel pressure boosting speed Vspeed is suppressed to be equal to or lower than the minute valve opening maintenance limit speed VTH (hard limit value) of the relief valve 15 by setting the rail volume volume (see FIG. 13), whereby the engine stop period It suppresses the relief valve 15 from fully opening inside.

When the boosted amount ΔP due to heat reception after the engine is stopped is larger than the predetermined pressure α, the valve opening pressure Po may be set to a value on the high pressure side of the boosted amount ΔP or more than the system fuel pressure Px (Po ≧ Px + ΔP). By designing the relief valve 15 so that the valve opening pressure Po is within the above range in consideration of the boosting amount ΔP, it is possible to prevent the relief valve 15 from unintentionally opening due to heat reception during the engine stop period. it can.

-The relief valve 15 may be provided on the rail 16. In this case, as the relief valve 15 opens, the fuel in the rail 16 returns to the low pressure portion through the return pipe 17.

-As the pressure of the high pressure portion, instead of using the actual rail pressure Pr, the pressure in the high pressure pipe 14 or the pressure in the fuel injection valve 52 may be used.

The controls and methods described herein are provided by a dedicated computer provided by configuring a processor and memory programmed to perform one or more functions embodied by a computer program. It may be realized. Alternatively, the controls and methods thereof described in the present disclosure may be implemented by a dedicated computer provided by configuring the processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and method thereof described in the present disclosure may be a combination of a processor and memory programmed to perform one or more functions and a processor composed of one or more hardware logic circuits. It may be realized by one or more dedicated computers configured. Further, the computer program may be stored in a computer-readable non-transitional tangible recording medium as an instruction executed by the computer.

10 ... Fuel supply system, 15 ... Relief valve, 16 ... Rail, 20 ... High pressure pump, 31 ... Rail pressure sensor (fuel pressure detector), 50 ... Engine (internal combustion engine), 52 ... Fuel injection valve, 60 ... ECU (fuel pressure) Control unit, drop determination unit, temperature determination unit).

Claims (5)

A high-pressure pump (20) that increases the pressure of the low-pressure fuel supplied from the fuel container (11) and discharges the high-pressure fuel, a pressure-accumulation container (16) that stores the high-pressure fuel discharged from the high-pressure pump, and the high-pressure fuel in the pressure-accumulation container. A fuel injection valve (52) that injects directly into the cylinder of the internal combustion engine (50) and a high-pressure portion (14, 16) downstream of the high-pressure pump are provided, and the fuel pressure of the high-pressure portion is a predetermined valve opening. Applied to fuel supply systems with a relief valve (15) that opens when the pressure is higher than the pressure.
During the injection stop period, by performing control to reduce the fuel pressure of the high pressure portion immediately before the injection stop period for stopping the injection of fuel from the fuel injection valve and at least during the injection stop period. A control device for a fuel supply system including a fuel pressure control unit that performs valve opening suppression control for suppressing the opening of the relief valve. The injection stop period is a period during which the injection of fuel from the fuel injection valve is stopped due to an engine stop request for stopping the operation during the operation of the internal combustion engine.
The fuel pressure control unit performs, as the valve opening suppression control, a stop delay control for stopping the operation of the internal combustion engine at a timing after the engine stop request when the engine stop request is made. The control device for the fuel supply system according to 1. A fuel pressure detection unit that detects the fuel pressure of the high pressure unit, and
Decrease determination for determining whether or not the fuel pressure detected by the fuel pressure detection unit after the engine stop request is lower than the predetermined decrease determination value set on the low pressure side with respect to the valve opening pressure. With a department,
The fuel pressure control unit continues the operation of the internal combustion engine until the fuel pressure of the high pressure portion is determined to be lower than the reduction determination value by the reduction determination unit, and is said to be lower than the reduction determination value. The control device for a fuel supply system according to claim 2, wherein the operation of the internal combustion engine is stopped when the determination is made. A temperature determination unit for determining whether or not the fuel temperature of the high-pressure unit is lower than a predetermined temperature when the engine stop request is made is provided.
The control device for a fuel supply system according to claim 2 or 3, wherein the fuel pressure control unit performs the stop delay control when the temperature determination unit determines that the fuel temperature is lower than the predetermined temperature. When the fuel pressure of the high-pressure unit becomes higher than a predetermined increase determination value set on the low-pressure side with respect to the valve-opening pressure during the injection stop period, the fuel pressure control unit controls the valve opening. The control device for a fuel supply system according to any one of claims 1 to 4, wherein injection start control for injecting fuel from the fuel injection valve is performed.

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