JP2009079514A - Fuel pressure control device for cylinder injection type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the ease of restarting after an idling stop while reducing a fuel leak (oil tightness leak) from a fuel injection valve during the idling stop as much as possible, in a cylinder injection engine with an idling stop function. <P>SOLUTION: A relief valve 41 for reducing fuel pressure in a high pressure fuel system is provided at a predetermined section of the high pressure fuel system supplying high pressure fuel to a fuel injection valve 34 from a high pressure pump 14 (a delivery pipe 33 in an embodiment). The open and close action of the relief valve 41 is controlled to reduce fuel pressure in the high pressure fuel system detected by a fuel pressure sensor 35 to predetermined fuel pressure at a time of the idling stop, and a manual stop by turning off an ignition switch 38. The easiness of restarting after the idling stop is improved while reducing an oil tightness leak during the idling stop as much as possible by setting set fuel pressure during the idling stop higher than set fuel pressure at a time of the manual stop. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention provides a cylinder having a function of controlling idle stop (automatic stop and automatic restart) of a cylinder injection internal combustion engine and a function of reducing the fuel pressure in the high-pressure fuel system when the internal combustion engine (engine) is stopped. The invention relates to a fuel pressure control device for an internal injection internal combustion engine.

  An in-cylinder injection engine that directly injects fuel into a cylinder has a shorter time from injection to combustion and sufficient time to atomize the injected fuel compared to an intake port injection engine that injects fuel into an intake port. Therefore, it is necessary to atomize the injected fuel by increasing the injection pressure. Therefore, as described in Patent Document 1 (Japanese Patent Laid-Open No. 2003-322048), in a cylinder injection engine, the fuel pumped up from the fuel tank by the low pressure pump is driven by the engine camshaft. The high-pressure fuel discharged from the high-pressure pump is pumped to the fuel injection valve through the high-pressure fuel pipe.

  In general, a high pressure pump is provided with a check valve that prevents a reverse flow of discharged fuel so that the fuel pressure (fuel pressure) in the high pressure fuel pipe is maintained at a high pressure. If the fuel pressure is maintained at a high pressure, the amount of fuel leakage from the fuel injection valve (oil-tight leakage amount) tends to increase while the engine is stopped, and the leaked fuel accumulates in the cylinder and remains unburned at the next start-up. There is a problem that exhaust emissions at the time of start-up deteriorate.

As a countermeasure, as described in Patent Document 2 (Japanese Patent Laid-Open No. 10-89176), Patent Document 3 (Japanese Patent Laid-Open No. 2005-264902), etc., high-pressure fuel is supplied from the high-pressure pump to the fuel injection valve. An electromagnetically driven relief valve is provided at a predetermined part of the high-pressure fuel system (delivery pipe, high-pressure fuel pipe, high-pressure pump, etc.) so that the fuel pressure in the high-pressure fuel system is lowered by opening the relief valve when the engine is stopped. There is what I did.
JP 2003-322048 A Japanese Patent Laid-Open No. 10-89176 JP 2005-264902 A

  In recent years, in order to save fuel consumption, the engine is automatically stopped (idle stop) while the vehicle is temporarily stopped, and then the driver prepares for starting the vehicle (brake release, shift lever operation, etc.) and starts operation (accelerator depression, etc.) Vehicles equipped with an idle stop system that automatically restarts the engine when the operation is performed are put into practical use. When the techniques of Patent Documents 2 and 3 are applied to a vehicle equipped with such an idle stop system and an in-cylinder injection engine, the fuel pressure in the high-pressure fuel system is reduced during normal engine stop (ignition switch) even during idle stop. It is conceivable to reduce the fuel pressure to the set fuel pressure (when the engine is stopped by turning on the engine) to prevent fuel leakage from the fuel injection valve during idle stop.

  However, in general, the idling stop time is short and restarting is often performed immediately. Therefore, if the fuel pressure in the high pressure fuel system is reduced to the set fuel pressure at the time of normal engine stop at the time of idling stop, the driver Makes you feel the delay of restart after idle stop. In order to ensure good restartability (combustibility) during restart after idle stop, it is necessary to quickly increase the fuel pressure in the high-pressure fuel system to a fuel pressure suitable for restart. This is because if the fuel pressure in the inside high-pressure fuel system becomes too low, the time required to increase the fuel pressure at the time of restart increases accordingly. If the fuel pressure is insufficient at the time of restart, it becomes difficult to inject fuel into the cylinder in the latter half of the compression stroke, which is an injection timing suitable for starting an in-cylinder injection engine, or it was possible to inject in the latter half of the compression stroke However, the fuel spray shape and atomization deteriorate, and good restartability (combustibility) cannot be obtained.

  The present invention has been made in view of such circumstances, and therefore the object of the present invention is to reduce fuel leakage from the fuel injection valve during idle stop as much as possible in a cylinder injection internal combustion engine with an idle stop function. However, an object of the present invention is to provide a fuel pressure control device for a direct injection internal combustion engine that can improve the restartability after idle stop.

  In order to achieve the above object, an invention according to claim 1 is directed to idle stop means for controlling automatic stop and automatic restart of a direct injection internal combustion engine, and to supply high pressure fuel from a high pressure pump to a fuel injection valve. A pressure reducing mechanism for reducing the pressure of the fuel in the high pressure fuel system (hereinafter referred to as “fuel pressure”), a fuel pressure detecting means for detecting the fuel pressure in the high pressure fuel system, and a fuel pressure detected by the fuel pressure detecting means is set as a fuel pressure. In the fuel pressure control apparatus for a direct injection internal combustion engine, the control means includes a control means for controlling the pressure reducing mechanism so as to reduce the pressure until the automatic stop by the idle stop means (hereinafter referred to as “idle stop time”). ) Is set to a fuel pressure higher than the fuel pressure set at the time of manual stop by turning off the ignition switch.

  In this configuration, the set fuel pressure at idle stop is set to a fuel pressure higher than the set fuel pressure at manual stop, so compared to the case where the set fuel pressure at idle stop is set the same as the set fuel pressure at manual stop, The pressure difference between the fuel pressure at idling stop and the minimum fuel pressure necessary to ensure combustibility at restart is reduced, and the fuel pressure in the high-pressure fuel system is quickly secured at restart after idling stop. The required minimum fuel pressure can be increased, the restartability can be improved, and the driver can be prevented from feeling the delay in restarting (shaking). Moreover, in general, the idling stop time is short, and restarting is often performed immediately. Therefore, even if the set fuel pressure during idle stop is set higher than the set fuel pressure during manual stop, There is little fuel leakage from the fuel injection valve (hereinafter referred to as “oil-tight leakage”), and deterioration of exhaust emission due to oil-tight leakage can be prevented.

  In this case, as set forth in claim 2, the set fuel pressure at the time of idling stop is set to the minimum fuel pressure at which good combustion can be obtained when the first injection at the time of restart after idling stop is performed in the second half of the compression stroke. It is good to do so. In this way, good combustion can be obtained from the first injection at the restart after the idle stop, and a very quick restart can be realized.

  Further, as set forth in claim 3, the set fuel pressure at the time of idling stop may be set based on any one or a plurality of temperatures of the cooling water temperature, the oil temperature, and the outside air temperature at the time of idling stop. . In general, the higher the temperature of the air-fuel mixture at the time of restart or the temperature in the cylinder, the easier the air-fuel mixture burns. Therefore, the higher the temperature, the lower the minimum fuel pressure at which good combustion can be obtained. . Therefore, as set forth in claim 4, the set fuel pressure at the idle stop is set lower as the temperature used for setting the set fuel pressure at the idle stop among the cooling water temperature, the oil temperature, and the outside air temperature at the idle stop is increased. This makes it possible to set the set fuel pressure during idle stop to the lowest fuel pressure within the fuel pressure range where good combustion can be obtained according to the temperature of the mixture and the temperature in the cylinder. The oil-tight leak during idling stop can be further reduced while securing the property.

  In addition, if the duration of the idle stop state becomes too long, the effect of oil-tight leakage during the idle stop may appear in the exhaust emission. Therefore, the set fuel pressure at the idle stop is set to the idle stop as in claim 5. You may make it change according to the duration of a state. For example, if the set fuel pressure during idle stop is decreased stepwise or gradually as the duration of the idle stop state increases, the amount of oil-tight leak per unit time decreases as the duration of the idle stop state increases. Therefore, even if the duration of the idling stop state becomes longer, the deterioration of exhaust emission due to oiltight leakage during idling stop can be reduced.

  In this case, as described in claim 6, when the duration of the idle stop state continues for a predetermined time or more, the set fuel pressure at the idle stop is the same as the set fuel pressure at the manual stop by turning off the ignition switch or You may make it reduce to the near fuel pressure. In this way, after the duration of the idle stop state continues for a predetermined time or more, the same oil-tight leak prevention effect as that at the time of manual stop can be obtained, and the exhaust emission deterioration due to the longer idle stop time. Can be suppressed.

  Further, as in claim 7, the set fuel pressure at the time of manual stop is based on any one or a plurality of temperatures of the coolant temperature, the oil temperature, the outside air temperature, the fuel temperature, and the delivery pipe temperature at the time of manual stop. You may make it set. If the fuel pressure in the high-pressure fuel system during manual stop becomes too low, vapor (bubbles) is generated in the fuel in the high-pressure fuel system, which causes a decrease in startability. Further, there is a relationship that vapor is more likely to be generated as the fuel temperature in the high-pressure fuel system is higher, and vapor is more likely to be generated as the fuel pressure is lower. Therefore, as in claim 8, the higher the temperature used for setting the set fuel pressure during manual stop out of the coolant temperature, oil temperature, outside air temperature, fuel temperature, and delivery pipe temperature during manual stop, the higher the temperature during manual stop. If the set fuel pressure is set higher, the fuel temperature in the high-pressure fuel system becomes higher and the temperature environment is more likely to generate vapor. This makes it possible to effectively prevent deterioration of startability due to vapor.

Hereinafter, an embodiment embodying the best mode for carrying out the present invention will be described.
First, a schematic configuration of the entire high-pressure fuel supply system of a cylinder injection engine (internal combustion engine) will be described with reference to FIG.

  A low pressure pump 12 that pumps up the fuel is installed in the fuel tank 11 that stores the fuel. The low-pressure pump 12 is driven by an electric motor (not shown) that uses a battery (not shown) as a power source. The fuel discharged from the low pressure pump 12 is supplied to the high pressure pump 14 through the fuel pipe 13. A pressure regulator 15 is connected to the fuel pipe 13, and the discharge pressure of the low-pressure pump 12 (fuel supply pressure to the high-pressure pump 14) is adjusted to a predetermined pressure by the pressure regulator 15, and surplus fuel exceeding that pressure Is returned to the fuel tank 11 by the fuel return pipe 16.

  As shown in FIG. 2, the high-pressure pump 14 is a piston pump that sucks / discharges fuel by reciprocating a piston 19 in a cylindrical pump chamber 18. The piston 19 is fitted to a camshaft 20 of the engine. It is driven by the rotational movement of the cam 21. A fuel pressure control valve 23 is provided on the suction port 22 side of the high-pressure pump 14. The fuel pressure control valve 23 is a normally open type electromagnetic valve, and includes a valve body 24 that opens and closes the suction port 22, a spring 25 that urges the valve body 24 in the valve opening direction, and a valve body 24 in the valve closing direction. And a solenoid 26 that is electromagnetically driven.

  During the intake stroke of the high-pressure pump 14 (when the piston 19 is lowered), the fuel pressure control valve 23 is opened and fuel is sucked into the pump chamber 18, and during the discharge stroke (when the piston 19 is raised), the fuel pressure control valve. By controlling the valve closing time 23 (the valve closing state time from the valve closing start time to the top dead center of the piston 19), the discharge amount of the high-pressure pump 14 is controlled to control the fuel pressure (discharge pressure).

  That is, when increasing the fuel pressure, the valve closing start timing (energization timing) of the fuel pressure control valve 23 is advanced, thereby extending the valve closing time of the fuel pressure control valve 23 and increasing the discharge amount of the high pressure pump 14. Conversely, when lowering the fuel pressure, the valve closing start timing (energization timing) of the fuel pressure control valve 23 is retarded, thereby shortening the valve closing time of the fuel pressure control valve 23 and reducing the discharge amount of the high pressure pump 14. .

  On the other hand, a check valve 28 for preventing the backflow of discharged fuel is provided on the discharge port 27 side of the high-pressure pump 14. As shown in FIG. 1, the fuel discharged from the high-pressure pump 14 is sent to a delivery pipe 33 through a high-pressure fuel pipe 32, and from this delivery pipe 33 to a fuel injection valve 34 attached to the cylinder head of the engine for each cylinder. High pressure fuel is dispensed. The high-pressure fuel pipe 33 (or delivery pipe 33) is provided with a fuel pressure sensor 35 (fuel pressure detection means) for detecting the fuel pressure in the high-pressure fuel pipe 32 (inside the high-pressure fuel system). A cooling water temperature sensor 36 for detecting the above is provided. In addition, an outside air temperature sensor 39 for detecting the outside air temperature is provided.

  In the present embodiment, a relief valve as a pressure reducing mechanism for reducing the fuel pressure in the high pressure fuel system is provided in a predetermined portion of the high pressure fuel system that supplies high pressure fuel from the high pressure pump 14 to the fuel injection valve 34, for example, the delivery pipe 33. 41 (pressure reducing valve) is provided, and the discharge port of the relief valve 41 is connected to the fuel pipe 13 on the low pressure side via the relief pipe 42.

  As this relief valve 41, for example, a normally closed electromagnetic drive type is used, and on / off of energization to the relief valve 41 is controlled by an ECU 37 described later. When the fuel pressure in the high-pressure fuel system is higher than the set fuel pressure, by energizing the relief valve 41 and opening it, a part of the fuel in the delivery pipe 33 passes from the relief valve 41 through the relief pipe 42 to the low-pressure side. To the fuel pipe 13 and returned to the fuel tank 11 to reduce the fuel pressure in the high-pressure fuel system. Thereafter, when the fuel pressure in the high-pressure fuel system drops to the set fuel pressure, the energization of the relief valve 41 is turned off and the valve is closed to maintain the fuel pressure in the high-pressure fuel system at the set fuel pressure.

  In the configuration example of FIG. 1, the relief valve 41 is provided in the delivery pipe 33. However, in the case of a high-pressure fuel system from the high-pressure pump 14 to the fuel injection valve 34, the relief valve 41 is provided in a place other than the delivery pipe 33. For example, the relief valve 41 may be provided in the high-pressure fuel pipe 32 or the high-pressure pump 14. In the configuration example of FIG. 1, the outlet of the relief pipe 42 is connected to the discharge side of the low-pressure pump 12 in the low-pressure side fuel pipe 13, but the outlet of the relief pipe 42 is opened in the fuel tank 11. Thus, the fuel flowing out from the relief pipe 42 may be returned directly into the fuel tank 11.

  The vehicle of the present embodiment is equipped with the high-pressure fuel supply system and the in-cylinder injection engine, and automatically stops (idle stop) the engine during a temporary stop, and then the driver performs a preparatory operation for starting the vehicle. It is equipped with an idle stop system (idle stop means) that automatically restarts the engine when a brake operation (brake release, shift lever operation, etc.) or a start operation (accelerator depression, etc.) is performed.

  An engine control circuit (hereinafter referred to as “ECU”) 37 that controls the operation of the engine is configured mainly with a microcomputer, and the fuel pressure (fuel injection valve 34) in the high-pressure fuel system detected by the fuel pressure sensor 35 during engine operation. The discharge amount of the high-pressure pump 14 (the energization timing of the fuel pressure control valve 23) is feedback-controlled so that the pressure of the fuel to be supplied) matches the target fuel pressure.

  Further, the ECU 37 reduces the fuel pressure in the high-pressure fuel system detected by the fuel pressure sensor 35 to the set fuel pressure at the time of idle stop and at the time of manual stop by turning off an ignition switch (hereinafter referred to as “IG switch”) 38. Controls the opening / closing operation (energization on / off) of the relief valve 41.

  By the way, during idle stop, the fuel pressure in the high-pressure fuel system is reduced to the set fuel pressure during manual stop to prevent fuel leakage from the fuel injection valve 34 during idle stop (hereinafter referred to as “oil-tight leak”). Can be considered.

  However, in general, the idling stop time is short, and restarting is often performed immediately. Therefore, the fuel pressure in the high-pressure fuel system is reduced to the set fuel pressure at the time of manual stop by turning off the IG switch 38 during idling stop. If this happens, the driver may feel a delay in restart after idle stop. In order to ensure good restartability (combustibility) during restart after idle stop, it is necessary to quickly increase the fuel pressure in the high-pressure fuel system to a fuel pressure suitable for restart. This is because if the fuel pressure in the inside high-pressure fuel system becomes too low, the time required to increase the fuel pressure at the time of restart increases accordingly. If the fuel pressure is insufficient at the time of restart, it becomes difficult to inject fuel into the cylinder in the latter half of the compression stroke, which is an injection timing suitable for starting an in-cylinder injection engine, or it was possible to inject in the latter half of the compression stroke However, the fuel spray shape and atomization deteriorate, and good restartability (combustibility) cannot be obtained.

  Therefore, in this embodiment, the ECU 37 improves the restartability after the idle stop by setting the set fuel pressure at the idle stop to a fuel pressure higher than the set fuel pressure at the time of manual stop by turning off the IG switch 38. The oil pressure leakage during idle stop is reduced as much as possible, and the set fuel pressure at idle stop is the same as the set fuel pressure at manual stop (or By reducing the fuel pressure to a fuel pressure close to that, an increase in the amount of oil-tight leak due to an increase in idle stop time is suppressed.

  The fuel pressure control in the high-pressure fuel system at the idle stop and the manual stop described above is executed by the ECU 37 according to the engine stop fuel pressure control program of FIG. This program is repeatedly executed at a predetermined cycle while the power of the ECU 37 is turned on, and plays a role as control means in the claims. Incidentally, in order to execute this program for a while after the IG switch 38 is turned off, the main relay (not shown) of the power supply line is maintained in the on state, and the power supply to the ECU 37 is continued. Yes.

  When this program is started, first, in step 101, it is determined whether or not the IG switch 38 is turned on. If the IG switch 38 is turned on, the process proceeds to the next step 102, where an idle stop condition is established. It is determined whether or not the following condition (1) to (5) is satisfied, for example.

(1) The specified time has elapsed since startup (after engine warm-up is complete)
(2) The brake is being operated
(3) Accelerator OFF
(4) Being idle
(5) Being stopped If any one of these conditions (1) to (5) is not satisfied, the idle stop condition is not satisfied, and this program is terminated without performing the subsequent processing. To do.

  On the other hand, if all of the above conditions (1) to (5) are satisfied, the idle stop condition is satisfied and the routine proceeds to step 102, where the engine is automatically stopped (idle stop). Thereafter, the routine proceeds to step 104, where it is determined whether or not it is immediately after the idling stop (before the start of pressure reduction of the high-pressure fuel system), and if it is immediately after the idling stop, the routine proceeds to step 106 and the set fuel pressure Pt1 at the idling stop. Is calculated as follows.

  For example, as shown in FIG. 4, the cooling water temperature (or oil temperature) and the outside air temperature during idling stop detected by the cooling water temperature sensor 36 and the outside air temperature sensor 39 are read, and the cooling water temperature (or oil temperature) and the outside air temperature are parameters. Referring to the two-dimensional map for calculating the set fuel pressure Pt1a at the time of idling stop, the set fuel pressure Pt1a at the time of idling stop according to the coolant temperature (or oil temperature) and the outside air temperature at that time is calculated.

  In general, the higher the temperature of the air-fuel mixture at the time of restart or the temperature in the cylinder, the easier the air-fuel mixture burns. Therefore, the higher the temperature, the lower the minimum fuel pressure at which good combustion can be obtained. . In consideration of this characteristic, the two-dimensional map for calculating the set fuel pressure Pt1a at the idling stop is set so that the set fuel pressure Pt1a at the idling stop decreases as the cooling water temperature (or oil temperature) or the outside air temperature increases. ing. This makes it possible to set the set fuel pressure Pt1a at the time of idling stop to the lowest fuel pressure within the fuel pressure range where good combustion can be obtained according to the temperature of the air-fuel mixture and the temperature in the cylinder. Control that further reduces oil-tight leakage during idling stop is possible while ensuring startability.

  In this case, the set fuel pressure Pt1a at the time of idling stop is set to be set to the minimum fuel pressure at which good combustion is obtained when the first injection at the time of restart after idling stop is performed in the second half of the compression stroke. . Thereby, the set fuel pressure Pt1a at the time of idling stop is set within a range of 2 to 5 [MPa], for example.

  Further, in the example of FIG. 4, the set fuel pressure Pt1a at the time of idling stop calculated from the two-dimensional map is compared with the in-cylinder pressure Pt1b at the compression TDC position, and the larger one is finally set as the set fuel pressure Pt1 at the time of idling stop. select. This is because if the fuel pressure in the high-pressure fuel system (the injection pressure of the fuel injection valve 34) is lower than the in-cylinder pressure Pt1b at the compression TDC position, fuel cannot be injected from the fuel injection valve 34.

  In the present invention, the set fuel pressure Pt1 at the time of idling stop is set based on only one of the cooling water temperature (or oil temperature) and the outside air temperature, or the set fuel pressure Pt1 at the time of idling stop is set in advance. You may make it set to a fixed value.

  After calculating the set fuel pressure Pt1 at the time of idling stop, the routine proceeds to step 107 where the relief valve 41 is energized and opened to reduce the fuel pressure Ps in the high-pressure fuel system. Thereafter, the routine proceeds to step 108, where the fuel pressure sensor 35 detects the fuel pressure Ps in the high-pressure fuel system, and in the next step 109, the fuel pressure Ps in the high-pressure fuel system calculated in the above step 106 is the set fuel pressure Pt1 at idling stop. It is determined whether or not the fuel pressure Ps has decreased below. If the fuel pressure Ps in the high-pressure fuel system is still higher than the set fuel pressure Pt1 at the time of idling stop, the process returns to step 107 and the relief valve 41 continues to be opened (energized). Thus, the fuel pressure Ps in the high-pressure fuel system is continuously reduced.

  Thereafter, when the fuel pressure Ps in the high-pressure fuel system drops below the set fuel pressure Pt1 at the time of idling stop, the routine proceeds to step 110, the energization to the relief valve 41 is turned off and this is closed to close the inside of the high-pressure fuel system. The decompression of the fuel pressure Ps is terminated, and the fuel pressure Ps in the high-pressure fuel system is maintained at the set fuel pressure Pt1 at the time of idling stop.

  Thereafter, while the idle stop state continues, every time this program is started, it is determined as “No” in the above step 104 and proceeds to step 105, and whether the idle stop duration has reached the predetermined time T or more. If the idle stop duration has not reached the predetermined time T, the program is terminated as it is.

  Then, when the idle stop continuation time becomes equal to or longer than the predetermined time T, it is determined as “Yes” in the above-described step 105, and the processing of steps 113 to 117 described later is executed to set the fuel pressure Ps in the high-pressure fuel system. Then, the fuel pressure is reduced to the same fuel pressure as the set fuel pressure Pt2 at the time of manual stop which is lower than the set fuel pressure Pt1 at the time of idling stop.

  On the other hand, if it is determined in step 101 that the IG switch 38 is turned off (OFF), the process proceeds to step 111 and the engine is stopped (manually stopped). Thereafter, the routine proceeds to step 112, where it is determined whether or not it is immediately after the manual stop (before the start of pressure reduction of the high-pressure fuel system). If not immediately after the manual stop, the fuel pressure reduction of the high-pressure fuel system has already ended. The program is terminated as it is.

  On the other hand, if it is determined in step 112 that it is immediately after the manual stop, the routine proceeds to step 113, where the set fuel pressure Pt2 at the time of manual stop is calculated as follows.

  For example, as shown in FIG. 5, the cooling water temperature (or oil temperature) and the outside air temperature at the time of manual stop detected by the cooling water temperature sensor 36 and the outside air temperature sensor 39 are read, and the cooling water temperature (or oil temperature) and the outside air temperature are parameters. Referring to the two-dimensional map for calculating the set fuel pressure Pt2 at the time of manual stop, the set fuel pressure Pt2 at the time of manual stop according to the coolant temperature (or oil temperature) and the outside air temperature at that time is calculated.

  If the fuel pressure Ps in the high-pressure fuel system during manual stop becomes too low, vapor (bubbles) is generated in the fuel in the high-pressure fuel system, which causes a decrease in startability. Further, there is a relationship that vapor is more likely to be generated as the fuel temperature in the high-pressure fuel system is higher, and vapor is more likely to be generated as the fuel pressure Ps is lower.

  Taking these relationships into consideration, the two-dimensional map for calculating the set fuel pressure Pt2 at the time of manual stop is set so that the set fuel pressure Pt2 at the time of manual stop increases as the coolant temperature (or oil temperature) and the outside air temperature increase. Has been. As a result, as the fuel temperature in the high-pressure fuel system becomes higher and the temperature environment is more likely to generate vapor, it is possible to control to suppress the generation of vapor by setting the set fuel pressure Pt2 at the time of manual stop higher.

  In the example of FIG. 5, the cooling water temperature (or oil temperature) and the outside air temperature are used as temperature information for evaluating the fuel temperature in the high-pressure fuel system. In addition, the temperature of the delivery pipe 33 is measured by a temperature sensor. Detect and set the set fuel pressure Pt2 at the time of manual stop according to the temperature of the delivery pipe 33, or directly detect the fuel temperature in the high pressure fuel system with the temperature sensor, and according to the actual fuel temperature The set fuel pressure Pt2 at the time of manual stop may be set.

  After calculating the set fuel pressure Pt2 at the time of manual stop, the routine proceeds to step 114 where the relief valve 41 is energized and opened to reduce the fuel pressure Ps in the high-pressure fuel system. Thereafter, the routine proceeds to step 115, where the fuel pressure sensor 35 detects the fuel pressure Ps in the high-pressure fuel system, and in the next step 116, the fuel pressure Ps in the high-pressure fuel system calculated in step 113 is the set fuel pressure at the time of manual stop. It is determined whether or not the pressure has decreased to Pt2 or less. If the fuel pressure Ps in the high-pressure fuel system is still higher than the set fuel pressure Pt2 at the time of manual stop, the routine returns to step 114 and the relief valve 41 is opened (energized). Continue to reduce the fuel pressure Ps in the high-pressure fuel system.

  Thereafter, when the fuel pressure Ps in the high-pressure fuel system drops below the set fuel pressure Pt2 at the time of manual stop, the routine proceeds to step 117, the energization to the relief valve 41 is turned off and this is closed to close the inside of the high-pressure fuel system. The decompression of the fuel pressure Ps is terminated, and the fuel pressure Ps in the high-pressure fuel system is maintained at the set fuel pressure Pt2 at the time of manual stop.

  According to the present embodiment described above, since the set fuel pressure Pt1 at the time of idling stop is set higher than the set fuel pressure Pt2 at the time of manual stop, the set fuel pressure Pt1 at the time of idling stop is set to the set fuel pressure Pt2 at the time of manual stop. Compared to the same setting, the pressure difference between the fuel pressure at idle stop and the minimum fuel pressure required to ensure combustibility at restart is reduced, and the fuel pressure in the high-pressure fuel system is reduced at restart after idle stop. It is possible to quickly increase to the minimum fuel pressure necessary for ensuring the combustibility at the time of restart, improve the restartability, and prevent the driver from feeling the delay in restart it can. Moreover, in general, the idling stop time is short and the restart is often performed immediately. Therefore, even if the set fuel pressure Pt1 at the idling stop is set higher than the set fuel pressure Pt2 at the manual stop, the idling stop is performed. There is little oil-tight leakage (fuel leakage from the fuel injection valve 34), and deterioration of exhaust emissions due to oil-tight leakage can be prevented.

  Moreover, the set fuel pressure Pt1 at the time of idling stop is set to the minimum fuel pressure at which good combustion can be obtained when the first injection at the restart after idling stop is performed in the second half of the compression stroke. In the restart after the idle stop, good combustion can be obtained from the first injection, and a very quick restart can be realized.

  Furthermore, as the cooling water temperature (or oil temperature) at the time of idling stop and the outside air temperature become higher, the set fuel pressure Pt1 at idling stop is set to be lower, so the idling stop according to the temperature of the air-fuel mixture and the temperature in the cylinder It is possible to set the fuel pressure Pt1 at the time to the lowest fuel pressure within the fuel pressure range where good combustion can be obtained, and even more oil-tight leakage during idle stop while ensuring restartability after idle stop Can be reduced.

  Further, when the duration of the idle stop state continues for the predetermined time T or longer, the set fuel pressure Pt1 at the time of idle stop is switched to the set fuel pressure Pt2 at the time of manual stop. After continuing the above, it is possible to obtain the same oil-tight leak prevention effect as that at the time of manual stop, and it is possible to suppress the deterioration of exhaust emission due to the longer idle stop time.

  In this case, when the duration of the idle stop state continues for a predetermined time T or longer, the set fuel pressure Pt1 at the time of idle stop may be set to a fuel pressure slightly higher than the set fuel pressure Pt2 at the time of manual stop.

  In the present invention, the set fuel pressure Pt1 at the time of idling stop may be decreased stepwise or gradually as the duration of the idling stop state becomes longer, and as a result, the duration of the idling stop state becomes longer. Thus, it is possible to control to reduce the amount of oil-tight leak per unit time, and even if the duration of the idle stop state is increased, the deterioration of exhaust emission due to the oil-tight leak during idle stop can be reduced.

  In this embodiment, the set fuel pressure Pt2 at the time of manual stop is set higher as the temperature information (cooling water temperature, oil temperature, outside air temperature, fuel temperature, delivery pipe temperature) for evaluating the fuel temperature at the time of manual stop is higher. Therefore, as the fuel temperature in the high-pressure fuel system becomes higher and the temperature environment is more likely to generate vapor, the fuel pressure Pt2 is set higher at the time of manual stop and control can be performed to suppress the generation of vapor. The startability deterioration due to vapor can be effectively prevented.

It is a schematic structure figure of the whole high-pressure fuel supply system in one example of the present invention. It is a block diagram of a high pressure pump. It is a flowchart which shows the flow of a process of an engine stop time fuel pressure control program. It is a block diagram explaining the calculation method of the setting fuel pressure Pt1 at the time of idling stop. It is a block diagram explaining the calculation method of the setting fuel pressure Pt2 at the time of a manual stop.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Fuel tank, 12 ... Low pressure pump, 14 ... High pressure pump, 18 ... Pump chamber, 19 ... Piston, 22 ... Suction port, 23 ... Fuel pressure control valve, 27 ... Discharge port, 28 ... Check valve, 32 ... High pressure fuel Piping, 33 ... Delivery pipe, 34 ... Fuel injection valve, 35 ... Fuel pressure sensor (fuel pressure detection means), 36 ... Cooling water temperature sensor, 37 ... ECU (idle stop means, control means), 38 ... Ignition switch, 39 ... Outside temperature Sensor, 41 ... relief valve (pressure reduction mechanism), 42 ... relief piping

Claims (8)

Idle stop means for controlling automatic stop and automatic restart of the direct injection internal combustion engine, and the pressure of the fuel in the high pressure fuel system that supplies high pressure fuel from the high pressure pump to the fuel injection valve (hereinafter referred to as “fuel pressure”) A pressure reducing mechanism for reducing pressure, fuel pressure detecting means for detecting a fuel pressure in the high pressure fuel system, and control means for controlling the pressure reducing mechanism so as to reduce the fuel pressure detected by the fuel pressure detecting means to a set fuel pressure. In a fuel injection control device for a cylinder injection internal combustion engine,
The control means sets the set fuel pressure at the time of automatic stop by the idle stop means to a fuel pressure higher than the set fuel pressure at the time of manual stop by turning off the ignition switch, and controls the fuel pressure of the direct injection internal combustion engine apparatus.   The control means sets the set fuel pressure at the time of the automatic stop to a minimum fuel pressure at which good combustion is obtained when the first injection at the time of automatic restart is performed in the latter half of the compression stroke. The fuel pressure control device for a cylinder injection internal combustion engine according to claim 1.   The said control means sets the set fuel pressure at the time of the said automatic stop based on any one or several temperature among the cooling water temperature at the time of an automatic stop, oil temperature, and external temperature. 2. A fuel pressure control device for a direct injection internal combustion engine according to claim 2.   The control means sets the set fuel pressure at the time of the automatic stop to be lower as the temperature used for setting the set fuel pressure at the time of the automatic stop is higher among the coolant temperature, the oil temperature, and the outside air temperature at the time of the automatic stop. A fuel pressure control device for a direct injection internal combustion engine according to claim 3.   The fuel pressure control device for a direct injection internal combustion engine according to any one of claims 1 to 4, wherein the control means changes the set fuel pressure at the time of the automatic stop according to the duration of the automatic stop state. .   When the duration of the automatic stop state continues for a predetermined time or more, the control means sets the set fuel pressure at the time of the automatic stop to the fuel pressure that is the same as or close to the set fuel pressure at the time of manual stop by turning off the ignition switch. 6. The fuel pressure control device for a cylinder injection internal combustion engine according to claim 5, wherein the fuel pressure control device is reduced.   The control means is configured to set a set fuel pressure at the time of manual stop by turning off the ignition switch to one or more of a coolant temperature, an oil temperature, an outside air temperature, a fuel temperature, and a delivery pipe temperature at the time of manual stop. The fuel pressure control device for a direct injection internal combustion engine according to any one of claims 1 to 6, wherein the fuel pressure control device is set based on the above.   The control means is configured such that the set fuel pressure at the time of manual stop increases as the temperature used at the time of setting the set fuel pressure at the time of manual stop among the coolant temperature, the oil temperature, the outside air temperature, the fuel temperature, and the delivery pipe temperature at the time of manual stop is higher The fuel pressure control device for a direct injection internal combustion engine according to claim 7, wherein the fuel pressure control device is set high.

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