JP2021021360A - Control device of engine - Google Patents

Abstract

To provide a control device of an engine which can further surely supply a proper quantity of fuel by a fuel injection valve.SOLUTION: An engine having a high-pressure fuel pump 80 for pressure-sending fuel to a fuel injection valve 15, and a low-pressure fuel pump 70 for pressure-sending the fuel to the high-pressure fuel pump 80 performs pump rotation-number increase control for determining whether or not a pressure-sending force of the low-pressure fuel pump 70 is lowered, and when determining that the pressure-sending force of the low-pressure fuel pump 70 is lowered, increasing a rotation number of the low-pressure fuel pump 70 at an increase rate higher than an increase rate up until the determination is performed, and lower than a prescribed upper limit increase rate.SELECTED DRAWING: Figure 1

Description

The present invention includes an engine including a fuel injection valve that injects fuel into a cylinder, a high-pressure fuel pump that pumps fuel toward the fuel injection valve, and a low-pressure fuel pump that pumps fuel toward the high-pressure fuel pump. Regarding the control device of.

Conventionally, in an engine, fuel is pumped from a fuel tank to a high-pressure fuel pump by a low-pressure fuel pump, fuel is pumped at high pressure from a high-pressure fuel pump toward a fuel injection valve, and high-pressure fuel is pumped from a fuel injection valve to a cylinder. Injection is being done.

Here, if vapor (bubbles) is generated in the fuel, the vapor interferes with the pumping of the fuel by the fuel pump, so that the fuel may not be properly supplied to the fuel injection valve. On the other hand, for example, in Patent Document 1, a device for removing the vapor generated in the passage is provided in the passage between the low pressure fuel pump and the high pressure fuel pump, and the vapor in the passage is used as a fuel tank. A device for returning to is disclosed.

Japanese Unexamined Patent Publication No. 2006-200423

In the apparatus of Patent Document 1, no countermeasure is taken against the vapor generated in the fuel sucked by the low-pressure fuel pump. Therefore, even if this device is used, there is a possibility that fuel cannot be properly supplied to the fuel injection valve. Specifically, when vapor is generated in the fuel sucked by the low-pressure fuel pump, it is difficult to properly pump the fuel from the low-pressure fuel pump because the vapor inhibits the suction of fuel from the low-pressure fuel pump. Therefore, there is a risk that a sufficient amount of fuel will not be supplied to the high-pressure fuel pump and thus the fuel injection valve. In particular, when the rotation speed of the low-pressure fuel pump is low, it becomes difficult to remove the vapor from the periphery of the rotating body because the fuel flow rate pumped from the low-pressure fuel pump is small.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an engine control device capable of reliably supplying an appropriate amount of fuel by a fuel injection valve.

In order to solve the above problems, the present invention presents a fuel injection valve that injects fuel into a cylinder, a high-pressure fuel pump that pumps fuel to the fuel injection valve, and a low-pressure fuel pump that pumps fuel to the high-pressure fuel pump. An engine control device including the above, which includes a pump control means for controlling a low-pressure fuel pump and a determination means for determining whether or not the pumping force of the low-pressure fuel pump has decreased. When it is determined that the pumping force of the fuel pump has decreased, the low-pressure fuel has an increase rate larger than the rate of increase until the pumping force of the low-pressure fuel pump is determined to have decreased and smaller than a predetermined upper limit increase rate. It is characterized in that the pump rotation speed increase control for increasing the pump rotation speed is carried out (claim 1).

According to the present invention, when the pumping force of the low-pressure fuel pump decreases, the rate of increase is larger than the rate of increase before the pumping amount of the low-pressure fuel pump decreases, that is, the pressure is reduced so that the amount of increase per unit time increases. The number of revolutions of the fuel pump is increased. Therefore, even if vapors (bubbles) are accumulated in the low-pressure fuel pump due to the low rotation speed of the low-pressure fuel pump and the pumping force of the low-pressure fuel pump is reduced due to this, the rotation speed of the low-pressure fuel pump can be increased. The vapor can be removed from the low-pressure fuel pump by increasing the pressure, and the pumping force of the low-pressure fuel pump can be restored. Therefore, until the vapor is accumulated in the low-pressure fuel pump, the rotation speed of the low-pressure fuel pump can be lowered to keep the driving force of the low-pressure fuel pump small, and the pumping force of the low-pressure fuel pump can be secured. Fuel can be reliably pumped to the fuel pump.

However, if the rate of increase in the rotation speed of the low-pressure fuel pump is excessively increased, the pressure in the low-pressure fuel pump may drop sharply and new vapor may be generated in the low-pressure fuel pump. On the other hand, in the present invention, when the rotation speed of the low-pressure fuel pump is increased as the pumping force of the low-pressure fuel pump decreases, the rate of increase is made smaller than the predetermined upper limit increase rate. Therefore, when the vapor is accumulated in the low-pressure fuel pump, the vapor can be discharged quickly while preventing new vapor from being generated in the low-pressure fuel pump, and the pumping force of the low-pressure fuel pump is more reliable. Can be secured.

In the above configuration, preferably, the pump control means maintains the rate of increase in the rotation speed of the low-pressure fuel pump constant regardless of the operating state of the engine when the pump rotation speed increase control is performed (claim 2). ..

According to this configuration, the control configuration of the low-pressure fuel pump can be simplified, and the rotation speed of the low-pressure fuel pump can be avoided from becoming excessively high to surely prevent the generation of new vapor in the low-pressure fuel pump.

In the above configuration, preferably, the pump control means increases the rotation speed of the low-pressure fuel pump toward the maximum rotation speed of the low-pressure fuel pump when the pump rotation speed increase control is performed (claim 3).

According to this configuration, the rotation speed of the low-pressure fuel pump can be increased, and vapor can be removed more reliably from the inside of the low-pressure fuel pump.

In the above configuration, preferably, the detection means for detecting the pressure of the fuel discharged from the low-pressure fuel pump is provided, and the pump control means determines that the pumping force of the low-pressure fuel pump is not reduced by the determination means. If so, the target fuel pressure, which is the target value of the pressure of the fuel discharged from the low-pressure fuel pump, is set, and the pressure of the fuel detected by the detection means becomes the target fuel pressure of the low-pressure fuel pump. Feedback control of the number of revolutions is performed (claim 4).

According to this configuration, the pressure of the fuel discharged from the low-pressure fuel pump can be set to an appropriate pressure.

In the above configuration, preferably, the determination means is based on the feedback amount of the rotation speed of the low pressure fuel pump calculated when the determination means determines that the pumping force of the low pressure fuel pump is not reduced. It is determined whether or not the pumping force of the low-pressure fuel pump has decreased (claim 5).

According to this configuration, it can be easily determined whether or not the pumping force of the low-pressure fuel pump has decreased by using the control amount of the feedback control.

In the above configuration, preferably, when the determination means determines that the pumping force of the low-pressure fuel pump has decreased and then the time during which the engine is continuously stopped becomes equal to or longer than a preset determination time, the low pressure The determination of the decrease in the pumping force of the fuel pump is canceled (claim 6).

When the engine is stopped for a long period of time and the temperature of the fuel supplied to the low-pressure fuel pump drops sufficiently, the amount of vapor in the low-pressure fuel pump decreases and the pumping power of the low-pressure fuel pump is restored. Therefore, according to this configuration, the determination of the decrease in the pumping force of the low-pressure fuel pump is appropriately released.

In the above configuration, preferably, the pump control means includes a vapor determining means for determining whether or not vapor is generated in the low pressure side fuel passage which is a passage between the high pressure fuel pump and the low pressure fuel pump. When it is determined by the vapor determining means that vapor is generated in the low pressure side fuel passage, the rate of increase equal to or greater than the rate of increase in the number of rotations of the low pressure fuel pump when the control for increasing the number of pump revolutions is performed. (7), the number of revolutions of the low-pressure fuel pump is increased.

According to this configuration, the vapor in the fuel passage on the low pressure side can also be removed, the appropriate amount of fuel can be reliably supplied by the high pressure pump, and the vapor can be removed at an early stage.

As described above, according to the engine control device of the present invention, it is possible to reliably supply an appropriate amount of fuel to the fuel injection valve.

It is a schematic block diagram of the engine which concerns on one Embodiment of this invention. It is a schematic block diagram of a low pressure pump. It is an enlarged view of a part of FIG. It is a schematic block diagram of a high pressure pump. It is a block diagram which showed the control system of an engine. It is a flowchart which showed the control procedure of a high pressure pump. It is a flowchart which showed the determination procedure of the vapor generation flag in a passage. It is a flowchart which showed the first half part of the control procedure of a low pressure pump. It is a flowchart which showed the latter half of the control procedure of a low pressure pump. It is a graph which illustrated the range of the rotation speed of a low pressure pump. It is a time chart which showed the time change of each parameter at the time of the occurrence of air accumulation. It is a flowchart which showed the procedure of resetting the air accumulation generation flag.

(1) Overall Configuration of Engine FIG. 1 is a system diagram schematically showing the overall configuration of an engine to which the engine control device of the present invention is applied. The engine system shown in this figure is mounted on a vehicle and includes an engine body 1 as a power source for traveling. In the present embodiment, a 4-cycle gasoline direct injection engine is used as the engine body 1. In the engine system, in addition to the engine body 1, the intake passage 30 through which the intake air introduced into the engine body 1 flows, the exhaust passage 40 through which the exhaust gas discharged from the engine body 1 flows, and the exhaust gas flowing through the exhaust passage 40 The EGR device 50 is provided so as to return a part of the EGR device to the intake passage 30.

The engine body 1 is slidable back and forth between the cylinder block 3 in which the cylinder 2 is formed, the cylinder head 4 attached to the upper surface of the cylinder block 3 so as to block the cylinder 2 from above, and the cylinder 2. It has an inserted piston 5. The engine body 1 is a multi-cylinder type having a plurality of cylinders 2 (for example, four cylinders 2 arranged in a direction orthogonal to the paper surface of FIG. 1), but here, for simplification, only one cylinder 2 is used. The explanation will proceed focusing on.

A combustion chamber 6 is defined above the piston 5, and fuel containing gasoline as a main component is supplied to the combustion chamber 6 by injection from an injector 15, which will be described later. Then, the supplied fuel is burned while being mixed with air in the combustion chamber 6, and the piston 5 pushed down by the expansion force due to the combustion reciprocates in the vertical direction. As the fuel injected into the combustion chamber 6, a fuel containing gasoline as a main component is used. In addition to gasoline, this fuel may contain auxiliary components such as bioethanol. In this embodiment, the injector 15 corresponds to the "fuel injection valve" of the claim.

Below the piston 5, a crankshaft 7, which is an output shaft of the engine body 1, is provided. The crankshaft 7 is connected to the piston 5 via a connecting rod 8 and is rotationally driven around the central axis in response to the reciprocating motion (vertical motion) of the piston 5. The cylinder block 3 is provided with a crank angle sensor SN1 that detects the rotation angle (crank angle) of the crankshaft 7 and the rotation speed (engine rotation speed) of the crankshaft 7.

The cylinder head 4 is provided with an intake port 9 and an exhaust port 10 that open into the combustion chamber 6, an intake valve 11 that opens and closes the intake port 9, and an exhaust valve 12 that opens and closes the exhaust port 10. The valve type of the engine of the present embodiment is a 4-valve type of 2 intake valves x 2 exhaust valves, and the intake port 9, the exhaust port 10, the intake valve 11 and the exhaust valve 12 are 2 for each cylinder 2. It is provided one by one. The intake valve 11 and the exhaust valve 12 are opened and closed and driven in conjunction with the rotation of the crankshaft 7 by the valve operating mechanisms 13 and 14 including a pair of camshafts and the like arranged on the cylinder head 4. In the present embodiment, a swirl valve 18 that can be opened and closed is provided in one of the two intake ports 9 connected to one cylinder 2, and the swirl flow in the cylinder 2 (swirl that swirls around the cylinder axis). The strength of the flow) is changed.

The cylinder head 4 ignites an injector 15 that injects fuel (mainly gasoline) into the combustion chamber 6 and a mixture of fuel injected from the injector 15 into the combustion chamber 6 and air introduced into the combustion chamber 6. An ignition plug 16 is provided. The cylinder head 4 is further provided with an in-cylinder pressure sensor SN2 that detects the in-cylinder pressure, which is the pressure of the combustion chamber 6.

The injector 15 is a multi-injection type injector having a plurality of injection holes at its tip, and can inject fuel radially from the plurality of injection holes. The injector 15 is provided so that its tip portion faces the central portion of the crown surface of the piston 5. In the present embodiment, a cavity is formed in the crown surface of the piston 5 in which a region including the central portion thereof is recessed on the opposite side (lower side) of the cylinder head 4. The injector 15 is connected to the fuel tank 21, and fuel is supplied from the fuel tank 21 to the injector 15. The specific configuration for supplying fuel to the injector 15 will be described later. The spark plug 16 is arranged at a position slightly offset from the injector 15 on the intake side.

The intake passage 30 is connected to one side surface of the cylinder head 4 so as to communicate with the intake port 9. The air (intake air, fresh air) taken in from the upstream end of the intake passage 30 is introduced into the combustion chamber 6 through the intake passage 30 and the intake port 9.

The intake passage 30 includes an air cleaner 31 for removing foreign matter contained in the intake air (air) introduced into the combustion chamber 6 (cylinder 2), a throttle valve 32 for opening and closing the intake passage 30, and intake air in this order from the upstream side. A supercharger 33 that compresses and sends out the air, an intercooler 35 that cools the intake air compressed by the supercharger 33, and a surge tank 36 are provided. An air flow sensor SN3 for detecting the amount of intake air, which is the flow rate of intake air, is provided in a portion of the intake passage 30 between the air cleaner 31 and the throttle valve 32.

The supercharger 33 is a mechanical supercharger (supercharger) that is mechanically linked to the engine body 1. The specific type of the turbocharger 33 is not particularly limited, but any known turbocharger such as a Rishorum type, a roots type, or a centrifugal type can be used as the supercharger 33. An electromagnetic clutch 34 capable of electrically switching between engagement and release is interposed between the supercharger 33 and the engine body 1. When the electromagnetic clutch 34 is engaged, the driving force is transmitted from the engine body 1 to the supercharger 33, and the supercharger 33 performs supercharging. On the other hand, when the electromagnetic clutch 34 is released, the transmission of the driving force is cut off and the supercharging by the supercharger 33 is stopped.

The intake passage 30 is provided with a bypass passage 38 for bypassing the supercharger 33. The bypass passage 38 connects the surge tank 36 and the EGR passage 51, which will be described later, to each other. A bypass valve 39 that can be opened and closed is provided in the bypass passage 38. The bypass valve 39 is a valve for adjusting the intake pressure, that is, the boost pressure, which is introduced into the surge tank 36. For example, as the opening degree of the bypass valve 39 increases, the flow rate of the intake air passing through the bypass passage 38 increases, and as a result, the boost pressure decreases.

The exhaust passage 40 is connected to the other side surface of the cylinder head 4 so as to communicate with the exhaust port 10. The burnt gas (exhaust) generated in the combustion chamber 6 is discharged to the outside through the exhaust port 10 and the exhaust passage 40. A catalytic converter is provided in the exhaust passage 40. The catalytic converter includes a three-way catalyst 41a for purifying harmful components (HC, CO, NOx) contained in the exhaust gas, and a GPF (gasoline) for collecting particulate matter (PM) contained in the exhaust gas. Particulate filter) 41b is built in in this order from the upstream side.

The EGR device 50 has an EGR passage 51, an EGR cooler 52 provided in the EGR passage 51, and an EGR valve 53. The EGR passage 51 connects a portion of the exhaust passage 40 on the downstream side of the catalytic converter and a portion of the intake passage 30 between the throttle valve 32 and the supercharger 33. The EGR cooler 52 cools the exhaust gas (EGR gas) that is returned from the exhaust passage 40 to the intake passage 30 through the EGR passage 51 by heat exchange. The EGR valve 53 is provided so as to be openable and closable in the EGR passage 51 on the downstream side (the side closer to the intake passage 30) of the EGR cooler 52, and adjusts the flow rate of the exhaust gas flowing through the EGR passage 51.

(2) Fuel supply system A configuration for sharing fuel with the injector 15 will be described below with reference to FIGS. 1 to 4. FIG. 2 is a schematic configuration diagram of a low-pressure pump 70 described later. FIG. 3 is an enlarged view of a part of FIG. FIG. 4 is a schematic configuration diagram of the high pressure pump 80 described later. The low-pressure pump 70 corresponds to the "low-pressure fuel pump" of the claim, and the high-pressure pump 80 corresponds to the "high-pressure fuel pump" of the claim.

The injector 15 and the fuel tank 21 are connected to each other by a fuel supply passage 22 through which fuel flows, and fuel is supplied to the injector 15 from the fuel tank 21 via the fuel supply passage 22. The fuel supply passage 22 is provided with a low-pressure pump 70, a fuel filter 23, a high-pressure pump 80, and a fuel rail 17 in this order from the upstream side (the fuel tank side, that is, the side opposite to the injector 15).

The low-pressure pump 70 and the high-pressure pump 80 are both pumps for pumping fuel. The fuel filter 23 is a filter for removing foreign substances contained in the fuel. The fuel rail 17 is a member for storing high-pressure fuel.

The fuel stored in the fuel tank 21 is pumped to the high pressure pump 80 by the low pressure pump 70. During this pumping, some of the foreign matter in the fuel is removed by the fuel filter 23. The fuel pumped to the high-pressure pump 80 is further boosted by the high-pressure pump 80 and pumped to the fuel rail 17. The fuel pumped from the high-pressure pump 80 is stored in the fuel rail 17. Each injector 15 is connected to a fuel rail 17, and fuel is distributed from the fuel rail 17 to each injector 15. In this way, the low-pressure pump 70 pumps fuel to the high-pressure pump 80, and the high-pressure pump 80 pumps fuel to the fuel rail 17 and thus to each injector 15.

The fuel supply passage 22 and the fuel rail 17 are separately connected via a return passage 17b and a relief valve 17a that opens and closes the return passage 17, and excess fuel in the fuel rail 17 returns with the opening of the relief valve 17a. It is returned to the fuel supply passage 22 through the passage 17b.

The fuel rail 17 is provided with a rail pressure sensor SN4 for detecting the pressure of the fuel stored in the fuel rail 17 (hereinafter, appropriately, the fuel pressure in the fuel rail 17 is referred to as a rail pressure). Further, in the low pressure side fuel passage 22a, which is a passage between the low pressure pump 70 and the high pressure pump 80, among the fuel supply passages 22, the temperature of the fuel sent from the low pressure pump 70 to the high pressure pump 80 (hereinafter, appropriately, the low pressure side). A low-pressure side fuel temperature sensor SN5 and a low-pressure side fuel pressure sensor SN6 are provided for detecting the fuel pressure (referred to as fuel temperature) and the pressure of the fuel sent from the low-pressure pump 70 to the high-pressure pump 80 (hereinafter, appropriately referred to as low-pressure side fuel pressure). ing. Note that FIG. 4 shows a case where these sensors SN5 and SN6 are provided in the low pressure side fuel passage 22a separately from the high pressure pump 80, but these sensors SN5 and SN6 may be incorporated in the high pressure pump 80. .. That is, as the high-pressure pump 80, a pump provided with a sensor capable of detecting the temperature and pressure of the fuel to be sucked may be used. The low-pressure side fuel pressure sensor SN6 detects the pressure of the fuel discharged from the low-pressure pump 70, and the low-pressure side fuel pressure sensor SN6 corresponds to the "detecting means" of the claim.

(Low pressure pump)
The low-pressure pump 70 is a rotary pump, and includes a substantially cylindrical pump case 71, a disc-shaped impeller 72 housed in the bottom of the pump case 71, and an electric motor 73 for rotationally driving the impeller 72. .. The shaft 73a of the electric motor 73 is connected to the center of the impeller 72, and the electric motor 73 rotates the impeller 72 around its central axis. In the following, the low-pressure pump 70 will be described with the vertical direction of FIG. 2 being simply the vertical direction.

A fuel suction port 74 that communicates the inner space of the pump case 71 with the outside of the pump case 71 is provided in a portion of the bottom portion 71a (lower end portion) of the pump case 71 that faces the impeller 72. The fuel suction port 74 has a tubular shape that projects outward (downward) from the pump case 71 along a line parallel to the rotation center line of the impeller 72 from a position close to the bottom surface (lower surface) of the impeller 72. .. The fuel in the fuel tank 21 is pumped into the pump case 71 from the fuel suction port 74 as the impeller 72 rotates.

A pump filter 78 for removing foreign matter contained in the fuel is attached to the lower end of the fuel suction port 74. The fuel in the fuel tank 21 is pumped into the pump case 71 through the pump filter 78.

At the end (upper portion) of the pump case 71 opposite to the bottom 71a, a fuel outlet 75 for leading fuel from the inside to the outside of the pump case 71 is provided. The fuel outlet 75 is connected to the fuel filter 23. The fuel pumped into the pump case 71 and boosted by the rotation of the impeller 72 is sent to the fuel filter 23 and thus to the high-pressure pump 80 via the fuel outlet 75.

A vapor relief port 76 is further provided at a portion of the bottom portion 71a of the pump case 71 facing the impeller 72.

The vapor relief port 76 is for releasing the vapor (air bubbles) generated in the fuel suction port 74 to the outside of the pump case 71. That is, when the temperature inside the fuel tank 21 exceeds a predetermined temperature, vapor starts to be generated in the fuel tank 21 and the fuel suction port 74 communicating with the fuel tank 21. As shown in FIG. 3, when a large amount of vapor V is accumulated in the fuel suction port 74, the contact between the impeller 72 and the fuel is hindered. Therefore, if a large amount of vapor is accumulated in the fuel suction port 74, it becomes difficult for the low-pressure pump 70 to sufficiently pump up the fuel and boost the pressure. The vapor relief port 76 is for suppressing this, and the vapor generated at the fuel suction port 74 is configured to be discharged to the outside of the pump case 71 through the vapor relief port 76. Specifically, similarly to the fuel suction port 74, the vapor relief port 76 also extends from a position close to the bottom surface (lower surface) of the impeller 72 to the outside of the pump case 71 along a line parallel to the rotation center line of the impeller 72. It has a tubular shape that protrudes (downward). However, the inner diameter of the vapor relief port 76 is set smaller than the inner diameter of the fuel suction port 74. Further, the vapor relief port 76 is located close to the fuel suction port 74, and is provided on the outer peripheral side of the fuel suction port 74 in the radial direction of the impeller 72. The vapor relief port 76 and the fuel suction port 74 communicate with each other below the impeller 72. That is, the pump case 71 is formed with a communication passage 77 that communicates the opening at the upper end of the vapor relief port 76 and the opening at the upper end of the fuel suction port 74.

(High pressure pump)
The high-pressure pump 80 is a reciprocating pump, and is driven by a high-pressure pump cam 81 provided on a camshaft for driving the exhaust valve 12 to boost fuel.

The high-pressure pump 80 includes a main body 82 in which a pressurizing chamber 82a for pressurizing fuel is formed, a suction port 83 for introducing fuel pumped from the low-pressure pump 70 into the pressurizing chamber 82a, and a pressurizing chamber. It has a discharge port 84 for discharging fuel from the 82a, and a plunger 85 whose tip is inserted into the pressurizing chamber 82a.

The plunger 85 is arranged above the high-pressure pump cam 81 so as to be in contact with the plunger 85, and reciprocates up and down as the high-pressure pump cam 81 rotates. That is, in the present embodiment, the high-pressure pump 80 is arranged on the upper surface of the cylinder head 4 on the exhaust side so that the plunger 85 comes into contact with the high-pressure pump cam 81. When the plunger 85 reciprocates in the pressurizing chamber 82a, the volume in the pressurizing chamber 82a changes, whereby the fuel flowing into the pressurizing chamber 82a from the suction port 83 is boosted. The boosted fuel is discharged from the discharge port 84 toward the fuel rail 17. The discharge port 84 is provided with a check valve 86 so that fuel does not flow back from the fuel rail 17 side to the high pressure pump 80 side.

The suction port 83 is provided with a spill valve 87 that opens and closes the suction port 83. The spill valve 87 is a normally open type electromagnetic valve that closes the suction port 83 when energized. The amount of fuel pumped from the high-pressure pump 80 to the fuel rail 17, that is, the discharge amount of the high-pressure pump 80 is changed by the valve closing period of the spill valve 87. Specifically, the spill valve 87 opens during the period from the upper end position to the lower end position of the plunger 85, and then the spill valve 87 closes at a predetermined timing until the plunger 85 reaches the upper end position. By changing the valve closing timing, the valve closing period of the spill valve 87 is changed. For example, when the valve closing timing of the spill valve 87 is advanced and the valve closing period of the spill valve 87 is lengthened, the amount of fuel pushed back from the pressurizing chamber 82a to the suction port 83 side is reduced. As a result, when the valve closing period of the spill valve 87 is long, the amount of fuel pumped from the pressurizing chamber 82a to the fuel rail 17 is larger than when it is short.

(3) Control system FIG. 5 is a block diagram showing an engine control system. The PCM 100 shown in this figure is a microprocessor for comprehensively controlling an engine, and is composed of a well-known CPU, memory (ROM, RAM), and the like.

Detection signals from various sensors are input to the PCM100. For example, the PCM 100 is electrically connected to the crank angle sensor SN1, the in-cylinder pressure sensor SN2, the airflow sensor SN3, the rail pressure sensor SN4, the low pressure side fuel temperature sensor SN5, and the low pressure side fuel pressure sensor SN6 described above. The information detected by (that is, crank angle, engine speed, cylinder pressure, intake amount, rail pressure, low pressure side fuel temperature, low pressure side fuel pressure) is sequentially input to the PCM 100. Further, the vehicle is provided with an accelerator sensor SN7 that detects the opening degree of the accelerator pedal operated by the driver who drives the vehicle, and the detection signal by the accelerator sensor SN7 is also input to the PCM 100.

The PCM 100 controls each part of the engine while executing various determinations and calculations based on the input signals from the respective sensors. The PCM 100 includes an injector 15, a spark plug 16, a swirl valve 18, a throttle valve 32, an electromagnetic clutch 34, a bypass valve 39, an EGR valve 53, a low pressure pump 70 (specifically, an electric motor 73 of the low pressure pump 70), and a high pressure pump 80. It is electrically connected to a spill valve 87 (specifically, a drive mechanism for driving the spill valve 87) or the like, and outputs a control signal to each of these devices based on the result of the calculation or the like.

The PCM 100 functionally includes a determination unit 101, a vapor determination unit 102, and a low pressure pump control unit 103. The determination unit 101 corresponds to the "determination means" of the claim, the vapor determination unit 102 corresponds to the "vapor determination means" of the claim, and the low pressure pump control unit 103 corresponds to the "pump control means" of the claim.

(Control of high pressure pump)
The control of the high pressure pump 80 performed by the PCM 100 will be described with reference to FIG.

First, in step S1, the PCM 100 sets a target rail pressure, which is a target value of the rail pressure, according to the operating state of the engine. The PCM100 sets the target rail pressure based on, for example, the engine speed and the engine load (accelerator opening degree). The engine load is calculated by the PCM 100 based on the intake amount, the engine speed, and the like.

Next, in step S2, the PCM 100 calculates the basic spill valve closing period, which is the basic value of the valve closing period of the spill valve 87. For example, the PCM 100 corresponds to the target rail pressure set in step S1 and the current engine speed from a map that is preset and stored for the rail pressure, the engine speed, and the valve closing period of the spill valve 87. The value is extracted to determine the basic spill valve closure period.

Next, in step S3, the PCM 100 reads the actual rail pressure, which is the current rail pressure detected by the rail pressure sensor SN4.

Next, in step S4, the PCM 100 calculates the deviation between the target rail pressure set in step S1 and the actual rail pressure read in step S3. Here, the value obtained by subtracting the actual rail pressure from the target rail pressure is calculated. Hereinafter, the deviation between the target rail pressure and the actual rail pressure (= target rail pressure-actual rail pressure) is appropriately referred to as the deviation of the rail pressure.

Next, in step S5, the PCM 100 calculates the feedback amount of the spill valve 87 during the closing period based on the deviation of the rail pressure calculated in step S4. In the present embodiment, the valve opening period of the spill valve 87 is PI-controlled so that the actual rail pressure becomes the target rail pressure, and in step S5, the PCM 100 has a P term (proportional) proportional to the deviation of the rail pressure. Item) is calculated. Further, the PCM 100 calculates an I term (integral term) which is a value obtained by integrating an amount proportional to the deviation of the rail pressure. Specifically, the PCM 100 repeatedly performs the operations of steps S1 to S7 in a predetermined cycle, and calculates the I term by integrating the amount proportional to the deviation of the rail pressure for each calculation cycle.

As described above, in the present embodiment, the discharge amount of the high-pressure pump 80 is set to increase as the valve closing period of the spill valve 87 becomes longer. From this, when the deviation of the rail pressure is larger than 0 and the discharge amount of the high pressure pump 80 needs to be increased due to the target rail pressure being higher than the actual rail pressure, the P term is more than 0. It is calculated to a large value, and the value of the I term is increased to a value larger than the value calculated in the previous calculation cycle. On the other hand, when the deviation of the rail pressure is smaller than 0 and the discharge amount of the high pressure pump 80 needs to be reduced because the target rail pressure is lower than the actual rail pressure, the P term is smaller than 0. Calculated as a value, the value of item I is reduced to a value smaller than the value calculated in the previous calculation cycle.

Next, in step S6, the PCM 100 adds the value of the P term and the value of the I term calculated in step S5 to the basic spill valve closing period calculated in step S2 to obtain the final spill valve 87. The final spill valve closing period, which is the valve closing period, is calculated.

Next, in step S7, the PCM 100 drives the spill valve 87 (the drive mechanism that drives the spill valve 87) so that the spill valve 87 is closed only during the final spill valve closing period calculated in step S7. In the following, the value of the item I calculated in step S5, that is, the value of the item I in the feedback amount during the valve closing period of the spill valve 87 calculated from the deviation of the rail pressure is appropriately referred to as the high pressure side I term. ..

(Control of low pressure pump)
In the present embodiment, variable fuel pressure control is adopted as the control of the low pressure pump 70, and the rotation speed of the low pressure pump 70 (the rotation speed of the impeller 72) according to the pressure of the fuel pumped from the low pressure pump 70 to the high pressure pump 80. The PCM 100 changes the driving force of the electric motor 73 so that According to this control, the rotation speed of the low-pressure pump 70 can be made lower than the maximum rotation speed (the maximum value of the rotation speed of the low-pressure pump 70) while keeping the pressure of the fuel at an appropriate pressure. Therefore, the driving force of the electric motor 73 can be reduced to reduce the energy consumption of the entire engine system.

However, if the rotation speed of the low-pressure pump 70 is lowered, a large amount of vapor may be accumulated in the fuel suction port 74 of the low-pressure pump 70, so that the low-pressure pump 70 may not sufficiently pump fuel and may not be able to discharge sufficient fuel. .. Specifically, when the rotation speed of the low-pressure pump 70 is low, the amount of fuel sucked and discharged by the low-pressure pump 70 is reduced, which makes it difficult for the vapor to flow from the fuel suction port 74 to the vapor release port 76, and as a result, A large amount of vapor tends to accumulate in the fuel suction port 74. As described above, when a large amount of vapor is accumulated in the fuel suction port 74, it becomes difficult to sufficiently pump the fuel by the low pressure pump 70, and by extension, to boost the fuel and discharge the fuel. That is, the pumping force, which is the force for pumping the fuel of the low-pressure pump 70, is weakened. When the pumping force of the low-pressure pump 70 is weakened, sufficient fuel cannot be supplied to the high-pressure pump 80, and the injector 15 cannot inject an appropriate amount of fuel.

Further, when the fuel pressure becomes lower than the saturated vapor pressure, vapor may be generated in the low pressure side fuel passage 22a. Even when vapor is generated in the low-pressure side fuel passage 22a, the amount of injection from the injector 15 may become inappropriate because the fuel discharged from the low-pressure pump 70 is not properly supplied to the high-pressure pump 80.

Therefore, in the present embodiment, whether or not a large amount of vapor is accumulated in the fuel suction port 74 of the low-pressure pump 70, that is, whether or not the low-pressure pump 70 can appropriately discharge the fuel (the pumping force of the low-pressure pump 70 decreases). Whether or not it is done) is judged. This determination is functionally performed by the determination unit 101 of the PCM 100. Further, it is determined whether or not vapor is generated in the low pressure side fuel passage 22a, that is, whether or not the fuel discharged by the low pressure pump 70 is appropriately pumped to the high pressure pump 80. This determination is functionally performed by the vapor determination unit 102 of the PCM 100. Then, when a large amount of vapor is accumulated in the fuel suction port 74 or when vapor is generated in the low pressure side fuel passage 22a, the injection amount from the injector 15 is prevented from becoming inappropriate. Controls the low pressure pump 70. The control of the low pressure pump 70 is functionally performed by the low pressure pump control unit 103 of the PCM 100.

A procedure for determining whether or not vapor is generated in the low pressure side fuel passage 22a will be described with reference to FIG. 7.

In step S11, the PCM 100 calculates the average rate of increase of the high-voltage side I term, which is the average value of the rate of increase of the term I (increase amount per unit time) calculated in step S5.

Specifically, the PCM 100 sequentially calculates the amount of change in the high-voltage side I term per preset unit time, and this amount of change calculated at each time during the period from the present time to a predetermined time ago is calculated. On average, the average value of the amount of change in the high-voltage side I term per unit time is calculated. At this time, in the PCM 100, the side where the high-voltage side I term increases is a positive value, the side where the high-voltage side I term decreases is a negative value, and the amount of increase in the high-voltage side I term per unit time, that is, the average rate of increase in the high-voltage side I term. Calculate the value.

Next, in step S12, the PCM 100 determines whether or not the average increase rate of the high-voltage side I term calculated in step S11 is larger than the preset high-voltage side reference increase rate. The high-voltage side reference increase rate is set in advance to a value larger than 0 and stored in the PCM 100.

If the determination in step S12 is NO and the average increase rate of the high pressure side I term is equal to or less than the high pressure side reference increase rate, the process proceeds to step S13, and the PCM100 determines that no vapor is generated in the low pressure side fuel passage 22a. Judgment is made and the vapor generation flag in the passage is set to 0. On the other hand, if the determination in step S12 is YES and the average increase rate of the high pressure side I term is larger than the high pressure side reference increase rate, the process proceeds to step S14, and the PCM100 generates vapor in the low pressure side fuel passage 22a. It is determined that the fuel is installed, and the vapor generation flag in the passage is set to 1. The in-passage vapor generation flag is a flag indicating whether or not it is determined that vapor is generated in the low-pressure side fuel passage 22a in this way.

As described above, in the present embodiment, when the high pressure side I term tends to increase and the rate of increase is larger than the high pressure side reference increase rate on average, the PCM 100 is placed in the low pressure side fuel passage 22a. It is determined that vapor is generated. That is, since the high-voltage side I term is a value obtained by integrating values proportional to the rail pressure deviation, when the rail pressure deviation becomes small, the value proportional to this becomes small and the rate of change of the high-voltage side I term becomes small. .. On the other hand, as described above, when vapor is generated in the low pressure side fuel passage 22a, a sufficient amount of fuel is not pumped from the low pressure pump 70 to the high pressure pump 80, and the fuel rail is sent from the high pressure pump 80. A sufficient amount of fuel cannot be supplied to 17. Therefore, in this case, even if the high-pressure side I term is increased and the valve closing period of the spill valve 87 is lengthened as the actual rail pressure is lower than the target rail pressure, the actual rail pressure can be sufficiently increased. However, the high-voltage side I term continues to increase. Further, if a sufficient amount of fuel is not supplied from the high pressure pump 80, the pressure in the fuel rail 17 decreases, so that the deviation of the rail pressure increases and the high pressure side I term is further increased. From this, when the rate of increase of the high pressure side I term is larger than the predetermined value on average, it can be said that vapor is generated in the low pressure side fuel passage 22a.

8 and 9 will be used to describe other controls of the low pressure pump 70 performed by the PCM 100 (low pressure pump control unit 103).

First, in step S20, the PCM 100 determines whether or not the air accumulation generation flag described later is 0. If this determination is NO and the air accumulation generation flag is 1, the PCM 100 proceeds to step S36.

On the other hand, if the determination in step S20 is YES and the air accumulation generation flag is 0, the process proceeds to step S21. In step S21, the PCM 100 reads the injection amount of the injector 15 (the amount of fuel injected from each injector 15) and the low pressure side fuel temperature detected by the low pressure side fuel temperature sensor SN5.

Next, in step S22, the PCM 100 determines the low pressure side target fuel pressure, which is the target value of the fuel pressure in the low pressure side fuel passage 22a, that is, the discharge pressure of the low pressure pump 70, based on the low pressure side fuel temperature read in step S21. To set. The PCM100 sets the low-pressure side target fuel pressure to a value close to the minimum value of the pressure at which it is considered that vapor is not generated in the low-pressure side fuel passage 22a when the low-pressure side fuel temperature is the value read in step S21. In the present embodiment, the relationship between the low pressure side fuel temperature and the minimum value of the pressure is set in advance by an experiment or the like in a map and stored in the PCM 100, and the PCM 100 reads the low pressure side fuel from this map in step S21. The pressure corresponding to the temperature is extracted and set to the low pressure side target fuel pressure.

Next, in step S23, the PCM 100 calculates the basic discharge amount of the low-pressure pump, which is the basic value of the discharge amount of the low-pressure pump 70 (the amount of fuel pumped from the low-pressure pump 70 per unit time). The PCM100 calculates the low-pressure pump basic discharge amount based on the low-pressure side target fuel pressure calculated in step S22 and the injection amount read in step S21. The basic discharge amount of the low-pressure pump is calculated to be larger as the target fuel pressure on the low-pressure side and the injection amount are higher.

Next, in step S24, the PCM 100 reads the low pressure side fuel pressure detected by the low pressure side fuel pressure sensor SN6. Hereinafter, the low-pressure side fuel pressure detected by the low-pressure side fuel pressure sensor SN6 is appropriately referred to as an actual low-pressure side fuel pressure.

Next, in step S25, the PCM 100 calculates the deviation between the low pressure side target fuel pressure set in step S22 and the actual low pressure side fuel pressure read in step S24. Here, the value obtained by subtracting the actual low pressure side fuel pressure from the low pressure side target fuel pressure is calculated. Hereinafter, the deviation between the low pressure side target fuel pressure and the actual low pressure side fuel pressure (= low pressure side target fuel pressure-actual low pressure side fuel pressure) is appropriately referred to as the deviation of the low pressure side fuel pressure.

Next, in step S26, the PCM 100 calculates the feedback amount of the rotation speed of the low pressure pump 70 based on the deviation of the low pressure side fuel pressure calculated in step S25. In the present embodiment, the rotation speed of the low pressure pump 70 is PI controlled so that the actual low pressure side fuel pressure becomes the low pressure side target fuel pressure, and in step S26, the PCM 100 is proportional to the deviation of the low pressure side fuel pressure. Multiply the coefficient to calculate the P term (proportional term) that is proportional to the deviation of the low pressure side fuel pressure, and multiply the deviation of the low pressure side fuel pressure by a predetermined integration coefficient to obtain the amount that is proportional to the deviation of the low pressure side fuel pressure. The I term (integration term), which is the integrated value, is calculated. Specifically, the PCM 100 repeatedly performs the operations of steps S20 to S35 in a predetermined cycle, and calculates the I term by integrating the amount proportional to the deviation of the low pressure side fuel pressure for each calculation cycle.

Since the actual low-pressure side fuel pressure increases as the rotation speed of the low-pressure pump 70 increases, the deviation of the low-pressure side fuel pressure is larger than 0, and the low-pressure side target fuel pressure is higher than the actual low-pressure side fuel pressure. When it is necessary to increase the rotation speed of the low-pressure pump 70, the P term is calculated to a value larger than 0, and the value of the I term is increased to a value larger than the calculated value in the previous calculation cycle. ..

On the other hand, when the deviation of the low pressure side fuel pressure is smaller than 0 and the low pressure side target fuel pressure is lower than the actual low pressure side fuel pressure and it is necessary to lower the rotation speed of the low pressure pump 70, the P term is It is calculated to a value smaller than 0, and the value of the I term is reduced to a value smaller than the value calculated in the previous calculation cycle. In the following, the value of the item I calculated in step S26, that is, the value of the item I in the feedback amount of the rotation speed of the low pressure pump 70 calculated from the deviation of the low pressure side fuel pressure is appropriately referred to as the low pressure side I term. .. In the present embodiment, the low pressure side I corresponds to the "feedback amount of the rotation speed of the low pressure fuel pump" of the claim. Further, the value of the P term calculated in step S26 is appropriately referred to as a low pressure side P term.

When the air accumulation generation flag described later is 0, the rotation speed of the low pressure pump 70 is set to the rotation speed corresponding to the basic discharge amount, so that the actual low pressure side fuel pressure basically becomes the low pressure side target fuel pressure. However, when the low-pressure pump 70 and its peripheral equipment deteriorate, even if the rotation speed of the low-pressure pump 70 is changed to the rotation speed corresponding to the basic discharge amount (the electric motor 73 so that the rotation speed of the low-pressure pump 70 becomes the rotation speed corresponding to the basic discharge amount). However, the actual low pressure side fuel pressure may deviate from the low pressure side target fuel pressure due to a decrease in the discharge amount of the low pressure pump 70 due to deterioration of the low pressure pump 70 and its peripheral equipment. On the other hand, in the present embodiment, as described above, the low pressure side target fuel pressure is realized by feedback controlling the rotation speed of the low pressure pump 70 based on the low pressure side fuel pressure. That is, the feedback control of the rotation speed of the low-pressure pump 70 is mainly performed to correct the deviation of the low-pressure side fuel pressure due to the deterioration of the low-pressure pump 70 and the like. Here, if the proportional coefficient used for calculating the low-pressure side P term and the integration coefficient used for calculating the low-pressure side I term are large, the rotation speed of the low-pressure pump 70 excessively increases or decreases, and the low-pressure side fuel pressure becomes unstable. Since there is a risk, the proportional coefficient and the integration coefficient are set to small values.

Next, in step S27, the PCM 100 determines the target value of the rotation speed of the low pressure pump 70 from the basic discharge amount of the low pressure pump calculated in step S23 and the values of the P term and the I term calculated in step S26. Calculate the basic target low-pressure pump rotation speed, which is the basic value. Specifically, the rotation speed of the low-pressure pump 70 corresponding to the basic discharge amount of the low-pressure pump calculated in step S23 (hereinafter referred to as the rotation speed corresponding to the basic discharge amount) is calculated, and the P term calculated in step S26 is added to this calculated value. And the value of the item I are added to calculate the basic target low-pressure pump rotation speed. The relationship between the preset discharge amount of the low-pressure pump 70 and the rotation speed corresponding to the basic discharge amount is stored in the PCM100 as a map, and the PCM100 corresponds to the basic discharge amount of the low-pressure pump calculated in step S23 from this map. The value to be used is extracted, and the extracted value is set to the rotation speed corresponding to the basic discharge amount.

Here, in the present embodiment, the capacity of the low-pressure pump 70 is relatively large, and the basic target low-pressure pump rotation speed is sufficiently lower than the maximum rotation speed, which is the maximum rotation speed of the low-pressure pump 70. In other words, the capacity of the low-pressure pump 70 is set so that the basic target low-pressure pump rotation speed is sufficiently lower than the maximum rotation speed. FIG. 10 is a graph showing an example of the relationship between the engine load and the basic target low-pressure pump rotation speed when the engine speed is a predetermined value. As shown in FIG. 10, the range of the basic target low-pressure pump rotation speed is between the first rotation speed and the second rotation speed, which is lower than the maximum rotation speed of the low-pressure pump 70. Specifically, the higher the engine load, the larger the basic target low-pressure pump rotation speed, but even when the engine load is maximum, the basic target low-pressure pump rotation speed is higher than the maximum rotation speed of the low-pressure pump 70. Is also a low value. For example, while the maximum rotation speed of the low-pressure pump 70 is 7,000 rpm, the first rotation speed is about 3,000 rpm, the second rotation speed is about 5,000 rpm, and the basic target low-pressure pump rotation speed is in the range of about 3,000 rpm to 5,000 rpm. Become.

After step S27, the process proceeds to step S28. In step S28, the PCM 100 determines whether or not the I term calculated in step S26, that is, the low pressure side I term, is larger than the preset air accumulation determination value. The air accumulation determination value is preset to a value larger than 0 and stored in the PCM 100.

If the determination in step S28 is NO and the low pressure side I term is equal to or less than the air accumulation determination value, the process proceeds to step S31, and the PCM 100 determines that vapor is not accumulated in the fuel suction port 74 of the low pressure pump 70. And set the air pool generation flag to 0.

On the other hand, if the determination in step S28 is YES and the low pressure side I term is larger than the air accumulation determination value, the process proceeds to step S30, and the PCM 100 has vapor accumulated in the fuel suction port 74 of the low pressure pump 70. Is determined and the air accumulation generation flag is set to 1. As described above, the air accumulation generation flag is a flag indicating whether or not vapor is accumulated in the fuel suction port 74 of the low pressure pump 70.

As described above, in the present embodiment, when the low pressure side I term is larger than the air accumulation determination value, the PCM 100 determines that the vapor is accumulated in the fuel suction port 74 of the low pressure pump 70. That is, since the low pressure side I term is a value obtained by integrating a value proportional to the deviation of the low pressure side fuel pressure, when the deviation of the low pressure side fuel pressure becomes small, the value proportional to this becomes small and the low pressure side I term becomes small. On the other hand, when vapor is accumulated in the fuel suction port 74 of the low pressure pump 70, the low pressure pump 70 cannot pump up and discharge sufficient fuel, so that the actual low pressure is relative to the target fuel pressure on the low pressure side. Even if the rotation speed of the low-pressure pump 70 is increased as the side fuel pressure is low, the actual low-pressure side fuel pressure does not increase sufficiently, and the low-pressure side I term continues to increase. From this, when the low pressure side I term is larger than the predetermined value, it can be said that the vapor is accumulated in the fuel suction port 74 of the low pressure pump 70. Then, the air accumulation determination value is a value equal to or greater than the minimum value of the low pressure side I term realized when a predetermined amount of vapor is accumulated in the fuel suction port 74, which is the predetermined value from experiments and the like. Is set to.

After proceeding to step S30, that is, after determining that vapor is accumulated in the fuel suction port 74 of the low-pressure pump 70 and setting the air accumulation generation flag to 1, the PCM 100 proceeds to step S36.

On the other hand, after proceeding to step S31, that is, after determining that vapor has not accumulated in the fuel suction port 74 of the low-pressure pump 70 and setting the air accumulation generation flag to 0, the PCM 100 proceeds to step S32. ..

In step S32, the PCM 100 determines whether or not the value of the in-passage vapor generation flag is 1.

When the determination in step S32 is NO, the vapor generation flag in the passage is 0, and it is determined that no vapor is generated in the low pressure side fuel passage 22a, the process proceeds to step S33. In step S33, the PCM 100 sets the basic target low-pressure pump rotation speed set in step S27 to the final target low-pressure pump rotation speed.

On the other hand, when the determination in step S32 is YES, the vapor generation flag in the passage is 1, and it is determined that vapor is generated in the low pressure side fuel passage 22a, the process proceeds to step S34. In step S34, the PCM 100 sets the value obtained by adding the increase amount on the high pressure side to the target low pressure pump rotation speed (i-1) one calculation cycle before to the final target low pressure pump rotation speed (i). Specifically, the PCM100 repeatedly executes the operations of steps S20 to S38 in a predetermined cycle, and in step S34, the PCM100 increases the high-pressure side to the target low-pressure pump rotation speed calculated at the time of the calculation one calculation cycle before. The value obtained by adding the amounts is set to the target low pressure pump rotation speed. The amount of increase on the high pressure side is a value larger than 0, and in step S34, the target low pressure pump rotation speed is set to a value larger than the target low pressure pump rotation speed one calculation cycle before. The amount of increase on the high pressure side is preset and stored in the PCM 100.

After step S33 or step S34, the process proceeds to step S35.

On the other hand, when it is determined in step S20 that the air accumulation generation flag is 1, or when the air accumulation generation flag is set to 1 in step S30, that is, vapor is accumulated in the fuel suction port 74 of the low pressure pump 70. If it is determined to be present, the process proceeds to step S36 as described above.

In step S36, the PCM 100 determines whether or not the target low-pressure pump rotation speed is the maximum low-pressure pump rotation speed which is the maximum value of the rotation speed of the low-pressure pump 70.

When the determination in step S36 is NO and the rotation speed of the low pressure pump 70 is not the maximum low pressure pump rotation speed (when it is less than the maximum low pressure pump rotation speed), the process proceeds to step S37. In step S37, the PCM 100 sets the target low-pressure pump rotation speed (i) by adding the amount of increase on the low-pressure side to the target low-pressure pump rotation speed (i-1) one calculation cycle before. The amount of increase on the low pressure side is a value larger than 0, and in step S37, the target low pressure pump rotation speed is set to a value larger than the target low pressure pump rotation speed one calculation cycle before. A constant value is used for the low pressure side increase amount regardless of the operating state of the engine and the driving state of the low pressure pump 70.

The amount of increase on the low voltage side is preset and stored in the PCM 100.

The low-pressure side increase amount is realized when the rotation speed of the low-pressure pump 70 is increased with both the air pool generation flag and the vapor generation flag in the passage being 0, that is, the low-pressure side target fuel pressure set in step S22 is realized. As described above, when the rotation speed of the low-pressure pump 70 is feedback-controlled, the value is set to be larger than the increase amount of the rotation speed (the increase amount of the rotation speed in one calculation cycle). For example, the low-pressure side increase amount is set to a value at which the increase rate (increase amount per unit time) of the low-pressure side pump rotation speed is about 2000 rpm / min. In other words, the feedback control of the rotation speed of the low pressure pump 70 is carried out in a range in which the amount of increase in the rotation speed of the low pressure pump 70 caused by this feedback control is smaller than the amount of increase on the low pressure side.

Further, the low pressure side increase amount is set to be less than a preset upper limit increase amount. The upper limit increase amount is set to a value that can avoid the generation of new vapor at the fuel suction port 74 of the low pressure pump 70. Specifically, when the rotation speed of the low-pressure pump 70 is rapidly increased, the pressure in the fuel suction port 74 is rapidly reduced. In particular, in the present embodiment, since the pump filter 78 is provided at the lower end of the fuel suction port 74, that is, at the open end, when the rotation speed of the low pressure pump 70 suddenly increases, the pressure in the fuel suction port 74 becomes negative pressure. It becomes. Therefore, if the rotation speed of the low-pressure pump 70 is rapidly increased, a new vapor may be generated in the fuel suction port 74. The upper limit increase amount is set to the upper limit value of the increase amount of the rotation speed of the low pressure pump 70 or a value slightly smaller than this so that the generation of the new vapor does not occur. The upper limit increase amount is a value corresponding to the "upper limit increase rate" of the claim, and the upper limit increase rate is a value obtained by converting the upper limit increase amount into a time change.

Further, in the present embodiment, the low pressure side increase amount and the high pressure side increase amount are set to the same value.

After step S37, the process proceeds to step S35.

Returning to step S36, when the determination in step S36 is YES and the rotation speed of the low pressure pump 70 is the maximum low pressure pump rotation speed, the process proceeds to step S38. In step S38, the PCM 100 maintains the target low pressure pump speed at the maximum low pressure pump speed. After step S38, the process proceeds to step S35.

In step S35, the PCM 100 drives the electric motor 73 so that the rotation speed of the low pressure pump 70 becomes the target low pressure pump rotation speed set in step S33, step S34, step S37 or step S38. For example, the relationship between the rotation speed of the low-pressure pump 70 and the drive duty ratio of the electric motor 73 (the ratio of the time for energizing the electric motor 73 to the total period of the time for energizing the electric motor 73 and the time for stopping the energization) is It is set in the map and stored in advance in the PCM 100, and the PCM 100 extracts the drive duty ratio corresponding to the target low pressure pump rotation speed from this map so that the drive duty ratio of the electric motor 73 becomes the extracted value. Issue a command to the electric motor 73.

In this way, when both the air accumulation flag and the vapor generation flag in the passage are 0, the PCM 100 sets the target low-pressure pump rotation speed and thus the low-pressure pump 70 rotation speed, and the actual low-pressure side fuel pressure becomes the low-pressure side target fuel pressure. Feedback control to. As a result, the target fuel pressure on the low pressure side is basically realized. On the other hand, when the air accumulation flag is 1 and a large amount of vapor is accumulated in the fuel suction port 74 of the low pressure pump 70, the PCM 100 sets the target low pressure pump rotation speed and thus the rotation speed of the low pressure pump 70 to the maximum rotation of the low pressure pump 70. Control is performed to increase the amount of increase on the low voltage side toward the number. Then, the PCM 100 maintains the rotation speed of the low pressure pump 70 when it reaches the maximum rotation speed of the low pressure pump 70. The above-mentioned control performed when the air accumulation flag is 1 and a large amount of vapor is accumulated in the fuel suction port 74 of the low-pressure pump 70 corresponds to the "pump rotation speed increase control" of the claim.

FIG. 11 is a diagram schematically showing the time change of each parameter before and after the air accumulation flag changes from 0 to 1. Each graph of FIG. 11 is a graph of the low pressure side fuel pressure, the low pressure side I term, the air accumulation determination flag, and the rotation speed of the low pressure pump 70 in order from the top. Further, in the graph of the low pressure side fuel pressure, the solid line is the actual low pressure side fuel pressure, the broken line is the low pressure side target fuel pressure, and the chain line is a comparative example. FIG. 11 shows a state when the vapor starts to accumulate in the low pressure pump 70 at time t2.

The deviation of the actual low-pressure side fuel pressure up to time t2 from the low-pressure side target fuel pressure is due to deterioration of the low-pressure pump 70 or the like. As a result, the deviation is small, and until time t2, the actual low pressure side fuel pressure is generally set to the low pressure side target fuel pressure by feedback control, and the value of the low pressure side I term is suppressed to a small value. On the other hand, when the vapor starts to accumulate in the low pressure pump 70 at time t2, the actual low pressure side fuel pressure starts to decrease with respect to the low pressure side target fuel pressure. By implementing feedback control, the rotation speed of the low-pressure pump 70 is increased, and a significant decrease in the actual low-pressure side fuel pressure is suppressed, but the low-pressure side I term continues to increase, and air accumulation is determined at time t3. Exceeds the value. Along with this, at time t3, the air accumulation determination flag changes from 0 to 1, the rotation speed of the low-pressure pump 70 is rapidly increased, and the increase amount (increase amount per calculation cycle) is regarded as the low-pressure side increase amount. .. Here, as long as the low-pressure side I term does not exceed the air accumulation determination value, the amount of change in the control amount of the feedback control per calculation cycle, and thus the amount of change in the rotation speed of the low-pressure pump 70 per calculation cycle is small. The amount of increase in the rotation speed of the low-pressure pump 70 per calculation cycle is smaller than the amount of increase on the low-pressure side. After time t3, the rotation speed of the low-pressure pump 70 is gradually increased toward the maximum rotation speed while the increase amount (increase amount per calculation cycle) is maintained at the low-pressure side increase amount. In the present embodiment, when the air accumulation flag becomes 1, the low pressure side I term is reset to 0. When the maximum rotation speed is reached at time t4 after time t3, the rotation speed of the low-pressure pump 70 is maintained at the maximum rotation speed thereafter.

Here, the chain line of the low-pressure side fuel pressure shows the movement of the low-pressure side fuel pressure when the same feedback control as until the time t3 is performed without rapidly increasing the rotation speed of the low-pressure pump 70 after the time t3. As shown in this chain line, if the rotation speed of the low-pressure pump 70 is not rapidly increased, the low-pressure side fuel pressure continues to decrease as the vapor continues to accumulate in the fuel suction port 74 of the low-pressure pump 70. When a predetermined amount or more of vapor is accumulated in the fuel suction port 74 of the low-pressure pump 70, the fuel pumping force of the low-pressure pump 70 becomes very weak and the low-pressure side fuel pressure drops to a very low value.

Further, by the above control, in the present embodiment, even when the air accumulation flag is 0 but the vapor generation flag in the passage is 1 and the vapor is generated in the low pressure side fuel passage 22a, the target low pressure pump rotation is performed. As a result, the rotation speed of the low pressure pump 70 is increased. In the present embodiment, as described above, the high-pressure side increase amount and the low-pressure side increase amount, which are the increase amounts of the target low-pressure pump rotation speed and thus the rotation speed of the low-pressure pump 70 in this case, are set to the same value. Therefore, even when the air accumulation flag is 0 but the vapor generation flag in the passage is 1, the rotation speed of the low pressure pump 70 is rapidly increased and the low pressure side fuel pressure is rapidly increased.

Here, when the air accumulation flag is set to 1 in step S30, the air accumulation flag is reset to 0 only after the engine has stopped for a predetermined time or longer. Specifically, as shown in FIG. 12, the PCM100 determines in step S51 whether or not the air accumulation flag is 1. If this determination is NO and the air accumulation flag is 0, the process ends as it is. On the other hand, if this determination is YES and the air accumulation flag is 1, the process proceeds to step S52. In step S52, the PCM 100 determines whether or not the time during which the engine is continuously stopped is equal to or longer than a preset determination time. The determination time is preset and stored in the PCM 100. If the determination in step S52 is YES and the time during which the engine is continuously stopped is equal to or longer than the determination time, the process proceeds to step S53, and the PCM 100 sets the air accumulation flag to 0. On the other hand, when the determination in step S52 is NO and the time during which the engine is continuously stopped is less than the determination time, step S52 is executed again. In this way, the PCM 100 resets the air accumulation flag to 0 only after waiting for the continuous stop time of the engine to exceed the determination time. From this, even when the engine is stopped, if the engine is driven again before the determination time elapses after the engine is stopped, the air accumulation flag is maintained at 1 and the rotation speed of the low pressure pump 70 is increased. Increased towards maximum speed.

(4) Action, etc. As described above, in the present embodiment, the rotation speed of the low pressure pump 70 is higher than the maximum rotation speed of the low pressure pump 70 in the normal state (when the air accumulation flag is 0 and the vapor generation flag is 0). Is also a small value. Therefore, the driving force of the low-pressure pump 70 can be reduced and the energy consumed for driving the low-pressure pump 70 can be reduced as compared with the case where the low-pressure pump 70 is driven so that its rotation speed becomes the maximum rotation speed. In particular, in the present embodiment, in the normal state, the rotation speed of the low pressure pump 70 is feedback controlled in a range lower than the maximum rotation speed so that the low pressure side fuel pressure becomes the target value. Therefore, the driving force of the low-pressure pump 70 can be reduced while keeping the low-pressure side fuel pressure at an appropriate value.

Moreover, in response to the problem that vapor tends to accumulate in the low pressure pump 70 (inside the fuel suction port 74) when the rotation speed of the low pressure pump 70 is lowered, whether or not the vapor is accumulated in the low pressure pump 70 is determined. When it is determined that the vapor is accumulated in the low pressure pump 70, the rotation speed of the low pressure pump 70 is increased. In particular, the rate of increase in the rotation speed of the low-pressure pump 70 is made larger than the rate of increase in the normal state, that is, the rate of increase until the determination is made. Therefore, the rotation speed of the low-pressure pump 70 can be increased at an early stage to quickly remove the vapor in the low-pressure pump 70, and it is possible to prevent the fuel from being discharged from the low-pressure pump 70.

Further, when it is determined that the vapor is accumulated in the low pressure pump 70, the rate of increase in the rotation speed of the low pressure pump 70 is made smaller than the upper limit increase rate set as described above. Therefore, while increasing the rotation speed of the low-pressure pump 70, it is possible to avoid the generation of new vapor in the low-pressure pump 70, and the vapor in the low-pressure pump 70 can be reliably removed.

Further, in the present embodiment, when it is determined that the vapor is accumulated in the low pressure pump 70, the rotation speed of the low pressure pump 70 is increased toward the maximum rotation speed. Therefore, the rotation speed of the low-pressure pump 70 can be sufficiently increased so that the vapor in the fuel suction port 74 can be more reliably discharged to the outside of the low-pressure pump 70.

Further, in the present embodiment, it is determined whether or not the vapor is accumulated in the low pressure pump 70 by using the feedback amount of the low pressure pump 70. Therefore, it is possible to easily determine whether or not vapor is accumulated in the low-pressure pump 70 while setting the low-pressure side fuel pressure to an appropriate value as described above.

In particular, in the present embodiment, the above determination is made based on the value of the low-pressure side I term calculated when the rotation speed of the low-pressure pump 70 is PI-controlled. Therefore, the determination can be made with high accuracy. Specifically, the low pressure side I term is a value obtained by integrating an amount proportional to the deviation between the low pressure side target fuel pressure and the actual low pressure side fuel pressure, and even when the low pressure side target fuel pressure and the actual low pressure side fuel pressure suddenly change, the value is increased. The amount of change is small. Therefore, when the low-pressure side target fuel pressure or the actual low-pressure side fuel pressure changes temporarily due to disturbance (due to noise on the low-pressure side fuel pressure sensor SN6 or fuel pulsation, etc.), the low pressure is accompanied by this. It is possible to avoid a sudden increase in the side I term, and it is possible to avoid erroneously determining that vapor is accumulated in the low pressure pump 70 due to the sudden change.

Further, in the present embodiment, the rotation speed of the low pressure pump 70 is increased even when the vapor generation flag is 0 and the vapor is generated in the low pressure side fuel passage 22a. Therefore, when the vapor is generated in the low pressure side fuel passage 22a due to the pressure increase in the low pressure side fuel passage 22a, it can be extinguished, and the amount of fuel supplied from the low pressure pump 70 to the high pressure pump 80 is increased. The amount of fuel injected from the injector 15 can be reliably set to an appropriate amount. In particular, even when the rotation speed of the low-pressure pump 70 is increased, the rate of increase is made higher than the rate of increase in the steady state. Therefore, the vapor in the low pressure side fuel passage 22a can be eliminated at an early stage.

(5) Modification Example In the above embodiment, in step S28, when the value of the low pressure side I term is compared with a predetermined value (air accumulation determination value) to determine whether or not an air accumulation has occurred. However, instead of this, the determination may be made by comparing the average value of the increase rate of the low voltage side I term with a predetermined value as in steps S11 and S12.

Further, in the above embodiment, the case where the high pressure side increase amount and the low pressure side increase amount are set to the same value has been described, but these values may be different from each other. However, in order to remove the vapor in the low pressure side fuel passage 22a at an early stage, it is preferable to increase the amount of increase on the high pressure side and increase the rotation speed of the low pressure pump 70 at an early stage. Further, even if the rate of increase in the rotation speed of the low-pressure pump 70 is increased, no new vapor is generated in the low-pressure side fuel passage 22a. From this, it is preferable to set the high pressure side increase amount to a value equal to or larger than the low pressure side increase amount.

1 Engine body 2a Cylinder 15 Injector (fuel injection valve)
17 Fuel rail 70 Low pressure pump (low pressure fuel pump)
80 High-pressure pump (high-pressure fuel pump)
101 Judgment unit (judgment means)
102 Vapor determination unit (vapor determination means)
103 Low pressure pump control unit (pump control means)
SN6 Low pressure side fuel pressure sensor (detection means)

Claims (7)

An engine control device including a fuel injection valve that injects fuel into a cylinder, a high-pressure fuel pump that pumps fuel to the fuel injection valve, and a low-pressure fuel pump that pumps fuel to the high-pressure fuel pump.
A pump control means for controlling the low-pressure fuel pump and
A determination means for determining whether or not the pumping force of the low-pressure fuel pump has decreased is provided.
When it is determined by the determination means that the pumping force of the low-pressure fuel pump has decreased, the pump control means is larger and predetermined than the rate of increase until it is determined that the pumping force of the low-pressure fuel pump has decreased. An engine control device for carrying out pump rotation speed increase control for increasing the rotation speed of the low-pressure fuel pump at an increase rate smaller than the upper limit increase rate. In the engine control device according to claim 1,
The pump control means is an engine control device, characterized in that the rate of increase in the rotation speed of the low-pressure fuel pump when the pump rotation speed increase control is performed is maintained constant regardless of the operating state of the engine. In the engine control device according to claim 1 or 2.
The pump control means is an engine control device, characterized in that, when the pump rotation speed increase control is performed, the rotation speed of the low pressure fuel pump is increased toward the maximum rotation speed of the low pressure fuel pump. In the engine control device according to any one of claims 1 to 3.
A detection means for detecting the pressure of the fuel discharged from the low-pressure fuel pump is provided.
When the determination means determines that the pumping force of the low-pressure fuel pump has not decreased, the pump control means sets a target fuel pressure which is a target value of the pressure of the fuel discharged from the low-pressure fuel pump. An engine control device for feedback-controlling the rotation speed of the low-pressure fuel pump so that the fuel pressure detected by the detection means reaches the target fuel pressure. In the engine control device according to claim 4,
The determination means has a pressure feeding force of the low pressure fuel pump based on a feedback amount of the rotation speed of the low pressure fuel pump calculated when the determination means determines that the pumping force of the low pressure fuel pump has not decreased. An engine control device, characterized in that it determines whether or not the fuel has decreased. In the engine control device according to any one of claims 1 to 5.
After determining that the pumping force of the low-pressure fuel pump has decreased, the determination means reduces the pumping force of the low-pressure fuel pump when the time during which the engine is continuously stopped becomes equal to or longer than a preset determination time. An engine control device characterized in that the judgment is canceled. In the engine control device according to any one of claims 1 to 6.
A vapor determining means for determining whether or not vapor is generated in the low pressure side fuel passage, which is a passage between the high pressure fuel pump and the low pressure fuel pump, is provided.
When the pump control means determines that vapor is generated in the low pressure side fuel passage by the vapor determination means, the rate of increase in the rotation speed of the low pressure fuel pump when the pump rotation speed increase control is performed. An engine control device characterized in that the rotation speed of the low-pressure fuel pump is increased at the above rate of increase.

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