JP7356836B2 - engine control device - Google Patents

Description

The present invention provides an engine that includes 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. The present invention relates to a control device.

Conventionally, in an engine, a low-pressure fuel pump pumps fuel from a fuel tank to a high-pressure fuel pump, and from the high-pressure fuel pump, the fuel is then pumped at high pressure toward a fuel injection valve, and the high-pressure fuel is delivered from the fuel injection valve to a cylinder. Injection is being carried out.

Here, if vapor (air bubbles) is generated in the fuel, the vapor obstructs the pressure feeding of the fuel by the fuel pump, so there is a possibility that fuel cannot be appropriately supplied to the fuel injection valve. On the other hand, for example, Patent Document 1 discloses that a device is provided in a passage between a low-pressure fuel pump and a high-pressure fuel pump to remove vapor generated in the passage, and the vapor in the passage is removed from a fuel tank. Disclosed is an apparatus for reverting to .

JP2006-200423A

In the device of Patent Document 1, no measures are taken against 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 appropriately supplied to the fuel injection valve. Specifically, if vapor is generated in the fuel sucked by the low-pressure fuel pump, this vapor obstructs the low-pressure fuel pump's suction of fuel, making it difficult to properly pump the fuel from the low-pressure fuel pump. Therefore, there is a risk that a sufficient amount of fuel may not be supplied to the high-pressure fuel pump and, by extension, the fuel injection valve. In particular, when the rotational speed of the low-pressure fuel pump is low, the flow rate of fuel pumped from the low-pressure fuel pump is small, making it difficult to remove vapor from around the rotating body.

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 that can reliably supply an appropriate amount of fuel by a fuel injection valve.

In order to solve the above problems, the present invention provides 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 comprising: pump control means for controlling a low-pressure fuel pump; determining means for determining whether the pumping force of the low-pressure fuel pump has decreased; and pump control means for controlling a low-pressure fuel pump; a detection means for detecting fuel pressure , and when the determination means determines that the pumping force of the low-pressure fuel pump has decreased, an increase rate until it is determined that the pumping force of the low-pressure fuel pump has decreased; Pump rotation speed increase control is carried out to increase the rotation speed of the low pressure fuel pump at an increase rate greater than and smaller than a predetermined upper limit increase rate, and the determination means determines that the pumping force of the low pressure fuel pump has not decreased. If it is determined that this is the case, a target fuel pressure that is a target value of the pressure of the fuel discharged from the low-pressure fuel pump is set, and the low-pressure fuel is adjusted so that the fuel pressure detected by the detection means becomes the target fuel pressure. Feedback control of the rotation speed of the pump is performed, and the determining means controls the low pressure fuel based on the feedback amount of the rotation speed of the low pressure fuel pump, which is calculated when it is determined that the pumping force of the low pressure fuel pump has not decreased. It is characterized in that it is determined whether or not the pumping force of the pump has decreased (claim 1).

According to the present invention, when the pumping force of the low-pressure fuel pump decreases, the pumping amount of the low-pressure fuel pump increases at a higher rate of increase than the rate of increase before the decrease, that is, the amount of increase per unit time is larger. The fuel pump speed is increased. Therefore, even if vapor (air bubbles) accumulates inside the low-pressure fuel pump due to the low rotational speed of the low-pressure fuel pump, and this reduces the pumping force of the low-pressure fuel pump, the rotational speed of the low-pressure fuel pump can be reduced. By increasing the pressure, vapor can be removed from within the low-pressure fuel pump, and the pumping power of the low-pressure fuel pump can be restored. Therefore, until vapor accumulates in the low-pressure fuel pump, the rotational speed of the low-pressure fuel pump can be lowered to reduce its driving force, and the pumping force of the low-pressure fuel pump can be secured, allowing the low-pressure fuel pump to transfer high pressure Fuel can be reliably pumped to the fuel pump.

However, if the rate of increase in the rotational speed of the low-pressure fuel pump is made too high, the pressure within the low-pressure fuel pump may drop rapidly and new vapor may be generated within the low-pressure fuel pump. In contrast, in the present invention, when the rotational 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 vapor is accumulated inside the low-pressure fuel pump, it is possible to quickly discharge the vapor while preventing new vapor from being generated inside the low-pressure fuel pump, making the pumping power of the low-pressure fuel pump more reliable. can be secured.

Furthermore, when the determining means determines that the pumping force of the low-pressure fuel pump has not decreased, the pump control means sets a target fuel pressure that is a target value of the pressure of fuel discharged from the low-pressure fuel pump. Then, the rotation speed of the low-pressure fuel pump is feedback-controlled so that the fuel pressure detected by the detection means becomes the target fuel pressure.

Therefore, according to the present invention, the pressure of the fuel discharged from the low-pressure fuel pump can be adjusted to an appropriate pressure.

Further, the determining means determines whether the pumping force of the low-pressure fuel pump has decreased based on a feedback amount of the rotation speed of the low-pressure fuel pump, which is calculated when determining that the pumping force of the low-pressure fuel pump has not decreased. Determine whether or not.

Therefore, according to the present invention, by using the control amount of the feedback control, it can be easily determined whether the pumping force of the low-pressure fuel pump has decreased.

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 performing the pump rotation speed increase control (claim 2). .

According to this configuration, the control configuration of the low-pressure fuel pump can be simplified, and the rotational speed of the low-pressure fuel pump can be prevented from becoming excessively high, thereby reliably preventing 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 performing the pump rotation speed increase control (Claim 3).

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

In the configuration, preferably, after determining that the pumping force of the low-pressure fuel pump has decreased, the determining means is configured to reduce the low-pressure fuel when the engine is continuously stopped for a predetermined determination time or more. The determination of the decrease in the pumping force of the fuel pump is canceled (Claim 4 ).

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 a decrease in the pumping force of the low-pressure fuel pump is appropriately canceled.

The present invention also provides control of an engine that includes 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. The apparatus includes a pump control means for controlling the low pressure fuel pump, a determination means for determining whether or not the pumping force of the low pressure fuel pump has decreased, and a link between the high pressure fuel pump and the low pressure fuel pump. vapor determining means for determining whether vapor is generated in a low-pressure side fuel passage, which is a passage, and the pump control means determines that the pumping force of the low-pressure fuel pump has decreased by the determining means. Then, the pump rotation speed is increased by increasing the rotation speed of the low-pressure fuel pump at an increase rate that is larger than the increase rate until it is determined that the pumping force of the low-pressure fuel pump has decreased and smaller than a predetermined upper limit increase rate. When the control is executed and the vapor determination means determines that vapor is generated in the low-pressure side fuel passage, the rate of increase in the rotation speed of the low-pressure fuel pump when the pump rotation speed increase control is implemented. The rotation speed of the low pressure fuel pump is increased at the above increase rate (Claim 5 ).

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

As explained above, according to the engine control device of the present invention, an appropriate amount of fuel can be reliably supplied to the fuel injection valve.

1 is a schematic configuration diagram of an engine according to an embodiment of the present invention. It is a schematic block diagram of a low pressure pump. 3 is an enlarged view of a part of FIG. 2. FIG. FIG. 2 is a schematic configuration diagram of a high-pressure pump. FIG. 2 is a block diagram showing a control system of the engine. It is a flow chart showing a control procedure of a high pressure pump. 2 is a flowchart showing a procedure for determining an in-passage vapor occurrence flag. It is a flow chart showing the first half of a control procedure of a low pressure pump. It is a flow chart showing the latter half of a control procedure of a low pressure pump. It is a graph illustrating the range of rotation speed of a low pressure pump. 5 is a time chart showing changes over time in each parameter when air accumulation occurs. 12 is a flowchart showing a procedure for resetting an air accumulation 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 that serves as a power source for driving. In this embodiment, a four-stroke gasoline direct injection engine is used as the engine body 1. In addition to the engine body 1, the engine system includes an intake passage 30 through which intake air introduced into the engine body 1 flows, an exhaust passage 40 through which exhaust gas discharged from the engine body 1 flows, and exhaust gas flowing through the exhaust passage 40. The engine is equipped with an EGR device 50 that recirculates a portion of the air to the intake passage 30.

The engine body 1 is capable of reciprocating sliding between a cylinder block 3 in which a cylinder 2 is formed, a cylinder head 4 attached to the top surface of the cylinder block 3 so as to close the cylinder 2 from above, and the cylinder 2. It has an inserted piston 5. The engine main body 1 is of a multi-cylinder type having a plurality of cylinders 2 (for example, four cylinders 2 lined up in a direction perpendicular to the paper surface of FIG. 1), but here, for the sake of simplicity, only one cylinder 2 is shown. The explanation will focus 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. The supplied fuel is mixed with air and combusted in the combustion chamber 6, and the piston 5, which is pushed down by the expansion force caused by the combustion, reciprocates in the vertical direction. Note that the fuel injected into the combustion chamber 6 contains gasoline as a main component. This fuel may contain subcomponents such as bioethanol in addition to gasoline. In this embodiment, the injector 15 corresponds to a "fuel injection valve" in the claims.

A crankshaft 7, which is an output shaft of the engine body 1, is provided below the piston 5. The crankshaft 7 is connected to the piston 5 via a connecting rod 8, and is driven to rotate around a central axis in accordance with the reciprocating motion (up and down 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 rotational speed (engine rotational 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 this embodiment is a 4-valve type with 2 intake valves and 2 exhaust valves, and each cylinder 2 has 2 intake ports 9, 10 exhaust ports 10, 2 intake valves 11, and 2 exhaust valves 12. They are provided one by one. The intake valve 11 and the exhaust valve 12 are driven to open and close in conjunction with the rotation of the crankshaft 7 by valve mechanisms 13 and 14 that include a pair of camshafts and the like disposed in the cylinder head 4. In this embodiment, one of the two intake ports 9 connected to one cylinder 2 is provided with a swirl valve 18 that can be opened and closed. The strength of the current) can now be changed.

The cylinder head 4 includes an injector 15 that injects fuel (mainly gasoline) into the combustion chamber 6, and an injector 15 that ignites the mixture of the fuel injected into the combustion chamber 6 from the injector 15 and the air introduced into the combustion chamber 6. A spark 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 in the combustion chamber 6.

The injector 15 is a multi-hole 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 faces the center of the crown surface of the piston 5. In the present embodiment, a cavity is formed in the crown surface of the piston 5, with a region including the center thereof recessed on the opposite side (downward) from the cylinder head 4. The injector 15 is connected to a fuel tank 21, and fuel is supplied from the fuel tank 21 to the injector 15. A specific configuration for supplying fuel to the injector 15 will be described later. The spark plug 16 is arranged at a position slightly shifted toward the intake side with respect to the injector 15.

The intake passage 30 is connected to one side of the cylinder head 4 so as to communicate with the intake port 9. 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, in order from the upstream side, an air cleaner 31 that removes foreign matter contained in the intake air (air) introduced into the combustion chamber 6 (cylinder 2), a throttle valve 32 that opens and closes the intake passage 30, and an intake A supercharger 33 that compresses and sends out air, an intercooler 35 that cools intake air compressed by the supercharger 33, and a surge tank 36 are provided. An air flow sensor SN3 is provided in a portion of the intake passage 30 between the air cleaner 31 and the throttle valve 32 to detect the amount of intake air, which is the flow rate of intake air.

The supercharger 33 is a mechanical supercharger that is mechanically linked to the engine main body 1 . Although the specific type of the supercharger 33 is not particularly limited, any known supercharger such as a Lysholm type, a Roots type, or a centrifugal type can be used as the supercharger 33, for example. An electromagnetic clutch 34 is interposed between the supercharger 33 and the engine main body 1 and can be electrically switched between engagement and disengagement. When the electromagnetic clutch 34 is engaged, 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 supercharging by the supercharger 33 is stopped.

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

The exhaust passage 40 is connected to the other side of the cylinder head 4 so as to communicate with the exhaust port 10. Burnt gas (exhaust gas) generated in the combustion chamber 6 is exhausted 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 filter) for collecting particulate matter (PM) contained in the exhaust gas. particulate filter) 41b are built in in this order from the upstream side.

The EGR device 50 includes an EGR passage 51, an EGR cooler 52, and an EGR valve 53 provided in the EGR passage 51. The EGR passage 51 connects a portion of the exhaust passage 40 downstream 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 recirculated from the exhaust passage 40 to the intake passage 30 through the EGR passage 51 by heat exchange. The EGR valve 53 is provided in the EGR passage 51 downstream of the EGR cooler 52 (closer to the intake passage 30) so as to be openable and closable, and adjusts the flow rate of exhaust gas flowing through the EGR passage 51.

(2) Fuel Supply System The configuration for sharing fuel to the injectors 15 will be described next with reference to FIGS. 1 to 4. FIG. 2 is a schematic configuration diagram of a low-pressure pump 70, which will be described later. FIG. 3 is an enlarged view of a part of FIG. 2. FIG. 4 is a schematic configuration diagram of a high-pressure pump 80, which will be described later. Note that the low-pressure pump 70 corresponds to a "low-pressure fuel pump" in the claims, and the high-pressure pump 80 corresponds to a "high-pressure fuel pump" in the claims.

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

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

The fuel stored in the fuel tank 21 is pumped by the low pressure pump 70 to the high pressure pump 80. During this pressure feeding, 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 pressurized by the high-pressure pump 80 and is then pumped to the fuel rail 17 . 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, which in turn pumps fuel to the fuel rail 17 and thus to each injector 15.

The fuel supply passage 22 and the fuel rail 17 are connected via a separate return passage 17b and a relief valve 17a that opens and closes the return passage 17b, and excess fuel in the fuel rail 17 is returned when the relief valve 17a is opened. The fuel 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, the fuel pressure in the fuel rail 17 will be referred to as rail pressure). In addition, in the low-pressure side fuel passage 22a, which is a passage between the low-pressure pump 70 and the high-pressure pump 80 in the fuel supply passage 22, the temperature of the fuel sent from the low-pressure pump 70 to the high-pressure pump 80 (hereinafter referred to as appropriate on the low-pressure side A low pressure side fuel temperature sensor SN5 and a low pressure side fuel pressure sensor SN6 are provided to detect the pressure of the fuel sent from the low pressure pump 70 to the high pressure pump 80 (hereinafter referred to as low pressure side fuel pressure as appropriate), respectively. ing. Note that although 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, these sensors SN5 and SN6 may be incorporated in the high-pressure pump 80. . That is, as the high-pressure pump 80, a pump equipped 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 fuel discharged from the low pressure pump 70, and this low pressure side fuel pressure sensor SN6 corresponds to "detection means" in the claims.

(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 that rotationally drives the impeller 72. . A 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 explained with the vertical direction in FIG. 2 simply being 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 71 a (lower end portion) of the pump case 71 that faces the impeller 72 . The fuel suction port 74 has a cylindrical shape that protrudes outward (downward) from the pump case 71 from a position close to the bottom surface (lower surface) of the impeller 72 along a line parallel to the rotation center line of the impeller 72. . The fuel in the fuel tank 21 is pumped up into the pump case 71 from the fuel suction port 74 as the impeller 72 rotates.

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

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

A vapor escape port 76 is further provided in a portion of the bottom portion 71a of the pump case 71 that faces the impeller 72.

The vapor release port 76 is for releasing vapor (air bubbles) generated within 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 begins to be generated in the fuel tank 21 and the fuel suction port 74 communicating therewith. As shown in FIG. 3, when a large amount of vapor V accumulates in the fuel suction port 74, contact between the impeller 72 and the fuel is inhibited. Therefore, when a large amount of vapor accumulates in the fuel suction port 74, it becomes difficult for the low-pressure pump 70 to sufficiently pump and pressurize the fuel. The vapor release port 76 is for suppressing this, and is configured so that the vapor generated at the fuel suction port 74 is discharged to the outside of the pump case 71 through the vapor release port 76. Specifically, similar to the fuel suction port 74, the vapor release port 76 extends outward from the pump case 71 from a position close to the bottom surface (lower surface) of the impeller 72 along a line parallel to the rotation center line of the impeller 72. It has a cylindrical shape that projects downward. However, the inner diameter of the vapor escape port 76 is set smaller than the inner diameter of the fuel suction port 74. Further, the vapor escape 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 escape 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 upper end opening of the vapor escape port 76 with the upper opening 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 that drives the exhaust valve 12 to increase the pressure of the fuel.

The high-pressure pump 80 includes a main body 82 in which a pressurizing chamber 82a for pressurizing fuel is formed, an inlet 83 for introducing the 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 82a, and a plunger 85 whose tip is inserted into the pressurizing chamber 82a.

The plunger 85 is arranged above and in contact with the high-pressure pump cam 81, and reciprocates up and down as the high-pressure pump cam 81 rotates. That is, in this embodiment, the high-pressure pump 80 is arranged on the upper surface of the exhaust side of the cylinder head 4 so that the plunger 85 comes into contact with the high-pressure pump cam 81. As the plunger 85 reciprocates within the pressurizing chamber 82a, the volume within the pressurizing chamber 82a changes, thereby increasing the pressure of the fuel that has flowed into the pressurizing chamber 82a from the suction port 83. The pressurized fuel is discharged from the discharge port 84 toward the fuel rail 17 . Note that the discharge port 84 is provided with a check valve 86 to prevent fuel from flowing backward 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, and closes the inlet 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 depending on the period during which the spill valve 87 is closed. Specifically, the spill valve 87 is open during the period until the plunger 85 reaches the upper end position from the upper end position, and then the spill valve 87 is closed at a predetermined timing until the plunger 85 reaches the upper end position. By changing this valve closing timing, the valve closing period of the spill valve 87 is changed. For example, if the closing timing of the spill valve 87 is advanced and the closing period of the spill valve 87 becomes longer, the amount of fuel pushed back from the pressurizing chamber 82a to the suction port 83 side decreases. As a result, when the spill valve 87 is closed for a long time, the amount of fuel pumped from the pressurizing chamber 82a to the fuel rail 17 becomes larger than when it is short.

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

Detection signals from various sensors are input to the PCM 100. For example, the PCM 100 is electrically connected to the aforementioned crank angle sensor SN1, cylinder pressure sensor SN2, air flow sensor SN3, rail pressure sensor SN4, low pressure side fuel temperature sensor SN5, and low pressure side fuel pressure sensor SN6, and these sensors Information (ie, crank angle, engine speed, cylinder pressure, intake air amount, rail pressure, low-pressure side fuel temperature, and low-pressure side fuel pressure) detected by the PCM 100 is sequentially inputted to the PCM 100. The vehicle is also provided with an accelerator sensor SN7 that detects the opening degree of an accelerator pedal operated by the driver of the vehicle, and a detection signal from this accelerator sensor SN7 is also input to the PCM 100.

The PCM 100 controls each part of the engine while executing various determinations, calculations, etc. based on input signals from each of the 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 the spill valve 87 (specifically, a drive mechanism that drives the spill valve 87), etc., and outputs control signals to these devices based on the results of the calculations and the like.

The PCM 100 functionally includes a determination section 101, a vapor determination section 102, and a low pressure pump control section 103. The determination unit 101 corresponds to the “determination means” in the claims, the vapor determination unit 102 corresponds to the “vapor determination means” in the claims, and the low-pressure pump control unit 103 corresponds to the “pump control means” in the claims.

(High pressure pump control)
Control of the high pressure pump 80 performed by the PCM 100 will be explained using FIG. 6.

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 PCM 100 sets a target rail pressure based on, for example, the engine speed and engine load (accelerator opening). Note that the engine load is calculated by the PCM 100 based on the intake air amount, engine rotation speed, and the like.

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

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) will be referred to as the rail pressure deviation, as appropriate.

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

As described above, in this embodiment, the discharge amount of the high-pressure pump 80 is set to increase as the period in which the spill valve 87 is closed increases. From this, when the rail pressure deviation is larger than 0 and the target rail pressure is higher than the actual rail pressure and it is necessary to increase the discharge amount of the high pressure pump 80, the P term is larger than 0. The value of the I term is increased to a larger value than the value calculated in the previous calculation cycle. On the other hand, if the rail pressure deviation is smaller than 0 and the target rail pressure is lower than the actual rail pressure, and it is necessary to reduce the discharge amount of the high-pressure pump 80, the P term is smaller than 0. The value of the I term 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, and the final spill valve 87 is adjusted. 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 closes for the final spill valve closing period calculated in step S7. In the following, the value of the I term calculated in step S5, that is, the value of the I term of the feedback amount during the valve closing period of the spill valve 87 calculated from the rail pressure deviation, will be referred to as the high pressure side I term as appropriate. .

(Low pressure pump control)
In this embodiment, variable fuel pressure control is adopted as control of the low pressure pump 70, and the rotation speed of the low pressure pump 70 (the rotation speed of the impeller 72) is adjusted according to the pressure of the fuel fed from the low pressure pump 70 to the high pressure pump 80. PCM 100 changes the driving force of electric motor 73 so that . According to this control, it is possible to make the rotation speed of the low pressure pump 70 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, there is a risk that a large amount of vapor will accumulate in the fuel suction port 74 of the low pressure pump 70 and the low pressure pump 70 will not be able to pump enough fuel and be unable to discharge sufficient fuel. . Specifically, when the rotational speed of the low-pressure pump 70 becomes low, the amount of fuel that the low-pressure pump 70 sucks and discharges decreases, making it difficult for vapor to flow from the fuel suction port 74 to the vapor relief 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 accumulates in the fuel suction port 74, it becomes difficult to sufficiently pump the fuel by the low-pressure pump 70, and furthermore, it becomes difficult to pressurize and discharge the fuel. In other words, the pumping force of the low-pressure pump 70 that pumps the fuel becomes weaker. When the pumping force of the low-pressure pump 70 becomes weak, 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 pressure of the fuel 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 fuel discharged from the low-pressure pump 70 may not be properly supplied to the high-pressure pump 80, so that the amount of injection from the injector 15 may become inappropriate.

Therefore, in this embodiment, whether a large amount of vapor is accumulated in the fuel suction port 74 of the low-pressure pump 70, that is, whether the low-pressure pump 70 can appropriately discharge fuel (the pumping force of the low-pressure pump 70 is reduced) is determined. (or not). This determination is functionally performed by the determination unit 101 of the PCM 100. It is also determined whether vapor is generated in the low-pressure side fuel passage 22a, that is, whether 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. When a large amount of vapor accumulates in the fuel suction port 74 or vapor occurs in the low pressure side fuel passage 22a, an inappropriate injection amount from the injector 15 is avoided. Controls the low pressure pump 70. 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 vapor is generated in the low-pressure side fuel passage 22a will be described using FIG. 7.

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

Specifically, the PCM 100 sequentially calculates the amount of change in the high-pressure side I term per preset unit time, and calculates this amount of change calculated at each time during the period from the current moment to a predetermined time before. On average, the average value of the amount of change in the high pressure side I term per unit time is calculated. At this time, PCM100 takes the side where the high pressure side I term increases as a positive value and the side where it decreases as a negative value, and the increase amount of the high pressure side I term per unit time, that is, the average increase rate of the high pressure side I term. Calculate the value.

Next, in step S12, the PCM 100 determines whether the average increase rate of the high-pressure side I term calculated in step S11 is larger than a preset high-pressure 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 PCM 100 determines that vapor is not generated in the low-pressure side fuel passage 22a. The vapor generation flag in the aisle 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 PCM 100 determines that vapor is generated in the low-pressure side fuel passage 22a. It is determined that the passage vapor generation flag is set to 1. The in-passage vapor generation flag is a flag that indicates whether or not it has been determined that vapor is generated within the low-pressure side fuel passage 22a.

As described above, in this embodiment, when the high-pressure side I term tends to increase and the rate of increase is larger on average than the high-pressure side reference increase rate, the PCM 100 injects the fuel into the low-pressure side fuel passage 22a. It is determined that vapor is occurring. In other words, the high-pressure side I term is a value that is the sum of values proportional to the rail pressure deviation, so as the rail pressure deviation becomes smaller, the proportional value becomes smaller and the rate of change of the high-pressure side I term becomes smaller. . On the other hand, as described above, if 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 from the high-pressure pump 80 to the fuel rail. 17 cannot be supplied with sufficient amount of fuel. Therefore, in this case, even if the high pressure side I term is increased due to the actual rail pressure being lower than the target rail pressure and the valve closing period of the spill valve 87 is lengthened, the actual rail pressure will not increase sufficiently. First, the high-pressure side I term continues to increase. Furthermore, if a sufficient amount of fuel is not supplied from the high-pressure pump 80, the pressure within the fuel rail 17 will decrease, so the rail pressure deviation will increase and the high-pressure side I term will further increase. From this, it can be said that vapor is generated in the low pressure side fuel passage 22a when the increase rate of the high pressure side I term is larger than the predetermined value on average.

Other control of the low pressure pump 70 performed by the PCM 100 (low pressure pump control unit 103) will be described using FIGS. 8 and 9.

First, in step S20, the PCM 100 determines whether an air accumulation flag, which will be described later, is 0. If this determination is NO and the air pocket occurrence 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 flag is 0, the process advances 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. Set. The PCM 100 sets the low-pressure side target fuel pressure to a value close to the lowest pressure value at which 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 this embodiment, the relationship between the low-pressure side fuel temperature and the above-mentioned lowest pressure value is set in advance in a map through experiments or the like and stored in the PCM 100, and the PCM 100 stores the low-pressure side fuel read in step S21 from this map. The pressure corresponding to the temperature is extracted and set as the low pressure side target fuel pressure.

Next, in step S23, the PCM 100 calculates a low-pressure pump basic discharge amount, which is a 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 PCM 100 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 low-pressure pump basic discharge amount is calculated to be a larger value as the low-pressure side target fuel pressure and 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 fuel pressure detected by the low-pressure fuel pressure sensor SN6 will be referred to as the actual low-pressure 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, a 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) will be 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 this embodiment, the rotation speed of the low pressure pump 70 is controlled by PI so that the actual low pressure side fuel pressure becomes the low pressure side target fuel pressure, and in step S26, the PCM 100 performs a predetermined proportional Calculate the P term (proportional term) that is proportional to the deviation of the low pressure side fuel pressure by multiplying the coefficient, and also calculate the amount that is the amount obtained by multiplying the deviation of the low pressure side fuel pressure by a predetermined integral coefficient and is proportional to the deviation of the low pressure side fuel pressure. An I term (integral term), which is the integrated value, is calculated. Specifically, the PCM 100 repeatedly performs the calculations of steps S20 to S35 at a predetermined period, and calculates the I term by integrating an 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. If it is necessary to increase the rotational 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 value calculated in the previous calculation cycle. .

On the other hand, if 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, then 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. Hereinafter, the value of the I term calculated in step S26, that is, the value of the I term of the feedback amount of the rotation speed of the low pressure pump 70 calculated from the deviation of the low pressure side fuel pressure, will be appropriately referred to as the low pressure side I term. . In this embodiment, this low-pressure side I term corresponds to the "feedback amount of the rotation speed of the low-pressure fuel pump" in the claims. 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 pocket occurrence flag, which will be 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, if the low-pressure pump 70 and its peripheral equipment deteriorate, even if the rotation speed of the low-pressure pump 70 is set to the rotation speed corresponding to the basic discharge amount (the electric motor 73 Even if a command is issued), the actual low-pressure side fuel pressure may deviate from the low-pressure side target fuel pressure because the discharge amount of the low-pressure pump 70 decreases 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 rotation speed of the low pressure pump 70 is feedback-controlled based on the low pressure side fuel pressure, thereby achieving the low pressure side target fuel pressure. That is, the feedback control of the rotation speed of the low pressure pump 70 is mainly performed to correct a deviation in the low pressure side fuel pressure due to deterioration of the low pressure pump 70 and the like. Here, if the proportional coefficient used to calculate the low-pressure side P term and the integral coefficient used to calculate the low-pressure side I term are large, the rotation speed of the low-pressure pump 70 will increase or decrease excessively, making the low-pressure side fuel pressure unstable. Therefore, the proportional coefficient and integral 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 low pressure pump basic discharge amount calculated in step S23 and the value of the P term and the value of 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 low pressure pump basic discharge amount 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. The basic target low pressure pump rotation speed is calculated by adding the value of and the value of the I term. The PCM 100 stores the relationship between the preset discharge amount of the low-pressure pump 70 and the rotation speed corresponding to the basic discharge amount as a map, and the PCM 100 stores the relationship between the preset discharge amount of the low-pressure pump 70 and the rotation speed corresponding to the basic discharge amount, and the PCM 100 stores the relationship between the preset discharge amount of the low-pressure pump 70 and the rotation speed corresponding to the basic discharge amount, and the PCM 100 corresponds to the low-pressure pump basic discharge amount calculated in step S23 from this map. The extracted value is set as the rotation speed corresponding to the basic discharge amount.

Here, in this 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 value of the 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 rotation 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, and is set 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 at its maximum, the basic target low-pressure pump rotation speed is lower 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 7000 rpm, the first rotation speed is about 3000 rpm, the second rotation speed is about 5000 rpm, and the basic target low pressure pump rotation speed is in the range of about 3000 rpm to 5000 rpm. Become.

After step S27, the process advances to step S28. In step S28, the PCM 100 determines whether the I term calculated in step S26, that is, the low pressure side I term, is larger than a preset air accumulation determination value. The air pocket 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 accumulation 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 determines that vapor has accumulated in the fuel suction port 74 of the low-pressure pump 70. It is determined that the air pocket occurrence flag is set to 1. In this way, the air accumulation flag is a flag that indicates whether vapor is accumulated in the fuel suction port 74 of the low-pressure pump 70.

As described above, in this embodiment, when the low-pressure side I term is larger than the air accumulation determination value, the PCM 100 determines that vapor is accumulated in the fuel suction port 74 of the low-pressure pump 70. That is, the low-pressure side I term is a value obtained by integrating values proportional to the deviation of the low-pressure side fuel pressure, so as the deviation of the low-pressure side fuel pressure becomes smaller, the value proportional to this becomes smaller, and the low-pressure side I term becomes smaller. On the other hand, if vapor accumulates inside the fuel suction port 74 of the low-pressure pump 70, the low-pressure pump 70 cannot pump up and discharge sufficient fuel, so the actual pressure is lower than 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 vapor has accumulated in the fuel suction port 74 of the low-pressure pump 70. The air accumulation determination value is determined from experiments and the like to be the predetermined value, which is a value greater than or equal to the minimum value of the low-pressure side I term that is realized when a predetermined amount of vapor is accumulated in the fuel suction port 74. is set to .

After proceeding to step S30, that is, after determining that vapor has accumulated in the fuel suction port 74 of the low-pressure pump 70 and setting the air accumulation occurrence 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 is not accumulated in the fuel suction port 74 of the low-pressure pump 70 and setting the air accumulation occurrence flag to 0, the PCM 100 proceeds to step S32. .

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

If the determination in step S32 is NO, the in-passage vapor generation flag 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 as the final target low-pressure pump rotation speed.

On the other hand, if the determination in step S32 is YES, the in-passage vapor generation flag 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 final target low-pressure pump rotation speed (i) to a value obtained by adding the high-pressure side increase amount to the target low-pressure pump rotation speed (i-1) one calculation cycle before. Specifically, the PCM 100 repeatedly performs the calculations of steps S20 to S38 at a predetermined cycle, and in step S34, the PCM 100 increases the high-pressure side to the target low-pressure pump rotation speed calculated during the calculation one calculation cycle ago. Set the added value as the target low pressure pump rotation speed. The high-pressure side increase amount 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 set in advance and stored in the PCM 100.

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

On the other hand, when it is determined that the air accumulation flag is set to 1 in step S20, or when the air accumulation 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 that there is, the process advances to step S36 as described above.

In step S36, the PCM 100 determines whether 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.

If the determination in step S36 is NO and the rotational speed of the low-pressure pump 70 is not the maximum low-pressure pump rotational speed (less than the maximum low-pressure pump rotational speed), the process advances to step S37. In step S37, the PCM 100 sets the target low-pressure pump rotation speed (i) to a value obtained by adding the low-pressure side increase amount to the target low-pressure pump rotation speed (i-1) one calculation cycle before. The low pressure side increase amount 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 or the driving state of the low pressure pump 70.

The low pressure side increase amount is set in advance and stored in the PCM 100.

The low-pressure side increase amount is determined when the rotational speed of the low-pressure pump 70 is increased when both the air pocket generation flag and the passage vapor generation flag are 0, that is, the low-pressure side target fuel pressure set in step S22 is realized. When the rotation speed of the low-pressure pump 70 is feedback-controlled, the value is set to be larger than the increase in the rotation speed (the increase in the rotation speed in one calculation cycle). For example, the low pressure side increase amount is set to a value such that the increase rate (increase amount per unit time) of the low pressure side pump rotation speed is about 2000 rpm/min. In other words, feedback control of the rotation speed of the low pressure pump 70 is performed within 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 generating new vapor in the fuel suction port 74 of the low pressure pump 70. Specifically, when the rotational speed of the low-pressure pump 70 is rapidly increased, the pressure within the fuel suction port 74 is rapidly reduced. In particular, in this embodiment, the pump filter 78 is provided at the lower end, that is, the opening end of the fuel suction port 74, so that when the rotational speed of the low pressure pump 70 rapidly increases, the pressure inside the fuel suction port 74 becomes negative pressure. becomes. Therefore, if the rotational speed of the low-pressure pump 70 is rapidly increased, there is a risk that new vapor will be generated within 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 the upper limit value of the increase amount of the rotation speed of the low pressure pump 70 at which no new vapor is generated. The upper limit increase amount is a value corresponding to the "upper limit increase rate" in the claims, and the upper limit increase rate is a value obtained by converting the upper limit increase amount into a change over time.

Further, in this 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 advances to step S35.

Returning to step S36, if 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 rotation speed at the maximum low pressure pump rotation speed. After step S38, the process advances 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 when the electric motor 73 is energized to the combined period of the time when the electric motor 73 is energized and the time when this energization is stopped) is It is set in a map and stored in the PCM 100 in advance, 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. A command is issued to the electric motor 73.

In this way, when the air accumulation flag and the passage vapor generation flag are both 0, the PCM 100 adjusts the target low-pressure pump rotation speed and thus the rotation speed of the low-pressure pump 70 so that the actual low-pressure side fuel pressure becomes the low-pressure side target fuel pressure. feedback control. As a result, the target fuel pressure on the low pressure side is basically achieved. On the other hand, when the air accumulation flag is 1 and a large amount of vapor has 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 therefore the rotation speed of the low pressure pump 70 to the maximum rotation speed of the low pressure pump 70. Control is performed to increase the amount of increase on the low pressure side toward the number. Then, when the rotational speed of the low-pressure pump 70 reaches the maximum rotational speed of the low-pressure pump 70, the PCM 100 maintains this. The above-described 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 "pump rotation speed increase control" in the claims.

FIG. 11 is a diagram schematically showing changes over time in each parameter before and after the air accumulation flag changes from 0 to 1. Each graph in 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 the comparative example. FIG. 11 shows a situation when vapor begins to accumulate in the low pressure pump 70 at time t2.

The deviation of the actual low-pressure side fuel pressure from the low-pressure side target fuel pressure until time t2 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 made approximately equal 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 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 rotational speed of the low pressure pump 70 is increased and a significant drop 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. exceed the value. Accordingly, at time t3, the air accumulation determination flag changes from 0 to 1, the rotational speed of the low pressure pump 70 is rapidly increased, and the amount of increase (the amount of increase per one calculation cycle) is taken as the amount of increase on the low pressure side. . Here, in a range where the low-pressure side I term does not exceed the air pocket determination value, the amount of change in the control amount of the feedback control per one calculation cycle and the amount of change in the rotation speed of the low-pressure pump 70 per one calculation cycle are small. The amount of increase in the rotation speed of the low pressure pump 70 per one 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 amount of increase (the amount of increase per one calculation cycle) is maintained at the low-pressure side increase amount. In this embodiment, when the air accumulation flag becomes 1, the low pressure side I term is reset to 0. When the maximum rotational speed is reached at time t4 after time t3, the rotational speed of the low-pressure pump 70 is maintained at the maximum rotational 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 up to time t3 is performed without rapidly increasing the rotation speed of the low-pressure pump 70 after time t3. As shown by this chain line, if the rotational speed of the low pressure pump 70 is not rapidly increased, vapor continues to accumulate in the fuel suction port 74 of the low pressure pump 70, and the low pressure side fuel pressure continues to decrease. When more than a predetermined amount of vapor accumulates 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.

Furthermore, with the above control, in this embodiment, even when the air accumulation flag is 0 but the passage vapor generation flag is 1 and vapor is generated in the low pressure side fuel passage 22a, the target low pressure pump rotation The number of rotations and therefore the rotation speed of the low pressure pump 70 is increased. In this embodiment, as described above, the high-pressure side increase amount and the low-pressure side increase amount, which are the amount of increase in 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 if the air accumulation flag is 0 but the passage vapor generation flag 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 period of time or more. Specifically, as shown in FIG. 12, the PCM 100 determines whether the air accumulation flag is 1 in step S51. If this determination is NO and the air accumulation flag is 0, the process is immediately terminated. On the other hand, if this determination is YES and the air accumulation flag is 1, the process advances to step S52. In step S52, the PCM 100 determines whether the time period during which the engine is continuously stopped is longer than or equal to a preset determination time period. The determination time is set in advance and stored in the PCM 100. If the determination in step S52 is YES and the time period during which the engine is continuously stopped is 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, if the determination in step S52 is NO and the time period 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 trap flag to 0 only after the engine has been stopped for a period longer than the determination time. From this, even if the engine is stopped, if the engine is driven again before the determination time elapses after the engine stops, the air pocket flag is maintained at 1, and the rotation speed of the low pressure pump 70 is Increased towards maximum rotation speed.

(4) Effects, etc. As described above, in this embodiment, under normal conditions (when the air accumulation flag is 0 and the vapor generation flag is 0), the rotation speed of the low pressure pump 70 is lower than the maximum rotation speed of the low pressure pump 70. is also considered to be a small value. Therefore, compared to the case where the low pressure pump 70 is driven so that its rotational speed becomes the maximum rotational speed, 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. In particular, in this embodiment, under normal conditions, 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 reaches its 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.

In addition, to address the problem that vapor tends to accumulate inside the low-pressure pump 70 (inside the fuel suction port 74) when the rotation speed of the low-pressure pump 70 is lowered, it is necessary to check whether vapor has accumulated inside the low-pressure pump 70 or not. If it is determined that vapor has 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 rotational speed of the low-pressure pump 70 is set higher than the rate of increase in normal times, that is, the rate of increase until the above-mentioned determination is made. Therefore, the rotational speed of the low-pressure pump 70 can be increased quickly to quickly remove vapor in the low-pressure pump 70, and it is possible to prevent fuel from being no longer discharged from the low-pressure pump 70.

Furthermore, when it is determined that vapor has accumulated in the low pressure pump 70, the rate of increase in the rotational speed of the low pressure pump 70 is made smaller than the upper limit increase rate set as described above. Therefore, while increasing the rotational speed of the low pressure pump 70, it is possible to prevent new vapor from being generated within the low pressure pump 70, and vapor within the low pressure pump 70 can be reliably removed.

Further, in this embodiment, when it is determined that 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, by making the rotational speed of the low pressure pump 70 sufficiently high, the vapor in the fuel suction port 74 can be discharged to the outside of the low pressure pump 70 more reliably.

Furthermore, in the present embodiment, the amount of feedback of the low-pressure pump 70 is used to determine whether vapor is accumulated in the low-pressure pump 70. Therefore, it is possible to easily determine whether vapor has 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 this embodiment, the above-mentioned determination is made based on the value of the I term, which is the low pressure side I term and is calculated when the rotation speed of the low pressure pump 70 is controlled by PI. Therefore, the determination can be made with high accuracy. Specifically, the low-pressure side I term is a value that integrates 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 change suddenly, The amount of change is small. Therefore, when the target fuel pressure on the low pressure side or the actual fuel pressure on the low pressure side suddenly changes temporarily due to a disturbance (due to noise on the low pressure side fuel pressure sensor SN6 or pulsation of fuel, etc.), the low pressure A sudden increase in the side I term is avoided, and it is possible to avoid erroneously determining that vapor has accumulated in the low pressure pump 70 due to the sudden change.

Further, in this embodiment, the rotation speed of the low pressure pump 70 is increased even when the vapor generation flag is 0 and vapor is generated in the low pressure side fuel passage 22a. Therefore, even if vapor is generated in the low-pressure side fuel passage 22a due to an increase in the pressure inside the low-pressure side fuel passage 22a, it can be eliminated, 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 ensured to be an appropriate amount. In particular, even when the rotational speed of the low-pressure pump 70 increases, the rate of increase is set higher than the rate of increase during steady state. Therefore, the vapor in the low-pressure side fuel passage 22a can be quickly extinguished.

(5) Modification In the above embodiment, in step S28, the value of the low pressure side I term is compared with a predetermined value (air accumulation determination value) to determine whether or not 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 pressure side I term with a predetermined value, similarly to steps S11 and S12.

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

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 section (pump control means)
SN6 Low pressure side fuel pressure sensor (detection means)

Claims (5)

An engine control device comprising 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,
pump control means for controlling the low pressure fuel pump;
determining means for determining whether the pumping force of the low-pressure fuel pump has decreased ;
and detection means for detecting the pressure of fuel discharged from the low pressure fuel pump ,
The pump control means includes:
When the determining means determines that the pumping force of the low-pressure fuel pump has decreased, the rate of increase is greater than the rate of increase until it is determined that the pumping force of the low-pressure fuel pump has decreased, and is smaller than a predetermined upper limit increase rate. Implementing pump rotation speed increase control to increase the rotation speed of the low pressure fuel pump at an increasing rate;
If the determination means determines that the pumping force of the low-pressure fuel pump has not decreased, a target fuel pressure that is a target value of the pressure of fuel discharged from the low-pressure fuel pump is set and detected by the detection means. Feedback control of the rotation speed of the low pressure fuel pump so that the pressure of the fuel reached the target fuel pressure,
The determining means determines whether the pumping force of the low-pressure fuel pump has decreased based on a feedback amount of the rotation speed of the low-pressure fuel pump, which is calculated when it is determined that the pumping force of the low-pressure fuel pump has not decreased. An engine control device characterized in that it determines whether The engine control device according to claim 1,
An engine control device, wherein the pump control means maintains a constant increase rate of the rotation speed of the low-pressure fuel pump when the pump rotation speed increase control is performed, regardless of the operating state of the engine. The engine control device according to claim 1 or 2,
An engine control device, wherein 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 performing the pump rotation speed increase control. The engine control device according to any one of claims 1 to 3 ,
After determining that the pumping force of the low-pressure fuel pump has decreased, the determining means determines whether or not the pumping force of the low-pressure fuel pump has decreased, if the engine has been stopped continuously for a predetermined period of time or more. An engine control device characterized by canceling a determination. An engine control device comprising 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,
pump control means for controlling the low pressure fuel pump;
determining means for determining whether the pumping force of the low-pressure fuel pump has decreased;
vapor determination means for determining whether vapor is generated in a low-pressure side fuel passage that is a passage between the high-pressure fuel pump and the low-pressure fuel pump;
The pump control means includes:
When the determining means determines that the pumping force of the low-pressure fuel pump has decreased, the rate of increase is greater than the rate of increase until it is determined that the pumping force of the low-pressure fuel pump has decreased, and is smaller than a predetermined upper limit increase rate. Implementing pump rotational speed increase control that increases the rotational speed of the low pressure fuel pump at an increasing rate,
When the vapor determination means determines that vapor is generated in the low-pressure side fuel passage, the increase rate of the rotation speed of the low-pressure fuel pump is greater than or equal to the increase rate of the rotation speed of the low-pressure fuel pump when the pump rotation speed increase control is performed. An engine control device characterized by increasing the rotational speed of a low-pressure fuel pump.

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