Fuel pump control device

Abstract

The present invention provides a fuel pump control device that can properly transport fuel to the fuel injector. [Solution] The system includes a fuel pump 70 that pumps fuel to the fuel injection valve 15 and a control unit 100 that controls the fuel pump. The control unit includes a vapor determination unit 102 that determines whether or not vapor is being generated in the fuel pump, and a pump control unit 103 that, when the discharge flow rate, which is the flow rate of fuel discharged from the fuel pump, is greater than or equal to a predetermined high flow rate determination value and the vapor determination unit determines that vapor is being generated, lowers the rotation speed of the fuel pump compared to when no such determination is made.

Description

Technical Field

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[0007] To solve the above problems, the present invention provides a control device for a fuel pump provided in an engine having a cylinder in which a combustion chamber is formed and an intake passage for introducing air into the combustion chamber, comprising: a fuel injection valve for injecting fuel into the combustion chamber or the intake passage; a fuel pump for pressurizing fuel to the fuel injection valve; and a control unit for controlling the fuel pump, wherein the control unit comprises: a vapor determination unit for determining whether or not vapor is generated in the fuel pump; and a pump control unit that, when the discharge flow rate, which is the flow rate of fuel discharged from the fuel pump, is greater than or equal to a predetermined high flow rate determination value, and the vapor determination unit determines that vapor is being generated, the control unit lowers the rotational speed of the fuel pump to a lower speed than when no such determination is made (Claim 1).

[0008] In this invention, when vapor is generated in the fuel pump when the fuel pump's discharge flow rate is high, above a high flow rate threshold, that is, when the fuel pump's rotation speed is high and the fuel is strongly agitated, the rotation speed of the fuel pump is reduced. As a result, the agitation action of the fuel pump can be weakened, the temperature of the fuel inside the fuel pump which has become hot due to this agitation action can be lowered, and at least a portion of the generated vapor can be eliminated, reducing its amount. Consequently, the transport of fuel can be prevented from being obstructed by vapor, and fuel can be properly supplied to the fuel injector.

[0009] In the above configuration, preferably, when the discharge flow rate is less than a predetermined low flow rate determination value that is less than or equal to the high flow rate determination value, and the vapor determination unit determines that vapor is being generated, the pump control unit increases the rotational speed of the fuel pump to a higher level than when no such determination is made (Claim 2).

[0010] As described above, when the fuel pump discharge flow rate is high and the fuel pump rotation speed is high, vapor is more likely to be generated due to the agitation action of the fuel pump. On the other hand, when the fuel pump discharge flow rate is low, vapor is more likely to be generated due to the low fuel pressure caused by the weak fuel pump's pressurizing effect. In contrast, in this configuration, if vapor is generated in the fuel pump when the fuel pump discharge flow rate is low, below the low flow rate threshold, the fuel pump rotation speed is increased. Therefore, the fuel pressure is increased, the volume of vapor is reduced, or at least a portion of the vapor is eliminated, preventing the vapor from obstructing fuel transport.

[0011] In the above configuration, preferably, the fuel pump is provided with a vapor discharge section for discharging vapor from the inside to the outside of the fuel pump (Claim 3).

[0012] With this configuration, vapor is discharged from the vapor discharge section, preventing vapor from accumulating in the fuel pump and thus hindering fuel delivery to the fuel injector. However, when the fuel pump rotation speed is low, the fuel flow is weak, which may cause vapor to accumulate near the vapor discharge section. In contrast, as described above, in the present invention, when vapor is generated in the fuel pump when the fuel pump discharge flow rate is low, below the low flow rate determination value, i.e., when the fuel pump rotation speed is low, the rotation speed of the fuel pump is increased. Therefore, the fuel flow is strengthened, promoting the discharge of vapor to the outside of the fuel pump via the vapor discharge section.

[0013] In the above configuration, preferably, a fuel pressure detection device is provided to detect the fuel pressure, which is the pressure of the fuel discharged from the fuel pump, the pump control unit provides feedback control of the rotational speed of the fuel pump so that the actual fuel pressure, which is the fuel pressure detected by the fuel pressure detection device, becomes a target value, and the vapor determination unit determines that vapor is being generated in the fuel pump when the amount of feedback of the rotational speed of the fuel pump based on the deviation between the actual fuel pressure and the target value is greater than or equal to a predetermined vapor generation determination value (Claim 4).

[0014] This configuration allows for the control of the fuel pressure discharged from the fuel pump to an appropriate value, and also makes it easy to determine whether or not vapor is being generated using the feedback amount calculated in conjunction with this control.

[0015] In the above configuration, preferably, a fuel pressure detection device is provided to detect the fuel pressure, which is the pressure of the fuel discharged from the fuel pump, and the vapor determination unit determines that vapor is being generated in the fuel pump when the actual fuel pressure, which is the fuel pressure detected by the fuel pressure detection device, is less than or equal to a predetermined amount from the target value of the fuel pressure (Claim 5).

[0016] With this configuration, it is possible to accurately determine whether or not vapor is being generated based on the pressure detected by the fuel pressure detection device. [Effects of the Invention]

[0017] As described above, the fuel pump control device of the present invention can appropriately transport fuel to the fuel injection valve. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is a schematic diagram of an engine according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram of the low-pressure pump. [Figure 3] Figure 3 is an enlarged view of a portion of Figure 2. [Figure 4] Figure 4 is a block diagram showing the engine control system. [Figure 5] Figure 5 is a flowchart showing the control process for the low-pressure pump. [Figure 6] Figure 6 is a time chart showing the time evolution of each parameter before and after vapor generation. [Figure 7] Figure 7 is a time chart showing the time evolution of each parameter when vapor is generated when the discharge flow rate of the low-pressure pump is equal to or greater than the second flow rate. [Figure 8] FIG. 8 is a time chart showing the time change of each parameter when vapor is generated in a state where the discharge flow rate of the low-pressure pump is less than the first flow rate.

MODE FOR CARRYING OUT THE INVENTION

[0019] (Overall Configuration) FIG. 1 is a system diagram schematically showing the overall configuration of an engine E to which a control device 200 for a fuel pump according to the present invention is applied. The engine E shown in this figure is mounted on a vehicle and includes an engine body 1 used as a power source for running and the like. In the present embodiment, a four-cycle gasoline direct injection engine is used as the engine body 1. The engine E includes, in addition to the engine body 1, an intake passage 30 through which intake air introduced into the engine body 1 flows, and an exhaust passage 40 through which exhaust discharged from the engine body 1 flows.

[0020] The engine body 1 includes a cylinder block 3 in which cylinders 2 are formed inside, a cylinder head 4 attached to the upper surface of the cylinder block 3 so as to close the cylinders 2 from above, and pistons 5 respectively inserted into the cylinders 2 so as to be reciprocally slidable. 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 plane of FIG. 1), but here, for simplicity, the description will proceed by focusing on only one cylinder 2.

[0021] Above the piston 5, a combustion chamber 6 is defined. Fuel is supplied to the combustion chamber 6 from an injector 15 described later. The supplied fuel burns 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. The piston 5 is connected to a crankshaft 7 which is an output shaft of the engine body 1 via a connecting rod 8. The crankshaft 7 rotates around its central axis in response to the reciprocating motion of the piston 5. A crank angle sensor SN1 for detecting the rotation angle (crank angle) of the crankshaft 7 and the rotation speed (engine rotation speed) of the crankshaft 7 is provided in the cylinder block 3.

[0022] 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 intake valve 11 and the exhaust valve 12 are driven to open and close in conjunction with the rotation of the crankshaft 7. The cylinder head 4 is provided with an injector 15 that injects fuel into the combustion chamber 6. The injector 15 is connected to a fuel tank 21, and fuel stored in the fuel tank 21 is supplied to the injector 15. The cylinder head 4 is provided with a spark plug 16 that ignites the mixture of fuel injected from the injector 15 into the combustion chamber 6 and air introduced into the combustion chamber 6. The injector 15 described above corresponds to the "fuel injection valve" of the present invention.

[0023] The intake passage 30 is connected to one side of the cylinder head 4 so as to communicate with the intake port 9. The intake passage 30 is equipped with a throttle valve 32 (Figure 2) that adjusts the amount of intake air flowing through it, and an airflow sensor SN2 (Figure 2) that detects the intake air volume, which is the flow rate of the intake air.

[0024] The exhaust passage 40 is connected to the other side of the cylinder head 4 so as to communicate with the exhaust port 10. Although not shown in the illustration, the exhaust passage 40 is equipped with a catalytic converter and the like for purifying the exhaust gas.

[0025] (Fuel supply system) The configuration for supplying fuel to the injector 15 will be described below using Figures 1 to 3. Figure 2 is a schematic diagram of the low-pressure pump 70, which will be described later. Figure 3 is an enlarged view of a part of Figure 2. The low-pressure pump 70 corresponds to the "fuel pump" of the present invention.

[0026] Fuel is supplied to the injector 15 from the fuel tank 21 via the fuel supply passage 22. The fuel supply passage 22 is a passage through which fuel flows and connects the fuel tank 21 and the injector 15. The fuel supply passage 22 is equipped with, in order from the upstream side (fuel tank 21 side, i.e., opposite the injector 15), a low-pressure pump 70, a fuel filter 23, a high-pressure pump 80, and a fuel rail 17.

[0027] 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 matter contained in the fuel. The fuel rail 17 is a component for storing high-pressure fuel.

[0028] 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 process, 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 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 the fuel rail 17, and fuel is distributed from the fuel rail 17 to each injector 15.

[0029] In the low-pressure fuel passage 22A, which is the passage between the low-pressure pump 70 and the high-pressure pump 80 in the fuel supply passage 22, a fuel temperature sensor SN4 is provided to detect the fuel temperature, which is the temperature of the fuel flowing through it. The low-pressure fuel passage 22A is also provided with a fuel pressure sensor SN5 to detect the fuel pressure, which is the pressure of the fuel flowing through it. The fuel in the low-pressure fuel passage 22A is the fuel discharged from the low-pressure pump 70, and the fuel pressure detected by the fuel pressure sensor SN5 is equivalent to the pressure of the fuel discharged from the low-pressure pump 70. In addition, the fuel rail 17 is provided with a rail pressure sensor SN3 to detect the rail pressure, which is the pressure of the fuel stored in the fuel rail 17. The above-mentioned fuel pressure sensor SN5 corresponds to the "fuel pressure detection device" of the present invention.

[0030] (Low-pressure pump) The low-pressure pump 70 is a rotary pump. The low-pressure pump 70 comprises a substantially cylindrical pump case 71, a disc-shaped impeller 72 housed at the bottom of the pump case 71, and an electric motor 73 that rotates 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. The low-pressure pump 70 pumps fuel under pressure by the rotation of the impeller 72. The pumping force of the low-pressure pump 70 is roughly proportional to the rotational speed of the impeller 72. The rotational speed of the impeller 72 is proportional to the voltage applied to the electric motor 73, i.e., the driving voltage of the electric motor 73. In this embodiment, the rotational speed of the impeller 72 corresponds to the "rotational speed of the low-pressure pump" of the present invention. Hereinafter, the rotational speed of the impeller 72 will be referred to as the rotational speed of the low-pressure pump 70. Furthermore, the low-pressure pump 70 will be described using the vertical direction in Figure 2 simply as the vertical direction.

[0031] A fuel intake port 74 is provided at the bottom 71a (lower end) of the pump case 71, in the portion facing the impeller 72, connecting the inner space of the pump case 71 with the outside of the pump case 71. The fuel intake port 74 has a cylindrical shape that protrudes outward (downward) from the pump case 71 along a line parallel to the rotation centerline of the impeller 72, from a position close to the bottom surface (lower surface) of the impeller 72. Fuel in the fuel tank 21 is drawn up into the pump case 71 from the fuel intake port 74 as the impeller 72 rotates.

[0032] A pump filter 78 is attached to the lower end of the fuel intake port 74 to remove 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.

[0033] A fuel outlet 75 is provided at the end (upper part) opposite the bottom 71a of the pump case 71 for guiding fuel from the inside to the outside of the pump case 71. The fuel outlet 75 is connected to the fuel filter 23. The fuel, which is pumped into the pump case 71 and pressurized by the rotation of the impeller 72, is sent to the fuel filter 23 and then to the high-pressure pump 80 via the fuel outlet 75.

[0034] A vapor relief port 76 is provided in the bottom portion 71a of the pump case 71 that faces the impeller 72. The vapor relief port 76 is for releasing vapor, or air bubbles, generated in the fuel intake port 74 to the outside of the pump case 71. The vapor relief port 76 described above corresponds to the "vapor discharge section" of the present invention.

[0035] When the fuel temperature rises above the temperature on the vapor pressure curve, or when the fuel pressure falls below the saturated vapor pressure, vapor begins to form in the fuel tank 21 and the low-pressure pump 70. As shown in Figure 3, if a large amount of vapor V accumulates at the fuel intake port 74, contact between the impeller 72 and the fuel is obstructed. Therefore, if a large amount of vapor accumulates at the fuel intake port 74, it becomes difficult for the low-pressure pump 70 to adequately pump and pressurize the fuel.

[0036] The vapor relief port 76 is designed to suppress this, and is configured so that vapor accumulated in the fuel intake port 74, i.e., the low-pressure pump 70, is discharged to the outside of the pump case 71 through the vapor relief port 76. Specifically, similar to the fuel intake port 74, the vapor relief port 76 also has a cylindrical shape that protrudes outward (downward) from the pump case 71 along a line parallel to the rotational centerline of the impeller 72, from a position close to the bottom surface (lower surface) of the impeller 72. However, the inner diameter of the vapor relief port 76 is set to be smaller than the inner diameter of the fuel intake port 74. Furthermore, the vapor relief port 76 is located close to the fuel intake port 74 and is provided on the outer circumference side of the impeller 72 in the radial direction. The vapor relief port 76 and the fuel intake port 74 are in communication below the impeller 72. In other words, the pump case 71 has a communication passage 77 that connects the upper opening of the vapor relief port 76 and the upper opening of the fuel intake port 74.

[0037] Here, as described above, there are two locations where vapor is generated within the low-pressure pump 70: the low-pressure pump 70 itself and the fuel tank 21. However, in this specification, regardless of which of the two locations the vapor is generated in, the state in which vapor is present within the low-pressure pump 70 is referred to as "vapor being generated in the low-pressure pump 70."

[0038] (High-pressure pump) The high-pressure pump 80 is a reciprocating pump. In this embodiment, the high-pressure pump 80 is driven by a high-pressure pump cam, which is attached to the camshaft that drives the exhaust valve 12, to pressurize and pump fuel. Briefly describing the structure of the high-pressure pump 80, the high-pressure pump 80 comprises a pressurizing chamber and a plunger located inside it, and the fuel is pressurized by the reciprocating motion of the plunger. The high-pressure pump 80 also includes an electromagnetic spill valve that opens and closes its discharge port, and the amount of fuel discharged to the fuel rail 17 is changed by changing the opening period of this electromagnetic spill valve.

[0039] (Control system) Figure 4 is a block diagram showing the engine control system. The PCM100 shown in this figure is a microprocessor for comprehensively controlling the engine and is composed of a well-known CPU, memory (ROM, RAM), etc. The above PCM100 corresponds to the "control unit" of the present invention.

[0040] The PCM100 receives detection signals from various sensors. For example, the PCM100 is electrically connected to the crank angle sensor SN1, airflow sensor SN2, rail pressure sensor SN3, fuel temperature sensor SN4, and fuel pressure sensor SN5, and the information detected by these sensors (i.e., crank angle, engine speed, intake air volume, rail pressure, fuel temperature, and fuel pressure) is sequentially input to the PCM100. In addition, the vehicle is equipped with an accelerator sensor SN6 that detects the opening of the accelerator pedal operated by the driver, and the detection signal from the accelerator sensor SN6 is also input to the PCM100.

[0041] The PCM100 controls various parts of the engine while performing various judgments and calculations based on the input signals from the above-mentioned sensors. The PCM100 is electrically connected to the injector 15, spark plug 16, throttle valve 32, low-pressure pump 70 (specifically the electric motor 73 of the low-pressure pump 70), high-pressure pump 80, etc., and outputs control signals to each of these devices based on the results of the above calculations.

[0042] The PCM100 functionally comprises a determination unit 101, a vapor determination unit 102, and a low-pressure pump control unit 103. The low-pressure pump control unit 103 corresponds to the "pump control unit" of the present invention.

[0043] The determination unit 101 makes various determinations based on the engine operating status, etc. The vapor determination unit 102 determines whether or not vapor is being generated in the low-pressure pump 70, that is, whether or not vapor is present inside the low-pressure pump 70. The low-pressure pump control unit 103 controls the low-pressure pump 70.

[0044] (Control of low-pressure pumps) Figure 5 is a flowchart showing the control of the low-pressure pump 70 performed by the PCM100. Each step shown in Figure 5 is mainly performed by the low-pressure pump control unit 103.

[0045] First, the PCM100 calculates the target fuel pressure, the required flow rate, and the basic drive voltage (step S11). The required flow rate is the required value of the discharge flow rate, which is the flow rate of fuel discharged by the low-pressure pump 70, and corresponds to the discharge flow rate when the target fuel pressure is achieved. The basic drive voltage is the basic value of the drive voltage of the low-pressure pump 70. The PCM100 sets the target fuel pressure based on the fuel temperature and fuel injection amount detected by the fuel temperature sensor SN4. For example, the higher the fuel temperature and fuel injection amount, the higher the target fuel pressure is set to. The PCM100 also sets the required flow rate based on the target fuel pressure and fuel injection amount. For example, the larger the target fuel pressure and fuel injection amount, the larger the required flow rate is set to. The PCM100 also sets the basic drive voltage based on the target fuel pressure and required flow rate. For example, the higher the target fuel pressure and required flow rate, the higher the basic drive voltage is set to. The fuel injection amount is the amount of fuel injected from each injector 15, and is calculated based on engine speed, throttle opening, intake air volume, etc.

[0046] Next, the PCM100 calculates the fuel pressure deviation, which is the difference between the target fuel pressure set in step S11 and the actual fuel pressure (actual fuel pressure) (step S12). The PCM100 uses the fuel pressure detected by the fuel pressure sensor SN5 as the actual fuel pressure. The PCM100 calculates the fuel pressure deviation using the formula: fuel pressure deviation = target fuel pressure - actual fuel pressure, that is, by subtracting the actual fuel pressure from the target fuel pressure.

[0047] Next, the PCM100 calculates the amount of feedback (F / B amount) for the drive voltage of the low-pressure pump 70 based on the fuel pressure deviation calculated in step S12 (step S13). In other words, the drive voltage of the low-pressure pump 70, that is, the rotational speed of the low-pressure pump 70, is basically feedback-controlled so that the actual fuel pressure becomes the target fuel pressure, and this feedback amount is calculated in step S13.

[0048] In this embodiment, the required flow rate, and consequently the drive voltage and rotational speed of the low-pressure pump 70, are PI-controlled. Specifically, in step S13, the PCM 100 multiplies the fuel pressure deviation by a predetermined proportionality coefficient to calculate a P term (proportional term) that is proportional to the fuel pressure deviation, as one of the feedback quantities. That is, the PCM 100 calculates the P term using the formula P term = "fuel pressure deviation" × proportionality coefficient. The proportionality coefficient is set to a value greater than 0 and stored in the PCM 100. The PCM 100 also calculates an I term (integral term) as one of the feedback quantities by accumulating an amount that is proportional to the fuel pressure deviation, which is obtained by multiplying the fuel pressure deviation by a predetermined integral coefficient. That is, the PCM 100 calculates the I term using the formula I term = Σ fuel pressure deviation × integral coefficient. In this embodiment, the PCM 100 repeatedly performs the calculations in steps S11 to S17 shown in Figure 5 at predetermined intervals, and the I term is accumulated in each of these calculation cycles. The integral coefficient is set to a value greater than 0 and stored in the PCM100. Term I above corresponds to the "feedback amount" of the present invention.

[0049] Next, the PCM100 calculates the normal drive voltage based on the basic drive voltage calculated in step S11 and the P and I terms calculated in step S13 (step S14). Specifically, the PCM100 calculates the normal drive voltage as the sum of the basic drive voltage, the P term, and the I term. That is, the PCM100 calculates the normal drive voltage using the formula: Normal drive voltage = Basic drive voltage + P term + I term.

[0050] Next, in step S15, the PCM 100 determines whether or not vapor is generated within a range where vapor generation is likely. Specifically, the inventors of the present invention have found that vapor is more likely to be generated when the required flow rate, i.e., the discharge flow rate of the low-pressure pump 70, is small or large. Therefore, in step S15, the PCM 100 determines whether or not the required flow rate calculated in step S14 is within the range of a first flow rate or greater and less than the second flow rate (step S15). The first flow rate is preset and stored in the PCM 100 based on experimental results, etc. The second flow rate is preset to a value less than or equal to the first flow rate based on experimental results, etc., and stored in the PCM 100. In this embodiment, the first flow rate is set to a value smaller than the second flow rate. The determination in step S15 is performed by the determination unit 101. The first flow rate mentioned above corresponds to the "low flow rate determination value" of the present invention, and the second flow rate corresponds to the "high flow rate determination value" of the present invention.

[0051] If the determination in step S15 is YES, and the requested flow rate is greater than or equal to the first flow rate and less than the second flow rate, the PCM100 sets the normal drive voltage calculated in step S14 to the drive voltage of the low-pressure pump 70 (specifically, the electric motor 73 of the low-pressure pump 70) (step S16). After step S16, the PCM100 proceeds to step S17.

[0052] On the other hand, if the determination in step S15 is NO, and the requested flow rate is less than the first flow rate, or the requested flow rate is greater than or equal to the second flow rate, the PCM 100 determines whether or not vapor is being generated in the low-pressure pump 70 (step S20). This determination is performed by the vapor determination unit 102. Details of this determination will be described later.

[0053] If the result of step S20 is NO and no vapor is generated in the low-pressure pump 70, the PCM100 proceeds to step S16.

[0054] On the other hand, if the determination in step S20 is YES and vapor is being generated in the low-pressure pump 70, the PCM 100 determines whether the requested flow rate is less than the first flow rate (step S21). This determination is performed by the determination unit 101.

[0055] If the determination in step S21 is YES and the requested flow rate is less than the first flow rate, the PCM100 sets the drive voltage of the low-pressure pump 70 to the low flow rate voltage (step S22). The low flow rate voltage is preset and stored in the PCM100. The low flow rate voltage is set to a value greater than the maximum value of the normal drive voltage that can be set when the requested flow rate is less than the first flow rate and no vapor is generated in the low-pressure pump 70. Specifically, as described above, the higher the requested flow rate, the higher the value of the basic drive voltage, and the normal drive voltage calculated based on this is also generally set to a value greater as the requested flow rate increases. Thus, the low flow rate voltage is set to a value greater than the normal drive voltage set when the requested flow rate is the first flow rate. After step S22, the PCM100 proceeds to step S17.

[0056] On the other hand, if the determination in step S21 is NO, the PCM100 performs step S30. Here, step S21 is performed when the determination in step S15 is NO and the determination in step S20 is YES. Thus, the PCM100 performs step S30 when the requested flow rate is 2 or higher (determinations in steps S15 and S21 are NO) and vapor is being generated in the low-pressure pump 70 (determination in step S20 is YES). In step S30, the PCM100 sets the drive voltage of the low-pressure pump 70 to the high flow voltage. The high flow voltage is pre-set and stored in the PCM100. The high flow voltage is set to a value smaller than the minimum value of the normal drive voltage that can be set when the requested flow rate is 2 or higher and no vapor is being generated. Specifically, the high flow voltage is set to a value smaller than the normal drive voltage set when the requested flow rate is 2. Also, the high flow voltage is set to a value higher than the low flow voltage. After step S30, PCM100 proceeds to step S17.

[0057] In step S17, the PCM100 drives the low-pressure pump 70 (specifically, the electric motor 73 of the low-pressure pump 70) with the drive voltage set in step S16, step S22, or step S30. In this embodiment, the electric motor 73 of the low-pressure pump 70 is PWM controlled, and the drive duty cycle of the electric motor 73 is adjusted to a value corresponding to the drive voltage.

[0058] Here, the higher the drive voltage of the low-pressure pump 70, the higher the drive duty cycle is set to, and the higher the drive duty cycle, the higher the rotational speed of the low-pressure pump 70. Therefore, if step S22 is performed, the drive voltage is set to the low flow rate voltage, and as a result of performing step S17, the rotational speed of the low-pressure pump 70 is set to be higher than the rotational speed of the low-pressure pump 70 when the requested flow rate is less than the first flow rate and no vapor is being generated by the low-pressure pump 70. On the other hand, if step S30 is performed, the drive voltage is set to the high flow rate voltage, and as a result of performing step S17, the rotational speed of the low-pressure pump 70 is set to be lower than the rotational speed of the low-pressure pump 70 when the requested flow rate is the second flow rate or higher and no vapor is being generated by the low-pressure pump 70. After step S17, the PCM 100 terminates processing (returns to step S11).

[0059] Next, the specific procedure for determining whether or not vapor is being generated in the low-pressure pump 70, which is performed in step S20, will be explained using Figure 6. Figure 6 is a time chart showing the time changes of each parameter before and after vapor generation. Figure 6 shows graphs of fuel pressure, I term, P term, and required flow rate from top to bottom. In the fuel pressure graph in Figure 6, the solid line represents the actual fuel pressure, and the dashed line represents the target fuel pressure.

[0060] In the example in Figure 6, vapor is generated at time t1. During the period before time t1 when no vapor is generated, the drive voltage of the low-pressure pump 70 is set to a value corresponding to the requested flow rate, which is feedback-controlled based on the fuel pressure, so that the actual fuel pressure matches the target fuel pressure. Consequently, the P term immediately before time t1 is zero. On the other hand, the I term is not necessarily zero when the actual fuel pressure becomes the target fuel pressure, and in the example in Figure 6, the I term immediately before time t1 is a value greater than 0.

[0061] As described above, when vapor accumulates in the low-pressure pump 70, including the fuel intake port 74, it becomes difficult for the low-pressure pump 70 to adequately pump and pressurize the fuel. Consequently, when vapor accumulates in the low-pressure pump 70, the actual fuel pressure does not reach the target fuel pressure and becomes lower than the target fuel pressure. In the example in Figure 6, from time t1 onward, the actual fuel pressure decreases from the target fuel pressure. As the actual fuel pressure becomes lower than the target fuel pressure, terms P, I, and the required flow rate increase. Accordingly, although not shown in the figure, the drive voltage of the low-pressure pump 70 also increases. However, when vapor accumulates in the low-pressure pump 70, increasing the drive voltage of the low-pressure pump 70 does not raise the fuel pressure, and the difference between the target fuel pressure and the actual fuel pressure is not eliminated. Therefore, from time t1 onward, term I continues to increase.

[0062] Thus, as vapor accumulates in the low-pressure pump 70, term I continues to increase. Therefore, in this embodiment, in step S15 of the flowchart in Figure 5, the PCM 100 determines that vapor is being generated in the low-pressure pump 70 when the increase in term I reaches a predetermined vapor generation determination value. In other words, in the present invention, "vapor is being generated in the low-pressure pump 70" means that vapor has accumulated in the low-pressure pump 70 to the extent that it is hindering the suction and pumping of fuel by the low-pressure pump 70.

[0063] Specifically, the PCM100 sets the I term at the start of the increase as the initial I term. Furthermore, while the I term is increasing, the PCM100 calculates the difference between the initial I term and the current I term each time it is calculated. The PCM100 then determines whether this difference has reached the vapor generation threshold, and if the difference reaches a predetermined amount, it determines that vapor is being generated in the low-pressure pump 70. The vapor generation threshold is pre-set to a value greater than zero and stored in the PCM100. In the example in Figure 6, after time t1, the I term continues to increase, and at time t2, the increase in the I term reaches the vapor generation threshold. Therefore, it is determined that vapor is being generated in the low-pressure pump 70 at time t2.

[0064] The PCM100 controls both the low-pressure pump 70 and the high-pressure pump 80. To briefly explain the control of the high-pressure pump 80, the PCM100 sets a target rail pressure, which is the target value of the rail pressure, according to the engine's operating state. The PCM100 then provides feedback control to the driving force of the high-pressure pump 80 so that the actual rail pressure, which is the current rail pressure detected by the rail pressure sensor SN3, becomes the target rail pressure.

[0065] (action, etc.) Figure 7 is a time chart illustrating the time changes of each parameter when vapor is generated when the required flow rate, i.e., the discharge flow rate of the low-pressure pump, is equal to or greater than the second flow rate. Figure 7 shows graphs of fuel pressure, vapor generation flag, high flow rate flag, and the drive voltage of the low-pressure pump 70, from top to bottom. In the fuel pressure graph in Figure 7, the solid line represents the actual fuel pressure, and the dashed line represents the target fuel pressure. The vapor generation flag is set to 1 when the determination in step S20 is YES and it is determined that vapor is being generated in the low-pressure pump 70, and to 0 otherwise. The high flow rate flag is set to 1 when it is determined that vapor is being generated in the low-pressure pump 70 and the discharge flow rate of the low-pressure pump 70 is equal to or greater than the second flow rate, and to 0 otherwise.

[0066] In the example in Figure 7, vapor begins to be generated in the low-pressure pump 70 at time t11. From this point until time t11, the actual fuel pressure matches the target fuel pressure, but from time t11 onwards, the actual fuel pressure deviates from the target fuel pressure and decreases. Also, from time t11 onwards, as the actual fuel pressure is lower than the target fuel pressure, the drive voltage of the low-pressure pump 70 increases. In the example in Figure 7, it is determined that vapor is being generated in the low-pressure pump 70 at time t12, after time t11. Accordingly, at time t12, the drive voltage of the low-pressure pump 70 is set to the high-flow voltage. As described above, the high-flow voltage is set to a value smaller than the maximum drive voltage achieved when the required flow rate is 2 or higher and no vapor is being generated in the low-pressure pump 70. Therefore, at time t12, the drive voltage of the low-pressure pump 70 is reduced to the high-flow voltage. When the drive voltage of the low-pressure pump 70 decreases, the rotational speed of the low-pressure pump 70 decreases.

[0067] Thus, in the above embodiment, when vapor is generated in the low-pressure pump 70 when the discharge flow rate of the low-pressure pump 70 is high, that is, when the rotational speed of the low-pressure pump 70 is high, the rotational speed of the low-pressure pump 70 is reduced. Therefore, the vapor inside the low-pressure pump 70 can be reduced.

[0068] Specifically, when the rotational speed of the low-pressure pump 70 is high, the force with which the low-pressure pump 70 agitates the fuel is strong. Therefore, vapor generation when the rotational speed of the low-pressure pump 70 is high is mainly due to the rise in fuel temperature caused by the agitation action of the low-pressure pump 70. In contrast, in the above embodiment, when vapor is generated in the low-pressure pump 70 while the rotational speed of the low-pressure pump 70 is high, the rotational speed of the low-pressure pump 70 is reduced, weakening its agitation action. As a result, the fuel temperature inside the low-pressure pump 70 can be lowered, and the vapor inside the low-pressure pump 70 can be reduced. Accordingly, according to the above embodiment, it is possible to prevent fuel transport from being hindered by vapor, and the low-pressure pump 70 can properly supply fuel to the fuel injector. For example, in the example in Figure 7, at time t12, the drive voltage of the low-pressure pump 70 drops to a high flow rate voltage, so that after time t12, the vapor inside the low-pressure pump 70 decreases, and as a result, proper fuel transport resumes and the actual fuel pressure rises toward the target fuel pressure.

[0069] As described above, in the above embodiment, when it is determined that vapor is being generated inside the low-pressure pump 70 when the discharge flow rate of the low-pressure pump 70 is equal to or greater than the second flow rate, the rotational speed of the low-pressure pump 70 is lowered compared to when the determination is not made, thereby supplying an appropriate amount of fuel to the fuel injector.

[0070] Figure 7 is a time chart illustrating the time evolution of each parameter when vapor is generated when the required flow rate, i.e., the discharge flow rate of the low-pressure pump, is less than the first flow rate. Similar to Figure 8, Figure 7 shows graphs of fuel pressure, vapor generation flag, high flow rate flag, and the drive voltage of the low-pressure pump 70, from top to bottom. In the fuel pressure graph in Figure 7, the solid line represents the actual fuel pressure, and the dashed line represents the target fuel pressure.

[0071] In the example in Figure 8, vapor begins to be generated at the low-pressure pump 70 at time t21. From this point until time t21, the actual fuel pressure matches the target fuel pressure, but from time t21 onwards, the actual fuel pressure deviates from the target fuel pressure and decreases. Also, from time t21 onwards, as the actual fuel pressure is lower than the target fuel pressure, the drive voltage of the low-pressure pump 70 increases. In the example in Figure 8, it is determined that vapor is being generated at the low-pressure pump 70 at time t22, after time t21. Accordingly, at time t22, the drive voltage of the low-pressure pump 70 is set to the low flow voltage. As described above, the low flow voltage is set to a value greater than the maximum drive voltage achieved when the required flow rate is less than the first flow rate and no vapor is being generated at the low-pressure pump 70. Therefore, at time t22, the drive voltage of the low-pressure pump 70 is increased to the low flow voltage. As the drive voltage of the low-pressure pump 70 increases, the rotational speed of the low-pressure pump 70 also increases.

[0072] Thus, in the above embodiment, when vapor is generated in the low-pressure pump 70 while the discharge flow rate of the low-pressure pump 70 is low and its rotational speed is low, the rotational speed of the low-pressure pump 70 is increased. Therefore, vapor inside the low-pressure pump 70 can be reduced.

[0073] Specifically, when the rotational speed of the low-pressure pump 70 is low, the agitation action of the low-pressure pump 70 is weak, and vapor generation due to agitation is unlikely. On the other hand, when the rotational speed of the low-pressure pump 70 is low, the fuel pressurizing action of the low-pressure pump 70 is weak, and vapor generation is likely due to the low fuel pressure. In contrast to this, in the above embodiment, when vapor is generated in the low-pressure pump 70 when the rotational speed of the low-pressure pump 70 is low, the rotational speed of the low-pressure pump 70 is increased to strengthen its pressurizing action. Therefore, the fuel pressure in the low-pressure pump 70 is increased, reducing the volume of vapor or eliminating at least a portion of the vapor. Accordingly, according to the above embodiment, even when the discharge flow rate and rotational speed of the low-pressure pump 70 are low, it is possible to prevent fuel transport from being obstructed by vapor, and the low-pressure pump 70 can properly supply fuel to the fuel injector. For example, in the example shown in Figure 8, at time t22, the drive voltage of the low-pressure pump 70 increases to the low flow voltage, which reduces the vapor inside the low-pressure pump 70 from time t22 onward. Consequently, appropriate fuel transport resumes, and the actual fuel pressure rises towards the target fuel pressure.

[0074] As described above, in the above embodiment, when it is determined that vapor is being generated inside the low-pressure pump 70 when the discharge flow rate of the low-pressure pump 70 is less than the first flow rate, the rotational speed of the low-pressure pump 70 is increased compared to when no such determination is made, thereby supplying an appropriate amount of fuel to the fuel injector.

[0075] Furthermore, in the above embodiment, a vapor relief port 76 is provided in the low-pressure pump 70. This prevents vapor from accumulating in the low-pressure pump 70.

[0076] Furthermore, in the above embodiment, when it is determined that vapor is being generated inside the low-pressure pump 70 when the discharge flow rate of the low-pressure pump 70 is less than the first flow rate, the rotation speed of the low-pressure pump 70 is increased to strengthen the fuel flow. Therefore, at this time, the discharge of vapor to the outside of the low-pressure pump 70 via the vapor relief port 76 is promoted, and the vapor inside the low-pressure pump 70 can be reduced at an early stage.

[0077] Furthermore, in the above embodiment, the drive voltage of the low-pressure pump 70, i.e., the rotational speed of the low-pressure pump 70, is feedback-controlled so that the fuel pressure reaches the target value, the target fuel pressure. Therefore, the fuel pressure can be controlled to an appropriate value. In addition, the feedback amount calculated in conjunction with the implementation of the above feedback control is used to determine whether or not vapor is being generated. Therefore, this determination can be easily made.

[0078] (modified version) In the above embodiment, the case in which the injector 15 injects fuel into the combustion chamber 6 was described, but the injector 15 may also be installed in the intake passage 30 and fuel may be injected from the injector 15 into the intake passage 30.

[0079] In the above embodiment, a case was described in which the required flow rate is compared with the first or second flow rate, and based on the result of this comparison, the driving voltage of the low-pressure pump 70, i.e., the rotational speed of the low-pressure pump 70 (electric motor 73), is increased or decreased. However, instead of the required flow rate, the actual discharge flow rate of the low-pressure pump 70 may be used, and the increase or decrease of the driving voltage of the low-pressure pump 70 may be determined based on the result of comparing the actual discharge flow rate with the first or second flow rate. The actual discharge flow rate of the low-pressure pump 70 may be detected using a sensor or the like, or it may be estimated from fuel pressure, fuel injection amount, etc.

[0080] In the above embodiment, the drive voltage and rotational speed of the low-pressure pump 70 were controlled by PI control, and the I term obtained during this control was used to determine whether or not vapor was being generated in the low-pressure pump 70. However, the specific configuration of this determination is not limited to this. For example, this determination may be made using the P term.

[0081] Furthermore, the above determination may be made without using feedback quantities such as the P and I terms. For example, as shown in Figure 6, when vapor is generated in the low-pressure pump 70, the actual fuel pressure becomes smaller than the target fuel pressure and the difference between them becomes larger. Therefore, it may be determined that vapor is being generated in the low-pressure pump 70 when the actual fuel pressure is less than or equal to a predetermined amount compared to the target fuel pressure. In other words, the PCM 100 may determine that vapor is being generated in the low-pressure pump 70 when the fuel pressure deviation (fuel pressure deviation = target fuel pressure - actual fuel pressure) is greater than or equal to a predetermined determination value greater than zero. In this configuration, the determination value can be set in advance and stored in the PCM 100. Also, when the above determination is made using the fuel pressure deviation, it may be configured so that it is determined that vapor is being generated in the low-pressure pump 70 when a predetermined time has elapsed for the fuel pressure deviation to be greater than or equal to the determination value.

[0082] Furthermore, although the above embodiment described a case where the first flow rate is set to a value smaller than the second flow rate, the first flow rate may be set to the same value as the second flow rate. Also, the low flow rate determination value and the high flow rate determination value may be set to the same value as each other. In addition, although the above embodiment described a case where the drive voltage is set to a larger value as the required flow rate increases, the drive voltage may be changed in steps according to the required flow rate.

[0083] Furthermore, the specific structure of the low-pressure pump 70 is not limited to the above. Also, the detailed structure of engine E, such as the number of cylinders, and the type of fuel used are not limited to the above. [Explanation of Symbols]

[0084] 1. Engine body 2-cylinder 6 Combustion chamber 15. Injector (fuel injection valve) 70 Low-pressure pump (fuel pump) 76. Vapor relief port (vapor discharge section) 100 PCM (Control Unit) 102 Vapor detection unit 103 Low-pressure pump control unit SN6 Fuel Pressure Sensor (Fuel Pressure Detection Device)

Claims

1. In a control device for a fuel pump provided in an engine having a cylinder in which a combustion chamber is formed and an intake passage for introducing air into the combustion chamber, A fuel injection valve that injects fuel into the combustion chamber or the intake passage, A fuel pump that pressurizes fuel to the fuel injection valve, The system includes a control unit that controls the fuel pump, The control unit is A vapor determination unit that determines whether or not vapor is being generated inside the fuel pump, A fuel pump control device comprising: a pump control unit that, when the discharge flow rate, which is the flow rate of fuel discharged from the fuel pump, is equal to or greater than a predetermined high flow rate determination value, and the vapor determination unit determines that vapor is being generated, the pump control unit lowers the rotation speed of the fuel pump compared to when the determination is not made.

2. In the fuel pump control device according to claim 1, The fuel pump control device is characterized in that, when the discharge flow rate is less than a predetermined low flow rate determination value that is less than or equal to the high flow rate determination value, and the vapor determination unit determines that vapor is being generated, the pump control unit increases the rotation speed of the fuel pump to a higher level than when no such determination is made.

3. In the fuel pump control device according to claim 1 or 2, A control device for a fuel pump, characterized in that the fuel pump is provided with a vapor discharge section for discharging vapor from the inside to the outside of the fuel pump.

4. In the fuel pump control device according to claim 1, The system includes a fuel pressure detection device that detects the fuel pressure, which is the pressure of the fuel discharged from the fuel pump. The pump control unit provides feedback control to the rotational speed of the fuel pump so that the actual fuel pressure detected by the fuel pressure detection device reaches the target value. The control device for a fuel pump is characterized in that the vapor determination unit determines that vapor is being generated in the fuel pump when the amount of feedback of the rotational speed of the fuel pump based on the deviation between the actual fuel pressure and its target value is equal to or greater than a predetermined vapor generation determination value.

5. In the fuel pump control device according to claim 1, The system includes a fuel pressure detection device that detects the fuel pressure, which is the pressure of the fuel discharged from the fuel pump. The control device for a fuel pump is characterized in that the vapor determination unit determines that vapor is being generated in the fuel pump when the actual fuel pressure, which is the fuel pressure detected by the fuel pressure detection device, is less than or equal to a predetermined amount from the target value of the fuel pressure.

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