Fuel leak diagnostic system

Abstract

The objective is to provide a fuel leak diagnostic system with improved accuracy in diagnosing liquid fuel leaks from the in-cylinder injection valves of an engine. [Solution] A fuel leak diagnosis system comprising: a high-pressure pump for pressurizing liquid fuel supplied from a fuel tank; a pressure accumulator for storing the liquid fuel discharged from the high-pressure pump; an in-cylinder injection valve for directly injecting the liquid fuel in the pressure accumulator into the cylinder of the engine; and a diagnostic device for diagnosing liquid fuel leakage from the in-cylinder injection valve.

Description

Technical Field

[0001] The present invention relates to a fuel leakage diagnosis system.

Background Art

[0002] There is a technique for diagnosing leakage of gas fuel from a gas engine (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Liquid fuel may leak from an in-cylinder injection valve of an engine using liquid fuel.

[0005] Therefore, an object of the present invention is to provide a fuel leakage diagnosis system with improved diagnostic accuracy for leakage of liquid fuel from an in-cylinder injection valve of an engine.

Means for Solving the Problems

[0006] The system comprises a high-pressure pump for pressurizing liquid fuel supplied from a fuel tank, a pressure accumulator for storing the liquid fuel discharged from the high-pressure pump, an in-cylinder injection valve for directly injecting the liquid fuel in the pressure accumulator into the cylinders of the engine, and a diagnostic device for diagnosing liquid fuel leakage from the in-cylinder injection valve, wherein the diagnostic device includes an acquisition unit for acquiring a first temperature and a first pressure of the liquid fuel in the pressure accumulator when the engine is stopped, and a second temperature and a second pressure of the liquid fuel in the pressure accumulator after the engine has stopped and before the engine has started, a determination unit for determining whether the second temperature is higher than the first temperature, and in the case where the determination unit makes an affirmative determination... This can be achieved by a fuel leak diagnosis system that includes: a first calculation unit that calculates the ideal pressure of the liquid fuel in the accumulator before starting the engine, assuming that there is no leakage of liquid fuel from the in-cylinder injector while the engine is stopped, based on the first temperature, the second temperature, the second pressure, the volume of the accumulator, the thermal expansion coefficient of the liquid fuel, and the bulk modulus of the liquid fuel; a second calculation unit that calculates the amount of liquid fuel leakage from the in-cylinder injector while the engine is stopped, based on the difference between the ideal pressure and the second pressure; and a diagnosis unit that diagnoses liquid fuel leakage from the in-cylinder injector based on the amount of leakage.

[0007] The first calculation unit is, Pi = P1 + (β × K) × (T2 - T1) The ideal pressure is calculated using the following formula, where Pi represents the ideal pressure, P1 represents the first pressure, β represents the coefficient of thermal expansion, K represents the bulk modulus, T2 represents the second temperature, T1 represents the first temperature, and the second calculation unit is, ΔV = (1 / K) × (Pi - P2) × V The leakage amount may be calculated using the following formula, where ΔV represents the leakage amount, P2 represents the second pressure, and V represents the volume.

[0008] The system includes a measuring unit for measuring the starting time required to start the engine, a counting unit for incrementing a counter value when the amount of leakage is greater than or equal to a predetermined amount and the starting time is greater than or equal to a predetermined time, and a diagnostic unit which may diagnose that liquid fuel is leaking from the in-cylinder injection valve when the counter value is greater than or equal to a predetermined value.

[0009] The counting unit may decrement the counter value when the leakage amount is equal to or greater than the predetermined amount and the start time is less than the predetermined time.

[0010] The system may also include a low-pressure pump that pressurizes the liquid fuel stored in the fuel tank and supplies it to the high-pressure pump and the port injection valve of the engine. [Effects of the Invention]

[0011] According to the present invention, a fuel leak diagnostic system can be provided that offers improved diagnostic accuracy for liquid fuel leaks from the in-cylinder injection valves of an engine. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram of the fuel leak diagnostic system. [Figure 2] This flowchart illustrates the fuel leak diagnostic control for the in-cylinder injection valve performed by the ECU. [Modes for carrying out the invention]

[0013] [Outline configuration of a fuel leak diagnostic system] Figure 1 is a schematic diagram of the fuel leak diagnostic system 1. The fuel leak diagnostic system 1 includes an engine 10, a fuel tank 21, a low-pressure pump 22, a low-pressure pipe 25, a low-pressure delivery pipe 26, a high-pressure delivery pipe 36, fuel pressure sensors 28 and 38, a fuel temperature sensor 39, a high-pressure pump 40, and an ECU (Electronic Control Unit) 5, etc. The fuel leak diagnostic system 1 is installed in a vehicle that uses the engine 10 as a power source, for example, but is not limited to that.

[0014] Engine 10 is a spark-ignition type four-cylinder gasoline engine equipped with in-cylinder injectors 37 that inject fuel into each cylinder and port injectors 27 that inject fuel into each intake port. However, engine 10 is not limited to this, and may be a diesel engine, an alcohol engine, or a so-called direct injection engine without port injectors 27 or low-pressure delivery pipes 26. Engine 10 also includes a camshaft 15 that drives intake valves or exhaust valves in conjunction with a crankshaft which is linked to a plurality of pistons.

[0015] The fuel tank 21 stores gasoline, which is a liquid fuel. If the engine 10 is a diesel engine, the liquid fuel is diesel oil. If the engine 10 is an alcohol engine, the liquid fuel is alcohol. The low-pressure pump 22 pressurizes the fuel and discharges it into the low-pressure pipe 25. The fuel discharged into the low-pressure pipe 25 is supplied to the port injection valve 27 via the low-pressure delivery pipe 26, and also to the high-pressure pump 40 via the branch pipe 25a that branches off from the low-pressure pipe 25.

[0016] The high-pressure pump 40 pressurizes the fuel supplied from the branch pipe 25a and discharges it into the high-pressure delivery pipe 36. The fuel pressurized by the high-pressure pump 40 is supplied to the in-cylinder injection valve 37 via the high-pressure delivery pipe 36.

[0017] The fuel pressure sensors 28 and 38 detect the fuel pressure in the low-pressure delivery pipe 26 and the high-pressure delivery pipe 36, respectively. The fuel temperature sensor 39 detects the fuel temperature in the high-pressure delivery pipe 36. The ECU 5 acquires the detected values ​​from the fuel pressure sensors 28 and 38 and the fuel temperature sensor 39.

[0018] The ECU 5 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and a rewritable non-volatile memory. By executing the program stored in the ROM with the CPU, the ECU 5 performs abnormal diagnosis control of the fuel pressure sensor 38 described later. The abnormal diagnosis control of the fuel pressure sensor 38 is executed by an acquisition unit, a determination unit, a first calculation unit, a second calculation unit, a diagnosis unit, a measurement unit, and a count unit that are functionally realized by the CPU, ROM, RAM, and non-volatile memory. Details will be described later.

[0019] Also, the ECU 5 changes the in-cylinder injection rate, which is the ratio of the fuel injection amount injected from the in-cylinder injection valve 37 to the total fuel injection amount, according to the operating region of the engine 10. For example, when the operating region of the engine 10 is a low load region, the in-cylinder injection ratio is 0%, when it is a high load region, it is 100%, and when it is a medium load region, it is set to an intermediate value.

[0020] [Schematic Configuration of High-Pressure Pump] The high-pressure pump 40 will be described. The high-pressure pump 40 is provided with a cylinder 41, a plunger 42, a pressurizing chamber 43, a suction passage 45, a discharge passage 47, a relief passage 49, a suction valve 50, a discharge valve 60, and a relief valve 70.

[0021] The plunger 42 reciprocates within the cylinder 41 in conjunction with the drive of the engine 10. Specifically, the plunger 42 is biased by a spring toward the cam CP side that rotates with the camshaft 15, and reciprocates within the cylinder 41 due to the rotation of the cam CP.

[0022] The pressurizing chamber 43 is defined by the cylinder 41 and the plunger 42. When the plunger 42 rises, the volume of the pressurizing chamber 43 decreases, and when the plunger 42 descends, the volume of the pressurizing chamber 43 increases.

[0023] The intake passage 45 connects the branch pipe 25a, which branches off from the low-pressure pipe 25, to the pressurizing chamber 43. The intake passage 45 is equipped with a pulsation damper 44 to suppress fuel pressure pulsation. The relief passage 49 connects the pressurizing chamber 43 to the high-pressure delivery pipe 36. The discharge passage 47 connects the relief passage 49 on the pressurizing chamber 43 side of the discharge valve 60 to the relief passage 49 on the high-pressure delivery pipe 36 side of the discharge valve 60. In other words, the discharge passage 47 bypasses the relief valve 70.

[0024] The intake valve 50 is an electromagnetically driven on-off valve located on the fuel inlet side of the pressurizing chamber 43, which switches the communication state between the intake passage 45 and the pressurizing chamber 43. The intake valve 50 has a valve body 51, a coil 55 that drives the valve body 51, and a spring 53 that always biases the valve body 51 in the open direction. The energization of the coil 55 is controlled by the ECU 5. When the coil 55 is energized, the valve body 51 blocks the intake passage 45 and the pressurizing chamber 43 against the biasing force of the spring 53. When the coil 55 is not energized, the valve body 51 is maintained in the open state by the biasing force of the spring 53.

[0025] The discharge valve 60 is a check valve located on the discharge passage 47 that allows fuel to flow from the pressurizing chamber 43 to the high-pressure delivery pipe 36 but restricts flow in the reverse direction. Specifically, the discharge valve 60 opens when the fuel pressure in the pressurizing chamber 43 becomes higher than the fuel pressure in the high-pressure delivery pipe 36 by a predetermined amount.

[0026] During the intake stroke of the high-pressure pump 40, the intake valve 50 opens and the plunger 42 descends, filling the pressurizing chamber 43 from the branch pipe 25a through the intake passage 45. During the pressurizing stroke, the intake valve 50 closes and the volume of the pressurizing chamber 43 decreases as the plunger 42 rises, pressurizing the fuel in the pressurizing chamber 43. During the discharge stroke, when the fuel pressure force acting on the discharge valve 60 from the pressurizing chamber 43 side becomes greater due to the fuel pressure force acting on the discharge valve 60 from the high-pressure delivery pipe 36 side and the biasing force of the discharge valve 60's spring, the discharge valve 60 opens, and the pressurized fuel is supplied to the high-pressure delivery pipe 36.

[0027] The relief valve 70 is a check valve located on the relief passage 49 that allows fuel to flow from the high-pressure delivery pipe 36 to the pressurizing chamber 43 but restricts flow in the reverse direction. The relief valve 70 opens when the fuel pressure in the high-pressure delivery pipe 36 rises excessively to the point where it could cause malfunctions in the high-pressure delivery pipe 36 or the in-cylinder injection valve 37, thereby preventing malfunctions in these components.

[0028] As described above, high-pressure fuel is stored in the high-pressure delivery pipe 36, the space in the discharge passage 47 on the side of the high-pressure delivery pipe 36 beyond the discharge valve 60, and the space in the relief passage 49 on the side of the high-pressure delivery pipe 36 beyond the relief valve 70. Therefore, these are examples of pressure storage vessels for storing liquid fuel discharged from the high-pressure pump 40.

[0029] [Fuel leak diagnostic control] Therefore, the ECU 5 performs fuel leak diagnostic control of the in-cylinder injection valve 37 as follows. Figure 2 is a flowchart illustrating the fuel leak diagnostic control of the in-cylinder injection valve 37 performed by the ECU 5. The ECU 5 repeatedly performs this control at predetermined intervals while the ignition is on. The ECU 5 determines whether the engine 10 has changed from a running state to a stopped state (step S1). Note that the stopped state of the engine 10 includes cases where the vehicle has stopped due to the ignition being turned off, where the engine 10 has temporarily stopped due to the idle stop function, where the engine 10 has intermittently stopped in a hybrid vehicle, etc. If the answer in step S1 is No, this control is terminated.

[0030] If the answer to step S1 is Yes, the ECU 5 acquires the temperature T1 and pressure P1 (step S2). The temperature T1 [°C] is the temperature of the fuel in the high-pressure delivery pipe 36 detected by the fuel temperature sensor 39. The temperature T1 may be an estimated value based on, for example, the temperature of the coolant in the engine 10. The pressure P1 [Pa] is the pressure of the fuel in the high-pressure delivery pipe 36 detected by the fuel pressure sensor 38. The temperature T1 and pressure P1 correspond to the temperature and pressure of the fuel in the high-pressure delivery pipe 36 immediately after the engine 10 is stopped. Step S2 is an example of the processing performed by the acquisition unit.

[0031] Next, the ECU 5 determines whether or not there is a request to start the engine 10 (step S3). If the answer in step S3 is No, step S3 is executed again. If the answer in step S3 is Yes, the ECU 5 obtains the temperature T2 and pressure P2 (step S4). The temperature T2 [°C] and pressure P2 [Pa] correspond to the temperature and pressure of the fuel in the high-pressure delivery pipe 36 immediately before starting the engine 10. The temperature T2 and pressure P2 are also detected by the fuel temperature sensor 39 and the fuel pressure sensor 38, respectively. Note that the temperature T2 may be an estimated value.

[0032] Next, the ECU 5 starts the engine 10 (step S5), and the ECU 5 measures the start time TM (step S6). The start time TM is the time required from the starter to the completion of engine 10 startup. Engine 10 startup is considered complete when the rotational speed of engine 10 reaches or exceeds the rotational speed at which it can operate autonomously. Step S6 is an example of the process performed by the measurement unit.

[0033] The ECU5 determines whether temperature T2 is higher than temperature T1 (step S7). If the answer in step S7 is Yes, various processes are executed to diagnose fuel leakage from the in-cylinder injection valve 37, as described later. Here, temperature T2 being higher than temperature T1 means that the temperature T2 immediately before starting the engine 10 is higher than the temperature T1 immediately after stopping the engine 10. This is because if temperature T2 is higher than temperature T1, the residual heat from the stopped engine 10 causes the fuel temperature in the high-pressure delivery pipe 36 to rise, which in turn increases the pressure, potentially causing fuel leakage from the in-cylinder injection valve 37. Therefore, if the answer in step S7 is No, this control process ends. In other words, if the possibility of fuel leakage, where temperature T2 is lower than or equal to temperature T1, is low, the fuel leak diagnosis is avoided. This improves the accuracy of the fuel leak diagnosis. Step S7 is an example of the process executed by the determination unit.

[0034] If the answer in step S7 is Yes, the ECU5 calculates the ideal pressure Pi based on the following equation (1) (step S8). Pi = P1 + (β × K) × (T2 - T1) ... (1) β[1 / K] represents the thermal expansion coefficient of the fuel. K[Pa] represents the bulk modulus of the fuel. Pi[Pa] represents the ideal pressure of the liquid fuel in the high-pressure delivery pipe 36 before starting the engine 10, assuming that there is no leakage of liquid fuel from the in-cylinder injection valve 37 while the engine 10 is stopped (hereinafter referred to as the ideal pressure). The ideal pressure Pi is the fuel pressure when there is no leakage of liquid fuel from the in-cylinder injection valve 37. Step S8 is an example of the process performed by the first calculation unit.

[0035] Next, the ECU5 calculates the leakage amount ΔV based on the following equation (2) (step S9). ΔV = (1 / K) × (Pi - P2) × V ... (2) V [mL] is the total volume of the high-pressure delivery pipe 36, the space in the discharge passage 47 on the side of the high-pressure delivery pipe 36 beyond the discharge valve 60, and the space in the relief passage 49 on the side of the high-pressure delivery pipe 36 beyond the relief valve 70. In other words, volume V is the volume of the accumulator that stores the liquid fuel discharged from the high-pressure pump 40. The leakage amount ΔV [mL] indicates the amount of liquid fuel leaking from the in-cylinder injection valve 37. If the pressure P2 is lower than the ideal pressure Pi, it means that the pressure increase is insufficient despite the temperature T1 rising to temperature T2. Therefore, it is considered that an amount of fuel corresponding to the pressure deficit is leaking. Step S9 is an example of the process performed by the second calculation unit.

[0036] Next, the ECU 5 determines whether the leakage amount ΔV is greater than or equal to a predetermined amount Vt (step S10). The predetermined amount Vt is set to the minimum amount of leakage that is considered to have occurred when fuel leaked from the in-cylinder injection valve 37 while the engine 10 was stopped, taking into account calculation errors in the leakage amount ΔV. If the answer in step S10 is No, this control is terminated.

[0037] If the answer in step S10 is Yes, the ECU 5 determines whether the starting time TM is greater than or equal to a predetermined time TMt (step S11). If a large amount of fuel leaks from the in-cylinder injector 37 while the engine 10 is stopped, the starting time TM will be prolonged. The fuel that leaks from the in-cylinder injector 37 while the engine 10 is stopped vaporizes and fills the cylinder. If the intake valve is open, the vaporized fuel also fills the intake passage. When the engine 10 is started, the amount of fuel injected for starting and the vaporized fuel cause the air-fuel ratio of the mixture to exceed the ignition limit and become rich. Thus, if fuel leaks from the in-cylinder injector 37 while the engine 10 is stopped, the ignitionability of the mixture deteriorates and the starting time TM is prolonged. Therefore, the predetermined time TMt is set to the shortest possible starting time during which it is considered that fuel leaked from the in-cylinder injector 37 while the engine 10 was stopped.

[0038] If the answer in step S11 is Yes, the ECU 5 increments the counter value N by 1 (step S12). The counter value N is a counter value used to diagnose fuel leakage from the in-cylinder injection valve 37, as will be explained in more detail later. This is because if the starting time TM is longer than a predetermined time TMt, there is a high probability that fuel is leaking from the in-cylinder injection valve 37. Step S12 is an example of the process performed by the counting unit.

[0039] If the answer in step S11 is No, the ECU 5 decrements the counter value N by 1 (step S13). This is because if the starting time TM is shorter than the predetermined time TMt, there is a high probability that the cause is something other than the in-cylinder injector 37. Factors other than the in-cylinder injector 37 include, for example, a case where the fuel temperature in the high-pressure delivery pipe 36 rises significantly due to residual heat, resulting in the pressure exceeding the relief pressure of the relief valve 70. In this case, the relieved fuel returns to the intake passage 45 via the intake valve 50, or some escapes through the gap between the plunger 42 and the cylinder 41. This is normal behavior and does not leak into the cylinder, so the starting time does not worsen. Thus, the counter value is decremented when there is a possibility of fuel leakage due to factors other than the in-cylinder injector 37, improving the accuracy of diagnosing fuel leakage from the in-cylinder injector 37. Step S13 is an example of the process performed by the counting unit.

[0040] Next, the ECU 5 determines whether the counter value N is greater than or equal to a predetermined value Nt (step S14). The predetermined value Nt is set to a counter value that allows the system to rule out temporary factors and determine that there is a high probability of fuel leakage from the in-cylinder injector 37. Temporary factors include, for example, the temporary presence of foreign matter between the needle and the nozzle of the in-cylinder injector 37. In this case, temporary fuel leakage may occur. As will be explained in more detail later, such temporary factors are ruled out and fuel leakage from the in-cylinder injector 37 is diagnosed. This improves the diagnostic accuracy. If the result in step S14 is No, this control process ends.

[0041] If the answer in step S14 is Yes, the ECU 5 diagnoses that there is a fuel leak from the in-cylinder injection valve 37 (step S15). Step S15 is an example of the process performed by the diagnostic unit. If a fuel leak is diagnosed from the in-cylinder injection valve 37, the ECU 5 may notify the driver of this fact, for example, through the MIL (Malfunction Indicator Light), display, or speaker installed in the vehicle.

[0042] [Method for calculating ideal pressure] Next, we will explain the method for calculating the ideal pressure Pi shown in equation (1). The bulk modulus K of the fuel can be expressed as shown in equation (3) below. K = (-1) × (dP / dV) × V ... (3) Equation (3) can be transformed into equation (4) below. dV = (-1) × (1 / K) × dP × V ... (4) Equation (4) shows that as the fuel pressure increases, the volume of the fuel decreases by dV.

[0043] The thermal expansion coefficient β of the fuel can be expressed as shown in equation (5) below. β = 1 / V × dV / dT …(5) Equation (5) can be transformed into equation (6) below. dV = β × dT × V ... (6) Equation (4) shows that as the fuel temperature rises, the volume of the fuel increases by dV. Here, the volume of the accumulator, including the high-pressure delivery pipe 36 mentioned above, does not change. Therefore, the volume decrease in equation (4) and the volume increase in equation (5) cancel each other out, and the following equation (7) holds true. (-1)×(1 / K)×dP×V+β×dT×V=0…(7) By rearranging equation (7), we obtain the following equation (8). dP = (K × β) × dT ... (8) In this way, the pressure increase of the fuel in response to the temperature increase of the fuel, assuming that the volume of the fuel does not change, is calculated. Based on equation (8) above, equation (1) for calculating the ideal pressure Pi is specified.

[0044] One might consider calculating the ideal pressure Pi using the ideal gas law. However, the ideal gas law applies to ideal gases, and intermolecular forces act on real gases. Therefore, calculating the ideal pressure Pi using the ideal gas law may reduce its accuracy. In this embodiment, the ideal pressure Pi can be calculated accurately by considering the pressure increase of the fuel in response to the temperature increase of the fuel, assuming that the volume in which the fuel is stored does not change. This also improves the accuracy of fuel leak diagnosis of the in-cylinder injection valve 37. Note that equation (2) is defined based on equation (4).

[0045] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of Symbols]

[0046] 1. Fuel leak diagnostic system 5. ECU (Diagnostic device, acquisition unit, judgment unit, first calculation unit, second calculation unit, diagnostic unit, measurement unit, counting unit) 10 Engines 21 Fuel tank 22 Low-pressure pump 27-port injection valve 38 Fuel pressure sensor 39 Fuel temperature sensor 36. High-pressure delivery pipe (pressure accumulator) 37 In-cylinder injection valve 40 High-pressure pump

Claims

1. A high-pressure pump that pressurizes the liquid fuel supplied from the fuel tank, A pressure storage vessel for storing liquid fuel discharged from the aforementioned high-pressure pump, An in-cylinder injection valve that directly injects the liquid fuel in the pressure accumulator into the cylinder of the engine, The system includes a diagnostic device for diagnosing leakage of liquid fuel from the in-cylinder injection valve, The diagnostic device is An acquisition unit that acquires the first temperature and first pressure of the liquid fuel in the accumulator when the engine is stopped, and the second temperature and second pressure of the liquid fuel in the accumulator after the engine has stopped but before the engine has started. A determination unit that determines whether the second temperature is higher than the first temperature, If the determination unit makes a positive determination, a first calculation unit calculates the ideal pressure of the liquid fuel in the pressure accumulator before starting the engine, assuming that there is no leakage of liquid fuel from the in-cylinder injection valve while the engine is stopped, based on the first temperature, the second temperature, the second pressure, the volume of the pressure accumulator, the thermal expansion coefficient of the liquid fuel, and the bulk modulus of the liquid fuel. A second calculation unit calculates the amount of liquid fuel leakage from the in-cylinder injection valve while the engine is stopped, based on the difference between the ideal pressure and the second pressure. Includes a diagnostic unit that diagnoses liquid fuel leakage from the in-cylinder injection valve based on the amount of leakage, Fuel leak diagnostic system.

2. The first calculation unit is, Pi=P1+(β×K)×(T2-T1) The ideal pressure is calculated using the following formula: Pi represents the ideal pressure, P1 represents the first pressure, β represents the thermal expansion coefficient, K represents the bulk modulus. T2 represents the second temperature, T1 represents the first temperature, The second calculation unit is, ΔV=(1 / K)×(Pi-P2)×V The leakage amount is calculated using the following formula: ΔV indicates the amount of leakage, P2 indicates the second pressure, The fuel leak diagnostic system according to claim 1, wherein V represents the volume.

3. A measuring unit for measuring the starting time required to start the engine, A counting unit that increments a counter value when the amount of leakage is equal to or greater than a predetermined amount and the start time is equal to or greater than a predetermined time, The fuel leak diagnosis system according to claim 2, wherein the diagnostic unit diagnoses that liquid fuel is leaking from the in-cylinder injection valve when the counter value is greater than or equal to a predetermined value.

4. The fuel leak diagnosis system according to claim 3, wherein the counting unit decrements the counter value when the amount of leakage is greater than or equal to a predetermined amount and the starting time is less than a predetermined time.

5. The fuel leak diagnostic system according to claim 4, further comprising a low-pressure pump that pressurizes the liquid fuel stored in the fuel tank and supplies it to the high-pressure pump and the port injection valve of the engine.

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