Fuel leak diagnostic system

Abstract

A fuel leak diagnostic system is provided with: a high-pressure pump that pressurizes liquid fuel supplied from a fuel tank; a pressure storage container for storing the liquid fuel discharged from the high-pressure pump; an in-cylinder injection valve which directly injects the liquid fuel in the pressure storage container into a cylinder of an engine; and a diagnostic device that diagnoses leakage of liquid fuel from the in-cylinder injection valve.

Description

Technical Field

[0001] This invention relates to a fuel leak diagnostic system. Background Technology

[0002] There are techniques for diagnosing gaseous fuel leaks from gas engines (e.g., see Japanese Patent Application Publication No. 11-107860). Summary of the Invention

[0003] Liquid fuel may leak from the in-cylinder injection valves of engines that use liquid fuel.

[0004] Therefore, the object of the present invention is to provide a fuel leak diagnostic system that improves the diagnostic accuracy of liquid fuel leaks from the in-cylinder injection valve of an engine.

[0005] The above objectives can be achieved through the following fuel leak diagnostic system, which includes:

[0006] A high-pressure pump pressurizes the liquid fuel supplied from the fuel tank;

[0007] A accumulator container for storing liquid fuel discharged from the high-pressure pump;

[0008] An in-cylinder injection valve directly injects liquid fuel from the accumulator container into the engine cylinder; and

[0009] The diagnostic device diagnoses leaks of liquid fuel from the in-cylinder injection valve.

[0010] The diagnostic device includes:

[0011] The acquisition unit 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 is stopped and before the engine is started.

[0012] The determination unit determines whether the second temperature is higher than the first temperature;

[0013] The first calculation unit, upon a positive determination by the determination unit, calculates the ideal pressure of the liquid fuel in the accumulator before engine start-up, assuming no leakage of liquid fuel from the in-cylinder injection valve during engine shutdown, 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.

[0014] The second calculation unit calculates the amount of liquid fuel leakage from the in-cylinder injection valve during the engine shutdown period, based on the difference between the ideal pressure and the second pressure; and

[0015] The diagnostic unit diagnoses liquid fuel leakage from the in-cylinder injection valve based on the leakage amount.

[0016] Alternatively, the first calculation unit may calculate the ideal pressure using the following formula:

[0017] Pi = P1 + (β × K) × (T2 - T1), where,

[0018] Pi represents the ideal pressure.

[0019] P1 represents the first pressure.

[0020] β represents the coefficient of thermal expansion.

[0021] K represents the bulk modulus of elasticity.

[0022] T2 represents the second temperature.

[0023] T1 represents the first temperature, and,

[0024] The second calculation unit calculates the leakage amount using the following formula:

[0025] ΔV = (1 / K) × (Pi - P2) × V, where,

[0026] ΔV represents the leakage amount.

[0027] P2 represents the second pressure.

[0028] V represents the volume.

[0029] Alternatively, the diagnostic device may further include:

[0030] The measuring unit measures the starting time required to start the engine; and

[0031] The counting unit increments the count value when the leakage amount is above a predetermined amount and the start-up time is above a predetermined time.

[0032] The diagnostic unit diagnoses liquid fuel leakage from the cylinder injection valve when the count value is above a specified value.

[0033] Alternatively, the counting unit may decrease the count value when the leakage amount is above the specified amount and the start-up time is less than the specified time.

[0034] Alternatively, the fuel leak diagnostic 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 engine's intake injection valve.

[0035] According to the present invention, a fuel leak diagnostic system is provided that improves the diagnostic accuracy of liquid fuel leaks from the in-cylinder injection valve of an engine. Attached Figure Description

[0036] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, wherein the same reference numerals denote the same components, and wherein:

[0037] Figure 1 This is a schematic diagram of the fuel leak diagnostic system; and

[0038] Figure 2 This is a flowchart illustrating the fuel leak diagnostic control of the in-cylinder injection valve executed by the ECU. Detailed Implementation

[0039] Overview of the structure of a fuel leak diagnostic system

[0040] Figure 1 This 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 electronic control unit (ECU) 5. The fuel leak diagnostic system 1 is, for example, installed in a vehicle powered by the engine 10, but is not limited to this.

[0041] Engine 10 is a spark-ignition four-cylinder gasoline engine equipped with in-cylinder injection valves 37 for injecting fuel into each cylinder and intake port injection valves 27 for injecting fuel into each intake port. However, engine 10 is not limited to this; for example, it can be a diesel engine, an ethanol engine, or a so-called direct injection engine without intake port injection valves 27 and low-pressure delivery pipes 26. Furthermore, engine 10 has a camshaft 15 that drives the intake or exhaust valves in conjunction with the crankshaft, and the crankshaft is linked to multiple pistons.

[0042] Gasoline, as a liquid fuel, is stored in fuel tank 21. If engine 10 is a diesel engine, the liquid fuel is light oil. If engine 10 is an ethanol engine, the liquid fuel is ethanol. Low-pressure pump 22 pressurizes the fuel and discharges it into low-pressure pipe 25. The fuel discharged into low-pressure pipe 25 is supplied to intake injection valve 27 via low-pressure delivery pipe 26, and also to high-pressure pump 40 via branch pipe 25a branching from low-pressure pipe 25.

[0043] 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 then supplied to the in-cylinder injection valve 37 via the high-pressure delivery pipe 36.

[0044] 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. Fuel temperature sensor 39 detects the fuel temperature in the high-pressure delivery pipe 36. ECU5 acquires the detection values ​​from fuel pressure sensors 28 and 38, as well as fuel temperature sensor 39.

[0045] ECU5 includes a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and rewritable non-volatile memory. The CPU executes a program stored in the ROM to perform the abnormal diagnosis control of the fuel pressure sensor 38, which will be described later. The abnormal diagnosis control of the fuel pressure sensor 38 is performed by an acquisition unit, a determination unit, a first calculation unit, a second calculation unit, a diagnostic unit, a measurement unit, and a counting unit, which are functionally implemented by the CPU, ROM, RAM, and non-volatile memory. Details will be described later.

[0046] In addition, the ECU5 changes the ratio of the fuel injection quantity injected from the in-cylinder injection valve 37 to the total fuel injection quantity, i.e., the in-cylinder injection rate, according to the operating region of the engine 10. For example, the in-cylinder injection rate is 0% in the low-load region of the engine 10, 100% in the high-load region, and set to an intermediate value in the medium-load region.

[0047] General structure of a high-pressure pump

[0048] The high-pressure pump 40 is described below. The high-pressure pump 40 is equipped with a cylinder 41, a plunger 42, a pressurization chamber 43, a suction passage 45, a discharge passage 47, a pressure relief passage 49, a suction valve 50, a discharge valve 60, and a pressure relief valve 70.

[0049] The plunger 42 reciprocates within the cylinder block 41 in a drive linkage with the engine 10. Specifically, the plunger 42 is forced by a spring toward the cam CP, which rotates together with the camshaft 15, and reciprocates within the cylinder block 41 by the rotation of the cam CP.

[0050] The pressurization chamber 43 is defined by the cylinder block 41 and the plunger 42. As the plunger 42 rises, the volume of the pressurization chamber 43 decreases, and as the plunger 42 falls, the volume of the pressurization chamber 43 increases.

[0051] The intake passage 45 connects to the pressurization chamber 43 via a branch pipe 25a branching from the low-pressure pipe 25. A pulsation damper 44 is installed in the intake passage 45 to suppress fuel pressure pulsations. The pressure relief passage 49 connects the pressurization chamber 43 to the high-pressure delivery pipe 36. The discharge passage 47 connects the pressure relief passage 49 on the side closer to the pressurization chamber 43 than the discharge valve 60 and the pressure relief passage 49 on the side closer to the high-pressure delivery pipe 36 than the discharge valve 60. That is, the discharge passage 47 bypasses the pressure relief valve 70.

[0052] The intake valve 50 is located on the fuel inlet side of the pressurization chamber 43 and is an electromagnetically driven on / off valve that switches the connection between the intake passage 45 and the pressurization chamber 43. The intake valve 50 has a valve core 51, a coil 55 that drives the valve core 51, and a spring 53 that always applies force to the valve core 51 in the opening direction. The energization of the coil 55 is controlled by the ECU 5. When the coil 55 is energized, the valve core 51 overcomes the force of the spring 53 and cuts off the intake passage 45 from the pressurization chamber 43. When the coil 55 is not energized, the valve core 51 remains open due to the force of the spring 53.

[0053] The discharge valve 60 is located on the discharge passage 47 and is a check valve that allows fuel to flow from the pressurization 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 pressurization chamber 43 is higher than the fuel pressure in the high-pressure delivery pipe 36 by a predetermined amount.

[0054] During the suction stroke of the high-pressure pump 40, the suction valve 50 opens, the plunger 42 descends, and fuel is filled from the branch pipe 25a into the pressurization chamber 43 via the suction passage 45. During the pressurization stroke, the suction valve 50 closes, and as the plunger 42 rises, the volume of the pressurization chamber 43 decreases, pressurizing the fuel within it. During the discharge stroke, when the fuel pressure acting on the discharge valve 60 from the pressurization chamber 43 side is greater than the fuel pressure acting on the discharge valve 60 from the high-pressure delivery pipe 36 side and the spring force of the discharge valve 60, the discharge valve 60 opens, and the pressurized fuel is supplied to the high-pressure delivery pipe 36.

[0055] The pressure relief valve 70 is located on the pressure relief passage 49 and is a check valve that allows fuel to flow from the high-pressure delivery pipe 36 side to the pressurization chamber 43 side but restricts the flow in the reverse direction. The pressure relief valve 70 opens when the fuel pressure in the high-pressure delivery pipe 36 rises excessively to a level that would cause abnormalities in the high-pressure delivery pipe 36 and the in-cylinder injection valve 37, thereby suppressing abnormalities in the high-pressure delivery pipe 36 and the in-cylinder injection valve 37.

[0056] As described above, high-pressure fuel is pressurized within the high-pressure delivery pipe 36, in the space between the discharge valve 60 of the discharge passage 47 and the pressure relief valve 70 of the pressure relief passage 49. Therefore, these are examples of pressurized containers for storing liquid fuel discharged from the high-pressure pump 40.

[0057] Fuel Leak Diagnosis and Control

[0058] Therefore, ECU5 performs fuel leak diagnostic control of the in-cylinder injection valve 37 as follows. Figure 2 This is a flowchart illustrating the fuel leak diagnostic control of the in-cylinder injection valve 37 executed by ECU5. ECU5 repeatedly executes this control at predetermined intervals during ignition activation. ECU5 determines whether the engine 10 has changed from a driving state to a stopped state (S1). It should be noted that the stopped state of the engine 10 includes situations where the vehicle stops due to ignition shutdown, situations where the engine 10 temporarily stops via the idle stop function, and situations where the engine 10 intermittently stops in hybrid vehicles, etc. If the result in S1 is negative, this control ends.

[0059] If S1 is true, ECU5 acquires temperature T1 and pressure P1 (S2). Temperature T1 [°C] is the temperature of the fuel in the high-pressure delivery pipe 36 detected by fuel temperature sensor 39. Temperature T1 can also be an estimated value based on, for example, the temperature of the engine 10's coolant. Pressure P1 [Pa] is the pressure of the fuel in the high-pressure delivery pipe 36 detected by fuel pressure sensor 38. Temperature T1 and pressure P1 are equivalent to the temperature and pressure of the fuel in the high-pressure delivery pipe 36 immediately after the engine 10 has been stopped. S2 is an example of the process performed by the acquisition unit.

[0060] Next, ECU5 determines whether there is a start request for engine 10 (S3). If S3 is negative, S3 is executed again. If S3 is positive, ECU5 obtains temperature T2 and pressure P2 (S4). Temperature T2 [°C] and pressure P2 [Pa] correspond to the temperature and pressure of the fuel in the high-pressure delivery pipe 36 before engine 10 is about to start. Temperature T2 and pressure P2 are also detected by fuel temperature sensor 39 and fuel pressure sensor 38, respectively. It should be noted that temperature T2 can be an estimated value.

[0061] Next, ECU5 starts engine 10 (S5), and ECU5 measures the starting time TM (S6). The starting time TM is the time required from the start of the starter-based engine 10 to the completion of the starting process of engine 10. The starting process of engine 10 is considered complete when the engine speed reaches a speed that allows it to operate independently. S6 is an example of the processing performed by the measurement unit.

[0062] ECU5 determines whether temperature T2 is higher than temperature T1 (S7). If yes in S7, various processes for diagnosing fuel leakage from the in-cylinder injection valve 37, described later, are executed. Here, a higher temperature T2 than temperature T1 means that the temperature T2 before the engine 10 is about to start is higher than the temperature T1 immediately after the engine 10 stops. This is because when temperature T2 is higher than temperature T1, the temperature of the fuel in the high-pressure delivery pipe 36 rises due to the residual heat of the engine 10 during the shutdown period, and the pressure rises accordingly. As a result, there is a possibility of fuel leakage from the in-cylinder injection valve 37. Therefore, if no in S7, this control ends. That is, when the possibility of fuel leakage due to temperature T2 being lower than temperature T1 is low, fuel leakage diagnosis is avoided. As a result, the accuracy of fuel leakage diagnosis is improved. S7 is an example of the process executed by the determination unit.

[0063] If S7 is true, ECU5 calculates the ideal pressure Pi (S8) based on the following equation (1).

[0064] Pi=P1+(β×K)×(T2-T1)…(1)

[0065] β[1 / K] represents the thermal expansion coefficient of the fuel. K[Pa] represents the bulk modulus of elasticity of the fuel. Pi[Pa] represents the ideal pressure (hereinafter referred to as ideal pressure) of the liquid fuel in the high-pressure delivery pipe 36 before starting the engine 10, assuming no leakage of liquid fuel from the in-cylinder injection valve 37 during engine 10 shutdown. Ideal pressure Pi is the fuel pressure under the condition of no leakage of liquid fuel from the in-cylinder injection valve 37. S8 is an example of the process performed by the first calculation unit.

[0066] Next, ECU5 calculates the leakage amount ΔV (S9) based on the following equation (2).

[0067] ΔV=(1 / K)×(Pi-P2)×V…(2)

[0068] V[mL] is the total volume of the space within the high-pressure delivery pipe 36, the space in the discharge passage 47 relative to the side of the discharge valve 60 near the high-pressure delivery pipe 36, and the space in the pressure relief passage 49 relative to the side of the pressure relief valve 70 near the high-pressure delivery pipe 36. In other words, volume V is the volume of the accumulator container storing the liquid fuel discharged from the high-pressure pump 40. The leakage amount ΔV[mL] represents the amount of liquid fuel leaking from the in-cylinder injection valve 37. When pressure P2 is lower than the ideal pressure Pi, it means that although temperature T1 rises to temperature T2, the pressure increase is insufficient. Therefore, it is considered that a fuel amount equivalent to the insufficient pressure leaks. S9 is an example of the processing performed by the second calculation unit.

[0069] Next, ECU5 determines whether the leakage amount ΔV is greater than or equal to the specified amount Vt (S10). The specified amount Vt is set to the minimum leakage amount considered to occur when fuel leaks from the in-cylinder injection valve 37 during the period when the engine 10 is stopped, taking into account calculation errors of the leakage amount ΔV. If no, the control ends in S10.

[0070] If the condition in S10 is yes, ECU5 determines whether the starting time TM is greater than or equal to a predetermined time TMt (S11). Here, if there is a large amount of fuel leakage from the in-cylinder injection valve 37 during the engine 10's shutdown period, the starting time TM is prolonged. During the engine 10's shutdown period, the fuel leaking from the in-cylinder injection valve 37 vaporizes and fills the cylinder. With the intake valve open, the vaporized fuel fills the intake passage. When the engine 10 starts, due to the amount of fuel injected for starting and the vaporized fuel, the air-fuel ratio of the mixture exceeds the ignition limit and becomes rich. Thus, if fuel leaks from the in-cylinder injection valve 37 during the engine 10's shutdown period, the ignition properties of the mixture deteriorate, and the starting time TM is prolonged. Therefore, the predetermined time TMt is set to the shortest possible starting time when fuel is believed to leak from the in-cylinder injection valve 37 during the engine 10's shutdown period.

[0071] If S11 is true, ECU5 increments the count value N by 1 (S12). The count value N is used to diagnose fuel leakage from the in-cylinder injection valve 37, as detailed later. This is because if the start-up time TM is longer than a specified time TMt, the possibility of fuel leakage from the in-cylinder injection valve 37 is high. S12 is an example of the processing performed by the counting unit.

[0072] If S11 is not true, ECU5 decrements the count value N by 1 (S13). This is because if the start-up time TM is shorter than the specified time TMt, the possibility of a major cause other than the injection valve 37 is high. A major cause other than the injection valve 37 refers to, for example, a higher rise in fuel temperature in the high-pressure delivery pipe 36 due to residual heat, resulting in exceeding the pressure relief valve 70. In this case, the depressurized fuel returns to the intake passage 45 via the intake valve 50, or some escapes from the gap between the plunger 42 and the cylinder block 41. This is normal behavior and does not leak into the cylinder, so the start-up time does not worsen. In cases where there is a possibility of fuel leakage due to a major cause other than the injection valve 37, the count value decreases, thus improving the diagnostic accuracy of fuel leakage from the injection valve 37. S13 is an example of the processing performed by the counting unit.

[0073] Next, ECU5 determines whether the count value N is greater than or equal to the predetermined value Nt (S14). The predetermined value Nt is set to a count value that is considered high in terms of the likelihood of fuel leakage from the in-cylinder injection valve 37, excluding temporary causes. A temporary cause could be, for example, a foreign object temporarily lodged between the needle and the nozzle of the in-cylinder injection valve 37. In such cases, temporary fuel leakage may occur. This will be described in detail later, but by excluding such temporary causes, fuel leakage from the in-cylinder injection valve 37 can be diagnosed. Therefore, diagnostic accuracy is improved. If the result in S14 is negative, this control process ends.

[0074] If the condition in S14 is true, ECU5 diagnoses a fuel leak from the cylinder injection valve 37 (S15). S15 is an example of the processing performed by the diagnostic unit. It should be noted that if a fuel leak from the cylinder injection valve 37 is diagnosed, ECU5 may also report this to the driver via, for example, the MIL (Malfunction Indicator Light) installed in the vehicle, a display, or a speaker.

[0075] Calculation method of ideal pressure

[0076] Next, the calculation method for the ideal pressure Pi shown in equation (1) will be explained. The bulk modulus K of the fuel can be expressed as shown in equation (3) below.

[0077] K=(-1)×(dP / dV)×V…(3)

[0078] Equation (3) can be transformed as shown in Equation (4) below.

[0079] dV=(-1)×(1 / K)×dP×V…(4)

[0080] Equation (4) indicates that the volume of fuel decreases by dV when the fuel pressure increases.

[0081] The thermal expansion coefficient β of the fuel can be expressed as shown in equation (5).

[0082] β=1 / V×dV / dT…(5)

[0083] Equation (5) can be transformed as shown in Equation (6) below.

[0084] dV=β×dT×V…(6)

[0085] Equation (4) indicates that the volume of the fuel increases by dV when the temperature of the fuel rises.

[0086] Here, the volume of the accumulator container, including the high-pressure transmission pipe 36 mentioned above, remains unchanged. Therefore, the volume reduction in equation (4) is offset by the volume increase in equation (5), and equation (7) below holds.

[0087] (-1)×(1 / K)×dP×V+β×dT×V=0…(7)

[0088] If equation (7) is transformed, then equation (8) holds true.

[0089] dP = (K × β) × dT … (8)

[0090] Thus, the pressure rise of the fuel relative to the temperature rise of the fuel is calculated when the fuel volume remains unchanged. Based on the above equation (8), equation (1) is defined for calculating the ideal pressure Pi.

[0091] Here, we also consider using the equation of state for gases to calculate the ideal pressure Pi. However, the equation of state for gases is based on ideal gases, while intermolecular forces act on actual gases. Therefore, the accuracy of calculating the ideal pressure Pi may be reduced when using the equation of state for gases. As in this embodiment, we calculate the pressure rise of the fuel relative to the temperature rise of the fuel, assuming that the volume of the stored fuel remains unchanged, with high accuracy. As a result, the accuracy of fuel leak diagnosis of the in-cylinder injection valve 37 is also improved. It should be noted that equation (2) is based on equation (4).

[0092] The embodiments of the present invention have been described in detail above, but the present invention is not limited to these specific embodiments. Various modifications and alterations can be made within the scope of the spirit of the present invention as set forth in the claims.

Claims

1. A fuel leak diagnostic system, comprising: A high-pressure pump pressurizes the liquid fuel supplied from the fuel tank; A accumulator container for storing liquid fuel discharged from the high-pressure pump; The in-cylinder injection valve directly injects the liquid fuel in the accumulator container into the engine cylinder; and The diagnostic device diagnoses leaks of liquid fuel from the in-cylinder injection valve. The diagnostic device includes: The acquisition unit 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 is stopped and before the engine is started. The determination unit determines whether the second temperature is higher than the first temperature; The first calculation unit, upon a positive determination by the determination unit, calculates the ideal pressure of the liquid fuel in the accumulator before engine start-up, assuming no leakage of liquid fuel from the in-cylinder injection valve during engine shutdown, 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. The second calculation unit calculates the amount of liquid fuel leakage from the in-cylinder injection valve during the engine shutdown period, based on the difference between the ideal pressure and the second pressure; and The diagnostic unit diagnoses liquid fuel leakage from the in-cylinder injection valve based on the leakage amount.

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

3. The fuel leak diagnostic system according to claim 2, wherein, The diagnostic device also includes: The measuring unit measures the starting time required to start the engine; and The counting unit increments the count value when the leakage amount is above a predetermined amount and the start-up time is above a predetermined time. The diagnostic unit diagnoses liquid fuel leakage from the cylinder injection valve when the count value is above a specified value.

4. The fuel leak diagnostic system according to claim 3, wherein, When the leakage amount is above the specified amount and the start-up time is less than the specified time, the counting unit decreases the count value.

5. The fuel leak diagnostic system according to claim 4, wherein, It also includes a low-pressure pump that pressurizes the liquid fuel stored in the fuel tank and supplies it to the high-pressure pump and the engine's intake injection valve.

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