Fuel Pressure Control System

Abstract

A fuel pressure control system (91, 92) controls the fuel pressure of a fuel supply system (90f) that supplies fuel to an injector (35) of an engine (90), and includes a boost pump (29) that raises the fuel pressure (P) of a high-pressure system (30) which is part of the fuel supply system, a pressure reducing mechanism (37) that reduces the pressure of the high-pressure system, and a control device (50). It is configured such that when an abnormal discharge of the boost pump occurs (A) and the fuel pressure of the high-pressure system starts to rise, the rise in the fuel pressure of the high-pressure system stops by performing an abnormal situation coping process (Ac) by the pressure reducing mechanism. The control device, on the condition of a warning state (Wq) where it is determined that if an abnormal discharge were to occur, it is likely that the fuel pressure of the high-pressure system would exceed a threshold pressure (Px) which is below the pressure resistance of the high-pressure system before the rise in the fuel pressure stops due to the abnormal situation coping process, sets it to a warning state (W) where even if an abnormal discharge occurs, the fuel pressure of the high-pressure system will not exceed the threshold pressure before the rise in the fuel pressure stops due to the abnormal situation coping process.

Description

[0001] Cross-reference to Related Applications

[0002] This application is based on Japanese Application No. 2020-179135 filed on October 26, 2020, the contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a fuel pressure control system that controls the fuel pressure of a fuel supply system that supplies fuel to an injector of an opposed engine. Background Art

[0004] In a fuel pressure control system, there is a fuel pressure control system having a booster pump that raises the fuel pressure of a high-pressure system that is part of the fuel supply system, a decompression mechanism that decompresses the high-pressure system, and a control device that controls these booster pump and decompression mechanism. Moreover, as a document showing such a technique, there is the following Patent Document 1.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2010-190147 Summary of the Invention

[0008] In such a fuel pressure control system, when an abnormality occurs in which the ejection flow rate of the booster pump is larger than normal, that is, an ejection abnormality occurs and the fuel pressure of the high-pressure system starts to rise, the fuel pressure rise is stopped by performing a predetermined abnormality countermeasure process by the decompression mechanism. Therefore, during the time lag from the start to the stop of the fuel pressure rise caused by the ejection abnormality, the fuel pressure of the high-pressure system rises to a certain extent. Therefore, the high-pressure system is required to withstand the fuel pressure after the rise. Therefore, it is necessary to set the upper limit of the fuel pressure of the high-pressure system used during normal ejection when no ejection abnormality occurs to be low by a margin corresponding to the fuel pressure rise amount during the time lag.

[0009] The present disclosure has been made in view of the above circumstances, and a main object thereof is to be able to set the upper limit of the fuel pressure used during normal ejection higher.

[0010] The fuel pressure control system of the present disclosure controls the fuel pressure of a fuel supply system that supplies fuel to an injector of an engine. The fuel pressure control system includes: a boost pump that raises the fuel pressure of a high-pressure system by injecting fuel into the high-pressure system, which is part of the fuel supply system; a pressure reducing mechanism that reduces the pressure of the high-pressure system; and a control device that controls the boost pump and the pressure reducing mechanism. Moreover, the fuel pressure control system is configured such that when an abnormality occurs in which the injection flow rate of the boost pump is larger than normal, i.e., an injection abnormality, and the fuel pressure of the high-pressure system starts to rise, the pressure reducing mechanism performs a predetermined abnormality countermeasure process, thereby stopping the rise in fuel pressure.

[0011] The control device includes a state determination unit that determines whether it is a state requiring vigilance, which is a state in which there is a risk that the fuel pressure of the high-pressure system exceeds a predetermined threshold pressure that is equal to or lower than the pressure resistance of the high-pressure system before the rise in fuel pressure stops due to the abnormality countermeasure process assuming the occurrence of the injection abnormality. Moreover, the control device starts warning control to set a warning state on the condition that it is determined that it is the state requiring vigilance, and the warning state is a state in which even if the injection abnormality occurs, the fuel pressure of the high-pressure system does not exceed the threshold pressure before the rise in fuel pressure stops due to the abnormality countermeasure process.

[0012] According to the present disclosure, a state determination of whether it is a state requiring vigilance in which there is a risk that the fuel pressure of the high-pressure system exceeds a predetermined threshold pressure that is equal to or lower than the pressure resistance of the high-pressure system assuming the occurrence of the injection abnormality is performed, and warning control is started on the condition that it is determined that it is the state requiring vigilance. Through this warning control, a warning state is set in which even if the injection abnormality occurs, the fuel pressure of the high-pressure system does not exceed a predetermined threshold pressure that is equal to or lower than the pressure resistance of the high-pressure system. Therefore, the upper limit of the fuel pressure that the high-pressure system may reach due to the injection abnormality can be suppressed to be equal to or lower than the pressure resistance of the high-pressure system.

[0013] Moreover, since the warning control is executed in the state requiring vigilance in this way, in the normal state that is not the state requiring vigilance, it is not necessary to consider the situation when the injection abnormality occurs in the state requiring vigilance. Thus, in the normal state when the injection is normal, the upper limit of the fuel pressure used can be set higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above object and other objects, features, and advantages of the present disclosure will become more apparent by referring to the drawings and the following detailed description. The drawings are as follows.

[0015] Figure 1 It is a schematic diagram showing the fuel pressure control system of the first embodiment and its surroundings.

[0016] Figure 2 It is a diagram showing the reference for state determination.

[0017] Figure 3 It is a flowchart showing the control of the control device.

[0018] Figure 4 It is a graph showing the transition of each value when the warning control is executed and then the warning control is released.

[0019] Figure 5 It is a graph showing the transition of each value when the warning control is executed and then the abnormal response process is executed.

[0020] Figure 6 It is a schematic diagram showing the fuel pressure control system of the second embodiment and its periphery.

[0021] Figure 7 It is a graph showing the transition of each value when the warning control is executed and then the warning control is released.

[0022] Figure 8 It is a graph showing the transition of each value when the warning control is executed and then the abnormal response process is executed. Detailed implementation mode

[0023] Next, embodiments of the present disclosure will be described with reference to the drawings. However, the present disclosure is not limited to the embodiments, and can be appropriately modified and implemented without departing from the spirit of the disclosure.

[0024] [First Embodiment]

[0025] First, the key points of this embodiment will be described. Figure 1 The shown fuel pressure control system 91 is a system that controls the fuel pressure P of the fuel supply system 90f that supplies fuel to the injector 35 of the engine 90, and includes a boost pump 29, a pressure reducing mechanism 37, and a control device 50.

[0026] The boost pump 29 is driven by the engine 90. The boost pump 29 sprays fuel into the high-pressure system 30, causing the fuel pressure P in the high-pressure system 30 to rise. On the other hand, the pressure reducing mechanism 37 is a mechanism that reduces the pressure of the high-pressure system 30. The control device 50 controls the boost pump 29 and the pressure reducing mechanism 37. Specifically, the control device 50 has a target fuel pressure calculation unit 62 that calculates the target fuel pressure Pt, and controls the fuel pressure P in the high-pressure system 30 at the fuel injection start timing of the injector 35 to approach the calculated target fuel pressure Pt.

[0027] Moreover, the control device 50 is configured such that when an abnormality occurs in which the discharge flow rate Q of the boost pump 29 is larger than normal, i.e., a discharge abnormality A, and the fuel pressure in the high-pressure system 30 starts to rise, the fuel pressure rise in the high-pressure system 30 is stopped by performing a predetermined abnormality countermeasure process Ac by the pressure reducing mechanism 37.

[0028] Moreover, the control device 50 has a state determination unit 61 that determines whether or not it is in a predetermined warning required state Wq. This warning required state Wq is the state of the comparative example indicated by the dashed line in Figure 5 (b), i.e., the state in which there is a risk that the fuel pressure P in the high-pressure system 30 exceeds a predetermined threshold pressure Px that is equal to or lower than the pressure resistance of the high-pressure system 30 before the fuel pressure rise in the high-pressure system 30 stops due to the abnormality countermeasure process Ac when a discharge abnormality A occurs in the boost pump 29 while the control device 50 does not execute the predetermined warning control Wc.

[0029] Regarding the state determination, as Figure 2 shown, it is performed based on three parameters: the rotational speed of the engine 90, a predetermined injection relationship quantity, and the temperature of a predetermined part. The injection relationship quantity is the discharge amount per combustion cycle of the boost pump 29 or the fuel injection amount per combustion cycle of the injector 35. Usually, these discharge amounts per combustion cycle and the fuel injection amount are approximately the same. The temperature of the predetermined part is the temperature of the fuel, the cooling water of the engine 90, the lubricating oil of the engine 90, the outside air, etc.

[0030] In the state determination, as Figure 2 the difference shown in the horizontal axis direction of

[0031] shows, when the rotational speed of the engine 90 is high (towards the right), compared with the case where the rotational speed of the engine 90 is low (towards the left), the range in the vertical axis direction determined to be the warning required state Wq is larger, and it is easier to determine that it is the warning required state Wq. Figure 2 And, in this state determination, as

[0032] the difference shown in the vertical axis direction of Figure 2 shows, when the injection relationship quantity is small (towards the bottom), compared with the case where the injection relationship quantity is large (towards the top), the range in the horizontal axis direction determined to be the warning required state Wq is larger, and it is easier to determine that it is the warning required state Wq.

[0033] Moreover, Figure 1The control device 50 shown starts the warning control Wc on the condition that the state determination unit 61 determines that it is a state requiring warning Wq in the normal control Nc where the warning control Wc is not executed. This warning control Wc is used to set to Figure 5 the state indicated by the solid line in (b) of, that is, the state where even if an ejection abnormality A occurs, the fuel pressure P in the high-pressure system 30 will not exceed the threshold pressure Px before stopping due to the abnormal response process Ac for the fuel pressure rise, that is, the warning state W.

[0034] Specifically, in the warning control Wc, as Figure 4 indicated by the one-dot chain line in (b) of, while maintaining the same target fuel pressure Pt as in the normal control Nc where this warning control Wc is not performed, as Figure 4 shown in (d) of, the pressure reduction of the pressure reduction mechanism 37 is executed. Thus, inevitably, the ejection flow rate Q of the boost pump 29 increases as Figure 4 shown in (c) of to offset the decrease in the fuel pressure P in the high-pressure system 30 caused by this pressure reduction.

[0035] Thus, as Figure 4 shown in (b) of, while maintaining the fuel pressure P in the high-pressure system 30 in the same state as in the case of executing the normal control Nc, as Figure 4 shown in (c) of, the difference between the ejection flow rate Q of the boost pump 29 and the maximum ejection flow rate Qx which is the maximum flow rate that can be ejected by this boost pump 29, that is, the increased flow rate ΔQ, decreases. Thus, it becomes the aforementioned Figure 5 warning state W indicated by the solid line in (b) of, that is, the state where even if an ejection abnormality A occurs in the boost pump 29, the fuel pressure P in the high-pressure system 30 will not exceed the threshold pressure Px before stopping due to the abnormal response process Ac for the fuel pressure rise.

[0036] Next, the details of this embodiment will be described in a form that supplements the key points of the above-described embodiment.

[0037] Figure 1 is a schematic diagram showing the fuel pressure control system 91 of this embodiment and its surroundings. The fuel supply system 90f has, in addition to the above-described high-pressure system 30, a first low-pressure system 10 and a second low-pressure system 20. Moreover, a feed pump 19 for supplying the fuel in the first low-pressure system 10 to the second low-pressure system 20 is provided between the first low-pressure system 10 and the second low-pressure system 20, and the above-described boost pump 29 for boosting the fuel in the second low-pressure system 20 and supplying it to the high-pressure system 30 is provided between the second low-pressure system 20 and the high-pressure system 30.

[0038] The first low-pressure system 10 has a fuel tank 11 for storing fuel and a first pipe 12 for sucking up the fuel in the fuel tank 11 to the feed pump 19. The second low-pressure system 20 has a second pipe 22 connecting the feed pump 19 and the boost pump 29 to each other.

[0039] The high-pressure system 30 has a third pipe 32, a pressure accumulator chamber 33, a fourth pipe 34, and an injector 35. The third pipe 32 connects the boost pump 29 and the pressure accumulator chamber 33 to each other. The fourth pipe 34 connects the pressure accumulator chamber 33 and the injector 35 to each other.

[0040] The pressure reducing mechanism 37 has a return pipe 39 connecting the pressure accumulator chamber 33 and the second pipe 22 to each other and a pressure reducing valve 38 for opening and closing the return pipe 39. The pressure reducing valve 38 is provided, for example, at the connection portion of the pressure accumulator chamber 33 and the return pipe 39, the return pipe 39, etc. The pressure reducing valve 38 can be, for example, an electromagnetic valve or a butterfly valve.

[0041] When the pressure reducing valve 38 is an electromagnetic valve, when it is energized, the valve core (not shown) is pulled closer by an electromagnetic solenoid (not shown) to open the valve, and when the power supply is stopped, the valve is closed by releasing the pulling. In addition, when the pressure reducing valve 38 is a butterfly valve, the opening amount of the valve is adjusted by rotating a disk (not shown) provided in the return pipe 39 or the like.

[0042] Moreover, a fuel pressure sensor 43 for detecting the fuel pressure P in the pressure accumulator chamber 33 and various other sensors 40 are provided for the engine 90. As these various sensors 40, for example, a crank angle sensor, a flow sensor (air flow meter), various pressure sensors, various temperature sensors, an air-fuel ratio sensor, an accelerator opening sensor, etc. are exemplified.

[0043] More specifically, as various pressure sensors, an intake pressure sensor for detecting the intake pressure, an exhaust pressure sensor for detecting the exhaust pressure, an internal pressure sensor for detecting the pressure in the combustion chamber, a fuel pressure sensor for detecting the fuel pressure in the second low-pressure system, etc. are exemplified. In addition, as various temperature sensors, a water temperature sensor for detecting the temperature of the cooling water, a fuel temperature sensor for detecting the temperature of the fuel, an oil temperature sensor for detecting the temperature of the lubricating oil, an intake temperature sensor for detecting the temperature of the sucked-in gas, an exhaust temperature sensor for detecting the temperature of the exhausted gas, an external air temperature sensor for detecting the temperature of the external air, etc. are exemplified.

[0044] The control device 50 controls the injector 35, the boost pump 29, the pressure reducing valve 38, etc. based on the information input from these various sensors 40, 43.

[0045] The control device 50 includes an intake air amount calculation unit 51, a target air-fuel ratio calculation unit 52, an injection amount calculation unit 53, and an injection control unit 55 as parts for controlling the injector 35. The intake air amount calculation unit 51 calculates the intake air amount based on the intake pressure, the engine speed of the engine 90, etc. Based on the calculated intake air amount, the engine speed of the engine 90, the accelerator opening degree, etc., the target air-fuel ratio calculation unit 52 calculates the target air-fuel ratio. Based on the calculated intake air amount, target air-fuel ratio, etc., the injection amount calculation unit 53 calculates the target fuel injection amount per combustion cycle. Based on the calculated target fuel injection amount, etc., the injection control unit 55 controls the fuel injection performed by the injector 35.

[0046] The control device 50 includes a target fuel pressure calculation unit 62, an ejection amount calculation unit 64, and a pump control unit 65 as parts for controlling the booster pump 29. The target fuel pressure calculation unit 62 calculates the target fuel pressure Pt based on the accelerator opening degree, the intake air amount, the engine speed of the engine 90, etc. Based on the calculated target fuel pressure Pt, the current fuel pressure P, the engine speed of the engine 90, etc., the ejection amount calculation unit 64 calculates the target ejection amount of the booster pump 29 per combustion cycle. Based on the calculated target ejection amount, the pump control unit 65 controls the booster pump 29.

[0047] The control device 50 includes a valve opening necessity determination unit 72, a valve opening degree calculation unit 73, and a valve control unit 75 as parts for controlling the pressure reducing valve 38. The valve opening necessity determination unit 72 determines whether valve opening is necessary. Specifically, for example, when it is determined that the above-described ejection abnormality A has occurred, the valve opening necessity determination unit 72 determines that valve opening is necessary. Regarding the determination of whether it is the ejection abnormality A, for example, it can be performed based on the determination of the rising speed of the fuel pressure P in the high-pressure system 30, the state of the booster pump 29, etc.

[0048] In addition, for example, when the vehicle equipped with the valve opening necessity determination unit 72 is in a stopped state, since it is necessary to reduce the fuel pressure P in the high-pressure system 30, the valve opening necessity determination unit 72 determines that valve opening is necessary. In addition, for example, when the fuel pressure P in the high-pressure system 30 is much higher than the target fuel pressure Pt and it is assumed that it is difficult to reduce the fuel pressure P to the target fuel pressure Pt only by the fuel injection of the injector 35, the valve opening necessity determination unit 72 also determines that valve opening is necessary.

[0049] Then, when the valve opening necessity determination unit 72 determines that valve opening is necessary, or when the above-described state determination unit 61 determines that the warning state Wq is required, the valve opening degree calculation unit 73 calculates the required target valve opening degree based on various parameters such as the current fuel pressure P of the high-pressure system 30 and the rotational speed of the engine 90. For this calculation, either a mapping diagram showing the relationship between these various parameters and the target valve opening degree can be used, or a mathematical formula representing this relationship can be used.

[0050] The target valve opening degree can be either the target valve opening duty ratio or the target valve opening amount. Specifically, for example, when the pressure reducing valve 38 is a valve such as a solenoid valve that is controlled by two options of valve opening and valve closing, the valve opening degree calculation unit 73 calculates the ratio of the time for which the pressure reducing valve 38 should be opened in a unit time, i.e., the target valve opening duty ratio, as the valve opening degree. Additionally, for example, when the pressure reducing valve 38 is a valve such as a butterfly valve that can adjust the valve opening amount, the valve opening degree calculation unit 73 calculates the amount by which the pressure reducing valve 38 should be opened, i.e., the target valve opening amount, as the target valve opening degree.

[0051] Then, based on the target valve opening degree calculated by the valve opening degree calculation unit 73, the valve control unit 75 controls the pressure reducing valve 38.

[0052] Next, the warning control Wc will be described. When the state determination unit 61 determines that the warning state Wq is required, the warning control Wc is executed by the valve opening degree calculation unit 73, the valve control unit 75, the injection amount calculation unit 64, and the pump control unit 65. On the other hand, the target fuel pressure calculation unit 62, which is independent of the execution of the warning control Wc, calculates the same target fuel pressure Pt as in the case of the normal control Nc without executing the warning control Wc even when the state determination unit 61 determines that the warning state Wq is required.

[0053] Specifically, when the state determination unit 61 determines that the warning state Wq is required, the valve opening degree calculation unit 73 calculates the target valve opening degree required for executing the warning control Wc. As a result, the injection amount calculation unit 64 necessarily calculates a larger target injection amount of the boost pump 29 compared to the case of the normal control Nc in order to maintain the same fuel pressure P as in the case of the normal control Nc without executing the warning control Wc.

[0054] Through the above, in the warning control Wc, the valve control unit 75 opens the pressure reducing valve 38, and the pump control unit 65 increases the injection amount of the boost pump 29.

[0055] Next, the abnormal situation handling process Ac will be described. When the valve opening necessity determination unit 72 determines that it is the ejection abnormality A, the valve opening degree calculation unit 73 and the valve control unit 75 execute the abnormal situation handling process Ac. Specifically, when the valve opening necessity determination unit 72 determines that it is the ejection abnormality A, the valve opening degree calculation unit 73 calculates the valve opening degree required for the abnormal situation handling process Ac as the target valve opening degree. Based on the calculated target valve opening degree, the valve opening degree calculation unit 73 opens the pressure reducing valve 38. As a result, the rise of the fuel pressure in the high-pressure system 30 stops, and thereafter, the fuel pressure P decreases to the target fuel pressure Pt.

[0056] Figure 2 It is a graph showing an example of the determination criterion for the state determination by the state determination unit 61, that is, the determination criterion for whether it is the state Wq that requires vigilance. The horizontal axis of this graph represents the rotational speed of the engine 90, and the vertical axis represents the above-described ejection relational quantity, that is, the ejection amount of the boost pump 29 or the fuel injection amount of the injector 35 per combustion cycle. In this way, the faster the rotational speed of the engine 90, that is, the more to the right side in the horizontal axis direction, the easier it is to determine that it is the state Wq that requires vigilance. In addition, the smaller the ejection relational quantity, that is, the more to the lower side in the vertical axis direction, the easier it is to determine that it is the state Wq that requires vigilance.

[0057] Moreover, the boundary line X for determining whether it is the state Wq that requires vigilance changes according to the temperature of a predetermined unit such as fuel, cooling water, lubricating oil, and external air. That is, the lower the temperature of this predetermined unit, the more the boundary line X moves to the left, and the higher the temperature of this predetermined unit, the more the boundary line X moves to the right. Therefore, the lower the temperature of the predetermined unit, the easier it is to determine that it is the state Wq that requires vigilance. In addition, regarding the temperature of the predetermined unit here, from the viewpoint of facilitating more accurate state determination, the temperature of the fuel is preferred, and more specifically, the temperature of the fuel in the high-pressure system 30 is preferred.

[0058] Figure 3 It is a flowchart showing the control of the control device 50. First, the state determination unit 61 determines whether it is the state Wq that requires vigilance (S101). When it is determined in S101 that it is the state Wq that requires vigilance (S101: "Yes"), the vigilance control Wc is executed (S102), and the process proceeds to S201. That is, when the vigilance control Wc has not been executed, the vigilance control Wc is started and the process proceeds to S201. On the other hand, when the vigilance control Wc is already being executed, the vigilance control Wc is continued and the process proceeds to S201.

[0059] On the other hand, in Figure 3In S101, when it is determined that the situation is not the warning state Wq (S101: "No"), the warning control Wc is not executed, and the process proceeds to the next S201. That is, when in the state of the normal control Nc where the warning control Wc is not executed, the normal control Nc is still maintained and the process proceeds to the next S201. On the other hand, when the warning control Wc has been executed, the warning control Wc is ended and restored to the normal control Nc, and then the process proceeds to the next S201.

[0060] In S201, the valve opening necessity determination unit 72 determines whether it is an ejection abnormality A. When it is determined that it is an ejection abnormality A (S201: "Yes"), the abnormal situation response process Ac (S202) is executed, and the process ends. That is, when the abnormal situation response process Ac has not been executed, the abnormal situation response process Ac is started and the process ends. On the other hand, when the abnormal situation response process Ac has been executed, the abnormal situation response process Ac is still maintained and the process ends.

[0061] On the other hand, in Figure 3 In S201, when it is determined that it is not an ejection abnormality A (S201: "No"), the abnormal situation response process Ac is not executed and the process ends. That is, when the abnormal situation response process Ac has not been executed, this state is still maintained and the process ends. On the other hand, when the abnormal situation response process Ac has been executed, the abnormal situation response process Ac is ended, and the process ends.

[0062] Then, when the process ends, it returns to "Start" again, and the same process is repeated.

[0063] Figure 4 It is a graph showing the transition of each value when transferring from the normal state N to the warning state Wq, transferring from the normal control Nc to the warning control Wc, but then transferring from the warning state Wq back to the normal state N again without the occurrence of an ejection abnormality A. In addition, Figure 4 The dotted lines shown in (b) to (d) of

[0064] The fuel pressure P of the high-pressure system 30 decreases as shown in the first half of the V-shaped transition shown in (b) of Figure 4 when fuel is injected by the injector 35, and recovers as shown in the second half of the subsequent V-shaped transition when the boost pump 29 ejects fuel. Therefore, the part at the root of the first half of this V-shaped transition becomes the fuel injection start timing of the injector 35. The control device 50 controls in either the normal control Nc or the warning control Wc so that the fuel pressure P of the high-pressure system 30 at this fuel injection start timing approaches the target fuel pressure Pt.

[0065] As Figure 4 shown in (a) of Figure 4 , for example, when the rotational speed of the engine 90 increases, it transfers from the normal state N to the warning required state Wq, and from the normal control Nc to the warning control Wc. Thus, as Figure 4 shown in (d) of Figure 4 , the pressure reducing valve 38 opens, and the return flow rate of the pressure reducing mechanism 37 increases. At this time, as Figure 4 indicated by the one-dot chain line in (b) of Figure 4 , the target fuel pressure Pt is not changed. Therefore, as Figure 4 shown in (c) of Figure 4 , the discharge flow rate Q of the boost pump 29 necessarily increases to maintain the fuel pressure P in the high-pressure system 30 at the same flow rate as in the case of the normal control Nc. Thus, the discharge flow rate Q of this boost pump 29 approaches the maximum discharge flow rate Qx, and the increaseable flow rate ΔQ decreases.

[0066] After that, as Figure 4 shown in (a) of Figure 4 , for example, when the rotational speed of the engine 90 decreases, it transfers from the warning required state Wq to the normal state N, and from the warning control Wc to the normal control Nc. Thus, as Figure 4 shown in (d) of Figure 4 , the pressure reducing valve 38 closes, and the return flow rate of the pressure reducing mechanism 37 becomes zero. Thus, as Figure 4 shown in (c) of Figure 4 , the discharge flow rate Q of the boost pump 29 decreases and returns to the original discharge flow rate Q.

[0067] Figure 5 is a graph showing the transition of each value in the case where a discharge abnormality A has occurred after transferring from the normal state N to the warning required state Wq and from the normal control Nc to the warning control Wc. In addition, Figure 5 the dashed lines shown in (b) to (d) of Figure 5 show a comparative example in which the normal control Nc is maintained even in the warning required state Wq.

[0068] When transferring from the normal state N to the warning required state Wq and from the normal control Nc to the warning control Wc, similarly to the above-described case, as Figure 5 shown in (c) of Figure 5 , the discharge flow rate Q of the boost pump 29 increases, and the increaseable flow rate ΔQ decreases. Therefore, even if a discharge abnormality A occurs thereafter, the abnormal increase amount of the discharge flow rate Q of the boost pump 29 is suppressed within the range of the decreased increaseable flow rate ΔQ. Therefore, as Figure 5 shown in (b) of Figure 5 , the increase in the fuel pressure in the high-pressure system 30 is suppressed as compared with the comparative example.

[0069] After that, when the abnormality countermeasure process Ac is executed as Figure 5 shown in (d) of Figure 5 , the opening degree of the pressure reducing valve 38 increases. Thus, when the return flow rate of the pressure reducing mechanism 37 increases, as Figure 5As shown in (b), before the fuel pressure P of the high pressure system 30 reaches the threshold pressure Px, the fuel pressure P of the high pressure system 30 starts to decrease. As described above, the fuel pressure P of the high pressure system 30 is suppressed from exceeding the threshold pressure Px.

[0070] Hereinafter, the effect related to the implementation of the first disclosure at the time of application is referred to as the first effect, the effect related to the implementation of the second disclosure at the time of application is referred to as the second effect, and similarly, the effects related to the implementation of the third to eighth disclosures at the time of application are referred to as the third to eighth effects.

[0071] According to this embodiment, the following first effect is obtained. Figure 1 The fuel pressure control system 91 shown in the figure determines whether there is a situation such as when the discharge abnormality A occurs. Figure 5 As shown by the dotted line in (b), the fuel pressure P of the high pressure system 30 exceeds the predetermined threshold pressure Px below the withstand pressure of the high pressure system 30, which is a potential danger requiring an alert state Wq. Then, under the condition that it is determined to be a required alert state Wq, as Figure 4 As shown by the solid line in (b), the warning control Wc is started. By this warning control Wc, it is assumed that Figure 5 As shown by the solid line in (b), even if the ejection abnormality A occurs, the fuel pressure P of the high-pressure system 30 will not exceed the predetermined threshold pressure Px below the withstand pressure of the high-pressure system 30. Therefore, the upper limit of the fuel pressure P that can be reached by the high-pressure system 30 due to the ejection abnormality A can be suppressed to below the withstand pressure of the high-pressure system 30.

[0072] Furthermore, since the warning control Wc is executed in the required warning state Wq, it is not necessary to consider the case where the discharge abnormality A occurs in the required warning state Wq in the normal state N which is not the required warning state Wq. Therefore, in the normal state N when the discharge is normal, the upper limit of the used fuel pressure P can be set higher.

[0073] In addition, the following second effect is obtained. In the warning control Wc, if Figure 4 As shown in (d), the pressure is reduced by the pressure reducing mechanism 37, and as Figure 4 As shown in (c), the discharge flow rate Q of the booster pump 29 is increased compared to the comparative example in which the warning control Wc is not performed. Figure 4 As shown in (b), the fuel pressure reduction of the high pressure system 30 caused by the decompression and the fuel pressure increase of the high pressure system 30 caused by the increase in the discharge flow rate Q are offset by each other, and as shown in Figure 4 As shown in (c), by increasing the discharge flow rate Q, the difference between the discharge flow rate Q and the maximum discharge flow rate Qx, that is, the increase flow rate ΔQ, is reduced compared to the case where the warning control Wc is not performed.

[0074] Therefore, when the ejection anomaly A occurs, the ejection flow rate Q anomalously increases within the range of the increased flow rate ΔQ after the reduction, suppressing the rise in the fuel pressure of the high-pressure system 30. Further, in this warning control Wc, since the reduction in the fuel pressure of the high-pressure system 30 due to decompression and the increase in the fuel pressure of the high-pressure system 30 due to the increase in the ejection flow rate Q offset each other, the warning control Wc can be executed while maintaining the fuel pressure P at the desired level.

[0075] In addition, the following third effect is obtained. In the warning control Wc, as indicated by the one-dot chain line in (b) of Figure 4 , the target fuel pressure Pt is not changed, and decompression of the decompression mechanism 37 is performed as shown in (d) of Figure 4 . Inevitably, as shown in (c) of Figure 4 , the ejection flow rate Q of the boost pump 29 increases to offset the reduction in the fuel pressure P of the high-pressure system 30 due to this decompression. Therefore, the warning state W can be simply set while maintaining the fuel pressure P of the high-pressure system 30.

[0076] In addition, the following sixth effect is obtained. The boost pump 29 is driven by the engine 90, so when the rotational speed of the engine 90 is high, its maximum ejection flow rate Qx also becomes large. Therefore, when the ejection flow rate Q of the boost pump 29 is the same, the larger the rotational speed of the engine 90, the larger the increased flow rate ΔQ. And the faster the rotational speed of the engine 90, the stronger the ejection force, and pulsation etc. are likely to occur, and thus the maximum fuel pressure is likely to become large. Regarding this, as shown in Figure 2 , in the state determination, when the rotational speed of the engine 90 is high (to the right), it is easier to determine that the warning state Wq is required compared to the case where the rotational speed of the engine 90 is low (to the left). By focusing on the rotational speed of the engine 90 in this way, it is possible to efficiently determine whether the warning state Wq is required.

[0077] In addition, the following seventh effect is obtained. When the rotational speed of the engine 90 is the same, the smaller the ejection amount per combustion cycle of the boost pump 29, the larger the increased flow rate ΔQ. Moreover, the ejection amount per combustion cycle of this boost pump 29 is approximately the same as the fuel injection amount per combustion cycle of the injector 35. Regarding this, as shown in Figure 2 , in the state determination, when the ejection amount per combustion cycle of the boost pump 29 or the fuel injection amount per combustion cycle of the injector 35, that is, the ejection-related amount is small (downward), it is easier to determine that the warning state Wq is required compared to the case where the ejection-related amount is large (upward). By focusing on the ejection-related amount in this way, it is possible to efficiently determine whether the warning state Wq is required.

[0078] In addition, the following eighth effect is obtained. When the temperature of the fuel is low, since the bulk modulus of elasticity of the fuel becomes high, large pulsations and the like are likely to occur in the fuel pressure P, and the maximum fuel pressure is likely to increase. Moreover, when the temperatures of the cooling water, lubricating oil, outside air, etc. are low, the temperature of the fuel is also likely to become low. Regarding this point, as Figure 2 shown, in the state determination, when the temperatures of the fuel, cooling water, lubricating oil, outside air, etc. in the predetermined part are low (dashed boundary line X), it is easier to determine that it is the warning state Wq compared to the case where the temperature of the predetermined part is high (solid boundary line X). By focusing on the temperature of the predetermined part in this way, it is possible to efficiently determine whether it is the warning state Wq.

[0079] [Second Embodiment]

[0080] Next, the second embodiment will be described. In the following embodiments, the same reference numerals are attached to the components and the like that are the same as or corresponding to those in the previous embodiments. However, different reference numerals are attached to the fuel injection system itself for each embodiment. Regarding this embodiment, based on the first embodiment, the description will be centered on the structure different from the first embodiment.

[0081] As Figure 7 indicated by the dashed line in (b) of, in the warning control Wc in this embodiment, the target fuel pressure Pt is set lower than in the case of the normal control Nc without performing this warning control Wc, and the fuel pressure P in the high-pressure system 30 is reduced. Therefore, the difference between the current fuel pressure P in the high-pressure system 30 and the threshold pressure Px, that is, the fuel pressure margin ΔP, becomes larger. Thus, it is set to the above-mentioned warning state W, that is, a state where even if an ejection abnormality A occurs in the boost pump 29, the fuel pressure P in the high-pressure system 30 does not exceed the above-mentioned threshold pressure Px. More specifically, as follows.

[0082] Figure 6 is a schematic diagram showing the fuel pressure control system 92 and its surroundings in this embodiment. In this embodiment, the target fuel pressure calculation unit 62 is also related to the execution of the warning control Wc. On the other hand, the valve opening degree calculation unit 73 and the valve control unit 75 are not related to the warning control Wc. Therefore, the warning control Wc is executed by the target fuel pressure calculation unit 62, the ejection amount calculation unit 64, and the pump control unit 65. Specifically, when the state determination unit 61 determines that it is the warning state Wq, the target fuel pressure calculation unit 62 calculates a target fuel pressure Pt that is smaller than in the case of the normal control Nc as the warning control Wc. As a result, the ejection amount calculation unit 64 and the pump control unit 65 control the boost pump 29 to reduce the fuel pressure P.

[0083] Figure 7This is a graph showing changes in various parameters when the state is shifted from the normal state N to the required alert state Wq and from the normal control Nc to the alert control Wc, but the state is shifted again from the required alert state Wq to the normal state N without the discharge abnormality A occurring.

[0084] like Figure 7 As shown in (a), for example, when the engine 90 speed increases, the normal state N is transferred to the required alert state Wq, and the normal control Nc is transferred to the alert control Wc. Figure 7 The target fuel pressure Pt indicated by the dotted line in (b) is decreased. Figure 7 As shown in (c), the discharge flow rate Q of the booster pump 29 drops instantaneously. Figure 7 As shown in (b) of FIG. 1 , the fuel pressure P of the high pressure system 30 is reduced to the target fuel pressure Pt in the guard control Wc. As a result, the fuel pressure margin ΔP increases.

[0085] Afterwards, if Figure 7 As shown in (a), for example, when the engine 90 speed drops, the alert state Wq needs to be ended and the alert control Wc is restored to the normal control Nc. Figure 7 The target fuel pressure Pt indicated by the dotted line in (b) rises to the original state. Figure 7 As shown in (c), the discharge flow rate Q of the booster pump 29 increases instantaneously. Figure 7 As shown in (b) of FIG. 1 , the fuel pressure P of the high pressure system 30 is increased to the target fuel pressure Pt in the normal control Nc.

[0086] Figure 8 This is a graph showing the transition of each parameter when the discharge abnormality A occurs after the normal state N is shifted to the alert-needed state Wq and the normal control Nc is shifted to the alert control Wc.

[0087] When the normal state N is shifted to the alert state Wq and the normal control Nc is shifted to the alert control Wc, the same as the above case, Figure 8 As shown by the dotted line in (b) of FIG. 1 , the target fuel pressure Pt decreases, and the fuel pressure P of the high pressure system 30 decreases, thereby increasing the fuel pressure margin ΔP. Therefore, even if the ejection abnormality A occurs later and the fuel pressure P of the high pressure system 30 starts to increase, Figure 8 As shown in (b) of FIG. 1 , before the fuel pressure P of the high pressure system 30 reaches the threshold pressure Px, Figure 8 Execute the abnormal response process Ac as shown in (d) of Figure 8 As shown in (b), the fuel pressure of the high pressure system 30 changes from rising to falling. As a result, the fuel pressure P of the high pressure system 30 is suppressed from exceeding the threshold pressure Px.

[0088] According to the present embodiment, in addition to the above-described first effect and sixth to eighth effects, the following fourth effect is also obtained. As shown in Figure 7 (b) of FIG., in the warning control Wc, by reducing the fuel pressure P of the high-pressure system 30, the fuel pressure margin ΔP is increased, thereby setting the warning state W. Therefore, the warning state W can be achieved with a simple structure.

[0089] In addition, the following fifth effect is also obtained. As shown in Figure 7 (b) of FIG., in the warning control Wc, the target fuel pressure Pt is set low. As a result, the fuel pressure P of the high-pressure system 30 decreases. Therefore, the fuel pressure P of the high-pressure system 30 can be reduced with a simple structure.

[0090] [Other Embodiments]

[0091] The above embodiments can be implemented with the following modifications, for example. For example, as shown in Figure 1 etc., in each embodiment, the base end of the return pipe 39 (the end on the return source side) is connected to the accumulator 33. However, alternatively, the base end of the return pipe 39 may be connected to the third pipe 32, and a pressure reducing valve 38 may be provided at the connection portion of the return pipe 39 and the third pipe 32.

[0092] In addition, the front end of the return pipe 39 (the end on the return destination side) is connected to the second pipe 22. However, alternatively, it may be connected to the boost pump 29, the feed pump 19, the first pipe 12, or the fuel tank 11. In addition, for example, when a check valve is provided at the connection portion of the third pipe 32 and the accumulator 33 with the third pipe 32, the front end of the return pipe 39 may be connected to a position on the boost pump 29 side of the check valve in the third pipe 32.

[0093] In addition, for example, the decompression mechanism 37 is composed of the return pipe 39 and the pressure reducing valve 38. However, alternatively, the decompression mechanism 37 may be composed of the injector 35. That is, when reducing the fuel pressure P of the accumulator 33, the fuel pressure P may also be reduced by additionally injecting fuel by the injector 35.

[0094] In addition, for example, as shown in Figure 2 FIG., in each embodiment, the state determination is performed based on three parameters, i.e., the engine speed, the injection relationship amount, and the temperature. However, the state determination may be performed based on only two or one of these parameters. In addition, parameters different from these three parameters may be additionally used, or one of these three parameters may be replaced to perform the state determination.

[0095] In addition, for example, as shown in Figure 3As shown, in each embodiment, it is determined whether there is an ejection abnormality A (S201), and on the condition that it is determined that there is an ejection abnormality A (S201: "Yes"), the abnormality countermeasure process Ac is executed (S202). Alternatively, even if it is not determined whether there is an ejection abnormality A (S201), if the fuel pressure P in the high-pressure system 30 abnormally rises, the abnormality countermeasure process Ac may be automatically executed by fuel pressure feedback control or the like.

[0096] In addition, for example, as Figure 4 shown in (b) of etc., in the warning control Wc in the first embodiment, the target fuel pressure Pt is maintained the same as in the case of the normal control Nc, but the target fuel pressure Pt may be slightly changed. Thus, when shifting from the normal control Nc to the warning control Wc, it is also possible to make one of the decrease in the fuel pressure of the high-pressure system 30 due to the decompression of the decompression mechanism 37 and the increase in the fuel pressure of the high-pressure system 30 due to the increase in the ejection flow rate Q slightly larger than the other, and only offset a part of this one by the other.

[0097] The present disclosure has been described based on the embodiments, but it should be understood that the present disclosure is not limited to the embodiments and configurations. The present disclosure also includes various modifications and modifications within the equivalent scope. In addition, various combinations, modes, and other combinations, modes that include only one element, more than one, or less than one of them also fall within the scope and spirit of the present disclosure.

Claims

1. A fuel pressure control system controls the fuel pressure of a fuel supply system that supplies fuel to an injector of an engine. The fuel pressure control system includes: a boost pump that raises the fuel pressure of a high-pressure system, which is part of the fuel supply system, by injecting fuel into the high-pressure system; a pressure reducing mechanism that reduces the pressure of the high-pressure system; and a control device that controls the boost pump and the pressure reducing mechanism. The fuel pressure control system is configured such that when an abnormality occurs in which the injection flow rate of the boost pump is larger than normal (i.e., an injection abnormality) and the fuel pressure of the high-pressure system starts to rise, the pressure reducing mechanism performs a predetermined abnormality response process, thereby stopping the rise in the fuel pressure of the high-pressure system. The fuel pressure control system is characterized in that the control device has a state determination unit that determines whether it is a state requiring caution. The state requiring caution is a state in which, assuming the occurrence of the injection abnormality, there is a risk that the fuel pressure of the high-pressure system exceeds a predetermined threshold pressure that is equal to or lower than the pressure resistance of the high-pressure system before the rise in the fuel pressure stops due to the abnormality response process. The control device starts caution control to set a caution state on the condition that it is determined to be the state requiring caution. The caution state is a state in which, even if the injection abnormality occurs, the fuel pressure of the high-pressure system does not exceed the threshold pressure before the rise in the fuel pressure stops due to the abnormality response process. As the caution control, the control device reduces the pressure through the pressure reducing mechanism and increases the injection flow rate of the boost pump compared to the case where this caution control is not performed. Thereby, at least a part of the decrease in the fuel pressure of the high-pressure system caused by the pressure reduction and the increase in the fuel pressure of the high-pressure system caused by the increase in the injection flow rate are offset by the other. And by increasing the injection flow rate, compared to the case where this caution control is not performed, the difference between the injection flow rate and the maximum injection flow rate, which is the maximum flow rate that can be injected by the boost pump, i.e., the increase in flow rate, is reduced, thereby setting the caution state.

2. The fuel pressure control system according to claim 1, characterized in that the control device has a target fuel pressure calculation unit that calculates a target fuel pressure, and controls the fuel pressure of the high-pressure system to approach the calculated target fuel pressure. As the caution control, the control device maintains the same target fuel pressure as in the case where this caution control is not performed, and reduces the pressure through the pressure reducing mechanism, thereby increasing the injection flow rate of the boost pump compared to the case where this caution control is not performed, to set the caution state.

3. A fuel pressure control system controls the fuel pressure of a fuel supply system that supplies fuel to an injector of an engine. comprising: a boost pump that raises the fuel pressure in the high-pressure system by injecting fuel into the high-pressure system that is part of the fuel supply system; a pressure reducing mechanism that reduces the pressure in the high-pressure system; and a control device that controls the boost pump and the pressure reducing mechanism, the fuel pressure control system is configured such that when an abnormality occurs in which the injection flow rate of the boost pump is greater than normal, i.e., an injection abnormality, and the fuel pressure in the high-pressure system starts to rise, the pressure reducing mechanism performs a predetermined abnormality response process, thereby stopping the rise in the fuel pressure in the high-pressure system, the fuel pressure control system is characterized in that, the control device has a state determination unit that determines whether it is a state that requires caution, which is a state in which there is a risk that the fuel pressure in the high-pressure system will exceed a predetermined threshold pressure that is less than or equal to the pressure resistance of the high-pressure system before the rise in the fuel pressure stops due to the abnormality response process assuming that the injection abnormality occurs, the control device starts caution control to set it to a caution state on the condition that it is determined to be the state that requires caution, which is a state in which even if the injection abnormality occurs, the fuel pressure in the high-pressure system will not exceed the threshold pressure before the rise in the fuel pressure stops due to the abnormality response process, as the caution control, the control device reduces the fuel pressure in the high-pressure system compared to the case where this caution control is not performed, thereby increasing the difference between the fuel pressure in the high-pressure system and the threshold pressure, i.e., the fuel pressure margin, and thereby setting it to the caution state.

4. The fuel pressure control system according to claim 3, characterized in that, the control device has a target fuel pressure calculation unit that calculates a target fuel pressure, and controls the fuel pressure in the high-pressure system to approach the calculated target fuel pressure, as the caution control, the control device sets the target fuel pressure lower compared to the case where this caution control is not performed, thereby reducing the fuel pressure in the high-pressure system compared to the case where this caution control is not performed, and setting it to the caution state.

5. The fuel pressure control system according to any one of claims 1 to 4, characterized in that, the boost pump is a pump driven by the engine, the state determination unit performs the state determination based at least on the rotational speed of the engine. In the state determination, compared to the case where the rotational speed is a predetermined speed, it is more likely to be determined to be the state that requires caution when the rotational speed is faster than the predetermined speed.

6. The fuel pressure control system according to any one of claims 1 to 4, characterized in that, the state determination unit performs the state determination based at least on an injection relationship quantity that is the injection amount per combustion cycle of the boost pump or the fuel injection amount per combustion cycle of the injector. In the state determination, compared to the case where the injection relationship quantity is a predetermined amount, it is more likely to be determined to be the state that requires caution when the injection relationship quantity is less than the predetermined amount.

7. The fuel pressure control system according to any one of claims 1 to 4, characterized in that the state determination unit performs the state determination based at least on the temperature of a predetermined unit, and in the state determination, it is more likely to be determined that it is the state requiring vigilance when the temperature of the predetermined unit is lower than the predetermined temperature than when the temperature of the predetermined unit is the predetermined temperature.

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