JP7613274B2 - Fuel Pressure Control Device - Google Patents

Description

The present invention relates to a fuel pressure control device.

A fuel pressure control device is known that performs fuel pressure feedback control so that the fuel pressure detected by a fuel pressure sensor coincides with a target fuel pressure (see, for example, Patent Document 1).

JP 2002-047984 A

Some of these fuel pressure control devices diagnose abnormalities in the fuel pressure sensor. For example, when the target fuel pressure is set from the previous target value to the current target value, if the deviation between the detected fuel pressure detected by the fuel pressure sensor and the current target value is greater than a judgment value, it is judged that an abnormality has occurred in the fuel pressure sensor. Here, there is a response delay from when the current target value is set until the actual fuel pressure matches the target value. Therefore, a delay time corresponding to this response delay is calculated, and after the delay time has elapsed since the current target value was set, an abnormality diagnosis of the fuel pressure sensor is performed based on the deviation between the detected fuel pressure and the current target value. Here, the greater the difference between the previous target value and the current target value, the longer the calculated delay time is, and the larger the calculated judgment value is.

As the fuel pressure increases, the target fuel pressure may also change significantly. For example, if there is a large difference between the previous target value and the current target value, the delay time will also be long. For this reason, depending on the operating state of the internal combustion engine, for example, the target value may be set to a different value again before the delay time has elapsed, which may result in the fuel pressure sensor abnormality diagnosis not being completed and a decrease in the frequency of abnormality diagnosis.

Therefore, it is conceivable to ensure the frequency of abnormality diagnosis of the fuel pressure sensor by setting the delay time to a short time. In this case, for example, if the amount of change from the target value before last to the previous target value is large and the amount of change from the previous target value to the current target value is small, the judgment value is calculated to be small according to the small amount of change, and abnormality diagnosis is performed. Here, if the time between when the previous target value was set and when the current target value is set is short, it is conceivable that the actual fuel pressure cannot follow such a change in the target value in such a short time. Even in such a case, abnormality diagnosis is performed based on the judgment value calculated to be small as described above after the current target value is set, so that even if the fuel pressure sensor is actually normal, the deviation amount will be larger than the judgment value, and there is a risk of misdiagnosing that the fuel pressure sensor is abnormal.

The present invention aims to provide a fuel pressure control device that improves the accuracy of diagnosing abnormalities in the fuel pressure sensor.

The above object can be achieved by a fuel pressure control device for an internal combustion engine that feedback controls a fuel pump that supplies fuel to the internal combustion engine so that a fuel pressure detected by a fuel pressure sensor that detects the pressure of fuel supplied to the internal combustion engine coincides with a target fuel pressure, the fuel pressure control device including: a calculation unit that uses a second target value that is set before a first target value that is set as the target fuel pressure as a reference value, and calculates a longer delay time and a larger judgment value as a difference between the first target value and the target fuel pressure increases ; an abnormality diagnosis unit that diagnoses that the fuel pressure sensor is abnormal when a deviation amount of the detected fuel pressure from the first target value after the delay time has elapsed since the first target value was set of the target fuel pressure is greater than the judgment value; and a selection unit that selects, from a plurality of past target values that were set before the first target value was set as the target fuel pressure, a past target value that has a maximum difference from the first target value as the reference value.

When a new first target value is set immediately after the first target value is set, the selection unit may re-select as the reference value a first difference between the first target value and the new first target value that is equal to or greater than a predetermined value , and may re-select as the reference value a past target value that is set as the target fuel pressure before the new first target value is set and has the largest difference from the new first target value, and may use the reference value already selected when the first difference is less than the predetermined value.

The control device may further include an update unit that updates the first target value to the new first target value when the first difference is less than the predetermined value.

The selection unit may select, as the reference value, a past target value that has the largest difference from the first target value among a plurality of past target values that were set before the first target value was set and after fuel cut recovery.

The present invention provides a fuel pressure control device that improves the accuracy of diagnosing abnormalities in the fuel pressure sensor.

FIG. 1 is a schematic diagram of an engine system according to the present embodiment. 2A and 2B are timing charts showing abnormality diagnosis control in a comparative example. FIG. 3A is an example of a timing chart showing the abnormality diagnosis control of this embodiment, and FIG. 3B is a timing chart showing an example of the case where the detected fuel pressure behaves in the same manner as in FIG. 3A. FIG. 4 is a flow chart showing an example of the abnormality diagnosis control of this embodiment. FIG. 5A is an example of a map that defines the relationship between the difference ΔP and the delay time D, and FIG. 5B is an example of a map that defines the relationship between the difference ΔP and the determination value α. FIG. 6 is a flowchart showing an example of the calculation control of the difference ΔP. FIG. 7 is a flowchart showing an example of the selection control of the reference value Pr. 8A to 8C are timing charts showing examples in which the maximum target value Pmax, the minimum target value Pmin, and the target value P(n-1), respectively, are selected as the reference value Pr. FIG. 9 is a timing chart showing an example of a case where the target value P(n) is updated.

[General configuration of engine system]
1 is a schematic diagram of an engine system 1 of this embodiment. The engine system 1 includes an engine 10 and an ECU (Electronic Control Unit) 40 that controls the engine 10. The engine 10 is a spark ignition inline four-cylinder internal combustion engine equipped with a cylinder group 11 including cylinders 111 to 114 arranged in series, a direct injection valve group 37, and a port injection valve group 27. The ECU 40 is an example of a fuel pressure control device.

The in-cylinder injection valve group 37 includes in-cylinder injection valves 371-374 that inject fuel into the cylinders 111-114, respectively. The port injection valve group 27 includes port injection valves 271-274 that inject fuel into the intake ports 13 that communicate with the cylinders 111-114, respectively. Each of the in-cylinder injection valve group 37 and the port injection valve group 27 is an electromagnetically driven open/close valve in which the fuel injection amount is adjusted by energizing an electromagnetic coil for a predetermined energizing period to separate the valve body from the valve seat.

The engine 10 is formed with an intake passage 12 having a plurality of intake ports 13 corresponding to each of the cylinder groups 11, and an exhaust passage having a plurality of exhaust ports (not shown). Each of the cylinder groups 11 contains a piston (not shown) to define a combustion chamber. The combustion chamber is opened and closed by an intake valve and an exhaust valve. The engine 10 is also equipped with a spark plug (not shown). The engine 10 is also equipped with a crankshaft 14 linked to the plurality of pistons, and an intake camshaft 15 that drives the intake valve in conjunction with the crankshaft 14. A crank angle sensor 14a that detects the rotation angle of the crankshaft 14 and an air flow meter 12a that detects the amount of intake air Ga introduced into the intake passage 12 are provided.

The engine system 1 includes a fuel tank 21, a low-pressure fuel pump 22, a pressure regulator 23, a low-pressure fuel pipe 25, a low-pressure delivery pipe 26, and a fuel pressure sensor 28. The fuel tank 21 stores gasoline as fuel. The low-pressure fuel pump 22 pressurizes the fuel and discharges it into the low-pressure fuel pipe 25. The pressure regulator 23 adjusts the pressure of the fuel discharged into the low-pressure fuel pipe 25 to a preset low-pressure supply pressure. The operation of the low-pressure fuel pump 22 is controlled by the ECU 40.

The low-pressure fuel pipe 25 and the low-pressure delivery pipe 26 supply the fuel discharged from the low-pressure fuel pump 22 to the port injection valve group 27. The fuel is pressurized to a predetermined pressure level by the low-pressure fuel pump 22 and adjusted to the low-pressure supply pressure by the pressure regulator 23, and is introduced into the low-pressure delivery pipe 26 via the low-pressure fuel pipe 25.

The port injection valve group 27 is connected to the low-pressure delivery pipe 26 and injects fuel into the intake ports 13 corresponding to each cylinder group 11. The fuel pressure sensor 28 detects the fuel pressure value in the low-pressure delivery pipe 26.

The engine system 1 includes a high-pressure fuel pump 31, a high-pressure fuel pipe 35, a high-pressure delivery pipe 36, and a fuel pressure sensor 38. The high-pressure fuel pump 31 draws fuel from a branch pipe 25a branched from the low-pressure fuel pipe 25, and pressurizes the fuel to a high-pressure level higher than the supply pressure level from the low-pressure fuel pump 22. The branch pipe 25a is provided with a pulsation damper 29 that suppresses fuel pressure pulsation in the branch pipe 25a.

Specifically, the high-pressure fuel pump 31 includes a pump housing 31h, a plunger 31p that is slidable within the pump housing 31h, and a pressurization chamber 31a defined between the pump housing 31h and the plunger 31p. The volume of the pressurization chamber 31a changes according to the displacement of the plunger 31p. With the solenoid valve 32 open, fuel pressurized by the low-pressure fuel pump 22 is introduced into the pressurization chamber 31a via the branch pipe 25a. The fuel in the pressurization chamber 31a is pressurized to a high pressure by the plunger 31p and discharged into the high-pressure fuel pipe 35.

A pump cam 19 that drives a plunger 31p is attached to the intake camshaft 15 of the engine 10. The high-pressure fuel pump 31 has a follower lifter 31f that is raised and lowered by the pump cam 19, and a pump spring 31g that biases the follower lifter 31f toward the pump cam 19. The plunger 31p is linked to the follower lifter 31f, and the plunger 31p also rises and falls together with the follower lifter 31f.

The solenoid valve 32 is provided at the fuel inlet of the pressurization chamber 31a of the high-pressure fuel pump 31. The solenoid valve 32 has a valve body 32v, a coil 32c that drives the valve body 32v, and a spring 32k that constantly biases the valve body 32v in the open direction. The supply of electricity to the coil 32c is controlled by the ECU 40. When the coil 32c is energized, the valve body 32v cuts off the connection between the branch pipe 25a of the low-pressure fuel pipe 25 and the pressurization chamber 31a against the biasing force of the spring 32k. When the coil 32c is not energized, the valve body 32v is maintained in an open state by the biasing force of the spring 32k.

A spring-loaded check valve 34 is provided in the high-pressure fuel pipe 35 between the high-pressure fuel pump 31 and the in-cylinder injection valve group 37. The check valve 34 opens when the fuel pressure in the high-pressure fuel pump 31 becomes higher than the fuel pressure in the high-pressure fuel pipe 35 by a predetermined amount.

During the intake stroke of the high-pressure fuel pump 31, the solenoid valve 32 opens and the plunger 31p descends, filling the pressurized chamber 31a with fuel from the branch pipe 25a of the low-pressure fuel pipe 25. During the pressurized stroke, the solenoid valve 32 closes and the volume of the pressurized chamber 31a decreases as the plunger 31p ascends, increasing the pressure of the fuel in the pressurized chamber 31a. During the discharge stroke, when the force of the fuel pressure in the pressurized chamber 31a becomes greater than the spring force of the check valve 34, the check valve 34 opens and the pressurized fuel is supplied to the high-pressure fuel pipe 35 and the high-pressure delivery pipe 36. As described above, the elevation and lowering of the plunger 31p is achieved by the rotation of the pump cam 19, and since the pump cam 19 is linked to the crankshaft 14 via the intake camshaft 15, the high-pressure fuel pump 31 is driven in conjunction with the crankshaft 14.

High-pressure fuel pressurized by the high-pressure fuel pump 31 is stored in the high-pressure delivery pipe 36 via the high-pressure fuel piping 35. The high-pressure fuel piping 35 and the high-pressure delivery pipe 36 supply high-pressure fuel from the high-pressure fuel pump 31 to the in-cylinder injection valves 371 to 374.

The in-cylinder injection valve group 37 injects high-pressure fuel directly from the high-pressure delivery pipe 36 into each of the cylinders 111 to 114 in a predetermined sequence. The fuel pressure sensor 38 detects the fuel pressure in the high-pressure delivery pipe 36.

The ECU 40 is composed of a CPU (Central Processing Unit), a flash ROM (Read Only Memory), a RAM (Random Access Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), various interface circuits, etc. The ECU 40 executes abnormality diagnosis control (described later) based on information from sensors and information previously stored in the flash ROM and EEPROM, in accordance with a control program previously stored in the flash ROM. The ECU 40 also functionally realizes a calculation unit, an abnormality diagnosis unit, and a selection unit. Details will be described later. The ECU 40 is electrically connected to an accelerator operation amount sensor 41 for detecting the accelerator operation amount Acc, an ignition switch 42 for detecting the ignition ON/OFF, and the above-mentioned fuel pressure sensors 28 and 38.

The ECU 40 determines the fuel injection ratio of the in-cylinder injection valve group 37 and the port injection valve group 27 based on the rotation speed NE of the engine 10 detected by the crank angle sensor 14a and the accelerator operation amount Acc detected by the accelerator operation amount sensor 41. Next, based on the ratio, the rotation speed NE, and the accelerator operation amount Acc, it calculates the target injection amount Qdt of each of the in-cylinder injection valves 371 to 374 and the target fuel pressure P, which is the target value of the fuel pressure of the high-pressure delivery pipe 36 when injecting fuel from each of the in-cylinder injection valves 371 to 374. In principle, the target fuel pressure P is calculated to be higher when the rotation speed NE is high than when it is low, and is calculated to be higher when the accelerator operation amount Acc is large than when it is small. Next, the ECU 40 calculates the injection time Fdi, which is the execution time of each fuel injection of the in-cylinder injection valves 371 to 374, based on the target injection amount Qdt and the target fuel pressure P. The ECU 40 energizes the in-cylinder injection valves 371, 373, 374, and 372 in that order at a predetermined crank angle interval for the calculated injection time Fdi. In this way, the fuel injection amount of each of the in-cylinder injection valves 371 to 374 is controlled to the target injection amount Qdt.

Similarly, the ECU 40 calculates the target injection amount Qpt of each of the port injection valves 271-274 and the target fuel pressure Ppt in the low-pressure delivery pipe 26 based on the above-mentioned distribution ratio, the rotation speed NE, and the accelerator operation amount Acc. Next, the ECU 40 calculates the injection time Fpi of the port injection valves 271-274 based on the target injection amount Qpt and the target fuel pressure Ppt. The ECU 40 energizes the port injection valves 271, 273, 274, and 272 in that order at a predetermined crank angle interval for the calculated injection time Fpi. In this way, the fuel injection amount of each of the port injection valves 271-274 is controlled to the target injection amount Qpt. In principle, the target fuel pressures P and Ppt are set to high values during high-load operation and low values during low-load operation.

The ECU 40 feedback controls the high-pressure fuel pump 31 so that the detected fuel pressure Pd detected by the fuel pressure sensor 38 matches the target fuel pressure P in the high-pressure delivery pipe 36. This allows the actual fuel pressure in the high-pressure delivery pipe 36 to match the target fuel pressure P, and the actual injection amount of each of the in-cylinder injection valves 371 to 374 to match the target injection amount Qdt, thereby controlling the operating state of the engine 10 to a desired operating state. If an abnormality occurs in the fuel pressure sensor 38, even if the high-pressure fuel pump 31 is feedback controlled based on the detected fuel pressure Pd, the actual fuel pressure in the high-pressure delivery pipe 36 cannot be made to match the target fuel pressure P, and the control accuracy of the operating state of the engine 10 decreases. Therefore, the ECU 40 executes abnormality diagnosis control to diagnose whether or not an abnormality occurs in the fuel pressure sensor 38. First, before explaining the fuel pressure abnormality diagnosis control of this embodiment, the fuel pressure abnormality diagnosis control in the comparative example will be explained.

[Comparative Example of Abnormality Diagnosis Control]
2A and 2B are timing charts showing abnormality diagnosis control of a comparative example. In Fig. 2A and Fig. 2B, the vertical axis indicates fuel pressure and the horizontal axis indicates time. Fig. 2A and Fig. 2B also show the transitions of the target fuel pressure P and the detected fuel pressure Pd, with the target fuel pressure P indicated by a dotted line and the detected fuel pressure Pd indicated by a solid line. Fig. 2A and Fig. 2B also show the case where the fuel pressure sensor 38 is normal.

Figure 2A shows target values P(n), P(n-1), and P(n-2) that are set as the target fuel pressure P. Target value P(n) indicates the most recent target value. Target value P(n-1) indicates the target value that was set immediately before it was set to target value P(n). Target value P(n-2) indicates the target value that was set immediately before it was set to target value P(n-1). In other words, target values P(n-1) and P(n-2) are target values that were set in the past.

As shown in FIG. 2A, at time t1, the target fuel pressure P is set from the target value P(n-2) to a target value P(n-1) that is lower than the target value P(n-2). As a result, the detected fuel pressure Pd also gradually decreases to follow the change in the target fuel pressure P and converge to the target value P(n-1). After that, at time t2, when the target fuel pressure P is set to a target value P(n) that is higher than the target value P(n-1) and lower than the target value P(n-2), the detected fuel pressure Pd also rises to follow the target fuel pressure P and converge to the target value P(n).

Here, we will explain the case where the fuel pressure sensor 38 is diagnosed for an abnormality based on the deviation amount A of the detected fuel pressure Pd from the target value P(n). When the target fuel pressure P is set to the target value P(n) from the target value P(n-1) at time t2, the delay time D and the judgment value α are calculated based on the change in fuel pressure to the target value P(n) when the target value P(n-1) is selected as the reference value Pr, that is, the difference ΔP between the target value P(n-1) and the target value P(n). After time t3, when the delay time D has elapsed from time t2 when the target value P(n) was set as the target fuel pressure P, the abnormality diagnosis is performed based on whether the deviation amount A of the detected fuel pressure Pd from the target value P(n) is larger than the judgment value α. The delay time D is a time determined in response to the response delay of the actual fuel pressure. If the difference A is greater than the judgment value α before the delay time D has elapsed, the difference A may become greater than the judgment value α due to a response delay of the actual fuel pressure, and the fuel pressure sensor 38 may be diagnosed as abnormal, even though the fuel pressure sensor 38 is normal. The judgment value α is the upper limit of the difference between the detected fuel pressure Pd and the target value P(n) when the fuel pressure sensor 38 is normal. As will be described in detail later, the delay time D is calculated to be longer as the difference ΔP is larger, and the judgment value α is calculated to be larger as the difference ΔP is larger. If the difference A is greater than the judgment value α, the fuel pressure sensor 38 is diagnosed as abnormal. If the difference A is equal to or less than the judgment value α, the fuel pressure sensor 38 is diagnosed as normal. As shown in FIG. 2A, the difference A is equal to or less than the judgment value α at time t3, and the fuel pressure sensor 38 is diagnosed as normal. In this specification, the "difference" refers to an absolute value.

Figure 2B shows a case where the target fuel pressure P is switched in a short time. The target values P(n-2), P(n-1), and P(n) shown in Figure 2B are the same as the target values P(n-2), P(n-1), and P(n) shown in Figure 2A, respectively. At time t12, a short time after the target fuel pressure P is set from the target value P(n-2) to the target value P(n-1), the target fuel pressure P is set from the target value P(n-1) to the target value P(n). In this case as well, after time t13, when the delay time D has elapsed from time t12, an abnormality diagnosis is performed based on whether the deviation amount A is larger than the judgment value α. Here, as shown in Figure 2B, if the target fuel pressure P changes in a short time, the actual fuel pressure cannot follow such a change in the target fuel pressure P. As a result, the detected fuel pressure Pd cannot be tracked, and even if the fuel pressure sensor 38 is normal, the deviation amount A becomes larger than the judgment value α, resulting in a misdiagnosis that an abnormality has occurred in the fuel pressure sensor 38. In this way, in the comparative example, if the target fuel pressure P changes in a short period of time, there is a risk of a misdiagnosis.

[Abnormality Diagnosis Control of the Present Embodiment]
FIG. 3A is an example of a timing chart showing the abnormality diagnosis control of this embodiment. FIG. 3A corresponds to FIG. 2B. In this embodiment, unlike the comparative example shown in FIG. 2B, the target value P(n-1) is not used as the reference value Pr, but the target value P(n-2) is used as the reference value Pr, and the difference ΔP between the target value P(n-2) and the target value P(n) is used. The difference ΔP of this embodiment shown in FIG. 3 is larger than the difference ΔP of the comparative example shown in FIG. 2B. Therefore, the delay time D of this embodiment is calculated to be longer than the delay time D of the comparative example, and the judgment value α of this embodiment is calculated to be larger than the judgment value α of the comparative example. In addition, the measurement start time of the delay time D in this embodiment is the time t12 when the target fuel pressure P is set from the target value P(n-1) to the target value P(n). Therefore, the abnormality diagnosis is performed after the time t13a when the delay time D has elapsed from the time t12 . That is, it is determined whether the deviation amount A is larger than the judgment value α. As shown in FIG. 3A, since the deviation amount A is equal to or smaller than the judgment value α, the fuel pressure sensor 38 is diagnosed as normal.

FIG. 3B is a timing chart showing an example of the case where the detected fuel pressure Pd behaves in the same manner as in FIG. 3A. The behavior of the detected fuel pressure Pd in FIG. 3A is the same as that in the case where the target fuel pressure P is switched from the target value P(n- 1 ) to the target value P(n) at time t11 as shown in FIG . 3B. In this manner, in this embodiment, an appropriate target value is selected from among a plurality of target values set earlier than the target value P(n) as the reference value Pr that is the basis for calculating the difference ΔP. This allows abnormality diagnosis to be performed without being influenced by the target value (target value P(n-1) in the example of FIG. 3A) that was set between the setting of the target value as the reference value Pr (target value P(n-2) in the example of FIG. 3A) and the setting of the target value P(n). Therefore, even if the target fuel pressure P changes in a short time, the abnormality diagnosis of the fuel pressure sensor 38 can be performed with high accuracy. The selection of the reference value Pr will be described in detail later.

[Details of Abnormality Diagnosis Control in this Embodiment]
FIG. 4 is a flow chart showing an example of the abnormality diagnosis control of this embodiment. This control is repeatedly executed while the ignition is on. The ECU 40 calculates the delay time D and the judgment value α based on the difference ΔP (step S1). FIG. 5A is an example of a map that specifies the relationship between the difference ΔP and the delay time D. In FIG. 5A, the vertical axis indicates the difference ΔP and the horizontal axis indicates the delay time D. FIG. 5B is an example of a map that specifies the relationship between the difference ΔP and the judgment value α. In FIG. 5B, the vertical axis indicates the difference ΔP and the horizontal axis indicates the judgment value α. As shown in FIG. 5A and FIG. 5B, the greater the difference ΔP, the longer the calculated delay time D is, and the larger the calculated judgment value α is. The ECU 40 calculates the delay time D and the judgment value α by referring to these maps. In the maps of FIG. 5A and FIG. 5B, the delay time D and the judgment value α change linearly with respect to the difference ΔP, but are not limited thereto and may change in a curved line. In addition, the delay time D and the judgment value α may be calculated by an arithmetic expression that uses the difference ΔP as an argument. The calculation control of the difference ΔP will be described in detail later. Step S1 is an example of a process executed by the calculation unit.

Next, the ECU 40 judges whether the delay time D has elapsed since the reference value Pr, which is also the target value previously set as the target fuel pressure P, was switched to another target value (step S2). The timing at which the reference value Pr was switched to another target value will be described later. If the answer is No in step S2, the control ends. If the answer is Yes in step S2, the ECU 40 judges whether the deviation amount A is greater than the judgment value α (step S3). If the answer is Yes in step S3, the ECU 40 diagnoses that an abnormality has occurred in the fuel pressure sensor 38 (step S4). In this case, the ECU 40 may, for example, turn on a warning light provided in the vehicle cabin to execute fail-safe control. If the answer is No in step S3, the ECU 40 diagnoses that the fuel pressure sensor 38 is normal (step S5). Steps S2 to S5 are an example of processing executed by the abnormality diagnosis unit.

[Calculation control of difference ΔP]
6 is a flowchart showing an example of the calculation control of the difference ΔP. The ECU 40 determines whether or not the fuel supply to the engine 10 is being cut off (step S11). The fuel supply cut is a control for stopping the fuel supply to the engine 10 when the accelerator pedal is released while the vehicle is running.

If step S11 is No, i.e., if fuel injection is being performed normally, it is determined whether the amount of change in the target fuel pressure P, i.e., the difference between the target value P(n-1) and the target value P(n), is equal to or greater than a predetermined value (step S12). For example, if the driver operates the accelerator pedal to a large extent, i.e., if there is an acceleration or deceleration request, the amount of change in the target fuel pressure P is determined to be equal to or greater than the predetermined value. Also, when the vehicle is traveling at a constant speed, the amount of change in the target fuel pressure P is determined to be less than the predetermined value.

If the answer is Yes in step S12, the ECU 40 selects a reference value Pr (step S13). The selection control of the reference value Pr will be described in detail later. The ECU 40 also resets the measurement start point of the delay time D to the point when the new target value P(n) is set (step S13a). The ECU 40 calculates a difference ΔP based on the selected reference value Pr (step S14). The difference ΔP is the difference between the reference value Pr and the target value P(n) as described above.

If the answer is No in step S12, the ECU 40 determines whether the delay time D has not yet elapsed (step S15). If the answer is Yes in step S15, the ECU 40 updates the target value P(n) (step S16). The ECU 40 calculates the difference ΔP based on the target value P(n) thus updated (step S14). If the answer is No in step S15, the ECU 40 calculates the difference ΔP (step S14).

If the answer is Yes in step S11, the ECU 40 resets the selected reference value Pr, maximum target value Pmax, and minimum target value Pmin (step S17). If the selection of the maximum target value Pmax and minimum target value Pmin continues during fuel cut, the maximum target value Pmax and minimum target value Pmin may become larger than necessary, which may result in the delay time D becoming longer than necessary and affecting the detection accuracy. The maximum target value Pmax and minimum target value Pmin will be described later.

[Selection control of reference value Pr]
FIG. 7 is a flow chart showing an example of the selection control of the reference value Pr. The ECU 40 selects a maximum target value Pmax and a minimum target value Pmin from the history of the target fuel pressure P (step S21). The maximum target value Pmax is the maximum value among the past target values after the fuel cut is restored and before the target fuel pressure P is set to the target value P(n-1). The minimum target value Pmin is the minimum value among the past target values after the fuel cut is restored and before the target fuel pressure P is set to the target value P(n-1). That is, the target value P(n-1) is excluded from the candidates for the maximum target value Pmax and the minimum target value Pmin. Note that, instead of step S21, the target fuel pressure P may be monitored after the fuel cut is restored, that is, in an operating state in which fuel injection is being performed, and the maximum target value Pmax and the minimum target value Pmin may be updated as needed.

Next, the ECU 40 calculates the differences ΔP0, ΔP1, and ΔP2 expressed by the following equations (1) to (3) as candidates for the difference ΔP (step S22).
ΔP0=|P(n-1)-P(n)|...(1)
ΔP1=|Pmax−P(n)|…(2)
ΔP2=|Pmin−P(n)|…(3)

Next, the ECU 40 determines whether the difference ΔP0 is the largest among the differences ΔP0, ΔP1, and ΔP2 (step S23). If the answer is Yes in step S23, the ECU 40 selects the target value P(n-1) as the reference value Pr (step S24). If the answer is No in step S23, the ECU 40 determines whether the difference ΔP1 is the largest (step S25). If the answer is Yes in step S25, the ECU 40 selects the maximum target value Pmax as the reference value Pr (step S26). If the answer is No in step S25, the ECU 40 selects the minimum target value Pmin as the reference value Pr (step S27). In this way, the ECU 40 selects the value that has the largest difference from the target value P(n) among the target value P(n-1), the maximum target value Pmax, and the minimum target value Pmin as the reference value Pr. In the example of FIG. 3, the difference ΔP1 is determined to be maximum. Steps S21 to S27 are an example of the process executed by the selection unit.

Figures 8A to 8C are timing charts showing examples in which the maximum target value Pmax, minimum target value Pmin, and target value P(n-1) are selected as the reference value Pr. Figures 8A to 8C only show the target fuel pressure P, and the detected fuel pressure Pd is omitted. Figures 8A to 8C also show an example in which at time t21, the target fuel pressure P is set from the maximum target value Pmax to a value other than that, and at time t22, the target fuel pressure P is set from the minimum target value Pmin to a value other than that.

Figure 8A shows a case where P is set from the target value P(n-1) to the target value P(n) at time t23. In Figure 8A, the target value P(n-1) and the target value P(n) are both smaller than the maximum target value Pmax and larger than the minimum target value Pmin. In addition, the target value P(n) is smaller than the target value P(n-1). Therefore, the difference ΔP1 is maximum and the difference ΔP2 is minimum. Therefore, the maximum target value Pmax is selected as the reference value Pr, and the difference ΔP1 is used as the difference ΔP used to calculate the delay time D and the judgment value α. In this case, the start time of the delay time D is time t21 when the target fuel pressure P is set from the maximum target value Pmax to a value other than the maximum target value Pmax, but in the example shown in Figure 8A, it is not until time t23 or later that the difference ΔP1 is calculated to be maximum. Therefore, the abnormality diagnosis is performed after the delay time D has elapsed from time t23.

Figure 8B shows a case where the target value P(n) set at time t23 is higher than the target value P(n-1) but lower than the maximum target value Pmax. In this case, the difference ΔP2 is maximum and the difference ΔP1 is minimum, so the minimum target value Pmin is selected as the reference value Pr. Therefore, the start time of the delay time D calculated based on the difference ΔP2 is time t22, when P is set from the minimum target value Pmin to a value other than that, but it is not until time t23 that the difference ΔP2 is calculated to be maximum. For this reason, an abnormality diagnosis is performed after the delay time D has elapsed from time t23.

In FIG. 8C, before time t23, the target fuel pressure P is set to a target value P(n-1) that is smaller than the minimum target value Pmin, and then at time t23, it is set to a target value P(n) that is smaller than the maximum target value Pmax but larger than the minimum target value Pmin. In this case, since the difference ΔP0 is the largest, the target value P(n-1) is selected as the reference value Pr. Therefore, the start time of the delay time D calculated based on the difference ΔP0 is an abnormality diagnosis that is performed after the time t23 at which the target value P(n-1) was set to the target value P(n).

As described above, of the multiple past target values that were set before the target value P(n) was set as the target fuel pressure P, the past target value that has the largest difference from the target value P(n) is selected as the reference value Pr. This allows abnormality diagnosis to be performed without being influenced by the target values that were set between the setting of the reference value Pr and the setting of the target value P(n), improving the accuracy of the abnormality diagnosis.

In step S21, the maximum target value Pmax and the minimum target value Pmin are selected without including the target value P(n-1), but this is not limiting. For example, immediately after the target fuel pressure P is set to the target value P(n), the maximum target value Pmax and the minimum target value Pmin may be selected from the target values that are set after the fuel cut is resumed and before the target value P(n) is set, including the target value P(n-1). In this case, it is sufficient to determine which of the differences ΔP1 and ΔP2 is larger, using the above-mentioned equations (2) and (3).

[Updating target value P(n)]
Next, the update of the target value P(n) will be described. FIG. 9 is a timing chart showing an example of the case where the target value P(n) is updated. In FIG. 9, only the target fuel pressure P is shown, and the detected fuel pressure Pd is omitted. FIG. 9 corresponds to FIG. 3. The target value P(n) gradually decreases from time t12. For example, when the depression amount of the accelerator pedal gradually decreases, the target value P(n) gradually decreases as shown in FIG. 9. In this case, it is determined that No is present in step S12 shown in FIG. 6 and Yes is present in step S15, and the target value P(n) is updated as needed (step S16), and the difference ΔP is calculated based on the updated target value P(n) (step S14). Since the delay time D is calculated based on the difference ΔP calculated in this way, the difference ΔP gradually increases after time t12, and the delay time D also gradually becomes longer. When the delay time D calculated as needed from time t12 has elapsed at time t13b, an abnormality diagnosis is performed. However, in the case where the target value P(n) gradually increases from time t12, the delay time D remains constant. This is because if the delay time D is shortened as the target value P(n) increases after time t12, there is a risk that the diagnostic accuracy will decrease. As described above, even if the driving operation is such that the target value P(n) gradually decreases or increases, the fuel pressure sensor 38 can be appropriately diagnosed for an abnormality.

In the above embodiment, the measurement start time of the delay time D is reset to the target value P(n) in step S13a of FIG. 6. Specifically, in FIGS. 3A and 9, measurement of the delay time D starts at time t12, and in FIGS. 8A to 8C, measurement of the delay time D starts at time t23.

The fuel pressure control device in the above embodiment has been described as being applied to an engine system 1 for a vehicle, but it can be applied to anything that uses an engine as a power source, and can also be applied to engine systems installed in so-called hybrid vehicles and motorcycles, for example.

Although the 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 variations are possible within the scope of the gist of the present invention as described in the claims.

REFERENCE SIGNS LIST 1 engine system 10 engine 11 cylinder group 111 to 114 cylinder 22 low pressure fuel pump 25 low pressure fuel piping 26 low pressure delivery pipe 27 port injection valve group 271 to 274 port injection valve 28, 38 fuel pressure sensor 31 high pressure fuel pump 35 high pressure fuel piping 36 high pressure delivery pipe 37 in-cylinder injection valve group 371 to 374 in-cylinder injection valve 40 ECU (calculation unit, abnormality diagnosis unit, selection unit)
42 Ignition switch

Claims (4)

1. A fuel pressure control device for an internal combustion engine, which feedback controls a fuel pump that supplies fuel to the internal combustion engine so that a fuel pressure detected by a fuel pressure sensor that detects a pressure of fuel supplied to the internal combustion engine coincides with a target fuel pressure,
a calculation unit that calculates a delay time to be longer and a determination value to be larger as a difference between a second target value set earlier than a first target value set as the target fuel pressure and the first target value increases;
an abnormality diagnosis unit that diagnoses that the fuel pressure sensor is abnormal when a deviation amount of the detected fuel pressure from the first target value is larger than the determination value after the delay time has elapsed since the first target value was set ;
a selection unit that selects, as the reference value, from among a plurality of past target values that were set before the first target value was set as the target fuel pressure, a past target value that has a maximum difference from the first target value. 2. The fuel pressure control device for an internal combustion engine according to claim 1, wherein the selection unit, when a new first target value is set immediately after the first target value is set, reselects as the reference value a past target value that has a maximum difference from the new first target value among a plurality of past target values that were set as the target fuel pressure before the new first target value was set, when a first difference between the first target value and the new first target value is equal to or greater than a predetermined value, and uses the already selected reference value when the first difference is less than the predetermined value. 3. The fuel pressure control device for an internal combustion engine according to claim 2, further comprising an update unit that updates the first target value to the new first target value when the first difference is less than the predetermined value. 4. A fuel pressure control device for an internal combustion engine according to claim 1, wherein the selection unit selects, as the reference value, a past target value that has a maximum difference from the first target value, from among a plurality of past target values that were set before the first target value was set and after recovery from a fuel cut.

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