Control device for evaporated fuel treatment device

Abstract

To provide a control device for an evaporation fuel treatment device capable of early starting purge diagnosis.SOLUTION: A control device for an evaporation fuel treatment device includes: a fuel tank 30 that stores fuel of an internal combustion engine; a canister 31 that adsorbs evaporation fuel generated in the fuel tank; a vapor passage 32 communicating the fuel tank with the canister; a purge passage 33 communicating an intake passage of the internal combustion engine with the canister; a seal valve 42 for opening / closing the vapor passage; a purge valve 43 for opening / closing the purge passage; an outside air introduction passage 36 for introducing outside air into the canister; a changeover valve 46 for opening / closing the outside air introduction passage; and a differential pressure detector 50 for detecting a differential pressure between a pressure in the fuel tank and a pressure in the passage from the seal valve to the purge valve. The control device also includes a purge control section that executes purge processing by opening the purge valve while the purge valve and the seal valve are closed and the changeover valve is opened. On the basis of change amount of the differential pressure between before and after the purge valve is opened, whether the purge processing is normal is diagnosed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control device for an evaporated fuel treatment device. [Background technology]

[0002] BACKGROUND ART There is known a technique for diagnosing leaks between a fuel tank and a canister of an evaporated fuel treatment device based on a tank internal pressure sensor (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2012-149592 Summary of the Invention [Problem to be solved by the invention]

[0004] It is conceivable to perform a purge diagnosis to determine whether the purge process is being performed normally. In order to perform the purge diagnosis based on the above-mentioned tank internal pressure sensor, it is necessary to open the isolation valve and wait until the tank internal pressure reaches atmospheric pressure before performing the purge process and performing the purge diagnosis. For this reason, it takes time before the purge process starts, and as a result, it may also take time to start the purge diagnosis.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a control device for an evaporated fuel treatment system that can start purge diagnosis early. [Means for solving the problem]

[0006] The object of the present invention is to provide a fuel tank for storing fuel for an internal combustion engine, a canister for adsorbing evaporated fuel generated in the fuel tank, a vapor passage connecting the fuel tank and the canister, a purge passage connecting an intake passage of the internal combustion engine and the canister, a seal valve for opening and closing the vapor passage, a purge valve for opening and closing the purge passage, an outside air introduction passage for introducing outside air into the canister, a selector valve for opening and closing the outside air introduction passage, and a pressure in the fuel tank and a pressure in the seal This can be achieved by a control device for an evaporated fuel treatment device that has a differential pressure detector that detects the pressure difference between the pressure in the passage from the shut-off valve to the purge valve and the pressure in the passage between the shut-off valve and the purge valve, a purge control unit that performs purging by opening the purge valve with the purge valve and the shut-off valve closed and the switching valve open, and a purge diagnosis unit that diagnoses whether the purge process is normal or not based on the amount of change in the differential pressure before and after the purge valve is opened.

[0007] The purge diagnosis unit may further close the switching valve during execution of the purge process and diagnose whether the purge process is normal or not based on an amount of change in the differential pressure before and after the switching valve is closed.

[0008] The fuel tank leak diagnosis system may include a first leak diagnosis unit that performs a leak diagnosis of the fuel tank based on the differential pressure when the purge valve and the shut-off valve are closed and the switching valve is open, and a second leak diagnosis unit that performs a leak diagnosis of the canister based on the differential pressure when the pressure in the fuel tank is within a normal range, and the second leak diagnosis unit may perform a leak diagnosis of the canister based on the differential pressure after closing the switching valve and then opening the shut-off valve, and then closing the shut-off valve and then opening the switching valve.

[0009] The second leak diagnosis unit may determine that there is a leak abnormality in the canister when the differential pressure is substantially zero.

[0010] The differential pressure detector may include a diaphragm, a strain gauge that detects strain in the diaphragm, a housing that holds the diaphragm and the strain gauge, and a communicating passage connected to the housing, wherein the housing separates a tank chamber and a back pressure chamber via the diaphragm, the tank chamber communicating with the fuel tank, the back pressure chamber communicating with the communicating passage, and the communicating passage communicating with a passage between the shut-off valve and the purge valve. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a control device for an evaporated fuel treatment device that can start purge diagnosis early. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of an evaporated fuel treatment device applied to an engine. [Figure 2] FIG. 2 is a schematic diagram of the differential pressure detector. [Figure 3] FIG. 3 is a flowchart illustrating the purge diagnosis control. [Figure 4] FIG. 4 is a timing chart illustrating the purge diagnostic control. [Figure 5] FIG. 5 is a flowchart illustrating the leak diagnosis control. [Figure 6] FIG. 6 is a timing chart illustrating the second leak diagnosis. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Outline of the fuel vapor treatment device] FIG. 1 is a schematic diagram of an evaporated fuel processing device 3 applied to an engine 1. In this embodiment, the engine 1 and evaporated fuel processing device 3 are mounted on a vehicle. The engine 1 is provided with a fuel injection valve 12 that injects fuel into a combustion chamber 11, and a spark plug 13 that ignites an air-fuel mixture that is a mixture of the injected fuel and intake air. An intake passage 14 and an exhaust passage 15 are connected to the combustion chamber 11. A surge tank 16 that forms part of the intake passage 14 is provided midway in the intake passage 14. A throttle valve 17 that adjusts the amount of intake air is provided upstream of the intake of the surge tank 16.

[0014] The evaporated fuel processing device 3 includes a fuel tank 30 that stores fuel. The fuel in the fuel tank 30 is supplied to the fuel injection valve 12 via a fuel supply path. The fuel tank 30 is provided with a differential pressure detector 50 that detects the difference in pressure within the fuel tank 30 (hereinafter referred to as tank internal pressure), more specifically, the pressure within a passage between a shutoff valve 42 and a purge valve 43 (described later) (hereinafter referred to as passage internal pressure). The evaporated fuel processing device 3 prevents evaporated fuel generated within the fuel tank 30 from being released into the atmosphere.

[0015] The evaporated fuel treatment device 3 is provided with a canister 31 that adsorbs evaporated fuel generated in a fuel tank 30. The canister 31 and the fuel tank 30 are connected by a vapor passage 32. A shutoff valve 42 that opens and closes the vapor passage 32 is provided midway in the vapor passage 32. By opening the shutoff valve 42, the evaporated fuel in the fuel tank 30 is temporarily collected in an adsorbent provided in the canister 31.

[0016] The canister 31 and the surge tank 16 are connected by a purge passage 33. A purge valve 43 is provided in the purge passage 33 to adjust the flow rate of evaporated fuel flowing through the purge passage 33. An outside air introduction passage 36 that introduces outside air into the canister 31 is connected to the canister 31. An air filter 37 is provided at the open end of the outside air introduction passage 36.

[0017] A selector valve 46 that opens and closes the outside air introduction passage 36 is provided in the outside air introduction passage 36. The selector valve 46, which will be described in detail later, is an electromagnetic valve that opens the outside air introduction passage 36 when de-energized and closes the outside air introduction passage 36 when energized. During engine operation, the selector valve 46 is maintained so as to open the outside air introduction passage 36, i.e., so that outside air can be introduced into the canister 31.

[0018] The engine 1 and the evaporative fuel treatment device 3 are controlled by an ECU (Electronic Control Unit) 60. The ECU 60 is an electronic control unit including a processing circuit that performs various arithmetic operations related to vehicle driving control and a memory that stores control programs and data. The ECU 60 is connected to various sensors that detect the operating state of the engine 1, a differential pressure detector 50, an ignition switch 40 operated by the driver of the vehicle, and the like. The ECU 60 executes various controls of the evaporative fuel treatment device 3 and the engine 1 based on signals from these sensors and switches. The ECU 60, which will be described in detail later, is an example of a control device for the evaporative fuel treatment device, and functionally realizes a purge control unit, a purge diagnosis unit, a first leak diagnosis unit, and a second leak diagnosis unit.

[0019] When a predetermined condition is met, the ECU 60 performs a purge process during engine operation by opening the purge valve 43 while the switching valve 46 is open and the stop valve 42 is closed. This causes evaporated fuel to be desorbed from the canister 31, and the desorbed evaporated fuel is introduced into the surge tank 16 via the purge passage 33 and combusted in the combustion chamber 11.

[0020] [Outline of differential pressure detector] 2 is a schematic diagram of the differential pressure detector 50. The differential pressure detector 50 is attached to a mounting portion 302 that protrudes cylindrically from an outer wall surface 301 of the fuel tank 30. The differential pressure detector 50 includes a housing 51, a cover 52, a communication passage 53, a diaphragm 54a, a strain gauge 54b, a base 55, an adhesive 56, and terminals 57. The housing 51 is formed in a substantially cylindrical shape, and the diaphragm 54a is held within the housing 51. One end of the housing 51 is attached to the mounting portion 302 via an O-ring 58. A cover 52 is attached to the other end of the housing 51. A communication hole 52a is formed in the cover 52. The communication passage 53 is connected to the housing 51 via the cover 52. The communication passage 53 communicates with the interior of the housing 51 via the communication hole 52a in the cover 52.

[0021] A diaphragm 54a is held within the housing 51 via a cylindrical base 55. The peripheries of the diaphragm 54a and base 55 are fixed to the interior of the housing 51 with adhesive 56. This divides the interior of the housing 51 into a tank chamber TC that communicates with the interior of the fuel tank 30 via the diaphragm 54a, and a back pressure chamber BC that communicates with the communication passage 53. A strain gauge 54b that detects distortion of the diaphragm 54a is attached to the diaphragm 54a. The strain gauge 54b is connected to the ECU 60 via a terminal 57. The diaphragm 54a distorts in response to the differential pressure between the internal pressure of the tank chamber TC and the internal pressure of the back pressure chamber BC. The strain gauge 54b outputs an output value corresponding to the amount of distortion to the ECU 60, allowing the ECU 60 to detect the differential pressure between the internal tank pressure and the internal passage pressure. The ECU 60 detects the differential pressure by subtracting the internal pressure of the back pressure chamber BC from the internal pressure of the tank chamber TC based on the output value from the strain gauge 54b.

[0022] In the differential pressure detector 50, if the communication passage 53 is not connected to the cover 52 and the communication hole 52a is open to the atmosphere, the differential pressure detector 50 can detect the tank internal pressure based on atmospheric pressure. In other words, the differential pressure detector 50 can be manufactured by slightly modifying the tank internal pressure sensor based on atmospheric pressure. This prevents an increase in the manufacturing cost of the differential pressure detector 50.

[0023] The communication passage 53 is connected to the vapor passage 32 between the block valve 42 and the canister 31, but is not limited to this. The communication passage 53 may be connected to a passage between the block valve 42 and the purge valve 43. This passage includes the vapor passage 32 between the block valve 42 and the canister 31, the canister 31, and the purge passage 33 between the canister 31 and the purge valve 43. As will be described in detail later, when the block valve 42 is closed and the switching valve 46 is open, the passage from the block valve 42 to the purge valve 43 is open, and the pressure in this portion is the same at any position.

[0024] [Purge diagnostic control] FIG. 3 is a flowchart illustrating the purge diagnosis control. FIG. 4 is a timing chart illustrating the purge diagnosis control. FIG. 4 shows the transitions of the open / close states of the purge valve 43, the switching valve 46, and the stop valve 42, and the transitions of the differential pressure detected by the differential pressure detector 50 when the purge process is normal and when it is abnormal. The purge diagnosis control is continuously repeated while the ignition is on. The ECU 60 determines whether or not the preconditions for the purge diagnosis are met (step S1). The preconditions are, for example, when the engine 1 is running and there is a purge request. In this state, the stop valve 42 and the purge valve 43 are closed, and the switching valve 46 is open. If the answer is No in step S1, this control is terminated.

[0025] If the answer is Yes in step S1, the ECU 60 opens the purge valve 43 (step S2, time t1), thereby starting the purge process. Steps S1 and S2 are an example of the process executed by the purge control unit.

[0026] Next, the ECU 60 determines whether the amount of change in the differential pressure before and after the purge valve 43 is opened is equal to or exceeds a first threshold value. EndIf the purge process is normal, the opening of the purge valve 43 creates a negative pressure lower than atmospheric pressure in the passage between the stop valve 42 and the purge valve 43. As a result, as shown in FIG. 4, the differential pressure increases and the amount of change in the differential pressure becomes equal to or greater than the first threshold value. On the other hand, if there is some abnormality, such as the purge valve 43 being stuck in a closed state or the purge passage 33 being clogged, the amount of change in the differential pressure becomes less than the first threshold value. If the answer to step S3 is Yes, the ECU 60 determines that the purge process is normal (step S4). In this way, the purge process can be started immediately after a purge request is made, and purge diagnosis can be started.

[0027] If the result in step S3 is No, as described above, an abnormality may have occurred in the purge valve 43 or the purge passage 33. However, it is also possible that these are normal and the flow rate of evaporated fuel is low, causing the amount of change in differential pressure to be less than the first threshold. Therefore, the ECU 60 closes the switching valve 46 (step S5, time t2) and determines whether the amount of change in differential pressure before and after closing the switching valve 46 is equal to or greater than the second threshold (step S6). The second threshold may be the same as or different from the first threshold.

[0028] By closing the switching valve 46 while the purge valve 43 is open, if the purge valve 43 and the purge passage 33 are normal, the pressure inside the passage will drop significantly to the same negative pressure as inside the surge tank 16. As a result, the differential pressure will increase and the amount of change in the differential pressure will exceed the second threshold. Therefore, if the answer is Yes in step S6, the ECU 60 determines that the purge process is normal (step S4). If the answer is No in step S6, the ECU 60 determines that the purge process is abnormal (step S7).

[0029] In this way, if the answer is No in both steps S3 and S6, the purge process is determined to be abnormal, improving the accuracy of abnormality determination. Steps S3 to S7 are an example of processing executed by the purge diagnosis unit.

[0030] After determining whether or not the purge process is to be performed as described above, the ECU 60 closes the purge valve 43 (step S8, time t3). This ends the purge process. Next, the ECU 60 determines whether or not the switching valve 46 is closed (step S9). If the answer is Yes in step S9, the ECU 60 opens the switching valve 46 (step S10, time t4), and this control ends. If the answer is No in step S9, this control ends.

[0031] In the above-described purge diagnosis control, the accuracy of the abnormality determination is ensured by executing steps S5 and S6 when the answer is No in step S3. However, when early diagnosis is prioritized over the accuracy of the abnormality determination, the abnormality determination may be performed immediately when the answer is No in step S3 without executing steps S5 and S6.

[0032] [Leak diagnosis control] FIG. 5 is a flowchart illustrating the leak diagnosis control. The leak diagnosis control is continuously repeated while the ignition is on. The ECU 60 determines whether or not the preconditions for the leak diagnosis are met (step S11). The preconditions are conditions for determining whether the generation of evaporated fuel in the fuel tank 30 is stable. For example, the following conditions are met. The first condition is when the ignition is turned on after the engine 1 has been stopped for a long time, such as while parked, and is the period from when the ignition is turned on to immediately before the purge valve 43 is opened and the intake passage 14 is first purged. The second condition is when several hours have passed since the ignition was turned off, and the coolant temperature or the intake air temperature is below a predetermined temperature. Such a first condition or a second condition is set as the precondition. Note that the first condition and the second condition may also be a logical OR condition. Note that in this state, the stop valve 42 and the purge valve 43 are closed, and the switching valve 46 is open. If the determination in step S11 is No, this control is terminated.

[0033] If the result of step S11 is Yes, a first leak diagnosis is performed to determine whether or not the fuel tank 30 has a leak, as follows. The ECU 60 determines whether the tank internal pressure is within the normal range based on the differential pressure detected by the differential pressure detector 50 (step S12). Specifically, if the differential pressure is approximately zero, the tank internal pressure is determined to be outside the normal range. If the differential pressure is a positive or negative value other than approximately zero as described above, the tank internal pressure is determined to be within the normal range. Here, the passage internal pressure is atmospheric pressure because the switching valve 46 is open. However, if there is a leak in the fuel tank 30, the tank internal pressure is also atmospheric pressure, and the differential pressure is approximately zero. If there is no leak in the fuel tank 30, the tank internal pressure will be higher or lower than atmospheric pressure, and the differential pressure will be a positive value greater than zero or a negative value less than zero. Note that the value is set to approximately zero because the range in which the differential pressure can be considered to be zero is outside the normal range, taking into account the tolerance of the differential pressure detector 50.

[0034] If the answer is No in step S12, the ECU 60 counts up counter A (step S13). Next, the ECU 60 determines whether counter A is greater than a predetermined value (step S14). If the answer is No in step S14, the ECU 60 suspends the leak diagnosis (step S15). If the answer is Yes in step S14, the ECU 60 determines that there is a leak abnormality in the fuel tank 30 (step S16). In this manner, the first leak diagnosis is performed. Steps S12 to S14 and S16 are an example of processing executed by the first diagnosis unit.

[0035] If the answer is Yes in step S12, the ECU 60 performs a second leak diagnosis to determine whether or not there is a leak in the canister 31. FIG. 6 is a timing chart illustrating the second leak diagnosis. FIG. 6 shows the transitions in the open / close states of the purge valve 43, the switching valve 46, and the stop valve 42, and the transitions in the differential pressure when the canister 31 is normal and when it is abnormal. FIG. 6 shows a case in which the second leak diagnosis is performed when the differential pressure indicates a positive value, and a case in which the second leak diagnosis is performed when the differential pressure indicates a negative value. A positive differential pressure means that the tank internal pressure is higher than atmospheric pressure, and a negative differential pressure means that the tank internal pressure is lower than atmospheric pressure.

[0036] The ECU 60 closes the switching valve 46 (step S17, time t11), and then opens the shut-off valve 42 (step S18, time t12). As a result, the tank internal pressure is transmitted to the canister 31, the passage between the canister 31 and the switching valve 46 in the outside air introduction passage 36, and the passage between the canister 31 and the purge valve 43 in the purge passage 33.

[0037] Next, the ECU 60 determines whether a predetermined time has elapsed since the block valve 42 was opened (step S19). If the answer is No in step S19, the process of step S19 is executed again. As shown in Fig. 6, when the block valve 42 is opened, the differential pressure becomes approximately zero. In other words, the predetermined time is set to the time required for the tank internal pressure and the passage internal pressure to become the same after the block valve 42 is opened.

[0038] If the answer is Yes in step S19, the ECU 60 closes the block valve 42 (step S20, time t13) and opens the selector valve 46 (step S21, time t14). If there is no leak in the canister 31, the pressure inside the passage becomes atmospheric pressure. This increases the difference between the pressure inside the tank and the pressure inside the passage, and the differential pressure also becomes a positive or negative value. In contrast, if there is a leak in the canister 31, for example, when the block valve 42 opens at time t12 after the selector valve 46 is closed, both the pressure inside the tank and the pressure inside the passage become atmospheric pressure, and the differential pressure becomes approximately zero. Even if the selector valve 46 is then opened at time t14 after the block valve 42 is closed, the differential pressure remains approximately zero.

[0039] Next, the ECU 60 determines whether the internal passage pressure is within the normal range based on the differential pressure (step S22). Specifically, if the differential pressure is approximately zero, the internal passage pressure is determined to be outside the normal range. If the differential pressure is a positive value or a negative value other than approximately zero as described above, the internal passage pressure is determined to be within the normal range.

[0040] If the answer is No in step S22, the ECU 60 counts up counter B (step S23). Next, the ECU 60 determines whether counter B is greater than a predetermined value (step S24). If the answer is No in step S24, the ECU 60 reserves the leak diagnosis result (step S15). If the answer is Yes in step S24, the ECU 60 determines that there is a leak abnormality in the canister 31 (step S25).

[0041] If the answer is Yes in step S22, the ECU 60 determines that the fuel tank 30 and the canister 31 are normal in terms of leaks (step S26), and resets counters A and B (step S27).

[0042] As described above, leak diagnosis control can be performed based on one differential pressure detector 50. Therefore, compared to performing leak diagnosis control using pressure sensors that detect the tank internal pressure and the canister internal pressure, for example, an increase in costs is suppressed.

[0043] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0044] 1 engine 3. Fuel vapor treatment device 30 Fuel Tank 31 canister 32 Vapor passage 33 Purge Passage 36 Fresh air intake passage 37 Air Filter 42 Shut-off valve 43 Purge valve 46 Switching valve 50 Differential pressure detector 53 Communication path 60 ECU (control unit, purge control unit, purge diagnosis unit, first leak diagnosis unit, second leak diagnosis unit)

Claims

1. a fuel tank for storing fuel for the internal combustion engine; a canister for absorbing evaporated fuel generated in the fuel tank; a vapor passage communicating the fuel tank and the canister; a purge passage that connects an intake passage of the internal combustion engine and the canister; a shutoff valve that opens and closes the vapor passage; a purge valve that opens and closes the purge passage; an outside air introduction passage for introducing outside air into the canister; a switching valve that opens and closes the outside air introduction passage; a differential pressure detector that detects a differential pressure between the pressure in the fuel tank and the pressure in a passage between the sealing valve and the purge valve; A control device for an evaporated fuel treatment device, a purge control unit that executes a purge process by opening the purge valve while the purge valve and the stop valve are closed and the switching valve is open; a purge diagnosis unit that, when a change in the differential pressure before and after the purge valve is opened is equal to or greater than a first threshold value, diagnoses that the purge valve is not stuck in a closed state and that no clogging occurs in the purge passage; The purge diagnosis unit further closes the switching valve while the purge process is being performed if the amount of change in the differential pressure before and after the purge valve is opened is less than the first threshold value, and diagnoses that the purge valve is not stuck in a closed state and that the purge passage is not clogged if the amount of change in the differential pressure before and after the switching valve is closed is greater than or equal to a second threshold value, and diagnoses that the purge valve is stuck in a closed state or that the purge passage is clogged if the amount of change in the differential pressure before and after the switching valve is closed is less than the second threshold value.

2. The differential pressure detector includes a diaphragm, a strain gauge that detects strain in the diaphragm, a housing that holds the diaphragm and the strain gauge, and a communication passage connected to the housing; the housing separates a tank chamber and a back pressure chamber via the diaphragm; the tank chamber communicates with the fuel tank, the back pressure chamber communicates with the communication passage; 2. The control device for an evaporated fuel treatment device according to claim 1, wherein said communication passage is in communication with a passage between said closing valve and said purge valve.

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