Method and device for diagnosing the ventilation circuit of a fuel tank of a motor vehicle operated with an internal combustion engine

Abstract

The invention relates to a method and a device for diagnosing a ventilation line (2) of a motor vehicle which can be operated as an internal combustion engine and has a control unit (ECU), the ventilation line being arranged between a fuel tank (1) and an activated carbon filter (3), wherein the state of a vacuum switch (4) is evaluated for the purpose of diagnosis.

Description

Technical Field

[0001] The invention relates to a method and a device for diagnosing a ventilation circuit of a fuel tank of a motor vehicle which can be operated as an internal combustion engine. Background Art

[0002] Figure 1 , a known tank system of a motor vehicle that can be operated as an internal combustion engine is shown. The tank system has a fuel tank 1. A ventilation line 2 is arranged between the fuel tank 1 and the activated carbon filter 3. The hydrocarbons released from the fuel tank are combined in the activated carbon filter 3. The hydrocarbon gas is introduced from the activated carbon filter 3 into the air path of the internal combustion engine through the tank ventilation line 2. The tank ventilation valve 5, which is constructed as a switching valve or a linear valve, is controlled by the motor controller ECU to adjust the air flow from the activated carbon filter 3 to the air path of the internal combustion engine. A tank cover 6 is provided to seal the fuel tank 1 in an airtight manner. A tank pressure sensor 7 is located in the fuel tank 1. In addition, a filling level sensor 8 for obtaining the current fuel filling level is arranged in the fuel tank 1.

[0003] The engine control unit ECU is designed to determine the setpoint value of the flushing flow from the activated carbon filter 3 to the internal combustion engine for the respective current operating state. The engine control unit ECU is also designed to receive the pressure sensor signals provided by the tank pressure sensor 7 and to determine the intake pipe pressure in the intake duct with the aid of these output signals. The engine control unit ECU is also designed to determine the PWM value for controlling the tank ventilation valve 5 as a function of the pressure drop between the pressure at the fresh air connection of the activated carbon filter 3 and the introduction point in the air path of the internal combustion engine and the predefined flushing flow. The engine control unit ECU is also designed to calculate the amount of fuel to be injected for the respective current operating state of the internal combustion engine.

[0004] In order to meet country-specific legislative provisions, it is necessary to ensure or diagnose the functionality of a fuel tank ventilation system of a motor vehicle that can be operated as an internal combustion engine. This diagnosis includes checking the functionality or patency of a ventilation line 2 arranged between a fuel tank 1 and an activated carbon filter 3. If this ventilation line is blocked, it is not possible to ensure that hydrocarbon vapors generated in the fuel tank can be absorbed in the activated carbon filter. In addition, due to this blockage caused by the overpressure generated in the fuel tank, refueling of the motor vehicle can only be carried out to a very limited extent, which also subsequently leads to an increase in hydrocarbon emissions.

[0005] It is known to diagnose the ventilation circuit of a fuel tank of a motor vehicle that can be operated as an internal combustion engine by means of a tank pressure sensor 7 installed in the fuel tank 1. In this case, in certain operating states of the internal combustion engine, the tank ventilation valve 5 is controlled so that the fuel tank 1 is emptied by the resulting mass flow. Therefore, in order to check the quality of the ventilation circuit 2, the pressure drop in the fuel tank that occurs during the control of the tank ventilation valve is evaluated. If the tank pressure does not drop during the diagnosis, then the presence of a defective or blocked ventilation circuit 2 is detected. Summary of the invention

[0006] The object of the present invention is to specify a method for diagnosing a ventilation circuit of a fuel tank of a motor vehicle that can be operated as an internal combustion engine, wherein no pressure sensor installed in the fuel tank is required.

[0007] According to the invention, a method is provided for diagnosing a ventilation line arranged between a fuel tank and an activated carbon filter of a motor vehicle having a control device and operable with an internal combustion engine, wherein the state of a vacuum switch is evaluated for the purpose of diagnosis.

[0008] According to one embodiment of the invention, the state of a vacuum switch arranged on the fresh air side of the activated carbon filter is evaluated for diagnosis.

[0009] According to one embodiment of the invention, within the scope of the diagnosis, the state of the vacuum switch is evaluated and the change in the filling level of the fuel tank is evaluated.

[0010] According to an embodiment of the invention, the negative pressure switch is brought into its closed state before the state of the negative pressure switch is evaluated and before a change in the filling level of the fuel tank is evaluated.

[0011] According to an embodiment of the invention, during operation of the internal combustion engine, a diagnosis is performed while the motor vehicle is idling, and when a change in the fill level is recognized and the vacuum switch switches to its open position, the presence of a properly functioning ventilation circuit is detected, and when a change in the fill level is recognized and the vacuum switch remains in its closed position, the presence of a faulty ventilation circuit is detected.

[0012] According to an embodiment of the invention, during subsequent operation of the control device, a diagnosis is performed with the internal combustion engine switched off and, in the case of a change in the fill level being identified and the vacuum switch switching to its open position, the presence of a functioning ventilation circuit is detected, and in the case of a change in the fill level being identified and the vacuum switch remaining in its closed position, the presence of a faulty ventilation circuit is detected.

[0013] According to an embodiment of the present invention, after refueling the motor vehicle, a diagnosis is performed with the motor control unit switched off, wherein, after restarting the motor control unit, the fill level of the fuel tank measured at the previous shutdown time of the motor control unit is compared with the currently measured fill level of the fuel tank, and the position of the vacuum switch at the previous shutdown time of the motor control unit is compared with the current position of the vacuum switch, and when the vacuum switch switches from its closed position to its open position and a change in the fill level of the fuel tank is detected, the presence of a properly functioning ventilation circuit is detected, and when the vacuum switch remains in its closed position and a change in the fill level of the fuel tank is detected, the presence of a faulty ventilation circuit is detected.

[0014] According to an embodiment of the present invention, a time period between a previous shutdown of the motor control device and a restart of the motor control device is measured, and a diagnosis is performed only if the measured time period does not exceed a preset time period.

[0015] According to an embodiment of the present invention, a device for diagnosing a ventilation line arranged between a fuel tank and an activated carbon filter of a motor vehicle with an engine control device and operable as an internal combustion engine is provided, the device having a motor control device which is designed to control the method according to the present invention.

[0016] The advantages of the present invention are in particular that the method according to the invention makes it possible to diagnose the tank ventilation circuit of a motor vehicle that can be operated with an internal combustion engine without requiring a pressure sensor arranged in the fuel tank. In addition, the diagnostic method according to the invention is insensitive to large amounts of discharged fuel and the associated pressure increase in the fuel tank. In addition, there is no active intervention in the tank ventilation controller during operation with an internal combustion engine, which leads to an increase in the total mass flow and thus to improved flushing of the activated carbon filter. Since the diagnostic method according to the invention according to one embodiment of the invention is carried out during the refueling process and immediately after the start of the engine controller, that is, when the vehicle is stationary, there are no influences of pressure fluctuations in the fuel tank that may occur due to high vehicle transverse or vehicle longitudinal dynamics. Finally, the diagnostic method is independent of the current fuel filling level, which, depending on the installation position of the tank pressure sensor, has an influence on the quality or validity of the currently measured tank pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Further advantageous properties of the present invention are apparent from the following exemplary description thereof with reference to the accompanying drawings. In particular:

[0018] Figure 1 A sketch of a known box system is shown;

[0019] Figure 2 A sketch showing a box system according to an embodiment of the present invention is shown;

[0020] Figure 3 The box ventilation circuit is intact. Figure 2 The signal routing lines in the box system shown;

[0021] Figure 4 The following figure shows the situation when the box ventilation line is blocked. Figure 2 The signal routing lines in the box system shown;

[0022] Figure 5 The signal curve is shown, which illustrates the diagnostic process during the subsequent operation of the control device when the box ventilation line is intact;

[0023] Figure 6 A signal curve is shown which illustrates the diagnostic sequence during subsequent operation of the control device in the event of a blocked tank ventilation line;

[0024] Figure 7 A signal progression line is shown, which illustrates the diagnostic process after the control device is restarted when the box ventilation circuit is intact; and

[0025] Figure 8 A signal curve is shown which illustrates the diagnostic sequence after a restart of the control device in the case of a blocked tank ventilation line. DETAILED DESCRIPTION

[0026] Figure 2 A schematic diagram of a tank system according to an embodiment of the invention is shown. The tank system has a fuel tank 1, a tank ventilation line 2, an activated carbon filter 3, a negative pressure switch 4, a tank ventilation valve 5, a tank cover 6, a filling level sensor 8 and a motor control unit ECU.

[0027] The method described below for diagnosing the tank ventilation line 2 does not require a pressure sensor arranged in the fuel tank. The method according to the invention is based on the evaluation of the state of the vacuum switch 4 on the fresh air side of the activated carbon filter 3 in combination with the evaluation of the filling level changes of the fuel tank that occur when refueling the motor vehicle.

[0028] During operation of the internal combustion engine, the tank ventilation valve 5 is controlled to flush the activated carbon filter 3. As a result, the vacuum switch 4 is closed due to the resulting mass flow. The vacuum switch 4 remains closed until pressure balance occurs in the entire volume from the fuel tank 1 to the tank ventilation valve 5.

[0029] This pressure compensation can take place very slowly on the one hand due to the non-gas-tight connection between the activated carbon filter 3 and the ambient air, or can take place suddenly on the other hand by opening the tank cover 6 .

[0030] Since the tank lid 6 is opened each time the motor vehicle is refueled, the evaluation of the position of the vacuum switch 4 in combination with the evaluation of the filling level change caused by the refueling process allows the blockage of the tank ventilation line between the fuel tank 1 and the activated carbon filter 3 to be inferred. The prerequisite is that the vacuum switch 4 is closed before the refueling process. Since the refueling process can take place during engine operation and also in a subsequent operating phase of the engine control in which the ignition of the motor vehicle is switched off, the following states can be observed in the diagnostic sequence:

[0031] - monitoring the position of the vacuum switch 4 during operation of the internal combustion engine;

[0032] - During a stationary state of the vehicle in idling, an additional monitoring of the filling level change in the fuel tank 1 is carried out;

[0033] If during the refueling process the vacuum switch 4 switches from its closed position to its open position, it is concluded that there is an intact or properly functioning tank ventilation line 2 between the fuel tank 1 and the activated carbon filter 3;

[0034] If, on the other hand, the vacuum switch 4 remains in its closed position during the refueling process or a change in the filling level is detected, a blockage of the tank ventilation line 2 between the fuel tank 1 and the activated carbon filter 3 is inferred.

[0035] Figure 3 The box ventilation circuit is intact. Figure 2 The signal curves in the tank system are shown. Here, the curve K1 represents the ambient pressure, the curve K2 represents the pressure in the fuel tank, the curve K3 represents the state of the tank ventilation valve 5, the curve K4 represents the state of the negative pressure switch 4, the curve K5 represents the state of the tank cover, and the curve K6 represents the tank filling level. Figure 3 It can be seen that during the refueling process (in which a change in the filling level is detected), the vacuum switch 4 passes from its closed state into its open state. It can be seen here that the tank ventilation line arranged between the fuel tank 1 and the activated carbon filter 3 is in a functional, ie intact, state.

[0036] Figure 4 The following figure shows the situation when the box ventilation line is blocked. Figure 2 The signal curves in the tank system are shown. Here, the curve K1 represents the ambient pressure, the curve K2 represents the pressure in the fuel tank, the curve K3 represents the state of the tank ventilation valve 5, the curve K4 represents the state of the negative pressure switch 4, the curve K5 represents the state of the tank cover, and the curve K6 represents the tank filling level. Figure 4It can be seen that during the refueling process in which a change in the filling level is detected, the vacuum switch 4 remains in its closed state. It can be seen here that the tank ventilation line arranged between the fuel tank 1 and the activated carbon filter 3 is in a faulty, ie blocked, state.

[0037] The following describes the diagnostic sequence in the subsequent operation of the control device, in which the internal combustion engine is in the switched-off state and the control device is in the switched-on state. The following states can be observed here:

[0038] - monitoring the position of the vacuum switch 4 during operation of the internal combustion engine;

[0039] - additionally monitoring the filling level change in the fuel tank 1 during a vehicle standstill, in which the internal combustion engine is in its switched-off state and the engine control unit is in its switched-on state;

[0040] If the vacuum switch 4 switches from its closed position into its open position, it is concluded that an intact or properly functioning tank ventilation line 2 is present between the fuel tank 1 and the activated carbon filter 3 ;

[0041] If, on the other hand, during the refueling process the vacuum switch 4 remains in its closed position or a change in the filling level is detected, a blockage of the tank ventilation line 2 between the fuel tank 1 and the activated carbon filter 3 is inferred.

[0042] Figure 5 The signal curves are shown, which illustrate the diagnostic sequence during the subsequent operation of the control device when the tank ventilation circuit is intact. In this case, the curve K1 represents the ambient pressure, the curve K2 represents the pressure in the fuel tank, the curve K3 represents the state of the tank ventilation valve 5, the curve K4 represents the state of the negative pressure switch 4, the curve K5 represents the state of the tank cover, and the curve K6 represents the tank filling level. Figure 5 It can be seen that during the refueling process, in which a change in the filling level is detected, the vacuum switch 4 passes from its closed state into its open state. It can be seen here that the tank ventilation line arranged between the fuel tank 1 and the activated carbon filter 3 is in a functional, ie intact, state.

[0043] Figure 6 1 shows signal curves which illustrate the diagnostic sequence in the subsequent operation of the control device in the event of a blocked tank ventilation line. In this case, curve K1 represents the ambient pressure, curve K2 represents the pressure in the fuel tank, curve K3 represents the state of the tank ventilation valve 5, curve K4 represents the state of the negative pressure switch 4, curve K5 represents the state of the tank cover, and curve K6 represents the tank filling level. Figure 6It can be seen that during the refueling process (in which a change in the filling level is detected), the vacuum switch 4 remains in its closed state. It can be seen here that the tank ventilation line arranged between the fuel tank 1 and the activated carbon filter 3 is in a faulty, ie blocked, state.

[0044] The following is a description of the diagnostic sequence after restarting the engine control unit, during which refueling is carried out in the switched-off state of the engine control unit. The following states can be observed:

[0045] After the engine control unit has been switched on with the internal combustion engine switched off, a fuel filling level measured at the time the engine control unit was switched off is compared with the currently measured fuel filling level;

[0046] - after switching on the engine control unit with the internal combustion engine switched off, the position of the vacuum switch 4 at the time when the engine control unit was switched off is compared with the current position. If the vacuum switch 4 switches from its closed position to its open position and a refueling process with a change in the filling level is detected at the same time, it is concluded that there is a functioning, i.e. intact, tank ventilation line 2 between the fuel tank 1 and the activated carbon filter 3;

[0047] - the procedures described in the first two steps for evaluating the switch position of the vacuum switch 4 or evaluating the tank filling level are only carried out if the downtime of the internal combustion engine does not exceed an adjustable value. Observation of the downtime of the internal combustion engine should ensure that a change of the vacuum switch 4 due to the above-mentioned natural pressure equalization process in the fuel system does not lead to erroneous results;

[0048] If, during a refueling process with a change in the filling level, the vacuum switch 4 remains in its closed position, then a faulty, ie clogged, tank ventilation line 2 between the fuel tank 1 and the activated carbon filter 3 can be inferred.

[0049] Figure 7 The signal curves are shown, which illustrate the diagnostic sequence after a restart of the control device when the tank ventilation circuit is intact. In this case, the curve K1 represents the ambient pressure, the curve K2 represents the pressure in the fuel tank, the curve K3 represents the state of the tank ventilation valve 5, the curve K4 represents the state of the negative pressure switch 4, the curve K5 represents the state of the tank cover, and the curve K6 represents the tank filling level. Figure 7 It can be seen that during the refueling process, in which a change in the filling level is detected, the vacuum switch 4 passes from its closed state into its open state. It can be seen here that the tank ventilation line arranged between the fuel tank 1 and the activated carbon filter 3 is in a functional, ie intact, state.

[0050] Figure 81 shows signal curves which illustrate the diagnostic sequence after a restart of the control device in the case of a blocked tank ventilation line. In this case, curve K1 represents the ambient pressure, curve K2 represents the pressure in the fuel tank, curve K3 represents the state of the tank ventilation valve 5, curve K4 represents the state of the negative pressure switch 4, curve K5 represents the state of the tank cover, and curve K6 represents the tank filling level. Figure 8 It can be seen that during the refueling process (in which a change in the filling level is detected), the vacuum switch 4 remains in its closed state. It can be seen here that the tank ventilation line arranged between the fuel tank 1 and the activated carbon filter 3 is in a faulty, ie blocked, state.

Claims

1. A method for diagnosing a ventilation line (2) of a motor vehicle which can be operated as an internal combustion engine and has an engine control unit (ECU), the ventilation line being arranged between a fuel tank (1) and an activated carbon filter (3), wherein: The state of a vacuum switch (4) arranged on the fresh air side of an activated carbon filter (3) and changes in the filling level of a fuel tank (1) occurring when refueling a motor vehicle are evaluated for diagnosis purposes, In this case, when a change in the fill level is recognized and the vacuum switch switches to its open position, the presence of a properly functioning ventilation line is detected, and when a change in the fill level is recognized and the vacuum switch remains in its closed position, the presence of a faulty ventilation line is detected.

2. The method according to claim 1, characterized in that: Before evaluating the state of the negative pressure switch (4) and before evaluating a change in the filling level of the fuel tank (1), the negative pressure switch (4) is brought into its closed state.

3. The method according to claim 2, characterized in that During operation of the internal combustion engine, the diagnosis is carried out while the motor vehicle is idling.

4. The method according to claim 2, characterized in that: During subsequent operation of the control device, the diagnosis is carried out with the internal combustion engine switched off.

5. A method for diagnosing a ventilation line (2) of a motor vehicle which can be operated as an internal combustion engine and has an engine control unit (ECU), the ventilation line being arranged between a fuel tank (1) and an activated carbon filter (3), wherein: The state of a fresh air side negative pressure switch (4) arranged on the activated carbon filter (3) and the change in the filling level of the fuel tank (1) are evaluated for diagnosis, In this case, after refueling the motor vehicle, a diagnosis is performed with the engine control unit switched off, wherein after restarting the engine control unit, a fill level of the fuel tank measured at a previous shutdown time of the engine control unit is compared with a currently measured fill level of the fuel tank, and a position of the vacuum switch at a previous shutdown time of the engine control unit is compared with a current position of the vacuum switch, and if the vacuum switch switches from its closed position to its open position and a change in the fill level of the fuel tank is detected, the presence of a properly functioning ventilation circuit is detected, and if the vacuum switch remains in its closed position and a change in the fill level of the fuel tank is detected, the presence of a faulty ventilation circuit is detected.

6. The method according to claim 5, characterized in that A time period between a previous shutdown of the motor control device and a restart of the motor control device is measured, and a diagnosis is performed only if the measured time period does not exceed a predefined time period.

7. A device for diagnosing a ventilation line (2) of a motor vehicle that can be operated as an internal combustion engine and has a control unit (ECU), the ventilation line being arranged between a fuel tank (1) and an activated carbon filter (3), wherein the control unit (ECU) is designed to control a method according to any of the preceding claims.

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