TANK VENTING SYSTEM FOR A MOTOR VEHICLE AS WELL AS MOTOR VEHICLE AND METHOD FOR OPERATING A TANK VENTING SYSTEM

Abstract

A tank venting system (14) for a motor vehicle (10) has a filter (16) to filter a venting gas (15) of a fuel tank (12) of the motor vehicle (10), a pump (25) to generate a flushing air stream (29) in order to flush the filter (16), and a control unit (30) that, for purposes of performing a leak test, is configured to detect a pressure signal (34) that is dependent on the gas pressure (P) present in the fuel tank (12) and to check whether the pressure signal (34) meets a prescribed leakage criterion (33). The pump (25) is fluidically interconnected between the filter (16) and a shut-off valve (26), whereby the shut-off valve (26) is configured to fluidically couple the pump (25) to an inlet site (27) of a fresh air system (19) of an internal combustion engine (11) of the motor vehicle (10), and whereby the control unit (30) is configured to operate the pump (25) for flushing the filter (16) as well as for performing the leak test.

Claims

1. A tank venting system (14) for a motor vehicle (10), comprising a filter (16) to filter a venting gas (15) of a fuel tank (12) of the motor vehicle (10), a pump (25) to generate a flushing air stream (29) in order to flush the filter (16), and a control unit (30) that, for purposes of performing a leak test, is configured to detect a pressure signal (34) that is dependent on the gas pressure (P) present in the fuel tank (12) and to check whether the pressure signal (34) meets a prescribed leakage criterion (33) and, if the leakage criterion (33) has been met, to generate a fault signal, wherein the pump (25) is fluidically interconnected between the filter (16) and a shut-off valve (26), wherein the shut-off valve (26) is configured to fluidically couple the pump (25) to an inlet site (27) of a fresh air system (19) of an internal combustion engine (11) of the motor vehicle (10), and wherein the control unit (30) is configured to operate the pump (25) for flushing the filter (16) as well as for performing the leak test.

2. The tank venting system (14) according to claim 1, wherein: the pump (25) is a displacement pump, and the control unit (30) is configured so that, during the leak test, at least at times, it operates at a neutral speed which is greater than 0 but less than an operating speed which is prescribed for conveying the flushing air stream (29) and at which a gas flow being conveyed by the pump (25) has no effect on the pressure signal (34) and at which the pump (25) loses its sealing effect between the shut-off valve (26) and the filter (16).

3. The tank venting system (14) according to claim 2, wherein the pump (25) is a rotary vane pump.

4. The tank venting system (14) according to claim 2, wherein the pump (25) and the shut-off valve (26) are connected via a connecting line (35) that is configured so that it can be disconnected reversibly and non-destructively.

5. The tank venting system (14) according to claim 1, wherein the control unit (30) is configured so that, during the leak test, it operates the pump (24), at least at times, in order to generate the gas pressure (P).

6. The tank venting system (14) according to claim 4, wherein, in order to generate the gas pressure (P), the pump (25) is configured to reverse the direction of rotation as compared to the direction of rotation set for the flushing air stream (29), or else to reverse a conveyed gas flow by means of a switch-over valve.

7. The tank venting system (14) according to claim 1, wherein the control unit (30) is configured to receive the pressure signal (34) from a pressure sensor (32) of the tank ventilation system (14), whereby the leakage criterion (33) entails that a pressure build-up curve displays a prescribed time course during the conveying operation to generate the gas pressure (P) by means of pumping or suctioning-off and/or a pressure change displays a prescribed time course after the end of this conveying operation and after the shut-off valve (26) has been blocked.

8. A motor vehicle (10) comprising: a fuel tank (12) and an internal combustion engine (11) having a fresh air system (19) and a tank venting system (14) according to claim 1.

9. A method for operating a tank venting system (14) in a motor vehicle (10), the tank venting system (14) comprising a filter (16) to filter a venting gas (15) of a fuel tank (12) of the motor vehicle (10), a pump (25) to generate a flushing air stream (29) in order to flush the filter (16), and a control unit (30) that, for purposes of performing a leak test, is configured to detect a pressure signal (34) that is dependent on the gas pressure (P) present in the fuel tank (12) and to check whether the pressure signal (34) meets a prescribed leakage criterion (33) and, if the leakage criterion (33) has been met, to generate a fault signal, wherein the pump (25) is fluidically interconnected between the filter (16) and a shut-off valve (26), wherein the shut-off valve (26) is configured to fluidically couple the pump (25) to an inlet site (27) of a fresh air system (19) of an internal combustion engine (11) of the motor vehicle (10), and wherein the control unit (30) is configured to operate the pump (25) for flushing the filter (16) as well as for performing the leak test, the method comprising: operating, during a leak test, the pump (25) of the tank venting system (14); and operating the pump (25), at least at times, at a neutral speed not equal to 0 that is too low to convey gas, and/or, at least at times, in order to generate a gas pressure (P) to detect a leak in the tank venting system (14).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] An embodiment of the invention is described below. In this context, the following is shown:

[0020] FIG. 1 is a schematic view of a first embodiment of the motor vehicle according to the invention, and

[0021] FIG. 2 is a schematic view of a second embodiment of the motor vehicle according to the invention.

[0022] The embodiment elucidated below relates to a preferred configuration of the invention. In the embodiment, the described components of the configuration each constitute individual features of the invention which are to be considered independently of each other and which refine the invention likewise independently of each other, and which therefore are also to be considered as part of the invention, either individually or else in a combination different from the one shown. Moreover, the described embodiment can also be augmented by additional features of the invention already described.

[0023] In the figures, functionally identical elements are designated by the same reference numerals.

DETAILED DESCRIPTION OF THE INVENTION

[0024] FIG. 1 shows a motor vehicle 10 which can be, for instance, a motor vehicle, especially a passenger car or a truck. The motor vehicle 10 can have an internal combustion engine 11 which can be, for example, a diesel engine or an Otto engine. A fuel 13 (e.g. diesel or gasoline) can have been filled into a fuel tank 12 for the operation of the internal combustion engine 11. The fuel tank 12 can be vented via a tank venting system 14, that is to say, evaporated fuel 13 can be discharged from the fuel tank 12 via the tank venting system 14 so that a pressure build-up or excess pressure in the fuel tank 12 can be prevented. The air containing the evaporated fuel constitutes a venting gas 15 which can be released or conveyed into a fresh air system 19 of the internal combustion engine 11 after having passed through a filter 16, for example, an activated carbon filter, as well as via a tank venting valve 17 and a non-return valve 18. Moreover, a throttle valve 20 and a turbocharger 21 are shown in conjunction with the fresh air system 19. The internal combustion engine 11 can draw in ambient air from an air filter 22 via the fresh air system 19. Exhaust gas of the internal combustion engine 11 can be conveyed to an exhaust-gas system 24 in a known manner via the turbocharger 21 or alternatively via a bypass 23.

[0025] In order to flush the filter 16, gas exiting from the filter 16 can be conveyed to a shut-off valve 26 via a pump or flushing pump 23, independently of the tank venting valve 14. The shut-off valve 26 is connected to the fresh air system 19 at an inlet site 27. The inlet site 27 can be installed upstream from the turbocharger 21.

[0026] FIG. 1 shows an embodiment in which the filter 16 can have a shut-off valve 28 which can be open so that, for a flushing operation, the pump 25 can convey a flushing air stream 29 through the shut-off valve 28 and through the filter 16 to the open shut-off valve 16, from where the flushing air stream 29 flows into the fresh air system 19 at the inlet site 27. The flushing air stream 29 flushes or purifies or regenerates the filter 16 in a familiar manner. In this process, the pump 25 can be operated at an operating speed that conveys the flushing air stream 29. The shut-off valves 26, 28 and the pump 25 can be controlled by a control unit 30 which, for this purpose, can have a processor unit 31.

[0027] In order to perform a leak test of the tank venting system 14, the shut-off valve 28 can be closed and the flushing pump 25 can build up a gas pressure P in the tank venting system 14 via the open shut-off valve 26. For example, during this time and/or after the shut-off valve 26 has been closed, the control unit 30 can monitor the course of the gas pressure P over time by means of a pressure sensor 32. The course can be compared to a leakage criterion 33 which defines from which point onwards this course constitutes an indication of a leak or leakage in the tank venting system 14 and/or in the fuel tank 12. Such a leakage criterion can be determined on the basis of simple experiments. The pressure sensor 32 can be installed, for example, in the fuel tank 12. The pressure sensor 32 can emit a sensor signal 34 to the control unit 30 and, on the basis of this signal, the time course of the gas pressure P can be observed or determined by the control unit 30.

[0028] The flushing pump 25 can be a flow pump. However, if the flushing pump is a displacement pump, especially a rotary vane pump, then, during the measurement of the gas pressure P, the flushing pump 25 can be operated on the basis of the pressure signal 34 at a neutral speed which is less than said operating speed, especially less than 50%, preferably less than 40%, of the operating speed, but greater than 0. In this way, a change in the gas pressure P can be detected by means of the pressure sensor 32, also in a connecting channel or in a connecting line 35 between the flushing pump 25 and the shut-off valve 26, since the flushing pump 25 loses its sealing or sealing-off effect at the neutral speed, without itself building up or bringing about a pressure differential or at least a significant pressure differential that could have an effect on the pressure signal 34.

[0029] FIG. 2 shows an embodiment in which, instead of the shut-off valve 28 on the filter 16, there is an additional diagnosis pump 36 with which the gas pressure P can be generated. The diagnosis pump 36 can be part of a tank-leakage diagnostic module which can also generate the pressure signal 34. FIG. 2 shows a diagnosis pump 36 that can generate an excess pressure as the gas pressure P. It is also possible to provide a suction pump that can generate a negative pressure as the gas pressure P with respect to the ambient pressure. In other words, the implementation is independent of whether the described diagnosis of the tank tightness is going to be carried out with excess pressure or with negative pressure. The tank-leakage diagnostic module can also evacuate the system.

[0030] If the leakage criterion 33 has been met, a fault signal 37 can be generated. Therefore, the leakage criterion 33 can entail, for instance, that a pressure build-up or relief has to display a prescribed change over time, that is to say, a pressure gradient, in order for the leakage criterion 33 to have been met.

[0031] Specific embodiments of the method for leak testing will described once again below.

[0032] For purposes of the tank-tightness diagnosis or leak test, the tank venting system 14 is closed at the filter 16 by the tank-leakage diagnostic module. Moreover, the tank venting valve 17 and the shut-off valve 26 are closed downstream from the flushing pump 25, especially the rotary vane pump. During the active leak testing, the rotary vane pump is then operated at the low speed (neutral speed). Due to the low centrifugal forces, a rotary vane pump then conveys a small volume flow or gas flow but, in exchange for that, the sealing effect is eliminated so that the pressure between the connecting line 35 and the filter 16 can be equalized. As a result, the air space between the shut-off valve 26 and the rotary vane pump (flushing pump 25) can likewise be checked for leaks, whereby detection is possible down to a leakage size of 0.5 mm.

[0033] In an advantageous manner, the connections between a pump 25 and the shut-off valve 26 can also be constructed so as to be detachable since now the tightness can be checked. Otherwise, the connections would have to be constructed so as to be undetachable. Detachable connections, however, are more maintenance-friendly and reduce the complexity of the components.

[0034] Therefore, with a combination of the tank venting system with a rotary vane pump, the rotary vane pump can be operated during the leak test at a lower neutral speed than the operating speed specified for the pump operation in order to achieve a pressure equalization beyond the rotary vane pump. The centrifugal forces at the neutral speed of the rotary vane pump are not sufficient to close off the conveying chambers. The sealing effect of the rotary vane pump is thus eliminated.

[0035] A diagnostic module having its own diagnosis pump 36 can also be completely dispensed with by using the pump 25 for the regeneration of the filter 16 as well as for the diagnosis or leak test, that is to say, in order to generate the gas pressure P. The pressure charge needed to generate the gas pressure P can come from the fresh air system 19 at the inlet site 26 of the internal combustion engine 11 instead of coming from the ambient air. This also prevents icing of components of the tank venting system 14 during the leak test.

[0036] If a pump 25 is used with which no reversal of the direction is possible, a switch-over valve (not shown here) can be employed between the pump and the air filter. In this case, the switch-over valve allows a reversal of the air flow direction.

[0037] For the diagnosis, the shut-off valve at the filter 16 and the tank venting valve 18 are closed and the shut-off valve 26 is opened upstream from the pump 26. The pump 25 conveys air from the air filter 22 into the fuel tank 22 counter to the regeneration direction. The reversal of the conveying direction can be effectuated either by reversing the direction of rotation of the pump 25 or else by installing a separate switch-over valve between the pump 25 and the filter 16 (not shown in the figure). As an alternative to this, the air can be conveyed in the regeneration direction, thereby generating a negative pressure for the diagnosis.

[0038] By means of a pressure sensor 32 in the tank system, a conclusion can be drawn about the tightness of or leaks in the tank system consisting of the fuel tank 12 and the tank venting system 14. This can be done either on the basis of the course of the pressure build-up curve during the build-up or relief by the pump or else on the basis of the pressure drop after the conveying procedure has ended and the shut-off valve 26 between the pump 25 and the filter 16 has been blocked.

[0039] Therefore, the core element of the tank venting system 14 is a pump 25 situated between the filter 16 (activated carbon container) and the second inlet site 27 upstream from the exhaust-gas turbocharger 21. The pump 25 is thus arranged fluidically between the activated carbon container 16 and the regeneration valve (tank venting valve 26). First and foremost, the pump 25 has the function of regenerating the activated carbon container 16. The dual utilization of the pump 25 is characterized by its use for the leak test or leak diagnosis of the tank system as well as for the regeneration of the activated carbon container 16. Moreover, a simple shut-off valve 26 can be used as the tank venting valve between the activated-coal container 16, the pump 25 and the internal combustion engine 11.

[0040] All in all, the example shows how the invention allows a tank leakage diagnosis to be carried out by means of the tank venting pump that is integrated in the regeneration line.

LIST OF REFERENCE NUMERALS

[0041] 10 motor vehicle [0042] 11 internal combustion engine [0043] 12 fuel tank [0044] 13 fuel [0045] 14 tank venting system [0046] 15 venting gas [0047] 16 filter [0048] 17 tank venting valve [0049] 18 non-return valve [0050] 19 fresh air system [0051] 20 throttle valve [0052] 21 turbocharger [0053] 22 air filter [0054] 23 bypass [0055] 24 exhaust-gas installation [0056] 25 pump [0057] 26 shut-off valve [0058] 27 inlet opening [0059] 28 shut-off valve [0060] 29 flushing stream [0061] 30 control unit [0062] 31 processor unit [0063] 32 pressure sensor [0064] 33 leakage criterion [0065] 34 pressure signal [0066] 36 diagnosis pump [0067] 37 fault signal