GB2339291A

GB2339291A - Ventilated liquid storage installation with ventilation integrity checking

Info

Publication number: GB2339291A
Application number: GB9919237A
Authority: GB
Inventors: Helmut Schwegler; Andreas Blumenstock
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-08-16
Filing date: 1998-08-07
Publication date: 2000-01-19
Anticipated expiration: 2018-08-07
Also published as: GB9919237D0; GB2339291B

Description

2339291 VENTILATED LIQUID STORAGE INSTALLATION WITH VENTILATION INTEGRITY

CHECKING The present invention relates to a ventilated liquid storage installation.

The Californian Environmental Authority (CARB), like the American Federal Environmental Authority (Environment Protection Agency, EPA), demands checking of the functional capability of tank-ventilating systems in motor vehicles by on-board means (On-Board Diagnosis, OBDII). After the model year 2000, leaks above a size of 0.5 millimetres must be detected, signalled and filed in an on-board storage device of the motor vehicle for later off-board diagnosis.

A method and a device for the testing of the functional capability of a tank-ventilating system, in which the tightness of the system is checked by the introduction of an underpressure into the system and by comparison of the resulting pressure with the pressure produced by a reference leak, are disclosed in, for example, US 5 347 971. A disadvantage of this method is that evaporation of the fuel in the tank is increased by the underpressure.

A device for the checking of the functional capability of a tankventilating system, in which the checking is carried out with excess pressure introduced into the tank-ventilating system by means of a fluid flow engine, is disclosed in DE 195 02 776 C1. In this case, the introduced volume flow is measured by means of a pressure difference measurement at a diaphragm and it is subsequently decided by a comparison with a programmable threshold whether a leak is present or not. A problem with this device is that a workshop external testing of the tankventilating system, during which an excess pressure is introduced into the system by an external pressure source, is difficult as the system cannot be readily sealed against the environment and to that extent a leak is difficult to detect.

In German Patent Application P 196 36 431.0 (not prior published) there is disclosed a method and a device for the testing of the functional capability of a tank-ventilating system, which comprises a tank, an adsorption filter, which is connected with the tank by way of a connecting duct and a ventilation duct, a tank-ventilating valve connected with the adsorption filter by way of a valve duct, and an on- board pressure source by which the tank-ventilating system can be loaded by a pressure, in which - for ascertaining the 2 pressure course and/or the conveyed volume flow the operational characteristic magnitudes of the pressure source are detected on the introduction of the pressure and the presence of a leak is deduced therefrom.

With this device, too, the introduction of an excess pressure by an external pressure source entails problems, since the adsorption filter cannot be sealed off completely. In the case of a workshop test of the ventilating system, air escapes from the system and indicates a leak. No distinction can be made between an actually present leak and a simulated leak.

There is therefore a need to further develop the diagnosis of a tankventilating system such that a secure sealing, which can be realised in a manner which is as technically simple as possible, of the system relative to the environment is possible whenever a workshop test is performed, for example when the system is subjected to an excess pressure produced by an off-board pressure source.

According to one aspect of the present invention there is provided a device for the diagnosis of a tank-ventilating system of a vehicle, comprising a tank, an adsorption filter which is connected with the tank by way of a tank connection duct and has an aeration duct, a tankventilating valve which is connected with the adsorption filter by way of a valve duct and an on-board pressure source, by which the ventilating system is loadable by a pressure, characterised in that shut-off means are provided, which open only when the ventilating system is loaded by pressure by the on-board pressure source and which close when the system is loaded by pressure by a pressure source coupled on externally for functional testing.

By virtue of the shut-off or flow control means, an on-board diagnosis of the system is made possible in that the shut-off valve means opens only when the ventilating system is loaded by pressure by the on-board pressure source, and a leakage to the environment is prevented when the system is loaded by pressure by a pressure source coupled on externally for the functional test, which is the case, for example, when a workshop test of the system is carried out.

In order in particular to ensure a long service life of the shut-off means, this is preferably arranged outside the flow path of the regenerating air of the adsorption filter.

3 Consequently, the shut-off means is flowed through only during a diagnosis or checking procedure, which is undertaken perhaps only once for each driving cycle, so that it has only a little exposure to contamination and, in consequence thereof, a high service life.

In principle, there are various possibilities of disposition of the shutoff means in the system. In one advantageous embodiment, the shut-off means is disposed in flow direction directly downstream of the on-board pressure source. This has the advantage that all components present behind the shut-off means are also included in an on-board diagnosis. In another embodiment, the shut-off means can be disposed in flow direction directly upstream of the on-board pressure source. In this case, the pressure source must be as pressure-tight as possible relative to the environment.

According to a second aspect of the invention there is provided a device for the diagnosis of a tank-ventilating system of a vehicle, comprising a tank, an adsorption filter, which is connected with the tank by way of a tank-connecting duct and has an aeration duct, a tank-ventilating valve which is connected with the adsorption filter by way of a valve duct and an on-board pressure source by which the tank-ventilating system and a reference leak connected in parallel therewith can be loaded by pressure in alternation by way of a switching means, wherein shut-off means are provided, which open and are flowed through when the reference leak is loaded by pressure as well as when the system is loaded by pressure.

In this device, which makes diagnosis possible by a reference leak, throughflow of the shut-off means is achieved in an advantageous manner during a reference measurement, i.e. when the reference leak is loaded by pressure, as well as during a tank measurement, i.e. when the ventilating system is loaded by pressure.

Various forms of construction of the switching means are feasible, for example the switching means can be, for preference, a 3/2 way valve or can be a 4/2 way valve.

In a particularly advantageous embodiment, the reference leak is part of the switching means. This embodiment, in particular, makes possible a reduction in the required components for the performance of the reference measurement.

4 Advantageously, the switching means is so connected that the shut-off means are not flowed through during a regenerating process of the filter, for example an active carbon filter. Consequently, the shut-off means is flowed through only during a tank diagnosis procedure which is undertaken perhaps once for each driving cycle, from which a low exposure to contamination and a high service life of the shut-off means result.

In principle, the shut-off means can be constructed in diverse forms, for example, electrically controllable valves are feasible. In a particularly advantageous embodiment the shut-off means is a non-return valve. A mechanical non-return valve requires no electrical control and its simple mode of construction results in reliable functioning An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, the single figure of which is a schematic block diagram of a ventilated liquid storage installation embodying the invention.

Referring now to the drawing, there is shown a ventilated fuel tank installation of a motor vehicle, but the installation could equally well serve for storage of other fluids requiring ventilation and in a context other than a motor vehicle. The illustrated installation comprises a tank 10, an adsorption filter 20, for example an active carbon filter, which is connected with the tank 10 by way of a tank-connecting duct 12 and has an aeration duct 22 connected with the environment, and a tank- ventilating valve 30, which is connected on the one hand with the adsorption filter 20 by way of a valve duct 24 and on the other hand with an induction duct 40 of an internal combustion engine by way of a valve duct 42.

Hydrocarbons, which deposit in the adsorption filter 20, emanate from the tank 10 due to evaporation. The valve 30 is opened for regeneration of the adsorption filter 20 so that, due to the underpressure prevailing in the induction duct 40, atmospheric air is sucked by way of a filter 50 through the adsorption filter 20, whereby the hydrocarbons deposited in the filter 20 are sucked into the induction duct 40 and fed to the engine.

For diagnosis of this tank-ventilating system, a diagnosis module 70 is provided, which comprises pressurising means in the form of a motor 71 and a compressor 72, by which pressure can be introduced into the ventilating system through the aeration duct 22 of the filter 20 under the control of controllable switching means 73, for example a 3/2-way change-over valve drivable in suitable manner, for example electromagnetically. Arranged in parallel with the switching means 73, i.e. in parallel with the 3/2- way valve is a reference leak 75, which is loaded by pressure from the compressor 72 when the 3/2-way valve is disposed in a switch position in which the duct, which leads from the compressor 72 to the filter 20, is closed (as shown in the figure).

A comparison of the measurements obtained with two settings of the switching means 73 enables a conclusion to be drawn about the possible presence of a leak in the ventilating system. In this connection, reference is made to the not prior published German Patent Application P 196 36 431.0.

As is further evident from the figure, a non-return valve 80 is arranged before the branching-off to the reference leak 75 and directly behind the compressor 72 in the pressure duct, which leads to the 3/2-way valve and to the reference leak 75. The nonreturn valve 80 opens whenever the ventilating system is loaded by a pressure by the onboard pressure source, i.e. the compressor 72 driven by the motor 71. Due to the arrangement of the valve 80 directly behind the compressor 72, this valve is opened and flowed through during a reference measurement, i.e. when the reference leak 75 is loaded by a pressure by the compressor 72, and also during a tank measurement, i.e. when the ventilating system is loaded by pressure by the compressor 72 in the case of a different setting of the 3/2-way valve. As a result of this position of the non-retum valve 80, it is taken into consideration during the tank measurement as well as also during the reference measurement, so that no differences result between the tank measurement and the reference measurement due to the influences of the non-return valve 80.

In the case of a workshop measurement, i.e. when an excess pressure is introduced into the ventilating system from an external excess pressure source, for example a gas bottle 100 illustrated schematically in the figure, via an additional duct 110 which opens into the valve duct 24 leading to the valve 30, the non-retum valve 80 closes and thus seals the entire tank-ventilating system off against the environment. - The afore-described installation has the following advantages:

A workshop test is made possible in simple manner by the non-return valve 80 closing in the case of a loading of the ventilating system by an external pressure source 100 and thus seals the entire ventilating system against the environment.

6 The non-return valve 80 can be a mechanical valve, so that no additional electrical drive control is necessary.

The non-retum valve 80 does not influence the tolerances of the leakage diagnosis, since it is brought into action for a reference measurement, i. e. a measurement in which the reference leak 75 is pressure-loaded by the compressor 72, as well as for a tank measurement, i.e. when the compressor 72 pressureloads the ventilating system.

The non-return valve 80 is flowed through by only a small air current provided by the on-board pressure source pump (motor 71, compressor 72) and can therefore have a small cross-section.

The non-return valve 80 is arranged so that it is not flowed through by regenerating air, but flowed through only during the relatively infrequent diagnosis processes, which take place perhaps once each driving cycle. Consequently, a low rate of contamination occurs and a high service life of the valve 80 is achievable.

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Claims

1 A ventilated liquid storage installation comprising a storage tank, a ventilating system comprising an aeratable adsorption filter connected to the tank by a ventilation duct and an outlet valve connected to the filter by a regenerating flow duct, pressurising means, integrated in the installation, for pressurisation of the system and of a reference leakage point, switching means for controlling pressurisation of the system and the leakage point to take place in alternation, and flow control means arranged to open and permit flow therethrough when the system is pressurised and when the leakage point is pressurised.

2. An installation as claimed in claim 1, the switching means comprising a 3/2 way valve.

3. An installation as claimed in claim 1, the switching means comprising a 4/2 way valve.

4. An installation as claimed in any one of the preceding claims, wherein the reference leakage point is part of the switching means.

5. An installation as claimed in any one of the preceding claims, the switching means being operable to prevent flow through the flow control means during regenerating flow through the filter produced by the outlet valve.

6. An installation as claimed in any one of the preceding claims, the flow control means being a non-return valve.

7. An installation as claimed in any one of the preceding claims, wherein the tank is a motor vehicle fuel tank.

8. A ventilated liquid storage installation substantially as hereinbefore described with reference to the accompanying drawing.

9. A motor vehicle provided with a ventilated liquid storage installation as claimed in any one of the preceding claims.

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10. A ventilated liquid storage installation comprising a storage tank, a ventilating system connectible to an external pressure source, separate from the installation, for pressurisation of the system for leakage detection and comprising an aeratable adsorption filter connected to the tank by a ventilation duct and an outlet valve connected to the filter by a regenerating flow duct, pressurising means, integrated in the installation for pressurisation of the system for leakage detection, and flow control means arranged to open when the ventilating system is pressurised by the pressurising means and to close when the ventilating system is pressurised by the external pressure source.

11 An installation as claimed in claim 10, the shut-off means being disposed away from the path of a regenerating flow produced by the outlet valve.

12. An installation as claimed in claim 10 or claim 11, the shut-off means being disposed directly downstream of the pressurising means with respect to the flow direction of pressurising fluid provided by the pressurising means.

13. An installation as claimed in claim 10 or claim 11, the shut-off means being disposed directly upstream of the pressurising means with respect to the flow direction of pressurising fluid provided by the pressurising means.