Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
2003-02-03
2004-11-23
Garber, Charles D. (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
C702S051000
Reexamination Certificate
active
06820467
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and an arrangement for checking the tightness of a vessel and especially of a tank-venting system of a motor vehicle.
BACKGROUND OF THE INVENTION
Vessels must be regularly checked as to their tightness in the most different areas of technology. For example, vessels for liquid or gas are checked in the chemical processing industry and tank systems are checked in the motor vehicle industry.
Because of more stringent statutory requirements for the operation of internal combustion engines, it will be necessary to provide control arrangements in motor vehicles wherein also fuels such as gasoline are utilized and this control arrangement must be able to detect an existing leak of the magnitude of 0.5 mm in the tank or in the total fuel system utilizing on-board means.
A method of this kind for checking the tightness of a tank-venting system of a motor vehicle is disclosed, for example, in U.S. Pat. No. 5,890,474. In this method, a back pressure is formed in the region between an electrically operated pump and a reference leak. The back pressure reduces the pump rpm and simultaneously increases the electric current drawn by the pump. For checking, the current increase when pumping against the preconnected reference leak with reference to the idle current of the pump is compared to the current increase which results relative to the idle current when pumping into the tank. Tank leakages having an opening cross section of less than that of the reference leak lead to the reference current, which was determined previously, being exceeded; whereas, leaks having cross sections greater than that of the reference leak do not cause the current to increase so far.
It can take some minutes until the backpressure, which is required for a tank measurement, is built up in dependence upon the tank volume and the tank fill level which corresponds to the backpressure when pumping against the reference leak. Because the tightness check takes place during after-running (that is, when the engine is switched off), the battery of the motor vehicle is loaded by the long diagnosis time.
SUMMARY OF THE INVENTION
It is an object of the invention to improve upon the method mentioned initially herein for the tightness check of a vessel so that the diagnosis time is reduced. This vessel can be especially a tank-venting system of a motor vehicle.
The basic idea of the method of the invention is to reduce the diagnosis time as well as the pressure level at which measurements are made by changing the pumping power of the pressure source during a reference measurement and/or during a diagnosis measurement.
In an advantageous embodiment of the method, the pumping power of the pressure source is reduced during the reference measurement, whereupon (preferably during an early phase of the diagnosis measurement) the pumping power is increased over a pregivable time interval. After the elapse of the time interval, the pump power of the pressure source is reduced to the level present before the increase. The advantage here is that for generating the pressure introduced at reduced pumping power, a lesser air volume is required than at higher pressures whereat reference and diagnostic measurements are carried out known to the state of the art. In order to be able to introduce this lower air volume rapidly, the pumping power of the pressure source during the diagnostic measurement is increased over a pregiven time interval and after the elapse of this time interval, the pumping power is again reduced to the level in advance of the increase.
In a further advantageous embodiment of the method, a comparison of characteristic variables of the pressure source takes place on the basis of the reduced pumping power of the pressure source. In experiments, it has been determined that a significant shortening of the diagnostic time is achieved when the pressure source is driven at increased pumping power for the duration of the buildup of the reduced pressure during the diagnostic measurement. The characteristic variables are determined at reduced pumping power.
If the conclusion is drawn as to a pressure not sufficiently great for the diagnostic measurement for the result from the comparison of the characteristic variables at reduced pumping power, then, in another advantageous embodiment of the method, the pumping power is again increased over at least a pregivable time interval during the diagnostic measurement. In this way, the pressure buildup is significantly accelerated, whereby a further shortening of the diagnostic time is achieved.
In an advantageous embodiment of the method, the particular time intervals are determined in dependence upon the fill level and the volume of the vessel. In this way, the required air volume is precisely determined. From this air volume and the increased pumping power per time interval, the required length of the time interval (over which this air volume is introduced into the vessel at increased pumping power), can be pregiven with high accuracy. In this way, it is prevented that the required air volume and therefore the required pressure are exceeded because of a too long an operation of the pressure source at increased pumping power.
With respect to the change of the pumping power and the determination of characteristic variables, the most different configurations of the method are conceivable.
An advantageous embodiment of the method provides that the pumping power of at least an electrically-driven pump is changed in that the pump voltage is varied and that at least one pump current and/or at least one pump pressure is determined as a characteristic variable. In this way, already existing components can be used for carrying out the method and only minor technical changes need be made.
In a further embodiment, the pump voltage is varied in that the electrically operated pump is clock driven whereby, for example, a very precise adjustment of the pumping power takes place with a variation of the drive pulse duty factor.
An arrangement according to the invention for carrying out the method for checking the tightness of a vessel includes at least one means for changing the pumping power of the pressure source during a charge of the reference leak and/or of the vessel with pressure. It is advantageous that with this means, the diagnosis time and the pressure level are reduced by changing the pumping power.
In a preferred embodiment, this means is realized cost effectively and technically simply via at least one resistance which can be switched in and out in a current loop of an electrically-driven pressure source and/or by at least one means for clocking the at least one supply voltage of this pressure source. It is advantageous that only a resistance or switching means are to be mounted in or at a control unit which is anyway available. A control of the switching means and the detection of the pressure source current take place with existing components, especially by programming these components in a control unit.
In a further advantageous embodiment, a switching means for selectively connecting an electrically-operated pressure source to at least one of at least two different supply voltages is provided for changing the pumping power.
The supply voltages can be provided in different ways. Two supply voltages can be realized, especially in a motor vehicle with a two-voltage on-board electrical system, in a cost effective and technically simple manner. Since the two voltages are anyway available, only the supplementing of the arrangement by a switch for selectively connecting the pressure source to one of the two supply voltages is required.
REFERENCES:
patent: 3872712 (1975-03-01), Westervelt et al.
patent: 4441357 (1984-04-01), Kahn et al.
patent: 4523452 (1985-06-01), Brayman
patent: 5890474 (1999-04-01), Schnaibel et al.
patent: 6131550 (2000-10-01), Fritz et al.
patent: 6615808 (2003-09-01), Streib
Garber Charles D.
Ottesen Walter
Robert & Bosch GmbH
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