Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Reexamination Certificate
2001-04-12
2003-02-11
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
C123S516000
Reexamination Certificate
active
06516786
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and an arrangement for controlling the through flow of fluid material especially of venting gases and vapors in a tank-venting system of a motor vehicle having an engine and a fuel supply tank.
Furthermore, the invention relates to a corresponding through-flow control valve as well as a control unit for operating such an apparatus.
BACKGROUND OF THE INVENTION
In motor vehicles, which are driven by internal combustion engines, a venting or aerating of the fuel supply tank is absolutely necessary for a trouble-free fuel flow. When fuel is consumed, air must be able to flow into the tank because otherwise a vacuum would form and the flow of fuel would become intermittent. The tank also has to be aerated to permit the contents of the tank to be able to expand when there is warming. In addition, when tanking, sufficient air must be able to exit from the tank so that the fuel added to the tank does not again bubble out of the fill stub.
In motor vehicles, tank venting systems are increasingly used wherein the vaporizing or excess fuel vapor is not conducted into the ambient but is directed via a venting line into an active charcoal filter. The fuel vapor or the fuel gas is there stored and is supplied during operation of the vehicle via a clocked controllable electromagnetic tank-venting valve to an intake manifold of the engine and therefore to the combustion. The maximum through flow in overcritical pressure relationships in the valve is mostly in the range of 3 to 6 kilograms per hour (kg/h). In this way, an emission of the environmentally-damaging fuel vapor from the tank into the ambient is substantially prevented and, at the same time, the fuel vapor, which is supplied to the engine, is itself utilized as fuel whereby the fuel consumption is significantly reduced at least from time to time.
In such tank-venting systems, the vapor quantity, which flows via the tank-venting valve, is varied, in most instances, in a controlled (open loop or closed loop) manner within pregiven limits in dependence upon the fuel concentration present at a particular time as well as on the then present rpm/load operating point of the engine. An adequately precise meterability of the vapor flow, which flows out via the tank-venting valve, must be guaranteed even for a comparatively low total air flow, which is inducted by the engine. Such a comparatively small total air flow takes place, for example, when the engine is operated at idle. So-called “clocked valves” are preferably used as such valves.
A problem of the known clocked valves with the above-mentioned high throughput is a deficient small-quantity meterability. A through flow of approximately 0.2 kg/h can only be adjusted with a large tolerance of approximately +/−0.1 kg/h. The reason for these large through-flow tolerances lies especially in the naturally occurring draw delay of the valves whose tolerance lies in the range of approximately +/−1 millisecond (ms). The draw delay is the time duration between the electrical drive of the clocked valve and its mechanical opening.
The clock frequency of the valves is the frequency of an electrical drive signal of the clocked valve. This clock frequency of the valve should not drop below 8 Hertz (Hz) in order to especially avoid a defective time-dependent even distribution for the operation of the valve.
A short number comparison should make the relationships somewhat clearer. Assuming the above-mentioned tolerance of +/−1 ms, with two valves with respectively different through flows (or maximum throughputs), a throughput of 0.12 kg/h should be attained. A clock frequency of 10 Hz is assumed for both valves. In one valve having a nominal throughput of 6 kg/h, a mechanical opening duration of the valve of 2 ms results which yields a through-flow tolerance of +/−50% for the assumed draw-delay tolerance. In contrast thereto, for a valve having a nominal throughput of 2 kg/h, a mechanical opening duration of 6 ms results and, therefore, a through-flow tolerance of comparatively only +/−16.6%. The opening duration or open time of a valve is defined as the time duration during which the valve is mechanically opened and a through flow can accordingly take place. The open time is the difference of the drive time and the draw delay already defined above.
With respect to the above tolerances, reference can be made to U.S. Pat. No. 5,873,350 which is incorporated herein by reference.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method and an arrangement of the kind described above wherein a meterability of the through flow as fine as possible for very low throughputs as well as for very high throughputs of fluid substances (gases, vapors, liquids, et cetera) is made possible. At the same time, the arrangement should be manufacturable and operable at favorable costs. The drive of such an arrangement should especially be possible with the least amount of technical complexity and not only with respect to a use in motor vehicles.
The method of the invention is for controlling the through-flow of fluid substances including venting gases and/or vapors in a tank-venting system of a motor vehicle having a fuel supply tank and an internal combustion engine. The method includes the steps of: generating a time-dependent clocked first through flow of a first through-flow amount; generating a time-dependent clocked second through flow with the first through flow being nominally less than the second through flow; and, switching in the second through flow at a time delay relative to the first through flow.
The method of the invention has the steps of generating a first time-dependent clocked through flow as well as at least a second time-dependent clocked through flow. The first through flow is nominally less than the second through flow and the second through flow is switched in delayed in time compared to the first through flow. For short drive times, the method makes possible an exclusive activation of the first through flow which is nominally less than the second through flow and accordingly permits a higher accuracy in the metering of smaller through-flow quantities. The drive time is defined as the time duration for the electrical drive of the clocked valve for opening the valve. With the short drive times (relative to the delay of switching in the second flow), small through-flow rates can be controlled with a high precision. Longer drive times lead to the situation that also the second through flow is activated. only by means of the longer drive times are higher through-flow rates made possible which are controllable with adequately high accuracy referred to these large through-flow quantities. In total, the method of the invention permits a precise through-flow control for low as well as for high through flows or through-flow rates.
With respect to fluid substances, it is noted that these include gases, vapors, liquids or other substances having good flow characteristics.
The arrangement according to the invention includes especially a first through-flow control valve having a first nominal through flow and a second or several through-flow control valves having a second nominal through flow. The first nominal through flow is less than the second nominal through flow. The first and the second through-flow control valves can alternatively define a first and an at least second valve stage of an at least two-stage through-flow control valve.
In addition, control means are provided for the time-dependent delayed driving of the at least second through-flow control valve or of the at least second valve stage relative to the first through-flow control valve or the first valve stage.
For low pulse-duty factors, that is, for relatively short opening durations of a through-flow control valve, the time-dependent delay makes possible the exclusive activation of the smaller of the two nominal through flows, namely, that having the first (smaller) through flow. In this way, a small quantity met
Krimmer Erwin
Mallebrein Georg
Schulz Wolfgang
Schwegler Helmut
Gimie Mahmoud
Ottesen Walter
Robert & Bosch GmbH
Wolfe Willis R.
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