Measuring and testing – With fluid pressure – Motor part or auxiliary
Reexamination Certificate
1999-01-27
2001-10-16
McCall, Eric S. (Department: 2855)
Measuring and testing
With fluid pressure
Motor part or auxiliary
C073S118040
Reexamination Certificate
active
06301955
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to an on-board leak detection system for detecting fuel vapor leakage from an evaporative emission space of an automotive vehicle fuel system. More particularly the invention relates to a leak detection system comprising a module that contains a pump and a vent valve which share a common solenoid actuator driven by an electric circuit that produces a drive signal for operating both the pump and the vent valve.
BACKGROUND OF THE INVENTION
A known on-board evaporative emission control system for an automotive vehicle comprises a vapor collection canister that collects volatile fuel vapors generated in the headspace of the fuel tank by the volatilization of liquid fuel in the tank and a purge valve for periodically purging fuel vapors to an intake manifold of the engine. A known type of purge valve, sometimes called a canister purge solenoid (or CPS) valve, comprises a solenoid actuator that is under the control of a microprocessor-based engine management system, sometimes referred to by various names, such as an engine management computer or an engine electronic control unit.
During conditions conducive to purging, evaporative emission space that is cooperatively defined primarily by the tank headspace and the canister is purged to the engine intake manifold through the canister purge valve. A CPS-type valve is opened by a signal from the engine management computer in an amount that allows intake manifold vacuum to draw fuel vapors that are present in the tank headspace and/or stored in the canister for entrainment with combustible mixture passing into the engine's combustion chamber space at a rate consistent with engine operation so as to provide both acceptable vehicle driveability and an acceptable level of exhaust emissions.
Certain governmental regulations require that certain automotive vehicles powered by internal combustion engines which operate on volatile fuels such as gasoline, have evaporative emission control systems equipped with an on-board diagnostic capability for determining if a leak is present in the evaporative emission space. It has heretofore been proposed to make such a determination by temporarily creating a pressure condition in the evaporative emission space which is substantially different from the ambient atmospheric pressure, and then watching for a change in that substantially different pressure which is indicative of a leak.
Two basic types of vapor leak detection systems for determining integrity of an evaporative emission space are: a positive pressure system that performs a test by positively pressurizing an evaporative emission space; and a negative pressure (i.e. vacuum) system that performs a test by negatively pressurizing (i.e. drawing vacuum in) an evaporative emission space.
Commonly owned U.S. Pat. No. 5,146,902 discloses a positive pressure system. Commonly owned U.S. Pat. No. 5,383,437 discloses the use of a reciprocating pump to create positive pressure in the evaporative emission space. Commonly owned U.S. Pat. No. 5,474,050 embodies advantages of the pump of U.S. Pat. No. 5,383,437 while providing certain improvements in the organization and arrangement of a reciprocating pump. The latter patent discloses a leak detection system that comprises an electric-operated pump and an electric-operated vent valve.
SUMMARY OF THE INVENTION
A general aspect of the invention relates to an evaporative emission leak detection system for detecting leakage from an evaporative emission space of a fuel system of an automotive vehicle comprising: a pump comprising a reciprocal pumping mechanism for pumping gaseous fluid with respect to an evaporative emission space; a vent valve that is selectively operable to a first state that vents the evaporative emission space to atmosphere and to a second state that does not vent the evaporative emission space to atmosphere; and an electromechanical actuator for operating both the pump and the vent valve comprising, an electric device comprising an electromagnetic coil for receiving an electric control signal for controlling operation both of the pump and of the vent valve, a first electromechanical coupling operatively coupling the device with the pump such that the pump operation is controlled by the electric control signal, and a second electromechanical coupling operatively coupling the device with the vent valve such that the vent valve operation is controlled by the electric control signal; including an electric circuit providing the electric control signal to the coil wherein the electric circuit comprises a first current path to the coil comprising a controlled conduction device that is connected in series circuit relationship with the coil and is cycled alternately between different states of conductivity to reciprocate the reciprocal pumping mechanism of the pump, and a second current path to the coil comprising an electric circuit component for maintaining a threshold electric current in the coil.
The invention is further characterized by a number of more specific aspects including the controlled conduction device comprising a semiconductor, specifically a field effect transistor; the electric circuit component comprising a resistor; and a sensing circuit that provides a sensed signal for controlling application of a pulse waveform to the controlled conduction device according to pressure sensed in the evaporative emission space.
Another general aspect of the invention relates to an electric circuit for operating a reciprocal pumping mechanism of a pump for pumping gaseous fluid with respect to an evaporative emission space of a fuel system of an automotive vehicle and for operating a vent valve that is selectively operable to a first state for venting the evaporative emission space to atmosphere and to a second state not venting the evaporative emission space to atmosphere, wherein both the pump and the vent valve are operated by respective electromagnetic actuators that share a common electromagnetic coil, the electric circuit comprising: a first current path to the coil comprising a controlled conduction device for connection in series circuit relationship with the coil and cycling alternately between different states of conductivity to reciprocate the reciprocal pumping mechanism of the pump, and a second current path to the coil comprising an electric circuit component for maintaining a threshold electric current in the coil.
Still another general aspect of the invention relates to a method of detecting leakage from an evaporative emission space of a fuel system of an automotive vehicle, the method comprising: operating a pump and a valve from a commonly shared portion of an electromagnet coil that is operated by a driver circuit that comprises a first current path to the coil comprising a controlled conduction device in series circuit relationship with the coil and a second current path to the coil, including cycling the controlled conduction device alternately between different states of conductivity to operate the pump, and maintaining a threshold current in the coil via the second current path.
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PCT Search Report mailed Nov. 18, 1999 for International Application No. PCT/CA99/00068.
Boucher William J.
Cook John E.
Rasokas Raymond
McCall Eric S.
Siemens Canada Limited
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