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 collected 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.
During conditions conducive to purging, evaporative emission space that is cooperatively defined by the tank headspace and the canister is purged to the engine intake manifold through a canister purge solenoid valve connected between the canister and the engine intake manifold. The canister purge solenoid valve is opened by a signal from an engine management computer in an amount that allows intake manifold vacuum to draw volatile fuel vapors from the canister for entrainment with the combustible mixture passing into the engine's combustion chamber space at a rate consistent with engine operation 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 their evaporative emission control systems equipped with 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.
It is believed fair to say that there are two basic types of diagnostic systems for determining integrity of the evaporative emission space against leakage.
Commonly owned U.S. Pat. No. 5,146,902 "Positive Pressure Canister Purge System Integrity Confirmation" discloses one type: namely, a system and method for making a leakage determination by pressurizing the evaporative emission space to a certain positive pressure therein (the word "positive" meaning relative to ambient atmospheric pressure) and then watching for a drop in positive pressure indicative of a leak.
The other type makes a leakage determination by creating in the evaporative emission space a certain negative pressure (the word "negative" meaning relative to ambient atmospheric pressure so as to denote vacuum) and then watching for a loss of vacuum indicative of a leak. A known procedure employed by this latter type of system in connection with a diagnostic test comprises utilizing engine manifold vacuum to create vacuum in the evaporative emission space. Because that space may, at certain non-test times, be vented through the canister to allow vapors to be efficiently purged when the CPS valve is opened for purging of the canister, it is known to communicate the canister vent port to atmosphere through a vent valve that is open when vapors are being purged to the engine, but that closes preparatory to a diagnostic test so that a desired test vacuum can be drawn in the evaporative emission space for the test. Once a desired vacuum has been drawn, the purge valve is closed. Leakage is reflected by a loss of vacuum during the length of the test time after the purge valve has been operated closed.
In order for the engine management computer to ascertain when the desired vacuum has been drawn so that it can command the purge valve to close, and for loss of vacuum to thereafter be detected, it is known to employ an electric sensor, or transducer, that measures negative pressure, i.e. vacuum, in the evaporative emission space by supplying a measurement signal to the management computer. It is known to mount this sensor on the vehicle's fuel tank where it will be exposed to the tank headspace. For example, commonly assigned U.S. Pat. No. 5,267,470 discloses a pressure sensor mounting in conjunction with a fuel tank roll-over valve.
In one respect, the present invention is directed to a novel vapor collection canister vent valve that comprises both a device for providing an electric signal related to pressure, either positive, negative, or both, in evaporative emission space during a diagnostic test and an electric actuator for operating the vent valve closed during a diagnostic test.
In another respect, the present invention is directed to a novel evaporative emission control system in which both an electric actuator for closing a vapor collection canister vent valve during a diagnostic test and a device for providing an electric signal related to pressure, either positive, negative, or both, in evaporative emission pressure during a diagnostic test are embodied in a single assembly.
The invention provides a number of important advantages. Use of the inventive valve in an evaporative emission control system reduces the number of connections, both electrical and fluid, that are required to install the valve in a new vehicle in a vehicle assembly plant. Accordingly, less in-plant labor time is needed. Moreover, reliability is improved because fewer connections reduces the probability of a faulty connection with another system component. Because the pressure sensor is now physically disposed on the vent side of the flow path through the canister, it is believed to be less sensitive to pressure fluctuations on the evaporative emission space side of the canister, thereby providing a degree of damping of the pressure signal, while retaining signal accuracy. The inventive valve is well-suited for mass-production fabrication, including the use of automated assembly techniques, thereby providing for cost-effective manufacture. Other advantageous aspects relate to various constructional details of the valve.
The foregoing, along with additional features, advantages, and benefits of the invention, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.