A device and method for signaling differential pressure change occurring during leak testing of an evaporative emission control space in a motor vehicle fuel system. A casing has sensing ports one of which is communicated to a reference pressure, such as atmospheric pressure, and another of which is communicated to sense pressure in the evaporative emission control space. As difference between the reference pressure and the pressure in the control space changes, the net magnetic flux acting on a magnetoresistive sensor changes. The sensor is electrically connected to the vehicle electrical system for signaling the differential pressure. The device may be used for both positive and negative pressure leak testing.
CROSS REFERENCE TO RELATED APPLICATION AND PRIORITY CLAIM
This application claims the benefit of U.S. Provisional Application No. 60/414,513 filed on Sep. 25, 2002 in the name of Gary Everingham and entitled DIFFERENTIAL PRESSURE SIGNALING DEVICE AND METHOD EMPLOYING A MAGNETORESISTIVE SENSOR, which is incorporated by reference herein in its entirety.
A canister has: a canister body including an adsorbent case which is provided with an adsorption chamber filled with an adsorbent and a fuel steam introduction port, a purge port and an air communication port which are communicated with the adsorption chamber; and a filter body. The canister body and the filter body are communicated with each other through a communication passage, in which a leak detection valve is disposed to be detachable through an end opening formed to the communication passage.
A method of diagnosing a fuel tank leak in a fuel tank ventilation system, comprising a fuel tank, an accumulator for fuel vapors and a fuel tank ventilation valve opening out into an intake manifold of an internal combustion engine, wherein the fuel tank, the accumulator and the fuel tank ventilation valve are connected by way of a system of lines and wherein the accumulator has an aeration line with a check valve, the method comprising: immediately before turning off the internal combustion engine, closing the check valve and opening the fuel tank ventilation valve to generate a vacuum in the fuel tank ventilation system; acquiring a vacuum degradation at specifiable points in time when the fuel tank ventilation valve is closed; opening of the check valve in order to bring about a pressure equilibrium with the ambient pressure; renewed closing of the check valve; acquiring a pressure increase emerging over at least a specifiable time interval and determination of a compensation variable; and inference about the presence of a leakage from behavior of the vacuum degradation over time, while taking into account behavior of the compensation variable over time.
