Cannister Purge Valve Assembly

This invention relates to a cannister purge valve assembly for a vehicle emission controls valve system.

Existing vehicle emission regulations require that evaporative emissions from the vehicle fuel tank be substantially reduced from current levels. In order to accomplish this reduction in emissions, a cannister is installed on the vehicle and is filled with a desiccant material to absorb vapors which may accumulate in the vehicle fuel tank. However, to minimize the cost of the cannister and the space required for it, a purge valve is necessary. The purge valve normally prevents communication between the fuel tank and the cannister to thereby trap most of the fuel vapors in the fuel tank, but actuates to permit communication between the fuel tank and the cannister when the vapor pressure in the fuel tank rises above a predetermined level. When the vehicle engine is operating, the vapors are purged from the cannister. Other designs for a purge valve of this type have been proposed, but these designs are not able to effectively seal between the various inlets and outlets required on the purge valve housing.

Therefore, an important object of my invention is to provide a cannister purge valve assembly in which a more effective seal between the inlet and outlet of the valve is provided than is available with prior art designs.

Another important object of my invention is to provide a cannister purge valve assembly in which the outlet to the engine intake manifold vacuum and the inlet from the cannister comprise a pair of coaxial tubes which terminate in a substantially coplanar valve setting area which is adapted to be sealingly engaged by a valve diaphragm.

FIG. 1 of the drawing is a cross-sectional view of a purge valve assembly made pursuant to the teachings of my present invention; and

FIG. 2 is a cross-sectional view taken substantially along lines 2--2 of FIG. 1.

Referring now to the drawings, a purge valve assembly generally indicated by the numeral 10 includes a housing 12 having a first inlet port 14 communicated to a cannister assembly 16. The cannister assembly 16 is conventional and includes a simple housing open to the atmosphere in which the fuel vapor absorbing material or desiccant is housed. The housing 12 further includes a second inlet port 18, which is communicated to the sealed fuel tank of the vehicle, and an outlet port 20 which is communicated to engine intake manifold vacuum when the engine of the vehicle is running through the vehicle PCV valve line.

The peripheral edge 22 of a diaphragm 24 is clamped between the upper portion 26 and the lower portion 28 of the housing 12, and divides a chamber 30 defined within the housing 12 into an upper section 32 and a lower section 34. It will be noted that the inlet ports 14 and 18 and the outlet port 20 communicate with the section 34 of the chamber 30, while another port 36 communicates with the upper section 32 of the chamber 30. The port 36 is communicated to the spark port of the vehicle carburetor so that during normal running operation of the vehicle engine (other than at idle), the section 32 will be communicated to a vacuum pressure level.

The inlet 14 and the outlet 20 terminate in a pair of coaxial tubes, which include an outer tube 38 and an inner tube 40 which project into the lower section 34 of the chamber 30. The end 42 of the inner tube 40 is substantially coplanar with the end 44 of the outer tube 38 so that the ends 42, 44 of the tubes 40 and 38 define concentric valve seating surfaces or rings 46, 48. A spring 50 yieldably urges the sealing portion 52 of the diaphragm 24 into sealing engagement with the valve seating surfaces or rings 46, 48 to thereby prevent communication from the lower section 34 of chamber 30 into either the inlet 14 or the outlet 20. The opposite end 54 of the tube 40 terminates in a passage 56 which intersects the outer tube 38.

A flow restricting orifice 60 is provided in the end 54 of the tube 40. The orifice 60 is substantially coaxial with the tubes 40 and 38, and permits limited communication between the inlet 14 and outlet 20 even when the sealing portion 52 of diaphragm 24 sealingly engages the valve seating areas 46, 48.

Various components of the purge valve assembly 10 are illustrated in the drawings in the position which they assume when the vehicle engine is off and when the vapor pressure in the vehicle fuel tank is relatively low. In this condition, both the upper section 32 and lower section 34 of the chamber 30 are at substantially the same pressure, thereby permitting the spring 50 to urge the sealing portion 52 of the diaphragm 24 into sealing engagement with the seating surfaces or rings 46, 48, thereby preventing communication between the inlet 18, the inlet 14, and the outlet 20, except for the limited communication permitted through the orifice 60. If the vapor pressure in the vehicle fuel tank increases to some predetermined level sufficient to overcome the force exerted by the spring 50 of the diaphragm 24, the diaphragm 24 will be urged upwardly, viewing the Figure, thereby permitting communication between the chamber 30 and the inlet 14, thereby venting the vapors in the vehicle fuel tank to the desiccant material in the cannister 16. Excess vapors are absorbed by the desiccant material in the cannister, thereby preventing release of the fuel vapors into the atmosphere.

When the engine of the vehicle is started, the upper section 32 of the chamber 30 is communicated to the vacuum level at the spark port of the carburetor, and the outlet 20 is communicated through the vehicle PCV valve line to the vacuum level at the intake manifold of the vehicle engine. Consequently, because of the pressure differential across the diaphragm 24, the latter will be urged upwardly viewing the Figure, against the bias of the spring 50. Consequently, the cannister 16 will be communicated directly to the vacuum level at the engine intake manifold through the inlet 14, the tube 38, the tube 40, and the passage 56. Since the cannister 16 is also communicated to the atmosphere, atmospheric air will be drawn through the cannister 16, thereby purging the desiccant. Because of the concentric design of the tubes 38 and 40, effective sealing between the sealing portion 56 of the diaphragm 24 and the seating areas 46, 48 is assured when the pressure level in the lower section 34 of chamber 30 does not exceed the pressure level in the upper section 32 of the latter by more than the predetermined amount necessary to overcome the bias of the spring 50. Therefore, during engine-off condition, the inlet 14 and outlet 20 are sealed from the engine fuel tank when the vapor pressure in the latter is relatively low, thereby trapping the vapors in the tank. Consequently the size of the cannister 16 may be much smaller than that which would be required if uninhibited communication was permitted between the fuel tank and the cannister 16.