Under vane valve piston structure

A valve has a sleeve with at least one outlet port in a radially outer surface. A piston is moveable within the sleeve along an axis. The piston has a lip on a radially outer portion extending forwardly to an axially forward most end and a recess radially inward from the lip with respect to an axis of the piston. A vane pump is also disclosed.

BACKGROUND OF THE INVENTION

This application relates to improvements in the piston for an under vane pressure regulating valve.

Vane pumps in compressors are known and, typically, include a plurality of vanes that extend outwardly of a rotor. The vanes are brought into contact with a cam surface of a casing or stator. As the rotor turns, the vanes move radially inwardly and outwardly of the rotor moving an entrapped fluid. The rotor is mounted within the casing. The distance between the outer surface of the rotor and the cam surface changes, such that the vanes are driven inwardly and outwardly, allowing filling and pressurizing of a fluid.

One feature commonly used in vane pumps and compressors is under vane pressure. This assists in biasing a vane outwardly of the rotor.

Valves are known to regulate the pressure of the fluid delivered to the under vane cavities to properly bias the vane. These valves are generally comprised of a valve set, a piston installed into a sleeve, installed into a housing bore. Typically, these valves have had a piston with a flat forward face or sometimes a “nosed” face with a central protrusion. A pressure from fluid in the under vane cavity is placed on this forward face and may move the vane to allow this fluid to communicate with an outlet leading to a pump chamber. Fluids reacting off the flat or “nosed” face and moving toward the outlet have a significant axial component as well as a radial component.

Thus, in the past, contaminants entrained in this fluid have sometimes been forced into a space between a radially outer surface of the piston, and a radially inner surface of a sleeve by pressure delta and fluid forces.

This is undesirable and can lead to valve seizure.

SUMMARY OF THE INVENTION

A valve has a sleeve with at least one outlet port in a radially outer surface. A piston is moveable within the sleeve along an axis. The piston has a lip on a radially outer portion extending forwardly to an axially forward most end and a recess radially inward from the lip with respect to an axis of the piston. A vane pump is also disclosed.

DETAILED DESCRIPTION

A system20is illustrated inFIG. 1and includes a vane pump or compressor22. As known, a rotor24is mounted within a casing26. Vanes28extend radially outwardly of the rotor and contact an inner surface of the casing26. The distance between an outer surface of rotor24and the inner surface of the casing26changes such that the vanes move inwardly and outwardly. A fluid is found in chambers between adjacent vanes and is moved between a fluid inlet and a fluid outlet.

Fluid is tapped into an under vane chamber30to bias the vanes28toward the inner wall of the casing26. In system20, a pressure regulating valve34maintains a desired pressure in the under vane cavity30. As shown, a line32communicates the under vane cavity30to a forward chamber38of the valve34.

A piston40regulates the flow between the chamber38and an outlet port36in a radially outer wall of a sleeve41. A forward end of the piston40includes a radially outer peripheral surface42which is desirably closely spaced from a radially inner surface44of the sleeve41. A forward lip46of the piston40extends to an axially outermost end48. A cupped depression or recess50extends inwardly cylindrical the end48and at radially central regions of the piston40.

As shown, a chamfer51(seeFIG. 2) leads into a side wall52and then to a bottom surface54of the recess50.

As shown in this embodiment, fluid reacting off of the forward face and moving to the outlet36has a much smaller axial component than the prior art.

Thus, contaminants are much less likely to be forced into the space between surfaces42and44.

The recess50affects the shape of a stagnation region60at a center of the piston40. This, in turn, affects the flow stream of fluid such as shown by arrows inFIG. 1through the outlet port36. The fluid moves at an angle A relative to a central axis C along which the piston40moves.

In theFIG. 1piston, the stagnation region60generally includes the area of the recess and, thus, the fluid is directed radially outwardly at an angle much greater than the prior art. As an example, theFIG. 1piston has a fluid flow angle A of between 80 and 90° when measured from the axis of movement of the valve.

As shown inFIG. 3A, one prior art piston100has an outer peripheral surface102spaced from a casing103inner peripheral surface104. The outlet106is positioned similar to theFIG. 1embodiment. The piston100has a flat face108. The stagnation region110is forward of that region. The angle A is approximately 69°. This results in fluid, containing impurities, having a greater likelihood of being forced between the surfaces102and104, which is undesirable.

Similarly, as shown inFIG. 3B, a “nosed” piston120has a forward nose122, and a curving surface124leading to an outer peripheral surface126. The sleeve127has an inner peripheral surface128. The outlet130receives fluid at an angle A. The stagnation regions132and134are forward of the piston surfaces122and124. The angle A in this embodiment may also be approximately 69°. Here again, the likelihood of contaminants moving between surfaces126and128is increased due to this angle, has a greater axial component than theFIG. 1embodiment angle.

With theFIG. 1piston, less contaminants will reach the area between surfaces44and42.