PISTON SEAL AND METHOD OF REDUCING FRICTIONAL FORCES OF A PISTON SEAL

A piston seal includes an inner surface configured to extend proximate a perimeter of a piston. Also included is an outer surface disposed proximate a chamber wall, wherein the chamber wall defines a chamber for the piston and the piston seal to translate within. Further included is a first axial side exposed to a first pressure portion of the chamber. Yet further included is a second axial side exposed to a second pressure portion of the chamber. Also included is at least one pressure differential reducing hole extending radially through the piston seal from the inner surface to the outer surface.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIGS. 1 and 2, a pneumatic actuator system10is generally illustrated. The pneumatic actuator system10may be employed in numerous contemplated applications, with one example being a bleed valve system of an aircraft. The pneumatic actuator system10includes a chamber wall12that at least partially defines a chamber14for a piston16to translate within. The piston16may be formed in numerous geometries. In the illustrated embodiment, the piston16is a cylindrical structure. Irrespective of the precise geometry, it is to be understood that the shape of the piston16substantially corresponds to the shape of the chamber14. The piston16is employed to separate and control portions of the chamber14. As one can appreciate, the pneumatic actuator system10, and more particularly the chamber14, may include a plurality of pistons for defining more than two chamber portions.

In the exemplary embodiment, the piston16includes a first side18and a second side20. The first side18is exposed to a first pressure portion22of the chamber14and the second side20is exposed to a second pressure portion24of the chamber14. The pressures within each of the first pressure portion22and the second pressure portion24are distinct, with one pressure being higher than the other. For purposes of explanation, the first pressure portion22is at a higher pressure than the second pressure portion24.

The piston16is dimensioned to provide a gap between a piston outer surface26and the chamber wall12to account for tolerances and positional variance issues associated with manufacturing, thereby ensuring translation of the piston16within the chamber14. A piston seal28is included to seal the above-noted gap. The piston seal28is formed to correspond to the geometry of the piston16. In the illustrated embodiment, the piston seal28is a substantially circular ring that corresponds to the substantially circular piston. Of course, other shapes are possible. The piston seal28may comprise a single, continuous structure that completely surrounds the piston outer surface26, or may comprise a plurality of segments that are spaced around the piston outer surface26. As illustrated inFIG. 2, a break41is provided to define an embodiment comprising a plurality of segments. The break facilitates expansion or contraction of the piston seal28, as required during operation of the pneumatic actuator system10. Alternatively, the piston seal28may include breaks to segment the overall structure, but overlap of the segments is provided to reduce leakage during operation. Irrespective of the precise configuration, the piston seal28is disposed within an annular groove30that extends proximate the piston outer surface26. Specifically, an inner surface32of the piston seal28is disposed in close proximity with an annular groove base wall34.

The piston seal28comprises a first axial side36that is exposed to the first pressure portion22of the chamber14and a second axial side38that is exposed to the second pressure portion24of the chamber14. Additionally, the piston seal28includes an outer surface40that is disposed in close proximity to the chamber wall12. A slight gap is disposed between the outer surface40and the chamber wall12, as is the case with the interface between the inner surface32and the annular groove base wall34. The high pressure fluid imposes a force on the inner surface32and biases the piston seal28radially outwardly into contact with the chamber wall12, thereby causing friction as the piston16translates within the chamber14. The pressure differential between the first pressure portion22and the second pressure portion24also introduces a pressure force on the outer surface40, with the pressure profile along the outer surface40comprising a pressure gradient. The pressure gradient includes lower pressures proximate the second axial side38that is exposed to the second pressure portion24, relative to portions of the outer surface40that are proximate the first pressure portion22. The pressure gradient results in a pressure differential between the inner surface32and the outer surface40.

At least one, but typically a plurality of pressure differential reducing holes42extends radially within the piston seal28from the inner surface32to the outer surface40. The plurality of pressure differential reducing holes42are circumferentially spaced from each other around the piston seal28.

Referring toFIG. 3, a force diagram is illustrated with respect to a cross-sectional portion of a segment of the piston seal28. Specifically, the segment illustrates one of the plurality of pressure differential reducing holes42. As shown, the first pressure portion22of the chamber14is disposed along the first axial side36, while the second pressure portion24of the chamber is disposed along the second axial side38. The high pressure fluid effects the radial location of the piston seal28by interacting with the inner surface32and the outer surface40. The plurality of pressure differential reducing holes42allow fluid coupling, or communication, between the inner surface32and the outer surface40, such that the forces acting on these surfaces are more balanced, relative to a piston seal28without such holes. As illustrated, the plurality of pressure differential reducing holes42facilitates a majority of an axial width44of the outer surface40of the piston seal28having a substantially uniform pressure distribution46, with only a relatively small portion of the outer surface40experiencing a pressure gradient48.

Advantageously, the plurality of pressure differential reducing holes42reduces frictional forces exerted on the piston seal28which provides benefits associated with stability and control. Additionally, a more reliable and predictable displacement model may be established by decreasing hysteresis in the actuator and valve system(s) that the piston is associated with.

A method of reducing frictional forces of a piston seal100is also provided, as illustrated inFIG. 4and with reference toFIGS. 1-3. The pneumatic actuator system10and more specifically the piston seal28have been previously described and specific structural components need not be described in further detail. The method of reducing frictional forces of a piston seal100includes exposing102the first axial side36of the piston seal28to the first pressure portion22of the chamber14. The second axial side38of the piston seal28is exposed104to the second pressure portion24of the chamber14. The method100also includes reducing106a pressure differential between the inner surface32and the outer surface40by fluidly coupling the inner surface32and the outer surface40with at least one, but typically the plurality of pressure differential reducing holes42.