Pumps – Diverse pumps – Moving partition or cylinder of rotary pump forms or...
Reexamination Certificate
2000-09-29
2002-05-07
Vrablik, John J. (Department: 3748)
Pumps
Diverse pumps
Moving partition or cylinder of rotary pump forms or...
C418S225000
Reexamination Certificate
active
06382924
ABSTRACT:
The present invention relates to a mechanically driven roller vane pump used for operating an automatic transmission for motor vehicle in particular a continuously variable transmission (CVT)
BACKGROUND OF THE INVENTION
The roller vane pump comprises a pump housing, a carrier having a substantially circular cross section and being located in the interior of the pump housing, said carrier being rotatable by means of a drive shaft, a ring shaped cam ring having a non-circular inner surface and surrounding the carrier in radial direction, and substantially cylindrical roller elements being slidably provided in slots on the periphery of the carrier. The roller vane pump further comprises at least one feed aperture and at least one discharge aperture, said apertures being arranged in the pump housing and having a substantially elongated shape, the long axes of said apertures extending in a substantially tangential direction. Said apertures are divided into an inner aperture and an outer aperture by a narrow ridge. Said ridge supports the roller elements in axial direction.
On rotation of the carrier, the roller elements interact with an inner surface of the cam ring along contact lines there between, under influence of a pressure and/or a centrifugal force. The spaces between the pump housing, the carrier, the cam ring and the roller elements define pump chambers, which may arrive into communication with hydraulic channels in the pump housing through the feed apertures and the discharge apertures for allowing a flow of fluid to or from the pump chambers. The pump chambers are divided into cam chambers and carrier chambers, said cam chambers ranging from tangential centre planes of the roller elements radially outward, and said carrier chambers ranging from tangential centre planes of the roller elements radially inward, in which the tangential centre plane of a roller element is a plane that extends through the centre line of the cylindrical roller element in axial direction as well as in tangential direction, in other words, a plane that extends substantially parallel to the periphery of the carrier. Each roller element is associated with a leading cam chamber and a trailing cam chamber, the leading cam chamber ranging from a radial centre plane of the roller element in rotational direction, and the trailing cam chamber ranging from said radial centre plane of the roller element in anti-rotational direction, in which the radial centre plane of a roller element is a plane that extends in axial direction through the centre line of the cylindrical roller element as well as through the contact line between the roller element and the cam ring. Thus, a cam chamber that extends between two roller elements acts simultaneously as leading cam chamber for the roller element in anti-rotational direction and as trailing cam chamber for the roller element in rotational direction. As each roller element is associated with on the one side a carrier chamber and on the other side a leading cam chamber and a trailing cam chamber, each carrier chamber corresponds with a leading cam chamber and a trailing cam chamber.
The radius of curvature of the inner surface of the cam ring changes along the circumference of the cam ring. As a result, the volume of each pump chamber varies during rotation of the carrier, in connection with the tangential position of the pump chamber. When the volume of a pump chamber increases, the pressure in that chamber, i.e. the feed pressure, decreases, and fluid is drawn from a reservoir through hydraulic feed channels and the feed apertures into the pump chamber. Consequently, the tangential position of the feed apertures relative to the cam ring is such that the pump chambers arrive into contact with the feed apertures when the pump chamber volume increases. When the volume of a pump chamber decreases, fluid is discharged from said pump chamber through the discharge apertures and hydraulic discharge channels to a user of pressurised fluid, whereby a higher pressure, i.e. a discharge pressure, may be effected. Consequently, the tangential position of the discharge apertures relative to the cam ring is such that the pump chambers arrive into contact with the discharge apertures when the pump chamber volume decreases.
A roller vane pump as described in the above is known from the European patent 0.921.314 and is suitable for pumping automatic transmission fluid in hydraulically controlled and/or operated automatic transmissions for motor vehicles, in particular continuously variable transmissions. In a continuously variable transmission (CVT), such as a belt-and-pulley type CVT, a large flow of fluid may be required for control of the transmission ratio. Since the pump is driven by a shaft drivingly connected to the engine shaft, the pump is designed to be able to provide a desired pump yield, i.e. a desired flow rate at a desired pressure, even at the lowest rotational speed of the engine. On the other hand, the pump is also able to reliably cope with the extremely high pump yield that will be provided at the uppermost rotational speed of the vehicle engine.
Although the known roller vane pump functions satisfactory per se, it possesses the drawback that cavitation is apt to occur inside the known roller vane pump, amounting both to wear of pump parts and to noise generated by the pump.
SUMMARY OF THE INVENTION
At high rotational speeds of the vehicle engine, a high pump yield is provided, i.e. a large flow of fluid is discharged. To enable such large discharge flow, an equally large feed flow must be drawn to the pump. As the flow of the fluid through a feed aperture to a pump chamber is dependent of the level of an underpressure effected in the pump chamber and of the surface area of the respective aperture, wherein the surface area of the apertures in a pump is a constant, the underpressure required for drawing such large feed flow will be large as well, so that cavitation is apt to occur.
An aim of the invention is to reduce the noise generated by the pump and to reduce the wear of pump parts. This aim is, according to the insight underlying the present invention, achieved in enlarging the surface area of the apertures through which fluid is allowed to flow to and from the pump chambers. In particular, this aim is achieved in providing for a modified shape of the ridge, wherein at least one of an inner surface and an outer surface of the ridge extends substantially parallel to the cam ring surface over a substantial part of the tangential dimension of said ridge. At the same pump yield, a larger surface area of the apertures means a less extreme underpressure, i.e. a higher feed pressure in a pump chamber when in communication with the feed channels, which results in a reduction of noise generated by the pump and in a reduction of wear of pump parts. The surface area of the apertures in the known roller vane pump is smaller than said surface area in the pump according to the present invention, because in the known pump the ridge surfaces have the shape of a segment of a circle and extend substantially parallel to the circular periphery of the carrier. With this known shape of the ridge, the distribution of the flows of fluid among the inner aperture and the outer aperture is not well-balanced and not optimal for most tangential positions of the carrier.
In a preferred embodiment of the pump according to the invention, the surface area of the apertures is at a maximum, because the ridges are located such that the radial distance between the centre lines of the ridges and the cam ring surface is substantially equal to the radius of the roller elements. This configuration also provides an optimal axial support of the roller elements by supporting the roller elements centrally and over a maximum possible surface area of the roller elements for a given radial width of the ridges.
Another drawback of the known roller vane pump is that the roller elements are known to intermittently loose contact with the cam ring surface, which is particularly undesirable at the instance the
Van Der Sluis Francis Maria Antonius
Van Spijk Johannes Gerardus Ludovicus Maria
Deveau Todd
Schneider Ryan A.
Troutman Sanders LLP
Van Doorne's Transmissie B.V.
Vrablik John J.
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