Roller vane pump

Abstract: The invention relates to a roller vane pump for operating an automatic transmission for motor vehicles. The pump is provided with a pump housing (12), a rotor (4), a cam ring (2) and roller elements (7), which define a number of pump chambers (13). Fluid is communicated between a hydraulic channel (24) and a pump chamber (13) through suction ports (11 and 16) and discharge ports (17 and 18). According to the invention a circumference segment (30) of the pump rotor (4) in between two subsequent slots (6) is an essentially straight line as seen in axial direction.

Description: The invention relates to a roller vane pump used for operating an automatic transmission for motor vehicles and in particular for pumping automatic transmission fluid in a continuously variable transmission. The pump is provided with a pump housing, a rotor located in the pump housing and rotatable by means of a drive shaft, a cam ring located around said rotor and roller elements slideably accommodated with some tolerance in slots on the periphery of the rotor. On rotation of the rotor the roller elements interact in a sealing manner with the surface of the cam ring. The cam ring, the rotor, the roller elements and the pump housing define a number of pump chambers, which may arrive in communication with hydraulic channels in the pump housing for allowing flow of fluid to and from the pump-chambers. fluid is communicated between a hydraulic channel and a pump chamber either through one or more suction ports for allowing a predominantly axial flow of fluid to a pump chamber, or through one or more discharge ports for allowing a predominantly axial flow of fluid from a pump chamber. Such a roller vane pump is known from the European patent 0.555.909 and is in particular adapted for pumping of large volumes of fluid particularly automatic transmission fluid, while maintaining a high pressure in a hydraulically controlled and operated continuously variable transmission for motor vehicles. In a continuously variable transmission of the belt-and-pulley type a large amount of fluid at a high pressure is needed to control the transmission ratio and the belt pinching force, even at a low engine speed. 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 even at the lowest rotational speed of the engine. When the pump is operated, the rotor rotates and a low pressure or suction pressure is effected in a pump chamber. Due to the suction pressure fluid is drawn from a hydraulic channel through a suction port or ports into a pump chamber. The flow of the fluid is dependent of said suction pressure and of the surface area of the suction port or ports. Inside a pump chamber, fluid is compressed and subsequently discharged through a discharge port to a hydraulic channel. Although the known pump functions satisfactory per se, it possesses certain drawbacks. Both the amount of wear of pump parts and the level of noise generated by the pump are not optimal. The aim of the invention is to optimise the known pump by reducing at least one of wear of pump parts and noise generated by the pump. This aim is, according to the insight underlying the present invention, achieved in providing for a modified rotor, the modification being such as to effect an increase of the suction pressure and/or a reduction of the pressure gradient. When a roller element, located in a slot on the periphery of the rotor, has just passed a discharge port, the fluid pressure in a pump chamber in front of that roller element has changed from a high discharge pressure to a much lower suction pressure. The difference between the two pressures is relatively large, as is the pressure gradient associated with said pressure change. Due to said pressure difference and since a roller element is fitted with some tolerance inside a slot, the roller element moves towards the front of the slot as seen in rotational direction of the rotor, where it collides with the rotor generating noise and resulting in wear of the element and of the rotor. Furthermore, inside the known pump the suction pressure becomes low enough for cavitation to occur even at generally occurring pump parameters. Cavitation amounts both to wear of pump parts and to noise generated by the pump, as is commonly known. A pump according to the invention has an improved functionality, since its functional life is prolonged and less noise is generated by the pump during operation. In a first embodiment of the solution according to the invention, a circumference segment of the rotor in between two subsequent slots as seen in axial direction deviates at least partly from a convex shape such, that the surface area of a pump chamber as seen in axial direction is enlarged. According to the invention, said circumference segment is an essentially straight line. According to the invention the radial dimension of the front of a slot may be less than that of the back of the slot, since a roller element interacts only with the front of a slot when it is near the bottom of said slot. In this manner a large additional axial surface area is created, whilst the radial dimension of the back of a slot may be unaffected. To increase the axial surface area even further, said straight line is at least partly oriented radially inward in anti-rotational direction. A rotor according to the invention increases the surface area through which fluid is drawn to a pump chamber, thereby increasing the suction pressure. Therefore, the pressure gradient during pumping is reduced and the occurrence of cavitation is shifted towards a higher pump yield and/or operating temperature. Wear of pump parts and noise generated by the pump is reduced. It is remarked that in US-A-3.734.654 a roller vane pump is disclosed having a cylindrical pump chamber and a rotor provided therein. The rotor is made of molded plastic and on the rotor periphery in between slots substantial voids with central reinforcing ribs are provided. The voids are intended to lower the weight of the rotor thereby reducing the costs in manufacture and in shipping. It is further remarked that in US-A-3.066.608 a slipper-type vane pump is disclosed having a rotor whereof one axial side is provided with tapered notches that extend between the circumference of the rotor and slots for accommodating the slipper-type vanes. A rotor with slots according to the invention reduces the pressure gradient during pumping and the noise generated by the pump is reduced. The invention will now be explained in greater detail with reference to the non-restricting examples of embodiment shown in the figures. Figure 1 shows an axial view of the inner pump parts of a rotary pump according to the state of the art. Figure 2 shows the cross-section II-II of the pump according to figure 1. Figure 3 shows a partial view in axial direction of the inner pump parts with a rotor according to the invention. The rotary pump according to figures 1 and 2 is provided with a pump housing 12 composed of three pump housing parts 1, 8 and 9. The central pump housing part 1 contains a cam ring 2 with a cam surface 2a and a rotor 4 with slots 6, each of which accommodates a roller elements 7 such, that the roller element can slide in a radial direction. The cam ring 2, the rotor 4 and the roller elements 7 define a number of pump chambers 13 in axial direction bounded by the inner surfaces 14 and 23 of the outer pump housing parts 9 and 8 respectively, and which may arrive in communication with hydraulic channels 24 in the pump housing for allowing flow of fluid to and from the pump chambers. The pump is provided with a number of suction ports 11 and 16 and/or discharge ports 17 and 18 for allowing a predominantly axial flow of fluid between a pump chamber 13 and a hydraulic channel 24 in the outer pump housing part 9. The rotor 4 mounted rotatably inside the pump housing 12 is connected to a drive shaft 5 by means of a wedge 3. On rotation of the rotor 4, the volume of a pump chamber 13 varies between a minimum and a maximum value. The three pump housing parts 1, 8 and 9 can be secured to each other by means of bolts that are inserted in holes in the pump housing, e.g. hole 10. With a suitable manufacturing method pump parts can be constructed as a single piece. Figure 3 shows a partial view in axial direction of the inner pump parts with a rotor 4 according to the present invention. The dashed line 29 indicates the convex shape of a rotor 4 according to the state of the art. In the embodiment of the invention shown in figure 3, the circumference segment 30 of the rotor 4 in between two subsequent slots 6 is an essentially straight line, which is inclined radially inward in anti-rotational direction. The rotational direction being indicated by the arrow 34. The dashed area 31 indicates the additional surface area, through which fluid is allowed to flow to a pump chamber 13, thereby effecting a reduction of the suction pressure.

Claims: Roller vane pump for operating an automatic transmission for motor vehicles provided with a pump housing (12), a drivably rotatable rotor (4), a cam ring (2) located around said rotor (4) and roller elements (7) accommodated in slots (6) on the periphery of the rotor (4), wherein the cam ring (2), the rotor (4), the roller elements (7) and the pump housing (12) define a number of pump chambers (13) which may arrive in communication with a suction port (11) at least partly located radially outward from the rotor (4), characterised in that , as seen in axial direction, a circumference segment (30) of the rotor (4) in between two subsequent slots (6) is an essentially straight line, which is oriented radially inward in anti-rotational direction, whereby the radial dimension of the front of slots as seen in the direction of rotation is smaller than the radial dimension of the back of the slots, but larger than two thirds of the latter dimension. Automatic transmission for motor vehicles provided with a roller vane pump according to claim 1.

Inventors: VAN SPIJK JOHANNES GERARDUS LU, VAN WIJK ELIAS, VAN SPIJK, JOHANNES GERARDUS LUDOVICUS MARIA, VAN WIJK, ELIAS
Applicants: DOORNES TRANSMISSIE BV, VAN DOORNE'S TRANSMISSIE B.V.
Application year: 1997
Main classification: F04C2
IPC codes: F04C2, F04C15, F16H61