ROLLER VANE PUMP The present invention relates to a mechanically driven roller vane pump used for operating an automatic transmission for motor vehicles, in particular for pumping automatic transmission fluid in a continuously variable transmission (CVT). 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 curved 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 the curved 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. In the known pump, the inner surface more less shows an oval shape. 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 sudden pressure changes are apt to occur inside the known roller vane pump, amounting both to wear of pump parts and to noise generated by the pump.

These sudden pressure changes are at least party caused by the feature that in the known pump the pump chambers arrive in communication with an aperture rather suddenly, as a result whereof the fluid pressure prevailing in a pump chamber abruptly changes to the pressure prevailing in the respective aperture, or more accurately in the

feed or discharge channel respectively associated with said aperture. In other words, during operation a pump chamber arrives into fluid communication with the feed or discharge channel through the feed or discharge aperture, whereby the surface area of the respective aperture available for such fluid communication, almost instantaneously assumes a relatively large value causing an equally instantaneous equalisation of the pressures prevailing in the pump chamber and the respective channel. Moreover, a fluid flow is effected almost instantaneously with the pump chamber and aperture arriving into communication. Consequently, the fluid pressure in the pump chamber changes rather abruptly, which generally results both in wear of pump parts as well as a high level of the noise generated by the pump.

It is remarked that such problem is relatively well known in the technical field of rotary pump design, for instance from FR-A-2.095. 994 or EP-A-0.200. 294. In the art it is suggested as a solution to provide a groove in the pump housing adjoining the pump chamber and connecting to the respective aperture, extending in an anti-rotational direction therefrom. The radial width of the groove progressively increases in rotational direction, starting from approximately zero at the location where the groove starts.

Accordingly, the pressure in a pump chamber may be brought to the level prevailing in the hydraulic channel associated with the respective aperture in a defined and gradual manner by communication through the groove, whereby the groove may act as a hydraulic restriction, impeding sudden pressure communication. As a result said pressure equalisation is dampened, substantially without significant dynamic effects causing sudden pressure fluctuations or vibrations and essentially before the fluid flow to or from the pump chamber starts when the chamber arrives into communication with the actual aperture. A disadvantage of such groove is that it is relatively expensive to manufacture, since it represents an added feature to the pump design and requires accurate manufacturing.

Accordingly it is an aim of the present invention to reduce the noise generated by the pump as well as the wear of pump parts, by providing a gradual pressure equalisation between a pump chamber and an aperture essentially before the fluid flow to or from the pump chamber starts, whereby such aim is achieved in a favourable and relatively easy to manufacture pump design.

According to the invention this aim is achieved in a pump defined according to the characterising portion of claim 1. Such configuration may be manufactured relatively easily, because the mentioned additional and accurate design feature is not required.

The said slit-like opening-like opening may be formed merely by extending the respective aperture and by adequately positioning the thus created end part of the

aperture with respect to the cam ring.

The invention will now be explained in greater detail by providing preferred embodiments with reference to the non-restricting examples of embodiment shown in the figures, in which similar parts are indicated with same reference signs, and in which: figure 1 shows an axial cross section of the inner pump parts of a known roller vane pump; figure 2 shows a radial cross section ll-ll of the pump according to figure I ; figure 3 schematically indicates the use of a roller vane pump according to the invention in a transmission of a motor vehicle; figure 4 shows an axial cross section of the inner pump parts of an embodiment of the roller vane pump according to the invention; figure 5 shows a detail of the pump according to figure 4 showing a preferred embodiment as well as alternatives thereto in more detail.

The figures 1 and 2 show a known roller vane pump 1 provided with a pump housing 2, which pump housing 2 accommodates a substantially cylindrically shaped carrier 3 rotatable by means of a pump shaft 4. The rotational direction is indicated by arrow R. Furthermore, the known pump 1 is provided with a ring shaped cam ring 5 having a curved inner surface 5a that approximates an oval shape and that radially surrounds the carrier 3. On its radial periphery, the carrier 3 is provided with slots 6 extending radially inward from its radially outer surface 3a. Each slot 6 accommodates a cylindrical roller element 7, the roller element 7 being radially movable in the slots 6.

During operation of the pump 1, the volumes of the spaces between the pump housing 2, the carrier 3, the cam ring 5 and the roller elements 7 alternately increase and decease, and therefore said spaces act as pump chambers 8. Said pump chambers 8 comprise carrier chambers 8a and cam chambers 8b, said carrier chambers 8a ranging from tangential centre planes of the roller elements 7 radially inward, and said cam chambers 8b ranging from said tangential centre planes radially outward, in which the tangential centre plane of a roller element 7 is a plane that extends essentially parallel to the periphery of the carrier 3 and through the centre line of said roller element 7. Each roller element 7 is associated with a leading cam chamber 8b and a trailing cam chamber 8b, the leading cam chamber 8b ranging from a radial centre plane of the roller element 7 in rotational direction, and the trailing cam chamber 8b ranging from said radial centre plane in anti-rotational direction, in which the radial centre plane of a roller element 7 is a plane that extends in axial direction through the centre line of said roller

element 7 and through the line of contact between the roller element and the cam ring.

As each roller element 7 is associated with a carrier chamber 8a as well as a leading cam chamber 8b and a trailing cam chamber 8b, each carrier chamber 8a corresponds with a leading cam chamber 8b and a trailing cam chamber 8b.

Along its circumference, the curved inner surface 5a of the cam 5 is provided with feed parts having an increasing radius in the rotational direction R of the carrier 3, so that the volume of a pump chamber 8 passing said feed part increases, discharge parts having a decreasing radius in the rotational direction R, so that the volume of a pump chamber 8 passing said discharge part decreases, and intermediate parts adjoining each of said feed part and said discharge part having a substantially constant radius of curvature, whereby also the fulcrum point of such curvature coincides with the centre of rotation of the carrier, so that the volume of a pump chamber 8 passing an intermediate part is substantially constant. The intermediate parts are provided to prevent direct communication between a feed channel 11 for feeding fluid to the pump chambers 8 and a discharge channel (not shown) for discharging fluid from the pump chambers 8, as well as to allow a smooth transition between the underpressure and the overpressure of fluid present in a pump chamber 8.

The pump housing 2 is provided with feed apertures 9 and discharge apertures 10, for allowing a substantially axial flow of fluid between the pump chambers 8 and a hydraulic channel in the pump housing 2. The feed apertures 9 as well as the discharge apertures 10 have an elongated shape, the long axes of the apertures extending in a substantially tangential direction. Furthermore, the apertures 9,10 partially overlap the pump chambers 8 in axial direction. The tangential position of the apertures 9,10 is associated with the shape of the inner surface 5a of the cam ring, in particular the clearance between the carrier 3 and the cam ring 5, as said clearance is variable as a result of the circular shape of the radial periphery of the carrier 3 and the changing radius of curvature of the inner cam surface 5a. In order for the pump 1 to function properly, the feed apertures 9 are located in the area in which said clearance increases, whereas the discharge apertures 10 are located in the area in which said clearance decreases. Each feed aperture 9 is divided into an inner feed aperture 9a and an outer feed aperture 9b by a narrow ridge 12. The radial position of the inner feed apertures 9a corresponds to the radial position of the carrier chambers 8a, whereas the radial position of the outer feed apertures 9b corresponds to the radial position of the cam chambers 8b. Similarly, each discharge aperture 10 is also divided into an inner discharge aperture 10a and an outer discharge aperture 10b by a narrow ridge 12, the radial position of the inner discharge apertures 10a corresponding to the radial position

of the carrier chambers 8a, and the radial position of the outer discharge apertures 10b corresponding to the radial position of the cam chambers 8b. The narrow ridge 12 serves as an axial support for the roller elements 7.

During operation of the known roller vane pump 1, the carrier 3 is rotated by the pump shaft 4, wherein the roller elements 7 interact with the said inner surface 5a under influence of a centrifugal force, and the volume of each pump chamber 8 increases and decreases alternately. When the volume of a pump chamber 8 increases, an underpressure is effected, and fluid will flow from a fluid reservoir (not shown) through the feed channel 11 and a feed aperture 9 to the pump chamber 8, whereas fluid will be discharged through a discharge aperture 10 and a discharge channel (not shown) to a user of pressurised fluid (not shown) under the influence of an overpressure when the volume of the pump chamber 8 decreases.

The known roller vane pump 1 as depicted in the figures 1 and 2 comprises two feed apertures 9 and two discharge apertures 10, which are alternately provided in the pump housing 2, whereby two pumps are effectively obtained in one pump housing 2.

In figure 3 the preferred application of a pump 20 according to the invention in a transmission 30 particularly suited for application in a motor vehicle 40 is schematically illustrated.

Figure 4 shows an axial cross section of the inner pump parts of an embodiment of the roller vane pump 20 according to the invention. The roller vane pump 20 as depicted in figure 4 comprises a cam ring 5 with a radially inward oriented curved surface 5a comprising two feed parts and two discharge parts, thereby effectively functioning as two pumps. However, the number of feed parts as well as the number of discharge parts does not necessarily have to be two, under the condition that both numbers are at least one. In the roller vane pump 20 both the feed aperture 9 and the discharge aperture 10 comprise an inner 9a, 10a and an outer aperture 9b, 10b respectively.

Figure 4 further indicates the centre of rotation C of the carrier 3 as well as the direction R of such rotation. Also in figure 4 it is shown that both the outer feed aperture 9b, 9c and the inner discharge aperture 10a, 10c are provided with an end part, indicated by reference numerals 9c and 10c respectively, extending in anti-rotational direction of the carrier 3 and having a significantly reduced radial dimension available for fluid communication with respect to that of the main part 9b resp. 10a of the respective aperture 9b, 9c resp. 10a, 10c, such that the surface area available for fluid communication between a pump chamber 8 that arrives in communication with the said end part 9c resp. 10c is relatively small, at least during initial of such communication.

Section A of the pump 20 in figure 4, is shown in figure 5 in more detail. In this detail the edges or, alternatively, boundaries of the outer feed aperture 9b, 9c and of the inner feed aperture 9a are indicated as an axial projection by reference numeral 13. The end part 9c of the outer feed aperture 9b, 9c of the pump 20 according to the invention is shown in detail at the instance immediately before the cam chamber 8b arrives into communication with the end part 9c. Because at such instance the fluid pressure prevailing in said cam chamber 8b is relatively high with respect to the feed pressure prevailing at the location of the outer aperture 9b, 9c, the roller element 7 is forced in rotational direction where it contacts with the carrier 3.

The end part 9c partly overlaps with the cam ring 5 as seen in axial direction and extends in anti-rotational direction from the main part of the outer aperture 9b, such that at the location of the end part 9c a slit-like opening 14 is formed between the said inner surface 5a and the aperture edge 13, whereby a radial width Sw of the slit-like opening 14 is considerably less than a radial width available for fluid communication Aw of the said main part 9b of the aperture 9, e. g. less than 50% thereof. Hereby, the cam chambers 8b arrive into communication with the outer feed aperture 9b, 9c through the slit-like opening 14 during operation of the pump 20. According to the invention the claimed design may be advantageously realised by and outer feed aperture 9b, 9c having an overall radial width Ew at the location of the end part 9c that is less than an overall radial width Mw of the main part of the aperture 9b.

The construction according to the invention represents an advantageously simple and cost effective construction for realising the advantageous effects of a gradual pressure equalisation between the pump chamber 8 and the said feed channel 11 essentially before a fluid flow is effected there between. In the pump according to the invention this last feature expresses itself in that along a first part, as seen in rotational direction, of the tangential extend of the slit-like opening 14 the said curved inner surface 5a has an essentially constant radius of curvature and a fulcrum point that essentially coincides with the centre of rotation C of the carrier 3 such that locally a radial position of the roller elements 7 remains essentially constant.

Also shown in figure 5 are alternatives embodiments of the end part 9c and, consequently, of the slit-like opening 14. A first embodiment is indicated by the arc- shaped solid line 13a representing the radially inner edge of the end part 9c of the outer aperture 9b, 9c, whereas dashed lines 15 and 16 respectively indicate alternative embodiments or shapes of said end part 9c, in particular of the radially inner edge thereof that determines the size and shape of the slit-like opening together with the surface 5a of the cam ring 5. In the alternative embodiment defined by the contour of

the inner edge 16, the width in radial direction of the slit-like opening 14 is set approximately constant, which according to the invention was found to be particularly suitable for a continuously variable transmission 30 type application of the roller vane pump 20, wherein the pump 20 must be able to cope with high pressures and a widely variable rotational speed of the carrier 3.

The pump 20 according to the invention may further be provided with a small gap 17 in tangential direction between the roller elements 7 and the carrier 3, as is also illustrated in figure 5. The gap 17 forms a channel through which corresponding cam 8b and carrier chambers 8a are in communication. These small channels contribute to a smoothing of the pressure differences between the said chambers 8a and 8b and allow the gradual pressure equalisation, achieved by adopting the slit-like opening 14 in the cam chamber, to also advantageously influence the pressure prevailing in the carrier chamber 8a resulting in a smaller fluid pressure increase or decrease in such chamber 8a when it does arrive into communication with the inner feed aperture 9a. Thus in, such construction only the outer feed aperture 9b, 9c of the feed aperture 9 needs to be provided with the slit like opening 14 according to the present invention. In a preferred embodiment of the invention the width of the gap 17 in tangential direction is dimensioned such that the rate at which the fluid pressure changes in the cam chamber 8b during operation substantially corresponds to that in the carrier chamber 8a.

According to the invention the width of the gap 17 in tangential direction may also be dimensioned such, that it correspond to a minimum width in tangential direction required for allowing said pressure difference to become approximately zero. It is remarked, that taking a minimum width of the gap 17 for achieving the above mentioned requirements is highly advantageous, because then the amount of tangential movement and the tangential speed of the roller elements 7 is limited, thereby limiting pump noise and wear. A width of the gap 17 in tangential direction having a value in the range from 0.5 to 2.5 percent of a diameter of the roller element 7 was found to be particularly suitable.

In the design of the roller vane pump 20 presently favoured for application in said transmission 30 such range conforms to a width of about 0.04 mm to 0.18 mm.

It will be clear to a person skilled in the art that the scope of the present invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the invention as defined in the attached claims.