Facing material for wet clutch plate

Abstract: A groove pattern for the paper-based annular friction facing (38) on an annular plate (39) of a clutch plate (41) of a wet clutch to equalize the surface temperature of the friction facing and thus increase the thermal capacity of the clutch where there is continuous slippage. The groove pattern includes one or more continuous annular grooves (42, 43, 44, 45) dividing the friction area into at least three annular bands (46, 47, 48, 49, 50), an inner band (46), at least one intermediate band (47, 48, 49), and an outer band (50), and a plurality of cross grooves (51, 52) in each band which are angled with respect to a radius of the facing. The angled cross grooves extend at an acute angle (a, b), (10-60 degrees) to such radius. Slip of the friction pair of plates causes a viscous pumping action. The cross groove angle in each band of the facing is similar so as to keep all the grooves filled with cooling oil, and the cross-section of the cross grooves vary in their dimensions as between the bands. The angled cross grooves of this pattern also provides viscous pumping of oil through the facing. The annular bands are formed by molding before the facing is bonded to the annular plate, but the cross grooves are preferably formed continuously through the facing in a blanking operation before the facing is applied to the annular plate. When the cross grooves are formed by blanking, the facing is preferably formed with a radially thin runner strip on its outermost periphery to rigidify the facing for ease of handling before it is applied to the annular plate. The runner strip is removed after the facing is applied to the annular plate.

Description: The present invention relates to a rotatable clutch plate for a wet clutch. As is disclosed in US-A-4995500 (Payvar), the clutch plate for a typical wet clutch assembly is made up of an annular plate, usually of a metallic material, with an annular friction facing, usually of a resin-impregnated grade of paper, bonded to each of the opposed faces of the annular plate. The facing material has grooves or other recesses in its outwardly facing surface, and these grooves or recesses define oil flow passages extending from an inside diameter to an outside diameter of the facing. The oil flow passages permit oil within the clutch assembly to flow in contact with the facing of the clutch when the facing is in clutching engagement with the face of an adjacent separator plate, and serve to dissipate heat which will result from such clutching engagement. A grooved clutch plate is also disclosed in DE-A-2042289. A further example of the prior art is featured in EP-A-0447019 which generally discloses a rotatable clutch plate for a wet clutch comprising an annular metal plate and a paper-based annular facing on the metal plate, the facing extending from an outer diameter of the plate towards an inner diameter of the plate, the facing including a plurality of annular grooves dividing the facing into at least three annular bands, an inner band, at least one intermediate band, and an outer band, the facing also including a plurality of circumferentially spaced apart inner band and outer band cross grooves extending at an angle to a radius of the plate, the cross grooves causing viscous pumping of oil across the facing during rotation of the dutch plate. In accordance with the present invention as claimed, the aforesaid generally disclosed rotatable clutch plate is characterised in that the inner band cross grooves extend linearly from an annular inner edge of the facing to the outer band, and the outer band cross grooves extended linearly from an annular outer edge of the facing to the or at least one intermediate band. Typically, the grooves in a clutch plate are machined in the facing material after the facing material is bonded to the annular clutch plate. This is a rather time consuming and expensive manufacturing technique, and the necessary machining tolerances which are applicable to the machining of the grooves limit the depth of each of the grooves to something less than the thickness of the face of the material, to avoid damage to the underlying clutch plate. The limited groove depth, in turn, limits the rate of oil flow through the grooves, for a given groove surface area, and, thus, limits the cooling capacity of the clutch plate. Alternatively, a clutch plate facing can be formed with grooves therein by a moulding operation. However, this also limits the depth of each of the grooves to something less than the thickness of the facing material. In contradistinction a preferred embodiment of the present invention provides a facing material for a wet clutch plate, for example, a clutch plate for a start clutch used in connecting an automotive engine to a transmission of a continuously variable type, an application in which a clutch plate is subject to slippage over an extended period of time, which facing material has full thickness, generally radially extending cross grooves formed therein during a blanking operation, before the facing material is bonded to an underlying clutch plate. A radially thin annular runner portion is provided in the outermost periphery of the facing during the blanking operation to add rigidity to the facing for ease of handling before it is bonded to an underlying clutch plate. This runner portion, which extends beyond the free edge of the underlying clutch plate, is then sheared off after the facing material is bonded to the clutch plate. By blanking the generally radially extending cross grooves, each such groove will extend entirely through the thickness of the facing material to the underlying clutch plate, and this will increase oil flow rates through the cross grooves for a given groove surface area and pattern, and thereby increase the cooling of the clutch plate during its engagement with the separator plate. Further, in the preferred embodiment, each of the cross grooves is inclined at an oblique angle, in the normal direction of rotation of the clutch plate assembly, to a radius of the clutch plate assembly. This orientation of the cross grooves will increase the flow of oil therethrough by utilizing the tangential forces on the oil which will result from the rotation of the clutch plate assembly. Thus, the use of such inclined cross grooves also increases the oil flow through each such cross groove in relation to oil flow through through a radially extending groove of similar width and depth. In order that the invention may be well understood the preferred embodiment thereof, given by way of example, will now be described with reference to the accompanying drawings in which: Fig. 1 is a plan view of a clutch plate according to the preferred embodiment of the present invention; Fig. 2 is a sectional view taken on line 2-2 of Fig. 1; and Fig. 3 is a fragmentary plan view at an enlarged scale of a portion of the clutch plate of Fig. 1 illustrating the angles of the cross grooves with respect to a radius of the facing. A clutch plate, illustrated generally by reference numeral 41, is made up of a metal plate 39 which has an opening or annulus 40 therein and an annular facing 38 bonded to each of the opposed faces of the metal plate 39. Each annular facing 38 is preferably formed from a resin-impregnated grade of paper. The rotation of the present clutch plate 41 of a wet clutch (otherwise not shown) relative to the metal mating face of a mating plate of the clutch produces movement of cooling oil radially from an inner diameter of the clutch plate 41 to the outer diameter thereof. Each of the annular friction facings 38 of the clutch plate 41 has an annular inner edge 54 and an annular outer edge 53 and includes spaced apart, concentric annular grooves 42-45 between and concentric to the edges 54, 53. The annular grooves 42-45 separate the facing 38 into five adjacent annular bands 46-50. In each of the bands 46-50 are a plurality of circumferentially substantially equally spaced interleaved sets of cross grooves 51 and 52 formed in each of the facings 38, preferably by blanking, a forming technique which will ensure that the depth of each of the cross grooves 51, 52 is equal to the thickness of the facing 38. Each of the cross grooves 51 and 52 extends in a direction at angles "a" and "b", respectively, to a radius R of the annular plate 39, as illustrated in FIG. 3. Each of the angles "a" and "b" between the center line of the cross groove extending across the bands 46-50 and the radius R is in the range of 10-60 degrees. As is shown on FIG. 1, there are two types of angled cross grooves 51 and 52: one type 51 extending from the outer diameter 53 into the second annular band 47; the other type 52 extending from the inner diameter 54 into the outermost annular band 50. The angled cross grooves 51 and 52 extending through or into the annular bands 46-50 are equally spaced at an angle of approximately 6° to each other. Oil is pumped through the grooves 51, 52, 42-45 of the clutch plate 41 of a standard wet clutch (not shown) by centrifugal force, and when the clutch plate 41 is stationary, or even when it is operating at a relatively low speed (e.g. under 1000 RPM), there will be an inadequate flow of oil through the grooves for proper cooling. In the absence of oil flow through the grooves, the clutch face temperature will rise and this can lead to hot spots or thermal failure of the clutch facing. Excess temperature will also tend to cause decomposition of the cooling oil. In the present embodiment these effects are avoided principally by the relative slip of the mating friction pair which will cause a viscous pumping action induced by the velocity of the components running parallel to the groove axis. The distribution and design of angled cross grooves 51 and 52 and annular bands 46-50 bring about a substantially uniform temperature of the interface of the wet clutch and provides the clutch with high thermal capacity. Because the grooves 51 and 52 are at angles "a" and "b", respectively, to the radial direction, the relative slip of the mating steel plate causes viscous pumping of the oil through the various grooves. This is important for thermal performance of the groove system. The grooves 51 and 52 across the annular bands 46-50 may vary in one or both of their cross-sectional dimensions to achieve hydraulic balancing and heat transfer area balancing depending upon the design parameters for the clutch. The angled cross grooves 51 and 52 of the preferred embodiment are each of rectangular cross section: one type 51 preferably being approximately 0.76-0.94 mm (.030-,037 inches) deep and approximately 1.14 mm (.045 inches) wide; the other type 52 preferably being approximately 0.76-0.94 mm (.030-.037) inches deep and approximately 2.29 mm (.090 inches) wide. Placing a groove at an angle of 30° to radius R will pump approximately 0.063 litres per second (one U.S gallon per minute) at typical slip speeds between the matching plates of the wet clutch. Typical oil flow of other designs of wet clutch produce approximately 0.15 to 0.20 gallons per minute per clutch face. The present invention provides a marked improvement in cooling of the clutch and thereby improves the thermal capacity. This increases the overall capacity of the wet clutch. It also provides for some oil pumping even when the clutch is not under rotation, and this is especially important in preventing overheating in a CVT start clutch, a type of clutch which is used in relatively slow start applications. Further, the depth of both annular grooves 42-45 and cross angle grooves 51 and 52 may be varied to provide improved recirculation of oil within the grooves. The groove depth may vary between the annular bands 46-50 to achieve balancing of the flow of oil and prevent emptying the grooves of the oil due to centrifugal forces upon rotation of the clutch plate 40. This generally requires the angled groove depth to decrease between the inner band 46 and the outer band 50. The angled grooves 51 and 52 are shown in FIG. 1 in placement so as to aid oil flow from the inner edge 54 of each of the facings 38 to its outer edge 53 for a given direction of rotation of the clutch plate 41. To retard flow of the oil so as to decrease its flow rate through the grooves, or, in the alternative, to reverse the flow from outer edge 53 to inner edge 54 of the facing, the grooves in any or all of the annular bands 46-50 may be angled in an opposite direction with respect to the radius R and the direction of rotation. That is to say if the cross grooves 51 and 52 are placed as shown and the rotation of the clutch plate 41 is in a reverse direction, the pumping action will be reversed its direction. The clutch plate illustrated in FIG. 2 has a facing 38 of a friction material on each of its opposed outer faces. In the alternative, the clutch plate may be provided with single facing 38 depending upon the nature of the clutch and service requirements. In either event, the main principles of this invention will apply. In the manufacture of each of the facings 38, preferably the grooves 51 and 52 are formed therein before the facing 38 is bonded to the annular plate 39. This may be done readily in a blanking operation in which the material originally occupying the grooves 51 and 52 is cut away from the surrounding material of the facing by a mating punch and die, a technique which is known in the manufacture of other types of paper and paper-based products. As previously noted, when such a blanking operation is performed, the depth of each of the grooves 51 and 52 will be the full thickness of the material of the facing 38, in contrast to the formation of grooves in a facing material by machining, or by molding, which requires that the depth of each groove be somewhat less than the full thickness of the facing. The enhanced depth of the grooves 51 and 52, when formed by blanking, as described, and in relation to grooves formed by machining or molding, increases the flow rate of cooling oil through the grooves, for a given groove surface area and configuration. When the grooves 51 and 52 are formed in a facing 38 by blanking, as described, it is useful to provide the original facing 38 with an annular, endless runner strip 60 beyond the finished outside diameter 53 thereof. The runner strip 60 is sheared away from the facing 38 after the facing 38 has been bonded to the annular plate 39, but serves to rigidify the facing 38 and thereby facilitate its handling until the completion of the bonding of the facing 38 to the plate 39. As illustrated in the drawing, the outermost extremity of each of the grooves 51 extends into the runner strip 60. In any case, it is desirable to form each of the annular grooves 42-45 in the facing 38 by molding before the facing 38 has been bonded to the plate 39, or by machining after the facing 38 has been bonded to the plate 39. Groove shape, as well as groove pattern and manufacturing method, can affect shudder during engagement. A square corner groove is less prone to shudder than a rounded compacted edge. When the grooves 51 and 52 are formed by blanking, as described, it is possible to produce a square corner groove rather than a rounded compacted edge of a molded groove. Square corner grooves can also be produced by machining. However, a complex groove pattern such as the one herein described would typically be molded for volume production, not machined. This of course would cause the clutch plate 41 to be more prone to shudder than it is when manufactured according to the preferred embodiment of this invention.

Claims: A rotatable clutch plate for a wet clutch comprising an annular metal plate (39) and a paper-based annular facing (38) on the metal plate (39), the facing (38) extending from an outer diameter (53) of the plate (39) towards an inner diameter (54) of the plate (39), the facing (38) including a plurality of annular grooves (42-45) dividing the facing (38) into at least three annular bands, an inner band (46), at least one intermediate band (47,48,49), and an outer band (50), the facing (38) also including a plurality of circumferentially spaced apart inner band (52) and outer band (51) cross grooves extending at an angle to a radius of the plate (39), the cross grooves (51,52) causing viscous pumping of oil across the facing (38) during rotation of the clutch plate (41), characterised in that the inner band cross grooves (52) extend linearly from an annular inner edge (54) of the facing (38) to the outer band (50), and the outer band cross grooves (51) extend linearly from an annular outer edge (53) of the facing (38) to the or at least one of the intermediate bands (47-49). A clutch plate as claimed in Claim 1, wherein each of the angular cross grooves (51,52) extends at an angle (a,b) to a radius of the plate that is an acute angle. A clutch plate as claimed in Claim 1 or Claim 2, wherein each of the inner band cross grooves (52) connects the inner band (46) of the facing with at least some of the plurality of annular grooves (47-50), and each of the outer band cross grooves (51) connects the outer band (50) of the facing with at least some of the plurality of annular grooves (47-49), at least one of the annular grooves (47-49) being connected with each of the outer band cross grooves (51) and with each of the inner band cross grooves (52). A clutch plate as claimed in any of the preceding claims, wherein the inner band cross grooves (52) and the outer band cross grooves (51) are interleaved with one another. A clutch plate as claimed in any of the preceding claims, wherein the cross-sectional size of each of the inner band cross grooves (52) is greater than the cross-sectional size of each of the outer band cross grooves (51). A clutch plate as claimed in any of the preceding claims, wherein the inner band cross grooves (52) are circumferentially spaced substantially equally and wherein the outer band cross grooves (51) are circumferentially spaced substantially equally. A clutch plate as claimed in any of the preceding claims, wherein the inner band (52) and outer band (51) cross grooves and the plurality of annular grooves (42-45) extend entirely through the thickness of the facing material (38) to the underlying clutch plate (41).

Inventors: FANELLA ROBERT J, GHIDORZI ANTHONY J, HORNICK ROBERT W, LARSON CRAIG S, FANELLA, ROBERT J., GHIDORZI, ANTHONY J., HORNICK, ROBERT W., LARSON, CRAIG S.
Applicants: BORG WARNER AUTOMOTIVE, BORG-WARNER AUTOMOTIVE TRANSMISSION AND ENGINE COMPONENTS CORPORATION
Application year: 1992
Main classification: F16D13
IPC codes: F16D13