Clutch pressure plate with backing plate

Abstract: A friction clutch (50) having a friction plate (60) and a pressure plate (58) located within the friction clutch housing (52). The friction clutch has a backing plate (62) that is positioned between the friction plate and the pressure plate with the backing plate being made from a harder material, such as steel, than the pressure plate which is made from a softer material, such as aluminum.

Description: The present invention relates to a pressure plate for a clutch and more specifically to a clutch assembly having a die cast aluminum pressure plate for a friction clutch. Friction type clutches are well known in the art. Friction type clutches generally comprise two discs. The first disc is more substantial and is usually the engine flywheel; the other disk is usually lighter and commonly referred to as the pressure plate. The flywheel is bolted to a flange on the end of the crankshaft, while the pressure plate slides axially on the output shaft. A spring mechanism is used to press the pressure plate against the flywheel. In these general friction type clutches, engine torque is transmitted from the engine flywheel to the pressure plate by the friction between the two abutting faces. Because of this large amount of torque, the surface of the discs need to be formulated from a material having a high coefficient of friction, coupled with good wearing properties. The materials that are used to create these products often are too heavy and too expensive. In other applications, clutch systems are used as part of a transfer case in a four-wheel drive vehicle. The transfer case transmits power (torque) to the front wheels of the vehicle from the rear wheels. The clutch is used to transmit this power from the rear input shaft to the front output shaft. The pressure plate applies the force to the clutch so that it engages and power is transmitted. Methods and apparatus have been used to try to improve transfer case clutch systems and basic clutch systems in general. Some of these prior systems have tried to extend the life of the clutch disks, but they often proved to be too heavy and/or expensive. US-A-5048654 discloses a clutch mechanism in which clutch separator plates made of ceramic material, such as silicon nitride, aluminium oxide or zirconium oxide, are interleaved between clutch friction plates so as to increase the coefficient of friction of the friction plates without substantially increasing the wear of the friction lining by increasing the operating surface temperature of the friction plates. JP-A-60 053224 discloses a clutch mechanism having a pressure plate which is formed of aluminium - silicon alloy which has a high heat conductivity and a relatively high tension strength. A silicon reinforcing layer is formed on a friction surface of the pressure plate which, in use, abuts against a friction forcing of the clutch, whereby it is possible to obtain a compact and lightweight pressure plate which has a high durability. It is an object of the present invention to provide a pressure plate for a friction clutch that is lighter and less expensive than prior friction clutches. Another object of the present invention is to provide a friction clutch that is more durable and operates longer than prior friction clutches and is less expensive to manufacture. Still another object is to provide an improved clutch assembly for a transfer case for a four-wheel drive vehicle. A still further object of the present invention is to provide a transfer case clutch mechanism which has increased transmitted torque. According to the present invention, there is provided a clutch mechanism comprising a housing at least one friction plate positioned in said housing and a pressure plate positioned in said housing which is in communication with said at least one friction plate characterised by a backing plate positioned between said at least one friction plate and said pressure plate, said pressure plate being composed of an aluminium alloy and said backing plate being made of a steel material which is harder than said aluminium alloy. In order, that the invention may be well understood, there will now be described an embodiment thereof, given by way of example, reference being made to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a prior art clutch assembly; Figure 2 is a cross-sectional view of a clutch assembly in accordance with a preferred embodiment of the present invention; Figure 3 is a front view of a pressure plate in accordance with another preferred embodiment of the present invention; Figure 4 is a cross-sectional view of the pressure plate of along the lines 4-4 in Figure 3; and Figure 5 is an enlarged illustration of section A in Figure 4. Figure 1 illustrates a prior art friction clutch referred to generally by the reference number 10. The friction clutch 10 includes a clutch housing 12, which contains a clutch hub 14, a thrust washer 24, a pressure plate 18, and a plurality of friction plates 20. The clutch 10 is used to engagingly connect the adjacent ends of two coaxial shafts, such as an input shaft (not shown) in communication with the left side 22 of the pressure plate 18 and the hub 14, and an output shaft (not shown) in communication with the clutch housing 12. In operation, the input shaft (not shown) causes the pressure plate 18 to rotate via the hub 14 and the input shaft can be moved laterally to put pressure on the pressure plate 18. The pressure plate 18 is attached to the hub 14 by splines 26 or the like. The friction plates 20 are also attached to the clutch hub 14 by splines 28 or the like and they are also caused to rotate. The friction plates 20 allow slipping between themselves and the pressure plate 18 until they are both rotating at the same speed. The friction plates 20 are in communication with the output shaft (not shown) via the housing 12 and therefore drive the output shaft. Figure 2 illustrates a preferred embodiment of the present invention. The clutch assembly of the preferred embodiment is generally referred to by reference number 50. The clutch assembly 50 includes a clutch housing 52, which houses a clutch hub 54, a thrust washer 56, a pressure plate 58, a plurality of friction plates 60, and a backing core plate 62. Although the drawings illustrate 11 friction plates, it should be understood that more or less friction plates may be utilized. The pressure plate 58 of the preferred embodiment is manufactured from a die cast aluminum alloy, preferably 380 alloy. However, other aluminum alloys may also be used as well as other forming or machining processes. The aluminum pressure plate 58 of the present invention is approximately 1/3 the weight of conventional pressure plates that are manufactured from powdered metal. Additionally, the aluminum part is far less expensive to manufacture than the prior powdered metal pressure plates. Another advantage of using aluminum is its non-magnetic properties. Since it is non-magnetic, it does not absorb any of the magnetic flux from the engaging mechanism. As a result, greater force can be applied on the clutch which increases the transmitted torque. Aluminum is known for its softness and thus was not thought to be applicable for use in these applications because of the high friction forces and torque involved. It was previously thought that the aluminum would deform and thus would need to be replaced if it was subjected to clutch types of loads. However, a finite element analysis done on the aluminum pressure plate formed in accordance with the preferred embodiment demonstrated that the maximum VonMises stress was below the fatigue strength of the material indicating that the part would not fail under repeated loading. A pressure plate made in accordance with the present invention was also tested on an MTS stroker machine with repeated loading of 14 235 N (3200 lbs). Two samples were tested and no visible failure occurred in either sample within a million cycles. The part was checked every 300,000 cycles. The test was continued on one of the samples until failure was observed. Cracks were first observed after 50.1 million cycles. In conventional friction clutch transfer cases, the pressure plate 58 has force exerted on it by a ball cam mechanism (not shown). The pressure plate 58 in turn exerts this force to the multiple friction plates 60 in the clutch. The friction plates 60 of the present invention help to transfer torque from the input shaft (not shown) to the clutch housing 52 and then to the output shaft (not shown) through the use of a chain drive. The torque imparted to this output shaft is proportional to the force exerted by the pressure plate 58. In order to prevent friction wear to the aluminum part under constant slip conditions, a backing core plate 62 is preferably positioned between the pressure plate 58 and the first friction plate 60. An alternative arrangement can also be made with the friction plates turned in the other direction with the friction material on the side away from the pressure plate. As a result, the aluminum pressure plate rubs only with the steel side of the friction plate preventing any wear. The core backing plate 62 is preferably manufactured from steel or any other suitable material that is harder than the pressure plate 58. The core backing plate 62 is attached to the clutch hub 54 by splines 64 or the like. Torque tests with the core backing plate 62 inserted between the pressure plate 58 and the friction plate 60 have shown zero wear on the aluminum pressure plate. The core backing plate 62 adds additional strength to the friction plate 58 and thus the clutch assembly 50. Moreover, as the torque from the hub is imparted directly to the core backing plate 62, the spline 26 for the pressure plate 58 is no longer needed. As shown in Figures 3 through 5, the pressure plate 58 preferably has a plurality of ribs 66 formed on its outer surface 68. The ribs 66 are arranged both perpendicular to the circumference of the plate and also circular with different radii. The intersection of the ribs 66 form a plurality of pockets 70 in the surface of the plate. The ribs help to strengthen the pressure plate 58. By use of the aluminum pressure plate 58, the clutch assembly will be lighter and the cost of the clutch assembly will be lower. The lighter weight could also contribute to better vehicle fuel efficiency.

Claims: A clutch mechanism (50) comprising a housing (52); at least one friction plate (60) positioned in said housing (52); and a pressure plate (58) positioned in said housing (52) which is in communication with said at least one friction plate (60); characterised by a backing plate (62) positioned between said at least one friction plate (60) and said pressure plate (58), said pressure plate (58) being composed of an aluminium alloy and said backing plate (62) being made of a steel material which is harder than said aluminium alloy. A clutch mechanism (50) as claimed in claim 1, further comprising at least one strengthening rib member on said (66) pressure plate (58). A transfer case including a clutch mechanism as claimed in claim 1 or claim 2.

Inventors: DATTA JAYANTA, DATTA, JAYANTA
Applicants: BORG WARNER INC, BORGWARNER INC.
Application year: 1997
Main classification: F16D13
IPC codes: F16D13