192 clutches and power-stop control – Elements – Engaging surfaces
Reexamination Certificate
2001-06-29
2003-05-20
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Elements
Engaging surfaces
C192S070140, C192S113400
Reexamination Certificate
active
06564919
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a pressure plate for a friction clutch, wherein the pressure plate has at least one friction surface region which can be pressed against a friction facing arrangement of a clutch disk or the like, and wherein the pressure plate is formed at least partially from a first material, and wherein a second material having thermal contact with the first material is provided in the pressure plate at least in some areas.
2. Description of the Related Art
In friction clutches, pressure plates serve to clamp the friction facings of a clutch disk between a flywheel and the pressure plate. In this way, a torque transmission state is produced when the clutch is closed. In order to achieve this result, the pressure plates are acted upon by an energy accumulator, for example, a diaphragm spring, and are pretensioned in the direction of the friction facings and flywheel. During the engagement and disengagement processes, the different surface regions of the friction facings and pressure plate or flywheel enter into frictional engagement with one another resulting in friction heat.
Particularly when the friction clutch is used in a vehicle, heat is guided to one side of the pressure plate on its friction surface during the startup process. The flywheel is also heated on one side, so that the effects, disadvantages and steps described in the following can also apply to the flywheel.
Because of the heating on one side, a temperature difference occurs relative to the other side of the pressure plate which faces away from the friction surface. This temperature difference initially causes an elastic deformation of the pressure plate such that the radial outer area of the pressure plate draws back from the friction surface, so that the average friction radius decreases. This is known as “umbrella deformation”. This umbrella effect causes the pressure plate to deform in the manner of an umbrella such that its radial inner area is pressed in the direction of the flywheel, which means that this area can protrude in axial direction with respect to the radial outer area of the pressure plate.
However, this impairs reliable transmission of the clutch, because the latter can assume an unwanted slip state. Further, during subsequent cooling, the radial outer area of the pressure plate can remain deformed, so that the friction facings wear in a conical manner (usually more on the radial outer side than on the radial inner side).
Previously, in order to counter this problem the pressure plate was made as thick as possible. However, this resulted in a disproportionately heavy and expensive pressure plate. Further, a large space requirement resulted. In another suggested solution, the pressure plate was provided with a concave shape in the cold state. This solution also has a number of disadvantages, for example, inhomogeneous support in the cold state. Another suggestion consisted in providing the pressure plate with a ventilation system for cooling. This solution has the disadvantage that the pressure plates are usually produced from gray cast iron and that there is a poor transmission of heat between gray cast iron and air. Another grave disadvantage is that cooling begins too late to prevent umbrella deformation. It has also been suggested to produce the clutch with a greater diameter. However, this solution has the disadvantage that clutches with large diameters are heavier and more expensive and also have a large space requirement. Further, a larger clutch has an excessive mass moment of inertia, which in turn impedes engine acceleration.
In order to prevent negative effects of this kind which are induced by increased temperature in the friction region, U.S. Pat. No. 6,202,820 suggests a pressure plate for a friction clutch which initially has at least one friction surface region which can be pressed against a friction facing arrangement of a clutch disk or the like. In the friction surface region, the pressure plate is formed at least partially from a first material which ensures that the heat generated by friction is quickly carried away. In a body region adjoining the friction surface region, the pressure plate has a second material which has a high heat absorption capacity for the heat carried away from the friction surface region.
The solution described in the patent ensures that sufficient energy is conducted from the region contacting the friction facings during the engagement and disengagement processes which generally only take up very short periods of time (this means that the generation of heat energy or the conversion of kinetic energy into heat energy will also take place only for a very limited period of time). This energy is occasionally stored temporarily in the body region and is then guided away from the body region to the outside.
SUMMARY OF THE INVENTION
The object of the present invention is to provide another solution by which deformation of the pressure plate caused by heat can be prevented in a simple yet dependable manner.
A pressure plate for a friction clutch is suggested, wherein the pressure plate has at least one friction surface region which can be pressed against a friction facing arrangement of a clutch disk or the like, and wherein the pressure plate is formed at least partially from a first material, and wherein a second material having thermal contact with the first material is provided in the pressure plate at least in some areas. According to the invention, the second material has a different thermal expansion, particularly a greater thermal expansion, than the first material.
In this way, umbrella deformation of the pressure plate under thermal loading can be prevented. For this reason, the pressure plates are constructed so as to be thinner, which is a considerable advantage with regard to cost and the installation space requirement. Further, optimum dependability of transmission of the clutch is ensured at all times.
Due to the second material with a different coefficient of expansion, which will also be referred to in the course of the following description as counter-expansion mass, the friction radius is increased, or its reduction is prevented, over several successive starting processes. The design can be realized in a neutral manner with respect to installation space. Further, common mechanical engineering methods and materials can be used.
A basic idea of the present invention is that a region of the pressure plate is constructed from a second material (e.g., aluminum) which has a different, preferably greater, thermal expansion coefficient than the first material, e.g., gray cast iron, from which the pressure plate is made in part.
In U.S. Pat. No. 6,202,820, frictional heat is guided away as quickly as possible and stored temporarily so that deformations are prevented. For this purpose, the first material has a high thermal conductivity. The friction surface region made from this material is in frictional contact with the friction faces of the clutch disk during the engagement and disengagement processes. Due to the heat-conducting material of the friction surface region, the heat is quickly conducted away into the second material which is in thermal contact with the first material. The second material comprises a material with high specific thermal capacity. Accordingly, it is suitable for storing heat in a particularly effective manner without resulting in negative deformation. The second material must be suitable for intermediate storage of the large quantities of heat occurring briefly during the engagement and disengagement processes without resulting in deformations in the pressure plate. At the conclusion of the engagement or disengagement process, the heat can be given off to the outside.
In the solution suggested according to the invention, deformation due to the occurring friction heat is not eliminated. Instead, the effect achieved by the second material is that a counter-expansion occurs which is controlled via the arrangement, mass and construction of the
Diemer Matthias
Distler Frank
Lorence Richard M.
Mannesmann Sachs AG
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