192 clutches and power-stop control – Elements – Engaging surfaces
Reexamination Certificate
1999-10-21
2001-03-20
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Elements
Engaging surfaces
C192S070140, C192S113210
Reexamination Certificate
active
06202820
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pressure plate for a friction clutch, the pressure plate having a friction-surface region which can be pressed against a friction-lining arrangement of a clutch disk or the like.
2. Discussion of the Prior Art
A pressure plate of this nature is known, for example, from German reference DE 85 12 194 U1. When the clutch is being engaged and disengaged, pressure plates of this nature are moved onto or away from friction linings of the clutch disk by the action of an energy accumulator. During these movement states, there is slippage between the pressure plate and the friction linings, resulting in heating in the area of the friction lining and in the friction-surface region of the pressure plate.
Particularly where there is a tendency to increase the pressure force of such clutches, in order in this way to obtain increased clutch moments, there is also a tendency, when engaging and disengaging the clutch, for the thermal energy generated by the pressure plate and the friction linings rubbing against one another to increase, with the result that the temperature of the various components rises in this area. This may have a disadvantageous effect on the performance of the clutch, since the heat generated may cause various components to be deformed. There is also the risk in particular of reducing the service life of friction linings made from organic materials.
In order to counteract this problem, German reference DE 85 12 194 U1 proposes that a plurality of cooling ribs be arranged on the rear side of the pressure plate, in the form of a ventilator arrangement, so that intensified air circulation is produced in rotational mode, in order to allow the heat to be dissipated more successfully.
A further attempted solution consists in increasing the overall mass of the pressure plate or of the pressure-plate assembly, in order to be able to absorb the heat better. However, this entails increasing the size of the individual components, resulting in construction space problems and increased cost.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a pressure plate for a friction clutch, by means of which it is possible to avoid effects which are induced by an increase in the temperature in the friction area.
In order to achieve this object, the present invention provides a pressure plate for a friction clutch, the pressure plate having a friction-surface region which can be pressed against a friction-lining arrangement of a clutch disk or the like.
The pressure plate according to the invention, in the friction-surface region, is at least partially formed from a first material which provides rapid dissipation of the heat generated by friction. In a body region which adjoins the friction-surface region, the pressure plate according to the invention is formed from a second material which has a high heat absorption capacity for the heat dissipated by the friction-surface region.
In the case of a pressure plate which is constructed in this way, therefore, it is ensured that the heat which is generated when the friction-surface region of the pressure plate comes into frictional engagement with a friction lining is rapidly conducted through the friction-surface region, so that there is no build-up of heat, resulting in an excessively high temperature, in the friction-surface region itself. This heat which is dissipated or conducted onward from the friction-surface region can then be absorbed in the body region and stored for a short time, since this region has a high heat absorption capacity. Since the operations of engaging and disengaging the clutch generally only take up short times, i.e. the generation of thermal energy or the conversion of kinetic energy into thermal energy will also only take place for a very limited time, it is possible, with an arrangement of this nature, to ensure that sufficient energy is dissipated from that region of the pressure plate which comes into contact with the friction linings. This energy, which is temporarily absorbed in the body region, can then be dissipated further outward from the body region.
In order to be able to maintain this removal of thermal energy from the region of the friction linings in a uniform manner, it is proposed for the first material to completely cover that surface region of the pressure plate which can be brought into contact with the friction-lining arrangement or the like.
To maintain the preceding function, it is proposed for the first material to comprise a material with a high thermal conductivity &lgr;. In this case, it is advantageous if the thermal conductivity &lgr; of the first material lies in the range of at least 50 W/mK and higher. By way of example, the first material may comprise aluminum or copper or alloys thereof. This means that alloys which contain a material with good thermal conductivity are also able to achieve the effects described above.
Furthermore, it is advantageous if the second material comprises a material with the high specific heat capacity c. This specific heat capacity c of the second material may be in the range of 0.35 kJ/kg K and higher. By way of example, this second material may comprise gray cast iron or steel.
The capacity to absorb and temporarily store heat which is dissipated from the friction-surface region in the body region, i.e. in the region of the second material, can also be obtained by the second material having a melting point which lies in the range of temperatures which occur in the event of frictional engagement of the pressure plate on a friction-lining arrangement or the like. In an arrangement of this nature, therefore, when thermal energy is generated and dissipated into the body region, the second material is melted, so that at least some of the thermal energy which is conducted into the body region has to be employed for the phase transition and, should the case arise, a remaining amount of the thermal energy then leads to further heating of the melted material. When energy is no longer introduced, the second material solidifies again and, in the process, continuously emits the energy which was previously introduced.
By way of example, the melting point of the second material may lie in the range from 80° C. to 250° C. Recommended examples for the second material are sodium, tin or alloys thereof or non-metallic materials, such as for example salts.
In order to be able to avoid the occurrence of imbalance in the region of the pressure plate even in the molten state, it is proposed for the second material to be contained in at least one chamber provided on the pressure plate.
In this case, for example, the at least one chamber may be essentially completely surrounded by the first material. On the one hand, this allows the introduction of heat into the body region, i.e. into the second material, to take place as quickly as possible, due to the largest possible interfacial region between the two materials. On the other hand, this large interfacial region also has advantageous effects when energy is being emitted from the second material as it solidifies again. In particular, it is ensured that the second material is again adjoined by a layer through which the thermal energy produced during the solidification can rapidly be conducted away by the second material, so that in this case too there is no build-up of heat.
Since the volume of the second material will generally change during the phase transition from the solid phase to the liquid phase, it is proposed for the volume of the at least one chamber to be variable.
Even in an embodiment in which there is no phase transition of the second material, it is advantageous, for the removal of thermal energy from the body region, if a third material, which provides rapid dissipation of the heat stored in the second material, adjoins the body region on that side which is opposite to the friction-surface region and/or radially on the outside and/or radially on the inside.
By way of example, the third material may be th
Orlamunder Andreas
Peinemann Bernd
Cohen & Pontani, Lieberman & Pavane
Lorence Richard M.
Mannesmann Sachs AG
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