192 clutches and power-stop control – Clutches – Axially engaging
Reexamination Certificate
1999-07-09
2001-04-17
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Clutches
Axially engaging
C192S089220, C192S089230
Reexamination Certificate
active
06216839
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to friction clutches, in particular for motor vehicles with internal combustion engines, including a clutch casing, a pressure plate which is guided in a rotationally fixed manner with respect to the clutch casing, at least one clutch disk and a spring device comprising from about 40 to 65% nickel.
2. Background of the Invention
Internal combustion engines provide a torque which can be used for drive purposes only within the speed range between idling speed and nominal speed. Motor vehicles therefore generally require a transmission and a device for separating the engine from the drive train. In the case of manual transmissions, a friction clutch is typically used for this purpose, and this clutch also allows an initially stationary vehicle to be driven off. Friction clutches of the prior art comprise a clutch casing, in which a pressure plate is guided in a rotationally fixed manner and is acted on by spring elements, and at least one clutch disk which in the at-rest state, which in this case is the engaged state, is clamped between the pressure plate and the torque input part as a result of the spring action. The clutch disk, which is connected to the output part, e.g. the transmission shaft, is thus entrained with the pressure plate and the input part as a result of the friction and therefore executes essentially the same rotational movement as the input part and output part. The force generated by the spring devices therefore must not fall below a minimum level in operation, in order for the engine torque to be reliably transmitted. In addition, the elasticity of the spring material is important, since the friction clutch is disengaged by elastic deformation of the spring element or elements. Since the disengagement mechanism is subject to friction, it is often useful for it to be at least partly coated with low-friction, hard materials. The friction clutches of the prior art usually have spring devices made from heat-treated steel, such as for example 50CrV4. The coating of the spring devices with hard material, such as for example chromium, is known, for example, from P 35 42 847.3. However, it has emerged that the spring devices, particularly when used in high-power engines, are heated to temperatures at which these conventional spring device materials may lose their elastic properties and their strength in the high-temperature phase, and under certain circumstances this loss may even be irreversible. Such reversible or irreversible setting losses of the spring elements may reduce the pressure force which they exert. It is therefore necessary to use relatively strong spring devices which ensure high torque transmission even under high thermal loads. A disadvantage, however, is that they also increase the inertial mass.
SUMMARY OF THE INVENTION
An object of the invention is therefore to present a friction clutch in which the spring devices are largely insensitive to heat, and to present a method for producing such spring devices. A further object of the invention is to describe a suitable coating material for the spring material and to present a method for coating the spring material with the coating material. According to the invention, these and other objects are achieved by means of a friction clutch which is designed in particular for use in the drive train of a motor vehicle and which comprises a clutch casing, a pressure plate which is guided in a rotationally fixed manner with respect to the clutch casing, at least one clutch disk and a spring device, and in which clutch at least part of the spring device comprises 40-60% nickel. A nickel content of 50-55%, as specified in a preferred embodiment, has proven particularly advantageous. A further advantageous configuration consists in providing 10-30%, or preferably 15-25%, chromium in the spring device. A preferred embodiment furthermore comprises at least one of the elements iron, niobium and molybdenum. Suitably, the iron content may be 10-30%, the niobium content 2-8% and the molybdenum content 1-6%. Particularly if it is intended for the spring device to be heat treated, the spring device should additionally contain titanium and aluminum, suitably at levels of 0.5-5% and 0.1-5%, respectively.
In the following, suitable spring constructions for spring elements made from the nickel-chromium alloy are described. If there is only a small amount of space available, it may be expedient to design a spring element as a coil spring. This may be advantageous as a of the small amount of space which coil springs require in particular perpendicular to their direction of action. If, on the other hand, the amount of space available is limited in the direction of action, it is recommended for the spring device to be designed as a disk spring. Disk springs require only a small amount of space in their direction of action. Furthermore, their simple form makes their surface easier to treat, for example to produce a surface layer by fusion or electroplating. An advantageous configuration is to use a diaphragm spring as the spring element made from nickel-chromium alloy. Diaphragm springs are disk springs with integrated actuation levers, which have the further advantage that in this case it is possible to dispense with manufacture and assembly of the corresponding actuation devices.
Particularly in the case of the integrated actuation levers of the diaphragm spring, but also in the case of other spring devices, friction may occur when the clutch is engaged and disengaged. It is therefore often desirable for the spring elements to have low-friction, wear-resistant surfaces. One embodiment therefore provides for at least part of the spring-device surface to contain boride. In a preferred configuration, at least part of the spring-device surface consists of boride. Depending on the particular application, boride can be applied to the surface in the molten state, such as for example by means of powder-coating processes, or by electroplating, the former option transmitting higher temperatures to the spring element. This may be advantageous in the case of hot age-hardening nickel-chromium alloys. In other cases, for example if the heating is undesirable, the electroplating option is advantageous. Particular preference is given to a method for coating a nickel-chromium material, which is to be used in particular for coating a nickel-base spring element for friction clutches, and in which method the surface of the component made from nickel-chromium alloy is covered with boron powder and is then heated at 800-1000° C. for 3-7 hours, with the component situated in an inert-gas atmosphere.
Furthermore, in connection with the present invention, a method is proposed for producing a spring device from nickel-chromium alloy in which the spring device is preferably to be used in friction clutches for motor vehicles and in which the method includes a heat treatment of the nickel-chromium alloy. Due to the special thermal properties of nickel-chromium alloys, it may be expedient for the heat treatment to include the shaping of the spring device. An advantageous embodiment of the method according to the present invention provides for the spring device to be clamped into a fixture during the heat treatment, so that it is given the desired shape. In this case, it may be expedient to carry out the heat treatment of the method under an inert-gas atmosphere for at least part of the time. In this case, it may be advantageous to use nitrogen as the inert gas. Furthermore, the method may comprise at least one cooling operation as part of the heat treatment, which cooling operation is expediently carried out using a gaseous coolant. In this case, it may be advantageous to use nitrogen as this coolant. A preferred method comprises the following steps:
a) clamping the spring blank into the fixture
b) heating the clamped spring blank at 900-1000° C. for 0.5-1.5 hours
c) cooling the spring blank to room temperature in a nitrogen atmosphere
d) heating the spring blank at 700-750°
Betten Klaus
Friedrich Horst
Loibersbeck Jurgen
Rudolf Thomas
Cohen & Pontani, Lieberman & Pavane
Lorence Richard M.
Sachs Race Engineering GmbH
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