Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Mechanical measurement system
Reexamination Certificate
1998-12-18
2001-07-10
Shah, Kamini (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Mechanical measurement system
C702S033000, C702S105000, C702S113000, C701S067000, C192S03000R
Reexamination Certificate
active
06259995
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for determining wear on the clutch disk of a friction clutch, which is pressed by a pressure plate arranged in the clutch housing, against a flywheel of an internal combustion engine. The invention further relates to a device with which this process can be implemented.
2. Discussion of the Prior Art
In light of the longer maintenance intervals sought by automobile manufacturers, it is desirable to have a device for determining wear on a clutch lining, so that the clutch disk can be exchanged in a timely manner, without any visual examination being needed in the meantime. It is conceivable either to continually determine, check and display the friction lining wear, or else to determine only a maximum permissible wear limit that, when reached, is displayed via a signal device.
For clutches in commercial vehicles, it is helpful to know the state of clutch wear, because unforeseen downtime results in costs that could have been avoided with better planning. Unpredictable wear-related factors can arise when the clutch is subjected to unusual stress due to other or different drivers or temporarily harder conditions of use.
German reference DE 26 40 088 A1 discloses a device for determining wear on a clutch disk lining, in which the axial position of the pressure plate is detected by a sensor. There is a marking on the pressure plate, which marking consists of two marks that extend in the axial direction of the clutch and are located one after the other in the circumferential direction of the pressure plate and of a third mark that connects the front end of one of the two marks to the rear end of the other mark (i.e., a Z-shape). An inductive sensor is inserted in an opening of the clutch housing. The sensor and the marking are oriented to each other in such a way that when the clutch is closed and the clutch disk lining is new, the effective direction of the sensor overlays a center line of the Z-shaped marking. Connected to the sensor is an analysis unit that has a display unit. The marking is located on the edge of the pressure plate so that, when the clutch is rotated, the marking passes in front of the sensor at a uniform distance. The sensor detects three passages. When the friction lining is new, the passage signals are equidistant from each other. When the friction lining becomes worn, the pressure plate, and with it the Z-shaped marking, moves farther in the direction of the flywheel. As a result, the effective direction of the sensor deviates from the center line, and a different chronological passage sequence is detected. From the chronological signal sequence, it is possible, via the electronic analysis unit, to determine the axial movement distance of the pressure plate and thus the wear of the friction lining, which can then be displayed.
Because the marking and the mechanical device to which the marking is attached are subject to mechanical play as well as to the influences of temperature and speed, additional axial movements of the marking occur. These cannot be distinguished from movements that result from wear. In this event, the signals are erroneous and indicate either too much wear or too little wear. In the former case, the clutch will be overhauled prematurely (which may increase maintenance costs only insignificantly). However, in the latter case, the danger exists that the clutch disk will be overhauled too late and that damage will be suffered by the flywheel as the rivets securing the friction linings to the clutch disk work themselves into the flywheel.
German reference DE 29 16 807 A1 discloses a distance sensing device for a friction clutch, in which pins that rest on a compression spring, are let into in the flywheel. The movement of a pin is transmitted via a lever to a ring, which is movable in the axial direction and interacts with a stationary approach switch arranged on the clutch housing. When the clutch is closed, the pins are pressed by the clutch disk against the force of the compression spring into the flywheel. This distance sensing device is intended to determine, particularly in trucks, the exact operational point at which the clutch closes, so as to reduce the operational times of the pneumatic clutch, which can be operated quickly at first and then, after the contact for engagement, can again be operated slowly. With these sensors, wear on the friction lining of the clutch disk upon engagement can be taken into account, but not determined.
SUMMARY OF THE INVENTION
Starting from this problem, it is an object of the present invention to provide a process and a device for the contact-free determination of the friction lining wear of a friction clutch that use, as a measurement variable, the movement distance of the pressure plate that results from wear.
Pursuant to this object, and others which will become apparent hereafter, one aspect of the present invention resides in a process in which:
signals are supplied via a sensor, which is arranged outside the clutch housing and connected to an electronic analysis unit;
the signals are generated in dependence on three detecting elements that rotate with the friction clutch;
a first signal series comprises the pulses supplied when the sensor is passed by two detecting elements, which are arranged at a defined axial distance (X,) to each other and are connected to a first component;
a second signal series comprises the pulses supplied by the third detecting element, which is connected to a second component;
the pulses from the first and second signal series provide information on the axial position of the respective detecting elements relative to the sensor;
in the analysis unit, the actual axial distance (current distance) between the two detecting elements is determined from the first signal series, and then compared with the previously defined axial distance (reference distance), and a correction value is generated from the found difference;
after this, by comparing the pulses of the third detecting element in the second signal series with the pulses of one of the two detecting elements in the first signal series, the axial distance (A
1
) of these two detecting elements to each other is found, and is then compared with the distance (A
0
) between the two detecting elements when the clutch disk is new; and
the wear (V) on the clutch disk is calculated using the equation
V=A
0
−A
1
±&Dgr;
where &Dgr; supplies a correction for at least the temperature influence.
According to this process, first, the correction value is found that determines the temperature or speed influence to which the pressure plate is subject. When the clutch is new, the axial distance between the detecting element and the pressure plate to which the detecting element is connected is definitely fixed. The pulse supplied at axially different points in the sensor reflect this distance. Thus, by comparing the current distance with the reference distance, an error is eliminated that would have resulted in an incorrect conclusion about the wear on the friction lining. The current axial distance between the detecting element connected to the clutch housing, on the one hand, and a detecting element connected to the pressure plate, on the other, is also definitely fixed when the friction lining is in the new state. When this axial distance changes in the course of operation, the axial distance of the pulse emission on the sensor is enlarged. This enlargement in distance allows a conclusion to be drawn about the wear on the friction lining, because the pressure plate, due to wear, is moved with the sensors farther in the direction of the flywheel. By adding or subtracting the correction value, the actual amount of wear is then reproducibly established.
A device for determining the friction lining wear in a friction clutch with a clutch housing and a pressure plate arranged axially movably therein, which pressure plate presses a clutch disk equipped with friction linings against a flywheel of an internal combustion engine, is cha
Amberger Alfred
Hirschmann Frank
Cohen & Pontani, Lieberman & Pavane
Mannesmann Sachs AG
Shah Kamini
Vo Hien
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