DE9312119U1 - Pad wear detector for a compressed air operated disc brake - Google Patents

Description

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Knorr-Bremse AG Munich

Brake wear detector for a pneumatically operated disc brake

The invention relates to a pad wear detector provided for a pneumatically operated disc brake according to the preamble of claim 1.

Generic compressed air-operated or pneumatic disc brakes, for which the lining wear detector according to the invention is provided, are known, for example, from DE-OS 37 16 202 and from the unpublished DE-OS 40 32 885. In these known disc brakes, the main area of application of which is in commercial vehicles, a brake disc is surrounded by a brake caliper that is mounted so that it can move in the axial direction, with a compressed air-operated application device being arranged on one side of the brake caliper, when actuated, a brake shoe located on this side of the brake disc is pressed against the brake disc, whereupon the brake caliper moves in the opposite direction due to the reaction forces and thereby presses a brake shoe located on the opposite side against the brake disc.

The application device in these known disc brakes has a rotary lever as an actuating element, which is mounted so that it can pivot about an axis of rotation running parallel to the plane of the brake disc. The rotary lever rests on its side facing the brake disc by means of an eccentric approximately longitudinally on a cross member extending parallel to the axis of rotation, which is guided so that it can move relative to the brake disc and in which at least one adjusting spindle with an external thread is located in a respective

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because it is adjustably screwed onto the associated internal thread of the cross member, whereby the adjusting spindle acts on the brake shoe, which is mounted on the brake application side in the brake calliper so that it can move relative to the brake disc, via a pressure piece located at its brake disc-sixth end.

In order to keep the clearance, i.e. the distance between the brake shoes and the brake disc in the non-actuated state, constant while compensating for the changing lining thickness due to abrasion, an adjustment device is provided which is coupled to each adjusting spindle in a rotationally fixed manner and which rotates each adjusting spindle by a certain angle each time the rotary lever is operated if the brake shoe is not yet in contact with the brake disc after overcoming the target clearance. Each adjusting spindle is therefore screwed further towards the brake disc by the adjusting device as the lining wear increases. For further details on the structure of such an adjusting device, reference is made to the unpublished DE-OS 40 34 165 and is fully incorporated by reference.

In order to inform the driver at all times about the remaining lining thickness so that a possibly necessary lining change cannot be overlooked, it has already been proposed to provide lining wear detectors that are coupled with a corresponding display device in the driver's cab. The lining wear detectors used to date for pneumatically operated disc brakes are made of sensor elements that are built into the brake lining in such a way that as the brake lining wears away, contacts of the sensor elements are exposed, which cause a corresponding current flow that can be suitably evaluated. A disadvantage of such integrated sensor elements, however, is that they are located in the area of the disc brake where the greatest heat is generated, which can impair reliability through contact erosion.

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Furthermore, the achievable measurement accuracy depends heavily on the respective installation location in the brake pad; finally, the manufacturing costs of the brake pad are also significantly increased by such sensors.
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In the unpublished DE-OS 40 41 318, in order to avoid the problems explained above with contact sensors integrated in the brake pad, it is proposed to use the adjustment device to actuate a rotary encoder, the output signal of which is evaluated as a wear measure. This type of wear detection is based on the idea that the rotary movement of the adjustment device, which is transmitted directly to the spindle(s), is proportional to the adjustment movement of the spindle(s) and thus to the wear measure of the brake pad actuated by the application device. Since the opposite brake pad, pressed against the brake disc by the brake caliper, shows essentially the same wear behavior, the current total wear of the brake pads or the remaining pad thickness can be calculated using the output signal of the rotary encoder.

Although the wear detector known from DE-OS 40 41 318 is characterized by significantly higher accuracy and reliability compared to the contact sensors integrated in the brake pad and also helps to reduce the manufacturing costs of the brake pads, there is a certain disadvantage in that the output signal of the angle of rotation sensor cannot be used directly for a display: The adjustment device rotates the adjusting spindle(s) several times during the entire adjustment cycle, so that the course of the output signal of the angle of rotation sensor repeats itself accordingly often, i.e. the output signal is ambiguous. The display device must therefore be connected via appropriate evaluation electronics, which, for example, generates a

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Counter is appropriately scaled up. However, such evaluation electronics are comparatively expensive and also disadvantageous in that the counter must be reset every time the pad is changed in order to update the display; otherwise the correct pad thickness will no longer be displayed.

EP 0 460 378 A2 discloses a pad wear detector for an S-cam drum brake, in which the application force is applied directly, i.e. without the interposition of a force amplification mechanism, to a lever that actuates an S-cam shaft; such an application device is therefore not suitable for use with compressed air-operated or pneumatic disc brakes of the type in question. The adjustment device of this known drum brake is formed by a rotatably mounted shaft, which has an area provided with a circumferential worm, whereby the circumferential worm engages with a gear and is rotated by a certain amount when pad wear occurs; this causes the shaft to be displaced in the adjustment direction in such a way that the pivot point of the brake lever is displaced by a corresponding amount.

As a result of the above-mentioned operation of the adjustment device of this known drum brake, the adjustment movement distance of the shaft can be used directly as a measure of the lining wear. Accordingly, a distance sensor is provided as a lining wear detector, which records the distance traveled by the shaft; since the shaft has a relatively long bearing area, the distance can be recorded in a relatively simple manner if the distance sensor is placed within the bearing area, so that the lining wear detector can be implemented with little effort. In addition, the

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The signal delivered by the displacement sensor is unambiguous and therefore does not require any further processing by electronics.

The principle of pad wear detection known from EP 0 460 378 A2 cannot, however, be applied to a clamping device of this type, as the adjustment device only performs a rotary movement and does not change its axial position. It could therefore be considered to use the adjustment distance covered by one of the adjusting spindles as a measure of the current wear; however, a corresponding travel sensor would only be possible with great effort due to the thread surface of the adjusting spindle and would also cause problems with regard to installation options and maintainability.

The invention is based on the object of creating a pad wear detector for a pneumatically operated disc brake according to the preamble of claim 1, which is characterized by low manufacturing costs and provides a clearly analyzable measurement signal.

This object is achieved according to the invention with the measures specified in the characterizing part of claim 1.

According to the invention, the adjustment device is therefore coupled to a reduction gear that reduces the total number of revolutions carried out by the adjustment device during the entire adjustment cycle to a maximum of one revolution, with the output of the reduction gear actuating a rotation angle sensor. This ensures that the rotation angle sensor generates a clear, i.e. non-cyclically repeating, detection signal that can be evaluated easily or without the interposition of evaluation electronics. Since a suitable reduction gear is also comparatively cheap and

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Since the assembly including the angle sensor does not cause any significant problems, the lining wear detector according to the invention is also characterized by very low manufacturing costs, which are hardly significant compared to the total costs of the clamping device.

A particularly simple and cost-effective installation of the pad wear detector is ensured according to claim 2 if the adjustment device is directly coupled to the reduction gear with its end facing away from the brake disc. However, it is also possible to provide the reduction gear at another location or, in the case of a two-spindle application device, on the synchronized actuating shaft of the second spindle.

According to claim 3, it is preferably provided that the angle of rotation sensor has a rotary potentiometer; such a rotary potentiometer is not only characterized by low costs, but also has the advantage that the signal generated can be displayed immediately. For example, if the resistance value of the rotary potentiometer is suitably dimensioned, it is possible to connect it to an existing analog display instrument, such as the fuel gauge, using a switch, so that the driver receives a lining wear indicator by simply operating this switch. Since a separate display instrument is therefore superfluous, an extremely inexpensive lining wear indicator is thereby realized. When using such a rotary potentiometer, the reduction factor of the reduction gear is expediently selected so that the revolutions carried out by the adjustment device are reduced to an angle of rotation that essentially corresponds to the complete operating angle of the rotary potentiometer; this is about 300 degrees for common potentiometers. According to claim 4, the output of the reduction gear is preferably connected to the grinder

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of the rotary potentiometer, while its resistance layer is mounted stationary.

Instead of using a rotary potentiometer, the angle of rotation sensor according to claim 5 can also be implemented using an optical or magnetic angle of rotation sensor , in which case the reduction gear should reduce the total angle to a little less than 360 degrees in order to be able to clearly distinguish between the minimum and maximum values of the sensor. According to claim 6, such an angle of rotation sensor can be implemented in a simple manner in that, for example, the output of the reduction gear rotates an optical coding disk or a circumferential surface provided with magnets, which acts on at least one stationary sensor element.

The adjusting spindles of the generic disc brakes are subjected to certain pivoting movements in the brake disc plane during the application process due to the non-play-free bearing, in particular of the cross member. These pivoting movements are also partly transferred to the adjustment device, which is coupled in a rotationally fixed manner; as a result, the reduction gear is preferably mounted in a bearing device according to the further development of the invention specified in claim 7, which supports the reduction gear in a rotationally fixed manner, but while maintaining longitudinal and transverse displacement. This ensures that the pivoting movements mentioned have no influence on the accuracy of the detection signal; in particular, it prevents a noise signal from being superimposed on the detection signal during application, which could possibly lead to an incorrect display. Such a bearing device is advantageously formed according to claim 8 by providing a longitudinally displaceable longitudinal slide, in the middle of which a cross slide is mounted so that it can move transversely, which carries the reduction gear. Preferably, the

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A bearing device formed in this way is attached to a housing cover, which simultaneously serves to protect the detector. The features of claim 8 are also important and justify protection even without the characterizing features of the invention explained above, since such a bearing for a rotary encoder has not been known to date.

According to claim 10, it is further advantageous if the angle of rotation sensor is designed together with the reduction gear as an integral unit.

A very compact design of the detector according to the invention can be achieved according to claim 11 if a cycloidal gear is used for the reduction gear.

The invention is explained in more detail below using the description of embodiments with reference to the drawing. The drawing shows:

Fig. 1 shows, in cross-section, the schematic structure of the application device of a compressed air-operated (pneumatic) disc brake;
Fig. 2 is a longitudinal section of the clamping device shown in Fig. 1;

Fig. 3 is an enlarged detail of Fig. 2 to explain the basic structure and operation of the pad wear detector;
Fig. 4 is a cross-sectional view of a cycloid reduction gear including a rotary potentiometer operated thereby;

Fig. 5A and 5B two longitudinal sections through the cycloid reduction gear; and
Fig. 6 is a plan view of the bearing device of the cycloidal reduction gear.

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In order to clarify the problem underlying the invention, the basic structure and mode of operation of the generic disc brake and its application device will first be explained in more detail. Although the embodiment of the application device shown has two spindles, it should be noted that the invention can of course also be used with a single-spindle application device.

As can be seen from Figures 1 and 2, an (internally ventilated) brake disk l _r, which is attached to an axle of a commercial vehicle (not specified in more detail), is surrounded by a brake caliper 2, which, according to Figure 2, is mounted on the vehicle by means of a rigid guide bearing 52 and a compensating bearing 51 so that it can be moved axially with respect to the brake disk 1. Otherwise, the structure and function of the brake caliper are known, so that a more detailed explanation is unnecessary.

On the right side of the brake disc 1 in Fig. 1 or the lower side in Fig. 2, a (two-spindle) application device, designated schematically with the reference number 3, is arranged. In the brake calliper 2, an essentially semicircular pivot bearing 30 is provided, the axis of rotation of which runs parallel to the plane of the brake disc 1 and which accommodates the correspondingly rounded area of a rotary lever 4, so that the rotary lever 4 can be pivoted parallel to the plane of the brake disc 1. To actuate the rotary lever 4, a brake cylinder 40, shown only schematically, is provided, which engages with a piston in a suitably shaped recess of an actuating arm 4a of the rotary lever 4. When the brake cylinder 40 is pressurized with compressed air, the actuating arm 4a of the rotary lever 4 is consequently moved from its rest position into the position indicated in dashed lines in Fig. 1.

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The side of the rotary lever 4 facing away from the half-shell-shaped pivot bearing 30 is coupled via an eccentric 6 serving as a cam to a cross member 7 which extends inside the brake caliper 2 essentially parallel to the axis of rotation of the brake disc 1 and is mounted so as to be movable in this plane. At its end facing the brake disc 1, the cross member 7 has a blind hole-like recess which is surrounded by a tubular extension projecting in the direction of the brake disc 1. This extension of the cross member 7 is slidably mounted in a corresponding recess in the brake caliper 2 at right angles to the plane of the brake disc 1 while maintaining such a play that the cross member 7 can carry out slight pivoting movements in the plane of the drawing. A spiral spring 78 is arranged within the recess, which is clamped between the cross member 7 and the end of the brake calliper 2 facing the brake disc 1 and thereby pre-tensions the cross member 7 towards the rotary lever 4.

As can be seen in particular from the longitudinal section of Fig. 2, the cross member 7 has a bore on both sides provided with an internal thread, into which an adjusting spindle 72 or 73 is adjustable and whose external thread, designated 711 in Fig. 3, is guided in a correspondingly shaped internal thread of the cross member 7. At the end of each of the adjusting spindles 72 and 73 facing the brake disk 1, a conically widening pressure piece 70 or 71 is attached. Since the two adjusting spindles 72 and 73 extend perpendicular to the plane of the brake disk 1 due to their arrangement in the cross member 7, the pressure pieces 70 and 71 rest with their flat ends on a brake shoe 10.

Inside the adjusting spindle 72 there is an adjusting device 74 which is coupled to the adjusting spindle 72 in a rotationally fixed manner via an axial toothing, so that the axial adjustment

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the sliding ability of the adjusting spindle 72 is ensured. The adjusting device 74 is rotated by a certain angle each time the rotary lever 4 is actuated, which ensures continuous adjustment of the brake. A gearwheel engages in a corresponding axial toothing of the opposite adjusting spindle 73, which is coupled via a shaft to a synchronization device 75, which rotates the internal gearwheel and thus the spindle 73 synchronously with the adjusting device 74. This ensures that the pressure piece 71 is adjusted synchronously with the pressure piece 70.

In a single-spindle embodiment of the cross member 7, which consequently has only a single adjusting spindle and thus only one pressure piece, the adjusting spindle is arranged, for example, in the middle of the cross member 7, while the eccentric 6 and the bearing of the cross member 7, which has the compression spring, are each provided in duplicate on both sides of the central adjusting spindle.

The working principle of the application device is briefly explained below. When compressed air is applied to the brake cylinder 40, the actuating arm 4a is pivoted to the left as shown in Fig. 1, whereby the eccentric 6 acting on the rotary lever 4 is also moved to the left by a distance reduced in accordance with the lever laws. The cross member 7 is therefore pressed against the preload force of the spiral spring 78 by this distance towards the brake disk 1. The pressure pieces 70 and 71 attached to the cross member 7 via the adjusting spindles 72 and 73 consequently press the brake shoe 10 against the brake disc 1 while overcoming the clearance (which in practice is approximately 0.4 mm). If the actuating arm 4a is pivoted further to the left, the brake calliper moves to the right in Fig. 1 due to the force exerted on the brake disc 1, so that finally the left brake shoe 10 is also pressed against the brake disc 1.

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If the two brake shoes 10 have been moved by a predetermined distance corresponding to a target clearance during the application process explained above, the adjusting device 74 is actuated by the rotary lever 4. If the clearance is set correctly, both brake shoes 10 are in contact with the brake disc 1 at this point. As a result, a slip clutch provided in the adjusting device 74 is activated so that the adjusting spindle 72 and the adjusting spindle 73 synchronized with it are not adjusted. If, on the other hand, the clearance is too large, which is the case, for example, after a pad change or when the brake shoes become increasingly worn, the adjusting spindles 72 and 73 are rotated by the adjusting device 74 by a certain distance and thereby bring the clearance to the target value, if necessary after several actuations of the brake. In this way it is ensured that the disc brake according to the invention remains functional until the brake shoes 10 are completely worn out.

The instantaneous amount of pad wear is detected according to the invention by means of a pad wear detector, the precise structure of which is shown in Fig.3. It should be noted at this point that the pad wear detector, as indicated in Fig.3, is preferably provided at the end of the adjustment device 74 facing away from the brake disc; however, it is also possible in principle to provide the pad wear detector at another location, such as at the end of the shaft coupling the second adjusting spindle 73 to the adjustment device 74 facing away from the brake disc (the end of which is, however, preferably provided with a hexagonal rotary head for resetting the spindles, so that the end of the adjustment device appears to be more suitable for coupling the pad wear detector). In any case, care must be taken that the pad wear detector according to the invention is so

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is coupled in such a way that it detects a rotational movement synchronous to the rotation of the adjusting device.

As can be seen from Fig. 3 and 4, the end of the adjustment device 74 facing away from the brake disc engages by means of a pinion 51 in a corresponding axial internal toothing of a reduction gear 53 in such a way that this is driven with each rotary movement of the adjustment device 74. A rotation angle sensor in the form of a rotary potentiometer 54 is coupled to the output of the reduction gear 53 in such a way that a slider 542 (see Fig. 4) of the rotary potentiometer 54 is rotated by an angle of rotation reduced by the reduction factor of the gear 53. The coupling of the reduction gear 53 and rotary potentiometer 54 is adjusted so that the wiper 542 in the uppermost position of the rotary spindle 74 (“full lining thickness”) touches one end position of a resistance track 541, so that the rotary potentiometer 54 has, for example, the lowest resistance value; on the other hand, the reduction ratio of the gear 53 is selected so that the wiper 542 in the lowest position of the rotary spindle 74 (“brake lining completely used up”) touches the other end position of the resistance track 541, so that the rotary potentiometer 54 has its highest resistance value.

Of course, it is also possible to choose the ratio of the resistance values in reverse, which can be achieved in the same way by swapping the connections of the rotary potentiometer 54, which are led to the outside via a line 55 shown only schematically.

As can be seen in particular from Fig. 5A and 5B, the reduction gear 53 is designed as a cycloid gear, in which the drive shaft coupled to the pinion 51 of the adjustment device 74 acts on an eccentric 531, which drives an internal gear wheel 532 provided with external teeth in an eccentric orbit

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rotates so that only some of its teeth are in engagement with an external gear wheel 533, which has a corresponding internal toothing and at the same time serves as the housing of the gear 53. According to Fig. 5B, the internal gear wheel 532 acts via three pins on three associated holes of an output disk 534, which have approximately twice the diameter; this is coupled to the slider 542 of the rotary potentiometer 54. The structure of such a cycloidal gear is otherwise known, so that a more detailed explanation of its function is omitted. It should be noted, however, that any other gear can be used which has a compact design despite a high reduction factor, such as a planetary gear.

In order to prevent pivoting movements of the adjustment device 74 occurring during the application process from causing a falsification of the output signal of the rotary potentiometer 54, the reduction gear 53 is mounted in a bearing device 52 shown in more detail in Fig. 6, which supports the reduction gear 53 in a rotationally fixed manner, but while maintaining longitudinal and transverse displacement. According to the invention, the bearing device 52 consists of a longitudinally displaceably mounted longitudinal slide 521, in the middle of which a transverse slide 522 is mounted transversely, which in turn supports the reduction gear 53. The bearing device formed in this way is attached to a housing cover 50, which simultaneously serves to protect the lining wear detector. As can be seen from Fig. 6, the longitudinal slide 521 is supported on corresponding, inwardly directed projections of the housing cover 50. For the inventive construction of the bearing device 52, independent protection is also claimed.

Although the bearing device 52, as can be seen from Figs. 3 and 4, is attached to the housing cover 50,

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so that the rotary potentiometer 54 is arranged below the reduction gear 53, it is nevertheless also possible to provide a reverse arrangement if this is advantageous. In any case, the reduction gear 53 together with the rotary potentiometer 54 is preferably designed as an integrated unit, which ensures correspondingly simple assembly and storage.

The rotary potentiometer 54 is connected via line 55 to a display device (not shown in detail) in the driver's cab of the commercial vehicle, so that the driver receives precise information about the respective value of the brake pad thickness, if necessary with the interposition of evaluation or driver electronics. If evaluation electronics are used, it is possible to derive further information from the output signal of the rotary potentiometer 54, such as in particular the value of the clearance or any overheating of the disc brake. In the simplest case, a single signal line can be used to connect the rotary potentiometer 54, with the other contact of the potentiometer 54 being connected to the vehicle ground, so that the signal generated represents the resistance value in relation to the vehicle ground. It is of course also possible to feed both end contacts or also the center tap of the potentiometer 54 to the display device via a double or triple line if this is advantageous for the signal evaluation.

Instead of a rotary potentiometer, another type of angle sensor can be used, such as an optical or magnetic angle sensor, whereby the reduction factor of the reduction gear should be selected so that the total number of revolutions performed by the adjustment device 74 during the entire adjustment cycle is reduced to slightly less than a 360-degree revolution in order to obtain a clear signal.

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Using such a sensor, the output of the reduction gear 53 can be coupled to an optical coding disk or a peripheral surface provided with magnets, which acts on at least one stationary sensor element (light-emitting diode or Hall element). However, both the structure of such an angle of rotation sensor and the signal evaluation are significantly more complex than with the previously described rotary potentiometer, so that this is preferable in practice.

In the embodiment of the application device 3 explained, the force is transmitted by means of a pivoted lever 4, which acts on a cross member 7 via an eccentric; however, the principle of the invention can of course also be used in other application devices, for example in those in which the force is transmitted by means of an expanding wedge or a ball ramp. Likewise, the invention is not limited to the embodiments of the adjusting spindle and adjustment device shown; the reduction gear according to the invention can rather be used in all adjusting elements whose axial position relative to the brake disc is changed by a suitable drive device as the lining wear increases.

With regard to further features and effects of the invention not explained in detail, express reference is made to the figures.

Claims (11)

—i S S S SA 1 * i— Knorr-Bremse AGMunich Protection claims: 1. Lining wear detector for a pneumatically operated disc brake, which has a brake calliper (2) comprising a brake disc (1) , on one side of which an application device (3) is arranged, which acts via at least one adjusting spindle (72, 73) and a pressure piece (70, 71) seated at its brake disc-side end on a brake shoe (10) which is mounted displaceably in the brake calliper (2) on the application side with respect to the brake disc (1) , wherein an adjusting device (74) coupled in a rotationally fixed manner to the adjusting spindle (72, 73) keeps the air gap, which changes as a result of lining wear, essentially constant, characterized, that the adjusting device (74) is coupled to a reduction gear (53) which reduces the total revolutions performed by the adjusting device (74) during the entire adjusting cycle to a maximum of one revolution and whose output actuates a rotation angle sensor (54) . 2. Lining wear detector according to claim 1, characterized in that the end of the adjusting device (74) facing away from the brake disc is coupled to the reduction gear (53) . 3. Lining wear detector according to claim 1 or 2, characterized in that the angle of rotation sensor has a rotary potentiometer (54) , the reduction factor of the reduction gear (53) being selected such that the total number of revolutions performed by the adjustment device (74) during the entire adjustment cycle is reduced to an angle of rotation which essentially corresponds to the full m:KN0711a _ϕ #.,.- 2. ₉ - ,. ,, _##t , Knorr-Bremse AG * * « « «« « . » constant operating angle of the rotary potentiometer (54) . 4. Lining wear detector according to claim 3, characterized in that the output of the reduction gear (53) is coupled to a wiper (542) of the rotary potentiometer (54) . 5. Lining wear detector according to claim 1 or 2, characterized in that the angle of rotation sensor (54) has an optical or magnetic angle of rotation sensor, the reduction factor of the reduction gear (53) being selected _such that the total number of revolutions performed by the adjustment device (74) during the entire adjustment cycle is reduced to slightly less than a 360-degree revolution. 6. Lining wear detector according to claim 5, characterized in that the output of the reduction gear (53) rotates an optical coding disk or a circumferential surface provided with magnets, which acts on at least one stationary sensor element. 7. Lining wear detector according to one of claims 1 to 6, in particular according to the preamble of claim 1, characterized in that the reduction gear (53) is mounted in a bearing device f5.2,1 which supports the reduction gear (53) in a rotationally fixed manner, but while maintaining longitudinal and transverse displacement. 8. Lining wear detector according to claim 7, characterized in that the bearing device (52) is formed from a longitudinally displaceably mounted longitudinal slide (521) , in the middle of which a transverse slide (522) is mounted transversely displaceably, which carries the reduction gear (53) . m:KN0711a ,&idgr;*··;- £'-»*% «'%**·? Knorr-Bremse AS 9. Lining wear detector according to claim 7 or 8 , characterized in that the bearing device (52) is fastened to the inner wall of a housing cover (50) . 10. Lining wear detector according to one of claims 1 to 9, in particular 7 to 9, characterized in that the angle of rotation sensor (54) and the reduction gear (53) are designed as an integral structural unit. 11. Lining wear detector according to one of claims 1 to 10 , characterized in that the reduction gear (53) is a cycloidal gear.