DE9312128U1 - Air operated disc brake - Google Patents

Description

Knorr-Bremse AG Munich

Air-operated disc brake

The invention relates to a pneumatically operated disc brake according to the preamble of claim 1, which is intended in particular for road vehicles and preferably for commercial vehicles.

Compressed air-operated or pneumatic disc brakes of the generic type are known, for example, from DE-OS 37 16 202 and from the unpublished DE-OS 40 32 885. In these known disc brakes, a brake disc is surrounded by a brake caliper that is mounted so that it can be moved in the radial 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 it, 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 as to be pivotable 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 as to be displaceable with respect to the brake disc and in which at least one adjusting spindle with an external thread is adjustably screwed into an associated internal thread of the cross member, whereby the adjusting spindle is actuated by a pressure piece located at its end on the brake disc side on the

m:KN0704b - 2 - Knorr-Bremse AG

The brake shoe is mounted in the brake calliper on the application side and is movable relative to the brake disc.

The perfect functioning of the disc brake, which is exposed to all kinds of environmental influences, in particular road dirt and moisture, can only be guaranteed if at least the moving parts of the application device are reliably protected from these harmful influences. For this purpose, the application device of the known disc brakes forms an interior that is essentially closed on all sides, with an elastic seal, which is usually a bellows, being arranged between the circumference of each through-opening provided for the passage of the respective adjusting spindle and the circumference of the pressure piece. This ensures that the interior of the application device is reliably sealed despite the functionally necessary through-openings for each adjustment position of the adjusting spindle(s), which changes depending on the pad wear.

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However, such a bellows is at risk of damage, for example when replacing the brake shoes. It is quite possible that a slipping screwdriver or other assembly tool could damage the bellows so badly that dirt or moisture could penetrate into the interior of the adjustment device. Such damage to the bellows, which is usually relatively minor, is very easily overlooked by maintenance personnel. As a result, dirt and moisture penetrate into the interior of the application device, so that the highly sensitive moving parts, such as the thread guide of the adjusting spindle in particular, gradually become so dirty or corroded that the adjusting spindle can no longer be turned, so that the wear adjustment of the disc brake ultimately fails; this inevitably leads to a total failure of the disc brake and thus to brake failure.

m:KN0704b

Knorr-Bremse AG

The invention is based on the object of developing a pneumatically operated disc brake according to the preamble of claim 1 in such a way that even if maintenance is carried out improperly, brake failure can be largely avoided.

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

According to the invention, an additional seal is therefore arranged between the cross member and the circumference of each through-opening of the adjustment device. This ensures that if the outer bellows is damaged, only the already extended areas of the external thread of the adjusting spindle can become dirty or rusty of the functionally necessary moving parts of the adjustment device, while all other parts, such as in particular the areas of the adjusting spindle located inside the adjustment device, are still protected - and thus retain their full functionality. Safe wear adjustment is therefore still guaranteed, so that a total failure of the disc brake can be avoided. Only the next time the pads are changed may it be necessary to replace the adjusting spindles with a spare part or to clean their external threads, which is a negligible factor compared to the possible consequences of a brake failure.

According to the further development of the invention specified in claim 2, the additional seal is designed as an elastic membrane, which according to claim 3 is preferably essentially ring-shaped and is fastened on the cross member side to an annular shoulder formed on the brake disc-side end of the cross member and which surrounds the associated adjusting spindle in an essentially circular manner; this ensures a simple and at the same time very tight fastening.

m:KN0704b

Knorr-Bremse AG

The additional seal according to claim 4 is advantageously fastened to the circumference of the associated through-opening in a substantially annular recess in the circumferential surface, whereby this annular recess according to claim 5 can be used to simultaneously fasten the bellows. The bellows according to claim 6 can be fastened in the annular recess using an expansion clamp in such a way that a clamping fastening for the additional seal can be achieved at the same time. The additional seal according to claim 7 is preferably fastened to the annular shoulder of the cross member using a clamping ring, which is preferably formed by a metal ring fastened to the circumferential end of the additional seal and embedded in its material, the diameter of which is selected so that a press fit is produced on the annular shoulder.

According to a further aspect of the invention, specified in the characterizing part of claim 9, it can be advantageous if a circumferential seal is provided at the brake disc-side exit of each adjusting spindle from the relevant internal thread of the cross member. This ensures that in the event of any damage to the outer bellows, the areas of the adjusting thread that may still be accessible from this side - if there is a correspondingly large thread play - are also securely sealed, so that the adjustment device retains its full functionality under all circumstances. If, due to the arrangement of the cross member within the clamping device, it can be expected that no significant amount of dirt or moisture can reach the moving parts located further inside, it may be possible that such a circumferential seal is sufficient to maintain the functionality of the clamping device even without the measure specified in claim 1.

m:KN0704b - 5 - Knorr-Bremse AG

When using such a circumferential seal, it is preferably designed as a sealing lip, which together with the associated additional seal forms a unit, so that assembly is facilitated and the manufacturing costs are correspondingly low.

The invention is explained in more detail below using the description of embodiments with reference to the drawing.
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Fig. 1 shows the schematic structure of the clamping device in cross section;

Fig. 2 is a longitudinal section of the clamping device shown in Fig. 1 ;

Fig. 3 and 4 are enlarged details of Fig. 2 to explain the structure and position of the additional seal; and

Fig. 5A and 5B are enlarged details of Fig. 4 to explain the structure and position of an additional sealing lip.

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, a (internally ventilated) brake disc 1, which is attached to an axle of a commercial vehicle (not specified in more detail), is surrounded by a brake calliper 2. According to Figure 2, the brake calliper 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 disc 1. In addition,

m:KN0704b - &bgr; - Knorr-Bremse AG

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 caliper 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 to the position indicated in dashed lines in Fig. 1. It should be noted that the rotary lever 4 can of course also be operated via a brake linkage, so that the brake cylinder 40 can be placed at a different location if the available installation space for the disc brake or its application device is limited.

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 calliper 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 calliper 2 at right angles to the plane of the brake disc 1 while maintaining such a play that the cross member 7

m:KN0704b - 7 _ Knorr-Bremse AG

can perform 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 disk 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 7 2 and 7 3 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. The brake shoe 10 is guided in particular in the circumferential direction to the brake disc 1 via brackets (not shown) transverse to the brake disc 1, wherein the brackets can be assigned either to the brake calliper 2 or to a brake carrier.

An adjusting device 74 is arranged inside the adjusting spindle 72, which is coupled to the adjusting spindle 72 in a rotationally fixed manner due to an axial toothing and can be moved in the axial direction. 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.

m:KN0704b -R- Knorr-Bremse AG

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 according to the invention 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 laws of leverage. 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.

If the clearance is too large, which is the case, for example, after a pad change or when the brake shoes become increasingly worn, the adjustment device 74 ensures that the adjusting spindles 72 and 73 rotate until the clearance reaches its target value. This ensures that the disc brake remains functional until the brake shoes 10 are completely worn out.

m:KN0704b - 9 - Knorr-Bremse AG

Fig. 3 and 4 each show an enlarged section of Fig. 2, with Fig. 3 showing the case where the brake pads are still new and therefore have their full lining thickness; the adjusting spindle 72 shown is therefore almost completely screwed into the cross member 7 or is in the "retracted" state. In contrast, Fig. 4 shows the state with medium wear of the brake pads, in which the adjusting spindle has been unscrewed by a corresponding distance from the internal thread of the cross member 7 by the (only schematically indicated) adjusting device 74 due to the correspondingly reduced lining thickness. From a comparison of Fig. 3 and 4 it is clear that a bellows 90 sealing a through opening 21 is easily able to adapt to the changing opening ratio of the through opening 21 by appropriate unfolding.

The bellows 90 is fastened at one end by means of, for example, a screwable clamping ring (which can be shaped like a hose clamp) to an annular recess in the pressure piece 70, which in turn is detachably coupled to the adjusting spindle 72 via conical support surfaces 714 or 722 and a pin 713, since the pin 713 engages in an associated recess 720 in the pressure piece 70 with the interposition of a spring-shaped clamping device, which is only indicated schematically in the figure. At the other end, the bellows 90 is fastened in a substantially annular recess in the peripheral surface of the through-opening 21, for example by means of an expansion clamp.

The fastening of the bellows 90 can alternatively be carried out by fastening a metal ring to the respective end of the bellows 90, the diameter of which is slightly smaller (fastening on the pressure piece side) or slightly larger (fastening on the crossbeam side) than the outer circumference of the pressure piece or the inner circumference of the recess of the circumferential surface of the through-opening 21. In this case, the assembly of the bellows can be carried out extremely easily by means of a

m:KN0704b - 10 - Knorr-Bremse AG

Preferably, such a metal ring is formed in the material of the bellows 90 during its manufacture, so that corrosion protection of the metal ring is achieved at the same time.
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According to the invention, an additional seal 91 is provided, which is arranged so that it extends between the cross member 7 and the circumference of the through opening 21, as can be seen directly from Figs. 3 and 4. Since the fastening of the additional seal 91 on the cross member side is selected so that the corresponding end of the seal 91 surrounds the lower outlet of the internal thread for the adjusting spindle 72 in close proximity, it is consequently achieved that even if the bellows 91 is damaged, no dirt or moisture can get into the corrosion-sensitive areas of the interior of the clamping device; only those areas of the external thread of the adjusting spindle 72, which are already outside the internal thread of the cross member 7 due to lining wear, are exposed to the dirt or moisture penetrating via the bellows 90. However, any inability to function in these threaded areas caused by this only becomes apparent when the adjusting spindle 72 has to be screwed back again when changing the pads and is now blocked, so that the adjusting spindle 72 may need to be replaced or cleaned. In any case, the adjusting effect of the adjusting spindle 72, which is essential for the safe functioning of the disc brake, is fully retained in this case too, since the unscrewing of the adjusting spindle 72 to be carried out here is based on threaded parts that were previously located within the internal thread, the function of which is still not restricted due to the additional seal 91.

The additional seal 91 is preferably designed as an elastic membrane, the elasticity of which is selected to be at least large enough to compensate for the stroke of the cross member 7 that occurs during braking or clamping; this

m:KN0704b - 11 - Knorr-Bremse AG

However, it only weighs a few millimeters and therefore does not pose any problem.

As can be clearly seen from Fig. 3 and 4, the elastic membrane 91 is essentially ring-shaped and is attached at one end to a correspondingly shaped ring shoulder of the cross member 7, which is essentially ring-shaped and is designed at the end of the cross member 7 facing the brake disc so that it surrounds the internal thread for the adjusting spindle 7 2 at a sufficient distance. A clamping ring or another suitable screw-clamp connection can be used for attachment. However, it is also possible to form a metal ring with a suitably reduced diameter at this end of the membrane 91, possibly integrally inside the membrane material, so that the attachment can be carried out in an assembly-friendly manner by means of a press fit.

The other end of the membrane 91 is preferably secured in the recess provided for the bellows 90 in the peripheral surface of the through-opening 21. In addition to saving the manufacturing costs of an additional recess, this arrangement has the advantage that the membrane 91 can be secured together with the bellows 90 using a single expansion clamping ring, so that assembly is made much easier. If a metal ring is integrally formed in the material of the bellows 90, as explained above, the membrane 91 can be secured in a simple manner by simply inserting this end of the membrane 91 into the recess, whereupon the bellows 90 is pressed in, thereby simultaneously ensuring that the membrane 91 is held securely.

Furthermore, any other suitable fastening for the membrane 91 can be provided, for example by means of corresponding grooves or peripheral edges on the surrounding area of the through hole or the cross member 7, as long as this ensures a firm and tight fit.

m:KN0704b - 12 - Knorr-Bremse AG

In order to ensure that, in the event of damage to the bellows 90, the threaded areas of the adjusting thread accessible via the brake disc-side outlet of the adjusting spindles are not exposed to the risk of contamination or corrosion, it is possible according to a further development of the invention as shown in Figs. 5A and 5B to arrange a circumferential seal, for example in the form of a sealing lip 93, at the respective outlet of the adjusting spindle 72 or 73. As indicated in the figures, this can form an integral or one-piece sealing unit together with the membrane 91, whereby both the assembly effort and the manufacturing costs can be reduced. The area of the sealing lip 93 facing the external thread of the adjusting spindle in question should of course be so elastically deformable that the required smooth running of the thread is guaranteed with sufficiently high tightness.

In the event that only a very narrow gap is formed between the cross member 7 and the surrounding inner area of the clamping device 3 and consequently only a small or barely appreciable amount of dirt or moisture can reach the moving parts further inside, it may be possible to consider providing the circumferential sealing lip 93 without the additional membrane 91 and still maintaining the full functionality of the clamping device. However, in practice the additional membrane 91 will generally be more important for the tightness of the housing of the clamping device 3 than the sealing lip 93.

The bellows 90, the additional membrane 91 and the sealing lip 93 are preferably made of a material that is weatherproof and, if necessary, acid-resistant, so that long-term protection is guaranteed.

m:KN0704b - 12 - Knorr-Bremse AG

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

Claims (11)

m:KN0704a - 1 - Knorr-Bremse AG Knorr-Bremse AGMunich §Protection claims: 1. Pneumatically operated disc brake with a brake calliper (2) comprising a brake disc (1), on one side of which an application device (3) with a pivotably mounted rotary lever (4, 4a) is arranged, which rests by means of an eccentric (6) on a cross member (7) extending parallel to the axis of rotation (25) , which is guided displaceably with respect to the brake disc (1) and in which at least one adjusting spindle (72, 73) is adjustably screwed, which acts via a pressure piece (70, 71) seated at its end on the brake disc side on a brake shoe (10) which is displaceably mounted in the brake calliper (2) on the application side with respect to the brake disc (1) , wherein the application device (3) forms an interior space which is closed on all sides and wherein between the circumference of each through opening (21) provided for the passage of the respective adjusting spindle (72, 73) and the circumference of the pressure piece (70, 71) an elastic seal (90) extends, characterized, that an additional seal (91) extends between the cross member (7) and the circumference of each through opening (21) . 2. Pneumatically operated disc brake according to claim 1, characterized in that each additional seal is designed as an elastic membrane (91) . 3. Pneumatically operated disc brake according to claim 1 or 2, characterized in that each additional seal (91) is essentially annular and is arranged on the cross member side at a point on the brake disc side of the cross member (7). m:KN0704a - 2 - Knorr-Bremse AG formed, the associated adjusting spindle (70, 71) is attached to an annular shoulder which surrounds it in a substantially circular manner. 4. Pneumatically operated disc brake according to claim 3, characterized in that each additional seal (91) is fastened to the circumference of the associated through opening (21) in a substantially annular recess of the circumferential surface. 5. Pneumatically operated disc brake according to claim 4, characterized in that the annular recess of the circumferential surface is provided for the simultaneous fastening of the first-mentioned seal (90) designed as a bellows and the additional seal (91) . 6. Pneumatically operated disc brake according to claim 5, characterized in that the bellows (90) is fastened in the annular recess by means of an expansion clamp in such a way that a clamping fastening for the additional seal (91) can be achieved at the same time. 7. Pneumatically operated disc brake according to one of claims 3 to 6, characterized in that each additional seal (91) is attached to the annular shoulder by means of a clamping ring. 8. Pneumatically operated disc brake according to claim 7, characterized in that the clamping ring is formed by a metal ring fastened to the peripheral end of the additional seal (91) , preferably embedded in the material thereof, the diameter of which is selected such that a press fit is produced on the ring shoulder. 9. Pneumatically operated disc brake according to one of claims 1 to 8, characterized in that at the brake disc-side exit of each adjusting spindle (72, 73) from the m:KN0704a - 3 - Knorr-Branse AG A circumferential seal (93) is located on the relevant internal thread of the cross member (7) . 10. Pneumatically operated disc brake according to claim 9, characterized in that the circumferential seal (93) is designed as a sealing lip. 11. Pneumatically operated disc brake according to claim 9 or 10, characterized in that the circumferential seal (93) together with the associated additional seal (91) forms a unit.