GB2125496A

GB2125496A - Brake adjustment device

Info

Publication number: GB2125496A
Application number: GB08322210A
Authority: GB
Inventors: Wilhelm Hopf
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1982-08-18
Filing date: 1983-08-18
Publication date: 1984-03-07
Also published as: DE3230683C1; FR2532020A1; SE444352B; FR2532020B1; IT8348697A0; IT1172300B; SE8304434D0; GB8322210D0; GB2125496B; SE8304434L

Abstract

An adjusting and centering device on a through-feed lock of an internal expanding brake includes brake shoes 14, 16 each fitted to a bolt 18, 20 which is non-rotatably supported on the shoe and which is screw-threaded through a bush 28, 30 the threaded bushes in turn being guided non-rotatably, but axially adjustably in driving or adjusting elements 32, 34 which are rotatably and slidably mounted in the device 10. On their outer circumference these driving elements 32, 34 carry radial locking teeth 62 cooperating with a spring-suspended ratchet 66, 68 and they can be moved towards each other as far as a stops 54, 60. Movement over the teeth of the ratchet allows the bolt to rotate relative to the threaded bush to take up clearance. <IMAGE>

Description

SPECIFICATION Adjusting and centering device on a through-feed lock of an internal expanding brake.

The invention relates to an adjusting and centering device on a through-feed lock of an internal expanding brake, particularly but not exclusively for motor vehicles.

Adjusting and centering devices of this type are already known from a German Auslegeschriften (Published Patent Applications) 1 2 02 593 and 23 11 166.

Such devices have the advantage, in the event of brake lining wear on one of the brake shoes, of automatically increasing their axial length, relative to their centred position, on the respective side where a greater brake clearance arises in such a manner that this clearance is again compensated for or remains essentially constant on each of the two brake shoes. In this connection the shoes operate in both directions of travel.

A feature common to both the known embodiments is that the adjusting elements, which are equipped with external toothing and which form toothed discs, are fitted on the ends of threaded bushes projecting out of a guide bracket. The engaging elements, which turn both the toothed discs and the threaded bush and which coperate with the teeth of the external toothing, are formed by control tongues which, in one case, are provided on control plates pivotably mounted separately from one another on the guide bracket and, in another case, on a common control plate a separate spring arrangement being required each time in order to return control plates to their initial position after the toothed discs have been turned for the purpose of adjusting a threaded bolt.In this connection the control tongues come into operation if, during the displacement of the through-feed lock, a cam which is moulded to the control plate, engages with a component moving relative to the guide bracket.

An essential disadvantage of this construction is that its functionally essential parts are fully exposed. The severe accumulation of dirt in the brake interior caused by wear on the brake can result in the external toothing of the toothed discs becoming clogged and in the accumlated residue caking together because of the high operating temperatures of the brake so that driving of the toothed discs and thus the compensating axial adjustment of the threaded bolts are no longer ensured. Moreover, assembly proves to be complicated and time-consuming operation, with the control plates having to be also subjected to a separate heat and abrasive treatment for strength reasons, in view of the frictional connection and cooperation between their cams and axially displaced components during throughfeed.

Finally, the threaded bushes which guide the threaded bolts retained on the free ends of the brake shoes have to be rotatably mounted in a common guide bush which is axiably slidably mounted on the guide bracket. The problem underlying the invention is therefore to provide an adjusting and centering device having a simple construction ensuring great operational reliability.

According to the present invention is provided an adjusting and centering device on a through-feed lock of an internal expanding brake for motor vehicles, comprising two threaded bolts which are coaxially to one another in the through-feed direction, which are externally threaded and which, through ends directed away from one another, engage non-rotatably on the respective ends of a primary brake shoe and a secondary brake shoe, on each of which a threaded bush is thereadedly engaged, which threaded bushes are slidable or movable axially in a guide bracket in a through-feed direction, are retained inside the guide bracket element and carry on adjusting element provided with external teeth, the adjusting elements forming driving bushes which are arranged so as to be independently axially adjustable in the guide bracket and which are slidably mounted on their respective threaded bushes in the direction of the other driving bush in each case as far as a stop on their threaded bush, the external teeth of each driving bush being in the form of an inclined radial locking toothing cooperating with an associated springmounted ratchet radially movable in the guide bracket, and resilient means biasing the driving bushes towards a stop position in contact with a centering stop on the guide bracket, in which stop position the threaded bushes are kept in end contact with one another, in the plane of the centering stop, by the driving bushes, wherein after a driving bush covers greater than a maximum through-feed distance in the direction of its associated brake shoe, the associated ratchet engages over a further tooth of the locking toothing and, upon the subsequent centering of the through-feed lock by the resilient means, bears against the previously engaged tooth and rotates both the driving bush and the threaded bush relative to the threaded bolt, to thereby adjust the brake. In the construction according to the invention all the functionally essential components are accordingly housed in the guide bracket, the inclined radial locking toothing which is provided on the outer circumferences of the driving bushes being protected against dirt accumulation as a result of the driver bushes being axially guided within the guide bracket. In this case the driver bushes also take over the guidance of the threaded bushes so that the arrangement of the latter in a common guide bush to be guided in the guide bracket can be omitted.

Finally, an important advantage of the construction according to the invention is that it makes machine assembly possible by virtue of the coaxial arrangement of the bushes relative to one another in the guide bracket. If in this case the through-feed lock is caused to slide through by the brake shoe which acts as the primary brake shoe, the driver bush of the threaded bush associated with this brake shoe remains in its stop position on the centering stop during axial adjustment of the threaded bush, whilst the driver bush of the adjusting mechanism of the adjusting and centering device associated with the brake shoe which acts as the secondary brake shoe is moved, during axial adjustment of its threaded bush, with the latter relative to the ratchet and as a result, after the brake is released, the secondary brake shoe is adjusted when there is excessive brake clearance.A necessitated adjustment of the other brake shoe is effected in the same manner if the through-feed lock is caused to slide through by the brake shoe which previously operated as the secondary brake shoe.

Accordingly, adjustment of only one brake shoe always takes place in one of the two possible directions of travel, that is the respective direction of always the same brake shoe.

A fully enclosed or ideally dirt-proof arrangement of the functionally essential components of the device inside the guide bracket is achieved if such a guide bore for receiving the driving bushes in the guide bracket is closed by means of sealing covers, in which the outer end piece of each of the threaded bushes is guided. Preferably the sealing covers are located inside an annular collar and packing sleeve which tightly enclose the end pieces of the threaded bolts, projecting out of the threaded bushes, are retained on the annular collars. Preferably the resilient means comprises return spring, arranged on the threaded bushes and supported, on the one hand, on the driving bushes, and on the other hand, on the sealing covers.A reliable torsionproof axial guidance of the threaded bushes in the driver bushes is to be achieved wherein the driving bushes are slidably mounted on a multiple spline of the threaded bushes.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing which shows a longitudinal section of an adjusting and centering device on a through feed back.

This device is arranged between the ends of the brake shoes lying opposite the expanding mechanism of an internal expanding servo brake and comprises a guide bracket 10 which is rigidly connected to a brake cover plate and in which there is provided a through-feed lock 1 2 which is slidable or movable in its axial direction and in this embodiment transmits the brake application force from each primary brake shoe to the secondary brake shoe. The through-feed lock forms an adjusting and centering device, which in the event of wear on the brake lining of one of the brake shoes, increases its axial length, relative to its centering position, or the worn side and thus maintains a constan: brake clearance on each brake shoe.

The through-feed lock is equipped with threaded bolts 1 8 and 20 for brake shoes -14 and 1 6 respectively, which threaded bolts are arranged coaxially to one another in the guide bracket 10 and their outer ends project out of the latter. The bolt ends are non-rotatably connected to respective webs 22 of the two brake shoes 14, 1 6 for which purpose each bolt carries a locking element 24 to prevent rotation, which is provided with a slot 26 in which the end of the web 22 of the associated brake shoe engages.Equally, the outer ends of the threaded bolts can also be provided with a slot in which the web of the associated brake shoe engages, or can be designed in another suitable manner in order that, in particular, advantageous resetting of the threaded bolts 1 8, 20 may be effected manually with the aid of a suitable tool whenever a brake lining is changed.

The two threaded bolts, 1 8, 20 are guided in cylindrical threaded bushes 28 and 30, respectively, which are provided with an internal thread and on which driver bushes 32 and 34, respectively, are non-rotatably, but axially slidably mounted, by means of splines 52 on the outer circumference of the bushes 26, 30.

These driver bushes, with cylindrical parts of the circumference, are guided slidably through a cylindrical guide bore 36 which receives the through-feed lock 1 2. This bore is closed at its ends by means of two sealing covers 38, 40, the outer end piece of each threaded bush 1 8 or 20 being slidably guided in these covers. The two threaded bushes which are coaxial to one another are consequently guided in the guide bore 36 of the guide bracket by each of the driver bushes 32 or 34 and each of the sealing covers 38 or 40. The sealing covers are located inside an annular collar 42 or 44 of the guide bracket which retains therein a package sleeve 46 or 48 which protects the said covers and thus also the outer end pieces of the threaded bushes 1 8, 20 against dirt and which, in a circumferential groove 50, tightly enclose the end pieces of the threaded bolts, 1 8, 20 projecting out of the threaded bushes. The range of movement of the driver bushes 32,34 is limited in the direction of the other threaded bush by respective stops 54 with the threaded bush which carries the driver bush.

As arranged on the threaded bushes 1 8, 20 are compression springs 56, 58, respectively, which are supported, on the one hand, on the driver bushes, 32, 34 respectively. These two compression springs 56, 58 bias the driver bushes 32, 34 inside the guide bracket to a centering position defined by a centering stop 60 which is formed preferably by a snap ring fitted into a circumferential groove in the guide bore 36. With the driver bushes in this centering position, the two threaded bushes 28, 30 are kept in end contact with one another in the plane of the centering stop 60 as a result of the co-operation between their stops 54 and each of the driver bushes 32, 34, as long as the brake is released and the brake shoes are in a neutral initial position.

The driver bushes 32, 34 are each equipped on their outer circumference with an inclined radial locking toothing or rack 62 which acts in one direction and has teeth 64 with a sawtooth profile in cross-section and inclined at an angle to the direction of sliding movement of the bushes 32, 34. This radial locking toothing on each driver bush is associated with ratchets 66, 68 respectively, which are radially slidably guided in corresponding guide bores 70, 72 respectively in the guide bracket 10 against the bias of respective compression springs 74, 76.

It can be seen from the drawing that the surface or wall of the driver bushes 32, 34 has approximately twice the length of the bush component which is slidably guided along the multiple spline 52 of the threaded bushes.

Driver bushes 32, 34 and threaded bushes 28, 30 thus define an annular space 74 or 76 through which extend the compression spring 56, 58 supported on the sealing covers 38, 40.

As can be seen from the drawing, the radial locking toothing 62 on each of the driver bushes 32, 34 ends some distance fr6m the bush ends so that the bushes are guided, by cylindrical circumferential parts 32', 32" or 34', 34" at the ends, in the guide bore and the radial locking toothing is thereby fully enclosed.

The adjusting and centering device operates as follows: When the brake is actuated in the forward direction, the brake shoe 1 4 for example acts as the leading and primary shoe and slides the through-feed lock axially to the right, as shown in the drawing, to press the leading brake shoe 1 6 forming the secondary against the brake drum. This axial movement is introduced into the through-feed lock via the threaded bolt 1 8 and the threaded bush 28, the threaded bush 30 and the threaded bolt 20 being driven by the latter and also the driver bush 34 being moved out of its center ing position by the stop 54. On the other hand, the driver bush 32 arranged on the threaded bush 28 remains in the illustrated stop position on the centering stop 60.If, as a result of wear on the brake lining, the clearance between the brake drum and the brake shoe 1 6 has reached a value corresponding to a maximum through-feed distance which, in turn corresponds, to at least the tooth spacing between the radial locking toothing 62 of the driver bush 68, which is gradually lifred out of the radial locking toothing 62 during the through-feed movement, engages in the following toothing. Upon the release of the brake, the driver bush 34 is guided back into its stop position on the centering stop 60 by the compression spring 58 and in this connection the other previously displaced components of the through-feed lock 1 2 are also automatically moved back into the centering position.The force of the compression spring 58 overcomes the friction between the flanks of the radial locking toothing 62 and of the ratchet 68, whereby the driver bush 34 is accordingly turned together with the threaded bush 30. This turning movement causes an axial adjustment of the threaded bolt 20 out of the threaded bush 30 in the direction of the brake shoe 1 6 by the amount or degree of wear on the brake lining.

In the event of a braking action in the opposite direction, the brake shoe 1 6 acts as the primary shoe and, through the threaded bolt 20 and the threaded bush 30, causes the threaded bush 28, together with the threaded bolt 1 8 and the driver bush 32, to slide to the left as shown in the drawing, to apply the pressure to the brake shoe 1 4 which acts as the secondary shoe. In this case, in a manner similar to the previously described operating cycle, the driver bush 34 remains in its centering position.Should the clearance between the brake drum and brake shoe 14 have reached a value equivalent to the maximum through-feed, the ratchet 66 will also during the axial movement of the driver bush 32, ride over the radial locking toothing of the latter by one space and cause a corresponding adjustment of the brake shoe 1 4 upon resetting of the components 18, 28, 32 by the compression spring 56.

The primary function of the compression springs 56, 58 in this is to prevent relative adjustment in the axial direction between the associated bushes 28, 32 or 30, 34 during the through-feed of the through-feed lock 1 2 in one direction or the other and to cause the rotary movement of the driver bushes and threaded bushes which is necessary for the axial adjustment of the threaded bolts 18, 20 when the ratchets ride over and tooth spacing.

The adjusting and centering device according to the invention thus operates in such a manner that the brake shoe which acts as the secondary shoe is adjusted in each case in one of the two possible directions of travel if the clearance exceeds a permissible value.

Claims

1. An adjusting and centering device on a through-feed lock of an internal expanding brake for motor vehicles, comprising two threaded boltd which are arranged coaxially to one another in the through-feed direction, which have externally threaded and which, through ends directed away from one another, engage non-rotatably on the respective ends of a primary brake shoe and a secondary brake shoe, on each of which a threaded bush is threadedly engaged, which threaded bushes are slidable or movable axially in a guide bracket in a through-feed direction are retained inside the guide bracket and carry an adjusting element provided with external teeth the adjusting elements forming driving bushes which are arranged so as to be independently axially adjustable in the guide bracket and which are each slidably mounted on their respective threaded bushes in the direction of the other driving bush in each case as far as a stop on their threaded bush, the external teeth of each driving bush being in the form of an inclined radial locking toothing cooperating with an associated spring-mounted ratchet radially movable in the guide bracket and resilient means biasing the driving bushes towards a stop position in contact with a centering stop on the guide bracket, in which stop position the threaded bushes are kept in end contact with one another, in the plane of the centering stop, by the driving bushes wherein after a driving bush covers greater than a maximum through-feed distance in the direction of its associated brake shoe the associated ratchet engages over a further tooth of the locking toothing and, upon the subsequent centering of the through-feed lock by the resilient means, bears against the previously engaged tooth and rotates both the driving bush and the threaded bush relative to the threaded bolt, to thereby adjust the brake.

2. An adjusting and centering device according to Claim, wherein a guide bore for receiving the driving bushes in the guide bracket is closed by means of sealing covers, in which the outer end piece of each of the threaded bushes is guided.

3. An adjusting and centering device according to Claim 2, wherein the sealing covers are located inside an annular collar and packing sleeves which tightly enclose the end pieces of the threaded bolts projecting out of the threaded bushes are retained on the annular collars.

4. An adjusting and centering device according to Claim 2, or 3, wherein the resilient means comprises return springs arranged on the threaded bushes and supported, on the one hand, on the driving bushes and, on the other hand, on the sealing covers.

5. An adjusting and centering device according to any of the preceding Claims, wherein the driving bushes are slidably mounted on a multiple spline of the threaded bushes.

6. An adjusting and centering device on a through-feed lock of an internal expanding brake for motor vehicles substantially as described herein with reference to and as illustrated in the accompanying drawings.