GB2244530A

GB2244530A - Adjusting device for a brake

Info

Publication number: GB2244530A
Application number: GB9108319A
Authority: GB
Inventors: Rudolf Thiel
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1990-05-26
Filing date: 1991-04-18
Publication date: 1991-12-04
Anticipated expiration: 2011-04-18
Also published as: JPH04231735A; FR2662478B1; GB2244530B; GB9108319D0; DE4017065A1; FR2662478A1

Abstract

An adjusting device, in a brake, for taking up brake pad wear, enables resetting of the device by simply pressing the actuating piston (3) axially inwardly of housing (1) so that the piston need not be reset either by a special drive arrangement for turning the adjusting spindle (5), or by turning in the piston itself. The spindle (5) is accordingly rotatable during resetting of the piston, while during normal hydraulic or manual operation of the brake the adjusting spindle (5) is prevented from rotation by a removable screw (22) provided with a pin (23) which locks a splined member (9) against rotation. The splined connection between the member (9) and the spindle (5) permits axial sliding of the spindle. The member (9) may be rotated by a suitable tool to rotate the spindle (5) and retract the piston (3). <IMAGE>

Description

3C 1 ADJUSTING DEVICE FOR A BRAKE The present invention relates to an

automatic adjusting device for a brake.

In order not to avoid extending the brake pedal travel unnecessarily to achieve braking of a vehicle with worn brake linings, it is known to provide automatic adjusting devices whereby the initial position of the usual brake piston is readjusted automatically depending on the degree of brake lining wear. Such automatic adjusting devices may be furnished with a threaded spindle without self-locking engagement, as fully described in published German Patent Application No. 3802014 for example.

With automatic adjusting devices of this type the piston may have moved a relatively large distance from its original initial position when the worn brake linings are replaced. In order to obtain space for fitting new linings, it is known to restore the piston to its original initial position by means of resetting means. Such resetting means are known for example from published German Patent Applications Nos. 3713201, 1813560 and from German Patent No. 1675245. One shortcoming of these known resetting means is that either the screw spindle is supported unrotatably relative to the housing, or the known adjusting devices are equipped with a non-reversible thread between nut and screw spindle. Both arrangements suffer from the disadvantage that either the brake piston must be rotated back down to its original initial position by a screw movement, or that 2 the screw spindle must be rotated about its longitudinal axis on its end remote from the piston by means of a special drive in order to restore the piston to its initial position.

It is an object of the invention to enable resetting of the piston to be performed in an adjusting device of the type referred to above in a simple manner avoiding rotation of the piston.

According to the present invention there is provided an automatic adjusting device for a brake with adjusting members, such as a co-operating nut and screw spindle exposed to hydraulic pressure, on each of which adjusting members spring means acts in the axial direction thereof and which members are rotatable without self-locking engagement in relation to each other for the purpose of re-adjustment when the hydraulic pressure in the pressure chamber is below a predetermined value, whereas in excess of a predetermined hydraulic pressure relative movement of the adjusting member that is axially slidable in relation to the brake housing is prevented, characterised in that the screw spindle is freely rotatably supported in the housing of the brake but a releasable locking mechanism is provided in the housing normally to prevent rotation of the screw spindle.

The stop mechanism is used in order to prevent undesirable return movement of the piston, such as immediately af ter braking due to the reaction f orces exerted on the piston by the disc or the usual ring seal. Corresponding movement of the nut in relation to the screw spindle on actuation of the hand brake is also prevented.

Locking of the screw spindle movement may be achieved by jamming, pinning or by any other form-locking arrangement which though permitting movement of the screw in its longitudinal direction does not allow rotation thereof.

It may be expedient in many cases to not only allow pushing in of the piston into the associated cylinder for assembly purposes but also to provide for resetting of the piston by means of a drive making catch at the screw 11 1 1 1 3 spindle. This may be advantageous when f or any reason an attempt to push back the piston in its longitudinal direction fails due for instance to the friction forces to be overcome being too large or to the piston otherwise being impeded in its motion. The drive for the screw spindle may comprise a sprocket forming part of the releasable locking means and having teeth which mesh with teeth of the spindle to rotation of the latter, the sprocket being lockable by a detachable pin.

The sprocket may have a longitudinal extension having a recess therein for receiving a tool for exerting a torque on the sprocket to rotate the sprocket and the screw spindle. The sprocket may be housed in a cylindrical opening of the brake housing.

In order to increase rotatability of the spindle the sprocket may be completely removed f rom the opening to disengage the screw spindle, or it may be just shifted out of engagement with the spindle.

A locking stop screw may be provided which lockingly engages the sprocket extension to prevent rotation thereof.

By way of example one embodiment of this invention will now be described with reference to the accompanying single-figure drawing which shows a crosssectional view of a brake of the kind described for instance in German published patent applications 3802014 and 3943106. The disclosures made in the two published applications are herein considered to form part of the present disclosure so that the brake assembly units of the drawing will be described only insofar as this is necessary for comprehending the present invention.

The cross-sectional view of a brake shown in the drawing comprises a piston 3 which is guided in a cylinder opening of a housing 1, illustrated in cross-section.

Pressure fluid entering through the opening 19 urges the brake piston 3 to the left as viewed in the drawing and, in doing so, applies the brake pad or shoe 6 to the non- 4 1 illustrated brake disc. In the normal condition in which the vehicle is able to be braked. the screw spindle 5 - as will be explained later - is displaceable in the longitudinal direction thereof but is supported unrotatably in its direction of movement. In the absence of wear of the lining of the brake shoe, the piston 3 is reset to its initial position after braking by means of the restoring action of the ring seal 21. In the event that the travel of the piston needs to exceed the clearance provided in the adjustment by means of the threaded spindle, the nut 27 will rotate in relation to the spindle 5 to allow further movement of the piston 3.

In the return movement of the piston.. after the clearance has been overcome, rotation of the nut 27 in relation to the locked spindle 5 will be prevented so that the piston returns to its readjusted position.

When, for some reason (such as changing worn brake linings) the piston 3 is required to be moved back into the cylinder opening in the housing 1, this can only be carried out if the screw spindle 5 is locked by turning the piston 3 in the cylinder chamber,, the nut 27 being locked in relation to the piston 3 in the axial direction thereof and rotary movement of the nut only being possible if the piston 3 is turned.

However, such a rotary movement of the piston is not desirable, it is being desirable that the piston be simply slidable in its longitudinal direction into the cylinder opening. To this end the invention proposes to Permit a rotary movement of the screw spindle 5 for the purpose of resetting so that, although the nut 27 is retained unrotatably in the piston 3, the force exerted in the longitudinal direction of the piston into the cylinder chamber results in a rotary movement of the screw 5 thereby screwing into the nut and hence into the piston.

Since the thread between screw spindle 5 and nut 27 is a non-self locking type thread rotation between them is possible if locking of the screw is removed. This locking 1 1 is provided by a sprocket 15 which is locked in the direction of rotation and which has teeth meshing with teeth 17 of the spindle 5 and thereby locks the spindle 5 against rotation. To permit re-setting of the piston 3, the sprocket 15 is disengaged from the teeth 17 of the spindle by drawing the sprocket 15 out of the cylindrical opening 16 in the housing 1 to the right, as viewed in the drawing.

The sprocket 15 is furnished with an attachment 9 carrying an attachment head 25. Making locking engagement sideways at the attachment head 25 is a pin 23 of a stop screw 22 which by means of an external thread 13 is screwed into the housing thread 20 of an aperture 14. The stop screw 22 comprises a screw head 11 on its outwardly facing end, which head has a hexagonal external configuration or a hexagonal recess to permit of its unscrewing or screwing it tight, as the case may be. After detachment of the screw 22, the locking pin 23 is disengaged from the lateral surface of the attachment head 25 so that this locking engagement of the pin 23 with the sprocket 15 is removed so that the sprocket 15 is permitted to freely rotate in the cylindrical opening 16. Hence it follows that it is sufficient to disengage the screw 22 from the sprocket 15 in order to permit rotation of the spindle 5 without there being the need to take the sprocket 15 out of the cylinder opening 16.

In a case where the axial force available does not suffice to provide resetting of the piston 3 into the housing, the illustrated construction affords the possibilityof retracting the piston by means of the sprocket 15. To this end, af ter detachment of the stop screw 22 a tool can be applied to the attachment head 25 on the attachment 9,, as f or instance into a hexagonal recess or slot provided in the head 25. The attachment head 25 having a hexagonal recess or slot enables the sprocket 15 to be turned by the tool and to thereby cause the piston to adopt its original initial position in response to the spindle 5 turning so that the nut 27 is then screwed back and restores 6 the piston into its original initial position by way of elastic force or coil-bound spring force via the stop ring.

The screw spindle 5 must be locked again after the piston 3 has been reset. This is achieved by the screw 22 being screwed back so that the locking pin 23 is brought into locking engagement into the head 25 of the attachment 9. As a result both the sprocket 15 and via the teeth 17 the spindle 5 are supported to be unrotatable but the spindle 5 is axially slidable.

The brake according to the present invention permits ease of rotation of the screw 5 and thus also ease of moving the piston 3 in for resetting purposes. This invention is applicable to floating- caliper brakes and fixed-type caliper brakes and is not limited to the form of locking arrangement for the screw 5 shown in the drawing.

7 1

Claims

CLAIMS:

1. An automatic adjusting device for a brake with adjusting members, such as a co-operating nut (27) and screw spindle (5) exposed to hydraulic pressure, on each of which adjusting members spring means acts in the axial direction thereof and which members are rotatable without self locking engagement in relation to each other for the purpose of readjustment when the hydraulic pressure in the pressure chamber is below a predetermined value, whereas in excess of a predetermined hydraulic pressure relative movement of the adjusting member that is axially slidable inrelation to the brake housing is prevented, characterised in that the screw spindle (5) is freely rotatably supported in the housing (1) of the brake but a releasable locking mechanism (9 to 15) is provided in the housing (1) normally to prevent rotation of the screw spindle (5).

2. An adjusting device as claimed in claim 1, characterised in that the releasable locking mechanism (9 to 15) comprises a sprocket (15) having teeth (15) which mesh with mating teeth (17) of the screw spindle (5) in the sense of facilitating rotation of the spindle (5) about its longitudinal axis, with the rotation of the sprocket (15) being lockable by a detachable pin (23).

3. An adjusting device as claimed in claim 2, characterised in that the sprocket (15) has a longitudinal extension (9) having a recess (26) therein for receiving a tool for exerting a torque on the sprocket.

4. An adjusting device as claimed in claim 2 or claim 3, characterised in that the sprocket (15) is supported in a cylindrical opening (16) in the brake housing (1).

5. An adjusting device as claimed in claim 4, characterised in that the opening (16) extends into an eccentrically positioned recess (14) which is open relative to the housing surface and which is provided with an internal thread (20) into which a stop screw (22) can be screwed.

6. An adjusting device as claimed in claim 5, 8 characterised in that the stop screw (22) includes a locking pin (23) which protrudes into the housing and which in the screwed-in condition of the stop screw lockingly engages with the extension (9) and thus prevents rotary movement of 5 the sprocket (15).

7. An adjusting device as claimed in claim 5 or claim 6, charcterised in that the friction forces are dimensioned such that after removal of stop screw (22) and sprocket (15) a piston (3) of the brake-can be urged to assume its initial 10 position also by a corresponding force.

8. An adjusting device for a brake substantially as hereinbefore described with teference to the accompanying single figure drawing.

Published 1991 at The Patent Office. Concept House, Cardiff Road. Newport. Gwent NP9 IRH. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwnifelinfach. Cross Keys. Newport. NP1 7HZ. Printed by Multiplex technJques lid, St Mary Cray, Kent.