GB2423804A

GB2423804A - Mechanical parking brake assembly for a fixed calliper floating piston disc brake

Info

Publication number: GB2423804A
Application number: GB0604261A
Authority: GB
Inventors: Mark Matthews
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-03-03
Filing date: 2006-03-03
Publication date: 2006-09-06
Also published as: GB0604261D0; GB0504494D0

Abstract

A fixed calliper floating piston disc brake 10 comprises hydraulic pistons 20, 21 operable to urge friction pads 12, 13 into engagement with a disc 14 during service braking, and a mechanical park brake assembly 28 & 38, 29 & 39 inserted between the friction pad and its associated piston, wherein the park brake assembly is operable to move the respective friction elements into engagement with the disc. The park brake assembly comprises a pivotally mounted lever arm 38, 39 which has a nose 46 to engage the friction pads, and plate 28, 29. The tiltable levers maybe connected by a Bowden cable mechanism 48, 49 incorporating a spring 50. The brake may incorporate a screw threaded adjuster.

Description

AUTOMOTIVE DISC BRAKES

TECHNICAL FIELD OF THE INVENTION

This invention relates to automotive braking systems and in particular to disc brakes which are adapted to incorporate a mechanical park brake function in addition to an hydraulic service brake function.

BACKGROUND

In known automotive disc brakes a pair of friction elements are held by a calliper for frictional engagement with opposite sides of a rotatable brake disc. In fixed calliper disc brakes the calliper is mounted in a fixed position axially of the disc. Normally, the calliper is provided with at least one hydraulically operated piston on each side of the disc which acts to move the respective friction element into frictional engagement with the disc when the service brakes are applied, although fixed calliper systems are also known in which one of the friction elements is fixed relative to the calliper (referred to as "disc bender" callipers for obvious reasons). In fixed calliper systems there is generally no means for returning the pistons after the hydraulic pressure is released so that the friction elements automatically position themselves close to the brake disc. Such brake systems will thus be referred to herein as "fixed calliper floating piston disc brakes".

In the development of automotive disc brakes a great deal of design effort has been expended in attempting to provide a simple, effective and low cost mechanical park brake function which utilises the same friction elements as the hydraulic service brakes. In practice, the two functions are generally provided by separate brake systems, which is costly, wasteful of space, and, in the case of racing or high performance vehicles in particular, adds significantly to the weight of the vehicle.

The present invention seeks to provide a new and inventive form of disc brake system which is simple, compact and economical, and which, more particularly provides both park brake and service brake functions utilising the same friction elements.

SUMMARY OF THE INVENTION

The present invention concerns an automotive fixed calliper floating piston disc brake in which the calliper holds a pair of friction elements on opposite sides of a rotatable brake disc and the operation of the service brakes causes frictional engagement between the friction elements and the brake disc to impede rotational movement thereof, wherein the improvement lies in a mechanical park brake assembly inserted between a friction element and the associated operating piston or pistons, the said assembly being operable to mOve the respective friction element into frictional engagement with the brake disc on operation of the park brakes and further being arranged to transmit hydraulic braking force from the associated piston or pistons to the friction element during operation of the service brake.

In a disc bender type calliper only one park brake assembly would be used, between the piston or pistons and the associated friction element.

In the majority of fixed calliper systems, which have at least one floating piston associated with each friction element, such a park brake assembly would be inserted between each friction element and the respective operating piston or pistons.

The or each such park brake assembly preferably includes a lever arm having a pivot, an end which projects from the calliper for operation of the mechanical park brake function, and a portion which acts against the friction element to move it into frictional engagement with the brake disc.

The portion which acts against the friction element is preferably disposed between the pivot and said projecting end.

Said park brake assembly preferably includes a plate to which the lever arm is connected by the pivot. The plate is preferably mounted in the calliper for movement generally parallel to the operating axis of the piston.

Such movement may be achieved by slidably mounting the plate on one or more elongate guide elements, e.g. pins. The associated friction element may also be slidably mounted on the same guide element or elements. In a preferred arrangement the pivot and the guide element or elements are disposed on opposite sides of the piston such that pivotal movement of the lever arm causes tilting of the plate to frictionally engage the guide element or elements.

Where two such park brake assemblies are used the park brakes may be applied via a mechanical arrangement for moving the two lever arms towards each other. In disc bender callipers the mechanical arrangement may act between the single lever arm and the calliper.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. In the drawings: Figure 1 is an automotive fixed calliper floating piston hydraulic disc brake provided with a park brake function in accordance with the invention, shown in sectional view taken axially of the associated brake disc; Figure 2 is an elevation of one of the park brake assemblies which provide the park brake function, as viewed from the direction of the associated brake disc; Ficjure3 is a similar sectional view to Fig. 1, showing the operation of the park brake assemblies and Figure 4 is a detail of a modified form of the hydraulic disc brake.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring firstly to Fig. 1, the illustrated automotive disc brake assembly includes a fixed disc brake calliper indicated generally at 10, which includes a pair of friction elements 12 and 13 (commonly known as brake pads) which are arranged for frictional engagement with opposite sides of a rotatable brake disc 14. At any given time the friction elements may frictionally engage part of the annular periphery of the disc, shown in the drawings, while the remainder of said periphery is not subjected to such frictional engagement.

The calliper 10 may typically be formed of two substantially mirror-image metal castings 16 and 17 which are assembled together and held by bolts or other such means (not shown). The castings both include a cup- shaped cylinder or piston housing, 18, 19, which contain respective axially opposed hydraulic pistons 20 and 21, disposed opposite sides of the disc 14, and which may be urged towards the disc by pressure of hydraulic fluid flowing into the cylinders 18 and 19, in known manner. The pistons and 21 operate as hydraulic service brake actuators and act on the brake disc 14 via the friction elements 12 and 13, which the pistons urge into frictional engagement with the opposite sides of the disc to impede or brake the rotational movement of the disc.

The friction elements 12 and 13 are of the free-floating type which accommodate wear or axial movement of the brake disc 14 without causing a delay in the application of the service brakes or reducing the braking efficiency. For this purpose the friction elements are slidably mounted on a pin 25 which is inserted through both of the calliper castings 16 and 17 parallel to, but offset from, the common axis A of the two service brake actuator pistons 20 and 21, beyond the periphery of the brake disc 14. In some forms of calliper two such pins (or possibly more) may be provided. The pistons are arranged to act substantially cehtrally on the friction elements 12 and 13, 50 that normal operation of the service brakes will automatically move the friction elements along the pin 25 until they lie immediately adjacent to the opposite faces of the disc 14.

In the present disc brake a respective mechanical park brake actuator including a tilt plate 28, 29 is interposed between each of the service brake pistons 20 and 21 and the associated friction element 12, 13.

Referring to Fig. 2, each tilt plate is generally of the same outline as the associated friction element, with a tongue 30 at one edge and a pair of spaced lugs 33 and 34 at the opposite edge. The tongue 30 contains a hole 31 which receives the pin 25 as a close sliding fit, thereby locating the tilt plates within the calliper. The face of the tilt plate which is opposed to the associated friction element 12 or 13 further contains a channel 36 which extends from between the lugs 33 and 34 and along the tongue 30 to receive a respective lever arm 38, 39 of substantially rectangular transverse section. Each lever arm is pivotally connected to the respective tilt plate 28 or 29 by means of a pivot pin 40 which is inserted through the projections 33 and 34 and one end of the lever arm. The opposite end of each lever arm projects beyond the respective tongue 30 to receive at least one, and in this case two, cable fixing apertures 42.1 and 42.2. In addition, each lever arm contains a further hole 44 which is aligned with the hole 31 to receive the pin 25, but in this case the hole 44 is slightly oversize, or elongated, to permit unimpeded angular movement of the lever arm about the pivot pin 40. In the case of a brake calliper having two spaced pins 25 the tilt plate may be provided with a pair of tongues 30 to slidably receive the pins 25, on opposite sides of the lever arm 38, 39.

Referring back to Fig. 1, it will be noted that the free end of each lever arm 38, 39 is recessed into the respective channel 36, but in the approximate centre of each tilt plate the lever arm is stepped outwardly to form a nose 46 which lies substantially flush with the surface of the tilt plate. As will be explained shortly, this is important to the operation of the park brake function.

The park brakes are applied by moving the projecting ends of the lever arms 38 and 39 towards each other. This may be achieved in various ways. In Fig. I for example, a Bowden cable is used, with the inner core 48 being connected to one lever arm 39 and the outer sheath 49 connected to the other lever arm 38. The holes 42.1 and 42.2 provide a choice of fixing positions depending on the available actuating force and the required operating distance. When the park brakes are not being applied the lever arms attain a substantially parallel configuration as shown in Fig. 1. It is preferable to provide a weak return spring 50 which biases the two lever arms apart without moving the pistons to ensure that the arms are positively held out of contact with the friction elements 12 and 13. The compression spring 50 also acts to tension the inner part 48 of the Bowden cable. On operation of the service brakes, since the pistons 20 and 21 act on the central region of the tilt plates the pistons cause axial movement of the tilt plates 28, 29 and friction elements 12 and 13. Any wear of the brake disc 14 is accommodated by sliding movement of the tilt plates along the pin 25, in the same manner as the friction elements 12 and 13.

Application of the park brakes causes the lever arms 38 and 39 to rotate angularly about the pivot pins 40, as shown in Fig. 3. When this occurs the noses 46 act on the central region of the friction elements 12 and 13, moving the friction elements into braking contact with the disc 14 (omitted in Fig. 3). It is important to note that since the noses 46 act on the friction elements 12 and 13 at approximately the same position as the pistons 20 and 21, tilting of the friction elements is avoided and the braking force is therefore distributed across the friction elements. It should also be noted that although the pistons are normally capable of moving back into their housings during application of the park brakes, the braking reaction forces are resisted in several ways. Firstly, the pivoted ends of the lever arms 38 and 39 cause a small angular movement of the tilt plates 28 and 29, which in turn causes the close tolerance holes 31 to frictionally engage the pin 25. Thus, the tilt plates are no longer able to slide away from the friction elements 12 and 13. Furthermore, such angular movement of the tilt plates exerts an off-centre force on the pistons 20 and 21 causing them to frictionally engage the piston housings 18 and 19, within which the pistons are a close tolerance fit. As a result, application of the mechanical park brakes is both immediate and sustained.

Nevertheless, it might also be desirable to provide means for compensating for wear and manufacturing tolerances, as shown in Fig. 4.

One or more dome-headed adjuster screws 60 are inserted into the lower portions of the tilt plates 28/29, or the lever arms 38, 39. During fitting, the screws are adjusted so that the domed heads 61 make contact with the respective piston housings 18 and 19. The screws thus limit movement of the plates 28 and 29 away from the brake disc. As the brake pads wear the screws can be re-adjusted at regular service intervals to ensure that the park brake assemblies remain correctly positioned.

During braking, circumferential movement of the friction elements 12 and 13 relative to the disc 14 may be prevented by projections on the two castings (not shown). Alternatively, as shown in Fig. 2, the tilt plate may be provided with short pegs, 51 and 52, which locate in holes in the rear face of the friction elements 12 and 13. - Although the brake callipers may be manufactured with the mechanical park brake function it is also possible to retro-fit the park brake option to a suitable calliper. This is easily achieved by inserting spacers between the two parts of the calliper and fitting a longer pin 25, or pins, to accommodate the two park brake assemblies.

It should also be noted that although a two-piston calliper has been described by way of example the park brake facility can equally be applied to callipers of the kind in which two or more pistons operate on each of the friction elements.

It will be appreciated that the features disclosed herein may be present in any feasible combination. Whilst the above description lays emphasis on those areas which, in combination, are believed to be new, protection is claimed for any inventive combination of the features disclosed herein.

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Claims

1. An automotive fixed calliper floating piston disc brake in which the calliper holds a pair of friction elements on opposite sides of a rotatable brake disc and the operation of the service brakes causes frictional engagement between the friction elements and the brake disc to impede rotational movement thereof, wherein the improvement lies in a mechanical park brake assembly inserted between a friction element and the associated operating piston or pistons, the said assembly being operable to move the respective friction element into frictional engagement with the brake disc on operation of the park brakes and further being arranged to transmit hydraulic braking force from the associated piston or pistons to the friction element during operation of the service brake.

2. An automotive disk brake according to Claim I in which the park brake assembly includes a pivotally mounted lever arm having an end which projects from the calliper for operation of the mechanical park brake function and a portion which acts against the friction element to move the friction element into frictional engagement with the brake disc.

3. An automotive disk brake according to Claim 2 in which the portion which acts against the friction element is disposed between said projecting end a pivotally mounted end of the lever arm.

4. An automotive disk brake according to Claim 2 or 3 in which the portion which acts against the friction element comprises a nose on the lever arm.

5. An automotive disk brake according to Claim 2, 3 or 4 in which the park brake assembly includes a plate to which the lever arm is pivotally connected.

6. An automotive disk brake according to Claim 5 in which the plate is mounted in the calliper for movement generally parallel to the operating axis of the piston.

7. An automotive disk brake according to Claim 6 in which the plate is slidably mounting on one or more elongate guide elements.

8. An automotive disk brake according to Claim 7 in which the associated friction element is slidably mounted on the same guide element or elements.

9. An automotive disk brake according to Claim 7 or 8 in which the said pivotal connection and the guide element, or elements, are disposed on opposite sides of the piston, the arrangement being such that pivotal movement of the lever arm causes tilting of the plate to frictionally engage the guide element or elements.

10. An automotive disk brake according to any preceding claim in which the or each such park brake assembly has a screw-threaded adjuster which can be adjusted to contact a fixed portion of the calliper.

11. An automotive disk brake according to any preceding claim of the kind having at least one floating piston associated with each friction element, in which such a park brake assembly is inserted between each friction element and the respective operating piston or pistons.

12. An automotive disk brake according to Claim 11 in which the park brakes are applied via a mechanical arrangement for moving the two lever arms towards each other.

13. An automotive disk brake according to any of Claims I to 10 of the disc bender kind in which one of the friction elements is fixed relative to the calliper and the other friction element is operated by a floating piston, in which a single park brake assembly is inserted between the piston and the associated friction element.

14. An automotive disk brake according to Claim 13 in which the park brakes are applied via a mechanical arrangement for moving the lever arm relative to the calliper.

15. An automotive fixed calliper floating piston disc brake substantially as described with reference to the drawings.

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