GB1562911A

GB1562911A - Hydraulically operated disc brakes for vehicles

Info

Publication number: GB1562911A
Application number: GB4171875A
Authority: GB
Original assignee: Girling Ltd
Current assignee: Girling Ltd
Priority date: 1976-09-17
Filing date: 1976-09-17
Publication date: 1980-03-19

Description

(54) IMPROVEMENTS IN HYDRAULICALLY OPERATED DISC BRAKES FOR VEHICLES (71) We, GIRLING LIMITED, a British Company of Kings Road, Tyseley, Birmingham 11, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to improvements in disc brakes for vehicles of the kind in which a clamp member extending over the peripheral edge of a rotatable disc is guided for sliding movement with respect to the disc on a part of a relatively stationary drag-taking member which is located adjacent to the disc, and hydraulic actuating means housed in the stationary member are adapted to apply a first directly actuated friction pad assembly directly to the said one side of the disc and act through the movable clamp member to apply a second indirectly actuated friction pad assembly simultaneously to the opposite side of the disc with the clamp member moving with respect to the drag-taking member in a generally axial direction.

In one known disc brake of the kind set forth the clamp member is guided on spaced axially extending guiding surfaces on the stationary member which may comprise the adjacent inner ends of opposed complementary slots or grooves disposed in the circumferentially outermost sides of the stationary member and which are embraced by the clamp member and the indirectly actuated friction pad assembly is carried by the clamp member so that the drag on that pad assembly is transmitted through the clamp member and onto the guiding surfaces in the stationary member. The guiding surfaces are often exposed and are therefore subject to corrosion. Although it is known to protect the guiding surfaces by flexible boots and to include some lubricant, nevertheless, inevitably deterioration of the guiding surfaces occurs and periodic servicing is required.

Furthermore, the drag transfer through the clamp member tends to cause binding of the guiding surfaces and a friction force opposing the brake applying force from the actuating means is generated. Therefore, the structure supporting the guiding surfaces must be substantial to cater for the drag loads, and to be sufficiently rigid to prevent the guiding surfaces from jamming.

In another known disc brake of the kind set forth the indirectly actuated friction pad assembly is coupled to the clamp member and is also guided between guide extensions on the stationary member which extend over the peripheral edge of the disc and which take the drag on the said pad assembly when the brake is applied, the clamp member also being coupled to the hydraulic actuator so that it is guided on opposite sides of the disc on the stationary member respectively through the indirectly actuated friction pad assembly and the hydraulic actuator. Although no other guide means for the clamp member have to be provided, the stationary member is a substantial construction requiring additional space to accommodate it. Furthermore, when substantial clearance are provided between the indirectly actuated friction pad assembly and the guide extensions, the application of the brake is noisy due to a "clonk" which occurs when the pad assembly carried around with the disc engages with one of the guide extensions which forms a drag-taking abutment. That movement of the pad assembly with the disc is accompanied by the clamp member with which it forms an assembly of substantial mass developing considerable inertia. When the clearances are reduced to eliminate the "clonk" by reducing to a minimum the movement of the pad assembly with the disc, there is a tendency for the interengaging surfaces to rust or otherwise corrode which, in turn, will impede operation of the brake.

In another known disc brake of the kind set forth the clamp member is coupled to the hydraulic actuator so that it is guided with respect to the housing by the hydraulic actuator over an area within the housing which is not wetted by hydraulic fluid when the brake is in use, the guide surfaces being sealed by flexible boots to protect them from corrosion.

When one component of a brake has to move relative to another component the clearance between the components is critical as if it is too small seizure may occur and if it is too large rattle may occur. Thus there is a maximum and a minimum critical dimension for such a clearance which depend on the contact areas, mass of the parts and degree of exposure. A possible way of increasing the margin between the maximum and minimum critical clearance is to include rubber bushes between the components.

According to our invention in a disc brake of the kind set forth for vehicles the stationary member is located wholly on one side of the disc, and the hydraulic actuating means comprises first and second hydraulic pistons working in respective first and second bores in the stationary member, with at least one first piston acting on the directly actuated friction pad assembly and movable in a direction to urge the pad assembly into engagement with the disc and at least one second hydraulic piston coupled to the clamp member and movable in the opposite direction to apply the indirectly actuated friction pad assembly to the opposite face of the disc, the bores being in communication at all times, and a slidable connection is provided between the clamp member and the stationary member, the slidable connection including spaced drag-taking guiding surfaces on the stationary member and complementary dragtransmitting surfaces on the clamp member, the guiding surfaces including the second bore, with the second piston comprising the complementary drag-transmitting surface, and the guiding surfaces being wetted by hydraulic fluid of the actuating means at least when the brake is in use.

Thus the clearance between the interengaging slide parts is lubricated so as to reduce the critical minimum clearance between the parts.

As the permitted clearances are smaller the location of the parts is improved.

Since interengaging slide parts are fully sealed and continuously lubricated and protected the possibility of wear and corrosion occurring is reduced substantially. Service problems are eliminated as the pads are changeable without disturbing the hydraulic connections. Also the reduction in friction due to the lubricating effects of the hydraulic fluid facilitates operation of the brake and the operation of the brake is quiet since the slide clearances between the clamp member and the stationary member can be made smaller with no risk of seizure.

The stationary member in a brake of the kind set forth is always constructed very robustly so that the bore in which the pistons work retains its shape under the worst conditions. Our invention uses this inherent rigidity to provide the additional function of a rigid guide. The brake can be made of ordinary cast iron rather than a special high strength iron, and it is relatively inexpensive and easy to manufacture.

When the pistons comprise a pair of oppositely acting pistons the bores are coaxial and are equal in diameter. In such a construction the bore in which the second piston works and the second piston itself comprise the drag-taking guiding surfaces and the complementary drag-transmitting surfaces respectively, being of stepped outline with the portion of the piston which is of greater diameter being equal to that of the first piston and being spaced from the portion which is of smaller diameter, which projects into the interior of the first piston which is hollow, and a passage in the stationary member interconnects the bores at all times.

This ensures that the wetted guiding surfaces are of substantial length to ensure stability of the clamp member when the brake is applied and to provide a bearing area which is adequate to take the drag on the indirectly actuated friction pad which is carried by the clamp member.

Alternatively a first piston acts on the directly actuated friction pad assembly, and at least two second pistons of which the sum area is equal to that of the first piston act on the clamp member and the bores are interconnected by passage means in the stationary member, the second bores comprising the drag-taking guiding surfaces, with the second pistons comprising the complementary dragtransmitting surfaces. At least one of the second pistons is coupled to the clamp member and one of the second pistons may extend into a bore defined by the interior of the first piston which is hollow. In such a construction the remaining second piston works in a separate bore in the stationary member. Alternatively both second pistons work in bores on opposite sides of the bore for the first piston and one or both second pistons are coupled to the clamp member.

The brake according to this invention is symmetrical, so that the parts are the same for the brakes on both sides of the vehicle. It is easy to machine as it permits ready access to robustly supported machining tools.

Two embodiments of our invention are illustrated in the accompanying drawings in which: Figure 1 is a side elevation of an hydraulically operated disc brake for a vehicle; Figure 2 is a longitudinal section through the brake; Figure 3 is a plan view including a section on the line 23 of Figure 4; Figure 4 is an end elevation including a section on the line 44 of Figure 3; Figure 5 is similar to the sectioned part of Figure 3 but showing a modification; and Figure 6 is a transverse section through a further brake.

The hydraulically operated disc brake illustrated in Figures 1 to 4 of the drawings comprises a stationary drag-taking member 1 mounted on a stationary part adjacent to one face of a rotatable disc not shown. A onepiece clamp member 2 in the form of a yoke fits over the member 1 and the disc and comprises axially spaced inwardly directed radial limbs 3, 4 which are interconnected by an integral bridge piece 5 having a central portion removed. The drag taking member 1 is provided with a pair of circumferentially spaced forwardly directed arms 6 which terminate short of the disc and between which a directly actuated friction pad assembly 7 is guided for movement relatively to the disc.

An indirectly actuated friction pad assembly 8 is located on the opposite side of the disc and is coupled to the clamp member 2. Each friction pad assembly 7, 8 comprises a pad 9 of friction material carried by a rigid backing plate 10. The end edges of the backing plate of the assembly 7 engage directly with the arms 6 and the assembly is retained against radial movement by spaced pins 11 which are externally accessible and which are received in elongate openings 12 in the assembly 7. The assembly 8 is coupled to the clamp member 2 by a pair of roll pins 13 which extend through the limb 4 and are received at their ends in openings in the backing plate 10.

Hydraulic actuating means incorporated in the drag-taking member 1 are arranged to apply the pad assembly 7 directly to the disc and simultaneously act through the clamp member 2 to apply the indirectly actuated friction pad assembly 8 to the opposite face of the disc. The hydraulic actuating means comprise opposed pistons 14 and 15 working in co-axial bores 16 and 17 in the drag-taking member 1. The piston 14 is of cup-shaped outline and engages at its closed end with the backing plate 10 of the directly actuated friction pad assembly 7, and the piston 15 is of differential outline working in the bore 17 which is stepped. The bore 17 comprises a bore portion 18 of a diameter equal to that of the bore 16, and a bore portion 19 of reduced diameter extending through radial extension 20 of annular outline which projects into the interior or "dead space" of the piston 14 by a substantial distance but is spaced from the piston 14. Thus the piston 15 has a substantial length over which it is guided in the dragtaking member 1, and passages 21 in the extension 20 provide communication at all times between the bores 16 and 17 so that the lengths of the piston inboard of hydraulic seals 22 and 23 are permanently wetted by the hydraulic brake fluid within the bores.

Annular flexible boots 24, 25 are received in recesses at each end of the stationary member and in annular grooves in the pistons 14, 15 respectively, so that the bore portions are completely sealed from the atmosphere. The attachment surfaces are plain cylindrical surfaces.

The clamp member 2 is positively and rigidly coupled to the piston 15 by means of a bolt 26 which is passed through an opening in the limb 3 and is screwed into a tapped hole 27 in the piston 15. The bolt 26 comprises the sole connection between the clamp member 2 and the actuating means, and the piston 15 and the stepped bore 17 define the part of the slidable connection comprising the guiding surfaces between the clamp member 2 and the drag taking member 1. A recess 28 located in the end of the piston 15 which is adjacent to the clamp member 2 may receive a plug (not shown) to protect the bolt 26 from the elements. In a modification the limb 3 of the claml. member 2 may be extended so that it completely covers the recess 28.

As will be observed from the drawings there is otherwise a clearance 29 between the clamp member 2 and the drag-taking member 1, although opposite sides of the clamp member 2 carry pads 30 of relatively small area slidably engaging with plane surfaces 31 on the drag-taking member to prevent the clamp member 2 from moving angularly about the axis of the bores 16 and 17 as it is moved axially in the application of the brake. In a modification a splined engagement may be provided between the bore portion 19 and the portion of the piston 15 which is of smaller diameter.

When the brake is applied by pressurising a space communicating with both bores 16 and 17, the directly actuated friction pad assembly 7 is applied directly to the adjacent face of the disc by the piston 14 and because of a clearance between the pins 11 and the openings 12, the pad assembly 7 is carried round with the disc and urged into engagement with the arm 6 at the forward end of the brake which takes the drag on that pad assembly. Simultaneously the piston 15 is urged in the opposite direction and carries the clamp member 2 with it to apply the indirectly actuated friction pad assembly to the disc.

Since the pad assembly 8 is carried by the clamp member 2, the drag on that assembly is transmitted to the stationary member 1 through the piston 15 and the bore 17 which comprises the slide guiding surfaces, the drag being received by spaced cylindrical bore portions at the same forward end of the brake as the arm 6.

In the modified construction of Figure 5 the radial extension 20 is extended axially away from the piston 14 to increase the length of the bore portion 19 and the piston 15 is of two part construction comprising a hollow piston part 31 which works in the bore portion 18, and a piston part or core piece 32 which extends through an opening 33 in the outer end of the piston part 31 and works in the bore portion 19. The free outer end of the part 32 is provided with a radial flange 34 which is received in a recess 35 in the clamp member 2 and is clamped against an annular seal 36 in the outer end of the piston part 31 by means of a Belleville washer 37 which ensures that the seal 26 is constantly nipped.

Exact concentricity is required between the bore portions 18 and 19 and between the stepped piston diameters. This can easily by achieved. There is no exact concentricity requirement between the bores 16 and 18.

The construction and operation of the embodiment of Figure 5 is otherwise the same as that of Figures 1 to 4 and corresponding reference numerals have been applied to corresponding parts.

In the brake illustrated in Figure 6 the piston 15 is comprised of two separate piston parts 40 and 41 working in separate bores 42 and 43 of which the bore 43 is co-axial with and of smaller diameter than the bore 16, and the bore 42 is spaced to one side of the bores 16 and 43. The piston 41 extends into the "dead-space" of the piston 14 and the total area of the pistons 40 and 41 is equal to that of the piston 14. Both pistons 40 and 41 are coupled to the limb 3 of the clamp member 2 by means of a headed stud 44 which is received in the open outer end of the piston 41 which is of cup-shaped outline, and a bolt 45 which is screwed into a tapped bore 46 in the piston 40 through an opening 47 in the limb 3. All three bores 16, 42 and 43 are in permanent communication at all times through passages not shown.

In this construction the clamp member 2 is guided for axial movement relatively to the stationary member 1 through both pistons 40 and 41 through which the drag on the indirectly actuated friction pad assembly 8 is transmitted to the bores 42 and 43 when the brake is applied.

The construction and operation of the brake of Figure 6 is otherwise the same as those described above, and corresponding reference numerals have been applied to corresponding parts.

In a further modification the piston 41 may work in a further separate bore in the member 1 disposed in the clamp member 2 on the side of the bore 16 opposite the bore 42.

In the embodiments described above the stationary drag-taking member 1 containing the bores is very robust so that it retains its shape during the worst conditions to ensure that the pistons can always slide freely in the bores. The inherent rigidity of the member 1 provides a rigid slide for clamp member 2 through the piston to which it is rigidly coupled.

Thus the drag forces from the indirectly actuated friction pad assembly 8 can easily be sustained by the slides, without the necessity of providing a separate robust slide.

The space for accommodating the bridge piece of the clamp member 2 is substantially unrestricted. The bridge may be of a substantial circumferential width, thus permitting a reduced radial section. The clamp member 2 can therefore be constructed from a material, for example aluminium, which is light and easy to machine, but which is not as strong as more conventional material, for example steel. Furthermore manufacture is facilitated since the guiding surfaces are not formed or machined in or on the clamp member 2 itself.

WHAT WE CLAIM IS: 1. A disc brake of the kind set forth for vehicles in which the stationary member is located wholly on one side of the disc, and the hydraulic actuating means comprises first and second hydraulic pistons working in respective first and second bores in the stationary member, with at least one first piston acting on the directly actuated friction pad assembly and movable in a direction to urge the pad assembly into engagement with the disc, and at least one second piston coupled to the clamp member and movable in the opposite direction to apply the indirectly actuated friction pad assembly to the opposite face of the disc, the bores being in communication at all times, and a slidable connection is provided between the clamp member and the stationary member, the slidable connection including spaced drag-taking guiding surfaces on the stationary member and complementary drag-transmitting surfaces on the clamp member, the guiding surfaces including the second bore, with the second piston comprising its complementary drag-transmitting surface, and the guiding surfaces being wetted by hydraulic fluid of the actuator at least when the brake is in use.

2. A disc brake according to Claim 1, in which the pistons comprise a pair of oppositely acting pistons working in bores which are co-axial and equal in diameter.

3. A disc brake according to Claim 1 or 2, in which the bore in which the second piston works and the second piston itself comprise the drag-taking guiding surfaces and the complementary drag-transmitting surfaces respectively, being of stepped outline, with the portion of the piston which is of greater diameter being equal to that of the first piston and being spaced from the portion which is of smaller diameter, which projects into the interior of the first piston which is hollow, and a passage in the stationary member interconnects the bores at all time.

4. A disc brake according to Claim 3, in which the bore portion of smaller diameter

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. portion 18, and a piston part or core piece 32 which extends through an opening 33 in the outer end of the piston part 31 and works in the bore portion 19. The free outer end of the part 32 is provided with a radial flange 34 which is received in a recess 35 in the clamp member 2 and is clamped against an annular seal 36 in the outer end of the piston part 31 by means of a Belleville washer 37 which ensures that the seal 26 is constantly nipped. Exact concentricity is required between the bore portions 18 and 19 and between the stepped piston diameters. This can easily by achieved. There is no exact concentricity requirement between the bores 16 and 18. The construction and operation of the embodiment of Figure 5 is otherwise the same as that of Figures 1 to 4 and corresponding reference numerals have been applied to corresponding parts. In the brake illustrated in Figure 6 the piston 15 is comprised of two separate piston parts 40 and 41 working in separate bores 42 and 43 of which the bore 43 is co-axial with and of smaller diameter than the bore 16, and the bore 42 is spaced to one side of the bores 16 and 43. The piston 41 extends into the "dead-space" of the piston 14 and the total area of the pistons 40 and 41 is equal to that of the piston 14. Both pistons 40 and 41 are coupled to the limb 3 of the clamp member 2 by means of a headed stud 44 which is received in the open outer end of the piston 41 which is of cup-shaped outline, and a bolt 45 which is screwed into a tapped bore 46 in the piston 40 through an opening 47 in the limb 3. All three bores 16, 42 and 43 are in permanent communication at all times through passages not shown. In this construction the clamp member 2 is guided for axial movement relatively to the stationary member 1 through both pistons 40 and 41 through which the drag on the indirectly actuated friction pad assembly 8 is transmitted to the bores 42 and 43 when the brake is applied. The construction and operation of the brake of Figure 6 is otherwise the same as those described above, and corresponding reference numerals have been applied to corresponding parts. In a further modification the piston 41 may work in a further separate bore in the member 1 disposed in the clamp member 2 on the side of the bore 16 opposite the bore 42. In the embodiments described above the stationary drag-taking member 1 containing the bores is very robust so that it retains its shape during the worst conditions to ensure that the pistons can always slide freely in the bores. The inherent rigidity of the member 1 provides a rigid slide for clamp member 2 through the piston to which it is rigidly coupled. Thus the drag forces from the indirectly actuated friction pad assembly 8 can easily be sustained by the slides, without the necessity of providing a separate robust slide. The space for accommodating the bridge piece of the clamp member 2 is substantially unrestricted. The bridge may be of a substantial circumferential width, thus permitting a reduced radial section. The clamp member 2 can therefore be constructed from a material, for example aluminium, which is light and easy to machine, but which is not as strong as more conventional material, for example steel. Furthermore manufacture is facilitated since the guiding surfaces are not formed or machined in or on the clamp member 2 itself. WHAT WE CLAIM IS:

1. A disc brake of the kind set forth for vehicles in which the stationary member is located wholly on one side of the disc, and the hydraulic actuating means comprises first and second hydraulic pistons working in respective first and second bores in the stationary member, with at least one first piston acting on the directly actuated friction pad assembly and movable in a direction to urge the pad assembly into engagement with the disc, and at least one second piston coupled to the clamp member and movable in the opposite direction to apply the indirectly actuated friction pad assembly to the opposite face of the disc, the bores being in communication at all times, and a slidable connection is provided between the clamp member and the stationary member, the slidable connection including spaced drag-taking guiding surfaces on the stationary member and complementary drag-transmitting surfaces on the clamp member, the guiding surfaces including the second bore, with the second piston comprising its complementary drag-transmitting surface, and the guiding surfaces being wetted by hydraulic fluid of the actuator at least when the brake is in use.

extends through a radial extension of annular outline on the stationary member, the extension projecting into the bore of the first piston but being spaced from it, and passages in the extension interconnecting the bores.

5. A disc brake according to Claim 1, in which the hydraulic actuating means comprises a first piston acting on the directly actuated friction pad assembly, and at least two second pistons of which the sum area is equal to that of the first piston acting on the clamp member, the pistons working in bores which are interconnected by passage means in the stationary member, the second bores comprising the drag-taking guiding surfaces, with the second pistons comprising the complementary drag-transmitting surfaces.

6. A disc brake according to Claim 5, in which at least one of the second pistons extends into a bore defined by the interior of the first piston which is hollow.

7. A disc brake according to Claim 6, in which the remaining second piston works in a separate bore in the stationary member.

8. A disc brake according to Claim 5, in which both second pistons work in bores on opposite sides of the bore for the first piston and one or both second pistons are coupled to the clamp member.

9. A disc brake according to any of Claims 1 to 8, in which the clamp member is positively coupled to the second pistons or one of the second pistons by means of a bolt passing through an opening in a limb of the clamp member and screwed into a tapped hole in the second piston.

10. A disc brake according to Claim 9, in which a recess is located in the end of the piston which is adjacent to the clamp member.

11. A disc brake according to Claim 10, in which a plug is received in the recess to protect the bolt.

12. A disc brake according to Claim 10, in which the limb of the clamp member is extended so that it completely covers the recess.

13. A disc brake substantially as herein described with reference to and as illustrated in Figures 1 to 4 of the accompanying drawings.

14. A disc brake substantially as herein described with reference to and as illustrated in Figures 5 of the accompanying drawings.

15. A disc brake substantially as herein described with reference to and as illustrated in Figure 6 of the accompanying drawings.