GB1572153A

GB1572153A - Brake actuating means

Info

Publication number: GB1572153A
Application number: GB4261875A
Authority: GB
Original assignee: GKN Axles Ltd
Current assignee: Dana Spicer Europe Ltd
Priority date: 1976-12-06
Filing date: 1976-12-06
Publication date: 1980-07-23

Description

(54) BRAKE ACTUATING MEANS (71) We, GKN AXLES LIMITED, a British Company of Old Bromford Lane, Ward End, Birmingham, B8 2RQ, 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 brake actuating means including a wear adjuster.

According to the invention we provide brake actuating means comprising a housing, first and second coaxial piston and cylinder assemblies in the housing, the first piston being movable in a first axial direction to apply a brake by pressure fluid introduced into the first cylinder and being urged in a second axial direction opposite to the first direction to a rest position by return spring means, the second piston being urged in said first direction by actuating spring means stronger than the return spring means and being movable in the second direction against the actuating spring means to an inoperative position by pressure fluid introduced into the second cylinder; oppositely directed abutment surfaces on the pistons which are urged into engagement by the return spring means so that the inoperative position of the second piston determines the rest position of the first piston; and means for adjusting said inoperative position to compensate for brake wear, said means comprising a stepped formation on one of the second piston and a part of the housing, a recess in the other of said housing part and the second piston and an adjustment element engaged with said formation and received in said recess with a predetermined clearance, the inoperative position of the second piston being determined by engagement of the element with one wall of the recess, the arrangement being such that if during movement of the second piston in said first direction from its operative position by the actuating spring means said predetermined clearance is exceeded the adjustment element engages the opposite wall of the recess and the element is thus moved from one step of said formation onto another thus changing the inoperative position of the second piston and thus the rest position of the first piston.

The invention will now be described by way of example with reference to the accompanying drawings in which : - Figure 1 is a section on the line ; A-A of Figure 2 through a brake pack having actuating means embodying the invention; Figure 2 is an end view in the directon of the arrow A of Figure 1; Figure 3 is a diagram showing the positions taken up by a spring ring which forms part of the actuating means; and Figure 4 is a part section on the line B-B of Figure 2 to Figure 1 2.

Referring to Figures 1 to 4 these show a brake assembly embodying the invention which comprises a reaction housing 10 which is secured to an axle housing 11 by bolts 12 which extend through a circumferentially extending flange 13 which is welded to the axle housing 11. The reaction housing 10 is also provided with radially inwardly extending lugs 14 which project into slots in the flange 13. The lugs 14 also project axially beyond the end face proper of the housing 10 which is shown at 10a in Figure 1.

The housing 10 is provided with six circumferentially spaced cavities 15 one or more of which may house a disc brake pack 16 and brake actuating means 17 of the form shown in Figure 1. In the particular arrangement illustrated only four of the cavities 15a to 15d house operative brake packs and actuating means. The other two cavities 15e and 1St may either be empty of brake packs and actuating means or, if brake packs and actuating means are carried, for example as spares, these packs and actuating means will be rendered inoperative.

It will be appreciated that the capacity of the brake assembly can be varied by varying the number of brake packs, the more brake packs the greater the braking torque that can be applied.

Referring to Figure 1, a wheel hub 18 is carried on the axle housing 11 on a roller bearing 19. The hub is driven from a live axle 20 within the housing 11 by planetary reduction gearing (not shown).

Each brake pack 16 disposed in the cavities 15a to 15d comprises a plurality of discs some of which are indicated at 21 and are received on splines 22 provided on a shaft 23. Interleaved with the discs 21 are discs 24 which have cut-outs in their outer peripheries which engage the spacer sleeves 25 carried on bolts 26. The discs 21 have facings of friction material for engagement by the discs 24.

The shaft 23 is supported adjacent one end in the housing 10 by a needle roller bearing 27. The other end of the shaft 23 is of reduced diameter as indicated at 28 and is supported in a needle roller bearing 29 received in a boss 30 formed in an end plate 31 which closes the cavity.

A housing 32 is disposed between the end plate 31 and the spacing sleeves 25. The bolts 26, three of which are provided per cavity, extend through the end plate 31, the housing 32 and the spacing sleeves 25 and have threaded end portions 33 which engage tapped holes in the housing 10. A seal 34 prevents any escape of liquid from the cavity around the edge of the end plate 31.

The housing 32 is provided with a cyliridrical bore and a radially inwardly extending abutment 35 which divides the bore of the housing into first and second coaxial cylinders 36 and 37 respectively. A first piston 38 is disposed in the cylinder 36 and is maintained in sealed sliding contact therewith by a seal 41. The piston 38 has an end portion 39 outside the cylinder 36 which is of increased diameter and which may be brought into contact with the adjacent end disc 21 of the brake pack.

A second piston 40 provided with a seal 42 is slidable in the second cylinder 37.

The second piston has a shank portion 43 which projects through the abutment 35 and is sealed thereto by a seal 44. The shank portion 43 extends within a counterbore 45 in the first piston 38 and is sealed thereto by a seal 46. The first and second pistons engage at oppositely directed abutment surfaces indicated at 47 and formed by the end of the shank 43 and the base of the counterbore 45.

The first piston 38 is urged to the right as shown in Figure 1 by means of return spring means in the form of a number of return springs, one of which is shown at 48, which surround the pins 49 which are supported at one end in apertures 50 in the housing 10 and at the other end in apertures 51 in the housing 32. Each pin 49 passes through a hole 52 in the end portion 39 of the piston 38.

The springs 48 urge the surfaces 47 on the piston 38 and 40 into contact, the piston 40 being itself urged to the left by a pack of Belleville springs 53 forming actuating spring means and which are stronger than the return springs 45. The movement of the second piston 40 to the right is limited by the compressed thickness of the springs 53.

Circlips 54 and 55 are provided on the piston 40 and shaft 23 respectively and a ring member 56 is positioned between these circlips to locate the shaft 23 against movement to the left.

The left hand end of each shaft 23 is provided with a planet gear 57 which meshes with an annulus gear 58 carried by the wheel hub 18. Thus as the wheel hub 18 is driven from the axle 20 the shafts 23 are also rotated thus in turn rotating the brake discs 21.

Hydraulic fluid may be introduced into the part 59 of the first cylinder 26 in order to displace the first piston 38 to the left against the action of the return springs 48 and hence compress the interleaved pack of discs 21 and 24 against a reaction ring 60 thereby braking the rotation of the shaft 23 and hence the wheel hub 18. The cylinders 36 of the actuating means of all the operative disc packs are supplied with hydraulic fluid via an inlet 61 shown in Figure 2. The cylinders 36 are connected in series by circumferentially extending drillings 62 within the housing 10, these terminate in a bleeder 63. As can be seen the drillings 62 also communicate with the inoperative cavities 15e and 15f but do not apply any brake pack which may be disposed in these cavities.

Hydraulic fluid may be introduced into the part 64 of the second cylinder 37 to move the second piston 40 to the right to an inoperative position as shown in Figures 1 and 4 against the action of the Belleville springs 53. The cylinder 37 associated with each brake pack are supplied with hydraulic fluid via an inlet 65, the cylinders being interconnected in series by drillings 66 in the housing 10. Again the drillings 66 com- municste with the inoperative cavities 15e and 15f but do not have any effect therein.

The drillings 66 terminates at a bleeder 66o The cylinders 37 and the associated first pistons 38 constitute a service braking circuit while the cylinders 37 and the associ ated pistons 40 constitute an emergency or parking brake circuit. When hydraulic pressure is available, as when the vehicle is operating normally, this will be supplied to the cylinders 37 via the inlet 65 and will urge the second pistons 40 to the right to the position shown in Figure 1 thus compressing the Belleville spring packs 53.

Assuming that no hydraulic pressure is applied to the cylinders 26, the first pistons 38 will assume the position shown in Figure 1 in which the surfaces 47 are brought into contact under the action of the return springs 48 thus ensuring that the brake is not applied.

Assuming now that the driver wishes to apply the brake, he operates the brake pedal which will supply hydraulic pressure to the cylinders 36 via the inlet 61. This will move each first piston 38 to the left against the action of the springs 48 thus applying the brake by forcing the discs 21 and 24 into engagement with the pressure plate 60.

Should the supply of hydraulic pressure fail, thereby preventing the driver from activating the service circuit by pressurising the cylinders 36, the hydraulic pressure in cylinders 37 will also fail and thus the Belleville spring packs 53 will displace the second piston 40 to the left thereby in turn also displacing the first pistons 38 to the left and applying the brake under the action of the spring packs 53. This is thus a fail safe arrangement in which the brake is applied automatically in the event of an hydraulic failure.

A parking brake function can also be provided by exhausting the cylinders 37 and hence applying the brake under the action of the spring packs 53.

The brake packs in cavities 15a to 15d are cooled by a supply of cooling oil which enters each of the cavities 15a to 15d via an axial drilling 67 and radial drilling 68 in each shaft 23. The cooling oil is supplied to the drillings 67 by connections 69, which engage outlets 69a provided on a ring shaped manifold 70 which is connected via an inlet 71 with an oil cooler. The outlets 69a for the cavities 15e and 15f are plugged.

Cooling oil enters each disc pack at its inner periphery and leaves at its outer periphery.

The cavities 15 are interconnetced circumferentially and the cooling oil on leaving the cavities collects in a hollow bottom portion 72 of the housing 10 from which it is passed back to the cooler by an outlet 73.

With continued use, the friction surfaces on the brake discs 21 will wear. In order that the response time of the brake shall remain reasonably constant, it is therefore necessary to adiust the rest position which the first piston 38 occupies when the service braking circuit is not actuated and to which it is urged by the return springs 48, the rest position being determined by engagement of the abutment surfaces 47 and the inoperative position of the piston 40.

In the arrangement shown in Figure 1 automatic wear adjustment is provided by a spring ring 74 disposed in an annular recess 75 in the second piston 40. The spring ring 74 is also engageable with steps 76 to 79 provided on a boss 80 formed on the inside of the end plate 31 which forms part of the housing 32 and which is telescoped within the piston 40. This wear adjustment arrangement is shown on an increased scale in Figure 4.

The width of the recess 75 is greater than that of the spring ring 74 thus providing a predetermined clearance and when the brake assembly is initially assembled the ring 74 is positioned on the step 76. Each time the second piston 40 moves to the left, as will occur when the pressure in the cylinder 37 is exhausted in order to park the vehicle, the ring 74 will engage the wall 81 of the recess 75. As the friction facing on the discs 21 wears down the movement of the piston 40 to the left necessary to apply the brake will increase. Eventually this movement will be sufficient to cause the spring 74 to be displaced from the step 76 onto the step 77. This will in turn mean that when the cylinders 37 are pressurised the pistons 40 will not be displaced so far to the right and hence their inoperative positions and the axial positions at which the abutment surfaces 47 on the first and second pistons come into contact will have moved to the left. This will mean that the rest positions of the pistons 38 are closer to the reaction rings 60.

As further wear of the friction facings of the discs 21 occurs the rings 74 will be progressively displaced onto the steps 78 and 79 therefore also progressively moving the inoperative positions of the pistons 40 and the rest positions of the pistons 38 to the left. When the rings 74 reaches the steps 79 the disc brake packs are considered to be fully worn and must be removed for servicing.

Figure 3 shows the various positions of the ring 74. The position 74a corresponds to the ring being engaged with the step 76 while the position 74b corresponds to the ring being engaged with the step 79.

Figure 4 shows bolts 82, two of which are provided per cavity, which may be inserted through the end plate 31 and the housing 32 so that screw-threaded end portions 82a of the bolts engage in tapped holes 83 in the portion 39 of the piston 38.

With the bolts 82 in position the end plate 31, housing 32 first and second pistons 38 and 40, Belleville spring pack 53 and automatic wear adjusting device can be held together as an assembled sub-assembly thus allowing removal from and introduction into the associated cavity 15 as a single unit.

When the sub-assembly has been introduced into its cavity 15 the bolts 82 are removed and the bolt holes plugged by shorter bolts (not shown) which extend through the end plate 31 and engage larger diameter tapped portions 84 of the bores in the cylinder 32 through which the bolts 82 extend. The bolts 82 also have an additional use. As previously described in the event of a pressure failure the brake packs are applied by the Belleville spring packs 53.

If the bolts 82 are then inserted and tightened up to the position shown in Figure 4 this will draw the pistons 38 to the right thus releasing the brake packs and allowing the vehicle to be moved.

In an alternative wear adjustment arrangement, not illustrated, the stepped formation may be provided on the piston 40 and the recess 75 may be provided on the boss or having part 80. In such an arrangement, when the parts were assembled. the ring 74 would be placed on the step of smallest diameter and would be arranged to be moved progressively towards the step of the largest diameter to adjust the relative rest position as wear took place.

WHAT WE CLAIM IS:- 1. Brake actuating means comprising a housing, first and second coaxial piston and cylinder assemblies in the housing, the first piston being movable in a first axial direction to apply a brake by pressure fluid introduced into the first cylinder and being urged in a second axial direction opposite to the first direction to a rest position by return spring means, the second piston being urged in said first direction by actuating spring means stronger than the return spring means and being movable in the second direction against the actuating spring means to an inoperative position by pressure fluid introduced into the second cylinder; oppositely directed abutment surfaces on the pistons which are urged into engagement by the return spring means so that the inoperative position of the second piston determines the rest position of the first piston; and means for adjusting said- inoperative position to compensate for brake wear, said means comprising a stepped formation on one of the second piston and a part of the housing, a recess in the other of said housing part and the second piston and an adjustment element engaged with said formation and received in said recess with a predetermined clearance, the inoperative position of the second piston being determined by engagement of the element with one wall of the recess, the arrangement being such that if during movement of the second piston in said first direction from its operative position by the actuating spring means said predetermined clearance is exceeded the adjustment element engages the opposite wall of the recess and the element is thus moved from one step of said formation onto another thus changing the inoperative position of the second piston and thus the rest position of the first piston.

2. Brake actuating means according to Claim 1 wherein the second piston and the housing part are arranged telescopically, the adjustment element is a spring ring, said recess is annular and the stepped formation comprises annular steps of different diameters.

3. Brake actuating means according to Claim 2 wherein the second piston surrounds said housing part, said recess being formed in the second piston.

4. Brake actuating means according to any one of the preceding claims wherein the second piston bas a shank portion which extends within a counterbore in the first piston, the end of the shank portion and base of the counterbore providing said abutment surfaces.

5. Brake actuating means according to Claim 4 wherein said housing has a cylin drical bore which forms said first and second cylinders which are separated by a radially inwardly extending abutment which is seal ingly and slidably engaged with said shank portion.

6. The combination of brake actuating means according to any one of the pre ceding claims with a multiple disc brake and wherein the first piston is arranged to operate the brake.

7. Brake actuating means substantially as hereinbefore described with reference to and as shown in Figures 1 and 4 of the accompanying drawings.

8. A brake assembly substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. together as an assembled sub-assembly thus allowing removal from and introduction into the associated cavity 15 as a single unit. When the sub-assembly has been introduced into its cavity 15 the bolts 82 are removed and the bolt holes plugged by shorter bolts (not shown) which extend through the end plate 31 and engage larger diameter tapped portions 84 of the bores in the cylinder 32 through which the bolts 82 extend. The bolts 82 also have an additional use. As previously described in the event of a pressure failure the brake packs are applied by the Belleville spring packs 53. If the bolts 82 are then inserted and tightened up to the position shown in Figure 4 this will draw the pistons 38 to the right thus releasing the brake packs and allowing the vehicle to be moved. In an alternative wear adjustment arrangement, not illustrated, the stepped formation may be provided on the piston 40 and the recess 75 may be provided on the boss or having part 80. In such an arrangement, when the parts were assembled. the ring 74 would be placed on the step of smallest diameter and would be arranged to be moved progressively towards the step of the largest diameter to adjust the relative rest position as wear took place. WHAT WE CLAIM IS:-

1. Brake actuating means comprising a housing, first and second coaxial piston and cylinder assemblies in the housing, the first piston being movable in a first axial direction to apply a brake by pressure fluid introduced into the first cylinder and being urged in a second axial direction opposite to the first direction to a rest position by return spring means, the second piston being urged in said first direction by actuating spring means stronger than the return spring means and being movable in the second direction against the actuating spring means to an inoperative position by pressure fluid introduced into the second cylinder; oppositely directed abutment surfaces on the pistons which are urged into engagement by the return spring means so that the inoperative position of the second piston determines the rest position of the first piston; and means for adjusting said- inoperative position to compensate for brake wear, said means comprising a stepped formation on one of the second piston and a part of the housing, a recess in the other of said housing part and the second piston and an adjustment element engaged with said formation and received in said recess with a predetermined clearance, the inoperative position of the second piston being determined by engagement of the element with one wall of the recess, the arrangement being such that if during movement of the second piston in said first direction from its operative position by the actuating spring means said predetermined clearance is exceeded the adjustment element engages the opposite wall of the recess and the element is thus moved from one step of said formation onto another thus changing the inoperative position of the second piston and thus the rest position of the first piston.