Background Spring-actuated, hydraulically releasable brakes are known which employ actuating springs to urge brake pads against brake discs and hydraulic piston and cylinder assemblies for releasing the brake pads from fictional engagement with the brake discs against the action of the springs.

After repeated use, the brake pads become worn and consequently the effectiveness of the brakes is reduced. However, due to the high braking capacities, direct acting functions and small retracted lining clearances of spring-actuated, hydraulically releasable brakes, automatic wear adjusters have not been common in such brakes. Not only does lack of adjustment of the brakes result in reduced braking capacities, but it can also severely reduce the fatigue life of the actuating springs. It has therefore usually been necessary to counteract brake pad or lining wear by manual adjustment of the brakes.

However, manual brake adjustment is time-consuming and risky.

In United States Patent Number 5,076, 401, there is disclosed a spring-actuated, hydraulically releasable brake, comprising a brake disc extending between first and second brake pads, a spring assembly urging the first pad toward the brake disc, a hydraulic piston and cylinder assembly operable to effect a brake releasing displacement of the first brake pad from the brake disc against the action of the spring assembly and comprising a piston, and a brake adjustment mechanism responsive to the amount of the

brake releasing displacement for adjusting the first brake pad toward the brake disc so as to counteract wear of the first brake pad.

In this prior device, there are included levers which are intended only for manual release action and limit switch action but which are not suitable or intended for a self-adjusting action.

Disclosure of Invention It is, accordingly, an object of the present invention to provide a novel and improved spring-actuated, hydraulically releasable brake which is automatically self-adjusting so as to be maintained in proper adjustment, regardless of lining wear and without manual adjustment of the brake.

According to the present invention, a spring-activated, hydraulically releasable brake of the above-described type is characterized in that the brake adjustment mechanism comprises components for exerting a force acting at 90 degrees to the longitudinal axis of the piston for effecting the adjustment of the first brake pad.

In a preferred embodiment of the invention, the hydraulic piston and cylinder assembly includes a piston rod extending between the piston and the first brake pad and an adjustable connection is provided between the first brake pad and the piston rod, the brake adjustment mechanism serving to adjust the adjustable connection.

The brake adjustment mechanism preferably includes a mechanical motion sensor responsive to the operation of the hydraulic piston and cylinder assembly.

The brake adjustment mechanism may comprises a motion amplifier responsive to displacement of the piston for transmitting an amplification of such displacement.

Preferably, the adjustable connection comprises a threaded connection between the first brake pad and the piston rod and the brake adjustment mechanism includes a mechanism to the motion amplifier for rotatably adjusting the threaded connection.

The brake adjustment mechanism may comprise a motion amplifier responsive to displacement of the piston for transmitting an amplification of such displacement through a lost-motion connection to rotate a piston rod connected to the piston, a one-way clutch connected between the motion amplifier and the piston rod and a threaded connection between the piston rod and the first brake pad for adjusting the latter in response to the rotation of the piston rod.

A one-way clutch may be provided on a rotatable shaft which is co-axially connected to a plunger carrying the first brake pad through a connection allowing the plunger to slide longitudinally relative to the piston rod, the threaded connection being between the plunger and the piston rod.

The motion amplifier may comprise a lever which is pivotable in response to displacement of the piston and a link between the lever and the one-way clutch, a lost-motion connection being provided between the link and the one-way clutch.

The link may be displaceable against the action of a spring to allow disengagement of the lost motion connection.

The motion amplifier may be pivotally biassed by a spring into contact with the piston.

A shaft co-axial with a piston rod may be connected to the piston, the lost motion connection comprising a slot in a link connected to the motion amplifier and a pin projecting from the shaft into the slot.

Brief Description of the Drawings The invention will be more readily understood from the following description of preferred embodiments thereof given, by way of example only, with reference to the accompanying drawings, in which:- Figure 1A shows a view taken in vertical cross-section through a spring-actuated, hydraulically releasable brake embodying the present invention in a released condition; Figure 1B shows a plan view of the brake as shown in Figure 1A ; Figure 2B shows a view corresponding to that of Figure 1 A, but with the brake in a spring- actuated condition; Figure 2B shows a plan view of the brake as shown in Figure 2B; Figure 3A shows a view corresponding to that of Figure 1A, but with the brake out of adjustment ; Figure 3B shows a plan view of the brake as shown in Figure 3 A ; Figure 4 shows a view in perspective of a mechanical motion sensor in perspective; Figure 5 shows a view in vertical cross-section through a dual spring stack caliper Description of the Best Mode In Figures 1A and 1B there is shown a spring-actuated, hydraulically releasable brake in the form of a single spring stack sliding caliper brake indicated generally by reference numeral 10 which has a brake body 12 formed with a downwardly-open cylindrical recess 14 and with an upwardly open cylindrical recess 16. An hydraulic piston and cylinder assembly operable to effect a brake releasing displacement of the first brake pad 32, as described below, is formed by the cylindrical recess 16 and a piston 18 in the cylindrical recess 16, the piston 18 being connected to a piston rod 20 which extends downwardly

from the piston 18 through an intermediate cylindrical boring 22 into the cylindrical recess 14.

The piston rod 20 has a downwardly-open axial opening 24 and is connected to a plunger 26, and thus to the first brake pad 32, by an adjustable, threaded connection in the form of screw threads 28 formed on the interior of the piston rod 20 and the exterior of the plunger 26. At its lower end, the plunger 26 has a backing plate 30, on which is provided a first brake lining or pad 32. A brake disc 34 extends between the first brake pad 32 and a second brake lining or pad 36 on a caliper arm 38.

A shaft 40, which is coaxial with the piston rod 20 and the plunger 26, extends downwardly into an upwardly open recess 42 in the plunger 26 and is longitudinally slidably connected to the plunger 26 by means of a transverse pin 44 extending through the plunger 26 and through a downwardly open slot 46 in the lower end of the shaft 40.

A hexagonal nut 48, in threaded engagement with the upper end of the shaft 40, secures a one-way clutch, indicated generally by reference numeral 50, between the nut 48 and a disc 52 seated on the top of the piston 18.

The brake has a brake adjustment mechanism responsive to the amount of brake releasing displacement of the first brake pad 32 for adjusting the threaded connection between the piston rod 18 and the plunger 26 the brake pad 32 toward the brake disc 34 so as to counteract wear of the brake pad 32, the brake adjustment mechanism including a mechanical force transmitting motion amplifier, indicated generally by reference numeral 54, mounted on the brake body 12 and illustrated in greater detail in Figure 4, which is responsive to the displacement of the piston 18 for transmitting an amplification of such displacement.

As shown in Figure 4, the motion amplifier 54 comprises a mechanical motion sensor in the form of a pivotable member or block 56, which in response to the operation of the hydraulic piston and cylinder assembly is pivotal about a pivot pin 58, opposite ends of which are secured in a bracket 60 mounted on the brake body 12. As shown in Figure 1A,

the pivotal block 56 is undercut at its lower side to form a projecting nose 62, which rests on the top of the piston 18 so that, as the piston 18 is displaced upwardly, the pivotal block 56 pivots in an anticlockwise direction, as viewed in Figure 1A, about the pivot pin 58.

The pivotal block 56 is biased in a clockwise direction about the pivot pin 58 by a helical compression spring 64 acting between the bracket 60 and the pivotable block 56, so that the nose 62 is pressed against the top of the piston 18.

The brake adjustment mechanism further includes a adjustment pin 66 provided on the shaft 40 and projecting into a slot 68 formed in one end of a link 70, the opposite end of which is secured to a pivot pin 72 extending through the pivotable block 56.

Consequently, the pivotal movement of the pivotable block 56 causes the link 72 move relative to the pin 66, as described in greater detail below.

The pin 66 and the slot 68 form a lost motion connection between the link 70 and the one way clutch 50, and the motion amplifier 54, the link 70 and the pin 66 are components of the brake adjustment mechanism which exert a force acting at 90 degrees to the longitudinal axis of the piston 18 for effecting the adjustment of the first brake pad 32, as described in greater detail below.

The plunger 26, and therewith the backing plate 30 and the first brake pad 52, are urged toward the brake disc 34 by an assembly of disc springs 76 provided in the cylindrical recess 14, the lower end of this assembly being seated on an annular shoulder 78 on the lower end of the piston rod 20.

The operation of the brake 10 is as follows: When hydraulic fluid is supplied under pressure through a hydraulic port 80 into the cylindrical recess 16, the piston and cylinder assembly comprising the piston 18 and the cylindrical recess 16 is operated so that the piston 18 is displaced upwardly, as viewed in Figure 1A, and the piston rod 20 and, therewith, the first brake pad 32 are raised against the action of the springs 76, thus producing a brake releasing displacement of the first

brake pad 32 from the brake disc 34 against the action of the spring assembly 76 so as to provide a clearance 82 between the first brake pad 32 and the brake disc 34. The consequential pivotation of the pivotal block 56 displaces the link 70 to the left, so that the pin 66 becomes located at the right-hand end of the slot 68.

The pivotal block 56 thereby acts as a force transmitting motion amplifying lever, which causes the movement of the link 70 to be amplified with respect to the upward displacement of the piston 18. Therefore, the relatively small clearance 82 between the first brake pad 32 and the brake disc 34 is amplified by the motion amplifier 54 to an amount which can be better utilized for adjustment of the brake and which makes the adjustment less sensitive to manufacturing clearances and additional clearances between moving parts caused by wear.

When the hydraulic pressure is removed, the springs 76 urge the first brake pad 32 against the brake disc 34, so that the clearance between them is reduced to zero. The link 70 is thereby displaced to the right, as shown in Figure 2 A, so that the pin 66 becomes located at the left-hand end of the slot 68. The length of the slot 68 is selected to correspond to the amount of the displacement of the link 70 when the brake 10 is properly adjusted.

Consequently, when the brake is fully adjusted, no motion is transferred from the link 70 to the adjusting pin 66.

Figure 3A shows the brake 10 with the hydraulic pressure removed, so that the brake is spring-applied. In this case, the operation of the brake has caused wear of the brake pad 32, and the brake 10 is therefore out of adjustment by the amount of the wear of the brake pad 32. This wear causes extra downward displacement of the piston 18, and consequentially provides movement to the right of the link 70 through a distance greater than the length of the slot 68, so that the adjusting pin 66 is correspondingly deflected to the right, by the action of the spring 64 acting through the link 70. The force thereby applied to the link 70 is sufficient to cause rotation of an outer case 86 of the one-way clutch 50.

When the brake 10 is next released, hydraulic pressure is again applied to the piston 18, thereby returning the pivotal block 56 and the link 70 to the positions in which they are shown in Figures 2A and 2B. Although the piston 18 may extend to an out of adjustment condition, it always returns to the same position on release of the brake.

The adjusting pin 66 and, thereby, the outer case 86 of the one-way clutch 50 are subsequently deflected in the opposite direction during the motion of the piston 18 on release of the brake 10, and the one-way clutch 50 is thereby locked, to cause the outer case 86 to be locked to the shaft 40, so that the shaft 40 is correspondingly rotated until the piston motion is complete.

This rotation of the shaft 40 is transmitted through the pin 44 to the plunger 26, and as a result of the threaded engagement of the screw threads 28 on the plunger 26 and the piston 20, the plunger 26 is thereby adjusted longitudinally relative to the piston rod 20 toward the brake disc 34, thereby reducing the amount of the out of adjustment. The piston rod 20 is retained by the action of the springs 76 from rotating with the shaft 40.

This automatic adjustment will continue during the subsequent cycles of operation of the brake until the motion of the link 70 is equal to the length of the slot 68 and, therefore, no further deflection of the adjusting pin 66 occurs.

As shown in Figure 4, a compression spring 90 is provided between the pivotal block 56 and a spring clip 92 at one end of the pivot pin 72. The compression spring 90 biasses the link 70 axially of the pivot pin 72 towards the one-way clutch 50 to maintain the interengagement of the pin 66 and the slot 68, and the pivot pin 72 can be manually displaced axially of the pivot pin 72 against the action of the spring 90 to disengage the link 70 from the adjustment pin 66 and thereby to disengage the lost motion connection between the link 70 and the one-way clutch 50. Manual adjustment of the brake can then be effected by using the hexagonal nut 48 to turn the one-way clutch 50. Such manual adjustment is required for approximate initial adjustment of the brake and for returning the plunger 26 to a fully retracted position when the brake pads 32 and 36 are replaced.

Figure 5 shows a dual spring stack fixed caliper brake which comprises two brake mechanisms, indicated generally by reference numerals 10A and 1 OB, which as will be readily apparent each correspond to the above-described brake 10, and in which components identical to those described above with reference to Figure 1A have, for convenience of illustration, being indicated by reference numerals which correspond to those of Figure 1A, with the addition of the suffixes A and B.

In Figure 5, the second brake pad 36 and the caliper arm 38 of Figure 1A are replaced by the brake mechanism 1 OB, the brake mechanisms 1 OA and 1 OB being mounted at opposite sides of the brake disc 34.

As will be apparent to those skilled in the art, other modifications may be made in the above-described invention within the scope of the appended claims.