A DISC BRAKE

DESCRIPTION OF THE INVENTION

[0001] This invention relates to a retraction arrangement wherein first and second friction members in a disc brake are magnetically moved away from a rotor to define a running clearance after each brake application.

BACKGROUND OF THE INVENTION

[0002] Disc brakes have spaced apart first and second rails that extend from a support member that is fixed to a frame of a vehicle guide to align and position first and second friction members with respect to a rotor of which the structure in the following U.S. Patents 4,200,173 and 6,454,056 may be considered as representative of the prior art. In such disc brakes, first and second guide pins are fixed to a caliper and extend through ears on the support member with the guide pins being retained in corresponding first and second bores in the support member such that they are parallel with the first and second rails. A piston located in a bore of the caliper is connected to the first friction member and when pressurized fluid is presented to the bore, a force is created that pushes the piston toward the caliper while pulling the caliper toward the rotor to bring pads on the first and second friction members into engagement with the rotor and effect a brake application. On termination of the supply of pressurized fluid to the bore, a retraction seal acts on and moves the piston and caliper such that the pads on the first and second friction members are moved away from the rotor to define a running clearance. Such disc brakes function in an adequate manner however movement by the caliper and bringing the second friction pad into engagement with the rotor requires the caliper to move a greater distance than the piston and as a result the retraction of the pads on the first and second friction members away from the rotor may not always result in equal running clearances between each pad and rotor. Unfortunately unequal running clearances may occur if a vehicle is traveling on certain uneven terrain, therefore it is possible that a pad may inadvertently engage the rotor and cause unwanted wear or noise.

[0003] It has been suggested that equal retraction may be achieved by attaching arms on slipper members that are placed on the rails of a support member of which U.S. Patent 4,245,723 may be considered as typical. While such devices function in an adequate manner, no provision is provided to account for a change in the thickness of the pad of a friction member and as a result the resulting running clearance may vary as a function of the change in such thickness.

SUMMARY OF THE INVENTION

[0004] A primary object of the present invention is to provide a disc brake with a retraction arrangement whereby the friction pads are magnetically attached and moved as the result of a seal positioning an actuation piston to define equal running clearances after each brake application for first and second friction members on opposite sides of a rotor.

[0005] According to this invention, the disc brake assembly has a support member that is secured to a vehicle. A caliper retained in the support member has

an actuation section that is connected by a bridge to an arm. The actuation section has an actuation bore therein for retaining a piston to define an actuation chamber. A first friction member is connected to the piston and aligned with a first braking surface on a rotor associated with a wheel on the vehicle. A second friction member is connected to the arm and aligned with a second braking surface on the rotor. The actuation chamber on being presented pressurized fluid from a source acts on the piston to develop an actuation force that moves the piston and a pad on first friction member toward and into engagement with the first braking surface and acts on the actuation section such that the caliper moves a pad on the second friction member into engagement with the second braking surface to effect a brake application. On termination of the presence of pressurized fluid in the actuation chamber, a retraction arrangement that includes magnetic members moves the first and second friction members away from the rotor to define a first running clearance between the first pad and the first braking surface and a second running clearance between the second pad and the second braking surface.

[0006] An advantage of the disc brake in this invention resides in a plurality of magnetic members that move with a retraction arrangement to position pads associated with first and second friction members a same distance away from a rotor after each brake application.

[0007] A further advantage of this disc brake resides in a retraction arrangement that includes magnetic members whereby a first friction member and a second friction member are concurrently moved away from a rotor to define equilateral running clearances after each brake application in retraction of the pads.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a perspective view of a disc brake having been made according to the principals of the present invention;

[0009] Figure 2 is a sectional view of the disc brake of Figure I in a rest position taken along lines 2-2;

[0010] Figure 3 is a sectional view of the disc brake of Figure 1 taken along lines 3-3;

[0011] Figure 4 is a sectional view of the disc brake of Figure 3 taken along line 4-4; and

[0012] Figure 5 is a sectional view of a second embodiment of a piston and magnetic member.

DETAILED DESCRIPTION OF THE INVENTION

[0013] The disc brake 10 shown in Figures 1 , 2 and 3 is distinguished from disc brakes of the prior art such as U.S. Patent 4,200,173 by a magnetic retraction arrangement 70, 70' of the present invention whereby first 30 and second 32 friction members are moved away from a rotor 34 to assist in defining first and second running clearances after each brake application.

[0014] The anchor 12 is defined by a base 35 that is fixed to the housing 14 of a vehicle by bolts 15 (only one is shown) to position spaced apart first 36 and second 38 rails thereon along perpendicular planes with respect to rotor 34. An ear 29a on

a backing plate 29 of a first friction member 30 and ear 31a on backing plate 31 of a second friction member 32 are respectively located on the first rail 36 while ear 29b on backing plate 29 of the first friction member 30 and ear 31b on backing plate 31 of the second friction member 32 are respectively located on the second rail 38 such that face 3Of on the first friction member 30 and face 32f on the second friction member 32 are respective located in parallel alignment with face 34a and 34b on rotor 34.

[0015] The anchor or support 12 receives an integral caliper 16 of disc brake 10 such that an actuation section 18 is connected by a bridge 22 to arms 20, 20' that straddles the rotor 34. The actuation section 18 has a bore 24 therein for retention of a piston 26 to define an actuation chamber 28. The first friction member 30 is connected to piston 26 while the second friction member 32 is connected to arms 20,20' to respectively locate the first 30 and second 32 friction members adjacent to the first braking face 34a and the second braking face 34b of the rotor 34 which is connected to rotate with an axle of the vehicle. The alignment of the caliper 16 on the support member 12 is achieved by a first guide pin 42 that is connected to an ear 44 that extends from the actuation section 18 and is mounted to slide in a first bore 46 in the support member 12 and a second guide pin 48 that is connected to an ear 50 that extends from the actuation section 18 and mounted to slide in a second bore 52 in the support member 12. The first 46 and second 52 bores are spaced apart, parallel, and designed to respectively hold the first guide pin 42 and the second guide pin 48 in a perpendicular relationship with respect to the rotor 34 such that the first friction member 30 is held in a first plane that is parallel with the first braking surface 34a and the second friction member 32 is held in a second plane that is parallel with the second braking face 34b on rotor 34. [0016] When an operator desires to effect a brake application, pressurized fluid is supplied to the actuation chamber 28 that acts on a piston 26 and moves face 3Of of the pad 30a on the first friction member 30 into engagement with the first braking surface 34a and acts on caliper 16 to move the face 32f of the pad 32a on the second friction member 32 into engagement with the second braking surface 34b to develop a brake force to reduce the rotation of rotor 34. As long as pressurized fluid is presented to the actuation chamber 28, braking continues until the rotation of the rotor 34 is reduced to a level corresponding to the presentation of pressurized fluid to actuation chamber 28 under the control of an operator. On termination of or the absence of pressurized fluid in actuation chamber 28, seal 27 of the retraction arrangement 70 acts on piston 26 to urge the piston 26 toward a position of rest in the actuation chamber 28, at the same time the first 72 and second 74, 74' retraction members respectively act on backing plate 29 of the first friction member 30 and on backing plate 31 of the second friction member 32 to move pads 30a and 32a away from face 34a and 34b on rotor 34 to define first and second running clearances.

[0017] The first 72 and second 74, 74' retraction members of the retraction arrangement 70, 70' are defined by a magnetic material. The first retraction member 72 is defined by an end cap that is attached to piston 26 with the end cap being retained in a groove 33 as show in figures 2 and 4. Alternately, the first

retraction member 72 may be defined as a disc 72a that is retained in a piston 26a as illustrated in figure 5.

[0018] The second retraction member 74, 74' is defined by a plurality of buttons that are located in grooves 21 , 21 ' and on arms 20, 20' as illustrated in figures 2 and 3. The number and size of the buttons may vary but it is suggested that the effective area of the buttons be equal to the end cap such that metal backing plate 29 and metal backing plate 31 are held with a same force within the caliper 16. Thus, the metal backing plate 29 and the metal backing plate 31 move in the same manner as the piston 26 moves away from the rotor 34 to define running clearances X and X' as shown in figure 3.

MODE OF OPERATION OF THE INVENTION

[0019] When an operator desires to effect a brake application, pressurized fluid is supplied to an actuation chamber 28 that acts on piston 26 and acts on actuation section 18 to develop an actuation force that respectively move pad 30a on the first friction member 30 into engagement with face 34a and move pad 32a on the second friction member 32 into engagement with face 34b of rotor to retard the rotation of rotor 34 and effect a brake application. On termination of the application of pressurized fluid to the actuation chamber 28, seal 27 moves piston 26 away from rotor 34. At the same time, the magnetic attraction of retraction member 72 with metal plate 29 moves the first friction member 30 away from the rotor 34 and the magnetic attraction of retraction member 74, 74' with metal plate 31 moves the second friction member 32 away from the rotor 34 to define the desired running clearance as illustrated in figure 3.