COMPACT BRAKE PISTON-RETURN MECHANISM

Abstract: The compact brake piston-return mechanism (10) comprises a housing (22) having a bore (40) with a longi­ tudinal sleeve (50) received fixedly in said bore (40). The sleeve (50) has a through opening (56) receiving therein a piston (60) which extends exteriorily of the through opening (56) to an enlarged diameter portion (69) for engaging a brake stack (32, 35, 36). The piston (60) has an interior opening (66) in which is disposed a de­ formable member (80) connected by means of a ring (70) with the piston (60). A deforming member (90) is dis­ posed within said deformable member (80), deforming mem­ ber (90) extending axially through an aperture (63) at an end (62) of the piston (60) disposed within said bore (40). The deforming member (90) includes a radially extending member (94) which has an axially extending portion (95) that encircles interior ends (52, 62) of the sleeve (50) and piston (60). The axially extending por­ tion (95) extends into a shoulder (97) for abutting a resilient spring (100) which engages at an opposite end a shoulder (57) of the sleeve (50).

Description: The invention relates to a compact brake piston and return mechanism as defined in the preamble of Claim 1. Aircraft brake assemblies require automatic adjusters which compensate for brake wear in order to maintain the hydraulic brake fluid volume essentially constant during brake actuation. Prior automatic adjusters include tube adjusters which utilize a pressure plate assembly disposed between the adjuster and the stack of brake members. Such adjusters are disposed external to pistons, in their own separate bores, and engage the pressure plate assembly. Other automatic adjusters are combined with a piston wherein the piston is returned to the running clearance position against brake back pressure. Adjusters disposed internally of the pistons such as known for example from GB-A-2 017 844 are provided for present-day hydraulic systems which operate at approximately 200 bar maximum brake pressure, although in cases where back pressure is high the design may be marginal because it is difficult to provide a large enough spring in the available space to overcome system back pressure. Future aircraft systems will require much higher hydraulic brake pressures, such as in the order of 550 bar. Such pressures require smaller diameter pistons which preclude the use of internal automatic adjusters due to the lack of sufficient space inside the piston to enclose all of the adjuster parts. It is undesirable from a weight standpoint to revert back to using a pressure plate assembly and adjusters disposed externally of the piston, and therefore a need exists for an automatic adjuster disposed internally of the piston which will fit within the piston of a small diameter piston high pressure system. The present invention fills this need by the features of the characterising part of Claim 1. One way of carrying out the invention is described in detail below with reference to the drawings which illustrate an embodiment, in which: Figure 1 is a sectional schematic representation of an aircraft wheel and disc brake assembly embodying the present invention; Figure 2 is an enlarged sectional view of a portion of Figure 1; and Figure 3 is a section view of a spring and seal wiper mechanism of the disc brake assembly. The compact brake piston-return mechanism of the present invention is designated generally by reference numeral 10. An aircraft wheel (not shown) is suitably journalled on a rotatably fixed axle 18 carried by conventional aircraft landing gear structure (not shown). An annular brake carrier 20 suitably keyed to axle 18 is provided with a plurality of circumferentially spaced-apart housings 22, only one of which is shown, each suitably vented via a passage (not shown) to a source of pressurized fluid controlled by the aircraft pilot. A torque tube 24 having an integral backing plate 26 is secured fixedly to carrier 20 by a plurality of circumferentially spaced-apart bolts 30. A plurality of spaced-apart annular brake rotor members 32 are suitably keyed to a retaining member 31 comprising carbon-carbon composite rotors secured to the wheel and adapted to permit axial movement of the rotor members 32 relative to the wheel. A plurality of annular brake stator members 35 comprising carbon-carbon composite stators are suitably keyed for axial movement relative to torque tube 24. The rotor members 32 and stator members 35 are adapted to be actuated by a plurality of compact brake piston-return mechanisms 10. Upon energization of the mechanisms 10, the stators and rotors are compressed together to retard rotation of the wheel. The housing 22 of the compact brake piston-return mechanism assembly 10 comprises bore 40 extending to an open end 42. Received within bore 40 is a longitudinal sleeve 50 which extends longitudinally within bore 40 to an interior end 51, sleeve 50 extending exteriorily of the bore to exterior end 54 and including a through opening 56 which slidably receives therein a piston 60. Piston 60 has an interior opening 66 and at interior piston end 62 a sealing means 64 which slidably engages the interior surface of opening 56. Interior opening 66 includes radially inward abutment 67 including shoulder 68 which provides a stop for ring 70. Ring 70 engages an end flange portion 82 of deformable member 80. Deformable member 80 extends longitudinally within interior opening 66 and includes therein a deforming member 90. The deforming member 90 extends longitudinally through deformable member 80 and through piston end aperture 63 located at piston end 62. Member 90 includes at one end a ball 92 affixed thereto by a nut 93 and at the other end a radially extending member or enlarged diameter member 94. Radially extending member 94 includes a through opening 97 for permitting fluid to flow therethrough. The deformable member 80 and deforming member 90 comprise a ball-and-tube adjuster which causes tube 80 to expand radially outwardly when the tube 80 is displaced relative to the rod 90 and ball 92. Radially extending member 94 extends radially outwardly of interior end 52 of sleeve 50 and extends axially through axially extending portion 95 in order to encircle the sleeve interior end 52 and piston end 62. Axially extending portion 95 extends radially outwardly into radially extending end 96 to provide shoulder 97 which abuts a resilient spring 100. Sleeve 50 includes an outer diameter section 55 and an inner reduced diameter section 54 which define therebetween shoulder 57 that is abutted by the other end of spring 100. Sleeve 50 includes a groove 58 including therein sealing means 65. Piston 60 extends axially outwardly of through opening 56 and includes an enlarged diameter portion 69 positioned adjacent the stack of rotors 32 and stators 35. Piston end 74 includes a stop ring 61 for limiting the inward axial movement of the piston relative to sleeve 50. Sleeve end 51 includes a groove 59 which includes therein a wiper mechanism 110 (see Figure 3). Wiper mechanism 110 comprises a spring 112 disposed within a generally C-shaped seal 113. When the seal 113 and spring 112 are disposed within and compressed between groove 59 and the exterior surface of piston 60, spring 112 is squeezed radially so that it biases the seal 113 both radially inwardly and outwardly. The present invention operates as follows during a typical braking actuation. When pressurized hydraulic brake fluid is introduced into bore 40 by the aircraft operator, the pressurized fluid acts against the end 62 of piston 60 to bias piston 60 axially outwardly of bore 56 and into contact with the brake stack. As piston 60 moves in the direction of Arrow A (see Figure 2), ring 70 engaging flange 82 moves deformable member 80 along with piston 60. It should be noted that the distance X between the radially extending portion 69 and the stack of rotors and stators comprises a running clearance which corresponds approximately to the distance Y located between end 52 of sleeve 50 and an interior surface 99 of radially extending member 94. As piston 60 moves axially outwardly though the running clearance X, the piston displaces, by means of ring 70, deformable member 80, deforming member 90, and radially extending member 94 through the distance Y. Displacement of radially extending member 94 compresses spring 100 against shoulder 57. As the friction material of rotors 32 and stators 35 wears, piston 60 will extend further outwardly of through opening 56 and in doing so moves a distance greater than the running clearance defined by the individual distances X or Y, and causes tube 80 to be displaced relative to the ball 93 and rod 90 which are fixedly positioned relative to housing 22 once interior surface 99 engages end 52 of sleeve 50. Thus, as tube 80 is displaced axially relative to rod 90 and ball 93, the tube expands, and when the aircraft operator ceases actuation of the braking system, spring 100 biases the radially extending member 94 inwardly of bore 40 so that surface 99 moves away from sleeve end 52 to reestablish the running distance Y and the corresponding running clearance X. The present invention solves the problems posed by the implementation of high pressure braking systems in aircraft. Because the spring and radially extending member of the deforming member are disposed exteriorily of the piston, a reduced diameter bore 56 may be provided and a reduced diameter piston may be utilized in order to provide higher braking pressures required for the system. By providing a ball and tube adjuster mechanism disposed interiorily of the piston, considerable size and weight savings are accomplished and the pressure plate utilized in external adjusters is eliminated.

Claims: A brake piston return mechanism assembly, comprising a housing (22) having a cylindrical bore (40), longitudinal sleeve means (50) disposed fixedly in the bore (40) and having therein a through opening (56), a piston (60) disposed slidably within the through opening (56) and extending therefrom, and a deformable member (80) connected with said piston (60) and frictionally contacting a deforming member (90), the piston (60) comprising an interior opening (66) receiving therein said deformable member (80) and deforming member (90), the piston (60) having an aperture (63) at an end (62) disposed interiorily of the bore (40) and through which the deforming member (90) extends to a radially extending member (94), the sleeve means (50) including an outer diameter section (55) and a reduced diameter section (54) defining therebetween a shoulder (57), characterized by resilient means (100) disposed between said shoulder (57) and said radially extending member (94) in order to bias the radially extending member (94) axially inwardly of said bore (40) so that a gap (distance Y) is located between the radially extending member (94) and an end (52) of the reduced diameter section (54) of said sleeve means (50). The brake piston return mechanism assembly in accordance with claim 1, characterized in that an exterior end (51) of said sleeve means (50) disposed oppositely of said end (52) includes a wiping seal (110) disposed between said sleeve means (50) and an exterior surface of said piston (60). The brake piston return mechanism assembly in accordance with claim 1, characterized in that the radially extending member (94) includes an outer radial portion (95) which extends axially relative to the bore (40) to encircle the end portion (52) of said sleeve means (50) and extends further radially outwardly to define a shoulder (97) engaging said resilient means (100). The brake piston return mechanism assembly in accordance with claim 3, characterized in that the deformable member (80) comprises a tube connected by means of a ring (70) with the piston (60), the deforming member (90) comprising a rod (90) having a ball (92) at an end thereof, movement of the deformable member (80) relative to the deforming member (90) causing said ball (92) to expand said tube. The brake piston return mechanism assembly in accordance with claim 4, characterized in that said piston (60) extends exteriorily of said through opening (56) to an enlarged diameter end portion (69) for engaging a braking member (35).

Inventors: CHAMBERS, WARREN DALE C/O ALLIED CORPORATION
Applicants: ALLIED-SIGNAL INC. (A DELAWARE CORPORATION)
Application year: 1987
Main classification: F16D65
IPC codes: F16D55, F16D65