Abstract:
Inner and outer brake shoes are swivel-mounted on the arms of a yoke. When the yoke is rotated, the shoes move concurrently toward and away from inner and outer braking surfaces of a brake drum. The swivel mounting facilitates optimum seating engagement with the braking surfaces and in cases where the drum is warped, serves to maximize braking area and minimize wear. Stops positioned near opposite ends of the shoes limit their circumferential movement. An electric puck or a hydraulic actuator is used to rotate the yoke.

Description:
This is a continuation of application Ser. No. 487,232, filed July 10, 1974, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to brakes for vehicles, and more particularly, to an improved brake employing inner and outer brakes shoes to grip inner and outer braking surfaces on a rotatable drum. 
     2. Prior Art 
     A number of proposals have been made in the prior art to employ inner and outer brake shoes operating concurrently on the inner and outer surfaces of a cylindrical brake drum. One such proposal is presented in U.S. Pat. No. 2,783,858 issued Mar. 5, 1957 to John H. Murphy. 
     One drawback of most of these proposals is that the freedom of movement of the brake shoes is restricted, typically to a pivotal motion. This restricted mounting does not permit the shoes to &#34;float&#34; or self-align with the drum when braking engagement is initiated. If the brake drum is warped from heat or out of warpage, the restricted mounting can reduce the area of braking engagement between the drum and the shoes, can cause undue and uneven wear on the brake shoes an drums, and can diminish the effective operating life of the shoes and the drum. 
     Another disadvantage of prior art proposals which pin or otherwise securely connect the brake shoes to a stationary mount is that these connections complicate assembly and disassembly of the brake. The connections add to the cost of the brake and provide additional areas which are subject to wear. 
     Still another disadvantage of prior brake proposals is that they include a relatively large number of parts, many if not most of which must be accurately formed and machined. Some of these parts must be made with close tollerances to assure their proper operation, and this adds significantly to the cost of the assembled brake. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the foregoing and other drawbacks of the prior art and provides a novel and improved brake including swivel mounted inner and outer shoes. 
     The shoes are carried on a yoke. The yoke has inner and outer arms which respectively overlie the inner and outer braking surfaces of a rotatable brake drum. The arms have rounded projections which extend toward the braking surfaces. The shoes are centrally engaged by the rounded projections and are held in such engagement by springs. This type of connection is advantageous in that it permits the shoes to swivel relative to the yoke, whereby the shoes can &#34;float&#34; into optimum braking engagement with the drum when the brake is applied. 
     Unlike most prior art proposals, no connection is made between a stationary structure and the brake shoes which would defeat the floating action of the shoes. The only interaction between the shoes and a stationary structure is provided by stops carried near opposite ends of the shoes to limit their circumferential movement once they are engaged with the drum. 
     In the preferred embodiment of the invention, the springs which hold the shoes on the arms of the yoke are wire springs which have opposite end regions connected to the shoes. Central portions of the springs are received in grooves on the arms of the yoke. This type of spring mounting has the advantages of being quite simple to make and to repair. It greatly simplifies assembly and disassembly of the shoes. 
     A significant advantage of brakes constructed in accordance with the present invention is their low manufacturing cost. The number of parts is minimal. Very little machining is required. The yoke is a forging which has a machined mounting stem. No machining is required in forming the shoes other than to drill two small holes in each shoe to receive opposite ends of the mounting spring. No machining is needed on the stops. 
     Another advantage is that the brake may be applied by rotating the yoke in either of two directions. This capability permits the brake to be electrically applied through the actuation of an electromagnetic puck that frictionally drags on the drum. When the drum is rotating in one direction, the puck rotates the yoke clockwise to apply the brake. When the drum is rotating in the other direction, the puck rotates the yoke counterclockwise to apply the brake. 
     Conventional hydraulic or mechanical actuators may also be used to rotate the yoke to effect brake application. In short, the brake is well adapted for use with almost any conventional type of actuation system. 
     As will be apparent from the foregoing, it is a general object to provide a novel and improved brake. 
    
    
     Other objects and a fuller understanding of the invention may be had by referring to the following description and claims taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of an electrically actuated brake embodiment constructed in accordance with the present invention, as seen from the plane indicated generally by the line 1--1 in FIG. 2; 
     FIG. 2 is a cross-sectional view as seen from the plane indicated generally by the line 2--2 in FIG. 1; and 
     FIG. 3 is a cross-sectional view similar to FIG. 3 of a hydraulically actuated brake embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, a brake is shown generally at 10. The brake 10 includes a drum 12 which is rotatable about an axis indicated by the numeral 14. The drum 12 is of conventional flanged configuration, preferably formed from steel and having a cylindrical side wall including inner and outer braking surfaces 16, 18. 
     A stationary mounting plate 20 is positioned to the left of the drum 12 as viewed in FIG. 1, and behind the drum 12 as viewed in FIG. 2. In a typical installation, the mounting plate 20 is part of the frame of a vehicle, and the brake drum 12 is secured to a rotatable wheel. 
     A yoke 22 is rotatably carried on the mounting plate 20. A spherical bearing 24 is carried by the mounting plate 20. The yoke 22 is a forging which has a machined cylindrical stem 25. The stem 25 extends through and is journaled by the bearing 24. The yoke 22 has a pair of inner and outer arms 26, 28 which overlie the inner and outer braking surfaces 16, 18. Rounded projections 36, 38 formed on the distal ends of the arms 26, 28 extend toward the braking surfaces 16, 18. 
     An inner brake shoe 46 and an outer brake shoe 48 are carried on the arms 26, 28. The shoes 26, 28 are centrally engaged by the projections 36, 38. The inner arm projection 36 engages a concave inner surface 40 of the inner shoe 46. The outer arm projection 38 engages a concave recess 42 formed in an upstanding projection 44 on the outer surface of the outer shoe 48. 
     The shoes 46, 48 are held in engagement with the arms 26, 28 by a pair of springs 56, 58. The springs 56, 58 are wires formed from spring steel. A pair of depending ribs 50 are formed on the inner shoe 46. A pair of upstanding ribs 52 are formed on the outer shoe 48. Holes 60, 62 are drilled through the ribs 50, 52. Opposite end regions of the springs 56, 58 are received in the holes 60, 62. Notches 66, 68 are formed in the arms 26, 28 opposite the projections 36, 38. The central regions of the springs 56, 58 extend through the notches 66, 68. 
     The described spring-mounting of the shoes 46, 48 biases the shoes 46, 48 into engagement with the rounded projections 36, 38 and establishes swivel connections between the shoes 46, 48 and the arms 26, 28. When the shoes are brought into their brake-applied position as by rotating the yoke 22 about the axis of the stem 25, the shoes will &#34;float&#34; into optimum braking engagement with the drum surfaces 16, 18. If the drum is warped from heat or is out of round from wear, the swivel mounted shoes will maximize the surface area of contact with the drum thereby minimizing wear and prolonging the life of the brake. 
     The only restriction on the movement of the shoes 46, 48 imposed by a stationary structure is provided by inner and outer pairs of stops 76, 78 carried by the mounting plate 20. The stops 76, 78 are located near opposite ends of the shoes 46, 48 and serve to limit the circumferential movement of the shoes 46, 48 after they have engaged the braking surfaces 16, 18. The stops 76, 78 are preferably cast as integral parts of the mounting plate 20 and are provided with integral reinforcing ribs 80, 82. 
     A sleeve 85 is secured by a pin 75 to the yoke stem 25. As will be explained in conjunction with FIG. 3, an actuating lever 95 can be connected to the sleeve 85 to mechanically or hydraulically rotate the yoke 22 in applying the brake 10. 
     The brake actuation system shown in FIGS. 1 and 2 employs an electromagnetic puck 90. The puck 90 is of conventional design, including a mounting stem 91, and a housing 92 which carries an electromagnet 93. Electrical conductors 94 connect with the electromagnet 93. 
     The puck 90 is carried on a lever 96. The upper end region of the lever 96 is secured by threaded fasteners 97 to the yoke 22. The lower end region of the lever 96 is provided with an aperture 98 which receives the puck stem 91. A threaded fastener 99 secures the puck 90 to the lever 96. 
     When electricity is supplied through the conductors 94 to the electromagnet 93, the puck 90 is drawn into engagement with the drum 12 and frictionally drags on the inner face of the drum. If the drum 12 is rotating clockwise as viewed in FIG. 2, the drag of the puck 90 on the drum 12 will pivot the lower end of the lever 96 leftwardly causing the yoke 22 to rotate clockwise. If the drum 12 is rotating counterclockwise, the lower end of the lever will be moved rightwardly causing the yoke 22 to rotate counterclockwise. The yoke 22 is operative to move the shoes 46, 48 into braking engagement with the drum 12 regardless of the direction of its rotation by the lever 96. 
     Referring to FIG. 3, a hydraulic brake actuation system is shown for rotating the yoke 22. A lever 95 has one end connected to the sleeve 85. The other end of the lever 95 has a concave recess 101. The upper end of a piston 102 extends into the recess 102. The lower end of the piston 102 is engaged by a hydraulic actuator 103 of conventional design. When hydraulic fluid under pressure is supplied to the actuator 103, the piston 102 moves upwardly causing the lever 95 to rotate the yoke counterclockwise to apply the brake 10. 
     As will now be apparent, the present invention provides a brake of extremely simple construction, employing a minimal number of parts which require a minimal amount of machining. There are no threaded fasteners or pins or other complicated connectors used to hold the brake shoes in place. Assembly and disassembly of the brake shoes is easily accomplished by slipping the shoes into and out of position on the arms 26, 28. 
     While only one set of brake shoes 46, 48 has been shown on the drum 12 in the drawings, one or more additional sets may be provided at other spaced locations around the perimeter of the drum to provide increased braking capability. 
     Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.