Patent GB-439925-A (GB)
Title: Improvements in or relating to braking systems for motor vehicles
IPC: F16D51/66
Filed: 1934-09-29
Abstract: 439,925. Servo-shoe brakes. CLENCH, E. C. S., and AUTOMOTIVE PRODUCTS CO., Ltd., Brock House, Langham Street, London. Sept. 29, 1934, Nos. 7717/35 (divided out of 439,894), 34465/34, and 36145/34. [Class 103 (i)] In brakes of the kind comprising a servo-shoe adapted to apply main friction members through mechanism giving a mechanical advantage the servoshoe pivots about an axis parallel to the plane of the brake drum. The servo-shoe may be applied by a roller engaging an arcuate track on the shoe, the curvature of this track being such that the pressure applied to the shoe tends to diminish as the brake is applied. The servo-shoe 18 is pivoted at 19 to a radial arm 15 extending from a sleeve 14 free upon an inner sleeve 13 forming part of the fixed anchor plate 12 and is pressed against the drum by a roller 23 engaging an arcuate track 22 on the shoe and carried by an arm 24 on a spindle 26 passing through the anchor plate and having a pair of external arms 29, 30. The shoe can thus be engaged either by mechanical connections from the arm 29 or by a hydraulic cylinder 32 mounted on the anchor plate and engaging the arm 30. The sleeve 14 is provided with a cam member 33 engaged by toggle links 40, 41 connected to the main brake shoes 34, 35 which are pivoted at 36, 37. When the shoe 18 is pressed against the drum, the shoe with the arm 15 and the cam are carried to a limited extent about the drum axis and the toggle is expanded by the cam and applies the main shoes. In order that the centre line of pressure between the lining 21 of shoe 18 and the drum may not vary substantially thus varying the pressure applied to the main shoes the distance between the pivot 19 and the vertical plane containing the centre line of the lining should not be less than twice the width of the lining. This limitation may however be avoided if as shown in Fig. 4, the shoe has a pin-and-slot connection 61 with the arm 15 and the track 22 of the shoe is centrally disposed in relation to the lining. The radius of the track 22 engaged by the roller should be greater than corresponds with concentricity with the drum so that the pressure on the shoe tends to diminish with travel of the shoe thus preventing sudden application of the brake. The servo-shoe may instead engage the exterior or a radially extending surface of the drum. According to the second Provisional Specification where the servo-shoe comprises a flat plate applied to a radial surface of the drum, the thickness of the plate engaged by the applying means may vary so that the pressure tends to reduce as the shoe moves about the drum axis to apply the main shoes and in a brake such as described in Specification 214,086 the cam engaged surface on the radial arm that carries the servo-shoe may be formed eccentric to the drum axis for the same purpose. Specification 439,894 is referred to in the third Provisional Specification. Compensating for wear.-The shoes 34, 35 abut on pivoted eccentric stops 46, 47 and so that corresponding adjustment of the effective length of the links 40, 41 may be made these links each comprise a pair of members held by a bolt 51 secured to and passing eccentrically through a disc 54 freely mounted on the web of the shoe.