Patent GB-1241798-A (GB)
Title: Vehicle skid sensing means
Inventor: DAVIS JOHN WALTER
IPC: B60T8/72
Filed: 1967-10-31
Abstract: 1,241,798. Fluid-pressure brake control by skid-sensing. DUNLOP HOLDINGS Ltd. 24 Oct., 1968 [31 Oct., 1967], No. 49342/67. Heading F2F. A vehicle skid-sensing means and brakereleaser comprises a first speed-responsive governor-type mechanism adapted to rotate synchronously with a member rotating at a speed proportional to a wheel speed, and a second speed-responsive governor-type mechanism driven by the member independently of the first mechanism, the first mechanism releasing the brakes via a control element whenever the first mechanism is rotating at or below a certain critical speed, provided that at the same time the second mechanism is rotating at a speed greater than its own critical speed (the second critical speed being greater than the first critical speed); the second governor-type mechanism comprises means to render the first mechanism ineffective at vehicle speeds below a predetermined value. As shown, an axially-fixed but rotatable shaft 44 is driven at a rate proportional to the rate of rotation of a vehicle wheel. It has pivoted to it by ball ends 51 in sockets 52 the limbs 50 of a number of weights 47 constituting a first governor-type mechanism 45. The limbs are also pivoted to a sleeve 49 axially slidable on the shaft 44 and urged to the left by a spring 54. The sleeve 49 has an annular lip 62 at its righthand end, which may be engaged by latches 63 on a second governor-type mechanism 46 to be described. The shaft 44 has another sleeve 59 keyed to it, and to this sleeve is keyed, in turn, a friction ring 58 urged by a spring 60 into contact with a ring 55 journalled on ball bearings around shaft 49. To the ring 55 are pivoted the arms 57 of the weights 56 of the second mechanism, and these arms are urged radially inwards by leaf springs 64, and embody the latches 63. Leftward movement of sleeve 49 serves to move a push rod 53 which effects operation of a control valve to release the wheel brake, either by applying a counter pressure to the brakeapplying pressure, or by reducing or preventing fluid flow to the brake and releasing fluid therefrom. In operation, at low vehicle speeds, the second mechanism 46 remains collapsed, thus latching the sleeve 49 against leftward movement; the valve is consequently inoperative, and the wheel brake cannot be released by the skid-sensing means. Hence low-speed manoeuvring of the vehicle with normal braking is permitted. For vehicle speeds at which skidding would be dangerous, (e.g. above 10 m.p.h.), the rate of rotation of shaft 44 is such that both mechanisms are in fly-out position. Should there be locking of the associated wheel, the shaft 44 would come suddenly to rest, and the first mechanism would collapse to operate the valve and cause brake release. Meanwhile the rotational inertia of the second mechanism 46 would cause it to continue rotating for a time against the resistance of the friction ring 58, and by the time it collapsed, the sleeve 49 would already be axially displaced, and the latches 63 would not engage the lip 62, so the valve would remain operative. If on the other hand (again from speeds e.g. above 10 m.p.h.), the shaft 44 slows to rest at the uniform rate associated with a non-skid stop, the second mechanism 46 slows with the shaft 44 under the influence of the friction ring 58. Because of the leaf springs 64 acting on it, the second governor 46 collapses before the first governor 45 would, and thus latches the sleeve 49 before the first governor 45 can move it to the left. Thus the brake cannot be released in this situation. But any resulting loss of directional stability is unimportant as the vehicle stops before getting out of control.