Patent GB-962933-A (GB)
IPC: B60T13/52
Abstract: 962,933. Anti-skid devices; ratchet clutches. AUTOMOTIVE PRODUCTS CO. Ltd. May 9, 1963 [June 15, 1962 (2)], Nos. 23196/62 and 23199/62. Headings F2C and F2F. A liquid-pressure braking system comprises a master cylinder 12, Fig. 1, or other pressure source, a wheel brake cylinder 11, a non-return valve 15 closable to prevent liquid flowing from the pressure source to the wheel brake cylinder, means to vary the capacity of the part of the system between the non-return valve 15 and the cylinder 11, and a sensing device 17 operable in response to a change of conditions tending to produce wheel locking to cause the closing of the non-return valve and the increase of the capacity of the said part of the system. The capacity-varying means comprises a plunger 34, Fig. 2, urged towards a minimum-capacity position by a spring 46 which also acts to hold the non-return valve in the form of a spring-loaded ball 28 and seat 27 open and servo-means 16 are provided to compress the spring 46 so as to allow the non- return valve 15 to close and to allow the plunger to move in a capacity-increasing direction. The servo-means includes a housing 36 divided by a diaphragm 37 or a piston into two chambers 38, 39, the chamber 38 being maintained at a relatively lower pressure, e.g. connected to a vacuum source or atmosphere and the chamber 39 having air, e.g. atmospheric or compressed admitted at a higher pressure by a valve 22 controlled by actuation of the sensing device 17. As shown, the latter, which is operated by wheel deceleration, but which may be operated by a reduction in speed of a wheel or by the deflection of wheel mountings under braking loads, comprises a pulley 56 and casing 57 rotatable about the body of the valve 22 and a flywheel 58 rotatable on a sleeve 59 which is itself rotatable on a stub axle 61 fixed in the casing 57, and a slipping clutch device 62. When the vehicle is driven or only a light brake application is made the flywheel 58 is driven at the same speed as the pulley 56 and casing 57, a cam-plate 63 being driven by a pin 69 and driving the sleeve 59 through balls 67, the sleeve in turn driving the flywheel through the clutch 62 which is in the form of a resilient metal strip 65, Fig. 4, anchored to the sleeve and wrapped therearound. Rotation of the sleeve 59 to drive the flywheel causes the metal strip to unwind and increase its frictional grip on the flywheel so that the latter can be set into rotation. However, if the brakes are applied strongly so as to cause rapid deceleration of the wheels the pulley 56 and casing 57 are rapidly decelerated and the flywheel tends to over-run the pulley and casing applying rotational drag to the sleeve 59, the coils of the clutch strip 65 tending to wind up, allowing the flywheel to over-run the sleeve 59. If the drag applied to the sleeve is sufficient it will rotate through a small angle causing balls 67 to ride up cam faces on the plate 63 and displace the latter axially so as to move push-rod 64 against spring 60 to unseat valve closure member 52. Atmospheric air is admitted from pipe 55 via the pipe 49 to the chamber 38 of the servo-device, the chambers 38, 39 of which are normally connected to a vacuum source through a pipe 48 and the interconnection 51 in the diaphragm 37. The admission of air to the chamber 38 is greater than the rate at which it can escape through orifice 51 and thus the diaphragm unit 37, 42, 45 is moved downwardly. The plunger 34 being withdrawn along the bore 25 allows the ball 28 to seat and cut-off communication between the master cylinder connection 31 and the wheel brake cylinder connection 33. The volume of the system between the non-return valve 15 and the wheel brake cylinders is also increased. The pressure acting on the rear wheel brakes is thus reduced and the wheels tend to speed up again until the speeds of the flywheel and the pulley are the same when the valve 22 closes again to restore the pressure to the rear wheel brake cylinders. Thus if strong braking is maintained the brakes on the rear wheels are alternatively applied and released. In modifications the sensing device may actuate an electric switch in a circuit which operates the valve 22, a restriction may be formed in the valve 15 to avoid a rapid increase in pressure to the rear wheel brake cylinders when the valve 15 is re-opened, and the orifice 51 may be dispensed with, the chamber 38 being connected directly to the vacuum source by the pipe 49 and a connection above the valve member 52 which connection is automatically closed on the opening of the valve 22.