Patent GB-1271401-A (GB)
Title: Skid control system
IPC: B60T8/1763
Filed: 1969-03-27
Abstract: 1,271,401. Anti-skid braking systems. KELSEY-HAYES CO. 27 March, 1969 [20 Sept., 1968], No. 16214/69. Heading F2F. A skid control system for controlling vehicle fluid operated brakes in which a fluid pressure modulating valve 24 is actuated in response to an electrical signal indicating the occurrence of a predetermined deceleration rate which is varied depending on the surface condition which condition is sensed by sensing the spin-up rate of the wheel being controlled during the time of brake relief, comprises an electrical control circuit for actuating the modulating valve to relieve fluid pressure in response to deceleration of the wheel of a first predetermined magnitude, the circuit including means responsive to acceleration of the wheel, following actuation of the valve 24, for varying the said magnitude in accordance with variations in the magnitude of the acceleration. A vehicle speed analogue is provided which during each brake relief senses the linear velocity of the vehicle by sensing the velocity attained by the controlled wheels, which information is stored and used for the next cycle to vary the time at which the brakes are re-applied in accordance with velocity. A control module 26 receives information from sensors 28, 28<SP>1</SP> by means of toothed exciter rings 30, 30<SP>1</SP> associated with the brake drums the sensors being of a permanent magnet or electromagnetic construction to define a variable reluctance pickup and the module 26 senses the rate of change in signal to sense the deceleration rate of the wheels and provide an output signal in response to the said rate reaching a predetermined value corresponding to a skid condition, the output signal controlling the operation of valve 24. The modulator circuit includes first and second differentiator integrator sections 38, 38<SP>1</SP> associated with amplifier, clipper and inverter sections 36, 36<SP>1</SP> which receive the sinusoidal input of the wheel sensors and provide a square wave of constant amplitude but varying in frequency in accordance with the variations of the input wave. An output and driver section 76 provides a direct current output signal 76a to actuate and deactuate the valve 24. Since the skid condition can occur under surface conditions which vary widely a threshold selector 60 is used, the difference in spin-up rates on different surfaces providing different signals from a fourth rate detector section 58 to vary the threshold and a memory circuit is provided so that the threshold is varied for the next cycle. Provision is also made to vary the deactuation time for the output section 76 in accordance with vehicle velocity by the use of a velocity ramp section 62 which stores a signal in a circuit having a faster charge rate than discharge rate. A failsafe includes a hold-off section 68 and fail-safe section 70 connected to output section 76 to sense when the latter has been operated. As long as the relief of brake pressure occurs as a result of excessive deceleration in accordance with a skid-control cycle the section 70 will be rendered inoperative by a signal from the holdoff section 68 which is in turn operated as a result of a deceleration signal received from a second rate detector section 54. If however valve 24 is improperly actuated to relieve pressure through some malfunction section 70 will no longer be held off and will be actuated to provide a signal which will deactuate the modulating valve 24. A spike suppressor section 72 eliminates actuation of the output section as a result of transients. An ignition cycle circuit 44 is connected to a voltage regulator section 46 and is responsive to actuation of the vehicle ignition to provide a pulse to a summing amplifier section 42 whereby output section 76 is actuated each time the ignition is turned on so that the valves, seals &c. will be actuated to prevent deterioration.