GB1233746A - - Google Patents

Abstract

1,233,746. Anti-skid systems; testing braking systems. KELSEY-HAYES CO. 18 June, 1968 [19 June, 1967], No. 28921/68. Headings F2E and F2F. An anti-skid hydraulic control system for a vehicle includes a pressure modulating valve 24 which is caused to be cycled automatically each time the vehicle driver operates the vehicle ignition switch SW, a valve checking electrical circuit also being connected with the modulating valve 24 and responsive to a preselected deviation from the predetermined cycle of the valve 24 which is indicative of valve malfunction to provide an electric warning signal. As particularly described, the modulating valve 24 is connected between a master cylinder assembly 20 and the rear wheel brake cylinders 12. A solenoid 48 of the valve 24 is energizable by the output from wheel sensors 28 indicative of a skid condition to cause one side 50 of a diaphragm assembly 42 in a vacuum chamber housing 40 to be disconnected from vacuum and connected to atmosphere via line 56; this causes an hydraulic piston 46 to move within its cylinder housing 44 to increase the volume of cylinder housing 44 and simultaneously to close a check valve 76 to disconnect cylinder housing 44 from the master cylinder assembly 20. The pressure in cylinder 12 is thereby relieved. Cycling the valve: The coil 104 of solenoid 48 is also connected between earth and the positive terminal B+ of a battery via a transistor Q1 and switches SW1, SW2 of ignition switch SW. Switch SW2 and a further switch SW2a are closed when the ignition is turned on, and switch SW1 is also closed when the engine of the vehicle is started; hence when the engine is started the coil 104 is energized and the valve 24 is cycled. Checking the valve cycle: A switch SW3 is maintained open by contact with diaphragm assembly 42 when its side 50 is connected to vacuum and is closed when the assembly 42 moves a predetermined distance. Closing of switch SW1 on starting the engine causes a capacitor C1 of a first timing circuit to be charged and the charge after a pre-set time will cause a normally non-conductive uni-junction transistor UJ1 to conduct to trigger a siliconcontrolled rectifier SCR1 to light a warning lamp L. However, this will only happen if the switch SW3 has not closed-if this has occurred a transistor Q3 is rendered conductive through which the capacitor Cl will discharge. Thus in this part of the cycle ignition of the lamp L indicates that the assembly 42 has not been displaced or has been displaced too slowly. To check that the assembly 42 returns in a preset time a capacitor C2 of a second timing circuit is charged through a transistor Q2 from terminal B+ from the moment switch SW1 is opened and coil 104 is de-energized. After a preset time the charge on capacitor C2 will cause transistor UJ2 and rectifier SCR2 to conduct to lamp L, if a transistor Q4 is not rendered conductive in this time by re-opening of the switch SW3. Additionally the output from deceleration sensor 28 is connected to these circuits via a control module 26 to check the operation of the valve each time the sensor 38 transmits a signal.