Patent GB-1480249-A (GB)
Title: Anti-skid braking systems for vehicles
IPC: B60T8/1763
Filed: 1974-07-03
Abstract: 1480249 Anti-skid braking systems FIAT SpA 3 July 1974 [26 July 1973] 29504/74 Heading F2F An anti-skid vehicle braking system includes a threshold circuit 7 having a first threshold level to control brake release, the system providing a second threshold level controlling brake re-application, and further including a connection circuit 15 for applying to the threshold circuit 7 a correction signal dependent on at least the dynamic parameters of wheel speed and vehicle deceleration to vary the first threshold level. As shown in Fig. 1 a wheel speed sensor 1A comprises a pick-up which supplies alternating signals of frequency proportional to the speed of the wheel being controlled and the sensor 1A drives a tachometer 2A which supplies a voltage signal proportional to the speed of the wheel. A threshold circuit 3 determines the minimum intervention speed and the speed signal is passed to a memory circuit 5 which memorizes the wheel speed signal during a brake release stage. If two wheels on the same axle are controlled, an additional sensor 1B and tachometer 2B are used and a selector circuit 4 selects the signal representing the lower wheel speed to supply to circuit 5. Connected to circuit 5 is a differentiator circuit 6 to provide a signal representative of wheel acceleration or deceleration which signal is applied to threshold circuit 7. An automatic reset circuit 8 is connected to the circuit 7 to re-establish braking if the correct command from the circuit 7 is not received in time. A power stage 9 acts on a solenoid valve 10 to control the brake pressure applied to the or each wheel brake actuator. A generator 11 connected to a decelerometer 12 supplies the memory circuit 5 with an electrical current signal proportional to the deceleration of the vehicle. A control circuit 13 for circuit 5 controlled by power stage 9 is connected to the output of generator 11. The correction circuit 15 has an input circuit 15<SP>1</SP> connected to the output A of circuit 4 and an input circuit 15<SP>11</SP> connected to the output B of decelerometer 12, and the output of correction circuit 15 connects with the input IC of the threshold circuit 7. A further control circuit 16 is provided which co-operates with the correction circuit 15 during the braking stage so that the brake release threshold depends upon wheel speed and vehicle deceleration, while the control circuit does not co-operate with circuit 15 during the brake release stage. To this end the circuit 16 is connected to the power stage 9 so that the circuit 16 is controlled to afford co-operation with circuit 15 only when valve 10 is deenergized. When the deceleration signal produced by circuit 6 during braking reaches the first threshold level (as corrected) solenoid valve 10 is energized via power stage 9 to effect brake release, and the energization signal also acts via circuit 13 on memory circuit 5 which stores the wheel speed signal. The signal from generator 11 slowly discharges circuit 5, simulating the velocity decrease of the decelerating vehicle and when the wheel speed signal reaches the detected speed of the vehicle, the circuits 6-9, cause de-energization of valve 10 and erasure of the speed signal stored in memory circuit 5 whereby the wheel speed signal is re-applied to the differentiator circuit 6. In the embodiment illustrated in Fig. 4, the. correction circuit 15 and its input circuits 15<SP>1</SP>, 15<SP>11</SP> are constituted by respective resistances R, R1, R2 and the control circuit 16 is constituted by a transistor T which acts as a trip circuit. The threshold circuit 7 comprises a hysteresis comparator having an amplifier Q; + ST indicates a stabilized voltage and R4, R5, R6 the resistances which define the thresholds of intervention. During the brake release stage the power stage 9 supplies a control signal to transistor T which saturates, earthing the input end I of resistance R so that the brake application threshold in the constant are defined by +ST and resistances R4, R5, R6. During braking the power stage 9 sends an inter-diction signal to the transistor T, so that signals provided by A and B are summed in R and combine at point IC with signal of voltage + ST so as to cause variation of the brake release threshold. Signals proportional to other parameters (e.g. vehicle load) can also be supplied to point I.