Patent GB-1410127-A (GB)
Title: Anti-locking control systems
IPC: B60T8/173
Filed: 1973-02-02
Abstract: 1410127 Anti-skid control systems ROBERT BOSCH GmbH 2 Feb 1973 [4 Feb 1972] 5263/73 Heading F2F An anti-skid brake control system has an acceleration sensor associated with a braked wheel for providing an analogue signal, two limit switches 41, 42 connected to the sensor and each connected to a respective setting and return setting input of an accumulator 45, an inlet valve 13 for a brake cylinder being controllable by an OR gate 49 whose inputs are connected to the accumulator and the second limit switch, and an outlet valve 16 from the brake cylinder being controllable by the accumulator. During initial wheel deceleration, upon braking, the inlet valve 13 is open and the outlet valve 16 is closed so that brake cylinders 14, 15 for rear wheels are fed by a master cylinder 10. The whel signal is obtained from a pulse generator, situated on a cordan shaft to the rear differential, via an A.C./D.C. converter and a differentiator. This is fed via a low pass filter 34, to damp out spurious signals, to the limit switch 41. The limit switch comprises an amplifier having an inverse input E and an input V from a variable resistance bridge which can be also varied by a transistor. Under the present braking conditions, the input V is fixed at a value equivalent to a - 3g acceleration so that a deceleration greater than 3g produces a signal at an output A to set the accumulator 45 thus passing a signal to open the valve 16 and decrease brake cylinder pressure. Furthermore, a signal passes to the valve 13 to close. The limit switch 42 has a fixed valve of + 1g acceleration and, upon this value being attained from the sensor, resets the accumulator 45 so that the valve 16 is closed. For greater adaptability, e.g. for various road surfaces and friction coefficients, Fig. 3 shows further components. During actuation of the switch 41 a monostable trigger 35 is cleared; also, a signal passes from the accumulator 45 to another accumulator 47 which is set; its reset input being coupled to a pressure switch 22 associated with the cylinder 10. A third limit switch 43 being the input V from the trigger 35 and the input E direct from the sensor, emits a signal so that an AND gate 46 allows the valve 16 to be opened. Furthermore an AND gate 50 has both inputs energized and allows the valve 13 to be closed. During the pulse period of the trigger 35, the limit at the switch 42 is set at - 2g so that upon deceleration decrease, the signal changes to zero, thus arresting the actuation of the valve 16 causing the pressure in the brake cylinders 14, 15 to be constant. During further retardation decrease tuning to acceleration, the switch 42 operates and releases a trigger 36 to cause the comparison signal of the switch 41 to be - 6g for the pulse period. A pulse generator 48 energizes the valve 13 via the gate 49 for pulsed pressure in the next cycle. If the pressure is too great the original cycle is repeated but at a slower rate. For a front wheel drive vehicle, separate sensors for the rear wheels feed average value and extreme value selection circuits. A fourth limit switch having an input from the low pass filter supplies an AND gate direct and via a trigger, the AND gate output passing to the accumulator 45 via a gate with an input from the switch 41 and from the average value circuit. This is to avoid wheel locking on slow braking due to frictional variations for each wheel. The momentary change in the comparative value for the switch 41 to - 6g is to avoid brake release due to axle oscillations.