Wheel slide protection system

Claim 2

A wheel slide protection circuit comprising in combination first switch means driven from a first state to a second state when the deceleration of the wheel exceeds a predetermined value and driven back to its first state when the wheel accelerates, control means coupled to the first switch means and normally occupying a first state, the control means being driven to a second state when the first switch means is in its second state and then effecting release of the brakes from the wheel, the maximum time for which the control means is in its second state after the first switch means reverts to its first state being restricted, and circuit means operable when the first switch means reverts to its first state to maintain the control means in its second state for a period of time inversely related to the rate of acceleration of the wheel, said circuit means including second switch means driven from a first state to a second state at an acceleration level greater than the acceleration level at which the first switch means reverts to its first state, the control means reverting to its first state when the second switch means is driven to its second state, and in which the circuit means includes a capacitor which is held discharged while the first switch means is in its second state but when the first switch means reverts to its first state charges by way of the second switch means, the charging current of the capacitor holding the control means in its second state, whereby the control means remains in its second state until either the capacitor is charged or the second switch means is driven to its second state.

Claim 3

A circuit as claimed in claim 1 in which the first switch means is a transistor which is off and on in its first and second states respectively and when on provides an input signal to an amplifier constituting said circuit means.

Claim 4

A circuit as claimed in claim 2 in which the second switch means is a transistor which is on and off in its first and second states respectively and when on provides an input signal to the amplifier by way of said capacitor.

Claim 5

A wheel slide protection circuit comprising means for producing an electrical signal having a value dependent on the rotational speed of the wheel, a differentiating circuit to which said signal is applied, said differentiating circuit producing an output signal dependent upon the rate of change of rotational speed of the wheel, first switch means operable by way of the output signal from the differentiating circuit for releasing the brakes from the wheel when the deceleration of the wheel reaches a value at which the wheel is liable to slide, and for permitting re-application of the brakes when the wheel accelerates subsequent to release of the brakes, and timing means responsive to the rate of acceleration of the wheel subsequent to release of the brakes for ensuring that when said rate of acceleration of the wheel is below a predetermined value, the brakes are held off for a predetermined period of time after the differentiating circuit output signal permits re-application of the brakes said timing means comprising a capacitor and a second switch means responsive to said rate of acceleration and through which said capacitor may be discharged if said rate of acceleration exceeds said predetermined value, said predetermined period of time determined by the charging rate of said capacitor.

Claim 6

A wheel slide protection circuit comprising means for producing an electrical signal having a value dependent on the rotational speed of the wheel, a differentiating circuit to which said signal is applied, said differentiating circuit producing an output signal dependent upon the rate of change of rotational speed of the wheel, first switch means operable by way of the output signal from the differentiating circuit for releasing the brakes from the wheel when the deceleration of the wheel reaches a value at which the wheel is liable to slide, and for permitting re-application of the brakes when the wheel accelerates subsequent to release of the brakes, and timing means responsive to the rate of acceleration of the wheel subsequent to release of the brakes for ensuring that when said rate of acceleration of the wheel is below a predetermined value, the brakes are held off for a predetermined period of time after the differentiating circuit output signal permits re-application of the brakes said timing means comprising a capacitor and a second switch means responsive to said rate of acceleration and through which said capacitor may be discharged if said rate of acceleration exceeds said predetermined value, said predetermined period of time determined by the charging rate of said capacitor.

Claim 7

A wheel slide protection circuit for a wheel of a road vehicle, comprising in combination first and second d.c. supply lines, means for producing an electrical signal having a value dependent on the rotational speed of the wheel, a differentiating circuit to which said signal is applied, said differentiating circuit producing an output signal dependent upon the rate of change of rotational speed of the wheel, the output signal differentiating circuit being a d.c. signal having a value intermediate the potentials of the first and second supply lines when the wheel is rotating at a constant speed, this potential approaching the potential of the first line when the wheel decelerates and approaching the potential of the second line when the wheel accelerates, a first transistor coupled to the output from the differentiating circuit and biased to be off when the wheel is rotating at a constant speed, the first transistor being turned on by the potential at the output of the differentiating circuit when the deceleration of the wheel exceeds a predetermined value with which the wheel is likely to slide, an amplifier which is operated when the first transistor turns on and releases the brakes from the wheel, a second transistor which is coupled to the output from the differentiating circuit and is also coupled to the amplifier by way of a capacitor, the second transistor being conductive when the wheel is rotating at a constant speed, and remaining conductive when the wheel decelerates, but the capacitor de-coupling the second transistor from the amplifier, the first transistor serving when it is conductive to discharge the capacitor so that when the first transistor turns off again the second transistor provides an input to the amplifier by way of the capacitor, the second transistor being arranged to turn off at an acceleration level which is greater than the acceleration level at which the first transistor turns off.

Claim 8

A wheel slide protection circuit for a wheel of a road vehicle, comprising in combination first and second d.c. supply lines, means for producing an electrical signal having a value dependent on the rotational speed of the wheel, a differentiating circuit to which said signal is applied, said differentiating circuit producing an output signal dependent upon the rate of change of rotational speed of the wheel, the output signal differentiating circuit being a d.c. signal having a value intermediate the potentials of the first and second supply lines when the wheel is rotating at a constant speed, this potential approaching the potential of the first line when the wheel decelerates and approaching the potential of the second line when the wheel accelerates, a first transistor coupled to the output from the differentiating circuit and biased to be off when the wheel is rotating at a constant speed, the first transistor being turned on by the potential at the output of the differentiating circuit when the deceleration of the wheel exceeds a predetermined value with which the wheel is likely to slide, an amplifier which is operated when the first transistor turns on and releases the brakes from the wheel, a second transistor which is coupled to the output from the differentiating circuit and is also coupled to the amplifier by way of a capacitor, the second transistor being conductive when the wheel is rotating at a constant speed, and remaining conductive when the wheel decelerates, but the capacitor de-coupling the second transistor from the amplifier, the first transistor serving when it is conductive to discharge the capacitor so that when the first transistor turns off again the second transistor provides an input to the amplifier by way of the capacitor, the second transistor being arranged to turn off at an acceleration level which is greater than the acceleration level at which the first transistor turns off.