Anti-lock brake systems for wheeled vehicles

Claim 2

An anti-lock vehicle brake system comprising, means for deriving an electric signal related to the rotational movement of a vehicle wheel, means responsive to said signal for deriving a wheel speed voltage proportional to the wheel speed, control valve means for adjusting the vehicle brake pressure, a signal processing circuit coupled to said control valve means and responsive to said speed voltage to produce an output signal when the speed voltage indicates that wheel deceleration exceeds a predetermined value, and timing means coupled to the output of the signal processing circuit and to said control valve means and operable to increase the length of time that the control valve means is actuated in the event that the duration of said output signal exceeds a predetermined length of time which is indicative that braking is being effected on a surface having poor adhesion.

Claim 3

An anti-lock vehicle brake system as claimed in claim 1, wherein said timing means comprises an RC time constant element responsive to said output signal to produce a signal with a ramp waveform, transistor means controlled by said ramp signal so that, in the event the duration of said output signal exceeds said predetermined length of time, the ramp signal reaches a magnitude which operates the transistor means to maintain said output signal independently of its normal dependence on said signal processing circuit, said timing means further comprising a discharge circuit through which the ramp waveform can decay following the normal duration of said output signal.

Claim 4

An anti-lock vehicle brake system as claimed in claim 2, wherein the rate of decay provided by said discharge circuit is appropriate for resetting the time constant element during the periods between successive electrical outputs of successive anti-lock cycles.

Claim 5

An anti-lock vehicle brake system as claimed in claim 3, wherein the discharge circuit provides a resetting time approximately equal to the duration of a normal electrical output which will just not operate the timing means.

Claim 6

A vehicle anti-lock brake system comprising, means for producing an electric signal with a frequency proportional to wheel speed, means for converting said signal to a proportional speed voltage, control valve means actuable to relieve the vehicle brake pressure during an anti-lock cycle, a signal processing circuit connected between said signal converting means and said control valve means and responsive to the speed voltage to produce an output control signal for actuating said control valve means when the speed voltage indicates that wheel deceleration exceeds a predetermined reference value, and timing means responsive to said output signal for effecting prolonged actuation of the control valve means independently of said output signal whenever the duration of the output signal exceeds a predetermined time period indicative that the wheel is being braked on a road surface with poor adhesion.

Claim 7

A vehicle anti-lock brake system comprising, means for producing an electric signal with a frequency proportional to wheel speed, means for converting said signal to a proportional speed voltage, control valve means actuable to relieve the vehicle brake pressure during an anti-lock cycle, a signal processing circuit connected between said signal converting means and said control valve means and responsive to the speed voltage to produce an output control signal for actuating said control valve means when the speed voltage indicates that wheel deceleration exceeds a predetermined reference value, and timing means responsive to said output signal for effecting prolonged actuation of the control valve means independently of said output signal whenever the duration of the output signal exceeds a predetermined time period indicative that the wheel is being braked on a road surface with poor adhesion.

Claim 8

A system as claimed in claim 5 wherein said timing means comprises, a controlled switching device coupled to said control valve means for effecting said prolonged actuation thereof, a resistor and capacitor connected together to form an RC circuit and to the control electrode of said switching device to control the conduction therein, and means responsive to said output signal for connecting said RC circuit to a source of voltage in synchronism with the receipt of said output signal.

Claim 9

A system as claimed in claim 6 wherein said timing means further comprises, means for biasing said switching device into a cut-off state, and wherein said RC circuit produces a signal with a ramp waveform which triggers said switching device into conduction when the duration of the output signal exceeds said predetermined time period.

Claim 10

A system as claimed in claim 7 further comprising a second resistor couPled to said capacitor to provide a discharge circuit therefor, said discharge circuit being rendered effective by said connecting means to discharge the capacitor upon the termination of said output signal.