Claims
- 1. A vehicle braking system comprising a chamber having means therein movable by fluid pressure to apply at least one wheel brake; an electrically operable inlet valve and an electrically operable outlet valve for controlling the flow of fluid into and out of said chamber respectively; and an electrical circuit for controlling said valves, said circuit having a first variable signal input means responsive to driver operation of said braking system, a second variable signal input means responsive to the degree of brake application achieved by the fluid pressure, error signal generating means connected to said first variable input means and to said second variable input means for producing an error signal of polarity and magnitude corresponding to the difference between the signals received from said first variable input means and said second variable input means, and means for generating a pulse train of selected frequency including a pair of pulse width modulation devices each having an input from said error signal generating means, one of said pulse width modulating means having an output connected to said outlet valve, the other of said pulse width modulation means having an output connected to the inlet valve, and means responsive to the polarity of the error signal for determining which one of the pulse width modulation means is operated, said pulse width modulation means acting on said pulse train to produce a mark-space ratio determined by the magnitude of the error signal, whereby the degree of brake application may be varied to bring the error signal to substantially zero and excessive wheel deceleration detection means is connected to the pulse width modulation means associated with said outlet valve and is adapted to apply a continuous signal to said outlet valve to open the same when wheel deceleration greater than said predetermined valve is detected and is also connected to said error signal generating means to override the signal thereto from said variable input means.
- 2. A braking system as claimed in claim 1, including a common oscillator connected to said pulse width modulation means and adapted to determine the frequency at which said pulse width modulation means operate, said wheel deceleration detection means being further connected to said oscillator to inhibit oscillation of said oscillator when excessive wheel deceleration is detected.
- 3. A braking system as claimed in claim 2, in which said oscillator is a variable frequency oscillator, and said pulse width modulation means includes a control signal terminal connected to the oscillator, whereby a control signal at said terminal reappears at a controlled ramp rate following removal of said control signal on detection of excessive wheel deceleration.
Priority Claims (1)
Number |
Date |
Country |
Kind |
157/75 |
Jan 1975 |
GB |
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RELATED APPLICATION
The present application is a continuation of Ser. No. 642,382, filed Dec. 19, 1975, now abandoned for which all rights are claimed.
US Referenced Citations (4)
Continuations (1)
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Number |
Date |
Country |
Parent |
642382 |
Dec 1975 |
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