Skid control system

Claim 2

An antiskid braking system for a rotatable wheel equipped with a hydraulic pressure responsive braking unit and an associated electronically responsive control valve for adjustably restricting the hydraulic pressure supplied to said braking unit, said control system comprising the combination of, speed sensing means to represent the wheel rotation as an electrical signal, a normally balanced bridge circuit, and electrical circuit means coupled to said bridge and responsive to an excessive rate of change of the electrical signal for unbalancing said bridge circuit in response to a skidding deceleration of the wheel to thereby provide a control signal for the valve means to cause a dump of all but a predetermined portion of the hydraulic pressure applied to the braking unit.

Claim 3

An antiskid system according to claim 1 which includes an amplifier circuit to receive the control signal from the bridge circuit and pass it as a uniform magnitude signal to the valve means regardless of the magnitude of the unbalance on the bridge circuit.

Claim 4

A combination according to claim 2 where the amplifier circuit includes a feedback to effectively limit conduction thereof when the voltage from the bridge circuit reaches a predetermined level.

Claim 5

A combination according to claim 1 which includes a modulation circuit to adjust the valve means to a hydraulic pressure slightly lower than the which caused a skid upon returned braking operation after actuation of the valve means by the bridge circuit, and which modulator circuit further allows a slow increase in the pressure applied by the valve means until another skid condition is approached.

Claim 6

A combination according to claim 4 where the modulator circuit includes a first branch and a second branch wherein the first branch acts and responds to the initial skid to properly and initially set said modulator response, and the second branch operates in response to all subsequent minor or approaching skid conditions to provide a modulation signal.

Claim 7

A combination according to claim 5 where the modulation characteristics of both the first and second branches can be adjusted to provide desired response characteristics and circuit parameters.

Claim 8

A combination according to claim 1 where the bridge circuit can be adjusted to provide a selected response characteristic to wheel deceleration.

Claim 9

A combination according to claim 6 where all circuits include diodes to control current flow and provide temperature stability.

Claim 10

In an antiskid braking system the combination of a plurality of rotatable wheels, means to supply hydraulic braking pressure to each wheel, independent valve means to adjustably restrict the hydraulic pressure actually applied to each wheel, means to represent the speed of rotation of each wheel as a DC voltage, and a separate antiskid detection circuit for each wheel, each detection circuit including a normally balanced bridge circuit and a circuit means coupled to said bridge circuit and responsive to said DC voltage for increasingly upsetting the balance of said bridge in response to a skidding deceleration of its respective wheel, said bridge circuit causing a signal to be sent to the respective independent valve means to restrict the hydraulic pressure to the respective brake upon its balance being upset by a predetermined amount.

Claim 11

In an antiskid braking system the combination of a plurality of rotatable wheels, means to supply hydraulic braking pressure to each wheel, independent valve means to adjustably restrict the hydraulic pressure actually applied to each wheel, means to represent the speed of rotation of each wheel as a DC voltage, and a separate antiskid detection circuit for each wheel, each detection circuit including a normally balanced bridge circuit and a circuit means coupled to said bridge circuit and responsive to said DC voltage for increasingly upsetting the balance of said bridge in response to a skidding deceleration of its respective wheel, said bridge circuit causing a signal to be sent to the respective independent valve means to restrict the hydraulic pressure to the respective brake upon its balance being upset by a predetermined amount.

Claim 12

The antiskid braking system of claim 1 wherein said speed sensing means provides a DC voltage with an amplitude proportional to the instantaneous rotary speed of said wheel, said bridge circuit includes first and second parallel legs, an electronic switching device having an input circuit coupled between respective points on said first and second legs and an output circuit coupled to said valve, and means for supplying a respective quiescent current flow through each of said legs to establish across said points unDer quiescent operating conditions a potential difference of predetermined magnitude sufficient to maintain said switching device in a first state, said switching device being effective when switched to a second state to provide said control signal for said control valve, and said electrical circuit means includes rate sensing means coupled between said speed sensing means and said first leg of said bridge circuit, said rate sensing means causing a change in the potential difference existing across said points in a sense tending to switch said switching device to its second state in response to changes in the amplitude of said DC signal at rates in excess of a maximum deceleration rate while leaving said potential difference substantially at said predetermined magnitude in response to changes in the amplitude of said DC signal at all other rates.

Claim 13

The antiskid braking system of claim 10 wherein the control signal delivered to said control valve when said switching device is switched to its second state is of fixed amplitude, so that the hydraulic pressure supplied to said braking unit is reduced to a predetermined level whenever said switching device is switched to its second state.

Claim 14

The antiskid braking system of claim 11 wherein said braking unit comprises a pair of surfaces which are brought into contact to brake said wheel, and the predetermined level to which said hydraulic pressure is reduced when said switching device is switched to its second state is selected to be the pressure level at which clearance of said surfaces would begin to occur if the hydraulic pressure supplied to said braking unit was reduced any further, whereby the quantity of hydraulic fluid supplied to said braking unit is minimized and response time is improved.

Claim 15

The antiskid control system of claim 10 wherein said rate sensing means comprises a capacitor which is charged by said DC signal as the rotary speed of said wheel increases and discharged by the quiescent current flow through said first leg of said bridge circuit as the rotary speed of said wheel decreases, said quiescent current flow through said first leg of said bridge circuit being the only current flow required to discharge said capacitor at substantially the rate of change in the amplitude of said DC signal for all rates of change of said amplitude up to said maximum deceleration rate.

Claim 16

The antiskid braking system of claim 13 wherein additional current flow for discharging said capacitor is drawn through the input circuit of said switching device when the rate of change of said DC signal exceeds said maximum deceleration rate and after the potential difference between said points on said bridge circuit has changed by a predetermined amount. 15 The antiskid braking system of claim 14 wherein said braking unit comprises a pair of surfaces that are brought into contact to brake said wheel, and the control signal supplied to said valve when said switching device is switched to its second state has a predetermined amplitude selected to reduce the hydraulic pressure supplied to said braking unit to a pressure level at which clearance of said surfaces would begin to occur if the level of the hydraulic pressure supplied to said braking unit was reduced any further, whereby variations in the level of hydraulic pressure supplied to said braking unit are minimized.

Claim 17

An antiskid brake control system for a rotatable wheel equipped with a hydraulic pressure responsive braking unit and an associated electrically responsive proportional control valve for adjustably restricting the hydraulic pressure supplied to said braking unit, said control system comprising the combination of a skid detector means coupled to said wheel for providing an output signal of substantially fixed amplitude in response to any skidding deceleration of said wheel, an amplifier means coupled between said skid detector means and said control valve for applying a first control signal of substantially fixed amplItude to said control valve in response to said output signal to relieve all but a predetermined portion of the hydraulic pressure applied to said braking unit, thereby permitting said wheel to recover from said skidding deceleration, and modulator means coupled between said skid detector means and said control valve for supplying to said control valve a second control signal which gradually decays following recovery from a skidding deceleration from a level determined by the frequency and duration of the output signals from said skid detector means to thereby provide a gradually increasing upper limit for the hydraulic pressure supplied to said braking unit.

Claim 18

An antiskid brake control system for a rotatable wheel equipped with a hydraulic pressure responsive braking unit and an associated electrically responsive proportional control valve for adjustably restricting the hydraulic pressure supplied to said braking unit, said control system comprising the combination of a skid detector means coupled to said wheel for providing an output signal of substantially fixed amplitude in response to any skidding deceleration of said wheel, an amplifier means coupled between said skid detector means and said control valve for applying a first control signal of substantially fixed amplItude to said control valve in response to said output signal to relieve all but a predetermined portion of the hydraulic pressure applied to said braking unit, thereby permitting said wheel to recover from said skidding deceleration, and modulator means coupled between said skid detector means and said control valve for supplying to said control valve a second control signal which gradually decays following recovery from a skidding deceleration from a level determined by the frequency and duration of the output signals from said skid detector means to thereby provide a gradually increasing upper limit for the hydraulic pressure supplied to said braking unit.

Claim 19

The antiskid brake control system of claim 16 wherein said modulator means includes a first capacitor connected to supply said second control signal by discharging through said control valve, a first charging circuit coupled between said skid detector means and said first capacitor for charging said first capacitor during initial skidding deceleration of said wheel and during subsequent relatively long skidding decelerations of said wheel, and a second charging circuit coupled between said skid detector means and said first capacitor for charging said first capacitor during subsequent relatively short skidding decelerations of said wheel, whereby said first capacitor is charged at any given time to a voltage which is a function of the frequency and duration of and elapsed time since any past skidding decelerations of said wheel.

Claim 20

The antiskid control system of claim 17 wherein the discharge of said first capacitor through said control valve is effected through a first relatively long time constant circuit, and said first charging circuit includes a second capacitor a relatively long time constant circuit connected between said skid detector means and said second capacitor for charging said second capacitor in response to each skidding deceleration of said wheel to a voltage dependent upon the duration of said skidding deceleration, means coupled between said first capacitor and said second capacitor for establishing the proper initial charge on said first capacitor, and a relatively short discharge time constant circuit connected to said second capacitor for fully discharging said second capacitor between successive skidding deceleration of said wheel.

Claim 21

The antiskid control system of claim 18 wherein said second charging circuit includes a third capacitor, a first unidirectional relatively short time constant circuit coupled between said first and third capacitors for charging said third capacitor to a voltage proportional to the voltage on said first capacitor, a second relatively short time constant circuit coupled between said skid detector means and said third capacitor for changing the charge on said third capacitor in response to each skidding deceleration of said wheel, and a second unidirectional relatively short time constant circuit coupled between said first and third capacitors for discharging said third capacitor into said first capacitor to assure that the charge on said first capacitor is increased in response to each skidding deceleration of said wheel.

Claim 22

The antiskid control system of claim 17 wherein the discharge of said first capacitor through said control valve is effected through a first relatively long time constant circuit, and said second charging circuit includes another capacitor, a first unidirectional relatively short time constant circuit coupled between said first and said other capacitor for charging said other capacitor to a voltage proportional to the voltage on said first capacitor, a second relatively short time constant circuit coupled between said skid detector means and said other capacitor for increasing the charge on said other capacitor in response to each skidding deceleration of said wheel, and a second unidirectional relatively short time constant circuit coupled between said first capacitor and Said other capacitor for discharging said other capacitor into said first capacitor to assure that the charge on said first capacitor is increased in response to each skidding deceleration of said wheel.

Claim 23

In an antiskid control system including an electrically responsive control valve for regulating brake pressure applied to a rotatable wheel and a skid detector coupled between said wheel and said control valve for initiating a first control signal for said valve to reduce the brake pressure applied to said wheel in response to any skidding deceleration of said wheel, a modulator for supplying a second control signal for said valve to establish a gradually increasing upper relatively for said brake pressure between successive skidding decelerations of said wheel; said modulator comprising the combination of a capacitor connected first through said valve to thereby provide said second control signal, a first charging circuit coupled between said skid detector and said capacitor for charging said capacitor during initial skidding deceleration of said wheel and during any subsequent relatively long skidding decelerations of said wheel, and a second charging circuit coupled between said skid detector and said capacitor for charging said capacitor during any subsequent relatively short skidding decelerations of said wheel.

Claim 24

In an antiskid control system including an electrically responsive control valve for regulating brake pressure applied to a rotatable wheel and a skid detector coupled between said wheel and said control valve for initiating a first control signal for said valve to reduce the brake pressure applied to said wheel in response to any skidding deceleration of said wheel, a modulator for supplying a second control signal for said valve to establish a gradually increasing upper relatively for said brake pressure between successive skidding decelerations of said wheel; said modulator comprising the combination of a capacitor connected first through said valve to thereby provide said second control signal, a first charging circuit coupled between said skid detector and said capacitor for charging said capacitor during initial skidding deceleration of said wheel and during any subsequent relatively long skidding decelerations of said wheel, and a second charging circuit coupled between said skid detector and said capacitor for charging said capacitor during any subsequent relatively short skidding decelerations of said wheel.