Anti-lock brake systems

Claim 2

An anti-lock vehicle brake system comprising a wheel brake, a source of fluid pressure, means for applying pressure from said source to said brake for operating same, an anti-lock control valve for relieving said brake pressure when actuated, means connected to said control valve for detecting wheel locking so as to actuate said control valve and thereby relieve braking pressure, a fail-safe arrangement for reapplication of brake pressure to said brake in the event of prolonged actuation of said anti-lock control valve so as to allow full brake pressure to be restored to said brake, comprising a chamber, a differential pressure member accommodated within said chamber for displacement between a normal position and an operative position in response to difference in fluid pressure acting on opposite ends thereof, said differential pressure member having first and second surface areas at one end thereof and a third surface area at the other end thereof opposite said first and second surface areas, said second surface area being larger than said first surface area and said third surface area being larger than said second surface area, said source of pressure connected to said chamber for Establishing a first reference pressure at said third surface area of said pressure differential member, reference pressure means for establishing a second reference pressure at said second surface area of said pressure differential member, and a first connection extending between said anti-lock control valve and said chamber, said first connection being connected to said chamber at the side thereof having said second surface area of said pressure member, so that when the control valve is actuated fluid may be displaced into said first connection thereby progressively varying in value of said first reference pressure at said third surface area in proportion to the reduction of the fluid pressure at the wheel brake due to said control valve being actuated until said differential pressure member is displaced from its normal position to its operative position so that fluid pressure acting on said brake will be increased to full braking pressure as a result of said control valve remaining actuated and fluid being displaced through said first connection from said source of pressure to said brake.

Claim 3

The system as claimed in claim 1 wherein said control valve is connected in a pressure line for supplying fluid under pressure from said source of pressure to the brake, said control valve being operative to divert fluid from said pressure line when actuated so as to relieve braking pressure thereby preventing wheel locking,and wherein said first connection extending between said anti-lock control valve and said chamber forms a portion of a by-pass connecting said source of pressure with said control valve when said differential pressure member is in the operative position, said differential pressure member being arranged so as to seal off said by-pass connection when in its normal position and to unseal said by-pass connection to permit the application of fluid pressure therethrough and through the actuated control valve from said source of pressure to the brake when said pressure member is displaced to its operative position.

Claim 4

The system as claimed in claim 2, wherein said differential pressure member comprises a piston which is slidably accommodated in said chamber, and wherein said reference pressure means for establishing a second reference pressure comprises a fluid reservoir communicating at one side thereof with said chamber, said fluid reservoir further being connected via said first connection to said control valve for receiving fluid diverted from said pressure line when the control valve is actuated, the fluid pressure in said reservoir providing said second reference pressure at said second surface area of the differential pressure member through said first connection, and further comprising a second connection communicating between said chamber and said source of pressure for applying fluid pressure from said source of pressure to said third surface area of said differential pressure member, and a third connection for applying fluid pressure from said source of pressure to said first surface area of said differential pressure member, the fluid pressure from said source providing said first reference pressure, and a seal on said differential pressure member for isolating said third connection from said chamber when said member is in its normal position, said by-pass connection being formed by said first and said third connections when said member is displaced to its operative position to cause communication of said third connection with said chamber.

Claim 5

The system as claimed in claim 3, further comprising a fluid control device for causing said first reference pressure to fall at a slower rate than the rate at which braking pressure falls at the brake to relieve braking pressure when the control valve of the system is actuated.

Claim 6

The system as claimed in claim 4, wherein said fluid control device comprises a one-way valve in said second connection, and a restrictor element connected in a fluid connection in parallel with said one-way valve, said restrictor Arranged so as to permit fluid pressure to pass to said third surface area of said differential pressure member, and to prevent such fluid pressure being relieved from that area, said restrictor element operating to relieve said fluid pressure at a rate determined thereby.

Claim 7

An anti-lock vehicle brake system comprising a wheel brake for applying brake pressure to said wheel to cause deceleration thereof, a fluid pressure source and connection therefrom to said brake for applying brake fluid thereto under pressure in response to braking action applied to said fluid pressure source, wheel movement sensing means for detecting wheel rotational movement and producing an output function as a result thereof, an anti-lock control valve located within the connection between said fluid pressure source and said brake and arranged for actuation in response to said output function so as to divert brake fluid from said brake to thereby relieve braking pressure so as to avoid wheel locking, a fail-safe mechanism comprising a chamber, a differential member slidably mounted within said chamber for displacement between a normal and operative position said differential pressure member comprising first, second and third surface areas, said first surface area being smaller than said second surface area and said second surface area being smaller than said third surface area, said first and second surface areas being located on one end of said member and said third surface area being located on an end opposite thereto, a fluid reservoir connected to said control valve for receiving the fluid diverted from said connection between said fluid pressure source and said brake when said control valve is actuated to relieve brake pressure, a first connection between said reservoir and said chamber on a side thereof so that the fluid pressure from said reservoir may be applied to said second surface area thereby providing one of two reference pressures, a second connection between said fluid pressure source and said chamber for applying fluid pressure to said third surface area of said differential pressure member, and a third connection from said fluid pressure source for applying fluid pressure to said first surface area of said differential pressure member, the pressure applied from said fluid pressure source thereby providing the other of said two reference pressures, said differential pressure member being caused to be displaced from its normal to its operative position when said first reference pressure falls below said second reference pressure, a by-pass connection being established between said first and third connections when said differential pressure member is displaced to its operative position so that fluid pressure may be applied therethrough from said fluid pressure source to said reservoir and through said actuated control valve so as to reapply brake pressure to said wheel brake and restore full braking pressure to the wheel.

Claim 8

An anti-lock vehicle brake system comprising a wheel brake for applying brake pressure to said wheel to cause deceleration thereof, a fluid pressure source and connection therefrom to said brake for applying brake fluid thereto under pressure in response to braking action applied to said fluid pressure source, wheel movement sensing means for detecting wheel rotational movement and producing an output function as a result thereof, an anti-lock control valve located within the connection between said fluid pressure source and said brake and arranged for actuation in response to said output function so as to divert brake fluid from said brake to thereby relieve braking pressure so as to avoid wheel locking, a fail-safe mechanism comprising a chamber, a differential member slidably mounted within said chamber for displacement between a normal and operative position said differential pressure member comprising first, second and third surface areas, said first surface area being smaller than said second surface area and said second surface area being smaller than said third surface area, said first and second surface areas being located on one end of said member and said third surface area being located on an end opposite thereto, a fluid reservoir connected to said control valve for receiving the fluid diverted from said connection between said fluid pressure source and said brake when said control valve is actuated to relieve brake pressure, a first connection between said reservoir and said chamber on a side thereof so that the fluid pressure from said reservoir may be applied to said second surface area thereby providing one of two reference pressures, a second connection between said fluid pressure source and said chamber for applying fluid pressure to said third surface area of said differential pressure member, and a third connection from said fluid pressure source for applying fluid pressure to said first surface area of said differential pressure member, the pressure applied from said fluid pressure source thereby providing the other of said two reference pressures, said differential pressure member being caused to be displaced from its normal to its operative position when said first reference pressure falls below said second reference pressure, a by-pass connection being established between said first and third connections when said differential pressure member is displaced to its operative position so that fluid pressure may be applied therethrough from said fluid pressure source to said reservoir and through said actuated control valve so as to reapply brake pressure to said wheel brake and restore full braking pressure to the wheel.