Anti-lock brake systems

Claim 2

An anti-lock brake system for a wheeled vehicle comprising a fluid pressure source, a fluid pressure connection from said source to a wheel brake controlled by the system, an anti-lock control valve and actuator means for actuating the valve in response to an electrical output from a wheel sensor, a fluid connection from said brake, said fluid connection being adapted to be opened by said anti-lock control valve to allow fluid to be diverted from said brake through said fluid connection to thereby relieve braking pressure, and braking pressure control means operable as a consequence of fluid diverted through said fluid connection to control at least part of the rate at which braking pressure is increased when said anti-lock control valve is closed, said rate at which braking pressure is increased being controlled and dependent upon the volume of fluid displaced when braking pressure is relieved with respect to at least one antilock period, said braking pressure control means comprising a reservoir adapted to receive fluid diverted from the brake, variable restrictor means adapted to provide a variable restriction to flow of fluid in said fluid pressure connection, means for controlling said variable restrictor means in such manner as to determine the amount of restriction afforded thereby as a function of reservoir fluid volume, and a pump for extracting fluid from said reservoir, whereby said restriction is reduced, at the end of an anti-lock period at a rate determined by the volume of displaced fluid and the rate of pumping, second variable restrictor means coupled to the first and located in an outlet of said reservoir via which connection is made to said pump, said second restrictor means being effective to restrict the rate at which fluid is pumped from said reservoir by said pump so that the volume of fluid in said reservoir is reduced at a controlled rate.

Claim 3

A system as claimed in claim 1, wherein said first and second restrictors are both coupled to a plunger which is provided in said reservoir and is displaceable in accordance with the volume of fluid therein.

Claim 4

An anti-lock brake system for a wheeled vehicle comprising a fluid pressure source, a fluid pressure connection from said source to a wheel brake controlled by the system, an anti-lock control valve and actuator means for actuating the valve in response to an electrical output from a wheel sensor, a fluid connection from said brake, said fluid connection being adapted to be opened by said anti-lock control valve to allow fluid to be diverted from said brake through said fluid connection to thereby relieve braking pressure, and braking pressure control means operable as a consequence of fluid diverted through said fluid connection to control at least part of the rate at which braking pressure is increased when said anti-lock control valve is closed, and rate at which braking pressure is increased being controlled and dependent upon the volume of fluid displaced when braking pressure is relieved with respect to at least one anti-lock period, said braking pressure control means comprising a reservoir adapted to receive fluid diverted from the brake, variable restrictor means adapted to provide a variable restriction to flow of fluid in said fluid pressure connection, means for controlling said variable restrictor means in such manner as to determine the amount of restriction afforded thereby as a function of reservoir fluid volume, and a pump for extracting fluid from said reservoir, whereby said restriction is reduced, at the end of an anti-lock period at a rate determined by the volume of displaced fluid and the rate of pumping, and''''fail-safe'''' means for sealing the reservoir outlet from said pump during the time that said anti-lock control valve is actuated.

Claim 5

An anti-lock brake system for a wheeled vehicle comprising a fluid pressure source, a fluid pressure connection from said source to a wheel brake controlled by the system, an anti-lock control valve and actuator means for actuating the valve in response to an electrical output from a wheel sensor, a fluid connection from said brake, said fluid connection being adapted to be opened by said anti-lock control valve to allow fluid to be diverted from said brake through said fluid connection to thereby relieve braking pressure, and braking pressure control means operable as a consequence of fluid diverted through said fluid connection to control at least part of the rate at which braking pressure is increased when said anti-lock control valve is closed, and rate at which braking pressure is increased being controlled and dependent upon the volume of fluid displaced when braking pressure is relieved with respect to at least one anti-lock period, said braking pressure control means comprising a reservoir adapted to receive fluid diverted from the brake, variable restrictor means adapted to provide a variable restriction to flow of fluid in said fluid pressure connection, means for controlling said variable restrictor means in such manner as to determine the amount of restriction afforded thereby as a function of reservoir fluid volume, and a pump for extracting fluid from said reservoir, whereby said restriction is reduced, at the end of an anti-lock period at a rate determined by the volume of displaced fluid and the rate of pumping, and''''fail-safe'''' means for sealing the reservoir outlet from said pump during the time that said anti-lock control valve is actuated.

Claim 6

A system as claimed in claim 3, wherein said ''''fail-safe'''' means comprises a plunger which is located adjacent the reservoir outlet and between said reservoir and the fluid connection from the latter to said anti-lock control valve, said plunger being displaceable by fluid pressure in the fluid connection when the anti-lock control valve is actuated to seal the reservoir outlet from the pump.

Claim 7

A system as claimed in claim 4, wherein said plunger is so dimensioned as to permit flow of fluid past it from said fluid connection into said reservoir, and wherein displacement of said plunger to seal the reservoir outlet causes an immediate volume of fluid to be displaced into said reservoir, followed by a slower increase of said volume as fluid thereafter has to pass said plunger to enter the reservoir.

Claim 8

An anti-lock brake system for a wheeled vehicle comprising a fluid pressure source, a fluid pressure connection from said source to a wheel brake controlled by the system, an anti-lock control valve and actuator means for actuating the valve in response to an electrical output from a wheel sensor, a fluid connection from said brake, said fluid connection being adapted to be opened by said anti-lock control valve to allow fluid to be diverted from said brake through said fluid connection to thereby relieve braking pressure, and braking pressure control means operable as a consequence of fluid diverted through said fluid connection to control at least part of the rate at which braking pressure is increased when said anti-lock control valve is closed, said rate at which braking pressure is increased being controlled and dependent upon the volume of fluid displaced when braking pressure is relieved with respect to at least one anti-lock period, said braking pressure control means comprising a reservoir adapted to receive fluid diverted from the brake, variable restrictor means adapted to provide a variable restriction to flow of fluid in said fluid pressure connection, means for controlling said variable restrictor means in such manner as to determine the amount of restriction afforded thereby as a function of reservoir fluid volume, and a pump for extracting fluid from said reservoir, whereby said restriction is reduced, at the end of an anti-lock period at a rate determined by the volume of displaced fluid and the rate of pumping, and an auxiliary fluid pressure connection from said pressurized fluid source to said anti-lock control valve, said auxiliary fluid pressure connection having a housing portion in which is slidably accommodated a differential piston presenting a small area face towards said pressurized fluid source and a large area face towards said anti-lock control valve, the arrangement being such that when said anti-lock control valve is unactuated it allows connection between said fluid pressure connection and the large area face of the differential piston so that the latter is displaced towards the pressurized fluid source despite the fluid pressure from the latter due to the differential effect afforded by the respective areas of the piston faces, whereas when the anti-lock control valve is actuated it seals the fluid pressure connection from the large face of the piston so that fluid pressure at the locking value of pressure is present at the large face, with the result that when the anti-lock control valve is released at the end of an anti-lock period, braking pressure is immediately increased by movement of the piston towards the fluid pressure connection at a first, relatively high rate until the value of braking pressure reaches a certain fraction of the pressure of the pressurized fluid source, said fraction being determined by the ratio of the area of the small face of the piston to that of the large face of the piston and braking pressure thereafter increasing at a second slower, rate.

Claim 9

An anti-lock brake system for a wheeled vehicle comprising a fluid pressure source, a fluid pressure connection from said source to a wheel brake controlled by the system, an anti-lock control valve and actuator means for actuating the valve in response to an electrical output from a wheel sensor, a fluid connection from said brake, said fluid connection being adapted to be opened by said anti-lock control valve to allow fluid to be diverted from said brake through said fluid connection to thereby relieve braking pressure, and braking pressure control means operable as a consequence of fluid diverted through said fluid connection to control at least part of the rate at which braking pressure is increased when said anti-lock control valve is closed, said rate at which braking pressure is increased being controlled and dependent upon the volume of fluid displaced when braking pressure is relieved with respect to at least one anti-lock period, said braking pressure control means comprising a reservoir adapted to receive fluid diverted from the brake, variable restrictor means adapted to provide a variable restriction to flow of fluid in said fluid pressure connection, means for controlling said variable restrictor means in such manner as to determine the amount of restriction afforded thereby as a function of reservoir fluid volume, and a pump for extracting fluid from said reservoir, whereby said restriction is reduced, at the end of an anti-lock period at a rate determined by the volume of displaced fluid and the rate of pumping, and an auxiliary fluid pressure connection from said pressurized fluid source to said anti-lock control valve, said auxiliary fluid pressure connection having a housing portion in which is slidably accommodated a differential piston presenting a small area face towards said pressurized fluid source and a large area face towards said anti-lock control valve, the arrangement being such that when said anti-lock control valve is unactuated it allows connection between said fluid pressure connection and the large area face of the differential piston so that the latter is displaced towards the pressurized fluid source despite the fluid pressure from the latter due to the differential effect afforded by the respective areas of the piston faces, whereas when the anti-lock control valve is actuated it seals the fluid pressure connection from the large face of the piston so that fluid pressure at the locking value of pressure is present at the large face, with the result that when the anti-lock control valve is released at the end of an anti-lock period, braking pressure is immediately increased by movement of the piston towards the fluid pressure connection at a first, relatively high rate until the value of braking pressure reaches a certain fraction of the pressure of the pressurized fluid source, said fraction being determined by the ratio of the area of the small face of the piston to that of the large face of the piston and braking pressure thereafter increasing at a second slower, rate.

Claim 10

A system as claimed in claim 6, wherein the ratio of said piston faces is about 1 : 2.

Claim 11

An anti-lock brake system for a wheeled vehicle comprising a fluid pressure source, a fluid pressure connection from said source to a wheel brake controlled by the system, an valve and interconnected with said first housing portion by a neck portion, a stem of said piston extending through said neck portion and having the flap valve secured to it, and the flap valve controlling the passage of fluid from said pressurized fluid source to said brake via a second auxiliary fluid pressure connection, the arrangement being such that when said anti-lock control valve is actuated, it seals fluid pressure at the locking value in said first housing portion and in said resilient element at opposite sides of said piston respectively, the fluid pressure in said resilient element leaking through said neck portion during the anti-lock period to a final value, as determined by the length of this period, whereby when said anti-lock control valve is released at the end of the period and fluid pressure in said first housing is relieved, the fluid pressure remaining in the resilient element displaces said piston against its spring-loading to an extent determined by its final value, thereby opening the flap valve a corresponding extent, so that fluid pressure from said pressurized fluid pressure source passes via said second auxiliary fluid pressure connection to increase braking pressure at a high rate until the flap valve is closed again, and then at a second, slower rate.

Claim 12

An anti-lock brake system for a wheeled vehicle comprising a fluid pressure source, a fluid pressure connection from said source to a wheel brake controlled by the system, an valve and interconnected with said first housing portion by a neck portion, a stem of said piston extending through said neck portion and having the flap valve secured to it, and the flap valve controlling the passage of fluid from said pressurized fluid source to said brake via a second auxiliary fluid pressure connection, the arrangement being such that when said anti-lock control valve is actuated, it seals fluid pressure at the locking value in said first housing portion and in said resilient element at opposite sides of said piston respectively, the fluid pressure in said resilient element leaking through said neck portion during the anti-lock period to a final value, as determined by the length of this period, whereby when said anti-lock control valve is released at the end of the period and fluid pressure in said first housing is relieved, the fluid pressure remaining in the resilient element displaces said piston against its spring-loading to an extent determined by its final value, thereby opening the flap valve a corresponding extent, so that fluid pressure from said pressurized fluid pressure source passes via said second auxiliary fluid pressure connection to increase braking pressure at a high rate until the flap valve is closed again, and then at a second, slower rate.

Claim 13

An anti-lock brake system for a wheeled vehicle comprising a fluid pressure source, a fluid pressure connection from said source to a wheel brake controlled by the system, an anti-lock control valve and actuator means for actuating the valve in response to an electrical output from a wheel sensor, a fluid connection from said brake, said fluid connection being adapted to be opened by said anti-lock control valve to allow fluid to be diverted from said brake through said fluid connection to thereby relieve braking pressure, and braking pressure control means comprising a reservoir for receiving fluid diverted from the brake, means connecting said reservoir to said fluid connection for diverting fluid from the brake, restrictor means adapted to provide a restriction to flow of fluid in said fluid pressure connection when fluid is diverted from said brake, means for controlling said restrictor means so as to vary the amount of restriction produced thereby between maximum, minimum and intermediate values as a function of reservoir fluid volume thereby controlling at least part of the rate at which braKing pressure is increased when said anti-lock control valve is closed, said means for controlling said restrictor means being connected thereto and includes means responsive to the volume of fluid displaced for controlling the rate at which braking pressure is increased.

Claim 14

An anti-lock brake system for a wheeled vehicle comprising a fluid pressure source, a fluid pressure connection from said source to a wheel brake controlled by the system, an anti-lock control valve and actuator means for actuating the valve in response to an electrical output from a wheel sensor, a fluid connection from said brake, said fluid connection being adapted to be opened by said anti-lock control valve to allow fluid to be diverted from said brake through said fluid connection to thereby relieve braking pressure, and braking pressure control means comprising a reservoir for receiving fluid diverted from the brake, means connecting said reservoir to said fluid connection for diverting fluid from the brake, restrictor means adapted to provide a restriction to flow of fluid in said fluid pressure connection when fluid is diverted from said brake, means for controlling said restrictor means so as to vary the amount of restriction produced thereby between maximum, minimum and intermediate values as a function of reservoir fluid volume thereby controlling at least part of the rate at which braKing pressure is increased when said anti-lock control valve is closed, said means for controlling said restrictor means being connected thereto and includes means responsive to the volume of fluid displaced for controlling the rate at which braking pressure is increased.

Claim 15

A system as claimed in claim 9 further comprising a pump for extracting fluid from said reservoir said restriction thereby being reduced at the end of an anti-lock period at a rate determined by the volume of displaced fluid and the rate of pumping.

Claim 16

A system as claimed in claim 10 in which said pump is driven by a vehicle wheel to which the system is applied whereby the pumping action is at a rate which is related to wheel rotational speed.

Claim 17

A system as claimed in claim 9 in which the anti-lock control valve is a solenoid actuated valve having characteristics such that it acts as a pressure relief valve, the opening value thereof being dependent on solenoid current and set such that at zero current it will remain closed at the maximum braking pressure of the system but will be fully open when energizing current is applied to it for a time greater than a certain minimum, whereby to provide a fluid pressure leak path between said fluid pressure connection and said fluid connection, at a time immediately before each anti-lock cycle, to cause a slight relieving of braking pressure at this time, whereby to ''''tail-off'''' the rate of braking pressure increase between one anti-lock cycle and the next.

Claim 18

A system as claimed in claim 9 including an electrical control unit for effectuating actuation of said anti-lock control valve in response to electrical signals from said wheel sensor.

Claim 19

An anti-lock vehicle brake system as claimed in claim 9 provided for each road wheel of a vehicle.