Anti-skid vehicle braking system

Abstract

In a fluid pressure-operated anti-skid braking system for rail and other vehicles operating fluid from a supply for actuating a wheel brake is supplied to the brake through a fluid-flow control valve interposed in the line between the supply and the brake. Deceleration responsive sensors responsive to a skid signal are incorporated for operating the valve to relieve the brake pressure of the fluid supplied to the brake when the deceleration of the wheel is excessive and exceeds a predetermined value. The valve incorporates a fluid pressure memory chamber for sensing the skid pressure, and the memory chamber provides a datum or changeover point between first and second successive stages of brake re-application following a skid.

I claim: 
     
       1. A fluid pressure-operated anti-skid braking system for rail and other vehicles comprising at least one actuator for applying a wheel brake, a supply of operating fluid for operating said actuator, fluid flow control valve means interposed between said supply and said brake and through which fluid from said supply is supplied to said actuator, .[.deceleration responsive.]. means responsive to a skid signal for operating said valve means to relieve brake skid pressure applied to said actuator when the deceleration of said wheel is excessive and exceeds a predetermined value, a fluid pressure memory chamber for sensing said skid pressure applied to said actuator on the downstream side of said control valve means whereby said skid pressure sensed by said memory chamber can never exceed the said skid pressure applied to said actuator to cause excessive deceleration of said wheel, wherein said memory chamber provides a changeover point between first and second successive stages of re-application of fluid from said supply to said actuator, said first stage comprising re-application of said fluid at a normal original rate until an intermediate pressure less than said skid pressure is attained at said changeover point, and said second stage comprising continued re-application of said fluid but at a reduced rate, and wherein said valve means comprises a re-application valve in which said memory chamber is incorporated and having an inlet connected to said supply and an outlet, a dump valve assembly having an inlet connected to said outlet of said re-application valve assembly and an outlet connected to said actuator, and a control member for controlling the maximum opening of said re-application valve, said control member having opposed first and second areas exposed respectively to said memory chamber and to a second chamber on the opposite side of said control member from said memory chamber, first and second connections between both said chambers and said outlet of said dump valve assembly, and a first restrictor incorporated in said connection between said memory chamber and said outlet of said dump valve assembly, the arrangement being such that a difference in pressure between the said two chambers biasses said control member in a direction to reduce the maximum opening of said re-application valve. 
     
     
       2. An anti-skid braking system as claimed in claim 1, wherein a second restrictor is incorporated in series with said first restrictor in said first connection between said memory chamber and said outlet of said dump valve, and a one-way valve is connected in parallel between a point between said first and second restrictors and said second connection between said second chamber and said outlet of said dump valve. 
     
     
       3. An anti-skid braking system as claimed in claim 2, wherein said one-way valve permits flow in a direction from said first connection to said second connection so that the rate of decay of pressure in said memory chamber is greater than the rate of pressure rise therein. 
     
     
       4. A fluid pressure operated anti-skid braking system for rail and other vehicles comprising at least one actuator for applying a wheel brake, a supply of operating fluid for operating and actuator, fluid flow control valve means interposed between said supply and said brake and through which fluid from said supply is supplied to said actuator, .[.deceleration responsive.]. means responsive to a skid signal for operating said valve means to relieve brake skid pressure applied to said actuator when the deceleration of said wheel is excessive and exceeds a predetermined value, said valve means is incorporating a fluid pressure memory chamber for sensing said skid pressure, wherein said memory chamber provides a changeover point between first and second successive stages of re-application of fluid from said supply to said actuator, said first stage comprising re-application of said fluid at a normal original rate until an intermediate pressure less than said skid pressure is attained at said changeover point, and said second stage comprising continued re-application of said fluid but at a reduced rate, wherein said valve means comprises a re-application valve in which said memory chamber is incorporated and having an inlet connected to said supply and an outlet, a dump valve assembly having an inlet connected to said outlet of said re-application valve assembly and an outlet connected to said actuator, and a control member for controlling the maximum opening of said re-application valve, said control member having opposed first and second areas exposed respectively to said memory chamber and to a second chamber on the opposite side of said control member from said memory chamber, first and second connections between both said chambers and said outlet of said dump valve assembly, and a first restrictor incorporated in said connection between said memory chamber and said outlet of said dump valve assembly, the arrangement being such that a difference in pressure between the said two chambers biasses said control member in a direction to reduce the maximum opening of said re-application valve, and wherein said re-application valve comprises a seating and a valve member movable towards and away from said seating said control member comprising a movable abutment member which is engagable by said valve member to limit movement of said valve member away from said seating. 
     
     
       5. An anti-skid braking system as claimed in claim 4, wherein said first and second areas comprise opposite sides of a diaphragm secured to said abutment member. 
     
     
       6. An anti-skid braking system as claimed in claim 4, including a spring for resiliently biassing said abutment member out of engagement with said valve member. 
     
     
       7. A fluid pressure-operated anti-skid braking system for rail and other vehicles comprising at least one actuator for applying a wheel brake, a supply of operating fluid for operating said actuator, fluid flow control valve means interposed between said supply and said brake and through which fluid from said supply is supplied to said actuator, .[.deceleration responsive.]. means responsive to a skid signal for operating said valve means to relieve brake skid pressure applied to said actuator when the deceleration of said wheel is excessive and exceeds a predetermined value, said valve means incorporating a fluid pressure memory chamber for sensing said skid pressure, wherein said memory chamber provides a changeover point between first and second successive stages of re-application of fluid from said supply to said actuator, said first stage comprising re-application of said fluid at a normal original rate until an intermediate pressure less than said skid pressure is attained at said changeover point, and said second stage comprising continued re-application of said fluid but at a reduced rate, wherein said valve means comprises a re-application valve in which said memory chamber is incorporated and having an inlet connected to said supply and an outlet, a dump valve assembly having an inlet connected to said outlet of said re-application valve assembly and an outlet connected to said actuator, and a control member for controlling the maximum opening of said re-application valve, said control member having opposed first and second areas exposed respectively to said memory chamber and to a second chamber on the opposite side of said control member from said memory chamber, first and second connections between both said chambers and said outlet of said dump valve assembly, and a first restrictor incorporated in said connection between said memory chamber and said outlet of said dump valve assembly, the arrangement being such that a difference in pressure between the said two chambers biasses said control member in a direction to reduce the maximum opening of said re-application valve, incorporating a latch valve connected between the said two chambers and constructed and arranged to equalise the pressure in the said chambers during a normal brake application under non-skid conditions, thereby preventing said control member from closing said re-application valve. 
     
     
       8. An anti-skid braking system as claimed in claim 7, wherein said latch valve comprises a seating disposed between said two chambers, a valve member for engagement with said seating, a diaphragm for controlling operation of said valve member and having one side exposed to said supply of operating fluid to urge said valve member towards said seating against pressure acting on the opposite side of said diaphragm, and wherein said diaphragm is of an area larger than that of said seating so that a reduction in said pressure of said operating supply does not affect the mode of said latch valve. 
     
     
       9. An anti-skid braking system as claimed in claim 8, wherein a restriction is located between said latch valve and said memory chamber to enable pressure acting on opposite sides of said diaphragm to equalise after a delay following equalisation of the pressures on opposite sides of said control member. 
     
     
       10. An anti-skid braking system as claimed in claim 9, wherein a one-way valve is connected in parallel with said restriction to permit flow of fluid from said latch valve into said memory chamber. 
     
     
       11. An anti-skid braking system as claimed in claim 8, wherein a spring biasses said valve member away from said seating. .Iadd. 12. A fluid-pressure-operated anti-skid braking system for rail and other vehicles comprising at least one actuator for applying a wheel brake, a supply of operating fluid for operating said actuator, fluid flow control valve means interposed between said supply and said brake, fluid from said supply being supplied to said actuator through said valve means, and means responsive to a skid detection signal for operating said valve means to relieve brake skid pressure applied to said actuator when said skid detection signal exceeds a predetermined value to signal a skid condition, said valve means incorporating a fluid-pressure memory chamber for storing a pressure corresponding to said skid pressure, means through which said memory pressure decays during a skid condition by an amount dependent on the duration of said skid condition, said valve means also incorporating a second chamber, said second chamber containing a pressure corresponding to existing brake pressure, a predetermined relationship between said pressures in said memory chamber and said second chamber determining a changeover point between first and second stages of re-application of fluid from said supply to said actuator, said first stage comprising re- application of said fluid at a rapid rate of pressure increase until an intermediate pressure less than said skid pressure is attained at said changeover point, said second stage comprising continued re-application of said fluid at a reduced rate of pressure increase, and means for restoring pressure in said memory chamber upon re-application of fluid to said actuator. .Iaddend..Iadd. 13. An anti-skid braking system as claimed in claim 12, wherein said memory chamber stores a volume of said fluid at the skid pressure of an immediately preceding brake application or re-application, and a re-application valve for controlling flow from supply to said actuator is incorporated, said re-application valve being operated by a control member responsive to a differential between said pressure in said memory chamber and said pressure in said second chamber during a successive brake re-application. .Iaddend..Iadd. 14. A fluid-pressure-operated anti-skid braking system for rail and other vehicles comprising at least one actuator for applying a wheel brake, a supply of operating fluid for operating said actuator, fluid flow control valve means interposed between said supply and said brake, fluid from said supply being supplied to said actuator through said valve means, and means responsive to a skid detection signal for operating said valve means to relieve brake skid pressure applied to said actuator when said skid detection signal exceeds a predetermined value to signal a skid condition, said valve means incorporating a fluid-pressure memory chamber for storing a pressure corresponding to said skid pressure, said memory chamber providing a changeover point between first and second successive stages of re-application of fluid from said supply to said actuator, said first stage comprising re-application of said fluid at a rapid rate of pressure increase until an intermediate pressure less than said skid pressure is attained at said changeover point, said second stage comprising continued re-application of said fluid at a reduced rate of pressure increase, said valve means also incorporating means defining a passage, said passage means including a one-way valve, said memory chamber being pressurised during non-skid braking to a pressure corresponding to brake pressure through said passage means and said one-way valve, said valve means further incorporating a latch valve, said latch valve being operative after said skid detection signal exceeds said predetermined value to restrict the effective cross-sectional area of said passage means to an amount which still permits flow through said passage means. .Iaddend. .Iadd. 15. An anti-skid braking system as claimed in claim 14, wherein said memory chamber incorporates means through which pressure can decay during said skid condition so that the pressure at said changeover point will reduce automatically in the time interval between successive brake re-applications in a common braking sequence. .Iaddend..Iadd. 16. An anti-skid braking system as claimed in claim 14, wherein a volume of fluid at the skid pressure of an immediately preceding brake application or re-application is trapped in said memory chamber, and a re-application valve for controlling flow from the supply to the brake is operated by a control member responsive to a differential between the pressure in said memory chamber and the brake pressure during a successive brake re-application. .Iaddend..Iadd. 17. An anti-skid braking system as claimed in claim 14, wherein said passage means through which said memory chamber is pressurised incorporates at least one restrictor. .Iaddend..Iadd. 18. An anti-skid braking system as claimed in claim 17, wherein said valve means comprises a re-application valve assembly in which said memory chamber is incorporated, and having an inlet connected to said supply and an outlet, a dump valve assembly having an inlet connected to said outlet of said re-application valve, and an outlet connected to said actuator, and a control member for controlling the maximum opening of said re-application valve, said control member having opposed first and second areas exposed respectively to said memory chamber and to a second chamber on the opposite side of said control member from said memory chamber, said memory chamber and said second chamber being connected to said outlet of said dump valve assembly, and a restrictor incorporated in said connection between said memory chamber and said outlet of said dump valve assembly, said latch valve being connected between said two chambers, said one-way valve located between said latch valve and said memory chamber, said latch valve being operative during normal non-skid braking to equalise the pressures in said chambers, thereby preventing said control member from closing said re-application valve. .Iaddend..Iadd. 19. An anti-skid braking system as claimed in claim 18, wherein said latch valve comprises a seating disposed between said two chambers, a valve member for engagement with said seating, a diaphragm for controlling operation of said valve member, one side of said diaphragm being exposed to said supply of operating fluid to urge said valve member towards said seating against the pressure acting on the opposite side of said diaphragm, and the area of said diaphragm is larger than that of said seating. .Iaddend..Iadd. 20. An anti-skid braking system as claimed in claim 19, wherein a restriction is located between said latch valve and said memory chamber to enable the pressures acting on said opposite sides of said diaphragm to equalise after a delay following equalisation of the pressures on said opposite sides of said control member. .Iaddend..Iadd. 21. An anti-skid braking system as claimed in claim 18, wherein a second restrictor is incorporated in series with said first restrictor in said connection between said memory chamber and said outlet of said dump valve assembly, and a second one-way valve is connected in parallel with said first restriction, having a first connection with a point between said two restrictors and a second connection with said connection between said second chamber and said outlet of said dump valve assembly. .Iaddend. .Iadd. 22. An anti-skid braking system as claimed in claim 21, wherein said second one-way valve permits flow in a direction from said first connection to said second connection so that the rate of decay of pressure in said memory chamber is greater than the rate of pressure rise during a skid condition. .Iaddend.