Fluid-pressure operated anti-skid braking systems for vehicles

A fluid-pressure operated braking system for vehicles comprising a wheel, a brake for braking said wheel, a fluid-operated brake actuator for applying said brake, a supply of brake-operating fluid for supplying said actuator with brake-operating fluid, a skid control unit interposed in a line between said supply and said brake, sensors provided to detect a skid point, means responsive to a skid signal produced by any of the sensors incorporated for operating valve means to relieve the pressure of the fluid supplied to said brake at a skid point, said unit having first means for re-applying said brake in a first stage of brake re-application and second means for re-applying said brake in a second stage of brake re-application, said first means incorporating a memory chamber for storing a memory pressure dependent upon the pressure of control fluid occurring at said skid point to provide a datum or knee point between said first and second stages of brake re-application, said first and second means controlling the re-application of said brake by said actuator such that said first stage of brake re-application is at a relatively higher rate than said second stage of brake re-application, and wherein said second means controls the rate of brake re-application in said second stage to be at a reduced rate in comparison to that at which the brake is applied before said skid point is detected by said sensors, said skid control unit further comprising pressure decay means associated with said memory chamber, said memory pressure decay means causing said memory pressure stored in said memory chamber to decay when said skid point is detected from an initial value substantially equal to that of the brake-operating pressure immediately before said skid point was detected to a lower pressure, and wherein a passage communicates said memory chamber with said supply, and an isolating valve for isolating said memory chamber from said supply is provided in said passage, the portion of said passage extending between said supply and said isolating valve comprising a connection portion of said passage, and wherein when a skid signal is detected for said wheel said skid control unit closes said isolating valve to isolate said memory chamber from said supply and said connection portion continues to be pressurized by said supply during said skid, said memory pressure decay means allowing said memory pressure to decay at a rate which substantially balances and counteracts the pressure increase in said connection portion during said skid so as to compensate upon brake re-application in said first stage for the pressurisatior of said connection portion so that the pressure reduction in said memory chamber and the pressure increase in said connection portion substantially cancel each other out during said firsty stage or rake re-application thereby maintaining the pressure of said knee point of said control fluid applied in said first stage of brake re-application substantially constant, independent of the duration of said skid.

A fluid-pressure operated braking system for vehicles comprising a wheel, a brake for braking said wheel, a fluid-operated bake actuator for applying said brake, a supply of brake-operating fluid for supplying said actuator with brake-operating fluid, a skid control unit interposed in a line between said supply and said brake, sensors provided to detect a skid point, means responsive to a skid signal produced by any of the sensors incorporated for operating valve means to relieve the pressure of the fluid supplied to said brake at a skid point, said unit having first means for re-applying said brake in a first stage of brake re-application and second means for re-applying said brake in a second stage of brake re-application, said first means incorporating a memory chamber for storing a memory pressure dependent upon the pressure of control fluid occurring at said skid point to provide a datum or knee point between said first and second stages of brake re-application, said first and second means controlling the re-application of said brake by said actuator such that said first stage of brake re-application is at a relatively higher rate than said second stage of brake re-application, and wherein said second means controls the rate of brake re-application in said second stage to be at a reduced rate in comparison to that at which the brake is applied before said skid point is detected by said sensors, said skid control unit further comprising pressure decay means associated with said memory chamber, said memory pressure decay means causing said memory pressure stored in said memory chamber to decay when said skid point is detected from an initial value substantially equal to that of the brake-operating pressure immediately before said skid point was detected to a lower pressure, and wherein a latch valve is provided and controls the flow of operating fluid between said source of operating fluid and said skid control unit, closure of said latch valve restricting flow of operating fluid from said source to said unit to said reduced rate of said second stage of brake re-application, and wherein first and second brakes on opposite ends of a common axle are provided and are each controlled by a respective separate said skid control unit, and a single latch valve common to both units closes at the first skid point to be sensed by a sensor on either wheel, whereafter re-application of said first and second brakes is respectively controlled in response to signals from their respective sensors, but at individual rates of pressure increase determined by said memory chambers of the respective said units, and by restricted flows of brake-applying fluid, and wherein each memory chamber has its own independent memory pressure decay means.