GB1564510A - Fluid pressure operated anti-skid braking systems for vehicles - Google Patents

Description

(54) IMPROVEMENTS IN FLUID PRESSURE OPERATED ANTI-SKID BRAKING SYSTEMS FOR VEHICLES (71) We, GIRLING LIMITED, a British Company of Kings Road, Tyseley, Birmingham 11, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to improvements in fluid-pressure operated anti-skid braking systems for rail or other vehicles of the kind in which the supply of operating fluid to a wheel brake is controlled by a fluid-flow control valve assembly interposed in the line between the supply and the brake and means responsive to a skid signal are incorporated for operating the valve assembly to relieve the pressure supplied to the brake.

Hereinafter the pressure to be relieved under such conditions will be referred to as the "skid-pressure".

In known braking systems of the kind for vehicles set forth the valve assembly comprises a single control valve which is operable by a deceleration responsive device to cut-off supply to the brake and subsequently reduce the skid pressure when the predetermined value of deceleration is exceeded. Subsequently the brake is re-applied automatically during the same braking sequence at the same rate at least up to the skid pressure which is undesirable since, for the same conditions of wheel adhesion, such a re-application will again cause the wheel deceleration to be excessive.In more complex systems it is known to include a memory which senses the skid pressure and ensures that the braking pressure in a subsequent brake re-application will normally be less than the skid pressure attained in the immediately preceding application in the same braking sequence and can rise only gradu ally to a pressure greater than the skid pressure and then only after a substantial interval of time.

According to our invention in a fluidpressure operated anti-skid braking system tor rail or other vehicles, the control valve assembly comprises first and second separate fluid-flow control valves which are connected in the line in parallel, the first valve having a higher flow rate than the second valve, and each valve having a device responsive to a skid signal for operating that valve, the second valve being operable independently of. or simultaneously with, the first valve.

When the brake is applied initially both devices are inoperative and both valves are open so that full pressure is applied to the brake. When the skid signal is present both devices are actuated to close both valves and subsequently relieve the braking pressure until the skid signal is no longer present. Thereafter, the brake is re-applied automatically in two stages in the first of which both valves are open to allow the pressure to rise at a normal rate to an intermediate value less than the predetermined value at a changeover point at which one of the devices is actuated to close the valve which it controls, whereafter in the second stage the pressure continues to rise, but at a reduced rate controlled by the other valve.

By providing a two-stage re-application has the advantage that the brake can be re-applied relatively quickly and the reduced or more gradual rate of operative in the second stage after the changeover point has been reached is less likely to cause a skid signal to be generated. This is therefore achieved without the provision of a memory which would make the system more complex. Should that happen of course the other device is then operative to close the said other valve and reduce the brake applying pressure, whereafter the sequence described above is repeated.

Preferably the second control valve is open during the second stage and incorporates pressure relief means for reducing the pressure applied to the brake when both devices have been actuated simultaneously or upon actuation of the second control valve following previous closure of the first valve.

The two valves may be substantially identical in construction but with one of the valves provided with a restriction to reduce its flow rate, and an exhaust port for relieving the braking pressure when that valve is closed.

Preferably each valve is diaphragm operated and controlled by a signal pressure acting on one side of the diaphragm, the device responsive to the skid signal com prising a solenoid-operated valve for con trolling the application of the signal pres sure to the diaphragm.

One embodiment of our invention is illustrated in the single Figure of the accompanying drawing which is a layout of a por tion of fluid-pressure operated anti-skid braking system for a rail or other vehicle.

In the layout illustrated in the drawings air under pressure is supplied by wheel brake actuators through a line 1 in which first and second valves 2 and 3 are located in paral lel. The valve 2 has a higher flow rate than the valve 3.

The two valves are substantially identical in construction so that only the valve 3 which comprises a double-beat diaphragm controlled valve of known construction will be described, corresponding reference numerals being used for corresponding parts in the two valves. In the valve 3 a valve member 4 in a housing 5 is engageable alternatively with spaced seatings 6 and 7 to control communication between an inlet port 8 from the supply part of the line 1 and an outlet port 9 leading to the delivery part of the line 1, and between the outlet port 9 and an exhaust 10 to atmosphere.

The valve member 4 is mounted on a vertical spindle 20 on which is mounted a flexible diaphragm 11 which controls operation of the valve member 4 and which is subjected on its upper face remote from the valve member 4 to a signal pressure through a passage 12 leading from the inlet port 8.

A solenoid-operated valve 13 located in the passage 12 is open to allow fluid-pressure to act on the diaphragm when the solenoid is de-energised, and augment the closing force of a spring 14 which normally urges the valve member 4 into engagement witht the seating 7 so that the inlet port 8 is in communication with the outlet port 9 and the exhaust 10 is closed. In this position the solenoid operated valve 13 closes an exhaust port 15 which is opened when the solenoid is energised by a signal from means responsive to deceleration of the braked wheel to reduce the pressure acting on the diaphragm 11, ener4isation of the solenoid first closing the valve 13.Reduction in the pressure acting on the diaphragm 11 en ables the higher pressure acting on its under side to urge the diaphragm and the valve member 4 upwardly into engagement with '11 > seating 6 so that communication be- tween the ports 8 and 9 is cut-off and the pressure into the delivery part of the line is dumped to atmosphere through the exhaust 10.

A restriction in the form of an orifice 16 is located in a union leading into the inlet port 8 to reduce the flow rate at the valve below that of the valve 2, although in a modification, the restriction may be located in any convenient position on the upstream side of the valve member 4 but downstream of the common connection with the valve 2.

No restriction is incorporated in the valve 2 which is otherwise identical to the valve 3 and corresponding reference numerals have been applied to corresponding parts except that the exhaust 10 is omitted so that the seating 7 acts as a stop face. Thus the valve 2 acts as an on/off valve.

When the brakes are applied both valves 2 and 3 are in open positions so that the pressure fluid passes from the supply to the actuators through both valves 2 and 3, and the valve members 4 are both held against the seatings 7 by the forces in the springs 14 which are augmented by the pressure on the diaphragms 11.

Should the deceleration of a braked wheel become excessive and exceed a predetermined value, both solenoids are energised to close the solenoid valves 13 and exhaust the bias pressures to atmosphere. Both valve members then move into engagement with the seatings 6 to isolate the supply and delivery parts of the line, and subsequently exhaust the delivery part to atmosphere thereby relieving the brake force.

After the rate of wheel deceleration has dropped below the said value, the solenoids are de-energised and the valves 13 open to restore the bias pressures thereby opening the valves again to apply the brake. Initially the supply pressure is provided through both valves 2 and 3 until a changeover point is reached when the pressure in the delivery part of the line is less than the pressure which previously caused said predetermined value of deceleration. As the changeover point the solenoid in the valve 2 is ener gised automatically to close the valve 13 and exahust the bias pressure, in turn closing the valve 2 itself. Thereafter the pressure applied to the brakes increases but at a reduced rate determined by the size of the orifice 16. The pressure increase continues until the pressures of the supply and delivery parts of the line are equal or until deceleration of a braked wheel becomes excessive when the solenoid of the valve 3 will be energised to close the valve 3 and exhaust to atmosphere the pressure applied to the actuators, thereby again relieving the braking pressure.

A connecting line 17 is provided between the chambers above the two diaphragms 11 in the valves 2 and 3 and a spring-loaded one-way valve 18 is located in the line 17 to permit fluid to flow from the chamber above the diaphragm in the valve 2 to the chamber above the diaphragm in the other valve, but to prevent flow in the opposite direction.

In the event of a malfunction causing the solenoid of the valve 2 to be energised when the solenoid of the valve 2 is deenergised, the valve 3 closes and would normally exhaust to atmosphere the pressure applied to the actuators including the supply through the valve 2. This is prevented by the line 17 and the one-way valve 18 since, under such conditions, the signal pressure in the passage 12 of the valves 2 will be supplied to the chamber above the diaphragm in the valve 3 at a rate greater than that at which it can leak to atmosphere through the exhaust passage 15 at that valve. The diaphragm 11 will be urged downwardly to open the valve 3 again, urging the valve member 4 into engagement with the seating 7 to close the exhaust 10.

WHAT WE CLAIM IS: 1. A fluid-pressure operated anti-skid braking system of the kind set forth for rail or other vehicles, the control valve means comprises first and second separate fluidflow control valves which are connected in the line in parallel, the first valve having a higher flow rate than the second valve, and each valve having a device responsive to a skid signal for operating that valve, the second valve being operable independently of, or simultaneously with, the first valve.

2. A braking system according to Claim 1, in which both devices are actuated when the brake is initially applied and the skid signal is present and the brake is re-applied automatically in two stages when the skid signal is no longer present, both valves being open in the first stage to allow the pressure to rise at a normal rate to an intermediate value less than the predetermined value at a changeover point at which one of the devices is then actuated to close the valve which it controls, the pressure then continuing to rise at a reduced rate controlled by the other valve in the second stage.

3. A braking system according to Claim 2, in which the second control valve is open during the second stage and incorporates pressure relief means for reducing the pressure applied to the brake when both devices have been actuated simultaneously or upon actuation of the second control valve following previous closure of the first valve.

4. A braking system according to any preceding claim, in which the two valves are substantially identical in construction but with the second valve being provided with a restriction to reduce its flow rate, and an exhaust port for relieving the brake pressure when that valve is closed.

5. A braking system according to any preceding claim, in which the operation of each valve is controlled by the pressure in a chamber of the valve, the supply of fluid to the chamber being controlled by the device responsive to the skid signal and the respective chambers in the two valves being connected together by means of a line in which a one-way valve is located, the oneway valve acting so as to permit fluid to flow from the first valve chamber to the second valve chamber but to prevent flow in the opposite direction.

6. A braking system according to Claim 5, in which each valve is diaphragm-operated and controlled by a signal pressure acting in the chamber on one side of the diaphragm, the device responsive to the skid signal comprising a solenoid-operated valve for controlling the application of the signal pressure to the diaphragm.

7. A control valve assembly for use in a braking system according to any preceding claim, substantially as herein described with reference to and as illustrated in the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. the chambers above the two diaphragms 11 in the valves 2 and 3 and a spring-loaded one-way valve 18 is located in the line 17 to permit fluid to flow from the chamber above the diaphragm in the valve 2 to the chamber above the diaphragm in the other valve, but to prevent flow in the opposite direction. In the event of a malfunction causing the solenoid of the valve 2 to be energised when the solenoid of the valve 2 is deenergised, the valve 3 closes and would normally exhaust to atmosphere the pressure applied to the actuators including the supply through the valve 2. This is prevented by the line 17 and the one-way valve 18 since, under such conditions, the signal pressure in the passage 12 of the valves 2 will be supplied to the chamber above the diaphragm in the valve 3 at a rate greater than that at which it can leak to atmosphere through the exhaust passage 15 at that valve. The diaphragm 11 will be urged downwardly to open the valve 3 again, urging the valve member 4 into engagement with the seating 7 to close the exhaust 10. WHAT WE CLAIM IS:

1. A fluid-pressure operated anti-skid braking system of the kind set forth for rail or other vehicles, the control valve means comprises first and second separate fluidflow control valves which are connected in the line in parallel, the first valve having a higher flow rate than the second valve, and each valve having a device responsive to a skid signal for operating that valve, the second valve being operable independently of, or simultaneously with, the first valve.

2. A braking system according to Claim 1, in which both devices are actuated when the brake is initially applied and the skid signal is present and the brake is re-applied automatically in two stages when the skid signal is no longer present, both valves being open in the first stage to allow the pressure to rise at a normal rate to an intermediate value less than the predetermined value at a changeover point at which one of the devices is then actuated to close the valve which it controls, the pressure then continuing to rise at a reduced rate controlled by the other valve in the second stage.

3. A braking system according to Claim 2, in which the second control valve is open during the second stage and incorporates pressure relief means for reducing the pressure applied to the brake when both devices have been actuated simultaneously or upon actuation of the second control valve following previous closure of the first valve.

4. A braking system according to any preceding claim, in which the two valves are substantially identical in construction but with the second valve being provided with a restriction to reduce its flow rate, and an exhaust port for relieving the brake pressure when that valve is closed.

5. A braking system according to any preceding claim, in which the operation of each valve is controlled by the pressure in a chamber of the valve, the supply of fluid to the chamber being controlled by the device responsive to the skid signal and the respective chambers in the two valves being connected together by means of a line in which a one-way valve is located, the oneway valve acting so as to permit fluid to flow from the first valve chamber to the second valve chamber but to prevent flow in the opposite direction.

6. A braking system according to Claim 5, in which each valve is diaphragm-operated and controlled by a signal pressure acting in the chamber on one side of the diaphragm, the device responsive to the skid signal comprising a solenoid-operated valve for controlling the application of the signal pressure to the diaphragm.

7. A control valve assembly for use in a braking system according to any preceding claim, substantially as herein described with reference to and as illustrated in the accompanying drawing.