GB2130668A - Re-applying the brakes after anti-skid control in compressed air- operated braking systems for vehicles - Google Patents
Re-applying the brakes after anti-skid control in compressed air- operated braking systems for vehicles Download PDFInfo
- Publication number
- GB2130668A GB2130668A GB08330317A GB8330317A GB2130668A GB 2130668 A GB2130668 A GB 2130668A GB 08330317 A GB08330317 A GB 08330317A GB 8330317 A GB8330317 A GB 8330317A GB 2130668 A GB2130668 A GB 2130668A
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- United Kingdom
- Prior art keywords
- chamber
- skid
- control
- brake
- piston
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
- B60T8/32—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration
- B60T8/34—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition
- B60T8/50—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition having means for controlling the rate at which pressure is reapplied to or released from the brake
- B60T8/505—Pressure reapplication in a mu-split situation, i.e. a situation with different coefficients of friction on both sides of the vehicle
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
- B60T8/32—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration
- B60T8/34—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition
- B60T8/50—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition having means for controlling the rate at which pressure is reapplied to or released from the brake
- B60T8/5056—Pressure reapplication using memory devices
- B60T8/5062—Pressure reapplication using memory devices using memory chambers
- B60T8/5068—Pressure reapplication using memory devices using memory chambers having decay means
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- Transportation (AREA)
- Mechanical Engineering (AREA)
- Regulating Braking Force (AREA)
Abstract
Compressed air from a supply (2) for actuating a wheel brake (4) is supplied through a skid control unit (1) interposed in the line between the supply and the brake, and means, e.g. solenoid (50), responsive to a skid signal are incorporated for operating valve means (52, 53, 54) to apply pressure to chamber 42 thereby unbalancing piston 15 and operating triple valve (10) to relieve the pressure of the fluid supplied to the brake at a skid point. The unit (1) incorporates a memory chamber combination (40 + 42) for controlling the rate of brake re-application following correction of a skid, and the memory chamber (42) is charged with air from chamber (16) only when the skid signal is received (valve 52, 53 opens). When separate control units (1, 1a) are provided for the brakes (4) of wheels (5) at opposite ends of an axle, the respective memory chambers (40 + 42) are interconnected by a pneumatic connection incorporating a restrictor (40a or 42a) (Figs. 2 or 3 not shown). <IMAGE>
Description
SPECIFICATION
Improvements in fluid-pressure operated braking systems for vehicles
This invention relates to improvements in fluid-pressure operated braking systems for vehicles of
the kind in which operating fluid from a supply for actuating a wheel brake is supplied to the brake
through a skid control unit interposed in the line between the supply and the brake, and means
responsive to a skid signal are incorporated for operating valve means to relieve the pressure of the
fluid supplied to the brake at a skid point.
In known systems of the kind set forth, for example as disclosed in GB 1 591 166 and
GB 2 007 787, the skid control unit incorporates a memory chamber for storing a memory pressure
dependent upon the brake pressure occurring at the skid point to provide a datum or knee point
between first and second stages of brake re-application.
In the systems of GB 1 591166 and GB 2 007 787 the memory chamber is charged with air
during each and every brake application, irrespective of whether or not a skid signal is present. Since the volume of a memory chamber usually represents between 5% and 10% of the air required to actuate the
brake, such wastage of air is significant and must be taken into account when determining the size of an
air compressor and air reservoir required for any particular vehicle. In addition, in some systems of this
kind, air in the memory chamber does useful work on a control piston which controls operation of a
main valve assembly, in turn for controlling the supply of pressure from the supply to the wheel brake.
Some known systems such as US 3 950 035 include addition control elements so that the volume of the memory chamber can be reduced but, unfortunately, the minimum volume of the memory chamber
is then determined by the minimum restrictor size which will resist icing-up in cold conditions. If a single
skid control unit per pair of opposed wheels, known as the wheels per axle, is replaced by two smaller
units for individual wheel control, then the total memory volume of that axle will tend to be increased since the frictional losses in the units, and hence the effective areas of the control pistons which are
required, do not reduce in proportion to the sizes of the units. The proportion of air wasted is also
greater for light brake applications because the memory volume is fixed whilst the full displacement of a
brake actuator is only used during maximum brake applications.
According to one aspect of our invention, in a fluid-pressure operated braking system of the kind
set forth the skid control unit incorporates a memory chamber for controlling the rate of brake reapplication following correction of a skid, and the memory chamber is charged with air only when a skid
signal is received.
This conserves air by utilising spent air to determine the rate of brake re-application.
Normally the skid control unit is operated by the supply of a control pressure to an application
chamber in order to operate a main valve assembly, in turn for controlling the supply of pressure to a wheel brake, and the memory chamber acts in opposition to the application chamber in order to
reduce the control force and determine the position of the knee point during brake re-application following correction of a skid.
Preferably full control pressure is retained in the application chamber throughout the skid cycle.
This ensures that the re-application of braking pressure up to the knee point is especially rapid.
In a modification in which some air is supplied to the application chamber during re-application, the re-application of braking pressure up to the knee point will be less rapid, but will still be quicker than units of known type in which the application chamber is discharged completely during the skid cycle. The
rate of re-application of the brake following correction of a skid may be determined by the relative volumes of the memory chamber and the application chamber, and the characteristics of a flow-control
regulator valve which controls the rate at which pressure in the memory chamber can leak to atmosphere.
Normally the control pressure acts on one face of a main piston to operate the main valve
assembly and the application chamber is isolated from the memory chamber by a valve operable by the
means responsive to the skid signal, one wall of the memory chamber being defined by a face of a second piston, which face is arranged in opposition to the said one face of the main piston, with the two pistons being coupled together.
The pistons may be coupled together against relative axial movement, or they may be coupled together by means of a lost-motion connection.
When the pistons are coupled together against relative axial movement the main valve assembly is held in a normally open position by means of a spring to overcome the friction in seals but when a lost-motion connection is provided between the two pistons such a spring is unnecessary since the main piston is able to move without incurring friction losses from the second piston.
The memory chamber may be defined by a control chamber between the said face of the second piston and the wall of the bore in which it works or the memory chamber may comprise the total volume of the control chamber and a separate reservoir chamber which is normally in communication with the control chamber but which is isolated from it whilst a skid is being corrected.
When separate skid control units are provided for the wheels at opposite ends of an axle, particularly a steerable axle, according to another aspect of our invention, the memory chambers of the two units are interconnected by a pneumatic connection incorporating a restrictor.
This has the advantage that when the wheels are travelling over surfaces of different coefficients of friction (,u) and the wheel travelling over the surface of lower ,u skids, then air from the memory chamber of that unit passes through the connection and the restrictor into the memory chamber of the unit for the non-skidding wheel travelling over the surface of higher . This reduces the nett control force on the unit for the higher y wheel so that braking pressure and hence braking torque are reduced, in turn ensuring that the driver of the vehicle does not feel an adverse pull at the steering wheel.
Thus we are able to control the torque differential between braked wheels on a common axle, particularly a steerable axle.
Preferably the control chambers which constitute, or form part of, the memory chambers are interconnected by the connection.
Some embodiments of our invention are illustrated in the accompanying drawings in which:
Figure 1 is a layout of a pneumatically-operated anti-skid braking system including a section through a skid control unit;
Figure 2 is a layout of another braking system;
Figure 3 is a layout of a braking system similar to Figure 2 but showing a modification;
Figure 4 is a modified flow-control regulator valve for the skid control unit embodied in the braking system of Figure 1;
Figure 5 is a section through a modified skid control unit; and
Figure 6 is a section through another skid control unit.
In the pneumatically-operated anti-skid braking system illustrated in Figure 1 of the accompanying drawings a skid control unit 1 is adapted to regulate the supply of pneumatic fluid from a source 2 to an actuator 3 of a brake 4 in accordance with the behaviour of the wheel 5 braked by the brake 4.
As illustrated the unit 1 comprises a housing 6 incorporating fluid-flow control means 7, and a solenoid-operated valve 8.
The fluid-flow control means 7 comprises a relay valve 10 for controlling communication between an inlet supply passage 11, which is connected to a treadle valve 12 for controlling the supply of pressure from the source 2, and an outlet supply passage 13 which is connected to the actuator 3 of the brake 4.
The relay valve 10 comprises a bore 14 of stepped outline in which works a piston 1 5 of complementary outline. An application chamber 1 6 defined in the bore 14 between shoulders 17 and 18 at the respective steps in diameter is connected to the treadle valve 12 through a branch-line 19 and a one-way valve 20 is located in the branch line 19, on the downstream side of its connection to a line 21, between the treadle valve 12 and the passage 11. A valve head 22 on the face of the piston 1 5 which is opposite the chamber 1 6 is engageable with a valve head 23 comprising a radial flange at the inner end of a sleeve 24, and the sleeve 24 is guided in an inwardly projecting axial skirt 25 of a closure member 26 for the lower end of the housing 6.The head 23 is also engageable with a seating 27 on the housing and the seating 27 is interposed between the inlet and outlet supply passages 11 and 1 3 through a chamber 28 between itself and the end of greater area at the lower end of the piston 1 5. A compression spring 29 acts to urge the head 23 towards the head 22.
The end of the piston 15 which is of smaller area is coupled to a corresponding, smaller area end, of a second piston 30 of differential outline. The piston 30 works in a second stepped bore 31 in the housing above the bore 14 and of which the portion of smaller area is common to the smaller area portion of the bore 14. A bolt 32 provides a rigid coupling between the two pistons 1 5 and 30, with mating faces of the pistons clamped together between the head 33 and a nut 34. The stem 35 projects through clearance bores in the pistons 1 5 and 30, and the bolt 32 itself is provided with a through bore 36. This ensures that an atmospheric chambers 37 above the piston 30 is in communication at all times with atmospheric through the sleeve 24 and an exhaust port 38 in the closure 26.A compression spring 39 acts on the head 33 of the bolt 35 to urge both pistons 30 and 1 5 towards the closure 26 with the head 22 in sealing engagement with the head 23, in turn to hold the head away from the seating 27.
Thus the inlet supply passage 11 is normally in open communication with the outlet passage 1 3.
A reservoir chamber 40, which is normally at atmospheric pressure, communicates through a flow-control regulator valve 41 with the atmospheric chamber 37, and a control chamber 42 defined in the bore 31 between shoulders 43 and 44 at the respective steps in diameter of the bore 31 and the piston 30 communicates with the reservoir chamber 40 through the solenoid-operated valve 8.
The flow-control valve 41 comprises a spool 45 which is urged by a spring 46 against a stop 47 and is provided with an orifice 48, and the spool 45 is axially movable in a bore to control the effective size of a passage 49 leading to the atmospheric chamber 37, thereby to constitute a variable orifice.
As illustrated the solenoid-operated valve 8 comprises a coil 50 which is adapted to be energised in response to a current from an electronic control module 8a which, in turn, is dependent upon a skid signal from skid sensing means 5a responsive to the behaviour of the wheel 5. A core-piece 51 is movable axially in response to energisation of the coil 50, and the corepiece 51 carries a valve head 52 for alternate engagement with one of a pair of spaced valve seatings 53 and 54.
In the inoperative position shown in which the coil 50 is de-energised, the head 52 engages with
the seating 53 so that the application chamber 1 6 is isolated from the control chamber 42, and the
control chamber 42 is in communication with the reservoir chamber 40 through the valve seat 54. This is achieved by a force applied to the core-piece 51 by a spring 55. In this position, as described above, the head 22 seals against the head 23 and holds the head 23 away from the seating 27 to place the passages 11 and 13 in open communication. The actuator 3 is exhausted to atmosphere through an exhaust port 56 on the treadle valve 12, through which the application chamber is also exhausted through a bleed orifice 57 in the valve member 58 of the one-way valve 20.
When the brake 5 is to be applied the treadle valve 12 is operated to supply air under pressure straight to the actuator 3 through the passages 11 and 13. Simultaneously air under the same pressure is supplied to the application chamber 1 6 from the treadle valve 12 and through the one-way valve 20.
Since the areas of opposite sides of the larger diameter portion of the piston 1 5 are substantially equal the forces on the piston 1 5 normally balance.
Should a skid signal be received, the coil 50 is energised to urge the core-piece 51 in a direction to urge the head 52 away from the seating 53 and into engagement with the seating 54. This places the application chamber 1 6 in communication with the control chamber 42, thereby destroying the force due to pressure in the chamber 16 acting over the area of the face 18, since the same pressure is applied to the face 44. The pressure acting on the opposite lower side of the piston 1 5 urges the piston 1 5 relatively away from the closure 26, carrying the upper piston 30 with it.Initial movement of the piston 1 5 in this direction is accompanied by a corresponding movement of the sleeve 24 until that movement of the head 23 is arrested by engagement with the seating 27 to isolate the brake actuator 3 from the inlet supply passage 11, further movement of the piston 1 5 in the same direction urging the head 22 away from the head 23 to place the outlet supply passage 13 in communication with atmosphere through the exhaust port 38, whereby to relieve pressure applied to the brake 5.
When the skid signal is cancelled, the head 53 is urged by the spring 55, out of engagement with the seating 54 and into engagement with the seating 53. This isolates the application chamber 1 6 from the control chamber 42, and connects the control chamber 42 to the reservoir chamber 40 which, in this mode, together constitute a memory chamber. The air from the control chamber 42, which is at a higher pressure, flows into the reservoir chamber 40, which is at atmospheric pressure, and then leaks to the atmospheric chamber 37 through the flow-control regulator valve 41. The pressure in the memory chamber (40 + 42) is thereby reduced at a controlled rate.This permits the control pressure in the application chamber 1 6 to apply a force to the piston 15, in a direction to urge the piston 1 5 towards the closure 26, with the result that the head 22 reengages with the head 23 initially to isolate the outlet passage 13 from the exhaust port 38, and subsequently, to urge the head 23 away from a seating 27 thereby reconnecting the inlet supply passage 11 to the outlet supply passage 13 so that the brake 4 is re-applied.
The extent to which the piston 1 5 urges the head 23 away from the seating 27 with consequent increase in the pressure applied to the brake depends upon the rate at which the flow-control regulator valve 41 permits fluid in the memory chamber (40 + 42) to be displaced to atmosphere through the atmospheric chamber 37 and the exhaust port 38.
Assume the brake is applied with a pressure of 60 p.s.i. (4.14 bar) and that this causes a skid signal to occur.
Mode of Application Brake Control Reservoir
Operation Chamber(1 6) Pressure Chamber (42) Chamber (40)
p.s.i. bar p.s.i. bar p.s.i. bar p.s.i. bar
Normal 60 4.14 60 4.14 0 0 0 0
Skid signal 60 4.14 0 0 60 4.14 0 0
Skid cancelled 69 4.14 30 2.07 30 2.07 30 2.07
Slow re-apply 60 4.14 40 2.76 20 1.38 20 1.38
60 4.14 50 3.45 10 0.69 10 0.69
60 4.14 60 4.14 0 0 0 0
As can be seen the brake pressure is re-applied rapidly initially to a lower level and then slowly to the original level. If the volume of the reservoir chamber 40 is then relatively large in comparison with that of the control chamber the brake 4 will be re-applied rapidly to a higher level and, if relatively small, to a lower level.
If the vehicle is on a low friction surface but the applied pressure is high the valve 10 will operate to charge the reservoir chamber 40 to a higher level.
In another example, assume that the control pressure can attain a maximum value of 80 p.s.i.
(5.52 bar), and that a skid will occur when the brake pressure is 20 p.s.i. (1.38 bar).
Mode of Application Brake Control Reservoir
Operation Chamber (16) Pressure Chamber (42) Chamber (40)
p.s.i. bar p.s.i. bar p.s.i. bar p.s.i. bar
Initial application ,20(80) 1.38(5.52) 20 1.38 0 0 0 0
Skid signal 80 5.52 0 0 80 5.52 0 0
Skid cancel 80 5.52 20(40) 1.38(2.76) 40 2.76 40 2.76
Skid signal 80 5.52 0 0 80 5.52 40 2.76
Skid cancel 80 5.52 20 1,38 60 4.14 50 3.45
Skid signal 80 5.52 0 0 80 5.52 60 4.14
Skid cancel 80 5.52 10 0.69 70 4.83 70 4.83
Slow re-apply 80 5.52 15 1.03 65 4.48 65 4.48
80 5.52 20 1.38 60 4.14 60 4.14
In the example referred to above the figures in brackets refer to steady state pressures which would have been reached had a skid signal not have been issued.
In the system described above, preferably the piston 30 has a larger effective area than that of the piston 1 5 in order to provide sufficient force to overcome the friction of the seals carried by the pistons 1 5 and 30 and the force in the spring 39 when a skid is to be corrected.
Although the system described with reference to Figure 1 states that the unit 1 is interposed between a treadle valve 12 and a brake, the unit itself may comprise an "in-line" unit in that it can be added to an existing braking system with a minimum of change. In such an arrangement the unit 1 can be interposed in a line between an existing relay valve and the brake, or between a treadle valve and an existing relay valve.
Similarly two units 1, la can be installed in a system to control the difference in brake torque applied to wheels 5 of pairs on opposite sides of a vehicle, generally referred to in the field of
Automobile Engineering as wheels on opposite ends of an axle. This is achieved, in layouts illustrated in
Figures 2 and 3 in which separate units 1 are provided for the brakes of the wheels at opposite ends of an axle.
In the system of Figure 2 control chambers 42 of the two units 1 are interconnected through a restrictor 42a.
When the brakes are applied with the wheels at opposite ends of the axle running on surfaces of different u, the wheel on the surface of lower y will skid and the unit 1 associated with that wheel, hereinafter referred to as the "skid unit", will operate as described above. When the two control chambers 42 are interconnected through the restrictor 42a, air entering the control chamber 42 of the skid unit 1 from the application chamber 16 of that unit will pass through the restrictor to the control chamber 42 of the other unit 1 a, hereinafter referred to as the "non-skid unit", and thus into the total memory chamber (40 + 42) of non-skid unit 1 a, namely the volume of the control chamber 42 plus the volume of the reservoir chamber 40.This acts on the respective piston 30 to urge it and the piston 1 5 relatively away from the closure member 26 and tends to close the relay valve 10, thereby reducing the pressure applied to the brake of the wheel which is running on the surface of higher X. This reduces the brake torque on that wheel.
Such action may be sufficient to prevent the higher y wheel skidding at all, but if it does tend to skid, then the effect of the cross-axle interconnection will be to lower the knee point for the higher ,u wheel during brake re-application following correction of the skid since the reservoir chamber 40 of the non-skid unit 1 a will have been pre-charged to some extent. Any tendency for the characteristics of the skid unit 1 to be affected in the opposite sense will be minimal because of the restrictor 42a and
because the control chamber 42 of the skid unit 1 is replenished frem the supply 2, for example the treadle valve or other relay valve, during every skid cycle.
We are therefore able to control the torque differential by arranging for the memory chambers (40 + 42) normally to be isolated from the supply and to act in opposition to the pressure in the application chamber 16 which provides us with the ability to alter the gain of the relay valve 10. This is particularly useful on a steerable axle with a positive offset steering geometry.
The operation of the two units 1 is otherwise the same as described above with reference to
Figure 1 and, where appropriate, corresponding reference numerals have been applied to corresponding parts.
In the system of Figure 3 the two reservoir chambers 40 are interconnected through a restrictor 40a. In this system a similar effect is achieved to that of the system of Figure 2. However the effect is delayed since the reservoir chamber 40 of the skid unit 1 is pressurised only when the associated skid signal is cancelled. Thus, when the ground offset is large, it would probably be necessary to control the two units 1, 1 a synchronously for the first two or three cycles.
The construction andoperntion of the system of Figure 3 is otherwise the same as Figure 2 and corresponding reference numerals have been applied to corresponding parts.
In the modification shown in Figure 4 of the drawings a hollow piston 60 working in a bore 61 in the housing 6 is exposed on its upper face to pressure in the reservoir chamber 40 and on its opposite, lower, face to pressure in the control chamber 40. In addition, the piston 60 carries a piston-rod 62 which extends towards the spool 45 of the flow-control regulator valve 41, and a spring 63 urges the piston 60 relatively away from the flow-control valve 41.
Normally the piston 60 is spring-urged away from the flow-control valve 41 when the brake 5 is applied normally with the chambers 42 and 40 in open communication and the coil 50 is de-energised.
When the coil 50 is energised in response to a skid signal the control chamber 42 is isolated from the reservoir chamber 40. The piston 60 is then subjected to a pressure differential which urges it against the loading in the spring 63 in a direction to close the flow control valve 41 by the piston-rod 62 acting to urge the spool 45 axially in its bore to close the orifice 49. This isolates the reservoir chamber 40 from the atmospheric chamber 37 to prevent leakage from the reservoir chamber 40 during brake release periods. This prevents any tendency for the knee point to creep upwards during operation on low M surfaces when brake release periods are correspondingly longer.
Although the piston 60 is responsive to the pressure difference between the control chamber 42 and reservoir chamber 40 which exists when the coil 50 is energised, in a modification the piston 60 can be responsive to the movement of the core-piece 51 itself.
The unit illustrated in Figure 5 of the accompanying drawings is particularly suitable for controlling operation of a pair of brakes on the wheels on opposite ends of an axle. In the unit of Figure 5 the spring 39 is omitted and a lost-motion connection is provided between the two pistons 1 5 and 30. This is achieved by reducing the length of the portion of the piston 30 which is of reduced diameter so that the piston 30 can move relative to the bolt 35.
When the treadle valve 12 is operated the piston 1 5 moves towards the closure 26 independently of the upper piston 30 in order to apply the brakes.
If a skid signal is received the coil 50 is energised, and the head 52 engages with the seating 54 to isolate the reservoir chamber 40 from the control chamber 42, and place the application chamber 16 in communication with the control chamber 42. This action removes the pressure applied to the brake 4, so that the skid signal is cancelled. The brake 5 is then re-applied rapidly to a lower level, and then slowly to the original level.
In the unit of Figure 5 the pressure in the application chamber 1 6 remains constant and does not have to be re-applied, other than to make up the expanding volume of the control chamber 42 due to the relative movement between the pistons 1 5 and 30, and this will give a rapid re-apply signal.
The construction and operation of the unit of Figure 5 is otherwise the same as that illustrated in
Figure 1, and corresponding reference numerals have been applied to corresponding parts.
The reservoir chamber 40 is omitted from the unit illustrated in Figure 6 of the drawings, the control chamber 42, which constitutes the memory chamber, communicates with atmosphere through the flow-regulating control valve 41, and the control pressure is applied to the application chamber 1 6 through the solenoid-operated valve 8.
When a skid signal is received, the supply to the application chamber 1 6 is cut-off and the application chamber 1 6 is connected to the control chamber 42 thus cancelling the force applied to the relay valve 10 in an opening direction. Since the volume of the control chamber 42 is relatively large, the pressure level in the application chamber 1 6 falls rapidly.
When the skid is cancelled the control pressure is re-applied to the application chamber 1 6 but since trapped pressure still exists in the control chamber 42, the brake is only partially re-applied. As the air escapes from the control chamber 42 under the control of the flow-control regulator valve 41 the brake is gradually re-applied to a higher level.
The construction and operation of the unit of Figure 6 is otherwise the same as that of Figure 5 and corresponding reference numerals have been applied to corresponding parts.
The unit of Figure 6 is suitable for use only as a relay valve such as is described in the layout of
Figure 1.
The unit of Figure 6 is not suitable for application in an "in-line" unit. If adapted for use in this way the relay valve 10 would oscillate violently on re-application after a skid signal since the input pressure would fall when the relay valve 10 opens with the result that the downward force on the piston 1 5 would be difficult to establish.
Claims (21)
1. A fluid-pressure operated braking system of the kind set forth in which the skid control unit incorporates a memory chamber for controlling the rate of brake re-application following correction of a skid, and the memory chamber is charged with air only when a skid signal is received.
2. A system as claimed in Claim 1, in which the skid control unit is operated by the supply of a control pressure to an application chamber in order to operate a main valve assembly, in turn for controlling the supply of pressure to a wheel brake, and the memory chamber acts in opposition to the application chamber in order to reduce the control force and determine the position of a knee point between first and second stages of brake re-application following correction of a skid.
3. A system as claimed in Claim 1 or Claim 2, in which full control pressure is retained in the application chamber throughout the skid cycle.
4. A system as claimed in Claim 1 or Claim 2, in which some air is supplied to the application chamber during brake re-application following correction of a skid.
5. A system as claimed in any preceding claim including a flow-control regulator valve which controls the rate at which pressure in the memory chamber can leak to atmosphere, the rate of reapplication of the brake following correction of a skid being determined by the relative volumes of the memory chamber and the application chamber, and the characteristics of the flow-control regulator valve.
6. A system as claimed in any preceding claim in which the control pressure acts on one face of a main piston to operate the main valve assembly, and the application chamber is isolated from the memory chamber by a valve operable by the means responsive to the skid signal, one wall of the memory chamber being defined by a face of a second piston, which face is arranged in opposition to the said one face of the main piston, and the two pistons being coupled together.
7. A system as claimed in Claim 6, in which the pistons are coupled together against relative axial movement.
8. A system as claimed in Claim 6, in which the pistons are coupled together by means of a lostmotion connection.
9. A system as claimed in Claim 6, in which a spring is provided to hold the main valve assembly in a normally open position.
10. A system as claimed in any of Claims 6 to 9, in which the memory chamber is defined by a control chamber disposed between the said face of the second piston and the wall of the bore in which it works.
11. A system as claimed in any of Claims 6 to 9, in which the memory chamber comprises the total volume of a control chamber disposed between the said face of the second piston and the wall of the bore in which it works, and a separate reservoir chamber which is normally in communication with the control chamber but which is isolated from it whilst a skid is being corrected.
12. A fluid-pressure operated braking system for vehicles in which operating fluid from a supply for actuating brakes on wheels at opposite ends of an axle is supplied to the brakes through a pair of skid control units, each unit being disposed between the supply and the respective brake on the corresponding wheel, and means responsive to a skid signal is associated with each skid control unit to operate valve means for relieving the pressure of the fluid supplied to the respective brake at a skid point, each skid control unit incorporating a memory chamber for controlling the rate of brake reapplication following correction of a skid, and in which each memory chamber is charged with air only when a respective skid signal is received, and the memory chambers of the two units are interconnected by a pneumatic connection which incorporates a restrictor.
13. A system as claimed in Claim 12, in which each skid control unit comprises a housing having an application chamber to which a control pressure is supplied in order to operate a main valve assembly, in turn for controlling the supply of pressure to the respective brake, and the control pressure acts on one face of a main piston to operate the main valve assembly, the application chamber being isolated from the memory chamber by a valve operable by the respective means responsive to the skid signal, and one wall of the memory chamber being defined by a face of a second piston which is coupled to the first piston, the said face being arranged in opposition to the said one face of the main piston.
14. A system as claimed in Claim 13, in which the memory chamber is defined by a control
chamber disposed between the said face of the second piston and the wall of the bore in which it works,
and the control chambers of the two units are interconnected by the pneumatic connection.
1 5. A system as claimed in Claim 13, in which the memory chamber comprises the total volume of
a control chamber disposed between the said face of the second piston and the wall of the bore in which it works, and a separate reservoir chamber which is normally in communication with the control chamber but which is isolated from it whilst a skid is being corrected, the reservoir chambers of the twe units being interconnected by the pneumatic connection.
1 6. A pneumatically-operated anti-skid braking system substantially as described herein with reference to and as illustrated in Figure 1 of the accompanying drawings.
1 7. A pneumatically-operated anti-skid braking system substantially as described herein with reference to and as illustrated in Figure 2 of the accompanying drawings.
18. A pneumatically-operated anti-skid braking system substantially as described herein with reference to and as illustrated in Figure 3 of the accompanying drawings.
1 9. A pneumatically-operated anti-skid braking system substantially as described herein with reference to and as illustrated in Figure 1 of the accompanying drawings, including the modification illustrated in Figure 4.
20. A pneumatically-operated anti-skid braking system substantially as described herein with reference to and as illustrated in Figure 5 of the accompanying drawings.
21. A pneumatically-operated anti-skid braking system substantially as described herein with reference to and as illustrated in Figure 6 of the accompanying drawings.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB08330317A GB2130668B (en) | 1982-11-23 | 1983-11-14 | Re-applying the brakes after anti-skid control in compressed air-operated braking systems for vehicles |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8233385 | 1982-11-23 | ||
GB08330317A GB2130668B (en) | 1982-11-23 | 1983-11-14 | Re-applying the brakes after anti-skid control in compressed air-operated braking systems for vehicles |
Publications (3)
Publication Number | Publication Date |
---|---|
GB8330317D0 GB8330317D0 (en) | 1983-12-21 |
GB2130668A true GB2130668A (en) | 1984-06-06 |
GB2130668B GB2130668B (en) | 1985-10-23 |
Family
ID=26284478
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB08330317A Expired GB2130668B (en) | 1982-11-23 | 1983-11-14 | Re-applying the brakes after anti-skid control in compressed air-operated braking systems for vehicles |
Country Status (1)
Country | Link |
---|---|
GB (1) | GB2130668B (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0252789A1 (en) * | 1986-07-09 | 1988-01-13 | BENDIX France Société Anonyme dite: | Pressure memory for a hydraulic circuit |
EP0304265A2 (en) * | 1987-08-19 | 1989-02-22 | Grau Limited | Improvements in fluid-pressure operated anti-skid braking systems for vehicles |
US5240314A (en) * | 1990-10-02 | 1993-08-31 | Nissan Motor Co., Ltd. | Hydraulic brake system |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1335916A (en) * | 1970-02-07 | 1973-10-31 | Knorr Bremse Gmbh | Pneumatic anti-skid devices |
GB1356845A (en) * | 1970-02-07 | 1974-06-19 | Knorr Bremse Gmbh | Pneumatic anti-skid devices |
-
1983
- 1983-11-14 GB GB08330317A patent/GB2130668B/en not_active Expired
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1335916A (en) * | 1970-02-07 | 1973-10-31 | Knorr Bremse Gmbh | Pneumatic anti-skid devices |
GB1356845A (en) * | 1970-02-07 | 1974-06-19 | Knorr Bremse Gmbh | Pneumatic anti-skid devices |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0252789A1 (en) * | 1986-07-09 | 1988-01-13 | BENDIX France Société Anonyme dite: | Pressure memory for a hydraulic circuit |
FR2601419A1 (en) * | 1986-07-09 | 1988-01-15 | Bendix France | PRESSURE STORAGE DEVICE FOR A HYDRAULIC CIRCUIT |
EP0304265A2 (en) * | 1987-08-19 | 1989-02-22 | Grau Limited | Improvements in fluid-pressure operated anti-skid braking systems for vehicles |
EP0304265A3 (en) * | 1987-08-19 | 1989-08-30 | Lucas Industries Public Limited Company | Improvements in fluid-pressure operated anti-skid braking systems for vehicles |
US5240314A (en) * | 1990-10-02 | 1993-08-31 | Nissan Motor Co., Ltd. | Hydraulic brake system |
Also Published As
Publication number | Publication date |
---|---|
GB2130668B (en) | 1985-10-23 |
GB8330317D0 (en) | 1983-12-21 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19921114 |