US3588188A - Control means for braking devices - Google Patents

Abstract

AN ACCELERATION-SENSING DEVICE IN WHICH A CONTROL VALVE HAS A RESTRICTED FLUID INLET PORT, AN OUTLET PORT AND AN EXHAUST PORT, THE LATTER INCLUDING A THROTTLING ELEMENT, THE OPENING OF WHICH IS DEPENDENT UPON MOVEMENT OF A PENDULUM TO WHICH IT IS OPERATIVELY CONNECTED, MOVEMENT OF THE PENDULUM OCCURRING UPON ACCELERATION OR DECELERATION. A RELAY DEVICE IN-

CLUDING A PRESSURE RESPONSIVE MEMBER IS LOCATED BETWEEN THE INLET/EXHAUST PORTS AND THE OUTLET PORT, A CHANGE IN THE THROTTLING OPENING RESULTING IN MOVEMENT OF THIS PRESSURE-RESPONSIVE MEMBER TO VARY THE PRESSURE AT THE OUTLET PORT.

Description

United States Patent [72] inventor Charles F. B. Shattock London, England [211 App]. No. 790,824 [22] Filed Jan. 13, 1969 [45] Patented June 28, 1971 [73] Assignee Westinghouse Brake and Signal Company,

Limited London, England [32] Priority Jan. 19, 1968 [33] Great Britain 1 l 02929/68 [54] CONTROL MEANS FOR BRAKING DEVICES 11 Claims, 2 Drawing Figs.

[52] US. Cl 303/21, 137/45, 188/181. 303/24, 303/40, 303/71 [51] int. Cl B60t 8/14, B60t 15/00 [50] Field oISearch l37/38,45, 46; 303/21,24. 6, 71,40; 188/181 m INTAKE- -MAN/FOL0 TANK BOOSTER Gas/rm.- /0 -YALVE m uamvaes P0176 1? AMPLIFIER A94 SOLE/VOID FEEDBACK 1 PRESSURE CHAMBER [56] References Cited UNITED STATES PATENTS 2,088,184 7/1937 White 303/24 2,181,161 11/1939 Wolf 303/24X 3,292,977 12/1966 Williams l37/46X 1 FOREIGN PATENTS 476,585 12/1937 Great Britain 303/24 Primary ExaminerGeorge E. A. Halvosa Assistant Examiner-John J. McLaughlin Attorney- Larson, Taylor & Hinds ABSTRACT: An acceleration-sensing device in which a control valve has a restricted fluid inlet port, an outlet port and an exhaust port, the latter including a throttling element, the opening of which is dependent upon movement ofa pendulum to which it is operatively connected, movement of the pendulum occurring upon acceleration or deceleration. A relay device including a pressure responsive member is located between the inlet/exhaust ports and the outlet port, a change in the throttling opening resulting in movement of this pressure-responsive member to vary the pressure at the outlet port.

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SHEET 2 OF 2 CONTROL MEANS FOR BRAKING DEVICES This invention relates to devices responsive to changes in the velocity of their movement, and more particularly to control devices for vehicle brakes.

According to the invention there is provided a device responsive to a change in its velocity, including a support for a fluid pressure control valve having a restricted fluid flow inlet port, an outlet port and an exhaust port providing a valve seat, a throttling element movable with respect to the valve seat thereby to effect a varying degree of throttling to the passage of fluid through the exhaust port, and a pendulum suspended on the support to support the throttling element while moving in accordance with the displacement of the pendulum from a reference position with respect to the support, so that in operation of the device, when a fluid pressure pertains at the inlet port, the value of the fluid pressure at the outlet port is dependent on the rate of escape of fluid through the valve seat which rate is in turn determined by the degree of throttling effected by the throttling element consequent upon the degree of displacement of the pendulum when the support is subjected to a change of velocity in the pendulum's plane of vibration.

According to a particular aspect of the invention there is provided a vehicle speed control system including such a device as in the previous paragraph.

Embodiments of the invention will now be described with reference to the accompanying drawings in which:

FIG. 1 is a sectional elevation of an accelerometer and,

PK]. 2 is a sectional elevation of another accelerometer.

An accelerometer is a device responsive to a change in its velocity, and although the term decelerometer is sometimes used to indicate a device responsive only to reductions in velocity an accelerometer can usually be arranged to respond to changes of velocity in either direction by appropriate orientation with respect to the direction of motion and in many cases will respond to changes in either direction to give an output signal indicative of magnitude and direction of acceleration. The terms acceleration and accelerometer are used herein to cover both upward and downward velocity changes and devices responsive thereto.

Referring now to FIG. 1 there is shown a support frame 31 which may be secured to the object or vehicle whose acceleration is to be measured. The frame has a mounting 32 for a leaf spring support 33 for a pendulum bob 34. The motion of the bob 34 is constrained by two springs 351, 352, in spring holders 36. The positions of the spring holders are adjustable by screwing them in or out of the support 31.

Support 31 also supports blocks 50 and 51 in which fluid passages and inlet and outlet connections for fluid under pressure are provided. The inlet connection (not shown) leads to a passage 52 one end of which leads to a filter element 54 in a chamber 55. The passage 52 also leads to a chamber 56. The outlet from this chamber is controlled by a valve 71 normally urged against its seat 73 by a spring 72 to close this end of the passage. Thus fluid normally only passes from passage 52 through filter 54 into chamber 55. The outlet from chamber 55 is a choke 43. This choke is preferably in the form of a tube through which a fine wire 47 passes. The ends of the wire are constrained by the end face of valve block 48 and by filter 54 which is preferably of the sintered metal type. The outlet of choke 43 is the inlet port of a three-port valve with an outlet port 53 and containing valve block 48, which has an exhaust port 42 in the form of a valve seat and a transverse port 45. A relay valve, to be described below, is interposed between the inlet and exhaust ports and the outlet port. The annular part of chamber 46 connects transverse port 45 to conduit 44 and provides a bleed path between the inlet port and the relay chamber 62. The valve seat 42 is controlled by a ball 41. whose position relative to the seat determines the amount of fluid passing through to the atmosphere. The ball 41 is loosely located by a cup 40 mounted on the pendulum bob support 33 so that in operation the ball can centralize itself with the valve seat 42 without touching it. The axial and transverse bores in valve block 48 must be large compared with the gap between the ball 41 and its seat so that all the pressure drop between the inlet port and atmosphere occurs at the exhaust port.

Conduit 44 is connected to relay chamber 62 which is closed by one side of a diaphragm 63 and an O-ring seal around the outer wall of conduit 64, which conduit passes through the diaphragm. The other side of diaphragm 63 is exposed to chamber 65. Conduit 64 passes through chamber 65 and the outer wall of the conduit is then slidably supported in bore 66, from which bore an outlet port 53 proceeds. The right-hand end of valve 71 normally seals the end of conduit 64, so that bore 66 is connected to outlet port 53 and chamber 65.

The operation of the device in FIG. 1 will now be described when responding to a reduction of velocity assuming motion in direction of arrow 30. Fluid pressure at the inlet port passes through passage 52 to choke 43, valve 71 being closed by spring 72. The pressure supplied to chamber 46 is maintained at an approximately fixed value by the pressure drop across choke 43. Fluid in chamber 46 can only escape through the valve seat 42 past ball 41 so pressure in chamber 46 rises until the force exerted by the pendulum bob support 33 balances the thrust on the ball at the exhaust port, when an equilibrium is achieved. This equilibrium results in a steady pressure in chamber 62. This steady pressure is dependent upon the balance between the inward flow of air through choke 43 and the outward flow of air through valve block 48 and past the ball, 41, to atmosphere. Valve block 48 is adjustable during the assembly of the device and is so set in relation to the ball 41 that when the device is at rest or moving at constant velocity in a straight line sufficient fluid escapes through valve seat 42 to prevent diaphragm 63 being displaced. In one embodiment a gap of 0.005 inch was found suitable. Valve 71 therefore remains closed and no fluid reaches bore 66 and the outlet port. When the velocity of the device in the direction of arrow 30 decreases bob 34 moves against spring 351 and deflects bob support 33 to reduce the clearance between valve seat 42 and ball 41. The flow of fluid through valve seat 42 decreases, and therefore the pressure on diaphragm 63 increases. This diaphragm moves so conduit 64 is urged against the end of the stem of valve 71 if not already so placed. When the increased pressure overcomes the force of spring 72 valve 71 opens and fluid flows from the inlet port, via passage 52 into bore 66 and to outlet port 53 to release the brakes When the velocity becomes constant or zero again bob 34 returns to its initial position under the control springs 351 and 352 and the pressure in chamber 62 falls as valve seat 42 is opened wider. Diaphragm 63 returns to its initial position and valve 71 closes under the action of spring 72. Pressure in chamber 65 and bore 66 will prevent valve 71 seating on conduit 64 until this pressure is dissipated. This prevents the buildup of a fluid cushion in chamber 65 which would alter the response of the device. The movement of bob 34 can be controlled by the adjustment of caps 36 and the selection of springs 351 and 352 so that the change in fluid pressure in outlet port 53 caused by the progressive closing of valve 41 on to its seat 42 is linearly proportional to the rate of change of the velocity of the device.

Two springs are used so that the force on the bob 34 is a dif ference between the spring forces. The springs preload each other so that both work on straight portion of their load/deflection curve. The deflection of the bob is small, approximately 0.025 inch in one embodiment, so that a flexible bob support can be used. This avoids the problems of pivot friction and wear which arise when a rigid bob support is used.

The arrangement described so far is for use where fluid consumption is to be kept to a minimum. Where consumption is less of a problem the relay valve formed by diaphragm 63 and associated parts 71, 72 and 73, can be omitted and the fluid flow increased accordingly so that the fluid flow in outlet port 53 is derived from the inlet connection via choke 43 and not via chamber 56.

The operation described above is for a response to a reduction in a velocity of the device in the direction of arrow 30 or, equally, an increase in velocity in the reversedirection. By al tering the adjustment of springs 351 and 352 so that for example, the position of ball 41 relative to its seat 42 is such as to result in an intermediate pressure being registered in outlet port 53 when the device is at constant velocity, it will be responsive to increase and decrease of velocity in the same direction.

The fluid pressure variation outlet at port 53 can be coupled to an indicating device directly or to other equipment for example to control motion in accordance with the acceleration indicated. This coupling can be through a further relay valve if v the pressure variation at outlet port 53 is too small.

Referring now to FIG. 2, this shows a form of the device to give a step change rather than a continuous variation of fluid pressure at the outlet. This form is particularly suitable for limiting the change of velocity of a vehicle to a chosen value, for example, by modifying the application of a fixed braking force so that the applied braking force is reduced when change of velocity reaches a chosen value, and then allowing the reapplication of the full fixed force when the change of velocity is below the chosen value. This form of control is particularly useful when for example it is required to provide a uniform retardation rate for a plurality of vehicles on a track, irrespective of the individual loads of the vehicles. If the fixed braking force applied to each vehicle is arranged to be such that the heaviest vehicle is decelerated at a required rate, then the remaining vehicles may be decelerated too rapidly when lightly loaded. The reduction of the braking force when the vehicle is decelerated as above the required rate will produce a more uniform retardation rate for the plurality of vehicles.

The device shown in FIG. 2 is adapted to be mounted on a vehicle having a braking device comprising, inter alia, a braking cylinder or cylinders, the device being orientated relatively to the direction of motion 1 of the vehicle as shown in FIG. 2.

The device comprises a support body 2 fixed in position on the vehicle, and displaceable within a recess in said body 2, a mass 3 mounted on a free lower end of a leaf spring 4. The other or upper end of the leaf spring 4 is coupled to the body 2 via a suitable coupling 5 so that said leaf spring 4 depends substantially vertically as shown. The mass 3 and leaf spring 4 are respectively the bob and bob support of a pendulum and the arrangement is such that the mass 3 tends to move towards the left-hand side of the drawing, i.e. in the direction of motion 1, when the vehicle is retarded. Engaging the left-hand face of the mass 3, and tending to resist said movement of said mass 3, is a helical spring 6, the loading of which is adjustable by means of an adjusting cap 7 which is in screw-threaded en gagement with the body 2. The pressure in the spring 6 is arranged to be approximately equal to the force which acts on the mass 3 when retardation takes place. Some resistance to movement of the mass 3 is given by the flexibility of the leaf spring 4 and in the normal position of said leaf spring 4 it may be free and straight or flexed.

At an intermediate position along the leaf spring 4 is mounted thereon a resilient button 8 which, in the normal position of said leaf spring 4, is spaced by a small distance, say, about 0.0l5 inch, from an exhaust port valve seat 9 ofa threeport valve and a relay valve assembly mounted on the body 2. The arrangement is such that movement of the button 8 in the direction of motion 1 reduces the spacing between it and the valve seat 9. As shown, the relay valve assembly comprises a diaphragm 10 connected to a half ball valve 17. A space 11 on the right-hand side of the diaphragm l0 communicates with the valve seat 9. The space 11 is also connected via an inlet port and a choke 12 to an air source line connected to a chamber 13. The connection between the space 11 and exhaust valve seat 9 is via a conduit 14.

On the left-hand side of the diaphragm 10 is a space 15 connected to atmosphere through opening 20. The output port 16 of the three-port valve assembly is arranged to be connected to a brake releasing cylinder or cylinders of the vehicle through the intermediary of the relay valve. The output port 16 is coupled via the half-ball valve 17 to the supply opening 13 and via a further valve 21 on diaphragm W to the atmospheric space 15. When diaphragm 10 moves to the left, the valve 21 closes onto valve seat 22.

In the device illustrated in FIG. 2 provision is made for adjusting the spacing between the button 8 and valve seat 9, in the normal position of the leaf spring 4, by means of a setscrew 18 arranged to engage the right-hand face of the mass 3. In addition, the setscrew 18 is provided with a hole through which a probe can be inserted, the probe being calibrated to indicate the force exerted by the spring 6 and leaf spring 3 at a particular point, as will hereinafter be described.

The braking means, which may be a spring load, is arranged normally to be capable of supplying a braking force to the vehicle which is at least sufficient to retard the vehicle at a desired rate when the load on the vehicle is at a maximum. In the normal position of the device, which exists whenever the retardation of the vehicle is less than said desired rate, any force due to retardation on the mass 3 is overcome by the combined effects of the spring 6 and the leaf spring 4 and accordingly, the pendulum is in the reference position illustrated. In this position it is arranged that the button 8 is spaced from the valve seat 9 by a distance which is substantially the minimum which will allow a free flow of air from the space lll through the valve seat 9 to atmosphere to maintain the space 11 at atmospheric pressure. The setscrew 1b is accordingly adjusted to achieve this spacing. if this adjustment results in a deflection of the leaf spring 4 in its reference position, the restoring force due to the leaf spring has to be taken into account in adjusting the loading of the spring 6. More precisely, the result of subtracting the restoring force from the loading of the spring 6 gives the resultant spring force acting on the mass 3, and this resultant force opposes the force on said mass 3 due to retardation of the vehicle. Adjustment of the resultant spring force is required to be made so that said resultant force overcomes the force on the mass 3 due to retardation whenever said retardation is substantially less than the desired rate. This adjustment can be made by adjusting the loading of the spring 6 in a manner which will be described more fully hereinafter.

As previously stated, in the referenced position of the pendulum, the space 11 is at atmospheric pressure due to the free flow of air from the valve seat 9, and hence, the relay valve assembly is in the position shown in the drawing in which the half-ball valve 17 is closed so the port 16, and accordingly also the brake-releasing cylinder or cylinders, are at atmospheric pressure via the opening past valve 21 and space 15. Under these conditions a maximum braking force is applied to the vehicle.

As the retardation of the vehicle approaches the predetermined desired rate, the force on the mass 3 due to retardation begins to exceed the resultant spring force thereon and the mass 3 moves towards the left-hand side of the drawing. Hence, the button 8 is moved towards the valve seat 9, by leaf spring 4, hereby restricting the free flow of air from the space 11 so that the pressure in said space 11 builds up. The diaphragm 10 is arranged to be such that when a certain pressure is attained in the space 11 said diaphragm 10 snaps over to a position in which the half-ball valve 17 is opened to connect space 15 to supply opening 13 and the valve 21 of diaphragm 10 is closed. Hence, the pressure applied to the brake-releasing cylinder or cylinders through outlet port 16 is increased, this increase having the effect of reducing the braking force supplied by the fixed brake. This reduction is arranged to occur at or near the required rate of retardation of the vehicle.

The reduction in the net braking force reduces the rate of retardation of the vehicle and hence, the mass 3 moves back towards the right-hand side of the drawing. This causes the button 8 to move away from the valve seat 9 and so the pressure in the space 11 is reduced causing the diaphragm 10 to snap back to its original position in which the half-ball valve 17 is closed the valve 21 is opened and the space 16 returned to atmospheric pressure, The pressure in the braking cylinder or cylinders is consequently reduced and hence the net braking force increases. The cycle can then be repeated to maintain a rate of retardation approximately equal to the desired rate, irrespective of the load on the vehicle.

In order to adjust the loading of the spring 6 so that movement of the mass 3 occurs substantially at a desired rate of retardation of the vehicle, after the setscrew 18 has been adjusted to obtain the desired spacing of the button 8 from the valve seat 9 in the reference position of the pendulum, a probe (not shown) is inserted through the hole in the setscrew 18 and is set to produce a force equal to that exerted on the mass 3 when subjected to the required rate of retardation. The adjusting cap 7 is then screwed up, compressing a spring 6, until the force of the latter just overcomes the force due to the probe and the relay valve reverts to the position shown. The stop screw 19 can then be adjusted and locked so as to prevent the mass 3 from moving further than necessary towards lefthand side of the drawing and thus causing severe indentation and possible damage to the button 8.

The leaf spring 4 is arranged to be substantially vertical in its normal position to avoid any transverse component of the force on the mass due to gravity.

If the vehicle on which the control means described above is mounted in running down a hill, the rate of retardation applied to the vehicle will be less than the predetermined desired rate and conversely if the vehicle is running uphill the rate of retardation will be greater than said predetermined desired rate.

The device shown in FIG. 2 may be modified in various ways without departing from the scope of the invention. For example, the button 8 which controls operation of the relay valve assembly may, if desired, be mounted on a leaf spring 4 below the mass 3. This may be preferred in the event that hysteresis is required to be kept very low since the effect of the increase in spring loading of the spring 6 and leaf spring 4 when the mass 3 is deflected is less the nearer the mass 3 to the fixed end of the leaf spring 4 due to the reduced movement of said mass 3.

The device described above with reference to FIG. 2 is suitable for use in conjunction with spring-operated brakes in which the braking cylinder or cylinders are such that an increase of pressure therein partially cancels the braking force in order to reduce the rate of retardation of the vehiclev In the event of the brakes are such that a reduction in pressure is required to reduce the braking force, the embodiment described above may be modified by reversing the effect of the spring 6 and the direction of motion 1 as indicated on the drawing.

lclaim:

l. A device responsive to a change in its velocity, including a support for a fluid pressure control valve having a restricted fluid flow inlet port an outlet port and an exhaust port providing a valve seat, a throttling element movable with respect to the valve seat thereby to effect a varying degree of throttling to the passage of fluid through the exhaustport, and a pendulum suspended on the support to support the throttling element while moving it in accordance with the displacement of the pendulum from a reference position with respect to the support, so that in operation of the device, when a fluid pressure pertains at the inlet port, the value of the fluid pressure at the outlet port is dependent on the rate of escape of fluid through the valve seat which rate is in turn determined by the degree of throttling effected by the throttling element consequent upon the degree of displacement of the pendulum when the support is subjected to a change of velocity in the pendulums plane of vibration, said fluid pressure control valve including a relay valve, which is interposed between said inlet and exhaust port and said outlet port, and in which the relay valve includes a pressure-responsive member arranged such that in operation the difference in pressure between the fluid flow through the inlet and exhaust port acts on the pressure-res onsive member.

2. A evice as claimed in claim 1 m which the pendulum includes a pendulum bob suspended by a bob support member.

3. A device as claimed in claim 2 in which the bob support member is a further resilient means, a leaf spring.

4. A device as claimed in claim 1 in which the pendulum is urged by at least one resilient means to said reference position, against force of which means said pendulum is displaced by said change of velocity of the support.

5. A device as claimed in claim 4 in which the pendulum bob is maintained against an abutment by the or one resilient means, so that the device is only responsive to a change of velocity which displaces the pendulum bob from the abutment, and in which the position of the abutment in the support is adjustable.

6. A device as claimed in claim 4 in which the pendulum is urged by two resilient means acting in opposition, and in which the force exerted by the individual resilient means is adjustable.

7. A device as claimed in claim 1 in which the pressureresponsive member is a diaphragm, and in which the diaphragm is connected to a fluid flow control valve, which controls the flow through said outlet port.

8. A device as claimed in claim 7 in which the diaphragm is a snap-action diaphragm, and in which the fluid flow control valve is set to one or other of two operating positions by the snap action of said diaphragm.

9. A device as claimed in claim 7 in which said control valve controls the flow of a fluid under pressure from an inlet to an outlet, and in which, when said control valve is operated to cut off the said flow of fluid, the outlet is connected to a further exhaust port.

10. A device as claimed in claim 1 in which the throttling element is a ball, which ball is supported by but not attached to the pendulum.

11. A vehicle speed control system including a device responsive to a change of velocity as claimed in claim I mounted in a vehicle to generate an output signal for said system when the vehicle velocity changes, and in which said output signal acts upon said system to influence the speed of the vehicle.

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