ZA200804844B - Self adjusting brake cylinder - Google Patents

Description

THIS INVENTION relates to a piston and cylinder assembly. In particular, the ! invention relates to a method of varying an operational length of a piston and cylinder assembly, to a piston and cylinder assembly and to a brake system.

According to a first aspect of the invention, there is provided a method of varying an operational length of a piston and cylinder assembly, the method including selectively ; pressurizing and depressurizing a chamber of a piston and cylinder assembly to cause a piston of the piston and cylinder assembly to extend and retract an associated piston rod ; : relative to the rest of the piston and cylinder assembly, so as to perform work, selectively pressurizing another chamber of the piston and cylinder assembly to cause another piston : of the piston and cylinder assembly to displace another piston rod from one position to i another position relative to the rest of the piston and cylinder assembly thereby to vary a distance by which the other piston rod extends from the rest of the piston and cylinder assembly and retaining the other piston rod at the other position thereby to vary an operational length of the piston and cylinder assembly.

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Selectively pressurizing the other chamber of the piston and cylinder assembly to cause the other piston of the piston and cylinder assembly to displace another piston rod from one position to another position may include selectively permitting fluid flow from "the chamber to the other chamber when the chamber is pressurized.

The piston and cylinder assembly may define a passage extending between the chamber and the other chamber. Selectively permitting fluid flow from the chamber to the other chamber when the chamber is pressurized may then include selectively permitting fluid flow from the chamber to the other chamber through the passage.

The piston and cylinder assembly may include a non return valve arrangement in i the passage. Retaining the other piston rod at the other position thereby to vary the operational length of the piston and cylinder assembly may then include blocking fluid flow from the other chamber to the chamber by means of the non return valve arrangement in the passage.

Selectively permitting fluid flow from the chamber to the other chamber when the chamber is pressurized may include permitting fluid flow from the chamber to the other chamber when the chamber is pressurized and the piston rod is in a generally retracted condition and blocking fluid flow from the chamber to the other chamber when the chamber is pressurized and the piston rod is caused to extend from the generally retracted ! condition.

The piston and cylinder assembly may include a closure member secured to the piston and operatively associated with the passage. Permitting fluid flow from the chamber to the other chamber when the chamber is pressurized and the piston rod is in a ! generally retracted condition and blocking fluid flow from the chamber to the other chamber when the chamber is pressurized and the piston rod is caused to extend from the generally retracted condition may then include causing the closure member to block the passage in sympathy with the piston rod being caused to extend from the generally retracted condition.

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The closure member may be in the form of a shank defining a radially outwardly extending step formation. The piston and cylinder assembly may include a seal member in the passage. Causing the closure member to block the passage in sympathy with the piston rod being caused to extend from the generally retracted condition may then include causing the radially outwardly extending step formation to pass over the seal member.

The passage may be at least partially defined by a conduit extending from the chamber toward the other chamber. The shank may be received in the conduit. Causing the radially outwardly extending step formation to pass over the seal member may then : a]

include permitting the shank to displace along the conduit in sympathy with the piston rod being caused to extend from the generally retracted condition.

The piston and cylinder assembly may define a wall operatively positioned between the chamber and the other chamber. The passage may extend from the chamber to the other chamber through the wall. The conduit may be secured to the wall.

Permitting the shank to displace along the conduit in sympathy with the piston rod being caused to extend from the generally retracted condition may then include permitting the shank to displace through the wall.

The conduit may sealingly pass through the other piston. The method may include permitting the other piston sealingly to displace along the conduit in response to fluid flow into the other chamber.

The other piston rod may define a passage. The conduit may be telescopically received in the passage. The method may further include permitting the other piston rod to displace telescopically over the conduit in response to fluid flow into the other chamber.

The other piston rod may define a port leading from the passage in the other piston rod into the other chamber. Permitting the other piston sealingly to displace along the conduit in response to fluid flow into the other chamber may include permitting fluid flow from the passage in the other piston rod, through the port and into the other chamber.

The piston and cylinder assembly may include urging means urging the piston rod to retract. Selectively pressurizing and depressurizing the chamber of the piston and cylinder assembly to cause the piston of the piston and cylinder assembly to extend and retract the associated piston rod relative to the cylinder of the piston and cylinder assembly may then include pressurizing the chamber to cause the piston to extend an 3 i ;

associated piston rod against urging of the urging means. : i :

The urging means may be in the form of spring members positioned in the [ cylinder on a side of the piston opposed from the chamber. Pressurizing the chamber to | i cause the piston to extend the associated piston rod against urging of the urging means may then include pressurizing the chamber to cause the piston to extend the associated piston rod against urging of the spring members. _

According to another aspect of the invention, there is provided a piston and cylinder assembly including a cylinder, a chamber defined in the cylinder, a piston displaceably received in the cylinder, a piston rod associated with the piston, such that the piston rod is caused selectively to extend and retract relative to the rest of the piston and cylinder assembly in sympathy with displacement of the piston in the cylinder, in response to the chamber being pressurized and depressurized, another cylinder, a chamber defined in the other cylinder, a piston displaceably received in the other cylinder, a piston rod associated with the piston in the other cylinder, such that the piston rod is caused selectively to displace from one position to another position relative to the rest of the piston and cylinder assembly in sympathy with displacement of the piston in the other cylinder, in response to the chamber in the other cylinder being pressurized, and retaining means for retaining the other piston rod at the other position thereby to vary an operational length of the piston and cylinder assembly, in use.

The piston and cylinder assembly may define a passage extending between the chambers. The passage may be arranged to enable fluid flow from the chamber in the cylinder to the chamber in the other cylinder when the chamber in the cylinder is pressurized.

The retaining means may include a non return valve arrangement positioned in the passage. The non return valve arrangement may be arranged to block fluid flow from the chamber in the other cylinder to the chamber in the cylinder, thereby to retain the piston 4 a

] rod associated with the piston in the other cylinder at the other position.

The piston and cylinder assembly may further include interruption means arranged to interrupt fluid flow from the chamber in the cylinder to the chamber in the other cylinder when the piston in the cylinder is caused to displace beyond a predetermined position.The interruption means may be arranged to permit fluid flow from the chamber in the cylinder to the chamber in the other cylinder, when the chamber in the cylinder is pressurized and the piston rod associated with the piston in the cylinder is in a generally retracted condition, and to block fluid flow from the chamber in the cylinder to the chamber in the other cylinder, when the chamber in the cylinder is pressurized and the piston rod associated with the piston in the cylinder is caused to extend from the generally retracted condition.

The interruption means may include a closure member secured to the piston in thecylinder. The closure member may be operatively associated with the passage to block the passage when the piston rod associated with the piston in the cylinder is caused to extend from the generally retracted condition.

The closure member may be in the form of a shank defining a radially outwardlyextending step formation. The interruption means may further include a seal member in the passage. The step formation may be arranged to pass over the seal member when thepiston rod associated with the piston in the cylinder is caused to extend from the generally retracted condition.

The passage may be at least partially defined by a conduit extending from the chamber in the cylinder toward the chamber in the other cylinder. The shank may be displaceably received in the conduit. ;

:The cylinders may be defined by opposed portions of a common cylinder. The piston and cylinder assembly may define a wall operatively positioned between thechamber in the cylinder and the chamber in the other cylinder. The passage may extend i from the chamber in the cylinder to the chamber in the other cylinder through the wall.H

The conduit may be secured to the wall. The shank may extend through the wall into the conduit.The conduit may sealingly pass through the piston in the other cylinder so as toenable the piston in the other cylinder sealingly to displace along the conduit.The piston rod associated with the piston in the other cylinder may define a passage. The conduit may be telescopically received in the passage. ! The piston rod associated with the piston in the other cylinder may define a port

I leading from the passage into the chamber in the other cylinder.The piston and cylinder assembly may further include urging means urging the i piston rod in the cylinder into a retracted condition. The piston rod may be arranged to extend relative to the rest of the piston and cylinder assembly when the chamber in the cylinder is pressurized against urging of the urging means.The urging means may be in the form of spring members positioned in the cylinder on a side of the piston opposed from the chamber so as to urge the piston rod in the cylinder into a retracted condition.

The spring members may be in the form of spring discs.

According to yet another aspect of the invention, there is provided a brake system including a base, a wheel mounted for rotation relative to the base, a brake shoe mounting ;

mounted for displacement relative to the base, to be selectively displaceable between a braking condition, in which a brake shoe when mounted on the brake shoe mounting is applied to the wheel, and a released condition, in which a brake shoe when mounted on the brake shoe mounting is released from the wheel, and a piston and cylinder assembly operatively associated with the brake shoe mounting and arranged selectively to be pressurized and depressurized thereby to cause the brake shoe mounting to be displaced between the braking condition and the released condition, the piston and cylinder assembly defining length adjustment means for varying an operational length of the piston and cylinder assembly so as, in use, to compensate for brake shoe wear.

The piston and cylinder assembly may include a cylinder, a chamber defined in the cylinder, a piston displaceably received in the cylinder, a piston rod associated with the piston, such that the piston rod is caused selectively to extend and retract relative to ! the rest of the piston and cylinder assembly in sympathy with displacement of the piston in the cylinder in response to the chamber being pressurized and depressurized. The length adjustment means may include another cylinder, a chamber defined in the other cylinder, a piston displaceably received in the other cylinder, a piston rod associated with the piston in the other cylinder, such that the piston rod is caused selectively to displace from one position to another position relative to the rest of the piston and cylinder assembly, in sympathy with displacement of the piston in the other cylinder, in response to the chamber in the other cylinder being pressurized, and retaining means for retaining the other piston rod at the other position thereby to vary the operational length of the : piston and cylinder assembly.

The brake system may define a passage extending between the chambers. The passage may be arranged to enable fluid flow from the chamber in the cylinder to the chamber in the other cylinder when the chamber in the cylinder is pressurized.

The retaining means may include a non return valve arrangement positioned in the passage. The non return valve arrangement may be arranged to block fluid flow from the f i chamber in the other cylinder to the chamber in the cylinder, thereby to retain the piston rod associated with the piston in the other cylinder at the other position. '

The brake system may further include interruption means arranged to interrupt fluid flow from the chamber in the cylinder to the chamber in the other cylinder when the i piston in the cylinder is caused to displace beyond a predetermined position. i

The interruption means may be arranged to permit fluid flow from the chamber in : the cylinder to the chamber in the other cylinder, when the chamber in the cylinder is pressurized and the piston rod associated with the piston in the cylinder is in a generally retracted condition, and to block fluid flow from the chamber in the cylinder to the chamber in the other cylinder, when the chamber in the cylinder is pressurized and the piston rod associated with the piston in the cylinder is caused to extend from the generally retracted condition.

The interruption means may include a closure member secured to the piston in the cylinder. The closure member may be operatively associated with the passage to block the passage when the piston rod associated with the piston in the cylinder is caused to extend from the generally retracted condition.

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The closure member may be in the form of a shank defining a radially outwardly ! extending step formation. The interruption means may further include a seal member in the passage. The step formation may be arranged to pass over the seal member when the piston rod associated with the piston in the cylinder is caused to extend from the generally ; retracted condition. !

The passage may be at least partially defined by a conduit extending from the i p g chamber in the cylinder toward the chamber in the other cylinder. The shank may be displaceably received in the conduit.

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The cylinders may be defined by opposed portions of a common cylinder. The piston and cylinder assembly may define a wall operatively positioned between the chamber in the cylinder and the chamber in the other cylinder. The p.ssage may extend i i from the chamber in the cylinder to the chamber in the other cylinder through the wall.

The conduit may be secured to the wall. The shank may extend through the wall into the conduit.

The conduit may sealingly pass through the piston in the other cylinder so as to enable the piston in the other cylinder sealingly to displace along the coaduit.The piston rod associated with the piston in the other cylinder may define a passage. The conduit may be telescopically received in the passage.

The piston rod associated with the piston in the other cylinder may define a port leading from the passage into the chamber in the other cylinder.

The brake system may further include urging means urging the piston rod in the

I cylinder into a retracted condition. The piston rod may be arranged to extend relative to ; the rest of the piston and cylinder assembly when the chamber in the cylinder is pressurized against urging of the urging means. :

The urging means may be in the form of spring members positioned in the cylinder on a side of the piston opposed from the chamber so as to urge: the piston rod in the cylinder into a retracted condition.

The spring members may be in the form of spring discs.

The base may be defined by a rail vehicle body.

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The piston and cylinder assembly may be operatively associaied with the brake shoe mounting by means of a linkage pivotally mounted relative to the base. :

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Embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:Co

Figure 1 shows a schematic diagram indicating a brake system n accordance with | ! an embodiment of the invention, a brake shoe mounting of the brake system being shown in a braking condition and a brake shoe mounted on the brake shce mounting being | i ! shown in an unworn condition;

Figure 2 corresponds with Figure 1, the brake shoe mounting of the brake system! being shown in a released condition;

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Figure 3 corresponds with Figures 1 and 2, the brake shoe mounting of the brake | ! system being shown in a braking condition and a brake shoe mounted on the brake shoe mounting being shown in a worn condition; i

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Figure 4 shows a schematic side view of a piston and cylinder assembly in : accordance with an embodiment of the invention;

Figure 5 shows a schematic cross-sectional side view of the piston and cylinder :

I ' assembly shown in Figure 4 when viewed from a different angle; i

Figures 5A to 5D show schematic exploded views of certain features of the piston and cylinder assembly as shown in Figure 5;

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Figure 6 corresponds to Figure 5, with certain detail having been omitted for the sake of clarity, and shows a piston and an associated piston rod of the >iston and cylinder assembly having been caused to displace from a generally retracted condition; [

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Figures 6A to 6C show schematic exploded views of certain features of the piston and cylinder assembly as shown in Figure 6;

Figure 7 corresponds to Figure 6 and shows the piston and the associated piston rod of the piston and cylinder assembly having been caused to return to the generally : retracted condition;

Figures 7A to 7C show schematic exploded views of certain fez tures of the piston and cylinder assembly as shown in Figure 7; : Figure 8 corresponds to Figures 6 and 7 and shows the piston and the associated ! piston rod of the piston and cylinder assembly having been caused to return to the generally retracted condition and shows another piston and associated piston rod of thepiston and cylinder assembly having been caused to displace from one position, in a ) generally extended condition, to another position, toward a retracted condition; : Figures 8A to 8C show schematic exploded views of certain features of the piston i and cylinder assembly as shown in Figure 8;

Figure 9 corresponds to Figures 6 to 8 and shows the piston «nd the associated ; piston rod of the piston and cylinder assembly having been caused t> displace from a generally retracted condition while the other piston and associated pisto 1 rod of the piston and cylinder assembly is caused to be retained in the other position. !

Referring to Figures 1 to 3 of the drawings, a brake system, in a:cordance with an embodiment of the invention, is generally indicated by reference numeral 110.The brake system 110 includes a base 112, a wheel 114 mounted for rotation relative to the base 112 and a brake shoe mounting 116 mounted for displacement relative i a : to the base 112. The brake shoe mounting 116 is mounted for displ: cement relative to the base 112 to be selectively displaceable between a braking condition, in which a brake shoe 118, when mounted on the brake shoe mounting 116, is applied tc the wheel 114, as shown in Figures 1 and 3 of the drawings, and a released condition, in which a brake shoe 118, when mounted on the brake shoe mounting 116, is released from the wheel 114, as shown in Figure 2 of the drawings. The brake system 110 further includes a piston and cylinder assembly, generally indicated by reference numeral 10, ope atively associated with the brake shoe mounting 116. The piston and cylinder assembly 10 is arranged selectively to be pressurized and depressurized thereby to cause the brike shoe mounting 116 to be displaced between the braking condition and the released condition. The piston and cylinder assembly 10 defines length adjustment means, for vary. ng an operational length 1 of the piston and cylinder assembly 10, so as, in use, to conipensate for brake shoe wear, for example, as will be described in greater detail below.

As shown in Figures 1 to 3 of the drawings, the brake system 110 is shown, by way of example, in an application in which the brake system 110 is used as a brakesystem for a rail vehicle, such as, a locomotive, or a rail car, or the like, for example. In such a case, the base 112 can be defined by a rail vehicle body, such 1s a chassis of the rail vehicle, or the like, for example. The piston and cylinder assembly can be operatively associated with the brake shoe mounting 116 by means of a linkage 120 pivotally mounted relative to the base 112, as indicated at 122.

Typically, in an application in which the brake system 110 is used as a brake system for a rail vehicle, the brake system 110 is arranged to be what is colloquially ] referred to as a dead man’s braking system. Such a brake system is arranged such that ] brakes are normally applied, operator input being required to release the brakes.

Accordingly, without operator input, the brakes are applied. An actuator 124, such as alever, or the like, for example, is used to release the brakes. The actuator 124 is shown in i ea . . ] a neutral position in Figures 1 and 3 of the drawings, which corresponds to a normal position of the actuator 124 in the absence of operator input, in which gosition the brakes are applied. In Figure 2, the actuator 124 is shown in a position removi:d from the neutral : position in response to operator input, in which position the brakes aie released. When the actuator 124 is removed from the neutral position in response to operator input, as shown in Figure 2, the piston and cylinder assembly 10 is charged, or pressurized, by means of a fluid under pressure from a fluid pressurizing unit 126.

Referring now to Figures 4 and 5S of the drawings, in which like reference numerals are used to designate similar parts, or features, unless otterwise stated, the ] piston and cylinder assembly 10 includes a cylinder 12, a chamber 14 defined in the cylinder 12, a piston 16 displaceably received in the cylinder 12 and a piston rod 16.1 associated with the piston 16. The piston rod 16.1 is caused selectively to extend and retract, as indicated by arrows AA, relative to the rest of the piston and cylinder assembly 10, in sympathy with displacement of the piston 16 in the cylinder 12, in response to the chamber 14 being pressurized and depressurized.

The piston and cylinder assembly 10 defines length adjustmen means, generally indicated by reference numeral 20, for varying the operational length I of the piston and cylinder assembly 10, as indicated by arrows L1 and L2, so as, in use, to compensate for i brake shoe wear, for example. i ;

The length adjustment means 20 includes another cylinder 22, a chamber 26 defined in the other cylinder 22, a piston 24 displaceably received in the other cylinder 22 and a piston rod 24.1 associated with the piston 24. The piston rod 24.1 is caused selectively to displace from one position, at L1, to another position, at L.2, relative to the rest of the piston and cylinder assembly 10, in sympathy with displaceinent of the piston 24 in the other cylinder 22, in response to the chamber 26 in the other cylinder 22 being ! pressurized.

Retaining means, generally indicated by reference numeral 30, is provided for retaining the other piston rod 24.1 at the other position L2, thereby to very the operational : a i length L of the piston and cylinder assembly 10.

A passage B, as indicated by arrows B, extends between the chambers 14, 26 as will be described in greater detail below. The passage B is arranged to enable fluid flow from the chamber 14 in the cylinder 12 to the chamber 26 in the othe: cylinder 22 when the chamber 14 in the cylinder 12 is pressurized.

The retaining means 30 includes a non return valve arrangeme1t 32 defining two non return valves 32.1, 32.2 positioned in the passage B. The non return valve arrangement 32, is arranged to block fluid flow from the chamber 26 ir. the other cylinder 22 to the chamber 14 in the cylinder 12, thereby to retain the piston rad 24.1 associated with the piston 24 in the other cylinder 22 at the other position 1.2.

Interruption means, generally indicated at 34, is arranged to interrupt fluid flow from the chamber 14 in the cylinder 12 to the chamber 26 in the other cylinder 22 when the piston 16 in the cylinder 22 is caused to displace beyond a predeterrained position.

The interruption means 34 is arranged to permit fluid flow from the chamber 14 in the cylinder 12 to the chamber 26 in the other cylinder 22 when the chamber 14 in the : i cylinder 12 is pressurized and the piston rod 16.1 associated with th: piston 16 in the cylinder 12 is in a generally retracted condition. The interruption means 34 is further arranged to block fluid flow from the chamber 14 in the cylinder 12 to the chamber 26 in the other cylinder 22 when the chamber 14 in the cylinder 12 is pressurized and the piston rod 16.1 associated with the piston 16 in the cylinder 12 is caused to extend from the generally retracted condition.

The interruption means 34 includes a closure member 36 secured to the piston 16 in the cylinder 12. The closure member 36 is operatively associated with the passage B to block the passage B when the piston rod 16.1 associated with the piston 16 in the cylinder 12 is caused to extend from the generally retracted condition.

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The closure member 36 can be in the form of a shank 38 defining a radially outwardly extending step formation 40. The interruption means 36 can further include a seal member 42 in the passage B. The closure member 36 is arranged to pass over the seal member 42 when the piston rod 16.1 associated with the piston 1€ in the cylinder 12 is caused to extend from the generally retracted condition.

The passage B may be at least partially defined by a conduit 44 extending from the chamber 14 in the cylinder 12 toward the chamber 26 in the other cylinder 22. The shank 38 is displaceably received in the conduit 44. :

The cylinders 12, 22 can be defined by opposed portions 46.1, 46.2 of a common cylinder 46. The piston and cylinder assembly 10 defines a wall 48 operatively positioned between the chamber 14 in the cylinder 12 and the chamter 26 in the other cylinder 22. The passage B extends from the chamber 14 in the cylinder 12 to the

I chamber 26 in the other cylinder 22 through the wall 48.

The conduit 44 is secured to the wall 48 at 50. Conveniently, this can be achieved I : . . by screw-threaded engagement of an outer screw-threaded end portion of the conduit 44 with an internally screw-threaded aperture in the wall 48. The shank 38 extends through the wall 48 into the conduit 44.

The conduit 44 sealingly passes through the piston 24 in the other cylinder 22 so as to enable the piston 24 in the other cylinder 22 sealingly to displace along the conduit 44, as indicated by arrows BB.

The piston rod 24.1 associated with the piston 24 in the other cy inder 22 defines a passage 52. The conduit 44 is telescopically received in the passage 52.

The piston rod 24.1 associated with the piston 24 in the other cy inder 22 defines a nooo]

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TT TTT port 54 leading from the passage 52 into the chamber 26 in the other ¢/linder 22.

The piston and cylinder assembly 10 further includes urginz means, generally indicated by reference numeral 56, urging the piston rod 16.1 in the cylinder 12 into a | ' retracted condition. The piston rod 16.1 is arranged to extend relative to the rest of the piston and cylinder assembly 10 when the chamber 14 in the cylinder 12 is pressurized against urging of the urging means 56.

The urging means 56 can be in the form of spring members 58 positioned in the cylinder 12 on a side 16.2 of the piston 16 opposed from the chamber 4 so as to urge the piston rod 16.1 in the cylinder 12 into a retracted condition. The spring members can be in the form of spring discs, or spring washers, or the like. !

To form the piston and cylinder assembly 10, two lengths of honed tubing, or the like, for example, which can define the cylinders 12, 22 are secured together end-to-end at 60 to define the common cylinder, or cylinder barrel 46. The two lengths of honed tubing are machined to high tolerances so as to inhibit leakage past szals of the pistons 16, 24 and for location of the disc springs 58.

Two cylinder port formations, 62, 64 are secured to the cylinder barrel 46 by welding, or the like, for example. Typically, in an application such a: the brake system 110, the port formation 64 is connected in flow communication with a fluid pressurizing unit, such as the fluid pressurizing unit 126, or the like, for example, s1own in Figures 1 to 3 of the drawings. Pressurized fluid can then be fed selectively through the port formation 64 to feed pressurized fluid to the chamber 14, a VSTI 1” BSP, or the like, for example, as indicated at 66, and into the conduit 44 past the seal 42. Typically, the port formation 62 is used for manual adjustment for set up and commissioning purposes, as will be described in greater detail below. : The centre cap, or wall 48, is accurately positioned within end portions of the 16 id

_—mA Mm mM : cylinders 12, 22 so as to secure the wall 48 relative to the cylinders 12, 22 when the cylinders 12, 22 are secured together end-to-end. The wall 48 serve; as a stop for the pistons 16, 24 and holds the VSTI 1” BSP 66, and seal 42 through which the extension rod, or shank 38, passes.

Typically, the shank 38 is secured to the piston 16 by screw threaded engagement of an externally screw-threaded end portion of the shank 38 in a complementary internally screw-threaded aperture in the piston 16. The piston 16 and associatec’ piston rod 16.1 is located in the cylinder 12 by passing the shank 38 through an open en¢ of the cylinder 12 so as to extend through the VSTI 1” BSP 66 and the seal 42. The disc springs 58 are then positioned in the cylinder 12 behind the piston 16 and around the piston rod 16.1.

Spacers 70 are positioned between the disc springs 58 to inhibit the disc springs 58 frombeing compressed beyond their plastic deformation point.

An end cap, or gland 72, is then secured to an open end portion of the cylinder 12to close the end portion. Typically, the gland 72 is screw-threadedly secured to thecylinder 12. Typically, the gland 72 is screw-threadedly engaged to the cylinder 12 to apredetermined depth to cause the disc springs 58 to be pre-tensioned 10 a predetermined amount.A mounting formation, such as a female clevis formation 74%, or the like, forexample, is then secured to an end portion of the piston rod 16.1 which protrudes fromthe gland 72. Typically, this can be achieved by screw-threadedly securing the femaleclevis formation 74 to the end portion of the piston rod 16.1.

The non return valve arrangement, or cartridge check valve 32, is mounted on theconduit, or tube assembly 44, by screw-threaded engagement, or the like, for example.

The conduit 44 is then passed through an open end portion of the cylinder 22, over the shank 38 and is screw-threadedly engaged with the wall 48. i i i - i The piston 24 and the associated piston rod 24.1 is then passed through the open end portion of the cylinder 22 and over the conduit 44 such that the conduit 44 extends through the piston 24 and into the passage 52 in the piston rod 24.1. -

An end cap, or gland 76, is then secured to the open end portion of the cylinder 22to close the end portion. Typically, the gland 76 is screw-threadedly secured to the cylinder 22.

A mounting formation, such as a clevis formation 78, or the like, for example, is ; then secured to an end portion of the piston rod 24.1 which protrudes from the gland 76.Typically, this can be achieved by screw-threadedly securing the clevis formation 78 to the end portion of the piston rod 24.1. | :

The operation of the piston and cylinder assembly will now be described with reference to Figures 6 to 9 of the drawings, in which like reference numerals have been used to designate similar parts or features, unless otherwise stated. ! 1

The piston 16, the piston rod 16.1 and the shank 38 function as a single unit.

Similarly, the piston 24 and the associated piston rod 24.1 function as a single unit. Thecylinder 46, the wall 48, the end caps 74, 78, the conduit 44 and the non-return valve arrangement 32, together function as a single unit as well. .

Typically, when the piston and cylinder assembly 10 is to be brought into operation, the piston and cylinder assembly 10 is bled to release any ir which can be in the piston and cylinder assembly 10. Typically, this is achieved through the port formation, or bleed port, 62. Accordingly, fluid under pressure is chaiged into the piston and cylinder assembly 10 through the port formation 64 while the port formation 62 is in an open condition. In addition, the piston 16 is urged into a retracted condition by the spring discs 58 so that the step formation 40 on the shank 38 is space from the seal 42.

The fluid under pressure can then pass into the chamber 14, from the chamber 14 into the : , : -

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Co conduit 44 through a space between the shank 38 and the seal 42, then along the conduit [ 44, through the non return valve arrangement 32, into the passage 5Z, then through the port 54, into the chamber 26, and then from the chamber 26 through the port formation 62, thereby to bleed the piston and cylinder assembly 10. After air is bled from the piston and cylinder assembly 10 in this fashion, the port arrangement 62 is closed.

After the piston and cylinder assembly 10 has been bled in this fashion, the piston and cylinder assembly 10 can then be mounted in a position, such as, in the position shown in Figures 1 to 3 of the drawings, operatively between the linkage 120 and the base 112, so as to be brought into operation.

In use, and as can best be seen with reference to Figures 6 and 6A to 6C of the ! drawings, the discs spring 58 urge the piston rod 16.1 into a retracted condition. In ] consequence, when applied to a brake system as shown in Figures 1 to 3 of the drawings, the brakes are applied to the wheel 114. It will be appreciated that the siston and cylinder | : assembly 10 shown in Figures 6 and 6A to 6C of the drawings, represent the piston and cylinder assembly 10 when the brake shoe 118 is in an unworn conditicn.

To release the brakes, an operator actuates the actuator 124, thereby to cause fluid under pressure to flow into the chamber 14. When a fluid pressure in the chamber 14 reaches an amount greater than a pressure exerted by the spring discs 58, the piston rod | : 16.1 is caused to extend against urging of the disc springs 58, as can best be seen with reference to Figures 7 and 7A to 7C of the drawings, thereby to cause the brakes to be released from the wheel 114. When the operator releases the actuator 124, the actuator 124 returns to a neutral position and pressure in the chamber 14 is released. The spring discs 58 then urge the piston rod 16.1 back into a retracted position so as to apply the : brakes to the wheel 114, as can best be seen with reference to Figures 6 and 6A to 6C of the drawings.

It will be appreciated that the passage B from the chamber 14 tc the chamber 26 is

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open when the piston rod 16.1 is in a retracted condition. The step formation 40 of the shank 38 passes over the seal 42 when the piston rod 16.1 extends from the retracted : condition, thereby to cause the passage B to be blocked. Accordingly, the chamber 26 is subjected to a pressure generally the same as the pressure in the cha nber 14, which in turn is generally the same as the pressure exerted by the disc springs 5:3 on the piston rod 16.1. When the pressure in the chamber 14 increases to cause the piston rod 16.1 to displace from the retracted condition, the passage B is blocked by the step formation 40 passing over the seal member 42, thereby inhibiting the chamber 26 fiom being exposed to the increased pressure in the chamber 14. ! !

As the brake shoe 118 becomes worn, and as can best be seen with reference to

Figures 8 and 8A to 8C of the drawings, pressurized fluid flows from the chamber 14 to the chamber 26 through the passage B, when the chamber 14 is pressurized to release the brakes. In consequence, the piston 24 retracts the piston rod 24.1 to compensate for wear of the brake shoe 118. The non return valve arrangement 32 inhibits fluid from returning to the chamber 14 from the chamber 26. In this way, the operational length of the piston and cylinder assembly 10 is caused to vary so as to compensate for wear of the brake shoe 118 throughout the life of the brake shoe 118. Accordingly, when he chamber 14 is pressurized to release the brakes and depressurized to apply the brakes, as can best be seen with reference to Figures 9 and 9A to 9C, the brakes are released and applied at a varied operational length of the piston and cylinder assembly 10 which compensates for wear of the brake shoe 118. !

Claims (1)

1. Enc EE ——— ; ; _ Ce I] ; cL j

   I. A method of varying an operational length of a piston a 1d cylinder assembly, the method including: selectively pressurizing and depressurizing a chamber of a piston and cylinder assembly to cause a piston of the piston and cylinder assembly to extend and retract an associated piston rod relative to the rest of the siston and cylinder assembly, so as to perform work; I selectively pressurizing another chamber of the piston and cylinder assembly to cause another piston of the piston and cylinder assembly to displace another piston rod from one position to another position relative to the rest of the i : piston and cylinder assembly thereby to vary a distance by which the other piston rod extends from the rest of the piston and cylinder assembly; ad ! retaining the other piston rod at the other position therety to vary an operational length of the piston and cylinder assembly.

   : 2. The method of varying an operational length of a piston and cylinder assembly as claimed in claim 1, in which selectively pressurizing the othr chamber of the piston and cylinder assembly to cause the other piston of the piston and cylinder assembly to displace another piston rod from one position to another position includes selectively permitting fluid flow from the chamber to the other chamber i ’ when the chamber is pressurized.

   : 3. The method of varying an operational length of a piston and cy inder assembly as claimed in claim 2, in which the piston and cylinder assembly defines a passage extending between the chamber and the other chamber, selectively permitting fluid flow from the chamber to the other chamber when the chamber is i pressurized then including selectively permitting fluid flow from the chamber to the other chamber through the passage. H 2 i ¢

   4. The method of varying an operational length of a piston and cylinder assembly as claimed in claim 3, in which the piston and cylinder assemtly includes a non return valve arrangement in the passage, retaining the other piston rod at the other position thereby to vary the operational length of the piston and cylinder assembly then including blocking fluid flow from the other chamber to the chamber by means of the non return valve arrangement in the passage.

   5. The method of varying an operational length of a piston and cylinder assembly as claimed in any one of claims 2 to 4 inclusive, in which selectively permitting fluid flow from the chamber to the other chamber when the chamber is pressurized includes permitting fluid flow from the chamber to the other chamber when the chamber is pressurized and the piston rod is in a generally retracted condition and blocking fluid flow from the chamber to the other chamber wt en the chamber is pressurized and the piston rod is caused to extend from the ;zenerally retracted condition.

   6. The method of varying an operational length of a piston and cylinder assembly as claimed in claim 5, in which the piston and cylinder assembly includes a closure member secured to the piston and operatively associated with the passage, permitting fluid flow from the chamber to the other chamber when the chamber is pressurized and the piston rod is in a generally retracted cond tion and blocking fluid flow from the chamber to the other chamber when the chamber is pressurized and the piston rod is caused to extend from the generally retracted condition then including causing the closure member to block the passage in sympathy with the piston rod being caused to extend from the generally retracted condition.

   7. The method of varying an operational length of a piston and cy inder assembly as claimed in claim 6, in which the closure member is in the form of a shank defining a radially outwardly extending step formation and the piston and cylinder =

   EE : assembly includes a seal member in the passage, causing the :losure member to block the passage in sympathy with the piston rod being caused to extend from the generally retracted condition then including causing the radially outwardly extending step formation to pass over the seal member. X !

   : 8. The method of varying an operational length of a piston and cylinder assembly as claimed in claim 7, in which the passage is at least partially defined by a conduit extending from the chamber toward the other chamber and the: shank is received in the conduit, causing the radially outwardly extending step formation to pass over the seal member then including permitting the shank to displace along the conduit in sympathy with the piston rod being caused to extend from the generally retracted condition.

   ! 9. The method of varying an operational length of a piston and cylinder assembly as claimed in claim 8, in which the piston and cylinder assembly defines a wall operatively positioned between the chamber and the other ch:mber, the passage extending from the chamber to the other chamber through the wall and the conduit being secured to the wall, permitting the shank to displace along the conduit in sympathy with the piston rod being caused to extend from the generally retracted condition then including permitting the shank to displace through the wall.

   10. The method of varying an operational length of a piston and cylinder assembly as claimed in claim 8 or claim 9, in which the conduit sealingly »asses through the other piston, the method including permitting the other piston sealingly to displace along the conduit in response to fluid flow into the other chamber.

   11. The method of varying an operational length of a piston and cylinder assembly as claimed in any one of claims 8 to 10 inclusive, in which th: other piston rod defines a passage and the conduit is telescopically received i1 the passage, the method further including permitting the other piston rod to disglace telescopically over the conduit in response to fluid flow into the other chamber.

   12. The method of varying an operational length of a piston and cylinder assembly as claimed in claim 11, in which the other piston rod defines a port leading from the passage in the other piston rod into the other chamber, permitting the other piston | : sealingly to displace along the conduit in response to fluid flow into the other chamber including permitting fluid flow from the passage in the other piston rod, through the port and into the other chamber.

   13. The method of varying an operational length of a piston and cylinder assembly as claimed in any one of the preceding claims, in which the piston and cylinder assembly includes urging means urging the piston rod to -etract, selectively pressurizing and depressurizing the chamber of the piston and cylinder assembly to cause the piston of the piston and cylinder assembly to extend and retract the associated piston rod relative to the cylinder of the piston and cylinder assembly then including pressurizing the chamber to cause the pis on to extend an associated piston rod against urging of the urging means.

   14. The method of varying an operational length of a piston and cylinder assembly as claimed in claim 13, in which the urging means is in the form of spring members positioned in the cylinder on a side of the piston opposed from the chamber, pressurizing the chamber to cause the piston to extend the associated piston rod against urging of the urging means then including pressurizing the chamber to cause the piston to extend the associated piston rod against urging of the spring members.

   15. A piston and cylinder assembly including: a cylinder; a chamber defined in the cylinder; a piston displaceably received in the cylinder;

   : oo a piston rod associated with the piston such that the piston rod is caused i i selectively to extend and retract relative to the rest of the piston and cylinder assembly in sympathy with displacement of the piston in the cylinder in response | ! to the chamber being pressurized and depressurized; another cylinder; a chamber defined in the other cylinder; a piston displaceably received in the other cylinder; a piston rod associated with the piston in the other cylinder such that the piston rod is caused selectively to displace from one position o another position : relative to the rest of the piston and cylinder assembly in sympathy with displacement of the piston in the other cylinder in response to the chamber in the other cylinder being pressurized; and retaining means for retaining the other piston rod at the other position thereby to vary an operational length of the piston and cylinder assembly, in use.

   16. The piston and cylinder assembly as claimed in claim 15, which defines a passage extending between the chambers, the passage being arranged to enable fluid flow from the chamber in the cylinder to the chamber in the other cylinder when the chamber in the cylinder is pressurized.

   17. The piston and cylinder assembly as claimed in claim 16, in which the retaining means includes a non return valve arrangement positioned in the passage, the non return valve arrangement being arranged to block fluid flow from the chamber in the other cylinder to the chamber in the cylinder, thereby to retain the piston rod associated with the piston in the other cylinder at the other position.

   18. The piston and cylinder assembly as claimed in any one of claims 15 to 17 inclusive, which further includes interruption means arranged to interrupt fluid flow from the chamber in the cylinder to the chamber in the other cylinder when | : the piston in the cylinder is caused to displace beyond a predetermined position.

   ! : : i

   19. The piston and cylinder assembly as claimed in claim 8, in which the interruption means is arranged to permit fluid flow from tte chamber in the ! cylinder to the chamber in the other cylinder when the chamber in the cylinder is pressurized and the piston rod associated with the piston in tie cylinder is in a generally retracted condition and to block fluid flow from the chamber in the cylinder to the chamber in the other cylinder when the chamber in the cylinder is pressurized and the piston rod associated with the piston in the cylinder is caused to extend from the generally retracted condition. =

   20. The piston and cylinder assembly as claimed in claim 9, in which the interruption means includes a closure member secured to the piston in the cylinder, the closure member being operatively associated with the passage to block the passage when the piston rod associated with the piston in the cylinder is caused to extend from the generally retracted condition.

   21. The piston and cylinder assembly as claimed in claim 20, in which the closure member is in the form of a shank defining a radially outwarily extending step formation and the interruption means further includes a seal member in the passage, the step formation being arranged to pass over the seal member when the piston rod associated with the piston in the cylinder is caused io extend from the generally retracted condition.

   22. The piston and cylinder assembly as claimed in claim 21, in wich the passage is at least partially defined by a conduit extending from the chamber in the cylinder | : toward the chamber in the other cylinder and the shank is displiiceably received in the conduit.

   23. The piston and cylinder assembly as claimed in claim 22, in v:hich the cylinders are defined by opposed portions of a common cylinder and the piston and cylinder I ——————————————————.—, i assembly defines a wall operatively positioned between the. chamber in the cylinder and the chamber in the other cylinder, the passage extending from the i chamber in the cylinder to the chamber in the other cylinder through the wall.

   24. The piston and cylinder assembly as claimed in claim 23, in which the conduit is secured to the wall and the shank extends through the wall into the conduit. i

   25. The piston and cylinder assembly as claimed in claim 24, in ‘which the conduit y sealingly passes through the piston in the other cylinder so as tc enable the piston p in the other cylinder sealingly to displace along the conduit.

   26. The piston and cylinder assembly as claimed in claim 25, in which the piston rod associated with the piston in the other cylinder defines a passage and the conduit is telescopically received in the passage. ] 27. The piston and cylinder assembly as claimed in claim 26, in which the piston rod ! y P associated with the piston in the other cylinder defines a port leading from the passage into the chamber in the other cylinder.

   28. The piston and cylinder assembly as claimed in any one of claims 15 to 27 inclusive, which further includes urging means urging the piston rod in the cylinder into a retracted condition, the piston rod being arranged to extend relative to the rest of the piston and cylinder assembly when the chamber in the cylinder is pressurized against urging of the urging means.

   29. The piston and cylinder assembly as claimed in claim 28, in which the urging means is in the form of spring members positioned in the cylinder on a side of the piston opposed from the chamber so as to urge the piston rod in the cylinder into a retracted condition. oF —

   30. The piston and cylinder assembly as claimed in claim 29, in which the spring members are in the form of spring discs. .

   31. A brake system including: a base, a wheel mounted for rotation relative to the base; a brake shoe mounting mounted for displacement relative to the base to be selectively displaceable between a braking condition, in which a brake shoe when mounted on the brake shoe mounting is applied to the wheel, and a released condition, in which a brake shoe when mounted on the brake shoe mounting is released from the wheel; and a piston and cylinder assembly operatively associated with the brake shoe mounting and arranged selectively to be pressurized and depressurized thereby to cause the brake shoe mounting to be displaced between the braking condition and the released condition, the piston and cylinder assembly defining length adjustment means for varying an operational length of the piston and cylinder assembly so as, in use, to compensate for brake shoe wear.

   32. The brake system as claimed in claim 31, in which the piston and cylinder assembly includes a cylinder, a chamber defined in the cylinder, a piston displaceably received in the cylinder, a piston rod associated with the piston such that the piston rod is caused selectively to extend and retract relative to the rest of the piston and cylinder assembly in sympathy with displacement of the piston in the cylinder in response to the chamber being pressurized and depressurized and the length adjustment means includes: another cylinder; a chamber defined in the other cylinder; a piston displaceably received in the other cylinder; a piston rod associated with the piston in the other cyliider such that the piston rod is caused selectively to displace from one position to another position ® ]

   _— : relative to the rest of the piston and cylinder assembly i1 sympathy with displacement of the piston in the other cylinder in response to the chamber in the other cylinder being pressurized; and retaining means for retaining the other piston rod at the other position thereby to vary the operational length of the piston and cylinder assembly.

   33. The brake system as claimed in claim 32, which defines a passage extending between the chambers, the passage being arranged to enable fl iid flow from the chamber in the cylinder to the chamber in the other cylinder whzn the chamber in the cylinder is pressurized.

   34. The brake system as claimed in claim 33, in which the retaining means includes a non return valve arrangement positioned in the passage, the non return valve arrangement being arranged to block fluid flow from the chamber in the other cylinder to the chamber in the cylinder, thereby to retain the pision rod associated with the piston in the other cylinder at the other position.

   35. The brake system as claimed in any one of claims 32 to 34 inclusive, which further includes interruption means arranged to interrupt fluid flow from thechamber in the cylinder to the chamber in the other cylinder whea the piston in the cylinder is caused to displace beyond a predetermined position.

   36. The brake system as claimed in claim 35, in which the interruption means is arranged to permit fluid flow from the chamber in the cylinder io the chamber in the other cylinder when the chamber in the cylinder is pressurized and the piston rod associated with the piston in the cylinder is in a generally retracted condition and to block fluid flow from the chamber in the cylinder to the chamber in the other cylinder when the chamber in the cylinder is pressurized ¢nd the piston rod associated with the piston in the cylinder is caused to extend from the generally retracted condition. j

   / 37. The brake system as claimed in claim 36, in which the interruption means includes a closure member secured to the piston in the cylinder, the closure member being operatively associated with the passage to block the passage when the piston rod associated with the piston in the cylinder is caus=d to extend from the generally retracted condition. {

   38. The brake system as claimed in claim 37, in which the closure member is in the form of a shank defining a radially outwardly extending step jormation and the interruption means further includes a seal member in the passage, the step formation being arranged to pass over the seal member when the piston rod associated with the piston in the cylinder is caused to extend from the generally retracted condition.

   39. The brake system as claimed in claim 38, in which the passage is at least partially defined by a conduit extending from the chamber in the cylinder toward the chamber in the other cylinder and the shank is displaceably received in the i conduit. ! 40. The brake system as claimed in claim 39, in which the cylinders are defined by opposed portions of a common cylinder and the piston and cylinder assembly defines a wall operatively positioned between the chamber in the cylinder and the chamber in the other cylinder, the passage extending from the chamber in the cylinder to the chamber in the other cylinder through the wall.

   41. The brake system as claimed in claim 40, in which the conduit is secured to the wall and the shank extends through the wall into the conduit.

   42. The brake system as claimed in claim 41, in which the condui sealingly passes through the piston in the other cylinder so as to enable the piston in the other s0

   -_ nn TT cylinder sealingly to displace along the conduit.

   43. The brake system as claimed in claim 42, in which the piston rod associated with the piston in the other cylinder defines a passage and the conduit is telescopically received in the passage.

   44. The brake system as claimed in claim 43, in which the piston rod associated with the piston in the other cylinder defines a port leading from the: passage into the chamber in the other cylinder.

   45. The brake system as claimed in any one of claims 32 to 44 inclusive, which further includes urging means urging the piston rod in the cylinder into a retracted condition, the piston rod being arranged to extend relative to the rest of the piston and cylinder assembly when the chamber in the cylinder is pressurized against { urging of the urging means.

   46. The brake system as claimed in claim 45, in which the urging means is in the form of spring members positioned in the cylinder on a side of the pision opposed from ! the chamber so as to urge the piston rod in the cylinder into a retracted condition.

   47. The brake system as claimed in claim 46, in which the spring members are in the : form of spring discs.

   48. The brake system as claimed in any one of claims 31 to 47 inclusive, in which the base is defined by a rail vehicle body.

   49. The brake system as claimed in any one of claims 31 to 48 inclusive, in which the piston and cylinder assembly is operatively associated with the brake shoe mounting by means of a linkage pivotally mounted relative to the base.

   BE ————_—— _ —

   50. A method of varying an operational length of a piston and cylinéer assembly substantially as described and as illustrated herein.

   51. A piston and cylinder assembly substantially as described and as illustrated herein. j § H

   52. A brake system substantially as described and as illustrated herein. N & HARY INC. ; APPLICANT'S PATENT ATTORNEYS i i i ; i ! i [ i Lo ! SE