GB2128255A

GB2128255A - Brake cylinder for wedge expander brakes

Info

Publication number: GB2128255A
Application number: GB08326756A
Authority: GB
Inventors: Otto Rath; Manfred Ulrich
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1982-10-06
Filing date: 1983-10-06
Publication date: 1984-04-26
Also published as: SE453527B; SE8305212L; DE3236922A1; DE3236922C2; SE8305212D0; GB8326756D0; FR2534338A1; GB2128255B; FR2534338B1

Abstract

The cylinder (10) is vented outwardly in the interior of the diaphragm cylinder by a vent (29) which allows the intrusion of dirt and moisture. The diaphragm cylinder interior is isolated from the guide tube interim (12) by an annular sealing ring or spaced rings (31) seated between the guide tube (12) and the piston rod (14) and sealing the annular chamber (9). The ring is rigidly seated either on the piston rod (14) or in the guide tube (12) and has a resilient annular sealing portion (34) in the form of a sealing lip which lies against the internal circumferential surface (35) of the guide tube (12) or against the outer circumferential surface of the piston (14) under pressure by virtue of a certain amount of over-dimensioning and is thereby resiliently deformable and has a wiping-off ability. The ring has an arcuate or tapered tip. <IMAGE>

Description

SPECIFICATION Brake cylinder for wedge expander brakes The invention relates to a brake cylinder for wedge expander brakes of the type which comprises a diaphragm cylinder with a guide tube contiguous thereto, a piston rod which is longitudinally movably guided in the guide tube, and a movable diaphragm which is located in the diaphragm cylinder and which sealably closes the diaphragm cylinder at its axial end and which presses against that end of the piston rod which faces the movable diaphragm, the interior of the diaphragm cylinder being vented outwardly by way of at least one vent and being isolated from the interior of the guide tube by means of a protective device.

Brake cylinders of this kind, in the form of diaphragm cylinders and combination diaphragm cylinders, are mounted particularly in compressedair brake systems of vehicles, the piston rod of the diaphragm cylinder operating mechanically upon the wedge expander brake connected therebeyond. In brake cylinders of this kind, it must be ensured that any impurities, moisture, water, particles of dirt or the like entering through the vent cannot reach the wedge expander mechanism through the guide tube. For this purpose, known brake cylinders of this kind are provided with the protective device which isolates the interior of the diaphragm cylinder from the interior of the guide tube. This protective device has a bellows which overlaps the piston rod and is mounted on the end thereof. The interior of the beilows cylinder is necessarily vented through at least one opening.This results in the disadvantage that dirt and liquid can enter through the vent, especially since they are even drawn in through the vent. Moreover, the vent can be one clogged by dirt. A protective device in another known brake cylinder is a seal in the form of a plastics lip which is intended to wipe off the dirt, but which is not pressure-tight. This protective device has the disadvantage that the lip is subjected to wear intensified by the action of dirt and is no longer able to wipe off all the dirt. Furthermore, the sealing action is unsatisfactory.

An object of the invention is to provide a brake cylinder for wedge expander brakes, particularly for compressed-air brake systems of vehicles, in which a protective device reliably and permanently prevents the intrusion of dirt, other impurities, moisture and water and at the same time ensures ventilation and venting of the interior of the guide tube and the contiguous wedge expander mechanism by way of the interior of the diaphragm cylinder.

According to the present invention there is provided a brake cylinder for wedge expander brakes which comprises a diaphragm cylinder with a guide tube contiguous thereto, a piston rod which is longitudinally movably guided in the guide tube, and a movable diaphragm which is located in the diaphragm cylinder and which sealably closes the diaphragm cylinder at its axial end and which presses against that end of the piston rod which faces the movable diaphragm; the interior of the diaphragm cylinder being vented outwardly by way of at least one vent and being isolated from the interior of the guide tube by means of a protective device, which comprises at least one annular sealing arrangement which is mounted between the guide tube and the piston rod and which is resiliently deformable whereby to seal the annular space between the two parts consisting of the guide tube and the piston rod and which is secured to one of said parts and whose annular sealing portion lies against the circumferential surface of the other of said parts and with a wiping-off ability.

In the brake cylinder in accordance with the invention the annular sealing portion of the annular sealing arrangement always lies against the particular circumferential surface, namely either against the outer circumferential surface of the piston rod or the inner circumferential surface of the guide tube, under a certain amount of initial stress and pressure and thus reliably prevents dirt, impurities, moisture and water from entering the interior of the guide tube and the following wedge expander mechanism when the piston rod is not moving. This tightness is also ensured during operation and when the piston rod is moving.The annular sealing portion has a wiping function on the one hand, since it can wipe off adhering particles of dirt and also moisture or liquid during the relative movement and, on the other hand, the annular sealing arrangement is able to compensate for tolerances. This ensures reliable sealing and great durability even in the event of wear. When the piston rod changes its direction of movement, the annular sealing arrangement is able to flex in the region of the annular sealing portion and in this manner to fulfil the wiping and sealing function in a particularly satisfactory manner without larger, perceptible forces being necessary to flex the annular sealing portion upon a change in the direction of movement.

The ventilation and venting of the interior of the guide tube and of the contiguous wedge expander mechanism through the interior of the diaphragm cylinder is ensured in that, owing to its elasticity, the annular sealing arrangement permits the overflow of air in the region of its annular sealing portion. Hence, neither a vacuum nor overpressure is produced in the interior of the guide tube and the following chamber with the wedge expander mechanism. Further, the annular sealing arrangement is simple and inexpensive and, moreover, can be rapidly exchanged if required.

A particularly satisfactdry wiping action with simultaneous sealing, but with the flowby of air of ventilating and venting the interior of the guide tube, and satisfactory compensation for tolerances, are achieved if the sealing arrangement comprises a sealing ring which has an annular sealing portion provided with a sealing lip of thinned cross section.

A design in which an outer retaining edge of the sealing ring is held on a collar at the end of the guide tube is particularly advantageous, and its inner annular sealing portion is seated on, and seals, the outer circumferential surface of the piston rod. Advantageously, the internal diameter of the sealing ring is, for example, 0.3 mm smaller than the external diameter of the piston rod in this region. This is adequate for the desired pressure in the region of the annular sealing portion.

If the tasks of the annular sealing arrangement are split up between two sealing rings which are mounted axially one behind the other, the sealing ring located nearer to the interior of the diaphragm cylinder effect a pre-wiping operation and holds back coarse particles of dirt and water. The second sealing ring facing the wedge expander mechanism undertakes the sealing function in the static state and wipes off water and moisture and fine particles of dirt which the first sealing ring could not hold back.

The chamber region between the two sealing rings is preferably open towards the interior of the diaphragm cylinder, namely it is vented preferably in the top region on the one hand and, on the other hand, is open preferably in the bottom region, such that water and dirt can flow off if they should have entered the chamber region between the two sealing rings, and dirt is flushed out by water which has penetrated. Moreover, these openings serve to ventilate and vent the interior of the guide tube and the following wedge expander mechanism, namely by air passing the sealing ring, facing the wedge expander mechanism, in the region of the sealing lip.

The invention is further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic axial longitudinal section through a part of a brake cylinder for a wedge expander brake in accordance with a first embodiment, Figs. 2 and 3 are each a diagrammatic section through a detail of the brake cylinder in accordance with a second and third embodiment respectively, Fig. 4 is a section through a part of a sealing ring of Fig. 1, Fig. 2 or Fig. 3, drawn to a larger scale, Fig. 5 is a section, corresponding to Fig. 4, through a part of a sealing ring in accordance with a modified embodiment.

A brake cylinder 10 for a wedge expander brake is shown diagrammatically in Fig. 1. Wedge expander brakes are well known in the art, so that there is no need to describe them here. The brake cylinder 10 has a diaphragm cylinder 11 with a contiguous guide tube 1 2 which is disposed coaxially thereof. The wedge expander brake (not illustrated) is mounted at the right hand end of the guide tube 12, only a spring-loaded push rod 13 of the wedge expander brake being shown in Fig. 1.

A piston rod 14 is longitudinally movably guided in the guide tube 12 by means of two axially adjacent guide members 1 5, 16 made from plastics material. The piston rod 1 4 is of two-part construction. Its second part 1 7 is inserted into the free right hand end of the piston rod 14 with a spacer ring 1 8 interposed therebetween. The second part 1 7 has a depression 1 9 which the push rod 13 engages with its end of substantially the same shape. The left hand end of the piston rod 14 carries a plate 20 rigidly secured thereto.

The left hand axial end of the diaphragm cylinder 11 as viewed in Fig. 1 is sealingly closed by means of a movable diaphragm 21 which abuts against the facing surface of the plate 20. The thickened outer edge 22 of the diaphragm 21 is mechanically and sealingly clamped between the diaphragm cylinder 11 on the one hand and, on the other hand, a connecting housing 23 contiguous to the left hand end of the diaphragm cylinder. A plunger or piston 24 coaxial with the piston rod 14 is located in the connecting housing 23 and, when the parking brake is actuated, is displaced to the right in Fig. 1 and towards the diaphragm 21, the plate 20, and the piston rod 14 under the pressure of a spring which is then relieved of stress, to apply the wedge expander brake.To release the parking brake, a pressure chamber 25 in the connecting house 23 is subjected to compressed air whereby a valve plate secured to the plunger 24 is displaced to the left (as viewed in Fig. 1) together with the plunger 24 against the action of the said spring, and the wedge expander brake is thus released.

Compressed air is introduced into the chamber 26 at the left of the diaphragm 21 in the direction of the arrow 27 when the service brake is actuated.

The diaphragm 21 is thereby subjected to compressed air which, by way of the plate 21, displaces the piston rod 14 and, by way of the latter, the push rod 13 to the right, as viewed in Fig. 1 , to actuate the wedge expander brake disposed therebeyond. The interior space 28 of the diaphragm cylinder 11 closed by the diaphragm 21 is vented outwardly by way of at least one vent 29 located at the bottom, in order to enable the previously described operation to be performed as smoothly as possible and without having to overcome a large counter-pressure in the interior space 28. If the pressure causing the braking action drops in the chamber 26, the piston rod 14 together with the diaphragm 21 is moved back to the left (as viewed in Fig. I) into the starting position by way of the spring-loaded push rod 13, ambient air then flowing through the vent 29 for the purpose of pressure equalisation.

The at least one vent 29 required, means that dirt and moisture can pass therethrough into the interior chamber 28. in order to ensure the permanent operability of the wedge expander mechanism of the wedge expander brake (not illustrated) connected to the right hand end of the brake cylinder 10, dirt and moisture must be kept away from the wedge expander mechanism, at the same time retaining the described ventilation and venting. This is effected by an annular sealing arrangement 30 which is mounted between the guide tube 12 and the piston rod 14 and which seals the annular chamber 9 therebetween. In the present instance, the annular sealing arrangement 30 comprises at least one sealing ring 31 whose inner edge 32 engages an annular groove 33 in the piston rod 14 and is thus fixed on the piston rod 14 and moves together therewith.The outer edge of the sealing ring 31 carries an annular sealing portion 34 by which the sealing ring 31 is resiliently deformable and is seated on, and slides along, the inner circumferential surface 35 of the guide tube 12 with a certain wiping-off capacity.

As is shown in Fig. 1, the sealing ring 31 is of approximately plate-like or disc-like construction.

Its diameter is chosen such that the annular space 9 between the piston rod 1 4 and the inner circumferential surface 35 is sealed and shut off around the entire cross-sectional area. The external diameter of the sealing ring 31 is chosen to be, for example 0.3 mm larger than the internal diameter of the inner circumferential surface 35.

The outer annular sealing portion 34 of the sealing ring 31 is thereby seated under pressure on the circumferential surface 35 in the guide tube 12, namely to compensate for any tolerances between the piston rod 14 and the circumferential surface 35, and further to provide a seal against the intrusion of dirt, moisture and liquid and also with the ability to wipe off and clean. The sealing ring 31 is made from, for example, rubber having a thickness of, for example, 3 mm. Preferably, the outer annular sealing portion 34 is in the form of a sealing lip which has a thinner cross section and which, in accordance with Fig. 4 for example, has an arcuate cross section or, in accordance with Fig. 5, a cross section which tapers in the manner of an arrow head.

By virtue of the described over-dimension of the sealing ring 31, the outer annular sealing portions 34 of the latter always abuts reliably against the inner circumferential surface 35 and thus seals the interior of the guide tube 12 and the following wedge expander mechanism from the interior space 28. In the static state, the intrusion of dirt, moisture and water is reliably prevented in this manner. This tightness is also ensured during movement of the piston rod 14. The sealing ring 31 then flexes in the region of the outer annular sealing portion 34, although the tightness or sealing action is ensured as previously. The expenditure of force required for flexing action is relatively small, since the described overdimension of, for example, 0.3 mm, and the thickness of the sealing ring 31 are relatively small.Tightness is ensured even when the direction of movement of the piston rod 14 changes. The annular sealing portion 34 of the sealing ring 31 then flexes towards the other side.

Owing to the elasticity of the sealing ring 31 at least in the region of the outer annular sealing portion 34, air can flow by at this location, whereby the generation of a vacuum or overpressure in the interior of the guide tube 12 and in the chamber of the contiguous wedge expander maximum is prevented. Consequently, reliable sealing of the interior of the guide tube 1 2 against the intrusion of dirt and other impurities and against moisture, water or the like, is ensured, moisture and water being able to drain off downwardly from the interior space 28 of the brake cylinder 10 which, as before, is ventilated and vented in a simple manner. The surface cooperating for the purpose of sealing are kept clean by the wiping-off effect. This at the same time reduces wear. Furthermore, the sealing ring 31 can compensate for tolerances.It is a simple element which can be exchanged as required.

Reference numerals increased by 100 are used for those parts of the second embodiment of Fig. 2 which correspond to those of the first embodiment, so that reference is made to the description of the first embodiment in order to avoid repetition.

In the second embodiment, the conditions are the reverse of those of Fig. 1. In the present instance, the sealing ring 1 31 is provided with an outer retaining edge 140 which overlaps a radially projecting collar 141 on the left hand, free end of the guide tube 112. In this manner, the sealing ring 131 is fixed on the guide tube 112. The annular sealing portion 134, which can be an arcuate or wedge-shape tapered sealing lip, is located in the region of the inner edge of the sealing ring 1 31. It presses against the outer circumferential surface 1 36 of the piston rod 114 in a resiliently deformable manner and can perform a wipe-off function.In the present instance, the internal diameter of the sealing ring 131 is chosen to be smaller than the diameter of the piston rod 114 by for example, 0.3 mm, so that, in the manner described with reference to the first embodiment, the annular sealing portion 1 34 presses against the outer circumferential surface 136 of the piston rod 114.

For the reason given, reference numerals increased by 200 are used for those parts in the third embodiment of Fig. 3 which correspond to those of the first or second embodiment.

In the third embodiment, two similar, axially spaced sealing rings 231,231 are provided. The two sealing rings are fixed in a retaining ring 242 which is in turn secured to the guide tube 212 in, for example, the region of its left hand, free end where the collar 242 is provided.

The retaining ring 242 has an upper air inlet port 244 and a lower outlet port 245 in the chamber region 243 formed between the two sealing rings 231 and 231', both of which ports lead to the interior space 228 of the diaphragm cylinder 211. The circumferential surface of the retaining ring 242 incorporates two annular grooves 246, 247 which are engaged by the outer edge of a respective sealing ring 231 or 231'. The retaining ring 242 is made from metal, plastics material or, alternatively, rubber. In a modified embodiment (not illustrated), the retaining ring 242 and the two sealing rings 231,231' are a one-piece part which is then made entirely from rubber.

This third embodiment has the advantage that the individual functions are distributed to the two sealing rings 231,231 The left hand sealing ring 231 of Fig. 3 enables the preliminary wiping-off of coarse particles of dirt and impurities and also performs a coarse sealing function by wiping off moisture and water, at least within limits. If moisture, water, dirt and other impurities should have passed the first sealing ring 231 and entered the chamber region 243, they can be removed from the latter through the ports, particularly the lower outlet port 245. The upper air inlet port 244 facilitates the outflow, since it vents the chamber region 243 to the interior space 228 and enables equalisation of pressure. The sealing ring 231' on the right in Fig. 3 undertakes the sealing function in the static state and also in the dynamic state and, moreover, provides for the fine wiping-off of water, moisture and any particles of dirt which are still adhering. That outer circumferential region of the piston rod 214 which has thus passed the right hand sealing ring 231' during the movement to the right in Fig. 3, is clean and dry. Any impurities or moisture are reliably kept away from the interior of the guide tube 212.

The sealing ring 131 of Fig. 2 and/or the retaining ring 242 of Fig. 3 is secured to the guide tube 112 or 212 respectively by pressing-in, glueing, snapping-in, clamping, or in another manner. Nevertheless, when necessary, such as in the case of wear on the particular annular sealing portions of the sealing rings, it is possible to exchange the sealing rings without great difficulty.

Claims

1. A brake cylinder for a wedge expander brake which comprises a diaphragm cylinder with a guide tube contiguous thereto, a piston rod which is longitudinally movably guided in the guide tube, and a movable diaphragm which is located in the diaphragm cylinder and which sealably closes the diaphragm cylinder at its axial end and which passes against that end of the piston rod which faces the movable diaphragm, the interior of the diaphragm cylinder being vented outwardly by way of at least one vent and being isolated from the interior of the guide tube by means of a protective device, which comprises at least one annular sealing arrangement which is mounted between the guide tube and the piston rod and which is resiliently deformable whereby to seal the annular space between the two parts consisting of the guide tube and the piston rod and which is secured to one of said parts and whose annular sealing portion lies against the circumferential surface of the other of said parts and with a wiping-off ability.

2. A brake cylinder as claimed in claim 1, in which the annular sealing arrangement comprises at least one resilient sealing ring of plate-shaped or disc-shaped configuration.

3. A brake cylinder as claimed in claim 2, in which the annular sealing portion of the at least one sealing ring lies with pressure against the circumferential surface of the interior of the guide tube or of the piston rod and compensates for tolerances, performs a sealing action, and has a wiping-off ability.

4. A brake cylinder as claimed in claim 2 or 3, in which the at least one sealing ring is made from rubber.

5. A brake cylinder as claimed in any of claims 2 to 4, in which the annular sealing portion of the at least one sealing ring has a sealing lip of thinned cross section, such as an arcuate cross section or a cross section tapering in the manner of an arrow head.

6. A brake cylinder as claimed in any of claims 2 to 5, in which the at least one sealing ring incorporates the annular sealing portion on its inner edge and is indirectly or directly fixed on or in the guide tube.

7. A brake cylinder as claimed in any of claims 2 to 6, in which the annular sealing arrangement comprises a sealing ring having an outer retaining edge which is held on a collar at the free end of the guide tube and the inner annular sealing portion of which sealing ring lies against the circumferential surface of the piston rod.

8. A brake cylinder as claimed in any of claims 2 to 6, in which the annular sealing arrangement comprises two similar, axially spaced sealing rings.

9. A brake cylinder as claimed in claim 8, in which the two sealing rings are fixed in a retaining ring which is in turn secured to the guide tube, such as to a collar located at the free end thereof.

10. A brake cylinder as claimed in claim 9, in which the retaining ring in the chamber region between the two sealing rings has at least one opening which opens into the interior of the diaphragm such as an upper air inlet opening and a lower outlet opening.

11. A brake cylinder as claimed in claim 9 or 10, in which the retaining ring is made from metal, plastics or rubber.

12. A brake cylinder as claimed in any of claims 9 to 11, in which the retaining ring and the two sealing rings together form a one-piece part, made, e.g., from rubber.

13. A brake cylinder as claimed in any of claims 9 to 12, in which the internal circumferential surface of the retaining ring incorporates two axially spaced annular grooves each engaged by the outer edge of a respective sealing ring.

14. A brake cylinder as claimed in any of claims 2 to 5, in which the at least one sealing ring has the annular sealing portion at its outer edge and is fixed directly or indirectly on the piston rod.

1 5. A brake cylinder as claimed in claim 14, in which the piston rod has for the or each sealing ring an annular groove which is engaged by the inner edge of the sealing ring.

16. A brake cylinder for a wedge expander brake constructed and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.