GB2296946A

GB2296946A - Protective bellows

Info

Publication number: GB2296946A
Application number: GB9500606A
Authority: GB
Inventors: Bernard Renzo
Original assignee: Draftex Industries Ltd
Current assignee: Laird Holdings Ltd
Priority date: 1995-01-12
Filing date: 1995-01-12
Publication date: 1996-07-17
Anticipated expiration: 2015-01-12
Also published as: GB9500606D0; FR2729443B1; GB2296946B; FR2729443A1

Abstract

A protective bellows (5) has a plurality of bellows turns integrally extending from a small diameter fixing collar (22) at one of its ends to a relatively large diameter fixing collar (20) at its opposite end. The relatively large diameter fixing collar (21) is sealingly clamped to the outside of the casing (10) of a transmission joint. The relatively small diameter fixing collar (22) is sealingly clamped to the outside surface of a rotary shaft connected to and driven by the mechanism within the joint. The interior surface of the fixing collar (22) is provided with a plurality of generally rectangular raised profiles (30) the profiles ensure that small passageways (34) still exist between the profiles (30). These small passageways (34) enable excess air pressure to be relieved to the outside. At the same time, however, their staggered arrangement blocks the escape of grease.

Description

PROTECTIVE BELLOWS The invention relates to protective bellows. Examples of protective bellows embodying the invention, to be described in more detail below by way of example, are protective bellows for protecting a transmission joint (e.g. a universal joint) of the transmission of a motor vehicle.

According to the invention, there is provided a protective bellows having a fixing collar at one of its ends for embracingly clamping to a cylindrical shaft forming part of a mechanism to be protected, the interior surface of the fixing collar having a plurality of axially separated circumferentially extending regions, each of these regions having an arcuately extending section in contact with the cylindrical shaft and at least one arcuately extending section spaced from the cylindrical shaft to provide a gap, the gaps of adjacent regions being angularly offset with respect to each other about the axis of the shaft so as together to form a passageway enabling the escape of excess pressure from within the bellows through the interior of the collar but resisting the escape of any lubricating grease within the bellows.

Protective bellows embodying the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a longitudinal section through one of the bellows, in position for protecting a universal joint of a motor vehicle transmission; and Figure 2 is a cross-section of part of the bellows of Figure 1, but removed from the vehicle transmission.

Figure 3 is a longitudinal section through another form of the bellows in position for protecting a transmission joint of a motor vehicle; Figure 4 is a cross-section on the line IV-IV of Figure 3; Figure 5 is a cross-section on the line V-V of Figure 3; Figure 6 is a longitudinal section through a further form of the bellows in position for protecting a transmission joint for a motor vehicle; Figure 7 is a cross-section on the line VII-VII of Figure 6; and Figure 8 is a cross-section on the line VIII-VIII of Figure 6.

Figure 1 shows the protective bellows 5 in position for protecting a universal joint 6 of a motor vehicle transmission. The transmission comprises an input shaft 8 solid with and rotating a cup-shaped casing 10 of the universal joint 6. The transmission includes an output shaft 12 carrying an inner element 14 having grooves in which balls 16 are engaged, the balls being mounted in a cage 18 and also engaged in grooves 19 on the inner face of the casing 10. In this way, the universal joint, which is of standard construction, transmits the rotary drive between the two shafts 8 and 12. In addition, however, the balls 16 permit the shaft 12 to move so that its axis can be inclined with respect to the axis of the shaft 8, the angle of inclination having a maximum possible value of the order of 500.

The protective bellows 5 is made of relatively hard material of the thermoplastic elastomer type. It comprises a plurality of bellows turns 20 integrally extending between a large diameter fixing collar 21 at one end and a smaller diameter fixing collar 22 at the opposite end. Fixing collar 21 is a tight fit around the outside of a receiving surface, possibly grooved, on the outside of the casing 10 and is securely clamped in position by a peripheral clamp 24.

The fixing collar 22 engages the outside of the shaft 12 and is clamped to the shaft by a peripheral clamp 26.

The mechanism of the universal joint 6 must be well lubricated because of the mechanical stresses which it has to withstand, and it is therefore packed with suitable grease. The protective bellows 5 protects the mechanism of the universal joint 6 from ingress of moisture, dirt and other contamination, but is sufficiently flexible to allow the required angular movement between the axis of shaft 12 and the axis of shaft 8.

During operation of the vehicle transmission, mechanical stresses within the universal joint 6, particularly when the above-mentioned angular movement takes place, will result in the creation of elevated temperatures, principally owing to friction between the various parts of the mechanism. The high temperatures can increase the pressure of the air within the interior volume of the bellows and in turn this can cause significant deformation of the material of the bellows and premature rupture unless steps are taken to allow the excess pressure to be relieved to the exterior of the bellows. At the same time, though, care must be taken not to allow leakage or expulsion of the grease.

Figure 2 shows, to an enlarged scale, the formation of the interior surface of the fixing collar 22 of the bellows 5 of Figure 1. As shown in Figure 2, the interior surface is provided with a multitude of small substantially rectangular profiles 30 arranged so as to produce through passageways 34 which are of zig-zag configuration, the profiles being produced integrally in the bellows material during the moulding process. The presence of the profiles ensures that small passageways 34, extending between the profiles, still exist when the fixing collar 22 is firmly clamped onto the shaft 12 (see Figure 1), these small passageways 34 connecting the interior of the bellows with the exterior. The small passageways thus allow excess air pressure to escape during conditions of elevated temperature but resist escape of the grease.

Each profile 30 may be about 0.5mm in height, about 2mm in width and about 5mm in length.

In Figures 3 to 8, items corresponding to items in Figures 1 and 2 are correspondingly referenced. The forms of bellows 38 shown in Figures 3 to 8 are for protecting a transmission joint shown generally at 40. Its mechanism is not illustrated in detail. However, the joint 40 is of a type which permits limited axial movement (in the directions of the arrows F) of the shaft 12 relative to the shaft 8. The joint 40 may also permit angular movement (similar to that permitted by the joint shown in Figure 1).

The forms of bellows 38 of Figures 3 to 8 are made of relatively hard material of the thermoplastic elastomer type.

As for the universal joint of Figure 1, the mechanism of the transmission joint 40 must be well lubricated because of the mechanical stresses which it has to withstand. It is therefore packed with suitable grease. The bellows 38 protects the mechanism of the transmission joint 40 from contamination by moisture and dirt but is sufficiently flexible to allow the required axial movement between the shafts 8 and 12.

During operation of the vehicle transmission, the pressure of air within the interior volume of the bellows 38 can increase or decrease because of the "pumping" action created by the axially directed movement between shafts 8 and 12. This, causes significant deformation of the material of the bellows and may cause its premature failure unless steps are taken to allow the excess pressure to be relieved. However, leakage of the grease must be prevented or minimised.

Figures 4 and 5 show axially spaced cross-sections through the collar 22 of the bellows 38. As shown, the collar comprises two axially spaced shoulders 44 and 46. Each extends around the interior surface of the collar 22 and into contact with the shaft 8 but is interrupted to provide a respective recess 48,50, the recesses 48,50 being substantially rectangular in cross-section as shown in Figures 4 and 5. In addition, Figures 4 and 5 show how the recesses 48,50 are offset with respect to each other 0 around the axis of the shaft 12 by 180 . The recesses 48 and 50 thus together provide a tortuous passageway from the interior of the bellows to the exterior. This passageway allows excess air pressure to be released.

However, because of its tortuous configuration, the passageway resists the escape of the grease 42.

Figures 6,7 and 8 show a modified version of the bellows 38. In this case, the collar comprises five axially spaced shoulders 52,54,56,58 and 60. Again, each shoulder extends around the interior surface of the collar 22 and in contact with the surface of the shaft 12. In this case, however, each shoulder is interrupted to provide four recesss 64,66,68 and 70, which are substantially rectangular in cross-section.

Figure 7 shows the shoulder 54 and its four recesses, and Figure 8 shows the shoulder 60 and its four recesses. The four recesses of each shoulder are positioned at 900 intervals around the circumference of the collar 22. As shown by comparing Figures 7 and 8, the four recesses 64,66,68 and 70 of shoulder 54 are respectively offset by 450 with reference to the four recesses 64,66,68 and 70 of shoulder 60.

The recesses of shoulder 58 are arranged in the same way as the recesses of shoulder 54 shown in Figure 7.

The recesses of shoulders 52 and 56 are arranged in the same way as the recesses of shoulder 60 shown in Figure 8.

In the embodiment of Figures 6,7 and 8, therefore, a plurality of passageways are provided between the interior of the bellows and the exterior, the passageways passing through the four recesses of each shoulder 52,54,56 and 58. Again, therefore, each passageway allows excess air pressure to be released from the interior of the bellows.

The tortuous nature of each passageway resists the escape of grease. Each passageway in the embodiment of Figures 6 to 8 is more tortuous in configuration than the passageway of the embodiment of Figures 3 to 5.

Claims

1. A protective bellows having a fixing collar at one of its ends for embracingly clamping to a cylindrical shaft forming part of a mechanism to be protected, the interior surface of the fixing collar having a plurality of axially separated circumferentially extending regions, each of these regions having an arcuately extending section in contact with the cylindrical shaft and at least one arcuately extending section spaced from the cylindrical shaft to provide a gap, the gaps of adjacent regions being angularly offset with respect to each other about the axis of the shaft so as together to form a passageway enabling the escape of excess pressure from within the bellows through the interior of the collar but resisting the escape of any lubricating grease within the bellows.

2. A bellows according to claim 1 and for protecting the mechanism of a transmission joint in a motor vehicle transmission, the bellows having a plurality of bellows turns integrally extending between the said fixing collar at one axial end of the bellows and a second fixing collar at the opposite axial end, the second collar having a relatively larger diameter for sealingly clamping to the outside of a casing of the transmission joint.

3. A bellows according to claim 1 or 2, in which each circumferentially extending region comprises a plurality of profiles extending from the interior surface of the first-mentioned fixing collar into contact with the cylindrical shaft and each forming a respective one of the arcuately extending sections in contact with the cylindrical shaft, the profiles within each said region being separated from each other by respective gaps forming respective ones of the arcuately extending sections spaced from the cylindrical shaft.

4. A bellows according to claim 3, in which the profiles are rectangular in elevation and cross-section.

5. A bellows according to claim 3 or 4, in which each profile is about 0.5mm in height, about 2mm in width and about 5mm in length.

6. A bellows according to claim 1 or 2, in which the interior surface of the fixing collar carries a plurality of axially spaced radially inwardly directed shoulders each interrupted by at least one arcuate gap such that each shoulder and its gap or gaps constitutes one of the circumferentially extending regions, each shoulder constituting one of the arcuately extending sections in contact with the shaft and the or each gap constituting a respective said arcuately extending section spaced from the shaft.

7. A bellows according to claim 6, in which there are two shoulders, each having a single gap, the gaps being angularly offset with respect to each other about the axis of the shaft by 1800.

8. A bellows according to claim 7, in which there are first, second and third shoulders spaced axially in that order, each shoulder having four said gaps, the gaps in each said shoulder being angularly offset with respect to 0 each other about the axis of the shaft by 90 , the gaps of the first and third shoulders being aligned with each other and the gaps of the second shoulder being angularly offset by approximately 450 with respect to the gaps of the first and second shoulders.

9. A protective bellows, substantially as described with reference to Figures 1 and 2 of the accompanying drawings.

10. A protective bellows, substantially as described with reference to Figures 3,4 and 5 of the accompanying drawings.

11. A protective bellows, substantially as described with reference to Figures 6,7 and 8 of the accompanying drawings.