GB2353836A

GB2353836A - Friction clutch with wear indicator

Info

Publication number: GB2353836A
Application number: GB0027010A
Authority: GB
Inventors: Wolfgang Grospietsch; Gunter Neugebauer
Original assignee: Mannesmann Sachs AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1996-09-18
Filing date: 1997-09-18
Publication date: 2001-03-07
Anticipated expiration: 2017-09-18
Also published as: GB0027010D0; GB2353836B

Abstract

A pull-to-release friction clutch has a wear indicator comprising an axial eye 89, mounted on an outer surface of an actuating cylinder 50, a first marking element formed as a guide sleeve 91 which is mounted with frictional clamping in the eye 89 and a second marking element formed as a pin 93 slidably positioned in the guide sleeve 91. Spring 97 urges, via flange 95, pin 93 against stop plate 73 so that the pin 93 follows the movement of a withdrawal piston. When the clutch is new and either engaged or disengaged, the pin 93 projects beyond guide sleeve 91 by an amount X. As the clutch wears the amount by which the pin 93 projects reduces and becomes substantially zero when the maximum permissible clutch wear is reached, this may be viewed through an opening (1a, fig 1) in a bell housing (1). In other embodiments a spacer (55) or a gauge (fig 5) may be employed and the pin (93', fig 4) may be riveted to the stop plate (73').

Description

2353836 FRICTION CLUTCH WITH WEAR INDICATOR The invention relates to a

friction clutch assembly for a motor vehicle of the kind mounted in the vehicle drive train between an engine and a gearbox in a housing secured to the gearbox, the housing containing a friction clutch, a clutch withdrawal mechanism for engagement and disengagement of the clutch, the withdrawal mechanism being movable by an actuating mechanism between two predetermined limiting positions relative to the gearbox, and a means for indicating the wear of the friction clutch. Friction clutch assemblies of the kind set forth may be used as starting clutches or bypass clutches of hydraulic torque converters.

WO 95109311 shows an assembly of the kind set forth in which an indicating element coupled to the withdrawal piston of a withdrawal pistonlcylinder unit coaxial with the clutch projects through an opening in the housing. The reciprocating movement of the withdrawal. piston is indicated on the outside of the housing. However without accurate measurement of the amount of movement of the indicating element it does not reveal directly whether or not the clutch is fully worn.

For servicing, even under unfavourable installation positions of the clutch and poor visibility for the servicing personnel, it should be possible rapidly and easily to determine to what extent the clutch is worn and in particular whether the clutch is so badly worn that it must be replaced. The device of WO 95109311 only indicates a relative state of wear. To determine whether or not the clutch has achieved maximum permissible wear the degree of inclination of the indicating element relative to the surface of the housing must be measured. Manual measurement can be extremely difficult in poor visibility and unfavourable installation 2 positions of the clutch. Alternatively, an electric display coupled to the indicating element can be used, but the electric display is expensive.

Accordingly it is an aim of the invention to provide a friction clutch assembly of the kind set forth which allows a rapid and clear monitoring of the state of wear of the clutch, in particular the maximum permissible wear of the clutch.

According to the present invention, in a friction clutch assembly of the kind set forth the means for indicating wear comprises two marking elements, a first marking element defining a predetermined position relative to the gearbox and second marking element defining a predetermined position relative to the withdrawal mechanism such that on wear of the clutch the position defined by the second marking element moves towards the position defined by the first marking element, the arrangement being such that in one of the limiting positions the spacing between the predetermined positions defined by the marking elements with a new clutch is substantially equal to the travel of the withdrawal mechanism at maximum permissible clutch wear, and with a fully worn clutch is substantially equal to zero, and in which the clutch is a pullto-release clutch with the actuating mechanism including a withdrawal piston, and the second marking element is slidable with the withdrawal piston relative to the first marking element, such that on maximum wear and with the clutch withdrawn, the amount by which the second marking element projects beyond the first marking element is substantially equal to zero.

In a pull -to -release clutch, the withdrawal piston disengages the clutch by movement in a direction away from the engine. The state of wear is measured with the clutch withdrawn. The checking of the state of 3 wear takes place simply by determining the projection of the second marking element beyond the first. If the second marking element projects beyond the first the clutch is still operable, but if the amount of projection is substantially zero it is worn and must be replaced. No more detailed measurement of the spacing is necessary because a substantially zero spacing can be determined directly without any measurement, for example just be looking. No electric display is necessary, although an additional auxiliary means is not excluded.

For adjusting the spacing at least one of the marking elements, in particular the first element, may be adjustable in the direction of movement of the withdrawal mechanism, but adapted to be locked firmly during operation of the clutch. The adjustable marking element may be guided to slide in the direction of movement of the withdrawal mechanism and locked by friction.

In order to simplify adjustment preferably a first stop is- provided on one of the marking elements and a second stop is provided fixed relative to the other marking element, and with a new clutch in the one of the two limiting positions, the stops are adapted to engage, directly or through a spacer element which is removable for operation, in order to adjust the spacing of two marking elements. The spacer element can be detachably secured on the housing or the pre-assembled withdrawal mechanism. The first stop is preferably provided on the first marking element, and the second stop is preferably fixed relative to the withdrawal mechanism.

Preferably one marking element has a stop against which, by the mounting of the housing on the clutch or an initial withdrawal movement 4 of the clutch, it is forcibly adjusted to set the spacing relative to the other marking element.

In this way, on assembly of the housing onto the clutch, such as in manufacture or after replacement of the clutch during servicing, the positions of the marking elements are defined, taking into account manufacturing and installation tolerances, at a spacing which corresponds to the maximum permissible wear travel of the clutch. No subsequent adjustment is needed. This ensures that when the spacing between the two elements is reduced substantially to zero, the maximum wear of the clutch is indicated accurately.

The wear indicating means is independent in principle of the kind of clutch actuating mechanism, whether it be pure mechanical actuation or hydraulic actuation. Furthermore the indicating means is preferably mounted within the housing. The advantages of the invention are particularly marked where there is a hydraulic pistonlcylinder withdrawal unit mounted coaxially with the clutch, because such a unit is inside the housing and difficult to access from outside. Thus any monitoring from outside of the position of the withdrawal piston, dependent on wear of the clutch, is only possible with great difficulty. Where the actuating mechanism has a withdrawal piston and cylinder unit mounted coaxially with the clutch, the indicating means is mounted on the outside of the cylinder to be visible through an opening in the housing.

The second marking element may be secured to, or spring-loaded into engagement with a surface associated with the piston.

When the state of wear is to be measured with the clutch disengaged, the first marking element is preferably mounted slidably with a frictional clamping engagement in an eye on the withdrawal cylinder, and on the mounting of the clutch in the housing or on the initial withdrawal of the clutch, the first marking element is moved to a position in which an amount by which the second marking element projects beyond the first marking element corresponds to the spacing, and is then clamped frictionally in this position.. The spacing corresponds to the maximum wear travel of the clutch, and as the first marking element is frictionally held in the eye, on further actuation of the clutch it no longer moves relative to the second marking element. This provides a precise automatic setting of the spacing for the maximum wear travel, taking into account any possible manufacturing and installation tolerances of the clutch and of the piston/cylinder withdrawal unit.

For assembly of the withdrawal cylinder onto the pull-to-release clutch the cylinder must engage behind a central opening of a clutch diaphragm spring, on that side remote from the withdrawal cylinder, in order to be able to withdraw the diaphragm spring by a pulling action. The withdrawal cylinder usually has a radially outwardly-loaded ring spring which, on assembly of the withdrawal cylinder to the clutch, is forced through the central opening in the diaphragm spring under compression. The withdrawal piston is pushed by this back into the cylinder, which can influence the initial setting of the spacing. In order to avoid this at least one clamping pin is held on the withdrawal cylinder in a frictional clamping engagement, but movable axially of the clutch, the clamping pin supporting the withdrawal piston, during assembly to the clutch, in the withdrawal direction against the axial forces arising during assembly, on fo-rcing the ring spring through the central opening.

Alternatively only the clamping pin is provided on the withdrawal cylinder, so that on the first withdrawal of the pull-to-release clutch the 6 pin takes up a positive relative to the withdrawal piston which takes into account manufacturing and installation tolerances of the clutch and of the withdrawal cylinder. The spacing between an end face of the clamping pin remote from the clutch and a reference face of the withdrawal piston can be determined directly according to the construction of the withdrawal mechanism or alternatively by a measurement gauge which is adapted to be placed on the reference face through an opening in the housing for checking the wear. A scale can be provided on the gauge. At the point on the scale which corresponds to full wear of the clutch there may be a marking surface which on full wear of the clutch is flush with the end face of the clamping pin. The invention also relates to a method of measuring wear by means of this gauge.

According to a second aspect of the present invention, a method of measuring the wear of a friction clutch of the kind set forth in which the withdrawal mechanism is operated by a withdrawal piston and cylinder unit, the method comprising providing a mark on a marking element arranged fixed relative to the housing, engaging a gauge against the withdrawal piston through an opening in the housing, a spacing between the mark on the marking element and a further mark on the inserted gauge being substantially equal to zero on maximum wear of the clutch, and determining whether or not the mark on the gauge is flush with the mark on the marking element.

Various embodiments of a friction clutch assembly are illustrated by way of example in the accompanying drawings, in which:

7 Figure 1 shows a friction clutch assembly which does not fall within the scope of the invention, with a partial section through the axis of a wear indicating means on a withdrawal cylinder arranged concentric with a pushto-release clutch; Figure 2 shows a variant of the embodiment of Figure 1; Figure 3 shows a friction clutch assembly falling within the scope of the invention, with a-partial sectional view of the indicating means on a withdrawal cylinder arranged coaxially with respect to a pull-to-release clutch; Figure 4 shows a variant of the embodiment of Figure 3; and Figure 5 shows a further variant of the embodiment of Figure 3.

Figure 1 shows a means for indicating wear of a friction clutch 3 for a motor vehicle which falls outside the scope of the invention. The clutch 3 is mounted in a clutch bell housing 1 between an internal combustion engine (not shown, but on the left in Figure 1) and a gearbox (not shown but on the right in Figure 1). The friction clutch 3 connects a crankshaft of the engine on an axis A-A to an input shaft of the gearbox, also on the axis A-A. An hydraulic piston and cylinder unit 5 forms an actuating mechanism for the clutch. The unit 5 is arranged on the axis A- A between the clutch 3 and the clutch housing 1. The cylinder 7 of the unit 5 is screwed into a wall 9 of the bell housing 1 furthest from the clutch. The cylinder 7 comprises an outer cylinder support 11 and an inner cylinder tube 13. The cylinder support 11 and the cylinder tube 13 are sealed with respect to one another by means of an 0-ring 15. An annular pressure space 17 open towards the clutch side is formed radially 8 between them. The space 17 is connected through a connection 23 to a source of hydraulic pressure (master cylinder), not shown. A tubular withdrawal piston 19 slides in the pressure space 17 and is guided over its entire length by the cylinder tube 13. The piston 19 is sealed with respect to the pressure space 17 in a pressure-tight manner by means of an annular seal 21.

The clutch end (left hand end) of the withdrawal piston 19 carries a radially outwardly projecting flange 25. A compression spring 27 is inserted between the flange 25 and an axially opposing face of the cylinder support 11, and urges the piston 19 towards the clutch. Under the action of the spring 27 the flange 25 engages against a non-rotating bearing race 29 of a ball-bearing thrust bearing 31, which is sealed against the ingress of dust. The bearing 31 forms a withdrawal mechanism for the clutch 3, movable between two limiting positions relative to the gearbox by the actuating unit 5. A bearing race 33 of the withdrawal bearing 31 engages a diaphragm spring 35 of the friction clutch 3. A retaining sleeve 37 holds the bearing 31 so that it cannot be lost but is slidable radially on the flange 25 of the withdrawal piston 19.

A pressure washer 39 is accommodated axially between the flange 25 and the bearing race 29. Introduction of hydraulic fluid into the pressure space 17 through the connection 23 moves the piston 19 out of the cylinder 7 to the left in Figure 1. The piston 19 acts through the thrust bearing 31 to urge the diaphragm spring 35 towards the engine, thereby disengaging the clutch (push-to-release clutch).

A radial external surface of the piston 19 which is exposed as it emerges from the cylinder 7 is protected by two telescopic dust-shielding sleeves 41,43 which are movable axially. The outer telescopic part 41 carries a radial flange 45 which is clamped between the spring 27 and the 9 flange 25 of the piston 19, so that it follows the inward and outward movement of the piston 19.

The flange 45 of the outer dust-shielding sleeve 41 forms a movable marking element 47 of a wear indicator for the clutch 3. A cylindrical radially resilient guide pin 49 projects away from the cylinder support 11 towards the clutch parallel to the axis A-A. The pin 49 is arranged radially outside the element 47 but with a small spacing from it.

A slide 51 is slidably mounted on the guide pin 49, with a frictional clamping engagement so that it slides with difficulty. An end face 53 of the slide 51 adjacent the clutch forms a marking element 53 fixed relative to and axially aligned with the marking element 47, which is fixed relative to the withdrawal mechanism, but movable with it. Between the two marks 47, 53, there is a gauge or template in the form of a spacer element 55 having a predetermined axial length X. The spacer element 55 is releasably secured by means of a flexible U-shaped tongue 57 on the end of the guide pin 49 furthest from the clutch. On assembly of the unit containing the bell housing 1, the actuating unit 5 and the withdrawal bearing 31 onto the engine, on the crankshaft on which the clutch 3 is already mounted, the withdrawal piston 19 is pushed in the direction of the axis A-A against the action of the spring 27. The piston 19 takes the outer sleeve 41 and its mark 47 with it. As the clutch moves into the engaged position the mark 47 pushes the spacer element 55 and the slide 51 (overcoming its frictional engagement) towards the gearbox, to the right in Figure 1. With the assembly completed and the clutch engaged the slide 51 is now clamped frictionally on the guide pin 49 in a position such that its end face 53 forms a fixed mark axially aligned with the movable mark 47, and spaced from it by a spacing X. Its position depends on the prevailing manufacturing and assembly tolerances. To complete assembly the spacer element 55 is subsequently removed through a closable viewing opening Ia in the clutch housing 1.

Alternatively the spacing X can be set by means of a tool through the opening Ia after assembly of the bell housing 1.

The spacing X corresponds to the maximum permissible wear travel of the clutch 3. With increasing wear of the clutch 3, and with the clutch engaged, the marks 47, 53 approach one another. When the spacing is reduced substantially to zero the clutch is worn out and must be replaced.

This can be seen without difficulty through the viewing opening Ia. To check whether the clutch is ready for replacement or not it is sufficient to determine whether the spacing between the two marks has been reduced to zero or not. It is not necessary to make any measurement of the spacing between the marks. Any spacing between the marks indicates there is some travel left for wear.

Figure 2 also falls outside the scope of the invention, and shows a modification of the wear indicator of Figure 1 for a push-to-release clutch. Corresponding reference numerals have been applied to corresponding parts.

In Figure 2, before assembly of the bell housing I and the actuating unit 5 onto the engine with a pre-assembled new clutch a spacer element 55a is mounted on the guide pin 49. The element 55a has an axial length corresponding to the maximum permissible wear travel X of the clutch. On assembly the spacer element 55a is pushed along the pin 49 by the mark 47 towards the gearbox. Its end face 55a' adjacent the gearbox now takes up a position on the guide pin 49 which is dependent 11 on manufacturing and installation tolerances and which is distant from the movable mark 47 by the amount of the wear travel X.

Paint or other colour is then applied to the guide pin 49 in the region of the end face 55a' of the spacer element 55a. The resulting colour boundary 53a forms the fixed mark. The spacer element 55a is then removed through the viewing opening la shown in Figure 1.

Figures 3 to 5 show embodiments of the wear indicator for a so- lo called pull-to-release clutch falling within the scope of the invention. In Figure 3 an actuating unit 50 is arranged coaxially with the crankshaft axis A-A of an internal combustion engine (not shown but on the left of Figure 3) and an input shaft of an associated gearbox (not shown but on the right of Figure 3) between the clutch and the gearbox. The actuating unit 50 disengages the clutch by pulling the radially inner periphery of the diaphragm spring 60 of the clutch towards the gearbox, to the right of Figure 3.

The actuating unit comprises a piston and cylinder unit. The cylinder carries on its end remote from the clutch a flange 71 by which it is mounted in a bell housing. The piston (not shown) projects from the open end of the cylinder 50 nearest the clutch. The piston carries a stop plate 73 engaging outwards over the cylinder 50, and a withdrawal bearing 75 with a groove 77 in which there is arranged a radially outwardly pre-loaded ring spring 79.

On assembly of the bell housing with the pre-mounted actuating unit, to a withdrawal bearing 75 and ring spring 79 on the engine with the preassembled friction clutch, the ring spring 79 is pushed through a central hole 81 of an inner flange 83 of the diaphragm spring 60 and 12 consequently is squeezed radially inwards. After passing through the flange 83 the spring snaps outwardly to engage behind it, and can thereby transmit tension forces of the withdrawal piston to the spring 60 in order to disengage the clutch.

Two axial eyes are arranged integrally on the outer surface of the withdrawal cylinder 50, spaced apart by 1801. Radially resilient clamping pins 87 are inserted frictionally in the eyes 85 and on the insertion of the withdrawal bearing 75 together with the spring 79 through the central hole 81 they support the stop plate 73 against the resulting axial forces.

The first time the clutch is withdrawn the clamping pins 87 are pushed towards the gearbox by a distance such that they do not affect subsequent operation of the clutch depends on the currently existing tolerances. After a clutch replacement the pins 87 must be moved back into their original position, in which they extend to the left, in order to allow the spring 79 to snap behind the flange 83 again.

The outer surface of the cylinder 50 has a further integral axial eye 89 in which a guide sleeve 91 is slidably mounted but with a frictional clamping engagement. The guide sleeve 91 is less difficult to move than the pin 87. A pin 93 is mounted to slide in the sleeve 91. The pin 93 has an annular flange 95 spaced from the end adjacent the clutch. A compression spring 97 is mounted round the guide sleeve 91 between an end face 95a of the flange 95 and the face of the further eye 89 adjacent the clutch. The spring 97 urges the pin 93 against the stop plate 73 so that the pin 93 follows the movement of the withdrawal piston. The axial length of the pin 93 from the face 95a of the flange 95 to its end 99 remote from the clutch is equal to the length of the guide sleeve 91 plus the maximum wear travel X of the clutch.

13 The first time the clutch is withdrawn the face 95a of the flange 95 engages the face 91a of the guide sleeve 91, and moves the guide sleeve 91. The amount by which the end face 99 of the pin projects beyond an end 101 of the guide sleeve 91 remote from the clutch accordingly corresponds to the maximum wear travel X. On subsequent engagement of the clutch the guide sleeve 91 remains frictionally held in the eye 89. The guide sleeve 91 is set the first time the clutch is withdrawn depending on the prevailing installation tolerances. No further adjustment is required.

With increasing wear of the clutch the amount by which the end 99 of the pin projects beyond the end 101 of the guide sleeve 91 becomes smaller. When the projection is reduced substantially to zero the clutch is then fully worn and must be replaced. The amount of the projection can be seen through a viewing opening (not shown) such as opening la in Figure 1.

The function of one of the pins 87 can be taken by the pin 93 and the guide sleeve 91. However this makes it more difficult to return this pin to its position after the replacement of the clutch because the pin which projects towards the gearbox may hinder access to the guide sleeve 91.

Figure 4 shows a modification of Figure 3. Here the pin 93' is riveted to the stop plate 73' and consequently follows the withdrawal movement of the piston. The wear travel X of the clutch corresponds to an axial spacing between the end face 99' of the pin 93' remote from the clutch and an end face 87a' of the pin 87' remote from the clutch. A 14 spacing X which is reduced substantially to zero with the clutch withdrawn shows that the clutch is worn out.

Figure 5 shows a further modification of Figure 3, in which the pin 93 and the guide sleeve 91 of Figure 3 are eliminated. For checking wear with the clutch withdrawn a gauge 100 is introduced into the housing and an engaging face 101 of the gauge 100 which is nearest the clutch is placed against a face 73a" of the stop plate 7Y' remote from the clutch.

In the region of the end 87a" of the pin 87 remote from the clutch the gauge 100 carries a scale 103 against which the position of the end face 87a" can be read off. A matching of the end face 87a" of the pin with a corresponding mark 105 on the scale 103 or of a face of this gauge parallel to the end face 87"a of the pin shows the maximum wear of the clutch. is

Claims

1. A friction clutch assembly of the kind set forth, in which the means for indicating wear comprises two marking elements, a first marking element defining a predetermined position relative to the gearbox and a second marking element defining a predetermined position relative to the withdrawal mechanism such that on wear of the clutch the position defined by the second marking element moves towards the position defined by the first marking element, the arrangement being such that in one of the limiting positions the spacing between the predetermined positions defined by the marking elements with a new clutch is substantially equal to the travel of the withdrawal mechanism at maximum permissible clutch wear, and with a fully worn clutch is substantially equal to zero, and in which the clutch is a pull-to-release clutch with the actuating mechanism including a withdrawal piston, and the second marking element is slidable with the withdrawal piston relative to the first marking element,- such that on maximum wear and with the clutch withdrawn, the amount by which the second marking element projects beyond the first marking element is substantially equal to zero.

2. An assembly as claimed in claim 1, in which at least one of the marking elements is adjustable in the direction of movement of the withdrawal mechanism but is adapted to be located firmly during the operation of the clutch.

3. An assembly as claimed in claim 2, in which the adjustable marking element is guided to slide in the direction of movement of the withdrawal mechanism and is locked by friction.

16

4. An assembly as claimed in claim 2 or claim 3, in which the first marking element is adjustable.

5. An assembly as claimed in one of claims 2 to 4, in which a first stop is provided on one of the marking elements, and a second stop is provided fixed relative to the other marking element, and with a new clutch, in one of the two limiting positions, the stops are adapted to engage directly in order to adjust the spacing of the two marking elements.

6. An assembly as claimed in claim 5, in which the first stop is provided on the first marking element, and the second stop is fixed relative to the withdrawal mechanism.

7. An assembly as claimed in any of claims 2 to 6, in which one marking element has a stop against which, by the mounting of the housing on the clutch or by an initial withdrawal movement of the clutch, it is forcibly adjusted to set the spacing relative to the other marking element.

8. An assembly as claimed in any preceding claim, in which the actuating mechanism has a withdrawal piston and cylinder unit mounted coaxially with the clutch and the means are mounted on the outside of the withdrawal cylinder to be visible through an opening in the housing.

9. An assembly as claimed in any preceding claim, in which the second marking element is secured to, or is spring-loaded into engagement with a surface associated with the piston.

10. An assembly as claimed in claim 9, in which the second marking 30 element is slidable coaxially in the first marking element.

17

11. An assembly as claimed in any preceding claim, in which the first marking element is mounted slidably with a frictional clamping engagement in an eye on the withdrawal cylinder, and on the mounting of the clutch in the housing or on the initial withdrawal of the clutch, the first marking element is moved to a position in which an amount by which the second marking element projects beyond the first marking element corresponds to the spacing, and is then clamped frictionally in this position.

12. An assembly as claimed in claim 11, in which the second marking element carries a follower which takes with it the first marking element in its predetermined position on the mounting of the clutch in the housing or on the initial withdrawal of the clutch.

13. An assembly as claimed in any preceding claim, in which a radially pre-stressed clamping pin is held in a frictional clamping engagement on the withdrawal cylinder to be movable axially of the clutch, supporting the withdrawal piston against axial forces in the direction of withdrawal arising during assembly on pressing a radially outwardly -loaded ring spring through a central opening in the clutch.

14. An assembly as claimed in claim 13, in which the second marking element comprises a slide movable with the withdrawal piston parallel to the clamping pin, the spacing being determined by the distance between the end faces of the clamping pin and the slide remote from the clutch.

15. An assembly as claimed in claim 13, in which the spacing between an end face of the clamping pin remote from the clutch and a mark on a gauge adapted to be placed on a reference face of the withdrawal piston 18 through an opening in the housing for checking wear is substantially equally to zero on maximum wear of the clutch.

16. A method of measuring the wear of a friction clutch of the kind set forth, in which the withdrawal mechanism is operated by a withdrawal piston and cylinder unit, the method comprising, providing a mark on a marking element arranged fixed relative to the housing, engaging a gauge against the withdrawal piston through an opening in the housing, a spacing between the mark on the marking element and a further mark on the inserted gauge being substantially equal to zero on maximum wear of the clutch, and determining whether or not the mark on the gauge is flush with the mark on the marking element.

17. A friction clutch assembly of the kind set forth substantially as described herein with reference to and as illustrated in Figure 3 of the accompanying drawings.

18. A friction clutch assembly of the kind set forth substantially as described herein with reference to and as illustrated in Figure 4 of the accompanying drawings.

19. A friction clutch assembly of the kind set forth substantially as described herein with reference to and as illustrated in Figure 5 of the accompanying drawings.