GB2069656A

GB2069656A - Tensioning devices

Info

Publication number: GB2069656A
Application number: GB8101046A
Authority: GB
Original assignee: BorgWarner Ltd
Current assignee: BorgWarner Ltd
Priority date: 1980-02-11
Filing date: 1981-01-14
Publication date: 1981-08-26
Also published as: BR8100542A; MX151541A; DE3101279A1; GB2069656B; FR2475669B1; DE3101279C2; FR2475669A1

Abstract

A chain tensioning device comprises a pair of arms 2, 3 which are pivoted together and urged apart so that the arm 3 applies a tensioning force to a chain by means of a spring loaded cam block 5. Alternatively, a spring loaded block 32, Fig. 10, may be utilized with links 37 coupled between the block and the arms 25, 26. A catch disc 9 and rod 8 arrangement is provided to prevent return movement of the spring loaded block and hence collapse of the arm 3 under load reversals of the chain. <IMAGE>

Description

SPECIFICATION Tensioning devices This invention relates to tensioning devices for endless driving elements such as claims and belts.

A preferred tensioning device constructed in accordance with the invention (whose scope is defined in the appended claims) comprises a pivoted arm, an actuator slidably mounted on a rod, spring means biasing said actuator in one direction along said rod, said arm being caused to pivot in a tensioning sense in response to spring biased movement of said actuator in said one direction, and a catch disc mounted on said rod and tiltable into binding engagement therewith in response to return movement of said actuator against said spring bias along said rod, as would be caused upon return pivotal movement of said arm, by which to inhibit such return movement of said actuator and hence said return pivotal movement of said arm.

The actuator may take the form of a cam block which is urged by a compression spring in a direction such as to exert a wedge action upon the pivoted arm. Alternatively, a compression spring may be used to urge the actuator axially, and the actuator may be coupled to the pivoted arm by links which convert axial motion of the actuator into angular movement of the arm about its pivot axis, and vice versa.

In order that the invention may be well understood there will now be described some preferred tensioning devices, which are given by way of example of the invention, with reference to the accompanying drawings, in which: Figure 1 is a part sectioned plan view of a tensioning device; Figure 2 is an end elevation of the same tensioning device; Figure 3 is a side elevation section on the line ll-ll of Fig. 2; Figure 4 is a sectioned side elevation of an alternative tensioning device; Figure 5 is a side elevation of the alternative tensioning device directly tensioning a chain drive; Figure 6 is a side elevation of the same alternative tensioning device indirectly tensioning a chain drive; Figure 7 is a side elevation of a third tensioning device; Figure 8 is a section along the line Vlil-Vill of Fig. 7;; Figure 9 is an end elevation of the same tensioning device; Figure 10 is a part sectional side elevation of the same tensioning device; Figure 11 is a side elevation of the same tensioning device directly tensioning a chain drive; Figure 12 is a side elevation of an alternative version of the third tensioning device shown directly tensioning a chain drive; and Figure 13 is a side elevation of another modified version of the tensioning device of Figs. 7 to 11 when used to tension a longer chain drive.

As shown in Figs. 1 to 4, a tensioning device 1 has a pair of generally channelshaped lower 2 and upper 3 arms which are pivoted together at one end as by means of a pivot pin 4.

The arms 2 and 3 are pivoted apart by a cam block 5 which is mounted to slide longitudinally of the lower arm 2 and is urged by a compression spring 6 towards the pivotally interconnected ends of the arms.

The cam block 5 is apertured at 7 and is mounted at that aperture on a guide rod 8 which extends longitudinally of the lower arm 2. The compression spring 6 is mounted about the guide rod 8 and enters the cam block 5 to seat at its inner end against a catch disc 9 also mounted on that rod. Thereby, the spring 6 applies a biasing force through the catch disc 9 to the cam block 5.

The outer end of the spring 6 seats against a support flange 10 which is integral with the lower arm 2 and which slidably supports an outer end of the guide rod 8. The guide rod 8 at its inner end is slidably mounted in an axially immovable arm member 11 and has an enlarged head 1 2 by which to be prevented from withdrawal therefrom. The arm member 11 is fashioned as a channel bracket with its flanges 1 3 pivotally mounted about the pivot pin 4 and its web 1 4 receiving the guide rod 8.

If the tensioning device 1 is to be used to tension the timing chain of an engine, the lower arm 2 would be secured at its mounting apertures 1 5 in relation to the chain drive and the engine as may be convenient. The upper arm 3 would then be pivoted away from the lower arm 2 under the wedging action of the spring biased cam block 5. The upper arm 3 carries a shoe S rivetted to it and which directly engages the timing chain thereby to tension it.

With the aforesaid construction, the wedging action of the cam block 5 would be smooth and progressive, the block being free to slide along the guide rod 8, under the bias applied by the compression spring 6 through the catch disc 9, and also being guided by the base of the cam block 5 engaging and sliding along the base plate 1 6 of the lower arm 2.

The tensioning device 1 provides resistance to load reversals in the chain. Upon such a condition obtaining, return movement of the cam block 5 against the bias of the compression spring 6 and subsequent collapse of the upper pivoted arm 3 is prevented by the catch disc 9 which binds on the guide rod 8. At that time, the cam block 5, catch disc 9 and guide rod 8 can only move as one, and the abutment of the guide rod head 1 2 with the web 1 4 of the arm member 11 determines the extent by which the guide rod and hence the cam block can move rearwardly.

It should be noted that when the catch disc 9 is perpendicular with respect to the guide rod 8, it does not bind against the guide rod and relative longitudinal movement between the two can take piace. That condition obtains when the cam block 5 is being biased forwardly, by the compression spring 6 acting through the catch disc 9, to wedge open the upper arm 3. it is when the catch disc 9 is tilted relative to the guide rod 8 that it will bind against it, and that condition is ensured by the catch disc being located in a recess 1 7 in the cam block 5, the recess having an angled front face 1 8. Accordingly, upon the cam block 5 tending to rearwardly move along the guide rod 8, its angled recess face 1 8 will tilt the catch disc 9 into binding engagement with the guide rod.

To prevent overloading of the chain T, a degree of lost motion is provided in the tensioning device 1 by the guide rod 8 being free to slide in the web 1 4 of the arm member 11 to a predetermined limited extent which is governed bv the gap g between the head 12 of the guide rod and the pivot pin upon which the arm 3 pivots. Thus, although the cam block 5 and the catch disc 9 are free to slide along the guide rod 8 when they are being urged forwardly by the compression spring 6, there will be by frictional drag a tendency for the guide rod 8 also to move forwardly and slide within the bracket web 14 by the length of the gap g at which time the head 1 2 of the guide rod will abut the pivot pin 4, and the guide rod prevented from moving further inwardly.Accordingly, in the event of a load reversal condition obtaining, so causing the cam block 5 to move rearwardly and hence bind the then tilted catch disc 9 against the guide rod 8, since the guide rod 8 has previously been moved forwardly and hence its head 12 moved away from the bracket web 14, there is scope for rearward movement of the guide rod until its head 1 2 against abuts the web 14. Therefore, although the cam block 5, catch disc 9 and guide rod 8 can only be moved rearwardly as one, they can do so within the limit imposed by the srze uf the gap g.

As will be realized by suitable adaption of the construction, the size of the gap g can be varied. and hence the degree of lost motion available to the guide rod 8 likewise varied, as may be required in accordance with the oper acting characteristics of the engine to which the -tensioning device is to be fitted.

The tensioning device may be locked in its spring loaded condition for shipping purposes and unlocked aftei installation. For this purpose, a locking pin 1 9 is releasably inserted in apertured webs 2a of the arm 2 across the path of movement of the spring loaded cam block 5. The pin 1 9 would probably also be used when the tensioning device is to be removed for repair or replacement.

The catch disc 9 is provided with a pair of oppositely extending radial lugs 20 which, as shown in Fig. 1, project outwardly of the cam block 5. To release the tensioning device 1 from its locked spring loaded condition shown in Fig. 3, it is sufficient to insert a screwdriver (not shown) into the space 21 between the lower 2 and upper 3 arms and then twist the screwdriver in a clockwise sense as viewed in that Figure. To lock the tensioning device 1 in its spring loaded condition, a pulling force is applied by a suitable tool to the exposed lugs 20 so as to straighten the catch disc and pull the cam block 5 back against the bias of the compression spring 6, and the locking pin 1 9 inserted in the lower arm 2.

The upper and lower arms are preferably steel pressings. The cam block is preferably of a suitable synthetic plastics material. The guide rod and the catch disc would suitably be of metal and would be hardened to resist wear.

The alternative tensioning device 1A of Fig.

4 has functionally similar parts to the tensioning device which are indicated by like references and will only be described in relation to constructional differences of note.

One such difference is that the outer end of the spring 6 seats against a support plate 1 0a which is slidably mounted on the base plate 1 6 of the lower arm and which is also slidably mounted upon the guide rod 8 and held thereon against the bias of the spring by a clip retainer 1 orb. Instead of the inner end of the guide rod having an enlarged head, another clip retainer 1 2a is provided to determine the extent of rearward movement of the rod, the outer end face of the rod when engaging the arm pivot restricting forward movement. Further, a bush 4a is utilized instead of a pivot pin, and a standard bolt (not shown) would be passed through the bush and secured by a nut to hold the arms 2 and 3 and arm member 11 together.

The tensioning device 1 A may also be locked in its spring loaded condition. To this end, the top of the cam block 5 is notched at 22, and the upper arm 3 is provided with a depending lug 23. When the lug 23 is engaged in the notch 22, the bias of the compression spring 6 acting on the cam block 5 will angularly lock the upper arm 3 relative to the lower arm 2, as shown in Fig. 4. Therefore, it is the spring loading itself which is used to lock the alternative tensioning device in its spring loaded condition.

The shoe S of the tensioning device could be of rubber and directly moulded upon the upper arm 3. As can be seen from Fig. 5, the shoe S directly engages the timing chain T thereby to tension it. Alternatively, as shown in Fig. 6, the shoe could be omitted, and the upper arm 3 used to indirectly apply a tensioning force to the timing chain T by engaging a pivoted guide strip G which itself engages the chain, as is suitable for a long centre distance chain drive.

The tensioning device 1 could, of course, be functionally used, adapted as necessary, in the manner shown in Figs. 5 and 6.

Both the tensioning devices as so far described and illustrated comprise a pair of arms pivoted together at one end and which are urged apart by means of a cam block being spring loaded towards the pivot so as to exert a wedge action between the two arms. The tensioning device now about to be described does not use the wedging action of spring loaded cam block to urge a pivoted arm into tensioning engagement with a drive member but, instead, incorporates a member which is spring loaded away from the pivoted end of such an arm and which acts through a link means pivoted to the arm to swing the arm in a tensioning sense.The "link" embodiment of tensioning device is designed, as will appear, to give the facilities available with the "cam block" product of providing a resistance to load reversals in the driving element being tensioned and preventing overloading of the tensioned driving element.

As shown in Figs. 7 to 10, a tensioning device 24 has a pair of lower and upper arms 25 and 26, respectively, which are pivoted together at one end by a pivot pin 27. An intermediate arm 28 is pivotally mounted about the pin 27 and supports a rod 29 which extends generally parallel to the lower arm 25. The rod 29 has an enlarged end 30 which engages behind an abutment flange 31 of the arm 28 and is spaced a gap g from the pin 27. A block 32 is apertured by which to be slidably mounted on the rod 29 and is urged therealong away from the pin 27 by a compression spring 33. The spring 33 is mounted about the rod 29 to engage at one end the abutment flange 31 and to extend at the other end through an apertured region 34 of the block 32 to engage a catch disc 35 mounted in a transverse recess 36 of the block.Finally, a pair of links 37 are coupled between the block 32 and the upper arm 26 to pivot that arm relative to the lower arm 25 as the block is urged along the rod 29 by the spring 33 acting on the block via the catch disc 35. The links 37 are connected to the block 32 and the upper arm 26 by pivot pins 38 and 39, respectively.

When the tensioning device 24 is used to tension the timing chain of an engine, the lower arm 25 would be suitably mounted on the engine and affixed in position. The upper arm 26 would then be swung about the pivot pin 27 relative to the lower arm 25 under the biasing action of the coil spring 33 urging, through the catch disc 35, the block 32 along the rod 29, and the block, in turn, acting on the links 37 to move their lower ends forward and so exert a turning moment on the upper arm. The upper arm 26 may have a shoe in the form of a rubbing face 40 directly moulded upon it and of, for example, rubber or nylon. As shown in Fig. 11, that rubbing face 40 directly engages the timing chain T thereby tensioning it.

As will be realised, the spring loading decreases the more the spring 33 is extended.

However, the further the block 32 moves along the rod 29 under the spring bias, the more the links 37 are oriented towards the vertical. Therefore, the greater is the vertical component of the biasing force acting to swing the upper arm 26. Accordingly, the construction affords a degree of compensation for the gradual decrease in spring loading available to pivot the upper arm 26 and so tension the timing chain T.

The construction of the tensioning device 24 also provides resistance to load reversals in the timing chain T. First, any tendency of the upper arm 26 to collapse under a sudden reversal of movement of the chain will give rise to a vertical force component acting through the links 37 on the block 32 so causing the block to bind against the rod 29.

Furthermore, the block recess 36 has its front face 41 angled so that as the block 32 returns along the rod 29 against the bias of the spring 33, its angled face will tilt the catch disc 35 relative to the rod so that it will bind against it thereby preventing further return movement of the block.

Effectively, at that time the block 32, catch disc 35 and rod 29 can only move as one unit. Because of the gap g between the enlarged end 30 of the rod 29 and the pin 27, a restricted degree of rearward movement is available to the rod and hence the aforesaid unit. Thereby, a degree of lost motion is provided in the tensioning device serving to prevent overloading of the chain T, the size of the gap g determining the extent of that lost motion and hence the degree by which the upper arm 26 can collapse under the chain loading.

When the overloading condition is removed, the spring bias acting on the catch disc 35 will tilt the disc upright so freeing it from its locking frictional engagement with the rod 29 and will urge the block 32 along the rod so causing the links 37 to pivot the upper arm 26 outwardly. Through frictional drag the rod 29 will be carried forward until its enlarged end 30 again contacts the abutment flange 31, so that scope again exists for a degree of retraction of the upper arm 26 as determined by the size of the gap g.

The catch disc 35 and the block 32 would be suitably fashioned to enable the catch disc to be tilted upright by a suitable tool and so freed from its locked condition as and when required The links 37 act as levers and hence by varying their lengths different leverages can be imposed on the outer arm 26 for the same strength of compression spring. Thus, lighter springs could be used by increasing the lengths of the links 37. Varying the link length will also give different take ups for wear in the chain. Again, as the length of the chain is increased, the length of the upper arm 26 could also be increased in which case the links 37. acting as support struts, would be suitably lengthened to give support for the arm near to its free end.

It is not absolutely necessary that there should be a lower arm 25, and Fig. 1 2 shows a tensioning device 24A which omits such an arm. The function of a lower arm is to act as a support surface on which the block 32 can slide and as a means for mounting the tensioning device to the engine. The former function could be provided by suitable fashioning of the engine structure E or, for example, by a flange of an angle bracket affixed to that structure. The latter function could be served by mounting the ends of the pivot pin 27 in a support means integral with or affixed to the engine structure The upper arm 26 could also be omitted in the case of a long length chain T as shown in Fig. 1 3. Here, a guide strip G which is pivoted at P has a tensioning device 24B mounted near to its free end.That device is similar to the tensioning device of Figs. 7 to 10 except that the links 37 instead of being pivoted to an upper arm are pivoted at 39 direct to the guide strip G itself which is fashioned with depending lugs 42 for that purpose.

As an alternative, the tensioning device 24 of Figs 7 to 10 could have its upper arm 26 abut the guide strip G so that as the arm is pivoted outwards it will pivot the guide strip into tensioning engagement with the chain T.

As variations, the lower arm could be fashioned so as to wrap around the engine block rather than being a channel section, as shown. The intermediate arm could be formed as a suitably shaped block produced as a moulding or casting. The various components may be manufactured similarly to their counterparts in our aforementioned application.

When the intermediate arm is formed as a block the lost motion available to the guide rod could be provided by the rod having a head engaging in an elongated slot in the block. the length of the slot determining the degree of lost motion available.

Claims

1. A tensioning device for an endless driving element, comprising a pivoted arm. an actuator slidably mounted on a rnd spring means biasing said actuator in one direction along said rod, said arm being caused to pivot in a tensioning sense in response to spring biased movement of said actuator in said one direction, and a catch disc mounted on said rod and tiltable into binding engagement therewith in response to return movement of said actuator against said spring bias along said rod, as would be caused upon return pivotal movement of said arm, by which to inhibit said return movement of said actuator and hence said return pivotal movement of said arm.

2. A tensioning device as claimed in claim 1, including means permitting a limited extent of axial movement of said rod by which to permit a limited extent of return movement of said actuator when said catch disc is tilted into binding engagement with said rod and hence permit a limited degree of return pivotal movement of said arm.

3. A tensioning device as claimed in claim 2, wherein said actuator is in the form of a cam block which when biased by said spring means in said one direction exerts a wedging action upon said pivoted arm by which to pivot said arm in said tensioning sense.

4. A tensioning device as claimed in claim 3, wherein said spring means is a compression spring mounted about said rod and biasing said actuator towards the pivot of said arm.

5. A tensioning device as claimed in claim 4, wherein said actuator has an angled face adjacent said catch disc such as to effect said tilting of said catch disc into said binding engagement with said rod in response to said return movement of said actuator.

6. A tensioning device as claimed in claim 5, wherein said compression spring imparts its spring bias to said actuator via said catch disc.

7. A tensioning device as claimed in claim 6, wherein said catch disc is positioned in a recess in said actuator, said angled face defining one wall of said recess, said compression spring extending through the opposite wall of said recess to impart its spring bias direct to said catch disc and thence to said actuator.

8. A tensioning device as claimed in any of claims 3 to 7, including an arm member mounted on a pivot pin and slidably supporting an inner end of said rod, said rod having stop means thereon and cooperating with said pivot pin and said arm member by which together therewith to constitute said rod limiting movement means to permit said limited extent of axial movement of said rod.

9. A tensioning device as claimed in claim 8, wherein said pivoted arm is also mounted on said pivot pin by which to be pivotable in said tensioning and return senses.

10. A tensioning device as claimed in claim 9, including a second arm having means by which to mount said tensioning device to a support, said second arm also being mounted on said pivot pin, said cam block being supported on said second arm when exerting its said wedging action on said pivoted arm.

11. A tensioning device as claimed in claim 10, including an abutment member integral with said second arm and against which said spring means reacts when imparting its bias to said actuator, said abutment member slidably supporting an outer end of said rod.

1 2. A tensioning device as claimed in claim 1 0, including an abutment member slidably supported on said second arm and itself slidably supporting an outer end of said rod, said spring means reacting against said abutment mernber when imparting its bias to said actuator.

1 3. A tensioning device as claimed in any of claims 10 to 12, including releasable locking means for locking said pivoted arm in its spring loaded condition.

14. A tensioning device as claimed in claim 13, wherein said locking means comprises a pin releasably positioned in said second arm across the path of spring biased movement of said actuator.

1 5. A tensioning device as claimed in any of the preceding claims, including lug means on said catch disc and located for engagement by a tool by which said catch disc may be straightened from its tilted attitude to permit said return pivotal movement of said arm.

16. A tensioning device as claimed in any of the preceding claims, wherein said pivoted arm carries a shoe which, in use of said tensioning device, directly engages the endless driving element to tension same.

1 7. A tensioning device as claimed in any of claims 1 to 15, wherein said pivoted arm, in use of said tensioning device, indirectly applies a tensioning force to the endless driving element by directly engaging a pivoted guide strip which itself directly engages the driving element.

1 8. A tensioning device as claimed in claim 2, including link means coupled between said actuator and said pivoted arm by which to convert axial movement of said actuator into pivotal movement of said arm, and vice versa.

1 9. A tensioning device as claimed in claim 1 8, wherein said spring means is a compression spring mounted about said rod and biasing said actuator away from the pivotal axis of said arm.

20. A tensioning device as claimed in claim 19, wherein said actuator has an angled face adjacent said catch disc such as to effect said tilting of said catch disc into said binding engagement with said rod in response to said return movement of said actuator.

21. A tensioning device as claimed in claim 20, wherein said compression spring imparts its spring bias to said actuator via said catch disc.

22. A tensioning device as claimed in claim 21, wherein said catch disc is positioned in a recess in said actuator, said angled face defining one wall of said recess, said compression spring extending through the opposite wall of said recess to impart its spring bias direct to said catch disc and thence to said actuator.

23. A tensioning device as claimed in any of claims 1 8 to 22, including an arm member mounted on a pivot pin and slidably supporting an ainner end of said rod, said rod having stop means thereon cooperating with said pivot pin and said arm member by which together therewith to constitute said rod Imiting movement means to permit said limited extent of axial movement of said rod.

24. A tensioning device as claimed in claim 23, wherein said spring means is mounted between said arm member and said catch disc.

25. A tensioning device as claimed in claim 23 or claim 24, wherein said pivoted arm is also mounted on said pivot pin by which to be pivotable in said tensioning and return senses.

26. A tensioning device as claimed in claim 25, including a second arm having means by which to mount said tensioning device to a support, said second arm also being mounted on said pivot pin, said actuator being slidably mounted on said second arm.

27. A tensioning device as claimed in any of claims 1 8 to 26, wherein said pivoted arm carries a shoe which, in use of said tensioning device, directly engages the endless driving element to tension same.

28. A tensioning device as claimed in claim 23 or claim 24, wherein said pivoted arm has its pivotal axis remote from said pivot pin and constitutes a guide strip which, in use of said tensioning device, applies a tensioning force direct to the endless driving element.

29. A tensioning device as claimed in claim 28, including a second arm having means by which to mount said tensioning device to a support, said second arm also being mounted on said pivot pin, said actuator being slidably mounted on said second arm.

30. A tensioning device as claimed in any of claims 1 8 to 26, wherein said pivoted arm, in use of said tensioning device, indirectly applies a tensioning force to the endless driving element by directly engaging a pivoted guide strip which itself directly engages the driving element.

31. A tensioning device for an endless driving element, comprising a pivoted arm, a cam block supported for axial movement, a compression spring biasing said cam block in one axial direction by which said cam block exerts a wedging action upon said pivoted arm to pivot said arm in a tensioning sense, and means to inhibit return axial movement against the bias of said compression spring by which to inhibit return pivotal movement of said arm. said inhibit means comprising a rod and co-operating catch disc locking means.

32. A tensioning device for an endless dnving element, comprising a pivoted arm, an actuator supported for axial movement. a compression spring biasing said actuator in one axial direction. and link means coupled between said actuator and said pivoted arm by which to exert a pivotal force on said arm in response to said spring biased movement of said actuator.

33. A tensioning device as claimed in claim 32. including a rod and cooperating catch disc for inhibiting return axial movement of said actuator against the spring bias by which to inhibit return pivotal movement of said arm.

34. Any of the tensioning devices substantially as herein described with reference to the accompanying drawings