CA2229943C

CA2229943C - Tension device for traction means with cone-type sliding bearing

Info

Publication number: CA2229943C
Application number: CA002229943A
Authority: CA
Inventors: Peter Giese; Werner Petri; Mathis Racke
Original assignee: INA Waelzlager Schaeffler OHG
Current assignee: INA Waelzlager Schaeffler OHG
Priority date: 1995-11-02
Filing date: 1996-06-20
Publication date: 2002-08-13
Anticipated expiration: 2016-06-20
Also published as: EP0858563A1; JP3657995B2; DE29518314U1; CA2229943A1; DE59603805D1; KR19990066962A; ATE187232T1; DE19540706A1; JPH11515079A; KR100403522B1; WO1997016658A1; EP0858563B1; ES2142635T3

Abstract

A tension device for traction means includes a tension arm (1) having a tension roller (2) spring-loaded towards the traction means. The tension arm (1) is rotatably supported relative to a housing (4) by means of a sliding bearing (3). The sliding bearing surfaces (7, 12) are formed as parallel conical surfac es extending concentric to the tension arm shaft (5). A helical torsion spring (14) wound along the tension arm axis (5) and supported, on the one hand, by a tension arm fixed support (15) and, on the other hand, by a stationary support (16) exerts an axial force (F D) which is introduced into the slidin g bearing (2) as a reaction force (F R) perpendicular to the sliding bearing surfaces (7, 12).

Description

FIELD OF THE INVENTION

7 The present invention refers to a tension device for traction means such as 8 belts and chains, including a tension arm which carries a tensioning member, 9 preferably a tension roller, and is spring-loaded against the traction means, with the tension arm being rotatably supported relative to a stationary element by 11 means of a sliding bearing which exhibits sliding bearing surfaces in the form of 12 conical surfaces in parallel relationship to one another and positioned 13 concentrically to the tension arm shaft, and a helical torsion spring wound about 14 the tension arm shaft and supported, on the one hand, on a support secured on the tension arm, and on the other hand, on a stationary support.

19 A tension device of this type is known e.g. from US-A 46 98 049. The tension arm shaft and the stationary element each have a conical surface, with a 21 conical sliding bearing bush being disposed between these two conical surfaces.
22 A radial play in the sliding bearing caused by abrasive wear on the sliding bearing 1 surfaces requires that the conical surfaces of the sliding bearing be pushed 2 manually toward each other in axial direction and positioned until the radial play in 3 the sliding bearing again lies within an admissible tolerance range.

SUMMARY OF THE INVENTION

7 It is an object of the present invention to improve a tension device of this 8 type such that an automatic adjustment of the sliding bearing surfaces is ensured 9 in a simple manner. In accordance with the present invention, it is proposed to introduce the axial force exerted by the helical torsion spring, which is clamped 11 between these supports, into the sliding bearing in form of a reaction force acting 12 perpendicular to the sliding bearing surfaces. This arrangement has numerous 13 advantages. Firstly, it is ensured that upon abrasive wear of the sliding bearing 14 surfaces the axial force, i.e. the reaction force acting perpendicular to the sliding bearing surfaces, pushes the sliding bearing surfaces together so as to effect a 16 clearance-free sliding bearing. At constant angle of inclination of the sliding 17 bearing surfaces relative to their axis, the reaction force via the axial mounting 18 and the axial force of the helical torsion spring can be varied.
Frequently, conical 19 sliding bearing bushes of plastic material are provided which are subject to an increased wear by sliding friction during frictional contact as a consequence of the 21 perpendicular reaction force. This wear by sliding friction is compensated without 22 any problems by a self-adjusting motion of the tension arm and the stationary 1 element, respectively. When forming the tension arm shaft and the stationary 2 element each with a conical surface, with the conical sliding bearing bush being 3 disposed between these conical surfaces, then the sliding bearing bush may also 4 be loosely arranged therebetween. During operation, a sliding friction is normally encountered between the external conical surface area of the sliding bearing 6 bush and the adjoining stationary or tension arm fixed conical surface at same 7 friction conditions on the sliding bearing surfaces. The helical torsion spring of the 8 tension device according to the present invention is subject to a torsional load in a 9 same manner as described in the prior art and spring-loads the tension arm against the traction means.

12 U.S. Pat. No. 4,698,049 further discloses a damping unit for damping 13 swinging motions of the tension arm relative to the stationary element.
This ' 14 damping unit is formed by providing the stationary element and the tension arm shaft with terminal end faces that oppose each other, with a friction disk being 16 disposed between theses end faces. The end face associated to the stationary 17 element is formed on a separate disk. The tension device in accordance with the 18 invention effects a damping unit, without necessitating additional measures as 19 opposed to conventional tension devices. The sliding friction between the sliding bearing surfaces is increased as a result of the reaction force and the resulting 21 surface pressure, respectively, so that the desired damping effect is effected in 22 both rotational directions of the tension arm.

1 In a helical torsion spring which is e.g. axially compressed to exert an axial 2 force, a particularly advantageous arrangement of the supports and the sliding 3 bearing surfaces is attained when the sliding bearing surface associated to the 4 tension arm is disposed radially outwards, and the sliding bearing surface associated to the stationary element is disposed radially inwards, whereby in 6 direction from the tapered ends of the sliding bearing surfaces toward the 7 widened ends of the sliding bearing surfaces, the stationary support is positioned 8 ahead of the support fixed on the tension arm. In the event the helical torsion 9 spring is axially compressed to exert an axial pressure force, a simple as well as suitable arrangement is also created by providing the sliding bearing surface 11 associated to the tension arm radially inwards and the sliding bearing surface 12 associated to the stationary element radially outwards, whereby in direction from 13 the tapered ends of the sliding bearing surfaces toward the widened ends of the 14 sliding bearing surfaces, the support fixed on the tension arm is positioned ahead of the stationary support. Both described arrangements result advantageously in 16 the generation of the reaction force acting perpendicular to the sliding bearing 17 surfaces, without necessitating any additional components or measures.

19 Tension devices in accordance with the invention are often used for aggregate drives of engines of motor vehicles. The construction of such tension 21 devices requires consideration also i.a. of spatial needs.

1 An especially space-saving variation is effected by forming tension arm 2 shaft fixed on the tension arm radially within the sliding bearing with an axially 3 open recess for receiving the helical torsion spring, which recess is radially 4 overlapped by the stationary support. This variation is particularly advantageous because the radially outer sliding bearing exhibits a reduced surface pressure as 6 a consequence of the circumferentially increased sliding bearing surfaces, and 7 therefore is subject to a reduced abrasive wear.

9 In a tension device which is particularly advantageous with respect to installation, the tension arm fixed tension arm shaft is arranged in the stationary 11 element of pot-shaped configuration with a pot bottom, a pot casing and a pot 12 cover, with the stationary support being formed by the pot cover, and with the 13 stationary element being formed with a circumferential slot through which the 14~ tension arm is radially guided. The pot cover can be secured to the stationary element e.g. by means of bayonet fastener.

17 According to a further variation, the stationary tension arm shaft has one 18 end formed with a cylindrical outer surface area, with a conical bush being 19 secured, preferably detachably, to this end and formed with conical outer surface area and cylindrical inner surface area. The conical bush has a tapered end which 21 faces the tension arm shaft at one end that faces away from the tension arm, with 22 the tension arm shaft being formed with a coaxial throughbore. This ensures that 1 the tension arm, which is formed with a conical bore coaxial to the tension arm 2 shaft, and the tension arm shaft, which is formed in one piece with the tension 3 arm, can be placed together with the conical bush and the helical torsion spring 4 on the tension arm shaft. As a result of the axial force exerted by the torsion .
spring, the tension arm and the conical bush, respectively, must be secured 6 against sliding off axially from the tension arm shaft; for example, a screw which is 7 coaxial to the tension arm shaft may be screwed into the end face of the tension 8 arm end at the free end of the tension arm shaft, with the conical bush being 9 axially .supported with its one end face on the screw head. It may be suitable to guide this screw through the coaxial throughbore of the tension arm shaft and to 11 screw it into the engine block. In this arrangement, the screw accomplishes two 12 functions, that is, firstly, the securement of the tension arm shaft to the engine 13 block, and, secondly, the axial securement of the tension arm and the conical 14 bush, respectively.
16 In accordance with a further modification of the invention, a support disk 17 forming the support is secured to the tension arm shaft at an end facing away 18 from the tension arm, with the tapered ends of the sliding bearing surfaces facing 19 the support disk. In such a tension device, the stationary element is preferably formed with a conical bore which exhibits an expanded end facing the tension 21 arm. The tension arm shaft, formed preferably in one piece with the tension arm, 22 is inserted in the conical bore and has a free end axially extending beyond this 1 conical bore. Preferably press-fitted on this end is the support disk. In this case, 2 there is no need to secure the support disk against axial displacement on the 3 tension arm shaft. The conical bore wall of the conical bore forms in this case the 4 one sliding bearing surface.
6 There is no need to design the conical bush as a separate component. It 7 may also be suitable to form a sliding bearing bush through injection molding with 8 a casing with circumferentially spaced holes, with sliding bearing material being 9 sprayed onto the casing to penetrate therethrough and engaging behind the bore.
In this manner, an intimate connection e.g. between the tension arm and the 11 sliding bearing bush is effected.

13 Particularly favorable force relationships in the sliding bearing are 14 accomplished when the angle of inclination of the sliding bearing surfaces relative to the tension arm shaft ranges between 8° and 30°.

17 In some circumstances, it may be also suitable to provide at least one 18 bearing surface with circumferentially distributed lubricant pockets.
Lubricant is 19 filled in the lubricant pockets so as to ensure optimum damping and sliding properties over an extended period. The lubricant pockets may certainly also be 21 provided on a sliding bearing bush.

1 With respect to the load of the sliding bearing, it is suitable to securely 2 clamp both ends of the helical torsion spring. This ensures that the torsion of the 3 spring does not result in any radial forces which are directed into the sliding 4 bearing and cause undesired edges stress. This type of attachment can also be attained when each of both ends of the helical torsion spring under torsion is 6 acted upon by a pair of forces which acts transversely to the longitudinal axis of 7 the helical torsion spring. This is for example the case when the spring as a result 8 of its torsion is supported with its angled end by a tension arm fixed first point of 9 support, with one supporting force of one pair of forces acting thereon. The helical torsion spring has a winding connected to this end and bearing upon a second.
11 point of support, with the second supporting force of the one pair of forces acting .
12 thereon. The other pair of forces is formed in like manner on stationary points of 13 support. This also ensures that as a result of the clamped helical torsion spring, 14 no further radial forces act on the sliding bearing.
16 In tension devices according to the invention, the expanded ends of the 17 sliding bearing preferably face the tension arm. Certainly, even when reversing 18 this arrangement, the advantages effected by the invention are also achieved, 19 whereby, however, an increased surface pressure and a resulting increased abrasive wear can be encountered at the tapered end of the sliding bearing.

3 The invention will now be described in more detail with reference to three 4 exemplified embodiments shown in a total of ten figures, wherein:

6 FIG.1 shows a longitudinal section through a tension device 7 according to the invention, 9 FIG.2 shows the sliding bearing bush of the tension device according to the invention, 12 FIG. 3 shows a cross sectional partial view of the sliding bearing 13 bush of FIG. 2, FIG. 4 shows a modified tension arm shaft;

17 FIG. 5 shows a further modified tension arm shaft, 19 FIG. 6 shows a modified stationary element, 21 FIG. 7 shows the tension device according to FIG. 1, however with 22 modified tension arm fixed support.

1 FIG. 8 shows a further tension device according to the invention, 3 FIG. 9 shows a further tension device according to the invention, FIG. 10 shows the clamping of the ends of the helical torsion spring.

9 The exemplified embodiment according to the invention and shown in FIG. 1 includes a tension arm 1 on which a tensioning roller 2 is secured for 11 engagement on a not shown traction means. The tension arm 1 is rotatably 12 supported by a sliding bearing 3 relative to a housing 4. Formed in one piece with 13 the tension arm 1 is a tension arm shaft 5 which exhibits a conical external 14 surface area 6. The tension arm shaft 5 is received in the housing 4 within a conical bore 8 formed with a conical wall 7, with a sliding bearing bush 9 being 16 provided between the conical wall 7 extending parallel to the conical outer surface 17 area 6. A form-fitting connection of the sliding bearing bush 9 with the tension arm 18 shaft 5 is effected by a projection 10 of the sliding bearing bush 9 through 19 engagement in a recess 11 of the tension arm shaft 5. The conical wall 7 and the outer conical surface area 12 of the sliding bearing bush 9 form sliding bearing 21 surfaces for rotatable support of the tension arm 1 relative to the housing 4. The 22 tension arm shaft 5 has one end which faces away from the tension arm 1 and 1 extends beyond the conical bore 7, with a support disk 13 being press-fitted onto 2 this tension arm end. The support disk 13 may certainly also be connected in 3 form-fitting or material locking connection with the tension arm 1. A
helical torsion 4 spring 14 is arranged coaxial to the tension arm shaft 5 and clamped, on the one hand, to a support 15 provided on the support disk 13 and, on the other hand, to a 6 support 16 provided on the housing 4 for exerting a torsion force and an axial 7 pressure force Fo. The expanded ends of the sliding bearing surfaces 7, 12 face 8 the tension arm 1, whereby in direction from the tapered ends of the sliding 9 bearing surfaces 7, 12 towards the expanded ends of the extended sliding bearing surfaces 7, 12, the tension arm fixed support 15 is arranged ahead of the 11 housing-fixed support 16. The tension arm 1 and the tension arm shaft 5 formed 12 in one piece therewith are preferably made by a die casting process, with 13 aluminum alloy being used as suitable material.

FIGS. 2 and 3 show details of the sliding bearing bush 9 and the formed 16 projection 10, with the conical outer surface area 12 being provided with lubricant 17 pockets 16a for receiving lubricant.

19 FIG. 4 shows a modified embodiment of the tension arm 1 formed in one piece with the tension arm axis 5. The tension arm shaft 5 includes a cylindrical 21 tube 17, with the sliding bearing bush 9 being applied through injection molding 22 onto the cylindrical tube 17. Also in this case, the conical outer surface area 12 is 1 selected as sliding bearing surface. As a constant wall thickness should be 2 maintained, if possible, during injection molding, recesses 19 are provided within 3 the sliding bearing bush 9 in direction towards the expanded end of the sliding 4 bearing face 12.
6 If however the tension arm shaft 5 of FIG. 1 is preferred, it is certainly 7 possible to apply the sliding bearing bush 9 by injection molding onto the conical 8 outer surface area 6 of the tension arm shaft 5, as shown in FIG. 5. To effect an 9 intimate connection between the sliding bearing bush 9 and the tension arm shaft 5, holes 21 are formed in the jacket 20 of the tension arm shaft 5, whereby 11 sliding bearing material sprayed onto the outer conical surface area 6 penetrates 12 the holes 21 and engages therebehind.

14 The procedure described in FIG. 5 for forming the sliding bearing bush 9 can be applied in analogous manner also to the housing 4, as shown in FIG. 6.
In 16 this case, holes 22 are provided in a jacket 23 of the housing 4.

18 The exemplified embodiment according to FIG. 7 corresponds essentially 19 to the one according to FIG. 1, with the difference to the above-described embodiment residing in the formation of the tension arm fixed support which in 21 this case is effected by clamping the helical torsion spring 14 at its end facing the 22 support disk 13 in a groove 24 formed on the tension arm shaft 5, with the support 1 disk 13 engaging in this groove 24 and axially supporting the helical torsion 2 spring 14. A further difference to the above-described embodiment resides in the 3 loose fit of the sliding bearing bush 9 between the tension arm shaft 5 and the 4 housing 4. The sliding bearing bush 9 can thus freely rotate relative to the conical wall 7 as well as relative to the conical outer surface area 6 of the tension arm 6 shaft 5.

8 The embodiment according to the invention shown in FIG. 8 difFers from the 9 preceding embodiments essentially in the configuration of the tension arm shaft 5 which is formed with an axially open recess 25 extending coaxial to the tension 11 arm 1 for receiving the helical torsion spring 14. The pot-shaped housing 4 12 includes a pot bottom 26 and a pot jacket 27, with the stationary support being 13 formed on a pot cover 28 which exhibits a pot jacket 26 axially overlapping the pot.
14 jacket 27 and being secured thereto. A slot 30 formed in circumferential direction is provided on the pot jacket 27 and the pot cover 28, respectively, for radially 16 guiding the tension arm 1 therethrough. The helical torsion spring 14 is supported 17 on the other hand by a bottom 31 of the tension arm shaft 5.

19 While in the preceding embodiments, the tension arm shaft 5 is always fixedly secured to the tension arm 1, the embodiment according to FIG. 9 exhibits 21 a stationary tension arm shaft 32. The tension arm shaft 32 is provided, on the 22 one hand, with a support flange 33 for attachment to a not shown engine block. A

1 tension arm 35 is rotatably supported by means of a sliding bearing 36 on the 2 tension arm shaft 32 at one end formed with a cylindrical outer surface area 34.
3 The tension arm 35 includes a tension arm jacket 37 extending coaxial to the 4 tension arm shaft 32 and formed with a conical bore 38, with the tapered end of the conical bore 38 facing away from the tension arm 35. Arranged between the 6 tension arm jacket 37 and the tension arm shaft 32 is a conical bush 39.
This 7 conical bush 39 is formed with a conical outer surface area 40 and a cylindrical 8 inner surface area 41. Provided between the conical bush 39 and the tension arm 9 jacket 37 is a conical sliding bearing bush 42. The conical sliding bearing bush 42 and the conical bush 39 may certainly be made in one piece, for example through 11 injection molding, from plastic material. Sliding motions are effected also in this 12 case between the conical wall 43 of the conical bore 38 and an outer conical 13 surface area 44 of the conical sliding bearing bush 42. A coaxial helical torsion 14 spring 45 is clamped, on the one hand, to the support flange 33 and, on the other hand, to a tension arm fixed support 46 and exerts an axial pressure force and a 16 torsion force. The tension arm shaft 32 is provided with a coaxial throughbore 47, 17 with a screw 48 being directed through the throughbore 47 and screwed onto the 18 not shown engine block. It is certainly possible to provide a washer between the 19 screw head 49 and the sliding bearing bush 42 at the end face facing the screw head 49. This ensures that the sliding bearing bush 42 cannot slide off axially 21 from the tension arm shaft 32.

>~
1 FIG. 10 shows a cross section of the tension device according to the 2 invention, shown in FIG. 9, however without the screw 48. This clearly illustrates 3 the tension arm fixed support. The angled end of the helical torsion spring 4 engages in an opening 50 of the support flange 33 and is supported circumferentially therein. The helical torsion spring 45 has a winding 51 secured 6 to this end and bears spotwise on the tension arm shaft 32. Both these contacts 7 are impacted by support forces FS which form together a pair of forces. When 8 forming the stationary support for the helical torsion spring in analogous manner, 9 it is evident that the torsion of the helical torsion spring 45 does not generate a radial force that acts on the sliding bearing. The supports of the helical torsion 11 spring, as illustrated with reference to the embodiments according to FIGS.

12 and 10, are certainly applicable in the same advantageous manner for the other 13 embodiments.

Subsequently, the mode of operation of the tension device according to the 16 invention is described. As a result of the inventive arrangement of the helical 17 torsion spring 14, 45, the axial pressure force Fo is introduced into the sliding 18 bearing 3, 36 as a reaction force FR acting perpendicular to the sliding faces 7, 19 12, 43, 44. The resulting increased friction dampens in advantageous manner swinging motions of the tension arm 1, 35. The tension device according to the 21 invention ensures that the tension arm 1, 35 is constantly swingably supported 22 without significant clearance relative to the housing 3 and the stationary tension 23 arm shaft 32, respectively. As soon as a result of the abrasive wear on the sliding 1 bearing surfaces 7, 12, 43, 44 a play is encountered, an axial displacement of the 2 tension arm shaft 5, 28 is effected relative to the tension arm 1, 31 to press the 3 sliding bearing surfaces 7, 12, 43, 44 towards each other.

Reference PVumerals 1 Tension arm 27 Pot jacket 2 Tension roller 28 Pot cover 3 Sliding bearing 29 Cover jacket 4 Housing 30 Slot Tension arm shaft 31 Bottom 6 Tapered surface area 32 Tension arm shaft 7 Conical outer surface area33 Support flange 8 Conical bore 34 Cylindrical surface area 9 Sliding bearing bush 35 Tension arm Projection 36 Sliding bearing 11 Recess 37 Tension arm jacket 12 Outer conical surface area38 Conical bore 13 Support disk 39 Conical bush 14 Helical torsion spring 40 Conical outer surface area Tension arm fixed support 41 Cylindrical inner surface area 16 Stationary support 42 Conical sliding bearing bush 16a Lubricant pockets 43 Conical wall 17 Cylindrical tube 44 Conical outer surface area 18 (deleted) 45 Helical torsion spring 19 Recesses 46 Tension arm fixed support Jacket 47 Throughbore 21 Holes 48 Screw 22 Holes 49 Screw head 23 Jacket 50 Opening 24 Groove 51 Winding Recess 26 Pot bottom

Claims

1. Tension device for traction means such as belts and chains, including a tension arm (1, 35) which carries a tensioning member, preferably a tension roller (2), and is spring-loaded against the traction means, with the tension arm being rotatably supported relative to a stationary element (4, 32) by means of a sliding bearing (3, 36) which exhibits sliding bearing surfaces (7, 12, 43, 44) configured in the form of conical surfaces in parallel relationship to one another and positioned concentricallly to a tension arm shaft (5, 32), and a helical torsion spring (14, 45) wound about the tension arm shaft (5, 32) and supported, on the one hand, on a support (15, 46) secured on the tension arm, and, on the other hand, on a stationary support (16, 33), characterized in that, in the installed state, an axial pre-stress acts on the helical torsion spring in addition to the torsional pre-stress, the helical torsion spring (14, 45), clamped between these supports (15, 16, 33, 46) at exertion of an axial force (F D), introducing its axial force (F D) into the sliding bearing (3, 36) in form of a reaction force (F R) which acts perpendicular to the sliding bearing surfaces (7, 12, 43, 44) so that the sliding bearing surfaces (7, 12, 43, 44) are pressed against each other under the axial force (F D).

2. Tension device according to claim 1, characterized in that the helical torsion spring (14, 45) exerts an axial pressure force (F D).

3. Tension device according to claim 2, characterized in that the sliding bearing surface (43) associated to the tension arm (35) is disposed radially outwards, and the sliding bearing surface (44) associated to the stationary element (32) is disposed radially inwards, whereby in direction from the tapered ends of the sliding bearing surfaces (43, 44) toward the widened ends of the sliding bearing surfaces (43, 44), the stationary support (33) is positioned ahead of the tension arm fixed support (46).

4. Tension device according to claim 2, characterized in that the sliding bearing surface (12) associated to the tension arm (1) is disposed radially inwards, and the sliding bearing surface (7) associated to the stationary element (4) is disposed radially outwards, whereby in direction from the tapered ends of the sliding bearing surfaces (7, 12) toward the widened ends of the sliding bearing surfaces (7, 12), the tension arm fixed support (13, 15) is positioned ahead of stationary support (16).

5. Tension device according to claim 1, characterized in that the tension arm fixed tension arm shaft (5) is formed radially within the sliding bearing (3) with an axially open recess (25) for receiving the helical torsion spring (14), which recess is radially overlapped by the fixed support (16, 28).

6. Tension device according to claim 5, characterized in that the tension arm fixed tension arm shaft (5) is arranged in the stationary element (4) of pot-shaped configuration with a pot bottom (26), a pot casing (27) and a pot cover (28), with the fixed support being formed by the pot cover (28), and with the stationary element (4) being formed with a circumferential slot (30) through which the tension arm (1) is radially guided.

7. Tension device according to claim 1, characterized in that the stationary tension arm shaft (32) has one end formed with a cylindrical outer surface area (34), with a conical bush (39) being provided on this end and exhibiting a conical outer surface area (40) and cylindrical inner surface area (41) and having a tapered end facing the tension arm shaft (32) at one end that faces away from the tension arm (35), with the tension arm shaft (32) being formed with a coaxial throughbore (47).

8. Tension device according to claim 1, characterized in that a support flange (33) forming a support is secured to the tension arm shaft (32) at an end facing away from the tension arm (35), with the tapered ends of the sliding bearing surfaces (43, 44) facing the support flange (33).

9. Tension device according to claim 1, characterized in that a sliding bearing bush (9) is formed through injection molding with a casing (20, 23) with circumferentially spaced holes (21, 22), with sliding bearing material being sprayed onto the casing (17, 20) to penetrate therethrough and engaging therebehind.

10. Tension device according to claim 1, characterized in that the angle of inclination of the sliding bearing surfaces (7, 12, 43, 44) relative to the tension arm shaft (5, 32) ranges between 8° and 30°.

11. Tension device according to claim 1, characterized in that at least one of the bearing surfaces (12) is provided with circumferentially distributed lubricant pockets (16a).

12. Tension device according to claim 11, characterized in that the lubricant pockets (16a) are formed on a sliding bearing bush (9).

13. Tension device according to claim 1, characterized in that both ends of the helical torsion spring (14, 15) are securely clamped.

14. Tension device according to claim 1, characterized in that each of both ends of the helical torsion spring (45) subject to torsion is acted upon by a pair of forces (F S) directed transversely to the longitudinal axis of the helical torsion spring (45).