Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02229943 1998-02-19
1 TENSION DEVICE FOR TRACTION MEANS WITH CONE-TYPE SLIDING
2 BEARING
3
4
FIELD OF THE INVENTION
6
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.
16
17 BACKGROUND OF THE INVENTION
18
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
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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.
4
SUMMARY OF THE INVENTION
6
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
2
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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.
11
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.
3
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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.
18
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.
4
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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.
8
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.
16
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
5
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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
6
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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.
12
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°.
16
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.
7
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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.
8
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1 BRIEF DESCRIPTION OF THE DRAWING
2
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,
8
9 FIG.2 shows the sliding bearing bush of the tension device
according to the invention,
11
12 FIG. 3 shows a cross sectional partial view of the sliding bearing
13 bush of FIG. 2,
14
FIG. 4 shows a modified tension arm shaft;
16
17 FIG. 5 shows a further modified tension arm shaft,
18
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.
9
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1 FIG. 8 shows a further tension device according to the invention,
2
3 FIG. 9 shows a further tension device according to the invention,
4
FIG. 10 shows the clamping of the ends of the helical torsion spring.
6
7 DETAILED DESCRIPTION OF THE DRAWING
8
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
CA 02229943 1998-02-19
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.
14
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.
18
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
11
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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.
13
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.
17
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
12
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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.
7
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.
18
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
13
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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.
14
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>~
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
45
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.
9
12 and 10, are certainly applicable in the same advantageous manner for the
other
13 embodiments.
14
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
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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.
16
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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
17
