Tensioning device for belts and the like, in particular on motor vehicle engines

In a tensioning device for belts and the like, in particular on motor vehicle engines, including at least two housing parts that can be swivelled relative to one another, one of which can be mounted in a stationary manner, it is provided, for the sake of unproblematic storage and reliable automatable mounting, that a screw element penetrates the housing parts in such a way that a threaded portion of the screw element protrudes freely from the stationary housing, wherein the screw element engages a bore of a plate of plastic, cardboard or the like joined to the stationary housing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention is directed to a tensioning device for belts and the like, in 
particular on motor vehicle engines, including at least two housing parts 
swivelable relative to one another, one of which can be mounted so as to 
be stationary. 
2. The Prior Art 
Tensioning devices of this type are used primarily on motor vehicle 
engines, in order to lend the belt an approximately constant tension 
regardless of the particular operating state, and to absorb and damp 
vibration and shocks to the belt. 
Since known devices of this type comprise at least two housing parts 
swivelable relative to one another and thus not firmly joined to one 
another, care must be taken when they are stored, so that all the parts of 
such a device will remain together. This is particularly onerous when 
shipping them to the storage place and in the unloading process, which 
sometimes is done automatically. 
Mounting a multiple-part entity of the known type on a motor vehicle engine 
is even more problematic, because such constructions are unsuitable or at 
best poorly suited to automated mounting, and even mounting them manually 
takes a comparatively long time. 
SUMMARY OF THE INVENTION 
Taking this as the point of departure, the object of the invention to make 
a tensioning device, of the type initially described above, easy to handle 
and in particular to make it capable of being mounted in an automated 
process; for structural simplification, the mounting parts should also 
perform additional functions beyond those of simply mounting the device. 
According to the invention, this object is attained in that a screw element 
penetrates the housing parts such that a threaded portion protrudes freely 
from the stationary housing, the screw element engaging a bore in a plate 
made of plastic, cardboard or the like joined to the stationary housing. A 
thread corresponding to the external thread of the screw element may be 
cut beforehand into the bore of such a plate, or can be tapped by the 
screwing-in of the screw element itself, or the disk can simply be pressed 
on. In each case, in this way all the housing parts are held together by 
the screw axially penetrating them, because as a rule the head of the 
screw element rests on the outer, movable housing part, while the thread, 
via the plate, retains the other housing part, which is to be mounted so 
as to be stationary. 
By means of the selection of the material of the plate, the pre-assembled, 
practically one-piece tensioning device can thus be simply mounted on a 
threaded bore, a welded-on nut or some arbitrary protrusion of the engine, 
simply by rotating the screw element farther so that the thread of the 
plate is stripped. 
It is advantageously provided that the screw element forms the swivel 
bearing, or centrally penetrates it. In this way, the screw element not 
only peforms the function of holding the housing parts together and fixing 
them in position in the final mounting, but at the same time serves as a 
stable swivel bearing construction securely anchored to the housing. 
In order not to have to use an expensive rotating tool for the screw 
element, it can be provided that the screw element includes a conventional 
screw and a sheath partially fitting over it. These two latter parts can 
favorably be coated and can easily be assembled together in order to 
attain the desired configuration. 
In a construction of the tensioning device in which its belt diversion 
wheel is at least partially in alignment in the axial direction with the 
housing parts, or in other words where the swivel arm used is very short, 
a further feature of the invention provides that the belt diversion wheel 
has a opening for actuating the screw element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A device according to the invention includes a swivel arm 1, on one end 2 
of which a belt diversion wheel 3 is rotatably supported on a hub 5, 
having an opening 4 provided with axial protrusions, by means of a ball 
bearing 6. The diversion wheel 3 has a double-U profile, in a known 
manner. The opening 4 makes it possible to engage the hub 5 with a tool 
during assembly. 
Disposed on the other end 7 of the swivel arm 1 is a swivel arm housing 8, 
which cylindrically surrounds a bearing bush 9 that is connected to a 
stationary housing 10, in the exemplary embodiment being integrally 
embodied with this housing, the stationary housing 10 closing off the 
swivel arm housing 8. 
The stationary housing 10 has a protrusion 11, which for rotationally fixed 
connection is inserted into a corresponding recess in a vehicle engine or 
the like. A screw element 12 axially penetrates the bearing bush 9 and has 
a threaded portion 13 that protrudes beyond the stationary housing 10, the 
threaded portion engaging a plastic washer 14 disposed in countersunk 
fashion on the back side of the housing 10. 
The housing 10 and the swivel arm housing 8 are held together by this 
plastic washer 14, on the one hand, and the screw head 15 or a metal shim 
16 beneath the screw head and a rubber washer 17, so that the entire 
device can be stored and used for assembly pusposes as a compact unit. For 
assembly, the screw element 12 is rotated, and the threaded portion 13 is 
thereby screwed into a corresponding threaded bore on the engine. In this 
rotation, the thread and the plastic washer 14 is over-tightened, which 
because of the softness of the material can be done without difficulty and 
without damage to the threaded portion 13. 
The swivel arm housing 8 has an outer cylindrical section 18, which is 
connected to the swivel arm 1, as well as an inner cylindrical section 19 
spaced apart from the outer cylindrical section; these sections 18 and 19 
are joined via a radially extending end wall section 20, forming an 
annular gap 21 that is open toward the housing 10. 
A roller bearing 22 is fitted into the inner cylindrical section 19, 
including roller bearing housing parts 23 and 24 and pins 25. The outer 
roller bearing housing part 23 is fixed to the inner cylindrical section 
19 of the swivel arm housing 8 so as to prevent relative rotation with 
respect to one another, and the inner roller bearing housing part 24 is 
likewise fixed to the bearing bush 9 so that these element are 
rotationally fixed with respect to one another. 
The inner cylindrical section 19 of the swivel arm housing 8 has a stepped 
recess 26, into which a cylindrical friction bushing 27 is inserted such 
that it is rotationally fixed relative to the swivel arm housing 8; that 
is, the friction bushing 27 is connected to the stationary housing 10 in a 
rotationally fixed manner. The friction bushing is manufactured from an 
intrinsically elastic material, such as thermoplastics, having a 
relatively high coefficient of friction as compared with metal. 
The friction bushing 27 in turn has a stepped recess 28, so that its 
outside diameter on the end oriented toward the housing 10 is somewhat 
greater than farther outward. 
In the annular gap 21 formed by the outer cylindrical section 18, as well 
as by the inner cylindrical section 19 on the one hand and the friction 
bushing 27 on the other, there is a helical spring 33, the ends of which 
are fixed, one (the helical spring end 30) in a longitudinal groove 29 
closed off from the outside in the outer cylindrical section 18 of the 
swivel arm housing 8 and the other (the end 32) in a bore 31 of the 
housing 10. The helical spring 33 rests on the friction bushing 27 with 
only its first few windings, while some distance still remains between the 
other windings and the recessed portion of the friction bushing 27. 
The following description relates in particular to FIGS. 3-5. These figures 
show that a cam-like protrusion 35, shown on a larger scale in FIG. 5, is 
embodied on the inner wall 34 of the outer cylindrical section 18 of the 
swivel arm housing 8. 
In the state as shipped or otherwise delivered, shown in FIG. 3, or in 
other words when the swivel arm 1 is located in a first end position, 
defined on the one hand by a stop prong 36 on the stationary housing 10 
and on the other by a rib protrusion 37 on the swivel arm 1, the first and 
second spring winding of the helical spring 33 of he friction bushing 27 
rests along a region that is substantially 180.degree. opposite the 
cam-like protrusion 35. 
If the device according to the invention is now fastened to an engine in 
the manner described, the swivel arm 1 is deflected outward into the 
opening 4 by the use of a tool, and a belt, not shown in the drawing, is 
tightened. Because of the belt tension, which is in equilibrium with the 
tension of the helical spring 33, the swivel arm 1 is deflected outward by 
an angular range .alpha. relative to the housing 10, as shown in FIG. 4. 
In this outward deflection, the helical spring 33 is supported on the 
cam-like protrusion 35, and on the approximately opposite side, where it 
originally rested against the friction bushing 27, it is raised away from 
the friction bushing, so that an annularly encompassing gap 38 is produced 
between the helical spring 33 and the friction bushing 27. As a result, in 
this state corresponding to the basic position in the operating state, no 
static friction occurs between the friction bushing 27 and the inner 
cylindrical section 19 of the swivel arm housing 8, so that even small 
shocks, which would not be sufficient to overcome the static friction, are 
intercepted and damped. 
It is not shown in detail in FIGS. 10 and 11 that in accordance with a 
variant of the invention the cam-like protrusion 35' can also be embodied 
as a separate housing part, which presses with radial spring loading 
against the helical spring 33. In the embodiment of FIG. 10, the 
protrusion 35' is embodied as a leaf spring element 50, which is secured 
with a rivet 51. In the embodiment of FIG. 11, a plate spring assembly 52 
presses against the cam protrusion 35', which is supported against a 
retaining element 54 secured by means of screws 53. 
The embodiment shown in FIG. 6 is embodied substantially like the 
embodiment described above, except that the basic design is laterally 
reversed. 
In this embodiment, instead of the washer 16, a plate spring 39 is 
provided, which in the state in which the housing 10' or the swivel arm 
housing 8' is screwed on or in other words secured to the engine, presses 
the two housings against one another. Also in this embodiment, the 
friction bushing 27' is embodied such that it has an end wall section 40, 
which rests on an abutment face 41, in the form of an end face of the 
swivel arm housing 8', with a friction defined by the plate spring 39. The 
abutment face 41 is embodied in such a way, deviating from a flat 
configuration, that it has at least one cam protrusion 60 extending in the 
axial direction, which rests against a part of the swivel arm housing 8' 
in such a way that in the basic position of the operating state, the end 
wall section 40 of the friction bushing 27' does not rest against the 
abutment face 41, so that in this position, the occurrence of static 
friction is avoided. 
In FIGS. 12 and 13, respective sections through the vicinity of the end 
wall section 40 or the abutment face 41 are shown, for embodiments in 
accordance with FIGS. 6 and 9, respectively. FIG. 12a and FIG. 13a each 
show the basic operational state, while FIGS. 12b and 13b show an 
outwardly deflected state having increased frictional force. 
In a further embodiment, shown in FIG. 7, instead of the one-piece screw 
element 12, a conventional screw 12' having a thread is provided, over 
which a sheath 43 is placed. Also in this embodiment, the swivel arm 1' is 
made quite short, so that the belt diversion wheel 3' partly covers the 
swivel arm housing 8" in the radial direction. In this embodiment, the 
head of the screw 12' can be grasped from above by means of a wrench for 
assembly purposes. In these embodiments shown in FIGS. 8 and 9, the belt 
diversion wheel 3" has an opening 44, which enables actuation of the screw 
12', provided with a socket head, for fastening purposes. In these 
embodiments shown in FIGS. 8 and 9, plate springs 39' are disposed not 
beneath the head of the screw 12' but instead are supported against an end 
face 45 of the housing part 10'. It is also provided in this embodiment 
that the helical spring 33 is disposed in an annular gap 21' that is 
accommodated in the stationary housing 10'. Accordingly, this exemplary 
embodiment shows that a kinematic reversal of the elements essential to 
the function of the invention between the swivel arm housing 8" and 
stationary housing 10' can readily be accomplished, while retaining the 
advantages according to the invention. 
The embodiments of FIGS. 8 and 9 also differ in that in the embodiment of 
FIG. 9, in accordance with the above-described exemplary embodiments, a 
threaded portion 13 protrudes beyond the stationary housing 10', while in 
the embodiment of FIG. 8 the stationary housing 10' has a recess 45', 
which is engaged either by a retaining arm or by a nut 46 or the like 
welded to the engine block.