Assembly for transmitting rotational movements and for damping torsional vibrations

An assembly for transmitting rotational movements and for damping torsional vibration and including a damper housing, a connection section located radially inward of the damper housing for attaching the assembly to a to-be-damped part, with the connection section being formed integrally with the housing as a one-piece part, a cover for sealingly closing the housing and a damping weight located in the working chamber which is formed in the housing, in a viscose medium filling the working chamber, with the assembly being formed as a camshaft gear, and with the radial outer circumference of the housing being formed as a camshaft gear toothing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an assembly for transmitting rotational 
movements and for damping torsional vibrations and which includes a damper 
housing, a connection section located radially inward of the damper 
housing for attaching the assembly to a to-be-damped part, with the 
connection section being formed integrally with the housing as a one-piece 
part, a cover for sealingly closing the housing and which defines with the 
housing a working chamber, and a damping weight located in the working 
chamber in a viscose medium filling the working chamber. 
2. Description of the Prior Art 
An assembly of a type described above is disclosed in European Patent No. 0 
503 424 B1. This patent discloses a torsional vibration damper connected 
with a belt pulley and designed for use as a crankshaft damper. This 
assembly, except the damping weight and the damping housing cover, is 
formed as a single part having a pulley element, damper housing and hub 
region and which is preferably manufactured by a non-chipping process. 
This assembly represents a so-called viscose damper which is based on a 
shear flow of a fluid in an annular clearance between an oscillating 
weight and a housing provided at a free end of the crankshaft. The freely 
rotatable oscillating weight, as a result of its rotational inertia, is 
retarded in its rotation relative to the housing. As a result, the 
shearing energy of the high viscose fluid absorbs the oscillations of the 
crankshaft, thus damping the vibrations. 
The crankshaft torsional viscose vibration dampers include steel-rubber 
components the frequency of which is selected to coincide with the first 
oscillating frequency of the crankshaft to thereby minimize the crankshaft 
oscillation due to its amortization and damping. 
While the use of torsional vibration dampers for crankshaft is 
conventional, it was not considered to be necessary to use dampers, in 
addition to those for crankshafts, for a drive train to a camshaft. It is, 
however, known to use viscose dampers when drives are use for adjusting of 
the camshaft in order to adapt the ignition points to different rotational 
regions. The camshafts, which are driven from the crankshafts via toothed 
belt, chain or gear drives, provide for valve control when internal 
combustion engines are used. Such a drive train represents a system with 
distributed masses and has points of different stability, the operation of 
which is subjected to oscillation due to the intermittent mode of 
operation of the internal combustion engines. Wide fluctuations of the 
rotational speeds of the engine are observed due to the intermittent 
action of the gas forces during combustion in separate cylinders. This is 
particularly observed at low rotational speeds. This so-called rotational 
non-uniformity causes a low-frequency rigid body vibration of the entire 
camshaft which, e.g., in four cylinder, four-stroke engines, results in 
two gas pulses per revolution. This results in an oscillation angle of the 
free end of the crankshaft and, thus, of the camshaft drive of 
.+-.3.degree. and more, especially when the use of a multi-valve technique 
results in higher gas force pulses or when the mass inertia moment of a 
flywheel on the crankshaft is reduced by the use of two solid flywheels. 
In addition, high frequency torsional vibrations are generated in the 
camshaft due to the acceleration and deceleration of valve masses. This 
effect is reinforced in diesel engines because of the drive of the 
injection pump from the camshaft. The multi-valve technique reinforces 
these vibrations even more. 
Accordingly, an object of the present invention is to provide a damping 
assembly for a camshaft which would enable a simplified vibration damping 
of a camshaft, without the use of any adjusting means. 
Another object of the present invention is to provide a camshaft vibration 
damping assembly having the smallest dimensions possible. 
SUMMARY OF THE INVENTION 
These and other objects of the present invention, which will become 
apparent hereinafter, are achieved by forming the damping assembly as a 
camshaft gear, preferably by non-chipping technique, with the outer 
circumference of the damper housing being formed as a camshaft gear 
toothing. 
The present invention permits to integrate an vibration damping mechanism 
of a viscose damper into a camshaft gear, without forming a complicated 
and, therefore, difficult to produce assembly. The assembly can 
advantageously be produced by non-chipping processes which reduce 
manufacturing costs. Because of the integration of the viscose damper into 
the camshaft gear, the vibration damping mechanism requires very little 
constructional space. 
According to a particular preferred embodiment of the present invention, it 
is contemplated to form the inner side of the camshaft gear toothing as an 
internal toothing extending into the working chamber in which at least one 
outer lamella, extending radially inward, is received, with the damping 
weight being formed as at least one inner lamella extending radially 
outward. At that, it is advantageous to use several inner and outer 
lamellas arranged alternatively relative to each other. The outer 
lamellas, which are form-lockingly received in the internal toothing, 
form, together with the freely rotatable inner lamellas, a plurality of 
annular clearances which are filled with viscose fluid. By utilizing a 
lamella construction, the operational surface of the annular clearances is 
substantially increased in comparison with a conventional construction, 
without increasing the dimension of the oscillating weight. This makes 
possible, on one hand, to obtain the same damping characteristics with the 
use of a fluid having a lower viscosity and/or, on the other hand, to 
increase the manufacturing tolerances of the clearances (which enables the 
utilization of non-chipping manufacturing processes). 
Because the inner lamellas serve as an oscillating weight, they are made 
wider than the outer lamellas and, advantageously, are formed of steel. 
The outer lamellas are made much thinner and are formed, advantageously, 
of aluminum or a plastic material. 
To insure an adequate dimensions of the annular clearances, axial spacers 
are provided between the lamellas. The spacers can be integrated into the 
lamellas or made with respective lamellas as one-piece parts. 
According to another embodiment of the present invention, the inner side of 
the camshaft gear toothing, which limits the working chamber, is formed as 
a smooth annular surface, with the oscillating weight being formed as a 
ring-shaped member. In this embodiment, a conventional oscillating weight 
can be used, the essential being that the inner side of the camshaft gear 
toothing is formed as a smooth annular surface. 
It is further advantageously contemplated to use a slide bearing support 
for axial and radial support of the oscillating weight. The slide bearing 
support can be formed of separate bearing shells or be formed as a 
coating, e.g., of a Teflon.RTM. material. This slide bearing support 
should not in any way limit the rotational movement of the inner lamellas. 
However, it should provide for additional friction damping.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As mentioned above, FIGS. 1 and 2 show a first embodiment of an assembly 
for transmitting rotational movements and for damping torsional vibrations 
according to the present invention, which is formed as a camshaft gear 1. 
The camshaft gear 1 has a hub-shaped connection region 2 for mounting the 
camshaft gear 1 on a camshaft of a motor vehicle or the like. The 
hub-shaped connection region 2 passes into a damper housing 3 having a 
U-shaped cross-section. The damper housing 3 has its open sides sealingly 
closed with a disc-shaped cover 4, which is secured to the housing 3 by 
welding, gluing or the like. The damper housing 3, together with the cover 
4, form a closed working chamber for receiving a torsional viscose 
vibration damper, the construction of which will be explained in details 
below. The axial outer wall 3a of the damper housing 3 is provided on its 
outer side with a camshaft gear toothing 5 which on its inner side is 
formed as an internal toothing 6 facing the working chamber. The camshaft 
gear 1, which is described above, is formed, except the cover 4, as a 
one-piece member which is preferably formed by a non-chipping process. 
The internal toothing 6, which is provided on the inner side of the 
camshaft gear toothing 5, serves for form-lockingly receiving at least 
one, but preferably more (in the described embodiment-four) of extending 
radially inward, disc-shaped, spaced from each other, outer lamellas 7 
which are thus secured in the working chamber of the damper housing 3 
against rotation. To insure the spacing between the lamellas 7, there are 
provided in the base (bottom) regions of the lamellas 7 annual spacers 8. 
Alternatively, it is possible to form the spacers 8 as a single pieces 
insertable between lamellas 7. 
The damping weight of viscose dampers is formed of at least one, preferably 
more (in the embodiment shown-four, extended radially outward, disc-shaped 
inner lamellas 9 which are arranged between the outer lamellas 7. The 
inner lamellas 9 are rotatably supported in the working chamber of the 
housing 3. To this end, there is provided in the working chamber a sliding 
bearing support 10 arranged on a radially inward side of the housing 3. 
The sliding bearing support 10 can be formed of separate bearing shells or 
as coating, e.g., of a Teflon.RTM.. The inner lamellas 9 are spaced from 
each other at their radially inner side by axial spacers 11 which are 
formed in the shown embodiment as an integral part of the inner lamellas 
9. The spacers 8 and 11 insure that an annular clearance 12 of a constant 
width is maintained between the lamellas 7 and 9, respectively. After the 
installation of the lamellas and the closing of the housing 3 with the 
cover 4, the working chambers are filled in a known manner with a viscose 
fluid 13 which fills in particular the region of the annular clearances 
12. 
In comparison with a conventional construction of the viscose vibration 
dampers, providing of lamellas permits to increase the surface area of the 
operating clearance 12. Thereby it becomes possible to obtain the same 
damping effect with the use of a fluid having a lower viscosity, on one 
side, and/or to substantially increase the manufacturing tolerances of the 
clearances, on the other side. 
As shown in FIG. 1, in order to provide an adequate damping weight, the 
inner lamellas 9 are formed noticeably wider than the outer lamellas 7. 
The inner lamellas 9 advantageously are formed of steel, whereas the outer 
lamellas 7 are formed of aluminum or a plastic material. 
Another embodiment of camshaft gear is shown in FIGS. 3 and 4, where the 
same elements are designated with the same reference numerals as in FIGS. 
1 and 2 but with an index "'". 
The camshaft gear 1', which is shown in FIGS. 3 and 4, differs from the 
camshaft gear 1, which is shown in FIGS. 1 and 2, in that the outer wall 
3a.sup.1 of the damper housing 3.sup.1 has, on its outer side, a camshaft 
gear toothing 5.sup.1 the inner side 3b.sup.1 of which facing the working 
chamber is substantially ring-shaped and the damping weight 9.sup.1 is 
also ring-shaped. The damping weight 9.sup.1 is rotably arranged in the 
working chamber and is supported on its radially inner side in a slide 
support 10.sup.1. The working chamber is filled with a viscose fluid 
13.sup.1. 
Both embodiment provide a very compact assembly which does not practically 
increases the constructional dimensions of a camshaft gear and which can 
be easily mounted. Obviously, other modification are also possible, 
without departing form the spirit of the present invention. Thus, the 
number of lamellas in the embodiment of FIGS. 1 and 2 can be varied. 
Accordingly, though the present invention was shown and described with 
reference to the preferred embodiments, various modifications thereof will 
be apparent to those skilled in the art and, therefore, it is not intended 
that the invention be limited to the disclosed embodiments or details 
thereof, and departure can be made therefrom within the spirit and scope 
of the appended claims.