Motor vehicle drive unit support arrangement

In a motor vehicle, the drive unit is suspended on a transverse member resting on the wheel suspension struts of the vehicle. The suspension struts are secured to the vehicle body by means of a suspension mount which includes a damping block. The suspension mount has an inner portion connected with the suspension strut, an intermediate portion connected with the transverse member, and an outer portion connected with the vehicle body. The inner portion, the intermediate portion and the outer portion are joined to each other through a rubber member which is loaded, substantially, in shear.

TECHNICAL FIELD 
The invention relates to a motor vehicle whose drive unit is secured to a 
transverse member that is elastically supported on the suspension struts 
of the motor vehicle, and wherein the suspension struts in turn, are 
supported on the vehicle body by means of respective mounts which are 
subjected to shear-type stresses. 
BACKGROUND OF THE INVENTION 
A motor vehicle of the above type is described in French patent publication 
No. 2 284 476. In the motor vehicle according to this publication, the 
suspension struts are bearing against the vehicle body by means of 
respective elastic mounts. The transverse member is supported on the 
respective upper ends of suspension struts by means of respective damping 
blocks which are loaded in compression. Therefore, in this arrangement, 
the mass of the vehicle body and the engine mass are arranged in parallel 
with one another. 
In British Pat. No. GB-PS 851,873, an arrangement is disclosed wherein the 
transverse member supporting the drive unit is rigidly connected with the 
suspension struts of the motor vehicle. A form-locking connection of this 
type provides that the drive unit with its mass can be considered in its 
entirety as part of the spring mass. This arrangement results in a 
relatively large ratio between the sprung and the unsprung mass, so that 
the vibrations induced in the vehicle body by road irregularities are only 
of a minor nature. However, the drawback associated with this arrangement 
is that the form-locking connection causes stability problems to occur on 
the torque transmitting elements, especially the ball bearings of the 
suspension struts. Another potential problem associated with this 
construction is that due to the inherent engine vibrations, vibrations are 
caused in the vehicle body because the vehicle body itself is not directly 
articulated to a resting subsuspension. 
SUMMARY OF PRESENT INVENTION 
It is an object of the present invention to incorporate features into a 
motor vehicle of the type identified in the foregoing which provide that 
the tendency of the vehicle body to vibrate in response to road 
irregularity induced vibrations and engine vibrations is significantly 
reduced. Another object of the invention is to reduce the likelihood of 
stability problems to occur in the region of the suspension struts. 
In accordance with the present invention, these objects are attained by the 
elastic mount being designed to support the transverse member on 
respective suspension struts on opposite sides of the vehicle, and also to 
support the suspension strut on the vehicle body, and wherein the stresses 
to which the elastic member of the mount is subjected are, substantially, 
shear-type stresses. 
Since the elastic member is primarily subjected to shear stresses, it can 
be made substantially softer than the damping block according to the 
French patent publication No. 2 284 476 which is designed to withstand 
compressive stresses. The important advantage of employing a rubber member 
that is relatively soft is that it assists in controlling acoustic 
vibrations and that it prevents stability problems from arising in the 
region of the suspension struts. Moreover, the front end steadiness can be 
improved by relatively simple means. Another benefit gained through the 
arrangement according to the invention is that the vehicle is more compact 
in the suspension strut area, because there is no need for an additional 
damping block. 
Instead of the transverse member, it is also possible to employ, especially 
in the case of front-wheel drive vehicles with transversely mounted 
engines, a pair of individual support bars which are rigidly connected 
with the drive unit. This arrangement has the effect of better handling 
loads of different magnitude generated on the left and the right hand 
side. 
An arrangement particularly adapted to cope with conditions of this nature 
is one wherein the suspension mount has its outer portion connected with 
the vehicle body, its inner portion with the wheel suspension strut, add 
its intermediate portion, which is disposed inside a rubber member, with 
the transverse member. A configuration of this type is simple in structure 
and enables the lever arm ratio between the outer portion and the 
intermediate portion supporting the transverse member, as well as between 
the inner portion and the intermediate portion to be varied, so that an 
optimum spring characeristic ratio can be selected with respect, on the 
one hand, to the excitation by the wheels on the vehicle body and, on the 
other hand, the excitation by the wheels on the engine. The advantage of 
this feature is particularly significant when the mounts are subjected to 
different loads. 
Double isolation of the drive unit relative to the vehicle body, which 
enhances the acoustic comfort while maintaining the vibratory comfort, is 
provided in a relatively simple manner in that the drive unit is suspended 
on the transverse member by means of resilient engine mounts. The 
remaining degrees of freedom of the engine/transmission drive unit are 
controlled by a torque control member on the front axle. 
According to another feature of the invention, the suspension mount is of 
cylindrical cross section, and the outer portion, the inner portion and 
the intermediate portion are in the form of coaxially arranged sleeves 
which together results in a relatively simple construction.

FIG. 1 illustrates schematically a motor vehicle wheel 1 which is suspended 
by means of a spring 2 on a structural component 22. A drive unit 3 is 
supported on top of this component 22 by means of a spring 23. The 
component 22 itself supports the vehicle body 5 through the interposition 
of a spring 24. Thus, in this arrangement the mass of the drive unit and 
the mass of the vehicle body are arranged in parallel through the 
component 22. When the vehicle wheel 1 rolls over a road surface 8, the 
drive unit 3 vibrates according to curve 10, and the vehicle body 5 will 
vibrate according to curve 9. The springs 2, 23 and 24 are supplemented by 
shock absorbers which are symbolically inserted in the drawing parallel to 
these springs and which represent actual shock absorbers employed in the 
vehicle or, as the case may be, the shock absorbing characteristics of the 
springs themselves. 
FIG. 2, which is a representation of the conditions prevailing with the 
arrangement according to the invention, also illustrates schematically the 
vehicle wheel 1 which is supported by means of the spring 2 on the drive 
unit 3. The drive unit 3 is connected via spring 4 with the vehicle body 
5. Shock absorbers 6, 7 are arranged in parallel with springs 2 and 4, 
respectively. The wheel 1 rolls over the road 8 and is forced into 
vigorous up and down deflections in accordance with road irregularities. 
The mass of the drive unit 3 is counteracting those vibrations, so that 
the drive unit 3 already vibrates with less intensity than the wheel 1, as 
indicated by curve 9. Since the drive unit 3 itself is connected with the 
vehicle body 5 through a spring 4, and since the vehicle body 5 has a 
relatively large mass, the vehicle body vibrations will only be of a minor 
nature, as indicated by curve 10 in FIG. 2. Thus, unlike the arrangement 
described in the foregoing, the present invention provides that the 
vehicle body and the drive unit 3 are arranged in series. 
FIG. 3 illustrates the front axle assembly of a motor vehicle according to 
the invention. Numerals 1 and 1' designate a pair of front wheels which 
are each connected by way of respective control arms 11, 11' with a front 
axle 12. Furthermore, the vehicle wheels 1, 1' are suspended by way of 
respective suspension struts 13, 13' on the vehicle body 5. Between the 
upper end of each suspension strut 13, 13' and the vehicle body 5 there is 
arranged a pair of elastic mounts, 14, 14', respectively. 
The drive unit 3 is suspended by way of an elastic engine mount 15 on a 
transverse member 16 and is connected by way of a torque member 21 to the 
front axle 12. The transverse member 16 is supported by its respective 
ends on the elastic mounts 14, 14', which will now be described in greater 
detail in conjunction with FIG. 4. 
FIG. 4 illustrates the upper end of the suspension strut 13, the elastic 
mount 14, a portion of the vehicle body 5 and the end portion of the 
transverse member 16. The elastic mount 14 is comprised of an outer 
portion 17 connected to the vehicle body 5, an inner portion 18 connected 
to the suspension strut 13 and an intermediate portion 19 which is rigidly 
connected with the transverse member 16. The outer portion 17, the 
intermediate portion 19 and the inner portion 18 all have a sleeve-like 
configuration, are coaxially arranged relative to one another and are 
connected with one another by an elastomeric member 20 which may be split 
by the intermediate portion 19 into two annular, coaxially arranged 
elastomeric portions. Since the forces acting on the rubber member are 
transmitted exclusively through the lateral surface areas, the rubber 
member 20 is loaded primarily in shear. The outer member 17, the 
intermediate member 19 and the inner member 18 are of slightly conical 
configuration relative to one another, so that the rubber member 20 is 
also subjected, to a minor extent, to compressive loads, which will 
increase the service life of the rubber member 20. 
The above described preferred embodiment is illustrative of the invention 
which may be modified within the scope of the appended claims.