Reduced friction automotive suspension strut mounting

In an automotive vehicle suspension including a telescoping strut, means for reducing static friction within the strut by causing either the upper end or the lower end or both ends of the strut to be rotated outboard with respect to the balance of said strut, whereby friction within the strut will be reduced.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to a means for mounting automotive 
suspension struts so as to reduce operating friction within the strut. 
2. Disclosure Information 
Automotive suspension designs incorporating struts have taken a variety of 
forms. In the true MacPherson design, the strut is positioned between a 
wheel carrier, to which it is rigidly mounted, and the chassis, to which 
it is pivotally mounted. A coil spring is commonly mounted concentrically 
about the strut. In the "modified" MacPherson design, a spring mechanism 
is mounted between a lower control arm attached to the wheel carrier and 
the chassis. The strut is, nevertheless, rigidly fastened to the wheel 
carrier and pivotally mounted to the chassis at its upper end. The rigid 
mounting between the strut and the wheel carrier with both designs causes 
radially directed preloading of the strut pistion and bearing. This 
preloading is undesirable inasmuch as the static friction resulting 
therefrom increases the force necessary to initiate sliding of the pistion 
within the strut and therefore correspondingly increases the shock loading 
transmitted to the chassis of the vehicle when an obstruction is 
encountered on the roadway surface. Attempts to minimize this undesirable 
static friction have resulted in configurations wherein the spring is 
eccentrically mounted about the strut or the spring mounting pads are 
canted at an angle to the strut center line, as in U.S. Reissue Pat. No. 
31,184. Although these solutions can result in a reduction of the strut 
friction, an undesirable effect may arise inasmuch as the packaging volume 
of the strut assembly may increase with either of the aforementioned 
structures. 
The present invention is intended to effect a reduction of strut friction 
without causing an increase of the struts' package volume. A further 
object of the invention is the provision of a method for controllably 
reducing or modifying strut static friction characteristics. The present 
invention may be utilized with either MacPherson or modified MacPherson 
designs. 
SUMMARY OF THE DISCLOSURE 
In accordance with the present invention, a reduced friction automotive 
suspension strut mounting is intended for use with an accompanying 
suspension strut, a chassis, and a wheel carrier. The strut comprises a 
working cylinder rigidly attached to the wheel carrier, a piston slidably 
carried within the working cylinder, and a piston rod comprising a lower 
end attached to the piston and an upper end attached to the vehicle's 
chassis by means of a mounting plate. The piston rod is rotated outboard 
by the mounting plate about an axis which is generally parallel to the 
longitudinal centerline of the vehicle, so as to urge the locus of 
intersection of the longitudinal axes of the piston rod and the working 
cylinder in a direction outboard of the vehicle. This movement of the 
strut outboard is accompanied by a reduction in the operating friction 
within the strut.

DETAILED DESCRIPTION OF THE DRAWING 
As shown in FIG. 1, an example of an automotive suspension suitable for use 
with the present invention comprises wheel and tire assembly 10 rotatably 
mounted upon spindle 12 which is integral with wheel carrier 14. Wheel 
carrier 14 also includes socket 16 which accepts the lower end of strut 
18, which is rigidly mounted to the wheel carrier. Coil spring 20 is 
mounted about strut 18. Strut mounting plate 22 connects strut 18 to the 
chassis of the vehicle. As its lower end, the suspension includes lower 
control arm 24 having inner pivot 30 and outer pivot 28. Control arm 24 is 
connected at its inboard end to chassis 26 by pivot 30 and at its outboard 
end to wheel carrier 14 by pivot 28. 
FIGS. 2 and 3 show a portion of the strut from FIG. 1 in greater detail. As 
shown in FIGS. 2 and 3, strut 18 includes working cylinder 38 and pistion 
rod 32, upon which is attached piston 34. Piston rod 32 passes into the 
interior of working cylinder 38 through rod guide 36. 
As shown in FIG. 1, the force of the vehicle's weight, labeled F.sub.W, 
acts upward through spindle 12. This force creates an upward acting 
bending moment or torque which must be counteracted by strut 18. As shown 
in FIG. 2, this counteraction produces forces F.sub.A and F.sub.B acting 
radially upon piston 34 and piston rod 32, respectively. Forces F.sub.A 
and F.sub.B, can be of considerable magnitude and are undesirable because 
they result in friction forces F.sub.p and F.sub.R acting upon piston 34 
and piston rod 32, respectively, in a direction parallel to the telescopic 
motion of strut 18. These friction forces comprise a relatively 
unpredictable addition to the spring rate of coil spring 20. In other 
words, forces F.sub.A and F.sub.B produce frictional forces F.sub.P and 
F.sub.R resisting the telescoping action of strut 18 and thereby cause the 
vehicle suspension to have a harsher operating characteristic than would 
otherwise be possible were forces F.sub.A and F.sub.B to be minimized. 
Minimization of the effect of forces F.sub.A and F.sub. B by changing the 
point and magnitude of their application is accomplished by the present 
invention. 
FIG. 3 shows the effect of mounting suspension strut 18 according to the 
present invention. As shown in FIG. 3, rotation of the upper end of the 
pistion rod through angle .alpha. relative to the remainder of the strut 
in a direction outboard of the vehicle, about an axis which is generally 
parallel to the longitudinal centerline of the vehicle, produces a shift 
.beta. in the locus of intersection of the axes of working cylinder 38 and 
piston rod 32. In the event that the shift .beta. is of sufficient 
magnitude, forces F.sub.C and F.sub.D, acting upon piston 34 and piston 
rod 32 as indicated in FIG. 3, will be produced. The magnitude of forces 
F.sub.C and F.sub.D, and correspondingly, the magnitude of forces F.sub.P 
and F.sub.R, may be adjusted by changing the predeterminded angle of 
rotation of the upper mount, .alpha., to achieve the desired reduction in 
friction acting within the strut. The friction reduction of the present 
invention is thus a result of removing or easing the bending moment which 
would otherwise be caused by the weight of the vehicle acting through 
spindle 12. In practice, the shift .beta. will be of small magnitude and 
may thus be described as an urging of the locus of intersection of the 
longitudinal axes of piston rod 32 and working cylinder 38 in a direction 
outboard of the vehicle. 
The reverse loading shown in FIG. 3 as forces F.sub.C and F.sub.D is not 
likely to persist during dynamic loading of the suspension inasmuch as 
force F.sub.W increases considerably with impact loading. During this 
condition, loading may reverse from that shown in FIG. 3 to the situation 
of FIG. 2. Nevertheless, the beneficial effect of the present invention 
will not cease merely because the locus of application of force against 
piston 34 and piston rod 32 changes dynamically, because the friction 
forces F.sub.P and F.sub.R will generally be of lesser magnitude during 
operation of a strut mounted according to the present invention. Indeed, 
although in certain vehicles design constraints may prohibit rotation of 
sufficient magnitude to cause the force reversal shown in FIGS. 2 and 3, 
forces F.sub.A and F.sub.B will in all cases be reduced. 
Rotation of the upper end of the piston rod to accomplished the purposes of 
the instant invention may be accomplished in a variety of ways. FIG. 3 
discloses one means for rotating the piston rod. As shown in FIG. 3, 
mounting plate 22 has been rotated through an angle .alpha. by the 
introduction of tapered spacer 40 between plate 22 and body mounting 
surface 23. Alternatively, it is possible to alter the configuration of 
mounting plate 22 to accomplish the same result while eliminating tapered 
spacer 40. This may be done by canting flange 25 at an angle which 
duplicates the introduction of tapered spacer plate 40 between plate 22 
and body mounting surface 23. Finally, the desired rotation of strut 
mounting plate 22 may be obtained by canting body mounting surface 23 to 
yield the rotation otherwise produced by tapered spacer 40. 
Those skilled in the art of suspension design will appreciate that it is 
possible to practice the present invention by rotating the lower mount of 
the strut outboard by canting socket 16, into which the lower end of strut 
18 is fitted, in a direction outboard of the vehicle at a predetermined 
angle of rotation about an axis which is generally parallel to the 
longitudinal centerline of the vehicle. 
The present invention can be utilized to allow tuning of a vehicle's ride 
characteristics to yield a desired operating condition. More specifically, 
by altering the angle .alpha., the operational friction forces of the 
vehicle's struts may be modified in a desired manner. If the friction 
within the suspension including the strut is measured and either or both 
of the ends of the strut is then rotated with respect to the remainder of 
the strut in the manner prescribed herein, the friction within the 
suspension may then be remeasured and the mounting of the strut 
readjusted. Successive iterations of this process will yield the desired 
reduction of friction within the strut. 
The term "chassis", when used in the specification and claims, will be 
understood to refer to either a conventional vehicle chassis or to a 
conventional unitary chassis and body construction, and is intended to 
include vehicle structure and components connected to or supported upon 
the chassis structure and forming part of the sprung portion of the 
vehicle. 
While preferred embodiments of the present invention have been shown and 
described, it is obvious to one skilled in the art that various 
modifications and substitutions may be made without departing from the 
spirit of the invention which is limited only in the scope of the appended 
claims.