Steering system for tracking of wheels

A motor vehicle steering system having first and second linkage assemblies, each pivotally coupled to a steerable wheel to exert simultaneous pushes or pulls, depending upon the direction of a vehicle turn. The first linkage assembly has an inboard end which is pivotally coupled to a first T-shaped track-inducing member which is connected to the steering box of the vehicle. The second linkage assembly is connected to a second T-shaped track-inducing member. Ends of the track-inducing members opposite to the linkage assemblies are joined by an arm. Rotation of a vehicle steering wheel causes the first track-inducing member to rotate about a vertical axis defined by the steering box. The joinder of the track-inducing members results in displacements of the inboard ends of the linkage assemblies. Because the connections at the opposed ends of each track-inducing member are out of phase by less than 180.degree., displacements of the linkage assemblies along an axis parallel to the side-to-side extension of the vehicle are dissimilar, and both the first and second steerable wheels track the turn center of the vehicle.

DESCRIPTION 
1. Technical Field 
The present invention relates generally to steering systems and 
particularly to steering systems for the tracking of steerable wheels 
during a turn. 
2. Background Art 
During negotiation of a turn, a motor vehicle forms an arc about a center 
of rotation as the steerable wheels of the vehicle are pivoted. Because 
the steerable wheels are spaced apart laterally, the outside wheel traces 
a larger radius circle than the inside wheel. Thus, only one wheel of a 
pair of wheels on opposite sides of a vehicle can be aligned with a radius 
of the vehicle turn center when both wheels are pivoted equal degrees. 
A tire which "tracks" a turn center is one which is aligned with a radius 
of the turn center. Tire tracking is desirable since it directly affects 
the tire adhesion, thereby improving both the handling and the feel of the 
vehicle. A tire which does not track a turn center experiences tire slip. 
Tire slip prematurely deteriorates a tire and leads to tire slide and, 
when excessive, loss of control of the vehicle. 
Tires which are not in tracking alignment will also adversely affect the 
wear of suspension components. The factors which lead to tire slip produce 
a stress not only on the bead wires and side walls of the tire, but also 
upon pivot assemblies and other components of the vehicle suspension. 
Ideally, laterally spaced steerable wheels are turned unequal degrees so 
that each wheel is tangent to the respective turning circle and each axis 
of wheel rotation is directed at the center of a vehicle turn. Therefore, 
in the ideal situation, the outside wheel must be pivoted to a lesser 
degree than an inside wheel. 
Steering and suspension systems which provide some degree of tracking are 
known. Such tracking systems, however, are typically compromises between 
complete tracking and other effects. Also known are steering and 
suspension systems for banking of steerable wheels to find a motion center 
point above the level of the car. Such systems are taught in U.S. Pat. No. 
4,159,128 to Blaine, U.S. Pat. No. 2,852,268 to Johnson, U.S. Pat. No. 
2,689,747 to Kolbe and U.S. Pat. No. 1,556,531 McMillin. These banking 
systems decrease the strain upon tires and suspensions, but alone the 
banking systems do not cause a pair of steerable wheels to track a turn 
center. Blaine, for example, teaches that an "outside" wheel in a turn 
must be banked, or tilted, to a greater degree than an "inside" wheel. 
Thus, the tilting of a wheel about a horizontal banking axis contrasts 
with the pivoting of a wheel about a vertical steering axis where an 
inside wheel must be pivoted to a greater extent in order to obtain 
tracking alignment. 
An object of the present invention is to provide a steering system which 
causes a pair of laterally opposed steerable wheels to accurately track a 
turn center as a vehicle negotiates a turn. Another object is to provide 
such a steering system which can be retrofit to existing vehicles. 
DISCLOSURE OF THE INVENTION 
The above objects have been met by a steering system having members which 
compound displacement dissimilarities of wheel linkaging to provide 
complete tracking of a turn center. That is, the present invention 
includes a first assembly for pivoting an inside wheel to a greater degree 
than an outside wheel and includes a member to further exaggerate the 
differentiation, with the goal being one of providing perfect parallel 
tracking throughout the steering range. 
The first assembly includes a first T-shaped track-inducing member which is 
connected to the pitman arm shaft of a steering box so that rotation of a 
vehicle steering wheel rotates the track-inducing member about a vertical 
axis. A motion transfer segment of the track-inducing member is parallel 
to the longitudinal axis of a vehicle during straight-line driving. A tie 
rod is attached to a first pivot coupling at one end of the motion 
transfer segment. At the opposite end of the motion transfer segment is a 
second pivot coupling which is attached to an arm. A pivot extension 
segment of the track-inducing member projects horizontally from the motion 
transfer segment to form the T-shape and to attach to the pitman arm shaft 
of the steering box. Thus, the ends of the motion transfer segment are 
less than 180.degree. out of phase during rotation about the vertical axis 
and displacement of the end attached to the tie rod is dissimilar to the 
displacement of the end attached to the arm. 
The tie rod attachment to the motion transfer segment is at the inboard end 
of a tie rod which has an outboard end that exerts a turning force on a 
steering rod of a first wheel. The dissimilar displacements created by the 
track-inducing member cause a degree of pivot of the first steerable wheel 
which is different than the degree of pivot of a laterally opposed 
steerable wheel. 
The variations in degrees of pivot, moreover, are exaggerated by a second 
T-shaped track-inducing member. This second member includes a motion 
transfer segment which is parallel to the first member during 
straight-line driving. The forward ends of the two motion transfer 
segments are connected by the arm. A tie rod extending from the steering 
rod of a second wheel has an inboard end pivotally coupled to the rearward 
end of the second track-inducing member. Again, the ends of the motion 
transfer segment are less than 180.degree. out of phase during rotation 
about a vertical axis. The track-inducing members act together to pivot an 
inside wheel of a turn to a greater extent than an outside wheel. 
An advantage of the present invention is that both of a pair of steerable 
wheels track a turn center. The two tie rods are equal in length to act 
against undesired toe-in and toe-out fluctuations. Moreover, the tie rods 
attach to the track-inducing member at pivot points in alignment with the 
pivot shafts of control arms of the vehicle. This alignment of pivoting 
further promotes elimination of undesired toe-in and toe-out fluctuations. 
Tracking of a turn center improves maneuverability and control of a 
vehicle as tire slip is reduced. Reduction of tire slip also decreases the 
stress on tires and suspension components. Another advantage of the 
present invention is that the first track-inducing member is connected 
directly to the steering box, thereby facilitating retrofit of the 
steering system to existing structures.

BEST MODE FOR CARRYING OUT THE INVENTION 
With reference to FIG. 1, a vehicle steering system is shown for pivoting a 
left steerable wheel 10 and a right steerable wheel 12. Each wheel 10 and 
12 is associated with a conventional steering assembly that includes a 
kingpin 14 and 16, a steering rod 18 and 20, and a tie rod 22 and 24. Also 
conventional are the lower control arms 26 and 28 and upper control arms 
30 and 32. 
As will be explained more fully below, the tie rods 22 and 24 are 
operatively coupled to a steering box 34 so that rotation of a vehicle 
steering wheel causes generally opposed motion of the tie rods. The tie 
rod 22 associated with the left steerable wheel 10 has an outboard end 
connected to the steering rod 18 at a ball and socket joint 36. At the 
inboard end, the tie rod 22 is connected to a T-shaped track-inducing 
member 38. The connection of the track-inducing member 38 to the inboard 
end of the tie rod 22 is provided by a pivot coupling 40. 
Now referring to FIGS. 1 and 2, the track-inducing member 38 comprises a 
motion transfer segment 42 and a pivot extension segment 44 which is 
perpendicular to the motion transfer segment. The pivot extension segment 
44 is attached to a pitman arm shaft 46 of the steering box 34. The 
steering box is fixed to a vehicle frame 48 by bolts, not shown. 
Manipulation of a vehicle steering wheel, not shown, causes rotation of a 
steering column 52 which is forked at a lower end and connected to the 
steering box. The steering box is a conventional device having a worm gear 
which translates clockwise or counterclockwise rotation of the vehicle 
steering wheel into an opposite rotation of the pitman arm shaft 46. That 
is, counterclockwise rotation of a vehicle steering wheel causes clockwise 
rotation of the track-inducing member 38. 
During straight-line driving, the left tie rod 22 is parallel to a coupling 
arm 54 joined to the motion transfer segment 42 of the track-inducing 
member 38 by a pivot coupling 56. However, during negotiation of a turn, 
the tie rod 22 and coupling arm 54 are no longer parallel. A phantom 
illustration of a left turn is shown in FIG. 1 to demonstrate the position 
of parts. In the phantom illustration of the left turn, the angle formed 
by the tie rod 22 and the motion transfer segment 42 is significantly less 
than the angle formed by the coupling arm 54 and the motion transfer 
segment. In like manner, there is a dissimilarity in displacement of the 
tie rod 22 and the coupling arm 54 relative to an X-axis that is defined 
by the transverse extension of the vehicle frame 48. 
The method of achieving a greater displacement of the tie rod 22 relative 
to the coupling arm 54 along the X-axis is best illustrated in FIG. 2. As 
noted above, manual rotation of a vehicle steering wheel causes the 
T-shaped track-inducing member 38 to undergo an opposite rotation. Thus, 
the forward pivot coupling 56 follows the arc 58, while the rearward pivot 
coupling 40 follows the arc 60. The arcs 58 and 60 are portions of a 
circle about the rotational axis defined by the pitman arm shaft 46. The 
pivot extension segment 44 of the track-inducing member 38 is attached at 
the midpoint 62 between the opposed pivot couplings 40 and 56. During the 
right turn illustrated in FIG. 2, the midpoint 62 is moved away from the 
right steerable wheel of a vehicle as counterclockwise rotation takes 
place during the turn. Maneuvering of the vehicle steering wheel moves the 
midpoint 62 through the sequence indicated in FIG. 2 until the position 64 
is reached. With the midpoint 62 moving away from the right side of the 
vehicle, the pull on the coupling arm 54 at the joint 56 is greater than 
the pull on the tie rod 22 at the joint 40. Consequently, a tire 
controlled by motion of the coupling arm 54 pivots to a greater extent 
than a tire controlled by the tie rod 22. The opposite effect is 
experienced during return to straight-line driving and during execution of 
a left turn, as shown in FIG. 1. The T-shaped track-inducing member 38 
rotates clockwise during a left turn, and because the midpoint between the 
pivot couplings 40 and 56 moves toward the left steerable wheel 10, the 
tie rod 22 associated with the left steerable wheel provides a greater 
push than the push provided by the coupling arm 54 associated with the 
right steerable wheel. For both left and right turns, therefore, the 
inside wheel is steered a greater degree than the outside wheel. 
Another way of analyzing the same effect is to look to the arcs 58 and 60 
followed by the pivot couplings 40 and 56 in FIG. 2. In the initial 
straight-line driving position shown in FIG. 2, the pivot-extension 
segment 44 may be considered as defining an X-axis. The relevant Y-axis is 
parallel to the motion transfer segment 42 and cuts through the pitman arm 
shaft 46 which defines the vertical axis of rotation. In following the 
arcs 58 and 60, the pivot couplings 40 and 56 are significantly less than 
180.degree. out of phase. Thus, the pivot couplings have dramatically 
different X and Y components of motion as the pivot couplings sweep along 
the respective arcs. The right turn illustrated by the arcs in FIG. 2 
shows that the forward arc 58 has a much greater range along the X-axis in 
the direction of the left side of a vehicle than does the arc 60 in the 
direction of the right side of the vehicle. In a straight-line driving 
position, the pivot coupling 40 has already swept through that portion of 
the arc which maximizes motion in the direction of the right side of the 
vehicle. In contrast, the forward pivot coupling 56 is in the position to 
maximize the lateral movement of the associated coupling arm 54. As a 
result, the right turn causes a greater pull of the coupling arm 54 than 
the pull on the tie rod 22. 
While the relevant arcs are not shown in FIG. 2, a left turn has the same 
effect as described above. The rearward pivot coupling 40 is in a position 
to maximize the movement along the X-axis during negotiation of the left 
turn. The forward pivot coupling 56, on the other hand, has a 
comparatively high range of motion along the Y-axis but a low range along 
the X-axis. Again, the inside wheel of a turn is steered to a greater 
degree. 
It has been discovered that the dissimilarities in displacement of the left 
tie rod 22 and the coupling arm 54 along the X-axis, is insufficient to 
provide a true track of a turning center throughout the steering range. 
For this reason, a track-inducing member 66 is included at the right side 
of the vehicle. The second track-inducing member 66 functions in the same 
manner as the above-described member 38, having a motion transfer segment 
68 and a pivot extension segment 70. The end of the pivot extension 
segment opposite to the motion transfer segment is pivotally connected to 
a bracket 72 affixed to the vehicle frame 48. A forward pivot coupling 74 
and a rearward pivot coupling 76 at opposed ends of the motion transfer 
segment are significantly less than 180.degree. out of phase with respect 
to rotation of the track-inducing member 66 at the bracket 72. Thus, as 
described above, there is a dissimilarity of displacements of the two 
pivot couplings 74 and 76 along the X-axis as the vehicle negotiates a 
turn. For example, in the turn illustrated in phantom in FIG. 1, offset 
rotation of the first motion transfer arm 42 causes a greater displacement 
of the left tie rod 22 than the coupling arm 54. This dissimilarity of 
displacement of left and right linkage members is increased by the offset 
rotation of the second motion transfer segment 68. The rearward pivot 
coupling 76 is in a position to maximize motion along the X-axis during a 
right turn, but in the phantom left turn of FIG. 1, there is a 
comparatively high range of motion along the Y-axis rather than along the 
X-axis. 
Thus, the track-inducing members 38 and 66 combine to provide sufficient 
dissimilarities of wheel pivot. As shown in FIGS. 1 and 3, the left turn 
about a turn center 78 is executed with the steerable wheels 10 and 12 
being turned dissimilar degrees to track the turn center. In order for 
both wheels 10 and 12 to track the turn center 78, it is necessary that 
the inside wheel of the turn pivot to a greater degree than the outside 
wheel. Proper tracking occurs only when the rotational axes of all four 
wheels 10, 12, 80 and 82 intersect at the turn center 78. The present 
invention permits a precise tracking throughout the range of steering 
permitted by maneuvering of the steering column 52. 
In operation, a first dissimilarity of displacement along the X-axis is 
produced by the left track-inducing member 38, and a second dissimilarity 
is produced by the right track-inducing member. The track-inducing members 
are each rotated about a vertical axis which is aligned with the inboard 
extension of the associated lower control arm 26 and 28. The lower control 
arms are mounted on shafts 84 and 86 which are fixed to a cross member 88 
to permit relative movement between the control arms and the vehicle frame 
48. Equidistantly spacing an inboard end of a lower control arm 26 and 28 
with the pivot axis of the associated tie rod 22 and 24, promotes 
elimination of undesired toe-in and toe-out fluctuations. 
While the present invention has been illustrated as having track-inducing 
members 38 and 66 which have pivot extension segments 44 and 70 that are 
equal in length, this is not critical. However, the combined length of the 
two pivot extension segments is critical to proper tracking of a specific 
vehicle, so that after determination of the combined length a shortening 
of one pivot extension segment must be accompanied by a corresponding 
lengthening of the other. Moreover, the left and right tie rods 22 and 24 
should be of equal length to guard against undesired toe-in fluctuations.