Motorcycle front wheel suspension system

A suspension system for the front wheel of a motorcycle wherein a fork that carries the front wheel is connected to the frame in a manner that the steering axis of the fork in response to front wheel deflection by bumps is displaced parallel to itself relative to the frame. A specific example of such a suspension mechanism is a double A-arm connection. Handlebars are rotatably mounted to the frame. A connection between the handlebars and the fork is made in a manner so only rotation of the handlebars will cause rotation of the fork about its steering axis, and the connection does not affect suspension movement of the wheel relative to the frame. Examples of the steering connection are a folding bar and a hydraulic system.

BACKGROUND OF THE INVENTION 
This invention relates generally to the art of vehicle suspension systems, 
and more particularly to an improved front wheel suspension mechanism for 
motorcycles and the like. 
Many motorcycle and bicycle front wheel suspension systems have been 
proposed in the literature and adopted in use. However, for 30 years the 
principle motorcycle products sold in the world have had the same basic 
front wheel suspension system of telescoping front forks. Although some 
limitations of this system have been recognized in general terms, no 
improvements over it have come forth. Its limitations include front end 
dive upon applying a front wheel brake and heavy weight because it is 
structurally inefficient. 
Therefore, in order to provide motorcycle handling characteristics by 
improving the front wheel suspension system, the present invention has the 
following as its principal objects: 
1. To provide a suspension system that permits the direction of wheel 
movement upon hitting a bump to be set independent of the front wheel rake 
and trail, including a particular direction that minimizes motorcycle 
front end dive due to application of the front wheel brake; 
2. To provide a suspension system that permits trail to be independently 
set; 
3. To provide a design that minimizes instability and maintains a more 
constant force feedback to the rider through the handlebars, even when the 
motorcycle strikes bumps; 
4. To minimize structural weight and bulk by providing a suspension linkage 
that efficiently transmits forces from the axle to the frame; 
5. To provide a comfortable, soft ride and also be good for racing and 
other hard use; and 
6. To provide a simplified and reliable mechanism for the front wheel 
suspension which accomplishes the above objects. 
SUMMARY OF THE INVENTION 
These and additional objects are accomplished by a front wheel suspension 
mechanism that moves the fork in a manner that the fork's steering axis 
orientation with respect to the frame does not change substantially. The 
suspension system connects to the fork only at its top, above the front 
wheel. Rotation of the fork about its steering axis is due solely to 
actuation by a steering linkage operated by movement of a handlebar 
pivotably mounted to the frame. The front suspension operates 
independently of the rear suspension and its movement is accommodated by 
the steering linkage. In a preferred form the suspension system for the 
front wheel assembly utilizes two A-arm members extending between the 
frame and the fork assembly. 
Additional aspects and features of the present invention, as well as other 
objects and advantages thereof, will become apparent from the following 
detailed description of its preferred embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a schematic illustration of the side view of a two 
wheeled motorcycle is shown for the purpose of explaining the improved 
front wheel motion that results according to the present invention when 
the motorcycle hits a bump. It will be understood, however, that the 
principles of this invention have application to any vehicle wherein a 
single front wheel is steered by a handlebar or steering wheel. Besides 
motorcycles, the techniques of the present invention have application to 
bicycles, and to vehicles having two rear wheels with a single steered 
front wheel. 
The basic motorcycle of FIG. 1 includes a frame 11, a front wheel 13, and a 
rear wheel 15. A fork 41 rigidly carries the front wheel axle 35. A 
handlebar 17 is pivotably attached to the front portion of the frame 11. A 
steering linkage (not shown) connects the handlebar 17 to the fork 41, 
causing movement of the handlebar 17 to rotate the fork 41 about a 
steering axis 21. The steering axis 21 never moves with respect to the 
fork 41. A steering head 19 is supported by the frame 11 through a 
suspension linkage 23. The fork 41 either pivotably connects to the 
steering head 19, said pivot defining the steering axis 21, or the 
connection is rigid. As is conventional on present motorcycles, a front 
wheel brake 25 is provided. Subsequent references to the "fork assembly" 
will mean the unit composed of the fork 41, and steering head 19. 
Embodiments of the steering head 19, suspension linkage 23, and the 
steering linkage are described in detail hereinafter with respect to FIGS. 
2-4. 
The linkage system 23 permits controlled movement of the front wheel 
assembly with respect to the frame 11 when a bump is hit, as shown in 
dotted outline in FIG. 1. This movement is independent of any movement of 
the rear wheel 15 since the rear wheel is carried by its own independent 
suspension system 27. 
In order to maintain constant the steering force that the rider feels 
against the handlebars 17 when the front wheel assembly moves, the "rake" 
and "trail" should not change. This makes it easier for the rider to 
control the motorcycle and maintain stability. The "rake" is the 
inclination from vertical of the steering axis 21. The "trail" is the 
distance between a point 31 wherein the wheel 13 contacts the surface 29 
and a point 31 which is the intersection of the steering axis 21 with the 
surface 29. The rake and trail do not vary with suspension movement when 
the suspension linkage 23 is properly configured so it moves the steering 
head 19 in a manner that the orientation of the steering axis 21 with 
respect to the frame 11 does not change. That is, when the steering axis 
21 moves, it always moves parallel to itself. 
If the linkage system 23 is designed to cause the axle 26 to move 
vertically, which is the case shown in FIG. 1, then the system has the 
further advantage of eliminating the front end dive caused by braking 
forces exerted by the front brake 25. However, the techniques described 
herein and methods of implementation are general enough to permit almost 
any particular wheel movement upon proper design of the linkage system 23, 
while still maintaining constant rake and trail. This gives a designer 
tremendous freedom. 
The fork assembly and front wheel 13 are supported by the suspension 
linkage 23 only at the top of the fork assembly, at a position outside the 
circumference of the wheel 13 when viewed from the side. No suspension 
arms cross the wheel 13 and there is no need for any direct linkage 
between the axle 35 and the frame 11. This simplifies the suspension 
system, makes the motorcycle handle more easily and reduces the size of 
the suspension system. 
Referring to FIG. 2, a preferred embodiment of a suspension linkage system 
and associated components is illustrated for carrying out the principles 
described with respect to FIG. 1. A fork 41 with a front wheel axle 43 at 
one end has a steering head 45 as an integral part of it at the other end. 
The fork assembly 41 is attached to the frame 11 through a linkage system 
that includes two sets of "A" arms 47 and 49, so called because they form 
the shape of an "A" in plan view. Arm 49 is pivotally attached to the 
frame 11 by pivots 51 and 53 lying on a common axis. At its other end, the 
A-arm 49 is attached to the top of the fork assembly 41 with a ball joint 
55. The A-arm 47 is similarly attached, being pivotally mounted to the 
frame 11 by pivots 57 and 59 lying on a common axis, while being attached 
on its other end to the fork assembly 41 with a ball joint 61. The ball 
joints 55 and 61 permit steering rotations of the fork assembly 41 about 
the steering axis 63 as well as permitting the movement of the fork 
assembly 41 with respect to the frame 11 that has been described earlier 
with regards to FIG. 1. 
The suspension linkage system shown in FIG. 2 has two structural 
advantages: the load path from the axle 43 to the frame 11 is as short as 
possible, and the A-arms 47 and 49 act in pure tension and compression to 
resist front wheel reactions. Only the fork acts in bending, thus the 
whole mechanism can be made very stiff with a minimum of structural 
weight. Additionally, there is a low moment of inertia about the steering 
axis because the suspension linkage does not rotate. A low moment of 
inertia improves steering stability. 
The fork assembly 41 is held away from the frame 11 by a spring 71 that is 
mounted to the frame 11 at one end through a pivot 67. The other end of 
the spring 71 is pivotably mounted to the lower A-arm 47 at 69. The spring 
71 is held in compression and gives a downward force to the fork assembly 
41. The weight of the motorcycle and rider act to compress this spring. 
Similarly, bumps encountered will cause the spring 71 to momentarily 
compress further. 
A folding bar 73 provides a steering linkage between the handlebars 17 and 
the fork assembly 41. The folding bar 73 is joined at one end to a 
handlebar shaft 75 by a U-joint 77 that has two degrees of rotational 
freedom. Similarly, the other end of the folding bar linkage 73 connects 
to the fork assembly 41 with another U-joint 79. The resulting linkage 
causes motion of the handlebar 17 to rotate the fork assembly 41 about its 
steering axis 63, while at the same time permitting the fork assembly 41 
to move with respect to the frame 11 without further rotation of the fork 
assembly 41 about its steering axis 21. Other linkages can be utilized, 
such as one with a spline shaft used in place of the folding bar 73, so 
long as the various degrees of freedom as described herein are provided. 
Referring to FIG. 3, different types of handlebar linkage and suspension 
linkage are illustrated. The suspension linkage is composed of a sliding 
post 93 attached to a pivot 95 mounted on the frame 11, and a rigid link 
83 which pivots on frame 11 mounted hinges 88 and 90. The other end of the 
rigid link 83 is pivotally attached to the steering head 81 by connections 
92 and 94 while the post 93 slidably mates in an opening 97 of the 
steering head 81. The axes of pivots 95, 88, 90, 92 and 94 are all 
parallel, and the post 93 is oriented perpendicular to these axes. A 
spring 99 reacts between the frame 11 and steering head 81, countering the 
weight of the motorcycle and rider. 
The fork 85 has a cylindrical boss 87 that rotatably connects to the 
steering head 81. The axis of this rotation is the steering axis 89 and it 
is coincident with the axis of the cylindrical boss 87. 
A hydraulic steering linkage is employed in FIG. 3. A hydraulic master 
cylinder 101 has a piston mechanically connected to a lever 103 that moves 
with rotation of the handlebar 17. Hydraulic fluid is transferred through 
a line 105 to a slave hydraulic cylinder 107. The ends of this cylinder 
107 make ball joint connections to the fork 109 and rigid link 111. 
Because ball joint connection 111 lies on the axis of pivots 92 and 94, 
suspension movement and steering rotations about the steering axis 89 act 
independently of each other. 
Referring to FIG. 4, a different specific embodiment of a hydraulic 
steering linkage is illustrated in combination with yet another steering 
head linkage system. Referring to the steering head linkage system first, 
a rigid link 115 is pivotally mounted at one end to the frame 11 and at 
the other end to a steering head 117 as was discussed in reference to FIG. 
3. A cylindrical boss 121, which is part of the fork 119, rotatably 
connects to the steering head 117. One end of an "A" arm 123 is pivotally 
mounted to the frame 11 at 141 and 143 and its other end is joined to the 
top of the fork boss 121 by a ball joint 125. The steering axis 127 is 
coincident with the axis of the cylindrical boss 121 and ball joint 125. A 
spring 65 is utilized in the embodiment of FIG. 4 similar to that 
described hereinbefore with respect to FIG. 2. 
For the steering linkage in the system of FIG. 4, the same master cylinder 
101 and lever 103 as exists in the system of FIG. 3 is employed. A 
hydraulic fluid hose 129 connects the master cylinder 101 to the slave 
cylinder 131. The slave cylinder 131 is solidly attached to the boss 121 
of the fork 119. A reaction strut 137 is connected by spherical joints to 
the slave cylinder 131 and frame 11. Spherical joint 139 lies on the axis 
of pivots 141 and 143, while spherical joint 135 lies on a line passing 
through ball joint 125 which is parallel to the axis of pivots 141 and 
143. Fork rotation about the steering axis 127 is independent of 
suspension movement with this reaction strut geometry. 
The rigid links of FIGS. 3 and 4 provide an efficient load path to the 
frame 11. Longitudinal forces on the steering head pivots cause only 
tension and compression in the rigid link 115, while transverse forces on 
the steering head pivots cause a shear in the plane of the plate-like 
rigid link 115. Front wheel forces do not cause bending or torsion in the 
rigid link 115, hence it carries these loads with minimal flexing and 
stress. Additionally, there is a low moment of inertia about the steering 
axis 137 because the suspension linkage does not rotate with steering 
movement. 
Although several preferred embodiments of a motorcycle suspension system 
embodying the various aspects of the present invention have been 
described, it will be understood that there are certain variations thereof 
which do not depart from the essence of the invention, and thus that the 
invention is entitled to protection within the full scope of the appended 
claims. For example, it will be understood that the handlebar linkage 
system of the embodiment of FIG. 2 can be utilized with the steering head 
linkage system of the embodiments of either of FIG. 3 or FIG. 4. 
Similarly, a hydraulic steering linkage system could be used with the 
steering head linkage system of FIG. 2. Other various combinations and 
variations will become apparent from the foregoing description as well.