Steering mechanism

A steering mechanism for use in a vehicle, such as an industrial truck or the like, in which a two-way power steering actuator cylinder having a piston rod extending from both ends is supported from and above a steering axle by pivot tube and pivot shaft members which enable universal movement of the steering cylinder, the piston rod functioning also as a tie rod which is connected at each opposite end to a modified four-bar steering linkage which is in turn connected to a dirigible wheel. King post assemblies are secured to opposite ends of the steer axle which connect the four-bar linkages to the wheels. Each such linkage includes a steering link extended in length to connect the adjacent end of the actuator piston rod. One end of a guide link of the four-bar linkage is connected to the steering link intermediate the ends thereof.

BACKGROUND OF THE INVENTION 
The field of art of which the invention pertains includes steering 
mechanism, and more specifically steering mechanism for industrial lift 
trucks and other vehicles. 
Prior steering mechanisms, particularly for vehicles of the type primarily 
contemplated, have more or less successfully coped with several problems 
inherent in the design of such mechanisms, and predictably there have been 
several prior design approaches. 
One of the problems encountered and not fully resolved heretofore has 
concerned the provision of a steering geometry in a four wheeled vehicle 
capable, within a relatively confined space, of producing substantially 
ideal differential steering angles as between the dirigible wheels through 
a very wide range of angular movement of the wheels, such as 180.degree. 
from a full right cramp to a full left cramp position thereof. A typical 
prior steering mechanism for a lift truck using a four-bar linkage design 
is disclosed in Howell U.S. Pat. No. 2,191,961, which includes a rather 
full explanation of the theory of differential angular steering such that 
the wheels roll with relatively little lateral slip or scuffing during 
turning maneuvers of the truck. 
Another problem has been to provide in the limited space ordinarily 
available for steering such trucks a steering linkage and tie bar assembly 
which is effective with a relatively small variation in actuator force to 
turn the steering wheels to a high angle full cramp position. Heretofore 
the effective turning moment arm has approached a very small value at high 
maximum steering angles in conventional four-bar steering mechanisms, 
thereby requiring either a relatively large range of actuator force or a 
substantial limitation on steering angle. Prior steering mechanisms of the 
type contemplated have not been available to provide 180.degree. steering 
angles combined with accurate steering geometry. 
While some prior steering axles, such as shown in Gaulke U.S. Pat. No. 
3,480,100 and Matteo U.S. Pat. No. 3,768,585, have utilized a combination 
power actuator and tie rod construction, they are unable to effect 
180.degree. wheel swing with accurate steering geometry in a relatively 
small space. 
SUMMARY OF THE INVENTION 
My invention provides an extremely novel modification in four-bar linkage 
steering devices which involves the extension of a steering link element 
to a point of connection with a tie rod element which is beyond the point 
of connection of the steering link with a guide link of the four-bar 
linkage. It also provides a steering assembly mounted in generally 
inverted U-shaped configuration around a steering axle, which includes an 
actuator cylinder and tie rod mounted for pivotal movement about vertical 
and transverse horizontal axes. 
A number of important advantages are effected by my invention as follows: 
1. Improved steering geometry effecting minimum variation from 
theoretically ideal differential steering in 180.degree. steer angle 
assembly for a four wheel vehicle; 
2. Less variation in steering linkage actuator force requirements which in 
turn makes possible the use of both a smaller diameter actuator cylinder 
for any given maximum hydraulic pressure, and of a lighter design of the 
steering linkage. These advantages result because both the linkage and the 
actuator must be designed to resist maximum force, not average force; 
3. A combined tie rod and actuator cylinder mounted as a single unit above 
the steer axle and connected to the steering linkage in such a manner that 
combined pivotal movements thereof occur during steering maneuvers, the 
said movements being relatively small as a result of the improved four-bar 
linkage geometry which further results in minimizing any off-center thrust 
forces on the packing of the cylinder; 
4. Improved universal pivotal mounting of actuator and tie rod. 
It is therefore a primary object of the present invention to provide 
improved steering geometry, steering structure, and mounting structure for 
steering actuator means in vehicles of the type contemplated. 
Additional objects, features and advantages of the invention will become 
apparent from the following description and accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An exemplary vehicle with which my invention may be used is shown in FIG. 1 
as an industrial lift truck 10 having a main body and chassis 12 enclosing 
a prime mover, drive, and control means which may comprise a hydrostatic 
or electric system, for example, for driving a pair of drive wheels 14. 
The truck includes an elevatable upright and fork carriage assembly 16 
mounted from the forward end, an operator's station 18, and a pair of 
dirigible wheels 20 and 22 steered by an operator's steering wheel 24 and 
supporting, along with the steering mechanism of my invention, a steering 
axle 26 which is shown in FIG. 4 as being relatively massive for the 
purpose of providing in such a vehicle a non-deformable rigid structure as 
well as counterweight. The steer axle is secured to the truck frame by a 
central longitudinal plate member, a portion of which is shown at 28, and 
by a pair of tubular sleeve members 30 welded to an arcuate section 31 of 
the axle and to side frame members of the truck. 
The wheels 20 and 22 are mounted suitably for rotation both about 
horizontal and vertical axes on a pair of yokes 32 which are secured to a 
pair of king posts 34 extending through sleeves 30 and mounted suitably on 
bearings therein, the king posts terminating in reduced diameter upper 
ends 36. 
Mounted centrally of the axle in a recess 38 and secured as by welding in 
the axle at 40 is a support post 42 upon which is mounted a tubular member 
44 which is rotatable about the vertical axis of post 42 and to which is 
secured a pair of transversely extending stub shafts 46 on which are 
mounted for articulation a pair of laterally spaced vertical plates 48 
which are secured to a pair of longitudinally spaced vertical plates 50 
between which is mounted for articulation in a vertical plane on a pair of 
pivot pins 54 a double-acting hydraulic steer cylinder 52. Boss members 56 
are mounted on pins 54 and are secured centrally of and to the front and 
rear sides of the cylinder. Plate members 50 are mounted so that a 
substantial clearance is present between the plates 50 and the tubular 
member 44, as shown, so that fore and aft movement of the cylinder can be 
effected, as best shown in FIG. 5. 
It will now be apparent that the actuator cylinder 52 is mounted for 
universal movement in operation of the steering mechanism as may be 
required about any one or combination of three different axes, viz., 
twisting movement in a horizontal plane about the vertical axis of tube 
44, articulation in a transverse vertical plane about the axis of pin 54, 
and fore and aft movement in a substantially horizontally plane about the 
axis of stub shafts 46. Thus, cylinder 52 is capable of continuous and 
inherently correct adjustment to accommodate the steering mechanism in and 
into any mode of steering on relatively smooth or rough surfaces, and from 
any steer angle to any other, while minimizing off center forces or thrust 
in any mode of steering, as will become apparent as the description 
proceeds. 
Cylinder 52 contains a piston head mounted centrally of piston rod portions 
60 and 62 which extend from both ends of the cylinder, the cylinder being 
connected to a steering pump and control circuit, not shown, which is 
activated by the operator's wheel 24 in known manner. As will be apparent, 
pressure fluid entering one or the other ends of the cylinder casing will 
actuate the piston and rod to a selected right or left hand steer position 
as the steer wheels 20 and 22 are actuated by linkage to be described, 
cylinder and rod structure combining the functions of an actuator and tie 
rod of conventional steering arrangements and effecting in combination 
with the remainder of the steering mechanism to be described in a number 
of significant advances over the prior art. 
A significantly modified four-bar linkage is operatively connected to each 
end of the piston rod, to each of the steer wheels, and to the frame. 
Right-hand linkage 64 comprises a guide link 66 mounted pivotally at one 
end at 68 from the steer axle by a post 69 and pivotally at the opposite 
end at numeral 70 between the ends of a rigid extended intermediate link 
72 which is pivotably connected at its outer end 74 to a steering arm 76 
mounted at its opposite end to king post 36 for turning wheel 20. An 
inwardly extending portion 78 of link 72 is connected pivotably to a 
bifurcated end of piston rod 60 at 80. 
The linkage parts which connect the piston rod portion 62 to king post 36 
at wheel 22 are of the same design as and in allochiral relationship to 
the parts of linkage 64, and the parts thereof have been identified by the 
same numerals with a prime designation. 
FIG. 6 illustrates diagrammatically my steering mechanism with the steer 
wheels being represented in three different positions, viz., the 
straight-ahead position as represented by the solid lines, the elements of 
which are numbered the same as in FIG. 2, the parts of the mechanism in a 
full right turn position (which is full left cramp in rear wheeled 
steering) being represented by dotted lines and carrying the same 
numerical designations with the addition of the letter "R," and the parts 
of the mechanism shown in a full left turn position (full right cramp in 
rear wheel steering) being illustrated in broken lines, the numerical 
designation of the parts being the same with the addition of the letter 
"L." An outline of the wheels 20 and 22 is illustrated in straight-ahead 
position and the center lines thereof are shown in full right turn 
position at numerals 20R and 22R, and in full left turn position at 
numerals 20L and 22L. The angles of turn of each wheel in both right and 
left turn positions are illustrated, it being noted that an exemplary 
embodiment of an actual design is shown in FIG. 6; it illustrates a full 
180.degree. turning capability of each wheel from one full cramp position 
to the opposite full cramp position. 
If the tread and/or wheel base varies in any vehicle for which my invention 
is designed the length of the various steering links and of the actuator 
will, of course, be changed to meet the design requirements. If the wheel 
base to tread ratio remains constant as between any vehicles then the 
ratios of the various link lengths and of the actuator cylinders in 
steering mechanisms designed for such vehicles will remain substantially 
the same as shown in FIG. 6, for example, other factors remaining 
constant. If, however, the wheel base to tread ratio changes as compared 
with that used in designing the mechanism of FIG. 6, for example, then the 
ratios of the link lengths of the steering mechanism will change, all as 
will be apparent to persons skilled in the art. In addition, if there is a 
required variation in the length of any one or more links from that shown 
in exemplary FIG. 6, for example, which may result from such factors as a 
variation in force output requirement of the actuator and/or different 
space limitations or available configurations from that disclosed, then 
the ratios of the link lengths will vary as a function of the change in 
length of any given one link. This is by way of generalized exemplary 
design variation criteria which will be readily understood by any person 
skilled in the art following his awareness of the design concept herein 
disclosed. 
Outstanding and much improved geometric design accuracy and efficiency is 
achieved in the use of my invention, plus additional attendant advantages 
which are derived primarily from the use of the extensions 78 and 78' of 
intermediate extended guide links 72 and 72', and also from the manner of 
mounting cylinder 52 in relation to the steer axle. Although the use of my 
steering mechanism effects the greatest degree of improvement over the 
prior art in a four wheeled vehicle which requires 180.degree. of steer 
wheel turning capability, it is also of most significant advantage in such 
vehicles which may require substantially less than 180.degree. of such 
capability. The extent of advantage derived in the use of my invention 
decreases as the steer angle requirement decreases substantially below 
180.degree., but nonetheless advantages over the prior art persist through 
lesser steer angle requirements. The significance of the invention is 
however, best represented in a design as shown in the embodiment herein 
disclosed which utilizes 180.degree. total steer angle capability. 
On standard four-bar steer linkage design it will be understood that pivots 
70 and 80, viewing the right-hand rear wheel, are combined as a single 
pivot, there being no rigid extension 78 in the link. Only the one side of 
the linkage is discussed below for the present purpose, but it will be 
understood, of course, that the same applies to the opposite side linkage 
as well. As will be particularly apparent in FIG. 6, if piston rod 60 were 
connected at pivot 70 instead of at pivot 80 by eliminating extension 78, 
the moment arm for turning the wheel would rapidly decrease as a full 
right wheel turn position is approached. Prior four-bar steering linkage 
designs have utilized such a structure so that the turning arm moment 
becomes very small at high steer angles necessitating, among other things, 
heavier steering linkage parts, a larger hydraulic actuator, more space 
for assembly of the steering mechanism, and the like, as will be described 
in greater detail below. The use of an extension link portion 78 effects a 
significantly longer moment arm at all steer angles to both full cramp 
positions, as will be apparent from a consideration of the full cramp 
positions of the linkages of both the right and left rear steer wheels as 
illustrated most graphically in FIG. 6, and as illustrated best 
pictorially in comparing the straight-ahead position of FIG. 2 with the 
left full cramp position (right hand turn) of FIG. 3. 
The extension links 78 and 78' enable a steering linkage which produces 
almost perfect steering geometry not heretofore obtainable, particularly 
in high angle steering such as 180.degree. center point steering for which 
the preferred embodiment as disclosed is designed. It has not been 
possible heretofore to provide both 180.degree. total wheel swing in 
four-bar linkage steering devices for a pair of steer wheels combined with 
the degree of accuracy in steering geometry and relatively low and uniform 
actuator forces present in my invention. 
Certain of the dependent claims herein define geometric relationships of 
certain elements of the steering linkage, such as the direction of the 
intermediate link at a maximum cramp angle, the relationship of the guide 
link and the steering arm and the position of the steering arm both at 
0.degree. steer angle and at said maximum cramp angle, and the 
relationship of the guide link and the intermediate link at said cramp 
angle, all of which relationships may be best viewed in the showing of the 
steering elements of the right hand wheel in maximum cramp angle position 
in FIG. 3. 
In FIG. 6 numeral 90 denotes the path of movement of pivot 80 from one full 
cramp position to the opposite such position, it being particularly 
important to note the relatively small lateral and longitudinal distance 
traversed which translates in the device as combined twisting and 
longitudinal movement during such 180.degree. of movement of wheel 20, 
such twisting and longitudinal movement being effected about pivot tube 44 
and pivot shafts 46. The maximum and total movement of actuator cylinder 
52 is represented best in FIG. 2 by the single and double broken line 
positions thereof which are superimposed on cylinder 52 at numerals 52R 
and 52L. The various positions of the cylinder and yoke may also be seen 
in the side sectional view of FIG. 5, the positions of the cylinder, yoke, 
and pivot 46 being identified by the usual designations for 
straight-ahead, and left and right turn positions. It will be noted that 
the right and left full turn positions of cylinder 52, yoke 50 and pivot 
shaft 46 are included in the section of FIG. 5 in single and double broken 
lines, the same as in FIG. 2. 
FIG. 7 is a comparative graphical showing of the turn angles of the left 
and right-hand wheels during right-hand steering movement of the vehicle 
from straight-ahead to a full cramp wheel position. The broken line 
illustrates theoretically perfect differential wheel angle steering 
characteristic. The differential steering characteristic of my device is 
represented by Curve A, whereas a typical conventional such characteristic 
is illustrated by Curve B. Curve C represents the characteristic which 
would result if my four-bar linkage design were to be used without the 
extension 78 and 78' of links 72 and 72'. That is, it assumes the same 
design as disclosed except that the piston rod ends are connected at 70 
and 70', not at 80 and 80'. The major deviation from ideal steering 
geometry resulting in apparent, although, of course, such a design would 
not be used in practice. 
The FIG. 8 chart shows comparative results of actuator force output 
requirements as between full left and full right cramp positions for each 
of the steering mechanisms represented by the characteristic Curves A, B, 
C and Theoretical of FIG. 7. The numerical force figures are expressed in 
absolute units which, depending upon the particular embodiment and vehicle 
size may, of course, vary greatly as to measured force output required, 
but the ratios of absolute units will remain the same as between the 
steering mechanisms represented by the characteristics of the A, B, C and 
Theoretical curves illustrated. 
The significance of the unit force differences to actuate the wheels 
between full cramp positions for the steering mechanisms represented by 
the A and B characteristic curves are apparent. It will be noted that the 
total actuator force difference required is substantially more than 2:1 as 
between a typical conventional four-bar linkage and the present invention. 
In addition it will be noted that the actuator force required for my 
design A remains far more nearly constant during actuation to a full turn 
position than does the force required to actuate the conventional design 
of Curve B. That is, it will be noted that my design requires at the right 
rear steer wheel a force of 1.45 units in full right cramp and 1.50 force 
units in full left cramp, as compared with 1.94 force units in full left 
cramp and 5.13 force units in full right cramp for the exemplary 
conventional linkage. The closeness of the force unit requirements of my 
design to those of a theoretically perfect design, which would have 
uniform constant unit force output throughout the full range of steering, 
are apparent. 
Thus, in addition to much improved steering geometry as effected by my 
invention, the relative consistancy and lower force output requirements 
make it possible to use a substantially smaller diameter actuator cylinder 
than heretofore for any given maximum hydraulic pressure inasmuch as the 
actuator size is determined by the peak force requirement, and not by an 
average force requirement. The peak force requirement of design B, as 
shown in FIG. 8 at full left cramp, is more than three times the peak 
force requirement of this invention. In other words, the effective moment 
arm for turning the steering wheels remains relatively constant in my 
design, whereas with conventional four-bar steering mechanisms the moment 
arm approaches a very small value at maximum cramp angle in 180.degree. 
steering mechanisms. Therefore, in addition to the available use of 
smaller actuator cylinders, a significantly lighter design of steering 
linkage may be used because the steering linkage also is designed to 
resist peak force, not average force. The results are included for the 
design which produces Curve C in FIG. 7 as a matter of information. 
Furthermore, the relatively small fore and aft movement of pivots 80 and 
80' through the full range of steering, as illustrated for pivot 80 by 
curve 90 in FIG. 6, permits the tie rod 60, 62 to be used also as a piston 
rod of the actuating cylinder 52 which in turn supports the cylinder in a 
manner which virtually eliminates off-center thrust or reaction forces 
which would otherwise increase friction and wear at the cylinder packings. 
In other words, if the tie rod and actuator were separate, misaligning 
forces are induced either on the cylinder or on the tie rod or both which 
increases off-center thrust forces. 
Yet additionally, a significant saving in space for installation of the 
steering assembly may be realized. Adequate space for conventional 
four-bar steering may not be available in certain vehicle designs. The 
space saving is, of course, realized by the combination of structure which 
effects a reduction of actuator cylinder size, a combination of tie rod 
and actuator as a cylinder and piston rod assembly which moves a 
relatively small distance fore and aft in operation, and a lighter or less 
bulky steering linkage design. 
Although I have described and illustrated a preferred embodiment of my 
invention, it will be understood by those skilled in the art that 
modifications may be made in the structure, form and relative arrangement 
of parts without necessarily departing from the spirit and scope of the 
invention. For example, the embodiment disclosed herein is particularly 
adapted to rear wheel steering in a specific type of industrial lift truck 
in which space for installation of the steering mechanism is at a premium 
and in which my invention is of particular advantage for all of the above 
described reasons, including the combining of the actuator and tie rod as 
the hydraulic cylinder and piston rod structure. Of course, the invention 
may be found applicable to many vehicular types, at least some of which do 
not require and may not prefer the combination of actuator and tie rod as 
herein disclosed. The "tie rod means," as is set forth in some of the 
claims below, should not be interpreted, therefore, as in any sense being 
limited to the type disclosed herein, but may be any type of known tie rod 
with or without any type of combined actuator means. 
In addition, as a further example, the particular application disclosed 
herein for the lift truck design contemplated has made it advantageous to 
combine a steering axle and a generally inverted U-shaped steering 
mechanism having an actuator cylinder mounted for pivotal movement about 
different axes and above the steer axle. This structure is peculiar to 
certain vehicular types, such as the lift truck which is disclosed in the 
preferred embodiment, and is so claimed in some of the claims below. It is 
not, however, in any way essential to the broader aspects of the invention 
in relation to the four-bar linkage per se, such as is claimed in claim 1 
below. On the other hand, the design of my improved four-bar steering 
linkage is not essential to the practice of my invention of the novel 
mounting structure of the cylinder actuator and inverted U-shaped steering 
assembly in relation to the steer axle, as also claimed below. In other 
words, there are various important aspects of this invention which must be 
considered independently of other aspects, as well as in combination 
therewith, when considering the claims hereof. Accordingly, it should be 
understood that I intend to cover by the appended claims all such 
modifications which fall within the scope of my invention.