Detent centering compensator for vehicle steering systems

A compensating apparatus resists movement of the steered wheels of a vehicle to either side of a selected center position, and returns them to this center position after such movement. The apparatus includes a cam member connected to the steered wheels for movement therewith and having a cam surface with a centering depression. A follower member is pivotally mounted on one end of an elongated rocker member and may be received in the centering depression to define the center position. An actuator assembly applies a resilient force against the other end of the rocker member to press the follower member into the centering depression in response to the pressing of a resilient mechanism by a fluid pressure system. The amount of the resilient force may be varied remotely either by the driver during vehicle operation or automatically in response to vehicle speed. The center position also may be changed during vehicle operation.

FIELD OF THE INVENTION 
This invention relates to vehicle steering systems and more particularly to 
a centering device for controlling the steerable wheels of a vehicle such 
as a motor home, bus, truck, automobile or the like so that a center 
steering position is selected and maintained in spite of spurious steering 
inputs, such as those caused by variable crosswinds, crown curvature or 
slant of the highway, or other factors tending to adversely affect vehicle 
steering by the driver. 
BACKGROUND OF THE INVENTION 
The steering systems of highway vehicles and the like are designed 
primarily for driver control. In these systems, the steering force 
required on the steering wheel and the ratio between steering wheel 
movement and movement of the steerable ground wheels depend upon the 
characteristics of the particular vehicle and the conditions under which 
it will usually be operated. A wide variety of extraneous forces can act 
on a vehicle steering system and spurious steering inputs caused by these 
forces must be dealt with satisfactorily in order to provide stable and 
controllable steering of a vehicle. As vehicle speed increases, the 
effects of any spurious steering inputs are magnified, making it necessary 
for the driver to exercise more precise and careful driving control. 
Vehicles with steering systems having positive caster generally track 
relatively straight ahead and generally resist normal steering inputs away 
from center, including those of the driver. Intentional turning maneuvers 
by the driver therefore require sufficient turning force to overcome this 
positive resistance to movement away from center.. When the driver relaxes 
the turning force applied to the steering wheel, a positive caster system 
has a definite tendency to return to its straight ahead position, although 
it may overshoot the neutral or center position if the steering wheel is 
entirely released. 
However, with such conventional steering, the smallest amount of erratic 
steerable wheel movement is passed on directly to the driver who must 
provide counter-active corrections through the steering wheel. The 
negative action of the steerable wheels is caused by spurious steering 
inputs from crosswinds, slanted or crown roads, bad road surfaces, and 
other adverse dynamic steering forces. Inherent geometric steering 
characteristics may also be responsible for spurious steering inputs. 
In other words, when the steered wheels are not able to hold a straight 
line, the problem is passed back through the system for driver correction. 
The result of such unruly behavior of the steerable wheels is known as 
"road wander". Heavy vehicle drivers know about road wander, crosswind 
steering, and steering wheel pull; and so does every front end specialist 
who must endeavor to solve these built-in problems. 
While positive caster is desirable in some respects, it is not without 
compromises over the full steering spectrum. For example, the adverse 
effects of strong gusty cross winds are usually more pronounced with 
positive caster. As its name would imply, the vehicle tends to caster 
towards the side of the roadway to which it is being pushed by the wind. 
Similarly, a high crown at the center of the roadway or a slanted roadway 
can cause vehicles to turn toward the edge of the roadway, that is, in the 
downhill direction. In addition, generous positive caster provides 
significant resistance to small radius turns, which can make city driving 
quite fatiguing. These three adverse effects are some of the negative 
aspects of achieving steering stability through generous amounts of 
positive caster. 
On the plus side, motor vehicles with positive caster are less fatiguing to 
drive over long distances and are safer and more controllable at highway 
speeds, as compared to vehicles without caster or with negative caster. 
This is because, by tracking straight, virtually no driver effort is 
required to keep a positive caster vehicle from swerving unless one of the 
foregoing sources of extraneous forces are present. 
Another drawback of prior art steering systems is that spurious inputs 
transmitted from the roadway through the steerable wheels affect 
substantially the entire steering assembly before encountering any 
stabilizing resistance from the steering wheel. The transmission of these 
various inputs between the steerable wheels and the steering wheel causes 
the inter-connecting components of the steering system to repeatedly 
oscillate between states of tension and compression. Such oscillations 
cause wear and slack in ball joints and other connections and have long 
been considered a primary source of stress fatigue which can lead to 
premature failure of various steering system components. Mechanical slack 
due to worn parts can also be a cause of steering system oscillations and 
vehicle wandering that require constant corrections and therefore produce 
driver fatigue. 
The ideal driving situation is therefore one where the steering system 
inherently causes the vehicle to travel in an unswerving straight line 
unless the driver intentionally turns the vehicle in another direction. 
Thus, the ideal steering system would require relatively little attention 
from the driver as the vehicle progresses along a straight line path down 
the roadway. From a steering standpoint, the vehicle should not respond to 
anything but the driver's steering commands and these must be of 
sufficient magnitude to overcome a significant resistance to turning away 
from center. In the absence of a steering input by the driver, the vehicle 
should literally do nothing but progress straight ahead. 
SUMMARY OF THE INVENTION 
The invention provides improved on-center control of the steerable wheels, 
and significantly reduces driver fatigue because it results in a major 
reduction in driver steering inputs. This is accomplished by allowing the 
driver to easily make small adjustments in the centered position of the 
steering system to fine tune steering of the vehicle during its operation. 
Fine tuning can only be made while driving, and makes driving more 
pleasurable and less fatiguing. It also prevents unnecessary trips to a 
front-end shop. 
The invention thus comprises a centering compensator having a center 
position which is remotely adjustable to permit the driver of the vehicle 
to change and reset the center position of the steering system to 
compensate for new or changed steering forces which would otherwise cause 
the vehicle to deviate from its straight ahead course. Such changes in the 
center position of the steering system may be necessitated by component 
wear, in addition to changes in the external forces acting upon the 
vehicle or its steerable wheels as described below. Even a change of tires 
may necessitate a change in the center position of the steering system to 
achieve straight ahead travel of the vehicle. Remote adjustment permits 
the center position maintained by the compensator to be fine tuned while 
the vehicle is in operation from a location near the driver, which is 
"remote" relative to the location at which the compensator is connected to 
the steering system of the vehicle. 
When a driver turns the steering wheel of modern over-the-road vehicles, 
power steering does the work. If these vehicles utilize the present 
invention and the steering wheel is released, the centering compensator 
goes to work and makes the steered wheels track straight with great 
accuracy by counteracting spurious steering inputs as described below. 
Gusty crosswinds cause the castered front wheels of a motor vehicle to 
steer downwind requiring constant driver corrections. With the centering 
compensator to stabilize the front wheels and to hold a straight course, 
crosswind driving is dramatically improved. In addition, use of the 
compensator permits a substantial reduction in the caster angle of 
vehicles with positive caster, thereby significantly reducing the 
crosswind effect. 
When driving on a crowned or slanted road, the driver must hold against 
wheel pull mile after mile. The culprit here is the hundred year old 
steering geometry that is responsible for the automatic, never failing 
pull to the low side of the roadway. With the present invention, the 
driver easily trims out such steering wheel pull by the simple touch of a 
trim switch. 
Because of their high-roll center dynamics, trucks, buses, motorhomes and 
other large vehicles are especially susceptible to a condition known as 
"dynamic sway". Dynamic sway is caused by steered wheels that will not 
hold a straight line because of vehicle geometry. Attempts to solve this 
steering problem have universally been made by making the chassis stiffer 
in the roll axis. However, there are practical limits to how rigid the 
roll axis can be made. There are no limits, however, to how straight a 
vehicle can be made to track. With the stabilized, on-center straight 
track steering provided by the present invention, the ultimate in sway 
control can be achieved. The reduction in the sway of buses and motorhomes 
means that passengers can move about without being thrown off balance, and 
those with a tendency for motion sickness will be more able to enjoy the 
pleasures of road vehicle travel. 
Road wander is similar to dynamic sway in that it is caused by steered 
wheels that are not holding a dedicated straight line. It may be caused by 
wear or slack in the steering system and, where power steering is used, 
because of dead space travel of the power steering valve before it opens 
the fluid ports of the power steering unit. When the steered wheels 
wander, the problem is passed on to the driver causing constant steering 
corrections. This problem is also cured by the present invention which 
provides precision centered steerable wheels that track super straight, 
preventing unstable wheel behavior that causes road wander. The invention 
is also capable of generating sufficient compensating forces to properly 
control steering with offset wheels having oversized tires. 
The centering compensator of the invention provides remotely adjustable 
levels of resistance for opposing off-center steering movements and of 
centering force for returning the steering system to its center position 
after a turning movement. The adjustment means provides for different 
levels of steering force to initiate or breakaway into a steering movement 
away from center. This level of force is sometimes referred to in this 
specification as the "break away" or resistance force. Different levels of 
break away resistance may be appropriate to compensate for different 
steering system characteristics on the same or different types of vehicles 
and/or for changes in the forces acting upon the vehicle. The level of 
break away resistance to movement away from center may be remotely 
adjusted either by a control mechanism operable by the driver or by a 
speed control mechanism responsive to the speed of the vehicle. 
The level of centering force for returning the steering system to center 
may also be remotely adjusted either by a control mechanism operable by 
the driver or by a speed control mechanism responsive to the speed of the 
vehicle. Both the resistance force and the centering force provided by the 
centering compensator are increased or decreased to provide a level of 
force sufficient to overcome any spurious steering inputs and to suit 
driver road feel, particularly a feel of the steering wheel that lets the 
driver know when the steered wheels are beginning to move away from center 
and are closely approaching return to center. 
The centering compensator may be left on continuously because it will 
automatically turn off with the ignition and come back on when the engine 
is started. With any malfunction of the vehicle's power steering, an 
automatic disabling feature of the invention shuts the compensator 
completely off. 
In order to effectively resist spurious wheel movements and prevent such 
spurious inputs from reaching the steering gear and other steering 
components located between the tie rod and the steering wheel, the 
compensator of the present invention is connected downstream of the 
steering gear on the slow side of its ratio. The steerable wheels are 
therefore maintained in their straight ahead position irrespective of any 
spurious inputs or mechanical slack that may be present in the upstream, 
fast ratio portion of the steering assembly. In the absence of the 
compensator, such spurious inputs to and/or mechanical slack in the 
steering assembly require almost constant manipulation of the steering 
wheel by the driver and make it almost impossible for the driver to hold 
the vehicle on a true straight ahead course. 
To properly compensate for the various adverse steering forces and inputs 
that may be encountered during operation of a vehicle, the centering 
compensator of the present invention therefore includes the following 
features: 
(a) Dynamic resistance force opposing turning movement away from either 
side of a preselected center position, the amount of resistance force 
being sufficiently large to prevent such turning moments in response to 
spurious inputs from either the steerable wheels or the steering wheel but 
sufficiently small to allow intentionally created turning inputs to be 
transmitted from the steering wheel to the steerable wheels. 
(b) Dynamic centering force toward the center position from either side of 
center, the amount of centering force from either side of center being 
sufficiently large to override spurious steering inputs tending to cause 
turning movements away from center. 
(c) Remotely operated means for initializing and varying the resistance 
force and the centering force to permit the driver to selectively activate 
and fine tune these forces while the vehicle is in operation so as to 
satisfy driver road feel preferences and to adequately compensate for 
changes in driving conditions and steering system characteristics. 
(d) Remotely operated trimming means to permit the driver to selectively 
vary and fine tune the preselected center position with great accuracy 
while the vehicle is in operation so as to precisely compensate for 
changes in driving conditions and steering system characteristics tending 
to alter forward movement of the vehicle away from a true straight ahead 
course. 
(e) Precision centering with no substantial overshoot past center when the 
steering system returns to a preselected center position. 
(f) Free return to the center position from either side of center. 
(g) Fail-safe mode for rendering the centering compensator inoperative so 
that it in no way affects movement of the steering system if the vehicle's 
power steering unit has failed or is otherwise inoperative. 
(h) Precision centering independent of mechanical slack in the reduction 
gear, power steering unit, and/or other steering system components between 
the pitman arm and the steering wheel. 
(i) Slack-free trimming of center position. 
(j) Damping of erratic steering movements, at least near the center 
position. 
(k) Retrofitting of existing vehicles. 
(l) Relatively little space required for installation. 
(m) Centering assistance for vehicles with or without power steering 
systems. 
(n) Resistance and centering forces through a predetermined range of 
turning movement to either side of the center position. 
(o) Distinctive driver road feel, including a sufficient feel through the 
steering wheel to let the driver know when the steered wheels are 
beginning to move away from center and are closely approaching return to 
center. 
The preferred embodiments of the invention therefore have the features (a) 
through (o) listed above, namely, resistance force for opposing steering 
movement away from center and centering force for return to center 
sufficient to overcome spurious steering inputs, remotely variable level 
of resistance force and centering force through a predetermined range of 
turning movement, remotely trimmable center position, no substantial 
overshoot, free return to center position, fail-safe mode for disabling 
the compensator in the absence of power steering, precision and slack-free 
centering, slack free trimming, damping of erratic steering movements, 
compact size, utility for old and new vehicles with or without power 
steering, and distinctive driver road feel. 
It follows that a principal object of the present invention is to provide a 
centering compensator having the foregoing features and attachable to a 
vehicle steering system to reduce automatically the driver inputs required 
to maintain a preselected straight ahead course for the vehicle. To 
accomplish this, the present invention offsets spurious steering inputs 
with an opposing resistance force sufficient to keep the steerable wheels 
or other steering member in a preselected center position for maintaining 
straight ahead vehicle travel. Accurately holding the steerable wheels on 
center prevents road wander, slanted road steering wheel pull, steering 
over-control, crosswind steering effect, and steering induced dynamic 
sway. Improvement in rutted road steering may also be realized. The 
positive centering feature gives the steering system designer greater 
latitude in reducing the caster angle of the king pin, which reduces the 
crosswind steering effect. 
The manner in which the present invention accomplishes the foregoing 
objectives and advantages will now be described. The compensator comprises 
a housing assembly enclosing a chamber for housing a cam means, a cam 
follower means, and an actuator means for actuating the cam follower. The 
cam means includes a cam member which is preferably pie-shaped and has an 
outer cam surface extending around at least a portion of its outer 
periphery. The cam member is mounted for rotation with and is fixed to a 
centering shaft rotatably supported between opposing walls of the housing. 
A portion of the centering shaft extends beyond the housing and there is 
connected to a centering lever. The centering lever is attached to a 
centering rod, which in turn is attached to the vehicle's pitman arm or 
tie rod for movement therewith. 
The cam follower means includes an elongated rocker member mounted at an 
intermediate portion for pivotal movement around an off-center bearing 
fixed to a smaller diameter trimming shaft, which in turn is rotatably 
supported between opposing walls of the housing. A cam roller is rotatably 
mounted on one end portion of the rocker member and confronts the cam 
periphery so as to ride on its outer cam surface. The cam roller is of a 
size and shape to allow the roller when centered to contact simultaneously 
opposite sidewalls of a centering depression formed as part of the outer 
cam surface. 
The other end portion of the rocker arm is connected by a pusher member and 
a spring or rod to a centering piston which is arranged for reciprocal 
movement within a centering cylinder formed in the housing. During 
operation, a pressurized fluid is delivered to the centering cylinder and 
biases the centering piston toward the pusher member. Movement of the 
centering piston thereby serves to pivot the rocker member about its 
eccentric bearing. As the rocker member pivots, it causes the cam roller 
at its opposite end portion to engage the cam surface of the cam member. 
When the cam member is its center position, which corresponds to the 
center position of the steering system, the cam roller is pressed into the 
centering depression so that contact between the cam roller and the 
sidewalls of the depression generates a resistance force which resists 
movement of the cam member and of the steering system to which it is 
connected. 
By selectively varying the pressure within the centering cylinder, the 
pressure and resulting forces between the cam roller and the cam member 
may be varied, thereby varying the resistance to off-center movement of 
the steering system. In a preferred embodiment, the centering piston is 
connected to the rocker member by a compressible spring, and a stop is 
preferably provided to limit compression of the spring, thereby providing 
an upper limit to the resistance force that may be generated by contact 
between the cam roller and the cam member depression. 
The turning resistance of the present invention is provided by delivering 
fluid under pressure to the centering cylinder from a fluid pressure 
control device which may take a variety of forms and may be either 
hydraulic or pneumatic. The pressure control device permits the level of 
resistance to movement away from center to be controllably varied, either 
by a hand mechanism operable by the driver or by a speed control mechanism 
responsive to the speed of the vehicle. In a hydraulic embodiment of the 
invention, the centering cylinder is preferably pressurized by the power 
steering system of the vehicle. In a pneumatic embodiment, the centering 
cylinder is preferably pressurized by an air brake system of the vehicle. 
It is also within the scope of the present invention to provide hydraulic 
fluid or air pressurization systems separate from other fluid systems of 
the vehicle. For example, a pressure accumulator system of the type 
described in my prior U.S. Pat. No. 4,410,193 may be employed for storing 
and providing hydraulic fluid under pressure to the centering piston. 
Regardless of the type of fluid pressurization system employed, the system 
should generate sufficient pressure to return the cam roller to its center 
rest position in the centering depression of the cam member upon cessation 
of intentional steering inputs. The pressurization system should also 
constantly bias the centering piston assembly into engagement with the 
rocker member and the cam roller into engagement with the cam surface of 
the cam member at all time when the compensator is activated so that there 
is no slack in the compensator linkages at any time during its operation. 
Spurious steering inputs tending to move the tie rod in either direction 
are therefore resisted by a corresponding resistance force generated by 
interaction between the cam member and the cam roller. Only when 
intentional steering wheel forces exceed a preselected break away level 
will the pitman arm of the steering system generate sufficient rotational 
force on the cam member to rotate it about its rotational axis, thereby 
causing the centering depression to move relative to the cam roller. 
After rotational movement of the cam member is initiated, the steering 
force required to sustain movement is a function both of the shape of the 
cam surface along the sides and shoulders of the centering depression and 
of the shape of the cam periphery beyond the respective shoulders of the 
centering depression, as well as of other centering phenomena acting on 
the steering system, such as positive wheel caster. The shape of the 
centering depression and other compensator parameters may be chosen so 
that a break away steering force of at least about 20 pounds, preferably 
at least about 50 pounds, and more preferably at least about 70 pounds 
must be applied to the tie rod by the pitman arm in order to initiate 
break away turning movement of the steerable wheels. 
If the steerable wheels are provided with positive caster, the sides and 
shoulders of the depression may be fared into a circular portion of the 
outer cam surface which is adjacent to the depression and will provide no 
supplemental cam centering force. In this case, the sides and shoulders of 
the depression are preferably shaped to provide a decreasing level of cam 
centering (and resistance) force until the caster centering force, which 
increases in proportion to turning angle with positive caster, is of 
sufficient magnitude to alone provide a rapid return of the steering 
system toward its center position. For example, there may be sufficient 
positive caster to permit the cam return force to go to zero at turning 
angles greater than about 20.degree., preferably greater than about 
15.degree., and more preferably greater than about 10.degree. on either 
side of center. 
However, the cam surface outside of the centering depression may be such 
that the cam return force does not go to zero, but instead may be 
effective over the entire range of turning angles, which for highway 
vehicles is usually limited to about 45.degree. on either side of the 
centered wheel position (the 0.degree. position). 
Another important feature of the present invention is the provision of a 
remotely operable trimming means for controllably varying the preselected 
center position of the steerable member to be maintained by the 
compensator. The actuator for the remotely adjustable trimming means may 
comprise a reversible electric motor assembly pivotally mounted on the 
vehicle frame. The electric motor assembly includes drive means for 
reciprocating a trim rod connecting the motor assembly to a trim lever, 
which in turn is fixed to a trimming shaft that is fixed to an eccentric 
bearing of the rocker member of the centering assembly. 
Upon selective actuation of the electric motor via an electrical system 
with a switch means conveniently positioned to the vehicle operator, the 
trim rod is caused to extend or retract relative to the motor assembly. 
Movement of the trim rod causes the attached trim lever and trimming shaft 
to pivot about the axis of the shaft. Because the rocker member of the 
centering assembly is rotatably mounted on the eccentric bearing and the 
eccentric bearing is fixed to the trimming shaft in an off-center position 
relative to its rotational axis, rotation of the latter produces 
longitudinal movement of the rocker member and alters the position of the 
cam roller relative to the rotational axis of the centering cam and its 
shaft. Altering the position of the cam roller causes the rest position of 
the cam depression and the centering shaft to rotate about the rotational 
axis of the latter, creating a new center position for both the centering 
lever and the vehicle steering system connected thereto. 
While a reversible electric motor is one preferred means for affecting the 
trimming operation, it is also within the scope of the present invention 
to employ any type of remotely controllable linear actuator for the 
trimming means. For example, hydraulic actuators may be used similar to 
those disclosed in my prior U.S. Pat. No. 4,410,193. In particular, the 
trim rod may be connected to a trim piston reciprocally carried within a 
hydraulic trim cylinder pivotally mounted on the vehicle frame. Hydraulic 
fluid from a fluid system accumulator or other pressurized fluid source 
may then be used to create differential pressure in either direction 
across the trim piston and thereby cause corresponding longitudinal 
movement of the trim rod. The direction and level of differential pressure 
may be controlled by inlet and outlet orifices in combination with 
solenoid stop valves. A liquid trimming fluid is preferred because it is 
substantially incompressible as compared to a gaseous trimming fluid and 
therefore provides the capability of locking the trimmed position without 
appreciable slack. 
A driver control panel makes it possible for steering corrections to be 
made while driving. The panel may be conveniently located near the driver 
and provides three basic functions, namely, a switch to turn the system on 
and off, a centering effectiveness control and gauge, and a momentary trim 
switch. Activating, adjusting and trimming the centering system is 
therefore an easy and natural driving function. Should the driver sense a 
degree of steering wheel pull that becomes a bother, it is then quickly 
eliminated by pressing the trim switch. 
The invention provides a distinctive feel when approaching or leaving the 
center position. Thus, the sense of touch is added to the visual sense to 
aid control of the vehicle and reduce driver fatigue. A turning resistance 
of at least about 20 pounds, preferably about 30 to about 150 pounds, 
should be available at the tie rod for small turning angles away from 
center, preferably 0.degree.-5.degree., more preferably 
0.degree.-3.degree., and most preferably within one degree on either side 
of center. The turning resistance selected should satisfy the road feel 
desired by the driver and be sufficient to overcome anticipated spurious 
inputs. 
When connected to weak or soft steering systems, i.e. those with no or 
negative caster, the invention thus provides the driver with a positive 
touch control not heretofore attainable with those types of systems. 
Positive stability is thereby achieved for previously unstable steering 
systems. 
Although the present invention is particularly useful as a centering 
mechanism for large motor vehicles, it can be employed to position any 
steerable member moveable to either side of a preselected position. For 
example, the centering compensator can keep an outboard motor centered so 
that a boat follows a straight course over the water in the presence of 
spurious steering forces produced by wind and wave action. The compensator 
can also be used to center such steerable members as the rudders of ships 
or airplanes and the tongues of tandem trailers or railway cars. The 
compensator is useable with both power and non-powered steering systems, 
with the level of compensating forces provided usually being less for 
vehicles without power steering. 
The invention may be used with steering systems having a reduction gear 
between the steering wheel and the steerable wheels. In this application, 
the apparatus is preferably connected to the steering system at a location 
between the steerable wheels and the reduction gear so as to be unaffected 
by any slack in the reduction gear or in components and connections 
between the reduction gear and the steering wheel. 
The centering compensator is preferably connected between the steering 
system and a frame member of the vehicle in a position that allows the 
steerable member to move through its full range of steering movements 
while providing sufficient leverage for the apparatus to resist movement 
of the steerable member away from the center position producing straight 
ahead travel of the vehicle. The steering system connection may be made to 
any steering system component providing appropriate range and leverage, 
such as a tie rod which joins the two front steerable wheels of a highway 
vehicle, or the pitman arm connected to the steering gear. The frame 
connection may be made to any component serving as a fixed mounting 
relative to the steering system. This fixed component may be a transverse 
frame member, or a fixed axle or some other part carried by the vehicle 
frame instead of an actual frame member. 
The apparatus includes control means for remotely and selectively varying 
both the amount of resistance to movement away from center and the 
selected center position of the steerable member(s) relative to the 
vehicle frame. Both of these remote adjustments are preferably made by the 
driver while the vehicle is in operation. Therefore, electrical control 
and fluid control systems are employed for remotely operating the 
centering and trimming units of the centering compensator. The controls 
for actuating the control systems are preferably located at the driver's 
station of the vehicle. The electrical controls may comprise one or more 
switches preferably having a toggle design that is spring-biased to a 
circuit-open position. Such switches are closed only momentarily when the 
toggle is held in a depressed position against the spring bias. Thus, the 
adjusting means, such as a motor or solenoid, is actuated only while the 
toggle is depressed. Release of the toggle opens the circuit and stops the 
adjustment at the point selected. 
My earlier U.S. Pat. Nos. 4,410,193, 4,418,931, and 4,534,577, the entire 
contents of which are expressly incorporated herein by reference, solved 
many of the shortcomings existing in the prior art. The present invention 
provides improvements over these earlier patents, especially in the areas 
of simplicity, precision, and reliability.

DETAILED DESCRIPTION OF THE INVENTION 
The detent centering compensator of the present invention comprises a 
centering unit, generally designated 8, which may be connected between the 
frame 9 and the pitman arm 10 of a conventional motor vehicle as shown in 
FIG. 1 of the drawings. Intentional steering inputs by the driver are 
transmitted from the pitman arm 10 to a tie rod 11 through a steering rod 
12. The steering rod 12 and the other steering system components connected 
thereto are conventional and include bell cranks 22, 22 carried by 
knuckles 24, 24, which support front steerable wheels 26, 26 for pivotal 
turning movement about respective king pins (not shown) mounted on the 
vehicle frame 9. 
The compensator includes a housing 13 having a centering lever 14 extending 
transversely from a rotatably mounted cam shaft 15 and a trimming lever 16 
extending transversely from a rotatably mounted trim shaft 17. The 
projecting end of the centering lever 14 is connected to the pitman arm 10 
by means of a connecting rod 18, while the projecting end of the trimming 
lever 16 is connected to a trimming rod 19 associated with a trim control 
mechanism having a pivotally mounted gear box 20 and a reversible electric 
motor 21. Gear box 20 and motor 21 are mounted on frame 9 by a pivot 
connection 23 to permit pivotal movement of rod 19 in the pivot plane of 
trimming lever 16. 
As shown in FIG. 2, compensator housing 13 is bolted to the vehicle frame 9 
by bolts 25 and includes an outer wall 27 enclosing and defining an 
interior chamber 28 which contains a generally pie-shaped centering cam 32 
fixed to centering shaft 15. Centering cam 32 includes an outer peripheral 
cam surface 33 having a centering depression 34 of a particular 
cross-sectional configuration as described below. Centering shaft 15 is 
rotatably mounted in housing wall 27 by conventional bearing assemblies, 
which are not shown for purposes of simplicity. 
Interior chamber 28 further contains a cam follower assembly comprising a 
rocker member 36 pivotally carried by an off-center bearing 35 fixed to 
trimming shaft 17, which is also rotatably mounted in housing wall 27 by 
conventional bearing assemblies that are not shown for purposes of 
simplicity. At its distal end, rocker member 36 carries a cam roller 38, 
and at its proximate end a pivotally mounted pusher member 40 engaged by a 
spring 42. Cam roller 38 is rotatably mounted on rocker member 36 and 
preferably has a substantially cylindrically-shaped outer surface capable 
of providing line contact with at least some portions of the cam surface 
33, such as the sidewalls of the centering depression 34 as shown in FIGS. 
5A-5D. 
As may be seen best in FIGS. 3 and 4, spring 42 is arranged to be 
compressed by a piston 44 having an elastomeric cup 46, a groove 48 for 
receiving an O-ring seal 50, and a sleeve 52 for receiving the end of 
spring 42 opposite from pusher member 40. Piston 44 reciprocates in a 
cylinder shell 54 between an annular stop 56 and the lower portion of 
shell 54 which is closed by a housing extension 58. The upper portion of 
shell 54 is press fitted into a cylindrical sub-chamber 60 defined by 
outer housing wall 27 and an interior housing wall 62. 
The lower portion of cylinder shell 54 between piston cup 46 and the lower 
end of housing extension 58 defines a reservoir chamber 64 for receiving 
hydraulic fluid from a hydraulic system 65, which is preferably 
pressurized by a conventional power steering pump 66. The hydraulic system 
comprises a supply line 68 containing a supply check valve 70 and 
connecting a high pressure outlet 71 of pump 66 to the inlet of a pressure 
accumulator 72 having a spring 74 for storing dynamic energy when 
compressed by a piston 76. Since power steering pumps only operate when 
the steerable wheels are turned by the steering wheel, accumulator 72 must 
store the dynamic energy it receives from the pressurized fluid that may 
pass from pump outlet 71 through check valve 70 only during intermittent 
pump operation. An inlet supply line 78 contains a solenoid actuated stop 
valve 80, a pressure gauge 82 and an inlet check valve 84, and connects 
the outlet of accumulator 72 with reservoir 64. A return line 86 contains 
a solenoid actuated stop valve 88 and connects reservoir 64 to a low 
pressure inlet 90 of pump 66. 
It is to be understood that the hydraulic system components described 
herein are connected together by appropriately sized fluid conduits and 
that these conduits are represented by the lines interconnecting these 
components as shown in FIG. 2. It is also contemplated that pump 66 may be 
a specialty pump which is independent of a vehicle's power steering system 
and could be electrically operated or operated with a belt driven by the 
vehicle engine. However, it is preferable to use the power steering pump 
when available because the centering compensator is automatically 
deactivated when the vehicle engine is cut off or when either the engine 
or the pump fails. If a separate specialty pump is used, these cut off 
features may be provided by a correspondingly actuated switch for 
deactivating the system as described below in connection with the 
embodiment of FIG. 7. 
The solenoid of stop valve 80 is electrically connected by a line 90 to a 
pressurizing switch 92, which preferably has a spring biased button 93 
that must be pushed and held in to briefly open the valve and thereby 
pressurize reservoir 64 to a selected fluid pressure between ambient and 
that of accumulator 72 as indicated by gauge 82. The solenoid of stop 
valve 88 is electrically connected by a line 94 to an on/off switch 96, 
which in turn is connected to a source of electrical power by a line 97. 
The off position of switch 96 opens valve 88 and thereby depressurizes 
reservoir 64 as shown in FIG. 3 by causing the fluid therein to be 
returned to the low pressure inlet 90 of pump 66. Switches 92 and 96, 
along with pressure gauge 82, are mounted on a control panel 100, which is 
preferably located at or near the driver's station within the vehicle in a 
position easily reached by the driver during operation of the vehicle. 
FIG. 3 shows the position of the rocker member 36 and related components 
when the centering system is deactivated by turning off switch 96, thereby 
opening valve 88 and depressurizing reservoir 64. In order to move 
centering piston 44 toward pusher member 40 and thereby compress spring 
42, switch 96 is turned on to close valve 88 and hydraulic fluid is 
selectively introduced into reservoir 64 by briefly actuating pressurizing 
switch 92 to open valve 80 until the desired pressure is registered on 
gauge 82. The maximum compression of spring 42, and thereby the maximum 
centering force, is achieved when piston 44 is forced into engagement with 
stop 56. 
As spring 42 is compressed, it acts through pusher member 40 to pivot 
rocker member 36 about eccentric bearing 35 in a counter-clockwise 
direction with respect to the orientation of FIGS. 2-3. This pivoting 
movement of rocker member 36 serves to press cam roller 38 at its distal 
end toward and into the aligned depression 34. Cam roller 38 then 
continues toward the bottom of depression 34 until it comes to rest 
against opposite sidewalls thereof as seen best in FIG. 5. In this seated 
position, there is preferably line contact between roller 38 and each of 
the opposing sidewalls 106, 106 of depression 34 as shown in FIGS. 5A-5D. 
Such line contact provides zero slack centering of the steering system. 
Line contact forces between roller 38 and depression 34 are therefore 
generated by the compression of spring 42, and these forces effectively 
prevent rotation of cam 32 and a corresponding pivoting of centering lever 
14 in either direction until a steering force on lever 14 is of sufficient 
magnitude to rotate cam 32 and thereby initiate relative movement between 
roller 38 and the portion of cam surface 33 forming depression 34. 
By selectively varying the pressure within reservoir 64, the line contact 
forces between cam roller 38 and sidewalls 106, 106 of centering 
depression 34 may be varied, thereby varying the resistance to off-center 
movement of the vehicle steering system. However, the maximum contact 
force, and therefore the maximum steering input required to initiate 
relative motion between roller 38 and depression 34, is limited by the 
annular stop 56, which is positioned along the axis of shell 54 to limit 
the compressive movement of piston 44 and thereby limit the compression of 
spring 42. 
Thus, even though contact between roller 38 and depression 34 prevents 
rotation of cam 32 in response to spurious steering inputs, an intentional 
steering input force above a predetermined or "break away" level will 
initiate rotation of cam 32. In particular, a sufficiently strong steering 
force transmitted through pitman arm 10, connecting rod 18, centering 
lever 14 and centering shaft 15 to cam 32 will initiate rotation of cam 32 
in spite of the resistance provided by the interaction between cam roller 
38 and depression 34. By way of example, the shape of centering depression 
34 and other compensator parameters may be chosen so that a total break 
away steering force of at least twenty pounds, preferably at least fifty 
pounds, and more preferably at least seventy pounds must be applied to the 
tie rod 11 by the compensator connecting rod 18 to initiate turning 
movement of wheels 26, 26. 
Pivotal rotation of cam 32 causes cam roller 38 to ride up one of the 
inclined sidewalls 106, 106 of depression 34 and over a corresponding one 
of its shoulders 107, 107 until the roller leaves the depression and rides 
on the outermost peripheral extension 108 of cam surface 33 as shown in 
FIG. 4. While roller 38 is being forced to ride up a sidewall of 
depression 34, the force transmitted from spring 42 through rocker member 
36 provides a centering force seeking to return roller 38 to its seated or 
"centered" position in which it simultaneously contacts both sidewalls of 
the centering depression. As a result, while roller 38 travels along one 
or the other sidewalls and shoulders of depression 34, a continuous 
centering force acts through the cam 32 and its connections to tie rod 11 
to bias the vehicle's steerable wheels 26, 26 toward their preselected 
center positions. 
The centering depression 34 is preferably shaped or "cut" so as to provide 
a supplemental centering force which blends with the return force provided 
by the usual steering geometry of the front end of a roadway vehicle, 
which may or may not include a power steering unit. Therefore, once cam 32 
pivots through a sufficient angle for roller 38 to pass over shoulders 
107, 107 of depression 34 and completely leave the depression, the 
centering force generated by spring 42 decreases and the magnitude of this 
force depends on the shape or "cut" of the outermost extensions 108, 108 
of cam surface 33. If the cut of cam surface extensions 108, 108 is 
substantially circular about the rotational axis of centering shaft 15 as 
shown in FIG. 5A, roller 38 will be equally susceptible to movement in 
either direction relative to cam 32 when out of the depression 34. 
However, a circular cut of the outermost cam surface extensions may only 
be appropriate for vehicle steering systems designed to provide strong 
geometric centering forces, such as those with strong positive caster. In 
the latter case, the only force seeking to return cam 32 to its original 
position at turning angles greater than about 10.degree. would be the 
positive caster acting directly on steerable wheels 26, 26. 
Geometric centering forces usually decrease to zero before a vehicle 
steering system returns to its center position. As illustrated by the 
indicia of scales 112 and 113 in FIGS. 5A-5D, which indicate in degrees 
the amount that the steerable wheels 26, 26 have been turned to the left 
and right, respectively, the interaction between the centering depression 
34 and roller 38 substantially increases the centering force available at 
and immediately adjacent to either side of the straight ahead position of 
the steerable wheels 26, 26. In the example shown, geometric centering 
forces have decreased to substantially zero at about 13.degree. on either 
side of the center position "C" as indicated by a left turn position line 
114 and a right turn position line 115. At greater turning angle 
positions, the centering force provided by cam 32 may taper off as a 
positive geometric centering force increases as described in more detail 
in my prior U.S. Pat. No. 4,418,931, the entire contents of which are 
expressly incorporated herein by reference. 
If, for example, steerable wheels 26, 26 are provided with strong positive 
caster, the sides and shoulders of centering depression 34 may be fared 
into circular cam surface extensions, such as represented by lines 108A, 
108B and 108C in FIGS. 5A, 5B and 5C. The cam depression 34 may then have 
a shape that provides a decreasing level of cam centering force until the 
caster centering force, which increases in proportion to turning angle 
with positive caster, is of sufficient magnitude to alone provide a rapid 
return of the steering system toward the center position. 
Alternative cam surface extensions 108A, 108B and 108C illustrate that the 
radial extent and shape of depression sidewalls 106, 106, as well as the 
shape and intermediate peripheral extent of depression shoulders 107, 107, 
will vary, depending on where the geometric centering force goes to zero 
and on other inherent steering system characteristics. In this regard, 
there preferably is sufficient geometric centering force for the cam 
centering force provided by centering depression 34 to be effective over 
the range 0.degree.-20.degree., more preferably 0.degree.-15.degree., and 
most preferably 0.degree.-10.degree. on either side of center C (the 
0.degree. position). However, such geometric centering forces are usually 
not available in the steering systems of large trucks, buses and motor 
homes. 
By appropriately contouring the peripheral cam surface portions on either 
side of centering depression 34, the cam centering force generated by cam 
roller 38 need not go to zero, but instead may be effective over the 
entire range of turning angles, which for road vehicles is usually limited 
to about 45 degrees on either side of the center position C, i.e., the 
zero degree (0.degree.) position, of the steering system. Such a contour 
is illustrated by alternative cam surface extensions 108D in FIG. 5D. 
These peripheral portions are not fared into a circular periphery and 
therefore provide a cam centering force over the entire range of turning 
angles. Extensions 108D also illustrate a steering system wherein the 
geometric centering force goes to zero at about 20.degree. on either side 
of center C. 
As also shown in FIGS. 5A-5D, a gap 109 is preferably provided between the 
fully seated roller 38 and the bottom of depression 34 to ensure that line 
contact is provided between roller 38 and the sides of depression 34. Gap 
109 also ensures that if true line contact is lost due to wearing of the 
depression sidewalls, the seated roller is kept out of contact with the 
bottom of the depression and therefore will continue to provide zero-slack 
centering of the steering system. 
Movement of cam 32 to either side of center in response to intentional 
turning movements is illustrated in FIG. 4. When an intentional turning 
movement transmitted through pitman arm 10 has ceased to act on steering 
rod 12, tie rod 11 and steerable wheels 26, 26, a positive caster of 
wheels 26, 26 (or other positive centering geometry) will automatically 
seek to return these wheels and the steering system toward their original, 
center tracking positions. This initial travel toward the center position 
C would be assisted by peripheral cam surface extension such as 108D in 
FIG. 5D. Because any return movement of wheels 26, 26 is transmitted to 
cam 32 via connecting rod 18 and centering lever 14, return movements of 
wheels 26, 26 cause cam 32 to rotate toward an orientation wherein a 
shoulder 107 of depression 34 will intersect the peripheral path of travel 
of cam roller 38 along cam surface 33. 
As soon as a shoulder 107 of centering depression 34 intersects roller 38, 
compressed spring 42 begins (or continues) to rotate rocker member 36 
counter-clockwise to press roller 38 into depression 34 in the same manner 
as when the system is activated as discussed above with reference to FIG. 
3. Thus, when roller 38 re-enters centering depression 34, the centering 
force generated by spring 42 becomes effective again (or becomes more 
effective upon leaving a cam surface portion like 108C). This force 
quickly re-establishes the position wherein roller 38 contacts the 
opposite sidewalls 106, 106 of depression 34, this position corresponding 
to the straight ahead or "centered" orientation of wheels 26, 26. 
Any additional rotation of cam 32 beyond the 0.degree. position of 
alignment between the seated cam roller 38 and the centering depression 34 
is resisted by interaction of the roller with the opposite wall of 
depression 34. Thus, the cam and follower arrangement of the present 
invention significantly reduces the chance of over shooting the center 
position, and thereby over-steering the vehicle, by providing an 
increasing resistance to movement in either direction away from the center 
position corresponding to straight ahead movement of the wheels 26, 26. 
An important feature of the present invention is that it may use fluid 
pressure provided by the power steering pump of a conventional power 
steering system. In this application of the invention, there is therefore 
no need to provide special hardware for deactivating the centering system 
as it is automatically turned off by a failure of the power steering pump 
or a leak in the power steering system. However, it is also within the 
scope of the invention to employ a special fluid pump separate from the 
power steering system and to provide an optional deactivation control 101 
(FIG. 2) for turning off the centering system automatically in response to 
a power steering sensor (not shown) connected to control 101 by a line 
105. The power steering sensor is capable of sensing inoperative 
conditions, such as a loss of pressure or a failure of the pump, in the 
separate power steering system. 
Another important feature of the present invention is the provision of a 
remotely operable trimming means for controllably varying a selectable 
center position of the steerable wheels as achieved by the interaction of 
cam roller 38 with cam 32. The actuator for the remotely adjustable 
trimming means comprises the reversible electric motor assembly 21 
pivotally supported by the vehicle frame 9. The gear box 20 serves as a 
drive means for reciprocating the trimming rod 19 and the trim lever 16 as 
shown in FIG. 6. 
Referring now to FIG. 2, a conventional three position toggle trim switch 
102 is mounted on control panel 100 and connected to trimming motor 21 by 
electrical power lines 104, 104. Switch 102 preferably has a toggle 103 
which is spring biased into a center normally off position from an up 
position for driving trimming rod 19 to the right in the direction of 
arrow R, and a down position for driving trimming rod 19 to the left in 
the direction of arrow L. 
Therefore, upon selective actuation of switch 102 from its off position to 
its up position, reversible electric motor 21 is activated to drive 
trimming rod 19 in a retraction direction with respect to gear box 20 as 
indicated by arrow R. Similarly, upon selective actuation of switch 102 
from its off position to its down position, reversible electric motor 21 
is activated to drive trimming rod 19 in an extension direction, opposite 
to the retraction direction, with respect to gear box 20 as indicated by 
arrow L. Gear box 20 may employ a conventional worm screw gear train or 
the like (not shown), which is rotated by motor 21 for extending and 
retracting trimming rod 19. 
The linear movement of trimming rod 19 in the respective directions 
indicated by arrows R and L causes attached lever 16, attached shaft 17 
and attached eccentric bearing 35 to rotate in a clockwise and a 
counter-clockwise direction, respectively, relative to the rotational axis 
of shaft 17 as viewed in FIG. 6. Because bearing 35, on which rocker 
member 36 is pivotally mounted, is fixed eccentrically to shaft 17, 
rotation of shaft 17 causes a corresponding transverse alteration of the 
pivot axis of rocker member 36, which in turn moves roller 38 linearly in 
corresponding directions, which are represented by the double-ended arrow 
T and are generally parallel to retraction direction R and extension 
direction L. 
In this manner, clockwise and counter-clockwise rotations of shaft 17 and 
the fixedly attached eccentric bearing 35 cause cam roller 38 to shift the 
center position C of cam depression 34 in corresponding rotational 
directions relative to the rotational axis of centering shaft 15, as 
represented by the double-ended arrow S in FIG. 6. In other words, as a 
result of linear displacement of cam roller 38 relative to the rotational 
axis of trimming shaft 17, a new rest position of cam roller 38 is 
achieved because of its corresponding lateral movement relative to the 
rotational axis of cam 32 and centering shaft 15. By so altering the rest 
position of cam roller 38, cam depression 34 when engaged by roller 38 is 
forced to rotate about its rotational axis, thereby creating a new center 
position for both cam 32 and the steerable members 26, 26 connected 
thereto. 
With the centering unit 8 mounted on the rear side of frame member 9 as 
shown in FIG. 1, the front wheels 26, 26 are trimmed toward the right side 
of the vehicle by temporarily holding the trimming switch 102 in its up 
position and thereby causing clockwise rotation of trimming lever 16. The 
front wheels 26, 26 are trimmed toward the left side of the vehicle by 
temporarily holding switch 102 in its down position and thereby causing 
counter-clockwise rotation of trimming lever 16. When the desired course 
correction is achieved by such actuation of switch 102, the switch toggle 
103 is released and moves to its center off position in response to its 
spring bias. 
While the embodiment of FIGS. 1-6 employs a coiled spring 42 to apply a 
resilient force to the proximate end of rocker member 36, the present 
invention is not to be limited to the coil spring arrangement shown in 
these drawings. Rather, the present invention is directed to any 
arrangement by which a resilient means applies a resilient force to the 
proximate end of rocker member 36. For example, in the alternative 
centering unit 110 of FIG. 7, pressurized air is trapped in an air chamber 
120 to provide an "air spring" which functions as a resilient means for 
providing a resilient centering force that increases with downward 
compressive movement of an air piston 122. For purposes of simplicity, 
components employed in the embodiment of FIG. 7 that are similar to the 
components shown in other figures have been given the same numeral 
designation. 
As shown in FIG. 7, the cylinder shell 54 is closed by a threaded cap 124, 
and the air piston 122 includes a groove mounted O-ring seal 126 and a 
groove mounted wear ring 128. The push member 40 pivotally mounted on 
rocker member 36 is connected to a push rod 130 having a free (unsecured) 
and rounded lower end portion 132 for engaging a conically-shaped upper 
end surface 134 of centering piston 122. All other components connected to 
rocker member 36 are the same as previously described in connection with 
the embodiment of FIGS. 1-6. 
Air chamber 120 is connected to a supply of pressurized air, such as air 
tank 135 of a vehicle airbrake system, by air lines 136 and 137. Air line 
136 contains a solenoid operated supply valve 138 and connects tank 135 to 
the inlet of a pressure regulator 141. Air line 137 contains a check valve 
139 and connects the outlet of pressure regulator 141 to air chamber 120. 
A vent line 145 is connected to a T-connector 143 in line 137 and contains 
a solenoid operated vent valve 140. Supply valve 138 is opened and vent 
valve 140 is closed by turning on a system on-off switch 142 connected to 
electrical power line 97 and located on a control panel 150 at the 
driver's station within the vehicle. The pressure maintained in chamber 
120 is indicated by a gauge 148 connected to an outlet passage of 
regulator 141. 
When switch 142 is in its off-position, supply valve 138 is closed and vent 
valve 140 is open such that air chamber 120 is vented to atmospheric 
pressure. When chamber 120 is vented, air piston 122 rests against 
cylinder cap 124 and roller 38 is disengaged from depression 34, similar 
to the deactivated position of rocker member 36 as shown in the embodiment 
of FIG. 3. In order to move air piston 122 upward through cylinder 54, 
switch 142 is moved to its on-position, thereby closing vent valve 140 and 
opening supply valve 138 to pressurize air chamber 120 to the outlet air 
pressure set by the pressure regulator 141. This outlet pressure may be 
adjusted manually by a knob 149 on the face of control panel 150, or may 
be controlled by an on-board computer 160 as described below. 
As air piston 122 moves upward through cylinder 54 in response to air 
pressure in chamber 120, rounded end portion 132 of push rod 130 slides 
within conical surface 134 until it becomes fully seated in the apex 
formed by the central portion of this conical surface. Further upward 
movement of air piston 122 serves to upwardly displace push rod 130, 
causing attached rocker arm 36 to pivot about eccentric bearing 35 in the 
counter-clockwise direction. Such pivotal movement of rocker member 36 
displaces cam roller 38 toward cam 32 and causes it to enter centering 
depression 34 when wheels 26, 26 are in or turned into their centered 
position. 
As soon as cam roller 38 contacts the opposite sidewalls 106, 106 of 
centering depression 34, the air piston 122 functions to press the cam 
roller into line contact with the centering depression with a resilient 
centering force that seeks to restrain cam 32 from rotating in either 
direction as previously described. By selectively varying the pressure 
within air chamber 120 by adjusting the setting of air pressure regulator 
141, the centering force between roller 38 and the sidewalls 106, 106 of 
depression 34 may be varied, thereby varying the resistance to off-center 
movement of the steerable wheels 26, 26. 
As an alternative to manual adjustment, the output pressure of air pressure 
regulator 141 may be adjusted by a reversible electric motor (not shown) 
controlled by the on-board computer 160, which comprises a microprocessor 
161, an encoder 162 and a decoder 163. Encoder 162 converts to digital 
signals an analog signal 164 input from a pressure sensor 165 in air 
supply line 137, an analog signed 168 input from a vehicle speed sensor 
169, and an analog signal 172 input from a position sensor (not shown) 
within regulator 141. Decoder 163 converts digital control signals 
generated by microprocessor 161 to an analog signal 174 for controlling 
the reversible electric motor which adjusts the output pressure provided 
by regulator 141. The air pressure in chamber 120 and the resulting 
resistance and centering forces are thereby made automatically responsive 
to the speed of the vehicle to provide "speed sensitive centering" of the 
vehicle's steering system. For reasons already explained above, it is 
preferable that the resistance to turning movements away from the center 
position C be increased automatically as the speed of the vehicle 
increases. 
The particularly important trimming feature of the invention may be 
achieved through drive means other than the gear box 20 driven by the 
reversible electric motor 21. For example, movement of the trimming lever 
16 may be accomplished by controllably varying its position with a piston 
carried by a hydraulic cylinder pivotally mounted to the vehicle frame 9 
in place of gear box 22. One such hydraulic trimming piston and cylinder 
arrangement is described in the my prior U.S. Pat. No. 4,418,931, which is 
incorporated herein by reference. However, the reversible electric motor 
arrangement shown in the drawings is preferred for its simplicity in 
avoiding the need for a more complicated hydraulic system. 
As it is best to deactivate compensator 110 in the event of a failure of 
the power steering system, a switch 152 for interrupting electrical power 
to solenoid valves 138 and 140 may be provided for vehicles with power 
steering systems. Switch 152 is connected by a line 154 to a pressure 
sensor (not shown) located in a hydraulic line in fluid communication with 
the outlet of the power steering pump. A loss of pressure at the pump 
outlet causes switch 152 to open, thereby causing supply valve 138 to 
close and vent valve 140 to open for depressurizing chamber 120. Vent line 
145 and vent valve 140 are preferably of larger capacity than supply lines 
136 and 137 to ensure that air chamber 120 will be depressurized even if 
supply valve 138 fails to close with the opening of pressure switch 152. 
It is also important to recognize that the centering compensators of the 
present invention engage the vehicle steering system at a location between 
the steerable wheels and the steering gear assembly from which extends the 
pitman arm 10. As a result, spurious inputs from the steering column 
and/or from a power steering unit are absorb by the compensator before 
these inputs can reach the steerable wheels. Likewise, spurious forces 
transmitted from the roadway are immediately absorbed in the compensator, 
rather than being transmitted through the entire steering assembly before 
encountering any stabilizing resistance from the steering wheel. As a 
result, the centering compensator protects the interior components of the 
steering assembly from the wear caused by repeated oscillations between 
states of tension and compression. 
By varying the contact pressure between roller 38 and cam 32 through 
control of fluid pressure in either liquid reservoir 64 or air chamber 
120, the break away resistance and the centering return force produced by 
the invention can be increased or decreased as desired. Manual pressure 
control in either of the embodiments may be provided by a hand held switch 
biased to the off position, such as switch 92, or by a manually adjustable 
fluid pressure regulator, such as regulator 141. The range of pressures 
available should be selected so that break away resistance can be varied 
from relatively low at low speeds to relatively high at high speeds. In 
either embodiment, the fluid pressure also may be controlled automatically 
in response to vehicle speed, such as by using computer 160 to control a 
reversible electric motor for operating a pressure regulator in direct 
response to vehicle speed. 
Both embodiments of the invention also may be used with other tie rod 
arrangements and with steering systems that do not require tie rod 
arrangements, such as those with only one steerable member, such as the 
rudder of a ship or an airplane. Without the centering compensator of the 
present invention, spurious steering forces of relatively small magnitude 
can cause the steering systems of all human occupied vehicles to move to 
one side or the other of center or to oscillate back and forth, thereby 
producing corresponding movements of the vehicle away from the desired 
direction of vehicular travel. In the operation of roadway motor vehicles, 
such spurious inputs may be caused by road forces acting on the vehicle 
wheels, environmental forces acting on the vehicle body, driver forces 
acting on the steering wheel, off-center bias inherent in the steering 
system itself, or any combination of one or more of these forces. 
The centering components can be used alone as a centering mechanism without 
the remote trimming feature. On the other hand, the remote trimming 
features of the present invention are useable not only with the 
compensators disclosed herein, but also in combination with centering 
mechanisms of the prior art. Thus, the remotely operable trimming 
components of the present invention can be combined with centering devices 
of known types to provide adjustment of the center position during vehicle 
operation. In addition, a number of other modifications to both the 
centering components and the trimming components specifically described 
herein are possible without departing from the scope of the invention, as 
defined by the claims below.