Vehicle steering system

A hydraulic servo axially biases a rack and pinion steering housing to add an additional amount of steering to the front wheels of a vehicle in response to one of (a) the amount of steering wheel rotation, (b) the rate of steering wheel rotation, or (c) the vehicle yaw rate, to compensate for the effect of cross winds or the like.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a steering system for correcting 
or compensating for side winds and the like and more specifically to a 
system which is applied to a rack and pinion steering system and which 
does not interfere with normal steering in the event of a malfunction 
thereof. 
2. Description of the Prior Art 
A previously proposed arrangement for compensating for the effect of side 
winds and the like is shown in FIG. 1 of the drawings. In this arrangement 
a so called "parallel link" type steering arrangement including, a 
steering gear 1, a pitman arm 2, a cross rod 3, an idler arm 4, side rods 
5 and a servo mechanism 6, is mounted on the chassis of the vehicle. As 
shown, the servo mechanism 6 is controlled by a circuit arrangement 
including a conversion and compensation circuit 7 which receives an input 
indicative of the angle of the road wheels with respect to the vehicle 
chassis, and a yaw rate sensor 8 which senses the rotation of the vehicle 
about an axis essentially normal to the chassis thereof. The outputs of 
the compensation circuit 7 and the yaw rate sensor 8 are fed to a mixer 9 
which in turn outputs an appropriate signal in accordance with the 
difference between the signals. With this arrangement the servo mechanism 
6 applies an additional amount of steering to the front wheels 10 to 
compensate for any deviation from the intended course due to side winds or 
the like. 
However, this arrangement has suffered from a notable drawback in that in 
the event the servo mechanism 6 malfunctions, its interposition between 
the pitman arm 2 and the cross rod 3 severely hampers efforts to steer the 
vehicle. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a steering system which 
compensates for any undesired deviations from an intended course due to 
the effect of side winds and the like and which, in the event of 
malfunction, does not interfere with normal steering. 
In brief, the the present invention features a hydraulic servo which 
axially biases a rack and pinion steering housing in a manner to add an 
additional amount of steering to the front wheels of a vehicle in response 
to one of (a) the amount of steering wheel rotation, (b) the rate of 
steering wheel rotation, or (c) the vehicle yaw rate, to compensate for 
the effect of cross winds or the like. 
More specifically, the present invention takes the form of a steering 
system for an automotive vehicle, comprising a housing supported on a 
chassis of the vehicle by an elastomeric member, a rack slidably disposed 
in the housing, a pinion disposed in the housing, the pinion being 
arranged to mesh with the rack, a steering wheel operatively connected 
with the pinion for synchronous rotation therewith, a source of hydraulic 
fluid under pressure, a hydraulic servo fluidly connected with the source 
and operatively connected with the housing for selectively biasing same in 
first and second axial directions, a control valve fluidly interposed 
between the servo and the source for selectively pressurizing the servo in 
a manner to bias the housing in the first and second axial directions, and 
control means operatively connected with the control valve for controlling 
the control valve in response to a sensed vehicle operating parameter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning now to FIGS. 2 to 4 a first embodiment of the present invention is 
shown. In this arrangement a servo mechanism generally denoted by the 
numeral 11 is operatively connected between the chassis 12 of the vehicle 
and the housing 14 of a rack and pinion steering arrangement. As shown, 
the housing 14 is mounted on the chassis 12 through elastomeric bushes 18 
so as to be axially displaceable by a small amount and simultaneously 
prevent road shocks being directly transmitted to the chassis. The ends of 
the rack 20 are connected to the front (steerable) wheels 22 in a 
conventional manner. The pinion 24 of the steering arrangement is 
rotatably mounted within the housing 14 so as to mesh with the rack teeth 
of the rack 20 and operatively connected with the steering wheel 22 of the 
vehicle through a suitable steering column 124. 
The servo mechanism in this embodiment, takes the form of a hydraulic 
cylinder 26 fixedly connected to the chassis 12 and a piston 28 which is 
connected to the housing 14. As shown, the piston 28 defines first and 
second variable volume chambers 30,32 within the cylinder 26 which are 
selectively pressurized by an electromagnetic spool valve 34 (see FIG. 4). 
The spool valve 34 is provided with solenoids 36, 38 at either end thereof 
which are operatively connected to a suitable amplifier 40. This amplifier 
may be of the type which outputs a square wave signal the duty cycle of 
which is varied in response to a suitable sensed parameter. In this 
embodiment a steering wheel angular displacement sensor 42 is operatively 
connected to the steering column 124 and arranged to output a suitable 
voltage signal which varies with the degree of rotation of the steering 
wheel from a neutral steering position. This signal is fed to the 
amplifier 40 which accordingly energizes the solenoids 36, 38 in a manner 
to reciprocate the spool of the valve so that the communication between a 
line pressure inlet port 44 and the discharge ports 46, 48 is controlled 
in a manner that the pressure discharged from the ports 46, 48 to the 
chambers 30, 32 is regulated or controlled to a level for inducing the 
appropriate amount axial displacement of the housing 14. 
Thus, with this arrangement should the steering wheel 22 be rotated in the 
clockwise direction (for example) to induce the vehicle to traverse to the 
right, the angular displacement sensor 42 will output a voltage signal to 
the amplifier 40. Subsequently, solenoid 36 will be energized with a 
frequency suitable for inducing the spool 50 to reciprocate in a manner to 
modulate the output from port 48. Accordingly, the pressure discharged 
from the spool valve 34 via port 48 will pressurize chamber 26 of the 
servo mechanism 11 and displace the piston 28 to the left as seen in the 
drawings. The movement of housing 14 due to the movement of the piston 28 
moves the rack and pinion steering arrangement as a whole laterally with 
respect to the vehicle chassis 12 in a manner which adds to the steering 
induced by the relative movement of the rack 20 with respect to the 
housing 14. Rotation of the steering wheel 22 in the reverse direction of 
course produces a similar effect. 
Accordingly, in the case that the vehicle is steered to traverse an arcute 
path, the inevitable compliance steering effect will tend to be 
compensated for by the extra rotation (steering) of the front wheels. 
According the present invention it is possible to replace the angular 
displacement sensor 42 with a rate of angular displacement sensor so that 
very rapid steering requirements induce an increased amount of additional 
steering as compared with more gradual rotations. Further, it is possible 
to replace and/or supplement the steering demand parameter mentioned above 
with a yaw rate sensor 52 (shown in phantom). With this arrangement any 
undesirable drifting of the vehicle under the influence of strong cross 
winds may be negated without the driver being required to manually 
compensate for same via rotation of the steering wheel. 
With the above disclosed embodiment, it will be appreciated that should the 
the pump 54, conduiting or the like of the servo mechanism 11 fail, normal 
manual steering will be in no way interfered with. 
FIG. 5 shows a second embodiment of the present invention. In this 
arrangement a power steering system is incorporated with the rack and 
pinion steering arrangement. This arrangement features the advantage that 
a pump 60 and suitable steering sensor in the form of a power steering 
control valve 62 are already provided whereby an additional servo 
mechanism denoted by the numeral 64 may be pressurized with the same 
pressures fed to the power steering servo 66. Thus, as shown the servo is 
connected to a cylinder defining part of the power steering servo 
mechanism which, due to its function, is associated with the rack and 
pinion housing in a manner to be movable therewith. Thus, upon the 
steering wheel being rotated in a direction (for example in the counter 
clockwise direction) both of the servos are pressurized in a manner to 
move the pistons 68, 70 thereof to the right as seen in the drawings. The 
movement of the piston 70 assists the relative movement between the rack 
20 and the housing 14 while the movement of the piston 68 moves the 
housing 14 and power steering servo 66 as a unit laterally with respect to 
the vehicle to add to the steering induced by the first mentioned relative 
movement. Of course it will be appreciated that the arrangement shown in 
FIG. 5 is purely schematic and that a number of design variations are 
encompassed thereby.