BACKGROUND OF THE INVENTION The present invention relates to steering systems for wheeled vehicles, particularly such vehicles with at least two steerable wheels under manual control of a driver and in which the steerable wheels are independently suspended from the vehicle body frame. More generally, the invention is applicable to steering systems for wheeled vehicles with at least two steerable wheels. By the present invention, the necessary forces for causing each of the steerable wheels to properly respond to the steering control provided by the driver is effectuated between the vehicle body and the (usually independently suspended) steerable wheel control arm by a fluid pressure or electrically powered actuator. The coordination of the left wheel and right wheel motion is attained, not with the usual mechanical link between steering control arms for the wheels, but rather by two distinct control signals provided to each of the actuators. These two signals and, hence, the motions imparted by the respective actuators have a predetermined non-linear relation which can be produced by an electronic digital or analog device. An advantage of the system of the invention is that the necessity for a conventional steering column is eliminated along with the safety hazard that such columns present for the driver in the event of a mishap. Another advantage is that it facilitates a very large angle of vertical travel for independent suspension arms which is desirable for some vehicles and virtually impossible to obtain in conventional steering systems.

The present invention is in sharp contrast to the traditional wheeled vehicle steering system. The structure, adjustment, and alignment of the steering mechanism of a wheeled

vehicle is a somewhat complicated matter involving various relationships of each steerable wheel axle to the vehicle body referred to as caster, camber, toe-in, Ackerman angle and the like. No attempt is made here to present a detailed discussion of all these factors, except as they relate to the improvements of the present invention.

For many decades, the steering system for automotive vehicles has utilized a front axle which does not rotate about a vertical axis when the vehicle is steered to the right or the left. Rather, each front wheel is provided with a stub axle which is rotatable about a vertically disposed king-pin. Accordingly, it is necessary to provide means by which the front wheels turn to the left or turn to the right together in a coordinated fashion. It was long ago determined that optimum steering was not achieved with strictly parallel motion of the front wheels because the outwardly turning wheel is closer to the vehicle turning center than the inwardly turning wheel and needs to rotate through a greater angle. This refinement and provision for steering control is referred to as the Ackerman angle provision.

The present invention eliminates reliance upon a track rod or other direct mechanical linkage between the left and right steerable wheels by causing the turning motion of each wheel to be effected by its own independent actuator. The hand lever actuated manual steering system of the present invention provides the advantage of removing the necessity of a steering wheel . The control of the vehicle may be accomplished with one or two hands.

2 . Prior Art .

Patent Nd. 5,094,312 to Hakel dated March 10, 1992 (U.S. Cl. 180/132) shows a vehicle steering system in which the left and right steering control arms for the front wheels are both operated by a single double-acting hydraulic piston with oppositely directed piston rods each coupled by a mechanical link to a respective steering control arm.

Patent No. 5,090,512 to Mullet et al . , dated February 25, 1992 (U.S. Cl. 180/236) , like the patent to Hakel, relies on a direct mechanical connection from the left side to the right side of the steering system including a rotatable shaft and cam pulleys operating a cable arrangement for wheel steering. Patent No. 4,006,664 to Brown has hydraulic operated steering, but like the patent to Hakel has only a single cylinder for left and right wheels, the coordinated motion of which must be provided by a linkage connecting left and right wheels with the single cylinder provided for their operation.

Patent No. 2,757,014 to Schmitz, dated July 31, 1956 (U.S. Cl. 280/87) discloses a steering system for a tractor having pairs of control cylinders and operating cylinders for providing steering motion to the respective front wheels which is independently controlled. The objective of the Schmitz system is solely to arrive at an extreme or limit position for the wheels in which the left wheel is turned by ninety degrees and the right wheel is turned by about fifty degrees (or vice versa) . Any slight steering movement of the wheel 24 will be transmitted to the wheels 13 and 14 equally.

SUMMARY OF THE INVENTION In addition to providing the features and advantages described above, it is an object of the present invention to provide a wheeled vehicle steering system which achieves coordination between the steering motion of the left and right wheels by providing independently controlled actuators, the motions of which are coordinated through the control systems thereof, thereby avoiding the necessity of direct mechanical linkage extending between the right side and left side wheels of the vehicle. It is another object of the present invention to provide a steering system for a wheeled vehicle wherein steering motion of each of the steerable wheels is provided by a hydraulic or electric actuator positioned near or at such wheel together with means remote from the steerable wheels for coordinating the motion of the actuators to have a predetermined non-linear relation and obviating the necessity for a direct mechanical linkage between the left steerable wheel and the right steerable wheel.

BRIEF DESCRIPTION OF THE DRAWINGS In addition to the objects and advantages described above, other objects and advantages of the invention will be apparent from consideration of the following description in conjunction with the drawing in which:

FIGURE 1 is a schematic diagram of a steering lever operated hydraulic steering control system for a wheeled vehicle according to the invention.

DETAILED DESCRIPTION

Referring now to FIGURE 1, a steering system 611 for a vehicle with a right front steerable wheel 613 and a left front steerable wheel 615 is shown. Wheels 613 and 615 are mounted so that they are rotatable about a generally vertical axis to turn the vehicle to the left or to the right.

Prior copending application Serial No. 08/230311, filed April 20, 1994, now U.S. Patent No. 5,435,407, provides a description of an exemplary relation of actuators for wheels 613 and 615 to their independent suspension and that Patent is an appropriate reference for details of vehicle construction not included herein.

The steering system according to the invention shown diagrammatically in FIGURE 1 is particularly adapted to the use of electrical actuators for providing steering motion to the wheels 613 and 615 but the apparatus of FIGURE 1 could be modified to use hydraulic actuators or servomotors.

Actuator 631 and actuator 641 preferably take the form of electrical servomotors with respective actuator rods 633 and 643 for imparting motion to wheels 613 and 615. A steering angles computer 660 provides digital or analog signals to actuators 631 and 641 through signal transmission lines 635 and 645 respectively. Transmission lines 635 and 645 will normally be physical conductors dedicated to transmitting control signals to actuators 631 and 641. As indicated the arrows on lines 635 and 645, the primary information flow is from steering angles computer 660 to actuators 631 and 641, but this does not preclude the use of feedback signals or other signals propagating in the opposite direction.

In mathematical terms, the Ackerman angle relation generally desired for the outside wheel (OW) and the inside wheel (IW) is:

OW = arctan L

(R + t/2)

IW = arctan L

(R - t/2) where L is the length of wheel base (front axle to rear axle) , t is the transverse vehicle dimension (tire to tire) , and R is the turning radius. A radius substantially greater than L and zero toe-in is assumed above. Usual implementation of the Ackerman angle provision by mechanical linkages achieves a fairly good but imperfect result for small wheel angles (large turning radius) . Actuator rod 633 is provided with a force sensor 630 and actuator 643 is provided with a force sensor 640. Force sensors 630 and 640 may utilize a strain gage apparatus to provide an electrical signal representative of the force imparted to wheels 613 and 615 by actuators 631 and 641 or on the other hand road contact forces on wheels 613 and 615 transmitted back to actuators 631 and 641. Electrical transmission lines 637 and 647 convey the signals from force sensors 630 and 640. back to the steering angles computer 660.

Optionally the steering angles computer 660 may also receive vehicle velocity and acceleration from a velocity and acceleration package 650. Vehicle velocity may be obtained from wheel rotation rate or other data and accelerations both lateral and longitudinal may be obtained from accelerometers, gyroscopes, or other well known sensing devices. Availability of velocity and acceleration data enables the steering angles computer 660 to generate warning of hazardous steering motions, skidding or incipient skidding, and, if desired, could initiate corrective

corrective steering action to regain control of the vehicle.

The steering levers 671 and 673 shown in FIGURE 1 are indicated somewhat schematically as they can take numerous forms. They may be substantially the same as shown in FIGURE 1 or may be pivoted about the lateral horizontal axis. Steering levers 671 and 673 are pivotally secured relative to the vehicle frame by brackets 681 and 683. As steering lever 671 is moved by the vehicle driver, its motion is imparted to actuation rod 653 which is free to reciprocate with respect to position sensing device 651 connected by signal transmission line 659 to steering angles computer 660. Preferably formed integrally with position sensor 651 is an artificial feel device 655 and these two devices are restrained relative to the vehicle frame by bracket 685. Position signals from position sensor 651 are transmitted to steering angles computer 660 over signal transmission line 659, and artificial feel signals derived from force sensor 630 are transmitted by computer 660 to artificial feel element 655 by means of signal transmission line 675.

A major advantage of the steering lever type system over the steering wheel type system resides in the fact that the space forward of the driver position is cleared of all obstacles related to the steering system, thereby improving crash safety of the vehicle. Another less apparent advantage of the steering lever system is that, with appropriate vehicle body design and steering lever positioning, the vehicle could be entered from directly in front rather than from the side. This releases constraints on the design of the roll-over cage for the body associated with permitting side entry into and exit from the vehicle. Typically, side entry into the vehicle is difficult at

best and a front entry vehicle would be substantially more accessible. These considerations are, of course, of greatest consideration in respect to an all terrain vehicle.

In a substantially identical fashion, symmetrically disposed left steering lever 673 is pivotally mounted relative to the vehicle frame by bracket 683 and the position of actuation rod 663 is sensed by position sensor 661 the signal of which is transmitted over transmission line 669 to the steering angles computer 660. Left wheel artificial feel signals are transmitted from computer 660 over signal transmission line 677 to artificial feel element 665 which, together with position sensor 661, is restrained relative to the vehicle body by a pivotal connection at bracket 687.

While a hydraulic cylinder steering system as shown in U.S. Patent No. 5,435,407 inherently provides feel of the road feedback to the vehicle driver, this is desirably accomplished in the system utilizing electrical actuators 631 and 641 by the artificial feel components of the system described above. Artificial feel systems are particularly well known, particularly with respect to aircraft controls and many versions of such systems could be adapted by one skilled in the art to provide the desired degree of feedback and artificial feel to the driver operating steering levers 671 and 673. Artificial feel systems for aircraft controls, sometimes known as force feel systems have been well known for decades as illustrated, for example, by Patent No. 3,463,423 for "Electromechanical Force Feel System For Aircraft Control Stick", issued August 26, 1969 (U.S. Cl. 244/83) and U.S. Patent No. 3,733,039 for "Feel Augmentation Control System For Helicopters", issued May 15, 1973 (U.S. Cl. 244/77d) .

Of course, the system of FIGURE 1 could be simplified by eliminating the elements for providing artificial feel at the steering levers 671 and 673 and the remaining system would be totally operational and reliable without the improvement provided by the artificial feel features. In the system of FIGURE 1, the artificial feel elements 655 and 665 or other means may be relied upon to coordinate the motions of steering levers 671 and 673 to be substantially equal and opposite, or one may choose not to constrain the relative motions of steering levers 671 and 673 relative to one another, but to take the difference in the position of the steering levers to be the indication of vehicle turning control from which wheel-steer angles are computed.

Whereas, the present invention has been described in relation to the drawing attached hereto, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of this invention.