Abstract:
A steering system ( 10 ) and a method of dampening the forces transmitted to a steering wheel ( 20 ) of a vehicle when a steerable wheel ( 22 ) of the vehicle collides with an obstacle using the steering system ( 10 ). The method includes steering a vehicle via a steering wheel ( 20 ) operably connected to a steerable wheel ( 22 ), with the steering wheel ( 20 ) defining an input angle. The method also includes monitoring the rate of change of a steering angle ( 40 ) as defined by the steerable wheel ( 22 ), with the ratio of the input angle to the steering angle ( 40 ) defining a steering ratio. The method further includes reducing an amount of torque transmitted to the steering wheel ( 20 ) from the steerable wheel ( 22 ) when the rate of change of the steering angle ( 40 ) exceeds a maximum rate by adjusting the steering ratio ( 40 ).

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a vehicle steering system, and in particular to a steering system that reduces the kickback transmitted to a steering wheel from a steerable wheel when the steerable wheel encounters an obstacle. 
   Vehicle steering systems typically include a steering wheel coupled to at least one steerable wheel via a plurality of mechanical linkages and mechanisms. These linkages and mechanisms allow for the transfer of an input from the operator via the steering wheel, to be transmitted to the steerable wheel, as well as the transfer of forces from the steerable wheel to the steering wheel. Heretofore, the steering wheel systems that allow the transfer of forces from the steerable wheel to the steering wheel required the operator to exert significant force onto the associated steering wheel to counter forces transferred thereto. In situations of extreme driving, the steerable wheels of a vehicle may collide or strike obstacles causing the steering wheel to rotate violently overcoming the operators ability to hold the steering wheel, resulting in injury to the operator or loss of control of the vehicle. 
   SUMMARY OF THE INVENTION 
   A steering system for a motor vehicle includes a steering shaft having a first portion and a second portion, wherein the first portion of the steering shaft is adapted to receive an input from an operator, and a rotational coupler connecting the first portion of the steering shaft to the second portion of the steering shaft, wherein the rotational coupler allows the first portion of the steering shaft to rotate independently of the second portion of the steering shaft when a rotational torque that exceeds a maximum torque value is exerted on the second portion of the steering shaft. The steering system also includes at least one wheel that pivots to define a steering angle, wherein the steering angle is determined, at least in part, by the input to the steering shaft by the operator, and wherein the first portion of the steering shaft and the steering angle have a given original alignment therebetween. The steering system further includes a motor operatively connected to the wheel, wherein the steering angle is determined, at least in part, by an input from the motor, and a controller operatively connected to the motor and adjusting the input of the motor to the steering angle, and realigning the steering angle with the first portion of the steering shaft to the original alignment therebetween subsequent to a torque that exceeds the maximum torque value being exerted on the second portion of the steering shaft to rotate independently of the first portion of the steering shaft. 
   Another aspect of the present invention is to provide a steering system for a motor vehicle that includes a steering shaft adapted to receive an input from an operator, and at least one wheel that pivots to define a steering angle, wherein the steering angle is determined, at least in part, by the input to the steering shaft by the operator, and wherein the steering shaft and the steering angle have a given original alignment therebetween. The steering system also includes at least one sensor for sensing the exertion of a force on a component on the steering system that exceeds a maximum set value, a motor operatively connected to the wheel, wherein the steering angle is defined, at least in part, by an input from the motor, and an actuator operatively connected to the motor and in operable communication with the sensor, wherein the actuator reduces the amount of the force exerted on the component as transmitted to the steering wheel by allowing a misalignment of the steering shaft and the steering angle. 
   Yet another aspect of the present invention is to provide a method of dampening the forces transmitted to a steering wheel of a vehicle when a steerable wheel of the vehicle collides with an obstacle, that includes steering a vehicle via a steering wheel operably connected to a steerable wheel, wherein the steering wheel defines an input angle, and monitoring the rate of change of a steering angle as defined by the steerable wheel, wherein the ratio of the input angle to the steering angle defines a steering ratio. The method also includes reducing an amount of torque transmitted to the steering wheel from the steerable wheel by adjusting the steering ratio when the rate of change of the steering angle exceeds a maximum rate. 
   The present inventive vehicle steering system results in a significant reduction in kickback as transmitted from a steerable wheel to the steering wheel of a vehicle. The steering system described herein reduces the possibility of injury to the operator, while simultaneously allowing the operator to maintain control of the associated vehicle, and is particularly well adapted for the proposed use. 
   These and other advantages of the invention will be further understood and appreciated by those skilled in the art by reference to the following written specification, claims and appended drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partially schematic view of the steering system embodying the present invention. 
       FIG. 2  is a perspective view of the steering system, wherein a steerable wheel defines a steering angle greater than 0°. 
       FIG. 3  is a diagram of steering angle versus steering wheel angle for the present inventive system. 
       FIG. 4  is a partially schematic view of an alternative embodiment of the steering system. 
       FIG. 5  is a partially schematic view of the alternative embodiment of the steering system, wherein the steerable wheel defines a steering angle greater than 0°. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in  FIG. 1 . However, it is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. 
   The reference numeral  10  ( FIG. 1 ) generally designates a vehicle steering system embodying the present invention. Steering system  10  includes a steering shaft  12  having a first portion  14  and a second portion  16 . First portion  14  of steering shaft  12  is adapted to receive a rotational input in a direction and represented by an arrow  18  via a steering wheel  20  coupled therewith. Second portion  16  of steering shaft  12  is operably coupled to a pair of steerable front wheels  22  via a rack-and-pinion system  24  and a plurality of steering links  26 . Rack-and-pinion system  24  includes a rack  28  and a pinion gear  30 . Steering links  26  include drag links  32  and steering arms  34 . Although the present example utilizes a rack-and-pinion steering system, it should be noted that other steering systems compatible with the inventive steering system  10  described herein may be substituted therefore. 
   Each steerable wheel  22  ( FIG. 2 ) pivots about a pivot point  36  with respect to a vehicle frame  38 . Each wheel  22  defines a steering angle  40  between the longitudinal axis  42  of the associated vehicle and a central travel axis  44  of wheel  22 . It should be noted that while steering angle  40  is defined by the pivotable movement of each of front wheels  22 , a steering angle may be defined by pivotable rear wheels if the vehicle is so equipped, and/or any other pivotable wheels. 
   The steering system  10  further includes a clutch system  46  operable connecting first portion  14  with second portion  16  of steering shaft  12 . Clutch system  46  includes a first clutch plate  48  and an abutting second clutch plate  50  having a frictional coefficient therebetween. Clutch system  46  allows first portion  14  of steering shaft  12  to rotate independently of second portion  16  of steering shaft  12  when a rotational torque in a direction and represented by a directional arrow  52  that exceeds a maximum torque value, or the frictional coefficient between first clutch plate  48  and second clutch plate  50 , is exerted on second portion  16  of steering shaft  12 . By allowing first portion  14  to rotate independently of second portion  16  of steering shaft  12  under prescribed conditions, the amount of torque transmitted to steering wheel  20  is reduced as described below. 
   The steering system  10  further includes an active front steering system  54  that includes a controller  56  in operable communication with a steering assist motor  58  operably connected to second portion  16  of steering shaft  12  via a mechanical coupler  60 . The active front steering system  54  assists in pivoting wheels  22  depending on various driving parameters. Although a particular kind of basic steering system is illustrated in the examples herein, other systems known in the art may be utilized. In basic operation, active front steering system  54  augments the input from the operator as applied to steering wheel  20 , via motor  58 . As illustrated in  FIG. 3 , the steering angle  40  as defined by wheel  22  follows a particular ratio along line  21 . Active front steering system  54  augments the input from the operator, thereby adjusting steering angle  40  by increasing the steering angle, as illustrated by line  23 , or by decreasing the steering angle, as illustrated by line  25 . Lines  27  and  29  represent the combined effects of line  21  with lines  23  and  25 , respective, and indicate the total input into steering angle  40 . 
   In operation, a plurality of sensors  62  are utilized to monitor the alignment between steering wheel  20  and wheels  22 , and therefore the alignment between steering wheel  20  and steering angle  40 . As a result of the high return efficiency of rack-and-pinion steering systems, injuries may occur when a high torque is transmitted to the steering wheel from a front wheel, or steerable wheel, that collides with an obstacle. To eliminate a high torque from being transmitted to steering wheel  20  when wheels  22  collide with an object, clutch  12  allows first portion  14  of steering shaft  12  to rotate separately from second portion  16  of steering shaft  12  if a sufficient force is exerted on second portion  16 , thereby overcoming the frictional coefficient between first clutch plate  48  and second clutch plate  50 . Allowing first portion  14  and second portion  16  of steering shaft  12  to rotate separately causes a misalignment from the original alignment between steering wheel  20  and steering angle  40 . Preferably, at least one sensor is in operable communication with a controller that monitors the application of a torque being applied to the first portion  14  of the steering shaft  12  and allows for disengagement of the clutch system  46  and locking the rotation of the first portion  14  of the steering shaft  12  with the second portion  16  of the steering shaft  12  when the vehicle is not running to thereby prevent misalignment when a driver of the vehicle grabs the steering wheel  20  and torques the steering wheel  20  as the driver enters the passenger compartment of the vehicle. Alternatively, at least one sensor can measure the speed of the vehicle and lock the rotation of the first portion  14  of the steering shaft  12  with the rotation of the second portion  16  of the steering shaft  12  when the vehicle is not moving to prevent misalignment as the driver enters the vehicle. In the alternative situation, a sensor can monitor to position of the driver&#39;s door to only lock rotation of the first portion  14  with the second portion  16  when the driver&#39;s door is open and when the velocity of the vehicle is zero. 
   To compensate for this misalignment the active front steering system  54  augments the input from the operator via steering assist motor  58  and returns wheels  22  and the associated steering angle  40  to the original alignment with first portion  14  of steering shaft  12  and steering wheel  20  over a finite period of time. The amount of time required to return steering angle  40  to the original alignment with first portion  14  of steering shaft  12  and steering wheel  20  depends on parameters such as the amount of misalignment therebetween, current road conditions, braking conditions, speed of the vehicle, etc. However, in some situations, the first portion  14  and the second portion  16  of the steering shaft  12  do not have to be realigned. Typically, no realignment is necessary when other systems of the vehicle are not hampered by misalignment. 
   The reference numeral  10   a  ( FIG. 4 ) generally designates another embodiment of the steering system of the present invention. Since steering system  10   a  is similar to the previously described steering system  10 , similar parts appearing in  FIGS. 1 and 2  and  FIGS. 3 and 4  respectively are represented by the same, corresponding reference numeral, except for the suffix “a” in the numerals of the latter. Steering system  10   a  operates similarly to steering system  10 , with the main exception being that any misalignment between steering wheel  20   a  and steering angle  40   a  from the original alignment is compensated directly by active front steering system  54   a  rather than a clutch system. 
   In operation, the striking of an obstacle by wheels  22   a  is monitored by sensors  52   a . Sensors  62   a  may be adapted to monitor the rate of change of steering angle  40   a , and/or a strain upon any of the components of steering system  10   a , including steering links  26   a , rack-and-pinion system  24   a , etc. This information is then relayed to controller  56   a  which compensates for and reduces the amount of the force exerted on wheels  22   a  as transmitted to steering shaft  12   a  and steering wheel  20   a , by controlling steering assist motor  58   a  accordingly. It should be noted that the active front steering system  54   a  and the components thereof of the present example are utilized herein for basic illustrative purposes only and that numerous active front steering systems are known in the art and may be utilized in conjunction with the present invention steering system  10   a.    
   The present inventive vehicle steering system results in a significant reduction in kickback as transmitted from a steerable wheel to the steering wheel of a vehicle. The steering system described herein reduces the possibility of injury to the operator, while simultaneously allowing the operator to maintain control of the associated vehicle, and is particularly well adapted for the proposed use. 
   In the foregoing description it will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed herein. For example, the force between the first clutch plate  48  and the second clutch plate  50  can preferably be altered, either continuously or discretely, to thereby provide the clutch system  46  with more than one setting, depending on the friction between the plates  48  and  50  set by the force between the plates  48  and  50 . Such modifications are to be considered as included in the following claims, unless these claims by their language expressly state otherwise.