Abstract:
A method and apparatus for a damped steering assembly are provided. The damped steering assembly includes a steering wheel attached to a steering column. Disposed between the steering wheel and the steering column is an active vibration control mechanism. The active vibration control mechanism damps vibration transmitted from the steering column to the steering wheel.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/220,272 filed on Jul. 24, 2000, the contents of which are incorporated herein by reference thereto. 
    
    
     TECHNICAL FIELD 
     The field of this disclosure relates to vibration control, and more particularly, to an apparatus and method for controlling the vibration of a steering wheel. 
     BACKGROUND 
     Vibrations are propagated through the mechanical structure of vehicle steering systems. The vibrations are created by the engine and by the interface of tires on road surfaces. The vibrations are transmitted to the steering system components and are ultimately transmitted to the steering wheel. 
     Improvements to the steering system performance can be gained by reducing the vibration of the steering system transmitted to the steering wheel. Passive isolation would make the structure softer which could also increase the transmission at the resonant frequency. A passive isolator will require that the isolation system be so flexible that the structural integrity of the system would make this system infeasible or performance must be sacrificed. These passive vibration control techniques make the steering system more bulky in applications where increasing the weight of the structures in the system is undesirable. Thus, there is a need in the art for improved control of the vibration transmitted to the steering wheel. 
     SUMMARY 
     A method and apparatus for a damped steering assembly as disclosed herein. The damped steering assembly includes a steering wheel attached to a steering column. Disposed between the steering wheel and the steering column is an active vibration control mechanism. The active vibration control mechanism damps vibration transmitted from the steering column to the steering wheel. The above-described and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with references to the accompanying drawings, wherein like elements are numbered alike in the several figures in which: 
     FIG. 1 is a perspective view of an exemplary embodiment of a damped steering assembly; 
     FIG. 2 is a perspective view of an exemplary embodiment of a flexure element; 
     FIG. 3 is a section view of an exemplary embodiment of a damped steering assembly without the steering wheel; 
     FIG. 4 is a plan view of an exemplary embodiment of a damped steering assembly without the steering wheel; 
     FIG. 5 is a plan view of another exemplary embodiment of a damped steering assembly without the steering wheel; 
     FIG. 6 is a front view of an exemplary embodiment of a damped steering assembly without the steering wheel. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a steering assembly  10  is shown. Steering assembly  10  is configured to have an active vibration control system for damping vibrations in the steering assembly. A part of a steering column  12  or steering rod is connected with a rimless hub  14  at one end and a steering mechanism (not shown) at the other. 
     The rimless hub  14  is connected in any suitable manner to the steering column  12  so that there is no relative motion between the rimless hub  14  and the steering column  12 . The rimless hub  14  is attached to the steering column  12  distal to the remainder of the steering system components, such as the steering box (not shown). 
     In a preferred embodiment, the rimless hub  14  is a conventional steering wheel hub. Coupled to the rimless hub  14  is a flexure element  16 . In a preferred embodiment, there are four flexure elements  16  mounted to the rimless hub  14 . In other embodiments, there may be a plurality of flexure elements. 
     The flexure element  16  may be coupled to the rimless hub in any manner. In a preferred embodiment, the flexure element  16  is mounted to the rimless hub  14  by the use of an adapter  18 . There can be a plurality of adapters  18 . In a preferred embodiment, the adapter  18  is used to make a rigid connection between the flexure elements  16 , rimmed hub  20 , and the rimless hub  14 . 
     The adapter  18  is mounted to the rimless hub  14  and the flexure element  16 . In the preferred embodiment, the flexure element  16  is coupled to the adapter  18  by the use of a flexure mount  22 . 
     There can be a plurality of flexure mounts  22 . The flexure mount  22  may be any means of fixedly coupling a flexure element  16  to an adapter  18 . In the preferred embodiment, the flexure mount  22  is a threaded fastener and nut assembly. In another embodiment, the flexure element  16  and the flexure mount  22  can be formed together to accomplish coupling to the rimless hub  14 . 
     The rimmed hub  20  is coupled to the flexure element  16  distal to the rimless hub in relation to the steering column  12 . The rimmed hub  20  is coupled to the flexure element  16  in a manner that fixes the rimmed hub  20  relative to the rimless hub  14 . Rotation about the long axis of the steering column  12  by the rimmed hub  20  translates to rotation about the long axis of the steering column  12  by the rimless hub  14  and in turn, rotation of the steering column  12  about its long axis. 
     The primary movement of the rimmed hub  20  is in the rotation of the steering column  12  of the damped steering assembly  10 . Flexure element  16  is coupled to the rimmed hub  20  by a plurality of flexure mounts  22 . In an exemplary embodiment, each flexure element  16  is secured by two flexure mounts  22  and two adaptors  18 . Of course, the number of flexure mounts  22  and adapters  18  may vary. In a preferred embodiment, the rimmed hub  20  is mounted to four flexure elements  16  by use of at least two flexure mounts  22  and two adapters  18  for each flexure element  16 . 
     A steering wheel  24  is connected to the rimmed hub  20 . The steering wheel  24  is coupled in any manner that fixes the steering wheel  24  to the rimmed hub  20  such that the steering wheel  24  and the rimmed hub  20  move in unison, in directions relative to one another. 
     Thus, in the steering assembly  10 , the torque of the steering wheel  24  is translated through the rimmed hub  20  through the flexure element  16  and through the rimless hub  14  to the steering column  12  to rotate the steering column  12 . In the operation of the steering wheel  24  of one embodiment, the operation of turning the steering wheel in order to control the tires of a vehicle is similar in function to a conventional steering system. Rotation of the steering wheel  24  controls the direction of the vehicle&#39;s tires (not shown). 
     The flexure elements  16  provide for rigid support of the rimmed hub  20  and steering wheel  24  when a torque is applied to the steering wheel and the rimmed hub  20 , in a manner similar to turning the steering wheel to control the tires of the vehicle (not shown). The flexure elements  16  allow for flexible support of the rimmed hub  20  and steering wheel  24  in a direction substantially parallel to the long axis of the steering column  12 . 
     Turning now to FIG. 2, an exemplary embodiment of a flexure element  16  is illustrated. Flexure element  16  is shown including a flexure body  26 . Flexure body  26  is shown in a preferred embodiment as being substantially planar in shape (a plate). Flexure body  26  has a mechanical structure that makes it rigid enough to translate the rotational force applied to the steering system. 
     Flexure body  26  has a mechanical structure that makes it flexible enough to dampen vibrations from the steering column  12 , thus decreasing vibrations in the steering wheel  24 . These flexures were designed to be stiff in the horizontal direction but flexible in the vertical direction. They were vertically flexible for two reasons. One reason is so that the resonant frequency of the isolation system needs to be lower than that of the unmodified system to take advantage of the passive isolation effects. 
     In a preferred embodiment, the flexure body  26  is an aluminum alloy plate that has a thickness of one thirty-second of an inch ({fraction (1/32)} inch). Flexure body  26  has a platen shape as shown in the FIGS. 1-6. Of course, it is contemplated that the flexure body  26  may be a variety of materials and shapes that provide both flexibility and rigidity to the forces encountered in the steering system. Disposed on or through the flexure body  26  is the flexure mount  22 . There may be a plurality of flexure mounts  22 . A preferred embodiment has four flexure mounts  22  disposed through the flexure body  26  to couple the flexure body  26  to two adaptors  21  (see FIG.  1  and FIG.  6 ). 
     In the preferred embodiment, the flexure mount  22  is a hole or passage that allows for a fastener to insert through the flexure body  26  and into or through the adaptor  18 , thereby securely fastening it. In some embodiments, the flexure mounts  22  function to hold the flexure body  26  to the adaptor  18  which is mounted to the rimmed hub  20  and the adaptor  18  mounted to the rimless hub  14 . In other embodiments, the flexure mounts  22  secure the flexure body  26  directly to each of the rimmed hub  20  and the rimless hub  14 . 
     Disposed on flexure body  26  is a first actuator  28 . Opposite first actuator  28  is a second actuator  30 . There may be a plurality of actuators or a single actuator. 
     Actuators  28  and  30  are electromechanical transducers that convert electrical energy to mechanical energy. The electromechanical transducers may use an electrostrictive element, a magnetostrictive element or a piezoelectric element. In a preferred embodiment, the actuators are piezoelectric ceramic strain transducers. Piezoelectric elements contract and expand in proportion to applied voltage. The actuators are mounted on the flexure body  26  to provide an electrical signal responsive to the vibration of the flexure body  26 . 
     In the preferred embodiment, as shown in FIG. 2, there is a first actuator  28  and a second actuator  30  on opposite faces of the plate-shaped flexure body  26 . The first actuator  28  and the second actuator  30  may be connected to the flexure body  26  by being bonded to the flexure body  26 . The orientation of the actuators on the flexure body is such that they are in a position to substantially cancel the vibration that is translating along the flexure body  26  from the rimless hub  14  to the rimmed hub  20 . 
     In the preferred embodiment, the actuators are located at optimum points along the transmission path between the disturbances (vibrations from the steering column  12 ) and the steering wheel  24 . Coupled to the first actuator  28  is a controller  32 . Typically, there is one controller  32  for each actuator. The controller  32  may be remotely coupled to the actuator. In an exemplary embodiment, second actuator  30  also has a controller  32 . 
     The controller  32  electrically communicates with the actuators. The controller  32  sends electrical signals to the actuator. Each controller  32  is of a simple design that makes the controller  32  robust to small system changes. In one embodiment, the electrical signal may be applied to a damping resistor connected across the transducer output terminals, or the signal may be fed to electronic processing circuitry (not shown) for developing an appropriate control signal which is fed back to the actuator. 
     In a preferred embodiment, the flexure element  16  uses active vibration control techniques to reduce the vibrations in the structures of the damped steering assembly  10 . The flexure element  16  senses the motion of the structure (rimless hub  14 , rimmed hub  20 ) with sensors  34  (see FIG. 3) such as accelerometers, and then calculates the bending vibrations from the sensed motion using a computer or controller such as the controller  32 . The flexure element  16  then produces canceling bending vibrations generally equal in amplitude and opposite in phase to the calculated bending vibrations. 
     In an exemplary embodiment, the actuators are piezoceramic actuator plates. The piezoceramic plates bendably vibrate the flexure body  26  to produce the canceling bending vibrations. In one embodiment, the piezoceramic plate (actuator  28 ) is driven by a signal such that when the signal is positive, the actuator  28  causes the flexure body  26  to bendably deflect in a first direction from its resting state, and when the signal is negative, the actuator  28  causes the flexure body  26  to bendably deflect in the opposite direction. 
     In an exemplary embodiment, the vibration characteristics of the damped steering assembly  10  can be empirically measured and stored. Preset values may be encoded (programmed) into the controller  32 . The programmed controller  32  can provide signals to the actuator  28 . The control signals are based on the empirical or theoretical (in other words, another embodiment uses a mathematical model derived from physics) data gathered which is specific to the vibration and structural characteristics of the damped steering assembly  10 . When the damped steering assembly  10  experiences the vibration during operating conditions, the controller  32  can communicate the signals to the actuators to generate the canceling bending vibration. The flexure element  16  actively controls the vibration being transmitted with the actuators and controllers  32 . For example, performance of steering system  10  with controller  32  off resulted in a 5 dB reduction from shaft  12  due to the passive damping effects of the isolation system as compared to a steering shaft without the isolation system. Additionally, performance of steering system  10  with controller  32  on resulted in a total 22 dB reduction from shaft  12  due to the active and passive damping effects of the isolation system as compared to a steering shaft without the isolation system. 
     Turning now to FIGS. 3 and 4, a cross sectional view of a portion of steering assembly  10  is shown. FIG. 3 is a sectional view from one side of the damped steering assembly  10  without the steering wheel  24 . Steering column  12  is shown connected to the rimless hub  14  which is coupled to the flexure element  16 . Flexure element  16  is coupled to the rimmed hub  20 , and the steering wheel  24  (not shown) would be connected to the rimmed hub  20 . Disposed on opposite sides of the flexure body  26  are the actuators  28  and  30  (controller  32  not shown in FIG.  3 ). The flexure element  16  is coupled to both the rimless hub  14  and the rimmed hub  20  by flexure mounts  22  (adapters  18  not shown in this embodiment). 
     In an exemplary embodiment, rimless hub  14  and flexure elements  16  lengthens the entire steering assembly  10  by about one and a half inches (1.5 inches). 
     As an alternative, as shown in FIG. 3, a load limiter  36  can be added to the steering assembly  10  to allow for high static loads while not changing the stiffness of the flexure elements  16 . The load limiter  36  is coupled to the rimless hub  14  and coupled to the flexure elements  16 . 
     The load limiters  36  or mechanical stops are added to impede the motion of the flexure body  26  up to a certain amount of deflection of the flexure element  16 . In one embodiment, the load limiter  36  allows about five tenths of a millimeter (0.5 mm) of tolerance for the flexure elements  16  to move or flex while in motion. This deflection value is below the tensile stress limit of an aluminum alloy plate which corresponds to about eighty-eight hundredths of a millimeter (0.88 mm) when under a deflection load. FIG. 4 shows a diagram of an embodiment from a top view. The same elements are shown in FIG. 4, as are also shown in FIG. 3, with the addition of the controller  32  and the deletion of the actuator  30  and load limiter  36 . The embodiment shown in FIG. 4 depicts the flexure mounts  22  connected to the rimless hub  14  at a position distal from the steering column  12 . 
     FIG. 5 illustrates an alternative embodiment of the steering assembly  10 . Here the flexure mounts  22  are connected to the rimless hub  14  more proximate to the steering column  12 . This reduces the total length of the damped steering assembly  10 . Accordingly, rimmed hub  20  is positioned closer to the rimless hub  14  as compared to the embodiment shown in FIG.  4 . 
     FIG. 6 shows a front view of a diagram depicting an alternative embodiment of the damped steering column  10  without the steering wheel and other elements. In this figure, the relationship of the flexure body  26  and the adapter  18  can be seen. In the preferred embodiment, fasteners  38  are used to attach the adapters  18  to the rimmed hub  20  and the rimless hub  14 . The flexure mounts are also depicted in relationship to the adapters and the fasteners. A thru-hole  38  is disposed in the rimless hub  14  to couple the rimless hub  14  to the steering column  12 . The rimmed hub  20  may also have a thru-hole  40 . 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.