Abstract:
A steering assembly for a vehicle, including an input shaft connectable to a steering input system, an output shaft connectable to a steering output system, a torsion device connecting the input shaft and the output shaft and allowing relative rotation movement between the input shaft and the output shaft based upon a torque applied to the input shaft or the output shaft, a first sensor of sensing relative rotational movement of the input shaft and the vehicle, and a second sensor for sensing relative rotational movement of the output shaft and the vehicle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present invention claims priority to U.S. Provisional Application Serial No. 60/266,979, filed on Feb. 7, 2001 and entitled “Method and Device for Detecting Steering Torque.” 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention generally relates to power assisted steering systems and, more specifically, to power assisted steering systems that differentiate between forces originating at a steering input and forces originating at a steering output.  
         BACKGROUND  
         [0003]    As an attempt to increase fuel-efficiency of automobiles, electric power assisted steering systems have been introduced to the automotive market. These systems assist in steering vehicles by applying additional torque to the steering system whenever torque is sensed in the steering shaft. Although these systems have increased fuel-efficiency, they are unable to differentiate between torque created by forces at the steering input and at the steering output. Forces originating at the steering output may be the result of the road wheel coming into contact with a curb or a large bump in the road, while forces originating at the steering input are those forces that a driver applies. Because the currently existing systems are unable to differentiate between these forces, the forces originating at the steering output (e.g. a road wheel) are sensed as an input torque and cause the system to apply additional torqu to the steering shaft in the same direction, thereby causing vibration in the steering input (e.g. a steering wheel) and decreasing stability of the system.  
           [0004]    While it is important to reduce the effort drivers must use to steer a vehicle, it is of equal importance to resist forces that originate at the steering output. Forces originating at the steering output sometimes steer the vehicle in an unintended direction and applying additional torque to the steering shaft may exacerbate this problem. For these reasons, there is a need in the automotive art, if not other arts, for a power assisted steering system that is able to distinguish between forces originating at the steering input and the steering output and to react to these forces differently. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a schematic top view of the preferred embodiment;  
         [0006]    [0006]FIG. 2 is a detailed view of the torque sensing subsystem of the preferred embodiment; and  
         [0007]    [0007]FIG. 3 is a cross-sectional view of the torque sensing subsystem of FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0008]    The following description of the preferred embodiment of the invention is not intended to limit the scope of this invention to this embodiment, but rather to enable any person skilled in the art of power assisted steering systems to make and use the invention.  
         [0009]    As shown in FIG. 1, the steering system  10  of the preferred embodiment includes a steering input subsystem  12 , a steering output subsystem  14 , a steer assist subsystem  16 , and a torque sensing subsystem  18 . The steering system  10  is capable of determining the magnitude and origination of an applied torque on the steering system  10 , which decreases the vibration and increases the stability of the steering system  10 .  
         [0010]    The steering input subsystem  12  of the preferred embodiment includes a steering input device  20  and an input shaft  22 . The steering input device  20  functions to receive forces from a driver of the vehicle and transfer those forces to input shaft  22 . The steering input device  20  is preferably a conventional steering wheel, but may alternatively be any suitable device for receiving forces from the driver of the vehicle. The steering input device  20  is preferably fastened to the input shaft  22  with conventional fasteners. The input shaft  22 , which functions to transfer the forces from the driver through the steering system  10 , is preferably a conventional solid shaft, but may alternatively be any suitable device.  
         [0011]    The steering output subsystem  14  of the preferred embodiment includes an output shaft  23 , a rack-and-pinion device  24 , and road wheels  26 . The output shaft  23 , which functions to receive torque from the input shaft  22  and transfer the torque to the rack-and-pinion device  24 , is preferably a conventional solid shaft, but may alternatively be any suitable device. The output shaft  23  is preferably fastened to the rack-and-pinion device  24  with conventional fasteners. The rack-and-pinion device  24 , which functions to convert the rotational movement of the output shaft  23  into a pivoting movement of the road wheels  26 , is preferably a conventional device. In alternative embodiments, any suitable device, such as a recirculating-ball device, may be used to pivot the road wheels  26 . The road wheels  26 , which function to communicate with a road surface, are preferably connected to the rack-and-pinion device  24  with conventional fasteners. The road wheels  26  are preferably conventional road wheels, but may alternatively be any suitable device to communicate with a surface, such as a ski on a snow mobile or a rudder on a watercraft.  
         [0012]    The steer assist subsystem  16  of the preferred embodiment includes a power supply  28 , a control unit  30 , and an assist motor  32 . The steer assist subsystem  16  functions to assist the steering output subsystem  14  and turn the road wheels  26  according to the intent of the driver. The power supply  28  is preferably a conventional battery within the vehicle, but may alternatively be a dedicated power supply for the steering system  10 , or may be any suitable device able to power the control unit  30  and the assist motor  32 . The control unit  30 , which functions to receive data signals from a computational unit (discussed below) and to control the torque and direction of the output of the assist motor  32 , is preferably connected to assist motor  32  with conventional wires. The control unit  30  is preferably a conventional microprocessor with a look up menu that determines an appropriate command for the assist motor  32 . The assist motor  32  is preferably coupled to the rack-and-pinion device  24  and in communication with the control unit  30 . The assist motor  32  functions to apply torque to the rack-and-pinion device  24  in accordance with the commands received from the control unit  30 . The additional torque serves to decrease the effort required by the driver to steer the vehicle and/or to reduce the effects of external forces acting on road wheels  26 . The assist motor  32  preferably applies torque directly to the rack-and-pinion device  24 . Alternatively, the assist motor  32  may indirectly apply torque to the rack-and-pinion device  24 . For example, assist motor  32  may apply force directly to output shaft  23 , thereby resulting in increased or decreased torque within the rack-and-pinion device  24 . The assist motor  32  is preferably a conventional electric motor, but may alternatively be any suitable device with a significant output to assist in the steering or reduce the vibrations of the steering system  10 .  
         [0013]    As shown in FIGS. 2 and 3, the torque sensing subsystem  18  of the preferred embodiment includes a torsion device  34 , an input indicator  36 , an output indicator  38 , an input sensor  40 , an output sensor  41 , and a computation unit  42 . The torque sensing subsystem  18  is capable of determining the amount of torque being applied to the input shaft  22  and to the output shaft  23 . In addition, the torque sensing system  18  is capable of determining where the torque originated.  
         [0014]    The torsion device  34  connects the input shaft  22  to the output shaft  23  and functions to allow relative rotational motion between the input shaft  22  and the output shaft  23 . The torsion device  34  is preferably a conventional torsion bar, but may alternatively be any suitable device capable of allowing relative rotational movement between the input shaft  22  and the output shaft  23  based upon a torque applied to the input shaft  22  or the output shaft  23 .  
         [0015]    The input indicator  36  and the output indicator  38  are preferably located on the input shaft  22  and the output shaft  23 , respectively. The purpose of the indicators  36  and  38  is to facilitate measurement of the rotational movement of the input shaft  22  and the output shaft  23  at the location of the indicators  36  and  38 . The indicators  36  and  38  are preferably barcodes. Alternatively, any other mark capable of being tracked and having its rotational movement measured may be used, such as formed grooves or striations.  
         [0016]    The input sensor  40  and the output sensor  41  are preferably connected to the computation unit  42 . The sensors  40  and  41  function to measure movement of the indicators  36  and  38  and transmit movement data to the computation unit  42 . Preferably, the sensors  40  and  41  are conventional optical sensors. Alternatively, any other suitable device capable of measuring the movement of the indicators  36  and  38  and transmitting the movement data may be used.  
         [0017]    The computation unit  42  functions to convert the movement data that it receives from the sensors  40  and  41  into torque measurements based upon a predetermined relationship between applied torque and relative rotational movement. Preferably, the computation unit  42  contains a look-up menu to accomplish this purpose. Upon receiving the movement data from the sensors  40  and  41 , the computation unit  42  locates the torque measurement within the look-up menu that correlates with the particular movement data that is received. Alternatively, the computation unit  42  may use any suitable method to determine torque based on the movement data.  
         [0018]    The computation unit  42  also functions to determine the location at which the measured torque was first detected. In other words, the computation unit  42  determines if the torque on the torsion device  34  originated from the road surface through the road wheels  26  or from the driver through the steering input device  20 . If rotational movement was first detected at the input indicator  36 , it may be concluded that the originating source was the steering input subsystem  12 . Likewise, if the rotational movement was first detected at the output indicator  38 , it may be concluded that the originating source was steering output subsystem  14 .  
         [0019]    The computation unit  42  further functions to transmit commands to the assist motor  32  based on the determinations of the magnitude and origination of the applied torque. If the computation unit  42  concludes that the originating source was the steering input subsystem  12 , then it will transmit a signal to the control unit  30  commanding it to have additional torque applied to the rack-and-pinion device  24  in the same direction as the measured torque. Otherwise, if the computation unit  42  concludes that the originating source was steering output subsystem  14 , then it will transmit a signal to the control unit  30  commanding it to reduce the external torque applied to the rack-and-pinion device  24 . The reduction of the torque is preferably accomplished by applying an opposing torque with the assist motor  32 , but may be alternatively accomplished by negating at least some of the torque. The computation unit  42  is preferably connected to the control unit  30  by conventional wires, but may alternatively be connected by any suitable means, such as fiber optics. Further, the computation unit  42  and the control unit  30  may be embodied in a single device, which would allow the single device to transmit commands directly to the assist motor  32  without any external connection.  
         [0020]    As any person skilled in the art of power assisted steering systems will recognize from the previous detailed description and from the FIGURES and claims, modifications and changes can be made to the preferred embodiment of the invention without departing from the scope of the invention defined in the following claims.