Abstract:
An electric power steering system, comprising: a steering wheel in operable communication with a mechanical linkage; a steering shaft in operable communication with the mechanical linkage, and in operable communication with at least one road wheel; a first transmission in operable communication with the steering shaft; a unidirectional electric motor in operable communication with the first transmission; wherein the electric power steering system is configured such that when the steering wheel is turned in a first direction, the motor&#39;s power is transmitted in the first direction to the steering shaft, and when the steering wheel is turned in a second direction, the motor&#39;s power is transmitted in the second direction to the steering shaft. A method for providing power assist for an electric power steering system, the method comprising: rotating a first body in a first direction with a unidirectional motor; rotating a second body in a second direction with the unidirectional motor; providing a power assist from the first body when a steering wheel is turned in a first direction; and providing a power assist from the second body when a steering wheel is turned in a second direction. n a third direction when a steering wheel is turned in a third direction thereby providing a power assist to the steering shaft in the third direction.

Description:
BACKGROUND  
       [0001]     The disclosed method and system relates generally to a power steering system, more particularly, to a method and system for an electric power steering system.  
         [0002]     Electric power steering (“EPS”) has been the subject of development by auto manufacturers and suppliers for well over a decade, due in part to its potential advantages of fuel economy and ease-of-control when compared with traditional hydraulic power steering (“HPS”). However, commercialization of EPS systems has been slow and is presently limited due to cost and performance challenges. Among the most challenging technical issues are the pulsating feel at the steering wheel and the audible noise associated with the type of high performance electric drives needed to meet steering requirements.  
         [0003]     Current EPS systems use expensive components to reduce the pulsating feel at the steering wheel and audible noise associated with the electric drives. These expensive components include, but are not limited to: a high powered controller, a low inertia motor, and very high precision gears and bearings.  
       SUMMARY  
       [0004]     The disclosed system relates to an electric power steering system, comprising: a steering wheel in operable communication with a mechanical linkage; a steering shaft in operable communication with the mechanical linkage, and in operable communication with at least one road wheel; a first transmission in operable communication with the steering shaft; a unidirectional electric motor in operable communication with the first transmission; wherein the electric power steering system is configured such that when the steering wheel is turned in a first direction, the motor&#39;s power is transmitted in the first direction to the steering shaft, and when the steering wheel is turned in a second direction, the motor&#39;s power is transmitted in the second direction to the steering shaft.  
         [0005]     The disclosed system also relates to an electric power steering system, comprising: a steering wheel in operable communication with at least one road wheel; a first transmission in operable communication with the at least one road wheel; a unidirectional electric motor in operable communication with the first transmission; wherein the electric power steering system is configured such that when the steering wheel is turned in a first direction, the motor&#39;s power is transmitted in the first direction to the at least one road wheel, and when the steering wheel is turned in a second direction, the motor&#39;s power is transmitted in the second direction to at least one road wheel.  
         [0006]     The disclosed method relates to providing power assist for an electric power steering system, the method comprising: rotating a first body in a first direction with a unidirectional motor; rotating a second body in a second direction with the unidirectional motor; providing a power assist from the first body when a steering wheel is turned in a first direction; and providing a power assist from the second body when a steering wheel is turned in a second direction.  
         [0007]     The disclosed method also relates to providing power assist for an electric power steering system, the method comprising: rotating a first body in a first direction with a unidirectional motor; rotating a second body in a first direction with a unidirectional motor; contacting a driven disk with the first body in order to turn the driven disk in a second direction when a steering wheel is turned in a second direction thereby providing a power assist to a steering shaft in the second direction; and contacting a driven disk with the second body in order to turn the driven disk in a third direction when a steering wheel is turned in a third direction thereby providing a power assist to the steering shaft in the third direction.  
         [0008]     Additionally, the disclosed method relates to providing power assist for an electric power steering system, the method comprising: rotating a driver body in a first direction with a unidirectional motor; changing the contact angle between the driver body and a driven body such that the driver body turns the driven body in a second direction when a steering wheel is turned in a fourth direction thereby providing a power assist to a steering shaft in the fourth direction; and changing the contact angle between the driver body and a driven body such that the driver body turns the driven body in a third direction when a steering wheel is turned in a fifth direction thereby providing a power assist to a steering shaft in the fifth direction. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0009]     Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures:  
         [0010]      FIG. 1  is a schematic view of a flywheel embodiment of the disclosed electric power system;  
         [0011]      FIG. 2  is a schematic view of a planetary gear embodiment of the disclosed electric power system;  
         [0012]      FIG. 3  is a schematic view of a driven disk embodiment of the disclosed electric power system;  
         [0013]      FIG. 4  is a schematic view of the driven disk embodiment of  FIG. 3  in a different mode of operation;  
         [0014]      FIG. 5  is a schematic view of a driven body embodiment of the disclosed electric power system; and  
         [0015]      FIG. 6  is a schematic view of the driven body embodiment of  FIG. 5  in a different mode of operation. 
     
    
     DETAILED DESCRIPTION  
       [0016]     By going back to the fundamentals of how a conventional HPS system operates, a simplified EPS system has been created that does not require the expensive components mentioned. The disclosed solution is an electric motor equivalent to a conventional hydraulic system in which there is a power source (hydraulic pump) moving an inertia (hydraulic fluid) in a single direction and then mechanically directing (through a hydraulic valve) the kinetic energy from the inertia to provide assist to the driver in the desired direction.  
         [0017]     Referring to  FIG. 1 , one embodiment of the disclosed steering system  10  is shown. A steering wheel  14  is in operable communication with a first linkage  54 . The first linkage  54  converts rotational displacement of the steering wheel to linear movement of the linkage and steering shaft  22 . The first linkage  54  may comprise a torsion bar and a cam. The cam may be selected from any of a number of cam devices, including, but not limited to: a ball in helical groove, 4-bar linkage, and ball screw. The first linkage  54  is in operable communication with a steering shaft  22 . The steering shaft is in operable communication with at least one road wheel (not shown). A first flywheel  26  and a second flywheel  30  are in operable communication with the steering shaft  22  via a first bearing  28  and a second bearing  32 , respectively. The bearings  28 ,  32  are configured to allow the shaft  22  to move axially with respect to the flywheels  26 ,  30  while allowing the flywheels  26 ,  30  to rotate freely about the steering shaft  22 . A motor  34  is in operable communication with both the first flywheel  26  and second flywheel  30 . Through a torque transfer system, such as, but not limited to, a gear system, the motor  34  is configured to rotate the first and second flywheels  26 , 30  in opposite directions. In this embodiment, the first flywheel may be configured to rotate counter-clockwise, as one looks from the steering wheel  14  to the steering shaft  22 . The second flywheel may be configured to rotate clockwise, as one looks from the steering wheel  14  to the steering shaft  22 . A first clutch  38  is in operable communication with the steering shaft  6  and the first flywheel  26 . Similarly, a second clutch  42  is in operable communication with the steering shaft  6  and the second flywheel  30 . In this disclosed embodiment, upon operation of the automobile, the motor  34  rotates both the first and second flywheels  26 ,  30 . It should be noted that the flywheels  26 ,  30  are rotating in opposite directions. When an operator turns the steering wheel  14 , in a clockwise direction for instance, the first linkage  54  may be configured to axially move the steering shaft  22  to the left, e.g. in the direction of the left arrow  46 . As the steering shaft  22  moves to the left, the second clutch  42  engages the second flywheel  30 , thus transferring the rotative energy of the flywheel  30  to the steering shaft and thereby providing a power assist for the clockwise turning of the steering wheel. Similarly, when the operator turns the steering wheel  14  in a counter-clockwise direction, the first linkage  54  is configured to axially move the steering shaft  22  to the right, e.g. in the direction of the right arrow  50 . As the steering shaft  22  moves to the right, the first clutch  38  engages the first flywheel  26 , thus transferring the rotative energy of the flywheel  26  to the steering shaft  22  and thereby providing a power assist in the counter-clockwise turning of the steering wheel. Of course, the first linkage  54  may be configured such that a clockwise turn of the steering wheel  14  axially moves the steering shaft  22  to the right, however in that case the flywheels  26 ,  30  would be configured to rotate in directions opposite to what was stated above. In this embodiment, the first flywheel  26  and first clutch  38  may be referred to as a first transmission and the second flywheel  30  and second clutch  42  may be referred to as a second transmission  
         [0018]     In another embodiment, there may be only one flywheel  26  in operable communication with the steering shaft  22 . In still another embodiment, the flywheel(s) may be omitted, and instead the inertia of the motor itself may be used to transmit a power assist to the steering shaft.  
         [0019]      FIG. 2  shows another embodiment of the disclosed steering system. A steering wheel  14  is in operable communication with a first linkage  54 . The first linkage  54  may comprises a torsion bar  18 , and a cam  56 . The cam may be selected from any of a number of cam devices, including, but not limited to: ball in helical groove, 4-bar linkage, and ball screw. The cam  56  shown happens to be a ball in helical groove. In this schematic diagram, the torsion bar  18  is shown radially displaced from the cam  56 , however, it is contemplated that the torsion bar  18  would be concentric with the cam  56 . The first linkage  54  is in operable communication with the steering shaft  22 . The steering shaft  22  is in operable communication with at least one road wheel (not shown). The steering shaft is also in operable communication with a steering shaft sleeve  58 . The steering shaft sleeve is in operable communication with a first clutch  38  and a second clutch  42 . A motor  34  is in operable communication with a first sun gear  62 . The first sun gear is in operable communication with a first planet gear  66 . The first planet gear  66  is in operable communication with a first ring gear  72 . The first ring gear is in operable communication with the first clutch  38 . The first sun gear  62 , first planet gear  66 , and first ring gear  72  all comprise a first planetary gear  76 . The motor  34  is also in operable communication with a gear system  80  which changes the rotation input to an output rotation in the opposite direction. The gear system  80  is in operable communication with a second sun gear  84 . The second sun gear  84  is in operable communication with a second planet gear  88 . The second planet gear  88  is in operable communication with a second ring gear  92 . The second ring gear  92  is in operable communication with the second clutch  42 . The second sun gear  84 , second planet gear  88 , and second ring gear  92  all comprise a second planetary gear  96 . When the steering system  10  is in operation, the motor  34  is configured to rotate the first ring gear  72  in one direction, which for this example may be clockwise, looking from the steering wheel  14  to the steering shaft  22 . Since the output of the motor  34  is going through the gear system  80 , the output of the gear system  80  causes the second ring gear  92  to rotate in the opposition direction from the first ring gear  72 . Thus, when the steering wheel  14  is turned in a clockwise direction, for example, the steering shaft  14  and steering shaft sleeve  58  may be configured to move axially to the left, in the direction of the left arrow. Although the steering shaft  22  and steering shaft sleeve  58  are axially moveable, the motor  34  and planetary gears  76 ,  96  are axially stationary. As the steering shaft sleeve  58  moves to the left, the first clutch  38  will engage the first ring gear  72 , thus transferring rotative energy from the ring gear to the steering shaft sleeve  58 , and ultimately to the steering shaft  22 , thereby providing power assist to the steering wheel operator. Similarly, when the steering wheel  14  is turned in a counter-clockwise direction, the steering shaft  14  and steering shaft sleeve  58  may be configured to move axially to the right, in the direction of the right arrow  50 . As the steering shaft sleeve  58  moves to the right, the second clutch  42  will engage the second ring gear  92 , thus transferring rotative energy from the ring gear  92  to the steering shaft sleeve  58 , and ultimately to the steering shaft  22 , thereby providing power assist to the steering wheel operator.  
         [0020]      FIG. 3  shows another embodiment of the steering system  10 . A steering wheel  14  is shown in operable communication with a first linkage  54 . In this view the torsion bar  18  is shown concentric with the cam  56 . The first linkage  54  is in operable communication with a steering shaft  22 . The steering shaft is in operable communication with a second linkage  100 . The steering shaft is also in operable communication with a driven disk  104 . Additionally, the steering shaft  22  is also in operable communication with at least one road wheel (not shown). A motor  34  is in operable communication with a third linkage  108 . The motor is also in operable communication with a first driver disk  112  and a second driver disk  116 . The motor  34  is configured to rotate both discs  112 ,  116  in the same direction, e.g. clockwise or counter-clockwise. The third linkage  108  is in operable communication with the second linkage  100 . The steering system may be configured such that when the steering wheel is turned clockwise (as one looks from the steering wheel  14  to the steering shaft  22 ), the first linkage  54  moves to the left in the direction of the left arrow  46 . This causes the second linkage  100  and the third linkage  108  to act in concert and cause the first driver disk  112  and second driver disk  116  to move radially in the direction of the down arrow  120  such that only the first driver disk  112  is in contact with the driven disk  104 . If the motor is configured to turn the driver disks  112 ,  116  in a counter-clockwise direction, (as one looks from the driver disks  112 ,  116  towards the motor), then the first driver disk  112  will turn the driven disk  104  in a clockwise direction (as one looks from the steering wheel  14  to the steering shaft  22 ), thereby providing a power assist to the clockwise turning of the steering wheel  14 . Referring now to  FIG. 4 , when the steering wheel is turned counter-clockwise (as one looks from the steering wheel  14  to the steering shaft  22 ), the first linkage  54  moves to the right in the direction of the right arrow  50 . This causes the second linkage  100  and the third linkage  108  to act in concert and cause the first driver disk  112  and second driver disk  116  to move radially in the direction of the up arrow  124  such that only the second driver disk  116  is in contact with the driven disk  104 . Since in this embodiment, the motor  34  is configured to turn the driver disks  112 ,  116  in a counter-clockwise direction, (as one looks from the driver disks  112 ,  116  towards the motor), then the second driver disk  116  will turn the driven disk  104  in a counter-clockwise direction (as one looks from the steering wheel  14  to the steering shaft  22 ), thereby providing a power assist to the counter-clockwise turning of the steering wheel  14 . When the steering wheel is not being turned, the steering system  10  will be positioned such that neither the first driver disk  112  nor the second driver disk  116  will be in contact with the driven disk  104 , thus in this position, no power steering assist is being provided.  
         [0021]      FIG. 5  shows another embodiment of the steering system  10 . A steering wheel  14  is shown in operable communication with a first linkage  54  and a torsion bar  18 . The torsion bar  18  is in operable communication with a steering shaft  22 . The steering shaft is in operable communication with a driver sphere linkage  128 . The steering shaft is also in operable communication with a driven gear  132 . The steering shaft is also in operable communication with at least one road wheel (not shown). A motor  34  is in operable communication with the driver body linkage  128 . Additionally the motor  34  is in operable communication with a driver body  136 , and is be configured to rotate the driver body  136  in one direction. For this embodiment, the driver body  136  is rotated clockwise (as one looking from the motor to the driver sphere). The driver body  136  is operable communication with a driven body  140 . The driven body has a curved surface that is in contact with a curved surface of the driver body  136 . The driven body also has a worm gear  144  that is in operable communication with the driven gear  132 . The driver body  136  and driven body  140  are configured such that when the contact angle of the driver body  136  to the driven body is perpendicular to the surface of the driven body, then the rotating driver body will not rotate the driver body  140 . However, if the contact angle between driver body  136  and the driven body  140  is less than perpendicular, as shown in  FIG. 5 , then the clockwise rotating driver body  136  will rotate the driven body  140  in a counter-clockwise direction (as one looks in the direction of the up arrow  124 ). Similarly, if the contact angle between driver body  136  and the driven body  140  is greater than perpendicular, as shown in  FIG. 6 , then the clockwise rotating driver body  136  will rotate the driven body  140  in a clockwise direction (as one looks in the direction of the up arrow  124 ). The driver body and driven body may be comprised of any of a variety of curved shapes, including, but not limited to: ovoid, spherical and semi-spherical. The worm gear  144 , when rotating counter-clockwise (as one looks from the steering wheel to the steering shaft) will rotate the driven gear clockwise (as one looks from the steering wheel to the steering shaft), and when the worm gear  144  is rotating clockwise (as one looks from the steering wheel to the steering shaft), it will rotate the driven gear counter-clockwise (as one looks from the steering wheel to the steering shaft). Of course, these gears may be configured differently for other embodiments, e.g. when the worm gear  144  is rotating counter-clockwise, the driven gear  132  may rotate counter-clockwise, etc. Thus, the steering system  10  may configured such that when the steering wheel is turned clockwise (as one looks from the steering wheel  14  to the steering shaft  22 ), the first linkage  54  moves to the left in the direction of the left arrow  46 . This causes the driver body linkage  128  to move the driver sphere out of perpendicular contact with the driven body  140 , and take a contact angle less than perpendicular with respect to the driven body, thereby causing the driven body  140  to rotate in a counter-clockwise direction (as one looks in the direction of the up arrow  124 ). This causes the worm gears  144  to also rotate in a counter-clockwise direction (as one looks in the direction of the up arrow  124 ), thereby causing the driven gear  32  to rotate in a clockwise direction (as one looks from the steering wheel  14  to the steering shaft  22 ) and thus provide power assist to the clockwise turning of the steering wheel  14 . Referring now to  FIG. 6 , when the steering wheel  14  is turned counter-clockwise (as one looks from the steering wheel  14  to the steering shaft  22 ), the first linkage  54  moves to the right in the direction of the right arrow  50 . This causes the driver body linkage  128  to move the driver sphere  136  out of perpendicular contact with the driven body  140 , and assume a contact angle greater than perpendicular with respect to the driven body  140 , thereby causing the driven body  140  to rotate in a clockwise direction (as one looks in the direction of the up arrow  124 ). This causes the worm gears  144  to also rotate in a clockwise direction (as one looks in the direction of the up arrow  124 ), thereby causing the driven gear  32  to rotate in a counter-clockwise direction (as one looks from the steering wheel  14  to the steering shaft  22 ) and thus provide power assist to the counter-clockwise turning of the steering wheel  14 .  
         [0022]     The disclosed power steering system allows for the use of low cost components such as standard inertia single direction motors. Also, since the electric power steering system essentially uses a mechanical coupling between the steering wheel and motor, there is no need for expensive components such as a torque measuring device to measure the torque an operator exerts on a steering wheel or a position measuring device to indicate how far the steering wheel is being turned. Further, the disclosed power steering system can use a motor that is constantly running in one direction during the operation of the vehicle. There is no need to start and stop the motor, even when changing the steering wheel direction. Therefore, since the motor and components being driven by the motor do not need to start and stop, the power consumption required to overcome the stand-still inertia and stand-still load is no longer necessary, thereby lowering the power consumption of the disclosed power steering system. Additionally, since the motor is unidirectional, there is very little backlash among the coupled components. Also, since the motor is unidirectional and constantly running during vehicle operation, electromagnetic interference (“EMI”) issues are minimized. In addition, the motor can be connected directly to the power supply and so the controller can be greatly simplified or eliminated completely.  
         [0023]     While the invention has been described with reference to an exemplary 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. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another.