Abstract:
A clutch system is described wherein a two-way roller clutch system transmits torque in from one direction (i.e., input side) only, and allows the clutch system to be physically decoupled from the power steering system when torque is forced in from the output side, e.g., during loss of electrical power to the power steering motor. Additionally, the clutch system can include a torque limiting system that permits slip when overall torque exceeds a preset limit. Both the clutch system and the torque limitation system are especially useful in conjunction with automotive power steering systems.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    The present invention claims priority to U.S. Provisional Patent Application Serial No. 60/308,022 filed Jul. 26, 2001, the entire specification of which is expressly incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to clutches such as those used in conjunction with automotive power steering systems and more particularly to a new and improved clutch system and torque limitation system, both especially for useful in conjunction with automotive power steering systems. The new and improved clutch system includes a passively actuated system that permits torque transmission from one direction only. The torque limitation system includes a feature for allowing slip, for example, at or above a preset torque level.  
         BACKGROUND OF THE INVENTION  
         [0003]    The advent of automotive electric power assisted steering (EPAS) systems will greatly enhance the ease of steering and overall drivability of modern automobiles. This is especially true for individuals, such as the elderly and the disabled, who may not possess the requisite physical strength to turn an unassisted (i.e., un-powered) automobile steering wheel in a reasonably safe and effective manner.  
           [0004]    However, there are several problems with electrical power steering systems. For example, in the event of a failure of the automobile&#39;s electrical system or the electrical power assist motor; the torque necessary to turn the steering wheel would be relatively unsafe due to the high-speed reduction ratio in the system. Such difficulty in turning the steering wheel could potentially result in an increased frequency of accidents.  
           [0005]    Additionally, “kickback” from impact with road hazards, such as curbs, bumps, potholes, and so forth, can potentially damage the power steering system&#39;s speed reduction system.  
           [0006]    Therefore, there exists a need for a new and improved power steering system wherein torque is transmitted from one direction (e.g., input side) only, and allows the system to be decoupled completely from the power steering motor when torque is forced in from the output side. Additionally, the new and improved power steering system should include a torque limiting system that permits slip when overall torque exceeds a preset and/or predetermined limit.  
         SUMMARY OF THE INVENTION  
         [0007]    In accordance with the general teachings of the present invention, a clutch system is provided wherein torque transmission is permitted out in one direction only (i.e., output side), thus eliminating feedback (e.g., kickback). Also in accordance with the general teachings of the present invention, a torque limiting system is provided wherein slip is permitted when the overall torque of the system exceeds a preset and/or predetermined level.  
           [0008]    In accordance with further teachings of the present invention, a clutch system for a power steering system is provided wherein torque transmission is permitted out in one direction only (i.e., output side), thus eliminating feedback (e.g., kickback) while also limiting overall torque to a preset and/or predetermined level. The present invention is preferably installed between the electric power steering motor and the speed reduction device on the rack of the electrically assisted power steering system, e.g., for automotive applications.  
           [0009]    In accordance with the first embodiment of the present invention, a clutch system having a power input member and a power output member is provided, comprising:  
           [0010]    a clutch member being coaxially disposed about the power input member, the clutch member being in physical cooperation with the power input member and the power output member, the clutch member being capable of rotating in either a first or a second direction in response to a torque force from the power input member;  
           [0011]    an inner race member being coaxially disposed about the clutch member, the inner race member being in physical cooperation with the clutch member, the inner race member being capable of rotating in either a first or a second direction in response to a torque force from the power input member;  
           [0012]    an outer race member being coaxially disposed about the inner race member, the outer race member being in physical cooperation with the inner race member, the outer race member being capable of rotating in either a first or a second direction in response to a torque force from the power input member; and  
           [0013]    a roller member disposed between the inner and outer race members;  
           [0014]    wherein the roller member is selectively operable so as to physically engage at least a portion of a surface of the outer and inner race members so as to cause the clutch member to physically disengage from the power output member in response to a torque force being applied to the power output member in either a first or a second direction.  
           [0015]    In accordance with a second embodiment of the present invention, a clutch system for use in conjunction with a power assisted steering system for a vehicle is provided, wherein the power assisted steering system includes a power steering motor, a power input member capable of rotating in either a first or a second direction in response to a torque force, and a power output member, the power input member being in physical cooperation with the power steering motor, comprising:  
           [0016]    a clutch member being coaxially disposed about the power input member, the clutch member being in physical cooperation with the power input member and the power output member, the clutch member being capable of rotating in either a first or a second direction in response to a torque force from the power input member;  
           [0017]    an inner race member being coaxially disposed about the clutch member, the inner race member being in physical cooperation with the clutch member, the inner race member being capable of rotating in either a first or a second direction in response to a torque force from the power input member;  
           [0018]    an outer race member being coaxially disposed about the inner race member, the outer race member being in physical cooperation with the inner race member, the outer race member being capable of rotating in either a first or a second direction in response to a torque force from the power input member; and  
           [0019]    a roller member disposed between the inner and outer race members;  
           [0020]    wherein the roller member is selectively operable so as to physically engage at least a portion of a surface of the outer and inner race members so as to cause the clutch member to physically disengage from the power output member in response to a torque force being applied to the power output member in either a first or a second direction.  
           [0021]    In accordance with a third embodiment of the present invention, a power assisted steering system for a vehicle is provided, comprising:  
           [0022]    a power steering motor;  
           [0023]    a power output member capable of rotating in either a first or a second direction in response to a torque force, the power output member being in physical cooperation with the power steering motor; and  
           [0024]    a clutch system disposed between the power steering motor and the power output member, the clutch system member being coaxially disposed about the power output member, the clutch system being in physical cooperation with the power output member;  
           [0025]    wherein the clutch system is selectively operable to physically disengage from the power output member in response to a torque force being applied to the power output member in either a first or a second direction.  
           [0026]    In accordance with a fourth embodiment of the present invention, a power assisted steering system for a vehicle is provided, comprising:  
           [0027]    a power steering motor;  
           [0028]    a power input member capable of rotating either in a first or a second direction in response to a torque force, the power input member being in physical cooperation with the power steering motor;  
           [0029]    a clutch system disposed between the power steering motor and a power output member, the clutch system member being coaxially disposed about the power output member, the clutch system being in physical cooperation with the power output member, wherein the clutch system comprises:  
           [0030]    a clutch member being coaxially disposed about the power input member, the clutch member being in physical cooperation with the power input member, the clutch member being capable of rotating in either a first or a second direction in response to a torque force from the power input member;  
           [0031]    an inner race member being coaxially disposed about the clutch member, the inner race member being in physical cooperation with the clutch member, the inner race member being capable of rotating in either a first or a second direction in response to a torque force from the power input member;  
           [0032]    an outer race member being coaxially disposed about the inner race member, the outer race member being in physical cooperation with the inner race member, the outer race member being capable of rotating in either a first or a second direction in response to a torque force from the power output member; and  
           [0033]    a roller member disposed between the inner and outer race members;  
           [0034]    wherein the roller member is selectively operable so as to physically engage at least a portion of a surface of the outer and inner race members so as to cause the clutch member to physically disengage from the power output member in response to a torque force being applied to the power output member in either a first or a second direction.  
           [0035]    In accordance with a fifth embodiment of the present invention, a torque limitation system is provided, comprising:  
           [0036]    a housing member;  
           [0037]    a power output member capable of rotation in response to a torque force, the power output member being capable of rotating relative to the housing member; and  
           [0038]    at least one clutch member in physical cooperation with the housing member and the power output member, the clutch member having a compressive force applied thereto so as to establish a preset torque level between the housing member and the power output member;  
           [0039]    wherein the at least one clutch member is selectively operable so as to slip in response to the application of a torque force in excess of the preset torque level.  
           [0040]    In accordance with a sixth embodiment of the present invention, a torque limitation system for use in conjunction with a power assisted steering system for a vehicle is provided, comprising:  
           [0041]    a housing member;  
           [0042]    a power output member capable of rotation in response to a torque force, the power output member being capable of rotating relative to the housing member; and  
           [0043]    at least one clutch member in physical cooperation with the housing member and the power output member, the clutch member having a compressive force applied thereto so as to establish a preset torque level between the housing member and the power output member;  
           [0044]    wherein the at least one clutch member is selectively operable so as to slip in response to the application of a torque force in excess of the preset torque level.  
           [0045]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0046]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0047]    [0047]FIG. 1 is a cross-sectional view of the clutch system for an exemplary power steering system, in accordance with the general teachings of the present invention;  
         [0048]    [0048]FIG. 2 is an axial view of the clutch system for an exemplary power steering system depicted in FIG. 1, in accordance with the general teachings of the present invention; and  
         [0049]    [0049]FIG. 3 is a partial cross-sectional view of a detail of the clutch system for an exemplary power steering system depicted in FIG. 1, in accordance with the general teachings of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0050]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0051]    While the present invention is described primarily as a torque-limited, unidirectional drive clutch system in conjunction with an electrical power assisted steering system for automotive applications, it should be appreciated that the present invention can be practiced with any type of power, force, or torque transmission system where torque limitation and/or unidirectional drive are desired in the event of the loss of system electrical power and/or the like. For example, the present invention can be practiced with pumps, such as but not limited to water pumps, mills, such as but not limited to watermills or windmills, and/or the like.  
         [0052]    Referring generally to the Figures, there is shown a clutch system  1 , in accordance with the general teachings of the present invention. It should be appreciated that one or more of the following list of general components of the clutch system  1  may be modified, substituted, or eliminated without substantially affecting the performance and/or operation of the present invention.  
         [0053]    The general components shown are, optionally, at least one pan-head screw  10  or other suitable fastener, a bearing  20 , at least one Belleville washer  30 , optionally, a bushing  40 , a clutch disk  50 , a drag spring  60 , at least one friction pad  70 , a housing assembly  80 , an inner race  90 , an outer race  100 , an output disk  110 , a retaining ring  120 , a centering or return spring  130 , at least one roller  140 , a roller cage  150 , optionally, a spacer  160 , optionally, a spring backing  170 , optionally, a spring retainer  180 , and, optionally, a wave spring  190 .  
         [0054]    Because the two-way clutch system  1  of the present invention can drive in both directions, torque from the power steering motor (not shown) is provided in both directions of rotation.  
         [0055]    In accordance with a preferred embodiment of the present invention, the inner race  90  is preferably cammed and the outer race  100  is preferably relatively smooth and cylindrical, although it should be appreciated that these particular features could be reversed, i.e., the inner race  90  can be smooth and cylindrical, and the outer race  100  can be cammed.  
         [0056]    In accordance with a preferred embodiment, the roller cage  150  is provided with pockets or depressions to accommodate the rollers  140 . During normal conditions, the return spring  130  preferably urges the roller cage  150  into the disengaged position, generally keeping the rollers  140  in the middle of the cammed surfaces.  
         [0057]    However during operation of the present invention (e.g., during kickback), as the inner race  90  rotates relative to the housing assembly  80 , the friction from the drag spring  60  preferably overcomes the return spring  130 , allowing the roller cage  150  to lag behind the inner race  90 , thus forcing the rollers  140  into engagement between the cammed inner race  90  and the cylindrical outer race  100 .  
         [0058]    In accordance with one embodiment of the present invention, the outwardly directed tangs of the substantially omega-shaped return spring  130  fit into notches on adjacent axial faces of the inner race  90  and the roller cage  150 . The drag spring  60  with inwardly bent tangs also fits into the notch on the roller cage  150 . However, by virtue of the friction that the drag spring  60  generates against the stationary housing assembly  80 , it will overcome the return spring  130  and allow the roller cage  150  to rotate relative to the inner race  90 , forcing the rollers  140  to wedge between the cammed surfaces and the inner surface of the outer race  100 . When torque comes in from the outer race  100 , the drag spring  60 , return spring  130 , roller cage  150  and inner race  90  are unaffected, so no torque is transmitted through the clutch. The drag spring  60  can also be any simple friction element that contacts the stationary housing assembly  80  to overcome the force of the return spring  130 .  
         [0059]    The clutch system  1  of the present invention preferably operates in all potential failure modes of the power steering system of the vehicle. In normal operation, when the power steering motor is providing supplemental torque to the power steering system, the torque from the power steering motor is brought into the clutch section through a connection between the power steering motor shaft and the clutch inner race. However, in the event of a failure of the automobile&#39;s electrical system or the power steering motor, then torque from the steering wheel is back fed into the two-way clutch system of the present invention. If not for the action of the two-way clutch system of the present invention, the inertia of the power steering motor being driven back through the speed reducer (now acting as a speed increaser because it is being driven in reverse) would be relatively large, requiring extraordinary effort from the driver to turn the steering wheel even slightly.  
         [0060]    However, with the two-way clutch system of the present invention in place, the back driving torque simply rotates the outer race of the clutch, without engaging any other components of the power steering system that would substantially interfere with manual operation of the steering wheel.  
         [0061]    In some cases under normal operation, such as highway cruising, the EPAS system is not really necessary, as the driver input is sufficient to make the needed minor directional changes without assistance. In this case, the electric motor can be inactive and the clutch will disconnect the EPAS from the steering system, effectively leaving the vehicle with relatively old-fashioned manual (i.e., non-power) steering, which would be sufficient for such operation.  
         [0062]    In certain other cases, the speed reduction section of the EPAS could be damaged by shock impact being fed back through the system when the clutch is engaged and driving in one direction. For instance, if the vehicle is being turned with the EPAS engaged, impact with a pothole or curb forcing the wheel in the same direction as it is being driven would cause back-driven torque to be sent through the system. Thus, the worm gear and worm wheel in the speed reducer could be stripped of their teeth in such an isolated case. Therefore, a torque-limiting feature or system is provided for the clutch system  1  of the present invention.  
         [0063]    The torque-limiting system  300  is specifically shown in FIG. 3. The torque-limiting feature consists primarily of a housing  310  (that is integral to the two-way clutch&#39;s outer race  100 ), and a plurality of clutch disks  320  which are alternately splined to the output shaft  330  and housing  310 . A snap ring  340  and backing washer  350  hold a Belleville washer  360  in place at a preset and/or predetermined force level, compacting the clutch disks  320 , providing for a consistent torque level when the output shaft  330  and housing  310  are rotated relative to one another. By way of a non-limiting example, the maximum torque level of the clutch system  1  could be preset to 10N-m (i.e., torque limiter setting).  
         [0064]    As previously noted, the torque-limiting feature of the present invention consists of a series of clutch disks  320  clamped at a preset and/or predetermined level to slip at a specified torque. In accordance with one embodiment of the present invention, a pair of friction pads  370  is employed to selectively engage the output shaft  330  to achieve the torque-limiting function.  
         [0065]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.