Abstract:
A torque-to-thrust apparatus includes a one-way mechanism permitting free application of rotation to torque. A friction plate disposed between a portion of a one-way device and a stationary member of the torque-to-thrust apparatus inhibits reverse rotation at a predetermined torque level, which will maintain the thrust member of the torque-to-thrust apparatus in an engaged condition until a predetermined load is applied to the rotary side of the torque-to-thrust apparatus to overcome the friction load.

Description:
TECHNICAL FIELD  
       [0001]     This invention relates to one-way torque-transmitting mechanisms for use with torque-to-thrust apparatus.  
       BACKGROUND OF THE INVENTION  
       [0002]     One-way torque-transmitting mechanisms or mechanical diodes generally are sprag, roller, or strut type and are designed to prevent overrunning between two members in one direction of operation while permitting overrunning of a member in the opposite direction. These devices might either be torque-transmitting mechanisms of the rotating type or torque-transmitting mechanisms providing a stationary operation such as a brake. These one-way devices have found a lot of use in power transmission situations wherein it is desirable to establish at least one ratio such that on a ratio interchange, the one-way device will simply overrun permitting a change within the gearing of a power transmission.  
         [0003]     More recently, it has been proposed that the friction devices of a power transmission be actuated by torque-to-thrust mechanisms. Types of torque-to-thrust torque-transmitting apparatus or mechanisms are shown in U.S. Ser. No. 10/303,245 filed Nov. 25, 2002; U.S. Ser. No. 10/319,957 filed Dec. 16, 2002; U.S. Ser. No. 10/738,564 (GP-302316) filed Dec. 17, 2003; and U.S. Ser. No. ______ (GP 301854), filed ______. Each of these patent applications is assigned to the assignee of the present application.  
         [0004]     In a torque-to-thrust apparatus in an automatic transmission application, an electric motor is generally employed to provide input rotation through a rotary member, which is operatively connected with a linear thrust member through a cam arrangement such that upon rotation of the electric motor the linear member will provide an apply force to a friction torque-transmitting mechanism such as a clutch or brake. In order to retain the clutch or brake engaged, the electric motor must remain energized or a significant friction must be built into the torque-to-thrust apparatus.  
         [0005]     The present invention seeks to improve the torque-to-thrust apparatus by providing a mechanism for retaining the engagement of the torque-transmitting mechanism but with little friction on the apply stroke which determines the required motor size.  
       SUMMARY OF THE INVENTION  
       [0006]     It is an object of this invention to provide an improved one-way torque-transmitting mechanism having an overrun condition in one direction of operation and a limited holding mechanism in the opposite direction.  
         [0007]     In one aspect of the present invention, a friction mechanism is disposed between one race of the torque-transmitting mechanism and a stationary wall member.  
         [0008]     In another aspect of the present invention, the one race of the one-way device is held stationary by the friction mechanism in response to a thrust force being applied to a torque to thrust mechanism.  
         [0009]     In yet another aspect of the present invention, the one-way device provides a low resistance input in one direction of rotation and a high resistance to input in the opposite direction of rotation.  
         [0010]     In yet still another aspect of the present invention, the torque-to-thrust apparatus includes a friction actuated one-way device to provide a limited value holding force to maintain the torque-to-thrust apparatus in an operable position.  
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a cross-sectional elevational view of a portion of a torque-to-thrust apparatus incorporating the present invention.  
         [0012]      FIG. 2  is another embodiment showing a torque-to-thrust apparatus employing the present invention.  
         [0013]      FIG. 3  is yet another embodiment describing the torque-to-thrust apparatus employing the present invention.  
         [0014]      FIG. 4  is a further embodiment of the present invention wherein a torque-to-thrust apparatus employs the present invention and wherein the torque-to-thrust apparatus includes a hydraulic mechanism.  
         [0015]      FIG. 5  is a series of curves relating motor torque to clamp load describing some of the operating characteristics of the present invention. 
     
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0016]     Referring to the drawings, there is shown in  FIG. 1 a  torque-to-thrust apparatus generally designated  10 . The torque-to-thrust apparatus  10  has an electric motor  12  driving an input gear  14 , which meshes with an output gear  16 .  
         [0017]     A linearly moveable thrust plate  18  is operatively connected to the gear  16  by a cam mechanism  20 , which includes a surface or track  22  formed on the output gear  16  and a surface or track  24  formed on the thrust plate  18 . The output gear  16  has an inner diameter  26 , which is rotatably mounted on a surface  28  through a bearing  30 . The thrust plate  18  is disposed in abutment with a spring  32 , which is contacting a friction plate  34 , that is a member of a friction torque-transmitting mechanism  36 .  
         [0018]     The friction torque-transmitting mechanism  36  includes the friction plate  34  and friction plates  38 , which are interdigitated with friction plates  40 . The friction plates  34  and  38  are splined to a housing  42 , and the friction plates  40  are splined to a housing  44 . The friction plates  34 ,  38 , and  40 , as well as housings  42  and  44 , form a conventional friction operated torque-transmitting mechanism. The torque-to-thrust apparatus  10  provides the apply force, which creates the frictional engagement between the plates  34 ,  38 , and  40 . These types of devices have been disclosed in prior patent applications.  
         [0019]     The output gear  16  has a cylindrical portion  46 , which forms an inner race for a one-way mechanism or mechanical diode  48 . The one-way mechanism  48  has an outer race  50  and a plurality of roller, sprag, or strut members  52  disposed between the inner race  46  and the outer race  50 .  
         [0020]     A thrust bearing  54  is disposed between a radial face  56  of the output gear  16 . The thrust bearing  54  is an antifriction bearing, which creates very little resistance to relative rotation between the face  56  and the outer race  50 .  
         [0021]     A friction plate  58  is disposed between the outer race  50  and a stationary wall  60 . The friction plate  58  when abutted by the outer race  50  will restrain or inhibit rotation of the outer race  50 . However, if the outer race  50  is restrained, as is well known with one-way mechanisms, the inner race  46  will be free to rotate in one direction while retarded in rotation in the other direction.  
         [0022]     When the electric motor  12  provides forward rotation for the gears  14  and  16 , the torque-transmitting mechanism  36  will be engaged by linear movement of the thrust plate  18 . The thrust force at the plate  18  will be reacted through the gear  16  to the outer race  50  thereby enforcing engagement between the outer race  50  and the friction plate  58 . Once the torque-transmitting mechanism  36  is fully engaged, the electric motor  12  can be de-energized.  
         [0023]     In normal or conventional torque-to-thrust apparatus, the thrust imposed between the plate  18  and the gear  16  would cause reverse rotation of the gear  16  when the electric motor input force was discontinued. However, the one-way mechanism  48  through the operation of the outer race  50  and the friction plate  58  prevent reverse rotation of the gear  16  thereby retaining the torque-transmitting mechanism  36  engaged.  
         [0024]     The frictional characteristics between the outer race  50  and the friction plate  58  are such that the electric motor  12  upon reverse rotation can overcome this friction force thereby driving the gear  16  in the opposite direction to permit disengagement of the torque-transmitting mechanism  36 . As the gear  16  is driven in the reverse rotation, the thrust force of the interface of the tracks  22  and  24  reduces accordingly, thereby reducing the amount of energy required at the electric motor  12 . This force transfer can be seen in  FIG. 5 .  
         [0025]     If one assumes a frictionless position in  FIG. 5 , the dashed line A would represent both the on-coming motor torque needed and the off-going motor torque needed to provide the clamping force or clamping load shown on the vertical axis. However, since systems are not frictionless, the on-coming motor torque must pass or traverse along the line B, which, of course, requires a greater motor torque than the ideal situation.  
         [0026]     In order to release the clamp load, a motor torque along line C would be required in a conventional torque-to-thrust condition. Thus, the torque-to-thrust apparatus can disengage unless a force is maintained at the motor. While sufficient friction can be built into the system, it greatly increases the motor torque. The line D represents the motor torque required to provide sufficient friction such that the release load for the motor torque follows the line E. Thus, a considerable amount of energy represented by the distance F is required to provide the locking feature.  
         [0027]     With the present invention, the on-coming motor torque increases along line B, which is required by the friction and the clamp load within the system, and having reached the desired clamp load and the friction mechanism comprised of the outer race  50  and the friction plate  58  is engaged by reversal of direction of rotation. When the friction mechanism is rotated to remove the clamp load, the motor  12  can be de-energized. The one-way mechanism  48  and the friction mechanism is released by energizing the motor  12 , in the opposite direction, when it is desired to relieve the thrust load of the torque to thrust apparatus  10 . This will require a motor torque to be increased to the point G prior to the release load being present at the torque-to-thrust apparatus  10 . Thus, with the embodiment shown in  FIG. 1 , the torque-to-thrust apparatus is applied with the conventional motor torque and is released by a reversal of motor torque, which is great enough to overcome the friction plate  58 . However, it should be evident that the motor  12  does not have to be energized to hold the torque to thrust apparatus  10  in the actuated condition.  
         [0028]      FIG. 2  describes an alternative embodiment wherein rotation of the gear member  16 A is operable to provide a thrust force at thrust plate  18 A in a manner similar to that described in  FIG. 1 . The gear  16 A has a cylindrical surface  80 , which forms the outer race of a one-way device or mechanical diode  82 . The inner race of the one-way device  82  is a cylindrical component  84 . The one-way device  82  has a plurality of rollers, sprags, or struts  86  disposed between the outer race  80  and the inner race  84 . The inner race  84  is aligned axially to abut a friction plate  88 , which is held stationary by a housing  90 .  
         [0029]     As described with the device in  FIG. 1 , the friction plate  88  does not increase the required load of the input to the gear  16 A because the one-way device  82  is permitted to overrun, thereby bypassing the inner race  84  frictional engagement with the friction plate  88  via free rotation across thrust bearing  89 . However, once a thrust force is applied to the plate  18 A, the friction plate  88  is engaged such that at full engagement of an associated torque-transmitting mechanism, the friction force at the inner race  84  will maintain the gear  16 A stationary until an input force from the electric motor is present to cause disengagement.  
         [0030]     A torque-to-thrust in one-way mechanism  92  is shown in  FIG. 3 . A gear member  94  is operable in combination with a thrust plate  96  and a cam mechanism  98  to provide a thrust force to engage a conventional friction operated torque-transmitting mechanism. The gear member  94  has a cylindrical surface  100  forming the inner race of a one-way torque-transmitting mechanism or mechanical diode  102 . A cylindrical body  104  forms the outer race of the torque-transmitting mechanism  102 . A thrust bearing  106  provides an antifriction member between the gear member  94  and a stationary housing  108 .  
         [0031]     A Bellville or washer type spring  110  is disposed between a locating ring  112  secured to the housing  108  and a locating ring  114  secured to the outer race  104 . The spring  110  urges the outer race  104  leftward into engagement with a friction member or plate  116 . The spring  110  therefore supplies the axial force required to engage the friction plate  116 . This would provide a constant force at the friction interface between the outer race  104  and the friction plate  116 .  
         [0032]     The forward rotation of the gear  94  is uninhibited by this constant friction force since the thrust bearing  106  and one-way rollers, sprags, or struts  118  are essentially frictionless bearings in that direction of rotation. However, upon reverse rotation of the gear  94 , sufficient energy must be put into the system such that the point G is achieved on the curve shown in  FIG. 5 . The required input load, however, would be constant along the line H in this situation, since the friction force is not related to the thrust force between the gear  94  and the thrust plate  96 .  
         [0033]     A torque-to-thrust apparatus  200  is shown in  FIG. 4 . This mechanism includes an electric motor  202  having a stator  204  and a rotor  206 . The rotor  206  drives a sleeve shaft  208 , which has formed thereon a roller screw  210 . The roller screw  210  drives an output member  212  in a linear direction relative to the rotation of the rotor  206 . The member  212  includes a master cylinder  213  having a piston  214  slidably disposed in a cylinder  216 . The cylinder  216  is in fluid communication with a reservoir  218  through a passage  220  and with an output or outlet port  222  through a passage  224 .  
         [0034]     When the piston  214  is fully retracted, as shown in  FIG. 4 , the passage  220  is maintained open. When the piston  214  is driven rightwardly in the cylinder  216 , the passage  220  is closed and fluid within the cylinder  216  is driven or pumped through the outlet port  222  to a passage  226 , which is communicated with a chamber  228  disposed adjacent a slave cylinder  230 . The slave cylinder  230  moves axially to engage an apply spring  232 , which is a member of a conventional friction actuated torque-transmitting mechanism  234 .  
         [0035]     The pressure generated within the chamber  216  to provide engagement of the torque-transmitting mechanism  234  is reacted through a thrust bearing  236  and a sleeve  238  to a friction plate  240 . The friction plate  240  is connected to a stationary wall  242  through a sleeve  244 .  
         [0036]     The sleeve  238  is rotatably supported through a one-way device or mechanical diode  245  to a housing  246 , which is rotatable with the rotor  206 . The one-way device  245  permits substantially uninhibited relative rotation between the sleeve  238  and housing  246  when the rotor  206  is rotated in a direction to cause pumping between the piston  214  and the cylinder  216 . However, when the cylinder  216  is pressurized, the reaction load on the sleeve  208  is transmitted through the sleeve  238  to the friction plate  240  to cause engagement between the friction plate  240 , sleeve  244 , and the wall  242  thereby holding the outer race, represented by sleeve  238 , of the one-way device  245  stationary and maintaining the piston  214  in the extended position. Rotation in the apply direction causes relative rotational movement to occur through the bearing  236  but rotation in the release direction drives through the one-way clutch and causes the relative rotational movement to occur through the friction plate  240 . In order to retract the piston  214 , the torque at the motor  202  must be sufficient to overcome the friction represented by the friction plate  240 . This is accomplished in a manner similar to that described for the above systems.  
         [0037]     When the torque-transmitting mechanism  234  is fully engaged, of course, the electric motor  202  can be de-energized and the fluid pressure within the slave cylinder  230  is maintained by the torsional friction load at friction plate  240 , which prevents reverse rotation of the motor  202  and thus prevents movement of the master cylinder  213  in the release direction.