BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to magnetically-actuated one-way clutch, and, more particularly to a motor-generator that employs a magnetically actuated one-way clutch especially for use in a hybrid electric vehicle. 
     2. Description of the Prior Art 
     The powertrain of a hybrid electric vehicle (HEV) includes an electric motor-generator. This generator is used to start the vehicle when in electric motor mode and when in generator mode the electric generator produces ac electric current, which is converted to dc and stored in an electric storage battery. 
     Under certain vehicle operating conditions, the motor is used to drive the vehicle wheels. In other operating conditions the electric generator produces ac electric current, which is converted to dc and stored in an electric storage battery. 
     The generator&#39;s rotor exhibits unwanted rotation in some modes of operation. The rotor must be stopped from rotating in some modes of operation and must be allowed to rotate in either direction in other modes of operation. 
     Hybrid transaxles can achieve improved fuel economy by having an electric generator brake for modes of operation where the generator is at zero speed. 
     A need exists in the industry for a simple, reliable, low-cost device for controlling generator rotation. Preferably the device would be a direct acting, electrically actuated one-way clutch with one sliding element having self-energization capability after it is actuated. 
     SUMMARY OF THE INVENTION 
     A clutch including a rotatable member including a first ramp and first teeth, a second member held against rotation, axially displaceable, including a second ramp and second teeth, a spring urging the first and second members apart, and an electromagnet causing the first and second teeth to engage and prevent rotation in a first direction, rotation in a second direction separating the first and second members as the first ramp ascends the second ramp. 
     The one-way clutch provides a simple, reliable, low-cost selectable technique for controlling rotation of the rotor of a motor-generator. The clutch can be used in multiple applications where a magnetic field can be turned on and off in order to control the presence and absence of a drive connection across the clutch. 
     The clutch avoids need for clutch linkages and an electric solenoid to control an actuator of the clutch, minimizes the number of parts, and has a small rotating mass. 
     The clutch includes a rotatable plate and a non-rotatable plate that can move axially with the rotatable plate. The non-rotatable plate is pulled into its engaged position by the electromagnet, and returned by a spring. The clutch locks in one rotary direction and overruns in the opposite direction. 
     The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
         FIG. 1  is a cross section of a motor generator that includes a one-way clutch; 
         FIG. 2  is a cross section of the motor-generator of  FIG. 1  showing the dog clutch member engaged with the nut; 
         FIG. 3  is a cross section of the motor-generator of  FIG. 1  showing the dog clutch member disengaged from the nut; 
         FIG. 4  is a perspective end view of the inner axial face of the nut; 
         FIG. 5  is a perspective end view of the axial inner face of the clutch member; 
         FIGS. 6 and 7  are perspective views showing a ramp of the dog clutch member contacting a ramp of the nut; 
         FIG. 8  is a perspective end view of the axial inner face of the clutch member showing the clutch member installed in the end cover. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings,  FIG. 1  shows a motor-generator  14  arranged about a central axis  18  and located within a space bounded by a front housing cover  20  secured by bolts  22  and to a housing  24 , whose position is fixed. 
     The motor-generator  14  includes a stator  26 , secured by a series of bolts  28  to an extension of the housing  24  or another fixed member; electrically conductive wire wound in a coil  30  about axis  18 ; a rotor  32  surrounded by the stator; and a rotor shaft  34  supported for rotation about axis  18  on bearings  36 ,  38 . Each axial end of the rotor  32  is covered by an end cap  40 ,  42 . A ring  48  contacts the end cap  40 . A nut  50 , engaged by a screw thread with rotor shaft  34 , contacts ring  48 . 
       FIGS. 2 and 3  show a dog clutch  52  comprising nut  50  and a dog clutch member  58 . The coil of an electric conductor, preferably copper wire, is encased in a electromagnet assembly  54  secured by a first snap ring  56  on cover  20  and located adjacent the dog clutch member  58 . A Belleville spring  60 , contacting dog clutch member  58  and a second snap ring  62 , continually urges the dog clutch member  58  leftward away from nut  50 . 
       FIGS. 3 and 5  show that dog clutch member  58  is formed with projection  64 , spaced mutually and angularly about axis  18  and extending rightward axially away from the body of member  58  and toward the nut  50 .  FIGS. 3 and 4  show that nut  50  is formed with projections  66 , spaced mutually and angularly about axis  18  and extending leftward axially away from the body of nut  50  and toward the teeth  64  of member  58 . 
       FIG. 4  shows that the axial inner face of nut  50  is formed with nine of the angularly spaced projections  66 , each projection  66  being formed with an inclined ramp  72 , an angular length portion  74  that may have a flat surface, and dog clutch tooth  76 , located at the opposite end of the length portion  74  from the location of the ramp  72 . 
     Similarly,  FIG. 5  shows that the axial inner face of dog clutch member  58  is formed with three of the angularly spaced projections  64 , each projection being formed with an inclined ramp  78 , an angular length portion  80  that may have a flat surface, and a dog clutch tooth  82 , located at the opposite of the length portion  80  from the location of the ramp  78 . The dog clutch member  58  is also formed with lugs  86 , spaced angularly about axis  18  and extending radially outward from the axis. 
     The clutch member  58  is installed such that each of its projections  64  is located between first and second projections  66  of the nut  50 , with the clutch tooth  82  of the clutch member projection  64  aligned with and facing the clutch tooth  76  of the first one of the clutch member projections  64 , and with the ramp  86  of the clutch member projection  64  aligned with and facing the ramp  72  of the second one of the clutch member projections  64 . When installed in this manner and position ramps  72  and  78  are substantially parallel surfaces, as shown in  FIGS. 6 and 7 . 
       FIGS. 6 and 7  show a ramp  78  of dog clutch member  58  contacting a ramp  72  of nut  50 , and clutch teeth  82  of clutch member  58  spaced from clutch teeth  76  of the nut  50 . 
       FIG. 8  is an end view of the axial inner face of the dog clutch member  58  showing the clutch member installed in the end cover  20 . Each lug  86  of member  58  is fitted in a recess  88  formed in the end cover  20 , thereby preventing rotational displacement of member  58  relative to the cover  20  and nut  50 , but permitting axial translation of member  58  relative to the cover and nut. 
     In operation, when the coil of electromagnet  54  is energized, dog clutch member  58  translates rightward, when viewed as in  FIGS. 2 and 3 , toward nut  50  due to the effect of the magnet field produced by the electromagnet. When rotor shaft  34  and nut  50  rotate counterclockwise about axis  18  when viewed as in  FIG. 8 , the clutch tooth  76  of at least one of the projections  66  of the nut contacts a corresponding clutch tooth of one of the projections  64  of the clutch member  58 , thereby preventing rotation of the rotor shaft and nut. 
     When the coil of electromagnet  54  is deenergized, spring  60  urges dog clutch member  58  leftward, when viewed as in  FIGS. 2 and 3 , away from nut  50 . When rotor shaft  34  and nut  50  rotate clockwise about axis  18  when viewed as in  FIG. 8 , the ramp  72  of at least one of the projections  66  of the nut ascends the ramp  78  of one of the projections  64  of the clutch member  58 , thereby forcing the clutch member leftward, disengaging the nut from the clutch member, and allowing rotation of the rotor shaft and nut. 
     Leftward axial translation of the dog clutch member  58  is limited by its contact with the end cover  20 , as  FIG. 2  shows. Rightward axial translation of the dog clutch member  58  is limited by its contact with nut  50 , whose axial position is fixed. 
     In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.
A clutch including a rotatable member including a first ramp and first teeth, a second member held against rotation, axially displaceable, including a second ramp and second teeth, a spring urging the first and second members apart, and an electromagnet causing the first and second teeth to engage and prevent rotation in a first direction, rotation in a second direction separating the first and second members as the first ramp ascends the second ramp.