Abstract:
A differential device is provided with a case being capable of rotation around a rotation axis; a differential gear set housed in and drivingly coupled to the case, which includes first and second output gears and is configured to differentially transmit the rotation of the case to the first and second output gears; a clutch configured to controllably limit and free a differential motion between the first and second output gears, which is housed in the case; an actuator configured to actuate the clutch; and a notifying member configured to notify whether the differential motion is limited or freed to an exterior of the case.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2006-042853 (filed Feb. 20, 2006); the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a differential device applied to conveyance means such as automobiles, differential motion of which is controllable and detectable from the exterior thereof. 
     2. Description of the Related Art 
     As is known, an automobile is equipped with a differential to distribute a driving force of an engine to right and left output axles. The differential allows a differential motion between the axles and hence right and left wheels can maintain traction with the road while the automobile is turning. 
     To provide a driver with operability for temporary lock of the differential motion, a so-called “Lock-up Differential” is used. The lock-up differential in general has a clutch for locking the differential motion and an actuator for actuating the clutch under control by the driver. The lock-up differential may be required to be equipped with a means for canceling the lock of the differential motion and another means for detecting whether the differential motion is locked or freed. 
     Installing the clutch and these means in a casing of the differential leads to complexity of a structure and inaccessibility to these elements. These are considerable disadvantages on occasions of assembly, maintenance and repair. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the present invention, a differential device is provided with a case being capable of rotation around a rotation axis; a differential gear set housed in and drivingly coupled to the case, which includes first and second output gears and is configured to differentially transmit the rotation of the case to the first and second output gears; a clutch configured to controllably limit and free a differential motion between the first and second output gears, which is housed in the case; an actuator configured to actuate the clutch; and a notifying member configured to notify whether the differential motion is limited or freed to an exterior of the case. 
     In accordance with a second aspect of the present invention, a differential device is provided with: a case being capable of rotation around a rotation axis; a differential gear set housed in and drivingly coupled to the case, which includes first and second output gears and is configured to differentially transmit the rotation of the case to the first and second output gears; a clutch having an engaging position and a disengaging position, which is configured to limit a differential motion between the first and second output gears in the engaging position and free the differential motion in the disengaging position; an actuator configured to actuate the clutch between the engaging position and the disengaging position; and a follower member following the clutch to output whether the clutch is in the engaging position or the disengaging position to an exterior of the case. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 and 2  are sectional views of a differential device in accordance with an embodiment of the present invention, as being taken from a line I-I of  FIG. 4 ; where  FIG. 1  illustrates a state of freeing the differential motion and  FIG. 2  illustrates a state of locking the differential motion; 
         FIG. 3  is a front view of the differential device; 
         FIG. 4  is a side view of the differential device viewed from the right of  FIG. 3 ; 
         FIG. 5  is a sectional view of the differential device taken from a line V-V of  FIG. 3 ; 
         FIG. 6  is a perspective view of a plunger and a clutch ring for the differential device; and 
         FIG. 7  is another perspective view of the plunger and the clutch ring. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be described hereinafter with reference to the appended drawings. Throughout the specification, claims and the drawings, some terms are specially defined in accordance with the following definitions unless any other particular explanations are given. An axial direction is defined as a direction along an axis of a differential device, which is generally correspondent to lateral directions of  FIGS. 1-3 . Ends are defined as extremes in the axial direction. An end face is defined as a face visible in a projection drawn along the axial direction. 
       FIGS. 1-7  illustrates a differential device  1  in accordance with the embodiment of the present invention. In the following description, the right and the left are correspondent to those of  FIGS. 1-3 . 
     Referring to  FIGS. 1 and 2 , the differential device  1  is provided with a differential gear set  5  of, but not limited to, a bevel gear type so as to differentially transmit a driving force of an engine from a differential case  3  to right and left axles linked with side gears  31  and  33 , a clutch  7  for locking (or limiting) the differential motion of the differential gear set  5 , a solenoid  9  for actuating the clutch  7  into an engaging state, a return spring  11  for urging the clutch  7  into a disengaging state, and shafts  13  to output a motion of the clutch  7  to the exterior. Of course, the differential gear set is not limited to the bevel gear type but may use any other types such as a coupling type. 
     Boss portions  67  and  69  are formed in a unitary body with the differential case  3  so as to respectively project from right and left end faces of the differential case  3 . The whole of the differential case  3  with the boss portions  67  and  69  is housed in a differential carrier  21 . The boss portions  67  and  69  and the differential carrier  21  have bearings  23  interposed therebetween so that the differential case  3  is made rotatable relative to the differential carrier  21  around a rotation axis determined by the bearings  23 . 
     The differential gear set  5  is provided with pinion shafts  25 , pinion gears  29 , and a pair of side gears  31  and  33 . The differential case  3  supports the pinion shafts  25  in radial directions therein and bolts  27  respectively prevent the pinion shafts  25  from displacing. The pinion shafts  25  respectively rotatably support the pinion gears  29 . The side gears  31  and  33  engage with the pinion gears  29  from respectively left and right sides. Internal surfaces of the side gears  31  and  33  are splined so as to drivingly engage with left and right axles. Thereby, the differential gear set  5  differentially transmits a driving force of an engine received by the differential case  3  to the left and right axles via the side gears  31  and  33 . 
     Spherical washers  85  intervenes between the pinion gears  29  and the differential case  3  for smooth rotation of the pinion gears  29 . Further, washers  91  and  93  respectively intervene between the side gears  31  and  33  and the differential case  3 . Referring to  FIG. 3 , the differential case  3  has openings so dimensioned as to allow insertion of the gears  29 ,  31  and  33  therethrough. Oil reserved in the differential carrier  21  flows out of and into these openings of the differential case  3  to lubricate and cool meshing portions of these gears and any contact faces, such as contact faces  35  among the differential case  3  and the side gears  31  and  33 , contact faces around the washers  91  and  93  and the spherical washers  85 . For ease of circulation of the oil, an oil flow path  87  is held between the left side gear  31  and the differential case  3  and also an oil flow path  39  is held between the right side gear  33  and the differential case  3 . 
     Referring again to  FIGS. 1 and 2 , as facing to the left side gear  31 , a clutch ring  37  having teeth  39  is provided. Correspondingly the left side gear  31  is provided with teeth  41 . These teeth  39  and  41  compose the clutch  7  for locking and freeing the differential motion of the differential gear set  5 . In the present embodiment, though the clutch  7  is formed to be a dog clutch, any other clutch such as a frictional clutch or a multi-plate clutch may be also applicable. The clutch ring  37  is supported by the internal periphery of the differential case  3  to be axially movable. The clutch ring  37  is provided with projections  43  for receiving actuation by the solenoid  9 . 
     The left end face of the differential case  3  has a support portion  51  formed to be a circular internal periphery thereof for supporting the solenoid  9  in a radial direction. The solenoid  9  fits in the support portion  51  though they are capable of rotating relative to each other. Plural (three in this example) sets of plates  59  for engagement with the solenoid  9 , and pairs of bolts  57  for fixation of the plates  59  to the differential case  3 . The fixation of the plates  59  to the differential case  3  may be made by welding instead of the bolts  57 . The left end face of the differential case  3  has openings  45  through which the projections  43  of the clutch ring  37  and projections  75  of ring  65  (described later) are capable of abutting on each other. 
     The solenoid  9  slidably fits in and is hence supported by the support portion  51 . The solenoid  9  is provided with a winding for conducting an electric current and a core  49  incompletely enclosing the winding. A lead line  71  is led out of the solenoid  9  and further led out of the differential carrier  21  as shown in  FIG. 3 . The connector  73  is to link with a battery via a controller (not shown). Thereby the solenoid  9  generates a magnetic flux under control by the controller. A plunger  63  is axially movably fit in the core  49 . The core  49  in combination with the differential case  3  and the plunger  63  substantially completely encloses the winding to conduct the magnetic flux. The magnetic flux drives the plunger  63  in the axial direction toward the clutch  7 . 
     A ring  65  fits in the plunger  63  for transmitting the movement of the plunger  63  to the clutch ring  37 . Referring to  FIGS. 6 and 7 , the ring  65  is provided with plural (three in this example) projections  75  as facing to the projections  43  of the clutch ring  37 . The projections  43  and  75  slidably engage with the openings  45  of the differential case  3  so that the clutch ring  37  and the ring  65  are rotated unitarily with the differential case  3 . 
     Referring again to  FIGS. 1-3 , the core  49  of the solenoid  9  has anti-rotation members  53  for anti-rotation of the solenoid  9 , which are spot-welded with the core  49 . The anti-rotation members  53  respectively latch with recesses formed on a differential carrier so that the solenoid  9  is made anti-rotated. 
     As the projections  43  respectively face to the projections  75 , axial motion of the plunger  63  toward the clutch  7  (rightward in  FIGS. 1 and 2 ) is transmitted to the clutch  7  via the butted projections  43  and  75  so that the clutch  7  is made engaged. Both the projections  43  and the openings  45  have correspondent side faces formed obliquely to the rotation direction. A combination of these oblique side faces of the projections  43  and the openings  45  compose a cam  47  for converting torque of the differential case  3  into an axial force on the clutch ring  37  to assist the engagement of the clutch  7 . 
     Further referring to  FIG. 5 , plural (four in this example) shafts  13  movably penetrate the differential case  3  through through-holes  77  thereof along the axial direction. One end of each shaft  13  projects out of a right end face of the differential case  3  and another end abuts on the clutch ring  37  so as to follow the axial motion of the clutch ring  37 . The projecting ends of the shaft  13  are fixed with a ring plate  79 . The return spring  11  repulsively intervenes between the ring plate  79  and a snap ring  81  fixed with the differential case  3 . Thereby, the return spring  11  urges the shafts  13  toward the clutch ring  37  and consequently the clutch ring  37  is urged into the disengaging state. Thereby, the clutch  7  stays in the disengaging state unless the solenoid  9  gives a force to the clutch  7 . 
     The differential device  1  is further provided with a sensor  15  for detecting displacement of the shaft  13 . The sensor  15  is provided with a detector portion  17  and a retractable probe  19  forced outward by a spring. The probe  19  is in touch with the ring plate  79  to follow displacement thereof. The detector portion  17  detects and converts displacement of the probe  19  into ON/OFF signals and output the signals to the controller. 
     When the solenoid  9  is excited, the generated magnetic flux drives the plunger  63  in the axial direction to drive the clutch  7  from a disengaging state into an engaging state. Thereby, the differential motion of the differential gear set  5  is locked. Then the cam  47  converts torque of the differential case  3  into an axial force for pressing the clutch ring  37  toward the left side gear  31  so that the engagement of the clutch  7  is prevented from being cancelled by shock or such. Then the engaging state of the clutch  7 , which means that the differential gear set  5  is locked, is notified to the sensor  15 . The sensor  15  outputs the ON signal to the controller to notify the engaging state to the driver. 
     When excitation is cancelled, the return spring  11  urges the shafts  13  leftward in  FIG. 1  to return the clutch  7  into the disengaging state so that the clutch  7  is disengaged and the differential motion of the differential gear set  5  is freed. Then the disengaging state of the clutch  7 , which means that the differential gear set  5  is freed, is notified to the sensor  15 . The sensor  15  outputs the OFF signal to the controller to notify the disengaging state to the driver. 
     Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings.