Abstract:
A differential device is comprised of a casing with a first end wall and a side wall forming a corner with the first end wall; a differential gear set including an input gear and first and second side gears that are so meshed with the input gear to allow differential motion between the first and second side gears; and a clutch member being housed in and axially movable in the casing from a first position where the clutch member engages with the first side gear to limit the differential motion to a second position where the clutch member rests on the first end wall and frees the first side gear, the clutch member slidably fitting on the first side gear so as to keep the clutch member concentric with the first side gear.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2012-146628 (filed Jun. 29, 2012); 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 having a differential gear set and a clutch therein. 
     2. Description of the Related Art 
     As is known, an automobile is equipped with a differential device, which distributes a driving force of an engine and/or an electric motor to right and left output axles with allowing differential motion between these axles. Some differential devices, such as “locking differential” or “lock-up differential” for example, have clutches built therein, for the purpose of limiting differential motion between the right and left axles so as not to lose traction with the road particularly when one of the wheels loses contact with the road. 
     In a design for a lock-up differential, one of side gears has clutch teeth and a clutch member for meshing with these clutch teeth is axially movably disposed in a differential casing. As the clutch member is forced to follow the rotation of the differential casing, when these clutch teeth mesh together, differential motion is locked. U.S. Pat. No. 8,348,799 discloses a related art. 
     SUMMARY OF THE INVENTION 
     The casing in the aforementioned related art must have an axially straight internal face to guide the axial movement of the clutch member. This portion of the casing inevitably forms an angular corner with respect to an end wall of the casing. The present inventors found out that this angular corner gives rise to stress concentration. If increased thickness was given to the portion in question, this problem could be solved. This solution is, however, contrary to the constant need for downsizing. 
     The present invention has been achieved in view of the aforementioned problems. According to an aspect of the present invention, a differential device having an axis is comprised of a casing rotatable about the axis, the casing including a first end wall rising from the axis and a side wall forming a corner with the first end wall; a differential gear set being housed in and drivingly coupled with the casing and including an input gear and first and second side gears rotatable about the axis, the first and second side gears being so meshed with the input gear to allow differential motion between the first and second side gears; and a clutch member being housed in and axially movable in the casing from a first position where the clutch member engages with the first side gear to limit the differential motion to a second position where the clutch member rests on the first end wall and frees the first side gear, the clutch member slidably fitting on the first side gear so as to keep the clutch member concentric with the first side gear. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a differential device of an embodiment of the present invention. 
         FIG. 2  is an exploded cross sectional view of the differential device, which only shows a casing main body, a clutch member, a side gear, and a cover. 
         FIG. 3A  is a side view of the side gear. 
         FIG. 3B  is a side view of the clutch member. 
         FIG. 3C  is a side view of the casing main body. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Certain embodiments of the present invention will be described hereinafter with reference to the appended drawings. 
     A lock-up differential device  1  of a bevel gear type shown in  FIG. 1  will be exemplified to describe an embodiment of the present invention, whereas the present invention may be embodied in various types of differential devices. 
     The differential device  1  is comprised of a casing  3  rotatable about an axis (shown by a chain line), and a differential gear set  11  with pinions (input gears)  5  and left and right side gears  7 ,  9  housed in and drivingly coupled with the casing  3 . The casing  3  receives torque from an engine and/or an electric motor. The side gears  7 ,  9  are respectively drivingly coupled with left and right axles  73 ,  75 . As the differential gear set  11  allows differential motion between the left and right side gears  7 ,  9 , the torque of the engine/motor is distributed to both the axles  73 ,  75  without losing traction. 
     The lock-up differential device  1 , as with one of the prior art, is comprised of a clutch member  13  for limiting the differential motion. The clutch member  13  is made movable in the axial direction within the casing  3  so as to engage with and disengage from one of the side gears, namely the right side gear  9  in this example, thereby switching the differential device  1  between a lock-up mode and a differential mode. 
     The clutch member  13  slidably fits on the right side gear  9  so that the right side gear  9 , instead of an internal face of the casing  3 , guides the clutch member  13  and keeps the clutch member  13  concentric with the right side gear  9 . The casing  3  does not have to have a guiding internal face and can be therefore freely designed to avoid stress concentration. An internal face of a corner part between a right end wall and a side wall may be comprised of a rounded dent  17  for example. Rounded shapes such as the rounded dent  17  may relieve stress concentration. 
     More detailed descriptions will be given hereinafter. 
     Referring to  FIG. 1 , the whole of the differential device  1  is rotatably housed in a carrier  113  that is a stationary member relative to the vehicle. The casing  3  is comprised of paired boss portions  43 ,  45  axially projecting outward, which are used for rotatable support by the carrier  113 . Thereby the casing  3  is rotatable about its axis. For smooth support and suppressing frictional loss, ball bearings or roller bearings  47 ,  49  may be interposed. 
     The casing  3  is comprised of a flange portion  57  and is preferably dividable there into two parts  51 ,  53 . The parts  51 ,  53  along with a ring gear  55  are secured together by means of plural bolts and nuts so that torque input from an engine/motor to the ring gear makes the casing  3  as a whole to rotate about the axis. 
     This dividable configuration allows installation of internal members into the casing  3 . Referring to  FIG. 2 , internal members such as the pinions  7 , the side gears  7 ,  9 , and the clutch member  13  are inserted through the opening of the main part  53  opened when the covering part  51  is detached therefrom. 
     Referring again to  FIG. 1 , the main part  53  of the casing  3  is in general comprised of the boss portion  45 , an end wall  19  rising from the boss portion  45 , and a side wall generally parallel to its axis. These portions are preferably formed in a unitary body. The end wall  19  and the side wall define a cavity for housing the internal members. 
     The end wall  19  and the side wall form a corner generally at right angle. The internal periphery of the corner is formed in a rounded shape, which is so structured as to relieve stress concentration there. The rounded internal periphery may be formed as the rounded dent  17  receding from an outer periphery of the clutch member  13  to some degree. The rounded dent  17  may be formed to have a radius of R=5 mm but may be properly rounded in light of stress relief. 
     Referring to  FIG. 3C  in combination with  FIG. 1 , the end wall  19  is comprised of windows  21  for allowing access from the exterior into the interior. The windows  21  may be formed to penetrate the casing  3  in the axial direction and communicate with the rounded dent  17 . 
     In addition, the windows  21  may respectively have portions directed radially outward, which will be referred to as radial through holes  23 . Outer ends  103  of a detector  99  described later are led out through the radial through holes  23 . The radial through holes  23  may not directly but via the windows  21  communicate with the rounded dent  17 . 
     The pinions  7  are respectively supported by pinion shafts  41  inserted through bores on the side wall of the main part  53  and are respectively secured by pins  59  inserted in directions of traverse. The number of the pinions  7  may be arbitrarily determined but may be four as an example. 
     The pinion shafts  41  allow rotation of the pinions  7  thereabout. To assure smooth rotation and receive thrust force on the pinions  7 , each pinion  7  may have a spherical washer  61  interposed between the pinion  7  and the casing  3 . 
     The pair of side gears  7 ,  9  is so disposed in the casing  3  as to mesh with the pinions  7 . The side gears  7 ,  9  respectively have boss portions  63 ,  15  axially projecting, which are respectively rotatably supported by the casing  3 , and further have splined internal peripheries  69 ,  71  for the purpose of coupling with the left and right axles  73 ,  75 , respectively. To assure smooth rotation and receive thrust force on the side gears  7 ,  9 , each side gear  7 ,  9  may have a thrust washer  65 ,  67  interposed between the side gear  7 ,  9  and the casing  3 . 
     The pinions  7 , when meshing with the side gears  7 ,  9 , form the differential gear set  11  to allow differential motion between, and distribute input torque to, the side gears  7 ,  9 , and as well the left and right axles  73 ,  75 . 
     Referring to  FIG. 3B  in combination with  FIG. 1 , the clutch member  13  housed in the casing  3  is comprised of a base part  79  formed in a ring shape and is so disposed as to face the right side gear  9 . An internal periphery of the base part  79  slidably fits on the outer periphery of the boss portion  15  of the side gear  9 . The clutch member  13  is thereby made movable in the axial direction and also kept concentric with the side gear  9  without guidance by the internal periphery of the casing  3 . More specifically, the differential device  1  requires no means for bringing the clutch member  13  into axial alignment, excepting the boss portion  15  of the side gear  9 . 
     On the base part  79  formed are clutch teeth  81  projecting toward the side gear  9  and, referring to  FIG. 3A  in combination, the side gear  9  is correspondingly comprised of clutch teeth  83 . The combination of the clutch member  13  and the side gear  9  forms a locking means for locking up the differential gear set  11 . The combination of the clutch teeth  81  and the clutch teeth  83  forms a clutch  77  for the locking means  39 . 
     The clutch member  13  may be further comprised of a reinforcement part  27  axially standing around its outer periphery. As the reinforcement part  27  connects the clutch teeth  81  as a unitary body, not only the clutch teeth  81  but also the clutch member  13  as a whole are reinforced and stiffened. 
     On another side of the base part  79  formed are engaging projections  35 . The windows  21  on its end wall  19  are so formed as to respectively catch the engaging projections  35 , thereby making the clutch member  13  anti-rotated relative to the casing  3 . Thus, when the locking means  39  is in mesh, the side gear  9  is restricted to rotate with the casing  3  and therefore the differential motion is disabled. 
     Both or either of the engaging projections  35  and the windows  21  may be formed in a slope shape so as to form a cam that partially converts torque of the rotating casing  3  into axial force for assisting the locking means  39  to keep its meshing state. 
     Each of the engaging projections  35  may be further comprised of a slope  37  that makes the thickness of the projection  35  gradually greater toward the base part  79 . The slopes  37  of the projections  35  reinforce and stiffen the projections  35 . 
     To urge the clutch member  13  to depart from the side gear  9 , a repulsive member  25  such as a coil spring may be interposed between the clutch member  13  and the side gear  9 . In the absence of force exerted by an actuator  31  described below, the clutch member  13  rests on the end wall  19  and frees the side gear  9 . 
     The actuator  31  is provided to actuate the clutch member  13  toward the side gear  9 . An actuator with a solenoid is exemplified in the following description although any other type of an actuator such as a hydraulic device, a pneumatic device, or any mechanical device may be applied thereto. 
     The actuator  31  is comprised of a solenoid  29  and a moving part  85  actuated by the solenoid  29  to move the clutch member  13 . 
     The solenoid  29  is comprised of a coil  87  and a core  89  for conducting magnetic flux generated by the coil  87 . The solenoid  29  is disposed to be coaxial with the axis of the casing  3  and abuts on the end wall  19  of the casing  3 . The boss portion  45  may have a stepped cylindrical portion on which the solenoid  29  rests. A member  91  standing on the boss portion  45  keeps the solenoid  29  in place. 
     The coil  87  is comprised of a conductor wire wound in a circular shape and molded with proper resin. Both ends of the wire are led out of the solenoid  29  and connected with lead wires that are led to a battery via a controller (not shown). Under control by the controller, the solenoid  29  is excited. 
     The core  89  is made anti-rotated by any member secured to a stationary member of the vehicle body. The core  89  alone, or in combination with the end wall  19 , nearly thoroughly encloses the coil  87  but leaves a gap at the internal side thereof. The moving part  85  is so disposed as to face this gap so that the magnetic flux leaping over this gap drives the moving part  85 . Either the end wall  19  or the core  89  may be comprised of an elongated portion  33  so as to ensure combination therebetween. 
     The moving part  85  is formed in a ring shape and fits within the inner periphery of the solenoid  29 . The moving part  85  may be comprised of a plunger  93  of a magnetic material and a ring member  95  of a non-magnetic material, which are drivingly coupled together. The plunger  93  receives magnetic force to allow the solenoid  29  to actuate the moving part  85 . The ring member  95  prevents leakage of the magnetic flux to the casing  3 . Thus this combination improves energy efficiency. The member  91  prevents dislocation of the moving part  85  out of the actuator  31 . 
     The ring member  95  is elongated toward the clutch member  13  to form pressure portions  97  that respectively get into contact with the engaging projections  35  through the windows  21 . The pressure portions  97 , when the ring member  95  is actuated by the solenoid  29 , press the engaging projections  35  of the clutch member  13  to let the locking means  39  into the meshing state. 
     The moving part  85  may be, nevertheless, omitted. In such modified embodiments, the solenoid  29  may be configured to be movable by itself toward the side gear  9  to actuate the clutch member  13 . To mediate driving force of the solenoid  29 , any intervening member such as a needle bearing or a thrust washer may be used. 
     The differential device  1  may be further comprised of the detector  99  for detecting position of the clutch member  13 . The detector  99  may be formed in a strip-shape or a flange shape having the outer ends  103  and inner ends. The outer ends  103  are led out of the casing  3  through the radial through holes  23  and the inner ends are secured to the clutch member  13  by means of screws  101  or such. If any external sensor or switch is coupled with the outer ends  103 , the sensor or switch follows motion of the clutch member  13 , thereby the sensor or switch can detect whether the clutch  77  is in a meshing state or not. 
     The differential device  1  may be further comprised of a switch  111  for detecting the position of the clutch member  13 . The switch  111  may be secured to the carrier  113  or any other stationary member. The switch  111  is comprised of an elongated knob  117  and an engaging flange  115  at an end thereof, which is so formed as to engage with the detector  99 . When the clutch member  13  moves, the detector  99  follows its motion and accordingly pulls the knob  117 , thereby switching the switch  111  on or off. Thus the state of the clutch  77  can be electrically detected. A narrow gap may be held between the engaging flange  115  and the detector  99 , when the clutch member  13  rests on the end wall  19 . This is advantageous in avoiding frictional energy loss therebetween. Further the knob  117  may be structured to be rotational. This is advantageous in reducing energy loss even after the clutch member  13  moves toward the side gear  9  and thereby the detector  99  is forced to butt against the engaging flange  115 . 
     As the locking means  39  by itself brings the clutch member  13  and the side gear  9  into axial alignment, the casing  3  is not required to have a straight internal face to guide the clutch member  13 . Freedom of design about the casing  3  is therefore improved. The casing  3  can be consequently comprised of a structure for relieving stress concentration, such as the rounded dent  17 . Of course, any structure such as a rounded corner or an oblique corner may be used instead. The present embodiment can respond to the constant need for downsizing although strength of the structure will not be vitiated. 
     In addition, the rounded dent  17  functions as an oil reservoir. Further the windows  21  and the through holes  23  communicating with the rounded dent  17  promote oil circulation to the exterior. Centrifugal force assists this oil circulation. Therefore the present embodiment is further advantageous in light of lubrication quality. 
     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.