Patent Publication Number: US-6701804-B2

Title: Power switching apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a power switching apparatus which is preferable for switching a two-wheel drive state and a four-wheel drive state, in a vehicle. 
     2. Description of the Related Art 
     In power switching apparatuses for a vehicle, as described in Japanese Patent Application Laid-Open No. 2001-80385 (JP-A), there are structures having the following features. A differential transmits rotation of a drive shaft to a wheel pair. A first rotary member corresponds to an output member of the differential in a side of one wheel, and a second rotary member is arranged to be relatively rotatable to the first rotary member and which integrally rotates with one wheel. A third rotary member integrally rotates with a case of the differential rotating in correspondence to the rotation of the drive shaft. A dog clutch can be switched among a first position at which a connection between the first rotary member and the second rotary member is cancelled, a second position at which the first rotary member and the second rotary member are connected, and a third position at which the first rotary member, the second rotary member and the third member are connected. 
     In the prior art, a two-wheel drive state in which rear wheels are only driven may be established, during which time the dog clutch is at the first position. A differential free state (a four-wheel drive state capable of absorbing rotation difference between right and left front wheels during a vehicle turning operation) in which four wheels are driven is established when the dog clutch is at the second position. A differential lock state (a direct-connection four-wheel drive state capable of integrally rotating the right and left front wheels so as to improve traveling characteristics) in which four wheels are driven may be established when the dog clutch is at the third position. 
     In the conventional power switching apparatus, the differential mechanism for switching the two-wheel drive state, the four-wheel drive differential free state and the four-wheel drive differential lock state involves installation of a bevel gear. Therefore, the structure becomes complex and large in size. 
     Further, since the switching operation is executed by using the dog clutch, it is necessary to align phases for engagement and disengagement of a sleeve and a spline which constitute the dog clutch. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to easily switch between a complete two-wheel drive state and a complete four-wheel drive state based on a compact and simple structure. In this case, the complete two-wheel drive state means a state in which only two front wheels or only two rear wheels are driven. The complete four-wheel drive state means a state in which the two front wheels and the two rear wheels are driven, and the right and left wheels are driven based on the integral rotation. 
     According to the present invention, there is disclosed a power switching apparatus for switching a power transmitting state from a drive member to right and left two driven member, comprising the following structure. 
     A circumferential connection surface is provided in a drive member. Circumferential connection surfaces are provided in both of the driven members. The circumferential connection surface of the drive member and the circumferential connection surfaces of the driven members are coaxially arranged inside and outside. 
     An annular space forms a wedge-like gap in a peripheral direction between the circumferential connection surface of the drive member and the circumferential connection surfaces of both of the driven members in a repeated manner. 
     A cage is received in the annular space, and a plurality of rolling elements are held at a plurality of positions in a peripheral direction of the cage. 
     An energizing member brings each of the rolling elements into contact with the circumferential connection surfaces in the drive means and one of the driven members, and energizes each of the rolling elements in a direction in which the rolling elements are not in contact with the circumferential connection surfaces in the drive member and another of the driven members. 
     A switching means moves the cage in an axial direction due to a centrifugal force, brings an end surface of the cage into frictional contact with the drive member and another of the driven member so as to rotate together therewith, and wedge connects the circumferential connection surface of the drive member and each of the circumferential connection surfaces in both of the driven members according to an interposition of the rolling elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully understood from the detailed description given below and from the accompanying drawings which should not be taken to be a limitation on the invention, but are for explanation and understanding only. 
     The drawings 
     FIG. 1 is a cross sectional view which shows a power switching apparatus; 
     FIG. 2 is an enlarged view of a main portion in FIG. 1; 
     FIG. 3 is a cross sectional view along a line III—III in FIG. 2, and shows a non-wedge connection state; 
     FIG. 4 is a cross sectional view along a line III—III in FIG. 2, and shows a wedge connection state; 
     FIG. 5 is an exploded perspective view of the power switching apparatus; and 
     FIG. 6 is an enlarged view of a main portion in FIG.  5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     According to the invention, a vehicle to which the present invention is applied is structured such that a transmission is connected to an output side of an engine. A drive shaft is connected to an output side of the transmission. Right and left rear wheel sets are connected to an end of the drive shaft in a side of the rear wheels via a differential, and right and left front wheel sets are connected to an end of the drive shaft in a side of the front wheels via a power switching apparatus  10 . In this vehicle, an engine rotating force which is transmitted to the differential of the rear wheels from the drive shaft is always transmitted to the rear wheels, and a rotating force which is transmitted to the power switching apparatus  10  in the side of the front wheels from the drive shaft is transmitted to the right and left front wheels according to a switching operation of the power switching apparatus  10 . When the power switching apparatus  10  is in an off mode in which the power switching apparatus  10  does not transmit the rotating force to the right and left front wheels, the vehicle operates in a complete two-wheel drive state in which the vehicle is driven only by two rear wheels. When the power switching apparatus  10  is in an on mode in which the power switching apparatus  10  transmits the rotating force to the right and left front wheels, the vehicle operates in a complete four-wheel drive state in which the vehicle is directly driven by two front wheels and is driven by two rear wheels. 
     The power transmitting apparatus  10  is, as shown in FIG. 1 to FIG. 6, such that first and second housings  11 A and  11 B are integrally connected by a bolt  10 A. A pinion gear shaft  12  provided with a pinion gear  12 A is supported to the housing  11 A via bearings  13 A and  13 B. A yoke  14  is fixed to the pinion gear shaft  12  according to a spline connection, and the drive shaft mentioned above is connected to the yoke  14 . 
     A drive member  15  is supported to the housing  11 A and the housing  11 B via bearings  16  and  17 . The drive member  15  corresponds to an assembled body, in which a ring gear shaft  18  which is provided with a ring gear  18 A, and a case  19 , are integrally connected by a bolt  20 . The ring gear  18 A is engaged with the pinion gear  12 A. Accordingly, the drive member  15  is always driven by a rotation of the drive shaft. 
     Two left and right driven members  21  and  22  and a spacer  23  held between the driven members  21  and  22  are arranged between end surfaces which are opposed to each other on a center axis of the ring gear shaft  18  and the case  19  constituting the drive member  15 . A left front wheel set  24  is fixed to the driven member  21  through a spline connection, and a right front wheel set  25  is fixed to the driven member  22  through a spline connection. 
     At this time, the drive member  15 , both of the driven members  21  and  22  and the spacer  23  are coaxially arranged with each other. A step-like outer peripheral portion  21 A which is provided on an outward end surface of the driven member  21  in a protruding manner is coaxially fitted to a step-like inner diameter portion  18 B which is provided on a punched end surface of the ring gear shaft  18  in a recess manner, so as to be capable of relatively rotating. The outward end surface of the driven member  21  can be abutted against the punched end surface of the ring gear shaft  18  in an axial direction thereof. A step-like outer peripheral portion  22 A which is provided on an outward end surface of the driven member  22  in a protruding manner is coaxially fitted to a step-like inner diameter portion  19 A which is provided on a punched end surface of the case  19  in a recess manner, so as to be capable of relatively rotating. The outward end surface of the driven member  22  can be abutted against the punched end surface of the case  19  in an axial direction thereof. Further, step-like outer diameter portions  23 A and  23 B which are respectively provided on both side end surfaces of the spacer  23  in a protruding manner are coaxially fitted to step-like inner peripheral portions  21 B and  22 B which are provided on a punched end surface of the driven member  21  and the driven member  22  in a recess manner, respectively. The respective side end surfaces of the spacer  23  can be abutted against the respective punched end surfaces of the driven member  21  and the driven member  22  in an axial direction thereof. Accordingly, both of the driven members  21  and  22  and the spacer  23  are held in the drive member  15  (the ring gear shaft  18  and the case  19 ) in a state in which they can relatively rotate. The drive member  15  (the ring gear shaft  18  and the case  19 ), both of the driven members  21  and  22  and the spacer  23  are coaxially arranged in a state in which they are coaxially fitted to each other. 
     Further, in the power switching apparatus  10 , a circumferential connection surface  30  which is provided on an inner diameter surface of the case  19  constituting the drive member  15 , and circumferential connection surfaces  31  and  32  which are provided on outer diameter surfaces of both of the driven members  21  and  22  are coaxially arranged inside and outside, respectively, as shown in FIGS. 2 and 3. The circumferential connection surface  30  of the case  19  is formed in a polygonal shape. A wedge-like gap  33 A is formed in which both sides (a forward rotating direction and a backward rotating direction) in a circumferential direction are narrow, in an annular space  33  between the circumferential connection surface  30  of the case  19  and the circumferential connection surfaces  31  and  32  of both of the driven members  21  and  22 , in a repeated manner. 
     Further, the power switching apparatus  10  receives cages  41  and  42  respectively corresponding to both of the driven members  21  and  22  in the annular gap  33  between the drive member  15  (the case  19 ) and both of the driven members  21  and  22 . The power switching apparatus  10  holds roller-like rolling elements  43  and  44  in pockets  41 A and  42 A which are provided at a plurality of positions in a peripheral direction of the respective cages  41  and  42 , thereby constituting a roller clutch mechanism according to the following manner. 
     The power switching apparatus  10  is provided with annular grooves  43 A and  44 A in center portions of the respective rolling elements  43  and  44 . A ring-like energizing member  45  which is provided in the periphery of the driven member  21  is engaged with and attached to the groove  43 A of each of the rolling elements  43 . The power switching apparatus  10  is provided with a ring-like energizing member  46  which is provided in the periphery of the driven member  22  and is engaged with and attached to the groove  44   a  of each of the rolling bodies  44 . The energizing member  45  is engaged with and attached to the grooves  43 A of all the rolling elements  43  which are adjacent in the peripheral direction from the side of the driven member  21 , in a state in which one end bent portion is engaged with the groove  43 A of one rolling element  43 . The energizing member  45  energizes each of the rolling elements  43  in such a manner as to be in contact with the maximum inner diameter portion of the circumferential connection surface  30  in the case  19 . The rolling element  43  is in non-contact with the circumferential connection surface  31  of the driven member  21 , and is held in a neutral position. Accordingly, the energizing member  45  forms a racing state in which the drive member  15  (the case  19 ) and the driven member  21  are not engaged (FIG.  3 ). The energizing member  46  is engaged with and attached to the grooves  44 A of all the rolling elements  44  which are adjacent in the peripheral direction from the side of the driven member  22 , in a state in which one end bent portion is engaged with the groove  44 A of one rolling element  44 . The energizing member  46  energizes each of the rolling elements  44 , so as to be in contact with the maximum inner diameter portion of the circumferential connection surface  30  in the case  19 . The rolling element  43  is in non-contact with the circumferential connection surface  32  of the driven member  22 , and is held in a neutral position. Accordingly, the energizing member  46  forms a racing state in which the drive member  15  (the case  19 ) and the driven member  22  are not engaged (the same as FIG.  3 ). 
     The power switching apparatus  10  has a switching means  50 . The switching means  50  switches modes from an off mode (a mode capable of forming a complete two-wheel drive state in which the rear wheels are only driven) to an on mode (a mode capable of forming a complete four-wheel drive state in which the front and rear wheels are driven). In the off mode, the drive member  15  and both of the driven member  21  and  22  are placed in a disengaged state by the energizing members  45  and  46  mentioned above so as to be capable of racing. Power transmission from the drive member  15  to both of the driven members  21  and  22  can thus be cancelled. In the on mode, the drive member  15  and both of the driven members  21  and  22  are engaged, and the power transmission from the drive member  15  to both of the driven members  21  and  22  can be executed. 
     The switching means  50  can move the cages  41  and  42  slightly in an axial direction with respect to flanges  21 C and  22 C of both of the driven members  21  and  22 , in a state of the followings; the inner end surfaces of both of the cages  41  and  42  are placed back to back with each other; inner peripheral portions  41 B and  42 B of the inner end surface of both of the cages  41  and  42  are supported by an outer peripheral guide surface  23 C of the spacer  23 , when receiving both of the cages  41  and  42  in the annular gap  33  between the drive member  15  and both of the driven members  21  and  22 . In the on mode, the switching means  50  slides and guides both of the cages  41  and  42  by the guide surface  23 C of the spacer  23  so as to move them to an outer side in an axial direction. This also brings the outer end surfaces of the respective cages  41  and  42  into contact with the opposing flanges  21 C and  22 C of the driven members  21  and  22  so as to achieve friction contact. Then, the switching means  50  makes the respective cages  41  and  42  capable of rotating together with the respective driven members  21  and  22 . In this state, when the drive member  15  is rotated forward and a rotation phase difference is further generated between the drive member  15  and the driven members  21  and  22 , the rolling elements  43  and  44  of the respective cages  41  and  42  move relatively in a positive direction in a peripheral direction of the circumferential connection surface  30  in the case  19 . They wedge connect the circumferential connection surface  30  of the case  19  to the circumferential connection surfaces  31  and  32  of both of the driven members  21  and  22 , and integrally rotate the drive member  15  (the case  19 ) and the driven members  21  and  22  in a forward rotating direction (FIG.  4 ). On the other hand, when the drive member  15  is rotated backward and the rotation phase difference is generated between the drive member  15  and the driven members  21  and  22 , the rolling elements  43  and  44  of the respective cages  41  and  42  move relatively in a reverse direction in the peripheral direction of the circumferential connection surface  30  in the case  19 . They wedge connect the circumferential connection surface  30  of the case  19  to the circumferential connection surfaces  31  and  32  of both of the driven members  21  and  22 , and integrally rotate the drive member  15  (the case  19 ) and the driven members  21  and  22  in a backward rotating direction. 
     Accordingly, the switching means  50  moves both of the cages  41  and  42  in the axial direction based on a centrifugal force generated in the on mode. In particular, recess-shaped ball receiving portions  51  and  52  are provided in an inner diameter side of inner end surfaces which are back on to each other in both of the cages  41  and  42 . A ball  54  having a fixed weight is received in each of a plurality of positions in a peripheral direction of a ball receiving space  53  (for example 3 positions) formed by both of the ball receiving portions  51  and  52 . Both of the ball receiving portions  51  and  52  are provided with inner side flat surfaces  51 A and  52 A which are orthogonal in the axial directions of the cages  41  and  42 , and outer side ball abutment surfaces  51 B and  52 B which are angular in the axial directions of the cages  41  and  42 . When making both of the cages  41  and  42  back on to each other, the opposing flat surfaces  51 A and  52 A have wider widths than a diameter of the ball  54 . The opposing ball abutment surfaces  51 B and  52 B form a V groove against which the ball  54  can abut in an outer side in the diametrical directions of the cages  41  and  42 . Both of the cages  41  and  42  form a plurality of hole-like ball receiving spaces  53  which are separated in the peripheral direction at uniform intervals, in place of a circular ring-like ball receiving space  53  which is continuous in the peripheral direction. The ball  54  is provided and charged in each of the hole-like ball receiving spaces  53 . 
     Accordingly, the power switching apparatus  50  is switched to the on mode when the drive member  15  (the case  19 ) reaches a high rotation which is over a predetermined fixed value, from the off mode in which the energizing members  45  and  46  mentioned above energize and hold the respective rolling elements  43  and  44  at the neutral position at which the rolling elements  43  and  44  are brought into contact with the maximum inner diameter portion of the circumferential connection surface  30  of the case  19 . In the on mode, a predetermined level or more centrifugal force is applied to the ball  54 . As a result of this centrifugal force, the ball  54  which is displaced outward in the diametrical directions of the cages  41  and  42  pushes and opens both of the cages  41  and  42  via the abutment with the ball abutment surfaces  51 B and  52 B which form the ball receiving space  53  in both of the cages  41  and  42 . Both of the cages  41  and  42  are respectively slid and guided by the guide surface  23 C of the spacer  23  so as to be moved in an outer side in the axial direction, whereby the outer end surfaces of the cages  41  and  42  can be respectively pressed against the flanges  21 C and  22 C of the driven members  21  and  22 . 
     Accordingly, the power switching apparatus  10  operates in the following manner. 
     (A) Complete Two-Wheel Drive State 
     In a state in which drive member  15  is at a lower rotation than the predetermined fixed value, the switching means  50  is in the off mode. In the off mode of the switching means  50 , when the wedge-connection between the drive member  15  and the left and right driven members  21  and  22  is cancelled, the driving force to the left and right driven members  21  and  22  is not transmitted, and a complete two-wheel drive state is achieved. The racing in the bevel gear or the like of the differential does not take place, and fuel consumption is improved. 
     (B) Complete Four-Wheel Drive State 
     When the drive member  15  reaches a high rotation which is over the predetermined fixed value, the switching means  50  is switched into the on mode. In the on mode of the switching means  50 , when a rotation phase difference is generated between the drive member  15  and the driven members  21  and  22  due to a further sudden acceleration of the engine rotating force or the like, the following occurs. The drive member  15  and the left and right driven members  21  and  22  are immediately wedge connected, driving force to the left and right driven members  21  and  22  is transmitted, and a complete four-wheel drive state is achieved. Since both of the left and right driven members  21  and  22  are wedge connected to the drive member  15 , rotating forces transmitted to the left and right driven members  21  and  22  are uniform, and high speed straight traveling stability is improved. 
     Further, during a period of high rotation which is over the fixed value, since the connection state is maintained even during engine braking or during sudden speed reduction, straight traveling stability is maintained. 
     According to the present embodiment, the following effects can be obtained. 
     (1) Since the power switching apparatus  10  has no differential gear built-in, it is possible to make the structure compact and simple, and to reduce weight. 
     (2) The switching means  50  moves the cages  41  and  42  in the axial direction due to the centrifugal force, and brings the end surfaces of the cages  41  and  42  into frictional contact with the flanges  21 C and  22 C of the driven members  21  and  22  so as to rotate together therewith. The drive member  15  and the left and right driven members  21  and  22  can be wedge connected to each other according to an interposition of the rolling elements  43  and  44  immediately after the rotation phase difference is generated between the driven members  21  and  22  and the drive member  15  (a roller clutch mechanism). The wedge connection between the drive member  15  and the driven members  21  and  22  can be easily and lightly engaged and disengaged. 
     (3) Since the switching means  50  is structured to start moving the cages  41  and  42  in the axial direction based on the centrifugal force which is generated at the predetermined rotation number of the drive member  15 , it is possible to automatically switch into a complete four-wheel drive state at the predetermined rotation level. Also, it is possible to automatically secure high speed straight traveling stability. 
     (4) The switching means  50  can simply and securely move the cages  41  and  42  in the axial direction based on the simple structure (the ball cam mechanism) abutting the ball  54  to which the centrifugal force is applied against the ball abutment surfaces  51 B and  52 B which are provided in the cages  41  and  42 . 
     As heretofore explained, embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configurations of the present invention are not limited to the embodiments but those having a modification of the design within the range of the present invention are also included in the present invention. For example, the structure may be made such that the circumferential connection surface of the drive member and each of the circumferential connections of both of the driven members are wedge connected according to an interposition of the rolling elements. This may be caused by the followings; the rolling elements in each of the cages would be held in contact with the polygonal circumferential connection surface of the driven member by the energizing member so as to energize in a direction in which the rolling elements is not in contact with the circumferential connection surface of the drive member; and the end surface of the cage moved in the axial direction as a result of the centrifugal force at the switching time, would be brought into frictional contact with the drive member so as to rotate together therewith. Further, one cage may be commonly used. 
     As described above, according to the present invention, it is possible to easily switch between a complete two-wheel drive state and a complete four-wheel drive state, based on a compact and simple structure. 
     Although the invention has been illustrated and described with respect to several exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made to the present invention without departing from the spirit and scope thereof Therefore, the present invention should not be understood as limited to the specific embodiment set out above, but should be understood to include all possible embodiments which can be embodied within a scope encompassed and equivalents thereof with respect to the features set out in the appended claims.