Abstract:
A forward/reverse change-over mechanism ( 3 ) of an automatic transmission comprises a forward clutch ( 5 ) inside a drum ( 7 ) with the base ( 7   c ) which rotates together with an input shaft ( 1 ). The forward clutch ( 5 ) engages by driving a piston ( 9 ) housed in the drum ( 7 ) by the oil pressure of an oil chamber ( 10 ) between a base ( 7   c ) and the piston ( 9 ). Projecting bearings ( 16 ) which seat the piston ( 9 ) are formed by press-forming at equal angular intervals concentrically with the axial center of the drum ( 7 ) in the base ( 7   c ). By installing a sensor body ( 18 ) which responds to the passage of depressions ( 17 ) formed underneath the bearings ( 16 ), the forward/reverse change-over mechanism ( 3 ) can be made compact and manufactured with a small number of parts and machining steps.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a sensor which detects the input rotation speed of a vehicle automatic transmission.  
       BACKGROUND OF THE INVENTION  
       [0002]     Concerning sensor arrangements which detect the input rotation speed of a vehicle automatic transmission, Tokkai Hei 09-32918 published by the Japan Patent Office in 1997 discloses a rotation speed sensor comprising members which extend in a radial direction at intervals of a fixed angle from a clutch drum, and a sensor body facing these members. The sensor body outputs a signal whenever a member passes a specific position on a path. The rotation speed of the clutch drum is detected from the interval of this signal.  
       SUMMARY OF THE INVENTION  
       [0003]     According to the prior art, the sensor body is disposed outside the circumferential path of the member. Therefore, a space must be reserved for the sensor body outside the clutch drum, and the size of the automatic transmission in the radial direction increases correspondingly.  
         [0004]     To avoid increasing the size of the automatic transmission in the radial direction, a rotation speed sensor is also known wherein a rotor is pressed into the outer circumference of the clutch drum from the axial direction, fixed by welding, and the rotation of the rotor is detected by a sensor installed behind the clutch drum.  
         [0005]     This sensor requires a special rotor for detecting rotation speed, and as this rotor is fixed to the clutch drum by pressing and welding, the number of parts and machining steps required to install the input rotation speed sensor increase.  
         [0006]     It is therefore an object of this invention to provide an input rotation speed sensor for an automatic transmission which is compact, and has few parts and machining steps.  
         [0007]     In order to achieve the above object, this invention provides an automatic transmission which changes the rotation speed of an input shaft to output power. The transmission comprises a drum having a base which rotates together with the input shaft, a piston housed in the drum, and an oil chamber formed in the drum between the base and the piston. The piston displaces parallel to an axial center of the drum according to an oil pressure supplied to the oil chamber. The transmission further comprises plural projecting bearings which seat the piston formed at equal angular intervals concentrically with the axial center, depressions formed underneath the bearings, and a sensor body disposed facing the base which outputs a signal when the depressions pass by.  
         [0008]     The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a vertical cross-sectional view of the essential parts of an automatic transmission according to this invention.  
         [0010]      FIG. 2  is a vertical cross-sectional view of the essential parts of a forward/reverse change-over mechanism according to this invention.  
         [0011]      FIG. 3  is a vertical cross-sectional view of a forward clutch drum according to this invention.  
         [0012]      FIG. 4  is a rear elevation of the forward clutch drum.  
         [0013]      FIG. 5  is a vertical cross-sectional view of a bearing surface and a depression taken along a line V-V in  FIG. 4 .  
         [0014]      FIGS. 6A-6D  are diagrams describing a press process of the bearing surface and the depression.  
         [0015]      FIG. 7  is a rear elevation of the automatic transmission describing the spatial relationship of the sensor body according to this invention, and a chain which drives an oil pump. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     Referring to  FIG. 1  of the drawings, a vehicle automatic transmission is provided with an input shaft  1  connected to an internal combustion engine, a V-belt continuously variable transmission mechanism  2  which changes the rotation speed of the input shaft  1 , and a forward/reverse change-over mechanism  3  which changes over the direction of the rotation transmitted to the continuously variable transmission mechanism  2  from the input shaft  1 .  
         [0017]     The forward/reverse change-over mechanism  3  is disposed between the input shaft  1  and a primary pulley  2 A of the continuously variable transmission mechanism  2 .  
         [0018]     The forward/reverse change-over mechanism  3  comprises a planetary gear set  4 , a forward clutch  5  and a reverse clutch  6 .  
         [0019]     Referring to  FIG. 2 , the planetary gear set  4  comprises a ring gear  4   r , sun gear  4   s , plural pinions  4   p  interposed between the sun gear  4   s  and ring gear  4   r , and a planet carrier  4   c  supporting each rotation shaft  4   ps  of the pinions  4   p.    
         [0020]     The ring gear  4   r  is spline-jointed to the inner circumference  7   a  of a cylindrically-shaped forward clutch drum  7 . A sleeve  7   b  is formed in the center of this forward clutch drum  7 . The sleeve  7   b  is spline-jointed to the outer circumference of the input shaft  1 .  
         [0021]     The forward clutch  5  comprises a drive plate  5   a  and a driven plate  5   b . The drive plate  5   a  is spline-jointed to the inner circumference  7   a  of the forward clutch drum  7 . The driven plate  5   b  is fixed to a hub  15  formed in one piece with the sun gear  4   s.    
         [0022]     The drive plate  5   a  and driven plate  5   b  are laminated in the direction of the input shaft  1  to form a multi-plate clutch.  
         [0023]     The inner circumference of the sun gear  4   s  is joined to the fixed primary pulley  2 A of the continuously variable transmission mechanism  2 .  
         [0024]     The planet carrier  4   c  is constructed so that it can be connected to a case  8  of the automatic transmission via the reverse clutch  6 . The reverse clutch  6  is also a multi-plate clutch identical to the forward clutch  5 .  
         [0025]     The inner circumference  7   a  of the forward clutch drum  7  and the sleeve  7   b  are joined via a base  7   c . A piston  9  which presses the drive plate  5   a  parallel to the input shaft  1  is housed inside the forward clutch drum  7 . An oil chamber  10  is formed between the piston  9  and base  7   c  of the forward clutch drum  7 . The piston  9  displaces parallel to the input shaft  1  due to the oil pressure of the oil chamber  10 , pushes the drive plate  5   a  against the driven plate  5   b , and transmits the rotation of the input shaft  1  to the sun gear  4   s  by frictional force. An oil pressure is supplied to the oil chamber  10  via an oil passage  1   a  formed in the input shaft  1 .  
         [0026]     A hub  11  which slides on the inner circumferential surface of the piston  9  is fixed to the inside of the forward clutch drum  7 . A spring  12  is interposed between the hub  11  and piston  9 , and the piston  9  is pushed towards the base  7   c  parallel to the input shaft  1  by the reaction force of the spring  12 .  
         [0027]     When the forward clutch  5  is in the non-engaged state, the oil pressure of the oil chamber  10  is released, and the piston  9  is held in a retracted position by the pushing force of the spring  12 .  
         [0028]     The reverse clutch  6  comprises a drive plate  6   a , a driven plate  6   b  and a piston  13  which pushes the drive plate  6   a.    
         [0029]     An oil chamber  14  is formed between a piston  13  and case  8 . The piston  13  displaces parallel to the input shaft  1  due to the oil pressure of the oil chamber  14 , pushes the drive plate  6   a  against the driven plate  6   b , and restricts the rotation of the planet carrier  4   c  by frictional force. When the oil pressure of the oil chamber  14  is released, the piston  13  is pushed by a spring, not shown, and is held in a retracted position which releases the reverse clutch  6 .  
         [0030]     Due to the aforesaid construction, when the forward/reverse change-over mechanism  3  engages the forward clutch  5  and releases the reverse clutch  6 , the ring gear  4   r , sun gear  4   s  and planet carrier  4   c  rotate together so that the rotation of the input shaft  1  is transmitted to the primary pulley  2 A without changing direction. On the other hand, when the forward clutch  5  is released and the reverse clutch  6  is engaged, the planet carrier  4   c  is restricted, so the ring gear  4   r  and sun gear  4   s  rotate in opposite directions, and the rotation of the input shaft  1  is transmitted to the primary pulley  2 A in the reverse direction.  
         [0031]     Next, the main construction of the rotation speed sensor which is the subject matter of this invention, will be described.  
         [0032]     Referring to  FIG. 3 , the forward clutch drum  7  comprises plural bearings  16  which seat the piston  9  in a retracted position on the base  7   c . The bearings  16  are projections extending toward the piston  9 , and are formed at a constant angular interval on a circle having the input shaft  1  at its center. The height of the bearing  16  is set according to a design oil amount of the oil chamber  10 .  
         [0033]     Depressions  17  corresponding to the bearings  16  are also formed in the rear surface of the base  7   c . Referring to  FIG. 4 , a total of 24 sets of the bearings  16  and depressions  17  are formed in the base  7   c  having the input shaft  1  at its center. Referring to  FIG. 5 , the depth of the depressions  17  is equal to the height of the bearings  16 . The bearings  16  and depressions  17  are formed in one piece by press-forming.  
         [0034]     Referring again to  FIG. 2 , a sensor body  18  is disposed facing the path of the depressions  17  which rotate together with the rotation of the forward clutch drum  7 .  
         [0035]     The sensor body  18  outputs a signal when the depressions  17  pass by them, and detects the rotation speed of the forward clutch drum  7  based on the signal interval.  
         [0036]     The sensor body  18  is generally formed in a cylindrical shape. By placing the sensor body  18  in the path of the depressions  17  parallel to the input shaft  1 , the sensor body  18  need not be installed outside the forward clutch drum  7  with respect to the radial direction, so the dimensions of the automatic transmission or forward/reverse change-over mechanism  3  in the radial direction can be suppressed small.  
         [0037]     Referring to  FIGS. 6A-6D , the method of forming the bearings  16  and depressions  17  in the forward clutch drum  7  will now be described.  
         [0038]     A steel plate  19  is set in a die  20 , and the steel plate  19  is fixed by a flat clamp  22  elastically supported by a spring  21 . The steel plate  19  is then pressed by a punch  23  until the depressions  17  of predetermined depth are formed in the steel plate  19  as shown in  FIG. 6B .  
         [0039]     Subsequently, the punch  23  and flat clamp  22  are removed as shown in  FIG. 6C , and the bearings  16  and depressions  17  underneath them are formed in one piece with the forward clutch drum  7  as shown in  FIG. 6D .  
         [0040]     Next, referring to  FIG. 7 , the sensor body  18  is installed on the inner side of a chain  32  looped around a sprocket  30  fixed to the rotation axis of the primary pulley  2 A, and a sprocket  31  which drives an oil pump, in the vicinity of the rotation axis of the primary pulley  2 A.  
         [0041]     As described hereinabove, the rotation speed sensor according to this invention does not comprise a rotor outside the forward clutch drum  7 , and the passage of the depressions  17  in the base  7   c  of the forward clutch drum  7  is detected by the sensor body  18 . The forward/reverse change-over mechanism  3  can therefore be made more compact with respect to the radial direction.  
         [0042]     Further, the bearings and  16  and depressions  17  are formed in a one-piece construction, so machining and assembly steps are reduced, and the rotation speed sensor can be incorporated in the automatic transmission at low cost. As the depressions  17  are formed in one piece with the bearings  16 , the formation of the depressions  17  has no effect on the volume of the oil chamber  10 , so sufficient oil pressure can be made to act on the piston  9 .  
         [0043]     The contents of Tokugan 2004-101055, with a filing date of Mar. 30, 2004 in Japan, are hereby incorporated by reference.  
         [0044]     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, within the scope of the claims.  
         [0045]     For example, herein, an embodiment was described where this invention was applied to an automatic transmission comprising the V-belt continuously variable transmission mechanism  2 , but this invention may be applied also to an automatic transmission comprising a conventional automatic transmission mechanism that varies the rotation speed of the input shaft  1  through plural combinations of gears.