Abstract:
The present invention provides a starting clutch in which an input side element and an output side element are joined together by applying an axial load thereby to transmit a power, which clutch comprises an urging device for always providing the axial load, and a releasing device for releasing the input side element and the output side element from the axial load.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a starting clutch which can be used in place of a torque converter of a motor vehicle. 
     2. Related Background Art 
     Conventionally, in an AT (automatic transmission), a vehicle was started by transmission of torque in a torque converter. Since the torque converter had a torque amplifying effect and torque could smoothly be transmitted during increase and decrease of the torque, the torque converter was mounted to many AT motor vehicles. 
     On the other hand, the torque converter has a disadvantage that a slip amount is great during increase and decrease of the torque and thus not so efficient. 
     Thus, recently, use of a starting clutch in place of the torque converter has been proposed, and torque has been amplified at a low speed area by decreasing a gear ratio and increasing a transmission number. 
     FIG. 2 is an-axial sectional view of a conventional starting clutch. Now, such a starting clutch will be explained. The starting clutch  100  includes a multi-plate clutch  101 . Within a clutch case  106  of the multi-plate clutch  101 , friction plates  102  acting as output side friction engaging elements and separator plates  103  acting as input side friction engaging elements are alternately disposed. 
     Further, a backing plate  104  is provided at one axial end of the multi-plate clutch. The backing plate  104  is supported by a stop ring  105  at an axial outer side (left in FIG.  2 ). On the other hand, at an end opposite to the backing plate  104 , a piston  108  is disposed within an inner wall of the clutch case  106  through an O-ring  107 . The piston  108  is biased by a return spring  116  toward a direction (right in FIG. 2) along which an engaging condition between the separator plates  103  and the friction plates  102  is released. Further, a hydraulic chamber  109  is defined between the piston  108  and the clutch case  106 . 
     The starting clutch  100  further includes a housing  110  covering an outer periphery of the multi-plate clutch  101 , and a damper  117  disposed between the clutch case  106  and the housing  110 . Incidentally, the housing  110  is connected to an output shaft  111  of an engine (not shown) and the damper  117  is constituted by a spring  130 , a retainer plate  113  for holding the spring  130  and a pawl  114  engaging by the spring  130 . 
     In the above-mentioned starting clutch  100 , the piston  108  is operated by supplying hydraulic pressure into the hydraulic chamber  109  through an oil path  115 , thereby effecting frictional engagement between the separator plates  103  and the friction plates  102 . 
     As mentioned above, in the starting clutch  100 , the piston  108  is operated by supplying the hydraulic pressure into the hydraulic chamber  109  through the oil path  115 , thereby effecting the frictional engagement. That is to say, upon operation of the starting clutch (upon transmission of power), the hydraulic pressure always acts. A predetermined clearance is provided, and, since the clearance is maintained by a biasing force of the return spring  116  against the piston, torque is completely blocked upon releasing. 
     When it is desired to release the engaging condition between the separator plates  103  and the friction plates  102 , the hydraulic pressure is released. When the hydraulic pressure is released, the piston  108  can be moved freely and thus is shifted to the right in FIG. 2 by the biasing force of the return spring  116 . As a result, the engaging condition between the separator plates  103  and the friction plates  102  is released. 
     However, in order to maintain the frictional engaging condition between the separator plates  103  and the friction plates  102 , the hydraulic pressure must always be supplied. Further, an operating time of a pump for supplying the hydraulic pressure to maintain the hydraulic pressure becomes longer. And, a mechanism can be complicated. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a starting clutch in which hydraulic pressure is not required to always be supplied, and an operating time of a pump for supplying the hydraulic pressure can be shortened, and operating efficiency is enhanced. 
     To achieve the above object, the present invention provides a starting clutch in which an input side element and an output side element are joined together by applying an axial load thereby to transmit a power, which clutch comprises urging means for always providing the axial load, and releasing means for releasing the input side element and the output side element from the axial load. 
     Further the present invention provides a method for controlling a starting clutch, in which the clutch is released by supplying hydraulic pressure and the clutch is engaged by releasing the hydraulic pressure. 
     Since the input side element and the output side element are frictionally engaged together by the spring for always providing the axial load and a hydraulic cylinder for releasing the input side element and the output side element from the axial load is provided, in the operation of the starting clutch, the hydraulic pressure may be supplied only upon releasing the clutch, with the result that the operating time of the pump for supplying the hydraulic pressure is shortened thereby to enhance the operating efficiency. Further, since the urging load given by the spring is provided by the mechanical means, good stability can be achieved. Accordingly, stable control can easily be performed. 
     Since the clutch is released by supplying the hydraulic pressure and the clutch is engaged by releasing the hydraulic pressure, a starting clutch controlling method in which operating efficiency is enhanced can be provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an axial sectional view of a starting clutch according to an embodiment of the present invention; and 
     FIG. 2 is an axial sectional view of a conventional starting clutch. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be fully explained in connection with an embodiment thereof with reference to the accompanying drawings. Incidentally, it should be noted that the illustrated embodiment is merely an example and various alterations and modifications can be made within the scope of the invention. 
     FIG. 1 is an axial sectional view of a starting clutch according to an embodiment of the present invention. The starting clutch  10  includes a multi-plate clutch  11 . Within a clutch case  16  of the multi-plate clutch  11 , substantially annular friction plates  12  acting as output side friction engaging elements and substantially annular separator plates  13  acting as input side friction engaging elements are disposed alternately along an axial direction. At one axial end of the clutch case  16 , a substantially annular backing plate  14  is fixedly supported by a substantially annular stop ring  15  in the axial direction. 
     Although the multi-plate clutch  11  is constituted by four friction plates  12  and four separator plates  13 , it should be noted that the number of the input side and output side friction engaging elements can be changed in accordance with required torque. Further, a friction material or a plurality of friction materials  35  divided into plural segments are secured to each axial surface of the friction plate  12  by an adhesive or the like. Of course, in accordance with the required torque, the friction material may be secured to only one surface of the friction plate  12 . 
     On the other hand, in FIG. 1, at the right side in the axial direction, a piston  18  is disposed between the friction engaging elements and an inner surface of the clutch case  16 , and a spring  41  is disposed between the piston  18  and the clutch case  16 . The spring  41  is a coil spring having predetermined elasticity but may be a spring of other type. 
     The piston  18  is always biased toward a direction along which the friction plates  12  and the separator plates  13  are frictionally engaged or joined together by a mechanical urging force of the spring  41 . In order to release an engaging condition between the friction plates  12  and the separator plates  13 , a hydraulic mechanism (described later) is used. 
     The starting clutch  10  further includes the multi-plate clutch  11 , a housing  20  covering an outer periphery of the multi-plate clutch  11 , and a damper  17  acting as a shock damping mechanism and disposed between the clutch case  16  and the housing  20 . Incidentally, the damper  17  is provided on an inner wall of the housing  20  and is constituted by a retainer plate  22  for holding a spring  21  and a pawl  23  engaging the spring  21 . The retainer plate  22  is secured to the housing  20  by a rivet  37 . The housing  20  covers the multi-plate clutch  11 , the piston  18  and a cylinder portion which will be described later. 
     A thrust washer  24  is disposed between the clutch case  16  and the housing  20 . A needle bearing may be used in place of the thrust washer  24 . A driven rotary member  3  is fitted into the clutch case  16 . The driven rotary member  3  is rotatably supported by a fixed member  2  through a bearing  6 . The fixed member  2  is supported by an output shaft  1  through a seal bearing  8  and a bearing  5 . The seal bearing  8  may be an O-ring or other seal member. 
     A seal bearing  7  is provided an outer peripheral surface of the driven rotary member  3  to provide a seal between the driven rotary member  3  and the fixed member  2 . The seal bearing  7  may be an O-ring or other seal member. The output shaft  1  is provided with a lubricating oil supplying path  4  to supply lubricating oil to various parts of the starting clutch  10 . The lubricating oil can be supplied through a gap between the output shaft  1  and the fixed member  2 . An oil path  32  extending in the axial direction is formed in the fixed member  2  and hydraulic pressure is supplied from a pump (not shown) of a hydraulic circuit (not shown) through the oil path. The oil path  32  is communicated with an oil chamber  30  (described later) through an oil path  31  radially extending through the driven rotary member  3 , thereby supplying predetermined hydraulic pressure to the oil chamber  30 . 
     At one axial end, the output shaft  1  is provided at its outer periphery with a spline  9  onto which an inner peripheral portion of a hub  25  for holding the plurality of friction plates  12  at its outer periphery is fitted. That is to say, the hub  25  is rotated integrally with the output shaft  1 . A thrust washer  29  disposed between the hub  25  and the housing  20 . A needle bearing may be used in place of the thrust washer  29 . 
     Next, the hydraulic mechanism according to the illustrated embodiment will be explained. A cylinder case portion  27  is integrally formed with one axial end of the driven rotary member  3  positioned within the clutch case  16 . A cylinder plate  33  is slidably fitted into the cylinder case portion  27  constituting a hydraulic cylinder for an axial movement, thereby defining the oil chamber  30 . Two O-ring seals are disposed between the cylinder case portion  27  and the cylinder plate  33 , thereby providing an oil-tight condition of the oil chamber  30 . Incidentally, the cylinder case portion  27  may be independent from the driven rotary member  3 . 
     As mentioned above, the oil chamber  30  is communicated with the oil path  32  of the fixed member  2  and the oil path  31  of the driven member. Two seal bearings  34  are disposed between the fixed member  2  and the driven rotary member  3  on both sides of the oil path  31 , thereby sealing the oil path to prevent leakage of hydraulic pressure. A thrust washer  28  is provided between the axial end of the driven rotary member  3  and the hub  25 . A needle bearing may be used in place of the thrust washer  28 . 
     A radial outward extension  36  of the cylinder plate  33  is opposed to the piston  18  in the axial direction, and a thrust washer  26  is disposed between the extension  36  and the piston  18 . A needle bearing may be used in place of the thrust washer  26 . The hydraulic pressure supplied from the oil path  32  of the fixed member  2  is supplied to the oil chamber  30  through the oil path  31 . 
     The cylinder plate  33  is shifted in a direction along which the cylinder plate is separated from the cylinder case portion  27  in the axial direction, i.e., along which the piston  18  is urged, by the hydraulic pressure generated in the oil chamber  30 . When the piston  18  is urged by the cylinder plate  33 , the piston  18  is shifted to the right in FIG. 1 in opposition to a biasing force of the spring  41 . As a result, since the piston  18  is separated from the separator plate  13 , the engaging condition between the friction plates  12  and the separator plates  13  is released. 
     In the illustrated embodiment, the driving torque from the engine (not shown) is transmitted to the output shaft  1  through the housing  20 , damper  17 , clutch case  16 , separator plates  13 , friction plates  12  and hub  25 . 
     As mentioned above, in another aspect of the present invention, since the clutch is released by supplying the hydraulic pressure and the clutch is engaged by releasing the hydraulic pressure, a starting clutch controlling method in which operating efficiency is enhanced can be provided. 
     In the illustrated embodiment of the present invention as mentioned above, the clutch of the starting clutch in which the input side elements and the output side elements are frictionally engaged with each other by the axial load may be, for example, a wet type of dry type multi-plate clutch, a single plate clutch or a cone clutch, and the spring as the urging means may be, for example, a leaf spring, a coil spring or a wave spring. Further, the urging force of the urging means, i.e., spring pressure and the hydraulic pressure are set in consideration of properties such as a weight of a vehicle, coefficient of friction of the friction engaging elements of the starting clutch, an area of the friction engaging surface and the like. 
     The starting clutch of the present invention mentioned above has the following advantages. 
     In the operation of the starting clutch, since the hydraulic pressure may be supplied only upon releasing the clutch, the operating time of the pump for supplying the hydraulic pressure is shortened. Further, the operating efficiency and the controlling ability can be enhanced.