Abstract:
An infinitely variable power transmission comprising an input shaft, a layshaft driven by the input shaft via internal/external gearing, a toroidal variator, and gearing and clutches which implement a low/reverse variable ratio mode and a high range variable ratio mode. An additional clutch and gearing implement an optional fixed ratio mode.

Description:
FIELD OF THE INVENTION 
     This invention relates to the field of automatic transmissions for motor vehicles. More particularly, the invention pertains to transmissions which provide a continuous range of speed ratios, including zero, between the output speed and the input speed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a transmission according to the present invention. 
         FIG. 2  is a table showing the proposed tooth numbers for the gears and sprockets of the transmission illustrated in  FIG. 1 . 
         FIG. 3  is a table showing the speeds of various elements in various operating conditions when the gears and sprockets have the tooth numbers shown in  FIG. 2 . 
         FIG. 4  is a table showing the state of the clutches for each operating mode. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A transmission according to the present invention is illustrated schematically in  FIG. 1 . Input shaft  10  is driven by the vehicle engine, preferably via a torsional isolator that smoothes out torque fluctuations due to discrete cylinder firings. Output shaft  12  drives the vehicle wheels, preferably via a differential. 
     A dual cavity toroidal variator transfers power from variator input disk  26  to variator output disks  28  and  30 , which are both fixed to intermediate shaft  36 . The variator is capable of efficiently transferring power at any speed ratio within its ratio range. In the present embodiment, the ratio range of the variator includes 2.211:1 overdrive and 0.463:1 underdrive. Two sets of power rollers  32  and  34  transfer power between the input disk and the output disks. The output disks always rotate in the opposite direction of the input disk. The axes about which the power rollers rotate is tilted to control the speed ratio of the variator. In the condition shown in  FIG. 1 , the radius of the interface between the power roller and the input disk is greater than the radius of the interface between the power rollers and the output disks, causing the output disks to rotate at a faster speed than the input disk. When the power roller axes are tilted in the opposite direction, the output disks rotate slower than the input disk. 
     Two varieties of toroidal variator are well known: full-toroidal and half-toroidal. In a full-toroidal variator, the cavity between an input disk and an output disk is shaped like a torus. In a half-toroidal, as illustrated in  FIG. 1 , only the inner portion of the torus is used. The present invention is applicable with either variety of toroidal variator. 
     Power is transmitted from the input shaft to the variator input disk by means of at least one layshaft  16 . Layshaft  16  is driven by the input shaft through internal gear  18  which meshes with external gear  20 . Internal/external gear meshes are more efficient than external/external gear meshes. Internal gear  18  must have a relatively large diameter, but this is acceptable because it is located in the bell housing portion of transmission case  14 . Layshaft  16  drives variator input disk  26  through external gears  22  and  24 . A second layshaft  68 , with external gears  70  and  72 , causes the separating forces of the gear meshes driving the variator input disk to partially or completely counteract one another, reducing the side loads on the variator input disk and simplifying the necessary support bearings. 
     A front planetary gear set drives intermediate shaft  46  at a predetermined proportion of the input shaft speed. Sun gear  38  is fixed to input shaft  10 . Ring gear  40  is fixed to transmission case  14 . Planet carrier  42  is fixed to intermediate shaft  46 . A set of planet gears  44  is supported on planet carrier  42  and meshes with both sun gear  38  and ring gear  42 . 
     A rear planetary gear set combines the speeds of intermediate shaft  46  and intermediate shaft  36 . Sun gear  48  is fixed to intermediate shaft  36 . Planet carrier  52  is fixed to intermediate shaft  46 . A set of planet gears  54  is supported on planet carrier  52  and meshes with both sun gear  48  and ring gear  50 . The number of teeth on the various gears are selected such that ring gear  50  is stationary for some variator speed ratio within the variator&#39;s available ratio range. This variator speed ratio is called the geared neutral ratio. An example of suitable tooth numbers is provided in  FIG. 2 . When the variator ratio is set to a more underdrive ratio than the geared neutral ratio, ring gear  50  rotates in the same direction as the input shaft. Conversely, when the variator ratio is set to a more overdrive ratio than the geared neutral ratio, ring gear  50  rotates in the opposite direction as the input shaft. 
     Clutch  56  releasably connects ring gear  50  to output shaft  12 . Clutch  56  completes a power path that is suitable for reverse motion and low speed forward motion. Substantially the same result would be obtained by placing clutch  56  is other locations within this power path. For example, ring gear  50  could be fixed to output shaft  12  with clutch  56  replacing one of the other fixed connections, such as between input shaft  10  and sun gear  38 , between transmission case  14  and ring gear  40 , between planet carrier  42  and planet carrier  52 , or between intermediate shaft  36  and sun gear  48 . These alternative arrangements would result in different relative speeds when clutch  56  is disengaged, but identical behavior when clutch  56  is engaged. Clutch  58  releasably connects intermediate shaft  36  to output shaft  12 . Clutch  58  is applied for moderate to high speed forward motion. The number of teeth on the various gears are selected such that ring gear  50  and intermediate shaft  36  rotate at the same speed at a variator ratio that is close to the maximum underdrive variator ratio. 
     Intermediate shaft  63  is constrained to rotate at a speed proportional to layshaft  16  and in the same direction. Chain  64  meshes with sprocket  60 , which is fixed to layshaft  16 , and with sprocket  62 , which is fixed to intermediate shaft  63 . Clutch  66  releasably connects intermediate shaft  63  to output  12 . These elements form a fixed ratio power path suitable for highway cruising because it bypasses the variator and therefore has better mechanical efficiency. The number of teeth on the various gears and sprockets are selected such that intermediate shaft  63  and intermediate shaft  36  rotate at the same speed at a variator ratio that is close to the maximum overdrive variator ratio. 
     Clutches  56 ,  58 , and  66  are preferably hydraulically actuated friction clutches which transmit torque when hydraulic pressure is applied and permit relative motion with low drag torque when the hydraulic pressure is removed. However, since the speeds of the elements may be synchronized before engaging the oncoming clutch, other types of couplers, such as dog clutches or switchable one way clutches, may be substituted for some or all of these clutches. 
     The vehicle is prepared for launch in reverse by disengaging all clutches and setting the variator ratio slightly on the overdrive side of the geared neutral ratio such that ring gear  50  rotates slowly backwards. In response to driver demand, clutch  56  is gradually engaged, accelerating the vehicle in reverse. The launch is completed when the speed of the output shaft reaches the same speed as ring gear  50  and clutch  56  is completely engaged. As the vehicle accelerates further, the variator ratio is adjusted to obtain a target engine speed selected based on driving conditions. 
     Similarly, the vehicle is prepared for launch in forward by disengaging all clutches and setting the variator ratio slightly on the underdrive side of the geared neutral ratio such that ring gear  50  rotates slowly forwards. In response to driver demand, clutch  56  is gradually engaged. The launch is completed when clutch  56  is completely engaged. As the vehicle accelerates further, the variator ratio is adjusted to obtain a target engine speed. 
     As the vehicle continues to accelerate, a point will be reached where the variator ratio is near its underdrive limit. At this point, the transmission is shifted from low mode to high mode by releasing clutch  56  while engaging clutch  58 . Unlike a gear change in a traditional step ratio transmission, this transition does not involve a change in the speed ratio between the output shaft and the input shaft. Once the transition to high mode is complete, the controller resumes adjusting variator ratio to obtain a target engine speed. 
     Typically, fixed ratio gearing provides better mechanical efficiency than power paths that include a variator. As a result, it may be preferable to shift to the fixed ratio mode when the vehicle is cruising at a moderately high speed. The transmission is shifted from high mode to fixed ratio mode by releasing clutch  58  while engaging clutch  66 . As shown in  FIG. 3 , the tooth numbers shown in  FIG. 2  result in a fixed ratio mode that is slightly more overdrive than the most overdrive ratio in high mode. As a result, this shift is an upshift with a very small ratio change. However, different speed ratios of the fixed ratio mode, either higher or lower, may be selected by adjusting the number of teeth on sprockets  60  and  62  without departing from the inventive concept. 
     A shift from fixed ratio mode back to high mode is accomplished by releasing clutch  66  while engaging clutch  58 . Preferably, the shift should be accomplished with the variator ratio set to minimize the overall ratio change. Similarly, a shift from high mode back to low mode is accomplished by releasing clutch  58  and engaging clutch  56 . 
     In accordance with the provisions of the patent statutes, the structure and operation of the preferred embodiment has been described. However, it should be noted that alternate embodiments can be practiced otherwise than as specifically illustrated and described.