Abstract:
An infinitely variable power transmission comprising an input shaft, a layshaft, a variator transmitting power from the input shaft to the layshaft, an output shaft, and an internal/external gear pair transmitting power from the layshaft to the output shaft. The output shaft axis may be offset a limited distance from the input shaft axis.

Description:
FIELD OF THE INVENTION 
       [0001]    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 
         [0002]      FIG. 1  is a schematic diagram of a transmission according to the present invention. 
           [0003]      FIG. 2  is a table showing the proposed tooth numbers for the gears of the transmission illustrated in  FIG. 1 . 
           [0004]      FIG. 3  is a table showing the speeds of various elements in various operating conditions when the gears have the tooth numbers shown in  FIG. 2 . 
           [0005]      FIG. 4  is a table showing the state of the clutches for each operating mode. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0006]    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. 
         [0007]    A dual cavity toroidal variator transfers power from input shaft  12  to layshaft  14 . 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 variator input disks  26  and  28  are driven by input shaft  10 . Variator output disk  30  is located between the variator input disks and drives layshaft  14  via external toothed gearing. Two sets of power rollers  32  and  34  transfer power between the input disks and the output disk. The output disk always rotates in the opposite direction of the input  30  disks. 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 disks is less than the radius of the interface between the power rollers and the output disk, causing the output disk to rotate at a slower speed than the input disk. When the power roller axes are tilted in the opposite direction, the output disk rotates faster than the input disks. 
         [0008]    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. 
         [0009]    An internal/external gear pair  44 / 42  transfers power from the layshaft to the output axis  22 . Gear  44  drives the output shaft, via shell  56 , whenever high mode clutch  58  is engaged. Internal/external gear meshes are more efficient than external/external gear meshes. Highway driving and a large percentage of city driving occur in high mode, so efficient power transfer is especially important. 
         [0010]    If output shaft  12  is on the same axis as input shaft  10 , internal gear  44  will have a radius larger than the variator&#39;s radius. When interference with other vehicle components is an issue, a smaller internal gear is made possible by displacing the output axis  22  from the input axis  20 . 
         [0011]    Internal/external gear pair  40 / 38  transfers power from input shaft  10  to intermediate shaft  16  which rotates about output axis  22 . External/external gear pair  42 / 46  transfers power from layshaft  14  to hollow intermediate shaft  18  which is disposed co-axially with intermediate shaft  16 . Intermediate shaft  16  spins in the same direction as the input shaft while intermediate shaft  18  spins in the opposite direction. The speed of intermediate shaft  16  is a fixed proportion of the speed of the input shaft while the speed of intermediate shaft  18  also varies based on the variator speed ratio. Sun gear  48  is connected to hollow intermediate shaft  18 . Ring gear  50  is connected to solid intermediate shaft  16 . Carrier  54  supports a set of planet gears  52  which mesh with both sun gear  48  and ring gear  50 . Carrier  54  rotates about axis  22  at a speed which is a weighted average of the speeds of the two intermediate shafts. Carrier  54  drives output shaft  12 , via shell  56 , whenever low mode clutch  60  is engaged. 
         [0012]    Alternatively, carrier  54  could be solidly connected to output shaft  12  and the low mode clutch used to disconnect one of the other connections to the planetary gear set. Specifically, a clutch that releasably connects sun gear  48  to gear  46  or a clutch that releasably connects ring gear  50  to gear  40  would accomplish the same function as clutch  60 . 
         [0013]    A number of epicyclic gearing assemblies provide three elements that rotate about a common axis with the speed of one element equal to a weighted average of the speeds of the remaining two elements. These include double pinion planetary gear sets, stepped pinion planetary gear sets, and co-planar gear loops as described in U.S. Pat. Nos. 5,030,184 and 6,126,566. Any of these epicyclic gearing assemblies should be regarded as an equivalent of the simple planetary gear set of the described embodiment. 
         [0014]    The number of teeth on the various gears are selected such that carrier  54  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. With the tooth numbers as shown in  FIG. 2 , the geared neutral ratio is approximately 1:642:1. As a result, in low mode, variator ratios on the overdrive side of the geared neutral ratio will result in reverse drive and variator ratios on the underdrive side will result in forward drive. Furthermore, at a variator ratio near the variator&#39;s underdrive limit, the speed of carrier  54  and internal gear  44  are identical. This facilitates the transition from low mode operation to high mode operation. An example of tooth numbers that provide these properties is shown in  FIG. 2 . 
         [0015]    The vehicle is prepared for launch in reverse by disengaging both clutches and setting the variator ratio slightly on the overdrive side of the geared neutral ratio such that carrier  54  rotates slowly backwards. In response to driver demand, clutch  60  is gradually engaged, accelerating the vehicle in reverse. The launch is completed when the speed of the output shaft reaches the same speed as carrier  54  and clutch  60  is completely engaged. As the vehicle accelerates further, the variator ratio is adjusted to obtain a target engine speed selected based on driving conditions. 
         [0016]    Similarly, the vehicle is prepared for launch in forward by disengaging both clutches and setting the variator ratio slightly on the underdrive side of the geared neutral ratio such that carrier  54  rotates slowly forwards. In response to driver demand, clutch  60  is gradually engaged. The launch is completed when clutch  60  is completely engaged. As the vehicle accelerates further, the variator ratio is adjusted to obtain a target engine speed. 
         [0017]    As the vehicle continues to accelerate, a point will be reached where the variator ratio is at its underdrive limit. At this point, the transmission is shifted from low mode to high mode by releasing clutch  60  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. 
         [0018]    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.