Method for operating a traction drive automatic transmission for automotive vehicles

A method for operating an automatic traction drive transmission for use in motor vehicles having a first gear unit for operation in an infinitely variable mode and a second gear unit for operation in a continuously variable mode includes connecting the first gear unit to the transmission output, disconnecting the second gear unit from the first gear unit, and changing the speed ratio of the variator to produce low forward and low reverse ranges, or connecting the second gear unit to the first gear unit, disconnecting the first gear unit from the transmission output, and changing the speed ratio of the variator to produce high mode low and high forward ranges.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the field of automatic transmissions for 
motor vehicles. More particularly it pertains to a method for operating 
such a transmission having a traction drive variator of the toroidal type. 
2. Description of the Prior Art 
One type of a continuously variable transmission typically includes a 
toroidal drive having at least one pair of traction discs, which often 
react upon each other and are rotatably supported in a housing along an 
axis facing one another to define a toric cavity between them. A motion 
transmitting traction roller is disposed in the cavity. The traction 
roller is frictionally engaged with the discs in circles of varying 
diameters depending on the transmission ratio, and is so supportive that 
it can be moved to initiate a change in the transmission ratio. A traction 
drive continuously variable drive can have more than one cavity and may be 
used, for example, to form part of an infinitely variable transmission. 
A common type of continuously variable transmission includes a toroidal 
drive having dual cavities, which are defined by two torsionally coupled 
outboard traction discs, which react upon each other, and two inboard 
discs, which are positioned between the outboard discs and also react upon 
each other. One dual cavity toroidal drive of the "off-center type" is 
disclosed in U.S. Pat. No. 5,368,529. An off-center toroidal drive is 
usually considered to have an included angle of less than 180 degree 
between the traction contacts, i.e., where the roller contacts the discs. 
An on-center toroidal drive is usually considered to have an included 
angle of about 180 degree. The included angle is the angle formed by the 
lines between the center of the toric cavity and the traction contact on 
the engaged discs. The usual method for transmitting power through a dual 
cavity design of the "off-center type" is to input the power to the two 
outboard discs and use parallel shafting and gearing to transmit power 
from the inboard discs. 
One gear mesh used to effect this parallel shafting is usually trapped 
between the inboard discs. Such a two-shaft system is bulky and difficult, 
if not impossible, to fit into the available space provided for the 
transmission of a number of vehicles. In addition, it is often necessary 
to return to the original center line when transmitting power. In the 
past, this has required a second gear mesh to be used, in addition to the 
gear mesh between the inboard discs. Single cavity toroidal drives are 
also known to take up more space than desired. 
Therefore, there is a need for a toroidal type transmission capable of 
inputting and outputting power along the same axis without having to use 
parallel shafting. U.S. Pat. No. 5,607,372 describes an axial transmission 
of this type. Such a coaxial-axial drive transmission takes up less space 
than parallel shaft transmissions and can therefore be used in 
applications with tighter space constraints. In addition, it is easier and 
less expensive to package a coaxial-axial drive transmission in a housing 
than to package a parallel shaft transmission. 
Transmissions of this type in the prior art do not have enough speed ratio 
span to overdrive the variator output. Instead, in infinitely variable 
transmissions of this type, upon shifting from a low mode to a high mode, 
the speed ratio produced by the variator is reduced and the transmission 
speed ratio increases as a result of the increase in the speed ratio of 
the gearset. To reduce the variator speed ratio the rollers are rotated to 
the low mode configuration from the higher speed ratio configuration to 
which they had progressed while accelerating the vehicle from a stop. 
Transmissions operating in this way are difficult to control effectively. 
It is preferred that the variator speed ratio increase continually when 
the gearset is shifted to a higher speed range without being decreased to 
a low mode of operation. 
SUMMARY OF THE INVENTION 
One feature of the transmission controlled by the method of this invention 
is a planetary gearset having a carrier connected to the transmission 
input, and a sun gear connected to the output of a traction drive. The 
traction drive is a toroidal drive having two coupled traction discs, 
which react at least torsionally, preferably both torsionally and axially, 
with one another through the carrier. The toroidal drive can be a dual 
cavity type, with two outboard traction discs and one inboard traction 
disc element or two separate inboard traction discs disposed between the 
outboard discs. The toroidal drive can also be a single cavity type. One 
of the traction discs rotates with the input shaft; the carrier rotates 
with the input shaft and the other traction disc. 
It is an object of this invention to provide a coaxial traction drive 
transmission that operates in an infinitely variable mode including a 
geared neutral condition and in a continuously variable mode. It is 
another object to provide such a transmission in which transmission speed 
ratios are increased by progressively increasing the speed ratios produced 
by the variator as the motor vehicle accelerates from a stop. In 
accomplishing this result, the variator underdrives its output discs as 
the vehicle accelerates from a stop and continually increases the variator 
speed ratios into the overdrive range without decreasing the variator 
speed ratio, even upon changing the operating mode of the transmission at 
the synchronous point where the torque flow path changes by alternately 
engaging and disengaging two clutches that control the gearsets. 
In realizing these objects and advantages a method for operating a traction 
drive transmission, having a traction drive variator driveably connected 
to a transmission input, a first gear unit driveably connected to the 
transmission input and variator output, a second gear unit driveably 
connected to the first gear unit, includes the steps of driveably 
connecting the first gear unit and the transmission output; operating the 
variator to overdrive the variator output with respect to the speed of the 
transmission input such that the transmission output drives the vehicle in 
a rearward direction; and operating the variator to underdrive the 
variator output with respect to the speed of the transmission input such 
that the transmission output drives the vehicle in a forward direction.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a transmission according to this invention includes an 
input shaft 10 driven by an internal combustion engine, electric motor or 
other power source, and including a planetary gearset 12, a compound 
planetary gearset 14, a toroidal traction drive variator 16, various 
elements driveably connecting components of the gearsets and variator, and 
an output shaft 18. 
Toroidal variator 16 includes first input discs 20, driveably connected 
directly to the input shaft 10, and second input discs 22, driveably 
connected to shaft 10 and the carrier 24 of the planetary gearset 12. The 
variator output discs 26 are driveably connected through a sleeve shaft 28 
to a first sun gear 30 of gearset 12. The variator discs are mutually 
spaced axially and define toroidal cavities 36, 38, each cavity containing 
a set of spaced, rotating, angularly displaceable rollers 32, 34, each 
roller set driveably engaged with an input disc and output disc. Rollers 
of the set 32 transmit torque between input discs 20 and output discs 26; 
rollers of the set 34 transmit torque between input discs 22 and the 
output discs 26 A drive ratio control mechanism tilts or inclines the axes 
of the rollers through arcs, thereby changing the location of contact of 
the rollers on the discs, the speed of the output disc relative to the 
speed of the input discs, and the torque transmitted between the input 
discs and output discs. Output discs 26 rotate in the opposite direction 
from that of the input discs about the axis of input shaft 10. 
The dual cavity toroidal drive 16 includes two inboard traction discs 26 
formed as one integral element mounted on shaft 28. However, inboard discs 
26 can also be two separate discs which are positioned back-to-back and 
simply coupled together in a conventional manner to operate in unison. An 
example of a dual cavity toroidal drive having dual inboard discs is 
disclosed in U.S. Pat. No. 5,368,529, which is incorporated in its 
entirety herein by reference. 
A toric cavity is defined between each outboard disc 20 and 22 and the 
inboard disc element 26. Each pair of traction rollers 32, 34 are mirror 
images of the other pair. The rollers are so supported that they can be 
moved to produce a change in the transmission ratio. 
Each roller is actuated to vary its diameter and to provide a normal force 
at its contact with the corresponding discs to sufficiently support the 
traction forces needed to effect a change in speed ratio. The outboard 
discs 20 and 22 impinge on the traction rollers, causing the traction 
rollers to rotate. As they rotate, the traction rollers impinge on and 
rotate the inboard disc element 26 in a direction opposite to that of the 
rotating outboard discs. 
In addition to first sun gear 30, the first epicyclic gearset 12 includes a 
second sun gear 40; a ring gear 42; a long planet pinion 44 in continuous 
meshing engagement with sun gears 30 and 40; a second set of planet 
pinions 46 in continuous meshing engagement with ring gear 42 and planet 
pinion 44; and a carrier 24 driveably connected to input shaft 10 and 
output disc set 22 for rotatably supporting the planet pinion sets 44 and 
46. 
The second compound planetary gearset 14 includes a sun gear 48; ring gear 
50 surrounding the sun gear 48; a set of planet pinions 52 continually 
meshing with sun gear 48; a second set of planet pinions 54 in continuous 
meshing engagement with ring gear 50 and planet pinion set 52; and a 
carrier 56 driveably connected to output shaft 18 for rotatably supporting 
the planet pinions of sets 52 and 54. Ring gear is continually fixed to 
the transmission housing, and carrier 56 is fixed to output shaft 18. 
The operation of gearsets 12 and 14 is controlled by a first clutch 60, 
adapted to alternately driveably connect carrier 56 and ring gear 42 when 
the clutch is engaged and to release that connection by disengaging clutch 
60. A second clutch 62 is adapted alternately to driveably connect sun 
gear 40 and sun gear 48 by engaging the clutch and to release that 
connection when the clutch is disengaged. 
Throughout this description, reference is made to preferred gear and pinion 
sizes and to preferred overdrive and underdrive speed ratios produced by 
variator 16. In a preferred embodiment of this invention, sun gears 30, 40 
have 81 teeth, ring gear 42 has 199 teeth, and planet pinions 46, 44 each 
have 56 teeth. With regard to the components of gearset 14 in the 
preferred application, sun gear 48 has 47 teeth, ring gear 50 has 105 
teeth, and each of the planet pinions 52, 54 has 26 teeth. 
The transmission is capable of operating in a geared neutral condition with 
clutch 60 engaged and clutch 62 disengaged. In order to produce the geared 
neutral condition for the preferred embodiment, the roller sets 32, 34 of 
variator 16 are arranged angularly within the toroidal cavities 36, 38 
such that the speed of output discs 26 is approximately -1.457 times the 
speed of input shaft 10. This corresponds to a variator speed ratio of 
1.457. The variator speed ratio is defined as the absolute value of the 
ratio of the speed of the output discs 26 to the speed of the input shaft 
10. Sun gear 30 is driven at the speed of discs 26, carrier 24 is driven 
directly from input discs 20, 22 at the same speed as that of input shaft 
10 and the output is taken at ring gear 42. With the transmission so 
disposed, the speed of ring gear 42, carrier 56 and output shaft 18 is 
substantially zero. 
The vehicle accelerates or drives away in the forward direction from the 
geared neutral condition by changing the drive ratio of variator 16 to the 
low mode forward ratio. A low mode forward range, having an overall speed 
ratio of about 0.40, is produced by setting the angular position of 
rollers 32, 34 such that they contact variator discs 26 at a radially 
outer position and contact variator input discs 20, 22 at radially inner 
position, the opposite configuration from that showing in FIG. 1. In low 
mode forward, discs 26 and sun gear 30 are driven at approximately -0.47 
times the speed of input shaft 10, and carrier 24 is driven at the speed 
of shaft 10. With clutch 60 engaged, ring gear 42 drives carrier 56 and 
output shaft 18 through clutch 60 at approximately 0.402 times the speed 
of shaft 10. 
The vehicle accelerates from stop while the transmission continues to 
operate in the low mode forward condition, i.e., with clutch 60 engaged 
and clutch 62 disengaged. A synchronous point occurs when the rotational 
speeds of the components connected by clutch 62, sun gears 40 and 48, are 
substantially equal, and the speed of the components connected by clutch 
60, carrier 56 and ring gear 42, are substantially equal. At the 
synchronous point, clutch 62 is engaged and clutch 60 is disengaged, 
thereby placing the transmission in the high mode low condition. 
During a transition from the low mode forward mode to the synchronous 
point, the angular inclination of rollers 32, 34 is maintained 
substantially constant, and the output variator discs 26 are driven at 
approximately -0.470 times the speed of input shaft 10. 
The transmission operates in the forward high mode high condition with 
clutch 62 engaged and clutch 60 disengaged. In the high mode high 
condition, the angular inclination of rollers 32, 34 is changed gradually 
from the underdrive position described above with reference to the low 
mode forward and high mode low conditions to the overdrive position shown 
in FIG. 1 where the rollers 32, 34 contact the input discs 20, 22 at 
radially outer positions and contact the output variator discs 26 at 
radially inner positions. As the variator changes in this way from the 
underdrive to the overdrive positions, carrier 24 is driven at the speed 
of shaft 10 through variator input discs 20, 22 and sun gear 30 is driven 
directly from variator output discs 26 in a preferable range from 
approximately -0.470 to -2.120 times the speed of input shaft 10. The 
speed and torque of sun gear 30 is transferred through pinion set 44 to 
sun gear 40, which drives sun gear 48, due to the engagement of clutch 62, 
at the same speed as that of sun gears 30, 40. Ring gear 50 continually 
provides a torque reaction due to its engagement with the transmission 
housing. With variator 16 at the maximum overdrive position, the 
transmission output shaft 18 is driven by carrier 56 of gearset 14 at 
approximately 1.718 times the speed of the input shaft. 
The transmission of FIG. 1 can operate in a low mode reverse condition upon 
disengaging clutch 62, engaging clutch 60, and adjusting the variator to 
operate in the overdrive condition, i.e., with the rollers 32, 34 
generally in the position shown in FIG. 1. With the variator so disposed, 
sun gear 30 is driven at approximately -2.12 times the speed of input 
shaft 10, ring gear 50 provides the torque reaction, and the output is 
taken at ring gear 42, which drives carrier 56 and output shaft 18 at 
approximately -0.270 times the speed of input shaft 10, in the preferred 
embodiment. 
Although the form of the invention shown and described here constitutes the 
preferred embodiment of the invention, it is not intended to illustrate 
all possible forms of the invention. Words used here are words of 
description rather than of limitation. Various changes in the form of the 
invention may be made without departing from the spirit and scope of the 
invention as disclosed.