Continuously variable transmission and control

A variable diameter pulley and belt drive has a torque and pitch radius sensitive squeeze control. The variable diameter pulleys are interconnected by a flexible belt or chain. The input pulley is connected to a power source through a pair of meshing gears and a floating link. A hydraulic control mechanism establishes the desired diameter ratio of the pulleys while the floating link is responsive to the torque transmitted to adjust the center distance between the pulleys and establish the squeeze force on the belt.

BACKGROUND OF THE INVENTION 
This invention relates to control mechanisms for variable ratio belt drives 
and more particularly to controls for such drives wherein both the belt 
squeeze force and the pulley center distance is controlled. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide an improved control mechanism 
for a variable ratio pulley drive wherein the center distance between the 
pulleys is adjusted for each ratio and wherein the squeeze force on the 
belt is proportional to the torque transmitted. 
It is another object of this invention to provide an improved control 
mechanism for a variable ratio belt and pulley drive wherein one of the 
pulley members is mounted on a pivotal axis and connected through gearing 
to a torque transmitting shaft such that the center distance between the 
pulleys is adjusted and the pulley squeeze force is proportional to the 
torque transmitted. 
These and other objects and advantages of the present invention will be 
more apparent from the following description and drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, wherein like characters represent the same or 
corresponding parts throughout the several views, there is seen in FIG. 1 
a pair of variable diameter pulleys 10 and 12 which are connected by a 
flexible torque transmitting member such as a belt or chain 14. 
As is well-known in variable diameter pulley drives, the drive ratio from 
one pulley to the other is varied by moving the sheaves of the pulleys. 
For example, in FIG. 3, the pulley 10 has a sheave 16 and a sheave 18. The 
sheave 16 is fixed for rotation on a shaft 20. The sheave 18 is axially 
movable on the shaft 20 while being rotatable therewith. As the sheave 18 
moves axially away from the sheave 16, the belt 14 will operate at a 
smaller diameter on the pulley 10. 
As is well-known, when the operating diameter of pulley 10 is decreased, 
the diameter of pulley 12 is correspondingly increased. The pulley 12 is 
similar in construction to pulley 10 and is operatively connected with a 
shaft 22. The shaft 22 is the output shaft of the pulley drive. The shaft 
20 is rotatably supported in a pair of floating links 24 and 26 and has 
rotatably secured therewith a gear 28. The gear 28 meshes with a gear 30. 
The gear 30 is connected to shaft 32 which is rotatably supported in a 
transmission housing 34. The links 24 and 26 are rotatably or pivotally 
supported on the shaft 32. 
As best seen in FIGS. 1 and 2, the link 26 is operatively connected with 
the transmission housing 34 by a spring member 36. The link 24 is 
similarly connected to the transmission housing 34 by a spring, not shown. 
The springs 36 connecting the links 24 and 26 urge the links 24 and 26 to 
pivot counterclockwise, as seen in FIGS. 1 and 2, about the axis of shaft 
32. The pivoting of links 24 and 26 about the shaft 32 affects the center 
distance D between the pulleys 10 and 12. The center distance D is the 
distance between the axes of shafts 20 and 22. 
The spring 36 establishes a minimum tension force in the belt 14. This 
tension force establishes the minimum squeeze force between the pulleys 10 
and 12 and the belt 14. The spring 36 also establishes the minimum center 
distance between the pulleys 10 and 12. 
The shaft 32 is adapted to be connected to a prime mover such as an 
internal combustion engine or an electric motor. Therefore, the shaft 32 
has imposed thereon the input torque for the variable belt drive. The 
input torque at shaft 32 is transmitted through gears 30 and 28 to the 
shaft 20, and therefore to the pulley 10. This input torque is delivered 
in the direction of Arrow T. The input torque is balanced by a reaction 
force F imposed on the links 26 and 24. As seen in FIG. 2, this reaction 
force F urges the links 24 and 26 to pivot counterclockwise about the 
shaft 32 thereby increasing the tension force in belt 14 and the squeeze 
forces established between the pulleys 10 and 12 and the belt 14. As the 
input torque increases, the squeeze force on the belt will also increase. 
The pulleys 10 and 14 have their respective. movable sheaves, such as 18, 
controlled by a conventional hydraulic piston and cylinder arrangement 38. 
As seen in FIG. 3, the movable sheave 18 is operatively connected to a 
control lever 40 which in turn operates on a control valve 42. One end 44 
of control lever 44 abuts the movable sheave 18 while the other end 46 of 
the lever 40 is subject to operator controls B. The pulley 12 has a 
similar control arrangement. 
There is shown in FIG. 4 a schematic representation of a hydraulic control 
system which can be utilized to control the operating diameters of the 
pulleys. In FIG. 4 there is seen a pair of variable diameter pulleys 10' 
and 12' which are interconnected by a flexible drive member, such as belt 
14'. The pulley 10' has a conventional hydraulic control member 48, and 
the pulley 12' has a conventional hydraulic control member 50. The member 
48 is in fluid communication through a passage 52 to a hydraulic control 
valve 54. The hydraulic control valve 54 is operatively connected to a 
control lever 40'. 
The hydraulic control member 50 is in fluid communication via a passage 56 
with a hydraulic control valve 58. The hydraulic control valve 58 is 
operatively connected with a control lever 60 which in turn is operatively 
associated with the movable sheave component of the pulley 12'. The 
control lever 40' and 60 are preferably interconnected through a 
conventional linkage mechanism 62. The operator only has one control 
element to manipulate in order to establish the desired operating diameter 
of both pulleys. 
Both of the control valves 54 and 58 are essentially three-position 
four-way valves having a closed center position. The valves are shown in 
the closed center position, that is, the passages 52 and 56 are 
disconnected from either pressure or exhaust when the respective valves 
are in the center position shown. 
The valve 54 has an input port 64 and a return port 66. The valve 58 has an 
input port 68 and a return port 70. Both return ports 66 and 70 are 
connected to a hydraulic reservoir 72, while the input ports 64 and 68 are 
connected via a passage 74 with a conventional hydraulic pump 76. In the 
center position shown, the pump 76 communicates with the return passage 66 
to reduce the hydraulic losses in the system. 
If the control levers 40' and 60 are moved by the operator input to the 
left (under the influence of controls B) as seen in FIG. 3 and 4, the 
valve 54 will connect the control piston to pressure while the control 
piston 50 is connected to exhaust. Under this condition, the sheaves of 
pulley 10' will be moved closer together thereby increasing the operating 
diameter for the belt 14 while the sheaves of pulley 12' are allowed to 
separate thereby decreasing the operating diameter of the belt 14' on the 
pulley 12'. When this occurs, the center distance D between the pulleys 
10' and 12' has to be adjusted accordingly. This adjustment takes place 
automatically through the pivoting of the links 24 and 26 about the shaft 
32. Thus, the new operating condition or drive ratio within the pulley 
system is accommodated. With the use of an adjustable center distance 
mechanism, the operating diameters for the pulleys 10 and 12 or 10' and 
12' can be more accurately controlled. Movement of the control levers 40' 
and 60 to the right has the opposite effect on the operating diameters of 
the pulleys 10' and 12'. 
In prior art arrangements, the variable ratio pulley drives accommodate the 
apparent change in belt length by establishing one pulley as the command 
pulley and the other as a slave pulley. In other words, the operator 
establishes the operating diameter of the master pulley and a spring, 
mechanical cam or fixed pressure hydraulic system generally controls the 
positioning of the slave pulley. 
This makes it very difficult to provide a simple operator lever control 
which will establish accurate diameter relationships between the pulleys 
without providing sophisticated speed signals to ensure that the desired 
drive ratio is established. With the present invention, the control levers 
40' and 60 can be designed with an appropriate link system such that the 
hydraulic control valves 54 and 58 will establish the desired diameter 
ratio while the links 24 and 26 will establish the correct center distance 
D and in response to the torque T the links 24 and 26 will also operate to 
establish the proper squeeze force between the belt 14 and the pulleys 10 
and 12. 
This system provides a squeeze force having a magnitude proportional to the 
torque and proportional to the pitch radius on the output pulley. The 
reaction force created by the input torque T creates the tension in the 
drive belt 14. This tension is balanced by the squeeze force of the 
pulleys and therefore the squeeze force is also proportional to the 
transmitted torque. 
As seen in FIG. 2, the links 24 and 26 operate at an angle A relative to a 
plane connecting the centers of the pulleys 20 and 22 and represented by 
the line 78. The component of the reaction force F which establishes the 
tension in belt 14 is modified by the sine of the angle A such that the 
position of the pulleys is controlled in a manner such that the change in 
angle A is inversely proportional to the pitch radius. 
From the foregoing discussion, it should be apparent that the present 
system provides a control wherein the torque sensitivity is proportional 
to the reaction force and the pitch radius sensitivity is controlled by 
the position of the two pulleys. 
Obviously, many modifications and variations of the present invention are 
possible in light of the above teaching. It is therefore to be understood, 
that within the scope of the appended claims, the invention may be 
practiced otherwise than as specifically described.