1. A Continuously Variable Transmission
having a Four Bar Linkage and Spherical Rotors
Nogill Park
Department of Mechanical Design
Pusan National University

2. Continuously Variable Transmission
velocity
time
Step variable
transmission (SVT)
Continuously variable
transmission (CVT)

3. Motivation Poor torque capacity in CVT
Even though there are lots of excellent advantages in CVT,
poor torque capacity is a fatal weak point in applying to automotive vehicle

4. CVT used to automobile
Types
Variable pulley-belt
Toroidal

5. CVT used to automobile Torque capacity : 50 ~ 150 Nm
Limitations
Torque capacity : 50 ~ 150 Nm
Variator speed ratio : 0.5 ~ 2.0
Split power transmission
Multiple mode system is used to extend the overall speed ratio
The weight is increased
The number of clutches is increased
Torotrak front wheel drive CVT

6. Spherical rotor pairing
New type of CVT
Spherical rotor pairing
A pair of concave and convex spherical rotors is used to improve torque capacity
Four bar linkage
A four bar linkage is used to give precise movement of the counter rotor assembly and to extend the speed ratio range

7. New type of CVT
Continuously Variable Speed ratio from (-) to (+) including zero can be transmitted by the proper design of this new type of CVT without any additional device such as clutch

8. Transmission performances
Crank angle vs. follower angle
CVT speed ratio vs. crank angle

9. Improvement of torque capacity
Hertzian theory
Maximum comtact pressure
A pair of concave and convex spherical rotors is used to improve torque capacity
Maximum
Contact
Pressure
Summation of curvatures on the contact region

10. Improvement of torque capacity
Relative Evaluations
Note) * values under the worst condition
The case of radius ratio over 3.0 in toroidal type can’t be accepted in actual design

11. CVT for bicycle (developing)
Application
CVT for bicycle (developing)

12. Application

13. Summary
According to the selection of four bar linkage, various transmission performances with respect to the variator speed ration are studied
Crank-rocker mechanism
Double-rocker mechanism
Offset type
Coaxial type
Simplified relative evaluation on the maximum contact pressure are examined by comparing with disk-ball, ball-ball and toroidal contacts
For the bicycle usage, a split-powered system is studing