A Continuously Variable Transmission having a Four Bar Linkage and Spherical Rotors Nogill Park Department of Mechanical Design Pusan National University
Continuously Variable Transmission velocity time Step variable transmission (SVT) Continuously variable transmission (CVT)
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
CVT used to automobile Types Variable pulley-belt Toroidal
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
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
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
Transmission performances Crank angle vs. follower angle CVT speed ratio vs. crank angle
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
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
CVT for bicycle (developing) Application CVT for bicycle (developing)
Application
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