10 Mechanical CVTs: Launch clutch Transmission Final drive Transmitting Engine torque

with slip Reducing engine torque

fluctuation Reducing engine torque

peaks

Amplifying engine torque over a larger speed coverage

Reversing engine torque direction

Controlling of transmission ratio

Connect to PTO

Distribute drive torque between the wheels

Transmit drive torque to moving wheels

Transmit brake torque at the wheels

10.1 Used types

10.1.1 Pulley: (Audi Multitronic,- Power transmitted frictionally through chain running between two axially adjustable

taper discs- Disc adjustment diameter variation ratio variation

10.1.2 Cone ring:

10.1.3 Toroidal:

10.2 Geometry

10.3 Design- Tensional link chain: more efficient (less power to adapt the chain to ratio radii)- Thrust link chain: short pitch of chain elements needs more lost work. Low nois

generation-

10.4 Kinematics- Speed ratio: ispeed = np / ns

- Geometrical ratio: igeom = Rs/Rp

- Torque ratio: itorque = Ts/Tp

- Ratio coverage: iLOW / iOD

- Variogram:

10.5 ForcesCoulomb`s law of friction: Belt pulley interaction: push force build-up and release:

- Factor influencing the clamping force:o Engine torqueo Torque converter multiplication and clutch controlso Gear ratioo The lowest occurring friction coefficiento The torque transmitted by the wheels

- Belt pulley interaction and clamping force equation:

- Required minimum clamping force:

10.6 Efficiency- Typical efficiency vs ratio:

- Effect of overclamping on efficiency (66 rad/sec; Overdrive; Fsec=7.8 kN):

- Efficiency improvement:Reference CVT efficiency Reference CVT loss at 50 Nm in OD:

Pump loss: Pump displacement depends on:- CVT rated torque- Leakages- Hydraulics design- Auxiliary functionPump power loss ≈ all losses in mechanical transmission

Torque loss:- Overclamping needed to prevent slip

(safety factor Sf)- Ekĺastic deformations of pulley/shafts- Tilting play- Internal friction in V-belt- Minimum clamping force restricted by :

o Hydraulic limitations ~> 6 baro Low control band width at low

pressure due to oil aeration

Slip loss:

- Very small under normal use (<1%), especially at partial load

- Depends strongly on torque- Depends on ratio

-

10.7 Dynamics of CVT driveline.

Simple model reduction Fixed gear drive train