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► Vehicles with continuously variable transmissions (CVTs) are becoming more prevalent.
► A system that uses two or more power sources is a hybrid drive system.
► A hybrid vehicle may have the following functions: idle stop, torque smoothing, regenerative braking,
torque assist, and electric-only propulsion.
► Idle stop refers to engine shutoff when the driver stops (but does not turn off) the vehicle.
► A hybrid vehicle that uses an electric motor to smooth out internal combustion engine (ICE) power
pulses is using torque smoothing.
► Most hybrid vehicles use braking power to generate electricity to charge the battery (regenerative
braking).
► Torque assist refers to using torque to help propel the vehicle when additional torque is needed.
► Common hybrid vehicle systems include belt alternator starter (BAS), Honda integrated motor assist
(IMA), two-mode hybrid, Toyota and Lexus hybrids, and Ford hybrids.
► A BAS system uses a 42-volt battery and relies on the belt drive to help quickly crank the vehicle over
following an idle stop.
► The IMA system replaces the conventional flywheel with a thin electric motor to supplement the
engine’s torque during acceleration.
► The two-mode hybrid system uses approximately 300 volts to power the two generators inside the
transmission case.
► The Toyota, Lexus, and Ford hybrid systems are series-parallel systems because the ICE and the electric
generator can propel the vehicle, either individually or together.
► In Toyota, Lexus, and Ford hybrid systems, the PCM monitors battery voltage; if voltage is low, the ICE
is engaged.
► Ford hybrid systems have two electric motors attached through a set of transfer gears.
► A CVT is able to change gear ratios to suit vehicle speed and load conditions for optimum fuel economy
and performance.
► Types of CVTs are the electronic continuously variable transmission (ECVT), variable-diameter pulley
(VDP) CVT, and toroidal (or roller-based) CVT.
► The most common CVT in vehicles today is the VDP.
► A VDP has two pulleys (input and output) with movable drive faces that can be adjusted to change the
pulleys’ effective diameter.
► The output pulley of a VDP utilizes large springs to maintain belt tension.
► Manufacturers recommend replacing CVTs as a whole, rather than repairing internal components.
► Change CVT fluid and filters on a regular basis to maintain transmission functionality.
► Toroidal CVTs use curved discs (input and output) with a set of variable-angle rollers instead of pulleys.
► Toroidal CVTs are costly to manufacture, and production is limited.
► In some VDP CVTs, multidisc clutch packs and planetary gear sets are designed to allow transmission
operation in reverse and to create a low gear ratio.