Light throttle acceleration

Light throttle acceleration

The driver is at a fixed point in overdrive. Assuming the primary belt radius would be at a maximum, the secondary at a minimum. Light acceleration, by using the throttle pedal, will activate the ratio control motor acting upon the primary valve causing the primary pressure to drop. The transmission will down-shift slightly, which will result in higher pitot pressure and balance within the primary valve restored. The transmission up-shifts at the new constant engine rpm.

Kick-down

Fully depressing the throttle pedal will move the primary valve against its stop and the primary pressure will rapidly drop. The transmission shifts down completely. The sensor shoe on the primary pulley creates a high spring force onto the secondary valve, therefore, the secondary pressure is kept at a sufficient high level to avoid belt slip. The balance can only be restored with a higher engine speed.

Emergency stop

During design care has to be taken so that the vehicle, after an emergency stop, can take off again immediately. During an emergency stop situation the transmission has to down-shift very quickly. The plunger on the secondary pulley must be filled very quickly to push the secondary pulley halves towards each other and to clamp the belt. The most critical situation for the pump is an emergency stop from an overdrive condition. The down-shift is then maximum, for a minimum engine speed. The required pump flow increases with the amount of braking.

The speed of the engine can only be held constant when the transmission has the time to downshift. This can cause some problems when braking on a slippery surface, for example, on ice, as the wheels will lock very fast. The clamping force and the locked clutches make the engine speed decrease very fast, to a speed at which the clutches disengages (about 800 rpm), bringing the pulleys to a standstill. In the primary valve the primary pressure is bleeding as there is no pitot pressure. Due to secondary pressure, the transmission down-shifts, although the shift time will be greater as the pulleys are standing still, and the time to stop the vehicle will also be greater. This enables the transmission to be in a low ratio when the vehicle comes to a halt.

Reverse running

With the manual valve in reverse, the clutch pressure will be sent to the reverse clutches via the reverse inhibitor valve. Once the vehicle is running in reverse, the clutches will stay under pressure because the primary pitot tube opening is in opposite direction to the oil flow within the pitot chamber, and therefore can sense no pressure. This keeps the reverse inhibitor valve in balance in the open position. Consequently the primary pressure will be bleeding and the transmission will stay in a low ratio. In contrast to the earlier rubber drive belt CVT, this transmission does not up-shift in reverse.