Automatic transmission (Selecta): General information

GENERAL INFORMATION

The ECVT combines an electronically controlled magnetic clutch with a variable transmission (pulleys driven by a metal belt), to allow high performance coupled with low fuel consumption and ease of use.

The pressure of the hydraulic control system can modify the transmission from "high" to "low" and vice--versa in relation to the engine load and power demanded by the driver. To guarantee the best transmission efficiency and torque, the clutch is optimally controlled by a microcomputer.

The electromagnetic clutch has been exclusively designed for the ECVT. It is of the "closed at standstill" type, and contains magnetic powder. An electronic control unit continuously calculates the engine rpm, the vehicle speed and the throttle valve position.

The variable transmission is driven by a metal belt and a set of special pulleys. The effective diameter of the pulleys is gradually changed by the variation of hydraulic pressure. This ensures a continuous increase of the transmission ratio, from standstill up to the vehicle top speed. This is identical to that of a conventional gearbox, but has the advantage of always selecting the most efficient ratio for the operating conditions.

To assist servicing, the ECVT is equipped with a warning light that alerts the driver of transmission faults.

SPECIFICATIONS

Change of transmission velocity

The rate of change of velocity is not linear as in conventional manual gearboxes. It can be expressed as an area between the minimum and maximum transmission ratios allowed by the pulleys.

1. Manual transmission
2. Engine RPM
3. Vehicle speed
4. Low transmission ratio
5. 1st gear
6. 2nd gear
7. 3rd gear
8. 4th gear
9. 5th gear
10. High transmission ratio (Overdrive)

In the figure above, the MAX line indicates the ratio between the vehicle speed and the engine RPM under hard acceleration conditions. The MIN line indicates this ratio when the acceleration is light.

When travelling on a flat road at a constant velocity, the engine RPM stays on the MIN line, but can respond rapidly to accelerator pedal pressure by moving upwards into the enclosed CVT area.

Under maximum acceleration conditions, i.e. between start point (A) and end point (B), the engine RPM increases gradually as the vehicle speed increases.