CVT- Continuously Variable Transmission

CVT control

(a personal approach*)

The CVT makes possible to freely match any engine speedto any vehicle speed.
This is advantageous because the engine could operate permanently in it'soptimum engine speeds (and throttlepositions).
Therefore, it could maximize power output relative to fuel consumption (or reduce harmful exhaust emissions).

Why is control needed?

It is needed to regulate CVT ratio and throttle position, while ensuring maximum efficiency.
Therefore, it reads three variables: gas pedal position, engine speed and vehiclespeed (which depends on the road slope andexternal loads).

How to maximize engine efficiency:

In order to minimize fuel consumption, the engine must operatealong the optimum efficiencycurve in the engine performance map:

How to select the optimum throttleposition:

With the previous experimental information we can establish the optimum relationshipbetween the throttle position and the enginespeed:

What is the gas pedal role inthis control?

It will express the driver's desired vehicle speed. A greater difference to the actual vehicle speed will request a greater acceleration, thus greater powerdemand. A P.I.D. control will calculate this powerdemand:

Howis the power demand used?

It will be used to control the engine, indirectly. Firstof all, the engine must be tested experimentally to obtain it's power curve, whileusing optimum throttle positions. This diagram willbe used to convert any value of power demand intothe corresponding required engine speed:

Selecting proper CVT ratio will force theengine into the required enginespeed:

The instantaneous vehicle speed is measured. Andconsidering the required engine speed the controlwill calculate the necessary CVT ratio (~vs/res).

Thus:

The resulting engine speed will generate thegreater (or smaller) power demand,consequently the vehicle speed will increase (ordecrease), as requested by the driver.

Complete CVT control Diagram:

* Some remarks:
- This is a first personal approach and doesn't result from any scientific research;
- This approach may be largely improved / corrected;
- The control's dynamic response wasn't considered.
- Neutral mode isn't considered in this section, neither reverse gear;
- Engine breaking is not considered neither sport-mode;
- This web-page is under development, thus constructive commentsare welcome to improve this scratch;
- However you may find useful the researchinformation in the following web links: