Tech Briefs
CVT for MGF

Positioning of MGF Steptronic manual gear selection buttons.

Continuously variable transmission (CVT) and a sports car might seem an unlikely combination but the Rover Group is offering the system on its 1.8-L MGF Steptronic. The company describes it as a "major evolution" of the system with electro-mechanical control and stepped gear shifting via steering wheel-mounted buttons. Rover worked with transmission specialist ZFST of Belgium to develop the CVT. It can operate in the normal stepless mode or with six, pre-determined steps (fixed ratios), similar to a regular six-speed manual gearbox. There is a further choice or "normal" or "sport" modes.

If the selector is placed in the "D" position, the system operates as an automatic but with revs kept below 4500 rpm at road speeds below 113 km/h (70 mph); above that speed the engine operates up to 5500 rpm. If the selector lever is pushed to the left, "Sport CVT" is selected with 5500 rpm available at any road speed. To use "manual" mode, the driver can operate either one of two steering wheel switches or the selector itself. Up to 6000 rpm can be achieved. Upshift and downshift functions are available with both steering wheel buttons. Any downshift that would over-rev the system is inhibited and failure to manually upshift at the rev limit will result in an automatic upshift.

Rover says that normally, two dedicated electronic control units (ECUs) have been used to manage the engine and automatic transmission, but which "talked" to each other. For the MGF Steptronic, an MEMS 3-engine management ECU has been configured and programmed to handle both the engine and transmission so that only a simplified electronic interface unit is required for the transmission. Rover claims that integrating the powertrain electronics in this way gives a simpler, more reliable system, avoiding duplication of sensor inputs and facilitating the development of optimum derivability characteristics.