New BMW engines: No throttle

BMW AG is ready with a significant step forward in the ongoing advance of engine design with its innovative, all-new Valvetronic concept.

The new Valvetronic design eliminates the throttle as we know it.

Valvetronic electronically — and instantaneously — varies both lift and the timing of inlet valves, so the engine breathing is controlled completely by the intake valves. It eliminates the usual “butterfly” throttle valve — and with it a major cause of pumping losses.

According to advance, pre-release information, the inlet valves are operated by a conventional camshaft, but initially via intermediate levers carried on and positioned by eccentrics on a secondary shaft. Each spring-tensioned lever bears against a roller cam follower that depresses the valve through a hydraulic lash adjuster (see accompanying schematic).

The secondary shaft is turned by a small stepper motor, providing a rotary indexing motion of the eccentric to raise or lower the lever. This alters the height of its specially profiled contact area wiped by the inlet cam — in turn varying the amount of valve lift on each induction stroke.

Motor operation is controlled electronically by additional microcircuitry in the engine management system, which has inputs from the usual sensors. One of these is a rheostat linked to the accelerator pedal, where driver foot pressure (registering power demand) determines the exact amount of inlet valve opening needed to induct the required fuel mixture.

Hence, Valvetronic delivers genuine drive-by-wire throttle action.

The management unit also regulates valve timing; the lift control signal can be advanced and retarded according to sensor inputs for engine speed, power demand and other parameters. Exhaust valves have fixed lift and timing, and are symmetrically pitched against the inlets at a 30-degree included angle. There are four valves per cylinder, with the sparkplug in a central position.

As an entirely new generation of 4-cyl. BMW engines, the Valvetronic will be manufactured at the German company's purpose-built Hams Hall plant near Birmingham, England, where construction on the greenfield site started just three years ago. Production starts this month and will hit 60,000 engines in the first year, with an annual rate of 400,000 units to follow.