"Valvetronic" variable valve gear

Valvetronic was developed to reduce fuel consumption.

The quantity of air supplied to the engine when Valvetronic is active is adjusted by the variable valve lift on the inlet valve and not the throttle-valve actuator.

An electrically-adjustable eccentric shaft changes the action of the camshaft on the roller cam follower via an intermediate lever. The result of this is variable valve lift.

With Valvetronic, the throttle-valve actuator is activated for the following functions:

• Engine start (warm-up)
• Idle speed control
• Full load operation
• Emergency operation

In all other operating conditions, the throttle valve only remains open far enough to induce a slight low pressure.

This low pressure is required to ventilate the tank, for example.

The DME control unit calculates the associated setting of Valvetronic using the position of the accelerator pedal and other variables.

The DME control unit activates the Valvetronic actuator motor on the cylinder head via the Valvetronic control unit. The Valvetronic actuator uses a worm gear to drive the eccentric shaft in the cylinder head oil chamber.

The eccentric shaft sensor records the current position of the eccentric shaft. The eccentric shaft sensor is equipped with 2 angle sensors.

The Valvetronic control unit adjusts the current position of the eccentric shaft via the Valvetronic actuator until the nominal position is reached.

For safety reasons, 2 angle sensors are used with characteristic curves which have opposing directions. Both signals are digitally transmitted to the DME control unit. The DME control unit supplies 5 volts to both angle sensors.

Both signals from the eccentric shaft sensors are continuously monitored by the DME control unit.

Checks are made as to whether the signals are plausible in their own right and also in relation to one another. The signals may not differ. Where a short circuit or fault develops, the signals lie outside the measuring range.

The DME control unit continuously checks whether the actual position of the eccentric shaft corresponds with its nominal position. This makes it possible to detect any stiff movements in the mechanics.

In the event of a fault, the valves are opened as wide as possible. The air supply is controlled by the throttle valve.

If the actual position of the eccentric shaft cannot be detected, the valves are opened to the maximum extent without regulation (controlled emergency operation).

In order to achieve the correct valve opening, an adaptation must be made to balance all tolerances in the valve gear.

During this adaptation process, the mechanical stops on the eccentric shaft are adjusted.

The positions registered are subsequently saved. These positions are used as the basis for calculating the actual valve lift at any point during operation.

The adaptation process is automatic: Each time the engine is restarted, the position of the eccentric shaft is compared with the values registered. If following a repair, for example, a different position of the eccentric shaft is detected, the adaptation process is carried out. In addition, the adaptation can be initiated via the BMW diagnosis system.