Valve Gear

Valve Gear

Valve gear
Valvetronic consists of the fully variable valve lift timing and the variable camshaft timing (double VANOS), which enables a free choice of closing time for the intake valve. Valve lift timing only takes place on the intake side; camshaft timing takes placed on the intake and exhaust side. Throttle-free load control is only possible if the following variables can be controlled:
- Valve lift of the intake valve
- Camshaft adjustment of the intake and exhaust camshafts

Result: The opening duration of the intake valve is freely definable.

Brief description of components
The following components are described for the valve gear:

Eccentric shaft sensor
The eccentric shaft sensor works according to the magneto-resistance principle. Here, a ferromagnetic conductor changes its resistance due to a magnetic field. The sensor is designed as redundant. Both sensor elements are fitted in one housing.







One sensor element assumes the task of guidance and the second sensor element monitors. The sensor elements operate in opposite directions. If the eccentric shaft is adjusted from minimum lift to maximum lift, the guide sensor delivers rising angle values and the reference sensor delivers falling angle values. The sensor elements are supplied with 5 Volts and earth by the DME. All lines to the sensor are separately shielded.

Valvetronic actuator
The air flow to the engine during throttle-free operation is adjusted by the variable valve lift and not the throttle valve. Valvetronic is driven by an electric motor. The Valvetronic actuator is mounted on the cylinder head. The Valvetronic actuator uses a worm gear to drive the eccentric shaft in the cylinder head oil chamber. The eccentric shaft sensor provides the DME control unit with an indication of the position of the eccentric shaft.







The Valvetronic actuator motor is a DC motor with 12 Volts. The actuator motor is activated with a frequency of 15.6 kHz. The direction of rotation is reversed by the DME changing the polarity of the activation. The Valvetronic actuator motor is connected by 2 cables to the DME. The maximum current consumption can be up to 40 Amperes.
The Valvetronic relay ensures the power supply for the Valvetronic actuator motor. The Valvetronic relay is supplied with vehicle voltage with terminal 87 and is activated by the DME with earth.
The Valvetronic relay is located in the relay carrier in the engine compartment.

Intake camshaft sensor and exhaust camshaft sensor
The valve gear is equipped with variable camshaft control (double VANOS) for the inlet and exhaust camshaft. Both camshaft sensors record camshaft adjustment. To this end, a camshaft sensor gear is fixed to the camshaft. The camshaft sensor works according to the Hall effect. Power is supplied to the sensor by the DME with 5 Volts and earth. The sensor delivers a digital signal via the signal cable to the DME.







VANOS solenoid valve intake and VANOS solenoid valve exhaust
The variable camshaft control serves to enhance the torque in the lower and middle engine speed range. The VANOS solenoid valve activates a VANOS adjustment unit on the inlet side. The VANOS solenoid valves are activated by the DME control unit.







System functions
The following system functions are described for the valve gear:

Variable valve gear: Valvetronic
Valvetronic was developed to reduce fuel consumption. The control device for Valvetronic is now integrated into the DME control unit. With the Valvetronic active, the amount of air fed to the engine is not set by the throttle-valve actuator but by the variable valve lift of the intake valves.
An electrically adjustable eccentric shaft changes the effect of the camshaft on the roller cam followers 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 on the cylinder head. The Valvetronic actuator uses a worm gear to drive the eccentric shaft in the cylinder head oil chamber.

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 two signals must not deviate from each other. 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 determine when a valve is sticking. 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.

Variable camshaft timing control VANOS
The variable camshaft improves the torque in the lower and middle engine speed range. A greater valve overlap results in lower amounts of residual gas at idle speed. The internal exhaust-gas recirculation in the part-load range reduces the nitrogen oxides.

The following are also achieved:
- faster heating of the catalytic converters
- lower pollutant emissions after a cold start
- reduction in the fuel consumption

A controlled VANOS adjustment unit is fitted at both intake and exhaust camshafts. A VANOS solenoid valve activates the VANOS adjustment unit. The required positions of the inlet and exhaust camshafts are calculated from the engine speed and the load signal (depending on the intake-air temperature and engine temperature). The DME control unit activates the VANOS adjustment unit accordingly.

The control of the intake and exhaust camshaft is variable within their maximum adjustment range. Once the correct camshaft position has been reached, the VANOS solenoid valves ensure that the oil volume in the servo control cylinders in both chambers remains constant. This keeps the camshafts in this position.

To perform the adjustment, the variable camshaft control requires an information signal on the current position of the camshaft. Camshaft sensors on the intake and exhaust end record the position of the camshafts. On engine start, the inlet camshaft is in the end position ( late ). When the engine is started, the exhaust camshaft is pretensioned by a spring and held in the "advanced" position.

No liability can be accepted for printing or other errors. Subject to changes of a technical nature