Valvetronic
Valvetronic
Over the entire speed and load range, the gasoline engine needs a combustible fuel-air mixture within the ideal ratio (Lambda = 1). The mixture quantity must be altered to vary the speed and output. This variation is effected by the throttle valve. The mixture, which falls within the narrow range of Lambda = 1, is formed outside the combustion chamber using the fuel injection system (external mixture formation).
The mixture control is influenced by the throttle valve and is not optimal in all the different load ranges. This is particularly true in the idle to part-load ranges, since the throttle valve is only opened slightly in these ranges. The consequences are less than optimal cylinder filling, torque and increased fuel consumption.
Technical measures were previously introduced; such as the optimization of air/fuel mixing, improved valve overlap, introduction of DISA and the steady improvement of mixture control all depend on the throttle valve. This is where the new completely unique Valvetronic design comes in.
The Valvetronic system simultaneously varies the valve opening time and the valve opening lift between 0.3 mm and 9.85 mm, according to engine speed and load. This means that the air/fuel mixture volume is controlled according to engine requirements. This type of mixture and volume control makes the typical throttle valve control unnecessary.
Physical considerations:
On engines with throttle valve control, the throttle valve is slightly open in the idling and part load ranges. This results in the formation of up to 500 mbar vacuum in the intake manifold, which prevents the engine from aspirating freely and in turn prevents optimum cylinder filling. The Valvetronic system with an open throttle valve largely counteracts this disadvantage. The air-mass flow to the intake valves is unrestricted. The full ambient pressure is available directly at the intake valves for cylinder filling and scavenging.
The Valvetronic system primarily controls the fill by adapting the valve opening time and the valve lift (short opening time/small valve lift = lower fill, and vice versa). During the valve opening phase the engine aspirates more freely via the intake valves even with small valve lifts vs. a throttle valve which is continuously blocked.
The slower cylinder filling from the intake valves with partial lift results in more turbulence in the combustion chamber, thus faster and better mixture control and more efficient combustion. At lower engine speeds this effect is intensified by opening the intake valves later, after top dead center (ATDC) using VANOS. This increases vacuum in the combustion chamber which accelerates filling and turbulence when the intake valves are opened.
In summary, the additional variability of the Valvetronic system results in optimization of cylinder filling and scavenging throughout the engine's entire operating range. This has a positive effect on output, torque and a decrease in fuel consumption and exhaust emissions.
Features:
- Valve lift adjustment
- VANOS for intake and outlet
- Variable intake manifold
- Mixture control and ignition control
- Other individual engine design measures
The main benefits of these features are:
- Improved cylinder tilling with air/fuel mixture
- Improved mixture control before the cylinder inlet
- Improved combustion procedure
This results in:
- Improved engine idling
- Improved engine torque
- Improved engine torque curve
- Fewer pollutant emissions
These benefits result in a clear improvement in performance and fuel consumption reduction (14%) for the driver.
Principle of Operation
The Valvetronic system is a combination of VANOS and valve lift adjustment. This combination of abilities allows the ECM to control when the intake valves are opened and closed, and also the opening lift. The intake air flow is set by adjusting the valve lift while the throttle valve is fully opened. This improves cylinder filling still further and reduces fuel consumption.
Each cylinder head in the N62 engine has a Valvetronic assembly. This Valvetronic assembly consists of a bridge support with eccentric shaft, intermediate levers with retaining springs, drag lever and the intake camshaft.
In addition the following components belong to the Valvetronic system:
- A Valvetronic motor for each cylinder head
- A Valvetronic control module
- A Valvetronic sensor for each cylinder head
The intake valve lift can be adjusted to anywhere between 0.3 mm and 9.85 mm.
The cylinder heads are precision manufactured together to ensure precise flow rate and uniform distribution. The valve gear components on the intake side are precisely matched together to the tightest limits.
The bridge support, lower eccentric shaft and inlet camshaft bearings are matched together in the cylinder head once it is assembled. If the bridge support or the lower bearings are damaged, the entire assembly must be replaced.
Valvetronic Motors
One Valvetronic motor is located on top of each cylinder head towards the inside of the engine "V". The motors are capable of traveling from minimum to maximum lift in 300 milli-seconds.
NOTE: The Valvetronic motor must first be removed in order to remove the cylinder head cover. The eccentric shaft must be in the minimum lift position and the motor must be wound out from the eccentric shaft. The worm gear could otherwise be damaged when separating the worm shaft and the worm wheel as the eccentric shaft springs back (due to the torque compensation spring).
If it is not possible to remove the motor, due to mechanical failure or sticking, the worm shaft can be moved using an Allen key to release the motor. A hole must be drilled in the rear plastic motor cover in order to access the motor shaft (worm shaft) using the Allen key. The motor can then no longer be used.
The Valvetronic motor worm gear rotates the eccentric shaft clockwise or counterclockwise at a very quick rate (1).
Due to the progressive "lobe" on the eccentric shaft, this rotation positions the intermediate lever (2) closer or further to the camshaft lobe
Eccentric Shafts
The eccentric shafts (one per cylinder head) are driven by the Valvetronic motors and are supported by four caged needle bearing assemblies for a smooth rotation.
To assist in maintaining the set positions and counter the valve train torque, a torque compensation spring is mounted on the end of the shaft for tension.
Magnets are fitted in the (removable) magnetic wheel at the end of the eccentric shaft. Together with the position sensor, the Valvetronic Control Module determines the exact shaft position. The eccentric shaft sensor is mounted through the cylinder head cover (one per cylinder head) at the back.
The magnetic wheel is secured to the shaft by a bolt and is indexed by a tab (arrow) to prevent incorrect installation.
Intermediate Lever and Roller Finger
The intermediate lever is positioned further (minimum valve opening) or closer (maximum valve opening) to the camshaft by the the progressive "lobe" on the eccentric shaft as it is rotated. This offers a variable ratio effect for valve actuation. The roller finger is used to actuate the intake valve.
The intermediate levers and roller fingers are matched (by classification) to ensure uniform valve lift.
NOTE: When disassembling/assembling the valvetrain, the intermediate levers and roller fingers must be returned to the original positions to prevent uneven cylinder charging which can result in rough idle and engine performance complaints.
Refer to the Repair Instructions for tolerance numbers!
Valve Lift
The Valvetronic motor worm gear rotates the eccentric shaft clockwise or counterclockwise at a very quick rate (1).
Due to the progressive "lobe" on the eccentric shaft, this rotation positions the intermediate lever (2) closer or further to the camshaft lobe.
As the camshaft is rotating (3), the cam lobe will pivot the intermediate lever (4) and the "heel" of the intermediate lever will depress the roller finger. A spring is located on each intermediate lever to maintain constant contact with the camshaft.
The roller finger is cushioned by the HVA and will open the intake valve (5).
The Valvetronic system varies the valve opening lift between 0.3 mm and 9.85 mm by rotating the eccentric shaft during engine operation to increase or decrease intake (flow) into the cylinder based on throttle request.
* This is an assembly that affects all of the intake valves (per cylinder head) to work in unison.