Variable Valve Timing Actuator: Description and Operation

DESCRIPTION OF VANOS FUNCTION (VARIABLE CAMSHAFT SPREAD) (550 B30):

GENERAL:

VANOS has the task of adjusting the spread of the intake camshaft in a variable manner from advance to retard and vice versa.

Opening and closing times for intake camshaft are adjusted between advance and retard in a parallel fashion.

The VANOS system is controlled by a dedicated VANOS control unit which is connected by CAN (Controller Area Network) to DME (Digital Engine Electronics) M3.3.

In contrast to M50 VANOS, this adjustment is an infinitely variable process. Governed maximum speed of 250 km/h is also controlled by VANOS adjustment unit. Development of this system achieved following objectives:

• Increase in torque in central speed range, increased performance in higher speed range by extended timing intervals

• Less unburnt residual gases at idle speed achieved with smaller spread, thereby improving idle characteristics.

• Catalytic converter reaches operating temperature faster after cold starts

• Reduction of fuel consumption

OPERATION:

VANOS housing contains VANOS compressed-oil pump, two solenoid valves and adjustment cylinder.

The VANOS control unit determines the optimum position for the intake camshaft from the throttle valve position signal and the engine speed. Continuous sensing of notched gears by sensors checks the relative angle setting between the intake camshaft (adjustable shaft) and exhaust camshaft (reference shaft), compares this with the specified nominal value and, when required, energizes the solenoid valves.

Adjustment of intake camshaft is performed by a control piston which is connected to an adjustable splined shaft.

The camshaft and sprocket wheel with integral actuator transmission are connected by splined shaft. When control piston is displaced, splined shaft in actuator transmission rotates camshaft relative to sprocket wheel.

Oil pressure required for adjustment is generated by VAN OS compressed-oil pump (radial piston pump).

Function of VANOS hydraulic system:

Engine oil pump carries oil to VANOS compressed-oil pump. This pump is driven by exhaust camshaft and develops continuous pressure of 100 bar

To develop pressure immediately when a solenoid valve opens, hydraulic system is equipped with an oil accumulator.

If a calculation in VANOS control unit calls for a retard adjustment to intake camshaft, solenoid valve I remains closed and solenoid valve 2 opens.

Note:

Valves are closed when de-energized.

This means that oil pressure is only developed on reverse side of piston. Control piston in adjustment cylinder moves in direction of travel and splined shaft rotates camshaft in its retard direction. When engine is started, initially both solenoid valves are closed. Immediately after start, VANOS control unit decides whether camshaft adjustment is actually necessary.

At idle speed, intake camshaft points towards its retard setting.

If a calculation in VANOS control unit shows that an adjustment in advance setting is required (e.g. full throttle from central speed range), solenoid valve I is opened and solenoid valve 2 remains closed. Control

piston in adjustment cylinder moves in direction of travel and splined shaft rotates intake camshaft in its advance direction.

Once calculated adjustment is terminated, both solenoid valves close and camshaft remains in setting it has reached.

Function of VANOS electrical system:

VANOS control unit uses sensor I (exhaust camshaft) and sensor 2 (intake camshaft) in conjunction with notched wheels to determine current setting of the camshaft. Required setting of intake camshaft is calculated from engine-speed signal and throttle-valve position signal.

This setting is stored in a characteristics file. If nominal and actual values deviate from one another, an appropriate correction is made.

VANOS control unit is capable of diagnosis work.

Using a BMW Service Tester or MoDIC, the non-volatile fault memory can be interrogated.