System Components: VANOS: Notes
Performance, torque, idle characteristics and exhaust emissions reduction are improved by variable camshaft timing (VANOS). The S62 engine uses a double VANOS system for valve timing on both the intake and exhaust camshafts.
The S62 uses a high pressure (100 Bar) control system that ensures quick and reliable adjustments of the camshafts to meet the high performance requirements of the M Engines. The VANOS units are mounted directly on the front of the cylinder heads.
Each VANOS unit contains:
- High pressure radial oil pump (driven by the intake Camshaft)
- Two inlet solenoids
- Two outlet solenoids
- Two adjustment pistons
- Two hydraulically actuated adjustment shafts
Two solenoids are required for each adjusting piston circuit, one for advancing and one for retarding the camshaft timing. The solenoids are controlled by the ECM.
The adjustment shafts contain two sets of splines that engage with:
| 1. | Camshaft Sleeves (Straight Splines) |
| 2. | Chain Driven Sprocket (Helical Splines) |
The adjustment shafts have a total stroke of 25 mm.
The camshaft sleeves are bolted to the end of the camshafts and engage with the straight spline of the adjustment shaft shown above.
The chain driven sprocket and spacer sleeve assembly (one assembly per camshaft). The sprocket engages with the helical splines of the adjustment shaft shown above.
The intake camshaft sprocket assembly has two drive "lugs" that must be aligned with the radial piston oil pump during installation.
VANOS mechanical operation is dependent on oil pressure applied to position the control pistons. The double VANOS camshafts are infinitely adjustable within the mechanical travel limits of the drive gears.
When oil pressure is applied to the control piston, the piston moves causing the splined adjustment shaft to move. The straight splines slide within the camshaft sleeve. The helical splines rotate the camshaft drive sprocket changing the position in relation to the camshaft position which advances/retards the camshaft timing.
| The total adjustment range of the camshafts is 60° (as referenced to the crankshaft). |
The "default" mechanical stop position without VANOS influence is:
| Intake Camshaft | Retarded |
| Exhaust Camshaft | Advance |
Oil is supplied from the main gallery through the front of cylinder head (arrow) to the inlet pressure reducing valve.
Pressure Reducing Valve: The pressure reducing valve supplies oil to the radial piston high pressure oil pump. It is located between the cylinder head and the VANOS unit.
The valve ensures the oil pressure supply to the VANOS pump is 0.5 Bar regardless of the varying pressure from the main oil pressure gallery. The pressure reducing valve is pressed into the VANOS unit and secured by an "o-ring".
100 Bar Pressure Regulating Valve: The 100 Bar pressure regulating valve regulates the pressure produced by the radial piston high pressure oil pumps.
The 100 Bar pressure regulating valve is mounted in the center of the cylinder block "V" on the thermostat housing.
The valve ensures that the oil pressure for VANOS operation is maintained at 100 bar. One pressure regulator is used for both cylinder banks.
VANOS Accumulator: The VANOS accumulator ensures that there is a sufficient volume of oil under pressure to adjust the camshafts under all engine operating conditions.
The accumulator is Nitrogen charged and is located on the front of the 5-8 bank of the engine. It is connected to the VANOS oil pressure circuit by a high pressure line.
VANOS Accumulator with Electrical Shutoff Valve:
The VANOS accumulator with an electrical shutoff valve was phased into production on 2001 MY S62 engines.
This production change addresses the customer complaint of a rattling noise (from the VANOS units) in the first few seconds after starting the engine. The VANOS hydraulics can cause rattling noises after the engine start due to the varying torque of the camshaft before sufficient VANOS oil pressure has built up.
When the engine is stopped, the oil runs out of the high-pressure chamber in the adjustment cylinder. This can cause the VANOS adjustment piston to move freely against the housing during startup.
The shutoff valve prevents this because it will close (without electrical power) to reserve a volume of oil under pressure in the accumulator when the ignition is switched off. Upon the next engine start, the valve will be opened by the ECM allowing the stored accumulator release to "prime" the VANOS assemblies with pressurized oil.
This noise has no effect on the engine's power output or durability.
The affected vehicles are:
- E39 (M5), E52 (Z8)