M62 TU Vanos
OVERVIEW
The variable intake valve timing system on the M62 TU continues to be identified as VANOS. This acronym comes from the German words; VAriable NOckenwellen Steuerung, which means Variable Camshaft Control.
The M62 TU VANOS system is a new variant providing stepless VANOS functionality on each intake camshaft. The system is continuously variable within its range of adjustment providing optimized camshaft positioning for all engine operating conditions.
While the engine is running, both intake camshafts are continuously adjusted to their optimum positions. This enhances engine performance and reduces tailpipe emissions.
Both camshafts are adjusted simultaneously within 20° (maximum) of the camshafts rotational axis.
This equates to a maximum span of 40° crankshaft rotation. The camshaft spread angles for both banks are as follows.
VANOS BENEFITS
The design of a camshaft for a non adjustable valve timing system is limited to the required overall performance of the engine.
- An intake camshaft with an advanced (early) profile will provide a higher performing power curve at a lower engine speed. But at idle speed the the advanced position will create a large area of intake/exhaust overlap that causes a rough, unstable idle.
- On the other hand, an intake camshaft with a retarded (late) profile will provide a very smooth, stable idle but will lack the cylinder filling dynamics needed for performance characteristics at mid range engine speeds.
The ability to adjust the valve timing improves the engine's power dynamics and reduces tailpipe emissions by optimizing the camshaft angle for all ranges of engine operation. VANOS provides the following benefits:
- Increased torque at lower to mid range engine speeds without a loss of power in the upper range engine speeds.
- Increased fuel economy due to optimized valve timing angles.
- Reduction of exhaust emissions due to optimized valve overlap.
- Smoother idle quality due to optimized valve overlap.
BASIC FUNCTION OF BMW VANOS SYSTEMS
Vanos In Default Position (Retarded):
Vanos In Full Activated Position (Advanced):
All BMW VANOS systems are operated through electric/hydraulic/mechanical control.
Electric Control: The engine control module is responsible for activating a VANOS solenoid valve based on DME program mapping. The activation parameters are influenced by the following input signals:
- Engine speed
- Load (intake air mass)
- Engine temperature
- Camshaft position
- Oil temperature (MS 42.0 only)
Depending on the specific VANOS system, the solenoid valve is one of two types:
- Basic black/white (on/off) solenoid valve. Found on M50 TU and M52 engines.
- Variable position solenoid valve. Found on the M52 TU and M62 TU engines.
Hydraulic Control: The position of the solenoid valve directs the hydraulic flow of engine oil. The controlled oil flow acts on the mechanical components of VANOS system to position the camshaft.
Mechanical Control: The mechanical components of all VANOS systems operate under the same principle. The controlled hydraulic engine oil flow is directed through advance or retard activation oil ports.. Each port exits into a sealed chamber on the opposite sides of a control piston.
- The control piston on six cylinder engine systems (M50TU, M52 & M52TU) is connected to a separate helical gear cup.
- The control piston on the M62TU VANOS system incorporates the helical gear.
In its default position the oil flow is directed to the rear surface of the piston. This pulls the helical gear forward and maintains the retarded valve timing position.
When the oil flow is directed to the front surface of the piston, the oil pushes the helical gear in the opposite direction which rotates the matched helical gearing connected to the camshaft.
The angled teeth of the helical gears cause the pushing movement to be converted into a rotational movement. The rotational movement is added to the turning of the camshaft providing the variable camshaft positioning.
M62 TU VANOS COMPONENTS
M62 TU VANOS components include the following for each cylinder bank:
- New cylinder heads with oil ports for VANOS
- VANOS transmission with sprockets
- Oil distribution flange
- PWM controlled solenoid valve
- Oil check valve
- Camshaft position impulse wheels
- Camshaft position sensors.
VANOS CONTROL SOLENOID & CHECK VALVE: The VANOS solenoid is a two wire, pulse width modulated, oil pressure control valve. The valve has four ports;
1. Input Supply Port - Engine Oil Pressure
2. Output Retard Port - To rear of piston/helical gear (retarded camshaft position)
3. Output Advance Port - To front of piston/helical gear (advanced camshaft position)
4. Vent - Released oil pressure
A check valve is positioned forward of the solenoid in the cylinder head oil gallery. The check valve maintains an oil supply in the VANOS transmission and oil circuits after the engine is turned oft. This prevents the possibility of piston movement (noise) within the VANOS transmission system on the next engine start.
VANOS TRANSMISSION: The primary and secondary timing chain sprockets are integrated with the VANOS transmission. The transmission is a self-contained unit.
The controlled adjustment of the camshaft occurs inside the "transmission". Similar in principle to the six cylinder engine VANOS systems, controlled oil pressure moves the piston axially.
The helical gear cut of the piston acts on the helical gears on the inside surface of the transmission and rotates the camshaft to the specific advanced or retarded angle position.
Three electrical pin contacts are located on the front surface to verify the default maximum retard position using an ohmmeter. This is required during assembly and adjustment.
OIL DISTRIBUTION FLANGES: The oil distribution flanges are bolted to the front surface of each cylinder head. They provide a mounting location for the VANOS solenoids as well as the advance-retard oil ports from the solenoids to the intake camshafts.
CAMSHAFTS: Each intake camshaft has two oil ports separated by three sealing rings on their forward ends.
The ports direct pressurized oil from the oil distribution flange to the inner workings of the VANOS transmission.
Each camshaft has REVERSE threaded bores in their centers for the attachment of the timing chain sprockets on the exhaust cams and the VANOS transmissions for each intake camshaft as shown.
CAMSHAFT POSITION IMPULSE WHEELS: The camshaft position impulse wheels provide camshaft position status to the engine control module via the camshaft position sensors. The asymmetrical placement of the sensor wheel pulse plates provides the engine control module with cylinder specific position ID in conjunction with crankshaft position.
M62 TU VANOS CONTROL
As the engine camshafts are rotated by the primary and secondary timing chains, the ME7.2 control module activates the VANOS solenoids via a PWM (pulse width modulated) ground signal based on a program map. The program is influenced by engine speed, load, and engine temperature.
- Shown below: In its inactive or default position, the valves direct 100% engine oil pressure flow to achieve max "retard" VANOS positioning
Maximum Retard Position:
- Shown below: As the Pulse Width Modulation (PWM) increases on the control signal, the valve progressively opens the advance oil port and proportionately closes the retarded oil port.
Oil pressure pushes the piston toward the advance position. Simultaneously the oil pressure on the retarded side (rear) of the piston is decreased and directed to the vent port in the solenoid valve and drains into the cylinder head.
Mid Way Position:
- Shown below: At maximum PWM control, 100% oil flow is directed to the front surface of the piston pushing it rearward to maximum advance.
Maximum Advance Position:
Varying the pulse width (on time) of the solenoids control signals proportionately regulates the oil pressures on each side of the pistons to achieve the desired VANOS advance angle.
VANOS SERVICE NOTES
VALVE TIMING PROCEDURES
Refer to Valve Timing Procedures. M62 TU valve timing adjustment is similar to the previous non-VANOS M62 engine with the exception of setting the VANOS transmissions to their max retard positions with an ohmmeter and attaching the camshaft gears to each camshaft with single reverse threaded bolts.
- After locking the crankshaft at TDC, the camshaft alignment tools (P/N 90 88 6 112 440) are placed on the square blocks on the rear of the camshafts locking them in place.
- The exhaust camshaft sprockets and VANOS transmission units with timing chains are placed onto their respective camshafts.
- The exhaust camshaft sprockets and VANOS transmissions are secured to the camshafts with their respective single, reverse threaded bolt. Finger tighten only at this point. Install the chain tensioner into the timing chain case and tension the chain.
- Connect an ohmmeter across two of the three pin contacts on the front edge of one of the VANOS transmissions. Twist the inner hub of transmission to the left (counter clockwise). Make sure the ohmmeter indicates closed circuit. This verifies that the transmission in the default max retard position.
- Using an open end wrench on the camshaft to hold it in place, torque the VANOS transmission center bolt to specification.
CAMSHAFT IMPULSE WHEEL POSITION TOOLS
The camshaft impulse wheels require a special tool set to position them correctly prior to torquing the retaining nuts.
The impulse wheels are identical for each cylinder bank. The alignment hole in each wheel must align with the tool's alignment pin. Therefore the tools are different and must be used specifically for their bank.
The tool rests on the upper edge of the cylinder head and is held in place by the timing case bolts.
VANOS SOLENOID REPLACEMENT
The solenoids are threaded into the oil distribution flanges through a small opening in the upper timing case covers.
Special Tool 11 6 420 is required.
VANOS TRANSMISSION RETARD P0SITION SET UP TOOLS
Special Tool 11 6 440 is used to rotate the transmission to the full retard position when checking the piston position with an ohmmeter.
This tool engages the inner hub of the transmission provides an easy method of twisting it to the left for the ohmmeter test.
DIAGNOSIS
The VANOS is fully compatible with the diagnostic software providing specific fault codes and test modules. Additionally, diagnostic requests section provides status of the PWM of the VANOS solenoids and camshaft position feedback via the camshaft position sensors. The Service Functions section of the DIS/MoDiC also provides a VANOS system test.