The following is a description of how BMW's variable camshaft timing system (VANOS) works.
The VANOS system really isn’t as complicated as it’s made out to be. It uses the rising oil pressure created while revving the engine higher in the rpm's to hydraulically force the camshaft to rotate (12.5 degrees) advancing the timing and therefore increasing horsepower and torque. The VANOS system is activated by a solenoid controlled by the DME, when the RPMs rise to a certain amount, VANOS will kick in, thus explaining that jolt you get at about 3800 RPMs, you know what im talking about :D. On the m50 and m52 only the intake camshaft is VANOS controlled, on later cars with VANOS, the intake and exhaust camshafts are both VANOS controlled.
Its a bit more complicated than this, but that’s the basic idea.
This write up explains it quite well. Although before i actually saw pictures of the system i couldn’t grasp it all that clearly.
Here is the VANOS system installed in the engine. You are seeing the timing chains, VANOS unit, and the exhaust and intake timing sprocket assemblies in this picture.
Here is the VANOS sprocket (or cup gear as JC calls it in the above description). In this picture it is not pushed into the sprocket assembly located on the timing chain sprocket and the intake camshaft sprocket.
Here you can see the timing chain and camshaft VANOS sprocket assembly, with the VANOS system removed from the engine. The inner sprocket is directly connected to the camshaft, while the outer sprocket is connected to the timing chain assembly.
Here is the VANOS system removed from the car. Here you can also see inner teeth to the VANOS unit assembly, that mesh with the teeth on the end of the intake camshaft assembly.
Again, here you see the VANOS system removed from the engine, the VANOS sprocket is pushed in and out to advance the timing, when it is out the timing is 'normal', or how it would be at idle, when it is pushed into the timing chain and camshaft sprocket assembly, that is when it advances the timing. You can see quite clearly the ‘Helical’ nature to these teeth, when they are pushed into the timing chain sprocket and intake camshaft sprocket assembly, they force the intake camshaft to rotate 12.5 degrees forward. This rotation of the camshaft is what produces the added power felt in the mid range of the RPM’s. The VANOS unit is allowing the intake camshaft to be controlled somewhat independently from the crankshaft, thus allowing the timing to be advanced.
Here is a picture of the engine with the valve cover simply removed, incase you were having trouble grasping where the VANOS assembly was located. (It is the semi-circle metal box located in front on the timing chains.)
Thanks to pelican parts for the pictures, sorry they’re so big (Commentary is by me). I hope that explains it... it’s not too complicated after you begin to grasp the entire system.
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