| M3 Double Vanos Explained |
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| Extracted from AutoZine Technical School (Variable-valve timing) |
| Cam-phasing VVT is the simplest, cheapest and most commonly used mechanism at this moment. However, its performance gain is also the least, very fair indeed. Basically, it varies the valve timing by shifting the phase angle of camshafts. For example, at high speed, the inlet camshaft will be rotated in advance by 30° so to enable earlier intake. This movement is controlled by engine management system according to need, and actuated by hydraulic valve gears. Note that cam-phasing VVT cannot vary the duration of valve opening. It just allows earlier or later valve opening. Earlier open results in earlier close, of course. It also cannot vary the valve lift, unlike cam-changing VVT. However, cam-phasing VVT is the simplest and cheapest form of VVT because each camshaft needs only one hydraulic phasing actuator, unlike other systems that employ individual mechanism for every cylinder. Continuous or Discrete Simpler cam-phasing VVT has just 2 or 3 fixed shift angle settings to choose from, such as either 0° or 30°. Better system has continuous variable shifting, say, any arbitary value between 0° and 30°, depends on rpm. Obviously this provide the most suitable valve timing at any speed, thus greatly enhance engine flexiblility. Moreover, the transition is so smooth that hardly noticeable. Intake and Exhaust The BMW's Double Vanos system has cam-phasing VVT at both intake and exhaust camshafts, this enable more overlapping, hence higher efficiency. This explain why BMW M3 3.2 (100hp/litre) is more efficient than its predecessor, M3 3.0 (95hp/litre) whose VVT is bounded at the inlet valves. In the E46 3-series, the Double Vanos shift the intake camshaft within a maximum range of 40° .The exhaust camshaft is 25°. |
| signals the valve at the green chamber open, then hydraulic pressure acts on the thin piston and push the latter, accompany with the cap, towards the camshaft, thus shift the phase angle forward. Continuous variation in timing is easily implemented by positioning the cap at a suitable distance according to engine speed. |
| From the picture, it is easy to understand its operation. The end of camshaft incorporates a gear thread. The thread is coupled by a cap which can move towards and away from the camshaft. Because the gear thread is not in parallel to the axis of camshaft, phase angle will shift forward if the cap is pushed towards the camshaft. Similarly, pulling the cap away from the camshaft results in shifting the phase angle backward. Whether push or pull is determined by the hydraulic pressure. There are 2 chambers right beside the cap and they are filled with liquid (these chambers are colored green and yellow respectively in the picture) A thin piston separates these 2 chambers, the former attaches rigidly to the cap. Liquid enter the chambers via electromagnetic valves which controls the hydraulic pressure acting on which chambers. For instance, if the engine management system |
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| Advantage: Cheap and simple, continuous VVT improves torque delivery across the whole rev range. Disadvantage: Lack of variable lift and variable valve opening duration, thus less top end power than cam-changing VVT. |
| Which car makers use this: |
| Audi 2.0-litre - continous inlet Audi 3.0 V6 - continous inlet, 2-stage exhaust Audi V8 - inlet, 2-stage discrete BMW Double Vanos - inlet and exhaust, continuous Ferrari 360 Modena - exhaust, 2-stage discrete Fiat (Alfa) SUPER FIRE - inlet, 2-stage discrete Ford Puma 1.7 Zetec SE - inlet, 2-stage discrete Ford Falcon XR6's VCT - inlet, 2-stage discrete Jaguar AJ-V6 and updated AJ-V8 - inlet, continuous Lamborghini Diablo V12 since SV - inlet, 2-stage discrete Mazda MX-5's S-VT - continous inlet Mercedes V6 and V8 - inlet, 2-stage ? |
| Nissan QR four-pot and V8 - continuous inlet Nissan VQ V6 - inlet, continuous ? Nissan VQ V6 since Skyline V35 - inlet, electromagnetic Porsche Variocam - inlet, 3-stage discrete PSA / Renault 3.0 V6 - inlet, 2-stage Renault 2.0-litre - inlet, 2-stage discrete Subaru AVCS - inlet, 2-stage ? Toyota VVT-i - continuous, mostly inlet but some also exhaust Volvo 4 / 5 / 6-cylinder modular engines - inlet, continuous Volkswagen VR6 - inlet, continuous ? Volkswagen (Audi) W8 and W12 - continuous inlet, 2-stage exhaust |
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