Variable Timing 2
|The most frequent construction for the variable camshaft adjustment |
It's about time we dedicated a page solely to the, at the moment, probably most frequently used process. It has proved itself to be probably the most simple to realise. The manufacturer can choose freely, whether it is
utilised for the intake- or also for the exhaust camshaft as well. The oil pressure for the adjustment is, in all cases, provided through special channels by the camshaft and is determined through stroke-valves by the
|Strong at high- and at low revs|
In the meantime, adjustable camshafts are found in all possible petrol engines, right down to the smallest ones. Not only do they provide for more torque at lower RPMs and are more willing to rev higher, they are also
even responsible for internal exhaust gas recirculation due to larger valve overlapping. Their control has become a complete sub-division in the motor management, into which it is fully intergrated.
|Irrespective whether belt-, chain- or spur wheel drive|
In the above pictures the one visible camshaft is driven by a timing chain. A belt-drive or spur gears are also possible. The camshaft can be turned, in all cases, to a certain angle in relation to the drive-wheel, The RPMs
of the two are irrelevant. Hereby, there are single chambers and corresponding vanes, which travel a certain circumferential distance determined by the control device.
|Exact adjustment through pulse-width modulation possible|
The model in figure 3 and 4 makes it clear. Two wheels are turned in opposing directions, if in four chambers an oil pressure is built up. Thereby, you must imagine these chambers, as seen by the viewer, as being
closed. The return adjustment occurs either through spring-force, if the, pressure decreases through regulation by electro-magnets, it is however, also possible through the oil pressure in the chambers which lie
opposite to each other. With appropriate timing of the oil pressure valve, and a continuous cycle of course, interim positions, accurate to 1 degree, are possible. 08/10
|Adjustment is supervised by the control device using echo sensors.|