ENGINE K SERIES 1.8 VVC
Technical Academy
Page 2 of 28 01-34-RG-W-Ver:1
Variable Valve Control
Engine tuning is usually a compromise between low speed drive-
ability and high speed power, and an increase in one is normally
accompanied by a reduction in the other The main reason for this
'trade off is a phenomenon called 'Inertial Ram Effect'.
The VVC overcomes these basic restraints by employing a
continuously variable camshaft profile; opening the intake valve for
longer periods at high engine speeds and shorter periods for more
sedate conditions to enhance bottom end torque and idle stability.
How VVC Works
The inlet camshaft, (and there are four of them), still receives drive
from the crankshaft in the normal manner; restricted to the overall
ratio of one camshaft revolution to every two from the crankshaft.
Working within this basic restraint, Rover engineers were able to
squeeze around 20% more power over the standard engine by
varying the speed of the camshaft within each revolution; slowing it
down whilst the valve is open to give a longer duration and speeding
it up to give a 'snap' open and close condition.
A = Distance covered in first half of rotation
B = Distance covered in second half of rotation
The principle of operation is extremely simple; driving through an eccentric mechanism
gives the necessary variation in velocity throughout the camshaft revolution.
Changes in the position of the eccentric in relation to the camshaft lobe, either speeds up,
or slows down the valve's opening sequence. Having the position of the eccentric
controlled through a hydraulic rack and pinion enables the MEMS 2J ECM to control
exactly the open period of each pair of intake valves.
Rotation of the Camshaft Drive
The inlet valve cam drive is turned at half crankshaft speed by a toothed drive belt.
Rotation of the Drive Ring
Because the drive ring centre is offset from the camshaft centre, the drive ring rotates
eccentrically and speeds up and slows down during its turn.
Rotation of the Cam Lobe
The slot on the drive ring engages the crank on the cam lobe and the eccentric rotation
becomes even more pronounced.
The basic principle is relatively easy to explain around one cylinder and one intake valve.
Figure 2
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