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Nowadays, every engine
management system includes an idle control valve. The frequently fitted
valves for controlling the idle speed are adjustment motors, either 2 pole
or 3 pole.
Adjustment motor, 2 pole
An adjustment motor can be produced with a sliding or part rotating
armature. On this armature can be found a valve that supplies air to the
engine at idling speed. The adjustment motor is always fitted as a by-pass
parallel over the fuel valve. Simultaneously there is pulsating current
on these adjustment motors or, as is often termed, a duty-cycle. The adjustment
motor or LFR usually consists of an armature, a permanent magnet and a
spring. The spring holds the armature and attached valve closed. The current
(duty-cycle) on the armature provides for a rotation of the armature which
in this case is open. A duty-cycle is an on and off switching current,
in this case, at a fixed frequency of 100 Hz. This frequency remains stable
despite the control function of this current. The control of the adjustment
motor proceeds as follows. The ratio between the on and off times can be
changed electronically. The on/off ratio is expressed in percentage terms.
The value that is maintained in this case is the on time of this pulse.
There are also adjustment motors that are fitted with two coils on the
armature. These motors have no compression spring and the return movement
is provided by the second coil. The duty-cycle on this coil is exactly
the opposite of that of the first coil and provides the return operation
of the armature. This system is also fitted with a 100 Hz duty-cycle and
the currents on both coils provide a balance, thus a certain position on
the armature. |
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H.A.S MG ROVER
Ltd
