Volvo 819 E - Page 20

Group 28 Ign ition sys tem s
D
esign and funct ion - Components
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1
REX-I
General
Since it is not technically pract ic al to use the control unit to regulate the relatively hi gh current in the ignition coil pri·
mary , this function is performed by a power stage wh ich employs control signals from the control unit to vary both
the charging time of the coil and the instant at which it delivers its high- tens ion pulse. The power stage opens and
closes the primary circuit , in du cin g a high - tension voltage in the secondary each time the primary cu rrent is in-
terru pted.
Construction
The p ower stage (1) and igni tion coil (2) are assembled by means of screws (enabling t he units to be r ep laced indi -
vidually) . The power stage receives control signa ls from the control unit (g re en lead) across th e two - pole centre con -
nector (3) ( which is also used to ground the signal). The thr ee-pole co nnector ( 4) on the right supp lies the power
stage and igni t ion coil wilh battery voltage, grounds the coil and supplies the rev counter with a signal. The connec-
tor (5) on the left is not used .
The power s tage (1) i ncorporates the electrical circui ts which control the primary current in the ignition coil. Mount -
ed
on a bracket in the eng ine compartment, the power stagelignition coil assembly is provided with a large contac t
area
with the suspens ion strut hous ing to ensure that the heat generated is diSSipated.
The
ignition coil (2) is of the conv ent ion al type w i th a pr i mary and secondary wir ing. The high-tension induced in the
secondary is fed to the distributor from t erminal (6). As on most modern igni t ion systems , the HT voltage is of the
order of 30 kV .
Standing current protection
A functi on known as 's tand ing curren t prote ction' is provided 10 prevent overhea ti ng of th e igni t ion coil when the ig-
nition is s witch ed on with the en gine at rest. When the engine is st opped, the control unit receives no speed signals
-and delivers a 'low' cont rol signal to the power stage, whi ch responds by opening the p rimary circui t of the coil.
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