Volvo 819 E - Design and Function: Overview; Review of Electronic Ignition Systems - I

Group 28 Ignit;on systems
Design and function - Overview
Review of electronic ignition systems - I
A B
C
D
E F G H
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The above figure shows the major componen ts of each of the systems descri bed below .
Summary
Control system
The control unit (A) house s the electronic circuits and the various program functions nee ded to compute the timing .
The
power stage (Bl cont r ols the pr i mary current in t he ignition coil in response to con trol signals fr om the control
unit. The power stage may either be an integral part of the control unit or a separate unit assembled with it. The func-
t ion of the distr i butor (e) is to deliver t he high-tension pulse i ndu ced in the secondary winding of the ignition coil to
the correct spark plug . The distr i butor may be dr i ven ei ther by bevel ge aring (in whi ch case it is ins talled vertically) or
directly from the camshaft ( hor i zontally i nstalled units) . In systems in which the rotor arm is the only moving part
(such as
types which employ inductive speed pick- ups ) the lim ing ca nnot be varied by alter i ng the pos it io n of the
distributor .
Sensors
The rema ining components in the tab le (D-E) c omprise part of the senso r system. T ogethe r with the con tro l un it,
these
supply i nformat io n on prevailing engine running c onditions .
Bas ic parameters
The con trol unit is supplied with information on engine speed and crankshaft position (D) either by a Hall generator
activated by a trigger rotor (with four vanes) moun t ed on the rotor s haft or by an inductive pick- up mounted c lose to
the
flywheel (on manuals ) or ca rrier pIaIe (automatics) . In th is case, the periphery of the flywheel /c arrier plate is pro-
vided with a series of holes whose passage is detected by the p ick-up and ind icated in the form of electrical signals.
The
eng ine load (E) is measured either by means of a vacuum line anached to th e i ntake manifold or, if the eng ine is
equipped w i th an LH-J etron ic fuel inject io n system (i.e. most engine s equi pped with EZ-K i gnit i on systems ). by an
air mass
meter (see next ill ustration ). The var ious signals - engine speed, crankshaft posi tion and enQine load -
com pr ise information which is used by ignit i on systems of all types to compu te the tim ing.
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