Volvo 819 E, Руководство по обслуживанию

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Group 28 Ignition sys t ems
D es i gn and funct io n - Compensa t ion f unctions
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R EX-I
Load - controlled retardation
Function
Since a sudden increase in load greatly inc reases the risk of knock , the control un i t in corpo rate s a fun c t io n which
tards t he tim ing sharply f o r a brief period u nder these condit io ns . The fun c tion of load - controlled re t ardation is to
duce th e li ke li h ood o f knock when the accelerator is suddenly depressed .
Back g r o und
High engine loa d (equiva l ent t o the injection of a la r ge quanti t y of mixture) is a prerequis i te to the occurrence of the
more com mon type s of kn oc k . Thus, for examp l e , when t he accelerator is s uddenly depressed, t he co ntrol uni t may
be unab le ( by virtue o f i t s design) to retard t he ignition quick l y enough by an amount equiva l en t to the l oad increase .
For th is reason , certai n c ars may be su bje c t to what is known as ' transitional ' knock if driven in too high a gear with
the accelera t or to the fl oor.
Sharp retardat i on
To overcome this problem , th e con trol unit incorporates a program -co ntr o lled fun c tion wh ich retards the norma l
t iming by in response t o a loa d signallfrom the fue l co ntrol unit) in d ic ating a s udden pr ess ure drop the in -
take manifold.
Rap i d re ·a dvan ce
Th e con t rol uni t t hen restores t he t imi ng very rapidly t o th e normal value,
0..
This is car ried ou t in ste p s o f every
five engine revolut ions (bo th values approx i mate) . regardle ss of whether th e higher load condi t ion i s o f longer dur-
ation .
Should the rap id pressure drop be fo llow ed by full o pen i ng of the throttle , th e con tr ol unit will have sufficien t t ime t o
aga in retard the basic tim ing by a sufficien t amount w i th ou t any significant r i sk of f u rther knock .
systems
8re
equipped w i th
8
similar cont r ol
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