Volvo B 200 E - Page 37

Group 28 igni t ion systems
De sig n and funct io n Compensa t io n fun c tions
Reason for different re-advance rat es
'Faste r' re- advance rates are possible in the lower speed ranges since ig nit ion then takes place when the piston is
closer to TDC and t he risk of knock is, consequently, lower . Fa st re-advance is more advantageous since it serves to
increase
th e mean value of the t iming angle . ( As already described, advancing the tim ing point im proves t he effi-
ciency of fuel utilization .)
' Slower ' re- advan ce rates are chosen at higher speeds since igni ti on then takes place relat iv ely early as th e piston
move s upwards towards Toe (and th e attendant risk of knock is greate r ). I ncreasing th e rate of re- advance un der
these condi t ions wou ld grea tly inc rease t he likelihood of recurring knock.
• EZ -K sys tems employ more or less the same method of varying the re -advance r ates following knock-controlled retardation.
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