Volvo 819 E - Page 33

Group 28 Ignition systems
Design and function - Co mpensation funct io ns
B
c D
Variants
T he three different t ypes of knock sensor used are illustrated above.
Type (B) is used
on EZ -102K. and on EZ-117K and EZ-118K systems from 1985 to 1986.
Type (C) is
used on EZ-116K systems from 1987 on, as well as on EZ -l17K and EZ-118K, and on Rex -I from 1989 on.
A refinement of type (B ), th is variant is fined with a sleeve (5) which ensures that th e mount ing for ce is less easily
transmitted to the piezoelectric crys tal, making the unit less sensitive to the effect of th e ti gh t ening torque .
Type (
0) is used on the EZ - 11 5K system on the B280 eng ine. which is fitted with a knock sensor f or each bank of
cylinde r s. The only di ff erence between th is var iant and type (C) is that the connec t ion lead is integral wi th the unit .
• Type IC) and lD l sensors are less sensitive to t igh ten ing torque than earlier lypes . The design permits the torque to vary from 15
to 25 Nm '1 1- 18 ft.lb) w it hout any adverse effect on the performance of Ihe devi ce. Although production of type 181 was discon-
t
inu ed in 1986, it is fu lly interchangeab le wi lh type ICI. Particular care muSI be taken when fining the older type 01 sensor ; a
torq ue wrench must be used to li ghten Ihe device in pos i tion .
• Since
the ignition may be retarded in each i ndiv i dual cylinde r in the evenl of knock. the tIming In each may vary by as much as ap -
prox . 10--15·, Apart from the fact that knock control is i nherently a major advantage. the facility of eliminating it 10 an individual
cylinde r means Ihat fuel ut ilizati on can be maximized in relation to the knock Ihre shold in each. ThIS is importanl since condi tio ns
in the various cylinders may differ somewhat in terms of combustion temperature , fuel residue deposits on cylinder walls . in-
jecto r design , and so on.
• Re lardat ion of the ig nition in each indivi dual cylinder is a feature of all systems equipped w ith knock senso rs dealt with in this
manual.
• Sh ou ld the signals f rom the kno ck sensor be lost for any reason. most of the c ontrol units w ill retard the ignition by a pre-
programmed 'fail-safe' value 01 approx . let .
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