Volvo 819 E - Page 40

Group 28 Ignit ion systems
D esign a nd fun ction - Compensa t ion functions
If th e load t empo rar ily re verts to normal (b) during the adaptive retardation period (e.g. if the tra iler is uncoupled or
the road becomes downhill) , the tim i ng will be returned to the basic setti ng (a). If engine speed and load sub-
sequently change (wi thin the 10-mi nute period) so that cond i tions once more fall within the knock-sensitive zone (c),
the
control unit will again automati c ally retard th e timing by 1 ~ without the occurrence of knock.
If knock persists desp i te the intervention of the adapt i ve retardati on funct i on , the tim ing will be retarded as usual (as
indicated by the dashed downward steps) i.e. by 3" each time kn o ck occurs .
The
control unit always leaves the adapt i ve mode ( at the end of i nterval (a )) after a predetermined i nterval (approx.
10 mini regardless of load . If the load remains high, a new adapt i ve period w ill commence if knock recurs and the
cycle will be repeated from the start of interval (a ).
Advantages
On average, this mode of knock control permits a more advanced timin g setting to be used - an advantage in terms
of combus t ion, fuel economy , and so on - due to the fact that fewer knock- controlled retardation operations are re-
quired when the function is activated. Stated in simple terms, knock is prevented by detecting the inc reased risk of
th e phenomenon.
38