Volvo B 230 FT User Manual

Group 28 Ignition systems
Design and function - Compensation functions
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Knock control
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The kno ck sensor moniiors the combus t ion process contin uo usly. If knock occurs, the device delivers a special sig.
nal to the control unit, which takes corrective act ion by retard ing the ignition i~ the cylin der affected.
Knock control characteristic
The principle of knock control is more or less the same in the case of all systems equipped with knock sensors. (AI·
though the kn ock cont rol characteristic shown is that for the EZ·115K system, the description is generally applica-
ble.) The vertical coordina te shows the ignition setting in degrees in relation to the basic timing (i ndicated here by
the ang le <xl, while the horizontal coordinate is the time scale (which normally varies wi th eng i ne speed).
Stepped control
The control unit continuously compu tes the optimum t iming on the basis of the running conditions. On detecting
knock, the unit retards the ignition by a step of a few degrees (2_3° depending on the system) in the cylinder affected.
If
the phenomenon persists, the setting is retarded by a further step, and so on until the condi tion has been correct-
ed. The maximum retardation in relation to the basic t iming is approx. 10-16 ° in th e case of EZ -K systems.
Ae-advance following correction of knock
After knock has been eliminated, th e control unit maintains the retarded setting for a speci fied number of engine rev -
o
lut ions, depending on the speed (app lies to EZ-K systems). before re-advancing the igni t ion in small steps (0.1-1° ),
eithe r until the original characteristic has been restored or until the engine again starts to knock .
• The maximum retardation must not deviate excessively from the basic setting if an excessive rise in exhaust gas temperature is to
be avoided . Informa t ion on engine speed and for load is also essential to enable the cont rol unit to impose the maximum retarda -
tion , if necessary.
32

Volvo B 230 FT Specifications

General

Engine Type	Inline 4-cylinder
Fuel System	Electronic Fuel Injection
Cylinder Bore	96 mm
Piston Stroke	80 mm
Turbocharger	Yes
Displacement	2.3 L (2316 cc)
Valvetrain	SOHC, 8-valve