GF07.10-P-1016MTC | Camshaft adjustment, function | 10.5.12 |
ENGINES 270.9 in MODEL 242 with CODE (924) Monovalent natural gas drive
Function requirements for camshaft adjustment, general points
Circuit 87M (engine control ON)
Engine running
Camshaft adjustment, general points
Camshaft adjustment allows the intake camshaft to be adjusted by up to a 40° CKW (crank angle) towards "advance" and the exhaust camshaft by up to 40° crank angle towards "retard". This means the valve overlap in the event of a gas exchange can be varied within wide limits.
In this way the engine torque curve is optimized, the fuel consumption reduced and the exhaust characteristics improved.
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Valve overlap
The intake valves open before the exhaust valves close.
For camshaft adjustment, the ME-SFI [ME] (N3/10) control unit reads the following sensors:
- intake camshaft Hall sensor (B6/15)
- exhaust camshaft Hall sensor (B6/16)
- coolant temperature sensor (B11/4)
- pressure sensor downstream of throttle valve (B28/7), engine load
- crankshaft Hall sensor (B70) (with direction of rotation recognition), motor rpm
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Function sequence for camshaft adjustment
To achieve the camshaft adjustment, the intake camshaft solenoid (Y49/1) and the exhaust camshaft solenoid (Y49/2) are actuated by the ME-SFI {ME} control unit with a PWM signal at 150 Hz.
Actuation takes place according to a performance map in the partial and full-load range, and allows continuous adjustment of the camshafts depending on the duty cycle of the PWM signals.
When actuated, the camshaft adjustment pistons are moved by the buildup of magnetic force, and engine oil flows into the control plungers. This causes the control plungers to be twisted axially backward, moving along a helical cut in the direction of camshaft rotation.
The position of the intake camshaft is detected by the intake camshaft Hall sensor and the position of the exhaust camshaft by the exhaust camshaft Hall sensor, and these are sent to the ME-SFI control unit as voltage signals.
Engine oil pressure regulation
The engine oil pressure is regulated via the engine oil pump valve (Y130) in order to ensure an adequate oil supply and to lower the oil pressure if necessary (a saving on fuel).