Function of camshaft adjuster - RA05001202160X(05-2160)
| Engine speed | Adjustment of camshafts | Effect on combustion cycle |
|---|---|---|
| up to approx. 2000 rpm | retarded | Idling improved, lower residual gas quantity, smaller valve overlap |
| from 2000 to 4400 rpm | advanced | More torque, fewer fresh gas losses |
| as of 4400 rpm | retarded | Intake valves open and close later, cylinder charge improved (turbo effect) |
| Engine switched off | retarded | - |
| above 250 km/h | advanced | - |
In selector lever position P/N the shift point in retarded direction is at 2500/min.
Function
When the engine is running, the camshaft adjuster hydraulically/mechanically advances and retards the intake camshaft by 32° crank angle relative to the camshaft sprocket. The camshaft adjuster is controlled electromagnetically by the LH-SFI control module. The adjustment time of approx. 1 second is dependent on the engine oil pressure at the camshaft adjuster and on the oil viscosity and oil temperature.
The intake camshaft is rotated as a result of the screw effect of the helical gearing on the camshaft sprocket (13), adjusting piston (14) and flange shaft (16). At the same time the engine oil in working chamber (B) is pushed by the adjusting piston (14) and flows through 2 bores in the adjusting piston (14), flange shaft (16) and control piston (18) through the control piston (18) and 2 bore in the camshaft flange (23).
Leak oil flows off over control and adjusting piston surfaces through the control piston bores and 2 bores in the camshaft flange (23).
Engine switched off ("retarded")
The control piston (18) is pushed by the compression spring (17) against the circlip (19). The engine oil pressure in the camshaft adjuster is reduced. The engine oil level is fixed by the oil return lock in the cylinder head.
Up to approx. 2000 rpm ("retarded")
The torque of the internally helically geared camshaft sprocket (13) acting in the direction of rotation of the camshaft, applies a pressure to the cover (12) as a result of the screw effect of the externally helically geared adjusting piston (14). As a result, the internally helically toothed adjusting piston (14) also holds the externally helically toothed flange shaft (16) with the bolted camshaft (22) in the "retarded" position. The compression spring (17) pushes the control piston (18) against the circlip (19). The engine oil flows through 2 sloping bores in the camshaft flange and in the flange shaft (16) into the working chamber (A) and, as the engine oil pressure drops, additionally holds the adjusting piston (14) in the "retarded" position.
Leak oil flows off through the control and adjusting piston surfaces through the control piston bores and 2 bores (23) in the camshaft flange.
"Retarded" position
Solenoid (2) de-energized.
Control piston (18) at rear stop.
Adjusting piston (14) at front stop. Oil pressure in working chamber (A).
From 2000 to 4400 rpm ("advanced")
The control piston (18) is pulled forward by the actuator (2) against the compression spring (17) as far as the stop in the flange shaft (16).
The control piston (18) closes the oil feed to the working chamber "A" and at the same time allows oil to flow to the working chamber "B" through 2 bores in the flange shaft (16) and in the adjusting piston (14). The engine oil pressure moves the adjusting piston (14) up to the stop on the flange shaft (16).
As a result of the axial movement of the adjusting piston (14), the camshaft (22) bolted to the flange shaft (16) is rotated into the "advanced" position. The rotation is the result of the effect of the helical gearing on the camshaft sprocket (13), adjusting piston (14) and flange shaft (16).
The engine oil in working chamber "A", pushed by the adjusting piston (14), flows off through the flange shaft (16) and 2 bores (23) in the camshaft flange.
"Advanced" position
Solenoid (2) energized.
Control piston (18) at front stop.
Adjusting piston (14) at rear stop. Oil pressure in working chamber (B).
From 4400 rpm ("retarded")
The actuator (2) is de-energized and releases the control piston. The compression spring (17) pushes the control piston (18) against the circlip (19). The oil supply to working chamber "B" is closed off and oil is allowed to flow to working chamber "A" through 2 bores in the flange shaft (16). The engine oil pressure moves the adjusting piston (14) up to the cover (12).
This axial movement of the adjusting piston (14) rotates the camshaft (22) bolted to the flange shaft (16) into the "retarded" position.