Variable Camshaft Timing (VCT)

Variable Camshaft Timing (CT) Unit





The use of the new variable camshaft timing optimizes the combustion procedure by improving gas exchange in the cylinders. As a result of this exhaust emissions regulations can be met without the use of a pulse air system or exhaust gas recirculation system (EGR system).
The mechanical principles behind variable camshaft timing (VCT) are relatively simple. The valve timing for the opening and closing of the exhaust valves is influenced by a hydraulic cylinder which is riveted to the timing sprocket. This cylinder connects the timing pulley with the camshaft through a hydraulic piston. The hydraulic piston is guided along its axis by the helical gears on the exhaust camshaft and the hydraulic cylinder. The helical gear transfers the up and down motion. As the timing sprocket is fixed in place by the timing belt, the position of the exhaust camshaft is rotated in relation to the timing sprocket, and the exhaust valve timing is therefore adjusted. The hydraulic piston is moved by supplying pressurized engine oil from the engine oil circuit to both pressure chambers of the hydraulic cylinder. The engine management system controls a solenoid valve which in turn supplies the pressurized oil to the pressure chambers.
The return spring ensures the hydraulic piston goes back towards its original position when the engine is switched off.
The VCT unit must be in its original position before the valve timing can be adjusted. Turn the exhaust camshaft in the normal direction of the engine rotation to bring the VCT unit to its original position. When doing this the crankshaft must not be turned.