Fig. 5.39. Duratec-V15 engine with 2.5 l capacity and variable valve timing system elements: 1 – timing mechanism drive cover; 2 – cylinder head cover; 3 – intake camshaft position sensor; 4 – exhaust camshaft position sensor; 5 – electromagnetic valve for adjusting the position of the intake camshaft; 6 – electromagnetic valve for adjusting the position of the exhaust camshaft; 7 – mechanism for adjusting the position of the exhaust camshaft; 8 – intake camshaft position adjustment mechanism; 9 – intermediate pulley of the timing belt; 10 – toothed pulley of the timing belt on the crankshaft; 11 – timing belt tensioner; 12 – toothed pulley of the coolant pump; 13 – timing belt drive.
The 2.5-litre Duratec-V15 engine (Fig. 5.39) is a five-cylinder, 20-valve, 2522 cm³ turbocharged engine with dual electronically controlled variable valve timing (VCT). By using variable valve timing for the intake and exhaust camshafts, maximum torque is achieved over a wide range of engine speeds.
The main engine components are made of aluminum.
The cylinder head consists of two parts. Maintenance-free mechanical valve tappets are installed in the cylinder head. The upper section of the cylinder head consists of a cover with built-in camshaft bearing caps. The spark plug wells are additionally sealed with rubber rings. A cover is installed above the spark plug wells to protect them from dirt and water.
The cylinder block consists of three parts.
This is the cylinder block itself, the lower section of the crankcase (the main bearing frame) and the oil pan. Five cast iron cylinder liners are inserted into the cylinder block, which are not replaced during repairs.
The lower section of the crankcase acts as a reinforcing element. In addition, it serves as a housing for the lower main bearing shells.
The oil pan with developed fins serves as an additional reinforcing element.
A replaceable cylinder head gasket is installed between the cylinder head and the cylinder block. Gaskets between other mating surfaces of the engine are seals based on a sealant.
The camshafts are mounted in six bearings, with the lower bearing shells of the camshafts located in the cylinder head and the upper bearing shells in the cylinder head cover.
Each camshaft is equipped with an electromagnetic hydraulic valve for controlling the oil supply to the VCT system, which is controlled by the electronic engine control unit (ECU). The electronic unit receives information about the current crankshaft speed and engine load from the system sensors. Based on these input signals, the hydraulic valves set a larger or smaller dynamic angle of rotation of the camshaft relative to the crankshaft.
The timing belt is tensioned automatically by a mechanical tensioner. The tension of the two poly V-belts of the auxiliary drive is also automatic.
The water pump is driven by the timing belt.
The crankshaft rotates in six main bearings. The thrust half rings of the crankshaft, limiting its axial movement, are installed in the fifth main bearing.
The front end of the crankshaft has two toothed rims. The inner rim serves to drive the oil pump.
A pulley for the timing belt is installed on the outer splined crown.
NOTE: The timing belt pulley can only fit onto the shaft splines in one position. For this purpose, one spline in the timing belt pulley hub bore and one spline on the crankshaft are made wider than the others.
The pistons are made of aluminum alloy and have a graphite coating, which serves to reduce friction and reduce noise. The pistons are cooled from below by jets of oil from oil nozzles screwed into the cylinder block.
The valve timing control system has a hydromechanical drive.
Engine oil is supplied from the oil pan through the electromagnetic valves of the VCT oil supply control to the control mechanisms of the intake and exhaust camshafts in the amount necessary to change the dynamic position of the shafts in the mechanisms. The valve timing for the camshaft is set by the electronic control unit (ECU) of the engine with advance or retardation depending on the signals received by the sensors of the engine management system.
The VCT control mechanisms for the intake and exhaust camshafts are self-setting to the locked home position when the intake camshaft is locked by engaging a special spring-loaded locking pin with the shaft.
The movement of the VCT mechanisms to the locked initial position is provided by the tension force of the timing belt.
In the locked initial position, the intake camshaft VCT control mechanism is in the "intake lag" position, and the exhaust camshaft VCT control unit is in the "exhaust advance" position.
When the engine is started, the lock is hydraulically released when a certain engine oil pressure is reached.
NOTE: The intake and exhaust camshaft VCT control mechanisms may only be replaced as complete units during repair.
When the engine is started, engine oil is pumped by the oil pump from the oil sump, supplied to the oil channels of the camshaft through the oil channels in the cylinder block and the engine block head, and then directed from there to the electromagnetic valve for controlling the oil supply 7 (Fig. 5.40) VCT and to the locking pin 2. The locking pin is returned to its original position by oil pressure, resulting in a mechanical connection between the camshaft pulley 1 and the rotor 3.
When the VCT control mechanism operates in the "retard" mode, chamber b is filled with engine oil. Rotor 3 rotates clockwise, the engine oil pressure in chamber b is greater than that in chamber a. The engine oil returning from chamber a enters through the oil return channel to the VCT oil control solenoid valve and from there returns to the oil sump.
When the VCT control mechanism operates in the "advance" mode, chamber a is filled with engine oil. Rotor 3 rotates counterclockwise, the engine oil pressure in chamber a is greater than that in chamber b. The engine oil returning from chamber b enters through the oil return channel to the VCT oil supply control solenoid valve and from there returns to the oil sump.
When checking the valve timing, make sure that the timing marks are precisely aligned (Fig. 5.41).
When checking and adjusting the valve timing, the timing cover must always be installed. In addition, the timing belt must be properly tensioned, as its outer surface has timing marks for the pulleys of both camshafts.
The mark on the timing belt pulley mounted on the crankshaft must be in exact alignment with the mark on the oil pump housing.
The timing belt tensioner mechanism includes a spring and a friction element. The latter serves to absorb small vibrations and fluctuations in engine crankshaft speed. The spring ensures correct timing belt tension regardless of belt wear and engine temperature.
The timing belt tension should be adjusted on a cold engine.
NOTE: If the engine temperature is higher or lower, remember that the timing belt tensioner mounting elements will take a different position than the original one at a temperature of 20°C (Fig. 5.42).
Fig. 5.40. Operation diagram of the electromagnetic valve for controlling the oil supply: 1 – pulley of the valve timing mechanism; 2 – spring-loaded locking pin; 3 – rotor; 4 – rotor blade; 5 – plunger; 6 – return spring; 7 – VCT oil supply control electromagnetic valve; A – channel connected to chamber a; B – channel connected to chamber b; C – oil supply channel; D – oil return channel.
Fig. 5.41. Timing marks (camshaft phases): 1 – timing mark of the exhaust camshaft pulley; 2 – timing cover with timing marks; 3 – timing mark of the intake camshaft pulley; 4 – toothed pulley of the intake camshaft; 5 – toothed pulley of the exhaust camshaft; 6 – timing mark of the timing gear pulley on the crankshaft; 7 – toothed pulley of the timing belt on the crankshaft; 8 – crankshaft.
Fig. 5.42. Positions of the timing belt tensioner installation elements of the 2.5L Duratec-V15 engine at different engine temperatures.
[The article was taken in its entirety from the specified website fordbook.ru]