Camshaft Control (CVVT)
Both intake camshafts and exhaust camshafts are regulated by the Engine Control Module (ECM). The intake camshafts are located in the middle of the engine, while the exhaust camshafts are located furthest out. The camshafts are divided into two banks.
Bank 1 (front cylinder row); cylinders 1, 3, 5 and 7.
Bank 2 (rear cylinder row, closest to the passenger compartment); cylinders 2, 4, 6 and 8.
The inlet camshafts are driven primarily by the crankshaft and chain, whilst the exhaust camshafts are driven by a chain from the inlet camshafts.
When each camshaft is set at the factory, it is aligned with the position of the crankshaft. The position of the camshaft in relation to the crankshaft is designated the camshaft 0 position (default setting). During camshaft control (CVVT) the camshaft 0-position is offset so that the cam timing changes. The opening and closing of the intake and exhaust valves can be changed to match the camshaft. Engine performance can be increased, idle quality increased and emissions reduced by regulating the camshaft timing changes.
The engine control module (ECM) detects the position of the camshafts by comparing the signals from the engine speed (RPM) sensor (1) (crankshaft position) and the camshaft position (CMP) sensors (2) (camshaft positions). The engine control module (ECM) then controls the angle of the camshaft by controlling the oil flow to the CVVT unit using the reset valve camshaft (3).
There are diagnostics for this function. See also: CAMSHAFT DIAGNOSTICS (CVVT)
Controlling, reset valve camshaft
1. Oil filter reset valve camshaft.
2. Oil duct (pressure, inlet).
3. Duct leading to CVVT unit chamber (deployment).
4. Duct leading to CVVT unit chamber (deployment).
The camshaft reset valve controls the oil flow to the continuous variable valve timing (CVVT) unit. The engine control module (ECM) uses a pulse width modulation (PWM) signal to control the valve. See also: CAMSHAFT RESET VALVE (CONTINUOUS VARIABLE VALVE TIMING (CVVT))
Controlling, CVVT units
The CVVT units are the "Vane" type which means that the CVVT unit rotors are turned by oil pressure on one, or the other, side of the rotor wings.
A. CVVT unit exhaust
B. CVVT unit inlet
1. Timing belt pulley inlet camshaft (primary, inlet camshaft driven by the crankshaft).
2. Timing belt pulley inlet -/exhaust camshaft (secondary, exhaust camshaft driven by inlet camshaft).
3. Oil duct reset valve camshaft (pressure).
4. Oil duct for controlling CVVT unit.
5. Oil duct for return CVVT unit.
6. Spring (CVVT unit exhaust camshaft only).
The continuous variable valve timing (CVVT) unit allows the position of the camshaft to be adjusted relative to the crankshaft.
The camshaft is secured to the CVVT unit rotor. The rotor (and with it the camshaft) rotates in relation to the timing belt pulley (1) by the oil pressure building up on one or both sides of the rotor vanes in the CVVT unit.
The difference in function between the exhaust camshaft (A) and inlet camshaft (B) CVVT unit is that the exhaust camshaft CVVT unit is equipped with a spring. The force of the spring makes the CVVT unit deploy the camshaft. The function causes faster deployment of the exhaust camshaft at engine start-up, before the oil pressure build in the engine.
Control occurs according to the following during deployment/return of the camshaft.
A. Exhaust camshaft
B. Inlet camshaft
- Oil pressure from the lubrication system (1) of the engine.
- The oil passes the filter for the camshaft reset valve (2) and then on to the reset valve (3).
- The engine control module (ECM) controls the oil flow to one of the CVVT unit chambers (4) depending on whether it is to be deployed/returned by the camshaft.
The reset valve is controlled by the engine control module (ECM) by high frequency, switching for deployment and return. This results in rapid and precise control. Both camshafts can be controlled up to 40 crankshaft degrees.