Multivalve, Variable Intake, and Valve Timing Systems
Multivalve Systems
Multivalve Systems involve using more than one valve for intake and exhaust (ESCP), operating either simultaneously or only when necessary. In a four-valve configuration, the valves are typically mounted in parallel, two by two, on the cylinder head. They are usually controlled by two camshafts: one for intake and one for exhaust.
Benefits of Multivalve Systems
- The intake cross-section is increased by at least 30%, improving airflow.
- Optimizes the size and shape of the combustion chamber.
- Smaller, lighter valves allow for faster opening and closing.
- Softer valve springs prevent rebound, resulting in quieter operation.
- Smaller valve size enhances cooling.
Variable Intake Systems
Variable Intake systems modify the intake manifold to suit different engine speeds, improving cylinder filling. There are two main types:
Inertia of Gases
As engine speed (Q) increases, the length of the intake duct should be reduced, and the diameter increased. This maintains the momentum of the gases and avoids pressure losses. Therefore, at low RPM, collectors are long and narrow, while at high RPM, they are wider and shorter.
Acoustic Resonances
This method is based on studying the oscillations of the gas mass inside the intake manifold. A device varies the dimensions of the collector based on these oscillations, achieving better filling at different engine speeds.
Variable Valve Timing Systems
Variable Valve Timing systems offer at least two distribution diagrams: one for low-to-medium RPM (improving cylinder filling) and another for high RPM (providing high performance). This results in a more flexible engine with a broader, more stable torque curve, and cleaner emissions.
VarioCam System
This system varies the valve timing using a hydraulic tensioner located on the chain that transmits rotation between the two camshafts. It acts on the intake camshaft. The system is controlled by the injection control unit, which uses an electrical signal to regulate the adjustable tensioner.
Operation
Below 1500 RPM or above 5500 RPM, the hydraulic tensioner is in the top position, so it does not affect the valve timing. At 1500 RPM, the tensioner moves to the lower position, advancing the intake camshaft by 7.5° relative to the exhaust camshaft. This changes the valve timing, resulting in greater cylinder filling as the valves open earlier and close later.
VTEC System
This system varies the valve opening height at different moments depending on the RPM.
Operation
This system, for a 4-valve configuration, incorporates three cams for intake and three for exhaust. The central cam has a higher lift and is only activated at high RPM. The injection control unit activates this, engaging all three cams. Because the central cam has a greater lift, the valves remain open longer, improving cylinder filling. When the RPM decreases, a return spring pushes the piston, disengaging the rocker arms.
VTEC-E System
This system is derived from VTEC but operates differently. It only affects the intake valves, opening only one valve at low RPM and both at high RPM, offering clear advantages.
Operation
When the engine exceeds 2500 RPM, the control unit sends a signal to open a valve, which leads to hydraulic pressure displacing a piston. This interconnects the rocker arms, opening both intake valves in unison. This system also often features a variable intake system to further improve engine performance.