Variable Valve Actuation
How do valves work?
IC (Internal Combustion) Engine either have a two-valve or four-valve arrangement dependent on the kind of bikes. A two-valve setup is most commonly seen on budget-friendly commuter motorcycles that focus on bottom end torque and fuel efficiency. A four-valve arrangement is typically offered on execution bikes for that top end snort. Valves work in conjunction with the engine and the carb/fuel-injection systems. However, the opening and closing of these valves are operated by either a single (SOHC) or dual overhead camshaft (DOHC) which control the feed of air/fuel mixture into the engine and the outlet of exhaust gases.
A four-valve arrangement utilizes two bigger valves for admission and two littler ones for exhaust. The arrangement is littler in measurement and lighter in mass contrasted with a two-valve setup. On account of this, the valves travel uninhibitedly and at a higher recurrence, empowering the motor to run at higher rpm and concentrate more execution.
Importance of valve timing:
The precise control over the opening and closing of these valves is called valve timing, and it's absolutely crucial. Camshafts, valves, pistons and crankshafts work together for proper combustion in a cylinder. Any inconsistency in this operation could lead to improper combustion which results in low fuel economy and lack of power.
In a four-stroke cycle, the camshaft needs to complete two full rotations (720 degrees), rotating a full 360 degrees every time the piston goes from top-dead-centre (TDC) to bottom-dead-centre (BDC) and back. In bikes, a cam chain is used to connect the camshaft to the crankshaft. As a result, the camshaft rotates in sync with the crankshaft which runs the piston.
How cam profiling affects valve timing and lift:
Cam rotation comprises of four key aspects - timing, duration, overlap and lift. Simply put, the ‘cam timing' controls when the valve opens while ‘lift’ controls the distance of the opening. More lift means the valve is open for a longer duration allowing for more air-fuel-mixture to get into the combustion chamber.
Simply put, the valve opening relies on the shape of the cam lobes, which force the valves to open as the camshaft rotates. The larger a cam profile, the longer a valve will remain open.
What is Variable Valve Timing:
A two valve engine offers better low and mid-range torque as opposed to a four-valve engine which generates better top end performance. This is where Yamaha’s VVA (another name for VVT) comes into play, it offers the best of both worlds. Variable Valve Actuation (VVA) makes the engine more flexible, offering better low-end grunt without compromising on top end performance.
How Variable Valve Timing works:
Essentially, the system works by shifting between two different intake cam lobes - one for low engine revs and the second for higher revs.
VVA utilizes the main cam between 0 rpm to 7400 rpm. This cam offers better low-end grunt. At 7400 rpm, an actuator pushes a pin in the rocker arm to activate the second cam profile with a larger lobe. The second camshaft also opens the intake valves by an additional 2 mm, letting in more air and fuel for higher combustion. The mechanism then disengages the pin when the revs drop below 7,400rpm, shifting back to the first cam.
The VVA on the Yamaha R15 V3 is a fairly complex setup but it delivers in spades in terms of performance and fuel efficiency. Shift Cam technology, on the other hand, steps it up a notch, so we’ll be covering that at a later stage.
IC (Internal Combustion) motors either have a two-valve or four-valve arrangement dependent on the kind of bikes. A two-valve setup is most commonly seen on budget-friendly commuter motorcycles that focus on bottom end torque and fuel efficiency. A four-valve setup is generally offered on execution bikes for that top end snort. Valves work in conjunction with the engine and the carb/fuel-injection systems. However, the opening and closing of these valves are operated by either a single (SOHC) or dual overhead camshaft (DOHC) which control the feed of air/fuel mixture into the engine and the outlet of exhaust gases.
A four-valve arrangement utilizes two bigger valves for admission and two littler ones for exhaust. The arrangement is littler in measurement and lighter in mass contrasted with a two-valve setup. Because of this, the valves travel unreservedly and at a higher recurrence, empowering the motor to run at higher rpm and concentrate more execution.
Importance of valve timing:
The precise control over the opening and closing of these valves is called valve timing, and it's absolutely crucial. Camshafts, valves, pistons and crankshafts work together for proper combustion in a cylinder. Any inconsistency in this operation could lead to improper combustion which results in low fuel economy and lack of power.
In a four-stroke cycle, the camshaft needs to complete two full rotations (720 degrees), rotating a full 360 degrees every time the piston goes from top-dead-centre (TDC) to bottom-dead-centre (BDC) and back. In Motorcycle, a cam chain is utilized to interface the camshaft to the crankshaft. Thus, the camshaft turns in a state of harmony with the crankshaft which runs the cylinder.
How cam profiling affects valve timing and lift:
Cam rotation comprises of four key aspects - timing, duration, overlap and lift. Simply put, the ‘cam timing' controls when the valve opens while ‘lift’ controls the distance of the opening. More lift means the valve is open for a longer duration allowing for more air-fuel-mixture to get into the combustion chamber.
Simply put, the valve opening relies on the shape of the cam lobes, which force the valves to open as the camshaft rotates. The larger a cam profile, the longer a valve will remain open.