Understand automotive engine VVT technology.

Often seen on the hood of the car “cvvt, dvvt, vvt, VVT-i, double VVT-i” and other words, these words sometimes appear in the configuration of new cars, today to talk about these words are what they mean, and what is the difference?

VVT (Variable Valve Timing Technology)

The full name of VVT is Variable Valve Timing. The advantage of a car engine with a VVT system is that it is fuel-efficient and has a large power-to-liter ratio; the disadvantage is that it has insufficient torque in the middle range of speed.

The VVT system regulates the cam phasing of an automotive engine based on a configured control and actuation system, which allows the valve opening and closing times to vary with engine speed, thereby improving charging efficiency and increasing engine power.

To put it bluntly, the so-called VVT variable valve timing is to find a way to change the cam, and then change the characteristics of the two curves, such as the starting point, the endpoint of the advance and delay, and the control of the maximum lift. When the car engine is at low speed, it is required to close the intake valve earlier, to meet the requirement of closing the intake valve earlier in low speed, which can increase the maximum torque; when the car engine is at high speed, it is required to close the intake valve a little later, which can increase the maximum power.

VVT-i (Variable Valve Timing Intelligence)

Toyota’s VVT-i technology has been widely used in its engines. Its main principle is to add a set of hydrodynamic mechanisms to the camshaft, and through the control of the ECU (engine computer), it regulates the opening and closing time of the valves within a certain angle, either opening earlier or delaying or keeping it constant. In this case, the outer rotor of the camshaft timing gear is connected to the timing chain, and the inner rotor is connected to the camshaft.

The switching between these is realized by the VVT solenoid valve, and the solenoid valve by changing the direction of oil flow to make the camshaft angle advance or delay, thus changing the valve opening time length.

 

Dual VVT-i

Dual VVT-i controls the engine’s intake and exhaust systems separately. When the car speeds up, the VVT-i system that controls the intake will advance the time of intake and delay the time of exhaust, which will increase the lift of the valves and increase the intake volume, so that the gasoline can be completely combusted, and realize the purpose of low carbon emission.

Dual VVT-i engine is an acronym for Toyota’s Intelligent Variable Valve Timing system. Most of the engines in the latest Toyota vehicles are now fitted with the VVT-i system. Even a small turbocharger can effectively boost the engine’s power. Its operating principle is that when the engine switches from low speed to high speed, the system’s electronic computer automatically presses oil into the small turbo inside the drive gear of the intake camshaft, and driven by pressure, the small turbo rotates at a certain angle in the opposite direction of the gear casing, so that the camshaft rotates forwards or backward in the interval of a 60-degree angle. This adjusts the timing of the intake valve opening and closing, allowing for continuity in adjusting valve timing.

CVVT (Continuously Variable Valve Timing)

Kia’s CVVT is an imitation of the VVT technology but with a different name. Currently, CVVT technology is widely used in modern cars. The CVVT system consists of the following parts: oil pressure control valve, intake cam disc, crankshaft main sensor, cam position sensor, oil pump, and engine electronic control unit (ECU).

 

The position of the oil pressure control valve is altered when the engine is started or shut down, causing the intake cam timing to be retarded.

When the engine is idling or under low-speed load, the timing is also in the retarded position, which enhances the stable working condition of the engine. When the engine is under low speed and high load, the cams are in the advanced position to increase torque output. When the engine temperature is low, the cam position is in the delayed position to stabilize the idle speed and reduce fuel consumption.

DVVT (Dual Variable Valve Timing)

The full name of DVVT is Dual Variable Valve Timing (DVVT), which means Continuous Variable Valve Timing (CVT). The engine with DVVT technology is more efficient, energy-saving and environmentally friendly than the engine with intake valve timing technology, which is more commonly used in the current market. DVVT technology can reduce fuel consumption and increase power at the same time; by controlling the gasoline and air mixture in the combustion chamber of the engine to achieve the most suitable air-fuel ratio, it can also significantly improve the idle speed stability and thus obtain better comfort.

DVVT not only regulates the intake valve timing but also the exhaust valves. The greatest advantage of this simultaneous intake and exhaust regulation technology is that it can realize high torque at low speeds, significantly improving the engine’s power output at low speeds. In addition, due to the realization of the exhaust valve timing adjustment, the DVVT engine’s emissions are also lower, and therefore more environmentally friendly.

DVVT engine is the continuation and development of VVT, which solves the technical problems that the VVT engine has not been able to overcome.DVVT that is, Double Continuously Variable Valve Timing (DVVT) for intake and exhaust, which can be said to be the most advanced form of the current valve variable timing system technology.

VTEC (Variable Valve Phase and Lift Control)

The full name of VTEC is Variable Valve Timing and Lift Electronic Control System. In 1989, Honda introduced the self-developed Variable Valve Timing and Lift Electronic Control System, or VTEC for short, which is the world’s first valve control system that can simultaneously control valve opening and closing time and lift.

VTEC is mainly composed of the TEC control system, which consists of a control part, an actuating part, and a sensor. The control part includes the engine control unit ECU and the VTEC solenoid valve; the actuating part includes the cams, rocker arms, and each piston. It includes the engine speed sensor, vehicle speed sensor, and coolant temperature sensor. When the engine is running, the control unit ECU determines whether it is necessary to change valve timing and valve lift based on signals from each sensor.

VTEC needs to be opened at a certain speed, and VTEC technology changes the timing of the engine’s intake and the size of the valve opening. When the engine is running at high speed, it needs more power. At this time, it needs to increase the amount of air intake and change the intake time. When VTEC works, the exhaust sound becomes very violent, so it will be called VTEC Explosion.

 

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