What do DVVT and CVVT of automobile engines mean?

CVVT is the abbreviation of English Continue Variable Valve Timing, which is translated into Chinese as continuously variable valve timing mechanism. It is one of many variable valve timing technologies that have been gradually applied to modern automobiles in recent years. For example, BMW is called Vanos, Toyota is called VVTI, and Honda is called VTEC, but whatever they are called, their purpose is to match the best valve overlap angle (valve timing) for different engine working conditions, but the methods are different.

CVVT, developed by Hyundai Motor Company of Korea, is a technology to control the required valve overlap angle by changing the time when the camshaft opens the intake valve in the morning and evening through the electro-hydraulic control system. This technology focuses on the initial letter C (Continue), emphasizing that the valve overlap angle is always controlled according to the continuous change of engine working conditions, thus changing the air intake of the cylinder. When the engine is running at low speed and small load (idle state), the opening time of intake valve should be delayed and the valve overlap angle should be reduced to stabilize the combustion state. When the engine is running at low speed and heavy load (starting, accelerating and climbing), the intake valve opening time should be advanced and the valve overlap angle should be increased to obtain greater torque. When the engine is running at high speed and heavy load (high speed), the opening time of the intake valve should also be delayed to reduce the valve overlap angle and improve the working efficiency of the engine. When the engine is in a medium working condition (medium speed and uniform driving), CVVT will also delay the opening time of the intake valve and reduce the valve overlap angle. The purpose at this time is to reduce fuel consumption and pollution emissions.

CVVT system includes the following parts: oil pressure control valve, intake cam gear, crankshaft sensor, cam position sensor, oil pump and engine electronic control unit (ECU).

The toothed disc of the air intake cam comprises an external gear driven by a timing belt, an internal gear connected with the air intake cam and a control piston which can move between the internal gear and the external gear. When the piston moves, the spiral gear on the piston will change the position of the external gear, thus changing the timing effect. The displacement of the piston is determined by the oil pressure control valve, which is an electronic control valve, and its oil pressure is controlled by the oil pump. When the computer (ECU) receives input signals such as engine speed, air intake, throttle position and engine temperature, it will determine the operation of the oil pressure control valve. The computer will also use the cam position sensor and crankshaft position sensor to determine the actual valve timing of the intake cam.

When the engine is started or shut down, the position of the oil pressure control valve changes, so that the intake cam timing is in a delayed state. When the engine is idling or loading at low speed, the timing is also in the delayed position, which improves the stable working state of the engine. The intake cam is in the advanced position when it is in the middle position, and it is in the advanced angle position to increase the torque output when it is in the middle, low speed and high load. When at high speed, it is in a delayed position to facilitate high-speed operation. When the engine temperature is low, the cam position is in the delayed position, which stabilizes the idle speed and reduces the fuel consumption.

The full name of DVVT is dual variable valve timing, which means the continuous variable timing technology of intake valve and exhaust valve. The engine with DVVT technology is more efficient, energy-saving and environmentally friendly than the engine with intake valve timing technology widely used in the market at present. Taking Roewe 550 as an example, DVVT technology can reduce fuel consumption by 5%, and at the same time increase power by 65,438+00%, reaching the power index of 2.0 displacement, and the exhaust emission reaches the national IV standard; By controlling the mixture of gasoline and air in the engine combustion chamber to achieve the most suitable air-fuel ratio, the idling stability can be obviously improved and better comfort can be obtained.