1, valve timing technology overview

Engine intake and exhaust valve opening and closing the beginning of the termination of the moment, usually expressed in terms of crank angle, known as the valve timing angle. From the valve timing diagram (see), it can be seen that the intake valve moves forward (α) and delay closes (β) during the intake process (light gray) of the piston moving from top dead center to bottom dead center. When the engine is finished, the exhaust valve moves forward (γ) and de-closes (δ) during the exhaust (dark gray) of the piston moving from the bottom dead center to the top dead center. Engine speed is very high, a four-stroke engine working stroke only a few thousandths of a second, such a short time will often lead to insufficient engine intake, exhaust is not net, resulting in power down.

Therefore, in order to solve this problem, the engine is generally used to extend the intake and exhaust valve opening time, increase the gas inlet and outlet capacity to improve the intake and exhaust valve working condition, in order to improve the performance of the engine.

Technology is gradually being applied to modern cars in recent years, a new technology, the use of intelligent variable valve timing engine at low speed, the valve overlap angle is relatively small, so that the valve ahead of time to open and delay off The valve overlap angle becomes larger, so that the valve ahead of time to open and delay the time to shorten the closure, so that the engine in all conditions can be fully into the air, thereby enhancing the The engine efficiency, but also to the engine at low speed to have sufficient torque output, high speed can have more powerful power output, so that the engine torque output more stable, the characteristic curve is more linear.

2, the engine intelligent variable valve timing system components and working principle

 2.1VVT-i system components

VVT-i system mainly consists of the following four parts:

 1) Sensor, crankshaft position sensor, intake manifold air pressure sensor, throttle position sensor, water temperature sensor and camshaft position sensor are responsible for collecting the engine load status and feedback information to the ECU.

2) The electronic control unit ECU, ECU stores the optimal valve timing parameter value, ECU collects the sensor information and carries on the contrast calculation with the predetermined parameter value, calculates the revision parameter and sends out the instruction to control the camshaft timing hydraulic control valve.

3) Camshaft timing hydraulic control valve, according to the ECU command to control the position of the oil tank valve, which is to change the hydraulic flow, the advance, lag, keep the same signal command to select the variable valve timing controller to the different oil Road.

Out of the advantages of this system, the development trend.

4) variable valve timing controller, installed on the exhaust camshaft, known as the blade variable valve timing controller, installed in the intake camshaft, known as the spiral groove variable valve timing Controller. The two structures are somewhat different, but have the same effect.

2.2VVT-i system control and working principle

From the 3 can be seen, VVT-i engine ECU stores the best valve timing parameter values, in a variety of driving conditions, ECU automatically search valve timing actual value, and its internal valve timing target value contrast correction, calculation A valve timing corresponding to the engine speed, the intake air amount, the throttle position and the cooling water temperature, and issues a command control camshaft timing hydraulic control valve which controls the position of the oil tank valve according to the ECU command, Change the hydraulic flow, the advance, lag, remain unchanged, and other signal command to select the delivery to the VVT-i controller of the different oil.

The ECU of the VVT-i engine simultaneously senses the actual valve timing by feedback information such as the crankshaft position sensor, the intake manifold air pressure sensor, the throttle position sensor, the water temperature sensor and the camshaft position sensor, and then executes the feedback control to compensate the system Error, the position to achieve the best valve timing, which can effectively improve the vehicle's power and performance, to minimize fuel consumption and emissions.

3, the engine intelligent variable valve timing system advantages

3.1 The whole engine operates more linearly

VVT-i engine valve timing is continuously variable, so the engine in all conditions can be obtained under the appropriate appropriate valve stacking angle, the engine power and torque output will be more stable, more linear characteristic curve.

3.2 better torque and power output

VVT-i engine at the same time taking into account the high and low speed power output. The engine speed can be designed to be higher, and thus get more power output. Low speed, the use of a larger valve stacking angle, can improve low-speed torque; high-speed valve with a smaller stack angle, can enhance the engine power. In this way, you can improve the engine at low speed and high speed of the valve condition, which can ensure that the engine at high and low speed torque and power output will exceed the traditional engine.

3.3 Better fuel economy

As the engine in each condition can be obtained under the most appropriate valve stacking angle, the fuel combustion efficiency is higher, so as to improve the torque and power output under the premise of reducing the effective fuel consumption and exhaust emissions.

3.4 enhanced low-speed operation flexibility

VVT-i system block diagram VVT-i system components at low speed to increase the torque output, greatly enhance the driving flexibility of the operation.

3.5 system structure is simple

Although the advantages of VVT-i many, but its technology is not complicated, the work of the engine did not put forward higher requirements. Process requirements than the traditional requirements of the engine is not much higher, so the manufacturing cost is not expensive. Its hardware cost is only in the camshaft on the assembly of a hydraulic valve, through the solenoid valve to control the rotation of the hydraulic valve to change the camshaft angle of purpose, thereby changing the engine valve timing.

4, summary

To sum up, VVT-i engine compared with the traditional engine. The main technical difference is the continuous variable valve timing. With the help of automatic control technology, the traditional engine fixed valve overlap angle, under the control of the computer with the traffic conditions change. Difficult to resolve the design contradictions in the past, now with the help of the computer to achieve the best of all conditions. The reason why many manufacturers do not have all the engines are matching VVT-i, because of software constraints - the design of a precise and appropriate gas distribution control software, not every engine can be easily done, it needs the overall design and match. Can be expected, the future direction of development of the car should be the automation of the control and operation of the intelligent.