1, the variable valve
automotive engine valve timing when the mechanisms and techniques, also called a continuously variable valve timing system.
Introduction 
illustrating a variable valve engine
The variable valve timing system. Today’s high performance engine is equipped with the universal system. The system, or the phase of the engine cam drive is adjusted by a valve with green control and execution system, so as to achieve the purpose of optimizing the process of engine valve.
Principle
because of high speed and low speed, the impact angle of the valve timing of the engine power and economy will be apparent, at high speed can take advantage of the inertia of the intake air amount, and proceeds to mention sweep gas efficiency, the late opening and early closing valve, low speed and vice versa, the engine now has mostly the art.
origin
four-stroke piston engine by intake, compression, power, exhaust four stroke is completed, we are concerned that the problem valve opening degree of the engine intake air. The basic principle of the cylinder intake air is “negative”, i.e. the gas pressure difference between inside and outside the cylinder. When the engine at low speed, the degree of opening of the valve must not be too large, so easily lead to internal and external pressure equalization cylinder, negative pressure decreases, the intake is not sufficient for the valve work is concerned, this “small degree on” needs a short trip controlled manner; and high-speed contrary, the speed at every turn 5000rpm, if still shy refused to open the valve, engine intake inevitable blocked, so we need a long stroke of valve lift. Often, engineers have to take into account not only the engine torque characteristics in the low-speed region, want to squeeze the power characteristics of the high-speed zone, but to take a “compromise” the idea, did not end the high-speed engine power, the lack of low-speed torque ……
Therefore, in such cases, a need for a device for valve lift adjustment is carried out, which is what we want to say “variable valve timing technology.” The technology can guarantee low speed high torque, high speed and high power can be obtained, for engines, it is a great breakthrough.
1980s, many companies began to put research at the positive variable valve timing, for the first time in 1989, Honda issued a “variable valve valve timing and valve lift electronic control system,” the English name “Variable Valve Timing and Valve LifeElectronic Control System, which is our common VTEC. Since then, various companies continue to develop the technology, and today has been very mature, Toyota also developed VVT-i, Porsche developed Variocam, modern developed DVVT …… almost every enterprise has a variable valve timing their technology . Although a series of variable valve timing technology trade names vary, but its design is extremely similar.
2. Category Description
Porsche VarioCam
911 variable valve timing car engine uses technology VarioCam
through the valve and we find its two positions, in each of FIG. intake valves were two kinds of maximum travel, green location is obviously a high-speed valve timing to achieve the maximum stroke. Control valve lift variation, two sets of the control cam, a high-speed cam is set, only the red portion of the cam; another group of low-speed cam, both cams between the high-speed cam.
When the engine at low speed condition, the control valve seat yellow top of the piston within the valve seat falls. Such speed cam drive only the downward stroke of the valve seat and the valve can not drive the whole operation, the entire top valve downward stroke valve drive by the low-speed cam, the valve opening degree obtained in this way is small. Conversely when the engine operating condition at high speed, driving the hydraulic control piston in the valve seat is pushed into the top of the valve, the valve seat and a valve connected to a rigid, high-speed driving of the cam driven valve seat can be obtained from the valve downstroke large valve opening.
Honda VTEC
with the same slightly Variocam Porsche, Honda VTEC proximity principle, different control mode.
are arranged on the camshaft is still low speed cam and the cam, but the Honda engine valve is driven by the rocker arm, it is not as compact as a Porsche. High and low speed cam switching control is a complex structure of the rocker arm, the rotational speed of the engine detected by the sensor, to the ECU is controlled by the control ECU instructs the rocker arm.
Briefly, this rocker arm is able to automatically select a row of intake valve operating the intake or 2 depending on the rotational speed2 rows of 4-valve work, so that the engine can be smooth and comfortable high and low speed conditions.
Generally, when the speed is less than 3500rpm, each with an intake and exhaust cam operating, when the engine is approximately a 2-valve engine, this benefit is possible to increase the negative pressure, the intake conducive; rotational speed exceeds 3500rpm when the hydraulic servo-based central controller to the engine ECU command oil pressure of the rocker arm, the timing of the pressure oil to promote movement of the plunger, the plunger such that the synchronous high-speed rocker arm and rigidly connected to the main and auxiliary rocker arm, this time low Although the rotation of the cam, but in the idle state, not involved in the work, work together so that the piston 4, to accommodate high-speed operation.
BMW Valvetronic
and Porsche VarioCam, Honda VTEC same technology there are many, for example, Toyota VVT-i, VVT general ECOtec series engine, etc., these techniques can alter the valve lift, but the limitation is that these technologies are only “two-stage” adjustable moment changes in the valve stroke will feel a sense of frustration. As a result, BMW took pains to adjust the valve stroke, we have developed a continuously variable valve timing technology, currently known as the most tech valve timing technology.
Unusually, BMW uses a motor-driven manner, movement of the motor circumference by a worm drive gear, the control angle changes becomes quasi rocker arm, then the rocker arm camshaft driven by the valve drive motion. By changing the angle of the rocker arm to vary valve stroke. As a result of motor control in the motor ECU instruction can be “Promise” angle changes, so changes the valve lift does not affect the engine work, there is no sense of frustration, but also targeted more careful with each speed range gas analysis.
Renault – Nissan CVTC
Renault, Nissan then combined for a number of common technologies are within the group. Including the Nissan painstaking research CVTC continuously variable valve timing system. Honda VTEC proximity principle, also uses hydraulic pressure to change the angle between the toothed pulleys synchronized with the camshaft end of the camshaft, thereby changing the valve timing angle.
When the camshaft timing with high pressure oil region and the low pressure area between the gear oil. As long as the oil pressure between the two adjustment zone differences, you can change the angle of the valve timing. Two hydraulic oil by the oil pressure control valve region regulated. When the high pressure oil passage (The red channel) is turned on, the entire oil chamber in a pressurized state, the deflection angle of the camshaft clockwise, valve timing is delayed, increasing the overlap angle, is suitable for low speed; yellow region when the solenoid valve control pressure when the pressure is higher than the red zone, the deflection angle of the camshaft counterclockwise, the valve timing is advanced, so that the overlap angle decreases, for high speed.
Type Manufacturer employed
Honda
VTEC variable valve lift hierarchical classification variable valve timing
i-VTEC classification variable valve lift continuously variable valve timing [123 ] TOYOTA
vvt-i continuously variable valve timing
dual VVTI continuously variable valve timing (intake and exhaust valves are independently controlled)
vvtl-i graded continuously variable valve lift varying valve timing of
BMW
The continuously variable valve lift Valvetronic
Double VANOS continuously variable valve timing (intake and exhaust valves are independently controlled)
mass
variable valve timing continuously variable valve timing (intake valve)
there seems audi fsi engine models has been employed comprises a variable valve lift, continuously variable intake valve, exhaust valve timing technique
Mitsubishi
MIVEC classification variable valve lift continuously variable valve timing
Mazda
s-vt classification variable valve lift continuously variable valve timing
Nissan
continuous CVTC variable valve timing