1. The variable valve timing system
automotive engine valve timing when the mechanisms and techniques, also called a continuously variable valve timing system.
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.
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 put the scavenging proceeds efficiency, the late opening and early closing valve, low speed and vice versa, the engine now has mostly the art.
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 is that the cylinder intake ldquo; rdquo ;, i.e. negative gas pressure difference inside and outside the cylinder. When the engine low speed, the degree of opening of the valve must not be too large, so easy to cause a pressure equalization inside and outside the cylinder, the negative pressure is reduced, so that the intake is insufficient, the valve for the work concerned, this ldquo; small degree of opening rdquo; requires short stroke 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 can only take a ldquo; compromise rdquo; thinking, in the end no high-speed engine power, the lack of low-speed torque hellip; hellip;
Therefore, in this case, it is a need for a device for adjusting the valve lift, that is to say we ldquo; variable valve timing technologies rdquo ;. This technique can ensure the low speed high torque, high speed and high power can be obtained, in terms of the engine is a great projectionbroken.
1980s, many companies began to put research at the positive variable valve timing, the 1989 Honda first released ldquo; variable valve valve timing and valve lift electronic control system English name rdquo ;, ldquo; Variable Valve Timing and Valve Life Electronic 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 DVVThellip; hellip; 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.
Variable Valve – Category Description
Porsche VarioCam
911 variable valve timing car engine uses technology Variocam we can find it through the valve has two positions, respectively, each intake valve has two kinds of maximum travel. 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. There is still disposed on the camshaft speed cam and the low speed cam, but the Honda engine valve is driven by the rocker arm, so as not PorscheLike compact. 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 an intake or exhaust valve operating in two rows of the second intake valve 4 depending on the working speed of the engine so that the high-low speed condition can smooth and comfortable.
Generally, when the speed is below 3500 rpm for, 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, facilitates the intake; when the speed exceeds 3500 rpm for, based hydraulic servo command to the engine ECU central controller, the 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 is rigidly connected to the main and auxiliary rocker arm, in this case, although the low-speed cam is rotated, 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, there are many, for example, Toyota VVT-i, VVT same general technique ECOtec series VTEC Honda engines, etc., these techniques able to change the valve lift, but the limitation is that these technologies are only ldquo; two-stage rdquo; 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 becomes quasi-angle change of the swing arm, and the lower roll is driven by the camshaft valve drive arm movement. By changing the angle of the rocker arm to vary valve stroke. As a result of motor control in the ECU commands the motor can ldquo; polar rdquo; angle changes, so changes the valve lift does not affect the engine work, there is no sense of frustration, but also more detailed targeted for each speed range analysis of gas distribution.
Renault Nissan CVTC
Renault, Nissan coAnd later, a number of technologies were shared 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 (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; when the solenoid valve control when the pressure is higher than the yellow red region of the pressure zone, the deflection angle of the camshaft counterclockwise, the valve timing is advanced, so that the overlap angle decreases, for high speed.