But we know the so-called variable valve timing technology, its function is mainly to change the time of engine valve opening and closing, in order to achieve a more reasonable control of the amount of air required for the corresponding engine speed, the main purpose is to reduce fuel consumption and improve economy. . The actual dynamic performance of the engine is related to the amount of oxygen that enters the cylinder per unit time. The variable valve timing system cannot effectively change this, so it does not help the power boost.
Since the variable valve timing system is powerless, it is now the turn of the main variable valve lift system in this article. Compared with variable valve timing, the valve lift system is still relatively rare, especially the continuously variable valve lift technology is only the top secret technology in the hands of several large manufacturers, so the equipment we can buy can be changed. There are not many models of the valve lift system. Let's take a look at which models are available.
Read the instructions before:
This article will mainly introduce the variable valve lift systems of the three major manufacturers. However, due to their different technical differences and different brand levels, the models of the models involved in this article are quite different. Therefore, we only do technical analysis and there is no comparison between the models. Please pay attention to netizens.
Honda variable valve lift technology: VTEC, i-VTEC
Application model: all domestic Honda and Acura models
"The engines of many models of Honda and Acura are equipped with VTEC or i-VTEC systems."
Honda is the first manufacturer to apply variable valve lift technology to on-board engines, and unlike other manufacturers who use variable valve timing and then add variable valve lift technology, Honda engineers at the beginning of the R&D project. The two technologies are synchronized. The simple structure and ingenious design are the characteristics of Honda's variable valve lift mechanism. The specific working methods will be introduced below.
However, it is somewhat regrettable that although it has been put into production for many years, Honda's variable valve lift technology does not seem to have much progress at present, and it still stays at a level of only two or three stages (depending on the model, the specific technology has The difference, while latecomers in the field of variable valve lift technology like Fiat, Toyota, Nissan and BMW have developed their own continuously variable valve lift technology. However, there is news that Honda has also developed its own continuously variable valve lift and timing system AVTEC, but it has not yet officially started to use.
"The Civic R18A single overhead camshaft engine"
Here we briefly introduce the working mode of the variable valve lift mechanism in the VTEC and i-VTEC systems. Honda and Acura currently sell models in both domestic SOHC and DOHC engines. Although they are equipped with VTEC or i-VTEC systems, the implementation is not the same.
Fit, Fengfan and Civic are all equipped with Honda's R-series engines, which use the SOHC single overhead camshaft structure. The two intake valves and the two exhaust valves are driven by a single camshaft. The first thing to note is that most of the current variable valve lift technology is applied to the intake valve end, and Honda's R series is no exception.
As can be seen from the above figure, there is a special rocker arm in the middle of the two intake valve rocker arms, which corresponds to a high angle cam on the camshaft, and two intake rocker arms at low engine speed. Separate from this special rocker arm, the intake rocker arm is only driven by a low angle cam, so the lift of the intake valve opening is small, which helps to improve fuel economy at low speeds. However, when the engine reaches a certain speed, the electro-hydraulic controlled connecting rod connects the two intake rocker arms with the special rocker arm, and the three rocker arms are simultaneously driven by the high angle cam, and the valve rises. The process will also increase, the amount of air intake per unit time is greater, and the engine power is stronger.
"The 2.4-liter DOHC double overhead camshaft engine on the Accord and Platinum Core"
In addition to the R series for small cars and compact cars, the Honda's Think Platinum, Accord and CR-V 2.4L models are equipped with DOHC double overhead camshaft K-series engines, all equipped with variable valve lifts. Process technology. In addition, Honda's VTEC system can adjust the valve lift at the intake and exhaust of the DOHC dual overhead camshaft engine. However, this function is not available on all Honda DOHC engines and is limited to certain models.
"Honda's variable valve lift function works on both the intake and exhaust ends, but it is limited to certain models."
The working principle is exactly the same as that of the R series engine. It is realized by the linkage and separation of the three rocker arms. However, since the exhaust valve lift can also be improved, it means that the exhaust effect will be higher at high speed. The engine's power output can be enhanced by a more tacit and efficient intake valve cooperation.
From the above introduction, we can see that Honda's variable valve lift system structure is not complicated. Engineers use the third rocker arm and the third cam to achieve a seemingly complicated valve lift change. But this principle is also the bottleneck of Honda's variable valve lift technology advancement, because it is impossible to add more cams to the camshaft to achieve more levels of adjustment, so both Nissan and BMW have a different approach, and eventually realized Let the valve lift continuously change, let's take a look at how Nissan does it.
Nissan Variable Valve Lift Technology: VVEL
Application model: Infiniti G37, Infiniti FX50
"At present, VVEL technology is only applied to two models of Nissan's high-end brand Infiniti."
Nissan is a latecomer in the field of variable valve lift, which has not been seen on Nissan models for many years. However, at the end of 2007, with the launch of the fourth-generation G37, Nissan finally released its own variable valve lift technology VVEL. This technology was first equipped on the G37's VQ37VHR engine, and VQ37VHR was also 2008 Ward. The winner of the top ten engine. The VK50VE engine of the FX50, which was subsequently launched, is the second engine to use VVEL. At the same time, Nissan also plans to popularize VVEL to its low-end models.
Honda's VETC uses different cams to achieve changes in valve lift at different speeds, while Nissan makes a fuss about the rocker that drives the valve movement. In order to achieve this variable function, it is necessary to develop a mechanism that can change the working condition steplessly. Nissan's VVEL system achieves this by using a simple screw and screw sleeve.
"Unique rocker arm structure that can realize VVEL continuously variable valve lift technology"
Screw can be understood as a common bolt in daily life, and the screw sleeve is a nut screwed on the bolt. The nut can move up and down along the thread on the bolt as it rotates. From another angle, this is a stepless adjustment method. . Nissan's engineers added a set of screws (bolts) and nuts (nuts) to the valve rocker arm of the engine to make the valve lift continuous (stepless) variable.
The specific implementation method is also very simple, and we have to admire the whimsy of these engineers. First, the onboard computer determines the position of the screw sleeve based on the current engine speed. The black DC motor is used to drive the screw sleeve. The threaded sleeve is connected to the control rod by a connecting rod, and the lateral movement of the threaded sleeve can drive the control rod to rotate. When the control rod rotates, the upper rocker arm rotates, and the rocker arm is connected with the link B (link B). When the rocker rotates counterclockwise, it will drive link B to the output cam at the upper end of the top lifter. Finally, the output cam will jack up the valve to change the valve lift. If you don't understand it, please read this paragraph together with the above two figures, it should be easy to understand.
Nissan's VVEL continuously variable valve lift system is within a certain range (the size of this range is determined by the length of the screw and the angle of the output cam) to achieve stepless continuous adjustment, with corresponding valves for different engine speeds. Lift, this form is undoubtedly more flexible and autonomous, but the VVEL system is currently only used at the intake end, so there is still room for evolution. Nissan also announced that it will apply VVEL technology to most of its models in 2010, and we are very much looking forward to it.
BMW Variable Valve Lift Technology: Valvetronic
Application model: BMW models other than M3 and M5 sold in China
"BMW's Valvetronic is equipped on most BMW models."
Compared with Nissan's VVEL, BMW's Valvetronic variable valve lift technology is more well known. This is BMW's own variable valve lift technology released in 2001. It is widely used in BMW engines and is currently sold in China. The engine of the BMW models outside the M3 and M5 has this function. Like Nissan's VVEL, BMW's Valvetronic is one of the few valve lift technologies that can be continuously variable.
BMW's Valvetronic system also relies on changing the rocker structure to control valve lift. Most of the traditional engines use the cam on the camshaft to squeeze the rocker arm to drive the valve lifter to move the valve up and down. BMW engineers add an eccentric camshaft between the camshaft and the traditional rocker arm. Part), the change in cam position on the eccentric camshaft is used to achieve a change in valve lift.
Nissan's VVEL range depends on the length of the screw, while BMW's Valvetronic's valve lift range is determined by the angle and height of the eccentric cam. According to the official introduction, this system can increase the valve lift by up to 10mm. It is helpful to increase the intake air volume at the speed.
When the engine is running, the computer controls the angle of the eccentric cam according to the engine speed. When it rotates to the right to the head, the valve rocker arm is also placed at the lowest position, and the valve opening is the largest.
Although it is a rocker mechanism that changes the camshaft and the valve lifter, BMW's Valvetronic and Nissan's VVEL design ideas are completely different. However, some people think that BMW's system structure is somewhat complicated, and its function in the high speed limit state is not ideal. This is why the M3 and M5 high-speed engines do not use Valvetronic. At the same time, like VVEL, Valvetronic is currently only used on the intake end of the engine, so the development of a more powerful and lighter new Valvetronic system may be what BMW is doing now.
to sum up:
In addition to the three vendors described in this article, Fiat, Audi, Porsche, Toyota, Mitsubishi and Subaru also realized the variable function of engine valve lift through their own technology exploration, but overall this technology is still far from the domestic Not to reach the level of popularity, I hope that with the growth of the Chinese market, major joint ventures will soon introduce the latest technology to domestic models for sale, and hope that our own brands can develop their own similar technologies as soon as possible.
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