Introduction to three types of variable valve lift technologies with similar functions

Among the models currently on the market, including many domestic brand models that we are familiar with, a large proportion of the engines are already equipped with variable valve timing systems. Although there is still a certain gap in the technical level between manufacturers and models, overall, the variable valve timing system has become a relatively popular technology and has become somewhat commonplace.

But we know that the so-called variable valve timing technology is mainly used to change the opening and closing time of the engine valves to achieve a more reasonable control of the amount of air required for the corresponding engine speed. Its main function is to reduce fuel consumption and improve economy. However, the actual power performance of the engine is related to the amount of oxygen entering the cylinder per unit time. The variable valve timing system cannot effectively change this, so it does not help much in improving power.

Since the variable valve timing system is powerless, it is now the turn of the protagonist of this article, the variable valve lift system. Compared with variable valve timing, the valve lift system is still relatively rare, especially the continuously variable valve lift technology, which is a top-secret core technology only mastered by a few large manufacturers. Therefore, there are not many models equipped with variable valve lift systems that we can buy. Let's take a look at what models are available.

Pre-reading instructions:

This article will mainly introduce the variable valve lift systems of the three major manufacturers. However, due to their respective technical differences and brand levels, the grades of the models involved in this article vary greatly. Therefore, we only conduct technical analysis and have no intention of comparing the models. Please pay attention.

Honda variable valve lift technology: VTEC, i-VTEC
Applicable models: All Honda and Acura models sold in China

"Many Honda and Acura models are equipped with VTEC or i-VTEC systems in their engines."

Honda is the first manufacturer to apply variable valve lift technology to vehicle engines. Unlike other manufacturers who first use variable valve timing and then add variable valve lift technology, Honda engineers simultaneously developed these two technologies at the beginning of the research and development project. Simple structure and ingenious design are the characteristics of Honda's variable valve lift mechanism. We will introduce the specific working method below.

Unfortunately, although Honda has been in production for many years, its variable valve lift technology does not seem to have made much progress, and still remains at the level of only two or three adjustable stages (depending on the model, the specific technology is different), while latecomers in the field of variable valve lift technology such as 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 been officially put into use.

『R18A single overhead cam engine equipped in Civic』

Here we briefly introduce the working method of the variable valve lift mechanism in VTEC and i-VTEC systems. Honda and Acura currently sell models in China with two types of engines, SOHC and DOHC. Although they are all equipped with VTEC or i-VTEC systems, the specific implementation methods are slightly different.

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Fit, City and Civic are all equipped with Honda's R series engine, which adopts SOHC single overhead camshaft structure, and two intake valves and two exhaust valves are driven by one camshaft. First of all, it should be noted 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 we can see from the above figure, there is a special rocker arm between the two intake valve rocker arms, which corresponds to a high-angle cam on the camshaft. When the engine is at low speed, the two intake rocker arms and this special rocker arm are separated and have nothing to do with each other. The intake rocker arm is only driven by the low-angle cam, so the lift of the intake valve is small, which helps to improve fuel economy at low speed. But when the engine reaches a certain speed, the connecting rod controlled by the electronic hydraulics will connect the two intake rocker arms and the special rocker arm into one. At this time, the three rocker arms will be driven by the high-angle cam at the same time, and the valve lift will increase accordingly, the intake volume per unit time will be larger, and the engine power will be stronger.

『Accord and Accord are equipped with 2.4-liter DOHC dual overhead camshaft engines』

In addition to the R series used in small and compact cars, the 2.4L models of Honda's Accord, Accord and CR-V in China are all equipped with DOHC dual overhead camshaft structure K series engines, which are also equipped with variable valve lift technology. In addition, Honda's VTEC system can adjust the valve lift at the intake and exhaust ends of the DOHC dual overhead camshaft engine, but this function is not available in all Honda DOHC engines, only limited to certain models.

"Honda's variable valve lift function works on both the intake and exhaust sides, but this is limited to certain engine models."

The working principle is exactly the same as the intake end of the R series engine, and is achieved through the connection and separation of three rocker arms. However, since the exhaust valve lift can also be improved, it means that the exhaust effect will be higher at high speeds, and the intake valve can cooperate more tacitly and efficiently to enhance the engine's power output.

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 seemingly complex valve lift changes. However, this principle is also the bottleneck that hinders the progress of Honda's variable valve lift technology, because it is impossible to add more cams to the camshaft to achieve more levels of adjustment. Therefore, Nissan and BMW have taken a different approach and finally achieved continuous variable valve lift. Let's take a look at how Nissan did it.

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Nissan Variable Valve Lift Technology: VVEL Applied Models: Infiniti G37, Infiniti FX50

"Currently, VVEL technology is only used in two models of Nissan's high-end brand Infiniti."

Nissan is a latecomer in the field of variable valve lift, and this feature has not appeared in Nissan models for many years. But 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 VQ37VHR engine of the G37, and the VQ37VHR was also the winner of Ward's Ten Best Engines in 2008. The VK50VE engine of the FX50 that was subsequently launched was the second engine to use VVEL. At the same time, Nissan also plans to popularize VVEL on its low-end models.

Honda's VETC uses different cams to achieve the change of valve lift at different speeds, while Nissan focuses on the rocker arm that drives the valve movement. In order to achieve the function of continuous variable, a mechanism that can steplessly change the working conditions must be developed. Nissan's VVEL system achieves this goal using a simple screw and screw sleeve.

『Unique rocker arm structure that enables VVEL continuously variable valve lift technology』

We can think of the screw as the bolts commonly seen in daily life, and the sleeve is the nut screwed on the bolt. As the nut rotates, it can move up and down along the thread on the bolt. From another perspective, this is a stepless adjustment method. Nissan engineers added a set of screws (bolts) and sleeves (nuts) to the valve rocker arm of the engine to make the valve lift continuously (steplessly) variable.

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The specific implementation method is also very simple. Here we have to admire the ingenious ideas of these engineers. First, the on-board computer determines the position of the screw sleeve according to the current engine speed. The black DC motor is used to drive the screw sleeve. The screw sleeve is connected to the control rod by a connecting rod. The lateral movement of the screw sleeve can drive the control rod to rotate. When the control rod rotates, the rocker arm above rotates accordingly. The rocker arm is connected to link B (connecting rod B). When the rocker arm rotates counterclockwise, it will drive link B to push the output cam at the upper end of the valve tappet. Finally, the output cam will push up the valve to change the valve lift. If you don’t understand, please read this paragraph again in conjunction with the two pictures above. It should not be difficult to understand.

Nissan's VVEL continuously variable valve lift system can achieve stepless and continuous adjustment within a certain range (the size of this range is determined by the length of the screw and the angle of the output cam), and has corresponding valve lifts for different engine speeds. This form is undoubtedly more flexible and independent, but the VVEL system is currently only used on the intake end, so there is still room for evolution. Nissan has also announced that it will apply VVEL technology to most of its models in 2010, and we are looking forward to it.

BMW Variable Valve Lift Technology: Valvetronic Applicable Models: BMW models sold in China except M3 and M5

"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 and is widely used in BMW engines. Currently, all BMW models sold in China except M3 and M5 have this function. Like Nissan's VVEL, BMW's Valvetronic is also one of the few technologies that can achieve continuously variable valve lift.

BMW's Valvetronic system also relies on changing the rocker arm structure to control valve lift. Most traditional engines use the cam on the camshaft to squeeze the rocker arm to drive the valve tappet to move the valve up and down, while BMW engineers installed an eccentric camshaft (the red part in the above picture) between the camshaft and the traditional rocker arm, and use the change in the position of the cam on the eccentric camshaft to achieve the change in valve lift.

The range of Nissan's VVEL depends on the length of the screw, while the valve lift range of BMW's Valvetronic is determined by the angle and height of the eccentric cam. According to official introduction, this system can increase the valve lift by up to 10mm, which is very helpful for increasing the intake volume at high speed.

When the engine is working, the computer controls the angle of the eccentric cam according to the engine speed. When it rotates to the right to the end, the valve rocker arm is also pushed to the lowermost position, and the valve opening range is the largest at this time.

Although both change the rocker arm mechanism between the camshaft and the valve lifter, the design ideas of BMW's Valvetronic and Nissan's VVEL are completely different, but they are similar in nature. However, some people think that the structure of BMW's system is a bit complicated and does not work well at high speed limits, which is why the high-speed engines of the M3 and M5 do not use Valvetronic. At the same time, like VVEL, Valvetronic is currently only used on the intake end of the engine, so developing a more powerful and lighter new Valvetronic system may be what BMW is doing now.

Summarize:

In addition to the three manufacturers introduced in this article, Fiat, Audi, Porsche, Toyota, Mitsubishi and Subaru have also achieved the variable valve lift function of the engine through their own technical exploration. However, overall, this technology is far from being popularized in China. It is hoped that as the Chinese market grows, major joint ventures can introduce the latest technology to domestic models as soon as possible, and we also hope that our own brands can develop their own similar technologies as soon as possible.