What's the mystery behind this amazing variable compression ratio engine?
It is said that the new QX50 is a secret weapon that Infiniti had just released, but when it was unveiled, the secret weapon became a signature weapon on the surface. As a cloud mushroom that has been powdered in the VQ series for a long time, it is not as exciting as seeing natural inhalation. However, when you see the counterattack of an internal combustion engine, you are also extremely expectant.
Why do we still insist on the research and development of internal combustion engines?
Increasing thermal efficiency and increasing the performance of the engine have always been the trend since the engine was developed. However, due to the increasingly stringent emission regulations in recent years, various companies have come up with energy-saving and emission-reduction technologies, so we can also see hybrid and pure electric vehicles. Quickly launched in the market. However, at the Infiniti QX50, which was officially unveiled at the end of last year, it exhibited a variable-compression-ratio internal combustion engine that Infiniti had spent US$20 billion and had spent nearly 20 years developing. This is still a bit out of place in all car companies that vigorously develop hybrid technology.
Mr. Jerry Hardcastle, Senior Director of Product Strategy at Infiniti's Business Development Strategy Group, interviewed Che Yunyu. Why did he still spend so much energy on sticking to traditional development? First of all, traditionally, although Infiniti currently uses Nissan's hybrid system on the QX60, we can see from the famous VQ engine that Infiniti has had its own insistence on the internal combustion engine.
At the time of opening the project, hybrid technology and pure electric power were still far less popular nowadays. Traditional internal combustion engines are the absolute mainstream. Even now, the electrification process is still not as fast as some people think. In combination with Nissan's tradition, technological innovation of the internal combustion engine is still the first choice. At the same time, Infiniti considered the relatively more complex structure of the hybrid system, with higher R&D costs and operating costs. Under comprehensive consideration, traditional power still has its own advantages.
In addition, in this advanced technology of the internal combustion engine, in the future will inevitably marry the hybrid technology, has a very broad application prospects. Therefore, with a more advanced foundation for internal combustion engines, with the addition of electric technology, such hybrid power may become more efficient in the future or in the future. Especially for the 4L fuel consumption standard of 100km in China in 2025, common hybrid systems may be very stressful.
So, for various reasons, the world’s first variable compression ratio turbocharged engine that was actually applied to a production car was born. Although it has already caused widespread concern, I will take a look at this engine again.
The key to the core: Diamond multi-link
The interior of the engine is coded as KR20, which can change the stroke of the crankshaft according to different driving requirements and change the angle of the connecting mechanism through the control handle so that the compression ratio is changed between 8:1 and 14:1, simulating the Atkinson cycle. And regular Alto cycle. Moreover, although the top dead center of the piston movement has changed by 6mm, the bottom dead center has actually changed by only 4.8mm, so the displacement of the engine in the lowest compression ratio mode is actually 1997cc, while that in the highest compression ratio mode is 1971cc. . Therefore, even after the variable compression ratio is equivalent to "variable displacement."
One of the most critical components is a diamond “multi-link†between the crankshaft and the piston, which is to change the invariable rigid connection between the piston and the crankshaft into a flexible and flexible connection to change the piston movement. The trip, thus changing the compression ratio. That is, it is the most thorny and time-consuming hardware in the entire R&D process. Mr. Hardcastle acknowledges that it is only the biggest difficulty, not only to consider the engineering connection problem, but also to constantly test wear and life.
And why do you have to change the compression ratio? The high compression ratio can improve the combustion efficiency, but due to the detonation and other reasons, it is not conducive to the output of the performance, and the performance of the low compression ratio engine is better, but the efficiency is low and the fuel consumption is low. Obviously this is a problem that cannot be shared by both fish and bear's paw. Therefore, each manufacturer is also choosing a balance in the compression ratio according to the positioning of the product.
Therefore, while it has a maximum torque of 268 horsepower and 380 Nm, it can have an average fuel consumption of 27 mpg in overseas surveys, which translates into an estimated fuel consumption of 8.7 L per 100 km. Although slightly inferior in power to the previous V6 naturally aspirated engine, but the torque is greater and the speed output range is earlier, the 0-60 mph acceleration performance can reach 6.7 seconds on the front drive model and 6.3 seconds on the four-wheel drive model. It seems that the effect is still good.
This concept has been developed by many other car companies such as Saab many years ago, but it has not yet been realized. Therefore, this engine with a variable compression ratio theoretically realizes the ideal of having both dynamic and fuel-efficient at the same time in our ideal, which can be said to be of extraordinary significance.
iPhone actually helped a lot?
From the point of view of our average consumer, is this engine, advanced in structure, costly? According to Mr. Hardcastle, the cost of the VC-T engine is necessarily higher than that of an ordinary four-cylinder engine. However, the cost is actually lower than that of the very complicated hybrid technology. And this engine is compared with the Infiniti V6 engine on the North American market, and the cost is also reduced. In addition, it is not ruled out that there will be parts with lower manufacturing costs to replace the most critical multi-linkages at present.
Although this technology was eventually developed by Infiniti, it took nearly two decades to complete the process, especially in the early stages of R&D. According to Mr. Hardcastle, the biggest breakthrough was in 2007, and it also benefited from the launch of the iPhone. The introduction of this revolutionary product by Apple at the same time led to a revolution in chip computing capabilities all over the world, which enabled Infiniti to achieve breakthroughs in the calculation of the model, so that the entire project could continue to progress.
Through this, we can also see that the influence of the software layer on technology is also growing. This not only reminds us of another Infiniti's landmark technology, the DAS-by-wire steering, but also the traditional structure. Improvements that can be flexibly regulated, but in fact are not very good from the user's feedback. The reason for this is actually that the software program of the DAS system has not been standardized enough. The use of variable valve timing, as it is widely used today, is also becoming more and more mature through continuous computer program training.
Therefore, the compression ratio of this computer-controlled VC-T engine will naturally face the same problem. Can we match this theoretically almost perfect technology with actual road conditions? It is also necessary for Infiniti's R&D department to further study it. .
Car cloud summary
At present, Infiniti refuses to disclose plans for the future. It also says that the VC-T engine will only be equipped on the QX50. However, such a heavy technology will surely gradually expand to more or even all models in the future. Infiniti plans to complete the electrification of all products in 2021. Before this, even after the electrification, it is believed that the VC-T engine will take the flag of the VQ series as the absolute main force.
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