Recently, the 2.0T variable compression ratio engine released by Infiniti has looted in the news, but when it comes to the variable compression ratio engine, the British Internal Combustion Engine Research Association began research in 1952. Later, there have been manufacturers to research related technologies. Today, let's take a look at the variable compression ratio engine.

● Why variable compression ratio?

1, what is the compression ratio

2, the disadvantage of fixed compression ratio

The general gasoline engine is most likely to produce knocking at full load, so the traditional engine should determine the maximum compression ratio based on the condition of the full load, generally around 10. However, the theory requires that the larger the compression ratio, the better. This destined fixed compression ratio can not make the engine run perfectly in a variety of complex conditions.

3, the advantages of variable compression ratio

Variable Compression Ratio (VCR), as it is literally meant, is the ability to change the compression ratio while the engine is running.

In fact, the variable compression ratio gasoline engine can accept a variety of fuels, but the higher the octane number of the fuel, the better the engine, because the higher the octane number, the less easy to trigger the knock, so the engine can be more High compression ratio operation, resulting in higher thermal efficiency and lower fuel consumption.

Because of the variable compression ratio technology, the use of a booster system is more efficient and there is no need to worry about knocks and other problems due to high pressure, so that the engine can use small-displacement turbocharger to squeeze out more performance and achieve large Displacement performance (many manufacturers now have this trend, adding variable compression technology is more efficient and more fuel-efficient).

In addition, at present, many manufacturers have realized the dynamic compression ratio by delaying the closing of the exhaust gas mixture by the intake valve (actually applied by Honda ten years ago). However, this method can only change the compression ratio unidirectionally, and the gas The amount of inhalation is equivalent to a reduction, and the displacement becomes smaller, so that the engine output power is reduced. Therefore, the geometric variable compression ratio engine still has a practical demand.

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2 variable compression ratio to achieve the program Part 1

● Variable Compression Ratio Implementation Scheme

1, SAAB SVC engine

However, the SVC engine has its advantages and disadvantages. It is because the engine is divided into upper and lower parts. The upper cylinder also needs a cooling system. The cooling system will become complicated, and the durability of the entire mechanism needs to be verified. Saab collapsed before these problems were resolved.

If you haven’t reacted yet, you can see the following video to understand how the SVC engine works:

2, Toyota

As the sales and profit champions of the previous year, Toyota will not ignore the important technical means of variable compression ratio. However, Toyota also knows that Toyota is no longer like Toyota in the 80's and 90's and Toyota's advanced technology. There is much to be cautious about, so the Toyota in the variable compression ratio engine is still in the stage of internal research. However, from the patents they applied for, we can see that Toyota's idea of ​​variable compression ratio is similar to that of Saab.

For Toyota's in-line variable compression ratio engine, similar to Saab's idea, it is easier to be understood, but the explosive force generated by the engine has a great impact on the control of the eccentric shaft, and the mechanism is also more complicated, so Toyota just stays in the Research phase.

3, modern

Of course, the method of realizing the variable compression ratio is not only the cylinder, some manufacturers think of hands and feet on the cylinder head. For example, Hyundai Motor Korea. Hyundai Motor (hereinafter referred to as Hyundai Hyundai Hyundai Motor) has a variable compression ratio by providing an auxiliary piston in the cylinder head and changing the combustion chamber volume by changing the position of the piston.

The modern idea is actually simpler and more feasible. In fact, this idea of ​​using a secondary piston or valve on the valve cover to change the volume of the combustion chamber and change the compression ratio was studied by Ford and Sweden's Lund Technical Institute long ago and was implemented on a two-valve engine. However, this type of solution is prone to seal problems. In order to ensure that the secondary piston can be used for long-term operation under high temperature and high pressure conditions, it must be cooled, and the unreasonable change of the combustion chamber arrangement will lead to a sharp increase in heat loss, resulting in a decrease in the thermal efficiency of the gasoline engine. .

3 Variable Compression Ratio Implementation Scheme Part 2

1. Infiniti VC-T engine

The topic of the variable compression ratio engine that has recently caused this is the Infiniti VC-T (Variable Compression Turbocharged) engine, which is expected to be equipped with the all-new QX50 debuted at the 2016 Paris Motor Show.

In fact, the Infiniti VC-T engine is highly similar to the VCR variable compression ratio engine that Nissan released in February 2005. After 10 years, Nissan felt that the technology had been optimized and matured, and that it could be put into mass production, so Infiniti was allowed to do it. The first person to eat crabs. Honda, which is also a car company of the island nation, also published its own variable compression ratio engine in 2005. It also added a variable mechanism to the crankshaft connecting rod. However, Honda has not produced any sound of mass production yet.

To see how Infiniti's VC-T variable compression ratio engine works, watch the following video:

2. MCE-5 VCRi engine

In 2005, the French company MCE-5 released an engine equipped with VCRi's variable compression ratio technology. It uses a manifold injection design with an in-line four-cylinder tandem twin-turbo with a displacement of 1.5L, a maximum power of 160kW, and a maximum torque. 420Nm, the compression ratio is variable from 7:1 to 20:1, and the combined fuel consumption is 6.7L/100km.

The biggest sponsoring partner behind MCE-5 is Peugeot, so VCRi's test car is also a Peugeot. At the 2009 Geneva Motor Show, Peugeot showed the 407 model equipped with a VCRi engine, but as to why Peugeot is still The lack of production of vehicles equipped with VCRi engines may be related to the cost of VCRi engines and the complexity of the organization.

For more information about the MCE-5 VCRi engine, watch the video below (PS: Sorry, this video is in French and no other alternative video TT can be found):

3, Gomecsys

The Gomecsys company in the Netherlands is also one of the companies eager to change the compression ratio. They proposed a way to change the variable compression ratio on the crankshaft. That is to add an eccentric ring to the big end of the connecting rod to control the eccentric ring. Turn to change the top dead center position of the piston.

Gomecsys' variable compression ratio scheme also understands the principle through video:

1, FEV variable compression ratio connecting rod

Germany's FEV Company is an independent engine engineering technology company. Global automotive OEMs provide advanced test equipment and accessories products as well as comprehensive technical consulting services. FEV is also one of the world's three authoritative internal combustion engine R&D institutions.

FEV has always studied variable compression ratio technology. Before they have announced a way to support the crankshaft on the eccentric shaft wheel, by turning the eccentric wheel, the crankshaft will drive the piston to change its top dead center, but this scheme of the engine The output shaft will appear to move, the actual use is inconvenient, so FEV company still gave up. Their latest idea is to add an eccentric ring to the piston pin and change the height of the piston by changing the position of the eccentric ring.

The FEV says that the change in piston height takes 0.6 seconds and can reduce fuel consumption by 5-7%. This solution has relatively few modifications to the entire engine. All systems are integrated on the connecting rod and the cost is not too high.

The working principle of FEV's variable compression ratio solution can watch the following understanding:

● Summary

The variable compression ratio engine can improve the engine's thermal efficiency, improve fuel economy, and promote the engine's small-displacement quantification. At present, the fuel engine has reached a bottleneck, and many new technologies are required to break through. The variable compression ratio has been studied for decades. It's time to test the water. Infiniti is the first one to eat crabs. Let's wait and see.

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