Variable compression ratio of the internal combustion engine. Engines with variable compression ratio: from Saab to Infiniti. Features of the compression change system

The unique compression ratio technology represents a real breakthrough in engine design - the 2-liter VC-Turbo constantly changes characteristics, adjusting the compression ratio for optimal power output and maximum fuel efficiency. In terms of traction, this 2.0-litre petrol turbo engine is quite comparable to advanced turbo-diesel engines of the same displacement.

The VC-Turbo engine constantly and completely imperceptibly changes the compression ratio using a system of levers that raise or lower the top dead center (TDC) of the pistons, thereby achieving the best power and economy.

A high compression ratio in principle makes the engine more efficient, but in certain modes there is a risk of explosive combustion (detonation). On the other hand, a low compression ratio avoids detonation and develops high power and torque. While driving, the compression ratio of the VC-Turbo engine changes from 8:1 (for maximum performance) to 14:1 (for minimum fuel consumption), emphasizing INFINITI's driver-centric philosophy.

INFINITI's VC-Turbo engine is the world's first production-ready variable compression ratio engine – and it makes its production debut on the new QX50. This unique variable compression technology represents a breakthrough in combustion engine design – the QX50’s 2.0-liter VC-Turbo continuously transforms, adjusting its compression ratio to optimize power and fuel efficiency. It combines the power of a 2.0-liter turbocharged gasoline engine with the torque and efficiency of an advanced four-cylinder diesel engine.

The unique combination of dynamics and efficiency makes the VC-Turbo a real alternative to today's turbodiesels, debunking the notion that only hybrid and diesel powertrains can provide high torque and economy. VC-Turbo develops 268 hp. (200 kW) at 5600 rpm and 380 Nm at 4400 rpm, which is the best combination of power and traction among four-cylinder engines. The VC-Turbo's power-to-weight ratio is higher than many competing turbo engines and comes close to that of some V6 petrols. The single-flow turbocharger guarantees instant engine response to increased fuel delivery.

The new INFINITI QX50 with VC-Turbo engine is the most efficient vehicle in its class with unsurpassed efficiency. The front-wheel drive version consumes just 8.7 l/100 km on the combined measurement cycle, which is 35% better than the previous generation QX50 with a V6 engine. The all-wheel drive version of the premium crossover with an average consumption of 9.0 l/100 km is 30% more efficient than its predecessor.

Other obvious advantages of the new motor design include compact dimensions and reduced weight. The block and cylinder head are cast from lightweight aluminum alloy, while the compression ratio components are made from high carbon steel. As a result, compared to the 3.5-liter INFINITI VQ engine, the new VC-Turbo weighs 18 kg lighter and also takes up less space in the engine compartment.

A lever system, an electric motor and a unique wave reduction gear are responsible for changing the compression ratio in the VC-Turbo engine. The electric motor is connected to the control lever through a gearbox. The gearbox rotates, turning the control shaft in the cylinder block, and that, in turn, changes the position of the rocker arms through which the pistons drive the crankshaft. The tilt of the rocker arms changes the position of the top dead center of the pistons, and with it the compression ratio. The eccentric control shaft regulates the compression ratio simultaneously in all cylinders. As a result, not only the compression ratio varies, but also the engine displacement ranging from 1997 cm3 (8:1) to 1970 cm3 (14:1).

The VC-Turbo engine also seamlessly switches between standard Otto and Atkinson duty cycles, further increasing power and efficiency. The Atkinson cycle has traditionally been used to improve the efficiency of hybrid power plants. During the operation of the internal combustion engine according to the Atkinson cycle, the intake valves overlap, allowing the working mixture in the cylinders to expand more, burning with greater efficiency. The INFINITI engine operates in the Atkinson cycle at high compression ratios, where, due to the longer piston stroke, the intake valves remain open for a short time already in the compression phase.

INFINITI's VC-Turbo engine is the world's first production-ready variable compression ratio engine and it makes its production debut on the new QX50. This unique variable compression technology represents a breakthrough in combustion engine design the QX50’s 2.0-liter VC-Turbo continuously transforms, adjusting its compression ratio to optimize power and fuel efficiency. It combines the power of a 2.0-liter turbocharged gasoline engine with the torque and efficiency of an advanced four-cylinder diesel engine.

When the compression ratio of the VC-Turbo is reduced, the engine returns to normal operation (Otto cycle), with clearly separated exhaust, compression, combustion and exhaust phases - thus, a higher power unit is achieved.

In addition to the variable compression ratio, the VC-Turbo engine uses a number of other advanced INFINITI technologies. The optimal balance between efficiency and power is provided by both the multiport injection (MPI) and direct injection (GDI) systems:

GDI improves fuel efficiency by preventing engine knock at high compression ratios
MPI, in turn, prepares the fuel mixture in advance, ensuring its complete combustion in the cylinders at low loads.

At certain speeds, the engine switches independently from one injection system to another, and at maximum loads they can work simultaneously.

The single-flow turbocharger increases engine power and efficiency by delivering fast throttle response at any rpm and compression ratio. Thanks to the turbocharging, the output is comparable to a six-cylinder naturally aspirated engine. The single-flow supercharger is characterized by compactness, as well as reduced losses of thermal energy and exhaust gas pressure.

The exhaust manifold integrated into the aluminum head also improves engine efficiency and keeps the engine compact. This solution allowed INFINITI engineers to place the catalytic converter just behind the turbine, thus shortening the exhaust gas path. Due to this, the converter warms up faster after starting the engine and enters the operating mode earlier.

Variable compression ratio technology represents a breakthrough in powertrain development. The QX50, powered by the VC-Turbo, is the first production vehicle ever to give drivers an engine that transforms on demand, setting a new benchmark for powertrain capability and refinement. This uncommonly smooth engine offers customers power and performance, as well as efficiency and economy.

Boost pressure is regulated by an electronically controlled valve (wastegate), which precisely controls the flow of exhaust gases passing through the turbine. This guarantees high power and economy, and helps to reduce harmful emissions.

Thanks to variable compression, the perfectly balanced VC-Turbo engine dispenses with the balance shafts normally required by four-cylinder engines. The VC-Turbo runs smoother than conventional in-line counterparts, and the noise and vibration levels are comparable to traditional V6s. This became possible, among other things, thanks to the layout with additional rocker arms, in which the connecting rods are almost vertical during the working stroke of the pistons (unlike the traditional crank mechanism, where they move from side to side). The result is a perfect reciprocating motion that does not require balance shafts. That is why, despite the use of a variable compression ratio, the VC-Turbo engine is as compact as a traditional 2-liter four-cylinder engine.

Of particular note is the extremely low vibration level of the new engine. In factory tests, during which INFINITI compared the performance of the VC-Turbo with four-cylinder engines of competitors, the revolutionary engine showed a significantly lower noise level - almost like a 6-cylinder unit.

This is the merit of INFINITI's "mirror" coating of the cylinder walls - it reduces friction by 44%, allowing the engine to run smoother. The coating is applied by plasma spraying, then hardened and honed to create an ultra-smooth surface.

The new INFINITI QX50 with 2.0-litre VC-Turbo engine is the world's first car to feature Active Torque Rod (ATR) active vibration reduction. The new QX50 is the only car in its class to feature this technology. Integrated into the upper engine mount, through which most of the noise and vibrations are usually transmitted to the body, the ATR is equipped with an acceleration sensor that detects vibrations. The system generates anti-phase reciprocating vibrations, allowing the four-cylinder unit to remain as quiet and smooth as the V6 engines, and reduces engine noise by 9 dB compared to the previous QX50. As a result, the VC-Turbo is one of the quietest and most balanced engines in the premium SUV segment.

INFINITI installed the world's first active mounts on a diesel engine back in 1998, confirming the brand's innovativeness in the field of powertrains. The INFINITI engineers developed the ATR system from 2009 to 2017, paying special attention to reducing the size and weight - on the first prototypes, the dimensions of the vibration motor were considered the main problem. However, the development of more compact reciprocating actuators has allowed the ATR to fit into a smaller package while retaining the system's full vibration damping capability.

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For more than a century of life, the internal combustion engine (ICE) has changed so much that only the principle of operation remains from the ancestor. Almost all stages of modernization were aimed at increasing the coefficient of performance (COP) of the engine. The efficiency indicator can be called universal. Many characteristics are hidden in it - fuel consumption, power, torque, exhaust gas composition, etc. The widespread use of new technical ideas - fuel injection, electronic ignition and engine management systems, 4, 5 and even 6 valves per cylinder - played a positive role in increasing the efficiency of engines.

Nevertheless, as shown by the Geneva Motor Show, the process of modernization of internal combustion engines is still far from being completed. At this popular international auto show, SAAB presented the result of 15 years of work - a prototype of a new engine with a variable compression ratio - SAAB Variable Compression (SVC), which became a sensation in the world of motors.

SVC technology and a number of other advanced and non-traditional technical solutions from the point of view of existing concepts of internal combustion engines made it possible to provide the novelty with fantastic characteristics. So, a five-cylinder engine with a volume of only 1.6 liters, designed for conventional production cars, develops an incredible power of 225 hp. and a torque of 305 Nm. Other, especially important today, characteristics turned out to be excellent - fuel consumption at medium loads was reduced by as much as 30%, CO2 emissions were reduced by the same amount. As for CO, CH and NOx, etc., they, according to the creators, comply with all existing and planned for the near future toxicity standards. In addition to this, the variable compression ratio gives the SVC engine the ability to run on a variety of gasoline grades - from A-76 to AI-98 - with virtually no degradation in performance and excluding the appearance of detonation.

Of course, a significant merit of such characteristics is in the SVC technology, i.e. the ability to change the compression ratio. But before we get acquainted with the device of the mechanism, which made it possible to change this value, let us recall some truths from the theory of the design of the internal combustion engine.

Compression ratio

The compression ratio is the ratio of the sum of the volumes of the cylinder and the combustion chamber to the volume of the combustion chamber. With an increase in the degree of compression, pressure and temperature increase in the combustion chamber, which creates more favorable conditions for the ignition and combustion of the combustible mixture and increases the efficiency of the use of fuel energy, i.e. efficiency. The higher the compression ratio, the higher the efficiency.

There are no problems with the creation of gasoline engines with a high compression ratio and there have never been. And do not do them for the following reason. During the compression stroke of such engines, the pressure in the cylinders rises to very high values. This, of course, causes an increase in the temperature in the combustion chamber and creates favorable conditions for the appearance of detonation. And detonation, as we know (see p. 26), is a dangerous phenomenon. In all engines created up to that time, the compression ratio was constant and was determined depending on the pressure and temperature conditions in the combustion chamber at maximum load, when fuel and air consumption are maximum. The engine does not always work in this mode, one might say, even very rarely. On the highway or in the city, when the speed is almost constant, the motor operates at low or medium loads. In such a situation, for more efficient use of fuel energy, it would be nice to have a higher compression ratio. This problem was solved by SAAB engineers - the creators of SVC technology.

SVC Technology

First of all, it should be noted that in the new engine, instead of the traditional block head and cylinder liners, which were cast directly into the block or pressed, there is one monohead that combines the block head and cylinder liners. To change the degree of compression, or rather, the volume of the combustion chamber, the monohead is made movable. On the one hand, it is mounted on a shaft that performs the function of a support, and on the other, it is supported and driven by a separate crank mechanism. The radius of the crank provides a displacement of the head relative to the vertical axis by 40. This is quite enough to change the volume of the chamber to obtain a compression ratio from 8:1 to 14:1.

The required compression ratio is determined by the SAAB Trionic electronic engine management system, which monitors the load, speed, fuel quality and, based on this, controls the crank hydraulic drive. So, at maximum load, the compression ratio is set to 8:1, and at minimum - 14:1. Combining the cylinder liners with their head, among other things, allowed SAAB engineers to give the channels of the cooling jacket a more perfect shape, which increased the efficiency of the process of removing heat from the walls of the combustion chamber and cylinder liners.

The mobility of the cylinder liners and their heads required changes to the design of the engine block. The joint plane of the block and the head has become lower by 20 cm. As for the tightness of the joint, it is provided by a rubber corrugated gasket, which is protected from damage by a metal casing from above.

Mal, yes daring

For many, it may become incomprehensible how more than two hundred “horses” were “charged” into an engine with such a small volume - after all, such power can adversely affect its resource. When creating the SVC engine, the engineers were guided by completely different tasks. Bringing the motor resource to the required standards is the business of technologists. As for the small volume of the engine, it is done in full accordance with the theory of internal combustion engines. Based on its laws, the most favorable mode of engine operation in terms of increasing efficiency is at high load (at high speeds), when the throttle is fully open. In this case, it maximizes the energy of the fuel. And since engines with a smaller displacement work mainly at maximum loads, their efficiency is also higher.

The secret behind the superiority of small engines in terms of efficiency is due to the absence of so-called pumping losses. They occur at low loads, when the engine is running at low speeds and the throttle is only slightly ajar. In this case, during the intake stroke, a large vacuum is created in the cylinders - a vacuum that resists the downward movement of the piston and, accordingly, reduces efficiency. With a wide open throttle, there are no such losses, since air enters the cylinders almost unhindered.

To avoid pumping losses by 100%, in the new engine, SAAB engineers also used high-pressure air "supercharge" - 2.8 atm., Using a mechanical supercharger - compressor. The compressor was preferred for several reasons: firstly, no turbocharger is capable of generating such boost pressure; secondly, the reaction of the compressor to a change in load is almost instantaneous, i.e. there is no deceleration characteristic of turbocharging. Filling the cylinders with a fresh charge in the SAAB engine was improved both with the help of today's popular modern gas distribution mechanism, in which there are four valves per cylinder, and through the use of an intercooler (Intercooler).

The prototype of the SVC engine, according to the German engine development company FEV Motorentechnie in Aachen, is quite functional. But despite the positive assessment, it will be launched into mass production after some time - after its refinement and fine-tuning to the needs of customers.

As it may seem at first glance, the modern internal combustion engine has reached the highest stage of its evolution. At the moment, various are mass-produced and, appeared, an additional opportunity has been realized.

The list of the most significant developments in recent years includes: the introduction of high-precision injection systems controlled by sophisticated electronics, obtaining high power without increasing the working volume thanks to turbocharging systems, increasing, using, etc.

The result was a noticeable improvement in performance, as well as a decrease in the level of toxicity of exhaust gases. However, that's not all. Designers and engineers around the world continue not only to actively work on improving existing solutions, but also try to create a completely new design.

Suffice it to recall attempts to build, get rid of in the device or dynamically change the compression ratio of the engine. We note right away that although some projects are still under development, others have already become a reality. For example, engines with a variable compression ratio. Let's look at the features, advantages and disadvantages of such internal combustion engines.

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Changing the compression ratio: why is it needed

Many experienced drivers are familiar with such concepts as the octane number for gasoline engines, as well as for diesel engines. For the less knowledgeable reader, we recall that the compression ratio is the ratio of the volume above the piston, which is lowered at BDC (bottom dead center) to the volume when the piston rose to TDC (top dead center).

Gasoline units have, on average, an indicator of 8-14, diesel engines 18-23. The compression ratio is a fixed value and is structurally incorporated during the development of an engine. Also, the requirements for the use of the octane number of gasoline in a particular engine will also depend on the degree of compression. At the same time, either supercharged or supercharged is taken into account.

If we talk about the compression ratio itself, in fact, this is an indicator that determines how much the fuel-air mixture will be compressed in the engine cylinders. Simply put, a well-compressed mixture ignites better and burns more fully. It turns out that increasing the compression ratio allows you to achieve engine growth, get improved engine performance, reduce fuel consumption, etc.

However, there are nuances. First of all, this. Again, if you do not go into details, normally the charge of fuel and air in the cylinders should just burn, and not explode. Moreover, the ignition of the mixture must begin and end at strictly specified moments.

In this case, the fuel has the so-called "knock resistance", that is, the ability to resist detonation. If, however, the compression ratio is greatly increased, then the fuel may begin to detonate in the engine under certain operating conditions of the internal combustion engine.

The result is an uncontrolled explosive combustion process in the cylinders, the rapid destruction of engine parts by a shock wave, a significant increase in temperature in the combustion chamber, etc. As you can see, it is impossible to make a high compression ratio constant precisely for these reasons. In this case, the only way out in this situation is the ability to flexibly change this indicator in relation to different engine operating modes.

Such a “working” motor was recently proposed by engineers of the premium brand Infiniti (an elite division of Nissan). Also, other automakers (SAAB, Peugeot, Volkswagen, etc.) have been and remain involved in similar developments. So let's look at a variable compression engine.

Variable engine compression ratio: how it works

First of all, the available ability to change the compression ratio allows a significant increase in the performance of turbo engines while reducing fuel consumption. In a nutshell, depending on the operating mode and loads on the internal combustion engine, the fuel charge is compressed and burned out in the most optimal conditions.

When the loads on the power unit are minimal, an economical "poor" mixture (a lot of air and little fuel) is supplied to the cylinders. A high compression ratio is well suited for such a mixture. If the load on the engine increases (a “rich” mixture is supplied, in which there is more gasoline), then the risk of detonation naturally increases. Accordingly, to prevent this from happening, the compression ratio is dynamically reduced.

In engines where the compression ratio is constant, a change is a kind of protection against detonation. This angle moves "back". Naturally, such an angle shift leads to the fact that although there is no detonation, power is also lost. As for the engine with a variable compression ratio, there is no need to shift the UOS, that is, there is no power loss.

As for the implementation of the scheme itself, in fact, the task boils down to the fact that there is a physical decrease in the working volume of the engine, however, all characteristics (power, torque, etc.) are preserved.

We note right away that different companies worked on such a solution. As a result, various methods of controlling the compression ratio have appeared, for example, variable combustion chamber volume, connecting rods with the possibility of raising the pistons, etc.

One of the earliest developments was the introduction of an additional piston into the combustion chamber. The specified piston had the ability to move, while changing the volume. The downside of the whole design was the need to install additional parts in. Also, changes in the shape of the combustion chamber immediately appeared, the fuel burned unevenly and incompletely.

For these reasons, this project was never completed. The same fate befell the development, which had pistons with the ability to change their height. These split-type pistons turned out to be heavy, and difficulties were added regarding the implementation of the control of the lifting height of the piston cover, etc.

Further developments no longer affected the pistons and the combustion chamber, maximum attention was paid to the issue of lifting the crankshaft. In other words, the task was to implement control of the crankshaft lift height.

The scheme of the device is such that the bearing journals of the shaft are located in special eccentric-type couplings. These clutches are driven by gears that are connected to an electric motor.

Turning the eccentrics allows you to raise or lower, which leads to a change in the height of the pistons in relation to. As a result, the volume of the combustion chamber increases or decreases, while the compression ratio also changes.

Note that several prototypes were built on the basis of a 1.8-liter turbocharged unit from Volkswagen, the compression ratio varied from 8 to 16. The engine was tested for a long time, but the unit never became a serial unit.

Another attempt to find a solution was an engine in which the compression ratio was changed by lifting the entire cylinder block. The development belongs to the Saab brand, and the unit itself almost did not even get into the series. The engine is known as SVC, 1.6 liter, 5-cylinder, turbocharged unit.

Power was about 220 liters. with., a torque of just over 300 Nm. It is noteworthy that fuel consumption in medium load mode has decreased by almost a third. As for the fuel itself, it became possible to fill in both the AI-76 and the 98th.

Saab engineers divided the cylinder block into two conditional parts. The upper part contained the cylinder heads and liners, while the lower part contained the crankshaft. A kind of connection of these parts of the block, on the one hand, was a movable hinge, and on the other, a special mechanism equipped with an electric drive.

So it was possible to slightly raise the upper part at a certain angle. Such an angle of elevation was only a few degrees, while the compression ratio varied from 8 to 14. At the same time, a rubber casing was supposed to seal the “joint”.

In practice, the parts themselves for lifting the upper part of the block, as well as the protective cover itself, turned out to be very weak elements. Perhaps this is what prevented the motor from getting into the series and the project was closed further.

Another development was further proposed by engineers from France. The turbo engine with a working volume of 1.5 liters was able to change the compression ratio from 7 to 18 and produced about 225 hp. The torque characteristic is fixed at around 420 Nm.

Structurally, the unit is complex, with a divided. In the area where the connecting rod is attached to the crankshaft, the part was equipped with a special geared rocker arm. At the junction of the connecting rod with the piston, a gear-type bar was also introduced.

On the other side, a piston rail was attached to the rocker, which implemented control. The system was driven from the lubrication system, the working fluid passed through a complex system of channels, valves, and there was also an additional electric drive.

In a nutshell, the movement of the control piston had an effect on the rocker. As a result, the lift height of the main piston in the cylinder also changed. Note that the engine also did not become serial, and the project was frozen.

The next attempt to create an engine with a variable compression ratio was the solution of Infiniti engineers, namely the VCT (Variable Compression Turbocharged) engine. In this motor, it became possible to change the compression ratio from 8 to 14. A design feature is a unique traverse mechanism.

It is based on the connection of the connecting rod with the lower neck, which is movable. Also used is a system of levers, which are driven by an electric motor.

The controller controls the process by sending signals to the electric motor. The electric motor, after receiving a command from the control unit, shifts the rod, and the lever system implements a change in position, which allows you to change the height of the piston.

As a result, the Infiniti VCT unit with a displacement of 2.0 liters with an output of about 265 hp. allowed to save almost 30% of fuel compared to similar internal combustion engines, which at the same time have a constant compression ratio.

If the manufacturer manages to effectively solve the current problems (design complexity, increased vibrations, reliability, high final cost of unit production, etc.), then the optimistic statements of the company's representatives may well come true, and the engine itself has every chance of becoming serial already in 2018-2019.

Summing up

Based on the information above, it is clear that variable compression engines can provide a significant reduction in fuel consumption in turbocharged gasoline engines.

Against the background of the global fuel crisis, as well as the constant tightening of environmental standards, these engines allow not only to burn fuel efficiently, but also not to limit engine power at the same time.

In other words, such an internal combustion engine is quite capable of offering all the advantages of a powerful gasoline high-speed turbo engine. At the same time, in terms of fuel consumption, such a unit can come close to turbodiesel counterparts, which are popular today, primarily due to their.