Motor with variable compression ratio. On what principles does the Infiniti engine with a variable compression ratio work, detailed information

As it may seem at first glance, modern engine internal combustion reached the highest stage of its evolution. On this moment Various ones are mass-produced and, additionally, the possibility has appeared.

In the list of the most significant developments for last years can be highlighted: the introduction of high-precision injection systems controlled by sophisticated electronics, obtaining high power without increasing the displacement due to turbocharging systems, increase, use, etc.

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

Suffice it to recall attempts to build, get rid of in a device, or dynamically change the engine compression ratio. Let us immediately note that although some projects are still in the development stage, others have already become a reality. For example, engines with variable degree compression. 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 necessary?

Many experienced drivers are familiar with concepts such as octane number for gasoline engines, as well as for diesel engines. For the less knowledgeable readers, remember that compression ratio is the ratio of the volume above the piston as it descends at BDC (bottom dead center) to the volume as the piston rises 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 determined during the development of a particular engine. Also, the requirements for use will depend on the degree of compression. octane number gasoline in one engine or another. Both are taken into account in parallel, or with supercharging.

If we talk about the degree of compression itself, this is actually an indicator that determines how much it will be compressed fuel-air mixture 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 performance from the engine, reduce fuel consumption, etc.

However, there are also nuances. First of all, this. Again, without going into details, normally the charge of fuel and air in the cylinders should 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 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, 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 modes engine operation.

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

Variable engine compression ratio: how it works

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

When the load is on power unit are minimal, an economical “lean” mixture (lots of air and little fuel) is supplied to the cylinders. A high compression ratio is good for this mixture. If the load on the motor increases (a “rich” mixture is supplied, in which 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 “backwards”. Naturally, such an angle shift leads to the fact that although there is no detonation, power is also lost. As for a motor with a variable compression ratio, there is no need to shift the OZ, that is, there are no power losses.

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

Let us immediately note that different companies worked on this solution. As a result, there were different ways compression ratio control, for example, variable combustion chamber volume, connecting rods with the ability to lift pistons, etc.

One of the earliest developments was the introduction of an additional piston into the combustion chamber. Said piston had the ability to move while simultaneously changing 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 there were additional difficulties regarding the implementation of control over the lifting height of the piston cover, etc.

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

The design of the device is such that the shaft support journals are located in special eccentric couplings. These couplings are driven by gears that are connected to an electric motor.

Rotating the eccentrics allows you to raise or lower, which leads to a change in the lifting height of the pistons in relation to. As a result, the volume of the combustion chamber increases or decreases, and at the same time the compression ratio changes.

Note that several prototypes were built based on 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 serial.

Another attempt to find a solution was an engine in which the compression ratio was changed by raising the entire cylinder block. Development belongs to Saab brand, and the unit itself almost didn’t even make it into the series. The engine is known as SVC, volume 1.6 liters, 5-cylinder unit, equipped with turbocharging.

The power was about 220 hp. s., torque 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 both AI-76 and 98.

Saab engineers divided the cylinder block into two conventional parts. The top contained the cylinder heads and liners, while the bottom contained the crankshaft. A unique connection between these parts of the block was a movable hinge on one side, and a special mechanism equipped with an electric drive on the other.

This made it possible to slightly raise the upper part at a certain angle. This angle of elevation was only a few degrees, while the degree of compression varied from 8 to 14. In this case, the “joint” had to be sealed by a rubber casing.

In practice, the parts themselves for lifting the top of the block, as well as the protective casing itself, turned out to be very weak elements. Perhaps this is what prevented the engine from entering the series and the project was subsequently closed.

The next development was further proposed by engineers from France. A turbo engine with a displacement of 1.5 liters was able to change the compression ratio from 7 to 18 and produced power of about 225 hp. The torque characteristic is fixed at 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 toothed rocker arm. At the junction of the connecting rod and the piston, a gear-type rack was also introduced.

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

In a nutshell, the movement of the control piston had an effect on the rocker arm. As a result, the lifting 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 engine (from the English Variable Compression Turbocharged). In this engine 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 journal, which is movable. A system of levers that are driven by an electric motor is also used.

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 thrust, and the system of levers implements a change in position, which allows you to change the height of the piston lift.

As a result, the Infiniti VCT unit with a displacement of 2.0 liters and a power of about 265 hp. made it possible to save almost 30% of fuel compared to similar internal combustion engines, which at the same time have constant degree compression.

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

Let's sum it up

Taking into account the above information, it becomes clear that engines with variable compression ratios can provide significant reductions in fuel consumption by gasoline engines with turbocharging.

Against the backdrop of global fuel crisis, as well as the constant tightening environmental standards These engines allow not only to burn fuel efficiently, but also not to limit engine power.

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 very close to its turbodiesel counterparts, which are popular today, primarily due to their efficiency.

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Turbocharger design, main design elements, turbine selection. Advantages and disadvantages of turbocharged gasoline and diesel engines.

Boosting the engine. Pros and cons of modifying an engine without a turbine. The main methods of boosting: tuning the cylinder head, crankshaft, compression ratio, intake and exhaust.

VC-T engine. Image: Nissan

Japanese automaker Nissan Motor introduced a new type of gasoline internal combustion engine, which in some respects is superior to advanced modern ones diesel engines.

The new Variable Compression-Turbo (VC-T) engine is capable of change the compression ratio gaseous combustible mixture, that is, to change the stroke pitch of the pistons in the cylinders of the internal combustion engine. This parameter is usually fixed. Apparently, VC-T will be the first in ICE world with variable mixture compression ratio.

Compression ratio is the ratio of the volume of the above-piston space of an internal combustion engine cylinder when the piston is positioned at bottom dead center ( the full amount cylinder) to the volume of the piston space of the cylinder when the piston is at the top dead center, that is, to the volume of the combustion chamber.

Increasing the compression ratio in general case increases its power and increases Engine efficiency, that is, it helps reduce fuel consumption.

In conventional gasoline engines, the compression ratio is usually from 8:1 to 10:1, and in sports cars And racing cars can reach 12:1 or more. As the compression ratio increases, the engine requires fuel with a higher octane number.

VC-T engine. Image: Nissan

The illustration shows the difference in piston pitch at different compression ratios: 14:1 (left) and 8:1 (right). In particular, the mechanism for changing the compression ratio from 14:1 to 8:1 is demonstrated. It happens this way.

If it is necessary to change the compression ratio, the module is activated Harmonic Drive and moves the actuator lever.
The actuator lever turns the drive shaft ( Control Shaft on the diagram).
When the drive shaft turns, it changes the angle of inclination multi-link suspension (Multi-link on the diagram)
The multi-link suspension determines the height to which each piston can rise in its cylinder. Thus, the compression ratio changes. The bottom dead center of the piston appears to remain the same.

Changing the compression ratio in an internal combustion engine can in some ways be compared to changing the angle of attack in controllable pitch propellers, a concept that has been used in propellers and propellers for many decades. The variable propeller pitch makes it possible to maintain the propulsion efficiency close to optimal, regardless of the speed of the carrier in the flow.

Degree change technology internal combustion engine compression makes it possible to maintain engine power while complying with strict engine efficiency standards. This is probably the most real way comply with these standards. “Everyone is now working on variable compression ratio and other technologies to significantly improve the efficiency of gasoline engines,” says James Chao, managing director for Asia Pacific and consultant for IHS, “at least for the last twenty years or so.” . It is worth mentioning that in 2000 Saab company showed a prototype of this Saab engine Variable Compression (SVC) for the Saab 9-5, for which it has won a number of awards at technical exhibitions. Then the Swedish company was bought by the concern General Motors and stopped working on the prototype.

Saab Variable Compression (SVC) engine. Photo: Reedhawk

The VC-T engine is promised to be launched on the market in 2017 with Infiniti QX50 cars. The official presentation is scheduled for September 29 at Paris Motor Show. This 2.0-liter four-cylinder engine will have about the same power and torque as the 3.5-liter V6 it replaces, but will deliver 27 percent fuel economy over it.

Nissan engineers also say the VC-T will be cheaper than today's advanced turbocharged diesel engines and will fully meet current emissions standards for nitrogen oxide and other emissions. exhaust gases- such rules apply in the European Union and some other countries.

After Infiniti new engines are planned to equip others Nissan cars and possibly partner company Renault.

VC-T engine. Image: Nissan

It can be assumed that the complicated design of the internal combustion engine is unlikely to be reliable at first. It makes sense to wait a few years before buying a car with a VC-T engine, unless you want to participate in testing experimental technology.

More and more authoritative opinions are being heard that the development of internal combustion engines has now reached highest level and it is no longer possible to significantly improve their performance. Designers are left to engage in creeping modernization, polishing the supercharging and injection systems, as well as adding more and more electronics. Japanese engineers do not agree with this. Infiniti has had its say, building an engine with a variable compression ratio. Let's figure out what the advantages of such a motor are and what its future is.

As an introduction, let us recall that the compression ratio is the ratio of the volume above the piston at the bottom “dead” point to the volume when the piston is at the top. For gasoline engines this figure ranges from 8 to 14, for diesel engines - from 18 to 23. The compression ratio is set fixedly by the design. It is calculated depending on the octane number of the gasoline used and the presence of supercharging.

The ability to dynamically change the compression ratio depending on the load allows you to increase efficiency turbocharged engine, ensuring that each portion air-fuel mixture burned at optimal compression. For light loads, when the mixture is lean, it is used maximum compression, and in loaded mode, when a lot of gasoline is injected and detonation is possible, the engine compresses the mixture minimally. This eliminates the need to adjust the ignition timing “backwards”, which remains in the most efficient position for removing power. Theoretically, the system for changing the compression ratio in the internal combustion engine makes it possible to reduce the engine displacement by up to two times while maintaining traction and dynamic characteristics.

Diagram of an engine with a variable combustion chamber volume and connecting rods with a piston lifting system

One of the first to appear was a system with an additional piston in the combustion chamber, which, by moving, changed its volume. But the question immediately arose about placing another group of parts in the head of the block, where camshafts, valves, injectors and spark plugs were already crowded. Moreover, the optimal configuration of the combustion chamber was disrupted, causing the fuel to burn unevenly. Therefore, the system remained within the walls of laboratories. The system with variable height pistons did not go further than the experiment. The split pistons were excessively heavy, and design difficulties immediately arose with controlling the lifting height of the cover.

Crankshaft lifting system on FEV Motorentechnik eccentric couplings (left) and traverse mechanism for changing the piston lift height

Other designers have gone the route of controlling the crankshaft lift height. In this system, the crankshaft bearing journals are placed in eccentric couplings driven through gears by an electric motor. When the eccentrics turn, the crankshaft rises or falls, which, accordingly, changes the height of the pistons to the cylinder head, increases or decreases the volume of the combustion chamber, and thereby changes the compression ratio. This motor was shown in 2000 German company FEV Motorentechnik. The system has been integrated into the turbocharged four cylinder engine 1.8 l from Volkswagen concern, where the compression ratio varied from 8 to 16. The engine developed a power of 218 hp. and torque 300 Nm. Until 2003, the engine was tested at Audi car A6, but did not go into production.

Wasn't too lucky reverse system, which also changes the lifting height of the pistons, but not by controlling the crankshaft, but by lifting the cylinder block. Operating motor similar design demonstrated in 2000 year Saab, and also tested it on the 9-5 model, planning to launch it in mass production. Dubbed Saab Variable Compression (SVC) five-cylinder turbocharged engine volume of 1.6 liters, developed a power of 225 hp. With. and a torque of 305 Nm, while fuel consumption at medium loads decreased by 30%, and due to the adjustable compression ratio, the engine could easily consume any gasoline - from A-80 to A-98.

Saab Variable Compression engine system, in which the compression ratio is varied by deflecting the top of the cylinder block

Saab solved the problem of lifting the cylinder block this way: the block was divided into two parts - the upper one with the head and cylinder liners, and the lower one, where the crankshaft remained. On one side, the upper part was connected to the lower part through a hinge, and on the other, an electric drive mechanism was installed, which, like the lid of a chest, raised the upper part at an angle of up to 4 degrees. The range of compression ratios during lifting and lowering could vary flexibly from 8 to 14. To seal the moving and stationary parts, an elastic rubber casing was used, which turned out to be one of the weakest points of the structure, along with hinges and lifting mechanism. After the acquisition of Saab by General Motors, the Americans closed the project.

Project MSE-5, which uses a mechanism with working and control pistons connected through a gear rocker arm

At the turn of the century, French engineers from MCE-5 Development S.A. also proposed their design for an engine with a variable compression ratio. The turbocharged 1.5-liter engine they showed, in which the compression ratio could vary from 7 to 18, developed a power of 220 hp. With. and torque 420 Nm. The design here is quite complex. The connecting rod is divided and equipped at the top (in the part mounted on the crankshaft) with a toothed rocker arm. Adjacent to it is another part of the connecting rod from the piston, the tip of which has rack. Connected to the other side of the rocker arm is the rack of the control piston, which is driven through the engine lubrication system by special valves, channels and electric drive. When the control piston moves, it acts on the rocker arm and the lifting height of the working piston changes. The engine was tested experimentally on a Peugeot 407, but the automaker was not interested in this system.

Now Infiniti designers have decided to have their say, presenting an engine with Variable Compression-Turbocharged (VC-T) technology, which allows you to dynamically change the compression ratio from 8 to 14. Japanese engineers used a traverse mechanism: they made a movable joint between the connecting rod and its lower journal, which, in in turn, connected by a system of levers driven by an electric motor. Having received a command from the control unit, the electric motor moves the rod, the system of levers changes position, thereby adjusting the height of the piston lift and, accordingly, changing the compression ratio.

Variable Compression System Design Infiniti engine VC-T: a - piston, b - connecting rod, c - yoke, d - crankshaft, e - electric motor, f - intermediate shaft, g - rod.

Thanks to this technology, the Infiniti VC-T two-liter gasoline turbo engine develops a power of 270 hp, being 27% more economical than the company's other two-liter engines with a constant compression ratio. The Japanese plan to put VC-T engines into mass production in 2018, equipping them with the QX50 crossover and then other models.

Note that efficiency is now the main goal of developing engines with variable compression ratios. At modern development technologies of supercharging and injection, it is not difficult for designers to increase the power in the engine big problems. Another question: how much gasoline in a supercharged engine will fly out the pipe? For conventional serial engines, consumption indicators may be unacceptable, which acts as a limiter for increasing power. Japanese designers decided to overcome this barrier. According to Infiniti, their VC-T petrol engine, is capable of acting as an alternative to modern turbocharged diesel engines, delivering the same fuel consumption at best characteristics in terms of power and lower exhaust toxicity.

What's the result?

Work on engines with variable compression ratios has been going on for decades - designers from Ford, Mercedes-Benz, Nissan, Peugeot and Volkswagen have been working in this area. Engineers research institutes and companies on both sides of the Atlantic have received thousands of patents. But so far not a single such motor has gone into mass production.

Not everything is smooth for Infiniti either. As the developers of the VC-T motor themselves admit, their brainchild still has common problems: the complexity and cost of the design have increased, vibration issues have not been resolved. But the Japanese hope to finalize the design and put it into mass production. If this happens, then future buyers will only have to understand: how much they will have to overpay for new technology how reliable such an engine will be and how much it will save on fuel.

Recently at the Paris Motor Show brand Infiniti(read, Renault-Nissan alliance) introduced an engine with a variable compression ratio. The proprietary Variable Compression-Turbocharged (VC-T) technology allows you to vary this very degree, literally sucking all the juice out of the engine.

In an “ideal universe” the rule is simple - the higher the compression ratio of the fuel-air mixture, the better. The mixture expands as much as possible, the pistons move as if wound up, therefore, power and Motor efficiency maximum. In other words, the fuel is burned extremely efficiently.

Everything would be great if it weren’t for the very nature of the fuel. During the course of bullying, his patience sometimes reaches its limit: the more evenly the mixture burns, the better, but high loads(high compression ratio, high speed) the mixture begins to explode rather than burn. This phenomenon is called detonation, and this thing is quite destructive. The walls of the combustion chamber and the piston itself experience serious shock loads and gradually, but quite quickly, collapse. In addition, the efficiency of the motor decreases - normal operating pressure falls on the piston.

Thus, the most profitable option- when the engine in any mode operates on the verge of detonation, preventing this phenomenon. Infiniti engineers have drawn up a graph on which they have identified for themselves the effective operating modes of the engine depending on the load, speed and compression ratio of the fuel-air mixture. (In fact, the efficiency of fuel combustion can be increased in other ways, for example, by increasing the number of valves per cylinder, adjusting their operating schedule, even choosing the place above the piston where the fuel injection is directed. Of course, we remember this.) The first two parameters, Clearly, they depend both on external factors and on careful selection of the transmission. And the third - the compression ratio - it was also decided to change in the range from 8:1 to 14:1.

Technically, this looks like an introduction to the design of the crank mechanism additional element- rocker arms between the connecting rod and the crankshaft. The rocker arm is controlled by an electric motor - the lever can be moved so that the piston stroke range varies within 5 mm. This is enough for significant change compression ratio.

There are no advantages without disadvantages. At first glance, they are obvious: an increase in the complexity of the design, some weight gain... However, it’s a shame to complain about these disadvantages - the engine turned out to be very balanced, thanks to which the balancing shafts were removed from the design. It is also likely that the engine is particularly sensitive to the brand and quality of fuel. It seems that this problem - at least to a large extent - can be solved using software methods.

Since the name of the technology contains the word Turbocharged, it is obvious that such engines will be turbocharged. The first of them, a two-liter 270-horsepower engine, will fit under the hood of the Infiniti QX50 crossover. They claim that an engine with a variable compression ratio consumes as much as 27% less fuel, how regular motor similar volume. The figure is extremely impressive. One must think that its environmental friendliness (the amount of emissions of harmful substances) is excellent.

Introduction

Currently, increasing the fuel efficiency of gasoline internal combustion engines (ICE) is still an urgent scientific and technical task. One of the ways to improve engine efficiency is to regulate the compression ratio at partial loads. In such internal combustion engines, the implementation of a variable compression ratio requires serious intervention in the design of both the engine itself and the power mechanism, which in a certain way affects the operating process parameters.

In developing power mechanism Some progress has already been made. In recent years, variable compression engines have used unconventional power mechanisms, which are characterized by complex, unreliable and inefficient designs. Many companies and research organizations are conducting research, the goal of which is to create a power mechanism that provides the best engine performance when regulating the compression ratio. From today’s point of view, the use of a crank-rotating power mechanism in an automobile internal combustion engine is promising.

This paper presents the first results of work aimed at developing a connecting rodless engine with a crank-rod mechanism that provides a change in the compression ratio over a wide range.

Review and analysis of work on engines with variable compression ratios

Work on the development of engines with a variable compression ratio (Ɛx) is carried out in the USA, Japan, Germany, Australia, Switzerland, Russia and other countries. To date, a large number of engines with different designs power mechanism providing Ɛx. Thus, in a two-stroke engine with counter-moving pistons, the compression ratio is changed using additional balancers with eccentrics connected to the crankshaft through connecting rods.

Working samples axial motors s Ɛx were created in the USA, Russia and other countries. In such engines, the drive mechanism is an oblique washer with a variable angle of inclination, which changes the stroke of the piston (S) and, accordingly, the compression ratio. The disadvantages of these engines are increased friction losses (up to 20%) and low reliability, as well as large inertial loads on the power shaft.

More interesting and reliable solutions for changing the compression ratio by adjusting S are found in internal combustion engine designs with flat mechanism. In the engine proposed by engineer N. Pouliot and developed by Sandia (USA) and ERDA (Australia), when the piston stroke changes within S = 25.4 ... 108 mm, the compression ratio changes from 6.3 to 8. Fuel efficiency of a car with an N engine. Pouliot for EPA driving cycles for city and highway is 20%.

In recent years, the DaimlerChrysler concern, together with the State Research Center NAMI, has developed an engine with a traverse mechanism for changing S. The compression ratio in this engine varies from 7.5 to 14, fuel economy exceeds 15%.

Analysis of engines with Ɛx due to regulation of S showed the following disadvantages:

According to friction losses in an engine with S = var, it is 40% greater than in a classic internal combustion engine, and this difference increases sharply with increasing crankshaft speed;

Significant losses of indicated engine power to the change drive S;

A decrease in S with a constant piston diameter leads to a decrease in turbulence in the cylinder due to a decrease in the speed in the intake valves. In this case, the combustion duration and heat transfer to the walls increase, which leads to an increase in the indicated fuel consumption;

As S decreases, CH emissions increase sharply due to an increase in the surface of the combustion chamber and a drop in combustion temperature.

Analysis of internal combustion engines with known power mechanisms indicates that the maximum value of the compression ratio in partial modes does not exceed 14 due to the high rate of increase in friction losses as Ɛx increases. This limits the possibility of further increases effective efficiency by increasing the compression ratio above 14.

Among other internal combustion engines, there is a connecting rodless engine with a crank-rotator power mechanism (KKM)

6, 7 has the greatest potential for using a variable compression ratio. A distinctive feature of the design of engines with PFC are low friction losses over the entire range of loads and rotation speeds, complete dynamic balance, compactness and low specific weight. In addition, this internal combustion engine implements a variable compression ratio much more simply and efficiently, which generally improves engine performance.

At ADI DonNTU, an experimental single-cylinder connecting rodless internal combustion engine with Ɛx was created on the basis of the engine. The engine (Fig. 1) is a two-shaft piston engine with a crank mechanism in which the force from the piston is transmitted to crankshafts through a rod, a mechanism for changing the compression ratio and a rocker with sliders mounted on the crank journals. The crankshafts are connected to each other through two identical gears.

Rice. 1. Diagram of a connecting rod engine

(the mechanism for changing the compression ratio is not shown):

1 – rod, 2 – rocker

The results of experimental studies showed:

– regulation of Ɛх at partial loads of a running engine in the range from 7 to 19 increases fuel efficiency by more than 30%;

– the device for changing Ɛx has high sensitivity and the ability to quickly respond to the occurrence of detonation. The initial stage of detonation development occurs in 1…3 engine operating cycles, and then detonation completely disappears;

– the drive of the mechanism for changing Ɛx requires little energy (approximately 0.1…0.2% maximum power engine);

– regulation of Ɛх during engine operation does not affect the kinematics of the PFC.

The influence of the power mechanism on the gas distribution in the engine

At the Department of Automobiles and Engines ADI DonNTU, computational, theoretical and experimental studies of connecting rod and

classic internal combustion engine with variable compression ratio.

One of the objectives of these studies was to identify the influence of the power mechanism on engine operation when regulating the compression ratio.

Application in crankless engine crank mechanism leads to a change in the kinematics of the piston. Unlike the classical

In a connecting rodless engine, the piston moves according to a cosine law. As a result, the piston speed near T.M.T. (Fig. 2) decreases, and around b.m.t. increases. This leads to a change in valve timing in a connecting rodless engine relative to a classic internal combustion engine.

Rice. 2. Dependence of piston speed on angle

crankshaft rotation for engines with PFC (=0) and

KShM at n = 4500 min-1

Changing the compression ratio by moving the cylinder relative to the crankcase leads in a two-stroke engine to a change in the opening height of the intake,

exhaust and purge ports and corresponding valve timing.

As calculations show, the kinematics of the piston has a significant impact on the valve timing. Application of KKM, reducing time-section

A' exhaust of the exhaust window by an average of 11% (Figure 3) relative to an engine with a crankshaft, enhances the influence of regulating the compression ratio on gas exchange processes.

However, the nature of the dependence of the time-section on the degree of compression remains unchanged. This allows, when changing the compression ratio from 7 to 17, to reduce the value of A’vyp by more than 30%, regardless of the power mechanism.

It should be noted that a decrease in A'vyp at partial loads and at low crankshaft speeds is positive, as it allows to reduce the loss of fresh charge during purging and improve engine efficiency.

Rice. 3. Changing the time-section of the outlet window from

compression ratios for engines with KKM and KShM

The influence of the power mechanism on the indicator and effective indicators of the engine

Changing the kinematics of the piston in a connecting rodless engine has a significant impact on the working process. In this engine, a decrease in piston speed in the area of TDC. leads to a decrease in heat losses during the combustion process and an increase in the degree of subsequent expansion.

The results of the experimental study showed the positive influence of the kinematics of the piston of a connecting rod engine on its indicator indicators. So, for example, at N e = 0.8 kW, n = 3000 min-1

and Ɛх = 7.7, the specific indicator fuel consumption is lower by more than 11% compared to the classic engine under study. Obviously, this is due to a reduction in direct losses of the mixture during gas exchange, as well as a better combustion process.

Analysis of the data obtained showed that an increase in the compression ratio in a connecting rodless engine is accompanied by a more uniform increase in indicator indicators. At high degrees compression, the influence of piston kinematics on improving engine indicators increases.

The increase in fuel efficiency of a connecting rod engine is associated not only with the kinematics of the piston, but also with low mechanical losses.

From the results of experimental studies of mechanical losses in crankless and classical engines, it is clear that in a crankless engine, mechanical losses at the same Ne and Ɛx are lower in all cases (Fig. 4). In addition, with increasing compression ratio, the difference in mechanical losses increases significantly.

Rice. 4. Influence of Ɛx on mechanical losses in

engines with PFC and KSHM: N e = 0.4 kW, n = 3000 min-1

Thus, with a compression ratio of 7.7, mechanical losses in a connecting rodless engine are lower than in a classic internal combustion engine by 1.5...2%, and at Ɛx = 17.1 - by 26%. This is due to the different nature of the dependence of the average pressure of mechanical losses p m for different internal combustion engines when the compression ratio changes. In a connecting rodless engine, the dependence p m = f(x) is almost linear, while in an engine with a crankshaft it is power-law in nature.

The identified advantages of a connecting rodless engine in terms of indicator indicators and mechanical losses are significantly manifested in its effective performance.

The experimentally obtained dependences of the indicator and effective indicators (Fig. 5) show the feasibility of using a crank mechanism in engines with compression ratio control.

In a connecting rodless engine, unlike a classic one, the specific effective fuel consumption decreases with increasing compression ratio above 14 at all speed and load modes. This allows you to set Ɛx in a crankless engine at the highest possible level - at the beginning of detonation (or self-ignition of the gasoline-oil mixture in a two-stroke engine).

Rice. 5. Dependence of performance of engines with crankshaft

and KKM from load during regulation

compression ratio: n = 3000 min-1

In the engine under study with a crankshaft, the compression ratio for various modes varied from 10 to 14 and was limited by an increase in g e due to an increase in mechanical losses. Thus, in an engine with a variable compression ratio, the use of Ɛx can increase fuel efficiency at low loads by more than 15% compared to an engine with a variable compression ratio, and in relation to classic engine with a fixed compression ratio - 30...45%.

Conclusion

The presented results show that application in gasoline engine adjusting the compression ratio in partial modes can significantly improve its fuel efficiency.

Options considered circuit diagrams power mechanism associated with the implementation of a variable compression ratio in relation to an automobile engine. In internal combustion engines with known power mechanisms, the maximum variable degree compression does not exceed 14 due to a significant increase in friction losses with increasing Ɛx, which limits the possibility of further improving the effective efficiency of the engine.

Higher fuel efficiency when adjusting the compression ratio, it is achieved in a connecting rodless engine with a crank-rod mechanism.

Using PFC in a two-stroke gasoline engine, it was possible to reduce mechanical losses by 26% and increase fuel efficiency by 30...45%. In addition, an analysis of the works indicates a significant

superiority of engines with PFC in terms of vibration and noise, balance, compactness and power density. In such engines, a variable compression ratio is structurally simpler and much more efficient.

In addition to the first results presented in this article, it is necessary to carry out a large amount of research and development work to develop and create a connecting rodless gasoline engine with a variable compression ratio.

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