Miller engine design features. Atkinson cycle: how it works

The Miller cycle was proposed in 1947 by American engineer Ralph Miller as a way to combine the virtues of the Atkinson engine with the simpler piston mechanism of the Otto engine. Instead of making the compression stroke mechanically shorter than the power stroke (as in the classic Atkinson engine, where the piston moves up faster than down), Miller came up with the idea of ​​shortening the compression stroke at the expense of the intake stroke, keeping the up and down movement of the piston the same. speed (as in the classic Otto engine).

To do this, Miller proposed two different approaches: either close the intake valve much earlier than the end of the intake stroke (or open it later than the beginning of this stroke), or close it significantly later than the end of this stroke. The first approach among engine specialists is conventionally called "shortened intake", and the second - "shortened compression". Ultimately, both of these approaches achieve the same thing: reducing actual the degree of compression of the working mixture relative to the geometric, while maintaining the same degree of expansion (that is, the stroke of the working stroke remains the same as in the Otto engine, and the compression stroke seems to be reduced - like in Atkinson, only it is reduced not in time, but in the compression ratio of the mixture) .

Thus, the mixture in the Miller engine compresses less than it should in an Otto engine of the same mechanical geometry. This allows the geometric compression ratio (and therefore the expansion ratio!) to be increased above the limits imposed by the detonation properties of the fuel - bringing the actual compression to acceptable values ​​due to the "shortening of the compression cycle" described above. In other words, with the same actual compression ratio (limited by fuel), the Miller engine has a significantly higher expansion ratio than the Otto engine. This makes it possible to more fully use the energy of gases expanding in the cylinder, which, in fact, increases the thermal efficiency of the motor, ensures high engine efficiency, and so on.

The benefit of increasing the thermal efficiency of the Miller cycle relative to the Otto cycle comes with a loss of peak power output for a given engine size (and mass) due to degradation of cylinder filling. Since a larger Miller engine than an Otto engine would be required to achieve the same power output, the benefit from the increased thermal efficiency of the cycle will be partly spent on mechanical losses (friction, vibrations, etc.) that increase with the size of the engine.

Computer control of the valves allows you to change the degree of filling of the cylinder during operation. This makes it possible to squeeze the maximum power out of the motor, with a deterioration in economic performance, or to achieve better efficiency with a decrease in power.

A similar problem is solved by a five-stroke engine, in which additional expansion is carried out in a separate cylinder.

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Jan 2016

Priorities

Ever since the first Prius, it seemed that Toyota liked James Atkinson much more than Ralph Miller. And gradually the "Atkinson cycle" of their press releases spread throughout the journalistic community.

Toyota officially: "A heat cycle engine proposed by James Atkinson (U.K.) in which compression stroke and expansion stroke duration can be set independently. Subsequent improvement by R. H. Miller (U.S.A.) allowed adjustment of intake valve opening/closing timing to enable a practical system (Miller Cycle)."
- Toyota informally and anti-scientifically: "Miller Cycle engine is an Atkinson Cycle engine with a supercharger".

Moreover, even in the local engineering environment, the "Miller cycle" has existed since time immemorial. How would be more correct?

In 1882, British inventor James Atkinson proposed the idea of ​​improving the efficiency of a piston engine by reducing the compression stroke and increasing the expansion stroke of the working fluid. In practice, this was supposed to be realized by complex piston drive mechanisms (two pistons according to the "boxer" scheme, a piston with a crank-rocker mechanism). The built versions of the engines showed an increase in mechanical losses, overcomplication of the design, and a decrease in power compared to engines of other designs, so they were not widely used. Atkinson's famous patents referred specifically to designs, without considering the theory of thermodynamic cycles.

In 1947, the American engineer Ralph Miller returned to the idea of ​​the idea of ​​reduced compression and continued expansion, proposing to implement it not due to the kinematics of the piston drive, but by selecting the valve timing for engines with a conventional crank mechanism. In the patent, Miller considered two options for organizing the workflow - with early (EICV) or late (LICV) closing of the intake valve. Actually, both options mean a decrease in the actual (effective) compression ratio in relation to the geometric one. Realizing that reducing compression would result in a loss of engine power, Miller initially focused on supercharged engines, in which the loss of filling would be compensated by the compressor. The theoretical Miller cycle for a spark ignition engine is exactly the same as the theoretical cycle for an Atkinson engine.

By and large, the Miller / Atkinson cycle is not an independent cycle, but a variation of the well-known thermodynamic cycles of Otto and Diesel. Atkinson is the author of the abstract idea of ​​an engine with physically different compression and expansion strokes. It was Ralph Miller who proposed the real organization of work processes in real engines, which is used in practice to this day.

Principles

When the engine is running on the Miller cycle with reduced compression, the intake valve closes much later than in the Otto cycle, due to which part of the charge is forced back into the intake port, and the actual compression process begins already in the second half of the cycle. As a result, the effective compression ratio is lower than the geometric one (which, in turn, is equal to the expansion ratio of the gases in the working stroke). By reducing pumping losses and compression losses, the thermal efficiency of the engine is increased by 5-7% and the corresponding fuel savings are achieved.

We can once again note the key points of difference between the cycles. 1 and 1 "- the volume of the combustion chamber for the engine with the Miller cycle is smaller, the geometric compression ratio and the expansion ratio are higher. 2 and 2" - the gases do useful work on a longer stroke, so there is less residual exhaust loss. 3 and 3 "- the intake vacuum is less due to less throttling and reverse displacement of the previous charge, therefore, pumping losses are lower. 4 and 4" - the intake valve closes and the compression begins from the middle of the cycle, after the reverse displacement of part of the charge.
Of course, reverse charge displacement means a drop in engine performance, and for atmospheric engines, operation in such a cycle makes sense only in a relatively narrow partial load mode. In the case of constant valve timing, only the use of boost can compensate for this throughout the entire dynamic range. On hybrid models, the lack of traction in adverse conditions is compensated by the traction of the electric motor.

Implementation

In classic Toyota engines of the 90s with fixed phases, operating on the Otto cycle, the intake valve closes at 35-45 ° after BDC (crankshaft angle), the compression ratio is 9.5-10.0. In more modern VVT engines, the possible intake valve closing range has expanded to 5-70 ° after BDC, the compression ratio has increased to 10.0-11.0.

In engines of hybrid models operating only on the Miller cycle, the intake valve closing range is 80-120° ... 60-100° after BDC. The geometric compression ratio is 13.0-13.5.

By the mid-2010s, new engines with a wide range of variable valve timing (VVT-iW) appeared, which can operate both in a conventional cycle and in the Miller cycle. For atmospheric versions, the intake valve closing range is 30-110 ° after BDC with a geometric compression ratio of 12.5-12.7, for turbo versions - 10-100 ° and 10.0, respectively.

The internal combustion engine (ICE) is considered one of the most important components in a car; its characteristics, power, throttle response and economy determine how comfortable the driver will feel behind the wheel. Although cars are constantly being improved, “overgrown” with navigation systems, fashionable gadgets, multimedia, and so on, the motors remain practically unchanged, at least the principle of their operation does not change.

The Otto Atkinson cycle, which formed the basis of the automobile internal combustion engine, was developed at the end of the 19th century, and since that time has not undergone almost any global changes. Only in 1947, Ralph Miller managed to improve the development of his predecessors, taking the best from each of the engine construction models. But in order to understand in general terms the principle of operation of modern power units, you need to look a little into history.

Efficiency of Otto engines

The first engine for a car, which could work normally not only theoretically, was developed by the Frenchman E. Lenoir back in 1860, was the first model with a crank mechanism. The unit ran on gas, was used on boats, its coefficient of performance (COP) did not exceed 4.65%. Later, Lenoir teamed up with Nikolaus Otto, in collaboration with a German designer in 1863, a 2-stroke internal combustion engine with an efficiency of 15% was created.

The principle of a four-stroke engine was first proposed by N. A. Otto in 1876, it is this self-taught designer who is considered the creator of the first motor for a car. The engine had a gas power system, while the Russian designer O. S. Kostovich is considered the inventor of the world's first carburetor internal combustion engine on gasoline.

The work of the Otto cycle is used on many modern engines, there are four strokes in total:

• inlet (when the inlet valve is opened, the cylindrical space is filled with the fuel mixture);
• compression (the valves are tight (closed), the mixture is compressed, at the end of this process, ignition is provided by the spark plug);
• working stroke (due to high temperatures and high pressure, the piston rushes down, makes the connecting rod and crankshaft move);
• release (at the beginning of this stroke, the exhaust valve opens, freeing the way for exhaust gases, the crankshaft continues to rotate as a result of converting heat energy into mechanical energy, raising the connecting rod with the piston up).

All strokes are looped and go in a circle, and the flywheel, which stores energy, helps to spin the crankshaft.

Although compared to the two-stroke version, the four-stroke scheme seems to be more perfect, the efficiency of a gasoline engine, even in the best case, does not exceed 25%, and diesel engines have the highest efficiency, here it can increase to a maximum of up to 50%.

Atkinson thermodynamic cycle

James Atkinson, a British engineer who decided to modernize Otto's invention, proposed his own version of the improvement of the third cycle (work stroke) in 1882. The designer set a goal to increase the efficiency of the engine and reduce the compression process, to make the internal combustion engine more economical, less noisy, and the difference in its construction scheme was to change the drive of the crank mechanism (KShM) and to go through all the cycles in one revolution of the crankshaft.

Although Atkinson was able to improve the efficiency of his motor in relation to Otto's already patented invention, the scheme was not put into practice, the mechanics turned out to be too complicated. But Atkinson was the first designer to propose the operation of an internal combustion engine with a reduced compression ratio, and the principle of this thermodynamic cycle was further taken into account by the inventor Ralph Miller.

The idea of ​​reducing the compression process and a more saturated intake did not go into oblivion; the American R. Miller returned to it in 1947. But this time, the engineer proposed to implement the scheme not by complicating the KShM, but by changing the valve timing. Two versions were considered:

• Intake valve lag stroke (LICV or short compression);
• early valve closing stroke (EICV or short intake).

By closing the intake valve late, a reduced compression is obtained in relation to the Otto engine, due to which part of the fuel mixture is forced back into the intake port. Such a constructive solution gives:

• more "soft" geometric compression of the fuel-air mixture;
• additional fuel economy, especially at low speeds;
• less detonation;
• low noise level.

The disadvantages of this scheme include a decrease in power at high speeds, since the compression process is reduced. But due to the more complete filling of the cylinders, the efficiency at low speeds increases and the geometric compression ratio increases (the actual one decreases). A graphic representation of these processes can be seen in the figures with conditional diagrams below.

Engines operating according to the Miller scheme lose power to Otto at high speeds, but in urban operating conditions this is not so important. But such motors are more economical, detonate less, run softer and quieter.

Miller Cycle Engine on a Mazda Xedos (2.3L)

A special valve overlapping mechanism provides an increase in the compression ratio (C3), if in the standard version, for example, it is equal to 11, then in a short compression engine, this figure, under all other identical conditions, increases to 14. On a 6-cylinder ICE 2.3 L Mazda Xedos (Skyactiv family) theoretically looks like this: the inlet valve (VK) opens when the piston is located at the top dead center (abbreviated as TDC), closes not at the bottom point (BDC), and later, remains open 70º. In this case, part of the fuel-air mixture is pushed back into the intake manifold, compression begins after the VC closes. When the piston returns to TDC:

• the volume in the cylinder decreases;
• pressure increases;
• ignition from a candle occurs at some specific moment, it depends on the load and the number of revolutions (the ignition advance system works).

Then the piston goes down, expansion occurs, while the heat transfer to the cylinder walls is not as high as in the Otto scheme due to the short compression. When the piston reaches BDC, gases are released, then all actions are repeated again.

A special intake manifold configuration (wider and shorter than usual) and a 70-degree EC opening angle at 14:1 NW makes it possible to set the ignition to 8º at idle without any perceptible detonation. Also, this scheme provides a greater percentage of useful mechanical work, or, in other words, allows you to increase efficiency. It turns out that the work calculated by the formula A \u003d P dV (P is pressure, dV is volume change) is not aimed at heating the walls of the cylinders, the block head, but is used to complete the working stroke. Schematically, the whole process can be seen in the figure, where the beginning of the cycle (BDC) is indicated by the number 1, the compression process - to point 2 (TDC), from 2 to 3 - heat supply with a stationary piston. When the piston goes from point 3 to 4, expansion occurs. The completed work is indicated by the shaded area At.

Also, the whole scheme can be viewed in the coordinates T S, where T means temperature, and S is the entropy, which increases with the supply of heat to the substance, and in our analysis this is a conditional value. Designations Q p and Q 0 - the amount of input and output heat.

The disadvantage of the Skyactiv series is that, compared to the classic Otto, these engines have less specific (actual) power; on a 2.3 L engine with six cylinders, it is only 211 horsepower, and even then, taking into account turbocharging and 5300 rpm. But the motors have tangible advantages:

• high compression ratio;
• the ability to install early ignition, while not getting detonation;
• ensuring fast acceleration from a standstill;
• high efficiency factor.

And another important advantage of the Mazda Miller Cycle engine is economical fuel consumption, especially at low loads and at idle.

Toyota Atkinson engines

Although the Atkinson cycle did not find its practical application in the 19th century, the idea of ​​​​its engine is realized in the power units of the 21st century. Such motors are installed on some models of Toyota hybrid passenger cars, which operate both on gasoline fuel and on electricity. It should be clarified that the Atkinson theory is never used in its pure form, rather, the new developments of Toyota engineers can be called ICEs designed according to the Atkinson / Miller cycle, since they use a standard crank mechanism. Reducing the compression cycle is achieved by changing the gas distribution phases, while the stroke cycle is lengthened. Motors using a similar scheme are found on Toyota cars:

• Prius;
• Yaris;
• Auris;
• highlander;
• Lexus GS 450h;
• Lexus CT 200h;
• Lexus HS 250h;
• Vitz.

The range of engines with the implemented Atkinson / Miller scheme is constantly replenished, so at the beginning of 2017, the Japanese concern launched the production of a 1.5-liter four-cylinder internal combustion engine running on high-octane gasoline, providing 111 horsepower, with a compression ratio in the cylinders of 13.5: 1. The engine is equipped with a VVT-IE phase shifter capable of switching Otto / Atkinson modes depending on speed and load, with this power unit the car can accelerate to 100 km / h in 11 seconds. The engine is economical, high efficiency (up to 38.5%), provides excellent acceleration.

diesel cycle

The first diesel engine was designed and built by the German inventor and engineer Rudolf Diesel in 1897, the power unit was large, even larger than the steam engines of those years. Like the Otto engine, it was a four-stroke, but it was distinguished by its excellent efficiency, ease of operation, and the compression ratio of the internal combustion engine was significantly higher than that of a gasoline power unit. The first diesel engines of the late 19th century ran on light petroleum products and vegetable oils, and there was also an attempt to use coal dust as fuel. But the experiment failed almost immediately:

• it was problematic to ensure the supply of dust to the cylinders;
• having abrasive properties, coal quickly wore out the cylinder-piston group.

Interestingly, the English inventor Herbert Aykroyd Stuart patented a similar engine two years earlier than Rudolf Diesel, but Diesel managed to design a model with increased cylinder pressure. The Stewart model in theory provided 12% thermal efficiency, while according to the Diesel scheme, the efficiency reached 50%.

In 1898, Gustav Trinkler designed a high-pressure oil engine equipped with a prechamber, this model is the direct prototype of modern diesel internal combustion engines.

Modern diesel engines for cars

Both the Otto cycle gasoline engine and the diesel engine have not changed the basic construction scheme, but the modern diesel internal combustion engine has been “overgrown” with additional components: a turbocharger, an electronic fuel supply control system, an intercooler, various sensors, and so on. Recently, Common Rail direct injection power units have been increasingly developed and launched into a series, providing environmentally friendly exhaust gases in accordance with modern requirements, high injection pressure. Diesels with direct injection have quite tangible advantages over engines with a conventional fuel system:

• economically consume fuel;
• have more power with the same volume;
• work with low noise level;
• allows the car to accelerate faster.

Disadvantages of Common Rail engines: rather high complexity, the need for repair and maintenance to use special equipment, demanding quality of diesel fuel, relatively high cost. Like gasoline internal combustion engines, diesel engines are constantly being improved, becoming more technologically advanced and more complex.

Video: The cycle of OTTO, Atkinson and Miller, what is the difference:

slide 2

Classic ICE

The classic four-stroke engine was invented back in 1876 by a German engineer named Nikolaus Otto, the cycle of operation of such an internal combustion engine (ICE) is simple: intake, compression, power stroke, exhaust.

slide 3

Indicator diagram of the Otto and Atkinson cycle.

slide 4

Atkinson cycle

British engineer James Atkinson even before the war came up with his own cycle, which is slightly different from the Otto cycle - its indicator diagram is marked in green. What is the difference? Firstly, the volume of the combustion chamber of such an engine (with the same working volume) is smaller, and, accordingly, the compression ratio is higher. Therefore, the highest point on the indicator diagram is located to the left, in the area of ​​\u200b\u200ba smaller over-piston volume. And the expansion ratio (the same as the compression ratio, only vice versa) is also larger - which means that we are more efficient, we use exhaust gas energy on a larger piston stroke and have lower exhaust losses (this is reflected by a smaller step on the right). Then everything is the same - the exhaust and intake cycles go.

slide 5

Now, if everything happened in accordance with the Otto cycle and the intake valve closed at BDC, then the compression curve would go up, and the pressure at the end of the cycle would be excessive - because the compression ratio is higher here! After the spark, not a flash of the mixture would follow, but a detonation explosion - and the engine, having not worked for an hour, would have died the explosion. But the British engineer James Atkinson was not like that! He decided to extend the intake phase - the piston reaches BDC and goes up, while the intake valve, meanwhile, remains open until about half the full piston stroke. At the same time, part of the fresh combustible mixture is pushed back into the intake manifold, which increases the pressure there - or rather, reduces the vacuum. This allows you to open the throttle more at low and medium loads. This is why the intake line in the Atkinson cycle diagram is higher and the engine pumping losses are lower than in the Otto cycle.

slide 6

The Atkinson cycle

So the compression stroke, when the intake valve closes, starts at a lower over-piston volume, which is illustrated by the green compression line starting at half of the lower horizontal intake line. It would seem that it’s easier: to increase the compression ratio, change the profile of the intake cams, and the trick is in the bag - the Atkinson cycle engine is ready! But the fact is that in order to achieve good dynamic performance over the entire operating speed range of the engine, it is necessary to compensate for the expulsion of the combustible mixture during an extended intake cycle by applying supercharging, in this case a mechanical supercharger. And its drive takes away from the motor the lion's share of the energy that can be won back on pumping and exhaust losses. The application of the Atkinson cycle to the naturally aspirated Toyota Prius hybrid engine is made possible by its light duty operation.

Slide 7

The Miller cycle

The Miller cycle is a thermodynamic cycle used in four-stroke internal combustion engines. The Miller cycle was proposed in 1947 by American engineer Ralph Miller as a way to combine the advantages of the Antkinson engine with the simpler piston mechanism of the Otto engine.

Slide 8

Instead of making the compression stroke mechanically shorter than the power stroke (as in the classic Atkinson engine, where the piston moves up faster than down), Miller came up with the idea of ​​shortening the compression stroke at the expense of the intake stroke, keeping the up and down movement of the piston the same. speed (as in the classic Otto engine).

Slide 9

To do this, Miller proposed two different approaches: close the intake valve much earlier than the end of the intake stroke (or open it later than the beginning of this stroke), close it significantly later than the end of this stroke.

Slide 10

The first approach for engines is conventionally called "shortened intake", and the second - "shortened compression". Both of these approaches give the same thing: reducing the actual compression ratio of the working mixture relative to the geometric, while maintaining the same expansion ratio (that is, the power stroke remains the same as in the Otto engine, and the compression stroke seems to be reduced - like in Atkinson, only decreases not in time, but in the degree of compression of the mixture)

slide 11

Miller's second approach

This approach is somewhat more beneficial in terms of compression losses, and therefore it is precisely this approach that is practically implemented in Mazda “MillerCycle” serial automobile engines. In such an engine, the intake valve does not close at the end of the intake stroke, but remains open during the first part of the compression stroke. Although the entire volume of the cylinder was filled with the air-fuel mixture on the intake stroke, some of the mixture is forced back into the intake manifold through the open intake valve when the piston moves up on the compression stroke.

slide 12

Compression of the mixture actually starts later, when the intake valve finally closes and the mixture becomes trapped in the cylinder. Thus, the mixture in the Miller engine compresses less than it should in an Otto engine of the same mechanical geometry. This allows you to increase the geometric compression ratio (and, accordingly, the expansion ratio!) Above the limits determined by the detonation properties of the fuel - bringing the actual compression to acceptable values ​​\u200b\u200bdue to the “shortening of the compression cycle” described above. Slide 15

Conclusion

If you look closely at the cycle - both Atkinson and Miller, you will notice that in both there is an additional fifth measure. It has its own characteristics and is, in fact, neither an intake stroke nor a compression stroke, but an intermediate independent stroke between them. Therefore, engines operating on the principle of Atkinson or Miller are called five-stroke.

View all slides

The internal combustion engine is very far from ideal, at best it reaches 20 - 25%, diesel 40 - 50% (that is, the rest of the fuel is burned almost empty). In order to increase efficiency (respectively increase the efficiency), it is required to improve the design of the motor. Many engineers struggle with this, and to this day, but the first were only a few engineers, such as Nikolaus August OTTO, James ATKINSON and Ralph Miller. Everyone made certain changes, and tried to make the motors more economical and productive. Each offered a certain cycle of work, which could be radically different from the opponent's design. Today I will try in simple words to explain to you what are the main differences in the operation of the internal combustion engine, and of course the video version at the end ...

The article will be written for beginners, so if you are a sophisticated engineer, you can not read it, it is written for a general understanding of the internal combustion engine cycles.

I would also like to note that there are a lot of variations of various designs, the most famous that we can still know are the cycle of DIESEL, STIRLING, CARNO, ERICKSON, etc. If you count the designs, then there can be about 15 of them. And not all internal combustion engines, but, for example, the external STIRLING.

But the most famous, which are used to this day in cars, are OTTO, ATKINSON and MILLER. Here we will talk about them.

In fact, this is a conventional internal combustion heat engine with forced ignition of a combustible mixture (through a candle), which is now used in 60-65% of cars. YES - yes, exactly the one you have under the hood works on the OTTO cycle.

However, if you dig into history, the first principle of such an internal combustion engine was proposed in 1862 by the French engineer Alphonse BO DE ROCHE. But it was a theoretical principle of operation. OTTO in 1878 (16 years later) embodied this engine in metal (in practice) and patented this technology

In fact, this is a four-stroke engine, which is characterized by:

• Inlet . Supply of fresh air-fuel mixture. The inlet valve opens.
• Compression . The piston goes up, compressing this mixture. Both valves are closed
• working stroke . The candle ignites the compressed mixture, the ignited gases push the piston down
• Exhaust gas outlet . The piston goes up, pushing out the burnt gases. Exhaust valve opens

I would like to note that the intake and exhaust valves work in strict sequence - EQUALLY at high and at low speeds. That is, there is no change in work at different speeds.

In his engine, OTTO was the first to apply compression of the working mixture to raise the maximum temperature of the cycle. Which was carried out along the adiabat (in simple words, without heat exchange with the external environment).

After the mixture was compressed, it was ignited by a candle, after which the process of heat removal began, which proceeded almost along the isochore (that is, at a constant volume of the engine cylinder).

Since OTTO patented his technology, its industrial use was not possible. To circumvent the patents, James Atkinson decided in 1886 to modify the OTTO cycle. And he proposed his own type of operation of the internal combustion engine.

He proposed to change the ratio of cycle times, due to which the working stroke was increased by complicating the crank design. It should be noted that the test specimen that he built was a single-cylinder, and was not widely used due to the complexity of the design.

If in a nutshell to describe the principle of operation of this internal combustion engine, it turns out:

All 4 strokes (injection, compression, power stroke, exhaust) - occurred in one rotation of the crankshaft (OTTO had two rotations). Thanks to a complex system of levers that were attached next to the "crankshaft".

In this design, it was possible to implement certain ratios of the lengths of the levers. In simple words, the piston stroke on the intake and exhaust stroke is MORE than the piston stroke in both compression and power stroke.

What does it give? YES, that you can “play” with the compression ratio (changing it), due to the ratio of the lengths of the levers, and not due to the “throttling” of the intake! From this, the advantage of the ACTINSON cycle is derived, in terms of pumping losses

Such motors turned out to be quite efficient with high efficiency and low fuel consumption.

However, there were also many negative points:

• The complexity and bulkiness of the design
• Low at low rpm
• Poor throttle control, be it ()

There are persistent rumors that the ATKINSON principle was used on hybrid cars, in particular by TOYOTA. However, this is a bit not true, only his principle was used there, but the design was used by another engineer, namely Miller. In its pure form, ATKINSON motors were more of a single character than a mass one.

Ralph Miller also decided to play with the compression ratio in 1947. That is, he, as it were, will continue the work of ATKINSON, but he did not take his complex engine (with levers), but the usual OTTO ICE.

What did he propose . He did not make the compression stroke mechanically shorter than the power stroke (as Atkinson suggested, his piston moves faster up than down). He came up with the idea of ​​shortening the compression stroke at the expense of the intake stroke, keeping the up and down movement of the pistons the same (classic OTTO engine).

There were two ways to go:

• Close the intake valves before the end of the intake stroke - this principle is called "Short intake"
• Or close the intake valves later than the intake stroke - this option is called "Shortened compression"

Ultimately, both principles give the same thing - a decrease in the compression ratio, the working mixture relative to the geometric! However, the degree of expansion is preserved, that is, the stroke of the working stroke is preserved (as in the OTTO internal combustion engine), and the compression stroke, as it were, is reduced (as in the Atkinson internal combustion engine).

In simple words - the air-fuel mixture at MILLER compresses much less than it should have compressed in the same engine at OTTO. This allows you to increase the geometric compression ratio, and accordingly the physical expansion ratio. Much more than is due to the detonation properties of the fuel (that is, gasoline cannot be compressed indefinitely, detonation will begin)! Thus, when the fuel is ignited at TDC (or rather dead center), it has a much higher expansion ratio than the OTTO design. This makes it possible to use the energy of gases expanding in the cylinder much more, which increases the thermal efficiency of the structure, which leads to high savings, elasticity, etc.

It should also be taken into account that pumping losses decrease on the compression stroke, that is, it is easier to compress fuel with MILLER, less energy is required.

Negative sides - This is a decrease in peak power output (especially at high speeds) due to worse cylinder filling. To remove the same power as OTTO (at high speeds), the motor had to be built larger (larger cylinders) and more massive.

On modern engines

So what's the difference?

The article turned out to be more complicated than I expected, but to summarize. THAT turns out:

OTTO - this is the standard principle of a conventional motor, which are now on most modern cars

ATKINSON - offered a more efficient internal combustion engine, by changing the compression ratio using a complex design of levers that were connected to the crankshaft.

BENEFITS - fuel economy, more flexible motor, less noise.

CONS - bulky and complex design, low torque at low revs, poor throttle control

In its pure form, it is now practically not used.

MILLER - proposed to use a lower compression ratio in the cylinder, with the help of a late closing of the intake valve. The difference with ATKINSON is huge, because he did not use his design, but OTTO, but not in its pure form, but with a modified timing system.

It is assumed that the piston (on the compression stroke) goes with less resistance (pumping losses), and geometrically compresses the air-fuel mixture better (excluding its detonation), however, the expansion ratio (when ignited by a candle) remains almost the same as in the OTTO cycle .

BENEFITS - fuel economy (especially at low speeds), elasticity of work, low noise.

CONS - a decrease in power at high speeds (due to the worst filling of the cylinders).

It is worth noting that now the MILLER principle is used on some cars at low speeds. Allows you to adjust the intake and exhaust phases (expanding or narrowing them using