In the automotive industry of passenger cars, for more than a century, standard use internal combustion engines. They have some drawbacks, over which scientists and designers have been struggling for years. As a result of these studies, quite interesting and strange "engines" are obtained. One of them will be discussed in this article.
History of the creation of the Atkinson cycle
The history of the creation of the motor with the Atkinson cycle is rooted in a distant history. Let's begin with first classic four-stroke engine was invented by the German Nikolaus Otto in 1876. The cycle of such a motor is quite simple: intake, compression, stroke, exhaust.
Just 10 years after the invention of the Otto engine, an Englishman James Atkinson proposed to modify the German motor. In fact, the engine remains a four-stroke. But Atkinson slightly changed the duration of two of them: the first 2 measures are shorter, the remaining 2 are longer. Sir James implemented this scheme by changing the length of the piston strokes. But in 1887, such a modification of the Otto engine did not find application. Despite the fact that the performance of the motor increased by 10%, the complexity of the mechanism did not allow the mass application of the Atkinson cycle for cars.
But the engineers continued to work on the Sir James cycle. American Ralph Miller in 1947 slightly improved the Atkinson cycle, simplifying it. This allowed the use of the engine in the automotive industry. It would seem more correct to call the Atkinson cycle the Miller cycle. But the engineering community left Atkinson the right to name the motor after his name on the principle of the discoverer. In addition, with the use of new technologies, it became possible to use a more complex Atkinson cycle, so the Miller cycle was eventually abandoned. For example, new Toyotas have an Atkinson engine, not a Miller one.
Nowadays, an engine that works on the principle of the Atkinson cycle is put on hybrids. The Japanese were especially successful in this, who always care about the environmental friendliness of their cars. Hybrid Prius from Toyota actively fill the world market. 
How the Atkinson cycle works
As mentioned earlier, the Atkinson cycle repeats the same cycles as the Otto cycle. But using the same principles, Atkinson created an entirely new engine.
The motor is designed so that the piston completes all four cycles in one rotation of the crankshaft. In addition, the strokes have different lengths: the piston strokes during compression and expansion are shorter than during intake and exhaust. That is, in the Otto cycle, the intake valve closes almost immediately. In the Atkinson cycle, this valve closes halfway to top dead center. In a conventional internal combustion engine, compression is already taking place at this moment.
The engine is modified with a special crankshaft, in which the attachment points are displaced. Due to this, the compression ratio of the motor has increased, and friction losses have been minimized.
Difference from traditional engines
Recall that the Atkinson cycle is four stroke(intake, compression, expansion, exhaust). A conventional four-stroke engine runs on the Otto cycle. Briefly, we recall his work. At the beginning of the stroke in the cylinder, the piston goes up to the upper operating point. The mixture of fuel and air burns, the gas expands, the pressure is at its maximum. Under the influence of this gas, the piston goes down, comes to the bottom dead center. The working stroke is over, the exhaust valve opens, through which the exhaust gas exits. In this place, output losses occur, because. the exhaust gas still has a residual pressure that cannot be used.
Atkinson reduced the release loss. In his engine, the volume of the combustion chamber is smaller with the same displacement. It means that the compression ratio is higher and the piston stroke is longer. In addition, the duration of the compression stroke is reduced compared to the power stroke, the engine is cycled with an increased expansion ratio (the compression ratio is lower than the expansion ratio). These conditions made it possible to reduce the loss of output by using the energy of the exhaust gases.
Let's go back to the Otto cycle. When the working mixture is sucked in, the throttle valve is closed and creates resistance at the inlet. This happens when the gas pedal is not fully pressed. Due to the closed damper, the motor wastes energy, creating pumping losses.
Atkinson worked on the intake stroke as well. By extending it, Sir James achieved a reduction in pumping losses. To do this, the piston reaches bottom dead center, then rises, leaving the intake valve open for about half the piston stroke. Part of the fuel mixture is returned to the intake manifold. It increases the pressure allows you to slightly open the throttle at low and medium speeds.
But the Atkinson motor was not released into the series due to interruptions in work. The fact is that, unlike the internal combustion engine, the engine only works at high speeds. At idle, it may stall. But this problem was solved in the production of hybrids. At low speeds, such cars drive on electric traction, and they switch to a gasoline engine only in case of acceleration or under load. Such a model both removes the shortcomings of the Atkinson engine and emphasizes its advantages over other internal combustion engines.
Advantages and disadvantages of the Atkinson cycle
The Atkinson engine has several benefits that distinguish it from the rest of the internal combustion engines: 1. Reduced fuel losses. As mentioned earlier, by changing the duration of cycles, it became possible to save fuel by using exhaust gases and reducing pumping losses. 2. Small probability of detonation combustion. The fuel compression ratio is reduced from 10 to 8. This allows you not to increase the engine speed by switching to a lower gear due to an increase in load. Also, the likelihood of detonation combustion is less due to the release of heat from the combustion chamber into the intake manifold. 3. Small consumption of gasoline. In the new hybrid models, gasoline consumption is 4 liters per 100 km. 4. Profitability, environmental friendliness, high efficiency. 
But the Atkinson engine has one significant drawback, which did not allow it to be used in the mass production of cars. Due to low power ratings, at low speeds, the engine may stall. Therefore, the Atkinson engine has taken root very well in hybrids.
Application of the Atkinson cycle in the automotive industry
By the way, about the machines on which they put Atkinson engines. In mass production, this modification of the internal combustion engine appeared not so long ago. As mentioned earlier, the first users of the Atkinson cycle were Japanese firms and Toyota. One of the most famous cars MazdaXedos 9/Eunos800, which was produced in 1993-2002.
Then, the Atkinson ICE was adopted by manufacturers of hybrid models. One of the most famous companies using this motor is Toyota, issuing Prius, Camry, Highlander Hybrid and Harrier Hybrid. The same engines are used in Lexus RX400h, GS 450h and LS600h, and Ford and Nissan developed escape hybrid And Altima Hybrid.
It is worth saying that in the automotive industry there is a fashion for ecology. Therefore, hybrids operating on the Atkinson cycle fully meet the needs of customers and environmental standards. In addition, progress does not stand still, new modifications of the Atkinson motor improve its pluses and destroy the minuses. Therefore, we can say with confidence that the Atkinson cycle engine has a productive future and hope for a long existence.
The Miller cycle is a thermodynamic cycle used in four-stroke internal combustion engines. The Miller cycle was proposed in 1947 by the American engineer Ralph Miller as a way to combine the advantages 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 give the same thing: reducing the actual compression ratio of the working mixture relative to the geometric one, while maintaining the same expansion ratio (that is, the stroke of the power stroke remains the same as in the Otto engine, and the compression stroke, as it were, is reduced - like in Atkinson, only it is reduced not in time, but in the degree of compression of the mixture). Let us consider in more detail Miller's second approach- since it is somewhat more profitable in terms of compression losses, and therefore it is precisely this that is practically implemented in Mazda “Miller Cycle” serial automobile engines (such a 2.3-liter V6 engine with a mechanical supercharger has been installed on the Mazda Xedos-9 car for a long time, and recently the newest "atmospheric" I4 engine of this type with a volume of 1.3 liters was received by the Mazda-2 model).
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 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. 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 makes it possible to increase the geometric compression ratio (and, accordingly, the expansion ratio!) above the limits due to 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, for 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.
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.
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. That is why Mazda engineers built their first production engine with a non-atmospheric Miller cycle. When they attached a Lysholm-type supercharger to the engine, they were able to restore the high power density with almost no loss of Miller cycle efficiency. It was this decision that made the Mazda V6 “Miller Cycle” motor, which is installed on the Mazda Xedos-9 (Millenia or Eunos-800), attractive. After all, with a working volume of 2.3 liters, it produces 213 hp. and a torque of 290 Nm, which is equivalent to the characteristics of conventional 3-liter atmospheric engines, and at the same time, fuel consumption for such a powerful engine on a large car is very low - 6.3 l / 100 km on the highway, 11.8 l / 100 km in the city, which is in line with the much less powerful 1.8-liter engines. Further development of technology allowed Mazda engineers to build a Miller Cycle engine with acceptable power density characteristics already without the use of superchargers - the new Sequential Valve Timing System, which dynamically controls the intake and exhaust phases, partially compensates for the drop in maximum power inherent in the Miller cycle. The new engine will be produced in-line 4-cylinder, 1.3-liter, in two versions: 74 horsepower (118 Nm of torque) and 83 horsepower (121 Nm). At the same time, the fuel consumption of these engines decreased by 20 percent compared to a conventional engine of the same power - up to four liters per hundred kilometers. In addition, the toxicity of the motor with the "Miller cycle" is 75 percent lower than modern environmental requirements. 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.
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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
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 bar. 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.
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