The Atkinson cycle engine is a type of reciprocating internal combustion engine invented by James Atkinson in 1882. It is practically a common Otto cycle engine, but with a crank modified crank to obtain greater efficiency at the expense of a reduction in the power. The objective was to compete with the Otto cycle without infringing any patent.
In its original version, the Atkinson cycle requires a single rotation of the crankshaft to complete a cycle of operation, keeping the phases of the Otto cycle engine intact: intake, compression, expansion (useful phase) and discharge. However, thanks to a particular geometry of the crankshaft mechanism, the expansion stroke is greater than the compression stroke, which allows the engine to have a higher efficiency compared to the Otto cycle.
Nowadays the term "Atkinson cycle" is misused to describe a normal Otto cycle engine in which different compression and expansion strokes are obtained by acting on the opening / closing of the intake valves, This cycle is described in place correctly by Miller cycle.
In the Miller cycle by keeping the inlet valve open for a greater angle of rotation than normal, the effect is obtained from a reflux of air sucked into the suction duct, or through an early closing of the valve during the phase of suction. In both cases, the effect is to reduce the filling of the cylinder and, therefore, the compression ratio, without modifying the stroke. So the expansion stroke is greater than the "current" compression, this results in a lower pressure and the temperature of the combustion gases at the end of the expansion phase, therefore, theoretically, a greater amount of heat it becomes mechanical work.
Atkinson rotary motor
The Atkinson cycle can also be applied to rotary engines with the consequent increase in power and efficiency compared to the Otto cycle. This type of motor retains an active phase per revolution of the crankshaft, along with the different compression and volume expansion of the original Atkinson cycle. The exhaust gases are expelled from the engine through compressed air, this modification of the Atkinson cycle allows the use of alternative fuels such as hydrogen and diesel.
Use of the Atkinson cycle
Very often this cycle is confused with the Miller cycle, which requires only a variation of the supply time, while the Atkinson cycle needs a particular crank structure, which is why many of the hybrid electric vehicles such as the Honda Jazz 2013 , the Toyota Prius, the hybrid Toyota Auris (front-wheel drive), the Toyota Yaris hybrid, the Lexus CT200h, the Lexus iS and the Ford exhaust (front-wheel drive and 4WD) using a Miller cycle engine are confused with the Atkinson engines, in fact, in all cases it is a common four-stroke engine with a delayed intake valve.
Currently, even non-hybrid vehicles are equipped with Otto cycle engines that can operate according to the Miller cycle, always confused for the Atkinson cycle, which acts on the opening / closing stages of the intake valves, allowing So the engine is to have a higher efficiency, while working in the Atkinson cycle, both develop maximum power while operating in the Otto cycle. An example of this possibility is given by the Mazda gasoline engines of the Skyactiv series.