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Hybrid Power for Mobile Systems
Published in Yatish T. Shah, Hybrid Power, 2021
Any combination of these three primary hybrid advantages may be used in different vehicles to realize different fuel usage, power, emissions, weight and cost profiles. The ICE in a HEV can be smaller, lighter, and more efficient than the one in a conventional vehicle, because the combustion engine can be sized for slightly above average power demand rather than peak power demand. The drive system in a vehicle is required to operate over a range of speed and power, but an ICE's highest efficiency is in a narrow range of operation, making conventional vehicles inefficient. On the contrary, in most HEV designs, the ICE operates closer to its range of highest efficiency more frequently. The power curve of electric motors is better suited to variable speeds and can provide substantially greater torque at low speeds compared with internal-combustion engines. The greater fuel economy of HEVs has implications for reduced petroleum consumption and vehicle air pollution emissions worldwide. Many hybrids use the Atkinson cycle, which gives greater efficiency, but less power for the size of the engine.
The End of Compromise
Published in Patrick Hossay, Automotive Innovation, 2019
As mentioned, more complete control of valve events can allow for a change in the fundamental parameters of the engine’s operation, even redefining the basic four-stroke process. Atkinson cycle engine operation offers a great example. The idea of an Atkinson cycle has long defined a variation from the classic Otto cycle four-stroke engine. Dating back to the mid-1800s, the basic idea is this: since there is more combustion power to be extracted at the end of the power stroke, the Atkinson Cycle allows for a longer power stroke rather than the equal length strokes of the Otto Cycle (Image 2.6). The extra piston travel allows the engine to usefully extract more energy from combustion. The Toyota Prius was notably the first to mimic this cycle in a production car by delaying the close of the intake valve. This allows some of the intake charge to return to the manifold, effectively shortening the intake stroke, and by relation, making the power stroke comparatively longer. The result is a significant improvement in efficiency, but a loss of power. Compressing the incoming air with a super or turbo charger can help compensate for this shorter compression stroke and recover lost power, defining a variant called the Miller Cycle. Multiple car manufacturers now use VVT to produce a variant of this Miller/Atkinson Cycle. So, this isn’t just about fine tuning engine operation; these systems are basically changing the fundamental operation of the four-stroke engine on the fly as conditions warrant. Is it just me, or is that really, really cool?
Internal Combustion Engines
Published in Mehrdad Ehsani, Yimin Gao, Stefano Longo, Kambiz M. Ebrahimi, Modern Electric, Hybrid Electric, and Fuel Cell Vehicles, 2018
Mehrdad Ehsani, Yimin Gao, Stefano Longo, Kambiz M. Ebrahimi
The original Atkinson cycle engine has a structure that allows the intake, compression, expansion (powering), and exhaust stokes to occur in a single revolution of the crankshaft, utilization of cylinder volume in expansion (power), and exhaust strokes that are larger than that in the intake and compression strokes. Figure 3.10 shows the conceptual structure and operation principle of an Atkinson cycle engine.
A theoretical study of the mechanism with variable compression ratio and expansion ratio
Published in Mechanics Based Design of Structures and Machines, 2018
Atkinson cycle means that engine cycles with expansion stroke longer than compression stroke. Define Δa as the effect of Atkinson. According to formula (4.1), Δa can be calculated as below: