Lexus RC F makes its European debut at Geneva; V8 with Otto-Atkinson cycle
2 March 2014
Lexus will stage the European premiere of the new RC F—which made its global debut at the North American International Auto Show in January—at the upcoming Geneva Motor Show. The RC F features an all-new 5.0-liter 32-valve V8 engine that, for the first time in a Lexus performance engine, uses the Atkinson cycle at cruising speeds for enhanced fuel economy and then switches to the Otto cycle at higher rpm to develop impressive performance levels.
The notion of combining the Atkinson cycle at part loads with the Otto cycle at full loads stretches back more than 30 years to a 1982 paper by a team of researchers from Tel-Aviv University and the Israel Institute of Technology.
With its expansion stroke longer than its compression stroke, the Atkinson cycle can achieve a higher thermal efficiency than its Otto counterpart; the downside is reduced power density. The Atkinson cycle has been used in combination with numerous hybrids, with unconventional valve timing to produce the effect of a shorter compression/longer expansion stroke.
In the 1982 paper, Luria et al. discussed the fundamentals of a new concept for an engine operating according to an hybrid thermodynamic cycle between the Otto cycle and the Atkinson cycle. Their objective was to deliver lowered fuel consumption and emissions.
At that time, their preliminary experimental results comparing the performance of the Otto engine with three experimental set-ups of the Otto-Atkinson engine operating at the same load and speed found that fuel consumption of the Otto-Atkinson engine was up to 19% lower, and that the CO and NOx were lower than in the conventional engine.
Over the years, various other research groups, including teams from the University of Sheffield, the University of Calgary, and Ford Motor Company, have worked with different mechanisms for implementing and optimizing the concept.
In a 1995 paper, Boggs et al. from Ford tested a modified 1.6L I-4 engine with retarded, but fixed, valve timings and increased, but fixed, geometric compression ratios to simulate the Otto-Atkinson cycle. The engine demonstrated 15% improvement in BSFC relative to the standard spark-ignition engine with 10% EGR at 1500 rpm, 2.62 Bar BMEP. Tests also revealed 50% reductions in BSNOx and BSCO emissions but a 60% increase in BSHC.
In 2005, Ford filed for a patent on Otto-Atkinson technology; the patent (EP 1754872 B1) was published in 2008.
The Lexus 5.0-liter engine develops well in excess of 450 DIN hp (336 kW) and more than 520 N·m (384 lb-ft) of torque, making it the most powerful V8 performance car yet developed by Lexus. Lexus is targeting fuel consumption lower than that of the IS F (the 2014 IS F, with its own 5-liter engine, is EPA-rated at 18 mpg US (13 l/100 km)).
The cylinder heads and all moving parts are newly designed to provide increased maximum power at higher engine revolutions than previously possible.
The RC F combines a newly calibrated eight-speed Sports Direct Shift (SPDS) transmission with the first installation of a Torque Vectoring Differential (TVD) in a front-engined rear-drive sports coupe, enhancing traction and control to guarantee extraordinary levels of handling and performance.
The TVD has three operating modes:
Standard, for a balance of agile performance and high-speed stability
Slalom, for an emphasis on nimble response to steering inputs
Track, for consistent, stable cornering behavior while circuit driving, with optimum driver control—a newly calibrated VDIM adds a vertical G-sensor to provide even greater vehicle stability
Luria, D., Taitel, Y., and Stotter, A. (1982) “The Otto-Atkinson Engine - A New Concept in Automotive Economy,” SAE Technical Paper 820352 doi: 10.4271/820352
Blakey, S., Saunders, R., Ma, T., and Chopra, A. (1991) “A Design and Experimental Study of an Otto Atkinson Cycle Engine Using Late Intake Valve Closing,” SAE Technical Paper 910451, doi: 10.4271/910451
Boggs, D., Hilbert, H., and Schechter, M. (1995) “The Otto-Atkinson Cycle Engine-Fuel Economy and Emissions Results and Hardware Design,” SAE Technical Paper 950089 doi: 10.4271/950089
M. D. Bassett, S. C. Blakey, and P. W. Foss (1997) “A simple two-state late intake valve closing mechanism,” Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering vol. 211 no. 3 237-241 doi: 10.1243/0954407971526399
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