Lexus RC F makes its European debut at Geneva; V8 with Otto-Atkinson cycle
02 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
Resources
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
Otto engine with variable valve actuation and Atkinson cycle operation EP 1754872 B1
Another fuel guzzling machine?
Posted by: HarveyD | 02 March 2014 at 06:54 AM
The problem is that to secure the resources required pay for the fuel this car comes with the optional 2.5 ton of armour plating and bullet proof glass.
This in turn requires a bigger engine further increasing the weight and fuel consumtion.
The best way to solve the escalating diabolical conundrum - predicted to end up using the entire world oil output, is to build a more efficient smoker.
It's obvious to some that a subcritical modular mox reactor would solve many technical issuues associated with this appliation.
I am curentlyn designing a nox (escape velocity) booster for the above mentioned application that already has substantial interest and not a few pre-orders being negotiated as we speak.
Interest has been expressed by govt agencies including overseers of various Overseas aid programs, quasi religious groups, private investigaters and middle school hockey teams.
Ongoing funding for the next four years has been sourced from various Sth American sponsers on a 'first available supply' basis.
Posted by: Arnold | 02 March 2014 at 05:55 PM
Surprisingly, there is not mentioned in the article regarding the compression ratios (CR) of the engine in Atkinson mode and of Otto mode. The ability to vary compression ratio is critical in an engine that is capable of both cycles. This is not easy to do, or else, it would have been done a long time ago. With fixed geometric compression ratio, an optimum CR of 13:1 to 15:1 at the Atkinson mode would be too high for the Otto mode. Here it is mentioned that the Otto mode is available at high rpm only, meaning that Toyota relies mainly on high rpm to stave off the potential for engine knocks associated with high CR. Engine torque, then, will be weak at lower rpm when only Atkinson mode is allowed, hence needing the 8-speed transmission. Furthermore, the engine must be built stronger, hence heavier, to deal with the higher compression pressures and the higher temperatures generated with high CR hence faster combustion in the Otto mode.
For utilizing the Otto mode at lower rpm hence boosting low-end torque, alcohol injection is another way of dealing with the higher effective CR in the Otto mode, and this was Ford's approach. Since the engine only rarely operates at high power level, a brief ethanol injection, using another fuel line for admitting the ethanol into the same injector can be done. The ethanol tank need not be large, since it is only rarely needed. When the ethanol runs out, then the engine computer will prohibit operation in the Otto mode.
An added advantage of having an ethanol container in your car is that when going to a party and forget to bring the booze...well, you know where you can get the alcohol! This should give ya additional incentive to keep the ethanol container filled-up!
Posted by: Roger Pham | 02 March 2014 at 10:18 PM
I was wondering the same thing as Roger concerning compression ratios. There must be some trickery that the engine can run normal Otto cycle for the high power figures.
Direct injection may help, EGR also. There was a article about dedicated EGR on petrol engine. The concept was that one valve is dedicated to EGR and that valve is run rich, to produce hydrogen that helps avoid knock problems. Probably no dedicated EGR on this engine, but running a little rich and using cooled EGR, may have some effect. Mazda did manage to get 14:1 CR (EU spec), and if I'm not mistaken it also uses Atkinson cycle during low load. So basicly the same recipe.
Posted by: GasperG | 03 March 2014 at 04:16 AM
Thanks, GasperG, for the information.
Another thought on this: another factor that plays in reducing knock potential at Otto mode at high rpm is that volumetric efficiency is less at high rpm than at lower rpm, meaning that the cylinder may be filled around 80%-85% instead of at near 100% at low rpm due to lack of time for air to move thru the intake valves. That's one of the reason that torque drops at higher rpm and lower risk of engine knock at high rpm.
Also, Toyota has new way to cool the exhaust valve and the area around the exhaust valve to reduce the risk of knock at high CR. See:
http://www.greencarcongress.com/2012/05/tmc-20120504.html
Posted by: Roger Pham | 03 March 2014 at 01:22 PM