Infiniti will introduce a production-ready variable compression ratio engine VC-T (Variable Compression-Turbocharged) at the 2016 Paris Motor Show (Mondial de l’Automobile) in September. Infiniti said that the new four-cylinder turbocharged gasoline VC-T engine has been in development for more than 20 years. (Nissan was awarded a patent in 1995 on compression ratio control for an engine.)
Interest in variable compression engines stretches back more than 40 years. In a 1976 SAE paper, Grundy et al. described the Teledyne Continental Motors (TCM) AVCR 1360-2 variable compression ratio (VCR) diesel engine, the culmination of fifteen years of VCR piston and high specific output research. Two main types of variable compression ratio systems have been proposed over the years: continuous and two-stage.
There have been a number of concepts proposed to enable such VCR systems. Broadly, they can be characterized into three groups: unconventional cranktrains; systems that vary the distance between the crankshaft and the cylinder head; and variable kinematic lengths. (Earlier post.)
Infiniti’s VC-T engine technology seamlessly raises or lowers the height the pistons reach. As a consequence, the displacement of the engine changes and the compression ratio can vary anywhere between 8:1 (for high performance) and 14:1 (for high efficiency). The engine control logic automatically applies the optimum ratio, depending on what the driving situation demands.
A series of earlier SAE papers published by Nissan engineers laid out the core approach of a new piston-crank system incorporating a multiple-link mechanism to vary the piston’s motion at top dead center and thereby obtain the optimum compression ratio matching the operating conditions.
Other attempts to to achieve variable compression ratio with this type of method ran into difficulties from issues such as an increase in the engine size, weight increases, increased engine block vibration due to a worsening of piston acceleration characteristics and increased friction resulting from a larger number of sliding parts.
Nissan, in a 2003 paper, said that its multi-link geometry resolved those previous issues.
This multiple-link variable compression ratio (VCR) mechanism can be installed without increasing the engine size or weight substantially by selecting a suitable type of link mechanism and optimizing the detailed specifications.
The piston stroke achieved with this multiple-link mechanism resembles simple harmonic motion, unlike that of conventional engines. This motion is characterized by slower piston speed near top dead center and faster piston speed near bottom dead center.
In a 2006 paper, the engineering team applied the multiple-link VCR mechanism to a turbocharged engine to investigate its effect on engine performance. In that study, they found that fuel economy and power output can both be improved by increasing the compression ratio and applying exhaust gas recirculation (EGR) under low loads and by lowering the compression ratio and applying higher boost pressure under high loads.
(In 2008, a team from Renault and Nissan published a study on the application of the use of this VCR technology for HCCI combustion in a diesel engine.)
VC-T technology is a step change for Infiniti. It is a revolutionary next-step in optimizing the efficiency of the internal combustion engine. This technological breakthrough delivers the power of a high-performance 2.0-liter turbo gasoline engine with a high level of efficiency at the same time.—Roland Krueger, president of Infiniti Motor Company
VC-T technology delivers multiple customer benefits including significantly reduced fuel consumption and emissions, greatly reduced noise and vibration levels; it is also lighter and more compact than comparable conventional engines.
Infiniti will present more information on the VC-T engine at Mondial de l’Automobile on September 29 during its press conference.
Gérard, D., Besson, M., Hardy, J., Croguennec, S. et al. (2008) “HCCI Combustion on a Diesel VCR Engine,” SAE Technical Paper 2008-01-1187 doi: 10.4271/2008-01-1187
Tanaka, Y., Hiyoshi, R., Takemura, S., Ikeda, Y. et al. (2007) “A Study of a Compression Ratio Control Mechanism for a Multiple-Link Variable Compression Ratio Engine,” SAE Technical Paper 2007-01-3547 doi: 10.4271/2007-01-3547
Hiyoshi, R., Aoyama, S., Takemura, S., Ushijima, K. et al. (2006) “A Study of a Multiple-link Variable Compression Ratio System for Improving Engine Performance,” SAE Technical Paper 2006-01-0616 doi: 10.4271/2006-01-0616
Takahashi, N., Aoyama, S., Moteki, K., and Hiyoshi, R. (2005) “A Study Concerning the Noise and Vibration Characteristics of an Engine with Multiple-Link Variable Compression Ratio Mechanism,” SAE Technical Paper 2005-01-1134 doi: 10.4271/2005-01-1134
Moteki, K., Aoyama, S., Ushijima, K., Hiyoshi, R. et al. (2003) “A Study of a Variable Compression Ratio System with a Multi-Link Mechanism,” SAE Technical Paper 2003-01-0921 doi: 10.4271/2003-01-0921
Compression ratio control for internal combustion engine US 5450824 A
Grundy, J., Kiley, L., and Brevick, E. (1976) “AVCR 1360-2 High Specific Output-Variable Compression Ratio Diesel Engine,” SAE Technical Paper 760051 doi: 10.4271/760051