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The End of Compromise
Published in Patrick Hossay, Automotive Innovation, 2019
There are nearly as many ways to accomplish VVT as there are manufacturers. Honda was an early adopter of variable valve profiles with its VTEC engine. The engine switched between two cam profiles, allowing smooth operation and efficiency at low rpm, with greater performance possibilities when the engine switched to the more aggressive cam at 4,500 rpm. Honda’s recent engines include a three-stage VTEC with separate cams for low, medium, and high engine speeds. GM’s Intake Valve Lift Control uses an adjustable cam to shift the pivot point of the rocker arms and thus vary valve lift. FIAT’s MultiAir system utilizes an electrohydraulic system, using pressurized engine oil to actuate the intake valves, allowing for control of both lift and timing.
Power Electronics Applications in Vehicle and Passenger Safety
Published in Ali Emadi, Handbook of Automotive Power Electronics and Motor Drives, 2017
D.M.G. Preethichandra, Saman Kumara Halgamuge
The most common and economical technique is the cam-changing and cam-phasing VVT system first used by Toyota and Porsche, which has now become the most popular in the family car range, used by many manufacturers.
Sensitivity of light duty vehicle tailpipe emission rates from simplified portable emission measurement systems to variation in engine volumetric efficiency
Published in Journal of the Air & Waste Management Association, 2021
Tongchuan Wei, H. Christopher Frey
VE is also affected by inter-vehicle variability in engine characteristics, such as VHP, FI, VPC, VVT, VT, CD, and CR (Chen et al. 2011; Heywood 2018; Hong, Parvate-Patil, and Gordon 2004; Pulkrabek 2003; Turner et al. 2004). VE tends to be higher for engines with larger VHP (Pulkrabek 2003). FI includes port fuel injection (PFI) and GDI for the current U.S. LDGV fleet (EPA 2021). GDI engines tend to have higher VE than PFI engines (Chen et al. 2011). An engine with more VPC tends to have higher VE (Heywood 2018). VVT is a process of changing the timing of valve opening and closing. Engines that have VVT have a higher VE than engines that do not (Hong, Parvate-Patil, and Gordon 2004). An engine valvetrain is a mechanical system that controls the operation of cylinder valves. VTs include overhead valves (OHV), single overhead camshafts (SOHC), and dual overhead camshafts (DOHC). VE tends to increase from OHV to SOHC and from SOHC to DOHC (Turner et al. 2004). VE is affected by a derived term based on Cylinder Displacement and Compression Ratio (CDCR). CDCR is the reciprocal of CD minus the reciprocal of the product of CD and CR, or . Larger CDCR indicates an engine with smaller CD and higher CR. VE is larger for smaller CD and for higher CR; thus, VE tends to increase as CDCR increases (Heywood 2018; Pulkrabek 2003). Details about the physics that explain these trends are described in Section SM.1 in the SM.
Operational feasibility of a spark ignition engine which is subjected to VTEC management strategy
Published in Australian Journal of Mechanical Engineering, 2020
Lucky Anetor, Edward E. Osakue
Research and practical engine operations have shown that various variable valve lift and timing (VVT) technologies can improve idle speed stability, low speed stability, emissions, power and fuel economy of the engine. In view of this, a lot of automobile manufacturers have started incorporating this technology into their products. Some of the automobile companies that have commercialised and incorporated the variable valve lift and timing technology in various forms are Toyota (i-VTEC), BMW (Vanos), Ford (VCT), Delphi (VCP), Nissan (CVVT), Hyundai (VVT) and Kia (CVVT). The mechanics of these variable valve lift and timing systems is based on camshaft phase modulation which adjusts the valve timing by changing the relative phase of the cam shaft and crankshaft. It is worth mentioning that this method of implementing the variable valve lift and timing can only adjust the valve timing over a certain/restricted range of angles. However, when compared with the traditional valve-cam systems, it does improve engine emissions and performance significantly.
Experimental analysis of the volumetric and thermal efficiency performance of a novel direct piezo-acting CVVT mechanism
Published in International Journal of Green Energy, 2023
A. Sürmen, M.I Karamangil, A Avcı, B. Dirim, F. Işıklı, M. Tekin, N. Türköz
If the valve timing is designed to provide high volumetric efficiency at partial load, the volumetric efficiency drops dramatically at higher loads due to higher pressure losses. Therefore, changing the valve timing, maximum valve lift, and lift profile with varying engine speeds have been an important research target since the early years of ICEs. Technologies with variations in valve timing are known as continuously variable valve timing (CVVT). All studies listed below are related to CVVT.