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The Honda variable valve timing and lift electronic control system VTEC is incorporated in the engine of the NSX sports car that is scheduled for sales in Europe this year. In the process of advancement of Honda's engine technology, VTEC was developed for much higher output and higher efficiency. This is actually the first system in the world that can simultaneously switch the timing and lift of the intake and exhaust valves.
Show all documents Gear Drive Mechanism for Continuous Variable Valve Timing of IC Engines In internal combustion engines, variable valve timing VVT , also known as variable valve actuation VVA , is a generalized term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine . In a standard engine, the valve events are fixed, so per- formance at different loads and speeds is always a com- promise between drivability power and torque , fuel economy and emissions.
Variable valve lift
Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. A variety of two-stage, or discrete, variable valve lift DVVL and continuously variable valve lift CVVL systems have recently been incorporated in production vehicles.
Several systems that have been introduced with the objective of reducing fuel consumption are described in this Appendix. CPS provides a means of switching the actuation of the intake valves between a standard high lift cam for maximum power operation and a low lift cam for efficient light load operation. The low lift cam for light load operation reduces fuel consumption by transferring air flow control from the throttle to the intake valves which results in reduced pumping losses. The incorporation of the CPS concept in numerous production applications is described in the following sections.
The VTEC system consists of a camshaft with a center high lift cam and outer low lift cams and associated rocker arms, as shown in Figure I. For light load operation, the valves are operated by the two outer, low lift cams and associated outer rocker arms. For higher power operation, hydraulic pressure is used to insert a pin to lock the middle rocker arm to the outer rocker arms for operation on the high lift cam. Cam phasing is accomplished with a hydraulic cam phaser.
Two different low lift cam lobes 5. The two sets of the low and high lift cams for each of the two intake valves of a cylinder are mounted on a single carrier piece so that the active cams depend on the longitudinal position of the carrier piece on the camshaft. Each cam carrier piece has two spiral grooves. A pin engages one of the spiral grooves to move the carrier axially from the low lift cam to the high lift cam position.
Another reverse spiral groove and pin are used to return the carrier to the low lift cam position. The pins are electrically actuated. The Audi AVS system was first introduced in the 1. Audi has indicated that the AVS system provides up to a 7 percent reduction in fuel consumption. In the Mercedes system, each cam carrier piece serves two adjacent cylinders, instead of only one cylinder as in the Audi AVS system. Mercedes introduced the Camtronic system on the new M series four-cylinder engine in The Chevrolet intake valve lift control IVLC system also uses the cam profile switching concept with low and high lift cams.
The system uses rocker arms consisting of two roller followers that are electro-hydraulically latched to the rocker arm for operation on either the low or high lift cams. Chevrolet introduced the IVLC system on their 2. Several different principles have been applied to develop continuously variable valve lift systems CVVL that range from mechanical systems to hydraulic systems.
Several systems that have been introduced in production with the objective of reducing fuel consumption are described here. The BMW Valvetronic system was the first continuously variable valve lift mechanism, which went into production in the BMW ti in The goal of Valvetronic was to reduce fuel consumption.
Since air flow, and thus engine output, is controlled by valve lift with the Valvetronic system, the conventional throttle valve is disabled which reduces pumping losses.
Overall, BMW claims that Valvetronic can provide a 10 percent reduction in fuel consumption Autozine Valvetronic adds an intermediate rocker arm between the camshaft and the roller finger follower that actuates the valve.
The pivot location of the intermediate rocker arm is varied with an eccentric shaft controlled by an electric motor through a worm gear set. Rotating the eccentric shaft to extend the pivot location of the intermediate rocker arm results in an increase in valve lift. Although Valvetronic reduces fuel consumption at part load, maximum power is not increased since the additional components result in additional friction and inertia.
The Valvetronic system adds significant height above the cylinder head so that packaging the engine is more difficult. The Toyota Valvematic system, shown in Figure I. Patent Application Publication The intermediate rocker shaft contains roller followers offset from the center of the intermediate rocker shaft and additional followers.
The angle between the roller follower and additional follower is controlled by an electric motor. Increasing this angle increases the resultant valve lift. Toyota implemented the Valvematic system on their 1. The Valvematic system was reported to improve fuel economy by 5 percent and increase power by 6 percent in the MY Corolla Borge The hydraulic chamber includes a solenoid valve. When the solenoid valve is closed, the oil in the line acts as a solid body and transmits the intake cam motion directly to the intake valve.
By opening the solenoid valve, the hydraulic pressure is relieved and the intake valve closes under the action of the valve spring. A dedicated hydraulic brake is used to provide a soft landing of the intake valve for all engine operating conditions.
A wide range of intake valve actuation modes can be obtained by controlling the solenoid valve, as illustrated in Figure I. Fiat Chrysler indicated that Multiair can provide a 10 percent reduction in fuel consumption with the elimination of pumping losses. Additionally, Multiair can provide up to a 10 percent increase in power when a power-oriented mechanical cam profile is used.
Low speed torque can be improved by up to 15 percent Murphy Multiair was first introduced in the MY 1. The next application was in the MY 2. Borge, J. Toyota engineers put a shine into the Corolla. Boutell, B. Variable valve Operation Control Method and Apparatus. Patent Application Publication No. Autozine Technical School. Accessed June 23, Accessed September 6, The VTEC breakthrough: solving a century-old dilemma.
Kelly Blue Book. Kelly Blue Book, September Accessed August 6, Murphy, T. WardAuto, March October 9. The light-duty vehicle fleet is expected to undergo substantial technological changes over the next several decades. New powertrain designs, alternative fuels, advanced materials and significant changes to the vehicle body are being driven by increasingly stringent fuel economy and greenhouse gas emission standards.
By the end of the next decade, cars and light-duty trucks will be more fuel efficient, weigh less, emit less air pollutants, have more safety features, and will be more expensive to purchase relative to current vehicles.
Though the gasoline-powered spark ignition engine will continue to be the dominant powertrain configuration even through , such vehicles will be equipped with advanced technologies, materials, electronics and controls, and aerodynamics.
And by , the deployment of alternative methods to propel and fuel vehicles and alternative modes of transportation, including autonomous vehicles, will be well underway. What are these new technologies - how will they work, and will some technologies be more effective than others? Cost, Effectiveness, and Deployment of Fuel Economy Technologies for Light-Duty Vehicles estimates the cost, potential efficiency improvements, and barriers to commercial deployment of technologies that might be employed from to This report describes these promising technologies and makes recommendations for their inclusion on the list of technologies applicable for the CAFE standards.
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Sign up for email notifications and we'll let you know about new publications in your areas of interest when they're released. Get This Book. Visit NAP. Looking for other ways to read this? No thanks. Page Share Cite. For maximum power at high speed, the solenoid valve is always closed so that full valve opening is obtained by following the intake cam.
For low speed torque, the solenoid valve is opened near the end of the cam profile to provide early intake valve closing to eliminate backflow into the intake manifold to maximize the air mass trapped in the cylinders.
At part load conditions, the solenoid valve can be opened earlier resulting in shortened valve open times to control trapped air mass as a function of the required torque without throttling partial valve opening. At idle, the solenoid valve can be closed after the mechanical cam has started and then opened early, resulting in partial valve opening so that air flows faster past the intake valve to enhance in-cylinder turbulence late valve opening. The last two actuation modes can be combined to open the intake valve twice during each intake stroke to enhance turbulence and combustion rates at light loads.
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Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. A variety of two-stage, or discrete, variable valve lift DVVL and continuously variable valve lift CVVL systems have recently been incorporated in production vehicles. Several systems that have been introduced with the objective of reducing fuel consumption are described in this Appendix. CPS provides a means of switching the actuation of the intake valves between a standard high lift cam for maximum power operation and a low lift cam for efficient light load operation. The low lift cam for light load operation reduces fuel consumption by transferring air flow control from the throttle to the intake valves which results in reduced pumping losses. The incorporation of the CPS concept in numerous production applications is described in the following sections.
engine called the variable valve timing and lift electronic control (VTEC) system [10,19,54]. VTEC uses two (or occasionally three) intake.
Variable valve timing
Variable valve lift VVL is an automotive piston engine technology which varies the height a valve opens in order to improve performance, fuel economy or emissions. There are two main types of VVL: discrete, which employs fixed valve lift amounts, and continuous, which is able to vary the amount of lift. Continuous valve lift systems typically allow for the elimination of the throttle valve. When used in conjunction with variable valve timing VVT , variable valve lift can potentially offer infinite control over the intake and exhaust valve timing. In Porsche made application for a German patent, also applied for and published as British Patent GB in
In internal combustion engines , variable valve timing VVT is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with variable valve lift systems. There are many ways in which this can be achieved, ranging from mechanical devices to electro-hydraulic and camless systems. Increasingly strict emissions regulations are causing [ citation needed ] many automotive manufacturers to use VVT systems.
VTEC variable valve timing and electronic control lift system developed by honda. It was invented by honda engineer ikuo kajitani. It improves the volumetric efficiency of 4 stroke diesel engine. It improves the volumetric efficiency of the engine by providing excess amount of air fuel in to engine at high speed.
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After multi-valve technology became standard in engine design, Variable Valve Timing becomes the next step to enhance engine output, no matter power or torque. As you know, valves activate the breathing of engine. The timing of breathing, that is, the timing of air intake and exhaust, is controlled by the shape and phase angle of cams. To optimise the breathing, engine requires different valve timing at different speed. When the rev increases, the duration of intake and exhaust stroke decreases so that fresh air becomes not fast enough to enter the combustion chamber, while the exhaust becomes not fast enough to leave the combustion chamber.
Engine development today necessitates both better fuel economy and advanced vehicle performance. Modern engines must also meet the social requirements of natural resource conservation and environment preservation. In , Toyota introduced the WT mechanism on its 4A-GE sports engines in order to increase engine torque and output. WT enables the intake valve to open and close in two steps, based on engine operating conditions. VVT-i is an improved version of the WT mechanism.
Вскоре слава о фугуся-кисай, гениальном калеке, облетела Токио. Со временем Танкадо прочитал о Пёрл-Харборе и военных преступлениях японцев. Ненависть к Америке постепенно стихала. Он стал истовым буддистом и забыл детские клятвы о мести; умение прощать было единственным путем, ведущим к просветлению. К двадцати годам Энсей Танкадо стал своего рода культовой фигурой, представителем программистского андеграунда.
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Потом, всего через несколько секунд, он должен был включить основные генераторы, и сразу же восстановились бы все функции дверных электронных замков, заработали фреоновые охладители и ТРАНСТЕКСТ оказался бы в полной безопасности.