In
internal combustion engineThe internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
s,
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 liftA valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
event within an internal combustion engine. VVT allows the
lift,
duration or
timing (in various combinations) of the
intakeAn intake , or especially for aircraft inlet, is an air intake for an engine. Because the modern internal combustion engine is in essence a powerful air pump, like the exhaust system on an engine, the intake must be carefully engineered and tuned to provide the greatest efficiency and power...
and/or
exhaustAn exhaust system is usually tubing used to guide reaction exhaust gases away from a controlled combustion inside an engine or stove. The entire system conveys burnt gases from the engine and includes one or more exhaust pipes...
valvesA poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide...
to be changed while the engine is in operation. Two-stroke engines use a power valve system to get similar results to VVT. There are many ways in which this can be achieved, ranging from mechanical devices to electro-hydraulic and
camlessMost four-stroke piston engines today employ one or more camshafts to operate poppet valves. The lobes on the camshafts operate cam followers which in turn open the poppet valves. A camless uses electromagnetic, hydraulic, or pneumatic actuators to open the poppet valves instead...
systems.
The valves within an internal combustion engine are used to control the flow of the intake and exhaust gases into and out of the
combustion chamberA combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...
. The timing, duration and lift of these valve events has a significant impact on
engineAn engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...
performance. In a standard engine, the valve events are fixed, so performance at different loads and speeds is always a compromise between driveability (power and torque),
fuel economyFuel efficiency is a form of thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is...
and emissions. An engine equipped with a variable valve actuation system is freed from this constraint, allowing performance to be improved over the engine operating range.
Strictly speaking, the history of the search for a method of variable valve opening duration goes back to the age of
steam engineA steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...
s when the valve opening duration was referred to as “steam cut-off”. Almost all steam engines had some form of variable cut-off. That they are not in wide use is a reflection that they are all lacking in some aspect of variable valve actuation.
The desirability of being able to vary the valve opening duration to match an engine’s
rotational speedRotational speed tells how many complete rotations there are per time unit. It is therefore a cyclic frequency, measured in hertz in the SI System...
first became apparent in the 1920s when maximum allowable RPM limits were generally starting to rise. Up until about this time an engine’s idle RPM and its operating RPM were very similar, meaning that there was little need for variable valve duration.
It was in the 1920s that the first
patentA patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....
s for variable duration valve opening started appearing – for example United States patent . A surprising fact is that from these first patents up until the appearance of the helical camshaft there has never been a really practical and useful variable duration camshaft.
Overview
Piston engines normally use
poppet valveA poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide...
s for intake and exhaust. These are driven (directly or indirectly) by
camA cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice-versa. It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path...
s on a
camshaftA camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...
. The cams open the valves (
lift) for a certain amount of time (
duration) during each intake and exhaust cycle. The
timing of the valve opening and closing is also important. The camshaft is driven by the crankshaft through
timing beltA timing belt, or cam belt , is a part of an internal combustion engine that controls the timing of the engine's valves. Some engines, such as the flat-4 Volkswagen air-cooled engine, and the straight-6 Toyota F engine use timing gears...
s,
gearA gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
s or
chainRoller chain or bush roller chain is the type of chain drive most commonly used for transmission of mechanical power on many kinds of domestic, industrial and agricultural machinery, including conveyors, wire and tube drawing machines, printing presses, cars, motorcycles, and simple machines like...
s.
The profile, or position and shape of the cam lobes on the shaft, is optimized for a certain engine
revolutions per minuteRevolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...
(RPM), and this tradeoff normally limits low-end
torqueTorque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
, or high-end
powerHorsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...
. VVT allows the cam timing to change, which results in greater efficiency and power, over a wider range of engine RPMs.
An engine requires large amounts of air when operating at high speeds. However, the intake valves may close before enough air has entered each combustion chamber, reducing performance. On the other hand, if the camshaft keeps the valves open for longer periods of time, as with a racing cam, problems start to occur at the lower engine speeds. This will cause unburnt fuel to exit the engine since the valves are still open. This leads to lower engine performance and increased emissions. For this reason, pure racing engines which are designed to idle at speeds close to 2,000 rpm, cannot idle well at the lower speeds (around 800 rpm) expected of a road car.
Pressure to meet environmental goals and fuel efficiency standards is forcing car manufacturers to use VVT as a solution. Most simple VVT systems advance or retard the timing of the intake or exhaust valves. Others (like
Hondais a Japanese public multinational corporation primarily known as a manufacturer of automobiles and motorcycles.Honda has been the world's largest motorcycle manufacturer since 1959, as well as the world's largest manufacturer of internal combustion engines measured by volume, producing more than...
's
VTECVTEC is a valvetrain system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine. The VTEC system uses two camshaft profiles and electronically selects between the profiles. It was invented by Honda R&D engineer Ikuo Kajitani, and was the first system...
) switch between two sets of cam lobes at a certain engine RPM. Furthermore Honda's i-VTEC can alter intake valve timing continuously.
Steam engines
The first variable valve timing systems came into existence in the nineteenth century on steam engines.
Stephenson valve gearThe Stephenson valve gear or Stephenson link or shifting link is a simple design of valve gear that was widely used throughout the world for all kinds of steam engine. It is named after Robert Stephenson but was actually invented by his employees....
, as used on early steam locomotives, supported variable
cutoffIn a steam engine, cutoff is the point in the piston stroke at which the inlet valve is closed. On a steam locomotive, the cutoff is controlled by the reverser....
, that is, changes to the time at which the admission of steam to the cylinders is cut off during the power stroke. Early approaches to variable cutoff coupled variations in admission cutoff with variations in exhaust cutoff. Admission and exhaust cutoff were decoupled with the development of the Corliss valve. These were widely used in constant speed variable load stationary engines, with admission cutoff, and therefore torque, mechanically controlled by a
centrifugal governorA centrifugal governor is a specific type of governor that controls the speed of an engine by regulating the amount of fuel admitted, so as to maintain a near constant speed whatever the load or fuel supply conditions...
and
trip valveTrip valve mechanisms are a class of steam engine valve gear developed to improve efficiency. The trip mechanism allows the inlet valve to be closed rapidly, giving a short, sharp cut-off. The valve itself can be a drop valve or a Corliss valve....
s. As
poppet valveA poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide...
s came into use, simplified valve gear using a
camshaftA camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...
came into use. With such engines, variable cutoff could be achieved with variable profile cams that were shifted along the camshaft by the governor. This is now coming in system.
Aircraft
Some versions of the
Bristol JupiterThe Bristol Jupiter was a British nine-cylinder single-row piston radial engine built by the Bristol Aeroplane Company. Originally designed late in World War I and known as the Cosmos Jupiter, a lengthy series of upgrades and developments turned it into one of the finest engines of its era.The...
radial engineThe radial engine is a reciprocating type internal combustion engine configuration in which the cylinders point outward from a central crankshaft like the spokes on a wheel...
of the early 1920s incorporated variable valve timing gear, mainly to vary the inlet valve timing in connection with higher compression ratios. The
Lycoming R-7755 engine had a Variable Valve Timing system consisting of two cams that can be selected by the pilot. One for take off, pursuit and escape, the other for economical cruising.
Automotive use
In 1958
PorschePorsche Automobil Holding SE, usually shortened to Porsche SE a Societas Europaea or European Public Company, is a German based holding company with investments in the automotive industry....
made application for a German Patent, also applied for and published as British Patent GB861369 in 1959. The Porsche patent used an oscillating cam driven via a push/pull rod from an eccentric shaft or swash plate. The cam was Desmodromic having opening and closing cam surfaces which operated the valve by a bifurcated rocker and ball joint. Being Desmodromic meant there was no valve spring. The cam pivot was adjustable for height, as the push/pull rod length was constant this rotated the cam so the lift and duration increased. A compensating link moved the rocker pivot to match the cam's position. The adjustment of the cam pivot could be by mechanical linkage to a screw thread, hydraulic from engine driven pump with spill valve or from a engine speed governor. At present it is unknown if any working prototype was ever made.
FiatFIAT, an acronym for Fabbrica Italiana Automobili Torino , is an Italian automobile manufacturer, engine manufacturer, financial, and industrial group based in Turin in the Italian region of Piedmont. Fiat was founded in 1899 by a group of investors including Giovanni Agnelli...
was the first auto manufacturer to patent a functional automotive variable valve timing system which included variable lift. Developed by Giovanni Torazza in the late 1960s, the system used hydraulic pressure to vary the fulcrum of the cam followers (US Patent 3,641,988). The hydraulic pressure changed according to engine speed and intake pressure. The typical opening variation was 37%.
In September 1975,
General MotorsGeneral Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...
(GM) patented a system intended to vary valve lift. GM was interested in throttling the intake valves in order to reduce emissions. This was done by minimizing the amount of lift at low load to keep the intake velocity higher, thereby atomizing the intake charge. GM encountered problems running at very low lift, and abandoned the project.
Alfa RomeoAlfa Romeo Automobiles S.p.A. is an Italian manufacturer of cars. Founded as A.L.F.A. on June 24, 1910, in Milan, the company has been involved in car racing since 1911, and has a reputation for building expensive sports cars...
was the first manufacturer to use a variable valve timing system in production cars (US Patent 4,231,330). The 1980
Alfa Romeo SpiderThe Alfa Romeo Spider is a roadster produced by the Italian manufacturer Alfa Romeo from 1966 to 1993 . Widely regarded as a design classic, it remained in production for almost three decades with only minor aesthetic and mechanical changes...
2.0 L had a mechanical VVT system in
SPICASPICA S.p.A. was an Italian manufacturer of fuel injection systems.- History :The company was founded by Francesco Cassani in 1932. SPICA fuel injection systems were used in diesel and petrol engines....
fuel injected cars sold in the United States. Later this was also used in the 1983
AlfettaAlfa Romeo GTV redirects here. For 916 series GTV see Alfa Romeo GTV & SpiderThe Alfa Romeo Alfetta is an Italian rear-wheel drive executive saloon car and fastback coupé produced from 1972 until 1987 by Alfa Romeo...
2.0 Quadrifoglio Oro models as well as other cars. The system was engineered by Ing Giampaolo Garcea in the 1970s.
Honda's REV motorcycle engine employed on the Japanese market-only Honda CBR400F in 1983 provided a technology base for
VTECVTEC is a valvetrain system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine. The VTEC system uses two camshaft profiles and electronically selects between the profiles. It was invented by Honda R&D engineer Ikuo Kajitani, and was the first system...
.
In 1986, Nissan developed their own form of VVT with the
VG30DE(TT)The VG engine family consists of V6 piston engines designed and produced by Nissan for several vehicles in the Nissan lineup. The VG series started in 1983 becoming Japan's first mass produced V6 engine. VG engines displace between 2.0 L and 3.3 L and feature an iron block and aluminum...
engine for their
MID4-History:First Unveiled at the 1985 Frankfurt Autoshow, the MID4 was a concept car designed by Nissan to originally go on sale in the mid-late 1980s. Nissan had aimed the MID4 to compete with European supercars from Porsche and Ferrari. The MID4 boasted a wide array of technology and features that...
Concept. Nissan chose to focus their NVCS (Nissan Valve-Timing Control System) mainly on torque production at low to medium engine speeds, because, the vast majority of the time, automobile engines will not be operated at extremely high speeds. The NVCS system can produce a smooth idle and high amounts of torque at low to medium engine speeds. The VG30DE engine was first used in the 300ZX (Z31) 300ZR model in 1987. It was the first production car to use electronically controlled VVT technology. In 1987 Nissan also sold the
GloriaThe Gloria is a large luxury car made from 1959 by the Prince Motor Company, and later by Nissan Motors since its merger with the former - hence being originally marketed as Prince Gloria and later as Nissan Gloria...
,
LeopardThe Nissan Leopard is a line of luxury sports cars built by Japanese carmaker Nissan. The Leopard began life in 1980 and was discontinued in 1999. Leopards were initially based on the Japanese market Nissan Skyline and Nissan Laurel and the American Datsun 910/Nissan Maxima, then later based on the...
, and
CedricThe Nissan Cedric is a large automobile produced by Nissan since 1960. It was developed to provide upscale transportation, competing with the Prince Skyline and Gloria which were later merged into the Nissan family...
, all of which could come powered by the VG20DET engine which also utilized Nissans NVCS valve timing system.
The next step was taken in 1989 by
Hondais a Japanese public multinational corporation primarily known as a manufacturer of automobiles and motorcycles.Honda has been the world's largest motorcycle manufacturer since 1959, as well as the world's largest manufacturer of internal combustion engines measured by volume, producing more than...
with the
VTECVTEC is a valvetrain system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine. The VTEC system uses two camshaft profiles and electronically selects between the profiles. It was invented by Honda R&D engineer Ikuo Kajitani, and was the first system...
system. Honda had started production of a system that gives an engine the ability to operate on two completely different cam profiles, eliminating a major compromise in engine design. One profile designed to operate the valves at low engine speeds provides good road manners, low fuel consumption and low emissions output. The second is a high lift, long duration profile and comes into operation at high engine speeds to provide an increase in power output. The VTEC system was also further developed to provide other functions in engines designed primarily for low fuel consumption. The first VTEC engine Honda produced was the B16A which was installed in the
IntegraThe Honda Integra is a compact luxury performance coupe made by Honda during the years 1985 to 2006. The sporty front wheel drive car is able to house five passengers with a two door hatch or four door sedan available.The Integra was on Car and Driver magazine's annual Ten Best list six times, in...
, CRX, and
CivicThe Honda Civic is a line of subcompact and subsequently compact cars made and manufactured by Honda. The Civic, along with the Accord and Prelude, comprised Honda's vehicles sold in North America until the 1990s, when the model lineup was expanded...
hatchback available in Japan and Europe. In 1991 the
Acura NSXThe Honda NSX, or Acura NSX, is a sports car that was produced between 1990 and 2005 by the Japanese automaker Honda. It is equipped with a mid-engine, rear-wheel drive layout, powered by an all-aluminium V6 gasoline engine featuring Honda's Variable Valve Timing and Lift Electronic Control ...
powered by the C30A became the first VTEC equipped vehicle available in the US. VTEC can be considered the first "cam switching" system and is also one of only a few currently in production.
In 1991,
Clemson UniversityClemson University is an American public, coeducational, land-grant, sea-grant, research university located in Clemson, South Carolina, United States....
researchers patented the Clemson Camshaft which was designed to provide continuously variable valve timing independently for both the intake and exhaust valves on a single camshaft assembly. This ability makes it suitable for both pushrod and overhead cam engine applications.
In 1992, Porsche introduced
VarioCamVarioCam is an automobile variable valve timing technology developed by Porsche. VarioCam varies the timing of the intake valves by adjusting the tension on the timing chain connecting the intake and exhaust camshafts...
its 968 model which provided continuously variable valve timing for the intake valves.
In 1992,
BMWBayerische Motoren Werke AG is a German automobile, motorcycle and engine manufacturing company founded in 1916. It also owns and produces the Mini marque, and is the parent company of Rolls-Royce Motor Cars. BMW produces motorcycles under BMW Motorrad and Husqvarna brands...
introduced the
VANOSVANOS is an automobile variable valve timing technology developed by BMW in close collaboration with Continental Teves. VANOS varies the timing of the valves by moving the position of the camshafts in relation to the drive gear...
system. Like the Nissan NVCS system it could provide timing variation for the intake cam in steps (or phases), the VANOS system differed in that it could provide one additional step for a total of three. Then in 1996 the Double Vanos system was introduced which significantly enhances emission management, increases output and torque, and offers better idling quality and fuel economy. Double Vanos was the first system which could provide electronically controlled, continuous timing variation for both the intake and exhaust valves.
Ford began using
Variable Cam TimingVariable Camshaft Timing is an automobile variable valve timing technology developed by Ford. It uses electronically controlled hydraulic valves that direct high pressure engine oil into the camshaft phaser cavity. These oil control solenoids are bolted into the cylinder heads towards the front of...
in 1998 for the
Ford Sigma engineThe Ford Sigma is a small straight-4 automobile engine sold by Ford Motor Company. First evolution of engines were sold as the "Zetec-SE" . After the upgrade Ford renamed Sigma to Duratec. Last upgrade of engine is named Duratec Ti-VCT...
and the
Ford Zetec engineFord Motor Company used the Zetec name on a variety of Inline-4-cylinder automobile engines. It was coined to replace "Zeta" on a range of 1.6 L to 2.0 L multi-valve engines introduced in 1991...
.
In 1999, Porsche introduced
VarioCamVarioCam is an automobile variable valve timing technology developed by Porsche. VarioCam varies the timing of the intake valves by adjusting the tension on the timing chain connecting the intake and exhaust camshafts...
Plus on its 911 Turbo which combined continuous valve timing and two stage valve lift on the intake valves.
In 2001, BMW introduced the
ValvetronicThe Valvetronic system is a variable valve timing system to offer continuous and precisely variable intake valve lift, from ~0 to 10 mm, and duration. It typically works in conjunction with the independent Double VANOS system that continuously varies the timing...
system. The Valvetronic system can continuously and precisely vary intake valve lift, and in addition, the independent Double VANOS system can concurrently vary the timing for both the intake and exhaust valves. The precise control the system has over the intake valves allows for the intake charge to be controlled entirely by the intake valves, eliminating the need for a
throttleA throttle is the mechanism by which the flow of a fluid is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases , but usually decreased. The term throttle has come to refer, informally and incorrectly, to any mechanism by which...
valve and greatly reducing
pumping lossParasitic loss is that which a parasite consumes from its host, for whom the loss may or may not be beneficial.- Parasitic loss in internal combustion engines :...
. The reduction of pumping loss accounts for a 10-15% increase in power output and fuel economy.
Ford became the first manufacturer to use variable valve timing in a pickup-truck, with the top-selling
Ford F-seriesThe F-Series is a series of full-size pickup trucks from Ford Motor Company which has been sold continuously for over six decades. The most popular variant of the F-Series is the F-150...
in the 2004 model year. The engine used was the 5.4 L 3-valve Triton.
In 2005, General Motors offered the first Variable Valve timing system for pushrod V6 engines,
LZE and
LZ4.
In 2007,
DaimlerChryslerDaimler AG is a German car corporation. By unit sales, it is the thirteenth-largest car manufacturer and second-largest truck manufacturer in the world. In addition to automobiles, Daimler manufactures buses and provides financial services through its Daimler Financial Services arm...
became the first manufacturer to produce a cam-in-block engine with independent control of exhaust cam timing relative to the intake. The 2008
Dodge ViperThe first prototype was tested in January 1989. It debuted in 1991 with two pre-production models as the pace car for the Indianapolis 500 when Dodge was forced to substitute it in place of the Japanese-built Stealth because of complaints from the United Auto Workers, and went on sale in January...
uses Mechadyne's concentric camshaft assembly to help boost power output to 600 bhp.
In 2009, Fiat Powertrain Technologies introduced the
MultiairMultiair is an electro-hydraulic variable valve actuation technology controlling air intake in petrol or diesel engines . It is compatible with both naturally aspirated and forced-induction engines....
system in Geneva Motor Show. The Multiair is a hydraulically actuated variable valve timing system, which gives full control over valve lift and timing. The new technology is available in Alfa Romeo MiTo starting from September 2009.
In 2009, Porsche introduced an enhanced version of
VarioCamVarioCam is an automobile variable valve timing technology developed by Porsche. VarioCam varies the timing of the intake valves by adjusting the tension on the timing chain connecting the intake and exhaust camshafts...
Plus on its 911 GT3 including the previous variable valve timing and two stage valve lift on the intake valves but with additional variable timing of the exhaust valves.
Diesel engines
In 2010,
Mitsubishiis a multinational automaker headquartered in Minato, Tokyo. In 2009 it was the fifth-largest Japan-based automaker and the 17th-largest in the world measured by production...
developed and started mass production of its
4N13The Mitsubishi 4N1 engine is a family of all-alloy four-cylinder diesel engines developed by Mitsubishi Motors, produced at the company's powertrain facility in Kyoto, Japan for use in Mitsubishi's small to mid-sized global passenger cars....
1.8 L DOHC I4 world's first passenger car
diesel engineA diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
that features a variable valve timing system.
["Geneva 2010: Mitsubishi ASX (Outlander Sport) Debuts in Geneva", autoguide.com]
Electro-mechanical
This method of valve control is often found in camless engine designs. A proponent of this technology is
ValeoValeo is a French automotive components manufacturer.-History:The Société Anonyme Française du Ferodo was founded in 1923 in Saint-Ouen, a suburb of Paris...
, which has indicated that its design will be utilized in volume production by 2009.
In this design the valves are opened and closed and held open or closed by means of electromagnets.
Some of the problems which may be encountered with this methodology are:
- Deceleration of the valve once set in motion is difficult to accomplish. This difficulty is exacerbated by the greatly increased magnetic pull of the magnets as the valves approach the end of their travel (magnetic pull increases dramatically as the distance from the magnet decreases). Inadequate slowing down of the valve can cause significant deterioration of the valve seat and other parts. Utilizing springs to effect valve deceleration limits the engine to lower speeds and on its own will not effect a gentle landing of the valve on its seat at all engine speeds.
- Springs utilized in this type of system may require very careful balancing with the valve movement in order to achieve gentle valve seating at differing engine speeds. As the springs deteriorate or the engine speed changes, the valve and spring balance
The spring scale apparatus is simply a spring fixed at one end with a hook to attach an object at the other. It works by Hooke's Law, which states that the force needed to extend a spring is proportional to the distance that spring is extended from its rest position...
may be compromised and ultimately lead to failure.
- The electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...
s will draw a significant amount of electrical energy, which may require a higher capacity alternatorAn alternator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current.Most alternators use a rotating magnetic field but linear alternators are occasionally used...
, which will in turn reduce the potential fuel efficiency of the engine.
- A powerful computer coupled with complex fast-acting control circuitry and devices will likely be necessary to control the valves in real time.
Hydraulic
This type of valve control has been advocated in the search for a camless engine. Sturman Industries, which incorporated its design into a large truck engine a number of years ago, is a proponent of this technology. (The truck did the hill climb at
Pikes PeakPikes Peak is a mountain in the Front Range of the Rocky Mountains, west of Colorado Springs, Colorado, in El Paso County in the United States of America....
)
Various methods have been explored to utilize hydraulic mechanisms to move the engine valves. Some claim to be successful at low engine speeds, but few claim to achieve that goal meaningfully at the higher RPM requirements of passenger vehicles.
Hydraulic systems suffer from two inherent problems :
- The faster a liquid is moved, the more it tends to act like a solid. A fast-acting hydraulic system
Hydraulic machines are machinery and tools that use liquid fluid power to do simple work. Heavy equipment is a common example.In this type of machine, hydraulic fluid is transmitted throughout the machine to various hydraulic motors and hydraulic cylinders and which becomes pressurised according to...
to activate automotive valves at the speeds required in passenger vehicles could require immense pressures, with all the incumbent problems, including the additional energy requirements of the hydraulic pump. Even if higher engine speeds were achieved, valve movement would likely be abbreviated and not fully follow the desired or optimum lift schedule.
- Temperatures can vary seasonally over a wide range. The hydraulic medium could change viscosity as the temperatures change, which could cause variances in the system's performance which may be difficult to control.
Utilizing springs to assist the hydraulic system may also prevent the engine attaining higher speeds.
In order to achieve gentle valve seating, hydraulic systems must be carefully controlled. This control may require the use of powerful computers and very precise sensors.
Stepper motors
This methodology of valve control has previously not been successful in camless engine design due to the limited RPM range inherent in the design.
The following link indicates that some measure of success has been achieved and a camless design for a medium to slow revving engine may be feasible.
Valves that open and close in fixed times cannot optimize engines running at differing speeds and importantly severely restrict engine speed. This is because the degrees of rotation for the valve events increase as the engine speed increases to the point where they are no longer practical.
Powertrain claim in their documentation at the above link that their device operates the valves “to 8,000 rev/min and beyond”. This figure was likely obtained under laboratory conditions. Real world engines using their devices with 7 ms valve open and close times may have useful speeds limited to well under 6,000 RPM, perhaps even under 5,000 RPM (7 ms at 8,000 RPM is 336 degrees of rotation which is currently unworkable in
passenger carAn automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
s). The engine may be able to run at higher RPM by limiting the lift and hence shortening the valve open close time but will most likely have a lower power output than is achieved at a lower RPM due to the lessening of breathing capability.
Pneumatic
Systems utilizing pneumatics to drive the engine valves would in all probability not be feasible because of their complexity and the very large amount of energy required to compress the air.
Cargine Engineering AB, a Swedish Company, has produced pneumatic valves and has fitted them into several different engines. One of these test engines is running in a test
Saab 9-5The Saab 9-5 is an executive car produced by the Swedish automobile maker Saab. The first generation was introduced in 1997 as the replacement to the Saab 9000 for the 1998 model year. At the time, the car represented a great leap forward for Saab...
.
The first prototype of the
Scuderi EngineThe Scuderi Engine is a split cycle, internal combustion engine invented by Carmelo J. Scuderi . Scuderi Group, an engineering and licensing company based in West Springfield, Massachusetts and founded by Carmelo Scuderi’s children, is testing a working prototype of the engine that was officially...
uses Cargine pneumatic valves for the intake and exhaust valves.
Implementations
- Aftermarket modifications — Conventional hydraulic tappet can be engineered to rapidly bleed-down for variable reduction of valve opening and duration.
- Alfa Romeo
Alfa Romeo Automobiles S.p.A. is an Italian manufacturer of cars. Founded as A.L.F.A. on June 24, 1910, in Milan, the company has been involved in car racing since 1911, and has a reputation for building expensive sports cars...
- Twin Cam
The all alloy Alfa Romeo Twin Cam engine series was an inline-4 cylinder engine produced by Alfa Romeo from 1954 to 1994. For earlier Alfa Romeo engines featuring twin camshafts, refer to the main Alfa Romeo page...
— latest versions are equipped with Variable Valve Timing technology.
- Twin Spark
Alfa Romeo Twin Spark technology was used first time in Alfa Romeo Grand Prix car in 1914. In the early 1960s it was used in their race cars to enable it to achieve a higher power output from its engines...
— is equipped with Variable Valve Timing technology.
- JTS
The JTS engine is a gasoline direct injection engine produced by Alfa Romeo. It exists in two forms, straight-4 and V6, and was introduced into the Alfa lineup in 2002.-2.0:...
— is equipped with Variable Valve Timing technology, both intake and exhaust.
- Multiair
Multiair is an electro-hydraulic variable valve actuation technology controlling air intake in petrol or diesel engines . It is compatible with both naturally aspirated and forced-induction engines....
continuously varies the timing of the inlet valve by changing oil pressure.
- BMW
Bayerische Motoren Werke AG is a German automobile, motorcycle and engine manufacturing company founded in 1916. It also owns and produces the Mini marque, and is the parent company of Rolls-Royce Motor Cars. BMW produces motorcycles under BMW Motorrad and Husqvarna brands...
- Valvetronic
The Valvetronic system is a variable valve timing system to offer continuous and precisely variable intake valve lift, from ~0 to 10 mm, and duration. It typically works in conjunction with the independent Double VANOS system that continuously varies the timing...
— Provides continuously variable lift for the intake valves; used in conjunction with Double VANOS.
- VANOS
VANOS is an automobile variable valve timing technology developed by BMW in close collaboration with Continental Teves. VANOS varies the timing of the valves by moving the position of the camshafts in relation to the drive gear...
— Varies intake timing by rotating the camshaftA camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...
in relation to the gear.
- Double VANOS — Continuously varies the timing of the intake and exhaust valves.
- Daihatsu
- DVVT — Daihatsu Variable Valve Timing. Continuously varies the timing of the intake camshaft, or both the intake and exhaust camshafts (depending on application).
- Ford
Ford Motor Company is an American multinational automaker based in Dearborn, Michigan, a suburb of Detroit. The automaker was founded by Henry Ford and incorporated on June 16, 1903. In addition to the Ford and Lincoln brands, Ford also owns a small stake in Mazda in Japan and Aston Martin in the UK...
- VCT Variable Cam Timing — Varies valve timing by rotating the camshaft.
- Ti-VCT Twin Independent Variable Camshaft with two fully variable camshafts used in Ford Sigma engine
The Ford Sigma is a small straight-4 automobile engine sold by Ford Motor Company. First evolution of engines were sold as the "Zetec-SE" . After the upgrade Ford renamed Sigma to Duratec. Last upgrade of engine is named Duratec Ti-VCT...
and Ford Duratec engineThe Duratec is a range of four, five, and six-cylinder gasoline engines produced by the Ford Motor Company, used in Ford, Mazda, Volvo, Caterham, Morgan, Tiger, Ginetta cars and by specialist engine tuner Cosworth....
.
- Chrysler
Chrysler Group LLC is a multinational automaker headquartered in Auburn Hills, Michigan, USA. Chrysler was first organized as the Chrysler Corporation in 1925....
— Varies valve timing through the use of concentric camshafts developed by Mechadyne enabling dual-independent inlet/exhaust valve adjustment on the 2008 Dodge ViperThe first prototype was tested in January 1989. It debuted in 1991 with two pre-production models as the pace car for the Indianapolis 500 when Dodge was forced to substitute it in place of the Japanese-built Stealth because of complaints from the United Auto Workers, and went on sale in January...
.
- General Motors Corporation (GM)
- VVT — Varies valve timing continuously throughout the RPM range for both intake and exhaust for improved performance in both overhead valve and overhead cam engine applications.(See also Northstar System).
- DCVCP (Double Continuous Variable Cam Phasing) — Varies intake and exhaust camshaft timing continuously with hydraulic vane type phaser; available on Family 1, Family 0, and Family II engines.
- Alloytec — Continuously variable camshaft phasing for inlet cams; continuously variable camshaft phasing for inlet cams and exhaust cams (High Output Alloytec).
- Honda
is a Japanese public multinational corporation primarily known as a manufacturer of automobiles and motorcycles.Honda has been the world's largest motorcycle manufacturer since 1959, as well as the world's largest manufacturer of internal combustion engines measured by volume, producing more than...
- VTEC
VTEC is a valvetrain system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine. The VTEC system uses two camshaft profiles and electronically selects between the profiles. It was invented by Honda R&D engineer Ikuo Kajitani, and was the first system...
— Varies duration, timing and lift by switching between two different sets of cam lobesA camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...
.
- VTEC-E — This system is designed solely for the purpose of improving fuel economy. A variation of the VTEC mechanism is used to create an offset of lift between the two intake valves, one valve opening only slightly to prevent accumulation of fuel in the intake port. The asymmetrical opening of the intake valves creates a powerful swirl in the combustion chamber and allows for a very lean intake charge to be used under certain conditions. Under normal operation the two intake valve rocker arms are locked together and both valves follow the normal lift cam profile.
- i-VTEC — In high-output DOHC 4 cylinder engines, the i-VTEC system adds continuous intake cam phasing (timing) to traditional VTEC. In economy-oriented SOHC and DOHC 4-cylinder engines the i-VTEC system increases engine efficiency by delaying the closure of the intake valves under certain conditions and by using an electronically controlled throttle valve to reduce pumping loss
Parasitic loss is that which a parasite consumes from its host, for whom the loss may or may not be beneficial.- Parasitic loss in internal combustion engines :...
. In SOHC V6 engines the i-VTEC system is used to provide Variable Cylinder ManagementVariable Cylinder Management is Honda's term for a variable displacement technology. It uses the i-VTEC system to disable one bank of cylinders during specific driving conditions to save fuel. The 2008 Accord takes this a step further allowing the engine to go from 6 cylinders, down to 4, and...
which deactivates one bank of three cylinders during low demand operation.
- Advanced VTEC
Advanced VTEC is a system designed to allow the variation of valve timing and lift. It is designed to improve engine Fuel efficiency without sacrificing performance...
— This is the latest Honda VVT system and is the most unusual of all the VTEC systems. Rather than switching between cam lobes the Advanced VTEC system uses intermediate rocker arms with a variable fulcrum to continuously vary intake valve timing, duration and lift.
- Hyundai MPI CVVT — Varies power, torque, exhaust system, and engine response.
- Iran Khodro
- CVVT-i - Continuous Variable Valve Timing Intelligence which is used for EF7 & EF4 engines of the IKCO EF
IKCO EF engines are four cylinders engines. The EF7 series are designed jointly by Iran Khodro Powertrain Company and F.E.V GmbH of Germany. The other models will be designed by IPCO itself. IPCO is the powertrain designing & producing company of Iranian car manufacturer Iran Khodro...
engines family.
- Kawasaki
is an international corporation based in Japan. It has headquarters in both Chūō-ku, Kobe and Minato, Tokyo.The company is named after its founder Shōzō Kawasaki and has no connection with the city of Kawasaki, Kanagawa....
— Varies position of cam by changing oil pressure thereby advancing and retarding the valve timing, 2008 Concours 14The Kawasaki 1400GTR, also known as the Concours 14 or ZG1400 in some markets, is a motorcycle produced by Kawasaki. The 1400GTR was introduced in September 2007 and is based on the ZX-14 platform....
(also known as the 1400GTR).
- Lexus
is the luxury vehicle division of Japanese automaker Toyota Motor Corporation. First introduced in 1989 in the United States, Lexus is now sold globally and has become Japan's largest-selling make of premium cars. The Lexus marque is marketed in over 70 countries and territories worldwide, and has...
VVT-iE — Continuously varies the intake camshaft timing using an electric actuator.
- Mazda
is a Japanese automotive manufacturer based in Fuchū, Aki District, Hiroshima Prefecture, Japan.In 2007, Mazda produced almost 1.3 million vehicles for global sales...
S-VTS-VT, or Sequential Valve Timing, is an automobile variable valve timing technology developed by Mazda. S-VT varies the timing of the intake valves by using hydraulic pressure to rotate the camshaft. S-VT was introduced in 1998 on the ZL-DE engine and is used in the B-, Z-, MZR- and J-families of...
— Continually varies intake timing and crank angle using an oil control valve actuated by the ECU to control oil pressure.
- Mitsubishi
is a multinational automaker headquartered in Minato, Tokyo. In 2009 it was the fifth-largest Japan-based automaker and the 17th-largest in the world measured by production...
MIVECMIVEC is the brand name of a variable valve timing engine technology developed by Mitsubishi Motors...
— Varies valve timing, duration and lift by switching between two different sets of cam lobes.
- The 4B1 engine series uses a different variant of MIVEC which varies timing (phase) of both intake and exhaust camshafts continuously.
- The 4N1
The Mitsubishi 4N1 engine is a family of all-alloy four-cylinder diesel engines developed by Mitsubishi Motors, produced at the company's powertrain facility in Kyoto, Japan for use in Mitsubishi's small to mid-sized global passenger cars....
engine family is the world's first to feature a variable valve timing system applied to passenger car diesel engines.
- Nissan
- N-VCT
Nissan Variable Cam Timing is an automobile variable valve timing technology developed by Nissan. N-VCT was first introduced in 1987 on the VG30DE and VG20DET engine. N-VCT varies the timing of the valves by rotating the cam shaft; valve lift and duration are NOT altered...
— Varies the rotation of the cam(s) only, does not alter lift or duration of the valves.
- VVL
Nissan Ecology Oriented Variable Valve Lift and Timing is an automobile variable valve timing technology developed by Nissan. VVL varies the timing, duration, and lift of valves by using hydraulic pressure switch between two different sets of camshaft lobes. It functions similarly to Honda's...
— Varies timing, duration, and lift of the intake and exhaust valves by using two different sets of cam lobes.
- CVTCS
Continuous Variable Valve Timing Control, which is known as CVTC or CVTCS, is an automobile variable valve timing technology developed by Nissan, similar to Toyota's VVT-i system. CVTC has been introduced with the HR15DE, HR16DE, MR18DE and MR20DE engines in September 2004 on the Nissan Tiida...
- introduced with the HR15DEThe HR is a family of straight-3 and straight-4 automobile engines co-developed by Nissan and Renault. Renault calls it the H engine. It is made by in Japan.-HR10DDT:...
, HR16DEThe HR is a family of straight-3 and straight-4 automobile engines co-developed by Nissan and Renault. Renault calls it the H engine. It is made by in Japan.-HR10DDT:...
, MR18DEThe MR is a family of straight-4 all-aluminum automobile engines with variable valve timing co-developed by Renault and Nissan. Renault calls it the M engine...
and MR20DEThe MR is a family of straight-4 all-aluminum automobile engines with variable valve timing co-developed by Renault and Nissan. Renault calls it the M engine...
engines in September 2004 on the Nissan TiidaThe Nissan Tiida is a compact car, manufactured by Japanese automaker Nissan, replacing the Pulsar and the Sunny, and marketed also as the Nissan Versa, prominently in the United States...
and North American version named Nissan Versa (in 2007); and finally the Nissan SentraThe Nissan Sentra is a compact car produced by automaker Nissan Motors and is generally a rebadged export version of the Japanese Nissan Sunny. The name "Sentra" is not used in Japan....
(in 2007). Also used on the new MR16DDTThe MR is a family of straight-4 all-aluminum automobile engines with variable valve timing co-developed by Renault and Nissan. Renault calls it the M engine...
- VVEL - introduced with the VQ37VHR Nissan VQ engine
The VQ is a V6 piston engine produced by Nissan with displacements varying from 2.0 L to 4.0 L. It is an aluminum block DOHC 4-valve design with aluminum heads. It is fitted with Nissan's EGI/ECCS sequential multi-point fuel injection system...
engine in 2007 on the Infiniti G37.
- Porsche
Porsche Automobil Holding SE, usually shortened to Porsche SE a Societas Europaea or European Public Company, is a German based holding company with investments in the automotive industry....
- VarioCam
VarioCam is an automobile variable valve timing technology developed by Porsche. VarioCam varies the timing of the intake valves by adjusting the tension on the timing chain connecting the intake and exhaust camshafts...
— Varies intake timing by adjusting tension of a cam chain.
- VarioCam Plus — Varies intake valve timing by rotating the cam in relation to the cam sprocket as well as duration, timing and lift of the intake and exhaust valves by switching between two different sets of cam lobes.
- Proton
Proton is a Malaysian automobile manufacturer headquartered in Subang Jaya and Shah Alam, Selangor, Malaysia, with a manufacturing plant in Tanjung Malim, Perak. Founded in 1983, it was Malaysia's only carmaker until the establishment of its competitor and arch-rival, Perodua, in 1993...
- Campro CPS — Varies intake valve timing and lift by switching between two sets of cam lobes without using rocker arms as in most variable valve timing systems. Debuted in the 2008 Proton Gen-2 CPS
Sometime after the launch of the standard Gen-2, comes the special edition. It is fitted with a full body-kit, leather seats and lightweight sport rims. Handling is slightly better with the broader tires fitted and it is more aerodynamic...
and the 2008 Proton Waja CPSThe Proton Waja is a saloon car designed in-house by Malaysian automotive company, Proton, first released in August 2000. The Waja is the first Malaysian-designed car. The name Waja, which means "the king", meaning it is the "king" of all of the previous models. The name was chosen partly to...
.
- VVT introduced in the Waja 1.8's F4P renault engine (Toyota supplies the VVT to renault)
- PSA Peugeot Citroën
PSA Peugeot Citroën is a French manufacturer of automobiles and motorcycles sold under the Peugeot and Citroën marques. Headquartered in the 16th arrondissement of Paris, PSA is the second largest automaker based in Europe and the number eight in the world.-History:In December 1974 Peugeot S.A....
CVVT — Continuous variable valve timing.
- Renault Clio Renault Sport 172, 172 Cup, 182, 182 Cup, Trophy, 197, 197 Cup, 200, and Clio V6 Mk2 VVT — Megane 1.6 vvt variable valve timing. Clio Mk4 Dynamique S 1.6 VVT. RS Twingo 133 1.6 VVT
- Rover
MG Rover was the last domestically owned mass-production car manufacturer in the British motor industry. The company was formed when BMW sold the car-making and engine manufacturing assets of the original Rover Group to the Phoenix Consortium in 2000....
VVCVVC is an automobile variable valve timing technology developed by Rover and applied to some high performance variants of the company's K Series 1800cc engine....
— Varies timing with an eccentric disc.
- Suzuki
is a Japanese multinational corporation headquartered in Hamamatsu, Japan that specializes in manufacturing compact automobiles and 4x4 vehicles, a full range of motorcycles, all-terrain vehicles , outboard marine engines, wheelchairs and a variety of other small internal combustion engines...
— VVT — Suzuki M engineThe Suzuki M engine family is a line of automobile engines from Suzuki. Ranging in displacement from 1.3 L to 1.8 L, it is a modern engine line with dual overhead cams, 16 valves, and multi-point fuel injection .-M13A:...
- Subaru
; is the automobile manufacturing division of Japanese transportation conglomerate Fuji Heavy Industries .Subaru is internationally known for their use of the boxer engine layout popularized in cars by the Volkswagen Beetle and Porsche 911, in most of their vehicles above 1500 cc as well as...
- AVCS — Varies timing (phase) with hydraulic pressure, used on turbocharged and six-cylinder Subaru engines.
- AVLS — Varies duration, timing and lift by switching between two different sets of cam lobes (similar to Honda VTEC). Used by non-turbocharged Subaru engines.
- Toyota
- VVT — Toyota 4A-GE 20-Valve engine introduced VVT in the 1992 Corolla GT-versions.
- VVT-i
VVT-i, or Variable Valve Timing with intelligence, is an automobile variable valve timing technology developed by Toyota, similar in performance to the BMW's VANOS. The Toyota VVT-i system replaces the Toyota VVT offered starting in 24 December 1991 on the 5-valve per cylinder 4A-GE engine. The...
— Continuously varies the timing of the intake camshaft, or both the intake and exhaust camshafts (depending on application).
- VVTL-i — Continuously varies the timing of the intake valves. Varies duration, timing and lift of the intake and exhaust valves by switching between two different sets of cam lobes.
- Valvematic
- Vauxhall
-Demography:Many Vauxhall residents live in social housing. There are several gentrified areas, and areas of terraced townhouses on streets such as Fentiman Road and Heyford Avenue have higher property values in the private market, however by far the most common type of housing stock within...
- VVT used in the facelift Vectra 1.8 engines, Astras and Corsas.
- Volkswagen Group
Volkswagen Group is a German multinational automobile manufacturing group. , Volkswagen was ranked as the world’s third largest motor vehicle manufacturer and Europe's largest....
— VVT introduced with later revisions of the 1.8t engine, and the 30-valve 2.8 L V6. Similar to VarioCamVarioCam is an automobile variable valve timing technology developed by Porsche. VarioCam varies the timing of the intake valves by adjusting the tension on the timing chain connecting the intake and exhaust camshafts...
, the intake timing intentionally runs advanced and a retard point is calculated by the ECU. A hydraulic tensioner retards the intake timing. Most modern VW Group petrol engines now include VVT on either the inlet cam, or both inlet and exhaust cams, as in their V6, V8 and V10 engines.
- Volvo
AB Volvo is a Swedish builder of commercial vehicles, including trucks, buses and construction equipment. Volvo also supplies marine and industrial drive systems, aerospace components and financial services...
- CVVT — Continuous variable valve timing on intake and/or exhaust camshafts (depending on application).
- CPS
-Australia:*Corporate Protective Services, Sydney based GPS monitoring company*Chatswood Public School, a school in Sydney-Bangladesh:*Criminology and Police Science, CPS is a discipline studied by the department at Mawlana Bhashani Science and Technology University in Tangail, Bangladesh. Md...
— Changes valve timing, duration and lift of the intake valves by switching between two different sets of cam lobes. Same basic technology as Porsches VarioCam Plus with switching direct-acting tappets. To date this is only used on Volvos short inline-6 (SI6) naturally aspirated 3.2 L engine.
- Yamaha
Yamaha may refer to:* Yamaha Corporation, a Japanese company with a wide range of products and services** Yamaha Motor Company, a Japanese motorized vehicle-producing company...
— VCT (Variable Cam Timing) Varies position of cam thereby advancing and retarding the valve timing.
See also
- Camless valve technology
Most four-stroke piston engines today employ one or more camshafts to operate poppet valves. The lobes on the camshafts operate cam followers which in turn open the poppet valves. A camless uses electromagnetic, hydraulic, or pneumatic actuators to open the poppet valves instead...
- Helical camshaft
A helical camshaft is a type of mechanical variable valve actuation system. More specifically it is a camshaft that allows the valve opening duration to be varied over a wide, continuous, step-less, range, with all of the added duration being at full valve lift.In this article a “variable duration...
- Corliss Orville Burandt
Corliss Orville Burandt is an American engineer who invented a system of variable valve timing in automobile engines. Working through a 1965 Chevrolet Corvair, he designed a system of putting a sensor into the cylinder to optimize the fuel-air mixture during combustion...
- Continuous variable valve timing
Continuous variable valve timing offers a unique ability to have independent control of the intake and exhaust valves in an internal combustion engine. For any engine load criteria, the timing of intake and exhaust can be independently programmed...
External links