Variable Valve Timing System 气门调节的认识，图片+video

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Variable valve timing
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In internal combustion engines, variable valve timing, often abbreviated to VVT, is a generic term for an automobile piston engine technology. VVT allows the lift, duration or timing (some or all) of the intake or exhaust valves (or both) to be changed while the engine is in operation. Two-stroke engines use a power valve system to get similar results to VVT.

Contents[hide] 1 Overview 2 History 2.1 Steam engines 2.2 Aircraft 2.3 Automotive use 3 VVT Implementations 4 See also 5 References 6 External links

[edit] Overview
The i-VTEC system found in the Honda K20Z3


Piston engines normally use poppet valves for intake and exhaust. These are driven (directly or indirectly) by cams on a camshaft. 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 belts, gears or chains.
The profile, or position and shape of the cam lobes on the shaft, is optimized for a certain engine revolutions per minute (RPM), and this tradeoff normally limits low-end torque, or high-end power. VVT allows the cam profile to change, which results in greater efficiency and power, over a wider rev-range.
At high engine speeds, an engine requires large amounts of air. However, the intake valves may close before all the air has been given a chance to flow in, reducing performance. On the other hand, if the cam 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 cannot idle at the low speeds (around 800rpm) expected of a road car, and idle speeds of 2000 rpm are not unusual.
Pressure to meet environmental goals and fuel efficiency standards is forcing car manufacturers to turn to VVT as a solution. Most simple VVT systems advance or retard the timing of the intake or exhaust valves. Others (like Honda's VTEC) switch between two sets of cam lobes at a certain engine RPM. Furthermore Honda's I-VTEC can alter intake valve timing continuously.

[ 本帖最后由 3-SGTE 于 2009-8-10 11:52 PM 编辑 ]

3-SGTE

History

[edit] Steam engines
The first variable valve timing systems came into existence in the nineteenth century on steam engines. Stephenson valve gear, as used on early steam locomotives, supported variable cutoff, 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 governor and trip valves. As poppet valves came into use, simplified valve gear using a camshaft came into use. With such engines, variable cutoff could be achieved with variable profile cams that were shifted along the camshaft by the governor. [1].


[edit] Aircraft
Some versions of the Bristol Jupiter radial engine of the early 1920s incorporated variable valve timing gear, mainly to vary the inlet valve timing in connection with higher compression ratios.[1] 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.


[edit] Automotive use
Fiat 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%.

n September 1975, General Motors (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 Romeo was the first manufacturer to use a variable valve timing system in production cars (US Patent 4,231,330). The 1980 Alfa Romeo Spider 2.0 L had a mechanical VVT system in SPICA fuel injected cars sold in the United States. Later this was also used in the 1983 Alfetta 2.0 Quadrifoglio Oro models as well as other cars. The system was engineered by Ing Giampaolo Garcea in the 1970s.[2]

Honda's REV motorcycle engine employed on the Japanese market-only Honda CBR400F in 1983 provided a technology base for VTEC.

In 1987,[citation needed] Nissan developed their own form of VVT with the VG30DE(TT) engine for their Mid-4 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.

The next step was taken in 1989 by Honda with the VTEC 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 Integra, CRX, and Civic hatchback available in Japan and Europe. In 1991 the Acura NSX 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 University 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.[3]

In 1992 BMW introduced the VANOS 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. In 2001 BMW introduced the Valvetronic system. The Valvetronic system is unique in that it can continuously vary intake valve lift, in addition to 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 throttle valve and greatly reducing pumping loss. The reduction of pumping loss accounts for more than a 10% increase in power output and fuel economy.

Ford began using Variable Cam Timing in 1998 for Ford Sigma engine. Ford became the first manufacturer to use variable valve timing in a pickup-truck, with the top-selling Ford F-series in the 2004 model year. The engine used was the 5.4L 3-valve Triton.

In 2005 General Motors offered the first Variable Valve timing system for pushrod V6 engines, LZE and LZ4.

In 2007 DaimlerChrysler 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 Viper uses Mechadyne's concentric camshaft assembly to help boost power output to 600 bhp (450 kW).

In 2009 Fiat Powertrain Technologies introduced the Multiair 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 will be available in Alfa Romeo MiTo starting from September 2009.[4]

3-SGTE

[edit] VVT Implementations
Aftermarket Modifications - Conventional hydraulic tappet can be engineered to rapidly bleed-down for variable reduction of valve opening and duration.
Alfa Romeo

Twin Cam - some versions are equipped with Variable Valve Timing technology.
Twin Spark - is equipped with Variable Valve Timing technology.
JTS - is equipped with Variable Valve Timing technology, both intake and exhaust.
Multiair continuously varies the timing of the inlet valve by changing oil pressure.
BMW

Valvetronic - Provides continuously variable lift for the intake valves; used in conjunction with Double VANOS.
VANOS - Varies intake timing by rotating the camshaft in relation to the gear.
Double VANOS - Continuously varies the timing of the intake and exhaust valves.
Fiat

"StarJet" FIRE-based engine.

Ford

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 and Ford Duratec engine.
Chrysler - Varies valve timing through the use of concentric camshafts developed by Mechadyne enabling dual-independent inlet/exhaust valve adjustment on the 2008 Dodge Viper.
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 (see also Ecotec LE5).
Alloytec - Continuously variable camshaft phasing for inlet cams. Continuously variable camshaft phasing for inlet cams and exhaust cams (High Output Alloytec).

Honda

VTEC - Varies duration, timing and lift by switching between two different sets of cam lobes.
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. In SOHC V6 engines the i-VTEC system is used to provide Variable Cylinder Management which deactivates one bank of 3 cylinders during low demand operation.
Advanced VTEC - This is the latest Honda VVT system and is the most unique 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.
Kawasaki
- Varies position of cam by changing oil pressure thereby advancing and retarding the valve timing, 2008 Concours 14.
Lexus

VVT-iE - Continuously varies the intake camshaft timing using an electric actuator.
Mazda

S-VT - Continually varies intake timing and crank angle using an oil control valve actuated by the ECU to control oil pressure.
Mitsubishi

MIVEC - 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.

Nissan

N-VCT - Varies the rotation of the cam(s) only, does not alter lift or duration of the valves.
VVL - Varies timing, duration, and lift of the intake and exhaust valves by using two different sets of cam lobes.
CVTC introduced with the HR15DE, HR16DE, MR18DE and MR20DE new engines in September 2004 on the Nissan Tiida and North American version named Nissan Versa (in 2007); and finally the Nissan Sentra (in 2007).
VVEL introduced with the VQ37VHR Nissan VQ engine engine in 2007 on the Infiniti G37.

Porsche

VarioCam - 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 Campro CPS

- Varies intake valve timing and lift by switching between 2 sets of cam lobes without using rocker arms as in most variable valve timing systems. Debuted in the 2008 Proton Gen-2 CPS[5][6] and the 2008 Proton Waja CPS.
PSA Peugeot Citroën
CVVT - Continuous variable valve timing.

Renault
Clio 182, Clio Cup and Clio V6 Mk2 VVT - variable valve timing.

Rover
VVC - Varies timing with an eccentric disc.

Suzuki
- VVT - Suzuki M engine

Subaru
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 - 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.

Volkswagen

Group - VVT introduced with later revisions of the 1.8t engine, and the 30v 2.8l V6. Similar to VarioCam, 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

- CVVT

Yamaha

- VCT (Variable Cam Timing) Varies position of cam thereby advancing and retarding the valve timing.

Proton

- VVT introduced in the Waja 1.8's F4P renault engine (toyota supplies the VVT to renault)

[ 本帖最后由 3-SGTE 于 2009-7-6 11:05 PM 编辑 ]

3-SGTE

An Imagery of the i-VTEC Implementation

EGR Effect: By swirling back some of the exhaust air back into the combustion chamber, combustion temperature is lowered, and NOx output is reduced.

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[ 本帖最后由 3-SGTE 于 2009-7-7 10:50 PM 编辑 ]

毛毛小子

VTEC的HEAD哦 哈哈 好料哦

3-SGTE

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Information

Valvetronic engines use a combination of hardware and software to eliminate the need for a conventional throttle mechanism.

Valvetronic varies the timing and the lift of the intake valves. The Valvetronic system has a conventional intake cam, but it also uses a secondary eccentric shaft with a series of levers and roller followers, activated by a stepper motor. Based on signals formerly taken mechanically from the accelerator pedal, the stepper motor changes the phase of the eccentric cam, modifying the action of the intake valves.

Valvetronic was introduced on the all-alloy 1.8-liter, 4-cylinder engine for the E46 316ti Compact, and it will subsequently be applied to most eight and 12-cylinder engines within a few years. The new E65 7 Series has Valvetronic engines.
The Valvetronic engine replaces the function of the throttle butterfly by using an infinitely variable intake valve lift. The Valvetronic engine does not require a timing belt or chain. Valvetronic has its own computer housed in a separate unit away from the engine management system, networked with the digital engine management system incorporating a 40-megahertz, 32-bit computer.

A unique set of images from BMW showing how Valvetronic was designed. Click for a larger image

Valvetronic reduces maintenance costs, improves cold start behavior, lowers exhaust emissions, and provides a  smoother running engine. Valvetronic does not need specific fuel grades or fuel qualities because of its fine atomization of fuel.
The entire Valvetronic system is pre-assembled and inserted as a module into its position in the cylinder head. Valvetronic engines are built at BMW's brand new engine plant at Hams Hall near Coventry, England.
Because Valvetronic allows the engine to breathe more freely, fuel consumption is reduced by 10%. The fuel savings are greatest at lower engine revs. Valvetronic is an important element in BMW's aim of meeting the 2008 carbon dioxide fleet requirements of 140 gm/km.
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V-8

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Here's how it works:

Fuel injection systems monitor the volume of air passing through the throttle butterfly and determine the corresponding amount of fuel required by the engine. The larger the throttle butterfly opening, the more air enters the combustion chamber.  

At light throttle, the throttle butterfly partially or even nearly closes. The pistons are still running, taking air from the partially closed intake manifold. The intake manifold between the throttle and the combustion chamber has a partial vacuum, resisting the [词语过滤-#17]ing and pumping action of the pistons, wasting energy. Automotive engineers refer to this phenomenon as "pumping loss". The slower the engine runs, the more the throttle butterfly closes, and the more energy is lost.

Valvetronic minimizes pumping loss by reducing valve lift and the amount of air entering the combustion chambers.

Compared with conventional twin-cam engines with finger followers, Valvetronic employs an additional eccentric shaft, an electric motor and several intermediate rocker arms, which in turn activates the opening and closing of valves. If the rocker arms push deeper, the intake valves will have a higher lift, and vice-versa. Thus, Valvetronic has the ability to get deep, long ventilation (large valve lift) and flat, short ventilation (short valve lift), depending on the demands placed on the engine.

Operating Parameters:

• Valve lift is variable between 0 and 9.7 mm.  
• Adjustment of the worm gear from one extreme to the other takes 300 milliseconds.
• Combined with double-Vanos valve timing technology, the camshaft angle relative to the crankshaft can be adjusted by up to 60?
• The intermediate arm is finished to a tolerance of 0.008 mm.
• The cams controlling the eccentric shaft are machined to tolerances of a few hundredths of a millimeter.

Additional Benefits:

• In Valvetronic engines coolant flows across the head, resulting in a temperature reduction of 60%.
• The water pump size is cut in half, reducing power consumption by 60%.
• The power steering fluid is warmed quickly, reducing the power used by the hydraulic pump.
• Mounting the water and power pump on the same shaft and a heat exchanger between coolant and engine oil reduces oil temperature by 30%.

The efficiency of Valvetronic engines drop rapidly at over 6,000 rpm since stronger valve springs are required. The stronger springs create higher friction losses. Don't expect to see Valvetronic in the "M" series engines any time soon.
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[ 本帖最后由 3-SGTE 于 2009-7-6 11:50 PM 编辑 ]

3-SGTE

What is MIVEC? In the early ‘90s, Mitsubishi Japan introduced a valve control system to combat Honda’s VTEC design. This system is labelled MIVEC (Mitsubishi Innovative Valve and Lift Electronic Control System). In its simplest form, MIVEC switches between two different intake and exhaust cam lobes depending on engine rpm. At low rpm, the valves receive relatively modest lift and opening duration. At high rpm, the secondary cam lobe is engaged and the valves receive greater lift and duration (which results in increased overlap). The purpose of the secondary cam lobe is to deliver greater engine breathing and the ability to maintain torque at very high rpm (which means greater power). The MIVEC system achieves its high power without the driveabililty, fuel consumption and emissions trade-offs typical in a conventional engine. In addition to the base MIVEC principle, Mitsubishi also released a sophisticated MIVEC-MD (Modular Displacement) system in the ‘90s. The MD system is an early form of cylinder deactivation which involves closing the intake and exhaust valves at light engine load. This means the driver must open the throttle further to maintain power and, as a result, pumping losses are reduced and active cylinder pressures are increased. This results in greater efficiency and fuel economy. Depending on conditions, the MIVEC-MD system can reduce fuel consumption by 10 – 20 percent.

[ 本帖最后由 3-SGTE 于 2009-7-11 10:23 AM 编辑 ]

毛毛小子

我对车没有什么研究，经过来看看而已

3-SGTE

HOME > Corporate Info > About Us > Technology > Driving Fun > MIVEC

MIVECRemarkable MIVEC Engine makes power performance and environmental protection compatible MIVEC = Mitsubishi Innovative Valve timing Electronic Control system The dual-intake valve camshaft enables changing between low-speed and high-speed modes, resulting in easy operation from low to high rpms, improving the driving experience when starting from a stop light, merging onto the freeway, or accelerating to overtake another car. In the pursuit of pure driving enjoyment, potentially incompatible goals like fuel economy, environment-friendliness, and clean driving have all been achieved. [Low-speed Mode] The difference in the dual-intake valve lift (low lift and medium lift) and enhanced in-cylinder streaming further stabilize combustion without compromising fuel economy, emissions, and torque. [High-speed Mode] Extending the injection valve opening time and expanding the valve lift range increases intake air mass and achieves output close to best in class. The Grandis is equipped with the 2.4L MIVEC and the Colt is equipped with with the 1.3 and 1.5L MIVEC. 4G69 MIVEC (2.4L SOHC 16-valve, 4-cylinder) (Grandis) MIVEC Switching Mechanism Grandis MIVEC Engine Performance Curve (4G69)

[ 本帖最后由 3-SGTE 于 2009-7-11 10:06 AM 编辑 ]