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VTEC is also an abbreviation for the verocytotoxin-producing Escherichia coli strain O157:H7.
For the education institution, see Virginia Techmarker.
VTEC (Variable Valve Timing and Lift Electronic Control) is a valvetrain system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine. This system uses two camshaft profiles and electronically selects between the profiles. It was invented by Honda R&D engineer Ikuo Kajitani. It can be said that VTEC, the original Honda variable valve control system, originated from REV (Revolution-modulated valve control) introduced on the CBR400 in 1983 known as HYPER VT EC. VTEC was the first system of its kind, though other variable valve timing and lift control systems have been produced by other manufacturers (MIVEC from Mitsubishi, VVTL-i from Toyota, VarioCam Plus from Porsche, VVL from Nissan, etc).

DOHC VTEC

The VTEC system is a simple method of endowing the engine with multiple camshaft profiles optimized for low and high RPM operations. Instead of one cam lobe actuating each valve, there are two: one optimized for low-RPM stability & fuel efficiency; the other designed to maximize high-RPM power output. Switching between the two cam lobes is controlled by the ECU which takes account of engine oil pressure, engine temperature, vehicle speed, engine speed and throttle position. Using these inputs, the ECU is programmed to switch from the low lift to the high lift cam lobes when the conditions mean that engine output will be improved. At the switch point a solenoid is actuated which allows oil pressure from a spool valve to operate a locking pin which binds the high RPM cam follower to the low rpm ones. From this point on, the poppet valve opens and closes according to the high-lift profile, which opens the valve further and for a longer time. The switch-over point is variable, between a minimum and maximum point, and is determined by engine load. The switch back from high to low rpm cams is set to occur at a lower engine speed than the up-switch to avoid a situation in which the engine is asked to operate continuously at or around the switch-over point.

Introduced as a DOHC system in the 1989 Honda Integra and Civic CRX SiR models sold in Japan and Europe, which used a variant of the B16A engine. The US market saw the first VTEC system with the introduction of the 1991 Acura NSX, which used a DOHC VTEC V6 with . DOHC VTEC engines soon appeared in other vehicles, such as the 1992 Acura Integra GS-R (B17A 1.7 liter engine). And later in the 1992 Honda Prelude VTEC (H22 2.2 liter engine with 195hp) and Honda Del Sol VTEC (B16 1.6 liter engine).Honda has also continued to develop other varieties and today offers several varieties of VTEC, such as i-VTEC and i-VTEC Hybrid.

SOHC VTEC

As popularity and marketing value of the VTEC system grew, Honda applied the system to SOHC (Single Over Head Cam) engines, which share a common camshaft for both intake and exhaust valves. The trade-off was that Honda's SOHC engines only benefitted from the VTEC mechanism on the intake valves. This is because VTEC requires a third center rocker arm and cam lobe (for each intake and exhaust side), and in the SOHC engine, the spark plugs are situated between the two exhaust rocker arms, leaving no room for the VTEC rocker arm. Additionally, the center lobe on the camshaft can only be utilized by either the intake or the exhaust, limiting the VTEC feature to one side.

However, beginning with the J37A4 3.7L SOHC V6 engine introduced on all 2009 Acura TL SH-AWD models, SOHC VTEC was incorporated for use with intake and exhaust valves. The intake and exhaust rocker shafts contain primary and secondary intake and exhaust rocker arms, respectively. The primary rocker arm contains the VTEC switching piston, while the secondary rocker arm contains the return spring. The term "primary" does not refer to which rocker arm forces the valve down during low-RPM engine operation. Rather, it refers to the rocker arm which contains the VTEC switching piston and receives oil from the rocker shaft.

The primary exhaust rocker arm contacts a low-profile camshaft lobe during low-RPM engine operation. Once VTEC engagement occurs, the oil pressure flowing from the exhaust rocker shaft into the primary exhaust rocker arm forces the VTEC switching piston into the secondary exhaust rocker arm, thus locking both exhaust rocker arms together. The high-profile camshaft lobe which normally contacts the secondary exhaust rocker arm alone during low-RPM engine operation is able to move both exhaust rocker arms together which are locked as a unit.

The secondary intake rocker arm contacts a low-profile camshaft lobe during low-RPM engine operation. Once VTEC engagement occurs, the oil pressure flowing from the intake rocker shaft into the primary intake rocker arm forces the VTEC switching piston into the secondary exhaust rocker arm, thus locking both intake rocker arms together. The high-profile camshaft lobe which normally contacts the primary intake rocker alone during low-RPM engine operation is able to move both intake rocker arms together which are locked as a unit.

The difficulty of incorporating VTEC for both the intake and exhaust valves in a SOHC engine has been removed on the J37A4 by a novel design of the intake rocker arm. Each exhaust valve on the J37A4 corresponds to one primary and one secondary exhaust rocker arm. Therefore, there are a total of twelve primary exhaust rocker arms and twelve secondary exhaust rocker arms.

However, each secondary intake rocker arm is shaped similar to a "Y" which allows it to contact two intake valves at once. One primary intake rocker arm corresponds to each secondary intake rocker arm. As a result of this design, there are only six primary intake rocker arms and six secondary intake rocker arms.

VTEC-E

It is a version of SOHC VTEC, which was used to increase efficiency at low RPM. At low RPM, one of the two intake valves is only allowed to open a very small amount, increasing the fuel/air atomization in the cylinder and thus allowing a leaner mixture to be used. As the engine's speed increases, both valves are needed to supply sufficient mixture. A sliding pin, which is pressured by oil, as in the regular VTEC, is used to connect both valves together and allows the full opening of the second valve.

3STAGE VTEC

It is a version using 3 different cams to control valve timing and lift. At low RPM, only one intake valve is used; at medium RPM, two intake valves are used; at high RPM, the high speed valve cam is used to increase power.

i-VTEC

(intelligent-VTEC) introduced continuously variable camshaft phasing on the intake cam of DOHC VTEC engines. The technology first appeared on Honda's K-series four cylinder engine family in 2001 (2002 in the U.S.).In the United States, Honda first debuted the technology on the 2003 Honda Civic Si EP3 with the economy version.

Valve lift and duration are still limited to distinct low- and high-RPM profiles, but the intake camshaft is now capable of advancing between 25 and 50 degrees (depending upon engine configuration) during operation. Phase changes are implemented by a computer controlled, oil driven adjustable cam gear. Phasing is determined by a combination of engine load and rpm, ranging from fully retarded at idle to somewhat advanced at full throttle and low rpm. The effect is further optimization of torque output, especially at low and midrange RPM.

K-series

The K-Series motors have two different types of i-VTEC systems implemented. The first is for the performance motors like in the RSX Type S or the TSX and the other is for economy motors found in the CR-V or Accord. The performance i-VTEC system is basically the same as the DOHC VTEC system of the B16A's; both intake and exhaust have 3 cam lobes per cylinder. However the valvetrain has the added benefit of roller rockers and continuously variable intake cam timing. Performance i-VTEC is a combination of conventional DOHC VTEC with VTC.

The economy i-VTEC is more like the SOHC VTEC-E in that the intake cam has only two lobes, one very small and one larger, as well as no VTEC on the exhaust cam. The two types of motor are easily distinguishable by the factory rated power output: the performance motors make around or more in stock form and the economy motors do not make much more than from the factory.

R-series

The new SOHC i-VTEC implementation is an entirely new implementation that was introduced on the 2006 Honda Civic's R-series four cylinder SOHC engines. This implementation uses the so-called "fuel economy cam" and "high output cam" on one of the two intake valves of each cylinder (another intake valve is fixed). The "fuel economy cams" are designed to retard the closure of one intake valve and are activated between 1000-3500RPM and under low load condition. When "fuel economy cams" are activated, the intake valve closes well after the piston has started moving upwards in the compression stroke. During this time, the drive-by-wire throttle valve is open wider than normal. Due to the delayed closing of intake valve, a part of the intake mixture that has entered the combustion chamber is forced out again into the intake manifold. That way, the engine "emulates" a lower displacement than its actual one (its operation is also similar to an Atkinson cycle engine, with uneven compression and combustion strokes), which reduces pumping losses thus reducing fuel consumption and increases its efficiency. VTEC-off on the R18A means it can be considered to be running "high output cams". When the right conditions are achieved for fuel economy, VTEC engages the 2nd set, the 'low' or 'economy' cams. Thus VTEC-on on the R18A means it is running low cams.

According to Honda, this measure alone can reduce pumping losses by 16%. Under heavier loads, the engine switches back into its "high output cams", and it operates like a regular 4 stroke Otto cycle engine. This implementation of i-VTEC was initially introduced in the R18A1 engine found under the bonnet of the 8th generation Civic, with a displacement of 1.8 L and an output of . Recently, another variant was released, the 2.0 L R20A2 with an output of , which powers the EUDM version of the all-new CRV. SOHC i-VTEC

With the continued introduction of vastly different i-VTEC systems, one may assume that the term is now a catch-all for creative valve control technologies from Honda.

i-VTEC VCM

In 2003, Honda introduced an i-VTEC V6 (an update of the J-series) that includes Honda's cylinder deactivation technology which closes the valves on one bank of (3) cylinders during light load and low speed (below ) operation. The technology was originally introduced to the US on the Honda Odyssey minivan, and can now be found on the Honda Accord Hybrid, the 2006 Honda Pilot, and the 2008 Honda Accord.

i-VTEC VCM was also used in 1.3L 4-cylinder engines used in Honda Civic Hybrid.

i-VTEC i

It is a version of i-VTEC with direct injection.

It was first used in 2003 Honda Stream.

AVTEC

The AVTEC (Advanced VTEC) engine was first announced in 2006. It combines continuously variable valve lift and timing control with continuously variable phase control. Honda originally planned to produce vehicles with AVTEC engines within next 3 years.

Although it was speculated that it would first be used in 2008 Honda Accord, the vehicle only used the older engines.

A related US patent (6,968,819) was filed in 2005-01-05.

DTEC

It is a version for diesel engine.

i-DTEC

It is a variant of i-CTDi diesel engine with exhaust gas recirculation, NOx catalytic storage, 2000bar injector.

The engine was unveiled in 2008 NAIAS.

The engine was first introduced in European 2008 Honda Accord as Honda N engine.

Honda originally announced the North American version of i-DTEC would be available in 2009 Acura vehicles, but it has yet to be introduced for that calendar year.

VTEC in motorcycles

Apart from the Japanese market-only Honda CBR400F Super Four HYPER VTEC, introduced in 1983, the first worldwide implementation of VTEC technology in a motorcycle occurred with the introduction of Honda's VFR800 sportbike in 2002. Similar to the SOHC VTEC-E style, one intake valve remains closed until a threshold of 7000 rpm is reached, then the second valve is opened by an oil-pressure actuated pin. The dwell of the valves remains unchanged, as in the automobile VTEC-E, and little extra power is produced but with a smoothing-out of the torque curve. Critics maintain that VTEC adds little to the VFR experience while increasing the engine's complexity. Honda seem to agree: their VFR1200, a model announced in October 2009 to replace the VFR800, abandons the V-TEC concept in favour of a large capacity narrow-vee "unicam" (i.e. sohc) motor.

References

  1. The Father of VTEC, Retrieved March 10, 2007
  2. Honda Worldwide | Technology Close-up
  3. acura.com
  4. Honda Civic Hybrid Technology
  5. Honda reveals the Advanced VTEC engine
  6. Honda Files Advanced VTEC Patent
  7. A-VTEC Details Break Cover at USPTO; TOV Analyzes
  8. 2008 Honda Environmental Annual Report
  9. ディーゼルエンジン「i-DTEC」
  10. Detroit 2008: Honda gives us a peek at the i-DTEC clean diesel
  11. Frankfurt2007 - 62nd International Motor Show (IAA) Cars Honda Press Conference (09:55)
  12. Acura Will Introduce Clean Diesel i-DTEC Engine in 2009




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