VTEC (Variable Valve Timing & Lift Electronic Control) is a system developed by Honda that is said to improve the volumetric efficiency of a four-stroke internal combustion engine, resulting in higher performance at higher RPM, and fuel consumption lower at lower RPM. The VTEC system uses two (or sometimes three) camshaft profiles and hydraulically selects between profiles. It was invented by Honda engineer, Ikuo Kajitani. This is clearly different from the standard VVT (variable valve timing) system that only changes the valve timing and does not alter the camshaft profile or valve lift in any way.
Video VTEC
Context and description
Japan levies taxes on the basis of engine displacement, and Japanese automakers thereby focus their research and development efforts to improve the performance of their smaller engine designs through means other than increased displacement. One method of improving performance to be static displacement includes forced induction, as well as models like the Toyota Supra and the Nissan 300ZX that use turbocharger applications and the Toyota MR2 that use superchargers for some models of the year. Another approach is the rotary engine used in Mazda RX-7 and RX-8. The third option is to change the cam time profile, where Honda VTEC is the first successful commercial design to change the profile in real-time.
The VTEC system provides engine with valve timing optimized for low and high RPM operations. In basic form, single cam lobes and follower/rocker arm from conventional engines are replaced with locking multi-part rocker arm and two cam profiles: optimized for low RPM stability and fuel efficiency, and the other designed to maximize high Output power -RPM. The transition operation between the two cam lobes is controlled by the ECU which takes into account engine oil pressure, engine temperature, vehicle speed, engine speed, and throttle position. By using this input, the ECU is programmed to switch from low lifts to high-lob cam when certain conditions are met. At the point of the switch, the solenoid is driven which allows the oil pressure of the spool valve to operate the locking pin that binds the RPM rocker arm high to the low RPM. From this point, the valve opens and closes according to the elevated profile, which opens the valve further and for a longer time. The switch-over point is a variable, between the minimum and maximum points, and is determined by the machine load. The back-down switch from high to low RPM cams is set to occur at lower engine speeds than switch-ups (representing hysteresis cycles) to avoid situations where the machine is required to operate continuously at or around the switch-over point.
The old approach to timing is to produce a camshaft with a valve timing profile that is more suitable for low RPM operations. Improvements in low RPM performance, where most road-driven automobiles operate most of the time, occur in trade for power and loss of efficiency over a higher RPM range. In line with that, VTEC seeks to combine low-fuel RPM efficiency and stability with high RPM performance.
Maps VTEC
History
VTEC, Honda's original variable valve control system, is derived from REV (Revolution-Modulated Valve Control) introduced on CBR400 in 1983 known as HYPER VTEC. On a regular four-stroke automobile engine, the input and exhaust valves are driven by lobes on the camshaft. The shape of the lobe determines the time, lift and duration of each valve. Time refers to the angle measurement when the valve is opened or closed against the piston position (BTDC or ATDC). Lift refers to how many valves are opened. Duration refers to how long the valve remains open. Because the behavior of the working fluid (mixture of air and fuel) before and after combustion, which has physical limitations on its flow, as well as its interaction with ignition sparks, the optimal valve timing, lift and duration under a low-operating RPM machine are very different from those below High RPM. Timing and setting duration of low optimal valve RPM will result in insufficient cylinder filling with fuel and air at high RPM, thus severely limiting engine power output. In contrast, optimal RPM settings and optimized high-valve RPM timing will result in extremely rugged low-limb RPM operations and poor idling. The ideal machine will have a fully variable timing, lifting, and duration of valves, where the valve will always open at exactly the right point, lifting high enough and remaining open only in the right amount of time for engine speed and load used.
DOHC VTEC
Introduced as a DOHC (Dual overhead camshaft) system in Japan on the 1989 Honda Integra XSi using the 160-bhp (120-kW) B16A engine. In the same year, Europe saw the arrival of VTEC on the Honda CRX 1.6i-VT, using a 150-bhp (110-kW) B16A1 variant. The US market saw the first VTEC system with the introduction of the Acura NSX 1991, which uses the 3-liter DOHC C30A V6 with 270 bhp (200 kW). The DOHC VTEC engine soon appeared in other vehicles, such as the 1992 Acura Integra GS-R (150 bhp (110 kW) B17A1), and then in 1993 Honda Prelude VTEC (195 bhp (145 kW) H22A) and Honda Del Sol VTEC (160 bhp (120 kW) B16A3). The Integra Type R (1995-2000) available in the Japanese market produced 197 bph (147 kW, 200 PS) using a 1.8 liter B18C engine, generating more horsepower per liter than most super cars at the time. Honda also continues to develop other varieties and currently offers several varieties of VTEC, such as i-VTEC and i-VTEC Hybrid.
SOHC VTEC
Honda also implemented systems for SOHC (single overhead camshaft) engines such as D-Series and J-Series Engines, which share a common camshaft for intake and exhaust valves. The trade-off is that the Honda SOHC engine benefits from the VTEC mechanism only on the intake valve. This is because VTEC requires a third center rocker arm and cam lobe (for every intake and exhaust side), and, in a SOHC engine, spark plugs are located between two rocker arm exhausts, leaving no room for VTEC rocker arms. In addition, the central lobe on the camshaft can not be used by the intake and exhaust, limiting the VTEC feature to one side.
However, starting with the 3.37L SOHC V6 J37A4 engine introduced on all 2009 Acura TL SH-AWD models, the SOHC VTEC is combined for use with inlet and exhaust valves, using a total of six cam lobes and six rocker sleeves per cylinder. Intake rocker intake and exhaust contains primary and secondary intake and armber armpipe exhaust, respectively. The main rocker arm contains a VTEC piston switching, while the secondary rocker arm contains the spring back. The term "primer" does not refer to the rocker arm that forces the valve to fall during low-engine RPM operation. Instead, it refers to a rocker arm containing a VTEC piston switching and receiving oil from a rocker axle.
The main exhaust rocker arm contacts the low-profile camshaft hole during low-engine RPM operation. After VTEC involvement occurs, the oil pressure flowing from the exhaust rocker shaft into the main exhaust rocker arm forces the VTEC piston to switch to the secondary rocker exhaust, thus locking both rocker exhaust arms together. The high-profile camshaft hole that normally exhausts the secondary rocker's exhaust during the operation of a low RPM machine is capable of moving the two shared exhaust sleeves that are locked as one unit. The same is true for rocker intakes, except that the high-profile camshaft lobe operates the primary rocker arm.
The J37A4 is capable of using VTEC's intakes and exhausts using the new design of the rocker arm intake. Each exhaust valve on J37A4 corresponds to one exhaust rocker primary and one secondary. Therefore, there are a total of twelve main exhaust rocker arms and twelve secondary exhaust rocker arms. However, each secondary artificial rocker arm shaped similarly to "Y" which allows it to contact two intake valves at once. One arm of the primary intake rocker corresponds to each arm of the secondary intake rocker. As a result of this design, there are only six main rocker intakes and six arms of secondary intake rockers.
VTEC-E
The earliest implementation of VTEC-E was a variation of SOHC VTEC used to improve combustion efficiency at low RPM while maintaining mid-range performance from non-vtec engines. VTEC-E is the first version of VTEC using the use of a rocker roller arm and therefore, it forgets the need to have 3 intake lobes to drive two valves - two lobes for non-VTEC operation (one small and one medium lobe) and one lobe for VTEC operation (largest lobes). In contrast, there are two different profiles of cam intake per cylinder: a very light cam lobe with slightly lift and normal cam leves with medium lifting. Because of this, at low RPM, when VTEC is not involved, one of the two intake valves is allowed to open only a very small amount due to the lightweight cam lobe, forcing most of the intake costs through other open entrance valves with normal cam lobes. This induces the rotation of the intake charge which increases the air/fuel atomization in the cylinder and allows for a slimmer fuel mixture to be used. As machine speed and load increases, both valves are required to supply a sufficient mixture. When using VTEC mode, the pre-determined threshold for MPH (must move), RPM and load must be met before the computer drives the solenoid that directs the pressurized oil to the sliding pin, as with the original VTEC. The sliding pin connects the intake follower rocker arm together so that, now, the two intake valves follow the "normal" camshaft lobe, not just one of them. When in VTEC, since the "normal" cam lobe has the same time and is lifted as a cam-intake lobe from a non-VTEC SOHC engine, both machines have identical performance in the upper powerband assuming the other is the same.
With VTEC-E implementation then, the only difference with the previous VTEC-E is that the second normal cam profile has been replaced with a more aggressive cam profile that is identical to the original high speed VTEC cam profile. This essentially replaces VTEC and previous VTEC-E implementations because of the fuel and low torque benefits of the previous VTEC-E combined with the original high performance VTEC.
VTEC 3-Stage
3-Stage VTEC is a version that uses three different cam profiles to control the time and lift the intake valve. Since this version of VTEC is designed around the SOHC valve head, space is limited; so VTEC can only modify the opening and closing of the intake valve. The improved VTEC-E low-end fuel economy and conventional VTEC performance are incorporated in this application. From idle to 2500-3000Ã, RPM, depending on load conditions, one intake valve is fully open while others open slightly, enough to prevent fuel pooling behind the valve, also called 12-valve mode. This 12 Valve mode produces an intake charge spin which improves the combustion efficiency, resulting in lower lower torque and better fuel economy. At 3000-5400 RPM, depending on the load, one of the VTEC solenoids is involved, which causes the second valve to lock into the first camshaft lobe of the valve. Also called 16-valve mode, this method resembles the normal machine operating mode and increases the mid-range power curve. At 5500-7000 RPM, the second VTEC solenoid is involved (both solenoids are now involved) so that the two intake valves use the third, middle camshaft lobe. The third lobe is set to high performance and provides peak power at the upper end of the RPM range.
i-VTEC
Honda i-VTEC (intelligent-VTEC) is a system that combines VTEC with Honda VTC (Variable Timing Control), a continuous variable camshaft staging system used on the DOHC VTEC engine intake camshaft. This technology first appeared in the family of Honda K-series four-cylinder engine in 2001 (2002 in the US). In the United States, this technology made its debut on the K24A1 engine at Honda CR-V 2002.
VTEC controls from valve lift and valve duration are still limited to different low and high RPM profiles, but the intake camshaft is now capable of advancing between 25 and 50 degrees, depending on engine configuration. Phasing is applied by cam-controlled cam sprocket, which is controlled by oil. Both machine load and RPM affect VTEC. The intake phase varies from fully backward when idle to slightly advanced at full speed and low RPM. The effect is the further optimization of torque output, especially in low and medium RPMs. There are two types of i-VTEC K series engines described in the next section.
The SOHC J-Series Honda'a engine uses a completely different system, confusing, marketed as i-VTEC. Honda J-Series engine using i-VTEC combines VTEC SOHC operation with Honda VCM (Variable Cylinder Management) variable displacement technology to improve fuel economy under light load.
K-series
K-Series engines have two different types of i-VTEC system implementations. The first type is for performance machines such as K20A2 or K20Z3 used in RSX Type S 2002-2006 or Si Civic 2006-2010 and the second type is for economic machines such as K20A3 or K24A4 used in Civic Si 2002-2005 or 2003-2007 Agreement. The performance of the i-VTEC system is essentially the same as the DOHC VTEC system of B16A. Intake and exhaust cams have 3 cam lobes per cylinder. However, valvetrain has the added benefit of roller rocker and VTC continuously variable time cam intake. The i-VTEC performance is a combination of conventional DOHC VTEC with VTC (which operates only for intake valves). VTC is available in economy and i-VTEC engine performance.
The i-VTEC economy used in K20A3/K24A4 engines is more like SOHC VTEC-E because cam intake has only two lobes, one is very small and one is larger, and there is no VTEC on the exhaust cam. At low RPMs only one valve on the intake is fully open, promoting the swirl of the combustion chamber and enhanced fuel atomization. This allows a slimmer air/fuel mixture to be used, improving fuel economy. At higher RPMs, both intake valves run from the larger incoming cam lobe, increasing total airflow and top-end power.
Both types of engines are easily distinguished from the power outputs rated by the manufacturer: performance engines produce about 200 hp (150 kW) or more in stock, while the engine does not make more than 160 hp (120 kW).
R-series
System i-VTEC engine R-Series SOHC VTEC system uses a modified consisted of one small and two large lobes. Large lobes operate intake valves directly while the small lobes move during VTEC. Unlike a typical VTEC system, the system in the R-Series machines operate in 'reverse' involved only in the low to mid RPM. At low RPMs, lock the small lobe into one of the larger lobes and make one of the valve intakes partially open during the compression cycle, similar to the Atkinson Cycle. Honda's ability to switch between Atkinson cycles and normal cycles allows excellent fuel efficiency without sacrificing too much performance.
i-VTEC with Variable Cylinder Management (VCM)
In 2003, Honda introduced the i-VTEC V6 (an update of the J-series) that included the Honda cylinder disabling technology that closes the valve on a bank (3) cylinder during light and low-speed loads (under 80 km/h (50 mph) ) operation. According to Honda, "VCM technology works on the principle that vehicles require only a fraction of the power output at cruising speeds.The system electronically disables the cylinder to reduce fuel consumption.This machine can run at 3, 4, or all 6 cylinders based on power requirements, basically getting the best of both worlds. Power V6 while accelerating or climbing, as well as smaller engine efficiency while sailing. "The technology was originally introduced to the US in the 2005 Honda Odyssey minivan, and now can be found on the Honda Accord Hybrid, the 2006 Honda Pilot , and Honda Accord 2008. Example: Estimated EPA for Accord V6 2011 (271 hp SOHC 3.5L) is a combined 24 mpg vs. 27 in two models equipped with 4-cylinder.
i-VTEC VCM is also used in the 1.3 liter LDA engine used in the Honda Civic Hybrid 2001-2005.
i-VTEC i
The i-VTEC version with direct injection, was first used on the 2004 Honda Stream. Direct injection 2.0L DOHC i-VTEC I gasoline engine.
DOHC 2-liter i-VTEC I integrates i-VTEC systems using VTEC and VTC using direct injection systems for up to 65: 1 fuel-to-air ratio for unprecedented ultra-thin burning rates. Stable combustion is achieved by using less fuel than a conventional direct injection engine that has a 40: 1 fuel-air ratio.
The oCombustion control through the use of high precision EGR valves and newly developed high performance catalysts enable the 2.0 liter DOHC i-VTEC I lean-burn direct injection engine that qualifies as an Ultra Low Emissions Vehicle.
AVTEC
AVTEC engine (Advanced VTEC) was first announced in 2006. It combines continuous variable valve lifts and time settings with continuous variable phase controls. Honda originally planned to produce vehicles with AVTEC engines in the next 3 years. Although it is speculated that it will be used for the first time in 2008 Honda Accord, this vehicle instead uses an existing i-VTEC system. By the end of 2017, no Honda vehicles are using the AVTEC system.
Associated US Pat. (6,968,819) filed on 2005-01-05.
VTEC TURBO
The VTEC TURBO engine series was introduced in 2013 as part of the Earth Dreams Technology range and includes new features such as direct injection of gasoline, turbochargers, and Dual Cam VTC. Turbo VTEC engine comes in three displacement capacities: 1 liter 1.0 liter, 1.5 liter 4-cylinder, and 2.0 liter 4-cylinder.
Initial implementation for European vehicles includes a 4-cylinder 2-liter engine used in the Honda Civic Type R, which includes Euro 6 emissions compliance.
VTEC in a motorcycle
Apart from the Honda CB400SF Super Four HYPER VTEC which is specialized in the Japanese market, introduced in 1999, the application of VTEC technology in the world's first in the world of motorcycles occurred with the introduction of Honda VFR800 motor sport in 2002. Similar to the style SOHC VTEC-E, one the intake valve remains closed until the 7000 RPM limit is reached, then the second valve is opened by the oil pressure regulator pin. The residence of the valve remains unchanged, as in the VTEC-E car, and a little extra power is generated, but with a smooth torque curve. Critics maintain that VTEC adds a bit of VFR experience, while increasing the complexity of the machine. Honda seems to agree, because their VFR1200, the model announced in October 2009, came to replace the VFR800, which abandoned the VTEC concept that supports a large capacity of narrow "unicam", ie , SOHC, engine. However, VFR800 2014 reintroduces VTEC system from VFR motorcycle 2002-2009.
Honda incorporated technology into the NC700 series, including the Integra NC700D, released in 2012, using a single camshaft to provide two time routines for the intake valve.
References
- General
External links
- Honda technology pages: VTEC, i-VTEC DOHC, S2000 2.0L DOHC VTEC, Type-R 2.0L DOHC i-VTEC, 2.0L DOHC i-VTEC I, V6 3.0L i-VTEC, V6 3.5 L VTEC
- Honda Technology Picture Book, VTEC
- Honda World: New i-VTEC Technology
- Ã,¿Is Honda VTEC?
Source of the article : Wikipedia
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