what is difference between sohc,dohc, and vtec?

Question

needs to be detailed. thank you for your answer!

Answer 1

VTEC (standing for Variable valve Timing and lift Electronic Control
* Single overhead camshaft (SOHC)
* Double overhead camshafts (DOHC)
Introduction to VTEC


In the regular four-stroke automobile engine, the intake and exhaust valves are actuated by lobes on a camshaft. The shape of the lobes determines the timing, lift and duration of each valve. Timing refers to when a valve is opened or closed with respect to the combustion cycle. Lift refers to how much the valve is opened. Duration refers to how long the valve is kept open. Due to the behavior of the gases (air and fuel mixture) before and after combustion, which have physical limitations on their flow, as well as their interaction with the ignition spark, the optimal valve timing, lift and duration settings under low RPM engine operations are very different from those under high RPM. Optimal low RPM valve timing, lift and duration settings would result in insufficient fuel and air at high RPM, thus greatly limiting engine power output. Conversely, optimal high RPM valve timing, lift and duration settings would result in very rough low RPM operation and difficult idling. The ideal engine would have fully variable valve timing, lift and duration, in which the valves would always open at exactly the right point, lift high enough & stay open just the right amount of time for the engine speed in use.

In practice, a fully variable valve timing engine is difficult to design and implement. Attempts have been made, using solenoids to control valves instead of the typical springs-and-cams setup, however these designs have not made it into production automobiles as they are very complicated and costly.

The opposite approach to variable timing is to produce a camshaft which is better suited to high RPM operation. This approach means that the vehicle will run very poorly at low rpm (where most automobiles spend much of their time) and much better at high RPM. VTEC is the result of an effort to marry high RPM performance with low RPM stability.

Additionally, Japan has a tax on engine displacement, requiring Japanese auto manufacturers to make higher-performing engines with lower displacement. In cars such as the Supra and 300ZX, this was accomplished with a turbocharger. In the case of the RX-7, a wankel rotary engine was used. VTEC serves as yet another method to derive very high specific output from lower displacement motors.


DOHC VTEC

Honda's 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, with the other designed to maximize high RPM power output. Switching between the two cam lobes is determined by engine oil pressure, engine temperature, vehicle speed, and engine speed. As engine RPM increases, a locking pin is pushed by oil pressure to bind the high RPM cam follower for operation. From this point on, the valve opens and closes according to the high-speed profile, which opens the valve further and for a longer time. The DOHC VTEC system has high and low RPM cam lobe profiles on both the intake and exhaust valve camshafts.

The VTEC system was originally introduced as a DOHC system in the 1989 Honda Integra sold in Japan, which used a 160 hp (119 kW) variant of the B16A engine. The US market saw the first VTEC system with the introduction of the 1990 Acura NSX, which used a DOHC VTEC V6. DOHC VTEC motors soon appeared in other vehicles, such as the 1992 Acura Integra GS-R.

SOHC VTEC

As popularity and marketing value of the VTEC system grew, Honda applied the system to SOHC engines, which shares a common camshaft for both intake and exhaust valves. The trade-off is that SOHC engines only benefit from the VTEC mechanism on the intake valves. This is because in the SOHC engine, the spark plugs need to be inserted at an angle to clear the camshaft, and in the SOHC motor, the spark plug tubes are situated between the two exhaust valves, making VTEC on the exhaust impossible.

SOHC VTEC-E

Honda's next version of VTEC, VTEC-E, was used in a slightly different way; instead of optimising performance at high RPMs, it was used to increase efficiency at low RPMs. At low RPMs, only one of the two intake valves is allowed to open, 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, as in the regular VTEC, is used to connect both valves together and allows opening of the second valve.


3-Stage VTEC

Honda also introduced a 3-stage VTEC system in select markets, which combines the features of both SOHC VTEC and SOHC VTEC-E. At low speeds, only one intake valve is used. At medium speeds, two are used. At high speeds, the engine switches to a high-speed cam profile as in regular VTEC. Thus, both low-speed economy and high-speed efficiency and power are improved.


i-VTEC

i-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.). 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 maximum advance at full throttle and low rpms. The effect is further optimization of torque output, especially at low and midrange RPMs.

In 2004, Honda introduced an i-VTEC V6 (an update of the venerable J-series), but in this case, i-VTEC had nothing to do with cam phasing. Instead, i-VTEC referred to Honda's cylinder deactivation technology which closes the valves on one bank of (3) cylinders during light load and low speed (below 80 mph) operation. The technology was originally introduced to the US on the Honda Odyssey Mini Van, and can now be found on the Honda Accord Hybrid and the 2006 Honda Pilot. An additional version of i-VTEC was introduced on the 2006 Honda Civic's R-series four cylinder engine. This implementation uses very small valve lifts at low rpm and light loads, in combination with large throttle openings (modulated by a drive-by-wire throttle system), to improve fuel economy by reducing pumping losses.

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.


Turbocharged VTEC

For 2007 models, Honda's Acura luxury division announced the RDX crossover SUV which will feature a new turbocharged 2.3 litre inline 4 cylinder i-VTEC engine. While Honda has used turbochargers before (previous examples include the Honda City Turbo and City Turbo II), this is a first for its Acura division.

VTEC in motorcycles

Apart from the Japanese market-only Honda CB400 Super Four Hyper VTEC, introduced in 1999, 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. Drivability is a concern for some who are wary of the fact that the VTEC may activate in the middle of an aggressive corner, potentially upsetting the stability and throttle response of the bike.

Answer 2

VTEC - Valve Timing(and Lift ) Electronically controlled. I-vtec is the same thing, but with VTC. Also known as Variable Cam phasing. I don't know why im going to sit here and actually type this out, but luckily I type pretty quick.. With a VTEC motor, at all times of acceleration 4 valves work per cylinder. With an I-VTEC motor, Below VTEC both Exhaust valves work and only 1 intake valve opens. This causes more suction from the one intake valve being open which also causes all the air that gets sucked in to be sucked in with a spirial like motion. The gas is then distributed through the combustion chamber more evenly. Creating better low end torque gains. This one intake valve working motion is known as VTC or Variable Cam Phasing. When VTEC is crossed over to the other intake valve opens and all 4 valve work. I've understood that the older VTEC just has the high-lift cam switchover, and the newer i-VTEC adds continuously variable cam phasing. Plus, the cam changeover RPM can vary depending on throttle position and whatnot; I'm not sure if that's only on i-VTEC or if it was also on the older versions of VTEC too. While the EP3's A3 motor doesn't have a high-lift cam for high RPM's (the 2200 rpm switch between 12 and 16 valves is for different reasons), it does advance/retard the cams' overlap as needed throughout the RPM range.

Answer 3

SOHC, mean single overhead Cam, DOHC means Double overhead cam, Vtec stands for Variable Timing and Lift electronic control. Basically all of these things deal with the amount of Horse power ur engines. VTEC is hondas way saying the same thing as SOHC & DOHC

Answer 4

SOHC is a single overhead cam,
DOHC is dual overhead cams (2 camshafts)
and Vtec is a variable valve timing system which is a 2 stage cam. It starts out on the lower profile for normal driving, and when the engine gets to a certain RPM it switches to the higher profile cam.

THeres also QOHC in some higher valve V engines, and various other kinds of Variable valve timing (like PiVVT aka porsche infinately variable valve timing)

Answer 5

the cam is what opens and closes the valves to let air/fuel/exhaust in and out of the engine cylinders.

sohc = single overhead cam, has one cam that operates all the valves for all cylinders.

dohc = double overhead cam, has two cams for each head (where the head is a group of cylinders). This is usually in engines with 4+ valves on each cylinder, where a single cam couldnt possibly operate all the valves at once.

vtec = variable valve timing and lift electronic control, which is an electronic system that allows the engine to use different parts of the camshaft so that the shape of the cam is best suited to engine RPM. The cam's shape determines which RPM it performs best at, so varying the shape allows a wider range of efficient performance.

See this article for more about cams.
http://auto.howstuffworks.com/camshaft.htm

Answer 6

sohc is single overhead camshaft
dohc is double overhead camshaft
vtec is honda's answer to the most basic disadvantage of a turbocharged engine, which is bad fuel economy. vtec allows the engine to extract turbo level specific output without eating up too much fuel. vtec has its own disadvantages, but for the pennywise, it's a godsend.

Answer 7

sohc single overhead cam
dohc dual overhead cam
v-tec variable timing electric cam

vtecs work like a regular engine until a certain rpm range is reached , then the valves(intake and exhaust are controlled by computer instead of a cam

Answer 8

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RE:
what is difference between sohc,dohc, and vtec?
needs to be detailed. thank you for your answer!

Answer 9

SOHC is single overhead cam (the camshaft for an engine)

DOHC is double overhead cam. I think this one is more powerful.

Vtec I don't know.

Answer 10

sohc (single over head cam) this is small engine.. like the regular civics. But the dohc(double over head cams) are more power full engines like, the ACURAs, and the civic Si. VTEC(variable timing electronic control) HONDAs and ACURAs has this...not a days the accord start having DOHC in their engine, give more a little bit more boost and fuel effiency

Answer 11

sohc or single over head cam is an internal combustion engine that has one cam, placed over the pistons to run the valves. a dohc or dual over head cam is the same principle, only two cans running twice as many valves. a vtec engine has an electronic cam that when you hit a certain rpms on the engine it opens the valves longer, or changes the duration of the valve opening