(Redirected from V6)
A 'V6 engine' is a
V engine with six
cylinders. It is the second most common engine configuration in modern cars after the
inline four. It is one of the most compact engine configurations and is well suited to the popular
front-wheel drive layout. It is becoming more common as the space allowed for engines in modern cars is reduced at the same time as power requirements increase, and has largely replaced the
inline-6, which is too long to fit in most modern engine compartments.
The first V6 was introduced by
Lancia in
1950 with the
Lancia Aurelia. Other manufacturers took note and soon other V6 engines were in use. In 1959,
GMC introduced a heavy duty 305
cubic inch (5
liter) 60-degree V6 for use in their pickup trucks and Suburbans, an engine design that was later enlarged to 478 cubic inches (7.8 liters) for heavy truck and bus use.
The design really took off after the 1962 introduction of the
Buick Special, which offered a 90 degree V6 with an uneven firing intervals that shared some parts commonality with a small Buick
V8 of the period. Though the
Buick Special was not a major success due to its excessive vibration, it was the first instance of a mass-produced V6 engine designed specifically for passenger automobiles. In 1983 Nissan produced Japan's first V6 engine with the
VG series.
Modern V6 engines commonly range in
displacement from 2.5 L to 4.0 L, though
larger and smaller examples have been produced.
Balance and smoothness
Due to the odd number of cylinders in each bank, V6 designs are inherently unbalanced and can benefit from some auxiliary
counterbalancing. A V6 is basically two
straight-3 engines running on the same crankshaft, and since the straight-3 suffers from a
dynamic imbalance which causes an end-to-end rocking motion, the V6 also suffers from the same problem. Unlike the V8, the V6 cannot be laid out so that the vibrations from the two banks cancel each other or can be offset by counterweights on the crankshaft. This vibration is particularly bad in V6s derived from V8 engines with a 90 degree angle between cylinder banks. As a result, V6s can develop significant odd-order
harmonic crankshaft
vibrations, which can be counteracted by the use of a heavy duty harmonic damper to avoid possible crankshaft failure at higher engine speeds. These vibrations can be reduced significantly by using more sophisticated crankshaft designs, and can be eliminated completely by adding a balance shaft. Unlike a straight-4 engine, which requires two balance shafts rotating in opposite directions at twice crankshaft speed to cancel its vibrations, a V6 needs only one rotating at crankshaft speed, which can be nestled between the cylinder banks in an
overhead camshaft design.
Six-cylinder designs are more suitable for larger displacement engines than straight-4s because the power strokes of pistons overlap. Since each power stroke lasts 180 degrees of crankshaft rotation, while a new piston starts its power stroke every 120 degrees, there are 60 degrees of overlap on each stroke in which one piston is finishing while the next is starting. This results in a smoother delivery of power than a four cylinder engine, in which each piston must come to a complete stop before the next piston commences its power stroke.
Modern
computer-aided design (CAD) techniques allow modern V6 engines to be designed to have far fewer vibration problems than older engines had, which is a major reason for their increase in popularity in recent years. As a result, V6 engines are generally used in mid-range cars where a big straight-4 would have too much vibration, and a V8 would be too large and expensive for the market.
V angles
60 degrees
The most efficient cylinder bank angle for a V6 is 60 degrees, which design is very compact and tends to minimize vibrations. 60 degree V6 engines do not usually require balance shafts to be acceptably smooth. While they are not as well balanced as
inline-6 and
flat-6 engines, modern techniques for designing and mounting engines have largely disguised their vibrations. The most common 60-degree V6s were built by
General Motors (the heavy duty commercial models, as well as a design used in many GM front wheel drive cars) and
Ford European subsidiaries (
Essex V6,
Cologne V6 and the more recent
Duratec V6). Other 60-degree V6 engines are the
Nissan VQ engine and the
Alfa Romeo V6 engine.
90 degrees
90-degree V6 engines are also produced, usually so they can use the same production-line tooling set up to produce
V8 engines (which normally have a 90-degree V angle). Although it is relatively easy to derive a 90-degree V6 from an existing V8 design by simply cutting two cylinders off the engine, this tends to make it wider and more vibration-prone than a 60-degree V6. The design was first used by
Buick when it introduced its
198 in³ ''Fireball V6'' as the standard engine in the
1962 Special. Other examples include the
Maserati V6 used in the
Citroën SM, the
PRV V6,
Chevrolet's
4.3 L ''Vortec 4300'' and
Chrysler's
3.9 L ''Magnum V6'' and
3.7 L ''PowerTech V6''. The Buick V6 was notable because it introduced the concept of uneven firing, as a result of using the 90 degree V8 cylinder angle without adjusting the crankshaft design for the V6 configuration. These engines were often referred to by mechanics as "shakers," due to the tendency of the engine to bounce around at idle speed. More modern 90-degree V6 engine designs avoid these vibration problems by using crankshafts with offset split crankpins to make the firing intervals even, and often add balancing shafts to eliminate the other vibration problems. An example is the 90-degree Mercedes-Benz V6 which, although designed to be built on the same assembly lines as the V8, uses split crankpins, a counter-rotating balancing shaft, and careful acoustic design to make it as smooth and quiet as the inline-6 it replaced.
120 degrees
120 degrees might be described as the ''natural'' angle for a V6 since the cylinders fire every 120 degrees of crankshaft rotation. However, this layout produces an engine which is too wide for most automobile engine compartments, so it is seldom used in cars. The 180-degree
flat-6 ''boxer'' engine is only moderately wider, and unlike the V6 is a fully-balanced configuration with no vibration problems, so it is more commonly used in aircraft and in cars where space allows.
The 120° V220/V300T V6 engines were designed by
Bombardier for use in light aircraft. This layout allows for a shorter crankshaft and a more compact engine. It also allows for the use of a firing order that is in harmony with the layout, unlike the opposed (180 degree) 6 cylinder engines it is meant to replace.
Other angles
Narrower angle V6 engines are very compact but can suffer from severe vibration problems unless very carefully designed. Notable V6 bank angles include:
★ The 10.6° and 15°
Volkswagen VR6, which is such a narrow angle it can use a single cylinder head and double overhead camshafts for both cylinder banks. With 7 main bearings, it is more like a staggered-bank in-line six rather than a normal V6, but is only slightly longer and wider than a straight-4.
★ The 45°
Electro-Motive 6 cylinder version of their model 567
Diesel locomotive engine.
★ The 54°
GM/Opel V6, designed to be narrower than normal for use in small
front-wheel drive cars.
★ The 65°
Ferrari Dino V6. A 60° angle limited the size of the carburetors which originally used in the engine, while a 65° angle allowed larger carburetors at the expense of a slight increase in vibrations.
Odd and even firing
Many older V6 engines were been based on
V8 engine designs, without altering the V angle or using a more sophisticated crankshaft to even out the firing interval. One characteristic of these engines was a notorious ''odd-firing'' behavior.
Purpose-built V6 engines use one
crankpin per cylinder for an even 120° ignition pattern. In contrast, most V8 engines share a common crankpin between opposite cylinders in each bank. That is, the
crankshaft has just four pins for eight cylinders, and a cylinder fires every 90° for smooth operation.
V6 engines derived from V8 engines often have three shared crankpins arranged at 120° from each other, similar to an
inline 3-cylinder, with two pistons per crankpin. If the cylinder banks are arranged at 90° (as they commonly are in V8-derived V6s), this leads to a firing pattern with groups of two cylinders separated by 90° of rotation, and groups separated by 150° of rotation.
An example is the
Buick 231 odd-fire, which has a
firing order 1-6-5-4-3-2. As the crankshaft is rotated through the 720° required for all cylinders to fire, the following events occur on 30° boundaries:
| 'Angle' | 0° | 90° | 180° | 270° | 360° | 450° | 540° | 630° |
| 'Odd firing' | 1 | 6 | 5 | 4 | 3 | 2 | ||
| 'Even firing' | 1 | 6 | 5 | 4 | 3 | 2 | ||||||||
Nissan uses the firing order 1-2-3-4-5-6 in some of the V6 engines they make.
In
1977,
Buick introduced a new "split-pin crankshaft" in the
231. Using a crankpin that is 'split' and offset by 30° of rotation resulted in smooth, even firing every 120°. However, in
1978 Chevrolet introduced a 90° 200/229 V6, which had a compromise 'semi-even firing' design using a crankpin that was offset by only 18°. This resulted in cylinders firing at 108° and 132°, which had the advantage of reducing vibrations to a more acceptable level and did not require strengthening the crankshaft. In
1985 Chevrolet changed it to a true even-firing V6 with a 30° offset, requiring larger crank journals to make them adequately strong.
In
1986 the similarly-designed 90°
PRV engine adopted the same 30° crankshaft offset design to even out its firing. Most recent 90° V6 designs use split crankpins to even out the firing intervals. Such a 'split' crankpin is weaker than a straight one, but modern
metallurgical techniques can produce a crankshaft that is adequately strong.
Racing use
The V6 engine was introduced into racing by the
Ferrari Dino V6.
Alfredo Ferrari (nicknamed Dino), the only legitimate son of
Enzo Ferrari, suggested to him the development of a 1.5 L
DOHC V6 engine for
Formula Two at the end of
1955. Soon afterwards, Alfredo fell ill, suffering from
muscular dystrophy. While in hospital, he discussed technical details with the engineer
Vittorio Jano. Dino would never see the engine; he died on 30 May 1956 at the age of 24.
The Dino V6 underwent several evolutions, including an increased
engine displacement to 2417 cc, for use in the
Ferrari 246 Formula One car in 1958.
[1][2]
The use of a wide 120° bank angle is appealing for racing engine designers as it permits a low
center of gravity. This design is even considered superior to the
flat-6 in that it leaves more space under the engine for exhaust pipes; thus the crankshaft can be placed lower in the car. The
Ferrari 156 built for new Formula One 1.5 L regulations used a Dino V6 engine with this configuration.
[3]
The Dino V6 engine saw a new evolution in
1966 when it was adapted to road use and produced by a Ferrari-Fiat joint-venture for the Fiat Dino and Dino 206 GT (this car was made by Ferrari but sold under the brand Dino). This new version was redesigned by
Aurelio Lampredi initially as a 65° 2.0 L V6 with an aluminum block but was replaced in
1969 by a 2.4 L cast-iron block version (the Dino car was renamed the 246GT).
The Fiat Dino and Dino 246GT were phased out in 1974, but 500 engines among the last built were delivered to
Lancia, who was like Ferrari already under the control of
Fiat. Lancia used them for the
Lancia Stratos which would become one of the most successful
rally cars of the decade.
The
Alfa Romeo V6 was designed in the 1970's by
Giuseppe Busso, the first car to use them being the
Alfa Romeo 6. The over-square V6, with aluminium alloy block and heads, has seen continuous use in road vehicles, from the
Alfetta GTV6 onwards. The 164 introduced a 3.0L V6, and in
1992, a 3.0L DOHC 24 valve version. The
Alfa 156 introduced a 2.5 L DOHC 24 valve version in
1997. The engine capacity was later increased to 3.2L, where it found application in the 156 GTA, 147 GTA and the Alfa GT. Production was discontinued in 2005.
Another influential V6 design was the
Renault-
Gordini CH1 V6, designed by
François Castaing and
Jean-Pierre Boudy, and introduced in
1973 in the
Alpine-Renault A440. The CH1 was a 90°
cast iron block V6, similar to the mass produced PRV engine in those two respects but otherwise dissimilar. It has been suggested that marketing purposes made the Renault-Gordini V6 adopt those characteristics of the PRV in the hope of associating the two in the public's mind.
Despite such considerations, this engine won the European 2 L prototype championship in
1974 and several European
Formula Two titles. This engine was further developed in a tubocharged 2 L version that competed in Sports car and finally won the
24 Hours of Le Mans in 1978 with a Renault-Alpine A 442 chassis.
The capacity of this engine was reduced to 1.5 L to power the Formula One Renault RS01. Despite frequent breakdowns that resulted in the nickname of the 'Little Yellow Teapot', the 1.5 L finally saw good results in 1979.
Ferrari followed Renault in the turbo revolution by introducing a turbocharged derivative of the Dino design (a 1.5 L 120° V6) with the Ferrari 126.
[4] However, the 120° design was not considered optimum for the
wing cars of the era and later engines used V angles of 90° or less.
Both Renault and Ferrari failed in their attempt to win the Drivers's Championship with V6 Turbo engines. The first turbocharged engine to win the championship was the
Straight-4 BMW.
They were followed by a new generation of Formula One engines, the most successful of these being the TAG V6 (designed by
Porsche) and the
Honda V6. This new generation of engines were characterized by odd V angles (around 80°). The choice of these angles was mainly driven by aerodynamic consideration. Despite their unbalanced designs these engines were both quickly reliable and competitive; this is generally viewed as a consequence of the quick progress of CAD techniques in that era.
Notes
1. Ferrari 246 F1 on www.f1technical.net
2. Ferrari engines on www.allf1.info
3. Ferrari Dino 156 F1 on www.f1technical.net
4. Ferrari 126CK on www.f1technical.net
External links
★
Understanding the odd-fire V6
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