Information AboutStraight-6 |
| CATEGORIES ABOUT STRAIGHT-6 | |
| piston engine configurations | |
| straight-06 | |
| motorcycle engines | |
|
The straight-6 (also '''inline-6''', '''I-6''', or '''I6''') is an Internal Combustion Engine with six cylinders aligned in a single row. The name '''slant-6''' is sometimes used when the cylinders are at an angle from the vertical. Usually a straight-6 was used for Engine Displacement s between about 2.5 and 4.0 L. It was also sometimes used for smaller engines but these, although very smooth running, tended to be rather expensive to manufacture and they were inevitably physically longer than alternative layouts. The smallest production straight-6 was found in the Benelli 750 Sei motorcycle, displacing 747.7 cc (0.75 L / 45.6 Cu in ). The largest are used to power ships and have displacements of 1,000 L or more. Straight-6 engines were historically more common than V6 s, mainly because the length of such engines was not such a concern in rear wheel drive vehicles, but also because V6s (unlike the Crossplane V8 ) of the time were difficult to run smoothly. The widespread use of front-wheel-drive and Transverse Engine ("east-west") configurations in smaller cars saw that the shorter engine length of the V6 became highly desirable, and currently most six-cylinder engines are made in the V configuration. BALANCE AND SMOOTHNESS Straight-6 Four-stroke Cycle engines are in perfect primary and secondary Balance and require no Balance Shaft . They are in primary balance because the two ends of the engines are mirror images of each other and the cylinders move up and down in pairs, one on the compression stroke and the other on the exhaust stroke. Piston #1 balances #6, #2 balances #5, and #3 balances #4, canceling the end-to-end rocking motion that would otherwise result. (This does not apply to Two-stroke Cycle engines.) Secondary imbalance occurs in Straight-4 engines because the two pistons on the upper 180 degrees of the crankshaft rotation move faster than the two pistons on the lower 180 degrees, creating an unequal motion. Straight-6 engines have cranks at 120 degrees to each other, so the differences in speed on different parts of the crankshaft rotation are offset by the changing number of pistons on each portion. The straight-6 is also smoother than engines with a fewer number of cylinders 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 smooth delivery of power, unlike a four cylinder engine in which each piston must come to a complete stop before the next piston commences its power stroke. This makes the straight-6 engine's delivery of power much smoother than a four-cylinder engine. This is the reason why 60 degree and 180 degree V12 Engine s are considered optimal for smooth power delivery; they allow for complete overlap of the power stroke between three cylinders at all time due to interleaving the overlap from their two component straight-6 banks. Eight cylinder engines also have even more power stroke overlap than six cylinder ones, but the improvement in smoothness is not as pronounced. STRAIGHT-6 ENGINES IN EUROPE BMW is a persistent maker of straight-6 Petrol and Turbo - Diesel Engine s, displacing from 2.0 to 3.8 L (122–231 cu in) ( As Of 2005 . Since BMW drivetrains are rear wheel drive, the straight-6 can mount lengthwise; therefore the width of the engine is not an issue. Volvo produced straight-6 engines like the Volvo B30 Engine for the Volvo 164 (1969-1975) and the B6304 engine for the 960/S90 ( RWD ). All vehicles in the Volvo lineup are front-wheel (or all wheel) driven thereafter, and yet, Volvo made it possible to mount their inline-6 engine transversely by using a very short Transaxle package and relocated engine-driven accessories. In 2006, Volvo announced a new 3.2 L straight-6 for the Volvo S80 that was only slightly longer than its straight-5, achieved by moving the camshaft drive to the back of the engine and sharing the same gear train with ancillaries mounted in otherwise unused space over top of the transmission. This resulted in a package that was not only extremely short for a straight-6, but also very narrow. Volvo says a transversely mounted inline engine leaves more crush space to protect against frontal impacts than a (shorter) transverse V6 or a longitudinally mounted inline-6. Mercedes-Benz built straight-6 engines as Gas and Diesel , but now prefers the V6 layout for its line of gasoline engines, while reserving the straight-6 for medium duty diesel applications, such as the MBE 906. (See List Of MB-engines ) Opel has also used a straight-6 engine in the 1970s until the early 1990s, ranging between 2.5 and 4.0 L (153–242 cu in). They powered Opel's top of the line models, including the Monza , the Omega and the Commodore . In 1959 , Saab had an experimental car with two transverse Straight-3 engines bolted together — the Saab Monster . Alfa Romeo used straight-6 engine in RL model (1922–1927) and between 1925–1954 in Alfa Romeo 6C series road and racing cars, the 1500 version had one of the smallest straight-6 engines (1487 cc). The last Alfa Romeo model using straight-6 was Alfa Romeo 2600 (1961–1969). STRAIGHT-6 ENGINES IN BRITAIN The straight-6 was the archetypal British engine for sports and luxury cars for many years. Rolls-Royce used straight-6 engines until changes in their design made the shorter V8 layout more suitable. Jaguar used them from 1949 until the mid-1990s, starting with the legendary twin-camshaft Jaguar XK6 Engine , followed by the AJ6 And AJ16 Engines . After Jaguar was acquired by Ford, they replaced these engines with the Ford Duratec -derived Jaguar AJ-V6 Engine . Aston Martin used a straight-6 for many years, as did Austin-Healey in their Austin-Healey 3000 . MG also used a straight-6 in their MGC . Bristol produced a straight-6 until 1961, based on a BMW design, that was also used by many small automakers. The compact Triumph straight-6 powered their high-end saloon and sports cars from the mid-1950s to the mid-1970s. It was available in 2.0 L and 2.5 L capacities. Triumph claimed that their TR5 model was the first car in the UK to come with fuel injection as standard; the TR5 has a 2.5 L Triumph straight-6. Other Triumph vehicles to use the Triumph straight-6 are:-
British sports car company TVR designed its own straight-6, known as the Speed Six , which powers its current range of cars. Land Rover used a 2.6 L (~159 cu in) straight-6 from 1967 in certain series Land Rover models. STRAIGHT-6 ENGINES IN THE UNITED STATES Engines of this type were popular before World War II in mid-range cars. Most manufacturers started building straight-6 engines when cars grew too large for the Straight-4 . After World War II , larger cars required larger engines, and buyers of larger cars tended to prefer V8s; performance sixes such as the Hudson Hornet engine were exceptions to the rule, and were not often top sellers. After Chevrolet introduced its V8 in 1955, the straight-6 became almost exclusively a base engine model pitched to economy-minded customers. Trucks (both light and heavy duty) also incorporated the straight-6 until the mid-1950s. The new wave of compact cars that started in the late 1950s provided a suitable home for straight-6 designs. The Chrysler Corporation had noteworthy Slant-6 Engines , used in the Plymouth Valiant and Dodge Dart A-body models of the 1960s and 1970s. This engine was extremely reliable and achieved some success in racing after engineers discovered that the 30-degree slant of the engine allowed them to use very long intake runners to achieve a significant horsepower boost by tuning the intake system. Part of the reason for its reliability was that it was originally designed to be built of aluminum, but after Chrysler had problems with manufacturing the engines in aluminum, the rest were built in cast iron without changing the design to compensate for the stronger metal. Although it only had four main bearings, these were the same size as those on the Hemi V8. It was discontinued in favor of V6 engines because it was expensive to manufacture and too long to mount transversely in front wheel drive cars. Another significant straight-6 engine family was introduced by , 2007 . A significant step was taken by Kaiser Jeep with the 1963 Tornado Straight-6 , the first U.S. designed mass-produced Overhead Cam (OHC) automobile engine. However, it was complex (by 1960s standards) for civilian vehicles in the U.S., but continued to be installed in military Jeeps and was also produced through 1982 by IKA in Argentina. Ford and General Motors straight-6s of the 1960s and 1970s were generally nondescript, except for the overhead cam Pontiac six of the late-1960s. Although the Pontiac six was one of the few straight-6s of its era to be advertised as exceeding 200 horsepower, it wooed few performance buyers away from V8s in the Muscle Car era and was eventually discontinued in favor of a less costly design. The predominance of the V8s in the muscle car era was largely a matter of marketing, since the seven-main-bearing design of the big sixes allowed racers to modify them to produce as much horsepower as small V8s, and the overhead cam of the Pontiac six allowed it to run at much higher speeds. However, automakers found it profitable to sell straight-6s as "economy" engines and V8s as "performance" engines regardless of their horsepower potential, since big, unsophisticated, overhead valve V8s were relatively cheap to manufacture, and fuel economy was not a concern during this period. When cars began to get smaller again as a result of the fuel crises in the 1970s, the trend was towards smaller cars with better fuel economy. Despite this, the straight-6 engines became rare in American cars although they continued to be used in trucks and vans. The decline of the straight-6 was in response to the more compact size of the V6 layout. The straight-6 required a longer engine compartment, which was more appropriate to a larger car. The shorter V6 could be used in a shorter engine compartment and therefore fit better in a more compact car. Jeep s were an exception to the rule, aside from AMC's 2.5 L, Jeep CJ's began offering AMC's 258, known as "High Torque," straight-6s as a common engine option in 1972. These engines continued to receive upgrades with an advanced for its time, high-performance 4.0 L (242 cu in) option in 1997. Usage of the AMC 4.0 has been declining in Jeep vehicles since the 2002 replacement of the Jeep Cherokee with the Liberty , which features the Chrysler 3.7 L V6 instead. It has declined further since the 2005 introduction of the third generation Jeep Grand Cherokee , which also uses the 3.7 L V6. The last application of the 4.0 was in the 2006 Jeep Wrangler ; for 2007 the engine has been replaced with a 3.8 L V6. Ford used a straight-6 in baseline Mustangs and in its other models for many decades. They were also found in F150 pickups (most notably the 300 cu in 4.9 L inline six) until 1997 when they were replaced with a V6. In 1989 Chrysler introduced the 5.9 L Cummins B Series Engine as an option on its pickup trucks. Displacing nearly 1 litre per cylinder, this straight-6 turbocharged diesel engine was an attractive alternative to the big gasoline V8s normally used on full-sized pickups because it got much better fuel economy and produced nearly twice as much low-speed torque. The usual marketing cachet of competing V8s from GM and Ford was offset by the feeling of truck owners that the Cummins was a ''real'' truck engine, since earlier diesel V8s derived from gasoline engines had reliability problems. The current 6.7 L version is the largest straight-6 engine ever produced for a passenger vehicle. In 2001 General Motors introduced a new family of straight engines, the '' Atlas '', for use in the newly-introduced Chevrolet TrailBlazer / GMC Envoy . The straight-6 was chosen for development because of the desirable operating characteristics of its self-balanced design. STRAIGHT-6 ENGINES IN ASIA The Japanese have used the straight-6 with great success since the 1960s in a wide range of applications, from passenger vehicles, to sports cars, to SUVs. Both Nissan and Toyota were among the first in this trend. They found it easy to create straight-6 designs by simply adding two more cylinders to their straight-4s. More recently, they have changed to V6s because the straight-6s were too long for the engine compartments in their newer vehicles. Toyota started with their (and others); the M and its replacement, the JZ, in the Toyota Supra (and others); and the F and its replacement, the FZ, in the Land Cruiser . In the 2000s, Toyota's still offers the FZ-series, G-series and the JZ-series engines. In Korea, GM Daewoo's FWD Magnus (sold abroad as the Chevrolet Evanda, Chevrolet Epica, Holden Epica or Suzuki Verona) comes with a Daewoo-designed straight-6. The Daewoo engine is unusual in that it is one of the few straight-6s designed to be installed transversely in front wheel drive cars. In order to do this, it is an extremely short engine for a straight-6. STRAIGHT-6 ENGINES IN AUSTRALIA Historically, all major manufacturers in Australia used straight-6s. BMC developed a straight six cylinder engine based on the B series engine in the late 1950's. It was developed from the MGA and other variants. This was after it was realised that in order to gain market share a six cylinder engine was required. It appeared in the Austin Freeway and Wolseley 24/80. Although successful in Australia nd tried successfully in the prototype MGC the cost of retooling meant that the engine remained indigenous to Australia. In the early 1970's the four cylinder engine from the Marina/Morris 1500 was also @cut and shut@ and a high performance but small six cylinder engine was developed for the Australian market. Chrysler had built the Slant 6 in Australia and the unique to Australia Hemi Straight-6 . These engines, made in 215, 245 and 265 cid capacity, were used in the Chrysler Valiant and the Valiant Charger producing up to 320 hp. Chrysler no longer owns any factories in Australia. Holden up until 1986 built their own straight-6s, adapted from a Chevrolet design. A 2.2 L unit (known as the 'grey' motor) was used until 1963 , replaced by a newer Chevrolet based design (known as the 'red' engine) which was offered in different capacities. Well known Holden engine sizes included the '173' (2.85 L - 1971-1984), '186' (3.0 L - 1968-1971) and '202' (3.3 L - 1971-1986) - the largest and most popular of the series. Vehicles using the Holden 'red' motor included the larger Holden models (Belmont, Kingswood, Premier, and commercial versions), the Torana and pre-1986 Commodores sixes. The engine was dropped by Holden due to it being outdated (especially in output and economy) when compared to rival engines, and perceived incompatibilities with unleaded fuel. While initially replaced by a Nissan designed straight-6, the large Holdens now use the V6 configuration. Ford Australia has been producing Straight-6s since 1960 and is the only manufacturer in Australia to still build them, however, production shall be discontinued in 2010 due to difficulty in meeting Euro-IV standards with the current configuration. Ford has built 144, 170, 188, 200, 221, 240 and 250 cu in engines, with the 240 being called the 3.9 L or 4.0 L and the 200 being called the 3.3 L. They have been used since 1960 in the Falcon , 1970-1982 in the Cortina and from 2004 in the Ford Territory . The current straight-6 engines in the Falcon and Territory are called the Barra and have a 4.0L displacement. The high-performance division of Ford Australia, Ford Performance Vehicles , produce vehicles equipped with the 4.0 L DOHC 24-valve turbocharged straight-6 with variable cam timing, which produces 270 kW (362 hp) @ 5250 rpm and 550Nm (406 ft·lbf) @ 2000 - 4250 rpm — the highest level of torque in any Australian production car to date (along with the HSV E Series). DIESEL STRAIGHT-6 ENGINES The straight-6 in Diesel form with a much larger displacement is commonly used for industrial applications. These include various types of Heavy Equipment , Power Generation , as well as Transit Bus es or Coaches . Virtually every medium-duty to large over-the-road truck employs an inline six diesel engine. Its virtues are superior low-end torque, very long service life, smooth operation and dependability. On-highway vehicle operators look for straight-6 diesels, which are smooth-operating and quiet. Off-highway applications such as tractors, marine engines, and electric generators need a motor that is rugged and powerful. In these applications, compactness is not as big a factor as in passenger cars, and reliability and maintainability are much more important concerns. As with everyday passenger vehicles, the smooth running characteristics of the straight-6 engine are what make it desirable for industrial use. In addition, a straight-6 engine is mechanically simpler than a V6 or V8. It has only one Cylinder Head and half as many Camshafts as a V engine. The fact that the the straight-6 is the simplest engine that is in both primary and secondary balance mean it can be scaled up to very large sizes without causing excessive vibration, and the fact that most of the engine components and accessories can be conveniently located along both sides, rather than on top of or underneath the cylinders, means that maintenance is easier than on a V-type engine. Notable versions include the 5.9 and 6.7 liter I-6 Cummins found in the Dodge Ram and the 3.2 liter straight-6 used in the Mercedes-Benz E320 CDI sold in America from 2004 through 2006. NOTES SEE ALSO Straight Engine |
|
|