Eight-cylinder engine
Eight cylinders are reciprocating piston engines that can work according to the Otto or diesel process .
Types
Today an eight-cylinder is mostly a V-engine , rarely a boxer or W-engine . Eight-cylinder in- line engines can only be found today as marine diesel engines due to their length .
Applications
The eight-cylinder engine is most commonly used as driving trucks from passenger cars of the upper middle class and the upper class as well as sports cars used. It is also used to drive rail vehicles , light aircraft (boxer engines from US manufacturers such as Lycoming and Continental ) and as a stationary power plant engine . During the First World War, Daimler-Motoren-Gesellschaft produced several hundred eight-cylinder in-line engines as Mercedes D IV aircraft engines , but these did not prove themselves in use.
Automobile manufacturing
In automotive engineering, the eight-cylinder engine is almost always liquid-cooled . Air-cooled models (for example, the V8 in the sedans Tatra Tatra 77 bis 700 ) were exceptions. Eight-cylinder in-line engines, especially as gasoline engines, have excellent running smoothness, as, as with the six-cylinder in-line engine, the free inertia forces of the first and second order are balanced. In addition, the ignition intervals are shorter. However, because of their length, crankshafts of in-line engines have problems with torsional vibrations and the torque to be transmitted. In the automotive industry, eight-cylinder in-line engines were therefore only manufactured for luxury vehicles in the 1920s and 1930s, and in the Bugatti Royale , for example, they achieved up to 220 kW (300 hp). There were a few in-line eight-cylinders in the USA until the 1950s ( Buick ), but then all suppliers switched to the V8 design. See also: In -line eight-cylinder .
The usual form of V8 engines is the so-called " crossplane " -V8 with four crankshaft throws offset by 90 degrees. With suitable counterweights on the crank webs , this type of V8 engine has a perfect balance of free inertia forces and moments of the first and second order. The ignition interval is uniform overall, but not within a cylinder bank . In connection with a double exhaust system (one exhaust pipe per cylinder bank) this leads to the typical "babbling" sound of V8 engines from US manufacturers. As a typical “cruiser engine”, the crossplane V8 runs very smoothly, but is not well suited for high speeds. Typical limit speeds of such engines are 6,500 or 7,000 min −1 , which are usually only achieved with engines whose valves are controlled by overhead camshafts ( OHC ). Easier engines whose valve control system with low-mounted camshaft, lifters , bumpers and rocker arms operates as were the rule in the US, often reach only 4,500 or 5,000 min -1 and achieve higher performance rather thanks to its large displacement, in cars up to 7.3 Liters, gasoline engines in small trucks up to 16 liters.
Large V8 diesel engines for trucks have a displacement of up to 19 liters in Europe, but are now being replaced by in-line six-cylinder engines because of their high consumption and pollutant emissions; their limit speeds are in the range of 2,300 or 2,500 min −1 .
The flat plane V8 with a crankshaft cranked by 180 degrees , which is mainly used in high-performance sports cars ( Ferrari F430 , Lotus Esprit V8 ), is less common . The firing order within a cylinder bank is as regular as that of a four-cylinder in-line engine; smaller counterweights are required on the crank webs than with crossplane engines. This allows higher speeds to be achieved. The running smoothness is worse, however, since free, unbalanced second-order inertia forces occur. Typical such motors limit speeds are 8,500 or 9,000 min -1 . These forces, in turn, can - as with four-cylinder engines - be balanced with the Lanchester balancer , i.e. with counter-rotating balancer shafts with unbalance that rotate at twice the crankshaft speed. Speeds such motors can min in racing 15,000 -1 reach ( Formula 1 ).
Every forged crankshaft for a V8 engine is initially "flat", forged flat. The crossplane design with the crank pins offset by 90 degrees is the result of a subsequent, complex "twist" process in the hot forming process , in which two of the four V-crankings out of the plane by 90 degrees in a second forging die device can be rotated by pushing up one crank from the central plane and down another crank. A crossplane crankshaft is therefore more expensive to manufacture. An alternative for less stressed engines is casting , which today is often performed as a hollow mold casting.
History, peculiarities
The first eight-cylinder engines were used as early as the 1910s, initially for racing purposes, later in luxury automobiles, initially in series. In-line eight-cylinder engines were also designed with four-valve technology for competition purposes very early on.
V8 engines were most widespread in the USA when, in the 1930s, Ford also offered a side-controlled V8 ( SV ) with 90 hp with the successor to the T-model , the Ford Model A.
In the 1920s and 1930s there were several offers, mainly from British suppliers of eight-cylinder engines with Knight valve controls . These motors work almost inaudibly.
Eight-cylinder engines achieved a high level of technical maturity from European car manufacturers who equipped the engines with gasoline injection ( Mercedes-Benz W100 from 1963), with overhead camshafts and four-valve technology (Aston Martin, Ferrari, Maserati from the 1960s), with adjustable cam drives (Mercedes -Benz from 1989) and with double ignition (Daimler-Chrysler from 1998), as well as with turbocharger from the 2000s.
From the end of the 1990s to around 2015, there was a short period of time in which eight-cylinder engines were introduced in the luxury segment as well as in upper middle-class cars ( BMW 5 Series , Mercedes E-Class , C 63 AMG). This was still the case with the top sports models (BMW M, Mercedes AMG) in 2018.
In the past, eight-cylinder engines were also built as boxer engines, as H engines with two connected four-cylinder boxer engines on top of each other, as two-stroke engines (until today mainly as outboard boat engines), as W engines (two VR4 banks, VW Passat W8 around 2003 ) and as compressed air motors (for torpedoes).
Present and future of eight-cylinder engines
Compared to engines with a smaller number of cylinders, the eight-cylinder engine has a higher friction loss, which requires a higher mean effective pressure for the same usable power and thus leads to consumption disadvantages. Overall, the eight-cylinder engine as a motor vehicle drive is therefore on the decline as a result of downsizing efforts to reduce CO 2 pollution and consumption. The eight-cylinder is seen as outdated technology, especially without a turbo charger. It is therefore increasingly being replaced by turbo-charged six-cylinder engines with direct injection in new vehicle offers.
As of 2018, it can only be found in new designs in very heavy vehicles ( SUV ), high-performance sports cars and extremely powerful sedans. The only German manufacturers of V8 engines for passenger cars are Audi , BMW and Daimler AG . Imports of V8 cars can be found at Toyota and Ford ( Ford Mustang ), as well as from Italian and British sports car suppliers and luxury vehicles ( Bentley , Aston Martin , Ferrari , Maserati , and Lamborghini ). According to the state of the art, such engines are often charged as V8s with a turbocharger, which makes the "package", the accommodation of all the units required for operation, extremely complex and repairs extremely expensive, as the complex peripherals of such engines almost consistently twice due to the two cylinder banks is to be accommodated (turbocharger, charge air cooling).
All of this relegates these engines, even more than before, to the luxury segment. In trucks, once the 500 hp limit has been exceeded with charged six-cylinder diesels, there is hardly any reason to use V8 engines. These engines will continue to be built in small numbers in order to be installed in tractors for heavy haulage and rail vehicles as well as in boats, and apart from vehicle technology they will also be used in combined heat and power plants and in emergency power generators in hospitals. But they will hardly touch normal vehicle technology in the future.
The eight-cylinder engine certainly has a future with medium-speed four-stroke diesel engines as ship propulsion and as propulsion in rail transport.
literature
- Peter Gerigk, Detlev Bruhn, Dietmar Danner: Automotive engineering. 3rd edition, Westermann Schulbuchverlag GmbH, Braunschweig, 2000, ISBN 3-14-221500-X
- Max Bohner, Richard Fischer, Rolf Gscheidle: Expertise in automotive technology. 27th edition, Verlag Europa-Lehrmittel, Haan-Gruiten, 2001, ISBN 3-8085-2067-1
Individual evidence
- ↑ Zima, Ficht: Unusual Motors, Vogel-Verlag Würzburg, 3rd edition 2010, p. 568 ff.
- ↑ MTZ Motorentechnische Zeitschrift, volumes 2011–2018
Web links
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