The Lexus NX is a compact luxury crossover SUV sold by Lexus, a luxury division of Toyota. It was introduced in late 2014 as an all-new, entry-level crossover model in Lexus' lineup, slotted below the mid-size RX crossover; the name NX stands for Nimble Crossover. The NX was revealed at the Beijing International Automotive Exhibition on 20 April 2014; the NX shares a small portion of parts with the Toyota RAV4 related to the structure and wheelbase, while the styling, suspension parts, some engines and level of luxury and craftsmanship are unique to the Lexus. Lexus NX variants sold in the United States feature altered fascias, which facilitate higher departure angles. US sales began in November 2014. Production commenced on 8 August 2014 at the Miyata plant in Fukuoka; the Lexus NX is available with various powertrains. In the US, it comes in NX 200t and NX 300h trims: The Lexus NX 300 features the newly developed 8AR-FTS 2.0L turbocharged inline four cylinder direct injection engine that can run on both Otto and Atkinson cycles.
The 8AR-FTS engine has Lexus’ ESTEC D-4ST fuel injection. With separate twin injectors for both direct and port injection, ESTEC D-4ST could perform high-pressure direct injection into the cylinder and conventional intake port injection, or direct cylinder injection only, according to engine speed. Mated to a 6-speed automatic transmission, this engine produces 175 kW at 4,800-5,600 rpm and 350 N⋅m at 1,650-4,000 rpm; the NX is the first Lexus vehicle to feature a turbocharged gasoline engine in the US market and many other markets around the globe. The Lexus NX 300h hybrid comes powered by a 2.5-liter inline-four 2AR-FXE engine mated to an electric motor and CVT that puts out a combined 145 kW and is shared with the Toyota Camry Hybrid. In addition, a 2.0-liter aspirated engine producing 112 kW will be available in Russian markets. The Lexus NX is liberally equipped. Notable features include: Advanced voice command Remote Touch with Touchpad Drive Mode Select Pre-Collision System with Dynamic Radar Cruise Control Blind spot monitor with Rear Cross-Traffic Alert Lane Departure Alert Radar Cruise Control with All-speed Tracking Function Premium triple-beam LED headlamps Backup camera Tire Pressure Monitor System In its first full year of sales the NX sold over 43,000 units in the USA.
It was successful in Europe where it sold over 28,000 in its first full year of sales, of which more than 17,000 were hybrids. This made it Lexus's best selling model in Europe, its success was strong in Russia, where in its first full year of sales it was the best selling luxury vehicle. Lexus NX international site
A V8 engine is an eight-cylinder V configuration engine with the cylinders mounted on the crankcase in two sets of four, with all eight pistons driving a common crankshaft. Most banks are set at a right angle to each other, some at a narrower angle, with 45°, 60°, 72° most common. In its simplest form, the V8 is two parallel inline-four engines sharing a common crankshaft. However, this simple configuration, with a flat- or single-plane crankshaft, has the same secondary dynamic imbalance problems as two straight-4s, resulting in vibrations in large engine displacements. Since the 1920s, most V8s have used the somewhat more complex crossplane crankshaft with heavy counterweights to eliminate the vibrations; this results in an engine, smoother than a V6, while being less expensive than a V12. Many racing V8s continue to use the single plane crankshaft because it allows faster acceleration and more efficient exhaust system designs. In 1902, Léon Levavasseur took out a patent on a light but quite powerful gasoline injected V8 engine.
He called it the'Antoinette' after the young daughter of his financial backer. From 1904 he installed this engine in a number of early aircraft; the aviation pioneer Alberto Santos-Dumont saw one of these boats in Côte d'Azur and decided to try it on his pusher configuration, canard-design 14-bis aircraft. Its early 24 hp at 1400 rpm version with only 55 kg of weight was interesting, but proved to be underpowered. Santos-Dumont ordered a more powerful version from Levavasseur, he changed its dimensions from the original 80 mm stroke and 80 mm bore to 105 mm stroke and 110 mm bore, obtaining 50 hp with 86 kg of weight, including cooling water. Its power-to-weight ratio was not surpassed for 25 years. Levavasseur produced its own line of V8 equipped aircraft, named Antoinette I to VIII. Hubert Latham piloted the V8 powered Antoinette IV and Antoinette VII in July 1909 on two failed attempts to cross the English Channel. However, in 1910, Latham used the VII with the same engine to become the first in the world to reach an altitude of 3600 feet.
Voisin constructed pusher biplanes with Antoinette engines notably the one first flown by Henry Farman in 1908. The V8 engine configuration was used in France by 1904, in race car and aircraft engines introduced by Renault, Buchet among others; some of these engines found their way into automobiles in small quantities. In 1905, Darracq built a special car to beat the world speed record, they came up with two racing car engines built on camshaft. The result was an engine with a displacement of 1,551 cu in, 200 bhp. Victor Hemery achieved the record on 30 December 1905 with a speed of 109.65 mph. This car still exists. Rolls-Royce built a 3,535 cc V8 car from 1905 to 1906, but only three copies were made and Rolls-Royce reverted to a I6 design. In 1907, the Hewitt Motor Company built a large five-passenger Touring Car, it was equipped with a V8 engine that developed 50/60 horsepower and had a bore of 4 in and a stroke of 4.5 in. The Hewitt was the first American automobile to be equipped with a V8 engine.
De Dion-Bouton introduced a 7,773 cc automobile V8 in 1910 and displayed it in New York in 1912. It inspired a number of manufacturers to follow suit; the limiting factor in mass production and sales of V8s was the difficulty in starting large engines using a hand crank. Not only does increasing the size of the engine make this harder, the number of pistons is a factor, because with a 4 cylinder engine, a piston comes into compression every half turn of the crank, overcoming this with the crank is not difficult. With eight cylinders, there is only 1/4 of a turn of the crank before another cylinder comes into compression. To overcome this problem, electric starters were developed; the first marque to equip its cars with electric starter motors was Cadillac, in 1912, Cadillac was the first production automobile with V8s, introduced 2 years later. It sold 13,000 of the 5.4 L L-head engines in its first year of production, 1914. Cadillac has been a V8 company since. Oldsmobile, another division of General Motors, introduced its own 4 L V8 engine in 1916.
Chevrolet introduced a 4.7 L V8 engine in 1917 and installed in the Chevrolet Series D. In February 1915, Swiss automotive engineer Marc Birkigt designed the first example of the famous Hispano-Suiza V8 single overhead cam aviation engines, in differing displacements, using dual ignition systems and in power levels from 150 horsepower to around 300 horsepower, in both direct-drive and geared output shaft versions. 50,000 of these engines were built in Spain, the United Kingdom, Italy. Wright Aeronautical built them in the United States during World War I, with the French-produced versions getting almost-exclusive use to power the SPAD S. VII and SPAD S. XIII fighter aircraft. E.5 fighters and Sopwith Dolphin fighters. The H. S. 8-series overhead cam valvetrain V8 aviation engines are said to have powered half of all Allied aircraft of the WW I era. By 1932, Henry Ford introduced one of his last great personal engineering triumphs: his "en block", or one piece, V8 engine, its simple design made possible the greatest production V8 to the masses.
Offered as an option to an improved 4-cylinder Mo
A supercharger is an air compressor that increases the pressure or density of air supplied to an internal combustion engine. This gives each intake cycle of the engine more oxygen, letting it burn more fuel and do more work, thus increasing power. Power for the supercharger can be provided mechanically by means of a belt, shaft, or chain connected to the engine's crankshaft. Common usage restricts the term supercharger to mechanically driven units. In 1848 or 1849, G. Jones of Birmingham, England brought out a Roots-style compressor. In 1860, brothers Philander and Francis Marion Roots, founders of Roots Blower Company of Connersville, patented the design for an air mover for use in blast furnaces and other industrial applications; the world's first functional tested engine supercharger was made by Dugald Clerk, who used it for the first two-stroke engine in 1878. Gottlieb Daimler received a German patent for supercharging an internal combustion engine in 1885. Louis Renault patented a centrifugal supercharger in France in 1902.
An early supercharged race car was built by Lee Chadwick of Pottstown, Pennsylvania in 1908 which reached a speed of 100 mph. The world's first series-produced cars with superchargers were Mercedes 6/25/40 hp and Mercedes 10/40/65 hp. Both models had Roots superchargers, they were distinguished as "Kompressor" models, the origin of the Mercedes-Benz badging which continues today. On March 24, 1878 Heinrich Krigar of Germany obtained patent #4121, patenting the first screw-type compressor; that same year on August 16 he obtained patent #7116 after modifying and improving his original designs. His designs show a two-lobe rotor assembly with each rotor having the same shape as the other. Although the design resembled the Roots style compressor, the "screws" were shown with 180 degrees of twist along their length; the technology of the time was not sufficient to produce such a unit, Heinrich made no further progress with the screw compressor. Nearly half a century in 1935, Alf Lysholm, working for Ljungströms Ångturbin AB, patented a design with five female and four male rotors.
He patented the method for machining the compressor rotors. There are two main types of superchargers defined according to the method of gas transfer: positive displacement and dynamic compressors. Positive displacement blowers and compressors deliver an constant level of pressure increase at all engine speeds. Dynamic compressors do not deliver pressure at low speeds. Positive-displacement pumps deliver a nearly fixed volume of air per revolution at all speeds. Major types of positive-displacement pumps include: Roots Lysholm twin-screw Sliding vane Scroll-type supercharger known as the G-Lader Positive-displacement pumps are further divided into internal and external compression types. Roots superchargers, including high helix roots superchargers, produce compression externally. External compression refers to pumps that transfer air at ambient pressure. If an engine equipped with a supercharger that compresses externally is running under boost conditions, the pressure inside the supercharger remains at ambient pressure.
Roots superchargers tend to be mechanically efficient at moving air at low pressure differentials, whereas at high pressure rations, internal compression superchargers tend to be more mechanically efficient. All the other types have some degree of internal compression. Internal compression refers to the compression of air within the supercharger itself, which at or close to boost level, can be delivered smoothly to the engine with little or no back flow. Internal compression devices use a fixed internal compression ratio; when the boost pressure is equal to the compression pressure of the supercharger, the back flow is zero. If the boost pressure exceeds that compression pressure, back flow can still occur as in a roots blower; the internal compression ratio of this type of supercharger can be matched to the expected boost pressure in order to optimize mechanical efficiency. Positive-displacement superchargers are rated by their capacity per revolution. In the case of the Roots blower, the GMC rating pattern is typical.
The GMC types are rated according to how many two-stroke cylinders, the size of those cylinders, it is designed to scavenge. GMC has made 2–71, 3–71, 4–71, the famed 6–71 blowers. For example, a 6–71 blower is designed to scavenge six cylinders of 71 cubic inches each and would be used on a two-stroke diesel of 426 cubic inches, designated a 6–71. However, because 6–71 is the engine's designation, the actual displacement is less than the simple multiplication would suggest. A 6–71 pumps 339 cubic inches per revolution. Aftermarket derivatives continue the trend with 8–71 to current 16–71 blowers used in different motor sports. From this, one can see that a 6–71 is twice the size of a 3–71. GMC made 53 cu in series in 2–, 3–, 4–, 6–, 8–53 sizes, as well as a "V71" series for use on engines using a V configuration. Dynamic compressors rely on accelerating the air to high speed and t
Toyota A engine
The A Series engines are a family of inline-four internal combustion engines with displacement from 1.3 L to 1.8 L produced by Toyota Motor Corporation. The series has cast iron engine blocks and aluminum cylinder heads. To make the engine as short as possible, the cylinders are siamesed; the 1A engine was only 550 mm long. The development of the series began in the late 1970s, when Toyota wanted to develop a new engine for the Toyota Tercel, successor of Toyota's K engine; the goal was to achieve good fuel efficiency and performance as well as low emissions with a modern design. The A-series includes one of the first Japanese mass-production DOHC, four-valve-per-cylinder engines, the 4A-GE, a version of the same engine was one of the first production five-valve-per-cylinder engines. Toyota joint venture partner Tianjin FAW Xiali still produces the 1.3 L 8A and resumed production of the 5A. The 1.5 L 1A was produced between 1978 and 1980. All variants were belt-driven 8-valve counter-flow SOHC engine with a single, twin-barrel downdraft carburetor.
Applications: AL10 Tercel Using Toyota TTC-C catalytic converter. Output: 59 kW at 5,600 rpm and 11.5 kg⋅m at 3,600 rpm Applications: AL10 Tercel/Corsa The 1.3 L 2A was produced from 1979 through 1989. 2A engines in 1982 onwards AL20 Tercels have a different valve cover and timing belt cover than early AL11 Tercels, as well as an automatic choke, automatically controlled hot air intake system. It has higher compression ratio, reformulated combustion chambers to improve the fuel economy and emissions. All variants used belt-driven SOHC eight-valve counter-flow cylinder heads with a single downdraft carburetor. Output: 48 kW at 6,000 rpm and 98 N⋅m at 3,800 rpm Applications: AE80 Corolla 1983–1985 AL11 Tercel 1979–1982 AL20 Tercel 1982–1984 Using Toyota TTC-C catalytic converter. Output: 55 kW at 6,000 rpm and 106 N⋅m at 3,600 rpm Applications: AE80 Corolla 1983–1985 AL20 Corolla II 1982–1986 AL11 Corsa AL20 Corsa 1982–1989 AE80 Sprinter 1983–1985 AL11 Tercel AL20 Tercel 1982–1989 The 1.5 L 3A was produced from 1979 through 1989.
The 3A engine is the successor of Toyota's first A engine, the 1A. All variants were belt-driven eight-valve counter-flow SOHC engines. Output: 52 kW at 5,600 rpm and 108 N⋅m at 3,800 rpm 44 kW at 4,500 rpm 46 kW at 4,800 rpm Applications: AL12 Tercel 1979–1982 AL21/25 Tercel 1982–1988 Using Toyota TTC-C catalytic converter. On some models marked as 3A-II. Output: 61.4 kW at 5,600 rpm and 118 N⋅m at 3,600 rpm Applications: AA60 Carina 1981–1987 AT150 Carina 1984–1988 AE70 Corolla 1979–1983 AE81/85 Corolla 1983–1987 AL21 Corolla II 1982–1986 AT140 Corona 1982–1987 AT150 Corona 1983–1987 AL12 Corsa AL21/25 Corsa 1982–1989 AW10 MR2 1984–1989 AE70 Sprinter 1979–1983 AE81/85 Sprinter 1983–1987 AL25 Sprinter Carib 1982–1988 AL21/25 Tercel 1982–1989 High compression version with Toyota TTC-C catalytic converter. Output: 63 kW at 6,000 rpm and 121 N⋅m at 4,000 rpm Applications: AL21 Corolla II 1982–1984 AL21 Corsa 1982–1984 AL21 Tercel 1982–1984 Twin carburetted swirl-intake version with Toyota TTC-C catalytic converter, introduced in August 1984 along with a facelift for the Tercel in Japan.
Features two variable-venturi carburetors, which Toyota wanted to test in Japan before launching them in export along E series engine, albeit in single carburetted version. Because of the swirl-intake, the sealing surface between cylinder head and valve cover is different from other SOHC A-engines, featuring vertical curves on the manifold side of the head. Thus, those parts are not interchangeable between each other; the swirl was supposed to improve burning of the air-fuel mixture, thus enabling cleaner emissions, improving fuel economy, increasing power. Output: 66 kW at 6,000 rpm Applications: AL21 Corolla II 1984–1986 AL21/25 Corsa 1984–1989 AL25 Sprinter Carib 1984–1988 AL21/25 Tercel 1984–1989 The 4A was produced from 1980 through 2002. All 4A engines have a displacement of 1,587 cc; the cylinder bore was enlarged from the previous 3A engines at 81 mm, but the stroke remained the same as the 3A at 77 mm, giving it an over-square bore/stroke ratio which favours high engine speeds. Numerous variations of the 4A design were produced, from basic SOHC 8-valve all the way to DOHC 20-valve versions.
The power output varied between versions, from 52 kW at 4,800 rpm in the basic California-spec 4A-C to 125 kW at 6,400 rpm in the supercharged 4A-GZE. The basic 4A is a SOHC inline 4 8-valve carburated engine which produces 58–67 kW at 4800 rpm and 115 N⋅m of torque at 2800 rpm, though the power and torque output figures vary between different regions of the world. At least in European versions, the combustion chambers were reformulated in early 1986, resulting in an increase of 2 hp (64 kW (86 hp.
The Pontiac Vibe is a compact automobile, sold by Pontiac from 2002 to 2010. It was jointly developed by General Motors along with Toyota, who manufactures the mechanically similar Toyota Matrix. Manufactured by the Toyota-GM joint venture NUMMI in Fremont, the Vibe succeeded the Chevrolet Prizm in production at NUMMI and like the Prizm, it was derived from the Toyota Corolla, making it the last of the GM and Toyota developed S-body cars. From 2002 to 2004, a rebadged right-hand drive variant of the Vibe was exported as the Toyota Voltz to the Japanese domestic market; the Voltz was not discontinued after two model years. Production of the Vibe ended in 2009 with the discontinuation of the Pontiac brand and the closing of NUMMI under the General Motors Chapter 11 reorganization, its twin, the Toyota Matrix, was in production for another three years for the American market and four years for the Canadian market, as the Matrix was manufactured by Toyota Motor Manufacturing Canada in Cambridge and was unaffected by NUMMI closing down operation.
The 2003–2006 Vibe was available in an economical base trim, an AWD mid-trim, the more powerful GT sport trim. Powertrains available for this car are a Toyota-built 1.8 L straight-4 16-valve engine producing 126 hp on the base model, 118 hp on the all-wheel drive model, or a version with VVTL-i producing 164 hp for the GT. The Vibe was at one time the most fuel efficient vehicle sold by GM in North America, but ceased to be the case with the revised United States Environmental Protection Agency testing procedures in 2008. Although the Vibe and Matrix are similar designs, the two brands use several different components, which are brand-specific, for their heating and air conditioning systems; these components include the air conditioning compressor and related hoses, the heater hoses, the heater core, the serpentine belt. There have been some minor changes between model years; the Vibe went on sale as a 2003 model. Power ratings for the first three model years were higher, with the GT up to 180 hp, the base model rated at 130 hp, the all-wheel drive model rated at 123 hp.
Engine power claims were decreased for 2006 as a result of Toyota's re-testing of its engines for the new Society of Automotive Engineers ratings standard. The GT and all-wheel-drive trims were discontinued for the 2007 model year due to poor sales and new federal emissions standards; the front fascia was freshened in the 2005 model year. In an attempt to'converge' the Pontiac look, the front grille was restyled to resemble the look of the Pontiac Solstice adopted by other vehicles in the Pontiac line; the 2003-2004 Vibes had a front grille more resembling the discontinued Pontiac Aztek. First generation Vibe/Matrix/Corolla odometers do not have the ability to "roll over" 299,999 km or 299,999 mi. No recall or "fix" is available for this. Mileage must be kept track of manually; the Vibe was produced in right-hand drive configuration and exported to the Japanese market as the Toyota Voltz from 2002 to 2004. The Vibe was redesigned, along with the Matrix, for the 2009 model year, debuted at the December 2007 LA Auto Show.
"The new Vibe's design is sporty yet functional," according to Ron Aselton, chief designer. "Clean lines, minimal overhangs and wheels pushed to the corners give the vehicle a muscular stance." The GT trim and AWD options return, two new inline-four engines are offered. This was Pontiac's last new model and remained as the brand's only remaining car for the 2010 model year; the second generation FWD Vibes offer computerized traction-control and anti-lock brakes. Rear disc brakes are standard on all models. Luggage racks are no longer standard order. Power outputs of the two engines are 158 hp respectively; the Vibe offers 91.4 cubic feet of passenger volume and 20.1 cubic feet of cargo volume, for a total of 111.5 cubic feet with rear seats that fold flat. The cargo area is 30 inches high and 40 inches wide, large enough to accommodate a standard-sized, North American washing machine or clothes dryer with enough extra room for an appliance dolly. First deliveries to dealerships were posted on GM's Website in April 2008, with comments that initial sales were brisk.
The first units were delivered to buyers in early March. On April 27, 2009, GM announced the discontinuation of Vibe production, as well as all other Pontiac models, by the end of 2010, it was announced that Vibe production would end in August 2009, the last Vibe left the assembly line on August 17, 2009, according to a source at genvibe.com. This left Toyota with a major problem as they had to scramble to relocate some of the tooling, jointly used to produce the Matrix in another factory. GM did not produce a compact hatchback to succeed the Pontiac Vibe, choosing to bracket it with the Chevrolet Sonic hatchback and Buick Encore small crossover. In Canada, GM followed the Vibe with the larger Chevrolet Orlando compact MPV, which replaced the Chevrolet HHR. Chevrolet introduced a hatchback version of the Chevrolet Cruze to North America in 2016. In January 2010, Autoblog.com reported that the 2009 and 2010 model year Pontiac Vibes are included in the 2009–2010 Toyota vehicle recalls related to unintended acceleration due to shared components with the Toyota Matrix.
The Atkinson-cycle engine is a type of internal combustion engine invented by James Atkinson in 1882. The Atkinson cycle is designed to provide efficiency at the expense of power density. A modern variation of this approach is used in some modern automobile engines. While seen in hybrid electric applications such as the earlier-generation Toyota Prius hybrids and some non-hybrid vehicles now feature engines with variable valve timing, which can run in the Atkinson cycle as a part-time operating regimen, giving good economy while running in Atkinson cycle, conventional power density when running as a conventional, Otto cycle engine. Atkinson produced three different designs that had a short compression stroke and a longer expansion stroke; the first Atkinson-cycle engine, the differential engine, used opposed pistons. The second and most well-known design, was the cycle engine, which used an over-center arm to create four piston strokes in one crankshaft revolution; the reciprocating engine had the intake, compression and exhaust strokes of the four-stroke cycle in a single turn of the crankshaft, was designed to avoid infringing certain patents covering Otto-cycle engines.
Atkinson's third and final engine, the utilite engine, operated much like any two-stroke engine. The common thread throughout Atkinson's designs is that the engines have an expansion stroke, longer than the compression stroke, by this method the engine achieves greater thermal efficiency than a traditional piston engine. Atkinson's engines were produced by the British Gas Engine Company and licensed to other overseas manufacturers. Many modern engines now use unconventional valve timing to produce the effect of a shorter compression stroke/longer power stroke. Miller applied this technique to the four-stroke engine, so it is sometimes referred as the Atkinson/Miller cycle, US patent 2817322 dated Dec 24, 1957. In 1888, Charon filed a French patent and displayed an engine at the Paris Exhibition in 1889; the Charon gas engine used a similar cycle without a supercharger. It is referred to as the "Charon cycle". Modern engine designers are realizing the potential fuel-efficiency improvements the Atkinson-type cycle can provide.
The first implementation of the Atkinson cycle was in 1882. In this, a single crankshaft was connected to two opposed pistons through a toggle-jointed linkage that had a nonlinearity. Thus, in each revolution, one piston provided a compression stroke and a power stroke, the other piston provided an exhaust stroke and a charging stroke; as the power piston remained withdrawn during exhaust and charging, it was practical to provide exhaust and charging using valves behind a port, covered during the compression stroke and the power stroke, so the valves did not need to resist high pressure and could be of the simpler sort used in many steam engines, or reed valves. The next engine designed by Atkinson in 1887 was named the "Cycle Engine" This engine used poppet valves, a cam, an over-center arm to produce four piston strokes for every revolution of the crankshaft; the intake and compression strokes were shorter than the expansion and exhaust strokes. The "Cycle" engines were sold for several years by the British Engine Company.
Atkinson licensed production to other manufacturers. Sizes ranged from a few up to 100 horsepower. Atkinson's third design was named the "Utilite Engine". Atkinson's "Cycle" engine was efficient. Atkinson realized an improvement was needed to make his cycle more applicable as a higher-speed engine. With this new design, Atkinson was able to eliminate the linkages and make a more conventional, well balanced, engine capable of operating at speeds up to 600 rpm and capable of producing power every revolution yet he preserved all of the efficiency of his "Cycle Engine" having a proportionally short compression stroke and a longer expansion stroke; the Utilite operates much like a standard two-stroke except that the exhaust port is located at about the middle of the stroke. During the expansion/power stroke, a cam-operated valve prevents pressure from escaping as the piston moves past the exhaust port; the exhaust valve is opened near the bottom of the stroke. After the exhaust port is covered the piston begins to compress the remaining air in the cylinder.
A small piston fuel pump injects liquid during compression. The ignition source was a hot tube as in Atkinson's other engines; this design resulted in a two-stroke engine with longer expansion stroke. The Utilite Engine tested as more efficient than Atkinson's previous "differential" and "cycle" designs. Few were produced, none are known to survive; the British patent is from 1892, #2492. No US patent for the Utilite Engine is known; the ideal Atkinson cycle consists of: 1–2 Isentropic, or reversible, adiabatic compression 2–3 Isochoric heating 3–4 Isobaric heating 4–5 Isentropic expansion 5–6 Isochoric cooling 6–1 Isobaric cooling In the late 20th century, the term "Atkinson cycle" began to be used to describe a modified Otto-cycle engine—in which the intake valve is held open lon
Overhead camshaft abbreviated to OHC, is a valvetrain configuration which places the camshaft of an internal combustion engine of the reciprocating type within the cylinder heads and drives the valves or lifters in a more direct manner compared with overhead valves and pushrods. Compared with OHV pushrod systems with the same number of valves, the reciprocating components of the OHC system are fewer and have a lower overall mass. Though the system that drives the camshafts may be more complex, most engine manufacturers accept that added complexity as a trade-off for better engine performance and greater design flexibility; the fundamental reason for the OHC valvetrain is that it offers an increase in the engine's ability to exchange induction and exhaust gases. Another performance advantage is gained as a result of the better optimised port configurations made possible with overhead camshaft designs. With no intrusive pushrods, the overhead camshaft cylinder head design can use straighter ports of more advantageous cross-section and length.
The OHC design allows for higher engine speeds than comparable cam-in-block designs, as a result of having lower valvetrain mass. The higher engine speeds thus allowed increases power output for a given torque output. Disadvantages of the OHC design include the complexity of the camshaft drive, the need to re-time the drive system each time the cylinder head is removed, the accessibility of tappet adjustment if necessary. In earlier OHC systems, including inter-war Morrises and Wolseleys, oil leaks in the lubrication systems were an issue. Single overhead camshaft is a design. In an inline engine, this means there is one camshaft in the head, whilst in an engine with more than one cylinder head, such as a V engine or a horizontally-opposed engine – there are two camshafts, one per cylinder bank. In the SOHC design, the camshaft operates the valves traditionally via a bucket tappet. SOHC cylinder heads are less expensive to manufacture than double overhead camshaft cylinder heads. Timing belt replacement can be easier since there are fewer camshaft drive sprockets that need to be aligned during the replacement procedure.
SOHC designs offer reduced complexity compared with overhead valve designs when used for multivalve cylinder heads, in which each cylinder has more than two valves. An example of an SOHC design using shim and bucket valve adjustment was the engine installed in the Hillman Imp, a small, early-1960s two-door saloon car with a rear-mounted aluminium-alloy engine based on the Coventry Climax FWMA race engines. Exhaust and inlet manifolds were both on the same side of the engine block; this did, offer excellent access to the spark plugs. In the early 1980s, Toyota and Volkswagen Group used a directly actuated SOHC parallel valve configuration with two valves for each cylinder; the Toyota system used hydraulic tappets. The Volkswagen system used bucket tappets with shims for valve-clearance adjustment; the multivalve Sprint version of the Triumph Slant-4 engine used a system where the camshaft was placed directly over the inlet valves, with the same cams that opened the intake valves directly opening the exhaust valves via rocker arms.
Honda used a similar valvetrain system in their motorcycles, using the term "Unicam" for the concept. This system uses one camshaft for each bank of cylinder heads, with the cams operating directly onto the inlet valve, indirectly, through a short rocker arm, on the exhaust valve; this allows a light valvetrain to operate valves in a flat combustion chamber. The Unicam valve train was first used in single cylinder dirt bikes and has been used on the Honda VFR1200 since 2010. A dual overhead camshaft valvetrain layout is characterised by two camshafts located within the cylinder head, one operating the intake valves and the other one operating the exhaust valves; this design reduces valvetrain inertia more than is the case with an SOHC engine, since the rocker arms are reduced in size or eliminated. A DOHC design exhaust valves than in SOHC engines; this can give a less restricted airflow at higher engine speeds. DOHC with a multivalve design allows for the optimum placement of the spark plug, which in turn improves combustion efficiency.
Engines having more than one bank of cylinders with two camshafts in total remain SOHC and "twin cam" unless each cylinder bank has two camshafts. Although the term "twin cam" is used to refer to DOHC engines, it is imprecise, as it includes designs with two block-mounted camshafts. Examples include the Harley-Davidson Twin Cam engine, Riley car engines from 1926 to the mid 1950s, Triumph motorcycle parallel-twins from the 1930s to the 1980s, Indian Chief and Scout V-twins from 1920 to the 1950s; the terms "multivalve" and "DOHC" do not refer to the same thing: not all multivalve engines are DOHC and not all DOHC engines are multivalve. Examples of DOHC engines with two valves per cylinder include the Alfa Romeo Twin Cam engine, the Jaguar XK6 engine and the Lotus Ford Twin Cam engine. Most recent DOHC engines are multivalve, with between five valves per cylinder. More than two overhead camshafts are not known to have been tried in a production engine. However, MotoCzysz has designed a motorcycle engine with a triple overhead camshaft configuration, with the intake ports descending through the cylind