An engine block is the structure which contains the cylinders, other parts, of an internal combustion engine. In an early automotive engine, the engine block consisted of just the cylinder block, to which a separate crankcase was attached. Modern engine blocks have the crankcase integrated with the cylinder block as a single component. Engine blocks also include elements such as coolant passages and oil galleries; the term "cylinder block" is used interchangeably with engine block, although technically the block of a modern engine would be classified as a monobloc. Another common term for an engine block is "block"; the main structure of an engine consists of the cylinders, coolant passages, oil galleries and cylinder head. The first production engines of the 1880s to 1920s used separate components for each of these elements, which were bolted together during engine assembly. Modern engines, however combine many of these elements into a single component, in order to reduce production costs; the evolution from separate components to an engine block integrating several elements has been a gradual progression throughout the history of internal combustion engines.
The integration of elements has relied on the development of machining techniques. For example, a practical low-cost V8 engine was not feasible until Ford developed the techniques used to build the Ford flathead V8 engine; these techniques were applied to other engines and manufacturers. A cylinder block is the structure which contains the cylinder, plus any cylinder sleeves and coolant passages. In the earliest decades of internal combustion engine development, cylinders were cast individually, so cylinder blocks were produced individually for each cylinder. Following that, engines began to combine two or three cylinders into a single cylinder block, with an engine combining several of these cylinder blocks combined together. In early engines with multiple cylinder banks — such as a V6, V8 or flat-6 engine — each bank was a separate cylinder block. Since the 1930s, mass production methods have developed to allow both banks of cylinders to be integrated into the same cylinder block. Wet liner cylinder blocks use cylinder walls that are removable, which fit into the block by means of special gaskets.
They are referred to as "wet liners" because their outer sides come in direct contact with the engine's coolant. In other words, the liner is the entire wall, rather than being a sleeve. Advantages of wet liners are a lower mass, reduced space requirement and that the coolant liquid is heated quicker from a cold start, which reduces start-up fuel consumption and provides heating for the car cabin sooner. Dry liner cylinder blocks use either the block's material or a discrete liner inserted into the block to form the backbone of the cylinder wall. Additional sleeves are inserted within, which remain "dry" on their outside, surrounded by the block's material. For either wet or dry liner designs, the liners can be replaced allowing overhaul or rebuild without replacement of the block itself, although this is not a practical repair option. An engine where all the cylinders share a common block is called a monobloc engine. Most modern engines use a monoblock design of some type, therefore few modern engines have a separate block for each cylinder.
This has led to the term "engine block" implying a monobloc design and the term monobloc itself is used. In the early years of the internal combustion engine, casting technology could produce either large castings, or castings with complex internal cores to allow for water jackets, but not both simultaneously. Most early engines those with more than four cylinders, had their cylinders cast as pairs or triplets of cylinders bolted to a single crankcase; as casting techniques improved, an entire cylinder block of 4, 6, or 8 cylinders could be produced in one piece. This monobloc construction was more cost effective to produce. For engines with an inline configuration, this meant that all the cylinders, plus the crankcase, could be produced in a single component. One of the early engines produced using this method is the 4-cylinder engine in the Ford Model T, introduced in 1908; the method spread to straight-six engines and was used by the mid-1920s. Up until the 1930s, most V engines retained a separate block casting for each cylinder bank, with both bolted onto a common crankcase.
For economy, some engines were designed to use identical castings for each bank and right. A rare exception is the Lancia 22½° narrow-angle V12 of 1919, which used a single block casting combining both banks; the Ford flathead V-8 — introduced in 1932 — represented a significant development in the production of affordable V engines. It was the first V8 engine with a single engine block casting, putting a V8 into an affordable car for the first time; the communal water jacket of monobloc designs permitted closer spacing between cylinders. The monobloc design improved the mechanical stiffness of the engine against bending and the important torsional twist, as cylinder numbers, engine lengths, power ratings increased. Most engines blocks today, except some unusual V or radial engines, are a monobloc for all the cylinders, plus an integrated crankcase. In such cases, the skirts of the cylinder banks form a crankcase area of sorts, still called a crankcase despite no longer being a discrete part. Use of steel cylinder liners and bearing shells minimizes
Cast iron is a group of iron-carbon alloys with a carbon content greater than 2%. Its usefulness derives from its low melting temperature; the alloy constituents affect its colour when fractured: white cast iron has carbide impurities which allow cracks to pass straight through, grey cast iron has graphite flakes which deflect a passing crack and initiate countless new cracks as the material breaks, ductile cast iron has spherical graphite "nodules" which stop the crack from further progressing. Carbon ranging from 1.8 to 4 wt%, silicon 1–3 wt% are the main alloying elements of cast iron. Iron alloys with lower carbon content are known as steel. While this technically makes the Fe–C–Si system ternary, the principle of cast iron solidification can be understood from the simpler binary iron–carbon phase diagram. Since the compositions of most cast irons are around the eutectic point of the iron–carbon system, the melting temperatures range from 1,150 to 1,200 °C, about 300 °C lower than the melting point of pure iron of 1,535 °C.
Cast iron tends to be brittle, except for malleable cast irons. With its low melting point, good fluidity, excellent machinability, resistance to deformation and wear resistance, cast irons have become an engineering material with a wide range of applications and are used in pipes and automotive industry parts, such as cylinder heads, cylinder blocks and gearbox cases, it is resistant to weakening by oxidation. The earliest cast-iron artifacts date to the 5th century BC, were discovered by archaeologists in what is now Jiangsu in China. Cast iron was used in ancient China for warfare and architecture. During the 15th century, cast iron became utilized for cannon in Burgundy, in England during the Reformation; the amounts of cast iron used for cannon required large scale production. The first cast-iron bridge was built during the 1770s by Abraham Darby III, is known as The Iron Bridge. Cast iron was used in the construction of buildings. Cast iron is made from pig iron, the product of smelting iron ore in a blast furnace.
Cast iron can be made directly from the molten pig iron or by re-melting pig iron along with substantial quantities of iron, limestone and taking various steps to remove undesirable contaminants. Phosphorus and sulfur may be burnt out of the molten iron, but this burns out the carbon, which must be replaced. Depending on the application and silicon content are adjusted to the desired levels, which may be anywhere from 2–3.5% and 1–3%, respectively. If desired, other elements are added to the melt before the final form is produced by casting. Cast iron is sometimes melted in a special type of blast furnace known as a cupola, but in modern applications, it is more melted in electric induction furnaces or electric arc furnaces. After melting is complete, the molten cast iron is poured into ladle. Cast iron's properties alloyants. Next to carbon, silicon is the most important alloyant. A low percentage of silicon allows carbon to remain in solution forming iron carbide and the production of white cast iron.
A high percentage of silicon forces carbon out of solution forming graphite and the production of grey cast iron. Other alloying agents, chromium, molybdenum and vanadium counteracts silicon, promotes the retention of carbon, the formation of those carbides. Nickel and copper increase strength, machinability, but do not change the amount of graphite formed; the carbon in the form of graphite results in a softer iron, reduces shrinkage, lowers strength, decreases density. Sulfur a contaminant when present, forms iron sulfide, which prevents the formation of graphite and increases hardness; the problem with sulfur is. To counter the effects of sulfur, manganese is added because the two form into manganese sulfide instead of iron sulfide; the manganese sulfide is lighter than the melt, so it tends to float out of the melt and into the slag. The amount of manganese required to neutralize sulfur is 1.7 × sulfur content + 0.3%. If more than this amount of manganese is added manganese carbide forms, which increases hardness and chilling, except in grey iron, where up to 1% of manganese increases strength and density.
Nickel is one of the most common alloying elements because it refines the pearlite and graphite structure, improves toughness, evens out hardness differences between section thicknesses. Chromium is added in small amounts to reduce free graphite, produce chill, because it is a powerful carbide stabilizer. A small amount of tin can be added as a substitute for 0.5% chromium. Copper is added in the ladle or in the furnace, on the order of 0.5–2.5%, to decrease chill, refine graphite, increase fluidity. Molybdenum is added on the order of 0.3–1% to increase chill and refine the graphite and pearlite structure. Titanium is added as a degasser and deoxidizer, but it increases fluidity. 0.15–0.5% vanadium is added to cast iron to stabilize cementite, increase hardness, increase resistance to wear and heat. 0.1–0.3% zirconium helps to form graphite and increase fluidity. In malleable iron melts, bismuth is added, on the scale of 0.002–0.01%, to increase how much silicon can be added. In white iron, boron is added to aid in the production of malleable iron.
A manual transmission known as a manual gearbox, a standard transmission or colloquially in some countries as a stick shift, is a type of transmission used in motor vehicle applications. It uses a driver-operated clutch engaged and disengaged by a foot pedal or hand lever, for regulating torque transfer from the engine to the transmission. A conventional 5-speed manual transmission is the standard equipment in a base-model vehicle, while more expensive manual vehicles are equipped with a 6-speed transmission instead; the number of forward gear ratios is expressed for automatic transmissions as well. Manual transmissions feature a driver-operated clutch and a movable gear stick. Most automobile manual transmissions allow the driver to select any forward gear ratio at any time, but some, such as those mounted on motorcycles and some types of racing cars, only allow the driver to select the next-higher or next-lower gear; this type of transmission is sometimes called a sequential manual transmission.
In a manual transmission, the flywheel is attached to the engine's crankshaft and spins along with it. The clutch disc is in between the pressure plate and the flywheel, is held against the flywheel under pressure from the pressure plate; when the engine is running and the clutch is engaged, the flywheel spins the clutch plate and hence the transmission. As the clutch pedal is depressed, the throw out bearing is activated, which causes the pressure plate to stop applying pressure to the clutch disk; this makes the clutch plate stop receiving power from the engine, so that the gear can be shifted without damaging the transmission. When the clutch pedal is released, the throw out bearing is deactivated, the clutch disk is again held against the flywheel, allowing it to start receiving power from the engine. Manual transmissions are characterized by gear ratios that are selectable by locking selected gear pairs to the output shaft inside the transmission. Conversely, most automatic transmissions feature epicyclic gearing controlled by brake bands and/or clutch packs to select gear ratio.
Automatic transmissions that allow the driver to manually select the current gear are called manumatics. A manual-style transmission operated by computer is called an automated transmission rather than an automatic though no distinction between the two terms need be made. Contemporary automobile manual transmissions use four to six forward gear ratios and one reverse gear, although consumer automobile manual transmissions have been built with as few as two and as many as seven gears. Transmissions for heavy trucks and other heavy equipment have 8 to 25 gears so the transmission can offer both a wide range of gears and close gear ratios to keep the engine running in the power band. Operating aforementioned transmissions use the same pattern of shifter movement with a single or multiple switches to engage the next sequence of gear selection. French inventors Louis-Rene Panhard and Emile Levassor are credited with the development of the first modern manual transmission, they demonstrated their three-speed transmission in 1894 and the basic design is still the starting point for most contemporary manual transmissions.
This type of transmission offered multiple gear ratios and, in most cases, reverse. The gears were engaged by sliding them on their shafts, which required careful timing and throttle manipulation when shifting, so the gears would be spinning at the same speed when engaged; these transmissions are called sliding mesh transmissions or sometimes crash boxes, because of the difficulty in changing gears and the loud grinding sound that accompanied. Newer manual transmissions on 4+-wheeled vehicles have all gears mesh at all times and are referred to as constant-mesh transmissions, with "synchro-mesh" being a further refinement of the constant mesh principle. In both types, a particular gear combination can only be engaged when the two parts to engage are at the same speed. To shift to a higher gear, the transmission is put in neutral and the engine allowed to slow down until the transmission parts for the next gear are at a proper speed to engage; the vehicle slows while in neutral and that slows other transmission parts, so the time in neutral depends on the grade and other such factors.
To shift to a lower gear, the transmission is put in neutral and the throttle is used to speed up the engine and thus the relevant transmission parts, to match speeds for engaging the next lower gear. For both upshifts and downshifts, the clutch is released; some drivers use the clutch only for starting from a stop, shifts are done without the clutch. Other drivers will depress the clutch, shift to neutral engage the clutch momentarily to force transmission parts to match the engine speed depress the clutch again to shift to the next gear, a process called double clutching. Double clutching is easier to get smooth, as speeds that are close but not quite matched need to speed up or slow down only transmission parts, whereas with the clutch engaged to the engine, mismatched speeds are fighting the rotational inertia and power of the engine. Though automobile and light truck transmissions are now universally synchronized, transmissions for heavy trucks and machinery, motor
Alfa Romeo Stelvio
The Alfa Romeo Stelvio is a front engine, all wheel drive, five door compact luxury crossover SUV manufactured and marketed by the Alfa Romeo subdivision of FCA since debuting at the 2016 Los Angeles Auto Show and entering production at the Cassino Plant at the end of 2016. It is current top Alfa sales with about 43,000 samples per year. Sharing the platform of the mid-size Giulia sedan, the Stelvio uses FCA's Giorgio platform to be shared with Maserati and Jeep; the name Stelvio derives from the Stelvio Pass, Italy's highest mountain pass, noted for its 48 circuitous switchbacks. Preceded by the Kamal concept car in March 2003, the Stelvio is Alfa Romeo's first production SUV, using a modified version of the Giorgio platform shared with the Giulia, available in both rear and all-wheel drive configurations. Alfa Romeo made its first off the Matta, in the 1950s; the sporting trim level of the Stelvio, the Quadrifoglio, was unveiled on 16 November 2016 at the Los Angeles Auto Show. The European versions of the Stelvio were presented at the Geneva Motor Show in March 2017.
The car's engine lineup is similar to that of the Giulia's, with a turbocharged 2.0 litre inline-four and a 2.2-litre diesel inline four. The Quadrifoglio trim level will offer a 2.9 litre twin-turbo V6 rated with 510 PS developed by Ferrari for Alfa Romeo. On January 18, 2017, Alfa Romeo began accepting orders for the Stelvio First Edition in the EMEA region. On November 2, 2017, the Stelvio Quadrifoglio went on sale in Italy. For the model year of 2019, diesel engines of the Stelvio got updates to meet the Euro 6d emission standards, with AdBlue technology introduced to tackle particulates in the exhaust. 150 PS and 180 PS versions got 10 PS more power. In the United Kingdom, all models have now an 8.8 inch infotainment system with Apple Car Play and Android Auto as standard, small tweaks have been made throughout the ranges. In Europe, consumption standards use now WLTP measuring system, which should give more accurate consumption and emission figures. For 2019 Model year Alfa introduced new trim level for Europe the Ti, this is different than Ti version for sale in United States, the Ti has 280 PS 2.0 Turbo Petrol engine, paired with an eight speed automatic transmission, Q4 all wheel drive.
The Stelvio uses the same Giorgio platform used by the Giulia, but modified and raised by 22 cm compared to the sedan. The Stelvio has the same engines and most of the mechanics, including a carbon fiber driveshaft. In addition, compared to the Giulia, its track has increased by 2.9 cm in the rear and 5.4 cm in the front. It has a boot capacity of 525 l, it has a 50/50 weight distribution between the two axles, a drag coefficient of 0.32. To help keep the Stelvio's weight in check, Alfa Romeo uses aluminum for many body parts such as the fenders and tailgate, as well as for mechanical parts such as the suspension, braking system, engine; the suspension, called AlfaLink, implements double wishbones in the front, an aluminum multi-link configuration in the rear. The springs are longer than those in the Giulia, but stiffer to account for the extra weight and ride height; the driver sits 190 mm higher from the road than in the Giulia. Alfa's "Q4" all wheel drive system, rear drive but sends up to 50% of power to the front in low grip conditions, is standard on all trim levels, except an entry level turbo petrol version.
The Stelvio weighs 1,660 kg with fluids, 145 kg less than an equivalent BMW X3 and 110 kg less than a four cyl Porsche Macan. In North America, the Stelvio will be available in three different trim levels: Stelvio, Stelvio Ti and Quadrifoglio. At the 2018 Geneva Motor Show, one limited edition was unveiled NRING edition of the Stelvio; the NRING edition has Carbon ceramic brakes, Sparco carbonfibre seats, carbonfibre interior trim, a Mopar branded gear shifter and Mopar floor mats, the cars are differentiated on the exterior by NRING badges as well as carbonfibre mirror caps and side skirts. Equipment is upgraded to include adaptive cruise control, a premium sound system. In April 2018, NYIAS was unveiled Nero Edizione' Package for Stelvio, a new exterior appearance through special blacked out wheels and other touches; the Nero Edizione package is available only for the 280 horsepower, 2.0 litre model. At the 2019 Geneva International Motor Show, Alfa Romeo Racing limited edition was introduced, which celebrate Alfa Romeo's legendary racing history and the entry of a new Italian driver onto the Formula 1 scene: Antonio Giovinazzi joins the "Alfa Romeo Racing" team with World Champion Kimi Räikkönen.
This special edition has exclusive paintwork, as a tribute to the Alfa Romeo Racing C38 Formula 1 car. It has some stylistic details like some carbon fibre parts and Akrapovič titanium exhaust system; the weight was shaved off about 28 kg from the standard Quadrifoglio version. The diet was backed up by a technical tune-up by Alfa Romeo engineers that has resulted more torque and power, which reaches 520 PS; the Stelvio was crash tested in July 2017 by Euro NCAP, with a score of 97% for the adult occupant protection. Overall, the Stelvio achieved five star results. For adult protection, the Stelvio did "exceptionally well", with its near perfect 97 percent score matching that of the Volvo XC90; the Stelvio is fitted with an autonomous emergency braking system as standard. On 29 September 2017, the Alfa
A drive shaft, driving shaft, propeller shaft, or Cardan shaft is a mechanical component for transmitting torque and rotation used to connect other components of a drive train that cannot be connected directly because of distance or the need to allow for relative movement between them. As torque carriers, drive shafts are subject to torsion and shear stress, equivalent to the difference between the input torque and the load, they must therefore be strong enough to bear the stress, while avoiding too much additional weight as that would in turn increase their inertia. To allow for variations in the alignment and distance between the driving and driven components, drive shafts incorporate one or more universal joints, jaw couplings, or rag joints, sometimes a splined joint or prismatic joint; the term drive shaft first appeared during the mid 19th century. In Stover's 1861 patent reissue for a planing and matching machine, the term is used to refer to the belt-driven shaft by which the machine is driven.
The term is not used in his original patent. Another early use of the term occurs in the 1861 patent reissue for the Watkins and Bryson horse-drawn mowing machine. Here, the term refers to the shaft transmitting power from the machine's wheels to the gear train that works the cutting mechanism. In the 1890s, the term began to be used in a manner closer to the modern sense. In 1891, for example, Battles referred to the shaft between the transmission and driving trucks of his Climax locomotive as the drive shaft, Stillman referred to the shaft linking the crankshaft to the rear axle of his shaft-driven bicycle as a drive shaft. In 1899, Bukey used the term to describe the shaft transmitting power from the wheel to the driven machinery by a universal joint in his Horse-Power. In the same year, Clark described his Marine Velocipede using the term to refer to the gear-driven shaft transmitting power through a universal joint to the propeller shaft. Crompton used the term to refer to the shaft between the transmission of his steam-powered Motor Vehicle of 1903 and the driven axle.
The pioneering automobile industry company, was the first to use a drive shaft in a gasoline-powered car. Built in 1901, today this vehicle is in the collection of the Smithsonian Institution. An automobile may use a longitudinal shaft to deliver power from an engine/transmission to the other end of the vehicle before it goes to the wheels. A pair of short drive shafts is used to send power from a central differential, transmission, or transaxle to the wheels. In front-engined, rear-drive vehicles, a longer drive shaft is required to send power the length of the vehicle. Two forms dominate: The torque tube with a single universal joint and the more common Hotchkiss drive with two or more joints; this system became known as Système Panhard after the automobile company Panhard et Levassor patented it. Most of these vehicles have a clutch and gearbox mounted directly on the engine, with a drive shaft leading to a final drive in the rear axle; when the vehicle is stationary, the drive shaft does not rotate.
Some vehicles, seeking improved weight balance between rear, use a rear-mounted transaxle. In some non-Porsche models, this places the clutch and transmission at the rear of the car and the drive shaft between them and the engine. In this case the drive shaft rotates continuously with the engine when the car is stationary and out of gear. However, the Porsche 924/944/928 models have the clutch mounted to the back of the engine in a bell housing and the drive shaft from the clutch output, located inside of a hollow protective torque tube, transfers power to the rear mounted transaxle, thus the Porsche driveshaft only rotates when the rear wheels are turning as the engine-mounted clutch can decouple engine crankshaft rotation from the driveshaft. So for Porsche, when the driver is using the clutch while briskly shifting up or down, the engine can rev with the driver's accelerator pedal input, since with the clutch disengaged, the engine and flywheel inertia is low and is not burdened with the added rotational inertia of the driveshaft.
The Porsche torque tube is solidly fastened to both the engine's bell housing and to the transaxle case, fixing the length and alignment between the bell housing and the transaxle and minimizing rear wheel drive reaction torque from twisting the transaxle in any plane. A drive shaft connecting a rear differential to a rear wheel may be called a half-shaft; the name derives from the fact. Early automobiles used chain drive or belt drive mechanisms rather than a drive shaft; some used electrical motors to transmit power to the wheels. In British English, the term "drive shaft" is restricted to a transverse shaft that transmits power to the wheels the front wheels. A drive shaft connecting the gearbox to a rear differential is called a propeller shaft, or prop-shaft. A prop-shaft assembly consists of a slip joint and one or more universal joints. Where the engine and axles are separated from each other, as on four-wheel drive and rear-wheel drive vehicles, it is the propeller shaft that serves to transmit the drive force generated by the engine to the axles.
Several different types of drive shaft are used in the automotive industry: One-piece drive shaft Two-piece drive shaft Slip-in-tube drive shaftThe slip-in-tube drive shaft is a new type that improves crash safety. It can be compressed to absorb energy in the event of a crash, so is known as a collapsible drive shaft
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
Sport utility vehicle
Sport-utility, SUV or sport-ute is an automotive classification a kind of station wagon / estate car with off-road vehicle features like raised ground clearance and ruggedness, available four-wheel drive. Many SUVs are built on a light-truck chassis but operated as a family vehicle, though designed to be used on rougher surfaces, most used on city streets or highways. In recent years, in some countries the term SUV has replaced terms like "Jeep" or "Land-Rover" in the popular lexicon as a generic description for light 4WD vehicles. Many SUVs have an upright built body and tall interior packaging, a high seating position and center of gravity, available all-wheel drive for off-road capability; some SUVs include the towing capacity of a pickup truck and the passenger-carrying space of a minivan or large sedan. The traditional truck-based SUV is more and more being supplanted by unitary body SUVs and crossovers based on regular automobile platforms for lighter weight and better fuel efficiency.
In some countries, notably the United States, SUVs are not classified as cars, but as light trucks. SUVs overtook lower medium segment cars to become the world's largest automotive segment in 2015, accounting for 22.9 percent of global light vehicle sales, or 36.8% of the world's passenger car market. Worldwide sales of SUVs grew from 5 million units in 2000 to 20 million in 2015 and are forecast to hit 42 million units by 2031. Becoming popular in the 1990s and early 2000s, SUVs combined with other light trucks, like pickups and minivans, supplanted many conventional large passenger cars and station wagons, changed the composition of America's vehicle fleet. SUV sales temporarily declined due to high oil prices and a declining economy, but by 2010, SUV sales around the world were growing again, in spite of gasoline prices; the market has overwhelmingly come to prefer 4/5-door models in favor of popular 2-door off-roaders. There is no universally accepted definition of the sport utility vehicle.
Dictionaries, automotive experts, journalists use varying wordings and defining characteristics, in addition to which there are regional variations of the use by both the media and the general public. The auto industry has not settled on one definition of the SUV either; the actual term "Sport Utility Vehicle" did not come into wide popular usage until the late 1980s — prior to such vehicles were marketed during their era as 4-wheel drives, station wagons, or other monikers. The American Merriam-Webster online dictionary offers three different definitions; the general definition of a "sport-utility vehicle", found under "SUV" reads: "a rugged automotive vehicle similar to a station wagon but built on a light-truck chassis", it is defined in the definition of sport-utility vehicle for students as: "an automobile similar to a station wagon but built on a light truck frame". However, the Merriam-Webster definition "for English Language Learners" reads: "a large vehicle, designed to be used on rough surfaces but, used on city roads or highways".
The Webster's New World Dictionary defines sport utility vehicle as "a passenger vehicle similar to a station wagon but with the chassis of a small truck and four-wheel drive". In recent years, the term SUV has come to replace the use of "jeep" as a generic trademark and description of these type of vehicles, a name that originated during World War II as slang for the light general purpose military truck. A Hemmings article defines the sport utility vehicle as bridging the gap between cars and trucks, "combining car-like appointments and wagon practicality with steadfast off-road capability". S. it only applies to the newer street oriented one, whereas "Jeep", "Land Rover" or 4x4 are used for the off-roader oriented ones. The German automaker BMW utilizes the term SAV to denote "Sport Activity Vehicles." Not all SUVs have four-wheel drive capabilities, not all four-wheel-drive passenger vehicles are SUVs. Although some SUVs have off-road capabilities, they play only a secondary role, SUVs do not have the ability to switch among two-wheel and four-wheel-drive high gearing and four-wheel-drive low gearing.
While automakers tout an SUV's off-road prowess with advertising and naming, the daily use of SUVs is on paved roads. In British English the terms "four-by-four" or "off-road vehicle" are preferred, for example the Chambers Dictionary has no entry for sport utility vehicle; the Collins English online dictionary defines sport utility vehicle as a "powerful vehicle with four-wheel drive that can be driven over rough ground" or "a high-powered car with four-wheel drive designed for off-road use", but the citations quoted by Collins are few. Other alternative terms are "four-wheel drive", or using the brand name to describe the vehicle. In the United States, many government regulations have categories for "off-highway vehicles" which are loosely defined and result in SUVs being classified as light trucks. For example, Corporate Average Fuel Economy regulations included "permit greater cargo-carrying capacity than passenger carrying volume" in the definition for trucks, resulting in SUVs being classified as light trucks.
This classification as trucks allowed SUVs to be regulated