In automotive engineering, an exhaust manifold collects the exhaust gases from multiple cylinders into one pipe. The word manifold comes from the Old English word manigfeald and refers to the folding together of multiple inputs and outputs. Exhaust manifolds are simple cast iron or stainless steel units which collect engine exhaust gas from multiple cylinders and deliver it to the exhaust pipe. For many engines, there are aftermarket tubular exhaust manifolds known as headers in American English, as extractor manifolds in British and Australian English, as "tubular manifolds" in British English; these consist of individual exhaust headpipes for each cylinder, which usually converge into one tube called a collector. Headers that do not have collectors are called zoomie headers; the most common types of aftermarket headers are made of mild steel or stainless steel tubing for the primary tubes along with flat flanges and a larger diameter collector made of a similar material as the primaries. They may be painted with a heat-resistant finish, or bare.
Chrome plated headers are available but these tend to blue after use. Polished stainless steel will color, but less than chrome in most cases. Another form of modification used is to insulate a aftermarket manifold; this decreases the amount of heat given off into the engine bay, therefore reducing the intake manifold temperature. There are a few types of thermal insulation but three are common: Ceramic paint is sprayed or brushed onto the manifold and cured in an oven; these are thin, so have little insulatory properties. A ceramic mixture is bonded to the manifold via thermal spraying to give a tough ceramic coating with good thermal insulation; this is used on performance production cars and track-only racers. Exhaust wrap is wrapped around the manifold. Although this is cheap and simple, it can lead to premature degradation of the manifold; the goal of performance exhaust headers is to decrease flow resistance, to increase the volumetric efficiency of an engine, resulting in a gain in power output.
The processes occurring can be explained by the gas laws the ideal gas law and the combined gas law. When an engine starts its exhaust stroke, the piston moves up the cylinder bore, decreasing the total chamber volume; when the exhaust valve opens, the high pressure exhaust gas escapes into the exhaust manifold or header, creating an "exhaust pulse" comprising three main parts: The high-pressure head is created by the large pressure difference between the exhaust in the combustion chamber and the atmospheric pressure outside of the exhaust system As the exhaust gases equalize between the combustion chamber and the atmosphere, the difference in pressure decreases and the exhaust velocity decreases. This forms the medium-pressure body component of the exhaust pulse The remaining exhaust gas forms the low-pressure tail component; this tail component may match ambient atmospheric pressure, but the momentum of the high and medium-pressure components reduces the pressure in the combustion chamber to a lower-than-atmospheric level.
This low pressure helps to extract all the combustion products from the cylinder and induct the intake charge during the overlap period when both intake and exhaust valves are open. The effect is known as "scavenging". Length, cross-sectional area, shaping of the exhaust ports and pipeworks influences the degree of scavenging effect, the engine speed range over which scavenging occurs; the magnitude of the exhaust scavenging effect is a direct function of the velocity of the high and medium pressure components of the exhaust pulse. Performance headers work to increase the exhaust velocity as much as possible. One technique is tuned-length primary tubes; this technique attempts to time the occurrence of each exhaust pulse, to occur one after the other in succession while still in the exhaust system. The lower pressure tail of an exhaust pulse serves to create a greater pressure difference between the high pressure head of the next exhaust pulse, thus increasing the velocity of that exhaust pulse.
In V6 and V8 engines where there is more than one exhaust bank, "Y-pipes" and "X-pipes" work on the same principle of using the low pressure component of an exhaust pulse to increase the velocity of the next exhaust pulse. Great care must be used when selecting the diameter of the primary tubes. Tubes that are too large will cause the exhaust gas to expand and slow down, decreasing the scavenging effect. Tubes that are too small will create exhaust flow resistance which the engine must work to expel the exhaust gas from the chamber, reducing power and leaving exhaust in the chamber to dilute the incoming intake charge. Since engines produce more exhaust gas at higher speeds, the header are tuned to a particular engine speed range according to the intended application. Wide primary tubes offer the best gains in power and torque at higher engine speeds, while narrow tubes offer the best gains at lower speeds. Many headers are resonance tuned, to utilize the low-pressure reflected wave rarefaction pulse which can help scavenging the combustion chamber during valve overlap.
This pulse is created in all exhaust systems each time a change in density occurs, such as when exhaust merges into the collector. For clarification, the rarefaction pulse is the technical term for the same process, described above in the "he
A V6 engine is a V engine with six cylinders mounted on the crankshaft in two banks of three cylinders set at a 60 or 90 degree angle to each other. The V6 is one of the most compact engine configurations ranging from 2.0 L to 4.3 L displacement, it is shorter than the inline 4. Because of its short length, the V6 fits well in the used transverse engine front-wheel drive layout; the V6 is commercially successful in contemporary mid-size cars because it is less expensive to build and is smoother in large sizes than the inline 4, which develops serious vibration problems in larger engines. The wider 90° V6 will fit in an engine compartment designed for a V8, providing a low-cost alternative to the V8 in an expensive car, while the narrower 60° V6 will fit in most engine compartments designed for an I4, proving a more powerful and smoother alternative engine to the four. Buyers of luxury and/or performance cars might prefer an inline 6, which has better smoothness, or a flat 6 which has a lower center of gravity.
Recent forced induction V6 engines have delivered horsepower and torque output comparable to contemporary larger displacement aspirated V8 engines, while reducing fuel consumption and emissions, such as the Volkswagen Group's 3.0 TFSI, supercharged and directly injected, Ford Motor Company's turbocharged and directly injected EcoBoost V6, both of which have been compared to Volkswagen's 4.2 V8 engine. Modern V6 engines range in displacement from 2.0 to 4.3 L, though larger and smaller examples have been produced, such as the 1991 Mazda MX3, the Rover KV6 engine. Some of the first V6-powered automobiles were built in 1905 by Marmon; this firm became something of a V-engine specialist producing, in the 1930s, a V16 engine, as one of the few automakers in the world. From 1908 to 1913, the Deutz Gasmotoren Fabrik produced gasoline-electric train sets which used a V6 as generator engine. In 1918 Leo Goosen designed a V6-powered car for Buick Chief Engineer Walter L. Marr. Only one prototype Buick V6 car was built in 1918.
The first series-production V6 was introduced by Lancia in 1950 with the Lancia Aurelia model. Lancia sought a more powerful engine that would fit into an existing narrow engine bay. Lancia engineer Francesco De Virgilio began analyzing the vibration of alternative V-angles for a V6 engine in 1943, he found that a V6 with its cylinders positioned at a 60° V-angle could be made uniquely smooth-running in comparison with other possible V-angles. There was resistance to his conclusion because the V6 was a unknown engine type in the 1950s, his design featured four main bearings and six crankpins, resulting in evenly spaced firing intervals and low vibrations. Other manufacturers took note and soon other V6 engines were designed. In 1959, General Motors' GMC Truck division introduced a new 60-degree heavy-duty 305 in3 gasoline-fueled 60° V6 for use in their pickup trucks and Suburbans; the use of the sweet spot of 60 degrees' V-angle maximized power while minimizing vibration and exterior dimensions of the engine.
In short, GMC introduced a compact V6 design at a time when the straight-six engine was considered the pinnacle of 6-cylinder design.1962 saw the introduction of the Buick Special, which offered a new 90° V6 with uneven firing intervals, derived from—and shared some parts with—a small Buick V8 engine of the period. To save design time and expense, it was built much like a V8; the combination of a 90° V-angle with only three crank pins—set at 120° apart, with opposing cylinders sharing a crank pin as most V8 engines do—the cylinders fired alternatively at 90 and 150° of crankshaft rotation. This uneven firing caused harmonic vibrations in the drive train that were perceived as a rough-running engine by the buyers. GM sold the engine tooling to Kaiser-Jeep in 1967. In 1977, Buick introduced a split pin crankshaft to implement an even-fire version of this engine in which cylinders fired every 120°; the V6 does not have the inherent freedom from vibration that the inline-six and flat-six have, but it can be modeled as two separate straight-3 engines sharing a crankshaft.
Counterweights on the crankshaft and a counter-rotating balance shaft are required to compensate for the first order rocking motions. Straight engines with an odd number of cylinders are inherently unbalanced because there is always an odd number of pistons moving in one direction while a different number move the opposite direction; this causes an end-to-end rocking motion at crankshaft speed in a straight-three engine. V6 designs will behave like two unbalanced three-cylinder engines running on the same crankshaft unless steps are taken to mitigate it, for instance by using offset journals or flying arms on the crankshaft or a counter-rotating balance shaft. In the V6 with 120° between banks, pairs of connecting rods can share a single crank pin, but the two cylinder banks run like two inline 3s, both having an end-to-end rocking couple. Unlike in a V8 engine with a crossplane crankshaft, the vibrations from one bank do not cancel the vibrations from the other, so a rotating balancing shaft is required to compensate for the primary vibrations.
Because the 120° V6 is nearly as wide as a 180° flat-6 but is not nearly as smooth, can be more expensive if a balancing shaft is added, this configuration is seen in production engines. In the V6 with 90° between cylinders, split crank pins are required to offset the connecting rods by 30° to achieve an 120° between firing intervals, crankshaft counterw
Radiator (engine cooling)
Radiators are heat exchangers used for cooling internal combustion engines in automobiles but in piston-engined aircraft, railway locomotives, stationary generating plant or any similar use of such an engine. Internal combustion engines are cooled by circulating a liquid called engine coolant through the engine block, where it is heated through a radiator where it loses heat to the atmosphere, returned to the engine. Engine coolant is water-based, but may be oil, it is common to employ a water pump to force the engine coolant to circulate, for an axial fan to force air through the radiator. In automobiles and motorcycles with a liquid-cooled internal combustion engine, a radiator is connected to channels running through the engine and cylinder head, through which a liquid is pumped; this liquid may be water, but is more a mixture of water and antifreeze in proportions appropriate to the climate. Antifreeze itself is ethylene glycol or propylene glycol. A typical automotive cooling system comprises: a series of channels cast into the engine block and cylinder head, surrounding the combustion chambers with circulating liquid to carry away heat.
The radiator transfers the heat from the fluid inside to the air outside, thereby cooling the fluid, which in turn cools the engine. Radiators are often used to cool automatic transmission fluids, air conditioner refrigerant, intake air, sometimes to cool motor oil or power steering fluid. Radiators are mounted in a position where they receive airflow from the forward movement of the vehicle, such as behind a front grill. Where engines are mid- or rear-mounted, it is common to mount the radiator behind a front grill to achieve sufficient airflow though this requires long coolant pipes. Alternatively, the radiator may draw air from the flow over the top of the vehicle or from a side-mounted grill. For long vehicles, such as buses, side airflow is most common for engine and transmission cooling and top airflow most common for air conditioner cooling. Automobile radiators are constructed of a pair of header tanks, linked by a core with many narrow passageways, giving a high surface area relative to volume.
This core is made of stacked layers of metal sheet, pressed to form channels and soldered or brazed together. For many years radiators were made from copper cores soldered to brass headers. Modern radiators have aluminum cores, save money and weight by using plastic headers; this construction is more prone to failure and less repaired than traditional materials. An earlier construction method was the honeycomb radiator. Round tubes were swaged into hexagons at their ends stacked together and soldered; as they only touched at their ends, this formed what became in effect a solid water tank with many air tubes through it. Some vintage cars use radiator cores made from coiled tube, a less efficient but simpler construction. Radiators first used downward vertical flow, driven by a thermosyphon effect. Coolant is heated in the engine, becomes less dense, so rises; as the radiator cools the fluid, the coolant falls. This effect is sufficient for low-power stationary engines, but inadequate for all but the earliest automobiles.
All automobiles for many years have used centrifugal pumps to circulate the engine coolant because natural circulation has low flow rates. A system of valves or baffles, or both, is incorporated to operate a small radiator inside the vehicle; this small radiator, the associated blower fan, is called the heater core, serves to warm the cabin interior. Like the radiator, the heater core acts by removing heat from the engine. For this reason, automotive technicians advise operators to turn on the heater and set it to high if the engine is overheating, to assist the main radiator; the engine temperature on modern cars is controlled by a wax-pellet type of thermostat, a valve which opens once the engine has reached its optimum operating temperature. When the engine is cold, the thermostat is closed except for a small bypass flow so that the thermostat experiences changes to the coolant temperature as the engine warms up. Engine coolant is directed by the thermostat to the inlet of the circulating pump and is returned directly to the engine, bypassing the radiator.
Directing water to circulate only through the engine allows the engine to reach optimum operating temperature as as possible whilst avoiding localised "hot spots." Once the coolant reaches the thermostat's activation temperature, it opens, allowing water to flow through the radiator to prevent the temperature rising higher. Once at optimum temperature, the thermostat controls the flow of engine coolant to the radiator so that the engine continues to operate at optimum temperature. Under peak load conditions, such as driving up a steep hill whilst laden on a hot day, the thermostat will be approaching open because the engine will be producing near to maximum power while the velocity of air flow across the radiator is low. Conversely, when cruising fast downhill on a motorway on a cold night on a light throttle, the thermostat will be nearly clos
Kei car is the Japanese vehicle category for the smallest highway-legal passenger cars. Similar Japanese categories existing for microvans, Kei trucks; the kei car category was created by the Japanese government in 1949, the regulations have been revised several times since. These regulations specify a maximum vehicle size, engine capacity of 660cc and power output, so that the kei car may enjoy both tax and insurance benefits. In most rural areas are exempted from the requirement to certify that adequate parking is available for the vehicle. Kei cars have become successful in Japan — consisting just over one third of domestic new car sales in fiscal 2016, in spite of dropping from a record 40% market share in 2013, just three years prior. However, in export markets, the genre is too specialized and too small for most models to be profitable. Notable exceptions exist though, for instance the Suzuki Alto and Jimny models, which were exported from ca. 1980. Most kei cars are designed and manufactured in Japan, however there have been overseas models that have been imported into Japan to be sold as kei cars.
Kei cars feature yellow license plates, earning them the name "yellow-plate cars" in English-speaking circles. Japanese government regulations limit the physical size, engine power and engine displacement of kei cars. Kei cars are available with forced-induction engines, automatic and CV transmissions, front-wheel drive and all-wheel drive; the Kei-car legal class originated in the era following the end of the Second World War, when most Japanese could not afford a full-sized car, but many had enough money to buy a motorcycle. To promote the growth of the car industry, as well as to offer an alternative delivery method to small business and shop owners, the kei car category and standards were created. Limited to a displacement of only 150 cc in 1949, dimensions and engine size limitations were expanded to tempt more manufacturers to produce kei cars. In 1955, the displacement limit increased to 360 cc for both two-strokes, as well as four-stroke engines, resulting in several new kei car models beginning production in the following years.
These included the 1955 Suzuki Suzulight and the 1958 Subaru 360, the first mass-produced kei car able to fill people's need for basic transportation without being too compromised. In 1955, the Japanese Ministry of International Trade and Industry set forth goals to develop a "national car", larger than kei cars produced at the time; this goal influenced Japanese automobile manufacturers to determine how best to focus their product development efforts for the smaller kei cars, or the larger "national car". The small exterior dimensions and engine displacement reflected the driving environment in Japan, with speed limits in Japan realistically not exceeding 40 km/h in urban areas; the class went through a period of increasing sophistication, with an automatic transmission appearing in the Honda N360 in August 1968, with front disc brakes becoming available on a number of sporting kei cars, beginning with the Honda Z GS of January 1970. Power outputs kept climbing, reaching a peak in the 40 PS Daihatsu Fellow Max SS of July 1970.
Sales increased reaching a peak of 750,000 in 1970. Throughout the 1970s, the government kept whittling away at the benefits offered to kei vehicles, which combined with stricter emissions standards to lower sales drastically through the first half of the decade. Honda and Mazda withdrew from the contracting passenger kei car market, in 1974 and 1976 although they both maintained a limited offering of commercial vehicles; until 31 December 1974, kei cars used smaller license plates than regular cars 230 mm × 125 mm. As of 1975, kei cars received the medium-sized standard plates. To set them apart from regular passenger cars, the plates were now yellow and black rather than white and green. Sales had been declining, reaching a low-water mark of 150,000 passenger cars in 1975, 80% less than 1970 sales. Many were beginning to doubt the continued existence of the kei car, with both Honda and Mazda withdrawing in the middle of the 1970s. Emissions laws were another problem for the kei car industry in the mid 1970s.
From 1973 to 1978, emissions standards were to be tightened in four steps. Meeting the stricter standards which were to be introduced in 1975 would be problematic for manufacturers of kei cars; this was hard for Daihatsu and Suzuki, which focused on two-stroke engines. Daihatsu, had both the engineering backing and powerful connections of their large owner, Toyota, to aid them in meeting the new requirements. All manufacturers of kei cars were clamoring for increasing the engine displacement and vehicle size limits, claiming that the emissions standards could not be met with a functional 360-cc engine. In the end, the Japanese legislature relented, increasing the overall length and width restrictions by 200 mm and 100 mm respectively. Engine size was increased to 550 cc, taking effect from 1 January 1976; the new standards were announced on 26 August 1975, leaving little time for manufacturers to revise their designs to take advantage of the new limits. Most manufacturers were somewhat surprised by the decision.
The Acura RDX is Acura’s first compact luxury crossover SUV, taking over from the MDX as Acura's entry-level crossover SUV, as the MDX grew in size and price. The RDX was built upon the same platform Honda uses for their Civic and CR-V passenger cars. Previewed as the Acura RD-X concept car, the production RDX had its debut at the 2006 New York Auto Show and went on sale on August 11, 2006. A facelifted 2010 model went on sale in August 2009, adopting Acura's power plenum grille seen on its sedan models. Front-wheel drive was added; the first generation RDX is powered by turbocharged gasoline engines. The 2.3-litre straight-4 K23A1 engine has all-aluminum construction, an i-VTEC head, dual balance shafts. It was one of the only four-cylinder powered luxury SUVs of its generation. Honda's variable flow turbocharger reduces turbo lag by using a valve to narrow the exhaust passage at low rpm, increasing the velocity of the exhaust flow and keeping the turbine spinning rapidly. At higher rpm, the valve opens to allow more exhaust flow for increased boost.
The engine features a top-mounted intercooler which receives air from the grille, channeled by ducting under the hood. The Acura RDX engine is rated at 240 bhp at 6,000 rpm with a torque peak of 260 ft⋅lbf at 4,500 rpm; the U. S. Environmental Protection Agency estimated fuel mileage is 19 mpg‑US city and 23 mpg‑US highway miles per gallon. Driving style and the terrain plays an important part in this Vehicle's fuel economy. Uphill driving, frequent lane changes and sudden accelerations can increase turbo usage to increase torque output to the SH-AWD system and thus cause much higher fuel consumption. New more recent EPA mileage estimates as of February 2007 are 17 mpg‑US city and 22 mpg‑US highway; the required fuel is premium 91 octane unleaded. The Acura RDX comes standard with a five-speed automatic transmission with Acura's SportShift sequential manual shift capability, activated by paddles mounted on the steering wheel; the paddles can be used in Drive to make a gear change with the transmission returning to automatic mode as soon as the vehicle resumes a steady-cruise state.
The Sport setting has higher shift points and quicker downshifts, using a paddle in “Sport” puts the transmission in full manual mode. The RDX has a version of Acura's Super Handling All-Wheel Drive, first seen on the flagship RL sedan; the system can vary the front/rear torque distribution from 90/10 to 30/70, depending on whether the vehicle is accelerating, hill climbing, taking a curve, or encountering poor road conditions. When taking a curve, a pair of magnetic flux clutches in the rear differential can transfer as much as 100% of the available rear torque to the outside wheel; that torque transfer, combined with a 1.7% rear over-rotation of the rear wheel helps rotate the RDX through a turn. The RDX seats five and comes standard with leather seating, a moonroof, automatic climate control, all the expected power features; the RDX 7-speaker audio system features an in-dash 6-CD changer, capable of playing standard Audio CDs, Data-CDs burned with either MP3 or WMA files, it plays DVD-A type CDs.
The RDX's sound system includes XM Satellite Radio with a complimentary 3-month subscription. Much of the interior technology introduced in the RL sedan is found in the optional "Technology Package"; this package includes the latest version of Acura's navigation system, complete with a rear view camera, XM Nav-Traffic real-time traffic monitoring, Zagat restaurant reviews. The package features a 10-speaker ELS Surround audio system with DTS and Dolby Pro Logic II surround sound; the audio system plays DVD-Audio discs as well. Both stereos come with a 1/8" auxiliary input jack, which may be used to plug in external sources such as iPods. For 2007, Acura offered an iPod adapter for the RDX, wired into the glove box, allowed the iPod to be controlled through the RDX's sound system interface. Due to hardware incompatibilities the Honda/Acura iPod musiclink has been discontinued as of model year 2008. 2010+ models come standard with a USB connection that interfaces with Apple iPod players and other USB mass storage devices, such as flash drives that contain MP3, WMA6 or AAC music files while being stored in the center console.
All of the ELS sound system's operations can be activated by voice command, as can most of the operations for the navigation and climate control systems. In addition, the vehicle will interact with most Bluetooth-equipped cell phones; the driver can receive calls through verbal command. During the call, the sound system will mute and channel the call through the speakers while caller and signal information is displayed on the instrument cluster; the tailgate opens over six-feet high and 60/40 rear seatbacks fold down for a flat cargo area. A hard cargo cover can fit flush on the floor when not needed and is reversible to carry wet or dirty cargo; the cabin includes several storage areas including a lockable center console that can hold a standard size laptop computer. The cargo hold is small size compared to most rivals and does not have the adjustable cargo tracks or a rear parcel shelf; the Acura RDX is the second Acura vehicle to feature the Advanced Compatibility Engineering body structure, designed to absorb energy from a collision.
The RDX comes standard with six airbags, including dual front airbags, front side airbags and dual side curtain airbags. The front airb
Aluminium alloys are alloys in which aluminium is the predominant metal. The typical alloying elements are copper, manganese, silicon and zinc. There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories heat-treatable and non-heat-treatable. About 85% of aluminium is used for wrought products, for example rolled plate and extrusions. Cast aluminium alloys yield cost-effective products due to the low melting point, although they have lower tensile strengths than wrought alloys; the most important cast aluminium alloy system is Al–Si, where the high levels of silicon contribute to give good casting characteristics. Aluminium alloys are used in engineering structures and components where light weight or corrosion resistance is required. Alloys composed of aluminium have been important in aerospace manufacturing since the introduction of metal-skinned aircraft. Aluminium-magnesium alloys are both lighter than other aluminium alloys and much less flammable than alloys that contain a high percentage of magnesium.
Aluminium alloy surfaces will develop a white, protective layer of aluminium oxide if left unprotected by anodizing and/or correct painting procedures. In a wet environment, galvanic corrosion can occur when an aluminium alloy is placed in electrical contact with other metals with more positive corrosion potentials than aluminium, an electrolyte is present that allows ion exchange. Referred to as dissimilar-metal corrosion, this process can occur as exfoliation or as intergranular corrosion. Aluminium alloys can be improperly heat treated; this causes internal element separation, the metal corrodes from the inside out. Aluminium alloy compositions are registered with The Aluminum Association. Many organizations publish more specific standards for the manufacture of aluminium alloy, including the Society of Automotive Engineers standards organization its aerospace standards subgroups, ASTM International. Aluminium alloys with a wide range of properties are used in engineering structures. Alloy systems are classified by a number system or by names indicating their main alloying constituents.
Selecting the right alloy for a given application entails considerations of its tensile strength, ductility, workability and corrosion resistance, to name a few. A brief historical overview of alloys and manufacturing technologies is given in Ref. Aluminium alloys are used extensively in aircraft due to their high strength-to-weight ratio. On the other hand, pure aluminium metal is much too soft for such uses, it does not have the high tensile strength, needed for airplanes and helicopters. Aluminium alloys have an elastic modulus of about 70 GPa, about one-third of the elastic modulus of most kinds of steel and steel alloys. Therefore, for a given load, a component or unit made of an aluminium alloy will experience a greater deformation in the elastic regime than a steel part of identical size and shape. Though there are aluminium alloys with somewhat-higher tensile strengths than the used kinds of steel replacing a steel part with an aluminium alloy might lead to problems. With new metal products, the design choices are governed by the choice of manufacturing technology.
Extrusions are important in this regard, owing to the ease with which aluminium alloys the Al–Mg–Si series, can be extruded to form complex profiles. In general and lighter designs can be achieved with Aluminium alloy than is feasible with steels. For instance, consider the bending of a thin-walled tube: the second moment of area is inversely related to the stress in the tube wall, i.e. stresses are lower for larger values. The second moment of area is proportional to the cube of the radius times the wall thickness, thus increasing the radius by 26% will lead to a halving of the wall stress. For this reason, bicycle frames made of aluminium alloys make use of larger tube diameters than steel or titanium in order to yield the desired stiffness and strength. In automotive engineering, cars made of aluminium alloys employ space frames made of extruded profiles to ensure rigidity; this represents a radical change from the common approach for current steel car design, which depend on the body shells for stiffness, known as unibody design.
Aluminium alloys are used in automotive engines in cylinder blocks and crankcases due to the weight savings that are possible. Since aluminium alloys are susceptible to warping at elevated temperatures, the cooling system of such engines is critical. Manufacturing techniques and metallurgical advancements have been instrumental for the successful application in automotive engines. In the 1960s, the aluminium cylinder heads of the Corvair earned a reputation for failure and stripping of threads, not seen in current aluminium cylinder heads. An important structural limitation of aluminium alloys is their lower fatigue strength compared to steel. In controlled laboratory conditions, steels display a fatigue limit, the stress amplitude below which no failures occur – the metal does not continue to weaken with extended stress cycles. Aluminium alloys do not have this lower fatigue limit and will continue to weaken with continued stress cycles. Aluminium alloys are therefore sparsely used in parts that require high fatigue strength in the high cycle regime.
The metal's sensitivity to heat must be considered. A routine workshop procedure involving heating is complicated by the fact that aluminium, unlike steel, will m
In automotive engineering a multi-valve or multivalve engine is one where each cylinder has more than two valves. A multi-valve engine has better breathing and may be able to operate at higher revolutions per minute than a two-valve engine, delivering more power. A multi-valve engine design has three, four, or five valves per cylinder to achieve improved performance. Any four-stroke internal combustion engine needs at least two valves per cylinder: one for intake of air and fuel, another for exhaust of combustion gases. Adding more valves increases valve area and improves the flow of intake and exhaust gases, thereby enhancing combustion, volumetric efficiency, power output. Multi-valve geometry allows the spark plug to be ideally located within the combustion chamber for optimal flame propagation. Multi-valve engines tend to have smaller valves that have lower reciprocating mass, which can reduce wear on each cam lobe, allow more power from higher RPM without the danger of valve bounce; some engines are designed to open each intake valve at a different time, which increases turbulence, improving the mixing of air and fuel at low engine speeds.
More valves provide additional cooling to the cylinder head. The disadvantages of multi-valve engines are an increase in manufacturing cost and a potential increase in oil consumption due to the greater number of valve stem seals; some SOHC multi-valve engines use a single fork-shaped rocker arm to drive two valves so that fewer cam lobes will be needed in order to reduce manufacturing costs. Three-valve cylinder headThis has two smaller intake valves. A three-valve layout allows better breathing than a two-valve head, but the large exhaust valve results in an RPM limit no higher than a two-valve head; the manufacturing cost for this design can be lower than for a four-valve design. The three-valve design was common in early 1990s; the Ducati ST3 V-twin had 3-valve heads. Four-valve cylinder headThis is the most common type of multi-valve head, with two exhaust valves and two similar inlet valves; this design allows similar breathing as compared to a three-valve head, as the small exhaust valves allow high RPM, this design is suitable for high power outputs.
Five-valve cylinder headLess common is the five-valve head, with two exhaust valves and three inlet valves. All five valves are similar in size; this design allows excellent breathing, and, as every valve is small, high RPM and high power outputs are theoretically available. Although, compared to a four-valve engine, a five-valve design should have a higher maximum RPM, the three inlet ports should give efficient cylinder-filling and high gas turbulence, it has been questioned whether a five-valve configuration gives a cost-effective benefit over four-valve designs. After making five-valve Genesis engines for several years, Yamaha has reverted to the cheaper four-valve design, examples of the five-valve engines is the various 1.8l 20vT engines manufactured by AUDI AG and the rare 1.6l 4A-GE engine of Toyota. Beyond five valvesFor a cylindrical bore and equal-area sized valves, increasing the number of valves beyond five decreases the total valve area; the following table shows the effective areas of differing valve quantities as proportion of cylinder bore.
These percentages are based on simple geometry and do not take into account orifices for spark plugs or injectors, but these voids will be sited in the "dead space" unavailable for valves. In practice, intake valves are larger than exhaust valves in heads with an number of valves-per-cylinder. 2 = 50% 3 = 64% 4 = 68% 5 = 68% 6 = 66% 7 = 64% 8 = 61% Turbocharging and supercharging are technologies that improve engine breathing, can be used instead of, or in conjunction with, multi-valve engines. The same applies to variable valve timing and variable intake manifolds. Rotary valves offer improved engine breathing and high rev performance but these were never successful. Cylinder head porting, as part of engine tuning, is used to improve engine performance; the first motorcar in the world to have an engine with two overhead camshafts and four valves per cylinder was the 1912 Peugeot L76 Grand Prix race car designed by Ernest Henry. Its 7.6-litre monobloc straight-4 with modern hemispherical combustion chambers produced 148 bhp.
In April 1913, on the Brooklands racetrack in England, a specially built L76 called "la Torpille" beat the world speed record of 170 km/h. Robert Peugeot commissioned the young Ettore Bugatti to develop a GP racing car for the 1912 Grand Prix; this chain-driven Bugatti Type 18 had three valves per cylinder. It produced appr. 100 bhp at 2800 could reach 99 mph. The three-valve head would be used for some of Bugatti's most famous cars, including the 1922 Type 29 Grand Prix racer and the legendary Type 35 of 1924. Both Type 29 and Type 35 had a 100 bhp 2-liter SOHC 24-valve NA straight-8 that produced 0.82 bhp per cubic inch. A. L. F. A. 40/60 GP was a working early racing car prototype made by the company now called Alfa Romeo. Only one example was built in 1914, modified in 1921; this design of Giuseppe Merosi was the first Alfa Romeo DOHC engine. It had four valves per 90-degree valve angle and twin-spark ignition; the GP engine had a displacement of 4.5-liter and produced 88 bhp at 2950 rpm, after modifi