North German Automobile and Engine
Norddeutsche Automobil und Motoren GmbH was a German automobile manufacturer, created in 1908 and owned by the Norddeutscher Lloyd shipping company. The factory was in Bremen. Many of the products of the company and its successors were badged with the Lloyd marque; the German Lloyd marque had no connection with the British Lloyd Cars Ltd company active between 1936 and 1951. The first cars were licence-built Kriéger electric vehicles. Petrol-engined models followed in 1908 with 3685 cc engines. In 1914 the company merged with Hansa to become Hansa-Lloyd Werke AG. Most of the cars made by the new company were sold as Hansa with the Hansa-Lloyd name attached to commercial vehicles only. Two cars, the 4-litre Treff AS and the 8-cylinder 4.6-litre Trumpf AS were badged as Hansa-Lloyds. The company was integrated in the Borgward group after the purchase of Hansa by Carl F. W. Borgward in 1929, car production ceased. Lloyd as a marque name only entered mass-production of cars and light trucks in 1950 with the company becoming Lloyd Motoren Werke GmbH – still in Bremen.
The first cars were wood and fabric bodied. Thin, rolled steel replaced the original fabric shell between 1953 and 1954, however wood framing was still used within the doors and elsewhere; the Lloyd 250 was called "Prüfungsangst-Lloyd" as they appealed to owners of older driving licenses who could drive it without having to pass a new driving test for cars with a cubic capacity of over 250 cc, a test, introduced in a legal reform of the mid-1950s. With a power of only 11 hp, the Lloyd's designers saw a need for saving weight, thus offered the LP 250 without a back seat, hub caps or trims. However, most buyers ordered the LP 250 V with these features as optional extras. Overall, the vehicles matched the need for small and cheap cars which were a characteristic of post-war Germany, they provided a comparatively high standard in comfort and reliability, they rose to third place in the annual licensing statistics for several years in the 1950s, behind only Volkswagen and Opel. In spite of this success, there was little prestige to be gained by driving a Lloyd.
In the vernacular, the Lloyd 300 was called "Leukoplastbomber" due to the owners' habit of repairing nicks in the fabric of the body with sticking plaster called LEUKOPLAST. A contemporary derisive verse went "Wer den Tod nicht scheut, fährt Lloyd". Pietro Frua designed a coupé on the basis of the Lloyd Alexander; the parent company failed in 1961 but cars were still made up to 1963. By this time, the LP 900 was named "Borgward Arabella" instead of "Lloyd Arabella"; the Lloyd 600 was assembled in Australia by a company formed as joint venture between Carl Borgward and Laurence Hartnett in the late 1950s. The car was introduced in December 1957 as the Lloyd-Hartnett and a total of 3000 cars were built before production ceased in 1962; the Lloyd Cars English HomePage LLOYD-FREUNDE-IG Deutschland Lloyd & Borgward Borgward history Lloyd Alexander Frua Coupé
International Standard Serial Number
An International Standard Serial Number is an eight-digit serial number used to uniquely identify a serial publication, such as a magazine. The ISSN is helpful in distinguishing between serials with the same title. ISSN are used in ordering, interlibrary loans, other practices in connection with serial literature; the ISSN system was first drafted as an International Organization for Standardization international standard in 1971 and published as ISO 3297 in 1975. ISO subcommittee TC 46/SC 9 is responsible for maintaining the standard; when a serial with the same content is published in more than one media type, a different ISSN is assigned to each media type. For example, many serials are published both in electronic media; the ISSN system refers to these types as electronic ISSN, respectively. Conversely, as defined in ISO 3297:2007, every serial in the ISSN system is assigned a linking ISSN the same as the ISSN assigned to the serial in its first published medium, which links together all ISSNs assigned to the serial in every medium.
The format of the ISSN is an eight digit code, divided by a hyphen into two four-digit numbers. As an integer number, it can be represented by the first seven digits; the last code digit, which may be 0-9 or an X, is a check digit. Formally, the general form of the ISSN code can be expressed as follows: NNNN-NNNC where N is in the set, a digit character, C is in; the ISSN of the journal Hearing Research, for example, is 0378-5955, where the final 5 is the check digit, C=5. To calculate the check digit, the following algorithm may be used: Calculate the sum of the first seven digits of the ISSN multiplied by its position in the number, counting from the right—that is, 8, 7, 6, 5, 4, 3, 2, respectively: 0 ⋅ 8 + 3 ⋅ 7 + 7 ⋅ 6 + 8 ⋅ 5 + 5 ⋅ 4 + 9 ⋅ 3 + 5 ⋅ 2 = 0 + 21 + 42 + 40 + 20 + 27 + 10 = 160 The modulus 11 of this sum is calculated. For calculations, an upper case X in the check digit position indicates a check digit of 10. To confirm the check digit, calculate the sum of all eight digits of the ISSN multiplied by its position in the number, counting from the right.
The modulus 11 of the sum must be 0. There is an online ISSN checker. ISSN codes are assigned by a network of ISSN National Centres located at national libraries and coordinated by the ISSN International Centre based in Paris; the International Centre is an intergovernmental organization created in 1974 through an agreement between UNESCO and the French government. The International Centre maintains a database of all ISSNs assigned worldwide, the ISDS Register otherwise known as the ISSN Register. At the end of 2016, the ISSN Register contained records for 1,943,572 items. ISSN and ISBN codes are similar in concept. An ISBN might be assigned for particular issues of a serial, in addition to the ISSN code for the serial as a whole. An ISSN, unlike the ISBN code, is an anonymous identifier associated with a serial title, containing no information as to the publisher or its location. For this reason a new ISSN is assigned to a serial each time it undergoes a major title change. Since the ISSN applies to an entire serial a new identifier, the Serial Item and Contribution Identifier, was built on top of it to allow references to specific volumes, articles, or other identifiable components.
Separate ISSNs are needed for serials in different media. Thus, the print and electronic media versions of a serial need separate ISSNs. A CD-ROM version and a web version of a serial require different ISSNs since two different media are involved. However, the same ISSN can be used for different file formats of the same online serial; this "media-oriented identification" of serials made sense in the 1970s. In the 1990s and onward, with personal computers, better screens, the Web, it makes sense to consider only content, independent of media; this "content-oriented identification" of serials was a repressed demand during a decade, but no ISSN update or initiative occurred. A natural extension for ISSN, the unique-identification of the articles in the serials, was the main demand application. An alternative serials' contents model arrived with the indecs Content Model and its application, the digital object identifier, as ISSN-independent initiative, consolidated in the 2000s. Only in 2007, ISSN-L was defined in the
Single- and double-acting cylinders
Reciprocating engine cylinders are classified by whether they are single- or double-acting, depending on how the working fluid acts on the piston. A single-acting cylinder in a reciprocating engine is a cylinder in which the working fluid acts on one side of the piston only. A single-acting cylinder relies on the load, other cylinders, or the momentum of a flywheel, to push the piston back in the other direction. Single-acting cylinders are found in most kinds of reciprocating engine, they are universal in internal combustion engines and are used in many external combustion engines such as Stirling engines and some steam engines. They are found in pumps and hydraulic rams. A double-acting cylinder is a cylinder in which the working fluid acts alternately on both sides of the piston. In order to connect the piston in a double-acting cylinder to an external mechanism, such as a crank shaft, a hole must be provided in one end of the cylinder for the piston rod, this is fitted with a gland or "stuffing box" to prevent escape of the working fluid.
Double-acting cylinders are unusual in other engine types. Many hydraulic and pneumatic cylinders use them where it is needed to produce a force in both directions. A double-acting hydraulic cylinder has a port at each end, supplied with hydraulic fluid for both the retraction and extension of the piston. A double-acting cylinder is used where an external force is not available to retract the piston or it can be used where high force is required in both directions of travel. Steam engines use double-acting cylinders. However, early steam engines, such as atmospheric engines and some beam engines were single-acting; these transmitted their force through the beam by means of chains and an "arch head", as only a tension in one direction was needed. Where these were used for pumping mine shafts and only had to act against a load in one direction, single-acting designs remained in use for many years; the main impetus towards double-acting cylinders came when James Watt was trying to develop a rotative beam engine, that could be used to drive machinery via an output shaft.
With a single-cylinder engine, a double-acting cylinder gave a smoother power output. The high-pressure engine, as developed by Richard Trevithick, used double-acting pistons and became the model for most steam engines afterwards; some of the steam engines, the high-speed steam engines, used single-acting pistons of a new design. The crosshead became part of the piston, there was no longer any piston rod; this was for similar reasons to the internal combustion engine, as avoiding the piston rod and its seals allowed a more effective crankcase lubrication system. Small models and toys use single-acting cylinders for the above reason but to reduce manufacturing costs. In contrast to steam engines, nearly all internal combustion engines have used single-acting cylinders, their pistons are trunk pistons, where the gudgeon pin joint of the connecting rod is within the piston itself. This avoids the crosshead, piston rod and its sealing gland, but it makes a single-acting piston essential. This, in turn, has the advantage of allowing easy access to the bottom of the piston for lubricating oil, which has an important cooling function.
This avoids local overheating of rings. Small petrol two-stroke engines, such as for motorcycles, use crankcase compression rather than a separate supercharger or scavenge blower; this uses both sides of the piston as working faces, the lower side of the piston acting as a piston compressor to compress the inlet charge ready for the next stroke. The piston is still considered as single-acting; some early gas engines, such as Lenoir's original engines, from around 1860, were double-acting and followed steam engines in their design. Internal combustion engines soon switched to single-acting cylinders; this was for two reasons: as for the high-speed steam engine, the high force on each piston and its connecting rod was so great that it placed large demands upon the bearings. A single-acting piston, where the direction of the forces was compressive along the connecting rod, allowed for tighter bearing clearances. Secondly the need for large valve areas to provide good gas flow, whilst requiring a small volume for the combustion chamber so as to provide good compression, monopolised the space available in the cylinder head.
Lenoir's steam engine-derived cylinder was inadequate for the petrol engine and so a new design, based around poppet valves and a single-acting trunk piston appeared instead. Large gas engines were built as blowing engines for blast furnaces, with one or two large cylinders and powered by the burning of furnace gas; these those built by Körting, used double-acting cylinders. Gas engines require little or no compression of their charge, in comparison to petrol or compression-ignition engines, so the double-acting cylinder designs were still adequate, despite their narrow, convoluted passageways. Double-acting cylinders have been infrequently used for internal combustion engines since, although Burmeister & Wain made 2-stroke cycle double-acting diesels for marine propulsion before 1930; the first, of 7,000 hp, was fitted in the British MV Amerika in 1929. The two B&W SCDA engines fitted to the MV Stirling Castle in 1937 produced 24,000 hp each. In 1935 the US submarine USS Pompano was ordered as part of the Perch class Six boats were built, with three different diesel engine designs from different makers.
Pompano was fitted with H. O. R. 8-cylinder double-acting engines that were a licence-built version of the MAN auxiliary engine
A cyclecar was a type of small and inexpensive car manufactured in Europe and the United States between 1910 and the early 1920s. The purpose of cyclecars was to fill a gap in the market between the car; the demise of cyclecars was due to larger cars – such as the Citroën 5CV, Austin 7 and Morris Cowley – becoming more affordable. Small, inexpensive vehicles reappeared after World War II, were known as microcars. Cyclecars were propelled by engines with a single cylinder or V-twin configuration, which were air-cooled. Sometimes motorcycle engines were used, in which case the motorcycle gearbox was used. All cyclecars were required to have variable gears; this requirement could be fulfilled by the simplest devices such as provision for slipping the belt on the pulley to act as a clutch, varying of the pulley diameter to change the gear ratio. Methods such as belt drive or chain drive were used to transmit power to the drive wheel to one wheel only, so that a differential was not required; the bodies sometimes offered minimal weather protection or comfort features.
The rise of cyclecars was a direct result of reduced taxation both for registration and annual licences of lightweight small-engined cars. On 14 December 1912, at a meeting of the Federation Internationale des Clubs Moto Cycliste, it was formally decided that there should be an international classification of cyclecars to be accepted by the United Kingdom, United States, The Netherlands, Italy and Germany; as a result of this meeting, the following classes of cyclecars were defined: From 1898 to 1910, automobile production expanded. Light cars of that era were known as voiturettes; the smaller cyclecars appeared around 1910 with a boom shortly before the outbreak of the First World War, with Temple Press launching The Cyclecar magazine on 27 November 1912, the formation of the Cyclecar Club. From 1912, the Motor Cycle show at Olympia became Cycle Car Show; the number of cyclecar manufacturers was less than a dozen in each of the UK and France in 1911, but by 1914, there were over 100 manufacturers in each country, as well as others in Germany and other European countries.
By 1912, the A. C. Sociable was described as "one of the most popular cycle cars on the road, both for pleasure and for business", though another source states that the "Humberette" was the most popular of cycle cars at that time. Many of the numerous makes were short-lived, but several brands achieved greater longevity, including Bédélia, GN and Morgan. By the early 1920s, the days of the cyclecar were numbered. Mass producers, such as Ford, were able to reduce their prices to undercut those of the small cyclecar makers. Similar affordable cars were offered in Europe, such as Austin 7 or Morris Cowley; the cyclecar boom was over. The majority of cyclecar manufacturers closed down; some companies such as Chater-Lea survived by returning to the manufacture of motorcycles. After the Second World War, economic cars were again in demand and a new set of manufacturers appeared; the cyclecar name did not reappear however, the cars were called microcars by enthusiasts and bubble cars by the general population.
Several motor racing events for cyclecars were run between 1913 and 1920. The first race dedicated to cyclecars was organised by the Automobile Club de France in 1913, followed by a Cyclecar GP at Le Mans in 1920; the Auto Cycle Union was to have introduced cycle car racing on the Isle of Man in September 1914, but the race was abandoned due to the onset of the war. Brass Era car Microcar Voiturette Worthington-Williams, Michael. From cyclecar to microcar the story of the cyclecar movement. Beaulieu Books. ISBN 0-901564-54-0. David Thirlby. Minimal Motoring: From Cyclecar to Microcar. Arcadia Publishing. ISBN 0-7524-2367-3
A transmission is a machine in a power transmission system, which provides controlled application of the power. The term transmission refers to the gearbox that uses gears and gear trains to provide speed and torque conversions from a rotating power source to another device. In British English, the term transmission refers to the whole drivetrain, including clutch, prop shaft and final drive shafts. In American English, the term refers more to the gearbox alone, detailed usage differs; the most common use is in motor vehicles, where the transmission adapts the output of the internal combustion engine to the drive wheels. Such engines need to operate at a high rotational speed, inappropriate for starting and slower travel; the transmission reduces the higher engine speed to the slower wheel speed, increasing torque in the process. Transmissions are used on pedal bicycles, fixed machines, where different rotational speeds and torques are adapted. A transmission has multiple gear ratios with the ability to switch between them as speed varies.
This switching may be done automatically. Directional control may be provided. Single-ratio transmissions exist, which change the speed and torque of motor output. In motor vehicles, the transmission is connected to the engine crankshaft via a flywheel or clutch or fluid coupling because internal combustion engines cannot run below a particular speed; the output of the transmission is transmitted via the driveshaft to one or more differentials, which drives the wheels. While a differential may provide gear reduction, its primary purpose is to permit the wheels at either end of an axle to rotate at different speeds as it changes the direction of rotation. Conventional gear/belt transmissions are not the only mechanism for speed/torque adaptation. Alternative mechanisms include power transformation. Hybrid configurations exist. Automatic transmissions use a valve body to shift gears using fluid pressures in response to speed and throttle input. Early transmissions included the right-angle drives and other gearing in windmills, horse-powered devices, steam engines, in support of pumping and hoisting.
Most modern gearboxes are used to increase torque while reducing the speed of a prime mover output shaft. This means that the output shaft of a gearbox rotates at a slower rate than the input shaft, this reduction in speed produces a mechanical advantage, increasing torque. A gearbox can be set up to do the opposite and provide an increase in shaft speed with a reduction of torque; some of the simplest gearboxes change the physical rotational direction of power transmission. Many typical automobile transmissions include the ability to select one of several gear ratios. In this case, most of the gear ratios are used to slow down the output speed of the engine and increase torque. However, the highest gears may be "overdrive" types. Gearboxes have found use in a wide variety of different—often stationary—applications, such as wind turbines. Transmissions are used in agricultural, construction and automotive equipment. In addition to ordinary transmission equipped with gears, such equipment makes extensive use of the hydrostatic drive and electrical adjustable-speed drives.
The simplest transmissions called gearboxes to reflect their simplicity, provide gear reduction, sometimes in conjunction with a right-angle change in direction of the shaft. These are used on PTO-powered agricultural equipment, since the axial PTO shaft is at odds with the usual need for the driven shaft, either vertical, or horizontally extending from one side of the implement to another. More complex equipment, such as silage choppers and snowblowers, have drives with outputs in more than one direction; the gearbox in a wind turbine converts the slow, high-torque rotation of the turbine into much faster rotation of the electrical generator. These are more complicated than the PTO gearboxes in farm equipment, they weigh several tons and contain three stages to achieve an overall gear ratio from 40:1 to over 100:1, depending on the size of the turbine. The first stage of the gearbox is a planetary gear, for compactness, to distribute the enormous torque of the turbine over more teeth of the low-speed shaft.
Durability of these gearboxes has been a serious problem for a long time. Regardless of where they are used, these simple transmissions all share an important feature: the gear ratio cannot be changed during use, it is fixed at the time. For transmission types that overcome this issue, see Continuously variable transmission known as CVT. Many applications require the availability of multiple gear ratios; this is to ease the starting and stopping of a mechanical system, though another important need is that of maintaining good fuel efficiency. The need for a transmission in an automobile is a consequence of the characteristics of the internal combustion engine. Eng
World War II
World War II known as the Second World War, was a global war that lasted from 1939 to 1945. The vast majority of the world's countries—including all the great powers—eventually formed two opposing military alliances: the Allies and the Axis. A state of total war emerged, directly involving more than 100 million people from over 30 countries; the major participants threw their entire economic and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. World War II was the deadliest conflict in human history, marked by 50 to 85 million fatalities, most of whom were civilians in the Soviet Union and China, it included massacres, the genocide of the Holocaust, strategic bombing, premeditated death from starvation and disease, the only use of nuclear weapons in war. Japan, which aimed to dominate Asia and the Pacific, was at war with China by 1937, though neither side had declared war on the other. World War II is said to have begun on 1 September 1939, with the invasion of Poland by Germany and subsequent declarations of war on Germany by France and the United Kingdom.
From late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or controlled much of continental Europe, formed the Axis alliance with Italy and Japan. Under the Molotov–Ribbentrop Pact of August 1939, Germany and the Soviet Union partitioned and annexed territories of their European neighbours, Finland and the Baltic states. Following the onset of campaigns in North Africa and East Africa, the fall of France in mid 1940, the war continued between the European Axis powers and the British Empire. War in the Balkans, the aerial Battle of Britain, the Blitz, the long Battle of the Atlantic followed. On 22 June 1941, the European Axis powers launched an invasion of the Soviet Union, opening the largest land theatre of war in history; this Eastern Front trapped most crucially the German Wehrmacht, into a war of attrition. In December 1941, Japan launched a surprise attack on the United States as well as European colonies in the Pacific. Following an immediate U. S. declaration of war against Japan, supported by one from Great Britain, the European Axis powers declared war on the U.
S. in solidarity with their Japanese ally. Rapid Japanese conquests over much of the Western Pacific ensued, perceived by many in Asia as liberation from Western dominance and resulting in the support of several armies from defeated territories; the Axis advance in the Pacific halted in 1942. Key setbacks in 1943, which included a series of German defeats on the Eastern Front, the Allied invasions of Sicily and Italy, Allied victories in the Pacific, cost the Axis its initiative and forced it into strategic retreat on all fronts. In 1944, the Western Allies invaded German-occupied France, while the Soviet Union regained its territorial losses and turned toward Germany and its allies. During 1944 and 1945 the Japanese suffered major reverses in mainland Asia in Central China, South China and Burma, while the Allies crippled the Japanese Navy and captured key Western Pacific islands; the war in Europe concluded with an invasion of Germany by the Western Allies and the Soviet Union, culminating in the capture of Berlin by Soviet troops, the suicide of Adolf Hitler and the German unconditional surrender on 8 May 1945.
Following the Potsdam Declaration by the Allies on 26 July 1945 and the refusal of Japan to surrender under its terms, the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki on 6 and 9 August respectively. With an invasion of the Japanese archipelago imminent, the possibility of additional atomic bombings, the Soviet entry into the war against Japan and its invasion of Manchuria, Japan announced its intention to surrender on 15 August 1945, cementing total victory in Asia for the Allies. Tribunals were set up by fiat by the Allies and war crimes trials were conducted in the wake of the war both against the Germans and the Japanese. World War II changed the political social structure of the globe; the United Nations was established to foster international co-operation and prevent future conflicts. The Soviet Union and United States emerged as rival superpowers, setting the stage for the nearly half-century long Cold War. In the wake of European devastation, the influence of its great powers waned, triggering the decolonisation of Africa and Asia.
Most countries whose industries had been damaged moved towards economic expansion. Political integration in Europe, emerged as an effort to end pre-war enmities and create a common identity; the start of the war in Europe is held to be 1 September 1939, beginning with the German invasion of Poland. The dates for the beginning of war in the Pacific include the start of the Second Sino-Japanese War on 7 July 1937, or the Japanese invasion of Manchuria on 19 September 1931. Others follow the British historian A. J. P. Taylor, who held that the Sino-Japanese War and war in Europe and its colonies occurred and the two wars merged in 1941; this article uses the conventional dating. Other starting dates sometimes used for World War II include the Italian invasion of Abyssinia on 3 October 1935; the British historian Antony Beevor views the beginning of World War II as the Battles of Khalkhin Gol fought between Japan and the fo
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