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== Technical description == [[File:Parts Unimog (7175790867).jpg|thumb|Scrapped Unimog 411 with plane frame]] [[File:Unimogantriebsstrang.jpg|thumb|Cutaway drivetrain model of a Unimog 401 showing [[torque tube]]s]] [[File:Unimog 404S, Unimog Museum.jpg|thumb|Chassis of a Unimog 404, showing the extreme axle angle offset]] [[File:Mercedes-Benz OM 636 JM 2023 08 12 5D410544.jpg|thumb|[[Mercedes-Benz OM636 engine|Mercedes-Benz OM636]], the original Unimog Diesel engine]] === Chassis === Like other trucks, but unlike agricultural tractors, the Unimog is a body-on-frame vehicle with short overhangs. The original Unimog was made with a plane ladder frame<ref name="Vogler_2014">{{cite book |author-first=Carl-Heinz |author-last=Vogler |title=Unimog 411: Typengeschichte und Technik |lang=de |publisher=GeraMond-Verlag |place=München |date=2014 |isbn=978-3-86245-605-5}}</ref>{{rp|82}} and a wheelbase of 1720 mm. Later, the wheelbase was extended several times to accommodate customer needs. Starting in the mid-1950s, with the introduction of the Unimog 404, the frame received a drop. Originally, this was done to make space for a spare tyre, but soon engineers found out that the new frame would improve the torsion performance, which is why all following Unimog series also received a frame with a drop.<ref name=Vogler_2016 />{{rp|45}} Several mounting brackets, additional cross members and tool boards were offered as factory options for the frame.<ref name=Vogler_2014 />{{rp|79}} === Suspension === The Unimog has live front and rear axles that have portal gears ([[portal axle]]s). Such axles have a lifted axle centre, but the wheels' centre remains unchanged, meaning that a high ground clearance can be achieved with small wheels and tyres. Unlike "regular" trucks, the Unimog has [[coil spring]]s with hydraulic [[shock absorber]]s rather than [[leaf spring]]s, as coil springs provide more spring travel. The axles themselves have only one longitudinal pivot point each, the so-called [[torque tube]]s. The torque tubes contain the drive shafts and connect the axles' differential gearboxes to the Unimog gearbox, but being also parts of the suspension system, the torque tubes prevent longitudinal movement of the axles, whilst still allowing limited vertical movement. Lateral axle movement is prevented by [[panhard rod]]s and [[transverse link]]s. This design results in extreme axle angle offsets of up to {{val|30|u=°}} possible.<ref name=Vogler_2016 />{{rp|36–40}} A wide variety of wheels and tyres were available for the Unimog. Originally, the first Unimog was equipped with 6.5–18 in tyres designed for both on- and offroad use.<ref name=Vogler_2014 />{{rp|48-49}} Later, bigger wheels and tyres with different tread patterns were available, reaching from agricultural tractor tread patterns to massive bar tyre treads to low pressure ballon tyre treads. Until 1973, drum brakes were standard for all Unimogs, until they were replaced by disc brakes, however, until 1989, drum brakes remained an option for Unimogs of the 406-family.<ref name=Vogler_2016 />{{rp|78}} The steering system used to be a screw-and-nut system until 1970. Then it was replaced by a power assisted ball-and-nut system for the 406-series.<ref name=Vogler_2016 />{{rp|77}} === Drivetrain === The classical Unimog is rear-wheel drive vehicle, meaning that the rear axle is directly connected to the gearbox. Turning on front wheel drive automatically locks both axles, without torque compensation. The mechanical lever that turns on all wheel drive has a third position that locks front- and rear differentials. As of 1963, a pneumatic power switch was used instead of a lever. Due to the reduction gears inside the portal axles, the rotational frequency of the driveshafts inside the torque tubes is relatively high, meaning that the amount of torque they have to withstand is fairly low.<ref name=Vogler_2016 />{{rp|23}} === Gearbox === Traditionally, the Unimog has a [[splitter gearbox]]. Over the years, three different ''base gearbox'' designs have been used, all following the same principle, and having four gears and two ranges (called ''groups'') and an additional direction gear. Those designs were ''UG-1/xx'', ''UG-2/xx'', and ''UG-3/xx''. UG is an abbreviation for ''Unimog-Getriebe (Unimog-Gearbox)'', the number after the slash resembles the input torque in [[Kilopondmetre|kp·m]] (=9.80665 N·m).<ref group="N">The kilopondmetre (kp·m) is the traditional technical unit of torque used in many European countries until the early 1980s. It equals the force that a mass of 1 kilogram applies. If the acceleration is exactly 9.80665 m·s<sup>−2</sup> (default gravitational acceleration), this equals 9.80665 N·m.</ref> Until 1955, the Unimog ''base gearbox'' UG-1 was a constant-mesh countershaft gearbox, it was then upgraded with synchroniser rings to a synchromesh gearbox. However, the synchromesh-version was only used for the [[Unimog 404|404-series]], and the constant-mesh version remained the standard gearbox for the 411-series. In 1957, the synchromesh-version became an option for the 411-series, before it became the standard gearbox for all Unimogs in 1959.<ref name=Vogler_2014 />{{rp|38-39}} The following gearbox versions UG-2 and UG-3 were made as synchromesh versions only. There are different ''layouts'' of the gearbox, namely ''F-layout'' and ''G-layout'' as well as their upgraded layouts, not having particular names. The F-layout is the original gearbox layout and is limited to the first two gears in the first range as it does not have selector sleeves, meaning that in total there are six forward gears. Instead of a reverse gear, the gearbox has its direction gear, which, in theory, can be used to reverse any gear. Due to the lacking shifting sleeves however, the reverse direction can only be used in the first range, which itself is limited to the first two gears, resulting in only two reverse gears (resulting in six forward and two reverse gears). To operate the gearbox, there is only one shift lever with a six-speed H-layout, the gearbox shifts its ranges automatically. An additional shift lever is used for shifting into reverse. The ''G-layout'' has an additional reduction gearbox, which can be used in all gears. This effectively doubles the number of gears (twelve forward and four reverse gears). This reduction gearbox was also available with an additional crawler gear, which can only be used in the first range (twenty forward and eight reverse gears). As of 1976, shifting sleeves were added and a four-speed-H-layout replaced the six-speed-H-layout, which allows using all gears in all ranges.<ref name="Gearbox">Helmut Schmitz: ''[https://www.unimog-community.de/2012/08/20/getriebevarianten-u-406u-421/ Getriebevarianten U 406/U 421]''. August 20th, 2012. Retrieved May 19th, 2017 (in German)</ref> With the introduction of the UG-3-gearbox, the standard gearbox-shifter-layout was changed to an eight-speed-H-H-layout, with eight gears on one lever, without any additional switches. When shifting from "4th" into "5th" gear, the gearbox automatically shifts into range 2 and back into gear 1. Crawler gearboxes were offered as a factory option for the UG-3 gearbox as well, resulting in 24 gears. The design with the additional direction gear was kept, which means that all 24 gears can also be used in reverse mode. Since the highest final gear ratio allows top speeds of up to 110 km/h, and the reverse gear only comes with a small reduction of 1:1.03, the top speed in reverse mode is more than 100 km/h. To prevent such high reverse speeds, a lock for the second range was available as a factory option, allowing only the first range (gears "1" to "4") in reverse mode.<ref>Oldtimer Traktor Heft 11-12/2012</ref> === Engine === The initial Unimogs were equipped with passenger car engines, the first Unimog series to receive a truck engine was the 406-series in 1963.<ref name="Wendeborn 1972 pp. 69–76">{{cite journal | title=The present state of development of the Unimog | journal=A.T.Z. Automobiltechnische Zeitschrift | publisher=Springer-Verlag | volume=74 | issue=2 | year=1972 | issn=0001-2785 | doi= | pages=69–76}}</ref> All engines use the [[Diesel engine|Diesel principle]], except for engines used for the Unimog 404-series and the first four Unimog prototypes, which use the [[Otto cycle|Otto principle]]. The following engines were used as of 1947, with ''M'' being Otto and ''OM'' being Diesel engines (the list is incomplete): {{col div|colwidth=23em}} * [[Mercedes-Benz M136 engine|M 136]]<ref name=Vogler_2015 />{{rp|13}} * M 130<ref name=Vogler_2015 />{{rp|46}} * M 180<ref name=Vogler_2015 />{{rp|47}} * [[Mercedes-Benz OM636 engine|OM 636]]<ref name=Vogler_2014 />{{rp|49}} * [[Mercedes-Benz OM621 engine|OM 621]]<ref name=Vogler_2015 />{{rp|89}} * [[Mercedes-Benz OM615 engine|OM 615]]<ref name=Vogler_2015 />{{rp|89}} * [[Mercedes-Benz OM616 engine|OM 616]]<ref name=Vogler_2015 />{{rp|89}} * OM 312<ref name=Vogler_2016 />{{rp|37}} * OM 314<ref name=Vogler_2016 />{{rp|107-108}} * [[Mercedes-Benz OM352 engine|OM 352]]<ref name=Vogler_2016 />{{rp}} * [[Mercedes-Benz OM352 engine|OM 353]]<ref name=Vogler_2016 />{{rp}} <!-- * OM 364 * [[Mercedes-Benz OM366 engine|OM 366]] * OM 902 * OM 904 * OM 924 * OM 934 * OM 936 --> {{col div end}} === Cab === Traditionally, three different cab options were available for the Unimog: An open roof cab (Cabrio), single cab and double cab, with the single cab being the most popular. Because the Unimog was designed to be a better agricultural tractor, its original design did not include a closed cab (as agricultural tractors in Germany usually did not have a closed cab in the 1940s). The first Unimog series to be officially offered with a cab was the 401-series. However, the first cabs were made by Westfalia in Rheda-Wiedenbrück and then shipped to the Unimog plant in Gaggenau for assembly. These cabs are known as ''Westfalia type B'' or simply {{Lang|de|Froschauge}} ('frog's eye'). Starting in 1957, a new cab with 30% more volume, called ''Westfalia type DvF'', Typ D, {{Lang|de|verbreitertes Fahrerhaus}} (Type D, widened cab), was used. Both Westfalia cabs were fairly narrow and came with the problem of engine heat causing high cabin temperatures.<ref name=Vogler_2014 />{{rp|44-47}} The first Unimog that was designed with a cab was the series 406. Just for the purpose of manufacturing cabs, Daimler-Benz built a new 1000-[[Megapond]]-sheet-panel-press in the Unimog plant.<ref name=Vogler_2016 />{{rp|60}} It was planned that the double cab parts would also be produced with this press, instead, the double cabs were manufactured by Wackenhut in Nagold.<ref name=Vogler_2016 />{{rp|89}} In 1974, the current heavy-duty-series' cab was introduced. Its basic design has not been changed since.<ref>{{cite web |url=https://media.daimler.com/marsMediaSite/de/instance/ko/Von-1963-bis-1992-Der-Unimog-waechst-zum-Komplettprogramm.xhtml?oid=9362073 |title=Von 1963 bis 1992: Der Unimog wächst zum Komplettprogramm |publisher=Daimler AG |lang=de |access-date=6 August 2017}}</ref> The equipment carrier versions' cab on the other hand has received several modifications since its introduction in the late 1980s, with the current version being introduced in 2000. <gallery class=center> File:UnimogU6.jpg|1948 Unimog U6, second oldest Unimog that still exists to this day, it is a Cabrio version without doors. File:Unimog 401 mit geschlossener Kabine bei Wischnewski.jpg|1954 Unimog 401 with Westfalia B cab File:Gaggenau 2016 -Unimog-Museum- by-RaBoe 102.jpg|1954 Unimog 402 with Westfalia B crew cab File:2009 08 22 Weelde 142240 - Beautiful blue vintage Unimog 406 pickup truck.jpg|Unimog 406 with Daimler-Benz cab File:HMH Unimog (cropped).jpg|1959 Unimog 411 with Westfalia DvF cab File:Unimog 401 (01) (cropped).jpg|1966 Unimog 411c with a self-made cab File:10 Jahre SRZ - Schutz & Rettung Zürich - 'Parade' 2011-05-13 20-34-22.jpg|1970s Unimog 416 with Wackenhut crew cab File:Unimog U 1300 L (1) (cropped).jpg|1975 Unimog 435 with single cab File:Unimog U417 (cropped).jpg|1988 Unimog 417 with single cab File:Unimog U90 turbo (1997, 122 PS) (cropped).JPG|1997 Unimog 408 with single cab File:Unimog 405 (UGN) in Germany used for forestry and arboriculture (cropped).jpg|2000 [[Unimog 405]] with single cab File:Heidelberg Airfield - Mercedes-Benz Unimog U5023 - RKF BLESES - 2018-07-20 17-52-27.jpg|2018 Unimog 437.4 with the same cab as the 1975 model </gallery> === Pneumatics and hydraulics === The original Unimog was offered with a pneumatic system. This system was used for powering all auxiliary devices as well as the three-point linkages.<ref name=Vogler_2014 />{{rp|77}} As of October 1961, a hydraulics system became an option,<ref name=Vogler_2014 />{{rp|76}} and as of 1963, the hydraulics system became standard, but unlike the pneumatics system, the hydraulics system was made by [[Westinghouse Air Brake Company]] in [[Hannover]]. With the introduction of the hydraulics system, the pneumatics system was solely used for operating the brakes.<ref name=Vogler_2016 />{{rp|27-28}}
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