Citroen 7 CV

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Citroen 7 CV
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Traction Avant monocoque

Front torsion bar suspension

The Traction Avant, French for "front wheel drive", was designed by André Lefèbvre and Flaminio Bertoni in late 1933 / early 1934. While not the first production front wheel drive car – Alvis built the 1928 FWD in the UK, Cord produced the L29 from 1929 to 1932 in the United States and DKW the F1 in 1931 in Germany – it was the world’s first front-wheel drive steel monocoque production car. Along with DKW’s 1930s models, the Traction successfully pioneered front-wheel drive on the European mass car market.

The Traction Avant’s structure was a welded monocoque (unitized body). Most other cars of the era were based on a separate frame (chassis) onto which the non-structural body ("coachwork") was built. Monocoque construction (also called Unit Body or "Unibody" in the US today) results in a lighter vehicle, and is now used for virtually all car construction, although body-on-frame construction remains suitable for larger vehicles such as trucks.
This method of construction was viewed with great suspicion in many quarters, with doubts about its strength. A type of crash test was conceived, taking the form of driving the car off a cliff, to illustrate its great inherent resilience.

The novel design made the car very low-slung relative to its contemporaries – the Traction Avant always possessed a unique look, which went from appearing rakish in 1934 to familiar and somewhat old fashioned by 1955.

The suspension was very advanced for the car’s era. The front wheels were independently sprung, using a torsion bar and wishbone suspension arrangement,[3] where most contemporaries used live axle and cart-type leaf spring designs. The rear suspension was a simple steel beam axle and a Panhard rod, trailing arms and torsion bars attached to a 3-inch (76 mm) steel tube, which in turn was bolted to the monocoque.

Since it was considerably lighter than conventional designs of the era, it was capable of 100 km/h (62 mph), and consumed fuel only at the rate of 10 litres per 100 kilometres (28 mpg-imp; 24 mpg-US).

Variants

Cabriolet

Traction Avant rear

1937 7C Coupe Traction Avant

A French "familiale" 11 F 1954, 6 windows, 9 seats

Citroën 11 Commerciale 5-door

Traction Avant rears. The boot was lengthened and its volume doubled in Autumn 1952.[4]
The original model, which was presented on 18 April 1934, was a small saloon with a 1,303 cc (79.5 cu in) engine. This model was called the 7A, which was succeeded in June 1934 by the 7B with a higher-power engine of 1,529 cc (93.3 cu in). The 7B in turn, was succeeded in October 1934 by the 7C with an even higher-output 1,628 cc (99.3 cu in) engine. Later models were the 11 (launched in November 1934), which had a 1,911 cc (116.6 cu in) four-cylinder engine, and the 15 (launched in 1938), with a 2,867 cc (175.0 cu in) six. The numbers refer to the French fiscal horsepower rating, or CV. The 11 was an 11 CV, but curiously the 15 was actually 16 CV. The 11 was built in two versions, the 11L ("légère", or "light"), which was the same size as the 7 CV, and the normal model 11, which had a longer wheelbase and wider track.

Citroën planned two variants that never entered production, since there was not enough funding available to develop them, except as running prototype vehicles. One was an automatic transmission-equipped model, based on the Sensaud de Lavaud automatic transmission, the other a 22 CV model with a 3.8 liter V8. The transmission (which was actually originally designed for the Citroen) was a "gearless" automatic, using the torque-converter alone to match engine revolutions to the drivetrain revolutions, much like the Dynaflow Transmission introduced later in the USA. The car was supposed to have a less spartan interior than the other Traction Avants and it was to feature Citroën’s own new V8 engine. About twenty prototypes were made, but when the project was canceled in 1935 due to Michelin’s takeover; they were probably all destroyed.[citation needed]

In addition to the 4-door body, the car was also produced as a 2-door coupé with a rumble seat, as a convertible and as an extended length Familial model with three rows of seats. There was even a hatchback-type Commerciale variant, in 1939, well ahead of its time, in which the tailgate was in two halves, the lower of which carried the spare wheel with the upper opening up to roof level. A one-piece top-hinged tailgate was introduced when the Commerciale resumed production in 1954 after being suspended during World War II.
Wartime disruption[edit]

In September 1939 France declared war on Germany and in June 1940 the German army rapidly invaded and occupied Northern France.[1] The war years were characterised by a desperate shortage of raw materials for civilian industry and of petrol,[1] but these factors were not apparent instantly. The Paris Motor Show scheduled for October 1939 was cancelled at short notice, but Citroën’s own planned announcements had involved the forthcoming 2CV model rather than any significant changes to the Traction.[1] For the Traction, the last “normal” year in terms of production levels was 1939, and 8,120 of the 2910mm wheelbase 1628cc engined 7C models were produced.[1] This tumbled to 1,133 in 1940, which was the first year when the plant suffered serious air-raid damage – on this occasion caused by a German attack – on 3 June 1940. Production of the cars was suspended in June 1941, by when a further 154 had been produced in the six-month period just ended. The 7C would continue to appear in Citroën price-lists until March 1944, but production of this smaller engined “7CV” version of the Traction was not resumed after the war.[1] For the more powerful 1911cc engined 11 B-light models, the equivalent figures were 27,473 units produced in 1939, 4,415 in 1940 and 2,032 for 1941, though for this model production in 1941 ended only in November 1941 so the figure for that year represents 11 months of production.[1]

In 1945 production restarted only slowly: the 11 B-light reappeared very little changed from the 1941 cars except that headlight surrounds were now painted rather than finished in chrome. By the end of December 1945 the year’s production had reached 1,525.[1] Currency depreciation is evident from the car’s listed price which had been 26,800 francs in January 1940, and had risen to 110,670 francs in October 1945.[1] In 1945 the car was the only model available from Citroën, and as another sign of the times, customers not able to supply their own tires were charged an additional 9,455 francs for a set of five.[1] In May 1946, presumably reflecting an easing of the war-time tire shortage, the car could at last be purchased with tires at no extra cost, but by now the overall price of an 11 B-light had risen to 121,180 francs.[1]

The 11 B-normal model, differentiated from the 11 B-light by its 3090mm wheelbase, experienced a similar drop off in volumes between 1939 and 1941, with just 341 cars produced during the first seven months of 1941.[1] After the war, a single 11 B-normal was produced in 1946, in time to be presented at the October 1946 Paris Motor Show: production built up during 1947, but during the car’s ten-year post-war period the shorter 11 B-light would, in France, continue to outsell the 11 B-normal.

Initially the French army lacked enthusiasm for the Citroën Traction, believing that it offered insufficient ground-clearance for their needs.[1] Nevertheless, by September 1939 roughly 250 had found their way into military service. With losses of cars at the frontier mounting, Citroën supplied a further 570 to the army between February and May 1940, and subsequent deliveries probably took place before military defeat intervened.[1] During the war many of the cars were reregistered with "WH…" (Wehrmacht Heer/Army command) license plates, having been requisitioned by the German Army.[1] These gave reliable service both in France and further afield, notably in Libya and Stalingrad. Tractions were also favoured by the Resistance, and as occupation gave way to Liberation they turned up all over France with FFI inscribed proudly on their doors. Less gloriously, the cars were known as favourites among gangsters such as the then infamous Pierrot le Fou, and his Traction gang.

UK built cars[edit]

Left-hand drive versions were built in Paris, in Forest, Belgium, in Copenhagen, Denmark for the Scandinavian market, and right-hand drive cars in Slough, England. The Slough version of the 11L was called the Light Fifteen and the long wheelbase 11 was called the Big Fifteen. This confusing terminology referred to the British fiscal tax rating of the time, which was higher than the French, so the 11CV engine was 15HP in England. The 15CV model was called "Big Six" in reference to its 6-cylinder engine. They were equipped with the leather seats and wooden dashboards popular in the UK, had a 12-volt electrical system and were distinguished by a different radiator grille and different bumpers. Some models also had a sliding sunroof.
A 1,911 cc (116.6 cu in) Light Fifteen tested by the British magazine The Motor in 1951 had a top speed of 72.6 mph (116.8 km/h) and could accelerate from 0–60 mph (97 km/h) in 29.7 seconds. A fuel consumption of 25.2 miles per imperial gallon (11.2 L/100 km; 21.0 mpg-US) was recorded. The test car cost GB£812 including taxes.[5]

A 2,866 cc (174.9 cu in) six-cylinder model was tested by the same magazine in 1954 and for this car the top speed found was 81.1 mph (130.5 km/h), acceleration from 0–60 mph (97 km/h) 21.2 seconds and fuel consumption 18.6 miles per imperial gallon (15.2 L/100 km; 15.5 mpg-US). The test car cost GB£1,349 including taxes.[6]
Engineering[edit]

Citroën 11 CV Légère

The Traction Avant used a longitudinal, front-wheel drive layout, with the engine set well within the wheelbase, resulting in a very favourable weight distribution, aiding the car’s advanced handling characteristics. The gearbox was placed at the front of the vehicle with the engine behind it and the differential between them, a layout shared with the later Renault 4 and 16 and first generation Renault 5 but the opposite way round to many longitudinal front-wheel drive cars, such as the Saab 96 and Renault 12 and 18 and most Audi models. The gear change was set in the dashboard, with the lever protruding through a vertical, H-shaped gate.[7] Because this vertical orientation could have resulted in the car dropping out of gear when the lever was in the upper positions (i.e., second or reverse gears), the gear shift mechanism was locked when the mechanical clutch was engaged and released when the clutch pedal was depressed. The result of this layout, along with pendant pedals, umbrella-type handbrake control and front bench seats, was a very spacious interior, with a flat and unobstructed floor. The low-slung arrangement also eliminated the need for running boards to step into or out of the vehicle. These features made them ideal for use as limousines and taxi cabs, and they were quite popular among drivers and passengers alike. Until 1953, black was the only color available.

Impact on Motorsport[edit]

Another technical significance of Tranction Avant was the cast aluminium alloy transaxle, which was pioneered by Hans Ledwinka in the early 1930s for Tatra V570 used in front of the engine located in the rear, but was quite radical at the time.

As well as being a considerable part of the weight savings, the manufacturing facility for this transaxle contributed to the below mentioned financial crisis. But when John Cooper looked for a light transaxle case for Formula One rear engine revolution, Traction Avant unit was about the only candidate, as Volkswagen magnesium alloy transaxle was much smaller and lacking the space needed to house heftier gears needed for Formula One. The Traction Avant transaxle was used on Cooper T43 which won a F1 championship race as the first mid-mounted engine car to do so in 1958, and on its successors Cooper T45, T51 and T53. Cooper T51 won the GP World Championship in 1959.

Unlike the Volkswagen alloy case used by Hewland, the Traction Avant case could not be used up side down, as the input shaft height was much higher in relation to the output shaft axis so that the oil level needed to lubricate the gears would exceed the then-unreliable input shaft oil seal height if used upside down. So the engine needed to sit high above the ground with the oil sump space below, which was not needed by dry-sump racing engines. But the French transaxle was used by several racing car constructors in the late 1950s to 60’s with various levels of success.

In the case of Jack Brabham, who personally visited the ERSA foundry in Paris to discuss a possibility to strengthen the case ,[8] the transaxle became known as "ERSA Knight" with an additional spur-gear set mounted in the bellhousing spacer (engine to transaxle adapter) suggested by Ron Tauranac, named for Jack Knight who designed the modification and made the straight-cut gears. The height offset created by the spur gear set enabled the engine to sit lower, and became the reason why Cooper T53 was called the ‘Lowline’, which not only made Brabham the World Champion in 1960 but also became the precursor to the establishment of Brabham as a Formula One constructor.

Impact on Citroën[edit]

1954 six-cylinder 15CV with hydropneumatic suspension fitted to the rear wheels – in ‘high’ position

Traction Avant as modern wedding car

The development costs of the Traction Avant, combined with the redevelopment of its factory, were very high and Citroën declared bankruptcy in late 1934. The largest creditor was Michelin, who then owned Citroën from 1934 until 1976. Under Michelin, Citroën was run as a research laboratory, a test bed for their radial tires and new automotive technologies.
In 1954 Citroën’s experiments with hydropneumatic technology produced its first result, the "15H" – a variant of the 6-cylinder model 15 with a self-leveling, height-adjustable rear suspension, a field trial for the revolutionary DS released the following year.

Directly after the introduction of the Citroën ID, a simplified and more competitively priced version of the still revolutionary DS, production of the Traction Avant ended in July 1957. Over 23 years, 759,111 had been built, including 26,400 assembled in Slough in England, 31,750 assembled in Forest near Brussels and 1,823 assembled at Cologne in Germany. The total reflects the production stoppage during World War II.

The Traction Avant today[edit]

Big Fifteen sedan

In 2006, the oldest surviving 7A has production number ("coque nr") AZ 00-18, and is displayed in partly dismantled shape (engine and front wheels detached) in the Citroën Museum in Paris. The oldest running 7A is probably number AZ-00-23, which was, until 1 September 2006, in possession of a Dutch owner and is now with a Slovenian owner.
Traction Avants are fairly robust vehicles even by modern standards; however, they are prone to leaking water inside the cabin and care needs to be taken when buying one. Every few years, Traction Avant enthusiasts ship their vehicles to an exotic location for a rally. In 2002, for example, a group of over 30 Traction Avants drove from Los Angeles to New York without incident. [1]

Image from page 50 of “Journal of electricity, power, and gas” (1899)
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Identifier: journalofele323271914paci
Title: Journal of electricity, power, and gas
Year: 1899 (1890s)
Authors: Pacific Coast Electric Transmission Association
Subjects: Electrical engineering Electricity Gas manufacture and works
Publisher: San Francisco : Technical Pub. Co.
Contributing Library: San Francisco Public Library
Digitizing Sponsor: California State Library Califa/LSTA Grant

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Text Appearing Before Image:
curvesshown in Figs. 1 and 2. What might be termed freakcurves, such as shown in Fig. 3, cannot be spaced togive uniform illumination efficiently. They are unde-sirable for general illumination. To determine the best k-value for curves as shownin Figs. 1 and 2, any slight irregularities should befirst eliminated and the dotted line curves shown in thefigures should be used. These dotted line curves arefor practical purposes the same as the solid line testcurves. After making this revision in the curve, itshould be compared with the critical angle curve Tabic I. Critical Angle. k. Critical Angle. k. 10° .35 31° 1.20 11° ,39 32° 1.25 12° .43 33° 1.30 13° .46 34° 1.35 14° .50 35° 1.40 15° .54 36° 1.45 16° .57 37° 1.51 17° .61 38° 1.56 18° .65 39° 1.62 19° .69 40° 1.68 20° .73 41° 1.74 21° .77 42° 1.80 22° ,81 43° 1.87 23° .85 44° 1.93 24° .89 45° 2.00 25° .93 46° 2.07 26° ,98 47° 2.14 27° 1.02 48° 2.22 28° 1.06 49° 2.30 29° 1.11 50° 2.38 30° 1.15

Text Appearing After Image:
Fig. 4. shown in Fig. 4. This curve is derived from the proto-type or original extensive, intensive and focusingcurves.1 The photometric curve (dotted line) shouldbe plotted to the scale 100 units downward; i. e., allthe values should be increased or decreased in the pro-portion which will make the downward intensity 100.Comparing this curve with the critical angle curve theangle of intersection should be observed. Referringthen to Table I the value of k can be obtained. This method has been found to give results suffi- v; j:iently accurate for all practical purposes, and with a :areful observance of the limitations pointed out above t may be used with confidence by the designer of 01, ! ighting systems. JSee Standard Relations of Light-Distribution; Arthur11 r. Sweet. Transactions Illuminating Engineering Society, No-i, -ember, 1909. ill. Uniform illumination is a result of correct designof the lighting appliance and its proper installation. Inwhat is known as direct lighting, the ar

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