BMW K4

BMW
Tubular frame ("rolling chassis") with body skeleton of the K4 comb car at Techno-Classica 2007 (replica)
K4
Presentation year:	1939/40 (test car / one-off)
Vehicle fair:
Class :	Upper class
Body shape :	limousine
Engine:	Otto engine : 3.5 liters (66 kW)
Length:	approx. 5000 mm
Width:	approx. 1700 mm
Height:	approx. 1500 mm
Wheelbase:	2984 mm
Empty weight:	approx. 1500 kg
Production model:	none

The BMW K4 was a test car made by Bayerische Motoren Werke AG ( BMW ) in 1939/40 based on the BMW 335 . The alternative spellings K-4 (with hyphen) or K 4 (with spaces) are also used, and more often the designation Kamm-Wagen K4 .

He was - similar to the test cars previously manufactured in BMW K1 - one designed for high travel speeds and low consumption four-door sedan of the luxury class with comfortable furnishings and five full-size seats, pontoon body in a streamlined shape (this time with integrated fenders ), comb-rear and 3.5 -Liter six-cylinder in - line engine (link to the picture :).

As with the K1 test car, the body of the K4 was not developed in the BMW main plant in Munich or in the BMW plant in Eisenach, which was responsible for automobile production at the time (the former Dixi plant ), but by Professor Wunibald Kamm in the Research Institute for Automotive Engineering and Vehicle engines ( FKFS ) in Stuttgart . Special features of the K4 - similar to the K1 - were its aerodynamically very favorable body and numerous technical innovations, some of which only entered series production decades later.

Background and history of the K4

The background and genesis of the BMW K4 test car correspond to those of the BMW K1 from 1938/39. The K4 was the fourth drivable result of the work of the FKFS and Kamm and after the K1 the second test car based on the "big" BMW 335 .

In between were the K2 and K3 models on the chassis of the smaller and lighter Mercedes-Benz 170 V , with the K2 resembling the K1 , which is extremely aerodynamically shaped , while the K3, similar to the K4, was somewhat more conservative.

The BMW K4 was also designed as a test car from the start, and therefore not designed for series production. Extensive test drives were carried out in 1939 and 1940, and at times - as with the K1 - two large vertical air guide fins were mounted at the end of the roof. The progressive bodywork and the technical innovations proved to be functional and efficient. However, even in this milder form, the external shape with its pontoon body, the unusual rear, the completely covered rear wheels and the temporarily mounted roof fins differed greatly from the series vehicles of the time. The appearance of this model also met with some harsh criticism from the audience. The K4 therefore also remained a one-off.

Typology

The BMW K4 bears, unlike intended for series production BMW cars before the war from 1933 starting with the Model 303 (1933-1934), no model number with three digits and a "3" at the beginning. Like numerous later concept vehicles, it was given a model designation with a letter and a single-digit number.

The K stands for "Kamm-Wagen" or "Kamm-Heck", the 4 for the fourth vehicle of this series of the FKFS .

Occasionally the K4 is incorrectly referred to as K2 in book and internet publications (possibly because it was the second BMW - based Kamm car ) - this is what happened with the publications for the special exhibition “100 Years Against the Wind” in the Prototype Collection in Hamburg from January 24th to March 25th, 2009. In book and internet publications it is occasionally confused with the smaller and lighter K3 Kamm car based on Mercedes that is still in existence today .

Vehicle model details

The BMW 335 sedan, presented in autumn 1938, in series production from 1939 - a pre-series chassis of this type provided by BMW provided the basis for the BMW K4 developed by Wunibald Kamm in Stuttgart in 1939/40

The BMW 335 , here as a four-door convertible, the conservatively designed series model for the innovative BMW K4 test car

Body and equipment

The most striking feature of the BMW K4 is its aerodynamically refined body, which was unusual, both then and now, with a very spacious and comfortable interior. The exact value has not been recorded, but lies between the excellent value of 0.23 for the K1 and the value of 0.37 for the shorter, closer -to- series Kamm car K3 . At that time, values ​​of 0.5 to 0.6 were common for sedans. ${\displaystyle c_{w}}$ ${\displaystyle c_{w}}$

The low drag coefficient was achieved by a streamlined pontoon body with a wing profile and modeled-in fenders, a relatively round and deeply drawn-down front with fitted headlights, fully clad rear wheel cutouts and a smooth, clad underbody. Another detail was the four-segment windscreen with only rounded elements on the sides, as curved glass was still expensive and unusual. In addition, there were relatively smooth body side parts as well as flush fitted front, rear and side windows. The relatively long, gently sloping hatchback with gently drawn-in side panels and a relatively straight cut-off rear end was particularly important. This created clear tear-off edges above the two-part rear window as well as in the side and lower body area.

Unlike the K1 , the K4 had the BMW kidney grille, which has been common on other models since 1933 . The arrangement of the four doors was just as typical, as had already proven itself in the model 326 : The front doors were hinged at the back (so-called “ suicide doors ”), while the rear doors were at the front. So the doors ran in opposite directions, the door hinges each attached to the B-pillar .

The two large vertical tail fins, which were temporarily mounted on the roof of the K4 , were supposed to guide the airflow over the roof and behind the vehicle more favorably; In practice, the advantages of the fins - as with the K1 - proved to be too small, since they also impaired crosswind stability and straight-line stability . Since the test drives took place during the Second World War, the large round headlights mostly had the headlight panels typical of the war, which only let the light out through a narrow slot.

In line with the goal of developing a comfortable touring sedan, the front and side windows were relatively steep and enabled a spacious interior. In the stern was a large trunk accessible from the outside. The interior was lavish and comfortable. Due to the larger body than the original BMW 335 and the complex interior, the weight of the K4 was relatively high at around 1500 kilograms and significantly higher than that of the standard 335 .

The design was very consistent aerodynamically; Compared to the aerodynamically even more favorable K1 , Kamm tried to take more account of contemporary taste in the K4 with the visible, uncovered front wheels and the modeled-in fenders at the front and rear. By dispensing with chrome elements , other ornaments and bumpers , the appearance did not correspond to the mass taste of the time.

The body was built in 1940 according to the plans of Kamm and the FKFS by the Stuttgart body works Reutter & Co. GmbH . The company is best known for the manufacture of car bodies for walkers and Porsches (before and after the Second World War ). It was one of the last civil vehicles before only officer or military vehicles were manufactured in Germany due to the Second World War.

Chassis and running gear

The BMW K4 had - like the K1 - a Vorserienchassis the model 335 , the BMW the FKFS presented under the direction of comb 1939 are available. It also had a drop-center box frame with a front suspension made up of upper wishbones and a transverse leaf spring at the bottom and a track width of 1306 millimeters. At the rear it had a rigid axle with two longitudinal spring bars and a track width of 1,404 millimeters. The wheelbase was 2984 millimeters. It had rack and pinion steering and hydraulically operated inner-shoe drum brakes on all four wheels with a cable-operated handbrake on the rear wheels.

An innovative feature of the Kamm cars K1 and K4 was a tire pressure control system , which made it possible to increase the tire pressure from the dashboard while driving and thereby reduce the rolling resistance of the tires ; This enabled fuel consumption to be reduced on the well-developed new motorways, especially at higher speeds.

engine and gears

The BMW K4 was - as the K1 - with the newly designed engine of the 335 provided, ie a water-cooled six-cylinder four-stroke -Reihenmotor with 3485 cc capacity and long excursion ( bore 82 millimeters Stroke 110 mm). With a compression of 1: 5.8, the engine equipped with two double register carburetors developed 66 kW / 90 PS at 3500 revolutions per minute. The power was transmitted in the usual way via a single-plate dry clutch to a manual four-speed gearbox with rear-wheel drive . An innovative feature of the Kamm cars K1 and K4 was a special lean mixture at constant speeds to further reduce consumption. A special overdrive made it possible to reduce the engine speed at higher speeds, thereby further reducing fuel consumption.

Design differences between the BMW K4 and the K1 in detail

• Pontoon body with fenders on the K4 (tapered to a point in the top view, softly rounded in the transverse profile) in contrast to the full pontoon body of the K1
• three-part front of the K4 (bonnet with BMW kidney grille, wide fenders with large, integrated headlights, reminiscent of the design of the VW Beetle from the front ) instead of the one-part front of the K1 with an oval air inlet
• Covered wheel cutouts on the K4 only at the rear (instead of the front and rear on the K1 )
• narrower, slightly inwardly recessed passenger cell with a smaller frontal area in the K4 , which partially compensates for the somewhat poorer value compared to the K1 ${\displaystyle c_{w}}$
• Larger, elongated third side window on the K4 that narrows towards the rear
• steep, two-part rear window on the K4 with a tear-off edge above the window, instead of a hatchback with a flat, lying rear window and a tear-off edge at the rear, lower end of the window

Influence on other vehicle models and whereabouts of the K4

Modern interpretation of a particularly energy-efficient multi-seat passenger car from BMW , the BMW Vision Efficient Dynamics from 2009 as the spiritual descendant of the innovative BMW K4

BMW's experience with the K1 and K4 flowed into the development of various planned series vehicles: the BMW 332 , the successor to the successful BMW 326 planned for 1940 , and the BMW 337 , the luxury or upper-class model planned for 1941 above the BMW 335 .

The track of the BMW K4 is lost at the end of the Second World War; today it is considered lost or destroyed. According to one source, the K4 was confiscated by French troops at the end of the war and dismantled for research purposes.

Individual design features of the K4 such as the basic idea of ​​the pontoon body and the aerodynamically influenced lines were found in the BMW 501/502 model series in the 1950s , even if these cars with their molded fenders in the style of contemporary Austin were already back in the 1950s looked classic (nickname: "Baroque Angel").

To date (as of March 2010) BMW has not presented a revolutionary and aerodynamically favorable design comparable to that of the K1 and K4 . It is possible that it was precisely the sometimes harsh criticism of the shape and the lack of understanding by contemporary car buyers that prompted BMW to maintain a more conservative design until the mid-1990s, before the designer Chris Bangle found the courage to use controversially discussed styling elements .

To date (as of March 2010), no efforts by BMW have become known to have a replica of the BMW K4 made, as happened, for example, with individual prestigious 328 racing versions.

BMW only picked up the idea of ​​a large hatchback sedan in 2007 with the BMW Concept CS concept vehicle and in series production with the BMW X6 and BMW 5 Series Gran Turismo models in 2008 and 2009, respectively. The idea of ​​a particularly energy-efficient, large, multi-seat model can be found again in the BMW Vision Efficient Dynamics concept vehicle presented in 2009 .

literature

• Halwart Schrader: BMW automobiles . tape 1 : From the Wartburg and Dixi to the BMW 3200 CS Bertone 1898–1962 . Motorbuch Verlag, Stuttgart 2003, ISBN 3-613-02343-1 , p. 86 .
• Werner Oswald, Eberhard Kittler: All BMW automobiles since 1928 . Motorbuch Verlag, Stuttgart 2000, ISBN 3-613-02080-7 , p. 83 (with picture).
• Ralf JF Kieselbach: BMW rarities. Cars that never went into production . GeraMond Verlag, Munich 2007, ISBN 978-3-7654-7806-2 , p. 45-47 .
• Ralf JF Kieselbach: Streamlined Cars in Germany: Aerodynamics in Car Construction 1900 to 1945 . Kohlhammer Verlag, Stuttgart 1982, ISBN 3-17-007626-4 , p. 24, 25, 34, 76 (with picture).
• Erik Eckermann: World history of the automobile . Society of Automotive Engineers, Inc., Warrendale, PA (USA) 2001, ISBN 0-7680-0800-X , p. 117, 119 (English, with picture).
• Princeton Institute for Historic Research (Ed.): Automobile quarterly. Volume 21, Issue 2, 1983, pp. 185, 189 (English).

Web links

• Pictures and backgrounds of the BMW K4 on the BMW-classic.de website under “BMW History” → “ Image Search” → “BMW K4” (8 photos) and under “BMW History” → “Search in the BMW Group Archive” → “BMW K4 ", accessed March 23, 2010
• P. Isermann: Aerodynamics - From the first beginnings to the current state of development. ( Memento of November 18, 2004 in the Internet Archive ) on fachreporte.de , March 2004, there in particular no. 2.5, accessed March 23, 2010.
• bmwclubsa.asn.au ( Memento from August 18, 2010 in the Internet Archive ) Report on the BMW 332 and the test car by Kamm and Jaray on the website of the BMW Driver's Club of South Australia , accessed on March 23, 2010 (English).

References and comments

1. ^ Image of the BMW K4 : motor-klassik.de (however incorrectly referred to as Kamm-Wagen K2 ), accessed on March 23, 2010
2. ↑ ^{a b c d e f g h} Werner Oswald, Eberhard Kittler: All BMW automobiles since 1928. Motorbuch Verlag, Stuttgart 2000, p. 83.
3. ↑ ^{a b} History and background to Wunibald Kamm and the FKFS ( Memento of August 14, 2010 in the Internet Archive ), accessed on March 23, 2010 (English).
4. ↑ Report by Motor Klassik magazine on the special exhibition “100 Years Against the Wind” in the Prototype Collection , accessed on March 23, 2010.
5. ^ Report by the Swiss trade magazine Auto Illustrierte on the special exhibition "100 Years Against the Wind" in the Prototype Collection , accessed on March 23, 2010.
6. ^ Syed Rafeeq Ahmed: Aerodynamics of the automobile. Fluid mechanics, thermal engineering, driving dynamics,…. 2005, p. 35 f.
7. ↑ P. Isermann: Aerodynamics - From the first beginnings to the current state of development. ( Memento of November 18, 2004 in the Internet Archive ) on fachreporte.de , March 2004, there in particular no. 2.5, accessed March 23, 2010.
8. ^ Report on the body manufacturer Reutter on the website of the BMW V8 Club ( memento from July 22, 2012 in the web archive archive.today ), accessed on March 23, 2010.
9. ↑ bmwclubsa.asn.au ( Memento from August 18, 2010 in the Internet Archive ) Report on the BMW 332 and the test car from Kamm and Jaray on the website of the BMW Driver's Club of South Australia , accessed on March 23, 2010 (English).