Last updated Original design incorporating a leather bellows which was replaced by a piston. This image was published 1908 and 1909A pair of SU carburettors from an MGB
The SU carburettor was a constant-depression carburettor made by a British manufacturer of that name or its licensees in various designs spanning most of the twentieth century.
Herbert Skinner (1872–1931), pioneer motorist and an active participant in the development of the petrol engine,[2] invented his Union carburettor in 1904.[3] His much younger brother, Carl (Thomas Carlisle) Skinner (1882–1958), also a motoring enthusiast, had joined the Farman Automobile Co in London in 1899.[4] He helped Herbert to develop the carburettor.[4] Herbert's son could remember his mother sewing the first leather bellows.[5] It would be given on loan to The Science Museum, South Kensington in 1934.[3][6] In 1905, Herbert applied for a patent,[5] which was granted in early 1906.[7] Later, Carl sold his interest in footwear business Lilley & Skinner and became a partner in G Wailes & Co of Euston Road, London, manufacturers of their carburettor.[4] Herbert continued to develop and patent improvements through to the 1920s, including the replacement of the leather bellows by a brass piston, even though he was a full-time director and divisional manager of Lilley & Skinner.[3][8][9]
S. U. Company Limited
S. U. Company Limited — Skinner-Union —[10][11][12][13] was incorporated in August 1910[note 1] to acquire Herbert's carburettor inventions, and it began manufacture[2] of the carburettors in a factory at Prince of Wales Road, Kentish Town, in North London.[14] Sales were slow.
Following the outbreak of war in 1914, carburettor production nearly stopped, with the factory making machine gun parts and some aircraft carburettors. With peace in 1918, production resumed, but sales remained slow and the company was not profitable, so Carl Skinner approached his customer, W. R. Morris, and managed to sell him the business.[11] Carl Skinner (T. C. Skinner) became a director of Morris's privately held empire, and remained managing director of S.U. until he retired in 1948 aged 65.[4] Production was moved to the W. R. Morris-owned Wolseley factory at Adderley Park, Birmingham. In 1936, W. R. Morris sold many of his privately held businesses, including S. U., to his listed company, Morris Motors.[15][16]
The S. U. Carburetter Company Limited
Manufacture continued, then by The S. U. Carburetter Company Limited, which was incorporated 15 September 1936,[17] as part of the Morris Organization, later known as the Nuffield Organization.[15] The company[clarification needed]became a subsidiary of British Leyland,[18][when?] and traded under the name SU Carburetters.
The S. U. Carburetter Company Limited of 1936[17] was voluntarily liquidated in December 1994.
In 1996, the name and rights were acquired by Burlen Fuel Systems Limited of Salisbury,[14] which incorporated an entirely new company with the name The S.U. Carburetter Company Limited,[19] which continues to manufacture carburettors, pumps and components, mainly for the classic car market.[citation needed]
SU carburettors feature a variable venturi controlled by a piston. This piston has a tapered, conicalmetering rod (usually referred to as a "needle") that fits inside an orifice ("jet") which admits fuel into the airstream passing through the carburettor.[20] Since the needle is tapered, as it rises and falls it opens and closes the opening in the jet, regulating the passage of fuel, so the movement of the piston controls the amount of fuel delivered, depending on engine demand. The exact dimensions of the taper are tailored during engine development.
The flow of air through the venturi creates a reduced static pressure in the venturi. This pressure drop is communicated to the upper side of the piston via an air passage. The underside of the piston is open to atmospheric pressure. The difference in pressure between the two sides lifts the piston. Opposing this are the weight of the piston and the force of a spring that is compressed by the piston rising. Because the spring is operating over a very small part of its possible range of extension, its force is approximately constant. Under steady state conditions the upwards and downwards forces on the piston are equal and opposite, and the piston does not move.
If the airflow into the engine is increased - by opening the throttle plate (also known as the "butterfly"), or by allowing the engine revs to rise with the throttle plate at a constant setting - the pressure drop in the venturi increases, the pressure above the piston falls, and the piston is pushed upwards, increasing the size of the venturi, until the pressure drop in the venturi returns to its nominal level. Similarly if the airflow into the engine is reduced, the piston will fall. The result is that the pressure drop in the venturi remains the same regardless of the speed of the airflow - hence the name "constant depression" for carburettors operating on this principle - but the piston rises and falls according to the rate of air delivery.
Since the position of the piston controls the position of the needle in the jet and thus the open area of the jet, while the depression in the venturi sucking fuel out of the jet remains constant, the rate of fuel delivery is always a definite function of the rate of air delivery. The precise nature of the function is determined by the profile of the needle. With appropriate selection of the needle, the fuel delivery can be matched much more closely to the demands of the engine than is possible with the more common fixed-venturi carburettor, an inherently inaccurate device whose design must incorporate many complex fudges to obtain usable accuracy of fuelling. The well-controlled conditions under which the jet is operating also make it possible to obtain good and consistent atomisation of the fuel under all operating conditions.
This self-adjusting nature makes the selection of the maximum venturi diameter (colloquially, but inaccurately, referred to as "choke size") much less critical than with a fixed-venturi carburettor.
To prevent erratic and sudden movements of the piston it is damped by light oil (20W Grade) in a dashpot, which requires periodic replenishment. The damping is asymmetrical: it heavily resists upwards movement of the piston. This serves as the equivalent of an "accelerator pump" on traditional carburettors by temporarily increasing the speed of air through the venturi when the throttle is suddenly opened, thus increasing the richness of the mixture.
SU carburettors do not have a conventional choke flap, which in a fixed-jet carburettor enriches the mixture for starting the engine from cold by restricting the air supply upstream of the venturi. Instead a mechanism lowers the jet assembly, which has the same effect as the needle rising in normal operation - increasing the supply of fuel so that the carburettor will deliver an enriched mixture at all engine speeds and throttle positions. The 'choke' mechanism on an SU carburettor usually also incorporates a system for holding the throttle plate slightly open to raise the engine's idling speed and prevent stalling at low speeds due to a rich mixture.
The beauty of the SU lies in its simplicity and lack of multiple jets and ease of adjustment. Adjustment is accomplished by altering the starting position of the jet relative to the needle on a fine screw (26TPI for most pre-HIF versions). At first sight, the principle appears to bear a similarity to that of the slide carburettor, which was previously used on many motorcycles. The slide carburettor has the same piston and main needle as an SU carburettor, however the piston/needle position is directly actuated by a physical connection to the throttle cable rather than indirectly by venturi airflow as with an SU carburettor. This piston actuation difference is the significant distinction between a slide and an SU carburettor. The piston in a slide carburettor is controlled by the operator's demands rather than the demands of the engine. This means that the metering of the fuel can be inaccurate unless the vehicle is travelling at a constant speed at a constant throttle setting - conditions rarely encountered except on motorways. This inaccuracy results in fuel waste, particularly as the carburettor must be set slightly rich to avoid a lean condition (which can cause engine damage). For this reason Japanese motorcycle manufacturers ceased to fit slide carburettors and substituted constant-depression carburettors, which are essentially miniature SUs. It is also possible - indeed, easy - to retrofit an SU carburettor to a bike that was originally manufactured with a slide carburettor, and obtain improved fuel economy and more tractable low-speed behaviour.
One of the downsides of the constant depression carburettor is in high performance applications. Since it relies on restricting air flow in order to produce enrichment during acceleration, the throttle response lacks punch. By contrast, the fixed choke design adds extra fuel under these conditions using its accelerator pump.
SU carburettor types
An SU fitted to an MZ in place of the original BVF slide carbThree 2-inch SU HD8 carburettors as installed on an E-type Jaguar
SU carburettors were supplied in several throat sizes in both Imperial (inch) and metric (millimetre) measurement.
The carburettor identification is made by letter prefix which indicates the float type:
"H": introduced in 1937 in which the float bowl has an arm cast into its base, which mounts to the bottom of the carburetor with a hollow bolt or banjo fitting. Fuel passes through the arm into the carburetor body. The bolt attaches to the carburetor body just behind the main jet assembly.
"HD": introduced in 1954 with the float bowl mounted with its arm fastening directly below, and concentric with, the main jet. The arm has a flange that fastens with 4 screws to the bottom of the carburetor, and sealed with a rubber diaphragm integral with the main jet.
"HS": introduced in 1958 the float bowl can be rigidly or rubber mounted to the main body, fuel is transferred by an external flexible pipe to the jet. The jet moves down to enrich the mixture for cold starting,when the 'choke' linkage is pulled.
"HIF": (1972) the float bowl is horizontal and integral (hence the name) Horizontal Integral Float. Example:[21] 1972-1974 MGB.
"HV" (1929), "OM" and "KIF" types also exist but were less commonly employed.[22]
The Imperial sizes include 1-1/8", 1-1/4", 1-1/2", 1-3/4", 1-7/8", and 2", although not every type (H, HD, HS, HIF) was offered in every size.
There were also H models made in 2-1/4" and 2-1/2", now obsolete. Special purpose-built carburetors (Norman) were made as large as 3".
To determine the throat size from the type number: If the final number (after one, two or three letters, beginning with H) has 1 digit, multiply this number by 1/8", then add 1". For example, if the type number is HS6, the final number is 6: 6/8 = 3/4", add 1, total is 1-3/4", etc.
If the final number has 2 digits, it is the throat size in mm. For example, if the type number is HIF38, the final number is 38, size is 38mm etc.
S.U. also produced carburettors for aircraft engines including the early versions of the Rolls-Royce Merlin, but these were of the conventional fixed-jet updraught type rather than the firm's patented constant-depression design.
Standard S.U. carburetors (American spelling) were also a popular upfit for Harley-Davidson motorcycles, given their space saving "side draft" design and superior ability to self-compensate for changes in air density/altitude. Many owners replaced the stock Linkert, Bendix or Keihin carbs with SU's until the Keihin Constant Velocity carb became stock in 1990.[citation needed]
S.U. carburetors remained on production cars through to 1994 in the Mini and the Maestro, by which time the company had become part of the Rover Group.
In 1929 SU introduced the Petrolift electric fuel pump, which could be fitted as a substitute for the vacuum type pumps common at the time.[citation needed] This was superseded in 1932 by the L type fuel pump, which used a solenoid to operate a diaphragm pump.[citation needed]
↑ S. U. Company Limited, 386—388 Euston Road, N.W. Capital £5,000 in £1 shares. Formed to acquire from G. H. Skinner certain inventions relating to carburettors for motorcars &c New Companies Registered. Private Companies. The Automotor Journal, 24 September 1910
Related Research Articles
A carburetor is a device used by a gasoline internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the Venturi tube in the main metering circuit, though various other components are also used to provide extra fuel or air in specific circumstances.
A float chamber is a device for automatically regulating the supply of a liquid to a system. It is most typically found in the carburettor of an internal combustion engine, where it automatically meters the fuel supply to the engine. However, this arrangement is found in many automatic liquid systems, for example the cistern of most toilets could be said to be a type of float chamber.
Aircraft engine controls provide a means for the pilot to control and monitor the operation of the aircraft's powerplant. This article describes controls used with a basic internal-combustion engine driving a propeller. Some optional or more advanced configurations are described at the end of the article. Jet turbine engines use different operating principles and have their own sets of controls and sensors.
A fuel pump is a component used in many liquid-fuelled engines to transfer the fuel from the fuel tank to the device where it is mixed with the intake air.
The Zenith Carburetter Company Limited was a British company making carburettors in Stanmore Middlesex, founded in 1912 as a subsidiary of the French Société du carburateur Zénith. In 1965, the company joined with its major pre-war rival Solex Carburettors, and over time, the Zenith brand name fell into disuse. The rights to the Zenith designs were owned by Solex UK.
Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere.
A ram-air intake is any intake design which uses the dynamic air pressure created by vehicle motion, or ram pressure, to increase the static air pressure inside of the intake manifold on an internal combustion engine, thus allowing a greater massflow through the engine and hence increasing engine power.
The Yamaha XS650 is a mid-size motorcycle made by Yamaha Motor Company. The standard model was introduced in October 1969,and produced through 1979. The "Special" cruiser model was introduced in 1978 and produced through 1985. The XS650 began with the 1955 Hosk SOHC 500 twin. After about 10 years of producing 500 twin, Hosk engineers designed a 650 cc twin. Later the Hosk company was acquired by Showa Corporation, and in 1960 Yamaha had bought Showa with Hosk's early design of 650 cc twin.
Carburetor icing is an icing condition which can affect carburetors under certain atmospheric conditions. The problem is most notable in aviation engines using float-type carburetors.
A nitro engine generally refers to an engine powered with a fuel that contains some portion of nitromethane mixed with methanol. Nitromethane is a highly combustible substance that is generally only used in very specifically designed engines found in Top Fuel drag racing and miniature internal combustion engines in radio control, control line and free flight model aircraft.
Weber Carburetors is an automotive manufacturing company founded in 1923, known for their carburetors.
In internal combustion engines with carburetors, a choke valve or choke modifies the air pressure in the intake manifold, thereby altering the air–fuel ratio entering the engine. Choke valves are generally used in naturally aspirated engines to supply a richer fuel mixture when starting the engine. Most choke valves in engines are butterfly valves mounted upstream of the carburetor jet to produce a higher partial vacuum, which increases the fuel draw.
A throttle is the mechanism by which fluid flow is managed by constriction or obstruction.
The Quadrajet is a four barrel carburetor, made by the Rochester Products Division of General Motors. Its first application was the new-for-1965 Chevy 396ci engine. Its last application was on the 1990 Oldsmobile 307 V8 engine, which was last used in the Cadillac Brougham and full size station wagons made by Chevrolet, Pontiac, Oldsmobile, and Buick.
Miss Shilling's orifice was a very simple technical device created to counter engine cut-outs experienced during negative G manoeuvres in early Spitfire and Hurricane fighter aeroplanes during the Battle of Britain. Officially called the R.A.E. restrictor, it was referred to under various names, such as Miss Tilly's diaphragm or the Tilly orifice in reference to its inventor, Beatrice "Tilly" Shilling.
AMAL was a British engineering company servicing the motorcycle and other light-engineering motor industries between 1927 and 1993 based in Birmingham, England.
A pressure carburetor is a type of fuel metering system manufactured by the Bendix Corporation for piston aircraft engines, starting in the 1940s. It is recognized as an early type of throttle-body fuel injection and was developed to prevent fuel starvation during inverted flight.
The Reece-Fish carburettor was a carburettor used by Mini Se7en racers in the 60s and 70s.
Of the three types of carburetors used on large, high-performance aircraft engines manufactured in the United States during World War II, the Bendix-Stromberg pressure carburetor was the one most commonly found. The other two carburetor types were manufactured by Chandler Groves and Chandler Evans Control Systems (CECO). Both of these types of carburetors had a relatively large number of internal parts, and in the case of the Holley Carburetor, there were complications in its "variable venturi" design.
Manifold injection is a mixture formation system for internal combustion engines with external mixture formation. It is commonly used in engines with spark ignition that use petrol as fuel, such as the Otto engine, and the Wankel engine. In a manifold-injected engine, the fuel is injected into the intake manifold, where it begins forming a combustible air-fuel mixture with the air. As soon as the intake valve opens, the piston starts sucking in the still forming mixture. Usually, this mixture is relatively homogeneous, and, at least in production engines for passenger cars, approximately stoichiometric; this means that there is an even distribution of fuel and air across the combustion chamber, and enough, but not more air present than what is required for the fuel's complete combustion. The injection timing and measuring of the fuel amount can be controlled either mechanically, or electronically. Since the 1970s and 1980s, manifold injection has been replacing carburettors in passenger cars. However, since the late 1990s, car manufacturers have started using petrol direct injection, which caused a decline in manifold injection installation in newly produced cars.
References
As of this edit, this article uses content from PESWiki, a source licensed under the terms of the GNU Free Documentation License which was imported into Wikipedia before November 2008 and is therefore validly licensed for use on Wikipedia. All relevant terms must be followed. The original article was at "PowerPedia:Carburetor".
1 2 Obituary. Mr. G. H. Skinner. The Times, Wednesday, Jan 06, 1932; pg. 12; Issue 46023
1 2 3 E A Forward, Handbook of the Collections illustrating Land Transport, II. Mechanical Road Vehicles, Science Museum South Kensington, 1936
1 2 3 4 Obituary. Mr. Thomas C. Skinner The Times, Saturday, Nov 15, 1958, Issue 54309, p.10.
1 2 H. Jones: Herbert Wakefield Banks Skinner. 1900-1960. Biographical Memoirs of Fellows of the Royal Society, Vol.6, (Nov. 1960), pp.259-268, publisher: The Royal Society
↑ SU Carburetors Owners Workshop Manual by Don Peers: Part 1 Chapter 2 and Part 2 Type H, Haynes Publishing Group, Spsrkford YEOVIL Somerset England. Copyright JH Haynes and Company Limited 1976
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
