Preselector

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A preselection gear is a manual gearbox in which the desired gear is first preselected with a gearshift lever and then engaged when another control element, for example a pedal, is actuated, without having to press a clutch pedal at the same time. It was widespread in car models, especially in the 1930s.

Most preselect transmissions do not require a driver-operated clutch. Some are connected to a starting clutch.

A preselection gearbox is not an automatic gearbox , even if there are similarities in structure. A fully automatic gearbox automatically selects a suitable gear ratio, while the pre-selection gearbox leaves the choice of the right gear in the hands of the driver. There were automatically shifting transmissions that could also be used as preselection transmissions (for example in the London AEC Routemaster double-decker bus from the 1960s).

There are different types of preselector gear, which differ significantly. The best known system is that of Wilson. Some preselector transmissions, such as the one from Cotal, engage the desired gear immediately after actuating the shift lever, without having to press an additional pedal beforehand. These are called “self-shifting transmissions”, but are considered preselection transmissions. In recent years, Tiptronic and similar automated transmissions have taken over the role of preselector transmissions. With them, the gear can be selected manually and is then automatically engaged immediately.

Advantages of the preselector

There are two advantages for the driver:

  • Quick gear changes with just a single operation. This requires less practice than double clutching, for example, and enables faster gear changes when racing.
  • Much greater engine power can be managed with less complex mechanics.

From a technical point of view, some types of preselector have particular advantages. In the case of the Wilson preselector, these are the following, some of which, however, also apply to some other, completely different types:

  • The friction components are brakes instead of clutches. These have a simpler structure because their wearing parts do not rotate.
  • The friction components are attached outside and not covered by the actuation mechanism. This makes maintenance and adjustment work easier.

There were preselector transmissions in Daimler cars and commercial vehicles, cars from Maybach , Alvis , Talbot-Lago , Delahaye , Ford France , Salmson , Hotchkiss , Bugatti and Armstrong Siddeley , as well as in many buses in London. In racing cars, such as the ERA R4D 1935 mountain race car she was found. From 1929 preselector gears were also installed in military vehicles, for example in the Panzerkampfwagen VI Tiger and the Panzerkampfwagen VI Tiger II in World War II . Modern tanks, such as the Challenger 2 , also have preselector transmissions.

Types

Planetary gear

Many preselect gears work with planetary gear sets .

Wilson

Wilson is the best known design and is often referred to when one speaks of the “preselector gear”.

Major WG Wilson (1874-1957) was one of the co-inventor of the tank in the First World War . His main focus was the development of gearboxes for tanks, especially the steering gears. He advocated planetary gears because they could transmit large torques with low actuating forces. In 1917 Wilson designed the Mark V with its planetary gearbox. Wilson saw the main advantage in being controlled by a brake instead of a clutch, because "a brake can withstand more mechanical stress than a clutch and its use is easier to assess." The Mark V was the first heavy tank that could be moved by just one driver without this having to pass on orders to his comrades who operated the gear shift.

From 1900 the Lanchester Motor Company had already built passenger cars with manual planetary gears, first with cone clutches, then with multi-plate flat clutches. They formed the individual speed levels of the drive. In 1918 a tank prototype , the Lanchester Gearbox Mashine or Experimental Machine K , was tested, which was equipped with a planetary gear from Lanchester.

After the war, Wilson had a good reputation as an engineer of genius, especially for gearbox design. In 1928 he patented his design of a pre-select gear. Many manufacturers manufactured preselector gears based on Wilson patents. Wilson himself teamed up with John Davenport Siddeley , co-owner of the automobile manufacturer Armstrong Siddeley , initially under the name "Improved Gears Ltd", later under the name " Self-Changing Gears Ltd".

The gear was selected by operating a selector lever. The selected gear was then engaged by pressing and releasing a “gear change pedal”, which was usually attached to the left of the pedal set instead of the normal clutch pedal.

The Wilson pre-selector could be used with a number of different clutches. The best known is the fluid coupling, for example in touring cars from Daimler or Armstrong Siddeley. Sports cars had a Newtonian centrifugal clutch. This was a multi-plate dry clutch, similar to the clutches used in racing cars together with manual transmissions, but with a pressure plate that was engaged by centrifugal forces at around 600 rpm. Racing cars like the ERA did not have a clutch and started off as the band brake of the first planetary set was increasingly closed.

The Wilson gearbox consisted of a series of planetary gear sets which - also according to an invention of Wilson - were connected in series. Each subsequent planetary set reduced the gear ratio further when it was switched on. A separate planetary set was provided for each gear stage; the highest gear instead had a cone clutch and the reverse gear also had a planetary gear set. At a time when most manual transmissions had three forward gears, the Wilson transmission offered four that were more closely spaced. The Wilson transmission has this planetary set structure in common with modern automatic transmissions, but the use of torque converters along with the broader power range and high output of the US V8 engines meant that the gear ratio spread was greater and thus fewer gear steps were required . In contrast to the spur gears of the first half of the 20th century, all gears in a preselector are constantly in mesh.

The gear change in a Wilson transmission is based on the control of the brake bands that hold the ring gears of the planetary gear sets. Each brake band was operated by a rotating cam that was moved by the shift lever. As a result, only one brake band was tightened at a time. However, the small gear lever couldn't transmit enough force to apply a brake band, so the extra pedal was needed. This was also the reason why a pedal that was moved by a strong leg muscle was used to change gears and not a hand lever. The movement of the brake band was controlled by a coupling mechanism, a special detail of the Wilson construction. When the pedal was pressed and then released, a series of finger-shaped levers were pushed up against a series of light coupling rods by a strong spring . The position of each coupling rod was controlled by the switch camshaft. When the gearshift cam (one for each gear position) held a coupling rod in place and prevented it from swinging away, it pressed via an actuation tappet on the levers that operated the brake band. These levers, under the force of the coil spring, provided the additional lifting force that was necessary to hold the brake band in place until the pedal was pressed the next time. Another characteristic of the Wilson design was the self-adjusting screws on each brake band to compensate for its wear. The continuous actuation and release of the brake bands was sufficient to adjust the ratchet mechanisms of the screws so that they could compensate for the elongation of the bands.

In some vehicles, you had to operate the gear change pedal like a clutch pedal to start off. Others could put first gear in when the engine was still idling, but the car wouldn't move even after pressing and releasing the gear change pedal. Then when you hit the gas, a centrifugal or fluid clutch engaged and the car drove off.

Talbot

The “accelerating gearbox” designed by Georges Roesch , which was built into some British Talbot models in the 1930s, automatically preset first gear as soon as reverse gear was engaged. After engaging the second gear, the third was automatically preselected, and after engaging the third, the fourth automatically. Then the transmission shifted automatically (depending on the driving speed) between third and fourth gear until another gear was selected manually.

This transmission had a centrifugal clutch , which Talbot referred to as the "Traffic Clutch". This clutch was a simple device with two radially movable shoes, similar to a drum brake.

De Normanville

This gearbox was manufactured by De Normanville and used in Humber automobiles . It was largely similar to Wilson's, but had direct, hydraulic actuation of the brake bands, which was controlled via a gearshift lever on the steering column of the car and thus required neither a gear change pedal nor a coupling mechanism.

De Normanville later became part of Laycock-de Normanville , a company that built overdrives for many automobile manufacturers, among other things .

Cotal

Cotal preselect gear (sectional drawing)
Switch of the electromagnetic cotal preselector in the Delahaye 135 MS

The Cotal preselector of the 1930s was a manual planetary gear like Wilson's. The difference was that it had electrically operated clutches instead of band brakes. The two clutches each consisted of a central steel disc and two rings each fitted with spiral springs, one of which was rotating and one was fixed. The latter could be viewed either as a clutch or a brake. Slip rings transmitted the current to the rotating coupling parts.

Unlike the Wilson pre-selector, these clutches were controlled by a simple switch mounted on the dashboard or steering column, described as a “cherry on a toothpick” and relay controlled. There was no servo mechanism, so no cams, no coupling mechanism and no gear change pedal as in the Wilson design.

In the 1950s and 1960s, Cotal used the same technology to build an electrically operated clutch for small Renault vehicles (with manual transmissions but without a clutch pedal). Vehicles like the Renault Caravelle or Dauphine were available with it. These electrically operated clutches were not very successful because the entire engine torque had to be transmitted through them, which meant that they had to be very large and powerful and constantly suffered from problems with the slip rings. There was also a gearbox similar to the Cotal preselector built by Ferlec . It worked with a magnetic particle clutch and switch buttons on the dashboard. Renault offered it in the Dauphine and in the Renault 8 and 10 .

The Cotal preselector was also used for light rail diesel multiple units, including in Wickham.

Multi-clutch transmission

A multi-clutch transmission avoids the difficulties of changing gears in that no gear changes are necessary. It works as a series of separate transmissions, each of which is switched on and off by its own clutch, with a control system preventing two transmissions from being engaged at the same time. The change of gears is accomplished by changing the clutches. An advantage of this arrangement is the easy remote control, because the shift lever does not have to be mechanically connected to the transmission.

One gear ratio per clutch

This type of transmission appeared in March 1917 during the Oldbury transmission tests on eight different tanks from the First World War . Each transmission had its own shaft and coupling. If the clutches are controlled so that only one can be engaged at a time, the system is very simple.

In the early 1980s, a similar system for city buses was developed in the United Kingdom of Great Britain and Northern Ireland under the name Maxwell ; it was a four-speed gearbox. The city buses in the United Kingdom were mostly double-decker buses with diesel engines installed across the rear. Stop-and-go operation is common, causing clutches for normal manual transmissions to wear out quickly. The advantage of this system was the four multi-disc oil bath clutches, all of which could be easily serviced from outside the engine compartment without removing the engine. However, the first gearboxes proved to be unreliable. In 1985, Brockhouse , the company that originally developed this gearbox, licensed Avon Maxwell Transmissions to build it . An upgraded version with a larger oil pump was offered for retrofitting on most buses in the UK. One unusual way this transmission could do was to engage first and second gears at the same time. The function of a retarder with 50 bhp output was thus implemented.

Panzerkampfwagen Tiger

The Panzerkampfwagen Tiger in World War II had a kind of pre-selection gearbox with eight gears. Clutches were used in combinations, which enabled many more gear ratios than there were actuators. Actuation was hydraulic to relieve the driver. There were three hydraulic cylinders, each of which could be brought into two positions, and which controlled positive-locking clutches for gear steps on four shafts. The cylinders were controlled with a ball valve and a simple gear lever and activated when the gear lever was pushed sideways into position. The combination of the three cylinders, actually a 3-bit binary code , made eight different translations possible. When reversing, only the bottom four were usable. The investigation of the gearbox of the Tiger No. 131 captured by the British Army in 1943 was carried out by Armstrong Siddeley , as experts in gearbox construction were available there.

Double clutch

The idea of ​​changing gears quickly by actuating only clutches is also used in double clutch transmissions in modern passenger cars. They are constructed almost as simply as normal manual transmissions and have the high switching speed of clutch systems. They consist of two sub-transmissions, each offering the odd (I, III and V) and the even (II, IV and R) gears. The two clutches then control which of the two sub-transmissions transfers the engine power to the drive. The gear change in the individual transmissions takes place automatically, as the disengaged transmission makes the next gear step available to the driver. If the next gear has been selected correctly (for example by an on-board computer that decides between upshifting and downshifting), the gear ratio change consists only in disengaging one clutch and simultaneously engaging the other. Unexpected driving maneuvers can throw the system out of sync and the correct gear ratio has to be selected before the relevant clutch is engaged. Then the gear change is much slower.

commitment

Car

  • Armstrong Siddeley was the last automobile manufacturer to use the Wilson selection gearbox.
  • All Daimler models from 1930 to the 1950s had this preselector, which was initially used in the Double-Six . The chairman of the board told shareholders at the annual meeting in November 1933:
"The Daimler Fluid Flywheel Transmission now has three years of success behind it and more than 11,000 vehicles, ranging from 10 hp passenger cars to double-deck omnibuses, aggregating over 160,000 hp, incorporate this transmission. (..) it has yet to be proved that any other system offers all the advantages of the Daimler Fluid Flywheel Transmission. Our Daimler, Lanchester and BSA cars remain what we set out to make them — the aristocrats of their class and type. (…) We have also received numerous inquiries from overseas markets. (Applause) ”.
[In German: “Daimler Fluid Flywheel Transmission has now had three successful years in more than 11,000 vehicles, from 10-bhp cars to double-deck buses, and transmitted more than 160,000 bhp. (…) It would have to be proven that any other system offers the same advantages as the Daimler Fluid Flywheel Transmission. Our Daimler, Lanchester and BSA cars remain what we created them for - the aristocrats of their class and type (...) We also received a lot of inquiries from overseas. (Applause) "]

City buses

A significant proportion of British city buses built between 1935 and 1960 had preselector transmissions, especially those from Daimler and AEC and some from Leyland. Some of these were mechanical, but the AEC Type RT , used almost exclusively in London at the time, had an air-operated gearbox (air was also used on this model to operate the brakes, windshield wipers, etc.) that gave off a characteristic blast of air when the gear change pedal has been pressed. It was typical of the London buses that they had a very low-geared first gear that was only used on inclines. Before driving off, the driver selected second gear, pressed the gear change pedal, released it and selected third gear, all while the bus was still stationary. To start off, all you had to do was press the gas pedal and, at around 24 km / h, the gear change pedal, which engaged third gear. With this thrust, the bus usually drove to the next stop, where it was brought to a stop with the gear engaged. When starting up again, the process started again.

Armored car

motorcycles

Some James motorbikes in the 1950s were Villiers - two-stroke engines equipped, had the preselector gearbox. You pressed the gear pedal down to select first gear and then pulled the clutch lever. If you let go of it, first gear was engaged and the motorcycle drove off. Then you could use the gear pedal to pre-select second gear, which in turn was only engaged as soon as you pulled and released the clutch lever.

Rail cars

Some early internal combustion engine ( Otto or Diesel ) railcars had Wilson pre- select gears . For example, the GWR 'Flying Banana' railcar powered by an AEC engine had such a transmission.

Individual evidence

  1. ^ The Autocar: The Autocar Handbook . 13th edition. Iliffe & Sons. London circa 1935. Clutch on Gear Box . P. 112
  2. ↑ a b c d e f g h Ian Ward (Ed.); L. Setright: Anatomy of the Motor Car . Orbis, 1976, ISBN 0-85613-230-6 , p. 91
  3. ^ Peter Banjo Meyer: The Wilson Preselector Gearbox, Armstrong-Siddeley Type . Pbm-Verlag, Seevetal 2011
  4. ↑ Both types are forerunners of the automatic transmission.
  5. ↑ Track test of 1935 ERA R4D vs Porsche 911 GT3. In: automobilemag.com. 2004, archived from the original on March 8, 2005 ; accessed on March 29, 2015 .
  6. ↑ David Fletcher: The British Tanks, 1915-1919 . Crowood Press, 2001, ISBN 1-86126-400-3 , p. 190.
  7. ↑ Fletcher, pp. 70-74
  8. ↑ Glanfield, p. 180
  9. ↑ Fletcher, p. 122
  10. ↑ John Glanfield: The Devil's Chariots . Sutton, 2001, ISBN 0-7509-4152-9 , p. 271
  11. ↑ Autocar, p. 98
  12. ↑ a b c Autcar, pp. 115/116
  13. ^ A b W. E. Blower: The Complete MG Workshop and Tuning Manual . Motor Racing Publications, 1952. 7th edition 1958. Pre-selector gearbox . Pp. 159-171
  14. ^ Anthony Blight: Georges Roesch and the Invincible Talbot . Grenville Publishing, 1970, ISBN 0-903243-01-6
  15. ↑ Autocar, pp. 98/99
  16. ↑ Autocar, p 120
  17. ^ GW Chapman: Modern High-Speed ​​Oil Engines . Caxton 1949. Volume II (June 2, 1956). Oil-engineered Locos and Railcars . P. 109
  18. ^ Fletcher, British Tanks, 1915-1919
  19. ^ Maxwell's at home abroad. Retrieved June 30, 2014 .
  20. ↑ Bryan Jarvis: No Longer a Pandora's Box . In: Commercial Motor . tape 163 , no. 4161 , March 8, 1986, p. 46/47 .
  21. ↑ Technical data on the gearbox and transmission of the Tiger I tank. Retrieved June 30, 2014 .
  22. ^ Rebuilding Tiger tank 131.Bovington Tank Museum, accessed June 30, 2014 .
  23. ^ The Manchester Guardian . April 22, 1931, p. 5
  24. ↑ Simpler and Safer Driving . In: The Times . May 1, 1930, p. 13; Edition 45501
  25. ^ A New Daimler Novel Transmission Combination . In: The Times . July 1, 1930, p. 14; Edition 45553
  26. ^ Birmingham Small Arms Company. The Times . November 17, 1933, p. 22; Edition 46604
  27. ^ British Diesel Rail Coaches. Eng Rail History , archived from the original on March 20, 2013 ; accessed on June 30, 2014 .

Web links

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