Wilson cockpit, with Wilson preselector gearbox The most common type of pre-selector gearbox was the Wilson, which used an
epicyclic design. A precursor to the Wilson gearbox was the manually-controlled epicyclic gearbox used in the 1901–1904
Wilson-Pilcher cars built in the United Kingdom. One of the company directors,
Walter Gordon Wilson, had become an advocate for the benefits of the epicyclic gearbox, which allowed large torques to be transmitted whilst still being controllable through a small input force. Walter Wilson was a major co-inventor of the armoured tank during and after
World War I, and was responsible for the 1918 British
Mark V tank using an epicyclic steering gearbox. The
Lanchester Motor Company in the United Kingdom also produced cars with manually-controlled epicyclic gearboxes from 1900 and built an experimental tank (the
Lanchester Gearbox Machine or
Experimental Machine K) fitted with an epicyclic gearbox. Walter Wilson continued experimentation with epicyclic gearboxes for cars and in 1928 his "Wilson gearbox" was invented. Walter and one of the co-owners of Armstrong Siddeley Motors formed the
Self-Changing Gears Ltd. company (initially called
Improved Gears Ltd.) to design and build the Wilson gearbox. The 1929
Armstrong Siddeley Thirty was one of the first cars to use the Wilson gearbox. The gearbox was also built under licence by other manufacturers including Cord, ERA, Daimler and Maybach. The driver pre-selected the next gear using a lever mounted to the steering wheel, then pressed the 'gear change pedal' (often located in place of the usual
clutch pedal) to activate the gearchange at the desired time. The Wilson gearbox was produced with a variety of clutches. The best-known is the
fluid flywheel, used for touring cars such as the Daimler (Armstrong Siddeley used a centrifugal clutch). Sports cars used a Newton
centrifugal clutch. This was a
multiple plate dry clutch, similar to racing manual clutches of the time, but with the pressure plate centrifugally actuated to engage at around 600rpm. Pure racing cars, such as the
ERA, avoided a clutch altogether and relied on the progressive engagement of the gearbox's band brake on lowest gear when starting. When fitted with a centrifugal clutch or fluid coupling, starting from a standstill involved simply selecting first gear, then the clutch would automatically engage once the accelerator pedal was pressed. On other cars, the gear change pedal functioned like a clutch when starting from a standstill. The Wilson gearbox relied on a number of epicyclic gears, coupled in an ingenious manner that was also Wilson's invention. Successive gears operated by compounding or 'reducing the reduction' provided by the previous gear. A separate epicyclic was required for each intermediate gear, with a
cone clutch for the straight-through top gear and a further epicyclic for reverse. Four gears were provided, at a time when many cars (especially American ones) usually only had a three speed gearbox. This was owing to the sporting, or indeed racing, market for the Wilson gearbox, so that the ratios could be more
closely spaced. Although this same arrangement of epicyclics would become the precursor for the post-war automatic transmission, the automatic transmission's use of a torque converter, together with the broad power band and excess power of US V8 engines, meant that wider-spaced, thus fewer, ratios were acceptable. Unlike the "crash" gearboxes of the first half of the 20th century, the gearwheels in a preselector box are permanently in mesh in an
epicyclic layout. Changing gear with the Wilson box relied on the control of the brake bands that held each epicyclic's annulus in fixed position. The brake band to be selected was controlled by a rotating cam, moved by the gear shift lever. Only one band was engaged for each gear selection. This small hand-operated lever could not provide enough power to engage and lock the brake band, thus the need for the foot pedal. The actual movement of the brake bands was controlled by the 'toggle' mechanism, a distinctive feature of the Wilson design. When the pedal was pressed and released, a series or 'busbar' of finger-like levers were pressed upwards by a strong coil spring, against a series of light linkages or 'operating struts'. The position of each linkage was controlled by the gear selection camshaft. If the cam (for each gear) held the linkage in place, rather than allowing it to swing out of the way, the busbar finger would then press, via the operating strut, onto the toggles controlling the brake bands themselves. These toggles provided the additional leverage necessary to hold the brake band in place, under the force of the coil spring, until the pedal was next pressed. A further characteristic of the Wilson design was the use of self-adjusting nuts on each band, to compensate for wear. The action of engaging and disengaging each band was sufficient to advance the ratchet nuts and so adjust for wear by taking up any slack.
Other epicyclic designs Cotal sportscar from 1935 2300S; gear selection lever mounted on the left side of the steering column During the 1920s and 1930s, several French luxury car manufacturers used three-speed or four-speed preselector gearbox manufactured by Cotal. A unique aspect of the Cotal gearbox was the use of
electromagnetic clutches (instead of band brakes) to engage the gears. A downside to this approach was that a loss of electrical power meant that the engine could no longer drive the wheels. The clutches were controlled by a simple dashboard or column-mounted switch, described as "a cherry on a cocktail stick", and relays. There was no mechanical servo action, so no need for the Wilson's cam or toggle arrangements and the change gear pedal.
De Normanville During the 1930s,
Humber cars were fitted with a four-speed preselector gearbox produced by
Laycock-de Normanville. It was broadly similar to the Wilson, but used direct hydraulic actuation of the brake bands (selected via a lever on the steering column) therefore avoiding the need for a change-gear pedal.
Talbot Several Talbot cars in the 1930s— such as the 1932–1935
Talbot AX65 Darracq— used an "accelerating gearbox" designed by Georges Roesch, based on the Wilson patents. The Roesch gearbox was vastly revised in both design and materials, resulting in a lighter gearbox that was able to withstand three times the power of the Wilson gearbox. This gearbox would automatically pre-select first gear when reverse was engaged. On engaging second gear, the gearbox would then pre-select third, and fourth when third was engaged. It would then cycle between third and fourth until another gear was pre-selected manually. Initial versions were produced without any form of clutch, however a centrifugal clutch was soon added to the design. Described by Talbot as the 'Traffic Clutch'. this was a simple device, with two radially swinging shoes (similar to a drum brake).
Viratelle An early pre-selector gearbox was a prototype three-speed motorcycle gearbox patented by
Marcel Viratelle in France in 1906. The design and production were very compact.
Tiger tanks The 1942–1945 German
Tiger I armoured tank used a form of pre-selective gearbox that was built by Maybach and offered 8 ratios. The shift mechanism was hydraulic, to reduce driver effort. Clutches were used in combinations, allowing many more ratios than actuators. There were three hydraulic cylinders, each with two positions and controlling dog clutches for gear trains arranged on four shafts. The cylinders were controlled by a rotary valve on a simple quadrant gear lever and activated by pushing the lever sideways into its gate. The combination of the three cylinders permitted eight different ratios, although in reverse these were limited to just the lowest four. When a captured Tiger I tank was studied by the British in 1943, the report on the gearbox was carried out by Armstrong Siddeley motors. == Comparison with other transmissions ==