PH Origins: The manual gearbox
Find out why you need to thank woodworking tools for the manual transmission
When the first automobiles began tentatively rolling out of workshops, their designs were mired in the past. Most were based on existing horse-drawn carriages or, if built from the ground up, adopted a similar visual appearance and layout. This meant, for the most part, that the only viable position for the engine was behind the rear seats. The Benz Patent Motor Car Type I of 1886, which is often regarded as the first production car, featured such a layout.
Its single-cylinder, 954cc four-stroke engine drove the rear wheels via a single-speed transmission. This consisted of an engine-driven belt that ran down to a pair of drums underneath the seat; one drum was effectively neutral, while the other was first. Moving the belt from one drum to the other would engage drive, channelling the engine's output into a pair of chains that ran back to the rear wheels. Flat out, with the 0.7bhp engine blatting away at 400rpm, Karl Benz's motor car could hit 10mph. There was no reverse but, as the car only clocked in at some 300kg, pushing it was backwards was hardly arduous.
French engineers Jean-Louis Perin, René Panhard and Émile Levassor had been watching the expanding German automotive and engine market with interest. They had long collaborated in the production of woodworking machinery and, in 1875, had begun producing stationary engines to capitalise on the rapidly advancing industrial marketplace. Perin died in 1886, so the large machine-building company - previously called Perin et Panhard - was renamed Panhard et Levassor.
It's reputed that the duo were not necessarily interested in producing their own vehicles at this point, with the plan being to solely manufacture and supply engines, but in 1888 things were to change. Armand Peugeot, then running a company called Peugeot Frères Aînés, was a leading manufacturer of bicycles. He, too, had expressed interest in the up-and-coming automobile industry. Panhard and Levassor, then producing Daimler engines under licence, subsequently approached him with a view to supplying engines in order to bolster their own sales.
Peugeot took up the offer and, in due course, prototypes began plodding around the countryside. These, however, conformed to the existing carriage-style design. As the engine was either mounted in the back or in the middle, there were limits to the size and complexity of the powertrain. Levassor, not convinced by existing configurations but inspired by the advances achieved by those around him, then set about coming up with a fresh layout for the motor car - no doubt aided by Panhard - with the aim being to design a complete automobile that could be marketed by their company.
His first step was to mount the engine at the front of the chassis. This created more room for the powertrain and put more weight on the steering wheels, helping improve the car's handling. Instead of mounting the engine transversely, between the wheels, Levassor mounted it longitudinally. Power would then be transmitted to the rear wheels.
Levassor wanted to make the most of the limited torque and crank speeds offered by the engines of the day, too, but was restricted by the available transmissions. Fortunately, he had plenty of experience with multi-gear transmissions in another field: woodworking. He had, in the past, worked on the design and construction of lathes, which featured basic transmissions - in which gears could be slid along shafts into different positions, altering the speed and torque of the chuck.
Drawing on this experience, Levassor then designed what is regarded as the first modern manual transmission. It had no casing, so the internal shafts and gears were exposed to the elements, and offered three forward ratios but no reverse. A foot-operated clutch was used to separate the engine from the transmission, drive from which would then be channelled into a differential. The outputs from the differential would then transmit power to the rear wheels via individual chain drives.
This unsynchronised 'sliding gear' transmission, unveiled in 1891, was a predictably agricultural affair that required precise throttle, clutch and gear actuation to avoid a horrible clashing of gears; these transmissions were originally called 'clash' gearboxes as a result - a moniker that would eventually evolve into 'crash'. Panhard or Levassor reportedly stated: 'It's brutal - but it works.' The new front-engined, rear-drive layout with a manual transmission was subsequently dubbed 'Système Panhard'. Besides being later adopted by Peugeot, it also established the standard vehicle configuration for countless vehicles for decades to come.
Later, in 1895, Panhard and Levassor would refine the manual transmission by enclosing the gears within their own casing. Rival Benz hadn't sat still, mind, and the later four-wheeled Benz Velo of 1894 featured a two-speed drum-based transmission - or, if you were willing to fork out a substantial premium from 1896 onwards, a planetary-based three-speed transmission was also available. This set-up also had a reverse gear, improving the Velo's ease of use. The sliding gear type of transmission would, however, become the far more common type in the coming years.
The next major advance was in 1918 when General Motors engineer Earl Thompson penned the 'Automatic gear shifting mechanism for sliding gear transmission' - an innovation that would later be renamed the synchromesh. This system allowed gears in the transmission to be moved into mesh with each other, while rotating, without clash. Besides making the manual transmission quieter, this innovation also made changing gears far easier.
It took some time to reach production, though, finally arriving in the 1928 Cadillacs and LaSalles. 'Gear-shifting made easy,' read the adverts. 'No mental strain, no clash, no noise - when a shift is made, it is simplicity itself!' Overdrive units were also soon introduced and, as time progressed, manufacturers continued to make manual transmissions more efficient and easier to use - increasing the number of ratios and continually adding synchromesh to more and more gears.
Development of manual transmissions for cars hasn't stalled entirely, either; in 2012, Porsche collaborated with ZF to produce a seven-speed manual transmission - a gearbox which was, somewhat ironically, based on an existing seven-speed dual-clutch transmission. For once, General Motors was lagging slightly behind the Europeans and followed suit in 2014, using the Tremec TR-6070 seven-speed manual in the then-new C7 generation of Corvette. As has always been the case, the addition of extra ratios allowed manufacturers to extract improved performance while potentially boosting efficiency. The first gear could potentially be shorter, improving off-the-line acceleration, while the seventh gear could be a substantial overdrive ratio - allowing for quiet, economical cruising at higher speeds.
That is not to say that the manual transmission has reached its peak, though; for example, the technology group Schaeffler is continuing to develop clutch-by-wire systems. Using this system would provide the driver with a familiar layout, unlike the semi-automatic clutchless manuals from Valeo and Saab's 'Sensonic', but allow for the automation of the clutch action. This would permit a manual car to enter a coasting mode at higher speeds, emulating the 'sailing' function offered in dual-clutch transmissions, without any input from the driver; real-world trials of this set-up, with the engine either dropping to idle or shutting off entirely, have so far demonstrated fuel efficiency savings of between two and six per cent.
A clutch-by-wire configuration would also help sate ever-increasing safety and comfort requirements by allowing for more advanced driver aids - such as stall-free emergency brake assist and automatic clutch operation in traffic. Schaeffler additionally states that, because the clutch is electronically operated, its actuation and response can be tailored to suit the conditions and further grants easy opportunities for hybridisation of the powertrain.
These advances will help prolong the remaining life of the manual transmission but, ultimately, it will go the way of manual ignition advance and unassisted brakes - in part due to ongoing automation, changing vehicle usage and market conditions. Manual transmissions will stick around in Europe for some time yet but, in countries such as the United States, expect their lifespan to be shorter. Case in point: a story called 'The disappearing stick shift', published in the LA Times in 2016, revealed that 47 per cent of new cars in the US were available with a manual transmission in 2006. By 2016, that number had dropped to 27 per cent. Sales were down, too; in 1992, manuals accounted for some 25 per cent of US car sales. In 2016? Just three per cent, a number that has no doubt continued to dwindle.
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