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Feature: Technology comes full circle – history of the gearbox

The advanced gearbox of today has reverted to what it was back in 1928 – three-speed and non-synchromesh. At least that is the way it is for Volvo Trucks. The development span between that first gearbox and the very latest – the I-Shift – encompasses a huge amount of work and many landmark accomplishments.
1928 saw the very first Volvo truck leave the factory. It was a very popular vehicle – in fact far more popular than its passenger car ancestor the ÖV4, whose driveline components were carried over into the truck in their entirety. This first truck, known simply as the Volvo Truck Series 1, produced 28 horsepower and had a three-speed non-synchromesh gearbox.

It was not until 1931 that Volvo built its first trucks without using driveline components from the company’s passenger cars. The gearbox in the new truck series was a robust four-speed unit specially designed for heavy vehicles. The new trucks also had sturdy rear axles with a reduction gear.

In these non-synchromesh gearboxes, it was necessary to press the clutch twice to change gears. This heavy double-declutching and shifting of gears solely by manual force put considerable physical strain on the driver. That is why it was hailed as an important leap ahead when synchromesh gearboxes appeared on the market in the 1950s.

“They marked an immense improvement in the driver’s working conditions: from a job requiring special training for gearchanging, it became more like driving a passenger car,” says Åke Zander, technical director at Volvo Powertrain and the person responsible for drivelines and hybrids. 

During the 1950s, Volvo also started experimenting with automatic transmissions. However, it would take another 40 years for automated transmission to make its breakthrough. Before that, auxiliary gears such as range-change and splitter transmissions made their entry into the truck cab.
However, auxiliary gears were really only a natural part of the development process and did not mark a major leap ahead. That at least is the view of Mart Mägi, former professor of automotive technology at the Chalmers University of Technology in Göteborg, Sweden.

“From a technological development perspective, the inclusion of additional mechanical gears behind and in front of the base gearbox was only a minor step in overall progress. The first truly revolutionary concept was the gearbox itself, which entered into use just over a century ago. The next significant technological advance was synchromesh, followed by automation,” explains Mägi.
The development of automatic transmissions for trucks progressed very slowly. However, once they arrived they were little short of epoch-making, says Mägi.

Volvo Trucks’ first automatic transmission – the Powertronic – arrived in 1992. Nine years later, Volvo took another decisive technological leap ahead with the introduction of the first generation of the I-Shift. Today this transmission is the jewel in Volvo Trucks’ crown, and has won widespread customer recognition.

Volvo Powertrain’s Åke Zander relates that it was only with the advent of the I-Shift that customers finally started appreciating automated transmission.

“Volvo has always had a strong selling point with its gearboxes, but when the I-Shift arrived in 2001, it received a particularly warm welcome. The I-Shift brought increased functionality, reliability, driveability and fuel efficiency, something that was entirely new on the market,” he explains.

The I-Shift is a splitter and range-change gearbox with three non-synchromesh gears in the main gearbox. With its splitter and range ratios, the transmission has a total of twelve forward gears, which are engaged and synchronised entirely electronically. The I-Shift communicates with the engine. For instance, it activates engine braking (the Volvo Engine Brake) as necessary, slowing down the engine and optimising each gearchange in a way that no driver with a manual gearbox can replicate.

The latest generation of the I-Shift was introduced in 2009 with the launch of Euro 5. Using a variety of software updates, it is optimised for various operating conditions, from highway to construction site. Today, more than 70 percent of all new Volvo FH and FM trucks sold are fitted with the I-Shift.

With this gearbox, the wheel comes full circle and Volvo has completed the journey from a three-speed non-synchromesh gearbox to the I-Shift, in which the mechanical heart of the unit is also a non-synchromesh three-speed gearbox.

However, Mägi prefers to look ahead beyond the I-Shift.

“In the future, the entire conventional gearbox may become obsolete – for instance in series hybrids, if or when we get a properly functioning hybrid system in trucks too. The next big step ahead is hybridisation, and that is already on its way in,” he says. Electric power transmission does not require any gears at all in the way they are used in today’s gearboxes. Computers take over control of power delivery from the engine to the driven wheels via intermediate electric motors and battery packs.

Zander agrees that hybrids are set to be the next major development step, but predicts that the gearbox is still going to be around.

“It will be needed together with an electric motor. Most of Volvo Trucks’ products are too heavy for electric power alone – the electric motor and batteries would be too big and expensive. And it is always customer benefit that determines when and if a technological paradigm shift is viable. Today Volvo Trucks’ hybrid trucks are equipped with the I-Shift,” he says.

November 1, 2010

Non-synchromesh or synchromesh transmission – what is the difference?
Before a gear can be changed, engine revolutions have to be adjusted to match the speed of the gearbox, otherwise the gears will scrape and the gearchange itself will be very clunky. This applies to all gearboxes.

The crucial difference between a non-synchromesh and a synchromesh gearbox is that in a non-synchromesh gearbox, the driver himself has to ensure that the engine’s speed matches the transmission speed.

This is done by pressing the clutch pedal twice (also known as double-declutching), allowing the driver to hear, feel or otherwise sense when the relative speeds of the gears that have to mesh are evenly matched with one another. The first time the clutch is pressed, the engine is disengaged; when the clutch is released, the driver can either rev the engine by pressing the accelerator, or can let the engine slow down by itself, depending on whether he intends to change down or change up. Once the relative speeds of the engine and transmission match one another, it is time to press the clutch pedal again and engage the next gear.

In a synchromesh gearbox, this adjustment of engine speed to suit the appropriate gear is done automatically through friction inside the gearbox.

Facts about the development of Volvo’s gearboxes:
1920s and ’30s: Manual, non-synchromesh gearboxes with few ratios.
1940s: With rising gross weights, increasing engine power and higher demands on fuel economy, the number of gears increases to four and then five. They are still manual and without synchromesh.
1950s: Synchromesh is gradually introduced in gearboxes.
1960s: Range-change gearboxes are launched. Introduction of the revolutionary R50 and R60 gearboxes with all-synchromesh changes.
1970s: SR61, a manual, 16-speed range-change and splitter gearbox.
1980s: The next generation of range-change and splitter gearboxes. The R1400, R1700, SR1400 and SR1700 had eight and twelve all-synchromesh ratios respectively, and either one or two crawler ratios.
1990s: Powertronic and Geartronic are introduced, Volvo Trucks’ first automatic gearboxes. Powertronic, an entirely new automatic transmission with torque converter. Geartronic, a traditional range-change gearbox with electronic gearchange control. Both had the advantage of both automatic and manual operation.
2000s: The I-Shift, the latest electronically controlled automated gearchanging system.

Link to photographs

For further information, please contact:
Marie Vassiliadis, Media Relations Europe, phone +46 31 322 41 27, e-mail
marie.vassiliadis@volvo.com