There’s more to auto gearboxes than meets the eye…
By Richard Robertson
In the ‘good old days’ of motorhoming, every transmission was manual and the biggest difference was the number of gears you had. Then automatics came along and suddenly, folks decided changing gears was too much like hard work. Almost overnight, manuals disappeared and any vehicle manufacturer without an auto in its range (think Ford and the Transit from 2006) faded from view. Today, trying to find a motorhome without an auto is like trying to find consensus on climate change…
When automatic transmissions first appeared here they were American and used a torque converter. One, two and three-speed autos were developed, followed by the mighty four-speed unit in the 90s. For decades, Europeans turned-up their noses at autos, but finally started to come around as much out of pragmatism than anything else. One of the biggest hurdles for them was fuel economy, which at the time in America and Australia wasn't much of an issue (older auto gearboxes were quite fuel-inefficient compared with their manual counterparts). However, ‘driven’ by ever-stricter emissions standards, European manufacturers got to work and came up with a more efficient type of self-shifting gearbox: the automated manual transmission or AMT. Essentially a manual transmission and clutch but without a clutch pedal, gear changes were made by a rudimentary computer. Shifts were clunky, slow and took some getting used to, but they were more efficient than the average driver, resulting in reduced fuel consumption and lower emissions.
Early AMTs were what we initially saw in the RV industry in Australia. Mercedes-Benz was first, I believe, with its Sprintshift transmission, followed by Volkswagen, Fiat and Renault. Ford also had a Transit with an AMT – called Durashift – prior to 2006, but it was pretty woeful and, unsurprisingly, dropped for the model’s Third Generation makeover.
In Australia at least, Mercedes’ Sprintshift was quickly replaced with a ‘proper’ (torque converter) automatic; I'm told primarily in response to various emergency services organisations telling the German manufacturer they wouldn't be ordering more Sprinters if it persisted with that "awful" gearbox. Volkswagen continued with its clunky six-speed AMT, which it called the Shiftmatic, until the demise of the original Crafter in 2017 (new Crafter has an eight-speed torque converter auto). Similarly, Fiat persisted for years with its six-speed ComfortMatic AMT in the Ducato, but has now replaced it with a ‘proper’ nine-speed automatic. Only Renault persists with a traditional AMT, in its Master range, but in its defence it’s arguably the smoothest such gearbox produced.
Today, AMTs in their original form are largely consigned to the history books and automotive automatic transmissions are primarily divided into two camps: Torque Converter and DCT (the latter a development of the AMT, which I’ll explain in a minute).
Torque Converter refers to ‘conventional’ automatics of the type in most cars (technically, the torque converter is just a part of the whole transmission, albeit the most important one). Seamlessly shifting gears, manufacturers have made huge strides in efficiencies and now, such autos can even surpass manual gearboxes in terms of fuel efficiency. Boasting anything up to 10 speeds (ratios) – but with 6-8 the norm – Torque Converter autos are also known as Fluid Autos, which refers to the gearbox being filled with a special transmission fluid that transmits the power from the engine. It works like this:
Picture a sealed housing with two turbines (propeller-like discs): One turbine is connected to a shaft from the engine and the other to a shaft on the gearbox. When the engine-turbine spins it forces the fluid to spin, which in turn spins the other turbine, and the vehicle moves. That’s a VERY basic description and there’s actually a lot more to it. There’s also a third, fixed piece called a Stator between the two turbines. It’s at the heart of Torque Converter technology and effectively acts as a reduction gear by the way it manipulates the flow of transmission fluid between the turbines. Suffice to say it works and works well, and is the usual North American/Japanese/Korean style of automatic. However, that’s changing…
Meanwhile, AMT development didn’t sit still and today the very latest units are highly sophisticated, effective and fuel-efficient. However, the old style AMT has been developed into what is known as a Dual Clutch Transmission or DCT. While DCTs trace their roots to a French engineer just before WW2, it was Porsche, developing them for racing in the late ‘70s, that made them practical. The first mass produced car with a DCT was the 2003 Volkswagen Golf R32 and VW is perhaps the manufacturer with the most invested in the technology, which it calls DSG (for Double Shift Gearbox).
In a nutshell, a DCT is still an automated manual transmission, but with two clutches: One that drives a shaft with even-numbered gears while the other drives a shaft with odd-numbered gears. The DCT pre-selects an odd gear while the vehicle is moving in an even gear (or vice-versa) and that means the speed of each gear shift is blindingly fast. By precisely timing the operation of both clutches, a DCT can shift gears in a few milliseconds and without interrupting the power supply to the wheels. Shifting-speed aside, a DCT is also more fuel-efficient than a torque converter auto because it doesn’t waste energy spinning fluid to drive the vehicle.
In the real world there is very little to choose these days between a torque converter auto and dual-clutch transmission. In an RV application, choice is driven by the make of base-vehicle a manufacturer chooses: Mercedes-Benz, Volkswagen, Iveco and Fiat have now all gone down the torque converter path, although VW uses a DSG in its Transporter series. As mentioned, only Renault continues with an original type of AMT, but it’s Master is a budget-priced bit player in the local RV scene and mainly found in rentals and entry-level models.
While old torque converter automatics were lethargic when shifting, the latest models are quick, crisp and rewarding to drive. Similarly, early DCTs were renowned for ‘dithering’ if unexpectedly asked to change gears, like suddenly putting your foot down at low speed. That trait largely seems to have been addressed and now there’s little noticeable difference between the two.
It’s worth mentioning there is a third type of auto becoming popular: the Continuously-Variable Transmission or CVT. However, it has yet to make an appearance in the RV world and appears better suited to cars and SUVs. Both CVTs and DCTs are making inroads in Korean and Japanese cars, but whether the trend spills over into the light commercial vehicle sector remains to be seen.
Although campervans and motorhomes with manual transmissions remain popular in Europe, their days are numbered. Increasingly strict emissions standards, significant advances in technology and the sheer convenience of having a gearbox do the work means the future is decidedly automatic. That’s until all vehicles become electric and the gearbox itself is consigned to museums as a technological curiosity…