The manual gearbox has been shifted even closer to the exit on the transmissions ward. It’s now been dealt another blow by Volvo’s latest innovation, a dual clutch (DC) gearbox. Automated manual transmissions (AMTs) have swept all before them in the last decade, and they are now the staple specification for everything from the owner-driver’s high-spec tractor, down to the common fleet truck. It will take a little while for devices like predictive cruise control to penetrate as far, but how long before the dual clutch stamps its authority in such broad style?
We’ve seen dual clutch transmission in cars for some time, but according to Jonas Odermalm, Volvo’s Heavy Transport Manager, it’s been a tortuous process to bring it to heavy trucks. He said, “It’s not been so easy for heavy truck development. Making a DC gearbox sufficiently robust and reliable has been difficult, with the development of the software having been especially tough.”
Volvo’s Astrid Drewsen, Product Manager, Powertrain, announced in late 2012, at the FH launch in Sweden, that the ‘I-Torque’ DC, would be about a year away as it wanted to get it right. However, in that time ZF has introduced the TraXon DC, which will be a direct rival.
How does it work?
The basic idea is to use two parallel drive paths through the gearbox, with two input shafts and each controlled by their own clutch. As one gear is in use, the next has already been pre-selected, so it is a simple action of closing one clutch and opening the other. The effect is to give a gearshift that has no break in torque, almost feeling like a fluid coupling automatic. But not all shifts can be carried out this way.
On a 12-speed gearbox, one clutch deals with gears 1,3,5,7, 9 and 11, and the other handles 2,4,6,8,10 and 12. This means that they can only execute seamless shifts when the traction is transferred from one clutch to another, usually between sequential gears. A block shift between second and fourth, for example, would involve the same clutch, so it would operate at conventional speed. In practice this is not an issue because the majority of gearshifts, particularly on long-distance transport, are between the top three or four ratios and usually move one gear at a time.
All these employ the DC function and, for the driver, the difference is immediately apparent. Typically, moving off with involve block shifting, possibly between second and fourth, but then a shift to fifth would be a fast DC shift, and so would all the rest, providing they were sequential up the gearbox.
Gain or pain?
We’ve heard a lot about the ‘incremental gains’ that have been squeezed out of Euro-6 engines and transmissions. In the hunt for every drop of fuel economy, compressors and alternators have been put on part-time working to save the waste of energy involved by having them running all the time. It’s possible that with two gear paths active inside this DC design, there must be an incremental loss of some sort, however small. That said, it must be more than outweighed by the slightly faster hill climbs achieved by I-Shift with a DC, and these will mount up over a period.
But Volvo is not claiming any fuel improvement for the DC innovation, saying that the prime advantages are ‘driveability and journey times.’ As always, technology like this comes with a price tag. The DC version of I-Shift will initially only be available on the top three horsepower versions of the FH-13 – at 460, 500 and 540hp. There’s no word from Volvo on when it will extend to other models, but economies of scale must be tempting .
As for the cost, it is expected to have a list price of around £4,000, on top of the regular chassis price, and I-Shift transmission. However, the transaction price, especially for any fleet deal, is likely to be negotiable. It’s important for Volvo to get at least some modest volumes of this currently unique feature into the market while it has the upper hand, but increasing costs won’t help sales figures.
There are a few haulage applications that might be looking at this device more closely than haulage fleets. Forestry and timber extraction operations – big business in Sweden – often only use a 6×2 drawbar, and it places a lot of responsibility on that single drive axle. Even with a double-drive, it’s easy to come unstuck on soft forest roads, many of which are often temporary.
Having no break in torque between shifts is an attractive prospect in these conditions, and it could speed up journey times by allowing higher gears to be used while a truck is making its way back to the blacktop. Heavy haulage specialists could also be interested as shifting gears on hills at STGO weights is a challenge. Either way, the DC is another opportunity to improve market dominance. Volvo’s Odermalm is now claiming that 95% of the heavy trucks it sells in Europe are fitted with one.
Improving shift comfort has been the aim, and the DC development certainly carries on that tradition. But to justify the extra expense, there should be a financial return for fleets, at least if this is not to end up as the preserve of owner operators, or SME fleets that want to reward their top drivers – a resource increasingly worth looking after.
Jeff Bird, Press Director at Volvo Trucks, says that the technology is based on that used in race car engineering, but employed in the FH for a totally different purpose.