The obvious answer to the question, ‘how many clutches do you need?’ would be one, but Volvo reckon there are advantages, in some cases, to using two clutches to improve driveline efficiency. The Volvo dual clutch technology has been available for some time in Europe, but has finally made its way here, after prolonged testing in Australian conditions.
There are now examples of the new gearbox option on the road and Diesel News took the opportunity to drive a B-double out of Brisbane, up the Toowoomba Range and along to Cunningham Gap, before returning down from the Dividing Range to Brisbane.
There have been dual clutch vehicles in Australia before. They are an option in Volkswagen cars and available as the Duonic option on the Fuso Canter model. Volvo’s introduction of the concept is a first for the heavy end of the market.
Volvo claim that by having two clutches in the gearbox most gear changes made can be power-shifts and there is no interruption of power as the change is made. Essentially this should make the driveline more efficient, but it can also reduce the number of times the driveline is interrupted during ratio changes.
The I-Shift Dual Clutch transmission consists of two input shafts and a dual clutch, which means that two gears can be selected at the same time. It is the clutch that determines which of the gears is currently active. I-Shift Dual Clutch is based on I-Shift, but the front half of the gearbox has been redesigned with entirely new components.
Essentially, the I-Shift Dual Clutch is two gearboxes linked together. During gear changing, the first gearbox is disconnected at the same instant as the second gearbox is connected, so gear changes take place without any interruption in power delivery.
The two clutches are connected to two different input shafts, operating independently of each other. Since the gearbox has 12 gears, one shaft holds the six odd numbered gears, while the other holds the six even numbered gears. The gear changes using the two clutches can be used for all single step gear changes apart from the one between sixth and seventh gear, as this involves a range change –from low to high, or vice versa.
When the transmission control unit decides it is a good idea to skip ratios, when the load is light and the going easy, either going up or down the box, the I-shift will change gears as it would normally without a second clutch.
According to Volvo, the I-Shift Dual Clutch makes a big difference when transporting moving or liquid cargo, such as livestock and tanker operations. The smoother uninterrupted gear changes create less movement in the cargo itself. The power-shifting on offer also means there is less risk of getting stuck on slippery or uneven roads, for instance when hauling timber in the forest.
The dual clutch does introduce a number of new components into the gearbox and, as a result, the transmission is 120mm longer than its single clutch equivalent. The extra componentry also adds 100kg to the weight of the gearbox.
When Ove Wikström, Volvo Global Heavy Duty Transmission and Rear Axle Manager came to Australia last year he spoke about the intended release of the dual clutch technology and gave examples of how it is working in Europe.
“We have some information from some of our customers that there is a fuel consumption saving with the dual clutch,” said Ove. “If you go on a flat road, you don’t save any fuel, but if the road is up and down you can save three or four per cent, and we had one customer saving five per cent on fuel. You also have some time saving and the smooth gear shifting is good for the driver and the load.
“We ran a trial in Sweden to see how much time could be saved. We went from Gothenburg in the east of Sweden to the west coast. This is a distance of 645km and we had an average speed of 70 km/h and it took 9.5 hours. The road was up and down, but not extreme, the normal landscape in Sweden, and the result was we saved them 15 minutes, which corresponds to a three per cent improvement.”