Volvo I-Shift Dual-Clutch Transmission: Review

We're accustomed to driving dual-clutch Fuso Canter light trucks, but now the first Volvo FHs with innovative I-Shift Dual Clutch transmissions have rolled off the Volvo production line at Wacol, Brisbane.

Before you get excited and send in emails about our lack of knowledge on this topic, a dual-clutch transmission (DCT) is not a twin-plate-clutch transmission and Volvo is indeed the first global heavy truck maker to introduce a series-production DCT 'box into Australia.

In a DCT the input shaft from the engine into the transmission is not a normal, solid shaft, but a hollow outer shaft with a second shaft running through the centre of it. One clutch pack of the dual-clutch assembly is splined to the outer shaft and the other clutch pack to the inner shaft.

Inside the 'box the outer shaft is geared to one set of reduction gears and the inner shaft to another set. The 'box can deliver torque through one clutch pack and geartrain while the other geartrain has already pre-selected the next gear.

When the first clutch pack is disengaged, the second clutch pack is engaged simultaneously and the shift happens seamlessly, with no break in torque flow through the transmission.

The obvious benefit is rapid, sequential, automated shifts without traction-breaking or momentum-losing delays in shifting. That's ideal for trucks operating in hilly terrain, but this snap-shifting ability also allows tall gearing to be used in applications where the normal shift delay between overdrive and direct would dictate shorter final drive gearing.

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Volvo: I-Shift Dual Clutch coming to Oz

DCT development dates back to the 1950s, but only after reliable electronic controls were developed did the concept see mass production. The first DCT-equipped series-production vehicle was VW's R32 Golf, in 2003.

Since then, several passenger car makers have adopted DCTs, but the take-up has had mixed success. Electric hybrid transmissions may well supplant car and SUV DCTs.

Fuso was the first truck maker with a DCT in a commercial vehicle, announcing the Duonic in 2010 and putting it in production the following year. In 2012 it won a Technological Development Award from the Japan Society of Automotive Engineers.

In the USA, Eaton launched the Class 6/7 Procision seven-speed DCT in 2015, behind the B-Series Cummins engine.

I remember seeing heavy-truck DCT exhibits for the first time at the 2012 IAA show in Hanover. ZF displayed its revolutionary Traxon transmission, along with different nose modules, including a DCT fitment for the front of the main transmission, known as the Traxon Dual.

ZF's primary objective was to minimise fuel consumption and so the DCT function was confined to only the top three gears (10-11-12) in the first development stage of the Traxon Dual. (Later development resulted in both clutches working simultaneously for the three gear changes 3-4, 6-7, and 9-10.)

Across the hall in the IAA in 2012, Volvo previewed its I-Shift Dual Clutch transmission that wasn’t officially released until 2014, so I suspect that the preview was prompted by ZF's release.

The display clearly showed that the DCT version was based on a normal I-Shift 'box, with a different clutch pack and twin input shafts.

In the Volvo DCT 12-speed gearbox, one clutch is linked to gears 1, 3, 5, 7, 9 and 11, and the other handles 2, 4, 6, 8, 10 and 12.

This means that the 'box can execute seamless shifts only when torque is transferred from one clutch to another: between sequential gears. A skip-shift between 2 and 4, for example, involves the same clutch, so it operates at conventional speed.

Also, the range-change shift, 6-7, is always done at normal shift speed, not rapid DCT speed.

In practice this is not an issue because the majority of gearshifts, particularly in long-distance transport, are between the top three or four ratios and usually move one gear at a time.

In 2016 Volvo began to promote the DCT in Europe and used a spectacular video production to do that.

During this Croatian-mountain climb, a DCT-equipped Volvo FH towed a para-glider up a steep mountain road and through a narrow bridge underpass. The feat called for precision driving at a constant cruising speed, without any possibility of gear-shifting error.

In late 2018 the Volvo DCT was released in Australia and I had the chance to drive the demonstration truck in February 2019.

Volvo's DCT is available on the FH and FM models, powered by Euro 5 D13 engines with 500 and 540 horsepower. The DCT was originally developed for Euro 6 engines and adapting the transmission electronics to Australian-market Euro 5 engines has taken some time.

FH and FM 13-litre trucks are normally fitted with direct-drive I-Shift transmissions, but DCT versions have overdrive 'boxes, resulting in lower engine revs at cruising speeds, with claimed fuel economy benefits.

When encountering a slight grade at cruising speed, the DCT-equipped Volvo snap-downshifts to maintain wind-resistance power and to reduce the road speed drop a slower downshift would cause.

Effectively, it becomes a direct-drive truck in undulating country and an overdrive economy machine on the flat.

That's the theory, but how does it work out in the real world?

My mentor for the test drive was Matt Wood, Volvo's Fuel Efficiency Manager. He'd coupled an FH540 demo truck to Volvo's six-axle B-Double set, shod with single tyres and loaded to 55 tonnes GCM. Final drive ratio was 3.4:1 and the overdrive gear was 0.78:1.

The test track was familiar to me: a very steep climb up the Toowoomba Range, an undulating run across to the Cunningham Highway intersection near Warwick and down the infamous Cunningham's Gap. Before and after these climbs is plenty of city, secondary highway and freeway driving. Perfect.

The stop-start and undulating drive to the Toowoomba Range didn't really show off the DCT's advantages to any great effect, other than imperceptible up and down shifts that didn't disturb the combination's smooth momentum. It never became confused at roundabouts, or when traffic conditions dictated regular speed changes.

The standard I-Shift is world class in the automated-shift world, so the DCT benefits weren't obvious at this stage. Then we hit 'The Hill'.

Matt told me that we'd be climbing up the Toowoomba Range in cruise control. I thought he was kidding, but he wasn't.

Dutifully, I engaged cruise control and, as the grade began to sap road speed the 'box shifted back progressively and without any driveline shock, did a slower shift into sixth in the bottom 'box and then dug in.

"Put the selector in manual now," said Matt. "Because when we get to the saddle section, it'll want to upshift."

I didn't need any encouragement, because the thought of swapping cogs on Toowoomba Hill was daunting.

However, cog-swapping was in store for us, because on the last section of the climb we came across Old Mate in a 10x4 ACCO tipper, doing it tough.

My instinct was to indicate out of the slow lane and preserve momentum but, rather than obstruct car traffic, I backed off the accelerator and braved a manual downshift.

It's something I wouldn't have dared normally, but Matt looked calm enough and hadn't opened his door in readiness, so I clicked the downshift button and the revs went up a bit, indicating that a shift had happened. I did it again and, now in fourth, the DCT Volvo settled into a slower climbing speed, behind the slug. Unbelievable!

Building up speed at the top of the climb was equally as smooth.

Going down Cunningham's Gap started off easily, with the box in sixth, using the combination engine/exhaust brake to keep speed at a safe 30km/h. Then we encountered a very slow rig and I worked the wondrous slick-shift-action again, dropping back to fourth, seamlessly, with no need to trim speed with the wheel brakes during the shifts.

For working in hilly terrain I've never experienced a safer, more driver-friendly 'box and one that apparently greatly reduces driveline shock and wear.

This test didn't provide an opportunity to measure real-world fuel consumption on a line-haul route against a direct-drive FH 540, but we're hoping to do that in the future.

Volvo FH16 with DCT specifications
Engine: 13-litre common-rail six-cylinder turbo-diesel
Horsepower: 540hp (265kW)
Torque: 1700Nm at 1050-1900rpm
Transmission: 12-speed + two crawler gears; AMT with DCT
Fuel capacity: 450lt
Emissions: Euro 5 – EGR and DPF
GVM: 28,000kg
GCM: 70,000kg
Cab: Sleeper cab
Suspension: Leaf front/ rear eight air springs
Axle ratio: 3.4:1 with diff lock.
Brakes: Six discs with ABS/EBS
Headlamps: Halogen H7 headlamps and LED tail, DRLs and position lamps
Safety: Advanced emergency brakes, stability control, traction control, lane departure warning, cruise control
Seat: Air suspension
Warranty: 12 months unlimited kilometres and powertrain warranty for 800,000km