Volvo Dual Clutch: a clutch of class

By: Steve Brooks


If you think automated transmissions don’t come any smarter or smoother than Volvo’s super-slick I-shift, well, you’ll have to think again following the release of a new ‘Dual Clutch’ version. But are quicker, slicker shifts Volvo’s only motivation for adding the significant cost and complexity of dual-clutch technology?

Volvo Dual Clutch: a clutch of class
‘Dual Clutch’ is barely evident as I-shift adopts its usual skip-shifting operation

 

Volvo’s dual clutch system is clever technology. No question. Launched in Sweden in 2014, which suggests any bugs have been well and truly ironed out by now, it remains a world first for heavy-duty trucks. As Volvo declares, "Transmissions with dual clutches are used in cars, but Volvo Trucks is the first and only manufacturer in the world to offer a similar solution for series-produced heavy vehicles."

Built on the remarkably, and deservedly, successful I-shift 12-speed transmission, the dual-clutch assembly makes Volvo’s supremely smooth and responsive automated shifter even smoother and more responsive. Some of the time!

But how much smoother and how much more responsive?

A little or a lot, the answer depends largely on where the truck is and what it’s doing.

Like, there were numerous occasions on a recent drive of a 13-litre FH540 B-double outfit when it was difficult to determine if there was any practical difference between this dual clutch version and the standard I-shift gearbox I’ve come to know and admire over many years in many trucks. Not just Volvo trucks either, but in the same transmission’s other identities as the Mack mDrive or UD’s strangely titled Escot.

Yet at other times during a busy stint that included hauling the 55-tonne combination up the formidable Toowoomba Range and down the unforgiving Cunningham’s Gap, the spontaneity of shifts through the dual clutch system was nothing short of outstanding.

Put simply, in the fluctuating flows of suburban traffic, where any modern automated shifter will routinely deliver multiple skip-shifts as traffic teeters between stop, go, fast and slow, the dual-clutch system showed little, if any, advantage over a standard I-shift.

Out in rolling country, though, and particularly where the grades came long and sharp both uphill and down, single-step shifts through the dual clutch system were breathtakingly quick and smooth. Sensationally seamless and, yes, appreciably more responsive than the standard I-shift.

Volvo refers to these single-step swaps as ‘power shifting’ – meaning no interruption to power and torque delivery during gear changes – and overall performance of the dual clutch system was effectively just as the press blurb said it would be.

Like, "When driving in conditions where it is optimal for the transmission to skip a few gears, the transmission changes gear just like a regular I-shift unit," Volvo’s press statement reads.

Conversely, as Volvo Trucks vice-president Tony O’Connell says in the same statement, "I-shift dual clutch … delivers seamless gear changes and uninterrupted engine power to the road when accelerating and climbing or descending tough grades."

And again, that’s just how it panned out on a run that started early on a weekday morning from Volvo’s Brisbane North dealership and ended 350km later at Volvo Group’s new headquarters at Wacol on the city’s western edge.

Riding shotgun was Volvo Group fuel efficiency manager Matt Wood (yes, the same Woody I’ve shared many travels with in his former life as a truck scribe) who had the 13-litre FH540 perfectly prepared, hooked to a B-double trailer set mounted on wide profile single tyres.

Exploded view of I-shift ‘Dual Clutch’. The dual clutch system adds around 100kg to overall vehicle weight and measures 12cm longer than a standard I-shift. Cost and complexity are significantly higher

DEFINING THE DETAIL

With just 1,600km on the clock, peak performance was probably still a few thousand kilometres away but that said, Volvo’s top 13-litre rating was typically lively and certainly not shy when required to dig deep.

Even so, this was an exercise primarily designed to showcase the merits of the dual clutch system over a relatively short but demanding route, and ideally, how this form of transmission technology can aid the efficiency and performance of Volvo 13-litre models at 500 and 540hp (373 and 403kW) in either FM or FH forms.

At this point it’s worth noting the dual clutch system is not available behind Volvo’s flagship 16-litre models.

So what exactly is ‘Dual Clutch’ and how does it work?

Its technical name is the SPO2812 transmission, meaning it’s a 12-speed box with input torque capacity of 2,800Nm. Most importantly, though, the ‘O’ signifies an overdrive gearbox whereas the standard I-shift behind the 13-litre engine in linehaul B-double applications is a direct-drive unit.

As Volvo puts it, the broad ratio coverage of the overdrive shifter – from a first gear of 11.73:1 to a relatively tall 0.78:1 top slot – provides good lift-off capability and critically at the other end of the spread, fuel efficient engine revs at cruising speed.

However, it needs to be also pointed out that this dual-clutch version of I-shift drove into a 3.4:1 rear axle ratio instead of the 3.09:1 final drive typically used behind the direct-drive box in 13-litre linehaul B-double combinations. That means the 13-litre dual clutch derivative uses the same gearbox and diff combination fitted in the vast majority of Volvo 16-litre B-double outfits.

Consequently, as our test run revealed, engine speed at 100km/h with the dual-clutch overdrive box is around 1,400rpm. By comparison, the standard direct-drive version of I-shift running through the 3.09:1 diff ratio notches 100km/h at a twitch off 1,600rpm.

Therefore, it shouldn’t surprise anyone that a prime goal for the dual clutch layout is to improve the fuel efficiency of 13-litre models in linehaul B-double roles.

Anyway, as for the details and actual workings of the I-shift dual clutch system, Volvo says, "I-shift dual clutch can be described as two gearboxes with two clutches, integrated into one unit.

"The two [dry type] clutches are connected to two different input shafts, operating independently of each other. Since the gearbox has 12 [forward] gears, one shaft holds the six odd numbered gears while the other holds the six even numbered gears.

"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."

Clutch of Class - Pic A.jpg

Power shifting!

There is, however, a significant exception in ‘power shifting’ availability. It does not operate on the range-change between 6th and 7th gears, which, as most drivers will confirm, is where fast shift speed is generally most beneficial.

What’s more, there are significant control components which operate the dual clutch arrangement and in addition to more mechanical parts, add substantially to I-shift’s complexity. As Volvo explains, "The clutches are controlled by the DCCA (Dual Concentric Clutch Actuator), which in turn is pneumatically controlled via the DCVU (Dual Clutch Valve Unit) while another device, the GCU (Gearbox Control Unit) controls gear changing."

Predictably, with complexity comes cost but unlike complexity, cost isn’t so easily uncovered in the corporate context.

In fact, Volvo’s official response when asked about the price premium for the dual clutch version of I-shift were a couple of rather lame lines about not speaking specifically about price and suggesting, "anyone interested in this unique offering … should contact their nearest Volvo dealer".

Following that advice, it seems there’s some ‘wriggle room’ when it comes to price but nonetheless, the dual clutch system won’t come cheap at between $10,000 and $12,000 over the cost of a standard direct-drive I-shift in the 13-litre Volvo.


Read about Volvo's release of its FH Globetrotter XXL cab, here


For the driver, however, nothing much has changed in operational terms. There’s a shift lever integrated on the left side of the seat, which has no mechanical contact to the actual transmission, and selecting auto, manual or reverse modes is as easy as pushing the short stick forward or back, with buttons on the side of the lever for fingertip shifts up or down when required.

There’s also a button for ‘Economy’ and ‘Performance’ modes, which give the driver the option of engine speeds tailored for fuel economy or, as Volvo states, "when extra engine power is needed". In reality, all ‘Performance’ mode does is increase the engine speed for upshifts made under full throttle.

Used correctly, the ‘economy’ and ‘performance’ functions of I-shift can be beneficial but it’s no secret that ‘performance’ mode has become something of a bane for Volvo and some of its customers. There are drivers who simply over-use ‘Performance’ in the mistaken belief of extracting more muscle from the engine – particularly the 13-litre engine – when, in fact, all they’re doing is using more fuel to gain marginally higher engine speeds.

In response, and obviously striving to improve fuel returns, Volvo some time ago introduced the option of dash-mounted transmission controls in place of the shift lever, a move which not only deleted ‘economy’ and ‘performance’ modes but also removed the ability to make manual shifts.

It’s easy to understand why Volvo developed the lever-less option but in practice, it also negates many of I-shift’s inherent attributes.

Fortunately, the ‘Dual Clutch’ test truck had the standard lever arrangement and as the exercise moved into the hard haul up Toowoomba Range before dropping down Cunningham’s, it was in manual mode that the dual clutch system showed its most impressive traits.

Clutch of Class - Pic D.jpg

Before then, of course, came the dawdle out of Brisbane’s northern ’burbs, where it was difficult to recognise the difference between a standard I-shift and its dual clutch counterpart.

Sure, there were occasional moments, such as the drag over the Gateway Bridge, when an almost imperceptibly fast single shift suggested what was to come, but for the most part, the run west through morning traffic was just another quiet stroll in another smooth Swede.

Likewise, the 13-litre engine was making relatively easy work of its 55-tonne gross weight, cantering comfortably in auto mode. Then again, the I-shift dual clutch transmission is rated to gross weights up to 80 tonnes, so if you’re out to showcase a transmission to its peak ability, why limit the combination to 55 tonnes instead of a B-double’s maximum of 62 tonnes and more?

The answer, apparently, is that the majority of linehaul B-double combinations hauling general freight rarely run at peak B-double weights anyway. So, given that a multitude of Volvo 13-litre B-double combinations haul general, 55 tonnes is probably an accurate indicator of real world operation.

FLASHBACK

In fact, a quick stroll into the recent archives revealed that Volvo’s thinking on its 13-litre model’s preferred place in the B-double business hasn’t changed at all over the past five years or so.

For instance, a road test on a 13-litre FH540 B-double in late 2013 – just months after the Australian launch of the new generation FH range – was run at a pinch over 55 tonnes, with Volvo even then making the point that it’s perhaps a typical gross weight for a B-double on general freight.

What’s more, the trucks then and now were run over much the same route, except the dual clutch version had a longer stint in the ‘burbs than the previous combination. Either way, the similarities were remarkable except, of course, for the dual clutch system with its different drivetrain and the fact that the earlier outfit at least had a few thousand more kilometres under its belt.

Like the previous test unit, the dual clutch Volvo was equipped with a swag of safety and efficiency features including the I-roll function, which under certain conditions puts the transmission into neutral, allowing the engine to coast at idle. The aim, of course, is to save fuel and in the undulations between Brisbane and the foot of the Toowoomba Range, I-roll certainly delivered many bouts of idle time … pardon the pun!

On a number of occasions, however, there was a slight ‘bump’ as the transmission re-engaged when the foot went back on the ‘go’ pedal. It wasn’t severe but it was definitely noticeable, at least to this nut behind the wheel, and certainly the first time I can recall anything of this nature in I-shift.

Clutch of Class - Fill Pic.jpg

Anyway, through the village of Withcott as the range rears up, with ‘Woody’ asserting the benefits of engaging cruise control at 80km/h and leaving the transmission in auto for at least the first half of the climb, the dual clutch system was soon strutting its stuff.

Suddenly, it was obvious what all the dual clutch hype was about, with ‘power shifts’ kicking in and each step down the box coming quicker and slicker than anything I’ve ever experienced in an automated box of any kind.

Still, as Volvo had already explained, the only exception in power shifting was in the range-change swap from 7th back to 6th. But seriously, the difference was negligible; such is the responsiveness of I-shift generally.

Halfway up and onto the saddle between the two climbs, experience determined a move to manual mode to hold the transmission in 6th gear and avoid an untimely and short-lived upshift before the tougher second stage of the ascent.

Beyond the saddle and with revs slowly peeling off as the grade grew, a manual swap to 5th went through in another silky smooth instant. Meantime, with engine speed dropping no lower than 1,550rpm on the sharpest pinch, it wasn’t long before an upshift to 6th went through with similarly spectacular speed while near the top, a manual move across the range-change to 7th might have been marginally less instant, but was nonetheless effortless.

From here on it was back to auto mode, through Toowoomba’s busy main artery and across the undulating tableland to the top of Cunningham’s Gap before a move down to 5th gear in manual mode for the drop over the lip.

Here again, the dual clutch system was every bit as impressive as it had been hauling up the range, delivering spectacularly fast, smooth single shifts, working in concert with flicks through the various stages of engine retardation to provide a safe, effortless descent of an historically difficult and dangerous grade. It just doesn’t get any easier.

Then on the run-off, a move back to auto and let I-shift just do its thing for the last leg to Volvo headquarters in Wacol. Simple!

CONCLUSION

As stated at the start, "Volvo’s dual clutch system is clever technology. No question."

In fact, if Volvo’s only goal with the system is to deliver the fastest, smoothest automated gear shifting transmission in the heavy-duty truck business, it has unequivocally succeeded.

There is, however, more to it than that and with the move to the same drivetrain – overdrive transmission and 3.4:1 final drive ratio – used in the great majority of its 16-litre B-double combinations, Volvo is obviously aiming to enhance fuel efficiency of its 540hp 13-litre outfit in linehaul B-double duties.

Similarly, perhaps, the characteristics of the dual clutch version of I-shift have the potential to at least partially reduce stress on the 13-litre engine in B-double combinations.

Still, if enhanced fuel efficiency is indeed a prime goal, does the dual clutch system achieve a gain worthy of the increased cost and complexity? Probably not!

Back in late 2013, our FH540 test unit running the standard direct-drive I-shift through a 3.09:1 rear axle ratio, at much the same weight over much the same highly demanding route, returned a fuel figure of 1.72km/litre, or 4.85mpg. By comparison, the overdrive dual clutch unit in this exercise returned a fuel figure of 1.64km/litre (4.63mpg), but given the severity of the route, neither figure is unacceptable.

Clutch of Class - Lead Pic.jpg

Yet even though the dual clutch truck had a couple of thousand fewer kilometres on the clock and travelled through marginally more traffic, it’s difficult to substantiate any fuel gain with the dual clutch transmission.

Most perplexing of all, though, is Volvo’s promotion of the dual clutch option when it has a perfectly good alternative to its 540hp 13-litre model for linehaul B-double work.

That option is a 540hp version of its 16-litre engine, which already runs an overdrive I-shift and 3.4:1 rear axle but, for whatever reason, remains a largely understated option in Volvo’s model menu.

From the outside looking in, the bigger cubes will almost certainly enhance long-term durability, and doing the job with considerably less stress than its smaller sibling, it’s entirely possible the 16-litre 540 will be better on fuel.

Finally, any consideration of the dual clutch option for B-double work should perhaps start with the simple fact that Volvo’s I-shift is still as good as it gets; a supremely successful and immensely intuitive automated shifter which from the moment of its release set a new standard in transmission technology.

As for the operational and economic value of ‘Dual Clutch’ … well, maybe it should be contemplated alongside a thought which jumped into the brain as the test truck ran up on a struggling, slower vehicle on the first long pinch up Toowoomba Range: If circumstance decreed a stop on such a severe grade, what would be the better addition to I-shift for a heavily loaded B-double – the dual clutch system or the crawler gear option released late last year?

For me, it’d be the crawler gear. Every time!

 

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