At the heart of the I-Save package is Volvo’s D13K500, TURBO-TC (Turbo-TurboCompound), an engine designed specifically for high mass, long-haul operations.
It is a 500hp 12.8 litre in-line six equipped with twin overhead camshafts, four valves per cylinder and common rail fuel injection. Optimum combustion efficiency is achieved by a wave-shaped piston crown which redirects the flame front to the centre of the combustion chamber.
With all this in mind it’s time to see if theory correlates with on-road reality as I step up into the cab of the Volvo I-Save for a return run from Volvo Group Australia’s (VGA) Wacol head office to Toowoomba.
On the subject of stepping up, a welcome upgrade of the step tread design provides a supremely solid and non-slip foothold, whether wet or dry, to ensure safe entry/egress at all times.
The prime mover is hitched to a curtain-sider B-double with the combination loaded to a GCM of 58 tonnes, a fairly typical weight for a line-haul runner.
Because this truck is a prototype unit fitted with the I-Save package, there are a few differences compared with the forthcoming production units. For example, production versions will have a push button gear selector rather than the traditional lever.
In addition, while the prototype’s transmission features a direct (1:1) top gear ratio, in line with all 13-litre models to date, word has it that an overdrive box will be used in production versions to provide the necessary down-speeding of the engine at highway cruising speed.
Initially VGA was planning to achieve this down-speeding by retaining the direct ‘box and fitting a European spec 2.83 ratio rear end. However, the company seemingly surmised that for our market the improved startability from the 3.09 diffs combined with the overdrive top gear was the way to go, effectively providing the best of both worlds.
Riding shotgun with me on the drive is Matt Wood, Strategic Projects and Communications Manager at VGA, who explains that the turbo-compounding on this vehicle is markedly different to that which Volvo introduced on its 12-litre engine more than 20 years ago.
Put plainly, there were a number of factors that adversely affected the long-term reliability of Volvo’s early 12 litre TC engines, including the propensity for trucks of that era to be driven somewhat above the legal 100km/h speed limit and the fact that most of them had manual transmissions fitted. Both of these factors, particularly in the hands of a ruthless driver, tended to put too much stress on the TC geartrain, leading to reliability and durability issues.
However, according to Matt Wood, those issues have now been well and truly rectified.
“There are significant differences between the two versions and probably the greatest of these is intent,” says Matt. “Back then TC was introduced to gain more horsepower and performance from the 12 litre engine, specifically for B-double duties, whereas today with the 13 litre it’s all about improving efficiency.
“In those days, many trucks were perhaps travelling a little faster than they should have been whereas today we have a largely compliant industry and I-Shift automated manual transmissions (AMT) are standard fare on all 13-litre Volvos.”
Matt goes on to emphasise that the greatest enemy of TC systems is overspeeding, which is why Volvo, this time around, is keen to promote the strengths of TC in terms of improved fuel efficiency and torque delivery at lower rpm.
“This engine produces peak torque between 900 and 1,300rpm so it needs to have a rear axle ratio that enables 100km/h cruising at or below 1,300rpm,” says Matt, asserting that the production version with the overdrive transmission should enable 100km/h cruising speed at around 1,250 to 1,300rpm.
Matt proceeds to explain that a number of other new features, in this engine designed specifically for high mass, long-haul operations, have enhanced Volvo’s latest TC unit over earlier versions the company produced.
“The housing is pressurised to reduce the likelihood of oil leaks and the turbine/compressor wheel has been tested to 124,000rpm, while in operation it rarely reaches 73,000rpm,” says Matt. “There is also a Voith fluid coupling in the system, rather than the previous direct mechanical connection, which mitigates vibrations and prevents shock loading on the gear train between the turbo and flywheel.”
