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Developmental Work on the New X15


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Diesel News Australia  /  November 2018

Instead of sitting on its hands, Cummins has decided to go on the front foot with specific developmental work on the new X15 engine to enable not only meeting the forthcoming regulations but also driving down fuel consumption.

It’s a fact that the vast majority of Cummins powered on-highway trucks in this country are hauling B-doubles up and down the eastern seaboard. Quite logically, this corridor linking the three eastern state capitals that collectively contain the vast majority of this country’s people is a well-trodden path for road transport.

Horses for courses

Mike Fowler, Director of Cummins On-Highway Engine Business, reveals that an important part of Cummins’ strategy for Euro 6 development has been to recognise and cater for two distinctly different sub-sectors at the heavy end of the heavy-duty truck market. 

“Firstly, there is the vocational sector largely encompassing tipper and dog and other short-haul single-trailer applications,” says Mike. “On the other side of the coin is the multi-trailer line-haul sector predominantly consisting of B-doubles but also including other configurations like Road Trains and various PBS (Performance Based Standards) combinations that demand really good performance as well as good fuel economy. 

“The vast array of different combinations and PBS combinations makes it very difficult to optimise the engine parameters to give the best fuel economy for each application .Therefore, to this end our goal has been to concurrently develop two distinctly different iterations of the X15 architecture for Euro 6. 

“When we further studied the breakdown of our market we realised the vast majority of our 15-litre product was in the B-double sector with much of it running up and down the east coast of Australia. So as we went through our Euro 6 plans we looked at how we could effectively optimise the X15 for fuel economy in that specific application.”

The consequential development of both 15-litre engine variants for Euro 6 is now at the stage of field testing, with a number of units placed in fleets around the country. The one that’s optimised for B-double line-haul work is for AMT (automated-manual transmission) powertrain only, the other is dedicated to vocational applications where an 18-speed manual RoadRanger is usually preferred.

“To optimise the fuel economy for the efficiency series we have ‘down-sped’ (reduced the cruise rpm of) the engine by running taller final drive ratios,” says Mike. “Due to our much higher gross vehicle weight limits this is a lot harder to do in Australia than in Europe or North America. In fact, the only way to achieve this is by increasing the torque output of the engine at lower rpm. So what we now have is power ratings of 550 to 570 hp (410 to 425 kW) and peak torque of 2050 ft lb (2779 Nm) arriving below 1000 rpm. 

“We’re also field testing with rear axle ratios as tall as 3.21:1 which is a massive departure from the traditional Cummins powered B-double ratios of 4.1, 4.3 and occasionally as tall as 3.9:1.”

Having said that, Mike goes on to say the 3.21 ratio is probably too tall for most ‘real world’ B-double prime movers in Euro 5 guise and a 3.73:1 ratio will be most likely the ideal solution for the application at this stage. 


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Gee, I showed my age, thought it was THE X-15  :)

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 “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’


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