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Cummins: New X15 Engine Offers High Performance, Economy, Reliability

July 24, 2016, by Tom Berg

A parade of X15-powered tractor-trailers led the press bus to presentations at the Transportation Research Center in central Ohio. Photos: Tom Berg
A parade of X15-powered tractor-trailers led the press bus to presentations at the Transportation Research Center in central Ohio. Photos: Tom Berg

Cummins officials say their next-generation X15 heavy-duty diesel series will offer new value through economy, performance, reliability and support when it replaces existing ISX15 models in January 2017. A year later, a new X12 will supersede the current ISX12.

Executives unveiled and demonstrated the new models at the Transportation Research Center in central Ohio Friday and Saturday. “Uptime” was a central theme in their presentations, and they said engineering and development teams devoted four years and almost 9 million test miles to be sure the engines will deliver on that promise.

Some individual trucks and engines racked up more than 500,000 miles, said Jim Fier, vice president of engineering. 2016-model diesels already meet federal greenhouse gas (GHG) and fuel-efficiency standards, and the 2017s will exceed those limits with further improvements in fuel economy.

The X15 engines will be up to 3% better in fuel economy than 2016 models, and as much as 20% better than 2012 models, officials said. Other benefits include extended service intervals and enhanced performance across a 400- to 605-hp ratings range.

Support will be available at more than 3,500 Cummins service locations in North America, said Amy Boerger, vice president of sales. Enhanced extended coverages for up to 6 years and 650,000 miles will be offered to original and second owners. Cummins recently realigned its support organization into eight operating regions for better administration efficiency.

Performance, Efficiency engines

The X15 will include two configurations, Performance and Efficiency, with hardware and software emphasizing the two requirements. Included are optimized compression ratios, air handling systems and cam profile to increase both fuel efficiency and performance capability.

The X15 Performance series, rated at 485 hp to 605 hp, provides power for heavy-haul, vocational and emergency vehicles. An upgraded high-flow air-handling system gives faster pedal response, for enhanced driveability at full payload and steep-gradient climbing. Peak torque of 1,650 to 2,050 lb-ft is delivered across a wide engine rpm range, so less shifting is needed and less fuel is used.

Engine brakes develop over 450 retarding horsepower at just 1,500 rpm and up to 600 hp at 2,100 rpm.

Except for white or black lettering and gloss or matte paint, X15 Efficiency (left) and Performance diesels look much alike. Displacement remains at 14.9 liters, like current ISX15 models. 
Except for white or black lettering and gloss or matte paint, X15 Efficiency (left) and Performance diesels look much alike. Displacement remains at 14.9 liters, like current ISX15 models.

For line-haul and regional applications, the X15 Efficiency series offers ratings of 400 to 500 hp and 1,450 to 1,850 lb-ft. Peak torque is available at 1,000 rpm. When integrated with the Cummins and Eaton SmartAdvantage powertrain, the company says, it achieves high fuel economy by precisely adjusting to grade, vehicle weight and driver input via throttle position.

Single-module aftreatment

A single-module aftertreatment system with in-line components replaces the multi-turn system now used. The oxygen catalyst, diesel particulate filter, and exhaust fluid injector and dosing chamber are close together so high temperatures needed for efficient operation are maintained, said Jim Nebergall, part of the engineering team that developed it.

A compact, lighter-weight single-module exhaust aftertreatment system replaces more complex devices. Systems are sized for medium- and heavy-duty engine models and horsepower ratings. 
A compact, lighter-weight single-module exhaust aftertreatment system replaces more complex devices. Systems are sized for medium- and heavy-duty engine models and horsepower ratings.

“The single aftertreatment module is simpler and exhaust flow is consistent no matter what the application,” he said. “So sensor readings are more reliable. We actually removed a temperature sensor because there’s less variation throughout the system.”

End caps can be side-entry and -exit or straight-through, or a combination of the two, to accommodate customer wishes and packaging demands. Side-entry/exit caps can be “clocked” or turned to line up with inlet and tail pipes to best suit an installation.

Twisting multi-piece exhaust aftertreatment system now used will be replaced by a single-module system.
Twisting multi-piece exhaust aftertreatment system now used will be replaced by a single-module system.

Efficiency and Performance engines can be up- and down-rated within their series by reprogramming their electronic controls. However, hardware differences – piston designs, for instance – preclude practical turning of an Efficiency engine into a Performance type or vice versa.     

Smart electronics

The X15 Efficiency series incorporates Adept, SmartCoast and Predictive Cruise Control (PCC) functions, to gain a further 3% fuel economy improvement over current ISX models. Low-rpm braking power is as much as 400 hp, and like any engine brake, retarding force rises with engine rpm’s.

X15 in-service reliability will be fully validated by over 9 million miles of real-world driving before the start of full production in January 2017. It’s the most extensive field-test program ever undertaken by Cummins, executives said.

Connected Diagnostics will be standard on all X15s, and will allow re-calibrations via telemetry and without having to visit a dealer. In practice, a calibration is transmitted to the truck and downloaded onto the engine’s control module; the driver is notified that it’s there, and accepts it by pushing a button, but only after he’s pulled off the road and parked, engineers explained. If the update is not successful, the controls revert to existing programming.

Higher engine efficiency

The X15 features an optimized cam profile to minimize inherent parasitic loss during combustion, in essence breathing easier, and thus increasing thermal efficiency. Applied to the X15, it results in the highest compression ratio in the industry, enabled by the Cummins VGT Turbo and XPI fuel system, to improve engine response and reduce fuel consumption.

Additional engine efficiencies have been gained by minimizing friction losses throughout the X15, including the water pump, gear train, lube system, piston and exhaust gas recirculation (EGR). The big-bore advantage of the 15-liter platform allows the highest level of performance without compromising durability, and has an important influence on maintaining the highest residual value of the truck, Cummins executives said.

Maintenance costs are expected to be reduced by almost half over an engine’s first 500,000 miles, compared to the 2010 engine, Fier said.

Oil-drain intervals for typical line-haul applications are extended up to 50,000 miles, depending on duty cycle, and will be able to extend to as much as 80,000 miles for trucks running at 6.5 mpg or higher with OilGuard – an oil analysis program to be introduced by Cummins. Fuel filter change intervals are also extended up to as much as 50,000 miles, and the crankcase breather filter is now maintenance-free.

A key X15 design goal was to increase uptime by reducing the number of components and simplifying systems wherever possible. A series of durability-focused upgrades were also made to components throughout the engine, including the camshaft lobes, piston cooling nozzles and air-handling system.

Cummins' variable-geometry turbocharger gets a stronger actuator and impeller, to boost transient response and substantially improve engine braking at lower rpms, engineers said. The exhaust-mounted fuel injector has been removed and thermal control is now activated inside the cylinders. A simple thermal recirculation device has been added to combat fuel waxing or gelling.

The X12 is a practically new engine, but will not enter the American and Canadian markets until 2018 because Cummins is concentrating on Mexico, Central America and other foreign areas where medium-bore diesels are more popular, a Cummins development technician said.  

X15 diesels showed quick throttle response and strong acceleration on the TRC's tracks. Engine brakes were impressively strong, even at low rpm's
X15 diesels showed quick throttle response and strong acceleration on the TRC's tracks. Engine brakes were impressively strong, even at low rpm's.

First Impressions

Driving some of the 2017 models on the TRC’s various tracks showed improved throttle response and snappier acceleration, particularly with the Performance engines, compared to current ISX15s. Retarding by the X15 engine brakes was especially strong, but less so on the single X12 engine available for driving. 

One demonstration with a bobtail tractor showed smooth reaction to X15 throttle inputs where one might expect some jerkiness with no trailer to “cushion” abrupt power and torque applications or reductions. More driving impressions will be posted soon on Truskinginfo.com.

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