December 2007, TruckingInfo.com - Feature
And North America gets the engine first. Here, it will be badged Detroit Diesel. The launch model, at 14.8 liters, is designated the DD15, with ratings between 455 and 560 horsepower.
The result of a five-year, 1.5 billion-dollar investment, the six-cylinder, in-line engine, weighs within a hundred pounds of the Series 60 it will ultimately replace at around 2,950 pounds. It is also 5 percent more economical, featuring a common rail fuel system and turbo-compounded output that contributes up to 50 horsepower to the engine flywheel from waste heat in the exhaust stream. The hollow double overhead camshafts are fabricated and driven by a cam and accessory drive mounted at the rear of the engine.
The DD15 covers power from 455 to 560 horsepower at 1,800 rpm. Torque ratings are 1,550 to 1,850 pounds-feet at a nominal 1,100 rpm, with several multi-torque models offering 450 horsepower, 1,550/1,750 pounds-feet and 475 horsepower, 1,650/1,850 pounds-feet ratings. Additionally there are now fewer than seven cruise power ratings that give the flexibility in high gear of dual power ratings at cruise.
The 14.8-liter displacement is only one of four that will ultimately fill out the Daimler Heavy Duty Engine Platform (HDEP) worldwide engine range.
Next up with be a stroked 15.6-liter for North America to be called the DD16. Later will be a DDC-manufactured 12.8-liter with the same bore centers but smaller cylinders and weighing 300-400 pound less than the DD15. It will replace the 4000-series engine and be designated the DD13.
Eventually a 10.6 liter will be added to the broad line-up. It is targeted toward Europe and may be less likely to appear in North America.
DD15 IS FIRST
Like all the engines, the first-to-appear DD15 is a clean sheet design, made to incorporate the technologies necessary to meet worldwide emissions requirements — here in 2010 and in Europe and Japan in 2012. The modular design is compact, even with the addition of the turbo-compound machinery.
According to officials at the Detroit launch in mid-October, the engine has more than 100,000 hours of testing and its durability and economy are assured. Furthermore, testing at the hands of regular road drivers confirms that the engines are very driver friendly, with excellent throttle response, flexibility and power.
The power and torque curves do not tell the full story, said David Siler, marketing director for the new engines. While the torque curves are impressive with peak torque flat over a wide 600 rpm band from 1,000 to 1,600 rpm, the power curve is flat from 1,600 to 2,000 rpm. But creating a new metric to describe the throttle response, Siler said, was important to describe the new type of performance.
Calling this the Get-Up-And-Go Challenge, engineers created the torque response parameter, measuring it to be 75 percent better than that of the Series 60. Torque response — the time the engine takes from mashing the throttle to reaching its torque output peak — is four seconds on the S60, where it is only 1.5 seconds for the new engine. This translates into a snappier and more powerful response from the engine, giving it a bigger feeling than the numbers alone would suggest.
Drivers also commented in the launch video that the engine is very quiet. That, said Mark Growneweg, senior manager of HDEP Development for NAFTA, is a consequence of the multi-event injection via the amplified common rail system, but it is also a result of less radiated combustion noise due to the rigid design on the cast iron block and the compacted graphite iron (CGI) one-piece head with its 38 clamping bolts.
The good throttle response is in part due to the use of a multiple combination of the low-inertia turbocharger with divided throat and no variable geometry or waste-gate complexity; the fuel common-rail injection system; and low inertia components like the hollow camshafts and lighter accessory drive.
The common-rail is fed by a two-stage pump that is fully lubricated by the fuel. In its first compression, pressure rises to 900 bar before the secondary filtration. It then is raised to rail pressure of 2,100 bar. Each electronically controlled fuel injection event has multiple pulses for precise control of fuel rate and shape, giving fine control of combustion and NOx generation, while lowering the diesel knock in the cylinders.
The engine features cooled exhaust gas recirculation for NOx reduction as well, and achieves the back pressure needed to force exhaust into the inlet stream — not with a VGT, but by utilizing the additional backpressure from the exhaust driven power turbo. PM emissions performance is assured using the same diesel particulate filter as is used on post-2007 Series 60s.
The key to the EGR flow is the turbo compounding, which provides back pressure to the exhaust exiting from the main turbo. As this gas flows through the axial downstream power turbo — from Holset, like the main turbo — it spins up to as much as 60,000 rpm, extracting energy from the hot exhaust, cooling it some as the exhaust expands through the turbine.
Gears and a fluid coupling reduce the rotational speed of the output shaft to couple through a gear train to the flywheel. The contribution of this additional element boosts both power — by 50 horsepower at its maximum — and fuel economy. But while the exhaust has given up additional energy that would otherwise be wasted out of the top of the exhaust stack, there is still sufficient heat to allow for passive regeneration of the DPF.
Detroit Diesel's Redford plant will machine the 14.8 blocks and liners for the North American engines. With its same cylinder bore spacing, the same tooling will be able to produce 12.8-liter engines on the same line at the same time. Machined heads come from the German plant in Mannheim, which also supplies the Japanese plant in Kawasaki. All connecting rods will be made at the Detroit plant, and such is the target capacity — 200,000 engines — Redford will be making 1.2 million rods a year.
The rods feature an angled bearing split, and are fractured across this split during manufacture. This provides matching granular surfaces that, when bolted up, are much stronger than mating ground surfaces.
At present, Redford production is just starting up and will ramp up from 20 engines a day to 160 as it goes into full production in the fourth quarter of this year. Because of lead times, this means that Daimler Trucks North America brands Freightliner, Sterling and Western Star will appear at dealerships with the engines in the second quarter of 2008.
First to get the DD15 will be Columbia, Century Class and, of course, the new Cascadia. It will also be early into Sterling A- and L-Line models. The third quarter 2008 will see it going in to Western Star 4900 and Freightliner Coronado.
The 12.8-liter DD13 and the 15.6-liter DD16 are timetabled for 2009 in North America.
The engines are designed to be inexpensive and easy to service. Oil drain and filter change are at 50,000 miles with fuel filters changes at the same interval. Oddly enough, adjustment to the overhead lash is called for at 60,000 miles. Aiding technicians and workshop cleanup, all filter housings are top-loading and are serviced above the frame.
Many of the subsystems on the engines are already in use on the Series 60. One such component is the DDEC6 electronic controls As such, much of the diagnostics is common and there is no need for new tools, said Tom Diefenbaker, director of Technical Support Development. There are a few new wrinkles, but technicians should feel comfortable from the start, he said.
ON THE TRACK
There were trucks with early versions of the 455-horsepower and 560-horsepower DD15 engines available for somewhat limited evaluation at the nearby Chrysler Proving Ground. Century Class and Cascadia models were on an oval test track to evaluate throttle-response, acceleration, cruising and noise. On a demanding hill section, the engines' ability to pull down and grunt at 1,000 rpm were amply demonstrated.
I found the engine in a Columbia was indeed very quiet, especially at idle. The noise changes a little as fuel is put to the engine, but it certainly bore out the contention that rigid structure of the block and head and the rate-shaped fuel injection make the DD15 a very refined engine.
It was tough to evaluate throttle response, mainly because there was no appreciable spooling up of the turbo: Put the pedal to the metal and the engine picked up the load immediately. Over the hill section, again the lack of any fuss was itself deceptive. Because there's no torque rise as the engine lugs back it has a different feel, but there is no question, this is one engine to hang on to the high gears in hilly terrain, saving the driver much gearshifting in a working day.
Jim Park, contributing editor, had the opportunity to put a lot more miles on a truck with this DD15 (story will appear in January HDT ). And we will do the same when the DD16 when it comes along.
So should other drivers. There's no question it will be popular. As one driver was quoted in the verbatim reports, after evaluating the unit: "I didn't want to give the truck back."