Driving Force

Medium-duty diesels are getting smaller, quieter, and more powerful for their displacement than ever before. Improvements in ring material and manufacturing techniques are allowing engines to live longer, and you’re seeing better “breathability” because of better injection strategies and turbocharging. Some of these advances are spin-off benefits from work in the heavy-duty world, but there’s a lot of R&D happening that’s specifically generated by the needs of medium-duty trucks.

The 1999 updates to meet new U.S. emissions standards coincided with some notable medium-duty diesel introductions. Other mid-range models have updates to fuel systems and electronics to meet the new emissions levels. Among the most extensively changed is the International six-cylinder engine line-up, which, despite the carry-over names and external appearance, are new engines.

An exciting development that will appear later this year is the Isuzu-designed Duramax diesel for GM full-size pickups and sport utilities. Due to launch in the 2001 model year, possible evolution of this line to address heavier applications will be followed with interest.

Ford pickups are also due for an engine update as International gets set to launch V-6 and V-8 versions of a new-technology diesel in 2002/2004.

Maker by maker, here’s a look at recent developments in the medium-duty marketplace:

CATERPILLAR

Cat’s 7.2-litre 3126B gets the big-bore ADEM-2000 electronic control module, adding customer-programmable features to the medium-duty power. Included are a real-time clock, a quick-stop recorder, fleet-information software capability for management purposes, and the ability to use the CatID driver information display.

Other features include an inter-lock to prevent the starter being keyed while the engine is running, and a fan-on with exhaust brake. Cat says an added benefit is the user’s ability to program shift points with Allison AT/MT automatic transmissions. The PTO capability is also enhanced with a multispeed feature allowing two additional PTO set speeds.

The 3126B has ratings from 175 to 330 horsepower, with torque from 420 to 860 pound feet. The 250-, 275-, and 300-horsepower ratings have been enhanced with the wastegated turbo from the 330 to enhance bottom-end response and fuel economy.

CUMMINS

After the introduction of the 24-valve OHC 5.9-litre ISB Series in 1997, followed shortly thereafter by the 8.3-litre ISC Series, it’s been status quo for Cummins Engine Co.’s midrange engine group. Both the ISB- and ISC-series in-service record has reportedly supported the maker’s claim of 15,000-mile oil-change intervals and generally lower maintenance costs. ISC chief engineer Jim Kahlenbeck reports that the only specific developments for his line have been recalibrations to demonstrate compliance with EPA consent-decree requirements (these revised ratings are reflected in the accompanying charts). Cummins emphasizes that the 9.0-litre ISL Series is not intended for the medium-duty world, being marketed for “heavy-seven vocational” and class-8 applications.

DETROIT DIESEL

New medium-duty diesels in the DDC line-up are just now appearing in the Bering truck chassis down in the States. The 3.75-litre six-cylinder diesels come from the VM Motori line-up, acquired by Detroit Diesel in the mid-1990s and currently available in a number of passenger cars and sport utilities in Europe.

GM

Isuzu has been named GM’s technology partner in the development of its new diesels, and the two have a 50-50 share in the Duramax 6600. This engine, set to debut later this year, is a 6.6-litre 90-degree V-8. It’s a four-valve engine with a common-rail injection system by Bosch. Electronic controls are featured, and it will be offered as a package with the new Allison-1000 automatic. The engine is claimed to be very quiet, due to rate-shaping of the injection and the additional stiffness of the deep-skirted block. Early reports suggest it is almost indistinguishable from a gasoline engine, in contrast to the 5.9-litre Cummins ISB in the Dodge Ram, or the International/ Powerstroke 7.3 in the Ford F-Series. GM has said nothing about power outputs, though to be competitive with Ford the engine will probably be around 235 horsepower and 500 pound feet of torque.

HINO

Hino Diesel upgraded power for 1999 along with cleaner emissions, and goes into 2000 with no changes. However, the company is unique in meeting both 1999 and 2002 standards with an all-mechanical injection control for its four- and six-cylinder engines, which gives customers fully emissions-compliant engines with a cost advantage. Also, because the engines are very light, they also have a weight advantage.

The engines are a removable, dry-sleeve design for easy rebuilds. The four-cylinder is a 5.3-litre overhead camshaft engine with four valves per cylinder. Designated J05C-TD, it produces 168 horsepower and 366 pound feet of torque. The six-cylinder engines both displace 8.0 litres, and are rated at 200 horsepower/456 pound feet for the J08C-TP, and 252 horsepower/550 pound feet for the J08C-TR.

Hino is on record that new engines due for 2003 will feature common rail systems and EGR to meet the emissions targets. Furthermore, these engines will be economical and more powerful, with passenger-car quietness.

FORD/INTERNATIONAL

The International T-444E V-8 diesel’s replacement-at least in Ford products-will be a revolutionary design. The fuel system is a joint venture between International and Sturman Engine Systems, and will feature Sturman’s digital valve technology in the injectors.

Little has been said publicly about the engines-there will be V-6 and V-8 versions for Ford’s sport utilities as well as the bigger work trucks. The smaller V-6 will be introduced first, and both engines are anticipated to be smaller than today’s 7.3-litre units.

International is also promising a breakthrough in exhaust aftertreatment, allowing for the optimization of engine performance. However, the catalysts in the exhaust will require fuel lower in sulfur than is currently available.

To get down to the necessary level makes the synthetic diesel fuel attractive, says International. Pointing to the Fischer Tropps fuel process, chief engineer Pat Charbonneau says the next wave of smaller, high-speed diesels will be car-quiet, with no exhaust smell and cleaner-than-natural-gas emissions.

MACK

Specs for the Renault-built E3 family of in-line-six diesels (two ratings available: 190- and 220-horsepower) are unchanged since our last report. These power the truckmaker’s popular Mid-Liner series of medium-duty conventionals and cabovers.

MERCEDES

MB power is standard for the Freightliner Business Class and the Sterling Acterra. Designated the MBE-900, the engine is available as a four-cylinder or a six-cylinder diesel. The 6.4-litre 906 is available now, rated at 190 to 300 horsepower and with a peak torque of 860 pound feet. The four-cylinder 904, expected to power Freightliner’s step-van chassis, has 150 to 190 horsepower and up to 520 pound feet of torque from its 4.3-litre displacement.

The engines are parent-bore designs with cast-iron cylinder blocks. Life to overhaul is predicted to be 500,000 miles, and the engines offer features such as molded rubber gaskets that are retained in machined channels for leak-proof joints. Unit-pump injection and electronic controls bring big-truck features such as fan control and electronic cruise control. An engine retarder incorporated into the three-valve heads is another highlight.

Engine weights are 860 pounds for the four-cylinder unit and 1168 pounds for the six-cylinder.

INTERNATIONAL

International has completely overhauled its six-cylinder DT-466 and -530. Both have new cylinder blocks, crank, and even revised bore and stroke, though they still come in at 466 and 530 cubic inches, respectively. The new engines retain the “E” suffix gained when they went to hydraulic-injection technology, but now they have added “HT” models, reflecting the high-torque output.

The DT-466E re-engineering gives it increased engine life with a short stroke for lower piston speeds. Redesigned block, bearings, and bearing supports lower weight to 1425 pounds, yet still offer increased engine strength for higher outputs.

International Diamond Logic controls and revised valve sizes across all engines are claimed to enable them to use fuel more efficiently, and provide drivers with more electronic features and advanced diagnostics.

The DT-466E has ratings from 175 to 230 horsepower, and peak torque from 460 to 620-pound feet. The high-torque DT-466E HT features the same design changes with a horsepower range from 195 to 250 horsepower and peak toques from 560 to 800 pounds-foot. The DT-466E HT engines’ lower governed speed results in up to 8% better fuel economy when compared to the DT-466E with a manual transmission.

The DT-530E now goes from 275 to 330 horsepower and 800 to 950 pound feet torque. Designed to compete with 10-litre engines, the 8.7-litre 530E offers significant weight savings.

Available features include a flywheel PTO and hydraulic pressure governor for fire truck applications. The 530E HT provides greater horsepower and torque for more specialized severe-service applications. It has heavy-duty ratings of 280, 300, and 330 horsepower, and a peak torque range of 950 to 1150 pound feet The available 575 pound feet clutch engagement torque gives it a big-engine feel.

“Around 2Q/2001 we expect to introduce a digital-control-valve injection system,” says Dan Webster, Canadian engine-sales manager at International. “This will be a brand-new capability in the whole world of mid-range engines, and a radical departure from the electro-magnetic solenoid assembly that we use today to create our split-shot HEUI system. The new design will use a digital ECM-controlled valve that can provide split-shot injection that will be infinitely more controllable than today’s systems.”

(reported with files from Steve Sturgess)