Powertrains 2007
THE NEW ENGINES
Much will change, but much will remain the same with engines that meet 2007 emissions standards. but cost is going only one way – up.
There's considerable consternation among fleet managers over 2007 diesels, especially the heavy duty models. Some '07 engines are currently running in builder's and customer's trucks. Builders say they're performing well, but fleets are still concerned about fuel economy, reliability and – probably most of all – cost.
Tom Berg
Senior Equipment Editor
Some fleet managers we talked to report that the new engines are reliable, but need more maintenance. Others say the '07 engines are trouble-prone and expensive to fuel and maintain.
The diesel particulate filters (DPFs) are heavy, bulky and might be difficult to "package" on certain trucks. Builders say the most difficult will be multi-axle dump trucks, whose lift axles consume frame space that could otherwise be used to hang the DPFs. However, the filters will also act as mufflers, so in most cases, they will be mounted where mufflers are now. A truck or tractor with lots of frame area or with a vertical stack should accommodate a DPF, provided the DPF's increased width and weight don't present problems. A DPF might weigh about 80 pounds and cost $1,500 or more to replace, although prices will come down as the devices go into volume production.
Then there's upfront price. Everyone anticipates higher prices for all classes of '07 trucks with the new diesels because of the expensive new anti-smog technology. But so far only two truck builders have announced estimated upcharges. General Motors says a diesel-powered medium-duty truck will cost $2,000 to $5,000 more than now. International says it will be $5,000 to $6,000 more for a medium-duty truck or school bus, and $7,000 to $10,000 more for a heavy duty truck or tractor.
All builders understand that such price hikes will be hard for customers to swallow, and they are lobbying furiously in Washington to get Congress to provide tax breaks for buyers. International says a Senate bill would provide a tax credit of 5 percent of the purchase price of a vehicle bought during 2007. That would offset part of an expected upcharge. But prospects for the legislation's passage are questionable, given the amount of federal money being spent on hurricane relief and the huge federal deficit in general. Stay tuned.
Driveability
Most builders we talked with said their 2007 heavy and medium-duty diesels will drive like current products. They'll have the same operating range, from torque peak to rated speed, and the same "sweet spots," where they are the most economical and powerful while cruising down the road. This means that if trucks with '07-spec diesels carry the same loads at the same speeds as now, their transmissions, axle ratios and wheel/tire sizes can stay the same.
One exception is Mack, which is introducing a new family of Mack Power engines starting in '06. First is an 11-liter MP7, which generally will run 100 to 150 rpm slower than current ASET engines. Thus axle ratios will have to be a bit "faster," or numerically lower, to get the same results.
David McKenna, marketing manager for powertrain products, said one example is a concrete mixer truck that now uses 4.64 axle ratio with an ASET Maxidyne engine. With the new MP7 Maxidyne – and assuming everything else on the truck stays the same, which isn't always the case – the truck would go to a 4.42 ratio. He said this type of change is so important that Mack has hired a powertrain sales manager whose duties will include training dealer sales people and customers on how to properly spec the drivetrain with the new engines.
Meanwhile, Allison Transmission is watching increased heat rejection expected with '07 engines. More EGR heat will be shrugged off into jacketwater coolers, raising coolant temperatures and perhaps hampering the work of water-to-transmission fluid coolers that keep torque converters from cooking. Regeneration heat from diesel particulate filters can also be a problem because heat radiating off a DPF could damage a nearby Allison. And engineers will have to be sure that transmission controls can still "talk" to revised programming in the electronic controls of engines.
Figuring Gearing
Any truck should be geared to let the engine spin at its sweet spot at the desired cruising speed. Builders usually figure that speed to be 65 mph, which is legal on interstate highways in most states. Gearing for faster or slower cruising speeds is also possible, but the faster the road speed, the more power is needed.
Trucks engaged in pick up and delivery, construction, trash-hauling or other urban tasks might do more accelerating and decelerating than cruising, so the engine's sweet spot might be different and so would the gearing. Medium- and light-duty diesels run faster than heavy duty engines, so their gearing is "slower," or numerically higher.
Some builders have on-line help for figuring. Cummins offers www.Powerspec.Cummins.com as a site that provides gearing advice based on use of a Cummins engine. If you're serious about buying a truck, a salesperson will use builders' software, which have equations built in to compute the proper powertrain design for any application. The plugged-in numbers, of course, are based on buyers' descriptions of how the truck will be used. If customers under- or overestimate the real cruising speeds of their trucks, the trucks might not be set up properly. Likewise, if buyers ignore the advice of the salesperson or builder, they might not get the performance or economy they want.
Other Considerations
Another consideration for gearing is startability, the ability of a truck to begin moving from a standstill on a specified grade, which is expressed as a percentage. The engine should pick up the load at idle, as the driver engages the clutch while the transmission is in the lowest forward gear. A dump or mixer truck might need startability of 20 percent (think of the slopes on building sites), a linehaul tractor might need 14 percent (ramps at loading docks can be steep) and a P&D truck might need 10 percent startability (ramps and driveway aprons might be less steep and the truck would often be less than fully loaded).
Another consideration is gradeability, which is the truck's ability to move up a hill in top gear with no need to downshift. For a linehaul tractor, Caterpillar recommends that this be 1.8 percent at peak torque and 1 percent at cruising speed in top gear. Most highway grades are 2 percent or higher, which is why most big-rig drivers have to downshift.
Hill Climbing
The gradeability of the Cat test tractor with the C15-550/1,800 thus was unusually high, as it marched up 3 percent to 4 percent grades with no downshifting needed. It would also accelerate in top gear on such upgrades with little apparent effort. Startability was also good, because I never needed the Fuller 9-speed transmission's Low gear. I used 1st gear when starting from a dead stop on level pavement and 2nd or even 3rd if we were rolling.
Sweet spots vary by engine make and model. In the case of the '07 Cat C15-550/1,800 that I drove, that spot is 1,325 rpm at 65 mph, according to Bob Keene, Caterpillar's manager for customer value. Multi-torque C15s should also be geared for 1,325 rpm at 65. C15s making less than 1,800 pounds-feet should run slightly faster – 1,400 rpm at 65 mph. And the C15 Heavy Haul, for rigs grossing 90,000 pounds or more, should spin at 1,500 to 1,650 rpm at 65. These are the recommendations for current C15s and they'll be true for '07.
The overall operating ranges of engines also vary by make and model. The C15 develops maximum torque at 1,200 rpm and will rev to 1,800. But that 550 version could lug to 1,100 and, Keene said, should be upshifted at 1,500 to get maximum fuel economy. This operating range is a bit slower than any other heavy duty diesel now being sold. But like I said, it's strong. Drivers who like the current version should also like the '07.
HDT editors will be test driving all the 2007 engines as they become available. Drive tests will appear in the April issue.
HDT would like to thank these people for supplying information for this article:
• Bob Keene, Caterpillar Engine
• Cyndi Nigh, Cummins Inc.
• Chuck Blake, Detroit Diesel Corp.
• Nick Richards, GM Powertrain
• Goeff Stigler, International Engine Group
• David McKenna, Mack Trucks
• Jim McNamara, Volvo Trucks
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