With Tier 3 in the field and Tier 4 in the wings, John Deere Power Systems is using several strategies to meet its customer’s needs for power and the EPA’s requirements for lower emissions. One of these strategies is to offer engines with three emissions solutions packages. These include:
- PowerTech M. The simplest of the JDPS engines, these have two-valve heads, standard turbochargers and mechanical fuel systems. Starting at 40 horsepower, PowerTech M engines are designed for the lower horsepower applications.
- PowerTech E. These engines retain the two-valve heads and standard turbos but introduce full- authority electronic controls and more sophisticated fuel delivery. The smaller engines (2.4 and 3 liter) use electronic unit pumps. The larger engines (4.5 and 6.8 liter) use high-pressure common-rail injection. There’s also an intercooler, which is used to reduce oxides of nitrogen (NOx) across Tier 3 platforms.
- PowerTech Plus. This top-of-the-line technology keeps the intercooler and the high-pressure common-rail fuel system of the other models and adds a four-valve head, variable geometry turbo and cooled exhaust gas recirculation. They are available in four displacements: 4.5, 6.8, 9 and 13.5 liters.
PowerTech Plus is also the top performer in what Deere refers to as its “power bulge.” Doug Laudick, product manager with John Deere Power Systems, defines the power bulge as an increase in power as you go down in speed. “With the larger displacement engines – primarily the 9- and 13.5-liter sizes – you’ll see anywhere from 7 percent to 14 percent power growth at 200 rpm below the rated speed, depending on the model,” he says.
And the advantage? “As you encounter a tough spot in your application, whether it’s hitting the pile with a loader or a big slug of material coming through a grinder, the power bulge gets you through it and back to rated speed quicker,” Laudick says.
So OEMs who use Deere engines can opt for a smaller, lower-cost unit. “If I have a customer who’s using an 8.1-liter engine with 250 horsepower, I can replace it with a 6.8 liter with the power bulge and get him back to where he was,” Laudick says. “The big driver here is the additional cost that accompanies greater engine displacement.”
Other cost benefits of the new engines are lower fuel consumption and service intervals equivalent to or better than Tier 2 engine models. The company cites fuel consumption as much as 13.4 percent lower than some competitive engines at full-load, rated speed and even greater fuel economy under partial load conditions. Service intervals can run up to 500 hours when end users employ premium oil, the proper John Deere oil filter and use fuel with sulfur levels of less than 1,000 parts-per-million.
Options for Tier 4
While Deere has settled on an array of design options for Tier 3 engines, it’s still assessing the pros and cons of different systems to meet Tier 4 standards. Part of the problem is that there are two Tier 4s.
The Interim Tier 4 arrives in 2011 for engines with more than 175 horsepower and the following year for engines between 75 horsepower and 175 horsepower. Final Tier 4 comes into play beginning 2014 in the same horsepower sequence as Interim Tier 4.
For the 75-horsepower-and-below market segment, Interim Tier 4 begins in 2008 and Final Tier 4 in 2012. In the 50- to 75-horsepower range, JDPS will provide Interim Tier 4 engines starting in 2008, with a final Tier 4 product in 2013.
Meeting Tier 4’s stringent standards will require exhaust after-treatment, but which one? “We have several choices, including diesel particulate filters and diesel oxidative catalysts,” says Gita Rao, manager of strategic product planning at JDPS. “We have selective catalytic reduction with some way of controlling particulate matter. And there are NOx traps.” (A lean NOx trap, or LNT, gathers oxides of nitrogen from the exhaust stream.) “Right now we’re evaluating all the technologies – we haven’t eliminated any of them,” she says.
After-treatment is no panacea, however. “Everyone is driving to get more NOx and particulate matter cleaned up in the engines,” Rao says. “You want to minimize the after-treatment as much as possible.” Minimizing reliance on after-treatment reduces initial costs by reducing the necessary capacity of the devices. It also reduces ongoing costs by extending service intervals for after-treatment components.
Reducing NOx and PM requires a more complete burn of the fuel in the cylinders at lower temperatures and a more homogenous charge. But there’s a dilemma. Lean conditions create NOx. Rich conditions create PM.
Kevin Resch, manager of product planning for Tier 4 at JDPS, says one technique being investigated is the use of pre-injection. “This puts fuel in the cylinder and allows mixing to take place, but it’s lean enough that it does not combust. Then comes the primary injection event that creates the right stoichiometric balance so you get ignition.” (A stoichiometric balance is the proper proportion of fuel/air mixture for efficient combustion.) Another method being explored is the injection of air with very high oxygen content.
After-treatment will put new demands on engine electronic controls. The heart of these electronic systems, the controller area network bus (CAN bus), is already a busy place. Sensors feed data on everything from coolant temperature to throttle position to weather conditions into the so-called “black box,” which responds by sending out signals that fine-tune engine performance thousands of times each second. Can these on-board information highways bear the burden of more data? “There’s going to be more CAN bus traffic,” Rao says. “But what we have today in terms of CAN bus architecture we think will be sufficient for where we’re going in the future.”
Servicing Tier 3 engines requires specialized knowledge, and Tier 4 designs will require even more of service technicians. Deere’s training packages address these matters. “The engine is a subset of our training system,” says Grant Suhre, manager of field service for JDPS. “Exhaust gas recirculation valves and variable geometry turbos and all the other
Deere has online and classroom training options and they’re available to OEMs and end users. Classroom training can be from one to several days and online training from one to several hours.
“The key to servicing equipment is that our Service Advisor is the same tool we’ve used since we started with electronically controlled engines,” Suhre says. “The diagnostic software goes right on a laptop. The current version has engine manuals on board. It comes with a monthly DVD that has the manuals all the way back to the mechanical models. You have the whole library of service tools on your laptop when you go to a machine.”