Engine Notebook: MaxxForce

International kicks off the year with a line of new engines for on-highway and vocational truck applications, the MaxxForce series. Like other engine manufacturers, International is being pressed by customer expectations – many of them related to fuel economy – and by Tier 3 emission standards starting this month. So MaxxForce is not an incremental change to a few engines. It’s a sweeping change to create an entire family of engines, including:

MaxxForce 5 is built on the company’s V-6 platform and delivers 200 horsepower and 440 foot-pounds of torque. It will be used in Class 4 and 5 International CityStar commercial trucks.

MaxxForce 9 is an inline six and will make its way into Class 7 and 8 DuraStar and WorkStar trucks. It can be configured for 300 to 330 horsepower and 800 to 950 foot-pounds of torque.

MaxxForce 10, another inline six is targeted specifically at Class 8 WorkStar and TranStar trucks with 310 to 350 horsepower and 1,050 to 1,150 foot-pounds of torque.

MaxxForce 11 and MaxxForce 13 are International’s new big-bore engines for the Class 8 market. The 11 will go into TranStar trucks while ProStar trucks will get the 13. The MaxxForce 11 and 13 engines will be available in the fall of ’07.

MaxxForce DT traces its heritage to International’s DT466 and can be spec’ed with 210 to 300 horsepower and 520 to 860 foot-pounds of torque. The DT will be found in Class 6 to 8 DuraStar and WorkStar trucks.

MaxxForce 7 is an all-new V-8 engine. Although a 300-plus-horsepower version will arrive in the fall of 2007, the 7 comes out of the gate with 200 to 230 horsepower and 560 to 620 foot-pounds of torque. That makes the 7 suitable for a broad range of applications. It will power Class 5 to 7 DuraStar series medium duty trucks, IC brand buses, International brand commercial buses, and the International MXT and RXT trucks.

Construction ready
The MaxxForce DT and 7 engines are those most likely to be on construction contractors’ short list when shopping for a new truck. While the DT has some upgrades over the DT 466 it replaces, the MaxxForce 7 is rich with innovation.

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The MaxxForce 7 uses parallel cooling circuits, as do the MaxxForce DT, MaxxForce 9 and MaxxForce 10. In the standard series cooling arrangement, coolant goes in at one point, cools engine components in sequence, and comes out of another point to return to the radiator. Because it collects heat from each component along the way, the coolant gets hotter as it travels through the engine.

International’s parallel design routes coolant coming into the engine past critical components simultaneously. The system provides tighter temperature control to those vital parts, which helps with emissions and should also prolong service life.

Excess heat is removed from the top of the piston with Directed Piston Cooling Jet Tubes and gallery-cooled pistons. This feature has trickled down from big-bore engine design to the MaxxForce 7. Cooling oil is circulated through a passage surrounding the combustion bowl to help cool the piston. This maximizes durability, reliability and cylinder life in the face of higher injection pressures.

Piezo trumps solenoids
The MaxxForce 7 also uses piezo injectors, a feature unique to the 7 within the MaxxForce family. Piezoelectricity has been the darling of engineers for years and can be found in products from the mundane (cigarette lighters) to the magnificent (acousto-optic modulators, which provide the Doppler shift necessary to fine-tune lasers). The underlying science for these applications is the same. Certain mineral crystals, when exposed to mechanical stress, generate electricity.

It’s the opposing characteristic that makes piezo systems so perfect for injectors. These same mineral crystals, when exposed to electrical stimulation, deform. These microscopic deformations are virtually instantaneous and can be precisely controlled.

One of the enabling technologies for emissions compliance is extremely tight control of the injection process. Piezo technology provides that control. In the early days of diesel injection, there was one sloppy squirt of fuel per combustion cycle. Quantity wasn’t crucial. Neither was timing. As long as enough fuel arrived within a few degrees of the ideal crank position, everything was fine. Old-style solenoid-driven injectors were up to the task, although efforts to improve control of solenoid-type injectors have been common over the past decade.

Now there may be as many as five injection pulses taking place in a few thousandths of a second. Some are tiny. Some are relatively large. All have to arrive at exactly the right moment, and the right moment varies with engine speed. Solenoid injectors are moving too much mass to keep pace with all this frantic opening and closing. Piezo to the rescue. Piezo architecture actuates the injector valve needle three times faster than solenoid design.

Smoother equals more efficient
Better injection reduces emissions, but it also reduces noise, vibration and harshness and is a key player in maintaining fuel economy. International says – depending on how the entire drivetrain is configured, – owners of MaxxForce engines may see significant fuel economy gains. “Our lab data verifies a double-digit fuel economy gain during pickup and delivery cycles,” says Helmut Endres, vice president engineering and product development, International Engine Group. “Even with increased displacement and the impact of exhaust aftertreatment devices, engine dynamometer and vehicle testing indicates the fuel economy of MaxxForce 7 powered products will not degrade, relative to the current V-8 product, under any operating condition.”

Service intervals are at 10,000 miles. CJ-4 oil is required. A new cartridge-type oil filter is top-mounted for easy access. The closed design keeps oil in the cartridge when the filter is changed. No more oil on the engine, the floor, or the mechanic’s forearms.

Hydraulic lifters on the MaxxForce 7 should never require adjustment. They’re also quieter than solid lifters, especially when the engine is first started and before it comes up to normal operating temperature.

Other features found on the MaxxForce engines, such as exhaust gas recirculation (EGR), variable geometry turbochargers (VGTs) and sophisticated electronic control modules (ECMs) used to be cutting edge technology. With the need to meet stringent new emissions standards, they’re now standard equipment and hardly worth a second mention.

The MaxxForce engines have the tricks you’d expect (EGR, VGT, ECM), and a few you never saw coming. The result is an engine family that meets the requirements of customers and the government, which is not an easy thing to do.