|Benefits of the D7E. Click to enlarge.|
Caterpillar Inc. presented the keys of the first AC electric drive track-type tractor in the industry to a long-time customer, TJ Lambrecht. TJ Lambrecht, headquartered in Joliet, Illinois, is one of the most recognized heavy, civil, and earthmoving contractors in the country, with one of the largest and most current fleets of Caterpillar equipment.
The D7E is in the 60,000-pound (27,000-kilogram) weight range and is powered by a Cat C9 engine producing 235 hp (175 kW) that drives a generator to produce electricity to power two AC electric drive motors connected to a differential steering system. (Earlier post.) The D7E delivers 10-30% lower fuel consumption and up to 50% longer drive life than a comparable conventional dozer.
Our customers are being challenged to do their work more efficiently with less impact on the environment. The D7E demonstrates Caterpillar’s commitment to the industry with a machine that does more work and consumes less fuel and parts, providing customers with lower owning and operating costs.
—Doug Oberhelman, Caterpillar Group President (Vice Chairman effective 1 January 2010)
|D7E electric powertrain. Click to enlarge.|
The Cat C9.3-liter ACERT diesel engine meets US Tier 3, EU stage IIIa, and Japanese MLIT standards. At 235 hp, it produces slightly lower power than the Cat 3176 engine in the conventional D7R—however, increase drivetrain efficiency allows the D7E to deliver better performance from less horsepower, resulting in improved productivity and lower fuel consumption.
The 175 kW engine runs in a narrow rpm range between 1,500 and 1,800 rpm, instead of between 1,600 rpm and 2,200 rpm in the conventional D7R Series 2. Because it drives a generator instead of a powershift transmission, the D7E’s engine doesn’t need to rev as high or low.
The D7E uses a distributed electro-hydraulics system, with multiple valves placed closer to their associated work tools. A valve at the front controls the blade, while another at the rear controls the ripper or winch. This design reduces the hydraulic line length, giving the D7E 30% faster blade cycle times and the best performing hydraulics in its class, according to Caterpillar.
Current flows from the generator through special armored cables and military-grade connectors to a solid-state inverter, then to the propulsion module. Within the propulsion module are two heavy-duty electric motors (using AC current) that drive through common gearing into the differential steering system.
Power from the steering system is transferred via axles to mechanical, double-reduction final drives to provide smooth, infinitely variable driving force to the tracks. The engine in the D7E is entirely beltless, eliminating the need for belt maintenance and replacement.
The D7E also has a new three-section aluminum radiator using separate circuits for the engine (jacket-water), charge-air system and electrical-power system-including the inverter and generator module. A variable-speed fan controls airflow through the radiator. The design of the radiator cooling systems reduces parasitic load and saves fuel. In addition, the electrical drive motors are cooled simply and effectively by power train oil.
Advanced electronics provide DC (direct) current to power the accessory system. The modular heating and air conditions system, water pump and battery charger are electrically powered for maximum reliability in varied conditions.