The Caterpillar D7E is the first hybrid dozer. It was developed by Caterpillar to meet new environmental and sound regulations in the U.S. and Europe. Caterpillar showed it off at a demonstration event in California on June 11, 2009.
The D7E is considered a midsize dozer with a broad array of applications. The D7E will replace the diesel-only D7R in the U.S. and European markets. Caterpillars range of tracked dozers goes from a D3K model, weighing 17,185 pounds, all the way up to the D11T, at 230,100 pounds. The D7E comes in at 56,669 pounds.
The D7E is a series hybrid, using this 9-liter diesel engine to generate electricity, powering its electric drive motors. The engine runs at a near constant speed, an optimal power band for fuel efficiency. A standard tractor's engine has to change speed whenever greater power is required.
The big metal tracks on the D7E are turned by a pair or electric motors contained in a module. They aren't directly connected to the tracks, going through a differential that lets the tracks send power back into the system. This mechanical regeneration merely sends power from one track to the other during turns, taking load off the motors.
These are the hydraulic lines controlling the D7E's rear ripper. A similar hydraulic system controls the blade on the front. The hydraulics rely on power from the diesel engine, as there isn't an equivalently efficient electric system to replace hydraulic pistons.
The cab of the D7E represents all the comforts of modern earth-moving equipment. The seat sits on shock absorbers, and there is air conditioning. Big windows allow good visibility all around, and there is also a rearview monitor.
This is the main drive controller for the D7E, handling steering and movement. With a dozer, you set the speed, then push a rocker switch for forward or reverse. The electric motors driving the D7E mean there is no gearbox to worry about.
A 40 year old D7G was also on hand at the demonstration site, showing an example of an older tractor fitted with a new, more efficient and less-polluting diesel engine. Unfortunately, older tractors won't be refitted with hybrid systems.