Hybrid Diesel-Electric Drivetrain for Small Agricultural Field Machines

Abstract

In this project, a series electric drivetrain sized for small agricultural machinery was developed and tested. Electric drives have noted benefits in simplicity, controllability, integration with other electronics such as those that provide autonomous action, and in efficiency over a wide operating range. Their biggest drawback for agricultural use is the limited capacity of electrical energy storage. A series hybrid drivetrain provides a method to overcome these capacity constraints through the use of chemical energy storage. The series hybrid drivetrain in this research was designed using well-established components. It consisted of a diesel-electric generator, a lead acid battery pack, a motor controller, and independent electric motors for each wheel with associated gearboxes to produce speeds and torques suitable for ground drive. Although these components are commercially available, they have not been integrated into a hybrid drivetrain before. The goal of this project was to test this drivetrain to determine its baseline performance and investigate the efficiencies of the various drivetrain components when operating under different conditions. The drivetrain efficiency was tested using a 2 × 2 × 2 factorial test in which the factors were average load level (30% or 40% of full load), load profile type (variable or constant), and size of the battery pack (170 or 340 A⋅h). The efficiencies of the three main components of the drivetrain were monitored in this testing: the diesel-electric generator, the battery system, and the ground drive. Of the tested factors, only load level had an effect on efficiency and then only on the overall efficiency and on the efficiency of the battery system. The other system components were not appreciably impacted by any of the factors. Large battery packs were not necessary to maintain efficiency even with variable loads, which indicates that future machines could consider more advanced (but more expensive) types of batteries, as less capacity would be required. Agricultural engineers interested in using electric motor drives because of their various benefits can use a series hybrid design to overcome their energy storage limitations and realize consistent efficiencies in a variety of operating conditions.