A typical layout for the hydraulic system of a self-propelled field spray consists of five pumps mounted front to back off the main hydrostatic pump, which connect directly to a diesel engine.
Next in line is a Linde MPR50 medium-pressure pump, which delivers hydraulic power to drive the spray pump. A special feature of this pump is that it can be adjusted right down to 0 cc at 0 bar—far from common with variable-volume pumps in open circuits. This results in zero energy loss when the pump is not running. There is also no pressure difference between pump pressure and load pressure (load-sense pressure difference is around 25 bar), which conserves energy.
At the end of the pump line are two gear pumps—fixed-displacement, of course. One provides the feed pressure maintain fluid volume in the closed circuit for the ground drive. It also distributes flow to an oil cooler and for pilot pressure to control the MPR 50 pump. The rearmost pump supplies hydraulic power to a fan drive.
All fluid return is combined in a small for subsequent filtering, cooling, and routing to a central reservoir. The manifold can be mounted in an easily accessible location for convenient access to hydraulic lines. The effective oil volume of the system is about 120 l.
Each of the four Linde wheel motors feature simultaneous swiveling of the pump and the drive motor to provide high torque when beginning motion or scaling an incline—causing the system to always operate at maximum efficiency. The system includes an anti-slip system to make a differential unnecessary. A rotational speed sensor fitted to each wheel motor detects when one wheel loses traction. Electronics will then cut power to that wheel, back to zero if necessary. This allows the other motors to transmit more torque. The electronics also ensures close speed control by automatically increasing or decreasing pump displacement as needed.
Material for this article was supplied by Motrac Hydraulics BV, Baak, Netherlands. For more information, visit the company's website.