Key components in Rexrothâs electrohydraulic hitch control are the EHR5 control panel, top, EHR-B controller, middle, and EHR5 control valve, above. The EHR5 control valve can be used in conjunction with directional control valves for a tractorâs working hydraulics at flow to 60 lpm and pressure to 220 bar.Placement was another challenge. Following extensive deliberation, the customer and we agreed to engineer an armrest ready to accept the control panel. This steadies the farmer’s hand when he presses the various buttons. We replaced the large actuator lever with a generously dimensioned switch with three positions: lift, lower, and off.
Another important consideration was service — primarily maintenance and troubleshooting. Most repair shops in India cannot run electronic fault diagnosis, so that function was incorporated into the control panel. So the control panel not only monitors operation, but also displays faults. Now the farmer can himself determine whether an electronic component is malfunctioning. To protect the entire control panel – especially the display – we fitted the unit with a tough film to keep out moisture, dust, and to resist mechanical damage.
Sealing electronics is always a challenge, and the IP-67 protection class used for the angular sensor would not withstand the extremely dusty conditions of these applications. As a result, we entirely re-engineered the sensor. Electronic components are now completely separate from the mechanical space.
We also developed the controller from the ground up. It is installed in the housing Bosch had designed for the Nano city car, manufactured by Tata Motors Ltd., Mumbai. That housing is already laid out to handle the Indian climate. The control’s software had to be adapted to the Indian market, too – shifting from the European lower linkage control to upper linkage control. This requires only one power regulation sensor instead of two and helps reduce costs.
Tackling Costs
To achieve a lower price for the Indian market, we turned to local suppliers who manufacture in India. We established local production capacities for the Bosch Rexroth’s EHR5 valve. This valve regulates hydraulic flow to the hitch cylinders, which raise and lower the hitch assembly. We also eliminated some automated manufacturing procedures. For example, the rear cover for the angular sensor cover would normally be an ultrasonically welded assembly. Instead, we to use an appropriate adhesive, thereby reducing the overall cost of the assembly.
Design options offered additional opportunities to reduce costs — material selection for example. Plastics prevalent in the Indian market are different from those typically found in Europe. In India, the strength of materials are matched to application requirements, and they are less expensive. Glass fiber reinforcement is seldom used.