What is in this article?:
High power density and design flexibility of hydraulics make a mine transport vehicle roomier and safer.
Safe at any speed
Moving the engine to the rear of the vehicle gives the driver an unobstructed view to the side previously blocked by the engine placement. A screen mounted in the driver’s compartment displays the view from a high-resolution rear facing camera when backing up the 15,000 lb (fully loaded) vehicle.
Just like speeding on a highway is illegal and may result in a speeding ticket, speeding in a man trip is totally unacceptable in a mine. Uncontrolled speeds caused by careless operation or equipment failure — coupled with a sudden stop — could result in serious injuries or even death for miners. Therefore, the Hydra-drive has a speed limiting function whenever it encounters a downward slope greater than 6°. This is accomplished by routing output from an inclinometer to the machine's electronic controller to limit displacement of the hydrostatic transmission's pump.
The hydraulic system was designed and implemented by P. J. Baumeister, senior design engineer, and Alan Grotefendt, IFPS certified fluid power specialist, both of Engineered Sales Inc., Maryland Heights, Mo., a subsidiary of Applied Industrial Technologies. ESI took full system design responsibility. They selected a Divelbiss HEC-4000- E-R controller to monitor and control the HST and steering because of its flexibility for the application.
The HST provides independent rear-wheel drive through a pair of Eaton 72450 (2.48 in.3/rev) variable speed axial-piston motors. The drive is powered by an Eaton 46 series (4.6 in.3/rev) pump that is capable of 50 gpm flow at 2500 rpm. The variable displacement pump and variablespeed motors give the drive a wide range of operating speed and torque. Pump flow feeds an integrated hydraulic circuit manifold containing valves for providing limited-slip operation to the motors and positivetraction control (when needed) via a 50-50 flow divider. A separate circuit in the manifold scavenges charge pump flow and pressure for pilot control of the motors.
The electrohydraulic controller reads hydraulic pressure from a pressure transducer in the pump and engine speed. As the operator depresses the accelerator pedal, engine speed increases, which the controller detects and then sends a signal to electrohydraulic valves to ramp down displacement of the motors. The result is smooth and accurate acceleration, deceleration, and vehicle speed control. Smooth starting and stopping occurs even with the car on an incline and fully loaded.
As the vehicle travels, the controller continuously monitors pump pressure to ensure that pump torque remains within the optimum range of the engine. If the driver continues depressing the accelerator pedal, the controller increases pump displacement until a maximum speed is reached. Even though the vehicle can reach 20 mph, top speed is typically factory programmed for something less for safety reasons. If the vehicle encounters a downhill grade, hydrostatic pressure will drop, and the controller will decrease displacement of the pump. The pump then acts as a dynamic brake to keep the vehicle under a predetermined speed limit.
The program was written by Divelbiss staff to meet requirements established by the ESI team, which later made modifications in the field due to the ease of programming afforded by the Divelbiss EZ Ladder software.
Controller handles harsh conditions
Electronic control of Wallace Mining’s Hydra-Drive man trip is provided by a pair of HEC- 4210-E-R controllers from Divelbiss. The HEC-4000 series controllers feature an environmentally sealed, water-tight NEMA-4X enclosure, high speed counting, and CAN network communication with J1939. Based on the company’s PLC on a Chip technology, the controllers are easy to apply and program using the company’s EZ Ladder PC-based software. The controllers can be mounted directly onto machines and are especially well suited to mobile equipment.
Additional features include four digital inputs (two for highspeed counting), four analog inputs (0 to 20 mA or 0 to 5 V), six digital outputs (four configurable as PWM), selectable 8- or 16-bit PWM resolution, J-1939 and OptiCAN connectivity, visual status indicator, and output monitoring for overloaded or open circuits.
Intended applications include off-highway equipment, engine driven pumps, compressors and generators, proportional valves, and monitoring and control in remote locations.