Photograph of the Caterpillar Electro-Hydraulic Test Bench



Each test bench is composed of an electric motor-driven pump which creates a supply pressure, pilot valves which control spool position, and spool valves which control the actuators. A hydraulic cylinder and a hydraulic motor are available that could be controlled using a manual or electronic joystick. The hydraulic motor has loads created by the hydraulic pump which it drives and the bypass valve. The load created by the hydraulic pump can be amplified by closing the restrictor valve. The restrictor, bypass, and electro-hydraulic pilot valves are all current-driven solenoid valves. An accumulator is used to help keep the supply pressure constant.

A Caterpillar Electronic Control Module (ECM) provides the current drivers as well as sensor feedback from an electronic joystick, pressure sensors, temperature sensor, cylinder position sensor, and motor speed sensor. All of the sensors output a PWM signal with the exception of the speed sensor which outputs an analog voltage signal in a similar fashion to an encoder. Control programs are first written in Simulink and then automatically converted into low-level code by compiling to an xPC targetbox, which runs the controller and communicates with the ECM via a CAN connection.

Schematic of CAT Caterpillar Electro-Hydraulic Test Bench