Modeling and Experimental Analysis of the Single-Shaft Coaxial Motor-Pump Assembly in Electrohydrostatic Actuators

Motor pump assemblies are key components of the electro hydrostatic activators. This protocol presents an efficient testing method on the output characteristics of the motor pump assembling and the wide working conditions. This protocol adopts accumulation of simulation and impairment, so which the performance of the model pump assembly can be quickly obtained.

This technology contribute to the development of the model pump assembly. When carrying out the experiment, protect yourself to prevent the harm of noise and oil. It is important to make sure that the oil pipes are connected tightly before loading.

Demonstrating the procedure will be Yuxuan Ma, a postgraduate student from the laboratory. To begin, set the main parameters of the motor pump assembly by entering the parameter mode, and set the main parameters by double clicking the specific component in the simulation model. Set the rotating speed and test pressure, as described in the text.

Set the pre-run parameters of the model as the start time of zero second, final time of one second, and print interval of one millisecond. Pre-run the simulation and check whether the system will reach the steady state at the end of the simulation. If the system reaches the steady state, check the Use old final values option in the Run Parameters window.

If not, reset the final time to two seconds or even longer, until the system reaches the steady state. Then set the run parameters of the model as the start time of zero seconds, final time of 0.2 seconds, and print interval of 0.002 milliseconds. To install the mechanical interfaces, connect the end face of the motor pump assembly with the test valve block and use at least four screws to ensure a good ceiling performance.

Fix the motor pump assembly and the test valve block on the workbench of the test bench. Connect the motor pump assembly and the test valve block to the dedicated tooling with four screws, and the tooling to the workbench with two screws. Install two groups of pressure and temperature sensors of port A and port B on the test valve block.

Connect these sensors directly to the leakage port for leakage monitoring. To connect the hydraulic interfaces, initially connect the two high pressure oil ports of the pump source with port A or B of the test valve block. Then connect the pressurized oil port with the leakage oil port of the pump.

For air exhaustion of the motor pump assembly, make sure the relief valve of the oil supply system is in the unloading state. Run the oil supply motor for three minutes to exhaust the air of the testing system and warm it. To check for leaks in the motor pump assembly, shut off the relief valve of the oil supply system and look for leakage in the motor pump assembly.

Adjust the oil supply pressure to two MegaPascal for more than one minute. To connect the electrical interfaces, first connect the power supply interface and the rotary signal interface to the motor pump assembly driver. Connect the driver to the controller via RS-442, working in a full duplex model, and then to a 270-volt DC power.

To perform the no load inspection of the motor pump assembly, run the oil supply pump and keep the relief valves of the oil supply and loading systems in the unloading state. Power on the driver and controller, and check whether the motor pump assembly can receive the control command normally. Set an instruction of 2000 rpm forward and then reverse to the motor pump assembly.

Observe the working state of the motor pump assembly and check whether there is leakage at the valve block. To set the oil supply system, run the oil supply pump and switch the relief valves of the oil supply system and loading system to the loading state. To determine the minimum oil supply pressure value, begin by adjusting the oil supply pressure to one MegaPascal or more, which is decided by the tested motor pump assembly.

Then adjust the rotational speed of the tested motor pump assembly to 9000 rpm, making sure that the pump flow is equal to the theoretical pump flow. Otherwise, increase the oil supply pressure to avoid cavitation. Slowly reduce the oil supply pressure and record the change of the pump flow.

Plot the relative pump flow versus oil supply pressure and find the inflection point of the pump flow denoted as the minimum oil supply pressure. Adjust the load relief valve to the minimum oil supply pressure. Turn on the temperature control system and adjust the oil temperature to 30 degrees Celsius.

Also, turn on the thermal imager to detect the surface temperature of the motor pump assembly. Send the control instructions to the motor pump assembly, to make it run continuously at a specific speed. Adjust the load relief valve gradually.

Increase the load pressure to a specific value and hold for four seconds at each critical measured pressure. After the pressure reaches the specific value of the speed, adjust the load relief valve back to one MegaPascal. Export the experimental flow data and plot the pump flow characteristic map of the motor pump assembly.

Calculate the overall efficiency of the motor pump assembly in different working conditions and plot the overall efficiency map. The simulation result of the discharge flow indicated that the flow decreased slightly, with an increase in pressure at a constant speed, while it increased linearly with increasing speed at constant pressure. A slight difference was observed in experimental and simulation results for the discharge flow.

When the speed is higher than 5000 rpm, where the output flow decreases first and then increases with the rising pressure. The volumetric efficiency was determined, which shows that the pump efficiency was higher at low pressure and speed. At 3000 rpm, the maximum output pressure was five MegaPascal, while at 8000 rpm, it was 23 MegaPascal.

The experimental results differ from the simulation, when the motor pump assembly works at high speed and low pressure. However, at 10 MegaPascal pressure, the volumetric efficiency decreases, with the increase in rotational speed. It was observed that the simulation and experimental results are closer at higher speed and almost coincide with the experimental results in the speed range of 3500 to 9000 rpm.

Experimental results of the overall efficiency show that under extreme conditions, such as low speed and high pressure, or high speed and low pressure, the total efficiency is relatively low. It is important to make sure that the pressure measuring points are close to the oil ports. Besides, pay attention to the inlet pressure to ensure that no cavitation exists.

Following this procedure, we can also adopt the fault injection method, to study the performance and failure mode of motor pump assembly under extreme working conditions.