# Fault Diagnosis Method for Aircraft EHA Based on FCNN and MSPSO Hyperparameter Optimization
## 5 Typical Fault Simulation and Fault Data Acquisition of EHA
### Typical Failure Simulation of EHA  
In this paper, a laboratory-built EHA-FPVS physical simulation model (Figure 10) is used for fault simulation, and the Supplementary Materials shows the model parameters of EHA-FPVS. Firstly, we obtained the data of EHA in normal operation mode and then injected the typical fault of EHA into the model to get the fault data. Six parameters characterizing the system performance were selected, including actuator cylinder displacement response, actuator cylinder velocity response, hydraulic pump pressure difference between two ports, hydraulic pump flow, motor speed, and accumulator outlet pressure, and the model diagnosed the EHA fault mode by learning the characteristics of these parameters.  
In the simulation, a displacement command of 2 s duration was given continuously to the actuator cylinder within 16 s, and the maximum action range of the actuator cylinder was \(\pm\)0.25 m. Figure 11a-c show the actuator cylinder displacement response, actuator cylinder velocity response, and motor speed under normal circumstances, respectively.  
Select six typical faults of EHA, including internal leakage of the hydraulic pump, oil mingled with air, internal leakage of the actuator cylinder, increased friction between the actuator cylinder piston and the cylinder body, decreased sensor gain, and increased motor winding resistance. Set the corresponding parameters to inject these faults into the EHA:  
1. Internal leakage of the hydraulic pump: The clearance between the plunger and the cylinder was set to 0.1 mm, 0.2 mm, 0.3 mm, and 0.4 mm to simulate different degrees of internal leakage of the hydraulic pump.
2. Oil mingled with air: The hydraulic oil air content is set to 2%, 3%, 4% and 5% to simulate different levels of air content.
3. Internal leakage of the actuator cylinder: The clearance between the piston and the barrel was set to 0.1 mm, 0.2 mm, 0.3 mm, and 0.4 mm to simulate different degrees of failure.  
Figure 9: (**a**) Schematic diagram of EHA-FPVS; (**b**) Picture of EHA-FPVS.  
* Increased friction between the actuator cylinder piston and the cylinder body: The Coulomb friction between the piston and the barrel was set to 1.1 times, 1.2 times, 1.3 times, and 1.4 times of the normal condition to simulate different degrees of friction increase.
* Decreased sensor gain: The displacement feedback loop gain was set to 0.9, 0.8, 0.7, and 0.6 to simulate different levels of gain reduction.
* Increased motor winding resistance: Set the winding resistance to 3.6 \(\Omega\), 4.6 \(\Omega\), 5.6 \(\Omega\), 6.6 \(\Omega\) to simulate different levels of failure.  
Figure 12 shows the speed response curves of the actuator cylinder under different faults.  
Figure 10: Physical simulation model of EHA-FPVS: **(a)** Model of hydraulic circuit; **(b)** Model of control unit.  
Figure 11: System response under normal circumstances: (**a**) actuator cylinder displacement response; (**b**) actuator cylinder velocity response; (**c**) rotation speed.  
Figure 12: Velocity response of actuator cylinder under different faults: (**a**) Internal leakage of hydraulic pumps; (**b**) Oil mingled with air; (**c**) Internal leakage of actuator; (**d**) Friction increases; (**e**) Loss of sensor gain; (**f**) Resistance increases.