# A Fault-Signal-Based Generalizing Remaining Useful Life Prognostics Method for Wheel Hub Bearings
## 4 Validation  
### Experimental Devices and Sensors  
The experiment is implemented in the LGM-15/45 wheel hub bearing fatigue testing rigs using mud, as shown in Figure 2. The main body of the testing rig adopts a cantilever structure. The test bearing is placed at the cantilever end of the main shaft, and the connection between the test main shaft and the drive shaft adopts the method of stop positioning and flange connection. This structure has strong simulation ability. This structure is also convenient in assembly and disassembly.  
The transmission system in the rigs controls the AC motor by the frequency converter. The belt drive is used to drive the bearing rotation, which facilitates the step-less speed regulation of the transmission system. The loading system uses the electro-hydraulic proportional system. The electro-hydraulic proportional loading system is a closed loop control system. The system has good dynamic performance, has fast response, and is stable within \(\pm\)0.01 kN.  
The speed control system adopts the microcomputer control VFD-A05543B intelligent frequency converter, which can switch the inverter Insulate-Gate Bipolar Transistor (IGBT) at high speed. It has multiple automatic protection functions, which can self-test current, voltage, and frequency. The rigs communicate with the microcomputer through the RS-485 serial port by the microcomputer output signal.  
The loading control system selects the BLR-42 load sensor with tension and compression style. The signal of 0-5 V is given by the microcomputer, and the given signal enters the proportional controller to continuously output the specified oil pressure under the action of the proportional amplifier and applies load to the test bearing by pushing the cylinder. This signal is converted into a voltage signal by the load sensor and the transmitter. The voltage signal is sent to the microcomputer to form a closed loop control. The system has a large control range and high precision, and can control the required load of the test bearing at a long distance and is continuously proportional.  
The temperature control system controls the temperature by using the temperature sensor with a semiconductor silicon PN junction. The temperature sensor changes the current of the heater through controlling the conduction angle of the triac with a voltage regulator.  
The vibration signal is collected with a model TD-3 accelerometer installed at the test point. The signal is amplified by the HD-7 charge amplifier to get the voltage value. The voltage value is input into the computer and processed according to the digital mode to reflect the amplitude of bearing vibration.  
The rigs adopt microcomputer automatic control and automatic test technologies. The test bearing types include tapered roller bearings, angular contact ball bearings, deep groove ball bearings, and wheel hub bearing units. The rotation modes include inner ring and outer ring rotation. The size of the test bearing inner diameter is 15-45 mm. The axial maximum load is \(\pm\)15 kN. The test bearing  
Figure 2: The wheel hub bearing fatigue test rigs using mud.  
maximum speed is 3000 r/min, and the measurement parameters include speed, load, temperature, vibration, and current.  
In the experiment, the rotating speed is 900 rpm. The media ratios are 10% loess, 84% water, and 6% sand with F100#. The water spray speed is 5 L/min. The axial pressure is 2.667 kN and the radial load is 4.445 kN. The test object is the front wheel hub bearings of a DAC4007440 automobile. The sampling rate is 6000.