Abstract: This paper introduces the composition and monitoring principle of the running gear on-board fault diagnosis system, and through the application in China Shenzhen Metro, it realizes the running gear status monitoring, fault diagnosis, application evaluation, and provides convenience for vehicle repair and maintenance.
Keywords: running gear; Status monitoring; fault diagnosis
With the development of cities, urban rail vehicles have become important public transportation tools. The short operating range and frequent starting, acceleration, deceleration, and braking of urban rail vehicles result in a larger range and frequency of dynamic load changes during mechanical operation. The failure of the running gear is particularly important for the operational safety of urban rail vehicles. Although urban rail vehicles are generally scheduled to be returned to the warehouse for maintenance every day, it is difficult to detect internal faults in bearings, wheel tread, and other issues in advance and in a timely manner solely through routine inspections and daily maintenance methods. Therefore, Shenzhen Metro has applied the running gear on-board fault diagnosis system on Shenzhen Line 1, 5 and 11 since 2016. Through long-term tracking, real-time and effective monitoring and fault diagnosis of the axle box bearing status, motor bearing status, gearbox bearing and gear status, and wheel tread of the running gear can be carried out, providing convenience for the maintenance and repair of key components of the vehicle running gear.
1. Composition and monitoring principle of on-board fault diagnosis system for running gear
The on-board fault detection system for the running gear mainly consists of composite sensors, front-end processors, vehicle extensions, train hosts, etc. The structural composition is shown in Figure 1.
Composite sensors are installed on the axle box, motor, and small gearbox to detect, process, and transmit multiple physical quantities such as temperature, vibration, and impact; The front-end processor is installed on the bogie, with 2 units per bogie for high-speed trains and 1 unit per bogie for trailers. It manages the sensors at each measuring point of the bogie, switches vibration and impact simulation channels, and transmits temperature and simulation signals through bus; Each vehicle has a vehicle extension, which enables the management of the front-end processor, signal acquisition, data storage, and fault diagnosis of the vehicle, as well as interactive communication with the train host; Each train has one train host to achieve centralized management of the onboard system, including receiving speed signals and distinguishing them, managing collaborative vehicle extensions, displaying diagnosis and alarms, centralized data storage and download, system updates and maintenance, etc.
Figure 1 Schematic diagram of the composition of the on-board fault diagnosis system for the running gear
The on-board fault diagnosis system for the running gear mainly adopts Chinese patented technologies such as "a resonance demodulation detection method for mechanical fault impact", "tracking and collection of time-domain samples from various information sources in the same and ordered dynamic information (group) group", and "speed tracking sampling and solidification spectrum analysis method for fault diagnosis of variable speed running machinery". Based on the above three patented technologies, the implementation of speed tracking sampling and filtering processing of vibration and impact signals aims to extract weak fault impact information of the running gear, perform periodic transformation of non periodic information, solidify theoretical abstract spectrum, and ultimately achieve early warning, graded alarm, and accurate diagnosis of monitoring objects.
2. System Application
Shenzhen Metro firstly installed the running gear on-board fault diagnosis system on the existing vehicles of Shenzhen Line 1 and Line 5 in combination with the unwheeling repair of vehicles. For the condition monitoring of the running gear after unwheeling repair, it deeply studied the running gear operation status to guide the vehicle operation and maintenance.
In addition, considering that Shenzhen Line 11 is the first 120km/h vehicle line in Shenzhen, in order to study the operating status of vehicles at a speed of 120km/h, an on-board fault diagnosis system for the running gear has also been introduced to evaluate the critical status of the running gear and achieve vehicle condition maintenance.
2.1 Monitoring of axle box bearing status
The on-board fault diagnosis system of the running gear collects real-time data, and achieves comprehensive judgment of bearing status through impact sample analysis, impact trend analysis, and temperature trend analysis.
The system analyzes the spectrum, and the time domain wave of bearing fault information forms a narrow comb shaped pulse, with each pulse equidistant. On the spectrum, the fault spectrum corresponds to the theoretical spectrum of the outer ring. And by analyzing historical trends, determine the historical occurrence and development status of faults, and guide the application and maintenance.
Figure 2 Axis shows the impact sample graph of outer ring fault characteristics
The monitoring of temperature information is the last barrier to ensure train safety. The temperature information of the on-board fault diagnosis system of the running gear is divided into two levels of processing. In the front processor, the conventional mode of MCU is divided into 5 seconds, and the temperature information of all connected sensors is read once with conventional accuracy.
Figure 3 Impact Trend of Bearing Outer Ring Obstruction Characteristics
If necessary, the on-board fault diagnosis system of the running gear will activate the box sealed temperature measurement mode. During each communication between the vehicle extension and the front-end processor, the vehicle extension obtains the temperature information of the front-end processor and its affiliated sensors on a per unit basis, thereby achieving parallel and rapid collection of temperature information.
Figure 4 Temperature Trend Graph
2.2 Motor bearing status monitoring
In recent years, motor bearings of Shenzhen Metro have frequently encountered various problems: electrical erosion of Siemens motor balls, overheating and seizure of bearings, etc. In order to grasp the real-time status of the motor during operation, the on-board fault diagnosis system of the running gear was applied to track and monitor the motor bearings, and analyze their health status during operation.
According to the structural geometry and Kinematics of the machine, the classical mathematical model of rolling bearing fault diagnosis is established by the resonance demodulation and speed tracking diagnosis technology, which can carry out deterministic and precise diagnosis of faults from both quantitative and qualitative perspectives.
In 2013, Siemens' traction motor bearings were monitored for faults through the on-board fault diagnosis system of the running gear, and fault information was found in the motor bearings, as shown in Figure 5; On site disassembly of the faulty bearing revealed a fault with the bearing cage, as shown in Figure 6.
Figure 5 shows the fault information displayed in the new system prompt for the hidden poetry of the train
Figure 6 Fault axis display on-site disassembly tracking
Shenzhen Line 11 was put into operation in June 2016. The on-board fault diagnosis system of the running gear found that early fault information of motor bearings was commonly present in the motors. Taking the 1116 train as an example, multiple motors of the train had early cage fault impact information. Through mechanical analysis of these faulty bearings, there was a shortage of oil in the motor bearing transmission end; As shown in Figure 7.
Figure 7: The on-board fault diagnosis system of the running gear indicates that there is a cage fault message for the bearing
In view of the lack of oil in the motor of Shenzhen 1116 car, Shenzhen Metro injected oil into the faulty motor. After oil injection, the fault information reflected by the data weakened significantly. The comparison before and after oil injection is shown in Table 1:
Table 1 Comparison of Fault Information of Cage Before and After Oil Injection
2.3 Gearbox status monitoring
Gearbox monitoring includes the monitoring of small gearbox bearings and gears, and the monitoring of small gearbox bearings has the same principle and spectral line as the monitoring of axle box bearings.
Analyzing the subway systems in various cities across the country, gear failures often occur, and the display characteristics of gear failures mainly include the following:
① Multiple impacts during a small gear rotation cycle indicate that more than one tooth has experienced a faulty impact.
② If there is only a single tooth fault, the pulse duty cycle of the shock wave in the time domain waveform of a gear cycle is very narrow, and the frequency domain will have rich multi order spectral characteristics. The impact at high speed is wider than at low speed, and under the same traction force, the impact value (primary diagnostic value) at high speed will also significantly increase.
③ Due to the simultaneous presence of multiple faults, the pulse duty cycle of time-domain impact pulses in the gear cycle is relatively wide, presenting multiple clusters of impacts; This leads to unclear higher-order spectral lines in the frequency domain.
The diagram below shows a typical single tooth crack fault and multiple gear faults.
By comparing the above fault graphs, it can be seen that when there is a single tooth (such as a crack) fault in a gear, a cluster of well located and sharp shock waves will appear within the sampling points of the gear cycle, with prominent frequency domain spectral lines and high order richness; When there are multiple faults in the gear, there are multiple clusters of impacts within the sampling points of the gear cycle, and higher order faults are not as abundant as single tooth (crack) faults.
Figure 8 Single tooth crack fault, with a small duty cycle of the time domain and a rich high-order spectrum of the peak spectrum
Figure 9: Multiple faults in the gear, with a large duty cycle of the time domain and reduced higher-order spectrum
During the operation of gears, when the faulty teeth mesh with adjacent teeth, there will be an impact. The shaft where the gear is located will produce such an impact every revolution at the fault location, which is received by the on-board fault diagnosis system of the running gear. The on-board fault diagnosis system of the running gear outputs a gear alarm through automatic diagnostic analysis. For a single tooth fault, the shaft on which the gear is located produces one impact per revolution, while when there are multiple faults in the gear, the shaft produces multiple impacts per revolution. So, when there are multiple faults in the gear, multiple clusters of impact pulses will appear during the gear cycle.
2.4 Monitoring of wheel tread condition
Wheel tread failures generally include tread scratches, tread peeling and wheel out of round. During the operation of Shenzhen Metro, wheel out of round and scratch peeling failures often occur, in which the wheel out of round is mostly characterized by high circular runout, and wheel out of round will cause regular periodic impact sound with the rail during vehicle operation, which not only causes abnormal vibration and impact of the wheel and rail, but also worsens the wheel rail relationship, It also affects ride comfort. For this reason, Shenzhen Metro applies the running gear on-board fault diagnosis system to comprehensively diagnose the tread for vibration and impact, analyze the development trend of wheel out of roundness, and guide wheel chain repair.
The on-board fault diagnosis system of the running gear analyzes the vibration spectrum of wheels with out of circle, and the impact spectrum in the data sample shows the impact state of the tread every ten revolutions of the wheel. When the wheel exhibits circular runout characteristics, the impact spectrum of the wheel will be generated every one revolution? A cluster of impact signals that trigger resonance demodulation waveform will have periodic repeatability, and the impact spectrum in the data sample will present ten equally spaced impact signals. Through this theoretical approach, it can be determined that there is a fault feature of wheel out of circle.
Taking the 112 vehicle of Shenzhen Line 1 as an example, in November 2016, the on-board fault diagnosis system of the running gear found that there was a tread out of circle fault feature information on the right side of the 1124 vehicle's 1 axis, and continued to track it. The system recommended plating repair at this location in February 2017, and the monitoring situation is shown in Figure 10.
According to on-site tracking of the chain repair on the right side of Axis 1 of Vehicle 1124, it was found that the circular runout at this position reached 0.91mm, severely exceeding the standard, as shown in Figure 10.
Figure 10 Impact Graph on the Right Side of Axis 1 of Car 1124
3 Conclusion
It is of great significance to monitor the status of vehicle running parts in a timely manner through the application of on-board fault monitoring system for running parts, excavate and repair hidden danger locations in a timely manner, reduce the accumulation of damage, improve the operating status of vehicle running parts, and reduce the occurrence of driving accidents and faults.
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2023-06-25