This article analyzes two representative types of automatic shutdown faults in electronic control systems related to R082 electronic speed controllers, namely "unforeseeable shutdown faults" and "overspeed faults", and studies solutions to effectively solve such problems.
1, Unforeseeable malfunction
1. Fault phenomenon. The definition of "unforeseeable fault" is that the speed is abnormally lower than 1500r/min and is effective under the microcomputer self-control state of the centralized control device. This fault can be manifested as an "unforeseeable fault" alarm appearing on the CRT display screen in the control room, causing the diesel engine to shut down.
2. Fault analysis. The shutdown alarm signals of the diesel engine electronic control system include comprehensive fault alarm, low oil pressure alarm, high fresh water temperature, overspeed alarm, and other alarm signals. The reason for the malfunction shutdown can be analyzed based on the alarm situation. The fault tree of electronic control alarm is shown in Figure 1.
Figure 1 Fault Tree of Diesel Engine Electronic Control System
From the fault phenomenon, the diesel engine executed the normal shutdown command. According to the fault tree diagram, this fault is in the "electronic control system alarm" ->comprehensive alarm "category. This type of malfunction is caused by the ECS (diesel engine control system) speed control module, which may be due to displacement sensor failure, speed sensor failure, circuit failure, etc. The working principle diagram of the R082 electronic governor for the speed control module is shown in Figure 2.
Figure 2R082 Working principle diagram of electronic governor
After the diesel engine speed is obtained by the speed sensor (24), the difference between the measured speed value (26) and the set speed value (1) is transmitted to the speed governor (3), which then controls the fuel supply regulator (6) to adjust the fuel supply to the diesel engine in order to achieve speed regulation. Therefore, the diagnosis and troubleshooting of faults should be carried out one by one along the module circuit according to the principle of primary to secondary, and in addition, the on-site conditions such as disassembly, replacement, and testing should be comprehensively considered.
The key control unit in this module is the electronic governor, which is the R082 electronic governor on this diesel engine. Based on this, the following troubleshooting route is formulated: ① Poor insulation of R082 electronic governor; ② R082 electronic speed regulator has its own fault; ③ Mistakenly sending a shutdown signal; ④ Signal failure of centralized control equipment; ⑤ Speed sensor malfunction.
3. Troubleshooting
(1) Check the inner and outer boxes of R082. The electronic control system of diesel engines has complex circuits, which often interfere with the transmission and reception of signals due to insulation issues. Check the inner and outer boxes of R082, which have good static insulation status and insulation resistance between 1-2M Ω, indicating that there is no signal interference.
(2) Check the electronic speed controller. 1) After swapping the faulty diesel engine governor with the normal operating diesel engine governor, the fault phenomenon shifted. 2) Thoroughly analyze the speed regulator, adjust the electrolytic capacitor of the speed regulator, and transfer the fault phenomenon again. Based on the above fault transfer phenomena, it can be concluded that the fault is caused by the failure of the electrolytic capacitor inside the governor. 3) After replacing the electrolytic capacitor spare parts, the high-speed train still experienced an unforeseeable malfunction and stopped after about half an hour. During operation, it was observed that the RZ electronic board parking signal light inside the governor box flickered at least 4 times, followed by continuous flashing until the diesel engine stopped. This indicates that there are other faulty components in the circuit.
(3) Check R082 and LOP board. 1) Upon inspection of R082 and LOP, it was found that the 13 plug D and F terminals (defined as diesel engine deceleration) of R082 are not conducting in both directions (normal diode effect is unidirectional conduction), indicating a fault in the plug. 2) After troubleshooting, it was discovered that one end of the capacitor on the R082 through-hole capacitor board was disconnected and had a grounding phenomenon. After replacement, the machine was turned on and tested for nearly 6 hours, but an emergency shutdown occurred again.
(4) Check the 13 # plug connecting the shutdown signal line to the central control device. 1) Unplug the aviation plug outside the 13th tree, the diesel engine runs for more than half an hour and works normally without any flashing signal lights. This phenomenon exacerbates the suspicion of the centralized control device sending false signals leading to shutdown. 2) Preliminary inspection of the external cables of the centralized control device, tightening and restoring the 13 aviation plugs, the high-speed train worked normally for an hour and a half, and no signal lights flickered; Subsequently, the external cables were thoroughly inspected and the aviation plug was cleaned, and no abnormalities were found. 3) The relay board of the centralized control device and the electronic board related to the starboard side microcomputer were replaced and inspected, and no abnormalities were found. 4) Swap the left and right side microcomputer (belonging to the centralized control device), and connect the shutdown signal and deceleration signal of Units 2 and 4 (belonging to the starboard side) in the junction box of the engine compartment below the ship. At the same time, start 4 diesel engines for full charging and run for 4 hours. Unit 4 stops urgently, and the fault is transferred, eliminating the possibility of problems with the local machine and microcomputer of Unit 2; Replace the relay B board of the control panel and continue to assess the operation of Unit 4. After running for more than 6 hours without stopping, it was confirmed that the problem was with the relay B board.
(5) Check the speed sensor. 1) Check if the speed sensor is faulty by swapping the speed sensors of the normal running diesel engine and the faulty engine. 2) Compare and measure the resistance values of two speed controllers to determine if it is a sensor malfunction.
This example shows that the occurrence of faults is often accompanied by multiple component errors. The diagnostic and troubleshooting process should focus on locking all fault sources from primary to secondary, in order to completely eliminate the faults.
2, Overspeed fault
1. Fault phenomenon. The position of the gear rack in the diesel engine governor test can only reach 5mm. Despite multiple tests, the phenomenon persists and causes the 24V power supply fuse on board to melt. After replacing the fuse and turning for many times, the governor test returns to normal. Starting the diesel engine, an overspeed shutdown occurred after running for about 5 minutes, and then the diesel engine could not be started normally, resulting in overspeed shutdown every time.
2. Fault analysis. When the speed signal received by the electronic governor of the diesel engine exceeds the speed limit value, the electronic control system will issue an overspeed alarm, and the diesel engine air cut-off butterfly valve will close and shut down. The overspeed alarm fault belongs to the electronic control system alarm (see Figure 1). The control system diagram of the electronic governor is shown in Figure 3.
Figure 3 Schematic diagram of electronic governor control system
The reasons for the overspeed alarm shutdown are summarized as follows: ① High lubricating oil level (according to previous experience of troubleshooting such faults, high lubricating oil level immersing the cylinder liner can cause the diesel engine to start and stop at an overspeed). ② Speed governor 2 fault; ③ Speed sensor 5 fault; ④ Electromagnetic actuator 3 fault; ⑤ Fuel injection pump 4 fault.
3. Troubleshooting
(1) Check the oil level. 1) Check the external surroundings of the diesel engine for any oil leakage; All wiring plugs are securely and reliably connected. 2) Check that the oil level is within the normal range.
(2) Check the speed regulator. 1) Check that the EMC box (governor board box) has good insulation to ground. Swap the four speed controller plug-in boards inside the speed controller boxes of Unit 1 (normal operation) and Unit 2 (faulty engine). Unit 1 is running normally, while Unit 2 is still running together, resulting in overspeed shutdown. The diesel engine speed did not stop at 1800r/min, and the fault did not transfer. It is preliminarily judged that it is not related to the diesel engine speed controller board. 2) Swapping the speed controllers 1 and 2 as a whole, the overspeed alarm still occurs in 2 #. The fault did not transfer with the governor, so the fault is not related to the governor.
(3) Check the speed sensor. Measure the resistance values of the speed sensors of two machines, and the resistance values are very close. Therefore, there is no problem with the speed sensor.
(4) Check the actuator. 1) Measure the resistance values of the actuator position sensors on two machines, and the resistance values are very close. The position sensor is normal. 2) Upon inspection of the actuator located in the V-shaped groove of the diesel engine, it was found that the plug of the actuator for the governor of two engines was loose, and the speed sensor was also loose. Tighten the plug and start the two engines again. Use the human-machine dialogue device to record the starting curve. It was found that when the diesel engine speed was 1500r/min, the rack position had already reached 0mm, but the overspeed alarm still sounded. 3) Dismantling and inspecting the actuators of two engines, removing dust from the actuators, and removing the upper end cover of the actuator intermediate body, it was found that the spherical cap (55) and locking washer spring (56) connecting the actuator push rod were missing (see the exploded view of the actuator intermediate body in Figure 4), which caused the actuator to push the fuel rack to 13 and unable to pull it back during the diesel engine starting process. After reaching the maximum fuel injection amount, it could not be adjusted back, and the diesel engine speed exceeded the limit value. 4) Reinstall the spherical cap and snap spring, and check to confirm that the snap spring is installed properly. Start the diesel engine and ensure normal operation. Use a human-machine dialogue device to record the starting curve and confirm that the starting process is normal. After multiple tests, the diesel engine operated normally. 5) During the mooring test, another engine experienced a situation where the governor test was normal but the diesel engine could not start - during the starting process, the displacement of the fuel rack was 0mm. After careful investigation, the cause is the same. With the guidance of previous troubleshooting experience, the fault was quickly and effectively eliminated. Analysis suggests that there are two reasons for the detachment of the spherical cap and locking clamp spring. One is that the clamp spring was not installed properly when replacing and installing the actuator; Secondly, the machining of the card spring groove exceeded the tolerance, and the diesel engine experienced vibration loosening after running for a long time (both engines ran for about 120 hours).
3, Conclusion
This article elaborates on the phenomena, causes, and solutions of two typical electronic control system failures and shutdowns of the 396 diesel engine, and summarizes the general approach to solving such problems: determining the type of fault based on the fault phenomenon, analyzing the cause of the fault, and determining the troubleshooting sequence from primary to secondary. For faults in the electronic control system, according to the working principle of the system, it is generally necessary to first check whether the insulation of the relevant signal components is good, determine whether it is a signal line fault or a fault of the components themselves, and then determine the faulty part by replacing the components. Taking into account the actual situation at the work site and drawing on past troubleshooting experience, this will greatly improve the efficiency of troubleshooting.