In my years of experience in EV repair, I have encountered numerous complex systems in hybrid electric vehicles, but the auxiliary charging system for power batteries in models like the Wuzhoulong hybrid bus stands out due to its intricate design and high failure rate. As an electrical car repair specialist, I have dedicated significant time to understanding and troubleshooting this system, which ensures the power battery remains charged without relying solely on external charging stations. This system incorporates a 11 kW generator driven by the engine to supplement the power battery when the state of charge (SOC) drops below certain thresholds. Failures in this system can lead to overcharging or undercharging, rendering the vehicle inoperable. In this comprehensive guide, I will delve into the system’s structure, operational principles, common faults, and detailed repair methodologies, emphasizing the importance of EV repair techniques and electrical car repair protocols. I will use tables and formulas to summarize key points, ensuring clarity for professionals in the field.
The auxiliary charging system is a critical component in modern hybrid vehicles, designed to maintain the power battery’s SOC through an onboard generator. My involvement in electrical car repair has shown that this system’s reliability hinges on proper maintenance and accurate diagnostics. The core components include an 11 kW generator, a power generation inverter, a programmable logic controller (PLC) board, a central processing unit (CPU226), and an optical encoder. Each element plays a vital role in converting mechanical energy from the engine into electrical energy for battery charging. In EV repair, understanding the interplay between these components is essential, as faults can arise from any part of the chain. For instance, the generator, produced by Dalian Tianyuan Motor Company, is a water-cooled, star-connected asynchronous motor with specific parameters that must be adhered to during electrical car repair procedures. Below, I present a table summarizing the key components and their functions based on my hands-on experience.
| Component | Function | Key Parameters |
|---|---|---|
| 11 kW Generator | Converts mechanical energy to AC power for battery charging | Rated power: 11 kW, Cooling: Water-cooled, Connection: Star |
| Power Generation Inverter | Rectifies AC to DC, monitors generator speed, provides control signals | Input: 350V AC, Output: DC, Fault code display |
| CPU226 | Processes CAN signals from BMS, outputs control voltages | Input signals: CAN bus, Output: Analog voltage |
| PLC Board | Acts as signal converter between CPU and inverter | Optical couplers for isolation, input/output terminals |
| Optical Encoder | Measures generator speed and direction | Input voltage: +15V, Signal output: Phase-shifted pulses |
The operational principle of the auxiliary charging system revolves around the battery management system (BMS) monitoring the SOC. In EV repair, I often reference the SOC value, which is calculated as the ratio of remaining capacity to total capacity, expressed as a percentage: $$SOC = \frac{Q_{\text{remaining}}}{Q_{\text{total}}} \times 100\%$$ where \(Q\) represents capacity in ampere-hours (Ah). When the SOC falls below 55%, the BMS sends a CAN signal to the CPU226, initiating auxiliary charging. If the SOC drops further to 50%, forced charging is triggered, and charging stops when SOC exceeds 69%. The control logic involves multiple signals: the CPU226 outputs a low potential to the REV terminal and a high potential to the FWD terminal of the inverter via the PLC board, enabling generation. Additionally, a torque signal from the EM232 module, typically around 3V, dictates the charging current. In electrical car repair, it’s crucial to verify these signals, as deviations can cause inefficiencies or failures. The power output of the generator can be related to voltage and current using the formula: $$P = V \times I$$ where \(P\) is power in watts, \(V\) is voltage in volts, and \(I\) is current in amperes. For the 11 kW generator, this translates to approximately 15A charging current under normal conditions.
During my EV repair practices, I have documented numerous fault scenarios, with one common issue being the generator not charging despite normal engine operation. In a typical case, the vehicle displayed a low voltage of 324V and an SOC of 40%, but no charging current was observed. As part of electrical car repair diagnostics, I first checked the inverter display, which showed “RUN” with no fault codes, indicating no immediate hardware failures. However, intermittent charging currents of a few amperes suggested underlying signal problems. Using a multimeter—essential in EV repair to avoid damaging sensitive components—I measured the FWD-CM voltage at 10V, significantly lower than the expected 20V, and the torque signal U12-11 at 2.27V, below the typical 3V. These measurements pointed to issues in the control circuit. To systematize such diagnostics, I have developed a table of common measurements and their implications, which aids in efficient electrical car repair.
| Measurement Point | Normal Value | Fault Indication |
|---|---|---|
| FWD-CM Voltage | 20V | Low voltage suggests control signal loss or PLC fault |
| REV-CM Voltage | 0V (during generation) | High voltage indicates incorrect CPU output |
| Torque Signal (U12-11) | 3V (normal), 4V (forced) | Low voltage may reduce charging current or prevent generation |
| Encoder Signals (YA, YB) | 7.2-7.3V pulses | Absence or imbalance indicates encoder or wiring faults |
| Generator Resistance | 0.63Ω per phase | Imbalance suggests winding faults |
In this specific EV repair case, further investigation revealed that the low FWD-CM voltage was due to a faulty optical coupler on the PLC board. The coupler, which acts as a switch, had developed a leakage resistance, causing a voltage drop. Using Ohm’s law, the voltage drop across the coupler can be modeled as: $$V_{\text{drop}} = I \times R_{\text{leakage}}$$ where \(I\) is the current and \(R_{\text{leakage}}\) is the unintended resistance. In normal operation, the coupler should have infinite resistance when off, but in this fault, it formed a voltage divider with the inverter’s internal pull-up resistor. This highlights the importance of component-level testing in electrical car repair. After replacing the coupler, the FWD-CM voltage returned to 20V, and charging resumed with currents around 15A, restoring the SOC to normal levels. This experience underscores that in EV repair, even minor components can cause significant system failures.
Another critical aspect of electrical car repair for this system is the encoder’s role in providing rotation feedback. The encoder outputs two phase-shifted pulse signals, YA and YB, with a 90-degree phase difference. The inverter uses this to determine the generator’s direction and speed. If these signals are swapped, generation may not occur. The frequency of these pulses relates to the rotational speed \(n\) in RPM by: $$f = \frac{n \times P}{60}$$ where \(f\) is frequency in Hz, and \(P\) is the number of pulses per revolution. In EV repair, verifying these signals with an oscilloscope is advisable, but a multimeter can suffice for basic checks. Additionally, the generator’s three-phase output must be correctly connected to the inverter; incorrect phasing can cause reverse rotation, preventing proper charging. As part of electrical car repair protocols, I often perform a direction test by temporarily using the generator as a starter motor, ensuring alignment with engine rotation.
When dealing with torque signals in EV repair, it’s essential to understand that they control the power output. The torque voltage \(V_{\text{torque}}\) from the EM232 module dictates the charging current \(I_{\text{charge}}\) according to a linear relationship: $$I_{\text{charge}} = k \times V_{\text{torque}}$$ where \(k\) is a proportionality constant specific to the system. In my electrical car repair experience, a \(V_{\text{torque}}\) of 3V typically results in a 15A charge, while 4V forces a higher current. However, excessive torque voltages can strain the engine drive belt, leading to slippage and wear. Therefore, in EV repair, calibrating this signal is crucial to avoid secondary damages. The BMS plays a pivotal role here; if it detects battery faults, such as zero voltage in some cells, it may command a reduced torque signal, halting generation. This interplay emphasizes the need for holistic diagnostics in electrical car repair, where battery health and control signals are assessed simultaneously.
In EV repair, safety is paramount, especially with high-voltage systems. Before any work, I always disconnect the high-voltage circuit and wait at least 20 minutes for capacitors to discharge. Using LED test lights instead of incandescent ones prevents overloading sensitive outputs like those from the EM232 or CPU226. Moreover, engine idle speed must be calibrated to 750 RPM for stable auxiliary generation; deviations can prevent the system from activating. For instance, if the engine control module (ECM) is replaced, re-calibration is necessary—a common oversight in electrical car repair. Additionally, when testing generator phasing, I follow a step-by-step procedure to avoid short circuits. This involves entering the inverter’s programming mode, adjusting parameters to use the generator as a motor, and observing rotation direction. Such meticulous steps are integral to effective EV repair.
To summarize the control logic mathematically, the auxiliary charging system’s operation can be represented using Boolean expressions. Let \(S_{\text{SOC55}}\) be a signal indicating SOC < 55%, and \(S_{\text{SOC50}}\) for SOC < 50%. The generation enable signal \(G_{\text{enable}}\) is given by: $$G_{\text{enable}} = S_{\text{SOC55}} \lor S_{\text{SOC50}}$$ where \(\lor\) denotes logical OR. The CPU226 then outputs signals to the PLC board, which converts them to inverter commands. The torque voltage \(V_{\text{torque}}\) is a function of SOC: $$V_{\text{torque}} = \begin{cases} 3V & \text{if } SOC < 55\% \\ 4V & \text{if } SOC < 50\% \end{cases}$$ These formulas help in simulating system behavior during EV repair diagnostics. Furthermore, the power efficiency of the charging process can be evaluated using the efficiency formula: $$\eta = \frac{P_{\text{output}}}{P_{\text{input}}} \times 100\%$$ where \(P_{\text{output}}\) is the power delivered to the battery, and \(P_{\text{input}}\) is the mechanical power from the engine. In my electrical car repair work, I aim for efficiencies above 90% to ensure optimal performance.
In conclusion, the auxiliary charging system in hybrid vehicles is a complex yet vital component that requires specialized EV repair skills. Through detailed analysis of its structure, principles, and fault cases, I have highlighted the importance of signal verification, component testing, and safety measures. Electrical car repair professionals must be adept at using multimeters, understanding control logic, and interpreting BMS data. The integration of tables and formulas in this guide serves as a reference for diagnosing and resolving issues efficiently. As EV technology evolves, continuous learning and adaptation in EV repair will be essential to maintain these systems reliably. My firsthand experiences reinforce that a methodical approach, combined with a deep understanding of electrical principles, is key to successful outcomes in electrical car repair.