Currently, all Dongfeng 4 series diesel locomotives used in China employ battery-powered series-wound electric motors to start the diesel engines. Due to the simple functionality of existing control systems and their susceptibility to human error, battery status, and relay lag, problems frequently arise, including difficulty starting the diesel engine, battery depletion, and poor combustion. This is particularly problematic in the cold winters of northern China, where battery depletion and starting difficulties have become major challenges for locomotive maintenance departments. Utilizing PCC technology for intelligent control of the locomotive diesel engine starting process can improve the starting process, reduce battery energy consumption, and improve combustion, thereby enhancing locomotive maneuverability, reducing fuel consumption, and minimizing harmful emissions. 1. Current Status of Locomotive Diesel Engine Starting Taking the Dongfeng 4C locomotive as an example, this paper illustrates the problems in diesel engine starting. This locomotive has a logic diesel engine starting control circuit composed of relays, contactors, and other contact-based electrical components. However, the circuit is simple in function, has a high failure rate, and cannot achieve optimized control of the diesel engine starting process. The locomotive is equipped with a starter oil pump specifically responsible for providing lubricating oil to the moving parts of the diesel engine during the starting process. The starter oil pump needs to start 45-60 seconds before the diesel engine starts, and the fuel pump needs to supply fuel to the diesel engine about 10 seconds in advance. Promptly supplying oil prevents damage to the moving parts of the diesel engine due to lack of lubrication when starting after a long period of inactivity; the early operation of the fuel pump provides the necessary fuel pressure for the high-pressure fuel pump to operate normally. The starter oil pump should not run for too long, otherwise it will consume a large amount of battery energy, which is detrimental to the starting of the diesel engine. The starter motor and fuel pump are synchronously controlled, and their starting circuit diagram is shown in Figure 1. [align=center] Figure 1 Schematic diagram of the starting circuit of the Dongfeng 4 locomotive diesel engine[/align] As can be seen from the figure, three conditions are required for the diesel engine to start: first, fuel supply; second, lubrication of moving parts; and third, sufficient battery energy to drive the starter motor and bring the diesel engine to a certain starting speed. Throughout the starting process, the control of the starter motor and fuel injection pump rack is achieved through the starter contactor QC. This control method has the following drawbacks: (1) The control circuit uses contact electrical components, resulting in limited functionality, complex structure, and high failure rate. It cannot meet the optimized control requirements of the diesel engine starting process and is incompatible with modern technological development. (2) Operators must observe and judge the success of the diesel engine start-up to control the starting process. Therefore, during startup, operators must judge the starting status by the sound, speed, and oil pressure of the diesel engine and control the starter motor's operating status through the starter button. Improper control may cause the diesel engine to fail to start, or the starter motor to operate for too long, causing the battery to discharge excessively and preventing further starting. This requires operators to have high qualifications and rich experience. (3) Premature fuel injection into the cylinder. When the diesel engine speed is low, the injection pressure is also low, the fuel injection quality is poor, the fuel cannot mix fully with air, delaying the ignition speed, resulting in high starting energy consumption, large exhaust volume, and even detonation. (4) After the diesel engine has started, the battery continues to supply power to the starter motor, causing over-discharge of the battery and affecting its lifespan. (5) If the diesel engine fails to ignite normally, holding down the start button for an extended period will cause damage to the starter contactor and battery depletion. Therefore, optimizing the starting process of the diesel engine is essential. 2. Advantages in Locomotive Control A Programmable Computer Controller (PCC) is a general-purpose industrial automatic control device with a microprocessor as its core. It can completely replace relay logic control devices, not only easily handling switching and analog quantities, but also realizing automatic timing, counting, and arithmetic operations. PCCs are equipped with large-capacity memory and can replace conventional relay logic control functions through software programming, making the control system intelligent. They are characterized by small size, light weight, high speed, high reliability, and easy debugging. They can also adapt to harsh working environments such as high and low temperatures, shock vibration, electromagnetic interference, and power fluctuations. The B&R 2000PCC series products manufactured by B&R GmbH of Austria are internationally advanced in terms of power supply, functionality, and safe operation. 2.1 PCC-based Optimized Control for Locomotive Diesel Engine Starting To address the deficiencies and shortcomings in the current diesel engine starting process, the starting process can be unfolded over time and programmed for control. A control system based on the PCC can be established to achieve detection and intelligent control of the starting process. The diesel engine starting process can be roughly divided into four stages: preparation, engine rotation, ignition, and stable operation after establishing oil pressure. The preparation stage mainly involves pre-supplying engine oil and fuel. The Dongfeng 4C locomotive uses a 45-60s delay to control the operation of the fuel pump and oil pump to pre-supply oil to the oil system before starting. Based on the different stages of the starting process, existing problems in the diesel engine starting process can be gradually optimized and resolved. 2.2 Control of the Starting Contactor (QC) During diesel engine starting, whether the starting contactor (QC) is energized depends on the oil pressure in the diesel engine pipeline. Ideally, oil pressure and fuel pressure should be used as control signals. This way, during the initial start-up, if a malfunction in the oil pump, pipeline, or other parts causes the oil and fuel pressures to fall below the required range, the starting contactor will not close to start the diesel engine. Currently, during the starting process, pressing the starter button 1QA activates the starter oil pump. After a 45-60 second delay, the starter relies primarily on manual observation of the oil and fuel pressure gauges to determine if the pressure meets the requirements and whether to stop starting. To some extent, the existing starting control logic is based on the assumption that the oil pressure will definitely build up within the 45-60 second delay time, and controls the starting contactor QC accordingly. Because the states of the oil system and the fuel system differ significantly, the time required to establish oil and fuel pressure also varies. Therefore, the above assumptions are unrealistic and cannot guarantee control accuracy. To address this, pressure sensors can be used to measure oil and fuel pressure, and the relevant signals can be input to the corresponding module in the PCC via an analog channel. The PCC then judges the pressure based on the set pressure range and controls the QC's action. 2.3 Optimized Control of the Starter Motor (QD) The success of diesel engine starting hinges on whether the diesel engine ignites. The termination of the start should be controlled by the diesel engine's ignition speed. If, for some reason, the engine cannot start normally, it should automatically stop to reduce battery discharge and prevent the starter contactor (QC) from burning out. Under normal circumstances, when starting the diesel engine of the Dongfeng 4 series locomotives, the ignition speed is around 150 r/min, and the minimum stable speed is 430 r/min. If a speed sensor is used to measure the diesel engine speed and the speed signal is input into the PCC, the PCC can control the QC to open/close based on the diesel engine speed, thus controlling the battery to supply power to the starter motor. This saves battery energy and extends battery life; furthermore, the motor changes from driving rotation to acting as a load on the diesel engine, reducing the speed shock during diesel engine starting. 2.4 Power Supply Control for the Electromagnetic Interlock DLS: During diesel engine starting, premature fuel injection into the cylinder at low speeds will have many adverse consequences. Firstly, the temperature and pressure at the compression end are low; secondly, the low injection pressure results in poor fuel atomization, preventing sufficient mixing with air to form a combustible mixture. This leads to incomplete combustion or even no combustion at all. Simultaneously, it lowers the temperature inside the combustion chamber, causing starting difficulties or even detonation. Therefore, it is essential to separately control the power supply to the starter contactor and the DLS electromagnetic interlock coil in the governor based on the diesel engine's starting speed. In this way, the fuel injection pump rack can be engaged only after the diesel engine reaches its ignition speed, thus achieving the goal of injecting fuel into the cylinder at the appropriate time. Since injecting fuel into the cylinder when the diesel engine, driven by the starter motor (QD), reaches the ignition speed is most beneficial for ignition, whether the DLS coil is energized should depend on the engine's driving speed. Different diesel engines, or even the same diesel engine operating under different environments and conditions, will have different ignition speeds. Factors affecting ignition speed mainly include cylinder temperature and pressure, oxygen content, and fuel atomization. The main factors affecting cylinder temperature are fuel and water temperature. In summer, diesel engines have higher fuel and water temperatures, making them easier to start; conversely, diesel engines are more difficult to start in winter. Therefore, the DLS electromagnetic interlock coil can be optimized and controlled based on the monitoring of fuel and water temperatures. 3. Logic Design and Flowchart of Diesel Engine Starting PCC Controller 3.1 Control Circuit As analyzed above, during diesel engine starting, the PCC can quickly calculate, process, and intelligently judge the detected signals by detecting the diesel engine speed, oil pressure, fuel pressure, and oil-water temperature to determine a reasonable ignition speed and perform real-time control on the starting contactor, DLS coil, etc. [align=center] Figure 2 Simplified Wiring Diagram of Diesel Engine Starting PCC Control Figure 3 Starting Flowchart[/align] The PCC is used as the core of diesel engine starting control, and its simplified wiring diagram is shown in Figure 2. As can be seen from the figure, compared with the original control method, the time relay 1SJ is reduced and implemented by the soft relay inside the PCC, and the speed sensor, temperature sensor, and pressure sensor are added. This circuit realizes starting delay control, battery power supply control, fuel supply rack control, and separation of the oil pressure protection circuit from the starting circuit. In the above process, the analog signal connected to the analog input terminal is converted into a digital signal by the analog-to-digital converter (ADC) in the module. 3.2 Starting Procedure Based on the working sequence of control signals during diesel engine starting, the starting procedure is shown in Figure 3. During starting, the timing is implemented by the counter inside the PCC to prevent the QC (starting contactor) from burning out due to prolonged holding of 1QA. 3.3 Determination of Ignition Speed ​​The ignition speed of the diesel engine can be determined based on the change in torque and speed. The relationship between the resistance characteristics, motion resistance torque, motor drive torque, acceleration torque, and motor speed of the Dongfeng 4 locomotive is shown in Figure 4. [align=center] Figure 4 Change curves of starting torque, resistance torque, and acceleration torque before and after ignition[/align] In the motion equation of the diesel engine starting system, Ms is the electromagnetic torque of the starter motor (Nm); Me is the diesel engine resistance torque of the starter motor (Nm). When the diesel engine accelerates, dMa/dn will gradually change from a negative value to a positive value. When dMa/dn = 0, its speed is the ignition speed. After actual measurement of parameters affecting locomotive diesel engine starting, the ignition speed was determined to be 150 r/min under calibrated atmospheric conditions. 4. Conclusion Simulation tests showed that using PCC to control locomotive diesel engine starting, compared to existing technologies, can reduce speed shocks during starting, decrease exhaust emissions, and achieve battery energy saving. The new control system also reduces the need for manual operation of holding down the 1QA button for extended periods. With technological advancements, both existing and newly manufactured locomotives require new methods for modification and equipment. For example, ① constant power control; ② resistance braking; ③ locomotive electrical fault diagnosis can all be implemented using PCC. Given the powerful functions and suitability for industrial control, PCC can be considered the core of intelligent control for the entire locomotive system. It is believed that the application of PCC technology will bring about significant improvements in locomotive control.