[Abstract]: This paper introduces the control scheme of a diesel engine electronic governor system. The differential transformer working principle is adopted, and the structure and signal conditioning circuit of the angular displacement sensor are designed. Through matching the angular displacement sensor with an angular displacement electromagnetic actuator and conducting three simulation experiments on the inner and outer loops of the electronic governor system, the optimal operating performance parameters of the angular displacement sensor are obtained, confirming that the steady-state and dynamic response performance indicators of the electronic governor system fully meet the requirements of normal diesel engine speed regulation. 0 Introduction Common displacement sensors for diesel engine electronic governors include eddy current, inductive differential, and resistive types, which are often used to measure linear displacement but rarely used for angular displacement. Currently, inductive differential displacement sensors are used to measure displacement in diesel engine electronic governor systems, but they still have the following shortcomings: large size, poor excitation stability, difficulty in zero-point handling, and low accuracy and reliability due to complex circuitry. These are not suitable for the high precision and high reliability requirements of diesel engine electronic governors. Therefore, improving the performance of displacement sensors has become the key to improving the performance of electronic governors. This paper describes a novel angular displacement sensor designed based on the performance requirements of an electronic governor for diesel engines. The sensor is required to measure the angular displacement of the electronic governor system. The sensor features a small size and a well-designed signal conditioning circuit. Optimal performance parameters are obtained through matching experiments with an angular displacement electromagnetic actuator. Simulation experiments of the inner and outer loops of the electronic governor system verify that the dynamic response of the entire system reaches 0.5 seconds, with a linearity of 0.%. This design has significant engineering application value. 1. Working Principle of the Electronic Governor System The electronic governor control scheme is shown in Figure 1. The diesel engine electronic governor system consists of a displacement sensor, a speed sensor and actuator, a PID control module, a potentiometer, and a voltage-to-frequency conversion circuit module (equivalent to the diesel engine). It is controlled by a dual-closed-loop PID control module consisting of an outer loop and an inner loop. The outer loop compares the given diesel engine speed n1 with the detected diesel engine speed n2, and adjusts it using the outer loop PID control. Its output is a setpoint signal for the position of the fuel injection pump rack, which is sent to the inner loop PI control module. The inner loop controls the rack position based on the difference between the displacement signal given by the outer loop and the actual rack position signal measured by the detection system. This difference is then applied to the actuator control circuit to adjust the rack position, thereby controlling the fuel injection quantity of the fuel injection pump, ultimately achieving speed adjustment n. 2. Angular Displacement Sensor Design The high-performance measurement requirement of the diesel engine electronic governor for angular displacement is ensured by the displacement sensing element and signal conditioning circuit of the angular displacement sensor. Therefore, the angular displacement sensor design should be divided into displacement sensing element design and signal conditioning/conversion circuit design. 2.1 Structural Design Based on the working principle of the differential transformer, this paper applies the differential transformer to the angular displacement sensor design. The coil assembly and its disk schematic diagram of the angular displacement sensor are shown in Figure 2. The coil assembly consists of a primary coil, two symmetrical secondary coils, a base, and a frame. The frame is made of cylindrical insulating material and uniformly wound with insulated enameled wire of diameter D=0.1mm (320 turns for the primary coil and 640 turns for each of the two secondary coils). The three coils are fixed by the iron core and the base, forming part of the magnetic circuit. The eccentric disk (equivalent to the iron core of a linear differential transformer) is fixed to the shaft. When the eccentric disk is in the middle position, the magnetic induction intensity of the two secondary coils is the same. As the shaft rotates, the eccentric disk rotates accordingly. The magnetic induction intensity on the side of the eccentric disk that rotates is greater than that on the other side. Therefore, the output signal changes with the rotation of the eccentric disk. 2.2 Signal Conditioning Circuit Design Currently, the displacement signal conditioning circuits in electronic speed controllers mostly use phase-sensitive detector circuits and differential rectification circuits. The former has stringent requirements for circuit conditions, affecting the detection accuracy; the latter is built with discrete components, which is not standardized. Furthermore, it suffers from drawbacks such as low integration, complex structure, poor linearity, difficulty in handling zero point, numerous components, and poor reliability. Figure 3 is a block diagram of the angular displacement sensor control. In the figure, the two ends of the primary coil of the angular displacement sensing element are connected to the input ports of the highly integrated new differential transformer signal conditioner AD598 in the displacement sensor signal conditioning circuit, respectively, to input the excitation voltage signal; the two ends of the two reverse-connected secondary coils are connected to the output ports of AD598, respectively, to generate the output voltage signal. In order to better solve the problems of zero point error, drift, and hysteresis, this paper designs an angular displacement sensor signal conditioning circuit with AD598 as the core. The peripheral circuit of AD598 mainly includes three major circuit modules. Its functions are as follows: Since the AD598 uses a bipolar ±12V power supply, a filter protection circuit module composed of diodes, electrolytic capacitors, resistors, and other components is designed to filter and protect the power supply, thereby preventing power supply interference from the conditioned signal; a signal symmetry circuit module composed of potentiometers can adjust the magnitude and symmetry of the positive and negative voltages after sensor signal conditioning; a signal amplification circuit module composed of potentiometers and capacitors adjusts the magnitude of the output voltage after signal conditioning and further filters it; the AD598 angular displacement signal conditioner circuit itself determines the excitation frequency and system bandwidth. This signal processing circuit is easy to adjust and widely applicable. 3 Experimental Verification 3.1 Parameter Matching Experiment Since the angular displacement sensor and the angular displacement electromagnetic actuator (for the design of the angular displacement electromagnetic actuator drive circuit, please refer to the literature) are coaxially mounted, they have advantages such as small size and working space. However, the structural positioning and parameter matching of the two are difficult during installation. Therefore, an angular displacement sensor and angular displacement actuator matching experiment is conducted to detect the zero point calibration, rotation direction, and optimal matching parameters. 3.1.1 Structural Positioning: As shown in Figure 2, the angular displacement sensor and its eccentric disk are coaxially mounted, with their center lines OO' aligned. This position is the zero-point calibration position of the angular displacement sensor. The clockwise rotation of the eccentric disk relative to the angular displacement sensor represents the positive direction of its movement; the counterclockwise rotation of the eccentric disk relative to the angular displacement sensor represents the negative direction of its movement. Since the angular displacement sensor and the angular displacement electromagnetic actuator are coaxially mounted and secured with fixing pins, the zero point and rotation direction of the angular displacement electromagnetic actuator are the same as those of the angular displacement sensor. 3.1.2 Experiment: The parameters of the electronic speed controller system are adjusted by changing the components of the displacement conditioning circuit and the mounting angle of the potentiometer. The adjustment results are as follows: When the angular displacement sensor is in its maximum negative position, the voltage after conditioning is -5V; the input voltage to the voltage-frequency converter is 0V, corresponding to a diesel engine speed of 0 r/min, and the rotation angle of the angular displacement electromagnetic actuator is -32°; when the angular displacement sensor is in its maximum positive position, the voltage after conditioning is 5V; the input voltage to the voltage-frequency converter is 5V, corresponding to a diesel engine speed of 3000 r/min, and the rotation angle of the angular displacement electromagnetic actuator is +32°; when the angular displacement sensor is in its zero position, the voltage after conditioning is 0V; the input voltage to the voltage-frequency converter is 2.5V, corresponding to a diesel engine speed of 1500 r/min, and the rotation angle of the angular displacement electromagnetic actuator is 0°. The angular displacement electromagnetic actuator rotates from its maximum negative position to its maximum positive position. The output voltage signal of the angular displacement sensor is detected every 2° of rotation. The performance curves of the angular displacement electromagnetic actuator and the angular displacement sensor are shown in Figure 4. As shown in the figure, the angular displacement electromagnetic actuator and the angular displacement sensor have good matching characteristics. When the rotation angle θ of the angular displacement electromagnetic actuator varies between -32° and 32°, the output voltage U of the angular displacement sensor varies between -4.5° and 5.0°, and shows a linear relationship with a linearity of 0.3%. During the experiment, its dynamic response was observed to reach 0.20s. 3.2 Inner Loop Experiment As shown in Figure 1, the working principle of the inner loop module is: the voltage signal Ur, which is the difference between the theoretical speed and the speed feedback from the speed sensor, is synthesized by the outer loop (PID) control module and the angle feedback signal from the angular displacement sensor. After passing through the inner loop (PI) control module, it controls the angular displacement electromagnetic actuator to rotate a certain angle θ. The system performance curve of the inner loop module is shown in Figure 5(a). As shown in the figure, when the voltage signal Ur of the speed deviation changes between -5 and 5V, the angular displacement electromagnetic actuator exhibits linear rotation within the range of -32° to 32°, with a linearity of 0.%. During the experiment, the dynamic response of the inner loop system reached 0.2s, and the repeatability error reached 2.0%, which proves that the inner loop system is working normally. 3.3 Outer Loop Experiment The outer loop PID control scheme diagram is shown in Figure 1. It represents the control relationship between the given speed signal n1 and the feedback signal n2 from the speed sensor, which are processed through a series of steps and then output by the voltage-to-frequency converter f. The performance curve of the outer loop is shown in Figure 5(b). As shown in the figure, when the voltage signal of the given speed n1 changes between 0 and 5V, the output frequency f of the voltage-to-frequency converter exhibits linear change within the range of 0 to 6kHz, with a linearity of 0.4%. During the experiment, the dynamic response of the outer loop system reached 0.5s, the repeatability error reached 3.0%, and the hysteresis error reached 3.5%, thus indicating that the outer loop system is working normally. 4 Conclusions This paper uses a diesel engine electronic governor system simulation experimental device as a platform. Through experiments on the parameter matching of the developed angular displacement sensor with the corresponding angular displacement electromagnetic actuator, as well as inner and outer loop experiments of the electronic governor system, the following conclusions are drawn: (1) The structure and displacement signal conditioning circuit design of the novel angular displacement sensor proposed in this paper are very suitable for use in electronic governors. At the same time, its optimal working parameters have also been verified; (2) When the designed angular displacement sensor is used in the electronic governor system, the system works normally. The dynamic response and steady-state performance indicators can meet the working requirements of normal speed regulation of diesel engines.