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Abstract
The electromagnetic actuator is the core component of modern fuel injectors, directly determining the response speed and accuracy of fuel injection events. However, under high-pressure and high-frequency working conditions, limitations in actuator dynamics often lead to delayed response, hysteresis, and unstable fuel delivery. This study proposes an improved design of the electromagnetic actuator to enhance its dynamic response characteristics, supported by both simulation and experimental validation.

1. Introduction
As emission regulations become increasingly stringent, fuel injection systems must achieve higher precision in injection timing and quantity. The dynamic response of the electromagnetic actuator is critical, as it governs needle valve motion and directly influences injection duration and repeatability. Conventional actuators often suffer from high inductance, insufficient magnetic force at small gaps, and slow armature return, which restrict overall system performance.

2. Design Improvements
The proposed design focused on optimizing three aspects:

• Magnetic circuit structure: The actuator core and armature geometry were redesigned to minimize magnetic reluctance and enhance flux density. A tapered pole piece was introduced to increase the magnetic force during initial attraction.

• Coil parameters: The number of turns and wire diameter were adjusted to balance inductance and current rise rate, ensuring faster energization.

• Spring preload and damping: The restoring spring was optimized to provide sufficient return force without causing excessive delay or oscillation.

Finite element analysis (FEA) of the electromagnetic field was conducted to evaluate magnetic flux distribution and force characteristics, ensuring improvements before prototyping.

3. Dynamic Response Simulation
A coupled electromagnetic–mechanical model was developed to analyze armature displacement and needle valve motion under different current excitation profiles. Results showed that the improved actuator design reduced response delay by approximately 18% and improved opening speed by 22% compared to the baseline model. Additionally, damping optimization effectively suppressed oscillatory motion, enhancing response stability.

4. Experimental Verification
A high-pressure injector test bench was established, integrating current drivers, displacement sensors, and high-speed data acquisition. Key response parameters such as opening delay, closing delay, and steady-state stability were measured. Experimental results confirmed the simulation predictions: the improved actuator achieved faster response, reduced hysteresis, and exhibited more consistent behavior under cyclic operation. In particular, closing delay was shortened by 0.12 ms, which significantly contributed to injection accuracy.

5. Discussion
The combined simulation and experimental results indicate that actuator performance is highly sensitive to magnetic circuit design and coil parameters. While stronger magnetic force improves response speed, excessive current may increase heat generation. Therefore, an optimal balance between force, efficiency, and thermal stability is necessary. Future work may involve integrating advanced materials with higher magnetic permeability and employing intelligent current control strategies to further enhance performance.

6. Conclusion
This study demonstrates that by redesigning the magnetic circuit, optimizing coil parameters, and adjusting spring characteristics, the dynamic response of injector electromagnetic actuators can be significantly improved. Both simulation and experimental verification confirm the validity of the proposed design. These improvements not only enhance injection accuracy but also support the development of cleaner and more efficient engines.