# An Electric Load Simulator for Engine
## 2 System Design  
### System Configurations  
The target force that the electric load simulator is required to reproduce is not very large, but the requirements of the bandwidth and accuracy are very high. On the other hand, the bearing object is the exhaust valve, which has a certain motion curve, the load simulator needs to follow the valve passively for linear motion. Therefore, the electric load linear simulator was selected as the load device to implement gas force on the exhaust valve under semi-physical conditions by comparing the advantages and disadvantages of different load simulators, as shown in Table 1[17; 18; 19; 20].  
The schematic diagram of the electric load simulator is shown in Figure 1. It was mainly composed of an electromagnetic actuator, a force sensor, an exhaust valve, a DSP controller, and a control computer. The exhaust valve was the carrying object. It was subjected to electromagnetic force F\({}_{mag}\), spring force F\({}_{s}\), damping force F\({}_{c}\), inertial force F\({}_{a}\), and gas force F\({}_{g}\) during the exhaust stroke. It was coaxially coupled to the electromagnetic actuator and the force sensor through the connecting shaft. The force sensor was connected with the electromagnetic actuator and exhaust valve by a bolt to measure the output force of the electromagnetic actuator. The concentricity of the force sensor, electromagnetic actuator, and exhaust valve was consistent to transmit the same displacement, speed, and force.  
The electromagnetic actuator was used to simulate gas force F\({}_{g}\) of the exhaust valve. When the exhaust valve moved in a certain displacement curve, the electromagnetic actuator followed the exhaust valve passively through the connecting shaft to achieve passive follow-up of the displacement. At the same time, the electromagnetic actuator simulated the gas force and loaded it onto the exhaust valve to realize the closed-loop control of the output force through the force sensor.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type** & **Advantages** & **Disadvantages** & **Applications** \\ \hline Mechanical load & Simple structure; no & Unable to track & Small loop experiment \\ simulator & extra torque & aerodynamic loads & Large loop experiment \\ Electro-hydraulic load & High operating & Complex structure; low & Large loop experiment \\ simulator & frequency; strong & energy efficiency & Small and medium load \\  & capability of output & & laboratory \\ Electric load simulator & Strong tracking ability; & Poor load accuracy & Small and medium load \\  & high resolution & & laboratory \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparisons of different load simulators.  
Figure 1: Schematic diagram of the electric load simulator.  
The control system requires high precision and fast response time to ensure the load simulator can reproduce gas force characteristics while moving with the exhaust valve. Since the DSP (Digital Signal Processing) controller has powerful digital signal processing capabilities, relatively complete event management capabilities, and embedded control functions, it is widely used in industrial control. Therefore, DSP was adopted as the core processor of the electric load simulator to use its rich peripheral design control system and powerful arithmetic processing capability. The signal processor and DSP controller were used to handle and convert signals to the control computer for further data analysis and to realize the control of output force.