# An Electric Load Simulator for Engine
## 1 Introduction  
The conventional valvetrains with camshafts use fixed cam profiles to get a reasonable compromise between speed stability, fuel economy, and torque performance. However, cam-driven valvetrains do not have efficiencies as large as camless valvetrains over a wide range of engine operation [1]. Camless valvetrains can achieve variable valve timing and opening duration by controlling individual valves. Therefore, in the face of increasingly scarce oil resources and serious environmental problems, studies on camless valvetrains have important research significance to improve the power and economy of automobiles and to reduce energy consumption and pollutant emissions [2]. During the engine exhaust stroke, there is a large pressure difference between the cylinder and exhaust passage when the exhaust valve starts to open. Under these circumstances, the exhaust valve is subjected to large gas force. Depending on the operating conditions of the engine, the combustion pressure in the combustion chamber changes between 0 and 7 bar when the exhaust valve begins to open [3]. Once the exhaust valve is opened, the exhaust gas flows out of the combustion chamber, and the pressure difference between the upper and lower end faces of the exhaust valve is gradually released [4]. As the exhaust valve opens, the gas force tends to decrease to zero gradually from a higher initial value [5]. [PERSON] and other scholars from the University of British Columbia in Canada conducted research on gas force. For a typical valve with a diameter of 25 mm, the initial pressure during the exhaust stroke is 5 bar, and the initial gas force acting on the valve is 250 N. [PERSON] and other scholars at the University of Alberta in Canada proposed that the energy lost by gas force is roughly the product of the valve lift and half of the initial force. Therefore, the gas force with an initial value of 250 N will dissipate 1 J of energy loss at a valve lift of 8 mm, which will dissipate half of the availablepotential energy during valve motion [3; 4; 5]. On the other hand, the gas force has a large influence on the trajectory and small contact velocity of the valve. The small contact velocity is correlated with noise and increased component wear, which is difficult to achieve under real operating conditions depending on various engine speeds and loads, as well as unknown gas forces acting on the valves [6; 7; 8; 9]. In order to test the static performance and dynamic characteristics of the camless valvetrains under load, to save research costs, and to shorten development cycle, it is necessary to carry out simulation and experimental research to reproduce the actual gas force of the valve. Two methods are generally available: physical test and semi-physical test. In the physical test, the engine needs to be burned and work. The stability of the control system is evaluated by actual measurements. This method requires much material, human, and financial resource, so it is difficult to collect the test data. The semi-physical test can simulate the performance of the valve under load by adopting the load simulator to reproduce gas force and load it onto the valve without the engine burning and working. This method can save research and development cost and improve test reliable. It turns destructive experiments into predictive studies under laboratory conditions and helps researchers foresee and detect the problems that occur in the mechanism and control system before they actually operate [10; 11; 12; 13]. [PERSON] and [PERSON] adopted the electro-hydraulic load simulator to generate desired torque profiles. A novel fuzzy logic controller was proposed to improve the transient performance and robustness of the load simulator control system. Simulation and experimental results showed that the load simulator could get faster and more accurate dynamic responses by using the designed controller, compared with the fixed fuzzy controller when the operating point and external disturbances were changed [14].