Conservation law-based air mass flow calculation in engine intake systems

In current engine controls, a number of control methods are based on the air charge estimation in engine intake systems. Since the derivative of the air mass flow through the throttle valve goes to infinity when the intake pressure is close to the upper stream pressure, the relatively large numerical error or oscillation occurs near the singularity point when using common algorithms. This paper develops an effective algorithm for calculating the air mass flow in engine intake systems. Utilizing the high-level model description (HLMD), the system is described by mass and energy conservation laws and therefor the singularity issue at the zero pressuredifference point is transformed into a singularity issue at the corresponding energy point. Then, the implicit midpoint rule, a special symplectic discrete method, is selected to integrate the energy and mass conservation system. The simulation results show that the numerical behaviour of the air mass flow is significantly improved at the singularity point by using the proposed algorithm. The experimental results also verify that the qualitative behaviour of the air mass flow calculated by the proposed algorithm is consistent with the actual physical system.