Modeling and Dynamic Characteristics Analysis of an Open-Center Pressure Control Valve for Heavy-Duty Automatic Transmission Considering Thermal Effects

An innovatively designed open-center pressure control valve with fast response, excellent flow-through capability, and outstanding reliability is utilized in gearshift hydraulic systems for heavy-duty vehicle automatic transmissions. This paper aims to demonstrate the influences of fluid temperature (20∼120°C) on the dynamic characteristics of critical components and the physical mechanism of their interaction with the pressure regulation process by using computational fluid dynamics (CFD) simulation and experimental research methods. Firstly, the flow area equation, the dependence of the flow coefficient on the fluid temperature, and the variation law of the jet angle along with the opening are derived by CFD simulation for a hollow spool with typical structural characteristics. Furthermore, a mathematical model is proposed to predict the gearshift performance with full consideration of temperature-induced variations in the flow force and viscous friction of the pressure control valve core control elements. Finally, the experiment is conducted to acquire the influence pattern of fluid physical parameters and valve throttling characteristics on the displacement, velocity, and clutch pressure. The results indicate that the simulation results of the clutch pressure are consistent with the data obtained from the real test bench with a maximum error of less than 5.6%; the spool inlet has the typical characteristics of a two-stage throttling, the inlet flow coefficient and the spool displacement approximately satisfies the exponential law variation, there is an approximately linear relationship between jet angle and displacement for larger spool openings; The pressure regulation time at an oil temperature of 120°C is 35% shorter than that at 20°C, but the starting and stopping pressure of the buffer boosting stage does not change significantly due to the change of oil temperature.