Thermal analysis of hydro-pneumatic suspension system for dumper based on a lumped-parameter thermal model

Abstract: Hydro-pneumatic suspension is an important part of off-highway dump trucks. It represents a compromise between ride comfort and handling stability via its nonlinear character. Off-highway dump trucks generally use the single air chamber hydro-pneumatic suspension system to achieve a vehicle's reliability and economy. But the effect of temperature changes on the output force characteristics of the hydro-pneumatic suspension, which results in ride comfort and ride height, is one of the urgent problems in its design and use. This paper presents a thermodynamic study of the hydro-pneumatic suspension using a lumped parameter model. It is known that this method is used to solve thermal problems by analyzing thermal networks by analogy to electrical circuits. This method has been used for a long time to calculate the temperature rises in electrical and spacecraft systems. Different from other studies, the cylinder and the piston rod thermal capacitance are taken into consideration in this study. During the study, the suspension system is divided into a number of lumped components. Each component has a thermal storage and interconnections to neighbor components through a linear mesh of thermal resistances. The heat is generated by oil flows through the damping orifices and nitrogen compression. Then, based on the gas state equation and thermodynamic theory, the nonlinear equations of the thermal model are established, which originally contain the heat capacity of the cylinder, the piston, and the oil. The simulation analysis is carried out under the model. The results show that, except for the oil in the bottom of the piston rod, while considering the thermal capacitance of the cylinder and piston, the temperature of the suspension system rises slower than if those capacitances are ignored. A validation experiment is performed to confirm the predicted results. The oil temperature in the initial stage of the experiment decreased first and then increased, which is different from the calculated value's monotonically upward trend. This may be caused by the fact that the oil from the static to flow requires a certain amount of energy in the initial stage of the experiment, while the external input of energy is shortage. Due to the measurement error, the lack of detail in lumped element division, and some other reasons, there are some differences between the experimental data and calculated values, but the tendencies of the experimental and calculated temperature rise of the suspension system are the similar. The comparison results show that the proposed model can describe the thermodynamic state of the hydro-pneumatic suspension more accurately than previous methods. The thermal capacitance of the cylinder and piston will increase the hysteresis effect of temperature changes.