Yoshiharu Inaguma

Oil temperature influence on friction torque characteristics in hydraulic pumps

This article presents a practical approach to the investigation of the influence of oil temperature on the friction torque in various types of hydraulic pumps using a mathematical model. Currently, an external gear, an internal gear or a vane pump is commonly used for an automatic transmission. These pumps have their own friction torque characteristics, which depend not only on pump-operating conditions such as operating pressures, pump speeds and oil temperature but also on structures and dimensions of the pumps. For various pumps, however, the friction torque characteristics can be represented by an identical mathematical model. In the pump-operating conditions, the oil temperature significantly and complicatedly affects them. The pump should be operated under conditions to obtain a higher mechanical efficiency, and the mathematical model is helpful to analyse how the oil temperature influences the friction torque. It is found that with an increase in oil temperature, the friction torque at a high pump speed decreases in a low oil temperature region, but it would not decrease in a high oil temperature region for all the tested pumps. This fact suggests that the pump overall efficiency would not improve at a high oil temperature, even if the volumetric efficiency does not go down.

A practical approach for analysis of leakage flow characteristics in hydraulic pumps

This article presents a practical approach to leakage flow analysing for various types of hydraulic pumps. In this study, the influence of pump-operating conditions such as operating pressures, pump speeds and oil temperature on the leakage flow characteristics is investigated and a mathematical model to calculate the leakage flow is proposed. Currently, an external gear, an internal gear or a vane pump is commonly used for an automatic transmission. These pumps have their own leakage flow characteristics, which depend not only on pump-operating conditions but also on structures and dimensions of the pumps. For various pumps having different constructions, the delivery pressure and the oil temperature differently affect the leakage flow characteristics and especially the delivery pressure also changes the clearances causing the leakage flow. A mathematical model for the leakage flow, which takes into account a change in the thickness of clearance according to the delivery pressure, represents accurately the actual leakage flow characteristics in various pumps. Also, it clarifies the influence of the pump-operating conditions on their leakage flow characteristics. In the external and internal gear pumps, the leakage flow would not approach zero due to an existence of the orifice flow leakage almost independent of the viscosity of oil, even at an extremely low oil temperature. This leakage flow influences significantly the volumetric efficiency at a low oil temperature in the gear pumps.

Friction of outer rotor affecting friction torque characteristics in an internal gear pump

This article presents the friction torque in an internal gear pump and the friction force between an outer circumference of an outer rotor and a body, which causes a significant loss, has been investigated. When in use at a high pressure, the pump has a large friction torque due to the friction force acting on the outer rotor circumference. This friction force is caused by imbalanced force acting on the outer rotor. As well as by a positioning suction and a delivery port, the force can be reduced by setting a suction pressure recess in a section of the outer rotor circumference. In this study, through the measurement of the friction torque in an actual pump and the pressure distribution on the outer circumference of the outer rotor, it is investigated how the suction pressure recess can change the force acting on the outer rotor. The actual internal gear pump without the suction pressure recess has a large friction torque, and it corresponds to a large force on the outer rotor, which is calculated from the pressure distributions on the inside and outside of the outer rotor. In addition, on the basis of the measured friction torque of the test pump and the force acting on the outer rotor, calculated using the results of the pressure distribution, the coefficient of friction between the outer rotor circumference and the body can be estimated.

Influence of leakage flow variation on delivery pressure ripple in a vane pump

This article describes the theoretical analysis and experimental verification of the influence of variations of leakage flow as well as ideal flow on delivery pressure ripple in a balanced vane pump. The analytical model for simulating the delivery pressure ripple of the pump is simplified. It is composed of only the ripple of the ideal flow based on the theoretical pump displacement determined from geometrical pump dimensions, the leakage flow variation dependent on the pump dimensions including clearances and pump-operating conditions, an oil chamber volume in the pump and the impedance of a hydraulic circuit with a throttle valve set close to a pump outlet. The purpose of this study is to predict the pump delivery pressure ripple at the design stage of the vane pump. This article reveals that the delivery pressure ripple can be theoretically predicted through the calculations of the leakage flow as well as the ideal flow. The waveform of the delivery pressure ripple calculated agrees well with the measured one. The leakage flow variation significantly affects the delivery pressure ripple and it can be also calculated accurately from the pump dimensions including the clearances and pump-operating conditions. In addition, the components of the leakage flow are clarified and their effects on the delivery pressure ripple are investigated.