An approach to determine the stable operating area for internal gear motors and pumps based on safe lubrication oil film thickness ☆

Designers and manufacturers always desire a simple method to verify the stable and unstable operating area for rotating machines at the early design stage. However, it is sometimes not easy due to lots of phenomena happened inside machines. This paper proposes an approach to determine the instability threshold for the internal gear motors and pumps based on the safe film thickness. By using the mobility method, the maximum eccentricity and the minimum oil lubrication film thickness can be determined, consequently, the minimum speed limit can be retrieved. From that, the stable operating area of internal gear motor and pump can be determined based on the lower speed limit. With proposal approach, the effect of geometry parameters on the stable operating area can be easily assessed. The numerical calculations of stable operating area are also compared to the experimental results of the stable operating area according to the manufacturer. The results show that the geometric parameters, e.g. radial clearance and L/D ratio, have significant effects on stable operating of the internal gear motors and pumps. These parameters, therefore, must be chosen correctly at the early design stage otherwise the stable operating area will be greatly reduced.