AMT | Application of Powder Metallurgy Structural Parts in Crescent-shaped Gear Pump

Date：2025-07-21   Views：1011

This type of gear pump is most commonly used in automotive transmissions. At first glance, the pump's gears appear to be a pair of ordinary large-pitch gears. The crescent-shaped gear design (Figure 9-40) is selected to meet the requirements of small volumetric output, high speed, minimal noise level, and lowest cost. However, when compared to the power transmission gears in the transmission, they are quite extraordinary in many aspects. The selection of large-pitch gears is based on the pump's displacement requirements rather than strength. Given the light load, wear resistance, and low cost considerations, gears are often manufactured using powder metallurgy materials. To reduce production costs, the inner gear was first converted to a powder metallurgy part, while the outer gear was still produced by tube drawing. Later, considering cost and material utilization efficiency, the outer gear was also converted to a powder metallurgy part.

Figure 9-40 Crescent-shaped Gear (this type of gear pump is most commonly used in automotive transmissions)

Due to the pump's unique internal sealing requirements, the outer diameter of the inner gear and the inner diameter of the outer gear must be machined to precise tolerances (Table 9-7). Additionally, the proper alignment of the two gears within the pump housing depends on the inner diameter of the inner gear and the outer diameter of the outer gear being machined to precise concentricity tolerances. Finally, the width, parallelism, and straightness of the two gears must be precision machined to ensure satisfactory sealing and appropriate operating clearances.

The material requirements for the two gears are not high. To reduce production costs and simplify the design of specific transmissions, steel or anodized die-cast aluminum can be used as pump cover materials. To enhance the wear resistance of the housing and cover, precision-machined rotors are typically tin-plated. Another material combination involves heat treatment to eliminate wear between the iron gears of the pump and the aluminum housing.

Table 9-7 Manufacturing Requirements for Crescent-shaped Gear Pumps (Dimensional Requirements)

 Note: The values in the table are a compilation of technical specifications from different gear pump manufacturers.