Pressure Pulsation Modelling of an External Gear Pump under Coupled Side-Clearance Leakage and Gear Tooth-Breakage Modulation

Abstract

Pressure pulsation in external gear pumps arises from periodic control-volume variation, intermittent communication between tooth spaces and inlet/outlet chambers, and shaft-rotation modulation of tooth-meshing components. Existing frequency-modulation models describe outlet pressure spectra under nominal conditions but rarely consider compound degradation. This paper develops an analytical model incorporating two physically meaningful fault parameters: a side-clearance parameter representing leakage-path enlargement caused by side-plate wear, and a tooth-breakage disturbance parameter representing additional hydraulic excitation from local tooth damage. Within the conventional rotational-frequency modulation framework, the model integrates leakage dynamics, outlet pressure evolution, rotational harmonics, tooth-meshing harmonics, and modulation effects. Side-plate wear is modelled as leakage-induced amplification of meshing components, whereas tooth breakage is represented by an additional periodic pressure disturbance and phase deviation. The resulting Fourier-series formulation extends the nominal pressure model to compound fault conditions. It shows that side-clearance growth mainly changes the amplitude envelope of meshing harmonics, while tooth breakage affects both amplitude and frequency characteristics. Experimental validation based on pressure-spectrum analysis, harmonic tracking, sideband observation, and model fitting supports the proposed mechanism without relying on unverified operating parameters or artificial diagnostic results.