Investigation of the Churning Power Loss Mechanism in a Standard Straight Bevel Gear Transmission System Under Splash Lubrication

To elucidate the energy dissipation mechanism of a Standard straight bevel gear transmission system under splash lubrication, this paper proposes a churning power loss prediction model tailored to such systems. This model decomposes the total power loss into three parts, namely circumferential resistance, end face stirring, and extrusion loss in the meshing area, and combines the control volume method with the bevel gear slicing method to achieve an engineering approximate quasi analytical model of stirring power loss. A transparent visualization test rig for churning power loss was developed, and systematic experiments were conducted over a range of rotational speeds (1000–4000 r/min), the dimensionless immersion depth (defined as the ratio between oil level and gear pitch radius) (0.5–1.5), and lubricant dynamic viscosities (0.0085–0.21228 Pa·s). The results show that, as the speed increases from 1000 r/min to 4000 r/min, the total churning power loss rises from 135 W to 5524 W; meanwhile, the proportion of end-face drag loss decreases from 51.6% to 38.7%, whereas the contribution of squeeze loss in the meshing region increases from 48.2% to 61.3%. At 2000 r/min, when the dimensionless immersion depth increases from 0.5 to 1.5, the total power loss increases from 283 W to 1559 W, and the share of mesh-region squeeze loss rises from 44.5% to 58%, becoming the dominant dissipation component. Under high-speed conditions of 4000 r/min and dimensionless immersion depth of 1.0, increasing the lubricant viscosity from 0.0085 to 0.21228 Pa·s causes the total power loss to increase from 774 W to 8176 W, with the dominant loss mechanism gradually transitioning from viscous shear to hydrodynamic squeeze. The theoretical predictions and experimental data trends are roughly consistent, confirming the accuracy and applicability of the proposed model under a wide range of operating conditions, and providing a quantitative basis for energy optimization of high-performance bevel gear transmission systems.