The power loss of the gearbox mainly includes oil stirring loss, wind resistance loss, gear meshing loss and bearing loss.
1.Loss of oil stirring power
The oil stirring loss of the gearbox mainly comes from the friction loss between the lubricating oil and the internal components of the gearbox. The influencing factors of the oil stirring loss mainly include the viscosity of the lubricating oil, the input speed, the working temperature, the helical angle of the gear and the oil immersion depth of the gear.
The calculation formula of oil stirring loss at high speed given by British standard AGMA iso14179-1 is adopted. Oil stirring loss includes 3 parts: oil stirring loss related to the outer diameter of the optical axis (such as the shaft); Oil mixing loss related to the smooth surface of the disc (such as the two sides of the gear); Oil mixing loss related to the tooth surface (such as the outer circumferential surface of large gear and small gear). The total power PC of oil stirring loss can be expressed as:
Where: FG – gear immersion factor; V – kinematic viscosity, CST; Ni – working speed of element, R / min; D0 – external diameter of element, mm; L – element length, mm; AG – configuration constant; B – tooth width, mm; RF – roughness factor; β— Helical angle of helical gear, when β ＜ At 10 °, β The value is taken as 10 °.
2.Wind resistance power loss
The wind resistance loss is the energy loss caused by the rotation of the pinion and the large gear in the oil-gas space of the gearbox. The factors affecting the wind resistance loss mainly include the diameter of the gear, the concentration of oil mist in the gear box and the speed of the gear. For the gear transmission of high-speed wheel drive system, the wind resistance loss accounts for a large proportion of the total power loss, so the analysis of the wind resistance loss can make the analysis of the total efficiency of the gearbox more accurate.
Anderson and Loewenthal gave the calculation method of wind resistance loss. This method considers the dynamic viscosity of the oil-gas mixture in the gear box, and then obtains the calculation formula:
Where: PW – wind resistance loss power, kW; B – gear width, m; R – radius of gear indexing circle, m; N – gear speed, R / min; μ— Dynamic viscosity of oil-gas mixture in gearbox, CP.
3.Average efficiency of helical gear engagement
The average efficiency formula of helical gear meshing transmission is derived by integral method, and the average efficiency formula of helical gear meshing is obtained as follows:
Where: K – coefficient of Z1, h * an, B; R1 — about h * an, Mn, Z1,α t. B function; R2 — about Mn, h * an, Z1, α t. B.
It can be seen from the formula that the meshing efficiency of helical gears is related to the number of driving teeth Z1, the number of driven teeth Z2, the transmission ratio I, and the helix angle β， Normal surface modulus Mn, tooth width b, normal surface pressure angle α n. The normal tooth crest height coefficient h * an is related to the friction coefficient F and other parameters.
4.Bearing power loss
Bearing efficiency η B is mostly measured directly by experiments. Under the condition of good lubrication, the efficiency value of rolling bearing is about 0.980-0.995; The efficiency value of the sliding bearing is about 0.970 to 0.990. Therefore, bearing efficiency η B is 0.990.