The speed of the input shaft of a wind turbine gearbox is generally 10-20 rpm. Due to the relatively low speed, it is often difficult to form an oil film on the input shaft bearing. The role of the oil film is to separate the two metal contact surfaces when the bearing is running to prevent direct metal-to-metal contact. We can introduce a parameter λ to characterize the lubrication effect of the bearing (λ is defined as the ratio of the oil film thickness to the sum of the roughness of the two contact surfaces).

If λ is greater than 1, it means that the thickness of the oil film is sufficient to separate the two metal surfaces and the lubrication effect is good; if λ is less than 1, it means that the thickness of the oil film is not sufficient to completely separate the two metal surfaces and the lubrication effect is not ideal. If the bearing is running under poor lubrication, it may be damaged. Since wind turbine gearboxes generally use circulating lubricating oil with a viscosity of ISOVG320, if λ is found to be less than 1, we can generally only improve the lubrication effect by reducing the roughness of the bearing raceway and roller.

In addition, when designing the gearbox, the support bearing should try to avoid the size of the bearing on one end being too small. In actual application analysis, we found that even if the life span meets the requirements, this design will cause the linear speed of the small bearing to be very low, and the oil film will not be able to form.