# Demand Analysis of Lubricating Oil in Spur Gear Pairs
## 5 Effect of Working Conditions  
The contact and oil film states between the tooth surfaces under different working conditions, including the input speed and input torque, exhibit significant differences. This situation results in different oil volumes for lubrication and cooling. Therefore, the influence of working conditions on the oil volumes for lubrication and cooling during the meshing process should be examined.  
An analysis method similar to that described in Section 4 is used to investigate the influence of input speed on lubricating oil demand. The input speeds are set to 4000, 8000, 10,000 and 12,000 rpm. The parameters of the gear and input torque are identical to those described in Section 3. The variations in the oil volume for lubrication during the meshing process at different input speeds are obtained through a series of simulations, as shown in Figure 9a.  
This figure indicates that the input speed of the gear has no effect on the meshing characteristics of the gear. The oil volume for lubrication increases as the input speed increases because the entrainment velocity and oil film thickness of each meshing tooth during the meshing process increases as the input speed increases. A series of simulations is performed to examine the influence of different input speeds on the friction coefficient during the meshing process, as shown in Figure 9b, and partially enlarged images are obtained concurrently.  
Oil film thickness and relative slide velocity increase as the input speed increases. The friction coefficient decreases as oil film thickness increases, but it increases as relative slide velocity increases. Figure 9b illustrates that the friction coefficient decreases slightly as the input speed increases because of the considerable influence of oil film thickness on the friction coefficient. The oil volume for cooling at different input speeds during the meshing process is compared, as shown in Figure 9c with a partially enlarged image.  
This figure indicates that the oil volume for cooling increases as the input speed increases because the relative slide velocity exerts a significant influence on the oil volume for cooling although the friction coefficient decreases as input speed increases. The oil for cooling increases as the relative slide velocity increases.  
To compare lubricating oil demand at different input torques during the meshing process, the input torques are set to 40, 60, 80 and 100 Nm. The parameters of the gear and input speed are the same as those described in Section 3. The variations in the oil volume for lubrication during the meshing process at different input torques are obtained using a series of simulations, as shown in Figure 10a.  
This figure illustrates that the oil volume for lubrication decreases as the input torque increases because oil film thickness decreases as the input torque increases. The thin oil film leads to an increase in the friction coefficient as the input torque increases, as shown in Figure 10b. A series of simulation models is used to examine the influence of different input torques on the oil volume for cooling during the meshing process, as shown in Figure 10c.  
Figure 9: Oil volume for lubrication (**a**), friction coefficient (**b**) and oil volume for cooling (**c**) at different input speeds during the meshing process.  
The oil volume for cooling increases as the input torque increases due to the friction coefficient, as shown in Figure 10c.