The heating of engine bearings is somewhat related to the engine rotation speed. During engine bearing selection, engineering technicians check the maximum and minimum rotational speeds of the bearings.
Checking the rotational speed takes into account factors such as the contact stress between the bearing rollers and the raceways, the centrifugal force under the rotational speed, and lubrication considerations. In these considerations, an inappropriate choice can lead to phenomena such as overheating of the motor bearings and excessively high temperatures.
It is important to note that when considering the upper and lower limits of motor bearing speed (maximum and minimum speeds), the impact of speed changes on bearing heating also needs to be taken into account.
Speed change conditions mentioned include starting, stopping, and acceleration/deceleration. In real operating conditions, this includes slow and fast speed changes as well as changes in the direction of rotation.
Typically, when a motor changes speed slowly in the same direction, the impact on the bearings is not significant.
First, the condition of frequent starts may involve unidirectional speed changes and rapid speed changes.
Secondly, it covers situations where the direction of rotation changes (forward and backward movement).
The main reason changing engine bearing speeds affects its heat generation is due to the impact of speed changes on oil film formation. We know that the formation of speed within the engine lubricating oil or bearing grease depends fundamentally on speed.
When the speed changes, there may be sliding friction between the bearing rollers and the raceway. Simultaneously, due to rapid fluctuations in speed or changes in direction, the internal lubrication film may not form effectively, resulting in direct contact between metal surfaces, leading to heat generation or bearing wear.
In the unidirectional speed change condition (speed change and frequent starts), if the engine bearings overheat, it can be checked whether the bearing selection is suitable for this condition.
In the case of speed changes, it is recommended to choose bearings with good cage resistance, preferably using cages made of lighter and softer materials. In this way, during bearing speed changes, the collision between the cage and the bearing rollers can be mitigated, consequently reducing additional damage and heat generation caused by this.
On the one hand, anti-wear additives can be selected for the lubricant to reduce friction, heat and wear caused by sliding friction between the various components within the bearing when the rotational speed changes.
For oscillating conditions, the bearing type needs to go through an additional verification process. Factors such as the static load of the bearing are considered, not just the rated fatigue life of the bearing.
For bearings with oscillating motion, it is essential to select a lubricant with extreme pressure additives to protect the friction surface when the rotational speed changes direction at low speeds.
When examining the above, it is evident that the focus is on lubrication considerations and improvements under unfavorable oil film forming conditions. The main objective is to form as much of an oil film as possible or, in cases where it is truly impossible to form an oil film, to use other measures (such as extreme pressure additives) to avoid direct contact and friction between the bearing metals. .
