*3.2.1 High-temperature operation*

The engine converts chemical energy into thermal/mechanical energy via the fuel-burning process. The engine operates at elevated temperatures due

to fuel burning. Engine bearings must have dimensional stability at elevated temperature in addition to other performance parameters. Bearing mounting and operating clearances are largely affected due to different materials and their expansion rates.

### *3.2.2 Varying loads and speeds*

Engine loads and speeds are varying during the operation. Bearing kinetic should be considered for varying speeds and loads. Rolling bearings use on crankshaft and camshaft is increased in recent time. However, at the connecting rod end, needle bearings or journal bearing are commonly used in an engine for multiple reasons including varying load and speeds.

### *3.2.3 Demanding operating conditions like contamination*

Crankshaft bearings are positioned bottom of the crankcase in the engine. The engine piston is reciprocating (sliding motion), so the wear of the engine part is not uncommon. However, wear particles are mixed in the oil contaminate the oil. Engine oil is the primary source of lubrication to bearings. The contaminated oil is having a negative influence on bearing operation and due consideration should be given to have good performance of bearing in this condition. Special heat treatment can be considered on the bearings rolling elements and raceways in such demanding operating conditions. Optimum ball pass frequencies selection is also important to ensure the hunting of rolling elements is not affecting the raceways or rolling element.

#### *3.2.4 Mounting and dismounting of bearings*

Engine bearing mounting and dismounting is one of the important considerations, not only from a service, assembly perspective but also from the operational performance perspective. Appropriate fits must be applied to the bearing to ensure bearing is loaded and operates in favorable clearance zone. Wrong selection of fits can lead to catastrophic damages to bearing with prolonged use.

#### **3.3 eMotors bearings**

Battery electric vehicles are using motors as prime mover of the vehicle. Hybrid powertrain vehicles are also uses motors to propel the vehicle. Traction motors used in vehicles are having many special technical requirements that are different from conventional motors.

Some typical requirements are discussed in the following session,

#### *3.3.1 Bearing arrangement*

Traction motors bearing arrangement plays an important role in bearing selection. In most of the traction motors application two bearing arrangement (drive and non-drive end) is preferred. However, integration of transmission and motors is also common practice in electric powertrain due to which three inline bearings arrangement is also implemented.

The bearing arrangement adds complexity to the overall bearing system and the need for the appropriate distribution of bearing loads. Comparatively, two bearing arrangement is simple compare to three bearings arrangements.
