**3. Aggregates bearings and its requirements**

Application and intended function in the aggregate is having an influence on the selection of bearings as well as on the performance of bearing. It is important to understand the bearing working environment, technical requirements, and application details for optimizing the performance [7]. Different aggregate applications are having different technical requirements that need to be fulfilled by bearing for optimum performance of the system. In this section, different aggregate and technical requirements of bearing in these aggregates are discussed,

#### **3.1 Transmission system bearings**

Automobile transmission facilitates speed and torque variation as per vehicle requirements and support engine to run in optimum performance range. The transmission system is having gears, shafts, shift system, and bearings arranged in the housing which perform speed and torque variation function together in coordination with the control system.

Transmission bearings are having multiple requirements to achieve the desired functions, some of them are mentioned below,

#### *3.1.1 Axial and radial load carrying capacity*

Transmission bearings experience combined axial and radial loads during the operation based on types of gears as well as shaft arrangement. The magnitude of the load depending upon the bearing position, gear arrangement, and torque transmission. The transmission bearings must be capable of handling these varying speeds and loads.

#### *3.1.2 Lower space and weight*

Vehicle powertrains are becoming compact due to the availability of space and emphasize on the reduction of the overall weight of vehicles. Power dense bearings that are capable to carry higher loads in a smaller size are the key selection criteria of bearings for modern transmission. Power density for the bearing is achieved with the usage of better material cleanliness from commonly used bearing materials like 100Cr6, 52100 with stringent specification of nonmetallic inclusions, oxygen content etc., optimized geometry, and precise manufacturing of bearings. It is worth mentioning here that each bearing manufacturer are having its own material specifications customized based on common bearing material chemistry. Most common bearing materials are SAE 52100, DIN 100Cr6, SUJ1, SUJ2 and many more.

#### *3.1.3 Optimized friction*

System efficiency is largely influenced by friction. Bearing contributes to the transmission system largely. Generally, Sealed bearings are having more friction compared to open bearings. Transmission bearings selection must have consideration of the friction.

#### *3.1.4 Lower NVH*

Modern automobiles particularly battery electric vehicles operate quietly. In the case of ICE, the engine noise suppresses some of the bearing noise, however, in modern automobiles bearings, noise is one of the major concerns. It is expected bearings with lower noise are implemented in the transmission system. In addition to noise, vibration and harshness are also to be given due consideration for the transmission bearings.

Automobile manufacturers specify the system level NVH requirements and typically bearing noise requirements are derived from system level requirements. However, very few manufacturers are having clearly defined NVH specifications for bearing. It is common practice in bearing industry to specify the bearing vibration level and measure at the end of the bearing assembly line. Each bearing manufacturer is having its specification for noise quality level of bearing. Low dB, Gen C, Q44 and other bearing manufacturer internal nomenclature of bearings quality

#### *Role of Bearings in New Generation Automotive Vehicles: Powertrain DOI: http://dx.doi.org/10.5772/intechopen.94222*

classes have been developed and specified accordingly [8]. Low-frequency noise is barely audible while high-frequency vibration does not audible to human ear. Hence noise problems at low frequency are categorized as "vibration problems" and at high frequency vibration are as "noise problems". As a rule of thumb, the arbitrary border separating vibration problems from noise problems is 1000 Hz. In other words, below 1000 Hz is vibration and above 1000 Hz is considered as sound or noise [8].
