Page 24 - needle bearings

Calculation of Bearing Loads
NTN

3. Calculation of Bearing Loads

3.1 Load acting on shafts
The loads acting on the shaft to be supported with the
bearing must be determined for calculation of bearing
loads. These loads include the self-weight of rotor assy,
loads inevitably resulting from a machine in running,
loads arising from power transmission, etc. These loads
are mostly difficult to calculate though some of them can Ks
be calculated numerically and theoretically.
The following paragraphs describe how to calculate
the loads acting on a power transmission shaft as one of Kt
the main bearing applications.
3.1.1 Load acting on gears Fig. 3.1 Load acting on spur gear
The loads acting on gears can be divided into
tangential load (Kt), radial load (Ks) and axial load (Ka).
The magnitude and acting direction of each load differ
depending on the types of gear. This paragraph
describes how to calculate the loads acting on parallel
shaft gears and cross shaft gears for general use.
For calculation of the loads acting on other gears, feel
free to contact NTN for inquiry.
Ks Ka
(1) Load acting on parallel shaft gear
Figs. 3.1 to 3.3 illustrate the loads acting on spur gear
and helical gear which are used with a parallel shaft. The
Kt
magnitude of each load can be determined using the
formulas (3.1) to (3.4).
Fig. 3.2 Load acting on helical gear

6
6
19.1ʷ10 ɾHP 1.95ʷ10 ɾHP
ʢ
ʣ
Ktʹʕʕʕʕʕʕʕʕʕ ʕʕʕʕʕʕʕʕʕ ʜʜʜʜʜʜ (3.1)
Dpɾn Dpɾn
KsʹKtɾtanЋ(Spur gear) ʜʜʜʜʜʜʜʜʜʜʜ(3.2a) Kt
tanЋ Ks
ʹKtɾʕʕʕʕ (for helical gear) ʜʜʜʜʜʜʜʜ(3.2b) Kr
cosЌ
Krʹ˽ʉʉʉ ʜʜʜʜʜʜʜʜʜʜʜʜʜʜʜʜ(3.3a) Dp
2
2
Kt Ks
KaʹKtɾtanЌ(for helical gear)ʜʜʜʜʜʜʜʜʜʜ(3.4)
where,
Kt ɿTangential load acting on gear
(Tangential force) N (kgf)
Ks ɿRadial load acting on gear Fig. 3.3 Composite radial force acting on gear
(separating force) N (kgf)
Kr ɿLoad acting perpendicularly on gear shaft
(composite force of tangential force and Table 3.1 Gear factor fz
separating force) N (kgf)
Types of gear fz
Ka ɿParallel load acting on gear shaft N (kgf)
HPɿTransmission power kw Precision ground gears 1.05ʙ1.1
n ɿRotational speed r/min (Pitch and profile errors of less than 0.02mm)
Dp ɿPitch circle diameter of gear mm
Ordinary machined gears
Ћ ɿGear pressure angle (Pitch and profile errors of less than 0.1mm) 1.1ʙ1.3
Ќ ɿGear helix angle

Actual gear load is determined by multiplying the
theoretical load by the gear factor described in Table 3.1,
because vibration and shock are added to each
theoretical load determined by the above formulas.

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