Page 249 - Analysis and Design of Machine Elements

(a) modulus Gear Drives 227
(b) torque transmitted
(c) number of the teeth of a gear
(d) load factor

3 In order to improve the contact fatigue strength of tooth surface, we can _____.
(a) reduce the pressure angle
(b) increase the centre distance a
(c) reduce the face width factor d
(d) increase the gear modulus m

4 For a pair of gears with hardness less than 350HBW, we usually _________.
(a) select the hardness of the pinion tooth surfaces < the hardness of the gear tooth
surfaces
(b) select the hardness of the pinion tooth surfaces = the hardness of the gear tooth
surfaces
(c) select the hardness of the pinion tooth surfaces > the hardness of the gear tooth
surfaces
(d) have no restriction on the hardness of the pinion and gear tooth
surfaces

5 In a cylindrical gear transmission, if the pitch diameters of the pinion and gear are
kept constant and the module is reduced, which of the following transmission qual-
ities will be improved? _____
(a) The gear tooth bending strength
(b) The gear tooth contact strength
(c) The gear transmission stability
(d) None of them

Calculation Questions

1 A pair of enclosed spur gears have z = 20, z = 80, m = 3 mm and face width fac-
1 2
tor of = 1.0. The pinion rotates at n = 970 rpm. The allowable contact stress of
d 1
the pinion and gear are [ ] = 700 MPa, [ ] = 500 MPa, respectively. The load
H1 H2
1/2
factor is K = 1.5, zone factor is Z = 2.5, elastic coefficient is Z = 189.8 MPa .
H E
Determine the power that can be transmitted by tooth surface contact strength
analysis.
2 The variables of a pair of standard spur gears are listed in the table as

Gear m z b Y Fa Y Sa [ ] [ ]
H
F
Units mm mm MPa MPa
1 4 19 65 2.85 1.54 410 650
2 4 50 60 2.34 1.70 380 570