Page 252 - Analysis and Design of Machine Elements

Analysis and Design of Machine Elements
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4 Design a pair of helical gears using data in Design Problem 3. Consider using both
soft tooth surface and case-hardened carburized surface gears.
Structure Design Problems
1 While designing a pair of spur gears, the face width of pinion is usually wider than
that of gear by 5–10 mm. The reason for this is ______.
(a) to ensure the strength of pinion is greater than that of gear
(b) to ensure the pinion and the gear have a similar strength
(c) to facilitate assembly and to ensure contact length
(d) to ensure stable transmission and to increase efficiency
2 The helix angle direction and rotational direction of gear 1 in a gear reducer are
shown in Figure P8.3. Gear 2 has a normal module of m n2 = 2 mm, 61 teeth and a
∘
helix angle of = 12.5 ; Gear 3 has a normal module of m n3 = 4mm and 19 teeth.
2
Do the following:

Figure P8.3 Illustration for Structure Design
n 1 Problem 2.

3
X X
1
4
X X 2

I II III

(a) To reduce the thrust force on shaft II, determine the helix directions of gears 2
and 3;
(b) Indicate the forces acting on gear 2 and 3;
(c) To ensure shaft II carries no thrust load, decide on the helix angle of
gear 3.

3 Design two layouts of gears in a reducer. In the reducer, the input shaft and output
shaft are concentric. The rotational speed of the input and output shafts are of the
same and opposite directions, respectively.
4 A pair of spur gears and a pair of helical gears are to be used in the gear reducer
shown in Figure P8.4. Should the pair of helical gears be arranged in the first stage
or in the second stage of power transmission?