3 Design of leaf springs

Design of leaf springs

1. Design of Leaf Springs

2. Leaf Springs Consists of flat plates/ leaves Longest leaf at top is called master leaf Bent at the end to form spring eyes U bolt and centre clip to hold the leaf together Master leaf, extra full length leaf, graduated leaf

3. Leaf Springs: Graduated leaves 𝜎 = 6𝐹 𝑔 𝑙 𝑔 𝑖 𝑏 ℎ 2 Eqn 11.28b Table 11.9 𝑦 = 6𝐹 𝑔 𝑙 3 𝑔 𝐸 𝑖 𝑏 ℎ 3 Eqn 11.28c Table 11.9 Load- Stress equation Load- Deflection equation 3

4. Leaf Springs: Extra full length leaves 𝜎 = 6𝐹 𝑓 𝑙 𝑓 𝑖 𝑏ℎ 2 Eqn 11.28b Table 11.9 𝑦 = 4𝐹 𝑓 𝑙 3 𝑓 𝐸𝑖 𝑏ℎ 3 Eqn 11.28c Table 11.9 Load- Stress equation Load- Deflection equation Taking 𝑦 𝑓 = 𝑦 𝑔 𝑎𝑛𝑑 𝐹 𝑔 + 𝐹 𝑓 = 𝐹 𝑔 𝜎 = 12 𝐹 𝑙 ′ 2 𝑓 𝑔 𝑏 ℎ ( 3 𝑖 + 2 𝑖 ) 𝑓 𝜎 = 1 8 𝐹𝑙 ′ 2 𝑓 𝑔 𝑏 ℎ ( 3 𝑖 + 2 𝑖 ) Eqn 11.30a Eqn 11.29d Eqn 11.30b 𝑦 = 12𝐹𝑙 3 ′ 3 𝑓 𝑔 𝑏 ℎ 𝐸 ( 3 𝑖 + 2 𝑖 ) Eqn 11.30c 4

5. Nipping of leaf springs Taking 𝑐 = 𝑦 𝑔 − 𝑦 𝑓 , 𝐸𝑞𝑢𝑎𝑙𝑖𝑠𝑖𝑛𝑔 𝑠𝑡𝑟𝑒𝑠𝑠 𝑣𝑎𝑙𝑢𝑒𝑠 𝜎 𝑏 6𝐹𝐿 = 𝑖𝑏 ′ ℎ 2 Pre-stressing by bending leaves to a different radii Initial gap between full length leaf and graduated length leaf before the assembly is called nip 𝜎 𝑏 𝑔 𝑔 𝑖 𝑏 ℎ ′ 2 𝑓 = 𝜎 𝑏 = 6𝐹 𝑔 𝑙 6𝐹 𝑓 𝑙 𝑓 𝑖 𝑏 ℎ ′ 2 Eqn 11.32b Eqn 11.32c 2𝐹𝑙 3 𝑐 = 𝐸𝑖𝑏 ′ ℎ 3 𝐹 𝑖 = 2𝑖 𝑔 𝑖 𝑓 𝐹 𝑖 2𝑖 𝑔 + 3𝑖 𝑓 Eqn 11.32a

6. Example. A truck spring has 12 number of leaves, two of which are full length leaves. The spring supports are 1.05 m apart and the central band is 85 mm wide. The central load is to be 5.4 kN with a permissible stress of 280 MPa. Determine the thickness and width of the steel spring leaves. The ratio of the total depth to the width of the spring is 3. Also determine the deflection of the spring. 6