You can find leaf springs in almost
all four wheelers. In this article we discuss how to design a leaf spring and
the typical guidelines for a leaf spring.
A leaf spring protects a four wheeler
from the unevenness of the road. Thus a leaf spring necessarily serves the
following purposes:
○ Increase service life of a four wheeler
○ Increase user comfort
Leaf spring design is based on the fundamental
beam theory. I already have an article on how to design plates based on
beam theory.
You have to use the following
two formulas for the leaf spring design process:
○ Bending stress produced in the whole spring:
Tb= (3*W*L)/ (b*N*t^2)
eqn1.1
○ Maximum deflection in the whole spring:
X= (6*W*L^3)/[{(2+(n/N)}*E*N*b*t^3]
eqn1.2
Where,
Tb maximum bending stress in the
leaf spring
W Applied load on the spring
t Thickness of the individual leaves
X Maximum deflection of the spring
due to applied load
L Span of the leaf spring
n Number of full-length leaves
N Number of graduated-length leaves
b Width of the spring
E Youngs modulus of the spring
material
Lets start with a leaf spring design
problem. We have the following data as input:
W= 24516 N
L= 0.445 M
N= 8
n= 2
E= 2.1E+11 N/m2
X= 0.13 M
Sa= 600000000 N/m2
Sa is the allowable bending stress for the
spring material.
You have to find out the width
(b) and the thickness (t) of the spring.
Solution:
Apply the eqn1.1 and
you will get the value of:
b*t^2 = 6.81 * 10^-6
eqn1.3
Now, apply the eqn1.2 and
you will get the value of:
b*t^3 = 2.63 * 10^-8
.eqn1.4
By solving the eqn1.3 and
eqn1.4 you will get:
t = 0.0038 m
b = 0.455 m
User comfort and the service life of
a four wheeler is dependent on the design of leaf spring. Leaf spring design
guidelines explained here is the simplest version of the whole leaf spring
design procedure. Nowadays, CAD and FEA tools are used
extensively in the industry for the design of leaf spring.