Design of Leaf Springprint

7/25/2019 Design of Leaf Springprint

1/9

DESIGN OF LEAF SPRINGFor TATA Marcopolo 912

ABSTRACT

Leaf springs are one of theoldest suspension components

they are still frequently used,

especially in commercial

vehicles. Weight reduction is

now the main issue in

automobile industries. In the

present work, existing mono

steel leaf spring of a Tata Bus is

taken for modelling and

analysis


2/9


3/9

I. INTRODUCTION

Leaf springs are widely used in automobile and in railway. The leaf spring shouldabsorb the vertical vibrations and impacts due to road irregularities by means of

variations in the spring deflection so that the potential energy is stored in spring as

strain energy and then released slowly so increasing the energy storage capabilities

of a leaf spring and ensures a more compliant suspension system. Leaf springs are

probably one of the oldest forms of spring-type suspension systems, having been in

use since medieval times. Until recently, leaf springs were a common rear

suspension component of most automobiles. The introduction of light-weight

front-wheel drive vehicles has basically made the use of leaf springs unnecessary,

and automobile manufacturers are now using coil springs for both front and rear

suspension systems. Leaf springs are now generally used only for heavier

commercial-type vehicles such as trucks, vans, trailers, and railroad cars.

There are two basic types of leaf springs:

Mono-leaf

Multi-leaf.

Multi-leaf:


4/9

Analytical Design of the Leaf Spring:

Physical properties of Spring Materials used:

Material Modulus of

ElasticityMN/m2

Ultimate strength

MN/m2

Allowable Stress

MN/m2

Chrome-Vanadiumalloy

Steel(0.5% C )

0.206 106 950

1250

550

Material Modulus ofElasticityMN/m2

Ultimate strengthMN/m2 Allowable StressMN/m2

C40 0.220 106 540

770

328

Design data of leaf spring:

Sl.No. Design parameter Value

1. Total Length of the spring eye to eye (2Lmm) 1610

2. No. of full length leaves(if) 0

3. No. of graduated leaves including master leaf(ig) 10

4. Youngs Modulus of the springmaterial (N/mm2) 0.206 106

5. Allowable stress 550

6. Free Camber(mm) 50.8

7. GVW(Fkg) 9000

8. Base width(mm) 492010. Band length (lbmm) 60


5/9

Design of Leaf Spring:

Data known:-

Total load = (Wt. of engine + Self wt of spring + Dead wt of vehicle chassis +

Dead weight of vehicle chassis + Wt. of passenger bus) F = 9000Kg = 88290N.

Assuming Centre of gravity at a distance of 2360mm behind front axle.


6/9

Free body diagram

By eqillibrium equations

Rf + Rr = 88920 N ------------------------ (a)

Taking moments about point O

Rb 4920 = 2360 88920

Rb = 42350.48 N

From eqn (a) we getRf = 8892042350.48 = 45939.52 N

Therefore the design is based on front axle since it is heavily loaded.

Hence F =.

= 22969.76 N (two leaf springs)

Length L=

=

11

= 775mm.

Considering the leaf spring as pre-stressed

g=

bh2=.

1= 9709.94 -------------------------- (b)


7/9

y =

()

bh3=.

.81= 305034.49------------------------(c)

Assuming the width to height ratio typically as 9:1

i.e= 9b=9h ------ (d)

Substituting in the above equations (b) & (c) we get

eqn (b) h = (9709.94)/9 = 10.25mm

eqn (c) h = (305034.49)/9 = 13.56mm

Refering the Data handbook

standard height h = 14mm

therefore from eqn (d) b = 9h

= 9 14 = 126mm.

Nip C =

=

.

1111= 149.39mm

Lengths of leaves:-

1stleaf =effective length

1+ ineffective length

=11

+ 60 = 238.88mm

2ndleaf =11

2+ 60 = 417.76mm

3rdleaf =11

3+ 60 = 596.64mm

4thleaf =11

4 + 60 = 775.52mm


8/9

5thleaf =11

5 + 60 = 954.4mm

6thleaf =11

5 + 60= 1133.28mm

7thleaf = 11 5 + 60 = 1312.26mm

8thleaf =11

5 + 60 =1491.04mm

9thleaf =11

5 + 60 =1669.92mm

Pin design

Since there is clearance between plate and eye

L2=L+4 = 126+4=130mm

We know that M=FL8

= .18

= 373258.6 N-mm.

Bending stress of Pin material (b) = 164 MPa.

We know that b =M

Where Z =d

Substituting these we get

164 =8.

d

d=28.51mm

Standard d=30mm

Therefore length of the master leaf = 2L + 2 (d+h) = 1610 + 276.46 = 1886.46mm


9/9

Conclusion:

In this work, we designed the leaf spring for Tata Marco polo 912 using analytical

approach. We determined different parameters of the leaf spring like thickness,

length using the analytical formulae. The values obtained by above approach

revealed that the closeness of the values were differing by 6.6% for

thickness(height), 3.07% for the width and also the length of each spring is

determined, the closeness of values are obtained by comparing the values with the

actual values.

Sl

no

Parameter Calculated value

mm

Actual value

mm

Error %

1. Thickness of

leaves

14 15 6.67

2. Width of theleaves

126 130 3.07

3. Length of

master leaf

188.6 195 3.28

4. Diameter ofthe pin

28.6 35

Design of Leaf Springprint

Documents

Transcript of Design of Leaf Springprint