product performance parameter (ppp) improvement of inner tie … · 2018-02-20 · product...

International Journal of Advanced Mechanical Engineering.

ISSN 2250-3234 Volume 8, Number 1 (2018), pp. 39-50

© Research India Publications

http://www.ripublication.com

Product Performance Parameter (PPP) Improvement

of Inner Tie Rod for Passenger Car

Saurabh Saraf1, U.S. Chavan2, Deepak Kulkarni3

1 Mechanical Engineering Department, Vishwakarma Institute of Technology, Pune, 2 Mechanical Engineering Department, Vishwakarma Institute of

Technology,Pune,411037, India. 3Engineering Manager, Kalyani Studio, Kalyani Nagar, Pune-411006

Abstract

The ratio of Tie Rod length to the radius of gyration of its cross section is

normally quite large, it would likely buckle under the action of compressive

forces. The aim of the project is to analyse tie rod for the active improvement

in the mass and buckling load of tie rod. This paper has the intention to

evaluate buckling strength and compare buckling performance of Tie rod for

different dimensions, theoretically calculate the critical buckling load of Tie

rod with different diameter of it and keeping the same material and length. We

have been compared & validated the theoretical results with the experimental

test results obtained by the natural frequencies on FFT analyser.

Keywords: Tie Rod, Load Carrying Capacity, FFT analyser

I. INTRODUCTION

Design of suspension components in an automotive is very critical as they are

constantly under varying loads. While designing the component we must ensure the

safety. Apart from design prospective it is important to focus on the weight and cost

of an individual component. The tie rod is an important part of suspension system. It

connects the steering to the suspension in order to transform the motion. In

MacPherson strut suspension and rack and pinion steering gears with tie rods connect

the end of the rack to the steering knuckle. A tie rod consists of an inner and an outer

end as shown in both figures. Tie rods transmit force from the steering centre link or

the rack gear to the steering knuckle, causing the wheels to turn. The outer tie rod end

mailto:[email protected]

40 Saurabh Saraf, U.S. Chavan, Deepak Kulkarni

connects with an adjusting sleeve, which allows the length of the tie rod to be

adjustable. This adjustment is used to set a vehicle’s toes, a critical alignment angle,

sometimes referred to as the caster and camber angles. A vehicle’s steering and

suspension systems should be checked regularly, at least once a year along with a

complete wheel alignment.

II. PROBLEM STATEMENT

Design and Optimize the Inner Tie Rod (ITR) by 15-20% in order to sustain it during

Cornering and Bumping and life of ITR should not go below 7 x 105 cycles and

maintain FOS in between 3 to 4.

III.OBJECTIVE

1. To Optimize the Weight of Existing ITR

2. Theoretical Calculations for

a. Shear Stress in Body

b. Fatigue life by Garber Equations

c. Critical Buckling Load

3. FEA Analysis Of ITR for validating Hand Calculation

4. Validate Software result and Hand Calculations on UTM and FFT Analyzer.

IV.DESIGN CALCULATIONS

Fig. 2. Tie Rod CATIA Model Table 1.Material Properties

Parameter Initial Design

Material Steel SM45C

E 210 x 103 MPa

Density 7700 Kg/m3

Tensile Yield Strength 360 Mpa

Tensile Ultimate Strength 569 MPa

Product Performance Parameter (PPP) Improvement of Inner Tie Rod for Passenger Car 41

(A) Steering movement ratio:

Where, R = 170 mm is the radius of the steering wheel, the output rack movement is:

Xo = 2 π r ---------------------------- (1)

40 = 2 π r

Then, the movement ratio (MR) can be calculated as input movement over output:

MR = Xi/Xo --------------------------- (2)

= 2 π R/2 π r

= 1068.11/40 = 26.70 Therefore the movement ratio is 26.70: 1.

For an effort of 40 N applied by both hands on the steering wheel and considering no

friction, the output load will be:

Fo = Fi * MR --------------------------- (3)

= 40*26.70= 1068.11 N

Therefore the load transmitted to the tie rods is 1068.11

(B) Design Calculations for Existing Tie Rod

(i) Stresses in Power Screw-Existing Inner Tie Rod

(a) Direct Compressive Stress:-

𝜎=𝑤/(𝜋/4 𝑑𝐶2 ) = 56.28 N/mm2 --------------------------- (4)

(b) Torsional Shear Stress:-

T=w dm/2 tan(ϕ+λ) = 11013.47 N-mm --------------------------- (5)

𝜏=16𝑇/(𝜋𝑑𝑐3 ) = 40.23 N/mm2 --------------------------- (6)

(c) Maximum Shear Stress in Screw Body:-

τMax=√((σc/2)2+τ2 ) = 49.09 N/mm2 --------------------------- (7)

So the Max. Shear stress is within Permissible Shear Stress. So we can say that our


design is safe for Shear stress criteria.

(d) Shear Stress in Threads:-

τs =w/(π∗dc∗t∗Z) = 5.059 𝑁/mm2 --------------------------- (8)

(e) Factor of Safety for Existing ITR

σmax= (F)max/(π/4)d2)=(25430) /(π/4)*(15.25)2) =126.18 N/mm2 ---------------- (9)

𝜎𝑚𝑖𝑛=((𝐹)𝑚𝑖𝑛/(𝜋/4)𝑑)2) = (6564/(𝜋/4)〖15.25)2)= 33.56 N/mm2 -------------- (10)

𝜎𝑚"= (𝜎𝑚𝑎𝑥+𝜎𝑚𝑖𝑛)/2= (126.2 +33.56)/2) = 79.88 N/mm2 ------------- (11)

𝜎𝑎 = (𝜎𝑚𝑎𝑥−𝜎𝑚𝑖𝑛)/2 = (126.2 -33.56)/2) = 46.32 N/mm2 -------------(12)

As we know that Gerber gives good predictions for ductile alloys, so I have used

Gerber formula for calculating Fatigue life.

((𝑓𝑜𝑠∗𝜎𝑚)/𝑠𝑢𝑡 ))2+((𝑓𝑜𝑠∗𝜎𝑚)/𝑠𝑒 ) = 1 ---------------- (13)

=((𝑓𝑜𝑠∗79.88)/569))2+((𝑓𝑜𝑠∗46.32)/270) = 1 ---------------- (14)

= FOS = 3.86

(f) Design of Component subjected to finite life

Pa = (Pmax - Pmin)/2 = (25430+6564)/2 ---------------- (15)

= 15997 N

Pm = (Pmax + Pmin)/2 = (25430-6564)/2 ---------------- (16)

= 9433 N

From Fig.

CF/FB = AE/EB


---------------- (17)

Log10 (N) = 5.915 = N = 8.912 x 105 cycles

(g) Critical Buckling Load for Existing ITR

Critical Load (Pcr ) = Pcr

= = 29360.25 N ---------------- (18)

(C) Design Calculations for Optimized Tie Rod

(a) Direct Compressive Stress:-

𝜎=𝑤/(𝜋/4 𝑑𝐶2 ) = 70.68 N/mm2 ---------------- (19)

(b) Torsional Shear Stress:-

T=w dm/2 tan(ϕ+λ) = 11013.47 N-mm ---------------- (20)

𝜏=16𝑇/(𝜋𝑑𝑐3 ) = 62.38 N/mm2 ---------------- (21)

(c) Maximum Shear Stress in Screw Body:-

τMax=√((σc/2)2+τ2 ) = 71.69 N/mm2 ---------------- (22)

So the Max. Shear stress is within Permissible Shear Stress. So we can say that our

design is safe for Shear stress criteria.

(d) Shear Stress in Threads:-

τs =w/(π∗dc∗t∗Z) = 10.473 𝑁/mm2 ---------------- (23)


(e) Factor of Safety for Existing ITR

As we know that Gerber gives good predictions for ductile alloys, so I have used

Gerber formula for calculating Fatigue life.

((𝑓𝑜𝑠∗𝜎𝑚)/𝑠𝑢𝑡 ))2+((𝑓𝑜𝑠∗𝜎𝑚)/𝑠𝑒 ) = 1 ---------------- (24)

=((𝑓𝑜𝑠∗79.88)/569)2+((𝑓𝑜𝑠∗46.32)/270) = 1 ---------------- (25)

=FOS = 3.75

(f) Design of Component subjected to finite life

Pa = (Pmax - Pmin)/2 = (25430+6564)/2 ---------------- (26)

= 15997 N

Pm = (Pmax + Pmin)/2 = (25430-6564)/2 ---------------- (27)

= 9433 N

From Fig.

CF/FB = AE/EB

---------------- (28)

N = 7.16 x 105 cycles


(g) Critical Buckling Load for Existing ITR

Critical Load (Pcr ) = Pcr

= = 24847.79 N ---------------- (29)

V. FEA Analysis of Tie Rod

To validate the Hand Calculations, we need to validate the all results in simulation

software (Ansys).

(a) FEA Analysis Of Existing ITR

Fig.4 Weight Of ITR-0.686 Kg Fig.5 Equivalent Stress – 90.85 Mpa

Fig.6 Maximum Shear Stress – 47.02 Mpa Fig.7 FOS – 3.96


Fig.8 Life – 8.66x105 Fig.9 Buckling Deformation-1.077 mm

(b) FAE Analysis Of Optimized ITR

Fig.10 Optimized ITR Model Fig11 Equivalent Stress- 100.38 Mpa

Fig.12 Maximum Shear Stress – 68.476 Mpa Fig.13 FOS -3.74


Fig.14 Life-7.16 x 105 Cycless

VI. TESTING & VALIDATION

(a) Buckling Test On Universal Testing Machine

Fig.15 Adjusting ITR on UTM Fig. 16 Buckling Test of ITR on UTM

Fig.17(a) Existing Tie Rod Fig.17 (b) Optimized Tie Rod


It is observed that the buckling deformation of existing tie rod obtained by analysis is

2.474 mm after applying 28868 N load & by experimentation the buckling

deformation is 2.8 mm and in our case cornering and bumping condition the buckling

deformation is

1.0773 mm. While the buckling deformation of optimized tie rod obtained by analysis

is 2.242 mm & by experimentation we got buckling deformation is 2.3 mm. From

Fig.17 (a) the Critical Buckling Load for Existing Tie rod is 29420 N. From Fig.17 (b)

it can be seen that the Critical Buckling Load of Optimized Tie Rod is 25430 N.

(b) Natural Frequency Test On FFT Analyzer

Modal analysis was performed on optimized model of tie rod to determine critical

natural frequency of tie rod and to avoid resonance.

Fig.18.Modal Analysis Test on FFT Analyser Fig.19. Existing Tie Rod

Fig.20.Optimized Tie Rod

The Modal analysis of Existing Tie Rod obtained

by analysis is in the range of 510 Hz. To 3620 Hz

and the Modal analysis obtained by

experimentally is in the range of 505 Hz. To 800

Hz. The Modal analysis of Optimized Tie Rod

obtained by analysis is in the range of 580 Hz. To

4024 Hz and the Modal analysis obtained by

experimentally is in the range of 560 Hz. To 810

Hz.


VII. RESULTS AND CONCLUSION

Inner

Tie Rod

Outer

Diameter

(mm)

Inner

Diameter(mm)

Stress

(MPa)

Life of

ITR

Cycles

(Laks)

FOS Buckling

Deformation

(mm)

Weight

(Kg)

Solid 16 0 90.86 8.66x105 3.96 1.0037 0.686

Iteration 1 16 8 94.43 6.85x105 3.45 1.0235 0.575

Optimized

ITR

15 8 100.38 7.16x105 3.75 1.1258 0.554

Table 3. Obtained results for Optimized Tie Rod

Fig.21 Max. Shear Stress Comparison Fig.22 Fatigue Life Of ITR Comparison

Fig.23 FOS Of ITR Comparison Fig.24 Buckling Load Of ITR Comparison

Tie rod plays important role in steering system and should be carefully selected. The

results we got for selected Optimized Tie Rod are showing good improvement

compare to Solid tie rod in terms of weight, High Strength. Optimized Tie rod with

ID 8.0 mm is selected for optimization purpose. Overall (Compare to existing model

with solid steel Tie rod) change in weight is 19.24 % for Steel- optimized tie rod. The

finite analysis result shows that in modal analysis natural frequency of proposed tie


rod is 10.00% more than natural frequency of existing tie rod. If we need to be

reduced the weight by 19.24% then we need to compromise the life by 17.23% but it

is within client acceptance limit. The life of a proposed ITR is 7.16 x 105 cycles.

VIII. REFERENCES

[1] A.H. Falah& et al., “Failure investigation of a tie rod end of an automobile

steering system”at Elsevier, Engineering Failure Analysis 14 (2007) 895–902.

[2] Wei Duan& et al., “Failure analysis of threaded connections in large-scale

steel tie rods” at Elsevier, Engineering Failure Analysis 18 (2011) 2008–2018.

[3] Soohyun Nam& et al., “Development of the light weight carbon composite tie

bar” at Elsevier, Composite Structures 134 (2015) 124–131.

[4] Manik A. Patil & et al., “FEA of Tie Rod of Steering System of Car” at

IJAIEM, Volume 2, Issue 5, May 2013, ISSN 2319 – 4847.

[6] M. Amabili& et al., “Estimation of tensile force in tie-rods using a frequency-

based identification method” at Elsevier, Journal of Sound and Vibration 329

(2010) 2057–2067.

[8] H.R. Kim& et al., “A study of the manufacturing of tie-rod ends with

casting/forging process”at Elsevier, Journal of Materials Processing

Technology 125–126 (2002) 471–476.

product performance parameter (ppp) improvement of inner tie … · 2018-02-20 · product...

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