Lightweight Design of the Vehicle Suspension Control Arm

Hongwang Zhao

1, 2, a

, Yuanhua Chen

1, b

and Xiaogang Liu

College of automotive and Transportation Engineering, Guilin University of Aerospace Technology, Jinji Road, Guilin,

China

Guangxi Colleges and Universities Key Laboratory of Robot & Welding, Guilin University of Aerospace Technology, Jinji

Road, Guilin 541004, China

Keywords: Control Arm, Lightweight, Structural optimization.

Abstract: The restraint relationship of the lower control arm of McPherson suspension under extreme conditions is

studied. The strength, stiffness and free mode of the control arm are analysed by using the finite element

software ANSYS. The structure optimization of the control arm is carried out. The results show that the

lightweight reduces by 0.5KG. Finally, the comprehensive effect of the lower control arm using advanced

high strength steel is better than that of aluminium alloy.

1 INTRODUCTION

Automobile lightweight is the design of reducing

structure quality based on guaranteeing strength and

stiffness. At the same time, economy should be

considered comprehensively. Lightweight design

includes structural design and selection of

lightweight materials. Lightweight can not only

improve the power performance of automobiles, but

also improve fuel economy, control stability and

collision safety. The data show that if the vehicle

weight is reduced by 10%, the fuel efficiency can be

increased by 6%-8% (Mitchell, Erik T, 2018). For

every 100 kg reduction in vehicle quality, the fuel

consumption of 100 km can be reduced by 0.3-0.6

liters. At present, due to the need of environmental

protection and energy saving, lightweight

automobile has become the trend of world

automobile development.

The lower control arm of McPherson suspension

is one of the most important parts of the whole

suspension system. It is mainly composed of

spherical hinges, bushing and control arm, which

transmits the force and moment acting on the wheel

to the body (Zhang Z, Chen R, Zhongming X U, et

al, 2017). In the process of vehicle movement,

especially in the complex and harsh road conditions,

the impact of road surface irregularity is transmitted

to the body through wheels and lower control arms.

It not only bears all kinds of forces and moments,

but also requires the strength, rigidity and fatigue

life of the control arm. At the same time, the lower

control arm has a direct impact on the vehicle's

maneuverability and comfort (Ragab K A, Bouaicha,

A, Bouazara, M, 2017).

2 ANALYSIS OF LOWER

CONTROL ARM

2.1 Static Load Acquisition under

Limit Conditions

The three supporting points of the lower control arm

are referred to as A, B and C respectively. As shown

in Figure1.

Figure 1. Three Connection Points of Lower Control Arm.

Zhao, H., Chen, Y. and Liu, X.

Lightweight Design of the Vehicle Suspension Control Arm.

DOI: 10.5220/0008849300210025

In Proceedings of 5th International Conference on Vehicle, Mechanical and Electrical Engineering (ICVMEE 2019), pages 21-25

ISBN: 978-989-758-412-1

Table 1. This caption has one line so it is centered.

Connection

point

Load(N)

Accelerated forward

Forward braking

Steady left

turn

Steady right

turn

1035

-1745

-37

410

-6365

12798

1763

-9833

568

-1061

-132

818

3777

-8405

-243

2708

5823

-12306

-347

3785

-279

477

-159

-4814

10167

280

-3121

541

-474

-1414

6045

-261

612

137

-631

Among them, A and B are connected to the sub-

frame with rubber bushing, and C is connected to the

steering knuckle with spherical hinges (Heo S J, D.

O. Kang, J. H. Lee, et al, 2013).

In this paper, the whole vehicle dynamics model

built by ADAMS of an enterprise is used for

reference. According to the design criterion of the

enterprise, the strength analysis basis of four

representative connection points to the lower control

arm is calculated based on the given height and

quality of the center of mass, classical formula of

automobile theory and dynamic equation of

automobile suspension. The linear mechanical

parameters of four typical working conditions are

simulated. As shown in Table 1:

2.2 Strength and Stiffness Analysis

Because the force on the lower control arm of the

suspension is complex in the actual movement of the

vehicle. Often multiple forces and moments coexist

at the same time. Among the four commonly used

strength theories in material mechanics, the third and

fourth strength theories of classical material

mechanics are closest to the lower control arm. The

steel of the original lower control arm is QSTE450,

which belongs to plastic yield material and has

medium performance index in high strength steel.

Yield failure is one of the most important failure

failures of the lower control arm of McPherson

suspension, because it does not refer to the effect of

the second principal stress. So the fourth strength

theory is more theoretical basis for composite

calculation. Therefore, the fourth strength theory is

used to evaluate the mechanical properties of the

original control arm.

Stress nephograms under four extreme

conditions are shown in Figure 2-5.

According to the finite element analysis of four

kinds of simulation under extreme conditions, the

worst condition is forward braking, and its

maximum stress value reaches 420 MPa. The

maximum stress is mainly concentrated in the first

rivet-Y direction. Understanding the stress

distribution of the control arm under extreme

conditions can provide a reference for lightweight

drilling and weight reduction.

3 LIGHTWEIGHT DESIGN OF

LOWER CONTROL ARM

3.1 Structure-based Lightweight

Figure 2. Accelerated Forward.

In the light-weight design, this paper mainly adopts

the way of drilling and lightweight. According to the

results of stress analysis of four representative

working conditions mentioned above, it can be

concluded that the working condition of forward

braking is the worst. Therefore, structural

optimization and lightweight are also optimized

based on the stress analysis results of forward

braking. In most areas where the stress value is

small, we can drill lightweight holes. The regions

with large stress values can be strengthened to

reduce the regions with large local stress values. At

the same time, the minimum safety factor is

ICVMEE 2019 - 5th International Conference on Vehicle, Mechanical and Electrical Engineering

minimized as much as possible. In the original and

optimized strength and stiffness analysis results, the

optimized performance can not be much worse than

the original. Before and after structural optimization,

as shown in Figure 6-7.

Figure 3. Forward Braking.

Figure 4. Steady Left Turn.

Figure 5. Steady right turn.

Figure 6. Stress nephogram before structural optimization.

Figure 7. Stress nephogram after structural optimization.

Through comparison, it can be seen that under

the same forward braking condition, the optimized

structure has little change in the maximum stress

value, and can still meet the yield conditions of raw

materials. At the same time, the lightweight drilling

arm is 0.5 kg lighter than the original control arm.

As shown in Table 2 and Figure 8-11.

Table 2. Quality comparison.

Quality(Kg)

original control arm

carbon fibre

4.1

Figure 8. Modal Analysis of Original Control Arm.

Lightweight Design of the Vehicle Suspension Control Arm

Figure 9. Optimized Modal Analysis.

Figure 10. Stiffness analysis of optimized Y-direction.

Figure 11. Stiffness analysis of optimized X-direction.

3.2 Material-based Lightweight

For cost research, cost models are usually

established. For a complete manufacturing industry

chain, the cost calculation begins with the raw

materials entering the factory, and then the direct or

indirect manufacturing cost generated during the

process of vehicle leaving the factory. According to

the material cost in NHTSA/EDAG LWV research:

HSLA350/450:$1.05/kgor$0.48/lb.DP350/600:$1.19

/kg or $0.54/lb. HF1050/1500 (aluminized): $1.6/kg

or $0.75/lb. Austenitic stainless steel: $4.65/kg or

$2.10/lb.Average cost of aluminium sheets: $4.71/kg

or $2.14/lb. The price of CHSS (HSLA350/450) is

about 13% higher than that of low carbon steel. The

increase from HSLA350/450 to AHSS DP350600

leads to the price of CHSS (HSI A350/450) higher

than that of low carbon steel by about 13%. Hot-

Formed (HF) aluminized steel prices have risen

sharply on the basis of dual-phase steel, but non-

aluminized HF is more within the price range of

dual-phase steel. The price of austenitic stainless

steel is very high, which is why it has not entered the

automotive structure market in large quantities.

Austenitic stainless steel can be regarded as the

second alternative to AHSS with very high strength

and elongation, but the problem with austenitic

stainless steel is that its cost is almost equal to that

of aluminium.

In this paper, the advanced high strength steel is

proposed to replace the high strength steel of the

lower control arm in the study of material

lightweight. The strength analysis is used to verify

whether the advanced high strength steel can meet

the requirements. As shown in Figure12-13.

Figure 12. Stress nephogram of high strength steel.

Two better materials 30CrMo and 7075

aluminium alloy were selected. The results of

strength analysis show that the yield strength of

7075 aluminium alloy does not meet the strength

requirements of the worst working conditions, and

30CrMo is selected as lightweight material for

lightweight selection. As shown in Table 3.

Figure 13. Stress nephogram of 7075 aluminium alloy.

ICVMEE 2019 - 5th International Conference on Vehicle, Mechanical and Electrical Engineering

Table 3. This caption has one line so it is centered.

Contrast before

and after

optimizing

structure

Quality

(Kg)

Volume

(10

)

Yield strength(MPa)

Elongation

(%)

QSTE450

460

Advanced

High Strength

Steel

4.1

780

7075

3.2

The optimized structure in the figure above uses

30CrMo to reduce the quality of lower control arm

by reducing the thickness of the structure while

meeting the strength requirements. It can be seen

that through structural optimization and the use of

advanced high strength steel lower control arm

quality reduction effect is good. Reducing the

thickness of the structure but still meeting the

strength requirements, the volume is reduced by

3000mm

4 CONCLUSIONS

In this paper, four limit conditions of the lower

control arm of a vehicle suspension are analyzed by

finite element method, and the worst condition of

forward braking is obtained. In the lightweight

optimization, the stress and deformation of the

control arm under forward braking are mainly

considered. In the structural optimization, the lower

control arm with small stress is lightweight by

drilling. The results show that it meets the use

requirements. In the analysis of the upper part of C

joint, the stress is relatively large, reaching 420 MPa,

which is strengthened by strengthening the closed

plate. In the aspect of material lightweight, advanced

high-strength steel is replaced by raw material high-

strength steel by studying its properties. Although

the density of advanced high-strength steel is larger

than that of raw material, lightweight treatment of

structure and thickness is carried out, and the final

result is reduced by 0.9 kg.

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Ragab K A, Bouaicha, A, Bouazara, M. Optimization of

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Lightweight Design of the Vehicle Suspension Control Arm