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KART STEERING SYSTEM OPTIMIZING AND SIMULATION

Arghavan Alireza*, Kheirkhahan Mohammadjavad ,Hemmati Mehran

Islamic Azad University of Semnan, Islamic Republic of Iran

Keywords: kart, steering system, spindle, dynamic loads, MSC Nastran/Patran

ABSTRACT

The main characteristic of kart is its simplicity, yet its design and adjustment can be more complicatedthan a standard automobile. In fact kart is a specific type vehicles without suspension system, differential,asymmetric position of engine and driver, and special kind of brake system.Because of the absence of differential the back wheel rises up while turning. Due to centrifugation severelateral forces are produced in wheels.These forces effect on steering system linkages and result in stress.

We made a model of kart in Visual Nastran and move it around a curve cornering radius equals with 15meter and speed equal with 40 km/h. One of performed studies in this software is determiningdependence among steering wheel angles and displacement of outer front wheel while cornering.

We use forces applied on spindle in finite element model in MSC/Patran so we can attain the stress valuedeveloped in steering system parts. In order to validate stress analysis result, we perform the sameanalysis by Visual Nastran software.

After loading and calculating of stresses we find out that stress doesnt exceed from allowable amount inmost of steering system parts such as stub axle, steering axle, joints, etc. but maximum value of stress isin steering pivot equal with 3.24*10

9and this is more than allowable stress.

In order to decrees stress, this part must be reinforced .thus we use from a sheet metal with 5 millimeterthickness instead of the sheet with 1.5 millimeters thickness for manufacturing mentioned part.

INTRODUCTION

The main characteristic of kart is its simplicity, yet its design and adjustment can be more complicated

than a standard automobile.In fact kart is a specific type vehicles without suspension system, differential, asymmetric position ofengine and driver, and special kind of brake system.Because of the absence of differential the back wheel rises up while turning. Due to centrifugation severelateral forces are produced in wheels.These forces effect on steering system linkages and result in stress. In one of the studies in mechanical

engineering department of torvergata university FEM and geometric models were used to compute

chassis resistance.

In 2004 in international automobile congress (FISITA) in Barcelona, in an article , kart dynamic analysis

has been presented by the use of Working Model 3D software and applying concentrated parameters

model consisting of 3 rigid objects connected by 2 elastic elements.

In September 2002 in 31st congress of AIAS in Parma in Italy an article has presented about kartintegrated dynamic analysis, and its driver. Then performed analysis indicates the effected of driver

movement on kart dynamic considering vertical forces on each wheel and in result on the acceleration and

motion trajectory (3).

KART VEHICLE

Geometric model of kart in solid works software is as shown below:

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Figure 1: geometric model of kart

Weight distribution and geometric characteristics of studied kart can be found in table

Table 1: distribution of the studied model of kart

MODELING IN VISUAL NASTRAN SOFTWARE

We made a model of kart in Visual Nastran and move it around a curve as seen in figure 2.Cornering radius equals with 15 meter and speed equal with 40 km/h (2)One of performed studies in this software is determining dependence among steering wheel angles anddisplacement of outer front wheel while cornering. Obtained diagram is almost adapted with similardiagram in (2) as seen in figure 3.

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Figure 2: model with constraints in Visual Nastran

Figure 3: relation among wheel hub and steering angle

MODELING INMSC/PATRAN SOFTWARE

We use forces applied on spindle in finite element model in MSC/Patran so we can attain the stress valuedeveloped in steering system parts, as seen in figure 4.

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Figure 4: finite element model in Patran

LOADING

Vertical load can be calculated by following equation:

Load: Translated longitudinal load while brakingm : Total mass: 152kga: longitudinal acceleration: 2.8m/s

2h : height of center of mass:246mmL : Wheel Base:1050mm

Load is equal with 98.9, that must add to vertical force applied on vehicle front tire when is in a staticstate.Fv= 355.6+98.9= 454.6N

Lateral force obtained by using of following equation:F = m.(V

2/R)

The calculated lateral force is applied on vehicle gravity center. The produced force in front wheel iscalculated by using of torque equilibrium equation in rear axle center.

RESULTS

In order to validate stress analysis result, we perform the same analysis by Visual Nastran software, asseen in figure 5, 6, 7.

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Figure 5: Distribution of stress in spindle

Figure 6: distribution of stress in a) Patran b) Visual Nastran

Figure 7: stress in joints a) small mesh b) big mesh

CONCLUSION

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After loading and calculating of stresses we find out that stress doesnt exceed from allowable amount inmost of steering system parts such as stub axle, steering axle, joints, etc. but maximum value of stress isin steering pivot equal with 3.24*10

9and this is more than allowable stress.

In order to decrees stress, this part must be reinforced .thus we use a sheet metal with 5 millimeterthickness instead of the sheet with 1.5 millimeters thickness for manufacturing mentioned part, as seen infigure 8.

Figure 8: increase of steering pivot sheet thickness

Therefore distribution of stress in this part is shown in following picture.

Figure 9: stress distribution in optimized pivot

REFERENCES

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(1) R. Baudille, M. E. Biancolini, L. Reccia, Integrated multi-body/FEM analysis of vehicle dynamicbehaviour , The 29th FISITA World Automotive Congress, Helsinki,Finland, June 2002.(2)C.Ponzo, F.Renzi, Parametric Multi-Body analysis of kart dynamics - FISITA world automotivecongress, Barcelona , may 2004 .(3)E. Pezzuti, L. Reccia, A. Ubertini, A. Gaspari, Analisi dell'interazione pilota-kart mediante la tecnicamultibody, Convegno AIAS 2002, Parma, Settembre 2002.