day8_frame_design.pdf

7/27/2019 DAY8_Frame_design.pdf

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Frame design

Erasmus LLPIntensive Programme

2011 2012 - 2013

Kalevi Vesterinen


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CONTENTS

Vehicle frames

Tasks of the vehicle frame

Main properties of the frame

Calculations/Measurements

Position of the centre of gravity

Strength

Stiffness

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DIFFERENT KIND OF FRAMES

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Arrangement of the wheels

With three wheels you have to decidehow to arrange the wheels

Possibilities

One wheel front Delta

Two wheel front Tadpole

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Delta

Because only one

wheel on the front

steering system iseasy to realise

Front wheel produces

the main part of the

braking force Driver CG is high and

near rear axle


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Tadpole

Two wheels on front

offers more brakingforce

Complicated steering

system

Drivelineconstruction is easier


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Location of the CG

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There is an

optimum place

for the CG


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Tasks of the Frame

Carries the driver and possible load

Connects different components

(component positions)

Transfers forces between different

components

between driveline components

between wheels

steering components 8


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Frame evaluation

One way to evaluate the frame of the

vehicle is to evaluate the stiffness and

strength properties of the frame

Stiffness is measure how much the frame

deflects under load

Strength measures how the frame withstand

the load


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Frame stiffness

Bending

stiffness

Torsionstiffness

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Calculation

Static bending

moment and shear

force diagramscalculated from the

positions and

masses of the

components andload

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Load cases

During different driving situations the loads on frame are

different

To handle that the designer defines load cases which

describes different driving situations and calculates the loads

which affect the vehicle

For example:

Road bump

Braking Cornering

Crash

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Road bump

Loads comes from road through wheels

The level of the forces depends on the

road condition and speed and how the

suspension is arranged

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Braking

Dynamical axle loads induce bending

moment to the frame

From brakes comes torque to the frame

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Dynamical Wheel Loads in

Braking

During braking weight transfers from

the rear axle to the front axle

The amount of the weight transfer

depends of the height of the CG and

the wheel base


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Cornering

In cornering side forces affects the

wheels

This force loads the frame whit the

moment witch tries to turn the wheels

around the vehicle longitudinal axle

In tadpole design this means that the

axle fork witch supports the lonely wheelhas to manage torsion loads

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Dynamical Wheel Loads in

Cornering

During cornering weight transfers from

the inner wheel to the outer wheel

The amount of the weight transfer

depends of the height of the CG and

the track width


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Driveline loads

It is an inner for witch tries to deform the

frame

If the frame is very flexible some energy

of the driver is lost when the frame bends

The pedal support and rear wheel fork

should be designed stiff enough to avoid

this

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Calculation

Whit those moment

diagrams and load case

forces designer can definethe strength and stiffness

needed and roughly define

the measures of the frame

members

When using 3D-modellingthe analyse can be easily

done whit FEM

calculations


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Properties of the frame

Wheelbase

Track

Mass

Material

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Wheelbase

Small wheelbase means smaller turning

radius

Seat angle is steep and so the CG of thedriver is higher

This means that the dynamical wheel

load changes are bigger


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Wheelbase

Longer wheelbase allows the driver to lie

down so the frontal area is smaller and the

height of the CG is lower The frame weights more and it is not so

stiff


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Track width

Track width affects the stability of the

vehicle Wider track stabilises the vehicle but also

means that the vehicle needs wider road

In tadpole design narrow wheelbase can

reduce the wheel steer angle

day8_frame_design.pdf

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