Aveneu Park, Starling, Australia

By follows: In the geometry the rack was displaced

By
calculating, the Actual Ackerman condition obtained varies by around 5% from
the Ideal Ackerman condition which is to be achieved. Hence the system is
almost accurate.

Cot(?)
– Cot(Ø) = L/B

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Ackerman
Condition,

Front
Track Width (B) = 1325mm

Wheelbase
(L) = 1565mm

Outer
wheel steer angle (?) = 32.20

Inner
wheel steer angle (Ø) = 520

From
the geometry,

 

C. Geometry Validation

 

Fig. Ackerman Geometry

The
final steering geometry is as follows:

 

In
the geometry the rack was displaced to its maximum possible position as it
would in an actual vehicle. At this displacement of rack, the steering angle
and turning radius of the vehicle was obtained through the geometry. After
performing several iterations by analyzing the effects of varying the steering
parameters such as length of tie-rod, rack, steering arm etc. a desired result
was obtained providing the turning radius least of all the iterations and all
following the Ackerman rule.

For
steering geometry design Dassault System Catia was used. It is better to use designing
software than using analytical method. By putting various steering parameters
like minimum wheelbase, track width and other chassis parameters regarding the
steering system a basic Ackerman geometry was obtained. In this we performed
numerous iterations until we get the desired result.

There
three types of steering geometries – Ackerman, Pro-Ackerman and Parallel steering.
Parallel steering is not considered as an option as it causes the vehicle to
understeer at a greater extent. As the formula student competitions require
considerably lower speed cornering in dynamic events, for this purpose Ackerman
Geometry is chosen. In Pro-Ackerman geometry, outer wheel steer angle being
greater than inner wheel steer angle, the inner wheel gets dragged while
cornering at lower speed and increase the steering effort.

 

B. Geometry Setup

 

·       
Considering the ease and cost of
manufacturing, type of gear-pair and material is selected for rack and pinion.

·       
For a steering system, selection of
geometry is a major factor. Implementing proper geometry according to the
cornering conditions is required.

·       
The main aim is to obtain the turning
radius as less as possible for maneuvering along a critical corner.

·       
Front track width should be greater than
rear track width to ensure that while close to any obstacle or vehicle, the
rear inner safely passes without dashing.

·       
The first step in designing the steering
system is to determine the Wheelbase and Track Width of the vehicle. In
accordance with formula student competition rules a minimum of 60 inches of
wheelbase is required.

A. Design Considerations

II. DESIGN

The
directional behavior of vehicle depends on the design of steering system. It
necessary to design a responsive steering mechanism which helps the driver in
obtaining complete control on the maneuvering of the vehicle. Since the
steering system is directly operated by the driver it is essential to take
human comfort into consideration while designing the steering. The goal is to
produce an optimal design to achieve higher strength to weight ratio. The
purpose of the steering system is to direct the vehicle in the desired path. A
purely mechanical rack and pinion mechanism is used for the vehicle. Steering
ratio can be altered using different gear ratios for rack and pinion. An
effective steering system should enhance the handling characteristics of the
vehicle. A lower steering ratio is required for continuously changing the
course throughout the race track. Steering effort and turning radius should
lesser to easily maneuver the vehicle along the tightest corner of the track.

I. INTRODUCTION

Index Terms = Ackerman,
Ergonomic, Maneuver, Turning radius, Steering ratio.

Abstract-
Steering system is used to direct the vehicle in the desired path. While
maneuvering, the vehicle should steer in response to the driver’s input
command. The goal of this project is to design a good
responsive steering system for high as well as low speed cornering for formula
student car and retain the moderate cost, manufacturability, and low weight. The main consideration in design of
the steering system is to produce pure rolling motion of the wheels while
maneuvering the tightest corners. A safe design should be developed to ensure
proper response to high speed cornering and heavy braking. It
is essential to take human comfort and safety into consideration while
designing. A steering system of lower steering ratio and weight as low as
possible is designed, analysed and fabricated.

x

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