design and construction of light vehicles steering system

design and construction of light vehicles steering system

PROCEEDINGS OF THE INSTITUTE OF VEHICLES 3(107)/2016
Michał Olszewski1, Wojciech Skarka2, Mateusz Wąsik3
DESIGN AND CONSTRUCTION OF LIGHT VEHICLES STEERING SYSTEM
1. Introduction
Vehicle's steering system is a set of mechanisms used for changing the direction of
driving direction as with the direction set by the driver. The process of changing the
movement direction takes place through a kinematic chain of:
 steering wheel,
 steering column,
 transverse rods,
 crossovers,
 vehicle wheels.
Main task given to the steering system are:
 The difference between the actual value of the steering angle and the theoretical
dependence should be minimal,
 Wheels derived from the equilibrium position, which is the direction of the
straight-ahead should automatically come back to it,
 The impact of side forces beyond the control of the driver cannot influence the
direction of the car,
 Vertical movement of the wheels as a result of driving over occurs when
inequality should not affect the direction of the car,
 Driving the process should be easy and efficient using small effort force by the
driver
 impacts caused by vertical movements of the wheels as a result of driving over
occurs when inequality should not be felt on the steering wheel.
Subject of this article is design of the new Steering system for HydroGENIUS
(fig. 1.) one of vehicles which competes in Shell Eco Marathon [1], an international
competition organised by Royal Dutch Shell which brings together students from many
countries and it main task is to cover the distance as long as it possible on one equivalent
of one litre of gasoline. Because of competition specification Car has been designed to
be as much energy co-efficient as it is possible.
Main reasons of changing actual system was the deflection of pitman arm noticed
when forces were applied into wheel on technical control which bring the need of the
steering systems optimization. Another important thing was a decision of modernization
of the car, among other things, applying to it a new suspension system. As a basis for the
design and further optimization was carried out discussion what should be the type of
new steering system and where it should be located. It was taken into account that car
Eng. Michał Olszewski, Institute of Fundamentals of Machinery Design, [email protected]
Prof. Wojciech Skarka, PhD, DSc, Eng., Institute of Fundamentals of Machinery Design, Silesian University
of Technology, [email protected]
3
Mateusz Wąsik MSc, Eng., Machine Technology Department, Silesian University of Technology,
[email protected]
1
2
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will have some changes which significantly reduce the available space in its front. For
this reason and the desire to obtain maximum content of system decision was taken to
make compact rack and pinion gear and locate it in front part of the vehicle. This
decision has imposed a specific geometry of crossover arm in an outward direction of the
centre of the car. The second factor taken into account at designing was decision of
changing of rigid suspension into double wishbone suspension. Solution used so far was
much simpler because it only requires observation of angle changes in one dimension.
During the design of the system it was necessary to take account changes in the
geometry of the vertical suspensions work. The basic principle of design steering is that
the work is not affected wheel alignment. There is a method of selection of such a
geometry to obtain the desired effect but it imposes some restrictions, length of the
crossover arm projection cannot be changed during a determining of the Ackerman
geometry.
Fig. 1. HydroGENIUS vehicle
`1.1. Ackerman geometry
Assumption of Ackerman convergence is that the car moves around a curve without
slipping wheels. The slip is undesirable phenomenon to due to the possibility of
abandoning the vehicle and premature wear on the tires. Sometimes imperfect
convergence of Ackerman is a desirable feature that allows better overcome the
cornering but in case of energy—efficient competition Ackerman angles should be full
well to minimize energy losses. Steering system should set the steered wheels in a way
that turning the steered wheels in curves with a common centre of curvature lying on the
extension of the axis of rotation of the rear wheels of the car. This condition is
understandable and it seems easy to achieve, but to provide such real kinematic system is
almost impossible without steering system consisting of several pivotally connected
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rods. In rack gear steering system, it is impossible to obtain Ackerman convergence for
each steering position. That's why in the cars there are applied simplified solutions. [4]
2. Design
As the main project input was taken into account geometrical parameters of
crossovers given by its designer and parameters imposed by rules of competitions [1, 2]
The following parameters arise from currently used solutions. Their modification may
not be possible without significant interference with the construction of the whole
vehicle:
 Rmin = 5500mm - minimum turning radius,
 rσ = 12mm – camber length resulting from construction of the suspension
system.
 b = 1053mm - front track width,
 l = 1500 mm - wheelbase,
 m = 280kg - the weight of the vehicle, including the driver,
 Vmax = 50km / h - the maximum speed that can develop the vehicle,
 μ = 1.08 - coefficient of static friction of the tire,
 δA.O = 15.86o - the maximum steering angle of the inner wheel calculated using
the formula (1).
(1)
First step of designing process was choosing such length of the projection of
crossover arm and the crossbar that provides constant steering geometry during work of
suspension. To achieve the desired effect, it was used descriptive geometry. sketch was
made in the Sketcher module of CATIA V5 (Fig. 2). By imposing appropriate constrains
it was possible to analyse the changes of geometry in motion.
Fig. 2. Kinematic sketch of suspension system [5]
Second step was choosing rest of geometry parameters to achieve as best as possible
Ackerman convergence. In order to do that the second sketch in CATIA has been made
(fig. 3.), it allows perform an optimization. Because of constant crossover arm angle and
length of crossbar only one geometrical parameter could be changed in that process,
length between front wheel axle and steering axle. It has been changed iteratively. For
each configuration inner wheel has been turned from position to drive forward to
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maximally turned. It has given a possibility to observe how offset from ideal geometry
changes when system works It allows to find optimal solution (tab. 1.).
Fig. 3. kinematic sketch of Ackerman convergence [5]
Table 1. Optimization table
As the optimal solution it has been selected arrangement in which the distance
between arm and front wheel axis is equal 42mm.
3. Design features
Possibility of reading up every else parameter from sketches allows to match
steering system design features. The crossbar used in the project has two male uniball
joints connected by aluminium pipe, each joint has another direction thread. That
solution allows to regulate it length without disassembly of the whole system. Steering
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gear was designed in the framework of this project as a a compact unit like a solutions
used in classic cars. As a construction material of the housing, an aluminium alloy
EN AW-7075 was selected due to its low weight and estimated low value of forces
which it will be exposed (fig. 4.).
Steering arm are threaded from both side, guide rollers with decimetre of 10mm
connected with a rack on one side and the transverse rods via the fork of the other.
elements are made from material steal S355JR (fig. 4).
Fig. 4. Steering system and steering arm visualization [5]
Toothed gear used in the project is composed of a rack and designed pinion.
Module, and the number of teeth of the elements have been chosen in such way that the
resulting range of motion of linear steering arm was consistent with the prescribed
geometry and the maximum range of movement of the steering wheel was 180 o in any
direction. The steering gear has been linked to the transmission shaft by using a double
Cardan joint (fig. 5).
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Fig. 5. Assembled steering system visualization
4. Verification
In order to verify the strength, it was determined the approximate values of the
forces acting on the steering arm. For calculations it was used critical case of braking of
the vehicle speeding to the maximum speed V = 50 km/h overcoming the bend
R = 5.5 m [6] (fig. 6.).
Fig. 6. Force distributions
(2)
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(3)
(4)
Calculated forces (3), (4) had been used for strength verification of the most tensed
part of the system which was a steering arm (fig. 7.).
Fig. 7. Steering arm force distribution
(5)
(6)
(7)
(8)
(9)
Most loaded component has been verified (9). Project is completed and ready for
manufacturing (fig. 8)
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Fig. 8. Steering system assembled with the rest of vehicle
5. Conclusions
Steering system is responsible for energy losses when car is taking bends. Well
prepared Ackerman geometry could increase the energy efficiency of the vehicle.
Another energy efficiency factor is changing of convergence caused by suspension
works. It is hard to design such steering geometry that provide constant convergence.
Other conclusion is that the steering system is responsible for driver safety and that’s
why it is necessary to design it as a solid construction which can withstand the impact of
external forces
References:
[1]
Official Shell Eco-marathon organizer web site: http://www.shell.com/energyand-innovation/shell-ecomarathon.html [08.01.2016].
[2]
Shell Eco Marathon rules http://www.shell.com/energyand- innovation/shellecomarathon/for-participants/rules-and-competition-overview/[08.01.2016].
[3]
Modelling of Machine Designs site: http://mkm.polsl.pl/[08.01.2016].
[4]
Reimpell J.; Betzel J. The Automotive Chassis: Engineering Principles,
Butterworth-Heinemann 2001
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[5]
[6]
W.F. Milliken, D.L. Milliken Chassis Design: Principles and Analysis (R-206)
SAE International ISBN of 978-0-7680-0826-5
L.G. Giordano L. Reggiani Vehicular Technologies - Deployment and
Applications InTech 2013
Abstract
Subject of work was to design and to construct a new steering system for light
Urban-concept vehicle HydroGENIUS. The car was designed and built by racing team
Smart Power from Silesian University of Technology to compete in international races
Shell Eco-marathon. New system has been designed to replace the old one. During the
designing phase it was taken into account that it should be lighter, smaller to ensure
lower energy losses due to influence of inertia. Another factor taken into account was to
achieve such solution which could cooperate with new suspension system designed in
parallel. Mechanism has been optimized to achieve best possible Ackerman angles
without changing the convergence when suspension system works. Last part was
creating of technical documentation which allow to begin manufacturing process. Each
task has been performed by using CATIA V5 software. Whole project has been verified
and It is ready for physical implementation.
Keywords: CAD, car suspension, car steering system, optimization, energy efficient
vehicle
PROJEKT I KONSTRUKCJA UKŁADU KIEROWNICZEGO LEKKIEGO
POJAZDU
Streszczenie
Przedmiotem pracy było zaprojektowanie i wybudowanie nowego układu
kierowniczego do lekkiego, miejskiego, koncepcyjnego pojazdu H6ydroGENIUS.
Samochód został zaprojektowany i zbudowany przez zespół wyścigowy Smart Power z
Politechniki Śląskiej, aby rywalizować w międzynarodowych wyścigach Eco-Marathon.
Nowy układ został zaprojektowany, aby zastąpić stary. W fazie projektowania zostało
wzięte pod uwagę to, że powinien on być lżejszy, mniejszy, aby zapewnić mniejsze
straty energii ze względu na wpływ bezwładności. Innym czynnikiem branym pod
uwagę było, aby to rozwiązanie mogło współpracować z nowym układem zawieszenia
projektowanym równolegle. Mechanizm został zoptymalizowany w celu uzyskania
możliwie najlepszych kątów Ackerman'a, bez zmiany zbieżności, w czasie działania
układu zawieszenia. Ostatnie zadanie to stworzenie dokumentacji technicznej, która
pozwala, aby rozpocząć proces produkcyjny. Każde zadanie zostało wykonane za
pomocą oprogramowania CATIA V5. Cały projekt został sprawdzony i jest gotowy do
realizacji fizycznej.
Słowa kluczowe: CAD, układ zawieszenia, układ kierowniczy, wysokosprawny pojazd.
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