Selection P arameter of AVT suspension system

International Research Journal in Engineering and Emerging Technology (IRJEET)
Volume – 01, Issue – 01, March – 2020
www.we-irjeet.com 2019 IRJEET – All Right Reserved 1 | Page
Selection Parameter of AVT suspension system
Punit Choudhary1
, Kuldeep Sharma2
1(Department of Mechanical Engineering / Jaipur Engineering College and Research Centre, India)
2(Training & Placement officer, Professor / Jaipur Engineering College and Research Centre, India)
Abstract The Suspension is the most vital sub-system in the automobile. its main function is to load transfer to
the wheels and protection of the driver from the road shocks .The purpose of this paper is to select proper
suspension system for front and rear of All Terrain vehicles (ATV) and to thereafter design, analyze, simulate
and test the suspension system for optimum performance of the vehicle, driver safety and maximum driver
comfort. The stability and road handling of vehicle is very important for parameters.
The system was designed to be durable enough to withstand with road shocks and vibration from harsh terrain
where ATV generally used. The springs were designed by calculation and the components were designed using
SOLID WORKS.
Keywords: Suspension, AVT, Spring, Anti-drive, Anti-squat, Rolling and Pitching
1. INTRODUCTION
Vehicle dynamics is the study of performance of an automobile in all of its motion like ride,
acceleration, braking and cornering. Suspension play a key role in all of these motion. The study of
vehicle suspension can be broken into two major parts: suspension kinetics and suspension
kinematics. Suspension kinetics is study of vibration analysis and suspension kinematics is study of
motion of tire as the suspension compress and extends. So for better motion of tire as they compress
and extends, some important parameters are considered. These parameters are motion ratio, ride
frequency, wheel travel, wheel rate, ride height, roll center, pitch center. The selection criteria of these
parameters for ATV are different from commercial vehicles.
1.1.STIFFNESS AND DAMPING
The tires stiffness and the tires viscous damping coefficient are important to the ride quality of the
vehicle, but more importantly to the handling performance of the vehicle. In typical passenger car
vehicles the stiffness of the tires is of an order of magnitude greater than the suspension stiffness. It is
typically the tire deflection that is important for the handling performance of the vehicle, because the
tire deflection is one of the parameters in which decides the tires grip capabilities. As the deflection of
the tire increases, the grip capabilities of the tire will decrease. It is very important to not allow the tire
to lose contact with the ground, because if it does the car will not be controllable in handling.
Typically, the damping coefficient of the tires is neglected because it is generally very low compared to
the other parameters in the system, and neglecting it results in a small error in the analysis in handling.
Typically, the damping coefficient of the tires is neglected because it is generally very low compared to
parameters in the system, and neglecting it results in a small error in the analysis.
1.2.CORNERING STIFFNESS
The tire cornering stiffness is an important parameter in determining the handling performance of
the vehicle. It is to some extent arbitrary; each tire has its own stiffness, and the tires on a vehicle can
be changed. Therefore the cornering stiffness can be chosen by the user to precisely predict turning
(cornering) characteristics of the vehicle. It is this parameter that will determine whether the car is an
understeering (the actual cornering radius increases with vehicle speed) or an oversteering (the actual
cornering radius decreases with vehicle speed) automobile because the center of mass of the vehicle is
a fixed parameter. It is generally better to have an understeering vehicle, because the vehicle is
normally more stable. In an oversteering case, the vehicle oversteers the turn, and the driver will be

forced to decrease the steering angle as he/she turns in order to stay on the desired path (the path the
vehicle takes when there is no lateral slipping). Oversteering and Understeering Vehicle There are also
more chances that the vehicle spins on the spot (about its own z-axis). In an understeering case, the car
understeers and the driver is forced to increase the steering angle in order to stay on the desired path.
There are several ways to determine the tires cornering stiffness. Two of these ways are by using the
magic tire model and second by using an estimation given the tires dimensions.
Fig 1. Difference between Understeering and Oversteering
1.3.SUSPENSION KINEMATICS
Suspension kinematics is the study of the motions of the tire. It describes the orientation of the tire
as a function of wheel travel and steering angle.
The motions of the tire are highly dependent on the type of suspension. In general there are two types
of suspension systems; solid axles and independent suspensions. A solid axle suspension is a
suspension where the movement of one wheel is transmitted to the other wheel causing them to move
together. This type of suspension is essentially a dependent suspension, the motion of the two wheels
are correlated to one another. The biggest advantage of this type is that the camber angle is not affected
by vehicle body roll. The major disadvantage of this type of suspension is the vibrations which are
induced into the system if the solid axle suspension also incorporates vehicle steering. Independent
suspension systems allow the left and right wheels to move independently; the movement of one wheel
will have no effect on the other wheel. The advantages of independent type of suspensions are: they
provide better resistance to steering vibrations; they provide a high suspension roll stiffness; steering
geometry is easily controlled; suspension geometry is easily controlled; and they allow for higher
wheel travel. The major disadvantages are: the camber angle changes quite a bit over suspension travel;
increased un-sprung mass; and the high cost of the system.
1.4.CAMBER THRUST
Camber on a wheel will produce a lateral force which is known as camber thrust. A rolling tire that is
cambered will produce a lateral force which is in the direction the tire is tilting in. When the camber
angle is generating a lateral force with no slip angle present it is known as camber thrust. Camber force
or camber thrust is a function of the following parameters: tire type, tire geometry, pressure, tread
pattern, camber angle, slip angles, traction or braking force, and the tire dimensions.
Path of vehicle
cornering with no
lateral slipping

Fig 2. Camber thrust angle
The camber thrust is the amount of force required to straighten out the contact patch so that it is
perfectly oval. Therefore, there are two things which generate a lateral force; camber angle and slip
angle. The lateral force generated by a slip angle will be greater than the lateral force generated by a
camber angle; that is the lateral force generated from 1 degree of slip angle will be greater than the
lateral force generated from 1 degree of camber angle. Typically the maximum amount of lateral force
or maximum (Fy/Fz) will occur at a camber angle between -2 and -7 degrees. In general, it is best to go
with a static negative camber angle because it improves the effective cornering stiffness of the tire and
it increase the maximum lateral force. For best performance the camber angle should remain between 2
and -7 degrees throughout the suspension travel.
1.5.CASTER ANGLE AND CASTER TRAIL
The caster angle is defined as the angle between the steering axis and the vertical plane viewed from
the side of the tire. It is important that the caster angle and caster trail be positive because both of these
quantities will affect the aligning moment. The aligning moment is the moment that will act against the
driver as he/she is trying to steer the vehicle. It is important that this moment acts against the driver so
that when the driver lets go of the steering wheel it will correct itself; the moment will force the tire to
re straighten itself. Caster trail is important because it defines how much of a moment will be applied
to the steering axis; as the caster trail increases, the moment arm increases and thus the moment acting
on the steering axis will increase. It is this moment that is acting to self-center the tire if the caster trail
is positive. However, if the caster trail is too large the driver will have a difficult time trying to turn the
wheels about the steering axis.
Fig 3. Caster angle

1.6.MOTION RATIO AND WHEEL RATE
The motion ratio describes the amount of shock travel for a given wheel travel. The motion ratio is
simply the shock travel divided by the wheel travel. A motion ratio of 0.6 implies that the shock will
compress 0.6 inches when the wheel compresses 1 inch. As the motion ratio decreases the control arms
will have to be built stronger because the effective bending moment acting on them will increase. The
effective bending moment will increase because the moment arm will increase; the moment arm is
defined as (d2 – d1).
Therefore it is more ideal to have a motion ratio as close to one as possible so that the load put on the
control arms is kept to a minimum so that they can be designed as light as possible thus decreasing the
un-sprung mass.
1.7.SUSPENSION KINEMATICS
Suspension kinematics is the study of the motions of the tire. It describes the orientation of the tire
as a function of wheel travel and steering angle.
The motions of the tire are highly dependent on the type of suspension. In general there are two types
of suspension systems; solid axles and independent suspensions. A solid axle suspension is a
suspension where the movement of one wheel is transmitted to the other wheel causing them to move
together. This type of suspension is essentially a dependent suspension, the motion of the two wheels
are correlated to one another. The biggest advantage of this type is that the camber angle is not affected
by vehicle body roll. The major disadvantage of this type of suspension is the vibrations which are
induced into the system if the solid axle suspension also incorporates vehicle steering. Independent
suspension systems allow the left and right wheels to move independently; the movement of one wheel
will have no effect on the other wheel. The advantages of independent type of suspensions are: they
provide better resistance to steering vibrations; they provide a high suspension roll stiffness; steering
geometry is easily controlled; suspension geometry is easily controlled; and they allow for higher
wheel travel. The major disadvantages are: the camber angle changes quite a bit over suspension travel;
increased un-sprung mass; and the high cost of the system.
𝑀𝑜𝑡𝑖𝑜𝑛 𝑟𝑎𝑡𝑖𝑜 = (
∆𝐿
∆𝑇
) ~ (
𝐵
𝐴
)
Fig 4. Motion ratio
The amount of force transmitted to the vehicle chassis is reduced when the motion ratio increases. This
implies that the wheel rate will increase as the motion ratio increases. Since the motion ratio relates
both the force and displacement of the spring to the wheel center, it must be squared to relate the wheel
rate (also known as wheel center rate) to the spring rate (if the motion ratio is reduced then the amount
of spring travel and the amount of force absorb by the spring will decrease).

1.8.SPRING RATE DETERMINATION
Spring rate determination the spring rate is one of the components of the vehicle where the designer
has control of its value. It is the spring rate along with the suspension geometry (motion ratio) which
determines the wheel rate. The wheel rate can be assumed to be equal to the ride rate because the
stiffness of the tires will be much greater than the effective stiffness of the suspension.
Therefore for good quality, the Maurice Olley criteria should be used when choosing the spring rates of
the front and rear suspension systems the front ride rate should be 30% lower than the rear ride rate.
The ride frequencies of the front and rear suspensions can be calculated once the front and rear ride
rates are known ride frequency Note in the equation above the weight is in lb and it is half of the
weight supported by the appropriate suspension (if the ride frequency calculation is for the front than
the weight is half of the weight supported by the front suspension). Also the ride rate is in lb/in in the
above equation and the frequency from the equation will be in hertz.
Note the ride frequency aid in determining the rear suspensions capable of catching up to the front
suspension when the vehicle goes over a bump thus minimizing the annoying motion felt by the driver
(pitch motion). Once the spring rates are known, the bounce, pitch, and roll natural frequencies can be
determined.
1.9.ANTI-DRIVE / ANTI-SQUAT
There will be weight transfer from the back to the front when the vehicle is braking and from the
front to the back when the vehicle is accelerating. The anti-dive/anti-squat properties of a suspension
are similar to the roll center concept applied. The anti-dive/anti-squat concept applies to the
longitudinal force whereas the roll center concept applies to the lateral force. A portion of the forces
will pass through the suspension components and be transferred to the frame, and this amount is
depicted by the amount of anti-dive or anti-squat present. In the study of anti-dive/anti-squat the roll
center is known as the pitch center. The definition of the pitch canter is the same as that of the roll
center except it is the longitudinal force and not the lateral force that is applied at the pitch center. The
pitch center is the location where the longitudinal forces can be applied without causing the vehicle to
pitch. The location of the pitch center is found in a similar way as that of the roll center except it is
calculated by looking at the vehicle from the side.
Fig 5. Anti-drive & Anti-squat geometry
The pitch center can be used to indicate the amount of pitch generated. The distance between the height
of the pitch center and the height of the center of mass of the vehicle gives an indication of the amount
of pitch. The smaller this distance is the smaller the amount of pitch generated will be. However, just
like with the roll center is the fact that the amount of jacking forces increases as the height of the pitch
center is increased. Thus there should be a compromise in the height of the pitch center; it should not
be too high because the jacking forces will be too high and it should not be too low because there will
be too susceptible to pitch.
The path of the tire in the longitudinal direction as a function of suspension travel will determine
whether the suspension is classified as anti-dive or anti-squat. If the suspension is classified as anti-

dive the point of contact of the tire will move forward (towards the front of the vehicle) as the
suspension compresses and with move rearward as the suspension extends (goes into rebound). If the
suspension is classified as anti-squat the point of contact of the tire will move rearward as the
suspension compresses and will move forward as the suspension extends (Figure 22: Anti-squat
suspension geometry). Anti-dive designed into the suspension system leads to harsh response over
bumps; the suspension will be trying to push into the bump instead of riding over it with ease. As the
suspension goes over a bump it will compress, and when the anti-dive suspension compresses it moves
forward and thus tries to push into the bump. This tends to cause a harsh response, and in some cases
can induce vibrations in the system which can be felt by the driver. However, anti-squat designed into
the suspension improves the performance of the suspension. The suspension will ride over bumps with
ease. As the suspension goes over a bump it compresses and moves rearward, thus it will follow the
path of the bump with ease and if anti-dive is designed into the suspension system it will prevent the
vehicle from diving; the vehicle dives when it is braking. If anti-squat is designed into the suspension
system it will prevent the vehicle from squatting. If anti-squat is designed into the suspension it will
assist the vehicle at diving, and if anti-dive is designed into the suspension it will assist the vehicle at
squatting. Therefore, it is common proactive to use a small percentage of anti-squat in the rear and a
small percentage of anti-dive in the front. The reason why anti-squat is designed in the rear is that
when the vehicle is squatting weight is transferred to the rear. Therefore the effect of designing the
suspension to prevent the vehicle from squatting will be greater by designing anti-squat into the rear
suspension because the weight is being transferred to the rear. This is the same reason why anti-dive is
designed into the front suspension; when the vehicle is diving weight is being transferred to the front.
However, since anti-dive leads to a harsh response over bumps which are detrimental to the suspension
system, therefore a small amount of anti-squat is typically designed into the suspension to optimize the
performance of the suspension. It is important that the amount of anti-squat be kept to a small
percentage in both the front and rear when they are both designed for anti-squat.
Fig 6. Anti-drive geometry

Fig 7. Anti-squat geometry
2. CALCULATION FOR SPRING RATE DETERMINATION
2.1.FRONT SUSPENSION SPRING RATE
GIVEN VEHICLE GEOMETRY DATA
Wheel travel (inches) 10
Spring travel (inches) 6
Motion ratio, MR 0.6
Angle correction factor (front view), Cf (deg) 0.90
Angle correction factor (side view), Cf (deg) 0.99
Corner sprung weight, CSW (lbs) 79.36
Assume frequency for AVT, N (hertx) 1.8
Installation ratio = MR * A * Cf = 0.6 * 0.90 * 0.99 = 0.54
Wheel rate = (CSW * (2 * 3.14 (N)^2) = 26.26 lbs/in
Spring rate = (Wheel rate) / (Installation ratio)^2 = 89.21 lbs/in
Droop travel = (CSW * gravity) / (Wheel rate) = 3 inches
Bump travel = Wheel travel – Droop travel = 7 inches
2.2.REAR SUSPENSION SPRING RATE
GIVEN VEHICLE GEOMETRY DATA
Wheel travel (inches) 10
Spring travel (inches) 6
Motion ratio, MR 0.65

Angle correction factor (front view), Cf (deg) 0.98
Angle correction factor (side view), Cf (deg) 0.987
Corner sprung weight, CSW (lbs) 109.34
Assume frequency for AVT, N (hertz) 2.178
Installation ratio = MR * A * Cf = 0.65 * 0.95 * 0.987 = 0.54
Wheel rate = (CSW * (2 * 3.14 (N)^2) = 52.98 lbs/in
Spring rate = (Wheel rate) / (Installation ratio)^2 = 139.81 lbs/in
Note: Front suspension should have a 30% lower ride rate than rear suspension. The reason for this is
that the front of the vehicle will ride over the bump (disturbance) first creating an excitation in the
front suspension, and then seconds later the rear suspension will ride over the bump creating an
excitation in the rear suspension. If the two suspension rates are identical the phase lag between the
front and the rear suspensions will create an undesirable motion in pitch. There have been studies that
have shown that the driver/passenger is/are very uncomfortable in pitch motion, it tends to cause neck
muscle strains. Therefore, by increasing the suspension rate in the rear suspension allows for the rear
of the vehicle to “catch up” to the front of the vehicle.
2.3.CALCULATION FOR REAR FREQUENCY
Calculation for rear ride frequency according to front ride frequency help in avoiding pitching
motion of vehicle.
Wheelbase = 55 inches
Velocity, V = 45 kph
Front frequency, f = 1.93 hz
Exit time to travel wheelbase, (t1) = wheelbase/velocity = .11 sec
Time period, (t2) = 1/f = 0.518 sec
Time period for rear suspension = (t2-t1) = 0.518 -0.11 = 0.4065 sec
Calculated rear frequency, (f) = 1/f = 2.45 hz
CONCLUSIONS
The primary work performed on the design clearly indicated that the desired goals were
achieved. According to design we have fabricated front and rear suspension for better performance of
ATV by considering all prominent design parameter. After initial testing it seems that all desired
properties achieved as considered while designing .we achieved rear ride frequency 22 % more than
front which help in avoiding pitching motion of the vehicle and provide good ride comfort to driver.
There were no major failure observed on the geometry for different configuration. The interference
made from the work clearly shown us the potential of the design and its feasibility to adapt without
having to modify major components. The selection parameter help us to select the proper design of
suspension system.
REFERENCES
[1] H. WALLENTOWITZ Vertikal-/Querdynamik von Kraftfahrzeugen Umdruck zur Vorlesung
Kraftfahrzeuge II Verlag fka ISBN 3-925 194-35-5 Aachen, 1. Auflage 1996

[2] W. MATSCHINSKY Radführung der Straßenfahrzeuge Springer Verlag ISBN 3-540-64155-6 Berlin,
Heidelberg, New York, 2. Auflage 1998
[3] J. REIMPELL, H. STOLL The Automotive Chassis: Engineering Principles SAE, Inc. ISBN 1-56091-
736-9 Warrendale, 1st edition 1996
[4] P. HOLDMANN, P. KÖHN, B. MÖLLER, R. WILLEMS Suspension kinematics and compliance -
measuring and simulation SAE 1998 International Congress and Exposition
[5] P. KÖHN, P. HOLDMANN Moderne Prüfstandstechnik für das Fahrwerk ATZ 100 (1998) Nr. 9
[6] P. HOLDMANN Kinematik und Elastokinematik moderner PkwRadaufhängungen Lecture within the
PhD-Procedure at the Aachen University of Technology, Aachen, May 2000
[7] Race car Vehicle Dynamics: Milliken and Milliken
[8] Car suspension and Handling: Geoffrey Donald Bastow
[9] Fundamental of vehicle dynamics: Thomas D. Gillespie

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