Suhas.Rao.Shyam.K | Automobile Engineering | suhasrao24@gmail.com | March 22, 2016

Innovations in Suspension Mechanisms

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Table of Contents.

1. Introduction. 1

1.1. Need of a Suspension system. 2

1.2. Functions of a Suspension system. 2

1.3. Requirements of a Suspension system. 2

1.4. Types of Suspension systems. 3

2. Scope of the Article. 4

3. Study of various Suspension systems. 5

3.1. Normal Terrain suspensions. 5

3.1.1. Leaf Springs. 5

3.1.2. Coil Springs. 6

3.1.3. Telescopic Shock Absorber. 6

3.1.4. Hydrolastic suspension. 7

3.1.5. Hydragas suspension. 8

3.1.6. Hydropneumatic suspension. 9

3.1.7. Solid Beam Axle. 10

3.1.8. Swing Axle 11

3.1.9. Trailing link suspension. 12

3.1.10. Macpherson Strut. 13

3.1.11. Wishbone suspension. 14

3.1.12. Air suspension. 15

3.1.13. Electromagnetic suspension. 16

3.1.14. Magnetic suspension. 17

3.1.15. Active body Control. 18

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3.1.16. Hydraulic Roll control. 19

3.2. Uneven Terrain suspensions. 20

3.2.1. Radius arm setup. 20

3.2.2. Parallel and Triangulated Four link. 20

3.2.3. Ford Twin Traction beam. 21

3.2.4. Semi-Active suspension with MR fluids. 22

3.2.5. Rocker-Bogie Suspension. 23

3.2.5.1. Design 24

3.2.5.2. Types of Rocker-Bogie system. 25

3.2.5.3. Structural Elements. 26

3.2.5.4. Working Principle. 27

3.2.6. Double-Lambda Mechanism. 28

3.2.6.1. Adaption of Double-lambda mechanism into Rocker-Bogie Suspension. 29

3.2.6.2. Various Design Possibilities with Linear Motion Bogie. 31

5. Suspension troubleshooting chart. 34

6. Conclusion. 35

7. References. 36

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List of Figures.

Figure 1: Semi-elliptical leaf spring. 5

Figure 2: Coil Spring. 6

Figure 3: Telescopic Shock Absorber. 6

Figure 4: Hydropneumatic Suspension. 7

Figure 5: Cross Section of a Hydragas suspension. 8

Figure 6: Hydropneumatic Suspension. 9

Figure 7: Typical beam axle design. 10

Figure 8: Illustration showing a swing axle suspension at different positions. 11

Figure 9: Single link trailing link rear suspension. 12

Figure 10: MacPherson Strut. 13

Figure 11: Wishbone suspension. 14

Figure 12: Block diagram of Air Suspension. 15

Figure 13: Bose suspension on front wheels. 16

Figure 14: Cross Section and working mode of GM’s Magneride. 17

Figure 15: Working action of a Mercedes’s Active Body Control. 18

Figure 16: Front and Rear DRC suspension. 19

Figure 17: Radius arm setup. 20

Figure 18: Parallel Four link. 21

Figure 19: Twin Traction beam. 21

Figure 20: Quarter car semi-active suspension model. 22

Figure 21: Rocker-Bogie suspension connected to six wheels. 23

Figure 22: Side View of Rocker-Bogie Configuration. 23

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Figure 23: Rocker-bogie suspension in action. 24

Figure 24: Rocker- Bogie system operated by a Differential Gearbox. 25

Figure 25: Rocker- Bogie system operated by a Differential Bar. 26

Figure 26: MER Suspension Nomenclature (Deployed Configuration). 27

Figure 27: A Rocker-Bogie Rover with deployed Suspension. 27

Figure 28: A rover climbing past the rocks without altering the body

directional vector. 28

Figure 29: (a) Connection between two lambda mechanisms,

(b) definition of ground clearance 29

Figure 30: Double-Lambda mechanism adapted into rocker-bogie suspension. 30

Figure 31: Differential gear mechanism between right and left rockers. 30

Figure 32: Different applications of lambda bogie suspension. 31

Figure 33: Solidworks model of a front loading vehicle operating on a

rocker bogie mechanism. 32

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1. Introduction

A suspension system connects your vehicle to its wheels. It is designed to counteract the

forces of gravity, propulsion and inertia that are applied to your vehicle as you accelerate,

slow down or stop in such a way that all four wheels remain on the ground. There have been

several methods developed in recent years to improve the comfort of the passengers by

maintaining the average pitch angle of the chassis.

The modern automobile has come along way since the days when “just being self-propelled”

was enough to satisfy the car owner. Improvement in suspension, increased strength &

durability of components, and advances in tire design and construction has made large

contributions to tiding comfort and driving safety.

Basically, suspension refers to the use of front and rear springs to suspend a vehicles frame,

body, engine & power train above the wheels. These relatively heavy assemblies constitute

what is known as “Sprung” weight. “Unsprung” weight, on the other hand, includes wheels

and tire, break assemblies and other structural members not supported by the springs.

The springs used in today's cars and trucks are engineered in a wide variety of types, shapes,

sizes, rates and capacities. Types includes leaf springs, coil springs, air springs and torsion

bars. These are used in sets of four per vehicle, or they are paired off in various combinations

and are attached to the vehicle by a number of different mounting techniques.

This article will provide a basic overview of just about all of the different types of front

suspensions that have been used on production vehicles and rovers since the inception of

the automobile. While some of the older styles are obsolete it is still important to learn

about them because it provides valuable insight into why the cutting edge suspensions of

today perform so much better

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1.1. Need of a Suspension.

A system of mechanical linkages, springs, dampers that is used to connect the

wheels to the chassis is known as suspension system. It also helps to maintain correct

vehicle height and wheel alignment. It also controls the direction of the vehicle and has to

keep the wheel in perpendicular direction for their maximum grip. The suspension also

protects the vehicle itself and luggage from damage and wear. The design of front and rear

suspension of a car may be different.

1.2. Functions of a Suspension System.

1. Maintain correct vehicle ride height.

2. Reduce the effect of shock forces.

3. Maintain correct wheel alignment.

4. Support vehicle weight.

5. Keep the tyres in contact with the road.

6. Control the vehicle's direction of travel.

1.3. Requirements of a Suspension System.

1. Low initial cost.

2. Minimum weight.

3. Minimum tyre wear.

4. Minimum deflection consistent with required stability.

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1.4. Types of Suspension Systems.

1) Independent Suspension System.

This system means that the suspension is set-up in such a way that allows the wheel on the

left and right side of the vehicle to move vertically independent up and down while driving

on uneven surface. A force acting on the single wheel does not affect the other as there is

no mechanical linkage present between the two hubs of the same vehicle. In most of the

vehicle it is employed in front wheels.

This types of suspension usually offers better ride quality and handling due to less unsprung

weight. The main advantage of independent suspension are that they require less space,

they provide easier steer ability, low weight etc... Examples of Independent suspension are

Double Wishbones

MacPherson Strut

2) Dependent Suspension System.

In Dependent Suspension there is a rigid linkage between the two wheels of the same axle.

A force acting on one wheel will affect the opposite wheel. For each motion of the wheel

caused by road irregularities affects the coupled wheel as well. It is mostly employed in

heavy vehicles. It can bear shocks with a great capacity than independent suspension.

Example of this system is

Solid Axle.

3) Semi-Independent Suspension System.

This type of system has both the characteristics of dependent as well as independent

suspension. In semi-independent suspension, the wheel move relative to one another as in

independent suspension but the position of one wheel has some effect on the other wheel.

This is done with the help of twisting suspension parts. Example of semi-independent is

Twist Beam.

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2.0. Scope of the Article

The sole purpose of a suspension system is to isolate the vehicle from road shocks and

hence pr0vide reasonable level of comfort to the passengers. This experience is amplified

when the vehicle is driven on well maintained and sophisticated roads. Some of the

important suspension systems that are used for this type of terrain is explained in the first

half of this article. Some of them are

Leaf springs.

Shock Absorbers.

Macpherson Strut.

Wishbone suspension.

Magnetic suspension.

Active and Dynamic Body control. Etc…

However for rough surfaces like a desert or any other rocky terrains or in outer-planetary

surfaces where gravity is of a lesser co-efficient than of the Earth’s, the vibrations produced

due to them cannot be damped or overcome by normal suspensions that are mentioned

above hence providing a poor degree of comfort. That being the case for conditions like

these a complete different system has to be applied. These have been explained in the other

half this article. Some of them are

Rocker-bogie suspension.

Twin-I Beam.

Double-lambda mechanism. Etc...

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3.0. Study of various Suspension systems.

3.1. Normal Terrain Suspensions.

3.1.1. Leaf Springs. The spring consists of number of leaves called blades. The blades vary

in length as shown. The composite spring is based upon the theory of a beam of uniform

strength. The lengthiest blade has eyes on its ends. This blade is called master leaf. All the

blades are bound together by means of steel straps as shown. The spring is supported on an

axle, front or rear by means of a U-bolt. One end of the spring is mounted on the frame with

a simple pin, while the other end, connection is made with a shackle. When the vehicle

moves up, deflecting the spring. This changes the length the spring eyes. If both the eyes

are fixed, the spring will not be able to accommodate this change of length. This is provided

for by means of a shackle at one end which gives a flexible connection. Generally rear springs

are kept longer than the front springs, this causes them to vibrate at different frequencies,

which prevents excessive bounce.

Figure 1: Semi-elliptical leaf spring.

Advantages Disadvantages

1. Lightweight, extremely strong.

2. Weighs 1/4th of the same strength.

3. Corrosion and chemical resistant

4. Excellent elastic properties.

5. Regains shape after bending till

certain limit, useful for spring

operation.

6. Internal friction provides damping.

1 High cost of fabrication,

complicated time consuming

process.

2. Repair procedure is complex.

3. Unpredictable mechanical

characterization.

4. Not isotropic, need more

parameters for evaluation.

5. Compressive strength not

dependable.

6. Prone to weaken over time.

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3.1.2. Coil Springs. Coil springs often find its application

with independent suspension. However due to lack of inner

friction some manufacturers have used it in rear suspension.

Coil springs are superior to leaf springs as far as the energy

storage is concerned. In front wheel drive car, the helical

springs are commonly used to support rear dead axle. The

spring takes shear as well as bending stresses. The coil springs

however cannot take torque reaction and side thrust, for which

alternative arrangements should be provided. A helper coil

spring is also sometimes used to provide progressive stiffness

against increasing load.

Fig 2: Coil Spring.

3.1.3. Telescopic Shock Absorber. The shock absorbers

widely used in the automotive suspension system are often

hydraulic shock absorbers, its working principle is that: when

the relative motion between the automobile frame (or

automobile body) and the driving axle occurs due to vibration,

the piston in the shock absorber moves up and down, the oil

in the cavities of the shock absorber repeatedly flows from one

cavity to another cavity via different holes, at this time, the

friction between the hole walls and the oil and between oil

molecules form the damping force, and the vibration energy

of the automobile is converted into heat energy of the oil and

then absorbed by the shock absorber and emitted to the

atmosphere. Under the condition of the same total sectional

area of oil channels, the damping force of the shock absorber

increases or decreases along with the increase or decrease of

the relative motion speed of the automobile frame and the

driving axle(or wheels), and is related to viscosity of the oil.

Modern shock absorbers are electrically controlled and are

velocity-sensitive i.e., the faster the suspension moves, the

more resistance the shock absorber provides. These allow the

driver to select the amount of shocker damping by simply

pressing a button on the instrument panel. The variation is

achieved by varying the size of orifices in the shock absorber

valves by means of small electric motor mounted on top of the

shock absorber.

Fig 3: Telescopic Shock Absorber.

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3.1.4. Hydrolastic suspension. Hydrolastic suspension - a system where the front and

rear suspension systems were connected together in order to better level the car when

driving. The principle is simple. The front and rear suspension units have Hydrolastic

displacers, one per side. These are interconnected by a small bore pipe. Each displacer

incorporates a rubber spring (as in the Moulton rubber suspension system), and damping

of the system is achieved by rubber valves. So when a front wheel is deflected, fluid is

displaced to the corresponding suspension unit. That pressurizes the interconnecting pipe

which in turn stiffens the rear wheel damping and lowers it. The rubber springs are only

slightly brought into play and the car is effectively kept level and freed from any tendency

to pitch. That's clever enough, but the fact that it can do this without hindering the full

range of motion of either suspension unit is even cleverer, because it has the effect of

producing a soft ride.

Fig 4: Hydropneumatic Suspension.

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3.1.5. Hydragas Suspension. The system replaces the separate springs and dampers of a conventional suspension system with integrated, space efficient, fluid filled, displacer units, which are interconnected between the front and rear wheels on each side of the vehicle Hydragas is an evolution of Hydrolastic, and essentially, the design and installation of the system is the same. The heart of the system are the displacer units, which are pressurised spheres containing nitrogen gas. These replace the conventional steel springs of a regular suspension design. The means for pressurising the gas in the displacers is done by pre-pressurising a hydraulic fluid, and then connecting the displacer to its neighbour on the other axle. This is unlike the Citroën system, which uses hydraulic fluid continuously pressurised by an engine-driven pump and regulated by a central pressure vessel. The difference is in the displacer unit itself. In the older systems, fluid was used in the displacer units with a rubber spring cushion built-in. With Hydragas, the rubber spring is removed completely. The fluid still exists but above the fluid there is now a separating membrane or diaphragm, and above that is a cylinder or sphere which is charged with nitrogen gas. The nitrogen section is what has become the spring and damping unit whilst the fluid is still free to run from the front to the rear units and back. The key improvement over conventional suspension is that the front/rear interconnection allows the vehicle to be stiffer in roll than in pitch. Hence it is possible to design a compliant suspension - giving a comfortable ride - without suffering a penalty in terms of excessive roll when cornering.

Fig 5: Cross Section of a Hydragas suspension.

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3.1.6. Hydropneumatic Suspension. It is a whole-car solution which can include the brakes and steering as well as the suspension itself. The system is powered by a large hydraulic pump, typically belt-driven by the engine like an alternator or an air conditioner. The pump provides fluid to an accumulator at pressure, where it is stored ready to be delivered to servo a system. This pump may also be used for the power steering and the brakes. The purpose of this system is to provide a sensitive, dynamic and high-capacity suspension that offers superior ride quality on a variety of surfaces. The suspension system usually features both self-leveling and driver-variable ride height, to provide extra clearance in rough terrain. At the heart of the system, acting as pressure sink as well as suspension elements, are the so-called spheres, five or six in all; one per wheel and one main accumulator as well as a dedicated brake accumulator on some models. Spheres consist of a hollow metal ball, open to the bottom, with a flexible desmopan rubber membrane, fixed at the 'equator' inside, separating top and bottom. The top is filled with nitrogen at high pressure, up to 75 bar, the bottom connects to the car's hydraulic fluid circuit. The high pressure pump, powered by the engine, pressurizes the hydraulic fluid (LHM) and an accumulator sphere maintains a reserve of hydraulic power. This part of the circuit is at between 150 and 180 bars. It powers the front brakes first, prioritized via a security valve. Pressure flows from the hydraulic circuit to the suspension cylinders, pressurizing the bottom part of the spheres and suspension cylinders. Suspension works by means of a piston forcing LHM into the sphere, compacting the nitrogen in the upper part of the sphere; damping is provided by a two-way 'leaf valve' in the opening of the sphere. LHM has to squeeze back and forth through this valve which causes resistance and controls the suspension movements. It is the simplest damper and one of the most efficient. Ride height correction (self levelling) is achieved by height corrector valves connected to the anti-roll bar, front and rear

Fig 6: Hydropneumatic Suspension.

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3.1.7. Solid beam axle. Just as it sounds, in the beam axle setup both of the front wheels

are connected to each other by a solid axle. This style was carried over to the first

automobiles from the horse drawn carriages of the past and worked well enough so that

initially no other suspension even needed to be considered. In fact the beam axle can still

be found today. New developments in springs, roll bars, and shocks have kept the solid axle

practical for some applications.

Fig 7: Typical beam axle design, showing

the wheels connected by the axle and the

whole assembly connected to the chassis

by the springs and shocks

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3.1.8. Swing Axle. After designers had come to realize the severe drawbacks of the solid

axle front suspension, they moved on to early attempts at an independent style of front

suspension. One of these attempts came to be known as a Swing axle suspension. It is, as

the name suggests, set up so that the axles pivot about a location somewhere near the center

of the car and allow the wheels to travel up and down through their respective arcs. This

system was eventually adapted for rear suspensions as can be found on the old beetles.

Fig 8: Illustration showing a

swing axle suspension at

different positions.

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3.1.9. Trailing link. Another early form of front independent suspension is called the

trailing link suspension. This suspension design uses a set of arms located ahead of the

wheels to support the unsprung mass. In essence the wheel “trails” the suspension

links. Hence the name. Since independent front suspensions were pioneered in production

cars to improve the ride characteristics of vehicles as well as minimize the space needed for

the suspension itself, early designs like the trailing link suspension attempted to excel in

those areas of improvement. Trailing link systems like the one in the front of the old beetle

were a success from the manufacturer standpoint as they did improve ride and reduce the

packaging size of the suspension. However, there were some considerable drawbacks to the

trailing link system when applied to vehicles that generate high cornering loads.

Fig 9: This image shows a single link

trailing link rear suspension

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3.1.10. MacPherson Strut. In the 70’s the MacPherson front suspension assembly became

a very popular design on front wheel drive cars. This strut based system, where the

spring/shock directly connects the steering knuckle to the chassis and acts as a link in the

suspension, offers a simple and compact suspension package. This is perfect for small front

wheel drive cars where space is tight and even allows room for the drive shaft to pass

through the knuckle. Today most small cars will use this type of suspension because it is

cheap, has good ride qualities, and has the compact dimensions necessary for front wheel

drive cars. Like the trailing link style independent suspension, the MacPherson assembly

works very well for production road going cars, but on performance cars it is less than ideal.

Fig 10: The illustration shows what a

typical MacPherson assembly looks like.

With the strut acting as the upper

suspension link

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3.1.11. Wishbone. The next evolution in suspension design was to move towards the equal

length A-arm setup. This is commonly referred to as a “double wishbone” suspension as the

A shaped control arms resemble a wishbone. The spring is placed between the lower

wishbone and the underside of the cross-member. The vehicle weight is transmitted from

the body and the cross-member to the coil spring through which it goes to the lower

wishbone member. A shock absorber is placed inside the coil spring and is attached to the

cross-member and to lower wishbone member. Because of the V-shape, the wishbones not

only position the wheels and transmit the vehicle load to the springs, but also resist

acceleration, braking and cornering (side) forces. The upper arms are shorter in length than

lower arms to keep the wheel-track constant and thereby minimizing tyre wear.

Fig 11: Image shows a wishbone suspension with

upper and lower wishbone arms and shock

absorber in the middle.

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3.1.12. Air suspension. In the front suspension, the air springs are installed between the

underside of each chassis side-member and the transverse axle beam. In the rear tandem

suspension, the air springs are mounted between each trailing arm and the underside of the

chassis. Two types of air springs are generally used, bellow or piston type. The air springs

which may be of either type are mounted on the same position where generally the coil

springs are mounted. An air compressor takes the atmospheric air through a filter and

compress it to a pressure of about 240MPa, at which pressure in the air in the accumulated

tank is maintained, which is also provided with a safety relief valve. This high pressure air

goes through the lift control valve and the levelling valves, to the air springs as shown. The

lift control valve is operated manually by means of a handle on the control panel, through

a cable running from the valve to the handle.

Fig 12: Block diagram of Air Suspension.

Advantages Disadvantages

1. The improved standard of ride

comfort and noise reduction

attained with air springs has

reduced driver fatigue.

2. The spring rate varies much less

between laden and unladen

conditions as compared to steel

springs. This reduces dynamic

loading.

1. High cost and complicated system

2. Higher maintenance cost.

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3.1.13. Electromagnetic (Bose) Suspension System. In a luxury sedan the suspension

is usually designed with an emphasis on comfort, but the result is a vehicle that rolls &

pitches while driving and during turning and braking. In sports cars, where the emphasis is

on control, the suspension is designed to reduce roll & pitch, but comfort is sacrificed. The

Bose suspension system includes a linear electromagnetic motor and power amplifier at

each wheel, and a set of control algorithms. This proprietary combination of suspension

hardware & control software makes it possible, for the first time, to combine superior

comfort & superior control in the same vehicle. A linear electromagnetic motor is installed

at each wheel of a Bose equipped vehicle. Inside the linear electromagnetic motor are

magnets & coils of wire. When electrical power is applied to the coils, the motor retracts

and extends, creating motion between the wheel & car body. The power amplifier delivers

electrical power to the motor in response to signals from the control algorithms. The

regenerative power amplifiers allow power to flow into the linear electromagnetic motor

and also allow power to be returned from the motor. Bose's front suspension modules use a

modified MacPherson strut layout and the rear suspension modules use a double-wishbone

linkage to attach a linear electromagnetic motor between the vehicle body and each wheel.

Torsion springs are used to support the weight of the vehicle. In addition, the Bose

suspension includes a wheel damper at each wheel to keep the tyre from bouncing as it rolls

down the road. Unlike conventional dampers, which transmit vibrations to the vehicle

occupants and sacrifice comfort, the wheel damper in the Bose system operates without

pushing against the car body, maintaining passenger comfort. The Bose suspension

demonstrates the ability to combine in one automobile a much smoother ride than any

luxury sedan and less roll and pitch than any sports car. This performance results from a

proprietary combination of suspension hardware and control algorithms.

Fig 13: Bose suspension on front wheels.

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3.1.14. Magnetic Suspension (Magneride). Magnetic suspension is described as the

fastest reacting suspension in the world as sensors monitor the road surface up to 1000 times

per second and an ECU can make variations within a few milliseconds resulting in the

possibility of multiple damping variations being made in a second. Magnetic ride control

uses a system known as magneto rheological technology for suspension damping. Each

absorber is filled with a polymer liquid containing many small magnetic particles

(MagnetoRheological (MR) fluid, a kind of synthetic oil containing tiny particles of iron in

suspension). An electrical charge is sent to the liquid in the absorber which immediately

changes the position of the particles in the liquid and its viscosity. The viscosity of the

polymer liquid can be changed to an almost solid state similar to plastic or rubber in

composition. As the viscosity of the liquid changes, it offers a difference in the damping.

Each of the four dampers are adjusted individually and independently even when it seems

that all of them are doing the same thing. This ensures a comfortable ride along various

road surfaces. Magnetic suspension reduces vibrations, bouncing, noise and body roll very

effectively on all road surfaces and at any speed that the vehicle could travel. The reduction

of body roll may reduce the need for anti-roll bars. Another benefit is that these dampers

easily offers the best of both worlds in the ride comfort/handling compromise that many

other suspension systems are subjected to. Although this type of suspension offers a very

comfortable ride, sport settings can be applied or tuned into the system to cater for

performance vehicles.

Fig 14: Cross Section and working mode of GM’s Magneride

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3.1.15. Active Suspension. Active Body Control, or ABC, is the Mercedes-Benz brand

name used to describe hydraulic fully active suspension, that allows control of the vehicle

body motions and therefore virtually eliminates body roll in many driving situations

including cornering, accelerating, and braking. In the ABC system, a computer detects body

movement from sensors located throughout the vehicle, and controls the action of the

active suspension with the use of hydraulic servomechanisms. The hydraulic pressure to the

servos is supplied by a high pressure radial piston hydraulic pump. A total of 13 sensors

continually monitor body movement and vehicle level and supply the ABC controller with

new data every ten milliseconds. Four level sensors, one at each wheel measure the ride

level of the vehicle, three accelerometers measure the vertical body acceleration, one

acceleration sensor measures the longitudinal and one sensor the transverse body

acceleration. At each hydraulic cylinder, a pressure sensor monitors the hydraulic pressure.

As the ABC controller receives and processes data, it operates four hydraulic servos, each

mounted in series on a spring strut, beside each wheel. Almost instantaneously, the servo

regulated suspension generates counter forces to body lean, dive and squat during various

driving maneuvers. A suspension strut, consisting of a steel coil spring and a shock absorber

are connected in parallel, as well as a hydraulically controlled adjusting cylinder, are located

between the vehicle body and wheel. These components adjust the cylinder in the direction

of the suspension strut, and change the suspension length. This creates a force which acts

on the suspension and dampening of the vehicle.

Fig 15: Working action of a Mercedes’s Active Body Control.

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3.1.16. Hydraulic Roll Control. The DRC system (known as Dynamic Ride Control -

DRC - by Audi) is a pure mechanical damping system which monitors road conditions and

cornering forces, and adjusts the suspension accordingly. This advanced damping system

counteracts movements of the vehicle along its longitudinal axis and transverse axis. Both

shock absorbers on the same side of the vehicle are connected with the diagonally opposed

dampers on the other side, each by means of one central valve. By connecting diagonally

opposed shock absorbers vehicle pitching and diagonal chassis movements are minimised.

The result is that the car is more stable at high speeds, as well as offering greater ride

comfort at any speed. When a corner is taken, a flow of oil, and thus a supplementary

damping force, is generated via the central valve between the diagonally opposed shock

absorbers. When the suspension is compressed on one side, the damper characteristic is

modified in such a way that rolling or pitching movements are almost entirely eliminated.

As a result, this mechanically active damping system ensures that the vehicle maintains

extremely good tracking stability when cornering and responds precisely to adjustments of

the steering wheel. Other advantages include: better handling, less tyre wear, lower

maintenance costs, preventing any tendency for over-steer and improved cornering ability.

Fig 16: Front and Rear DRC suspension.

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3.2. Uneven Terrain Suspensions.

3.2.1. Radius Arm Setup

Fig 17: Radius arm setup.

Some solid axle designs use coil springs instead of leaf springs. Coil springs are more compact than leaf springs but they only support the vehicle’s weight; they cannot locate the axle like leaf springs do. The suspension members need to locate the axle while also allowing it to move. The radius arm design uses two arms that run parallel to the frame. They mount to a perch on the frame and solidly to the axle housing and allow the axle to pivot up and down. A track bar runs from the frame to the axle perpendicular to the radius arms to keep the axle centered on the frame. Since the radius arms are fixed at the axle end, the caster angle changes when the suspension cycles up and down, shown in the figure to the right. Radius arm designs have been used by Ford and Dodge among others.

3.2.2. Parallel and Triangulated Four Link

A variation on the radius arm suspension is the parallel four link, shown in the figure to

the left. Aftermarket manufacturers make kits that retrofit an existing radius arm

suspension to a parallel four link design and use coil springs and a track bar to center the

axle. Instead of a radius arm with a fixed mount on the axle, it uses an upper and lower

link on each side with pivots on both ends. As the axle cycles up and down, the links allow

it to maintain the same relationship with the ground and the caster angle remains

constant. Anytime you add a pivot, you add a wear item and the potential for deflection.

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Fig 18: Parallel Four link.

What the parallel four link gives up in strength compared to the radius arm, it makes up

for in better ride quality and handling. Another four link design is the triangulated four

link. The parallel four link needs a track bar to locate the axle side to side. With a

triangulated four link design, if the links are mounted at great enough angles, a track bar

is not needed. When the top links are wider at the frame and narrow at the axle housing,

then the lower links are mounted with opposing angles. The greater the angles, the more

the links will resist side to side movement.

3.2.3. Ford Twin Traction Beam

Fig 19: Twin Traction beam.

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This Toyota Tundra was retrofitted with an I-beam setup usually found on Fords. Notice

the positive camber at full droop.

Ford has an independent suspension design that is part solid axle and part independent

suspension – the Ford Twin Traction Beam or TTB. The TTB is similar to a solid axle

except the drive axles and housing pivot in the center. It came from Ford with either leaf

springs or coils. The two wheel drive version is called the twin I-beam. The TTB design

works well as designed but has been maligned by many; usually due to modifications done

by the end user. Complaints of unusual tire wear and bump steer are typical after

installing a lift kit. Many times the culprit is the steering linkage, not the TTB design itself.

It may look strange but TTB is very strong due to the length of the beams. It spreads the

stresses out and has a much better shock ratio than A-arms. The passenger side beam

needs to be gusseted if you are doing a lot of off-roading but we have kits for that. It’s

important to maintain the bushings and steering components on a TTB suspension.

3.2.4. Semi Active Suspension with MR Fluids

The MagnetoRheological (MR) fluids can be quite pro- missing for vibration reduction

applications. Dampers with controllable fluids are often known as rheological fluids. MR

fluids are non-colloidal suspensions of particles having size in order of a few microns

(5 - 10μm). The properties of these fluids are determined by polarize- able particles within

nonconductive carrier fluid. These particles being polarized the fluid become very viscous

and difficult to move and responds faster, in milliseconds. In active suspension, the power

consumption is very large (at least 10% of engine power) but for Semi-Active Suspension

(SAS) the power from the battery is enough. At the time of power failure, the active

suspension is completely inactive. Because of the above reasons it has been considered and

observed that SAS very much useful in ATV suspensions.

Fig 20 : Quarter car semi-active suspension model.

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3.2.5. Rocker-Bogie Suspension.

The place, where the value of gravity remain lower than earth’s own gravitational

coefficient, at that place the existing suspension system fails to fulfil desired results as the

amount and mode of shock absorbing changes. To counter anti-gravity impact, NASA and

Jet Propulsion Laboratory have jointly developed a suspension system called the rocker-

bogie Suspension system. It is basically a suspension arrangement used in mechanical

robotic vehicles used specifically for space exploration. The rocker-bogie suspension based

rovers has been successfully introduced for the Mars Pathfinder and Mars Exploration Rover

(MER) and Mars Science Laboratory (MSL) missions conducted by apex space exploration

agencies throughout the world. The proposed suspension system is currently the most

favored design for every space exploration company indulge in the business of space

research. The motive of this research initiation is to understand mechanical design and its

advantages of Rocker- bogie suspension system in order to find suitability to implement it

in conventional loading vehicles to enhance their efficiency and also to cut down the

maintenance related expenses of conventional suspension systems.

Fig 21: Rocker-Bogie suspension connected to six

wheels.

Fig 22: Side View of Rocker-Bogie Configuration

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3.2.5.1. Design

The rocker-bogie design has no springs or stub axles for each wheel, allowing the rover to

climb over obstacles, such as rocks, that are up to twice the wheel's diameter in size while

keeping all six wheels on the ground. As with any suspension system, the tilt stability is

limited by the height of the center of gravity. Systems using springs tend to tip more easily

as the loaded side yields. Based on the center of mass, the rover can withstand a tilt of at

least 45 degrees in any direction without overturning, but automatic sensors limit the rover

from exceeding 30-degree tilts. The system is designed to be used at slow speed of around

10 centimeters per second (3.9 in/s) so as to minimize dynamic shocks and consequential

damage to the vehicle when surmounting sizable obstacles.

JPL states that this rocker bogie system reduces the motion of the main MER vehicle body

by half compared to other suspension systems. Each of the rover's six wheels has an

independent motor. The two front and two rear wheels have individual steering motors

which allow the vehicle to turn in place. Each wheel also has cleats, providing grip for

climbing in soft sand and scrambling over rocks. The maximum speed of the robots

operated in this way is limited to eliminate as many dynamic effects as possible so that the

motors can be geared down, thus enabling each wheel to individually lift a large portion of

the entire vehicle's mass.

In order to go over a vertical obstacle face, the front wheels are forced against the obstacle

by the center and rear wheels. The rotation of the front wheel then lifts the front of the

vehicle up and over the obstacle. The middle wheel is then pressed against the obstacle by

the rear wheels and pulled against the obstacle by the front until it is lifted up and over.

Finally, the rear wheel is pulled over the obstacle by the front two wheels. During each

wheel's traversal of the obstacle, forward progress of the vehicle is slowed or completely

halted. This is not an issue for the operational speeds at which these vehicles have been

operated to date.

Fig 23: Rocker-bogie system in action, the body remains horizontal irrespective of the surface.

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3.2.5.2. Types of Rocker-Bogie system.

The Rocker-Bogie suspension system is operated through two different types of

mechanism. They are

Differential Gearbox.

Differential Bar.

1) Differential Gearbox

Fig 24: Rocker- Bogie system operated by a Differential Gearbox.

The Mars Exploration Rovers (Spirit and Opportunity) use differential gearboxes. The

gearbox is inside the rover body, so you never see it. No wonder it is hard to figure out how

it works! In my Lego model rover shown here, I use a simple three-gear differential. Two

gears connect to the two rockers and the third (middle) gear connects to the body. If you

hold the model rover body steady in midair and tilt one rocker up, the gears will turn and

the other rocker will tilt down (see the animations below).

The real Mars Exploration Rovers use more complicated gearboxes with more gears but

they are functionally equivalent to this simple three-gear differential.

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2) Differential Bar

The Mars Science Laboratory (Curiosity) uses a differential bar. This is the big black bar that

you see across the deck of the rover.

Fig 25: Rocker- Bogie system operated by a Differential Bar.

The middle of the bar is connected to the body with a pivot and the two ends are connected

to the two rockers through some short links. If you hold the model rover body steady in

midair and tilt one rocker up, one end of the bar will go back, the other end will go forward,

and the other rocker will tilt down.

The Mars Exploration Rovers did not use a differential bar because it would interfere with

the solar panels. But the Mars Science Laboratory does not have that problem because it is

nuclear powered and has no solar panels.

3.2.5.3. Structural Elements.

As the name would suggest, the two primary components of this type of suspension are the rocker and bogie. These two structural elements are connected via a free rotating pivot dubbed the Bogie Pivot. The right and left sets of rocker-bogie assemblies are connected to each other via the vehicle’s differential, a passive, motion-reversal joint that constrains the two sides of the mobility system to equal and opposite motion. Three unique break points were selected: the Rocker-Bridge Joint, a mid-span rocker folding joint; the Rocker Deployment Actuator (RDA) Joint, a motor driven deployment joint on the forward rocker arm, and a telescoping prismatic joint on the bogie member. Thus, a total of six joints must be reliably locked and latched into place during deployment to provide the rover with a safe and stable platform for driving.

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Fig 26: MER Suspension Nomenclature (Deployed Configuration)

3.2.5.4. Working Principle.

The design of the suspension system for the wheels is based on heritage from the

“rocker-bogie" system on the Pathfinder and Mars Exploration Rover missions. The

suspension system is how the wheels are connected to and interact with the rover body. The

term "bogie" comes from old railroad systems. A bogie is a train undercarriage with six

wheels that can swivel to curve along a track.

Fig 27: A Rocker-Bogie Rover with deployed Suspension.

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The term "rocker" comes from the design of the differential, which keeps the rover body

balanced, enabling it to "rock" up or down depending on the various positions of the

multiple wheels. Of most importance when creating a suspension system is how to prevent

the rover from suddenly and dramatically changing positions while cruising over rocky

terrain. If one side of the rover were to travel over a rock, the rover body would go out of

balance without a "differential" or "rocker," which helps balance the angle the rover is in at

any given time. When one side of the rover goes up, the differential or rocker in the rover

suspension system automatically makes the other side go down to even out the weight load

on the six wheels. This system causes the rover body to go through only half of the range of

motion that the "legs" and wheels could potentially experience without a "rocker-bogie"

suspension system.

Fig 28: A rover climbing past the rocks without altering the body directional vector

The rover is designed to withstand a tilt of 45 degrees in any direction without overturning.

However, the rover is programmed through its "fault protection limits" in its hazard

avoidance software to avoid exceeding tilts of 30 degrees during its traverses. The rover

rocker-bogie design allows the rover to go over obstacles (such as rocks) or through holes

that are more than a wheel diameter (50 centimeters or about 20 inches) in size. Each wheel

also has cleats, providing grip for climbing in soft sand and scrambling over rocks. The rover

has a top speed on flat hard ground of 4 centimeters per second (a little over 1.5 inches per

second)

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3.2.6. Double-Lambda Mechanism.

New bogie design consists of two lambda mechanisms which are connected

symmetrically. Thus, wheels move on a straight line but in opposite direction of each other.

This design balances the reaction forces on each wheel; therefore the traction force remains

same for each wheel whether one wheel is on upper position.

Symmetric connection of two mechanisms is a critical process. Since the both sides of the

bogie will work in linear part of the curve, one side will be opposite position of other side.

While designing this connection we must avoid from singular configurations of the

mechanism.

Figure 29: (a) Connection between two lambda mechanisms, (b) definition of ground

clearance

3.2.6.1. Adaption of Double-lambda mechanism into Rocker-Bogie

Suspension.

Rocker-bogie mechanism has advantages while distributing load on the wheels

nearly equal. To obtain this useful property, double lambda mechanism can be combined

with former rocker-bogie design.

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Fig 30: Double-Lambda mechanism adapted into rocker-bogie suspension.

Linear Bogie Suspension (LBS) has nearly similar off-road capacity with linear bogie

motion. Small angular displacement of rocker which affects linear motion of bogie can be

neglected.

Two planar mechanisms are connected to each other by a differential mechanism.

When one side climbing over obstacle, this mechanism rotates the main body around the

rocker joints by average angle of two sides

Figure 31: Differential gear mechanism between right and left rockers

Gear A connected to left, gear B connected to right and C is assembled on the main platform.

In differential mechanisms, all gear ratios are same. That means if gear A rotates 10 degrees

and gear B rotates 20 degrees, main platform will rotate 15 degrees.

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3.2.6.2. Various Design Possibilities with Linear Motion Bogie.

1) Adapting to terrain parameters, there are different possibilities for rover suspension

like LBS. Spring and damper application to double lambda suspension good solution for

high-speed off-road vehicles.

Fig 32: Different applications of lambda bogie suspension.

2) The possibility to implement Rocker-Bogie suspension in Front Loading Vehicles.

Methodology

As per the research it is find that the rocker bogie system reduces the motion by half

compared to other suspension systems because each of the bogie's six wheels has an

independent mechanism for motion and in which the two front and two rear wheels have

individual steering systems which allow the vehicle to turn in place as 0 degree turning

ratio. Every wheel also has thick cleats which provides grip for climbing in soft sand and

scrambling over rocks with ease. In order to overcome vertical obstacle faces, the front

wheels are forced against the obstacle by the centre and rear wheels which generate

maximum required torque. The rotation of the front wheel then lifts the front of the vehicle

up and over the obstacle and obstacle overtaken. Those wheels which remain in the middle,

is then pressed against the obstacle by the rear wheels and pulled against the obstacle by

the front till the time it is lifted up and over. At last, the rear wheel is pulled over the obstacle

by the front two wheels due to applying pull force. During each wheel's traversal of the

obstacle, forward progress of the vehicle is slowed or completely halted which finally

maintain vehicles centre of gravity. The above said methodology is being practically proved

by implementing it on eight wheel drive ATV system in order to gain maximum advantage

by rocker bogie system.

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The main problem associated with current suspension systems installed in heavy loading

vehicles rovers (including those with active and semi active suspension systems) is their

slow speed of motion which derail the rhythm to absorb the shocks generated by wheels

which remain the result of two factors. First, in order to pass over obstacles the vehicle must

be geared down significantly to allow for enough torque to raise the mass of the vehicle.

Consequently, this reduces overall speed which cannot be tolerated in the case of heavy

loading vehicles. Second, if the vehicle is travelling at a high speed and encounters an

obstacle (height greater than 10 percent of wheel radius), there will be a large shock

transmitted through the chassis which could damage the suspension or topple down the

entire vehicle. That is why current heavy loading vehicles travel at a velocity of 10cm/s

through uneven terrain. The software based testing of rocker bogie suspension system

describes the momentum and efficiency related utilities in cumulative manner.

After optimizing the ground profile it can be assumed that each of the rocker working with

specified angle of inclination α, but can be changed by the users demand. The Genetic

Algorithm requires evaluates of the fitness of each arm in the population and therefore

justifies the goodness of each of these specific combinations of link lengths and variable

angles of the rocker-bogie suspension mechanism.

Fig 33: Solidworks model of a front loading vehicle operating on a rocker bogie mechanism.

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3) As an amphibious vehicle.

Design of mechanical system on land that took considers the features of water vehicle.

The wheel should be retracted to enhance the stability of vehicle while it in water mode.

Retractable wheels are designed to reduce the loss of the bow wave wheel. It increases

vehicle speed when maneuvering on the water's surface. If the wheels are deployed, the

water flow under the surface of the vehicle will be blocked and distracted by the wheel. The

wheel will disturb the water flow path causing a high pressure before the wheel and low

pressure after it. This produces a negative pressure that will affect the speed and stability of

the vehicle. A low-pressure hole will also reduce the speed of water flow, encouraging the

whirlpool flow and increase the loss of the bow wave. On the land mode, the vehicle should

be able to transverse smoothly on the uneven surface and overpasses the obstacle. The

wheel-track type vehicle are most suitable to use in uneven surface because the construction

are simplest and not required complicated algorithm control compare to the leg type vehicle

that equipped with lot of sensors and actuators. Rocker-bogie mechanism is an example of

passive linkage that been used in Mars Rover Exploration due to it stability and adaptive

ability on terrain surface (uneven surface). In a post- disaster relief, the road surfaces

become uneven and rough. It will disrupt the mobile stability and movement. The

intelligently designed wheel suspension allows the vehicle to traverse over very uneven or

rough terrain and even climb over obstacles. The rocker-bogie allows the chassis of the rover

to average its pitch overall wheel deflections while still maintaining load equalization on all

wheels and avoiding a low oscillation frequency. The rocker-bogie mechanism consists of

rocker that attached to a frame and a bogie that connects to rocker link with pivot joint.

The main advantage of this mechanism is that net load is distributed equally over all wheels.

These ensure even working condition on all wheels and prevents from excessive sinkage of

a wheel in a soft terrain (muddy). However, the uneven surface is not predictable; the

different configuration is needed for different terrain surface. The commons problem facing

while using this mechanism are wheel slip, slow in speed and power consumption.

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4. Suspension Troubleshooting Chart.

In this table the major defects that occur in the suspension system of the automobiles

will be discussed.

Table 1: Suspension Troubleshooting chart.

Problem Causes Remedies

Rough Ride.

1. The leaves of the spring may be rusted resulting in excessive friction.

2. In the case of torsion bars, they may have not been adjusted properly.

1. Immediate lubrication of the springs to reduce friction.

2. They should be adjusted properly.

Vehicle drag. 1. The spring on the sagging side may have broken or become weak due to constant use.

2. In case of independent systems, the coil soring may be incorrectly adjusted.

1. Replace.

2. They should be adjusted properly.

Vehicle bouncing after crossing bump

1. Worn out shock absorbers.

2. Damaged or slipped leaf springs.

1. Replace 2. Springs should be checked, repaired or replaced.

Knocking during crossing of bump.

1. The shock absorber or struts may have worn out.

2. Ball joints may be loose or worn out.

1. Shock absorbers and/or struts bearings have to be replaced.

2. Ball joints have to be checked and serviced or replaced as required.

Noises. 1. U-bolts may be loose. 2. There may be side play in shackles. 3. The shackle pins and bushes may be

loose. 4. There may be some defect in the

shock absorber.

1. Tighten wherever necessary.

2. Lubricate.

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5. Conclusion.

This article covers the suspension trends in the modern world. It can be seen that

Independent suspensions have been given primarily more importance than any other

suspension system. This is because of the high degree of comfort provided by the

independent motion of the wheels when passing over an obstacle. But Bose suspension has

proven itself as a winner in both fields of comfort and performance. But when it comes to

off-road vehicles the good old solid axle and Twin I beam has been preferred over other

types.

The work presented in this report shows that applications of rocker-bogie system are

enormous. It can be applied in a front loading vehicle with proper modifications and it can

also be used as post-disaster transportation vehicle as it also can be produced as an

amphibious vehicle. With the addition of double-lambda mechanism it can provide a

system with more degrees of freedom than a normal rocker-bogie system. This research also

shows that it is possible to construct useful mechanisms by arranging classical four-bar

mechanisms. These design possibilities can be discussed with new structural synthesis

formula, which has been introduced and applied on rover suspension design.

Future studies may continue to discuss dynamic behavior of the suspension

mechanisms.. The purpose of this study is to put another stone on the pyramid of

scientific knowledge. Although the art of mechanism design seems like it has lost its

popularity due to the powerful control algorithms, there is no doubt that future robotics

study will continue to search for new mechanisms.

36

6. References

The information in this article was obtained from the following sources.

1) Design analysis of Rocker Bogie Suspension System and Access the possibility to

implement in Front Loading Vehicles.by Nitin Yadav1, BalRam Bhardwaj, and Suresh

Bhardwaj. (May. - Jun. 2015)

2) Hong-an Yang, Luis Carlos Velasco Rojas*, Changkai Xia, Qiang Guo, School of

Mechanical Engineering, Northwestern Polytechnic University, Xi’an, China, Dynamic

Rocker-Bogie: A Stability Enhancement for High- Speed Traversal- Vol. 3, No. 3,

September 2014, pp. 212~220 ISSN: 2089-4856.

3) Design of a Mars Rover Suspension Mechanism by Fırat Barlas. June, 2004.

4) http://www.boseindia.com/the-bose-suspension-system/

5) J.C.Dixon, Tires, Suspension and Handling Second Edition, Society of Automotive

Engineers (Arnold – London – 1996).

6) The Challenges of Designing the Rocker-Bogie Suspension for the Mars Exploration

Rover by Brian D. Harrington* and Chris Voorhees*

7) ANALYSIS AND SIMULATION OF A ROCKER-BOGIE EXPLORATION ROVER by

Hervé Hacot1, Steven Dubowsky1, Philippe Bidaud, Department of Mechanical

Engineering, Massachusetts Institute of Technology

8) Mars Pathfinder: www.mpf.jpl.nasa.gov

9) http://www.whyhighend.com/magnetic-suspension.html.

10) 2015 IEEE International Symposium on Robotics and Intelligent Sensors (IRIS 2015)

System Modelling of Rocker-Bogie Mechanism for Disaster Relief by S. F. Toha1 and

Zakariya Zainol*

11) http://www.carbibles.com/suspension_bible_pg3.html.

12) Optimized Suspension Design of an Off-Road Vehicle 1Arindam Pal, 2Sumit Sharma,

3Abhinav Jain, 4C.D.Naiju School of Mechanical and Building Sciences, VIT University

Vellore Tamil Nadu

13) http://www.automotivearticles.com/Suspension_Design_Types_of_Suspensions.shtml.

14) T. Thueer and R. Siegwart (2010), Mobility evaluation of wheeled all-terrain robots,

Robotics and Autonomous Systems 58 (2010), pp. 508~519, ISSN: 0921-8890.