nitr shock absorber

Nitro Shock Absorbers

J.T.Mahajan Polytechnic College, Faizpur

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SYNOPSIS

In the present scenario of automobile industry manufacturers are trying to

produce comfortable and safe vehicles which the consumers are looking for. A

shock absorber is a damping element of the vehicle suspension, and its

performance directly affects the comfortability, dynamic load of the wheel and

dynamic stroke of the suspension. The conventional type of shock absorbers has

got the main drawback that it causes foaming of the fluid at high speeds of

operation. This results in a decrease of the damping forces and a loss of spring

control. The gas filled shock absorbers are designed to reduce foaming of the oil

and provide a smooth ride for a long period.



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CONTENTS -

INTRODUCTION 1

NEED FOR SHOCK ABSORBERS 2

SHOCK ABSORBER ACTION 5

GAS FILED SHOCK ABSORBERS 9

TYPES 10

WORKING 11

ADVANTAGES 14

CONCLUSION 15

REFERENCES 16



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INTRODUCTION-

For a smooth and comfortable ride the disturbing forces should be eliminated or

reduced considerably by using some devices. Shock absorbers are such devices

which isolate the vibrations by absorbing some disturbing energy themselves. Of

the many types telescopic shocks are widely used which has got the draw back

that the flow of oil in the cylinder can cause foam of oil and air to form. These

limit the optimum throughout of the flow in the valves. Gas shocks represent an

advance over traditional shocks. Nitrogen filled gas shock absorbers are the

results of years of extensive research and development with top flight shock

design engineers. They are designed for both lowered and stock vehicles to

provide shock absorbers that would out perform anything on the market today.

Nitro shock absorbers are high quality, nitrogen filled shocks designed and gas

charged specifically for each vehicle application. The addition of nitrogen under

pressure limits the foaming effect and increases efficiency.

NEED FOR SHOCK ABSORBERS-

Springs alone cannot provide a satisfactorily smooth ride. Therefore an additional

device called a “shock absorber” is used with each spring. Consider the action of

a coil spring. The spring is under an initial load provided by the weight of the

vehicle. This gives the spring an original amount of compression. When the

wheel passes over a bump, the spring becomes further compressed. After the

bump is passed the spring attempts to return to its original position. However it

over rides its original position and expands too much. This behaviour causes the

vehicle frame to be thrown upward. Having expanded too much, the spring

attempts to compress that it will return to its original position; but in compressing

it again overrides. In doing this the wheel may be raised clear of the road and the

frame consequently drops. The result is an oscillating motion of the spring that

causes the wheel to rebound or bounce up and down several times, after a bump



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is encountered. If, in the mean time, another bump is encountered, a second

series of rebounding will be started. On a bumpy road, and particularly in

rounding a curve, the oscillations might be so serious as to cause the driver to

lose control of the vehicle.

A shock absorber is basically a hydraulic damping mechanism for controlling

spring vibrations. It controls spring movements in both directions: when the

spring is compressed and when it is extended, the amount of resistance needed

in each direction is determined by the type of vehicle, the type of suspension, the

location of the shock absorber in the suspension system and the position in

which it is mounted. Shock absorbers are a critical product that determines an

automobile’s character not only by improving ride quality but also by functioning

to control the attitude and stability of the automobile body.

PRINCIPLE OF OPERATION-

The damping mechanism of a shock absorber is viscous damping. Viscosity is

the property of a fluid by virtue of which it offers resistance to the motion of one

layer over the adjacent on. The main components of a viscous damper are

cylinder, piston and viscous fluid. There is a clearance between the cylinder walls

and the piston. More the clearance more will be the velocity of the piston in the

viscous fluid and it will offer less value of viscous damping coefficient. The basic

system is shown below. The damping force is opposite to the direction of

velocity.

I-CLEARNCE, II-PISTON, III-VISCOUS FLUID



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The damping resistance depends on the pressure difference on the both sides of

the piston in the viscous medium. The figure shown below shows the example of

free vibrations with viscous damping.

The equation of motion for the system can be written as mx + cx +kx = 0

Energy dissipation in viscous damping :

For a vibratory body some amount of energy is dissipated because of damping.

This energy dissipation can be per cycle. Rate of change of work W is called

energy. For a viscously damped system the force F is expressed as

F= cx = cdx/dt, where x = dx/dt

Work done W = Fx = (cdx/dt) x

The rate of change of work per cycle

i.e. Energy dissipated

Let us assume the simple harmonic motion of the type x = Asinωt

(dx/dt) ² = ω²A²cos²ωt

The equation for

This shows that the energy dissipation per cycle is proportional to the square of

the amplitude of motion.

The total energy of a vibrating system can be either maximum of its potential or

kinetic energy. The maximum kinetic energy of the system can be written as E =

(KE) max = 1/2mx²max

= 1/2mω²A²



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SHOK ABSORBER ACTION-

Shock absorbers develop control or resistance by forcing fluid through restricted

passages. A cross-sectional view of a typical shock absorber is shown below. Its

main components and working is also given below.

The inside parts of a shock absorber-

The upper mounting is attached to a piston rod. The piston rod is attached to a

piston and rebound valve assembly. A rebound chamber is located above the

piston and a compression chamber below the piston. These chambers are full of

hydraulic fluid. A compression intake valve is positioned in the bottom of the

cylinder and connected hydraulically to a reserve chamber also full of hydraulic

fluid. The lower mounting is attached to the cylinder tube in which the piston

operates.

During compression, the movement of the shock absorber causes the piston to

move downward with respect to the cylinder tube, transferring fluid from the

compression chamber to the rebound chamber. This is accomplished by fluid

moving through the outer piston hole and unseating the piston intake valve.

During rebound, the pressure in the compression chamber falls below that of the

reserve chamber. As a result, the compression valve will unseat and allow fluid to

flow from the reserve chamber into the compression chamber. At the same time,



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fluid in the rebound chamber will be transferred into the compression chamber

through the inner piston holes and the rebound valve.

FORMS OF SUSPENSIONS AND TYPES OF SHOCK

ABSORBERS-

Various types of shock absorbers are available in the market. Out of that the

widely used types and their characteristics are given below.

Type

Product

Characteristics

Double-wishbone(Multilink)

Double-tube

The outer part of the double tube is used as a gas chamber, which is filled with

low- pressure nitrogen gas. This type can provide stable damping force.

Single-tube

Separation between oil and nitrogen gas by a free piston provides stable

damping force, as well as high performance.



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Strut

Double-tube

This type consists of double tubes that comprise part of the support structure of

the suspension. Filled with low-pressure nitrogen gas, it provides stable damping

force.

Inverted type

Structurally, this is a single-tube type placed upside down. Its large-diameter pipe

provides sufficient rigidity to bear the heavy load from the car body, characteristic

of a strut.

With a steering arm

When connected to the power steering system at a point higher than normal, this

type allows the cabin space to be expanded and the maneuvering stability

improved.

Type with separately mounted spring (rigid axle, etc.)

Unit damper

Because the spring is mounted separately, this type features a simple structure

comprised of a damping mechanism

WHY GAS FILLED SHOCK ABSORBERS?



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The rapid movement of the fluid between the chambers during the rebound and

compression strokes can cause foaming of the fluid. Foaming is the mixing of

free air and the shock fluid. When foaming occurs, the shock develops a lag

because the piston is moving through an air pocket that offers up resistance. The

foaming results in a decrease of the damping forces and a loss of spring control.

During the movement of the piston rod, the fluid id forced through the valuing of

the piston. When the piston rod is moving quickly, the shock absorbers oil cannot

get through the valuing fast enough, which causes pressure increases in front of

the piston and pressure decreases behind the piston. The result is foaming and a

loss of shock absorber control. The need for a gas filled shock absorber arises

here.

GAS FILLED SHOCK ABSORBER

The gas filed shock absorbers is designed to reduce the foaming of the oil. It

uses a piston and oil chamber similar to other shock absorbers. The difference is

that instead of a double tube with a reserve chamber, a dividing piston separates

the oil chamber from the gas chamber. The oil chamber contains a special

hydraulic oil and the gas chamber contains nitrogen at 25 times atmospheric

pressure. The schematic diagram showing the inside parts of a gas filled shock

absorber is shown below.

When the piston rod is moved into the shock absorber, oil is displaced as in

double tube principle. This oil displacement causes the dividing piston to press in

the gas chamber, thus reducing it in size. With the return of the piston rod the

gas pressure returns the dividing piston to its starting position.

Whenever the oil column is held at a static pressure of approximately 25 times

atmospheric pressure, the pressure decreases behind, the working piston cannot



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be high enough for the gas to exit from the oil column. Consequently, the gas

filled shock absorber operates without foaming.

TYPES OF GAS FILLED SHOCK ABSORBERS

Twin– tube with low pressure gas.

Single- tube with high pressure gas.

LOW PRESSURE TWIN- TUBE SHOCKS

Twin- tube gas technology design retains the classical twin-tube while adding at

the top of the reserve tube nitrogen under relatively low pressure 2.5- 5 bars

instead of 25- 30 bars used in high pressure shock absorbers. This pressure is

sufficient to radically improve the efficiency of the shock absorbers.

HIGH PRESSURE SINGLE- TUBE SHOCKS

Gas shock absorbers operate in the same principle of movement of the piston in

an oil filled tube but they contain at one end a small quantity of nitrogen under

high pressure (25 bars). The gas is prevented from mixing with the oil by a

floating piston. When the piston rod passes into the body and displaces oil, the

oil compresses the nitrogen even further. The volume of gas changes playing the

role as an equalization tube. The permanent pressure exerted on the oil by the

gas guarantees an instantaneous response and the quieter piston valve

operation. At the same time this constant pressure eliminates cavitations and

foaming which could momentarily degrade the effectiveness of the shock

absorber.

WORKING



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TWIN– TUBE SHOCK ABSORBERS :

The main components are:

Outer tube, also called reservoir tube

Inner tube, also called cylinder

Piston connected to a piston rod

Bottom valve, also called foot valve

Upper and lower attachment

How does it work?

Bump Stroke:

When the piston rod is pushed in oil flows without resistance from below the

piston through the orifices and the non-return valve to the enlarged volume

above the piston. Simultaneously, a quantity of oil is displaced by the volume of

the rod entering the cylinder. This volume of oil is forced to flow through the

bottom valve into the reservoir tube (filled with air (1 bar) or nitrogen gas (4-8

bar)). The resistance, encountered by the oil passing through the footvalve,

generates the bump damping.

Rebound Stroke:

When the piston rod is pulled out, the oil above the piston is pressurized and

forced to flow through the piston. The resistance, encountered by the oil on

passing through the piston, generates the rebound damping. Simultaneously,

some oil flows back, without resistance, from the reservoir tube through the

footvalve to the lower part of the cylinder to compensate for the volume of the

piston rod emerging from the cylinder.



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MONO- TUBE SHOCK ABSORBERS :

The main components are:

1. Pressure cylinder, also called housing

2. Piston rod connected to a piston rod

3. Floating piston, also called separating piston

4. Piston rod guide

5. Upper and lower attachment

How does it work?

Bump Stroke:

Unlike the bi-tube damper, the mono-tube has no reservoir tube. Still, a

possibility is needed to store the oil that is displaced by the rod when entering the

cylinder. This is achieved by making the oil capacity of the cylinder adaptable.

Therefore the cylinder is not completely filled with oil; the lower part contains

(nitrogen) gas under 20-30 bar. Gas and oil are separated by the floating piston.

When the piston rod is pushed in, the floating piston is also forced down the

displacement of the piston rod, thus slightly increasing pressure in both gas and

oil section. Also, the oil below the piston is forced to flow through the piston. The

resistance encountered in this manner generates the bump damping.

Rebound Stroke:

When the piston rod is pulled out, the oil between piston and guide is forced to

flow through the piston. The resistance encountered in this manner generates the

rebound damping. At the same time, part of the piston rod will emerge from the

cylinder and the free (floating) piston will move upwards.



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ADVANTAGES OF NITRO SHOCKS-

Instantaneous response :

Because the high pressure eliminates aeration (foaming), action is always is

immediate.

The low mass of gas and the single tube further improves response time.

Better fade resistance :

Since there is no outer tube, cooling is much better which gives a drastic

reduction in fade. Thus more consistent handling and control.

Better durability :

Single-tube construction also allows for a larger internal working area, reducing

stress and fatigue for better durability.

De Carbon’s monodisc valving system features a single moving part that

drastically reduces inertia and friction, to improve durability and performance.

Better cooling of the mono tube design results in lower operating temperatures

and thus longer life.

No need for re-adjustment:

The viscosity of hydraulic fluid changes as temperature changes. This may

because of climate, season (summer/winter) or heavy duty (motorway cruising).

The high pressure gas compensates immediately and automatically for changes

in viscosity.



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CONCLUSION-

In the current scenario of automobile industry the need for vehicles which

provides smooth and comfort ride is growing. Nitro shock absorbers are designed

to be ultimate in performance and comfort. In a country like ours whose roads are

not up to world standards the need for automotive components like nitro shocks

are necessary. It goes without saying that if the right choice is made the

improvements in vehicles ride and handling can be shocking.



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REFERENCES-

“In For A Shock”, S.B.L Beohar; Mechanical Systems and Signal Processing.

Automotive Encyclopedia; Tobolt, Johnson.

Auto Mechanical Fundamentals; Stockel.

nitr shock absorber

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