Hydro-Pneumatics Suspension System: Submitted By: Melanie P. Mandipol Submitted To: Prof. Antonio M. Merca

Hydro-pneumatics
Suspension System
Submitted by:
Melanie P. Mandipol
Merca
Submitted to:
Prof. Antonio M.
Definition of Hydro-pneumatic Suspension System

Hydro-pneumatic suspension system is a type
of automotive suspension system, invented by Citron, and fitted to
Citron cars, as well as being used under license by other car
manufacturers, notably Rolls-Royce (Silver
Shadow),Maserati (Quattroporte II) and Peugeot. It was also used
on Berliet trucks and is since recently used on Mercedes-Benz cars.
Similar systems are also used on some military vehicles. The
suspension was referred to asolopneumatique in early literature,
pointing to oil and air as its main components.
The hydro-pneumatic system uses an accumulator to generate spring
force (similar to the Hydractive suspension system of Citron) and a
remote valve block to generate damping force.
A hydraulic cylinder replaces the damper strut and springs of the
vehicle. The cylinder generates oil volume displacement towards the
accumulator. The oil is assumed to be incompressible and the volume
of the air chamber inside the accumulator is diminished which creates
a pressure increase by means of the ideal gas law.
To put it simply, the spring and shock absorber were replaced by
a sphere, which was filled with trapped gas on one side and
incompressible hydraulic fluid that was connected to the suspension
on the other.
Purpose of hydro-pneumatic suspension system
Is to provide a sensitive, dynamic and high-capacity suspension that
offers superior ride quality. Severe off-road vehicles superior ride
quality, handling, stability, and durability with low maintenance
requirement. The system provides a soft, comfortable, yet wellcontrolled ride.
Three Components of Hydro-pneumatic Suspension System

A hydraulic cylinder used to give a unidirectional force through a
unidirectional stroke, hydro-pneumatic accumulator is
a pressure storage reservoir in which a non-compressible hydraulic
fluid is held under pressure by an external source. The external
source can be a spring, a raised weight, or a compressed gas which
is directly, mounted on the cylinder and of course the hydraulic fluid.
In case cylinder and accumulator need to be separatedfor example
due to design space reason-additional oil lines and fittings are
necessary to provide the hydraulic connection.
Advantage of hydro-pneumatics Suspension System
Create a high level of comfort with a low stiffness
Provide smooth ride
Low weight and low space of suspension unit.
The whole system is virtually maintenance-free, and the suspension
does not have to be dismantled periodically for shock absorber
replacement.
Use of additional electronic sensors and driver control of suspension
performance.
Faster and more cost-effective development.
Improves vehicle handling
High off road speed capacity
Disadvantage of hydro-pneumatics Suspension System
One disadvantage is however that the gas tends to diffuse out of the
upper chamber through the diaphragm, causing a lack of pressure,
and when too much gas has escaped, the suspension tends to go
hard. This usually doesn't occur until after about 10 years or 100 000
km. The spheres can be replaced or recharged, which however
requires them to be removed from the car.
Application of hydro-pneumatics Suspension System
A level control is needed in particular for level readjustment after
major load changes,
A level control needs to work frequently and needs to react quickly,
A manual operator control for the suspension level is desired,
Little space is available for suspension elements,
How does it works?
The sphere in these systems is actually mounted at the end of the
strut. The strut itself acts like a syringe to inject fluid into the sphere.
When the wheel hits a bump it rises, pushes the piston back and this
squeezes fluid through the tiny hole in the sphere to let the gas spring
absorb the energy of the bump. Then when the car is over the bump,
the gas pushes the diaphragm back out, pushing the fluid down to the
strut, pushing the wheel down to the ground. The compression of the
gas acts like a spring, while the hydraulic fluid acts like a damper.
References:
http://www.butoba.net/homepage/hydraulike.html
Retrieved on January 19, 2015
http://www.mate.tue.nl/mate/pdfs/11189.pdf
http://www.quazoo.com/q/Hydropneumatic_suspension?
alt=Hydractive
http://www.argo-hytos.com/news/products-application/article/hydropneumatic-suspension-systems-faster-and-more-cost-effectivedevelopment.html
http://vintage.mitchell1.com/PClubData/chassis/chis79/V2I799123.pdf
http://www.hendrickson-intl.com/CMSPages/GetFile.aspx?
guid=6afe938b-2a5b-49ff-8e02-721c77a70933

Hydro-Pneumatics Suspension System: Submitted By: Melanie P. Mandipol Submitted To: Prof. Antonio M. Merca

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Hydro-pneumatics

Definition of Hydro-pneumatic Suspension System

Three Components of Hydro-pneumatic Suspension System

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