● Extended and renewed to meet all market demands
● Over 450 new references in the catalogue
● Coverage of up to 97% of the European car park
● Applications for 55 car makers

Magneti Marelli Parts & Services offers one of the most complete ranges of shock absorbers in the aftermarket. The new range includes products of OEM or equivalent quality, both for cars and for commercial vehicles, covering a wide range of applications and offering solutions for every type of vehicle.

The catalogue, also available in PDF format, includes:
•  applications by brand and vehicle;
•  OE/IAM comparison tables.

The applications and cross references are also available on the TecDoc web platform.

Gas and hydraulic shock absorbers are available in the following versions:

Mono-tube shock absorbers
•  High damping power
•  Rapid hydraulic valve response
•  Lower weight

Twin-tube shock absorbers
• Excellent suspension performance
• Friction reduced to a minimum thanks to the use of nitrogen
• Reduced cavitation

Structural shock absorbers
• Absorb vertical stress, braking and acceleration forces
• Contribute to vehicle safety
• Contribute to bearing the vehicle weight
 

1. Global structure

Marelli Ride Dynamics has a global presence comprising 15 manufacturing plants, 8 research and development centres and 9 sales offices. Our experience over many years and our presence in four continents enables us to offer world class quality and excellent technical and sales services.

2. Shock absorbers, an overview

The ride dynamics of a motor vehicle are determined by the forces generated by the contact between the tyre and the road surface. Controlling these forces provides the necessary conditions of safety and comfort. Without a suitable suspension system, all the stresses caused by irregularities in the road surface would be transmitted to the vehicle body, also compromising road holding and braking efficiency, as a result of the variations of transmitted forces.
Suspension systems make it possible to isolate the passenger compartment from the stresses transmitted from the wheels, absorbing terrain irregularities and thus ensuring that the tyres are subjected to a vertical force that is as constant as possible. This guarantees safe driving conditions for the vehicle.
The suspension system and its geometry makes it possible to control the interactions between the vehicle body (sprung mass) and all the components that are directly exposed to the road surface profile (unsprung mass), in other words tyres, wheels, brake discs and  calipers, and part of the drive shaft of the driving wheels.

The suspension, in a simplified description, is represented by an elastic element, the spring that generates a force proportional to the deformation to which it is subjected and by a damping element, the shock absorber that generates a force proportional to the speed of the deformation to which it is subjected.
If the damping element is not present in the suspension, when the wheel encounters an irregularity in the road profile, the energy stored by the compression of the spring would be released in its subsequent slackening.
The suspended mass, the vehicle body, will be  then pushed up and after would return to weigh on the elastic element, compressing it again.
A swinging motion of the vehicle would therefore be triggered, the damping of which would occur only progressively due to the dissipation coefficients of the tyre, spring and joints of the suspension arms.

The presence of the shock absorber allows the control and dampening of these oscillations characterized by frequencies and amplitudes determined by the masses involved and by the physical parameters of the suspension.

In addition, shock absorbers perform other primary suspension functions, such as bearing vertical, lateral and longitudinal loads, and limiting wheel travel in the two phases of extension and damping. The optimization of these functions plays an important part in determining the vehicle’s dynamic performance, helping to ensure the required level of comfort, and also governing driving characteristics.

The shock absorber operates both during spring compression and extension. When the spring is compressed as a result of the vehicle weight, the shock absorber closes, providing greater resistance than that exerted by the spring alone. When the wheel runs over a bump, the spring is compressed even more. The shock absorber reduces this movement without completely preventing it.

During compression, the shock absorber works together with the spring, helping it with its reactive force. During extension however, it has to exert a greater force to dampen the spring’s extension force. This is why, when applying a force manually, it is usually easier to compress a shock absorber than trying to extend it.
A shock absorber comprises several dozen high-precision components (dust seal, reservoir, pressure tube, base valve, piston valve, etc.). Particularly important production and design features comprise the sealing system, which has to create a perfect barrier preventing any leakage of hydraulic fluid, and the welded seams that give the structure a higher resistance to breakage.

3. Marelli technology

3.1 Conventional twin-tube shock absorbers
 

This type is the technical configuration most widely used in the automotive industry. Their simplicity of construction and their versatility enable them to be used in many different types of suspension layout, such as twist beam, multi-link, quadrilateral, and coil-over versions (for competition applications).
The twin-tube shock absorber consists of two nesting tubes: the space between them is partly filled by nitrogen which compensates for the piston volume during its telescopic movements when the suspension system is in operation. This type of shock absorber has a minimum axial distance between mounting points, and provides flexibility in defining the damping characteristics.
The presence of low-pressure nitrogen minimizes cavitation and emulsification, offering excellent performance in most rear suspension applications.
This configuration offers great flexibility in design and installation, with a wide range of possible mounting systems for fitting to the vehicle.
 

3.2 Conventional mono-tube shock absorbers
 

Mono-tube shock absorbers damp vertical stresses and limit travel of the suspension system.
The pressure levels are in excess of 10 bar. The principal benefits of this product configuration are:
· high damping power with respect to its size
· reduced weight
· high hydraulic valve response speed, due to the high pressurization values.

A mono-tube shock absorber comprises a single tube and a high-pressure nitrogen chamber. Oil and gas are separated by a floating piston that prevents emulsification in operating conditions and during high-frequency movements, thus providing better stability on particularly rough roads. The shock absorber can be fitted to the vehicle in any position. This enables greater design flexibility and use in many automotive applications. No cavitation is present. As a result, it provides greater stability in high-frequency vertical wheel travel.
Its principal characteristics include better heat dissipation, and higher damping stability in all operating conditions.
This type is generally used for high-performance and off-road vehicles.
 

3.3 Structural shock absorbers
 

Structural shock absorbers are widely used in the front suspensions of vehicles in the A, B and C segments, and in the rear suspension of some SUVs. This type of shock absorber has structural roles, such as supporting the vehicle’s weight and the vertical loads from the body, and absorbing stresses in the horizontal plane during braking, acceleration and cornering, in addition to the usual functions of damping and limiting wheel travel. The structure of this type of shock absorber has significant implications for user safety.
 

3.4 Smart Damping Control System

The SDC system allows the continuous real-time regulation of the shock absorber damping effect. It consists of 4 shock absorbers, 1 control unit and 5 accelerometers. The accelerometers, 3 on the body and 2 on the front wheel hubs, send data to an electronic control unit which calculates the damping requirements and operates the actuators mounted on the shock absorbers according to the road profile and the driving conditions.
 

3.5 Lifter System

The Lifter system is an axle lifting system for sports vehicles. It is used above all on the front axle in order to clear obstacles such as speed bumps and ramps so that the spoiler does not come into contact with the ground.
The system consists of a hydraulic actuator located below the suspension spring, a hydraulic pump and a control unit. It can be applied only on the front axle, or to the whole vehicle.

4. Shock absorber replacement

When clear problems are noticed while driving, such as reduced road holding when cornering, vehicle vibration, loss of grip, steering-wheel vibration, lower ride height, or dipping when braking, the suspension system should be checked in order to identify worn or defective parts that need replacement. Usually the scheduled vehicle maintenance programme includes a check of shock absorbers every 20,000 km, and their replacement every 80,000 km.

Typical problems that require shock absorber replacement.

• Persistent noise caused by friction between the piston rod and seal: caused by dryness of the material used for the seal.
• Metallic noise from inside the shock absorber: this can be caused by internal parts that have been assembled incorrectly, or whose functioning has changed.
• Breakage of the mounting rubber located in the eyelets of the rear shock absorbers.
• Oil leakage*.
• Loss of shock absorber pressure, reduced efficiency, no reaction force.

(*) A small degree of dampness on the piston rod can be considered normal, because it is caused by an evaporation process that occurs during shock absorber operation.