Safety has become a crucial element in automotive engineering, resulting from a number of rollover accidents on the roads. Today’s cars are manufactured to meet more stringent safety standards. But Monroe wants to meet an even threshold of safety. That is why 160 engineers from the Monroe Europe Technical Centre are developing and fine tuning new technologies that make Monroe shock absorbers among the most reliable and safest in the market. Monroe’s extensive research lab can rely on its comprehensive road test facilities, giving direct, measured, real performance feedback in the toughest driving situations.

Shock absorbers work on the principle of fluid displacement on both their compression and rebound stroke. This controls the suspension spring while accommodating various road surfaces and irregularities.

Suspension control is achieved by the shock absorber converting the energy absorbed by the spring, due to suspension movement, to heat energy and dissipating it into the air.

Valving Stages

As the velocity of the shock’s stroking increases, the level of damping control changes to the shock’s multi-stage valving.

Each Monroe valving system has a minimum of three valving stages of both compression and rebound.

The first valving stage is called the “bleed” stage which influences handling and it is also responsible for slow vehicle ride quality. When a shock absorber is extended and compressed by hand, the resistance you are feeling is due to the bleed stage valving.

The second valving stage is the “blow off” stage. This stage controls vehicle handling and highway ride quality and is effective in the mid-range stroking velocities.

The third valving stage is called the “orifice” stage which operates during high stroking velocities. It controls high-speed suspension movement, preventing the suspension from “bottoming out” and provide high-speed vehicle stability.

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Compression Stroke

During the compression stroke the piston is moving down.

There are two compression valves; one is the piston, while the other is located in the compression valve assembly. The multi stage valving located in the compression valve assembly is responsible for the shock damping during the compression stroke.

As the piston rod moves down the inner cylinder, high pressure oil is generated beneath the piston in chamber three, creating compressing damping control. The volume of oil equal to the piston rod entering the inner cylinder is forced to flow from chamber three, through the compression valve to the reservoir, chamber two.

At the same time, unrestricted oil flows from chamber three through the piston assembly to chamber one. This ensures the inner cylinder is always completely full of oil.

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Rebound Stroke

The piston moves up the inner cylinder during the rebound stroke. Both the piston and compression valve assemblies also have a rebound valve. This time the multi-stage valving responsible for the shock damping during the rebound stroke is located in the piston assembly.

As the piston moves upwards, rebound damping control is created by high-pressure oil being generated in chamber one. This due to the restriction of oil flowing through the piston valving in chamber three.

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The Benefits of Gas Pressurization

Even during normal driving conditions, a vehicle’s suspension works a shock absorber hard. One moment the shock absorber is on the compression a stroke, a fraction of a second later it has changed direction to the rebound stroke.

This happens thousands of times every kilometer. Imagine what the shock absorber has to cope with on rough roads and high speed conditions. It is estimated that a shock absorber cycles at least six million times in 20,000 kilometers.

Hydraulic shocks are quite efficient. However, when oil is forced to flow from a high to a low-pressure area as it does on both compression and rebound strokes, the sudden pressure drop causes bubbles to form in the oil. This is called the process of cavitation and aeration.

Air bubbles, unlike oil, are compressible. Therefore the initial piston rod travel of each stroke will simply compress the bubbles before the oil is forced through the valving. This produces a damping control lag, which compounds the problem and result in deterioration of shock absorber efficiency.

Pressurizing shock absorbers with nitrogen gas prevents bubbles forming in the oil, because the low pressures which support cavitation are eliminated. This significantly improves shock damping control and their fade characteristics.

Monroe has spent considerable time in designing and refining the Monroe valving system to optimize the feature of gas pressurization, providing a better ride, reduced noise, plus improved handling.

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