Suspension Damping(A Brief Insight)

In this brief article, we will discuss Suspension Damping and the types of Suspension Damping.

What is Suspension Damping?

Damping is the attribute of a suspension that controls vibration. A Vehicle, as it drives on different roads, is subject to numerous vibrations. Along with vibrations, there are road loads, or in other words, forces applied to the tires that are experienced by the suspension. 

The manner in which these loads hit the suspension can infinitely vary. For example, a large speed bump, or sleeping policeman, is felt in a certain way by the car occupants at the speed of, say 30 kmph. Now, another small-sized pothole on the road is felt in a different way at the speed of say 50 kmph. The difference between the two situations is the frequency content of the incoming road vibration. 

A suspension spring is an element that absorbs loads. Think of the suspension as a big foam block. Any load will need to pass through this foam before it affects you inside of the cabin. How the suspension spring absorbs the road load is by converting the force into elastic energy by compressing itself.

Now, road vibration is different from road load. It is the speed at which the road load hits the suspension. What a suspension Damper does, as the name suggests, is to literally “Dampen” or reduce the speed and intensity of the incoming vibration. A suspension Damper is a large contributor to the comfort feel that the car’s occupants get

One more function of damping is to adjust the vehicle’s cornering behavior. The reason why this is important is that at high speeds, the vehicle’s cornering ability is crucial when it comes to safely avoid obstacles and giving the driver a feeling of confidence that he/she has the vehicle under control. Apart from Spring stiffness and geometry, the front and rear dampers also contribute significantly to the car’s handling behavior.

What are the different types of Suspension Damping?

The 3 main types of damping are

  • Friction Damping
  • Hydraulic Damping
  • Magneto-Rheological Damping

Friction Damping

Friction Damping, also called ‘Coulomb Damping’, is the damping action that results from the friction coefficient between two objects sliding over each other. In the context of the Automotive suspension, a semi-elliptic leaf spring suspension contains a stack of many leafs that all bend together and also have to slide over each other at the contact surfaces.

Hydraulic Damping

The Hydraulic damper is the most common type of damping that can be seen on almost any vehicle. You could safely assume that almost every vehicle produced would have some form of hydraulic damping.

The Hydraulic suspension Damper or Shock-Absorber will convert the vibrational energy into heat energy by restricting the speed of the vibration. This speed reduction is achieved by restricting the damping fluid to pass through small orifices called valves.

Magneto-Rheological Damping

The Mangeto-rheological damper is actually a kind of Hydraulic damper, but very different in its functioning. Initially introduced by General Motors in 2002, the “Magnetic Ride Control” (MRC) Electronic Damping system, was developed by Delphi Systems. The MRC system’s Damper does not work on the concept of valve orifice size restriction. The MRC system’s Damper has an electromagnetic coil inside the piston valve which energized the special Magneto-Rheological metal-infused Damping fluid. The MR Fluid changes its viscosity depending on the magnetic field applied to the valve. 

This system has been continually refined and is now in its 4th generation. The system apparently has one of the fastest reactions of approximately every millisecond. The MagneRide has since found wide application in car models across multiple brands like Ferrari, Lamborghini, Ford, and Audi.

What are the Different Types of Hydraulic Dampers? 

The different types of Hydraulic Dampers are:

  • Monotube Dampers
  • Twin-Tube Dampers

MonoTube Dampers

This design uses a Tube which contains a floating divider to separate the oil and the gas volumes. The damper’s upper portion is a Rod, with a piston at its bottom. As the suspension moves, the rod and piston slide within the damper tube. During compression, oil is forced through a stack of shim-plates on the upper side of the piston. In rebound, shim-plate stacks on the bottom side of the piston restrict oil flow. Gas (nitrogen in most cases) in the chamber is squeezed during compression to make up for the oil displaced by the piston.

Twin-Tube Dampers

 a twin-tube damper’s body consists of two concentric tubes. The inner tube is similar to a monotube damper. The outer tube functions as an oil reservoir. The inner tube contains oil and guides the shaft and piston. The stack of shim-plates on the piston will restrict oil flow in both compression and rebound, creating a damping force. An additional stack of shim-plates at the bottom of the inner tube, called the base valve, allows oil to flow into the outer tube (reservoir) during compression, adding to the overall damping effect. 

On rebound, oil returns from the outer tube reservoir to the inner tube via a check valve. The outer tube is partially filled with a compressible gas. The compressed gas volume makes up for the volume occupied by the additional length of the shaft during compression and causes oil to flow from the outer tube into the inner tube while rebound. Damping force is influenced by the combined effects of the shim-plate stacks of the piston and the base valve. The twin-tube damping force adjustment is done by adding or removing shim-plates from the stack.

What is an Adjustable Damper?

An adjustable Damper is one in which parameters like Bump and/or rebound damping settings can be dialed in and adjusted by the owner himself by way of an adjustment knob located on the damper bottom tube.

Why is an Adjustable Suspension needed?

All Suspension systems are tuned by the manufacturer for an average mix of road conditions and usage patterns. The Road condition Mix that the manufacturer takes as reference for the purpose of suspension tuning is arrived at based on data acquired while testing the prototype car over selected routes and conditions that somewhat represent the usage pattern of the car model’s target customer. This Road Mix is arrived at based on years of feedback and issues that past customers reported. It has a lot of assumptions made for practical purposes and need not necessarily be the exact usage pattern of, say, 40% of the potential customers, who could be first-time car buyers.

So it implies that the Factory standard suspension tuning of most car models may not be to the liking of a large number of potential customers who may have likings and tastes that are different from the average mix that the OEM had selected.

This has opened up several possibilities for car and motorcycle enthusiasts who like to tweak and tune the suspension response of their vehicles to their own personal taste.

What are the Different Types of Adjustable Dampers?

There are basically 2 types of Solid Axles:

  • Manual Adjustable
  • Electronic Adaptive Suspension

Manual Adjustable Dampers

Manually adjustable Dampers are usually not available as original equipment from the car manufacturer. Adjustable Dampers are generally available in the aftermarket. Manually adjustable means that you would need to access the underbody in order to make changes to the suspension. The most commonly available adjustable suspension products allow the user to adjust either 

  • Coilover strut ride height or 
  • shock absorber damping, or 
  • Both of the above

Adjustable Damping Settings

A Suspension’s feel and response are often most influenced by the damping settings. The effect of a change in shock absorber settings is almost immediately felt while driving. Adjustable Dampers are a feature that almost no OE car manufacturer offers. One would have to invariably look into the aftermarket for a compatible and adjustable shock absorber/damper.

Adjustable dampers are of basically 2 types, namely “Single Adjustable” and “Double Adjustable”

  • Single Adjustable means that only the Rebound damping settings of the shock can be changed. This is done using a ‘dial’ on the shocks bottom tube with several adjustable steps, without removing the shock absorber from the vehicle.
  • Double Adjustable means that both the Rebound as well as Compression damping settings can be changed

If there are 10 adjustment steps available for bump as well another 10 for rebound, tuning both simultaneously could become rather confusing for those who are not familiar with suspension tuning. As a Pro-Tip: A good starting point for shock adjustment is to set the rebound damping adjuster knob to high damping and the compression/bump damping adjuster knob to fully low. Starting to tune from this point would be easier since this a good reference point that one can experience and remember as the ‘Worst’ setting. Any further setting changes will be easier to compare and improve against the initial reference point.

Electronically Controlled Suspension

An ‘Electronically Controlled suspension’ is the type of suspension that adjusts suspension parameters on its own during driving. It is also popularly called ‘Active’ or ‘Adaptive’ suspension. In most cases, the electronic suspension would also provide user-selectable settings to choose from like ‘Comfort’, ‘Sport’, ‘Sport plus’, etc.

Electronically Controlled Suspension systems are generally only available in the high-end high-performance models or luxury models in a given car manufacturer’s model lineup. Every OEM that provides Electronically controlled Suspension on its car models would have its own proprietary system and a name for it.

Adaptive Suspension is one term commonly used to describe the electronic suspension. Audi’s system is called ‘Predictive Active Suspension’. BMW calls its Adaptive suspension the ’Adaptive M Suspension’.  Mercedes Benz calls their Adaptive Suspension the ‘E-Active Body Control’. General Motors has different systems for electronic control of the suspension depending on the vehicle model. They are called ‘Adaptive Ride Control’, ‘Continuous Damping Control’ and ‘Magnetic Ride Control’.

How does the Active Damping Control work?

Adaptive Suspensions started appearing initially in the form of electronically adjustable Dampers, called Active dampers. The early versions of Active Dampers had a solenoid valve that was actuated based on a user-selected mode like “Comfort”, “Sport”, etc. Basically, the damping settings would be altered to predetermined values based on the selection and would remain until further selection by the user.

The Electronic dampers later evolved to an active system with its own dedicated Electronic Control Unit (ECU). The system comprised of 

  • Electronically variable valve damping
  • ECU
  • Wheel movement sensors and accelerometers

The ECU received inputs from the wheel sensors by which it would interpret the current vehicle driving condition. Based on this, its internal software would calculate the best setting suited to the given driving condition and accordingly send a signal to the Electronic Dampers. The Electronically variable dampers had a solenoid valve that could be set to multiple 10’s of positions depending on the signal it received from the ECU.

There have been alternative approaches to how the dampers’ damping settings are changed, which affect the speed at which the damper reacts to driving conditions. One of the first such alternative systems was the General Motors “Magnetic Ride Control” (MRC) Electronic Damping system

Conclusion

In this brief article, we have discussed Suspension Damping and the types of Suspension Damping.

In case of any queries or comments, please feel free to ask.

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