Theme: Suspension – Not As Good As It Sounds But Still An Improvement

Suspension systems are inherently reactive. One approach to managing the response of the body to road surface changes is adaptive ride suspension. Is it really any different from passive systems?

Mercedes-Benz S 63 AMG (W222) 2013: autoevolution.com
Mercedes-Benz S 63 AMG (W222) 2013: autoevolution.com

In both passive and active systems, the road surface’s variations are the main input to the body and suspension system. Passive systems are designed to build in to the suspension the capacity to absorb energy so that the body movement is controlled and tyre contact to the road surface is maximized. Active suspensions involve the use of actuators to change the height of the body at each corner of the car. This additional mechanism requires the use of variable-rate shock absorbers and dampers. The active ride system needs sensors to

2011 Hyundai Equus has active ride technology: source
2011 Hyundai Equus has active ride technology: source

monitor the car’s state and a computer to process the data which then sends appropriate signals to the suspension to moderate its settings. Is that really active ride though? While such a system incrementally reduces body roll and controls changes in roll, pitch and yaw it is really only an improvement in degree and not in kind compared to passive systems. What the active ride system is doing is adjusting extremely quickly to road inputs. While the actuators can vary the car’s ride height at each corner, the car is still changing in response to a variation on the road or both the road and the body’s reaction to a previous input.

This doesn’t take away from the advantages of adaptive, active and semi-active suspension but makes it clear that additional mechanisms are added to the standard elements of the suspension. What hasn’t changed is that the road surface is still an unknown quantity and the car, as whole, must be able to cope with the forces encountered from moment to moment. Some might point to the use of monitoring cameras and satellite navigation in certain new Mercedes that can be used to warn the on-board computer of changes in the road surface and changes in the road’s path and altitude. What this does is provide more time and data for the car’s suspension to react accordingly but really only pushes the problem a little further up the road, so to speak.

Author: richard herriott

I like anchovies. I dislike post-war town planning.

2 thoughts on “Theme: Suspension – Not As Good As It Sounds But Still An Improvement”

  1. There is presumably a new level of development around the corner.

    Some drive trains, such as BMW systems, use sat nav data to anticipate road conditions and inform gear changes.

    All those ‘autonomous’ Teslas are sending data back to the network, sharing information so that the Tesla hive mind can learn more about the roads they are driving on. This is a key part of Elon Musk’s stated goal for a Tesla to drive itself entirely from coast to coast in the US.

    Soon, cars will be able to record every action and movement made by the suspension, and share this data (alongside accurate mapping of the car’s location) to build up a detailed picture of every curve, pot hole, compression and surface change.

    Adding this data would surely create a genuinely active suspension – one that would be able to predict the behaviour of the suspension for the duration of a journey.

    1. When I follow other cars down our worn-out secondary road, I seldom follow the exact same path as they do, and I wouldn’t expect autononomous cars to either. Potholes can appear overnight in the freeze thaw cycle, cars have different tracks (treads or width between wheels) from model to model. Compressions and dips vary across the width of the lane surface as well, and then the bicyclists appear around the next sharp bend.

      I see where you’re coming from, but the accretion of trillions of data points not quite correlated with each other seems a giant exercise with not especially predictable results. Let’s just resurface the roads and go from there!

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