Your customer just wants a smooth ride and that’s not going well for them right now. You see wires to the shocks and struts and wonder if the problem is electrical or mechanical. You might even wonder how it even works for that matter. Then there’s the service manual acronym alphabet soup. There is CVRSS (GM’s Continuously Variable Road Sensing Suspension), KDSS (Toyota/Lexus Kinetic Dynamic Suspension System), BMW EDC (Electronic Damper Control), VW DCC (Dynamic Chassis Control) and on and on. How do they work? Are there really that many systems to master? What goes wrong when they fail?
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Aside from air ride systems and electronically controlled sway bar equipped vehicles, if we keep our discussion to only electronically controlled shocks and struts, the systems really fall only into three basic categories:
1. Manually Selectable Suspension
2. Semi Adaptive Suspension
3. Fully Adaptive Suspension
Before getting too deep, let’s review suspensions in general. Suspension system springs must compress and rebound with bumps and holes in the road surface. The softness or firmness of a spring is known as spring rate. Shock absorbers are used to return the suspension to its natural position quickly and smoothly. Not only do shock absorbers control the compression of the spring, but the rebound as well.
Shock absorbers dampen the movement of springs by using fluid or gas forced through holes in the shock absorber’s piston. The size of the holes determines the damping effect of the shock. As the shock absorber compresses, a piston inside moves through oil or hydraulic fluid. Because energy never goes away, it just only changes states, the mechanical energy of the spring oscillations is turned into heat energy via the action just described within the shock absorber to give you that 1 ½ compression/rebound cycles you’re familiar with when you move each corner of the vehicle up and down and then step back to watch the shock’s dampening performance.
On the subject of testing shocks/dampers on the vehicle, there is now an iPhone app for that. In case you hadn’t heard, just Google “I-Suspend” and for 99 cents you can download an iPhone app that has you lay the phone on the passenger floorboard, drive the vehicle as you press the start button and then accelerate and brake as instructed. The app records the spring oscillations via the GPS/shock sensor internal to the phone. The data is then recorded in graph form to help you determine if your customer’s ride needs new dampers.
Springs and shocks are matched to vehicle weight. Sometimes they are chosen to correspond with the weight of optional equipment added to individual vehicles as they are built. This is referred to as a tuned suspension. Because the lines of differentiation have blurred in the last few years between shocks and struts, for the purpose of this article from here on out we’ll just refer to their generic term of damper.
Some of today’s suspension systems include electronically controlled dampers that can produce a soft, medium or firm ride. The ride and handling of the car can be changed for different road conditions or to suit individual driver preferences.