Pressure Vs Height Control

In the last 3-4 years there have been a few electronic ride height control systems come available for air suspension systems. These systems can be generally categorized into either air pressure based or ride height based systems. With a pressure based system you are relying on air pressure to translate into the position of the airspring, which should then theoretically translate into the position of the suspension, which should then [again, theoretically] translate into the ride height of the vehicle. The problem with this type system is all of the translations and assumptions that are made.

When any change occurs to the load that the air spring sees then you can no longer assume that a given air pressure will mean a specific ride height. These load changes can be many things… actual weight change via passengers, luggage, or fuel, the vehicle sitting on an incline or a pothole, or just general suspension geometry or suspension bind that would require more air pressure to raise than it would to maintain ride height.

Another problem with active pressure based systems [the one that actively maintains a given air pressure while going down the road] is that they react completely wrong in a “long sweeping turn” scenario like an interstate off ramp or any other dynamic maneuver that increases the load on one side of the vehicle for a significant period of time. An active pressure based system will attempt to deflate the outside [loaded] airspring and inflate the inside [unloaded] airspring. Like a 2 way control system, this magnifies body roll and handling problems.

A pressure based system also sometimes struggles with a light vehicle with large airsprings [like an unloaded dually] and with very fast solenoid systems that raise the car quickly. In reality a pressure based control system works fine on many vehicles. If your vehicle seldom sees load changes and is reasonably well balanced it may be a good candidate for a pressure based system.

A ride height based system is much better but not without its limitations as well. By directly sensing the actual position of the vehicle suspension we have eliminated several “assumptions” based on air pressure. Now we know the precise relationship of the suspension compared to the chassis and therefore the precise ride height of the vehicle. The problem with a pure ride height based system is “crossloading”. This is when the ride height is achieved with radically different air pressures from corner to corner.

Although you will see some variation of air pressure from side to side because of unequal weights, etc, this difference should be within about 20%. It is possible to “fool” a ride height based system by “overinflating” 2 diagonal corners while leaving the opposing corners
significantly under-inflated. The vehicle is level but the handling characteristics will suffer greatly.

There is at least one electronic leveling system available now that addresses these problems. The LevelPro® system from Air Ride Technologies actually uses both air pressure AND ride height sensors to achieve the correct ride height at the appropriate air pressure. The beauty of this particular system is that it can be configured as a pressure based system to save cost and the ride height sensors can be added later if your vehicle proves troublesome.

The electronics portion of the LevelPro® electronic leveling systems includes the computer, control panel, air pressure sensors and ride height sensors. The LevelPro® system is unique in using both air pressure and ride height to achieve the appropriate vehicle ride height.