|Air-spring module uses a rollingdiaphragm air cylinder not only to isolate shocks and vibrations, but for controlling cab height as well. |
Whether it’s a truck negotiating the rough terrain of a construction site or a tractor traveling over deep ruts in a field, reaction forces and movement transmitted to an operator can feel more like punishment than a part of the job. Left unchecked, these dynamics can quickly wear out an operator and jeopardize safety.
Of course, a vehicle’s suspension is designed to damp much of the shock and vibration before it can be transmitted to the chassis. However, many applications can also benefit from cabin dampers that prevent shock and vibration from being transmitted from the chassis to the operator cabin.
When damping requirements are moderate, ZF Sachs, the power train and suspension components division of ZF Friedrichshafen AG, Germany, provides steel-spring modules. Steelspring modules are inexpensive and easy to install. However, ZF’s pneumatic springs provide a wider range of performance and greater operator comfort.
Air springs for higher demands An air-spring module is well suited for installation in vehicles that carry a wide range of different loads — including in the cabin itself. The working element of the air-spring module is a rolling-diaphragm air cylinder. The rolling diaphragm design eliminates the need for a complex seal and its potential for leakage. Instead, a diaphragm keeps air positively sealed within the cylinder.
Georg Memmel, director of engineering at ZF Sachs, says that standard air spring modules have a diameter of 125 or 140 mm, with a maximum stroke to 120 mm. He adds that they typically operate at a working pressure of 4 to 8 bar, but are rated for maximum working pressure to 10 bar.
Memmel explains that mounting an air spring module at each corner of an operator cabin isolates it from much of the shock that would otherwise be transmitted to it from the chassis. A leveling valve controls air pressure of the air spring to match cabin weight and pressure.
The proportional valves can regulate the pressure in the cylinders to control height of the cabin. ZF Sachs integrates its air-spring modules and a mechanical leveling valve for a ride-height control system for the cabin — a system called the Cabin Air Leveling Module (CALM).
Greater safety and comfort Vehicle damping must meet complex demands. On the one hand, it must improve driver comfort and safety, but on the other, it must maintain driving stability. Therefore, the optimum adjustment for shock absorbers is always a compromise between driving comfort and driving stability.
This is where ZF’s Continuous Damping Control (CDC) comes into play. The CDC is an electronically adjustable damping system that monitors all operating variables — such as driver actions and vehicle movements — and controls the CDC airspring module dampers accordingly. The electronic control unit enables damping forces to be adjusted in fractions of a second as required by any given driving situation.
The CDC improves ride comfort, such as when drivers face changing conditions (off-road, on-road, etc). Moreover, it reduces strain on vehicle components and, thus, lowers maintenance costs. Dynamic adjustment of the damping forces decreases driver fatigue, which keeps them alert for higher productivity longer.
For more information, contact ZF Industries, Vernon Hills, Ill., at (847) 478-6868, visit www.zf.com/na, or visit Booth S-16039 at ConExpo.