Suspension systems in commercial vehicles must accommodate a variety of road conditions, as well as full and empty loads and specific safety standards. Despite this, it is well recognised that conventional suspension damping in commercial vehicles is a necessary compromise between the requirement for safe handling and driver comfort. Wayne McCluskey, Technical Training Manager at ZF Aftermarket, looks at an alternative approach from ZF that negates the need for compromise.
Enhancing the damping characteristics of a commercial vehicle can pose an issue for suspension system designers. First, there’s the consideration of sufficiently protecting the driver, vehicle, and the freight from harsh impact, as well as the subsequent vibrations transmitted from the road surface or resulting from manoeuvres.
There is also maintaining driving safety and vehicle stability. This is particularly important during abrupt load variations such as starting from rest or braking, as well as handling tight bends or following
long curves in the road. Therefore, the necessary characteristics of conventionally damped suspension systems typically compromise comfort in order to stabilise the vehicle and maintain driver safety. For example, the standard damper specification is calculated to enable safe operation of a fully laden truck,
so when the vehicle is unladen or only lightly laden, the damping forces can be well in excess of those required.
Modern collision avoidance systems require vehicle stability and optimum tyre contact with the road surface. If shock absorbers don’t ensure the correct road-tyre contact, particularly in wet conditions,
this can in turn affect the anti-lock braking system (ABS). Modern collision warning systems will also be affected by poor suspension systems, compromising their ability to function correctly.
Highway damage
Ineffective suspension systems go beyond loss in driver comfort, and can also impact roads and tyre wear. Forceful suspension damping can result in cracks, hollows and bumps, which gradually form ruts, while incorrect suspension set up can accelerate tyre wear.
What’s more, poor suspension damping is contributing to the multi-billion damage to Europe’s highways. Ruts in the road can amplify hazards, turning routine manoeuvres such as changing lane or driving in poor weather conditions, into a potentially dangerous situation. On top of that, the ensuing damage is compromising the safety of other road users.
Variable damping
More frequently, a variable damping approach is being adopted, which takes into account the load and other dynamic forces which affect the vital role of increasing safety, maintaining comfort and reducing the damage to roads. Sachs Continuous Damping Control (CDC), an electronically adjustable damping system which was originally developed for passenger car applications, is now available for use in commercial vehicles.
There are numerous benefits of the early adoption of CDC technology for freight and passenger transit operators. Take fragile loads,for example, every care is taken to ensure the goods reach their destination
undamaged, and CDC systems help to reduce tyre wear, decrease operating costs and provide a less stressful driving experience, ultimately improving safety. For the PSV sector, drivers can enjoy a safer and more comfortable journey.
CDC system components and operation
The Sachs CDC damper is the active element within an intelligent suspension control system consisting of the damper, an array of sensors throughout the vehicle, and a control unit. The vehicles sensor system continuously monitors driving parameters including load conditions, driver actions and vehicle movements, transmitting data from the sensors to the vehicles Controller Area Network (CAN ) to provide the basis for damping force calculations.
At the core of the CDC damper itself, is an electromagnetically controlled proportional valve. Depending on the calculated damping requirements, the oil aperture in the valve is dilated to soften the level of damping or contracted to firm up the ride. The control unit constantly recalculates and dynamically adjusts the valve settings according to sensor data received. A combination of continuously variable valve positioning, plus the adjustment of damping forces within milliseconds, enables fine tuning of the damper rate to match the prevailing conditions.
Electronic control eliminates the need to choose between comfort and stability, removing the conflict between damping comfort and tyre-road contact for safe handling. For average driving conditions, damping forces can be reduced to permit comfortable cabin suspension. Where cabin variations change due to lane manoeuvres, braking or gear shifting, Sachs CDC helps maintain the stability by increasing damping forces to match. The system also contributes to efficiency, by enabling reduction of gear shifting times to maximise tractive force.
The far-reaching advantages of Sachs CDC
CDC systems offer a variety of benefits for drivers, passengers, fleet operators and the environment. The reduction of vehicle body and seat acceleration ensures driver fatigue can be avoided and results in a more comfortable and pleasant journey. Better wheel control, reduced roll angle and less pitching mean that accelerating, braking, and changing direction can all be achieved, enhancing safety through improved vehicle control and handling. The smoother ride protects freight and minimises transit damage, while vehicles run more economically, as chassis and suspension components are subjected to less stress and tyre wear. This also helps maximise service life and keep maintenance downtime and costs low.
