IPG at DaimlerChrysler
An Independent Front Suspension for Light Commercial Trucks
(Summary of article published in ATZ Issue 12/2001, December 2001 - Publication No. V112)
The majority of commercial trucks on the road today use rigid axles or air suspension systems, while independent front suspensions are usually reserved for passenger cars and trucks. This trend has historically been based on factors such as cost and maximum weight and load, yet for light commercial vehicles a rigid suspension might not be the best choice. This is because the vehicle dynamics and ride comfort of a commercial truck under 10 tons could be dramatically improved by using an independent front suspension, which are important factors for driver safety and accident prevention, among other things.
The DaimlerChrysler AG Division, Basic Engineering of Commercial Vehicles, was charged with assessing these very ideas, and by using simulation tools that were provided by IPG Automotive GmbH, did just that. The project objectives were to develop a system that had improved vehicle dynamics behavior, ride comfort, steering behavior and frame packaging in the cab and engine areas. Also, both air suspension and steel springing systems needed to be available for the same axle design. In addition, the cost of the system was not to exceed the costs of the traditional suspension design with a rigid axle; all very challenging requirements when taken as a whole.
The axle design consisted of a double wishbone suspension with a radial linkage. Steering was done via a rack and pinion system, which was chosen over a reticulating ball system because of the improved steering response. Additional bracing was required to secure the axle to the Atego front frame, as the Atego was originally designed for a rigid axle system. To avoid the use of an anti-roll bar the axle spring was coupled on the central axel, which increases stability when cornering.
Now that the initial design work was done, it was time to simulate. IPG-KINEMATICS was used to evaluate the kinematics, elasto-kinematics, steering kinematics and to optimize the design before building the first prototype. The optimization was geared toward minimizing the steering roll of the axle so that greater stability and response were achieved.
For the vehicle dynamics IPG simulation tools were used which contained a comprehensive library of vehicle models to simulate the DaimlerChrysler commercial fleet. Using steady-state cornering the simulations confirmed that no anti-roll bar was required and a roll angle that is equal to that of a rigid axle vehicle could be achieved. Also, the simulations showed that the steering behavior was not as directly effected by the vehicles load as a rigid axle system would be, and that ride comfort was clearly improved when driving on a simulated "bad and bumpy" country road.
When the simulation testing was complete the first prototype was built and installed. The same tests that were done with simulation were now performed on the real vehicle. Real world testing verified the results obtained with simulation and confirmed that the independent front suspension did, in fact, have clear advantages in ride comfort, steering behavior, and vehicle dynamics behavior.
The study showed that a front independent suspension system for light commercial trucks was indeed feasible, and has quantifiable benefits. The cost requirements of the design were unfortunately not met, but work has already been started to reduce the cost of such systems to make them comparable in price to rigid axle systems. However, it is clear that there is now evidence that using an independent front suspension system could be advantageous. In addition, this project shows that IPG's simulation tools can accurately predict the behavior of real systems and help to optimize the design long before the actual components become available. This time saving was important and significantly contributed to the successful aspects of the project.
