Experimental characterisation of front axle suspension systems for narrow-track tractors

Over the last few years, stricter comfort and stability standards for agricultural vehicles have generated tough challenges for manufacturers. Front axle suspensions can considerably improve tractor comfort. This solution has been typically installed on vehicles over 100 kW but recently, it has also been introduced for narrow-track tractors. These types of tractor require special features in terms of dimensions, manoeuvrability and stability; indeed, the small turning radius and the roll-over performance required present tough constraints. In addition, the lack of space for positioning suspension systems is a concern. A lack of background knowledge has forced companies to search for methods to systematically validate suspension performance. The aim of this work was to design and validate a test-set that can enable the front axle suspensions of these specialised tractors to be fully characterised. The proposed test-set comprises of two different bumps tests and a braking test which are designed to excite each tractor rigid mode selectively. In tests, a series of sensors was installed to measure accelerations at different tractor positions and other dynamic parameters (tractor speed, pitch rate and roll rate) in real-time. Aggregated data (root mean square and peak-to-peak values) were calculated from the acquired signals which allowed to compare two tractors of the same power class, one equipped with a front axle suspension, and one with a rigid front axle. The collected data could lead to a benchmark definition of the tractor class features, to be compared with newly designed, improved suspension systems.