Driving dynamics tests on agricultural machinery
The Cologne Laboratory for Construction Machines (KLB) is an integral part of the course of studies for mobile work machines at the Cologne University of Applied Sciences. It is involved in numerous research and industrial projects, including an examination and optimization of driving dynamics, driving safety and driving comfort in mobile work machines.
KLB's equipment for these projects includes two six-component measuring wheels manufactured by Kistler. They were purchased through the FHInvest funding program of the German Federal Ministry for Education and Research (BMBF).
The road tests in Fig. 1 are designed to demonstrate the possibilities offered by using these measuring wheels and additional sensors in combination with the catman AP software from HBM for examining driving dynamics in mobile work machines.
The goal of these road tests was to determine the tire parameters of the tractor under different operating conditions. These parameters are needed to perform the simulations. Determining these parameters, especially for large-volume agricultural tires, involves considerable effort. So a process was selected that could be used to determine the relevant tire parameters directly on the vehicle during simple road tests.
Measurement technology and software
A comprehensive examination of driving dynamics requires a wide range of different sensor equipment and the corresponding software to record and analyze the measurement data. A diagram of the measurement technology used for this examination is shown in Fig. 2. The HBM catman measurement software, the HBM QuantumX measuring amplifier system and the following sensors were used in the tests:
- Analog sensors for measuring force, displacement, and strain
- Two Kistler wheel force sensors for wheel loads up to 24 metric tons
- CAN inertial navigation system
- CAN speed sensors
- Video camera
In addition to supporting the QuantumX amplifier system, the catman data acquisition system also makes it possible to acquire measurement data from the Kistler wheel force sensors via an Ethernet interface and video data via a USB or Ethernet interface.
Since there is no room in the tractor cab to hold the necessary measuring equipment, it was placed in a control cabinet on the right side of the vehicle (Fig. 3). The QuantumX amplifier, the on-board electronics required for the measuring wheels and the voltage supply are also installed in the control cabinet. All of the measurement equipment is operated from a measurement PC installed in the driver's cab. A second person outside the tractor can access this PC during the road tests via a remote desktop connection.
To monitor the road tests as they were being conducted, an option of the catman software was used for visualizing measurement data during the test. An example of this is shown in Fig. 4 for the essential parameters of a measuring wheel, together with a video recording. The tests can be analyzed accurately from a safe distance using this function.
Three different road tests were performed with the measurement technology shown here. The tire pressure, travel speed and ballasting of the tractor were modified in the tests.
- Driving over an obstruction on one side to examine the vertical rigidity of the tires when subjected to a ramp-shaped stimulus
- Braking tests to examine the longitudinal forces depending on the measured slip
- Examination of the slip angle and lateral rigidity during quasi-steady-state circular travel with increasing lateral acceleration
The tire parameters required for the simulation and the momentum of the vehicle were successfully measured during the road tests. Fig. 5 shows some examples of lateral force curves over the slip angle for different wheel loads on the rear wheel of the tractor.
Using HBM measurement technology and catman software, it was easy to set up and operate synchronous data acquisition for different sensors including Kistler wheel force sensors.