Hardware-in-the-Loop test stand for controlled all-wheel drive at Ford
Quality and Reliability under any operating conditions, matched with time and cost efficiency - These are the central goals which stand high on the list for vehicle development. Therefore Ford counts on Hardware-in-the-Loop simulation for its new four-wheel-controls' functional tests. As a testing tool, they use a CarMaker/HIL test stand from IPG Automotive.
Controlled all-wheel-drive vehicles allow not only the best possible traction but also very good driving dynamics qualities and a high degree of driving stability. It is fundamental to realize, depending on the driving situation, the optimal force allocation at the front and rear axle. The exact force allocation at the front and rear axle is calculated by a four-wheel control unit, which receives information about the actual driving situation from different sensors over CAN. This configuration enables the creation of a vehicle with all the advantages of a four-wheel drive, fuel efficiency and the Ford-typical driving characteristic.
Hardware-in-the-Loop tests with CarMaker/HIL
Ford performs its Hardware-in-the-Loop tests (HIL tests) on IPG's CarMaker/HIL test stand to ensure the correct functioning of the control unit and the system elements. This test stand has already been successfully used to integrate an ESP system combined with an electronic parking brake (EPB), and has now been enlarged for the test of four-wheel controls. Thus Ford's engineers can make use of their experience with the ESP tests and perform further all-wheel and ESP tests together.
Integration of the four-wheel control in a virtual vehicle environment
CarMaker/HIL simulates the target vehicle and its vehicle dynamics behaviour in real time. Therefore CarMaker offers not only the driver and road models but also a complete vehicle model with its subsystems like chassis, drivetrain, brake system and tires. A four-wheel coupling model was integrated in this vehicle environment.
The four-wheel control unit is connected to CarMaker/HIL's real time system by I/O modules. The information about the vehicle situation, simulated by CarMaker, can be imported as well as the signals of the ESP control unit. The four-wheel control unit takes all factors into account to analyse the optimal force allocation of the axle and turns them over to the coupling model. The coupling reaction of these signals is simulated in real time and sent back as a new control variable to the control unit.
The testing program
The primary goals of HIL tests are, on the one hand to perform the Fail-Safe analysis of the four-wheel systems, and on the other hand to ensure the correct functioning of the interface communication. It must be guaranteed that an electrical fault of the four-wheel control unit sensors is exactly diagnosed and the according process initiated. Electrical faults are systematically inserted at the control unit to check this.
ESP and four-wheel control can be tested in together. The vehicle dynamics behaviour is influenced by both control systems that consequently interact with each other. To ensure a correct fault management for coherent systems, CAN signals are manipulated or several control units completely de-activated in the CarMaker/HIL test stand.
Quality Assurance thanks to Hardware-in-the-Loop tests
HIL simulation allows an comprehensive and far-reaching verification of the four-wheel control and the complete behaviour of the system. Possible problems with the electronic activation or the fault management can be discovered comfortably, and eliminated. As they can also be easily and rapidly reproduced by virtual test driving, the accordant fault analysis is clearly more efficient. Finally, HIL tests contribute to assure and strengthen Ford's high quality standards.
