Hardware-in-the-Loop Testing of Vehicle Dynamics Controllers – A Technical Survey 2005-01-1660

Hardware-in-the-loop (HIL) test benches are indispensable for the development of modern vehicle dynamics controllers (VDCs). They can be regarded as a standard methodology today, because of the extremely safety-critical nature of the multi-sensor and multi-actuator systems used in vehicle dynamics control. The required high quality standards can only be ensured by systematic testing within a virtual HIL environment before going into a real car.

This paper aims to provide a condensed technical over-view of state-of-the-art HIL test systems for VDCs, which are currently widely used in passenger cars, in the form of ABS and TCS, as well as ESP, or integrated chassis control, which is just coming onto the market. First, a short introduction to the basic functionality of these types of ECUs is given, and the reasons why HIL testing is necessary and especially useful for VDCs are discussed. Since most of the dominant suppliers of VDC systems like Bosch, TRW, and Continental Teves, have the same principle system architecture, the closed loop HIL system (including I/O interfaces, signal conditioning, real-time models, user Interface, and test automation) can be generalized. However, there is still a possibility depending on the module being tested that one must include module specific resources to the setup.

A more detailed description of the currently used sensor signals for steering wheel position, lateral/longitudinal acceleration, yaw rate, wheel-speeds (active/passive/intelligent) and the hydraulic pressure sensors (internal/external) is presented. For the synthetic simulation of these signals within a simulator setup, it is also necessary to take into account the diagnostic functions of the ECU, for example to properly simulate the self-adjusting procedures for some of these sensors.

Controlling brake forces at each wheel is the main task of such a system and it is normally performed by hydraulic valves actuated by solenoids. Since these devices are enclosed within the housing of the ECU itself, a special device, called a valve signal detection unit (VSD), is used to measure the valve actuation.

In order to close the loop, a model of the complete vehicle is required to provide consistent and precise sensor signals as a response to the current actuator and (simulated) driver input signals. Some parts of the model will be explained in more detail to show how it is possible to overcome the partly numerically stiff behavior of the governing equations and to emphasize their importance within test scenarios and standard test maneuvers.

In the last section of the paper, an example of the interactivity of systems like ESP, EPB (electrical parking brake), and ACC (automatic cruise control) will show how demanding today's chassis controls are and how HIL technology copes with these challenges.