Development time and costs can be reduced by the use of simulation tools. The capabilities of Hardware in the Loop simulation offer the opportunity to scrutinize each single component detached from its system.

Sophisticated closed loop control algorithms check the input data for physical correctness and realistic behaviour. A common static test algorithm is no longer sufficient to meet all requirements. Therefore the input data must be calculated and made available by a real-time simulation environment. To achieve a viable closed loop test-bench the output data of the ECU (electronic control unit) are led back to the real-time unit. These data are the basis for the next simulation cycle.

A HiL test-bench consists of the following components:  

  •  Hardware (real device)
  •  Real-time simulation environment
  •  Monitor and analysis unit 

Testing of closed loop controller with HiL simulation methods grants the following advantages:

  •  Reproducible results
  •  Simple modification of the system structure
  •  Safe and non-destructive study of extreme conditions
  •  Automation of test cycles
  •  Independence of boundary conditions
      (e.g. environmental influences)

The simulation results can’t be transferred to the real test in all respects. This disadvantage is due to the fact that the simulation has to work under real-time condition. The duration of each simulation cycle, which contains reading the input data, solving the model equations and generating the output data, must be less than one millisecond to achieve adequate results. Consequently the computer capacity is strongly limited and large simplifications of the simulation-model become necessary.

 The FTM HiL-ESP-test-bench

The hardware of this test-bench contains the entire brake system of a vehicle (ECU, hydraulic unit, brake hoses and callipers). All necessary input signals are handed over to the ECU by the simulation environment (vehicle model and driver model). The test-bench passes signals for the motor control unit and the brake-fluid pressures at the brake disks back to the simulation environment. The main goal of this research programme is to reduce the number of dangerous test drives at the limit of handling. The development process can thus be accelerated and the result be optimized.