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Goals of this final MSc. presentation :

System identification of the brake setup in the TU Delft Vehicle Test Lab (VTL ) Jean-Paul Busselaar MSc. thesis. Goals of this final MSc. presentation : Introducing the basics of ABS, tire dynamics and tire friction models related to the Feed Forward ABS controller

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Goals of this final MSc. presentation :

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  1. System identification of the brake setup in the TU Delft Vehicle Test Lab (VTL)Jean-Paul Busselaar MSc. thesis

  2. Goals of thisfinal MSc. presentation: Introducing the basics of ABS, tire dynamics and tire friction models related to the Feed Forward ABS controller Introducing the TU Delft VTL Describing the dSPACE data acquisition Presenting the results of the VTL measurement setup Presenting the conclusion

  3. ABS introduction • An Anti-lock Braking System (ABS) is a vehicle motion control system to increase the passive safety of a vehicle. • ABS intends to prevent wheel lock by regulating the hydraulic brake pressure of each wheel to increase the lateral stability.

  4. ABS introduction • ABS consists of mathematic models which are based on physical properties related to tire-road conditions. • Tire friction and road conditions are affecting the control schemes of the mathematic models.

  5. Tire dynamics • The dynamic behaviour of atire is suggested in a coordinate system. • The three forces are: The three moments are: • 1. Longitudinal force Fx 1. Overturning moment Mx • 2. Lateral force Fy2. Rolling moment My • 3. Normal force Fz3. Yawing moment / self-aligning torque Mz

  6. Tire dynamics • Side slip α is the angle between the tire longitudinal axis and the wheel velocity vector • Longitudinal slip is the normalized ratio of the slip velocity and vehicle velocity:

  7. Tire dynamics • A free rolling wheel is represented with . • A locked wheel is indicated by . • ABS controllers are optimized at the transition of the rising and falling slope • Identification of the algorithm for estimating the peak-value can provide a reliable estimation for ABS activation.

  8. Stationary friction models • Static friction is determined by the friction coefficient and the normal force • Coulomb force

  9. Quasi-physical dynamic friction model LuGre Tire friction model • The constant Coulomb friction force is replaced by the speed dependent sliding friction function . • The LuGre model is related to the bristle interpretation of friction. Friction is modeled as the average deflection force of elastic springs.

  10. Feed Forward ABS controller • The Feed Forward ABS controller model is used to do brake pressure dynamics measurements • Quarter car with LuGre tire friction • With • And is the linearized viscous damping • The term with is the non-linearity of the tire-road friction

  11. Feed Forward ABS controller • Flatness-based model inverse • Where is a function of the vehicle speed, acceleration, jerk and the third derivative of the speed

  12. TU Delft Vehicle Test Lab • The TU Delft VTL is used for testing tire behaviour and for prototyping ABS strategies

  13. TU Delft Vehicle Test Lab Tire setup room Control room • Close up brake caliper • Close up test wheel

  14. Brake setup Vehicle Test Lab • The VTL brake system consists of: 1. A hydraulic pump • A by-pass valve to (dis)connect the brake caliper hydraulically • A rubber brake hose in the original situation • A brake caliper with a brake disc, brake pads and forced air cooling • A piezo-electric brake pressure transducer

  15. Brake setup Vehicle Test Lab • A charge amplifier to receive charge form the piezo-electric transducer • An analog proportional controller to measure and adapt the error between the reference and measured brake pressure • A brake torque sensor and receiver

  16. Brake setup Vehicle Test Lab • The situation with design improvement: Stainless Steel braided brake hose

  17. dSPACE • dSPACE is used to control and measure the parameters of the VTL setup. dSPACE contains software as well as hardware components. • Brake pressure measurements are performed with an existing Feed-Forward ABS model in dSPACE. • Modifying the Feed-Forward controller by a signal generator for brake pressure actuation purpose. • Constant average brake pressures with varying amplitudes are used. To achieve this, a constant is added with the signal generator.

  18. dSPACE ControlDesk • To actuate and measure the test setup real-time, a control panel in ControlDesk has to be made. • From the existing Feed-Forward ABS model, the specific parameters has to be carefully chosen. • The control panel contains : • ON-OFF buttons • A constant pressure value slider • graphs with measuring parameters • settings of the actuating signal • data acquisition

  19. Brake pressure dynamicsresults • Sinus wave excitation measurements are executed to show possible differences in brake pressure dynamics. • These are relativelysimple and quick measurements to see the effects between frequencies, amplitudes and constant average in the originalsituation. • Twolast waves are taken to compare for the repeatabilityresult • About 3bar difference between the desired and the actual max pressure • 0,07bar max difference in one97bar case between nr77 and nr78 • 0,08% max difference in 60bar case between nr77 and nr78

  20. Brake pressure dynamicsresults • When the frequency increases with relative low amplitudes: little pressure difference is observed

  21. Brake pressure dynamicsresults • When the amplitude increases 2x, the max pressure dynamics decreases

  22. Brake pressure dynamicsresults • Further increase of the frequency with relative high amplitudes results into larger decrease in pressure dynamics

  23. Brake pressure dynamicsresults • With design improvements stainless steel braided brake hose • Shows an improved repeatability • 0,75bar improved compared to the original situation

  24. Brake pressure dynamicsresults • Random noise excitations to determine transfer functions • Best result of the original settings, cross over frequency 150Hz • Resonance frequency of approx. 84Hz • Bandwidth of approx. 118Hz • Time delay to approx. 250Hz

  25. Brake pressure dynamicsresults • Cross over frequency from 150Hz to 300Hz • Resonance frequency approx. 84Hz • Bandwidth approx. 116Hz when using relative low amplitudes • Time delay to approx. 400Hz

  26. Brake pressure dynamicsresults • Amplitude 1bar • Resonance frequency of approx. 75Hz • Bandwidth of approx. 120Hz • Time delay to approx. 300Hz

  27. Brake pressure dynamicsresults • Check channel 5 input signal with channel 6 with limited freq. content • Resonance frequency of approx. 33Hz • Bandwidth of approx. 115Hz • Time delay to approx. 300Hz

  28. Brake pressure dynamicsresults • Best overall results when changing gains • Resonance frequency of approx. 90Hz • Bandwidth of approx. 112Hz • Time delay to approx. 500Hz

  29. Brake pressure dynamicsresults • Best bandwidth result when changing gains • Resonance frequency of approx. 50Hz • Bandwidth of approx. 117Hz • Time delay to approx. 300Hz

  30. Conclusion • Sinus wave excitation results of the original situation show clearly decreased brake pressure dynamics when increasing the frequency. • Also relative small maximum pressure increase of 0,75bar for the stainless steel braided brake hose situation is observed. When applying relative high amplitudes of 20bar with a constant average 80bar @ 1Hz. • Decreasing the varying amplitude will improve the dynamical behaviour of the measurement setup. • Random noise excitation results with design improvements when increasing the cross over frequency to 300Hz the overall results are slightly decreased. • When changing the proportional gains, little difference in bandwidth is noticed in most cases. • Channel 6 with a limited frequency content has a comparable bandwidth, overall results of channel 5 show a better performance. • The upper knob gain setting of 2.00 shows the best overall results. • The upper knob gain setting of 5.00 shows the best bandwidth of 117Hz. • A cross over frequency of 150Hz and relative low varying amplitudes to 1bar show the best results of all measurements

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