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TECHNICAL PAPERS

Mixed Slip-Deceleration Control in Automotive Braking Systems

[+] Author and Article Information
Sergio M. Savaresi1

Dipartimento di Elettronica e Informazione, Politecnico di Milano, Piazza L. da Vinci, 32, 20133 Milano, Itallysavaresi@elet.polimi.it

Mara Tanelli

Dipartimento di Elettronica e Informazione, Politecnico di Milano, Piazza L. da Vinci, 32, 20133 Milano, Itally

Carlo Cantoni

 BREMBO S.p.A., Via Brembo, 25, 24035, Curno (BG), Italy

1

Corresponding author.

J. Dyn. Sys., Meas., Control 129(1), 20-31 (Jul 10, 2006) (12 pages) doi:10.1115/1.2397149 History: Received March 29, 2005; Revised July 10, 2006

In road vehicles, wheel locking can be prevented by means of closed-loop anti-lock braking systems (ABS). Automatic braking is extensively used also for electronic stability control (ESC) systems. In braking control systems, two output variables are usually considered for regulation purposes: wheel deceleration and wheel longitudinal slip. Wheel deceleration is the controlled output traditionally used in ABS, since it can be easily measured with a simple wheel encoder; however, the dynamics of a classical regulation loop on the wheel deceleration critically depend on the road conditions. A regulation loop on the wheel longitudinal slip is simpler and dynamically robust; moreover, slip control is perfectly suited for both ABS and ESC applications. However, the wheel-slip measurement is critical, since it requires the estimation of the longitudinal speed of the vehicle body, which cannot be directly measured. Noise sensitivity of slip control hence is a critical issue, especially at low speed. In this work a new control strategy called mixed slip-deceleration (MSD) control is proposed: the basic idea is that the regulated variable is a convex combination of wheel deceleration and longitudinal slip. This strategy turns out to be very powerful and flexible: it inherits all the attractive dynamical features of slip control, while providing a much lower sensitivity to slip-measurement noise.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Single tire/wheel diagram

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Figure 2

Shapes of μ(λ) in different road conditions (in the table, the corresponding parameters are listed)

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Figure 3

Equilibrium manifold η¯(λ¯) in the case of Fz=mg and dry asphalt (continuous line)

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Figure 4

Magnitude bode plots of Gλ(s), at different longitudinal speeds (dry asphalt; λ¯=0.05)

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Figure 5

General scheme of the MSD controller

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Figure 6

Graphical interpretation of slip control in the (λ,η) domain. The vertical dotted bold line represents the set point λ¯. The square dots represent the equilibrium points, for different road conditions.

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Figure 7

Graphical interpretation of deceleration control in the (λ,η) domain. The horizontal bold line is the set point η¯. The square dots represent the equilibrium points for different road conditions.

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Figure 8

Graphical interpretation of MSD control in the (λ,η) domain. The bold line is the set point ε¯. The square dots represent the equilibrium points for different road conditions.

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Figure 9

Expression 9 of the lower bound of α, as a function of λ for different road conditions.

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Figure 10

Sensitivity function features when α=1 and 0.80⩽α⩽0.95

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Figure 11

Bode plots of the sensitivity function. (a) v=30m∕s; (b) v=10m∕s.

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Figure 12

The behavior of Φ(α), in different working conditions

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Figure 13

An example of measurement noises on λ and η used in the simulator

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Figure 14

Behavior of the actual wheel slip during a hard-braking maneuver on dry asphalt

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Figure 15

(a) Hard-braking maneuver, with a sudden road-surface change high→low grip (MSD control). (b) Hard-braking maneuver, with a sudden road-surface change low→high grip (MSD control).

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