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Research Papers

Utilization of Actuators to Improve Vehicle Stability at the Limit: From Hydraulic Brakes Toward Electric Propulsion

[+] Author and Article Information
Mats Jonasson1

 Vehicle Dynamics and Active Safety, Volvo Car Corporation, SE-405 31 Gothenburg, Sweden; KTH Vehicle Dynamics, SE-100 44 Stockholm, Sweden e-mail: mjonass2@volvocars.com

Johan Andreasson

Modelon AB, Ideon Science Park, SE-223 70 Lund, Sweden

Stefan Solyom, Bengt Jacobson

 Vehicle Dynamics and Active Safety, Volvo Car Corporation, SE-405 31 Gothenburg, Sweden

Annika Stensson Trigell

 KTH Vehicle Dynamics, SE-100 44 Stockholm, Sweden

Dymola is registered trademark of Dynasim AB, Lund, Sweden.

MATLAB and Simulink are registered trademarks of The Mathworks, Inc., Natick, MA.

1

Corresponding author.

J. Dyn. Sys., Meas., Control 133(5), 051003 (Jul 27, 2011) (10 pages) doi:10.1115/1.4003800 History: Received October 26, 2009; Revised January 13, 2011; Published July 27, 2011; Online July 27, 2011

The capability of over-actuated vehicles to maintain stability during limit handling is studied in this paper. A number of important differently actuated vehicles, equipped with hydraulic brakes toward more advanced chassis solutions, are presented. A virtual evaluation environment has specifically been developed to cover the complex interaction between the driver and the vehicle under control. In order to fully exploit the different actuators setup, and the hard nonconvex constraints they possess, the principle of control allocation by nonlinear optimization is successfully employed. The final evaluation is made by exposing the driver and the over-actuated vehicles to a safety-critical double lane change. Thereby, the differently actuated vehicles are ranked by a quantitative indicator of stability.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

The methodology developed to investigate differently actuated vehicles

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Figure 2

(a) Different actuators setup in consideration. The physical designs are exemplified in sketches 1–4. Sketch 1 shows a conventional front axle design, sketch 2 an axle with individually actuated drive/brake, sketch 3 a conventional steering rack, and sketch 4 an axle with individually actuated steering. In (b) the functional description is presented with the wheel torque (Mfi from friction brakes and Mei from the primary power source) and steering inputs (δi).

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Figure 3

Principles of composed actuator and tire force constraints, denoted as S, for the configurations studied marked with green surfaces and curves. The dashed circles are assumed to be the friction circles. For purpose of illustration, the dots show the initial tire forces before the force distribution take place.

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Figure 4

The evaluation environment developed to investigate the potential of differently actuated vehicles. Force allocation to actuators (urefact) with global forces (frefglob) as input to follow a reference state (xref). The human driver acts in an outer loop to follow the global reference coordinates (Xref,Yref) and a heading reference angle Ψref.

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Figure 5

The control structure to handle the hard constraints

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Figure 6

Consumer union double lane change test

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Figure 7

Illustration of the vehicle behavior during maximum entry speed. The red sphere is representing the drivers preview point: (a) the NA vehicle configuration and (b) the AWD|S vehicle configuration.

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Figure 8

The path that the NA, AWB, and AWD|S vehicle configurations drive through under their maximum speeds (17.5, 21.0, and 23.0 m/s, respectively). Due to their deceleration (3 m/s2 ) under different entry speeds, they stop at different X positions. The red circles show the positions of the cones. The time interval between each vehicle plot is equal.

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Figure 9

The resulting wheel steering angles (δ1,δ2,δ3,δ4) and steering wheelangle (SWA) of the AWD|S vehicle configuration during maximum entry speed. Note that the AWD|S is a steered-by-wire configuration.

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Figure 10

The controlled RWD vehicle configuration: (a) reference states (dashed lines) from the reference vehicle model and actual states (solid lines); (b) reference wheel torques to the left rear (Me3) and the right rear (Me4) electrical machine

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Figure 11

Global vehicle forces are positioned at the boundary of the set of attainable forces at t = 2.5 s. The black dots represent a reconstruction and an estimate of the attainable set of vehicle forces for the RWD vehicle configuration. The red square represents frefglob and the yellow circle represents fglob.

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Figure 12

Variables plotted for the RWD configuration. (a) Actual lateral tire forces (solid lines) and actual lateral tire force limits (dotted red lines). (b) Allocation of tire forces at 2.5 s showing the assumptions of tire force constraints made by the force allocator. The vectors are pointed toward (fxi,fyi).

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