chapter  11
32 Pages

Active Suspensions

I. Introduction ...................................................................................................................... 328

II. Basics of Active Suspensions .......................................................................................... 328

A. Concepts ................................................................................................................... 328

B. Active and Semi-Active........................................................................................... 328

C. Design Considerations ............................................................................................. 330

III. Tilting Trains.................................................................................................................... 331

A. Concept and Equations ............................................................................................ 331

B. Mechanical Configurations ...................................................................................... 333

C. Control: Strategies and Assessment......................................................................... 334

1. Control Approaches........................................................................................... 334

2. Assessment of Controller Performance ............................................................ 336

D. Summary of Tilting.................................................................................................. 338

IV. Active Secondary Suspensions ........................................................................................ 338

A. Concepts and Requirements..................................................................................... 338

B. Configurations .......................................................................................................... 339

C. Control Strategies..................................................................................................... 339

1. Sky-Hook Damping........................................................................................... 339

2. Softening of Suspension Stiffness..................................................................... 342

3. Low-Bandwidth Controls .................................................................................. 342

4. Modal Control Approach .................................................................................. 343

5. Model-Based Control Approaches.................................................................... 344

6. Actuator Response............................................................................................. 344

7. Semi-Active Control ......................................................................................... 344

D. Examples .................................................................................................................. 345

1. Servo-Hydraulic Active Lateral Suspension..................................................... 345

2. Shinkansen/Sumitomo Active Suspension........................................................ 346

V. Active Primary Suspensions ............................................................................................ 347

A. Concepts and Requirements..................................................................................... 347

B. Configurations .......................................................................................................... 348

C. Control Strategies..................................................................................................... 349

1. Stability Control — Solid-Axle Wheelset ........................................................ 349

2. Stability Control — Independently Rotating Wheelset.................................... 349

3. Steering Control — Solid-Axle Wheelset ........................................................ 350

4. Guidance Control — Independently Rotating Wheelset .................................. 350

5. Integrated Control Design ................................................................................. 351

6. Assessment of Control Performance................................................................. 351

D. Examples .................................................................................................................. 352

VI. Technology....................................................................................................................... 353

A. Sensing and Estimation Techniques ........................................................................ 353

B. Actuators .................................................................................................................. 354

C. Controllers and Fault Tolerance .............................................................................. 355

VII. Long Term Trends ........................................................................................................... 355

Nomenclature................................................................................................................................ 355

References..................................................................................................................................... 356

It is clear from the preceding chapters that the subject of railway vehicle dynamics has developed

principally as a mechanical engineering discipline, but an important technological change is

starting to occur through the use of active suspension concepts. The use of advanced control has

been common for many decades in the power electronic control of traction systems, and it is now

firmly established as the standard technology which has yielded substantial benefits, but its

application to suspensions is much more recent. Although the term “active suspension” is

commonly taken to relate to providing improved ride quality in fact, it is a generic term which

defines the use of actuators, sensors, and electronic controllers to enhance and/or replace the springs

and dampers that are the key constituents of a conventional, purely mechanical, “passive”

suspension; as such it can be applied to any aspect of the vehicle’s dynamic system.