Railway Vehicle Active Suspensions

This paper reviews the state-of-the-art of active suspensions for use on railway vehicles. The primary focus of the paper is on ride quality control, both vertical and lateral, and on lateral stability control.

The section on theoretical considerations summarizes the results of a one-degree of freedom optimization and then investigates analytically the use of active suspensions for lateral ride and stability augmentation. It is shown that separate control structures using different measurements and actuator actions are very effective in controlling both ride quality and stability.

A section on a survey ofcurrent activities reviews published research on active railway suspension work around the world.

Finally a concluding section indicates future trends in active suspension applications.     

主动底盘系统的发展趋向（下）

本文论述“主动底盘系统”范畴内两个最现实的问题:悬架减振及四轮转向。关于悬架减振,首先探讨传统悬架的规律,然后阐述主动和半主动悬架系统对悬架可能作出的改进。对所谓“悬空阻尼”系统,着重作了介绍。四轮转向方面首先论述了比例四轮转向、质心侧偏角补偿和可调节的四轮转向等几种基本型式的理论基础。接着介绍了现有的四轮转向系统。     

Anti-Roll and Active Roll Suspensions

Full car roll model is used to show an anti-roll control like that in Citroen's Xantia Activa and the proposed active roll with an in-series active suspension. Computed responses to pulse-shaped anti-phase road unevenness as well as to lateral acceleration in comparison with passive suspension are given in the paper. Also stability values for all parameters can be found.     

Anti-Roll and Active Roll Suspensions

Full car roll model is used to show an anti-roll control like that in Citroen's Xantia Activa and the proposed active roll with an in-series active suspension. Computed responses to pulse-shaped anti-phase road unevenness as well as to lateral acceleration in comparison with passive suspension are given in the paper. Also stability values for all parameters can be found.     

Theoretical Limitations in Active Vehicle Suspensions

SUMMARY

Vehicle suspensions in which forces are generated in response to feedback signals by active elements obviously offer increased design flexibility compared to conventional suspensions using passive elements such as springs and dampers. It is often assumed that if practical difficulties are neglected, active systems could in principle produce arbitrary ideal, behavior. It is shown, using a simple linear two degree-of-freedom suspension system, model that even using complete state feed back and in the case of in which the system is controllable in the control theory sense, there still are limitations to suspension performance in the fully active case. If the ideal suspension performance is defined based on low-pass filtering of roadway unevenness inputs, an active suspension may not offer much better performance than a partially active or adaptive passive suspension depending upon the values of certain vehicle parameters.     

Theoretical Limitations in Active Vehicle Suspensions

Vehicle suspensions in which forces are generated in response to feedback signals by active elements obviously offer increased design flexibility compared to conventional suspensions using passive elements such as springs and dampers. It is often assumed that if practical difficulties are neglected, active systems could in principle produce arbitrary ideal, behavior. It is shown, using a simple linear two degree-of-freedom suspension system, model that even using complete state feed back and in the case of in which the system is controllable in the control theory sense, there still are limitations to suspension performance in the fully active case. If the ideal suspension performance is defined based on low-pass filtering of roadway unevenness inputs, an active suspension may not offer much better performance than a partially active or adaptive passive suspension depending upon the values of certain vehicle parameters.     

主动汽车悬架的非线性控制

本文采用１／４车模型对天棚阻尼器和主动悬架的动力学性能进行分析，针对执行器的非线性特性，探讨了微分几何法和反馈法线必互法在主动悬架控制中的应用，在系统控制设计中采用了离散滑模法，仿真结果显示非线性控制律能有效地改善主动悬架的隔振特性。     

主动悬架的参数估计自校正控制

本文采用二自由度的单轮模型，运用衰减记忆递推最小二乘法参数估计算法和广义加权最小方差自校正控制算法，通过控制律隐式结构直接估计控制器参数，再综合得到控制律，从而实现了主动悬架的参数估计自校正控制。经实例计算和数值仿真，证明了该控制方法的有效性和可行性。     

Active Suspensions Based on Fast Load Levelers

SUMMARY

A class of active suspensions is presented which provides near optimum isolation of base motion as well as zero static deflection for force disturbances using a simple type of feedback. The load leveling effect is rapid with the system stabilized using isolated mass velocity feedback both for a semi-active damper and for the load leveler. The system can be made energy conservative and fail safe since the system reverts to a reasonable passive isolator if the load leveling effect and even if the active damping effect is switched off. The system could be incorporated in automotive vehicles with some extension of the feedback control to account for several aspects of body motion.     

Optimal Linear Active Suspensions with Integral Constraint

This paper considers the application of linear optimal control to the design of an active automobile suspension system. By inclusion of an integral constraint in the performance index it is possible to achieve zero steady state axle to body response to both static body forces and ramp road inputs. Full state feedback is achieved by reconstructing the state variables from easily measured quantities.     

Technical Note: Force Control in Electrohydraulic Active Suspensions Revisited

The inner loop control for the actuator force can be quite simply compensated by means of a correction term to the desired force signal at the input. The correction requires only a measurement of the actuator piston velocity and is employed to cancel the loop disturbance caused by the oil flow to the actuator. Although an additional time constant is introduced by the integration in the inner loop force control, the overall performance is nevertheless quite close to that of an ideal optimal system.     

Technical Note: Force Control in Electrohydraulic Active Suspensions Revisited

The inner loop control for the actuator force can be quite simply compensated by means of a correction term to the desired force signal at the input. The correction requires only a measurement of the actuator piston velocity and is employed to cancel the loop disturbance caused by the oil flow to the actuator. Although an additional time constant is introduced by the integration in the inner loop force control, the overall performance is nevertheless quite close to that of an ideal optimal system.     

Active Suspensions Based on Fast Load Levelers

A class of active suspensions is presented which provides near optimum isolation of base motion as well as zero static deflection for force disturbances using a simple type of feedback. The load leveling effect is rapid with the system stabilized using isolated mass velocity feedback both for a semi-active damper and for the load leveler. The system can be made energy conservative and fail safe since the system reverts to a reasonable passive isolator if the load leveling effect and even if the active damping effect is switched off. The system could be incorporated in automotive vehicles with some extension of the feedback control to account for several aspects of body motion.     

Achievable Dynamic Response for Automotive Active Suspensions *

A complete set of constraints is derived for the road disturbance transfer functions in a quarter car model of an automotive active suspension, for typical choices of measured outputs. It is shown that any road disturbance responses which are achievable using “full state feedback” can be achieved, to within an arbitrary small tolerance, using a dynamic compensator measuring suspension deflection only. Also considered are the disturbance responses to loads acting on the sprung mass, and a complete set of constraints is derived for these. It is shown that road disturbance and load disturbance responses can be determined independently if suspension deflection and sprung mass velocity are measured. Indeed, any responses achievable separately with “full measurements” can be approximated together to an arbitrary small tolerance. Certain integral relationships are shown to follow from the derived transfer function constraints. These relationships imply fundamental limitations for certain responses (e.g. tyre deflection) no matter what measurements are available for feedback.     

Optimal Linear Active Suspensions with Multivariable Integral Control

In this paper, an optimal suspension system is derived for a quarter-car model using multivariable integral control. The suspension system features two parts. The first part is an integral control acting on suspension deflection to ensure zero steady-sate offset due to body and maneuvering forces as well as road inputs. The second is a proportional control operating on the vehicle system states for vibration control and performance improvement. The optimal ride performance of the active suspensions based on linear full-state feedback control laws with and without integral control together with the performance of passive suspensions are compared.     

Fuzzy Logic Active and Semi-Active Control of Off-Road Vehicle Suspensions

For off-road vehicles, minimizing the absorbed power is the main objective of suspension control. The primary cause of increase in the absorbed power in off-road vehicles driven at high speeds on harsh courses is the exhaustion of the suspension travel. Fuzzy-logic approach to active and semi-active off-road vehicle suspension control, with the goal of improving the speed of the vehicle over rough terrains are developed. The ride metric used for quantifying improvements is the absorbed power of the sprung mass. Particular attention is paid to the proper modeling of the suspension using both the full kinematic constraints and the more convenient two degree of freedom linear model of the quarter vehicle suspension. The nonlinearities due to the kinematic constraints on motion are accounted for by modifying the stiffness and damping coefficients of the suspension spring and dashpot in the linear model. The control laws are developed using the less complex model and demonstrated in the fully constrained environment. Nonlinearities of the suspension, including tire stiffness/damping and bumpstops are included at all stages of controller development.     

Performance Limitations and Constraints for Active and Passive Suspensions: a Mechanical Multi-port Approach

This paper develops a framework using mechanical multi-port networks to study the performance capabilities and constraints in vehicle suspensions. We seek to understand the set of dynamic responses which are achievable for both passive and active systems. To this end, we view a suspension system as a mechanical multi-port network and draw on concepts from electrical circuits such as passivity and reciprocity. We identify necessary conditions on the external behaviour of a quarter-car model for the suspension to be capable of passive realisation, and thereby establish that several behaviours or force laws cannot be implemented without an internal power source. We study the number of available degrees of freedom (i.e., independently specifiable impedances) in the quarter-, half- and full-car cases.     

Fuzzy Logic Active and Semi-Active Control of Off-Road Vehicle Suspensions

For off-road vehicles, minimizing the absorbed power is the main objective of suspension control. The primary cause of increase in the absorbed power in off-road vehicles driven at high speeds on harsh courses is the exhaustion of the suspension travel. Fuzzy-logic approach to active and semi-active off-road vehicle suspension control, with the goal of improving the speed of the vehicle over rough terrains are developed. The ride metric used for quantifying improvements is the absorbed power of the sprung mass. Particular attention is paid to the proper modeling of the suspension using both the full kinematic constraints and the more convenient two degree of freedom linear model of the quarter vehicle suspension. The nonlinearities due to the kinematic constraints on motion are accounted for by modifying the stiffness and damping coefficients of the suspension spring and dashpot in the linear model. The control laws are developed using the less complex model and demonstrated in the fully constrained environment. Nonlinearities of the suspension, including tire stiffness/damping and bumpstops are included at all stages of controller development.