Olugbenga Moses Anubi

DESIGN AND ANALYSIS OF A VARIABLE STIFFNESS MECHANISM

The design and analysis of a mechanism with variable stiffness is examined. The mechanism, which is a simple arrangement of two springs, a lever arm and a pivot bar, has an effective stiffness that is a rational function of the horizontal position d of the pivot. The external pure force acting on the system is constrained to always remain vertical. The effective stiffness is varied by changing d while keeping the point of application of the external load constant. The expression for the effective stiffness is derived. A reverse analysis is also carried out on the mechanism. Special design cases are considered. The dynamic equation of the system is derived and used to deduce the natural frequency of the mechanism from which some insights were gained on the dynamic behavior of the mechanism.Copyright

A new active variable stiffness suspension system using a nonlinear energy sink-based controller

This paper presents the active case of a variable stiffness suspension system. The central concept is based on a recently designed variable stiffness mechanism which consists of a horizontal control strut and a vertical strut. The horizontal strut is used to vary the load transfer ratio by actively controlling the location of the point of attachment of the vertical strut to the car body. The control algorithm, effected by a hydraulic actuator, uses the concept of nonlinear energy sink (NES) to effectively transfer the vibrational energy in the sprung mass to a control mass, thereby reducing the transfer of energy from road disturbance to the car body at a relatively lower cost compared to the traditional active suspension using the skyhook concept. The analyses and simulation results show that a better performance can be achieved by subjecting the point of attachment of a suspension system, to the chassis, to the influence of a horizontal NES system.

Roll stabilisation of road vehicles using a variable stiffness suspension system

A variable stiffness architecture is used in the suspension system to counteract the body roll moment, thereby enhancing the roll stability of the vehicle. The variation of stiffness concept uses the ‘reciprocal actuation’ to effectively transfer energy between a vertical traditional strut and a horizontal oscillating control mass, thereby improving the energy dissipation of the overall suspension. The lateral dynamics of the system is developed using a bicycle model. The accompanying roll dynamics are also developed and validated using experimental data. The positions of the left and right control masses are sequentially allocated to reduce the effective body roll and roll rate. Simulation results show that the resulting variable stiffness suspension system has more than 50% improvement in roll response over the traditional constant stiffness counterparts. The simulation scenarios examined is the fishhook manoeuvre.

Vehicle Roll Stabilization Enhancement Using a Variable Stiffness Architecture: Kinematic Control

A variable stiffness architecture is used in the suspension system to counteract the body roll moment, thereby enhancing the roll stability of the vehicle. The variation of stiffness concept uses the “reciprocal actuation” to effectively transfer energy between a vertical traditional strut and a horizontal oscillating control mass, thereby improving the energy dissipation of the overall suspension. The lateral dynamics of the system is developed using a bicycle model. The accompanying roll dynamics are also developed and validated using experimental data. The positions of the left and right control masses are optimally allocated to reduce the effective body roll and roll rate. Simulation results show that the resulting variable stiffness suspension system has more than 50% improvement in roll response over the traditional constant stiffness counterparts. The simulation scenarios examined is the fishhook maneuver.© 2013 ASME

Nonlinear Control of Semi-Active MacPherson Suspension System

This paper presents the control design and analysis of a non-linear model of a MacPherson suspension system equipped with a magnetorheological (MR) damper. The model suspension considered incorporates the kinematics of the suspension linkages. An output feedback controller is developed using an ℒ2-gain analysis based on the concept of energy dissipation. The controller is effectively a smooth saturated PID. The performance of the closed-loop system is compared with a purely passive MacPherson suspension system and a semi-active damper, whose damping coefficient is tunned by a Skyhook-Acceleration Driven Damping (SH-ADD) method. Simulation results show that the developed controller outperforms the passive case at both the rattle space, tire hop frequencies and the SH-ADD at tire hop frequency while showing a close performance to the SH-ADD at the rattle space frequency. Time domain simulation results confirmed that the control strategy satisfies the dissipative constraint.Copyright

Nonlinear Disturbance Rejection for Semi-Active MacPherson Suspension System

This paper presents the control design and analysis of a non-linear model of a MacPherson suspension system equipped with a magnetorheological (MR) damper. The model suspension considered incorporates the kinematics of the suspension linkages. A state feedback controller is developed using an L2-gain analysis based on the concept of energy dissipation. The controller is effectively a saturated PID. The performance of the closed-loop system is compared with a purely passive MacPherson suspension system and a semi-active damper, whose damping coefficient is tunned by a Skyhook-Acceleration Driven Damping (SH-ADD) method. Simulation results show that the developed controller outperforms the passive case at the rattle space, tire hop frequencies and the SH-ADD at tire hop frequency while showing a close performance to the SH-ADD at the rattle space frequency. Time domain simulation results confirm that the control strategy satisfies the dissipative constraint.© 2012 ASME

Disturbance observer design for a class of nonlinear system with application to active suspension system control

A systematic disturbance observer for a class of nonlinear affine systems subject to bounded exogenous input is designed. The main idea expounded upon is to design the “control law” for the observer dynamics such that the tracking error between the observer states and the original system states lies within a bounded set. It is then shown that, provided that the system satisfies some sufficient conditions, then the observer control authority will track the unknown exogenous input with the same order of magnitude of the error. In other words, the observer dynamics is designed to recreate the measured behavior of the original system to some order of accuracy. If this happens, then, under certain sufficient conditions, the control authority that reproduced this measured behavior will track the unknown disturbance input to the same order of accuracy. While the concepts developed in this paper can be used for a class of nonlinear system, the main application considered is the active suspension system control. The motivation is to eventually use the observed disturbance as a preview information for a cascaded suspension system.

A New Variable Stiffness Suspension Mechanism

A new variable stiffness suspension system based on a recent variable stiffness mechanism is proposed. The overall system is composed of the traditional passive suspension system augmented with a variable stiffness mechanism. The main idea is to improve suspension performance by varying stiffness in response to road disturbance. The system is analyzed using a quarter car model. The passive case shows much better performance in ride comfort over the tradition counterpart. Analysis of the invariant equation shows that the car body acceleration transfer function magnitude can be reduced at both the tire-hop and rattle space frequencies using the lever displacement transfer function thereby resulting in a better performance over the traditional passive suspension system. An H¥ controller is designed to correct for the performance degradation in the rattle space thereby providing the best trade-off between the ride comfort, suspension deflection and road holding.