M.M. ElMadany

Active vibration control of a flexible rotor

Abstract In this work, a finite element model of a multibearing rotor system is presented. The effects of rotary inertia, gyroscopic moments, internal viscous and hysteretic damping and shear deformations have been included. The characteristics of the fluid-film bearings are represented by eight stiffness and damping coefficients which are functions of Sommerfeld number. An optimal controller has been derived based on characteristics peculiar to rotor bearing systems which take into account the requirements for the free vibration and the persistent unbalance excitations. The controller uses as feedback signals, the states and the unbalance forces. A methodology of selecting the gains on the feedback signals has been presented based on separation of the signal effects: the plant states are the primary stimulates for stabilizing the rotor motion and augmenting system damping, while the augmented states representing the unbalanced forces are the primary stimulus for counteracting the periodically excited vibration. The results demonstrate that the proposed controller can significantly improve the dynamical behaviour of rotorbearing systems with regard to resonances and instabilities.

Optimal Linear Active Suspensions with Multivariable Integral Control

SUMMARY 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.

Stochastic optimal control of highway tractors with active suspensions

SUMMARY Stochastic optimal control and estimation theories are used to design an active suspension system for a cab ride in a tractor-semitrailer vehicle. A discrete-continuous vehicle model with eleven degrees of freedom is augmented by a stochastic road excitation model and a human perception of vibration shape filter. Both perfect measurement and estimated state cases are considered. The impact of the measurement noise on the design of the optimal controller is demonstrated. The performance of the optimally controlled system is compared with an optimal passive system. It is shown that significant improvements in ride comfort can be achieved through the use of actively controlled cab suspensions.

An analytical investigation of isolation systems for cab ride

Abstract The dynamic performance capabilities of heavy duty trucks with suspended cabs are identified using a linearized model of heave-fore-aft-pitch dynamics. Cab acceleration levels and dynamic deflections are determined for vehicle performance on a randomly irregular road surface. The important trade-offs that limit the overall design are illustrated.

Nonlinear ride analysis of heavy trucks

Abstract The problem of the dynamic interaction between the articulated vehicle and the road surface undulations is investigated using the equivalent linearization technique. The effects of the frictional forces generated in the laminated springs, bump-stops, wheel hop, road characteristics, loading condition and vehicle speed on the ride comfort and road safety are discussed and evaluated.

Integral and state variable feedback controllers for improved performance in automotive vehicles

Abstract An analytical investigation of a half-car model using an integral plus state variable feedback controller for tracking and regulation is performed. The potential benefits of incorporating, actively or semi-actively, such a controller to remedy the inherent problems associated with conventional passive suspensions and active suspensions based on state variable feedback controllers are examined. Both random and deterministic roadway inputs as well as deterministic body force and moment disturbances are used. The results demonstrate that an optimal suspension using an integral plus state variable feedback controller retains both excellent ride and attitude control characteristics.

RIDE PERFORMANCE POTENTIAL OF ACTIVE FAST LOAD LEVELING SYSTEMS

SUIMMARY The potential performance benefits of active high gain load levelers with specified configurations are investigated analytically using a quarter-car model. An analysis of the vehicle suspension systems is formulated for determining vehicle stability and response to body force and road disturbances. Both random and deterministic disturbances are considered Optimally controlled active suspensions with and without a derivative constraint in the performance index are also investigated. Results pertaining to the two optimal systems are presented and evaluated. It is shown that the load leveler offers a viable mechanism for controlling vehicle attitude without the necessity of reducing the isolation qualities and road-holding ability of the suspension.

Design of an active suspension for a heavy duty truck using optimal control theory

Abstract The optimal active suspension for the cab in a tractor-semitrailer vehicle model is obtained using the linear stochastic optimal control theory. Two state controllers, full state and limited state feedback, are determined. The control law minimizes a performance function representing operator discomfort and cab suspension travel. The randomly profiled road is modelled as a filtered white noise excitation and time delays due to the multiaxle excitation inputs are included. The performance of the optimally active controlled system is compared with the performance of an optimal passive system.

Design and optimization of truck suspensions using covariance analysis

Abstract The optimization of a six-degree-of-freedom plane linear heavy truck model subject to normally distributed stationary random road excitations is discussed. The analysis makes use of the technique of covariance analysis to obtain the variances of the state variables. A mathematical programming technique for the design of vehicle suspension systems is formulated and a computer program is developed for the optimization of vehicle suspension parameters to make vehicle response a minimum.

A Procedure for Optimization of Truck Suspensions

SUMMARY The purpose of this paper is to develop a procedure based on covariance analysis and nonlinear programming techniques which can be used for the parameter selection of optimum truck suspensions. The procedure is applied to explore the differences in parameter selection caused by the changes in the frequency content of the road input or by changes in the criteria for optimization. The equations of motion for a tractor-semitrailer truck are cast in state space form. The road excitations are represented by the output of a white noise excited shaping filter taking into consideration the time delays between the different vehicle axles. Shape filters to represent human perception of vibration in both the vertical and longitudinal directions in the time domain are presented and realized in terms of state variables. The suspension parameters of the road-vehicle-human body system are optimized using a direct search algorithm.