Avesta Goodarzi

An optimal torque distribution control strategy for four-independent wheel drive electric vehicles

In this paper, an optimal torque distribution approach is proposed for electric vehicle equipped with four independent wheel motors to improve vehicle handling and stability performance. A novel objective function is formulated which works in a multifunctional way by considering the interference among different performance indices: forces and moment errors at the centre of gravity of the vehicle, actuator control efforts and tyre workload usage. To adapt different driving conditions, a weighting factors tuning scheme is designed to adjust the relative weight of each performance in the objective function. The effectiveness of the proposed optimal torque distribution is evaluated by simulations with CarSim and Matlab/Simulink. The simulation results under different driving scenarios indicate that the proposed control strategy can effectively improve the vehicle handling and stability even in slippery road conditions.

Multi-objective optimization of a hybrid electromagnetic suspension system for ride comfort, road holding and regenerated power

This paper reports work on the optimization and performance evaluation of a hybrid electromagnetic suspension system equipped with a hybrid electromagnetic damper. The hybrid damper is configured to operate with hydraulic and electromagnetic components. The hydraulic component produces a large fail-safe baseline damping force, while the electromagnetic component adds energy regeneration and adaptability to the suspension. For analyzing the system, the electromagnetic component was modeled and integrated into a 2DOF quarter-car model. Three criteria were considered for evaluating the performance of the suspension system: ride comfort, road holding and regenerated power. Using the genetic algorithm multi-objective optimization (NSGA-II), the suspension design was optimized to improve the performance of the vehicle with respect to the selected criteria. The multi-objective optimization method provided a set of solutions called Pareto front in which all solutions are equally good and the selection of each one depends on conditions and needs. Among the given solutions in the Pareto front, a small number of cases, with different design purposes, were selected. The performances of the selected designs were compared with two reference systems: a conventional and a nonoptimized hybrid suspension system. The results show that the ride comfort and road holding qualities of the optimized hybrid system are improved, and the regenerated power is considerably increased.

Innovative Active Vehicle Safety Using Integrated Stabilizer Pendulum and Direct Yaw Moment Control

Basically, there are two main techniques to control the vehicle yaw moment. First method is the indirect yaw moment control, which works on the basis of active steering control (ASC). The second one being the direct yaw moment control (DYC), which is based on either the differential braking or the torque vectoring. An innovative idea for the direct yaw moment control is introduced by using an active controller system to supervise the lateral dynamics of vehicle and perform as an active yaw moment control system, denoted as the stabilizer pendulum system (SPS). This idea has further been developed, analyzed, and implemented in a standalone direct yaw moment control system, as well as, in an integrated vehicle dynamic control system with a differential braking yaw moment controller. The effectiveness of SPS has been evaluated by model simulation, which illustrates its superior performance especially on low friction roads.

Vehicle dynamics control by using a three-dimensional stabilizer pendulum system

ABSTRACT Active safety systems of a vehicle normally work well on tyre–road interactions, however, these systems deteriorate in performance on low-friction road conditions. To combat this effect, an innovative idea for the yaw moment and roll dynamic control is presented in this paper. This idea was inspired by the chase and run dynamics animals like cheetahs in the nature; cheetahs have the ability to swerve while running at very high speeds. A cheetah controls its dynamics by rotating its long tail. A three-dimensional stabilizer pendulum system (3D-SPS) resembles the rotational motion of the tail of a cheetah to improve the stability and safety of a vehicle. The idea has been developed in a stand-alone 3D stabilizer pendulum system as well as in an integrated control system, which consists of an ordinary differential braking direct yaw control (DYC) and active steering control that is assisted by the 3D-SPS. The performance of the proposed 3D-SPS has been evaluated over a wide range of handling manoeuvres by using a comprehensive numerical simulation. The results show the advantage of 3D-SPS over conventional control approaches, which are ineffective on low-friction road conditions and high lateral acceleration manoeuvres. It should however be noted that the best vehicle dynamics performance is obtained when an integrated 3D-SPS and DYC and AFS is utilised.

Vehicle dynamics control using an active third-axle system

This paper introduces the active third-axle system as an innovative vehicle dynamic control method. This method can be applicable for different kinds of three-axle vehicles such as buses, trucks, or even three-axle passenger cars. In this system, an actuator on the middle axle actively applies an independent force on the suspension to improve the handling characteristics, and hence, its technology is similar to slow-active suspension systems. This system can change the inherent vehicle dynamic characteristics, such as under/over steering behaviour, in the linear handling region, as well as vehicle stability in the nonlinear, limit handling region. In this paper, our main focus is to show the potential capabilities of this method in enhancing vehicle dynamic performance. For this purpose, as the first step, the proposed method in both linear and nonlinear vehicle handling regions is studied mathematically. Next, a comprehensive, nonlinear, 10 degrees of freedom vehicle model with a fuzzy control strategy is used to evaluate the effectiveness of this system. The dynamic behaviour of a vehicle, when either uncontrolled or equipped with the active third axle is then compared. Simulation results show that this active system can be considered as an innovative method for vehicle dynamic control.

A novel approach for the design and analysis of nonlinear dampers for automotive suspensions

This paper proposes an analytical technique for frequency analysis and the design of nonlinear dampers to further improve ride dynamics performance of vehicle suspensions over a wide range of excitation frequencies. Using the energy balance method (EBM), the proposed methodology estimates the equivalent linear damping coefficient of any nonlinear passive damper whose force is a general function of the damper’s relative displacement and relative velocity. Knowing the equivalent linear damping coefficient makes it possible to perform a frequency analysis of the suspension ride performance with any nonlinear damper. Some specific criteria are defined to design the desired form of equivalent linear damping coefficient which provides a high/small damping ratio at low-/high-frequency excitations, so the corresponding nonlinear damping force required to obtain improved ride performance of the suspension using a 1-degree-of-freedom quarter car model is also defined. A sensitivity analysis is then performed to provide a design guideline. The results show that the dependency of the equivalent damping coefficient either relative to the velocity of the suspension (velocity-dependent damper) or the relative displacement of the suspension (position-dependent damper) could provide a variable damping ratio leading to better vibration isolation over the excitation frequency. A noticeable ride dynamic performance can be reached over the entire range of the excitation frequency by designing a nonlinear damper such that its equivalent linear damping ratio becomes a desired function of both its relative displacement and relative velocity (position-velocity-dependent damper).

Vehicle Suspension System Technology and Design

The purpose of this book is to cover essential aspects of vehicle suspension systems and provide an easy approach for their analysis and design. It is intended specifically for undergraduate students and anyone with an interest in design and analysis of suspension systems. In order to simplify the understanding of more difficult concepts, the book uses a step-by-step approach along with pictures, graphs and examples. The book begins with the introduction of the role of suspensions in cars and a description of their main components. The types of suspensions are discussed and their differences reviewed. The mechanisms or geometries of different suspension systems are introduced and the tools for their analysis are discussed. In addition, vehicle vibration is reviewed in detail and models are developed to study vehicle ride comfort.

A novel integrated suspension tilting system for narrow urban vehicles

Narrow vehicles are proposed to resolve urban transportation issues such as congestion, parking, fuel consumption and pollution. They are characterized by a high ratio of centre of gravity height over track width. Such vehicles are vulnerable to rollover and stability issues when negotiating curves at a normal operating speed. Therefore, the tilting capability is crucial to such vehicles. Existing solutions, which mechanically connect the wheel module on both sides and synchronize their movement, still have room for further improvement. The extra links for synchronization not only take up space on compact urban vehicles, but also introduce additional mass to the light-weighted body. The novel tilting mechanism introduced in this work utilizes hydraulics to replace mechanical connections to generate the tilting motion. An interconnected hydro-pneumatic suspension system is adopted to provide the desired bump and roll stiffness for narrow urban vehicle applications. Two independently controlled hydraulic pumps are connected to the hydraulic suspensions to provide the tilting, as well as riding height change capabilities. The integration of the tilting system with suspension reduces the system weight and packing size, both of which are vital to the success of narrow urban vehicles. All the functionalities are illustrated, modelled and examined in the simulation studies, which prove the feasibility of the proposed system on narrow urban vehicle applications resulting in more functionalities with lower complexity and weight.

Vehicle yaw stability control using active rear steering: Development and experimental validation:

In this paper, a novel pulse active steering system for improving vehicle yaw stability is developed. In the proposed method, pulses are sent to the steerable rear wheels whenever the error between the expected and actual yaw rate is outside a predetermined range. The proposed method and its performance are verified experimentally by full vehicle testing. For this purpose, a simplified vehicle model and a rear suspension model are developed. Vehicle stability is investigated and the steering pulse parameters on the vehicle’s stability are studied. A control system is designed and numerical simulations are performed. Moreover, the active rear steering system is implemented on a Lexus for performing road experiments. Results from simulations and experiments indicate that considerable improvement in the yaw stability performance can be achieved by the proposed system. The proposed method is more cost effective and simpler for vehicle stability control.

Developing an active variable-wheelbase system for enhancing the vehicle dynamics

In order to enhance the vehicle dynamics, this paper presents a novel and innovative yaw moment control system in which the longitudinal positions of the wheels are individually controlled. For this purpose, the proposed concept is analytically and numerically studied first, and it is shown that the method can considerably modify the inherent characteristics of a vehicle, such as the handling and the steerability. This system can generate a stabilizing yaw moment, without any considerable changes in the total lateral force and the total longitudinal force of the vehicle. Finally, a comprehensive vehicle model together with an intelligent fuzzy control strategy are developed to evaluate the effectiveness of the active variable-wheelbase system in different driving conditions. Based on the simulation results, this system has the potential to be considered as a new alternative technique for vehicle dynamics control in the future.