An Active Roll-Moment Control Strategy for Narrow Tilting Commuter Vehicles

SUMMARY

An automatic tilt control strategy for a narrow commuter vehicle is described. Such a vehicle would be enclosed like a conventional car but would bank into turns like a motorcycle and so it would feel quite unconventional to drive. The proposed tilt control system uses the steering to tilt the car over like a motorcycle but this is augmented by actively generating a rolling moment about the pivot axis between the tilting upper body and non-tilting base. The provision of this active direct tilt control enables the vehicle to remain upright at low or zero speed and also permits the designer to fine tune the transient roll response. Although it appears complex the proposed tilting control relies on only a few simple sensor measurements, some modest, microprocessor based signal processing and low power, low bandwidth steering and tilt control actuators which might be derived from existing automotive components.     

Active Dual Mode Tilt Control for Narrow Ground Vehicles

Small, narrow commuter vehicles have attracted considerable interest in recent years as a means to increase the utilization of existing freeways and parking facilities. However, conventional narrow track vehicles are likely to have reduced stability against overturning during hard cornering. A possible solution to this problem lies in vehicles which tilt toward the inside of a turn. Two different ways to achieve this tilt will be analyzed. For direct tilt control (DTC) an actuator forces the upper part of the vehicle to tilt. Steering tilt control (STC) uses steering to control the tilt as is done by motorcycle or bicycle riders. At low speeds, only the DTC system is effective while at high speeds the STC offers less lateral acceleration for the passenger during transient cornering and may seem more natural. The two methods of control will be studied separately and it will be shown that even though the same steady state tilt can be achieved with either system, the transient behavior of the systems is very different. It also will be shown that it is possible to switch from one system to the other at an arbitrarily chosen speed with virtually no transient effects even when the vehicle is not in a steady state. Regardless of which control system is active, the driver simply communicates his desire to follow the road by moving the steering wheel and the control systems take care of the tilting either by using the tilt actuator or by actively steering the road wheels. Thus the driver does not need to leam how to stabilize the tilt mode of the vehicle.     

A fundamental investigation of tilt control systems for narrow commuter vehicles

One way of addressing traffic congestion is by efficiently utilizing the existing highway infrastructure. Narrow tilting vehicles that need a reduced width lane can be part of the solution if they can be designed to be safe, stable, and easy to operate. In this paper, a control system that stabilizes the tilt mode of such a vehicle without affecting the handling of the vehicle is proposed. This control system is a combination of two different types of control schemes known as steering tilt control (STC) and direct tilt control (DTC) systems. First, different existing variations of both STC and DTC systems are considered and their shortcomings analysed. Modified control schemes are then suggested to overcome the deficiencies. Then a new method of integrating these two control schemes that guarantees smooth switchover between the controllers as a function of vehicle velocity is proposed. The performance of the proposed STC, DTC, and integrated systems is evaluated by carrying out simulations for different operating conditions and some experimental work. The design of a second-generation narrow tilting vehicle on which the developed control system has been implemented is presented.     

A fundamental investigation of tilt control systems for narrow commuter vehicles

One way of addressing traffic congestion is by efficiently utilizing the existing highway infrastructure. Narrow tilting vehicles that need a reduced width lane can be part of the solution if they can be designed to be safe, stable, and easy to operate. In this paper, a control system that stabilizes the tilt mode of such a vehicle without affecting the handling of the vehicle is proposed. This control system is a combination of two different types of control schemes known as steering tilt control (STC) and direct tilt control (DTC) systems. First, different existing variations of both STC and DTC systems are considered and their shortcomings analysed. Modified control schemes are then suggested to overcome the deficiencies. Then a new method of integrating these two control schemes that guarantees smooth switchover between the controllers as a function of vehicle velocity is proposed. The performance of the proposed STC, DTC, and integrated systems is evaluated by carrying out simulations for different operating conditions and some experimental work. The design of a second-generation narrow tilting vehicle on which the developed control system has been implemented is presented.     

Steady-state steering of a tilting three-wheeled vehicle

The design of a narrow-track enclosed vehicle for urban transport was the subject of the CLEVER project. Due to its narrow track and requirement for car-like controls, an actively controlled tilting system was integrated into the chassis to allow for high lateral accelerations without rolling over. The cornering behaviour of this unique vehicle concept is investigated and compared with the ideal Ackermann response. The steer kinematics of this 1F1T (one front wheel, one wheel tilting) configuration are assessed through the use of a steady-state steering model, with attention focused on how steer parameters such as tilt axis height and inclination can be tuned to provide the required response. A prototype vehicle was designed and built and the results of experimental testing are presented to illustrate the real balancing performance of the combined steering and tilting approach used for the CLEVER vehicle. The experimental results follow the trends demonstrated in the model.     

Steady Turning of Two-Wheeled Vehicles

When driving along a circular path, the driver of a motorcycle controls the vehicle mainly by means of steering torque. If low steering torque is necessary, the driver feels that the vehicle is manoeuvrable. In this paper, a mathematical model concerning steering torque is developed; it takes into account the actual kinematic behaviour of the vehicle and the properties of motorcycle tyres. Tyre forces act at the contact points of toroidal tyres, which are calculated according to kinematic analysis. Non-linear equations are solved using an iterative approach. Several numerical results are presented, and the influence of tyre properties and some geometrical and inertial properties of the vehicle on steering torque are discussed.     

Steady Turning of Two-Wheeled Vehicles

When driving along a circular path, the driver of a motorcycle controls the vehicle mainly by means of steering torque. If low steering torque is necessary, the driver feels that the vehicle is manoeuvrable. In this paper, a mathematical model concerning steering torque is developed; it takes into account the actual kinematic behaviour of the vehicle and the properties of motorcycle tyres. Tyre forces act at the contact points of toroidal tyres, which are calculated according to kinematic analysis. Non-linear equations are solved using an iterative approach. Several numerical results are presented, and the influence of tyre properties and some geometrical and inertial properties of the vehicle on steering torque are discussed.     

Steering control of motorcycles using steer-by-wire system

This study proposes a steering control method to improve motorcycle handling and stability. Steer-by-wire (SBW) technology is applied to the motorcycle's steering system to remove characteristic difficulties of vehicle maneuvers. By examining computer simulation using a simplified motorcycle model, the actual rolling angle of the SBW motorcycle is controlled to follow the desired rolling angle intended by the rider. A state feedback control such as linear quadratic control gives the SBW vehicle a good follow-through performance compared with proportional-derivative control because it can decouple rolling motion from the other motions, which affect the rolling motion in the strongly coupled motorcycle system.     

New approaches to enhance active steering system functionalities: preliminary results

An important development of the steering systems in general is active steering systems like active front steering and steer-by-wire systems. In this paper the current functional possibilities in application of active steering systems are explored. A new approach and additional functionalities are presented that can be implemented to the active steering systems without additional hardware such as new sensors and electronic control units. Commercial active steering systems are controlling the steering angle depending on the driving situation only. This paper introduce methods for enhancing active steering system functionalities depending not only on the driving situation but also vehicle parameters like vehicle mass, tyre and road condition. In this regard, adaptation of the steering ratio as a function of above mentioned vehicle parameters is presented with examples. With some selected vehicle parameter changes, the reduction of the undesired influences on vehicle dynamics of these parameter changes has been demonstrated theoretically with simulations and with real-time driving measurements.     

Twenty First Century Transportation System Solutions - a New Type of Small,Relatively Tall and Narrow Active Tilting Commuter Vehicle

SUMMARY

There are many problems that face transportation systems as the twenty-first century approaches, and many solutions will be required. Mass transportation systems are one large area of research that will provide some solutions. This paper presents another possible solution at the other end of the spectrum, small relatively tall and narrow tilting commuter vehicles for individual transportation. A historical overview of the various types of tilting vehicles built or proposed over the last forty years is shown and the results of these studies are discussed. If one considers a relatively tall and narrow vehicle, (under 1.0 meters or 40“ wide), to maintain high speed performance in cornering it becomes necessary to bank the vehicle into a corner to prevent overturning. The design of a modem active tilting suspension and control law for a small narrow, one-half width, commuter vehicles is presented. Analysis of the static and dynamic tipping limits illustrates which vehicles are considered tall and narrow requiring active tilting. The performance of such vehicles as they enter a steady corner is considered and how tilt dynamics may feel to passengers is discussed.     

Twenty First Century Transportation System Solutions - a New Type of Small, Relatively Tall and Narrow Active Tilting Commuter Vehicle

There are many problems that face transportation systems as the twenty-first century approaches, and many solutions will be required. Mass transportation systems are one large area of research that will provide some solutions. This paper presents another possible solution at the other end of the spectrum, small relatively tall and narrow tilting commuter vehicles for individual transportation. A historical overview of the various types of tilting vehicles built or proposed over the last forty years is shown and the results of these studies are discussed. If one considers a relatively tall and narrow vehicle, (under 1.0 meters or 40“ wide), to maintain high speed performance in cornering it becomes necessary to bank the vehicle into a corner to prevent overturning. The design of a modem active tilting suspension and control law for a small narrow, one-half width, commuter vehicles is presented. Analysis of the static and dynamic tipping limits illustrates which vehicles are considered tall and narrow requiring active tilting. The performance of such vehicles as they enter a steady corner is considered and how tilt dynamics may feel to passengers is discussed.     

Electro-hydraulic braking system for autonomous vehicles

Reducing the number of traffic accidents is a declared target of most governments. Since dependence on driver reaction is the main cause of road accidents, it would be advisable to replace the human factor in some driving-related tasks with automated solutions. To automate a vehicle, it is necessary to control the actuators of a car, i.e., the steering wheel, accelerator, and brake. This paper presents the design and implementation of an electro-hydraulic braking system consisting of a pump and various valves, allowing the control computer to stop the car. It is assembled in conjunction with the original circuit for the sake of robustness and to permit the two systems to halt the car independently. This system was developed for installation in a commercial Citroën C3 Pluriel of the AUTOPIA program. Various tests were carried out to verify its correct operation, and an experiment showing the integration of the system into the longitudinal control of the car is described.     

Dynamic modelling and experimental validation of three wheeled tilting vehicles

The present paper describes the study of the stability in the straight running of a three-wheeled tilting vehicle for urban and sub-urban mobility. The analysis was carried out by developing a multibody model in the Matlab/SimulinkSimMechanics environment. An Adams-Motorcycle model and an equivalent analytical model were developed for the cross-validation and for highlighting the similarities with the lateral dynamics of motorcycles. Field tests were carried out to validate the model and identify some critical parameters, such as the damping on the steering system. The stability analysis demonstrates that the lateral dynamic motions are characterised by vibration modes that are similar to that of a motorcycle. Additionally, it shows that the wobble mode is significantly affected by the castor trail, whereas it is only slightly affected by the dynamics of the front suspension. For the present case study, the frame compliance also has no influence on the weave and wobble.     

解决N车型外后视镜调节失效问题

车辆后视系统由车外反射镜和广角透镜组成,在车辆安全系统中起着重要的作用。现有的汽车后视镜系统还存在许多问题亟待解决,如汽车转向过程中的盲区等。本文提出了一种新型的智能车辆后视系统的设计方案,该系统能够在不同的行驶条件下自动调节车辆外部镜头的角度。影响因素包括车辆转向角、行驶速度和车辆尺寸参数。本设计以AT90C516RD+单片机为核心控制单元。该系统增加了一个新的自动模式与现有的手动功能保留。通过理论仿真和模型试验,证明该设计完全可行,并已被具有工业潜力的客户调查所接受。     

Links between subjective assessments and objective metrics for steering

The characteristics of steering perception are decisive factors for overall driver preference and for vehicle safety. Car manufacturers are continuously required to tune the characteristics of the vehicle and have a strong need to be more effective in the design and evaluation of cars. Using only objective metrics (OM) can result in unwanted steering feel and using only subjective assessments (SA) is time-consuming, costly and non-repetitive. Before a tool can be built to predict the steering feel in front-end development and to improve design knowledge from the full vehicle level to the component level, links between subjective assessments and objective metrics must be found and analysed. The data collected for the study presented in this paper include subjective ratings from expert drivers and objective measurements made with steering robots, involving twelve expert drivers and over twenty vehicles across four different vehicle classes. Linear regression and neural network analysis (NN) have been used to explore reliable subjective-objective links. The tools and methods used in this research showed promising results. Most of the links found concern response and torque feedback. The preferred ranges of some crucial objective metrics leading to more desirable steering feel have been defined and presented. The results indicate that it would be possible for car manufacturers to develop new vehicles more effectively with a steering feel in line with the design criteria by using the tools and methods investigated in this paper.     

A Variable Free Control Characteristic Vehicle

A variable characteristic car (VCC) has been developed at Melbourne University for driverlvehicle handling research. The vehicle is unusual in that it has facilities for varying both its fixed control and free control dynamic characteristics over wide ranges. In this paper the servo systems used to effect these changes are described. The calibration methods used to relate the vehicle response characteristics to the variable servo settings are detailed. Sample calibration results are given for the fixed control parameters steering ratio, yaw response time and stability factor. Calibration of the free control parameters is also described and results are given for the steering torque gradient, and the time-to-peak and percentage overshoot of the steering wheel motion in response to a step input of torque.     

Handling Analysis of a Motorcycle with Added Cambering of the Front Frame

Through linear analysis, the handling characteristics of the motorcycle with fixed control of added cambering of front frame are investigated under the variation of fixed and free controls of steering axis. The cornering responses and stability characteristics of the motorcycle are presented with the aid of the handling diagram. From numerical results for a typical motorcycle, it is found that the influence of the cambering of front frame on the cornering response of fixed steering control is opposite to that of free steering control. Moreover, the design philosophy of a so-called semi-direct steering mechanism, which cambers the front frame for cornering, is studied.     

Advanced Steering System Adaptable to Lateral Control Task and Driver's Intention

This paper proposes an advanced steering system that adaptively varies the static gain and dynamics of the steering system. The steering system gain is adjusted, depending on whether the driver is in an aggressive or leisurely driving mood. The steering system dynamics is so designed that the command mode of the steering system will be either a rate-command or an attitude-command according to the lateral control task performed by the driver. The recognition system for lateral control tasks, a lane-following or lane-change task is proposed. The findings of simulator tests indicate proposed advanced steering system would remarkably improve the vehicle handling qualities.     

Advanced Steering System Adaptable to Lateral Control Task and Driver's Intention

This paper proposes an advanced steering system that adaptively varies the static gain and dynamics of the steering system. The steering system gain is adjusted, depending on whether the driver is in an aggressive or leisurely driving mood. The steering system dynamics is so designed that the command mode of the steering system will be either a rate-command or an attitude-command according to the lateral control task performed by the driver. The recognition system for lateral control tasks, a lane-following or lane-change task is proposed. The findings of simulator tests indicate proposed advanced steering system would remarkably improve the vehicle handling qualities.     

Active Roll Mode Control Implementation on a Narrow Tilting Vehicle

This paper describes work carried out on the development of a narrow tilting vehicle at the University of Minnesota. The project had two objectives. One objective was to better understand the dynamics of two-passenger leaning vehicles. The other was to use this understanding to design and implement leaning control on such a vehicle. The desire was to make a tilting vehicle as easy, in some sense, to drive as a non-leaning vehicle. The scope of this work was fourfold. First, a model of such a system was developed and linearized to obtain a fourth-order linear model. Second, a tilt controller was designed to stabilize a tilting vehicle's unstable rolling mode. Third, the system and controller were simulated using both Simulink and a real time simulator written with Visual Basic. Fourth, and most importantly, an experimental vehicle was built and used for implementation. Comparisons were made between the simulated system and the experimental vehicle. This illustrated the limitations encountered in the simulations but also showed similarities that validated the model. Also, experimental results showed that the vehicle was stabilized well by the controller within the limitations of our hardware.