Rear Axle Steering Research Articles

Model-based design of a rear axle steering (RAS) system using an electro-hydraulic actuator (EHA)

Model-based design of a rear axle steering (RAS) system using an electro-hydraulic actuator (EHA)

Model-free autonomous control of four-wheel steering using artificial flow guidance

Four-wheel steering (4WS) is an effective technique to improve handling performance and lateral stability of road vehicles. Conventionally, controllers utilise the driver's actions and vehicle dynamics to coordinate front and rear-axle steering. This paper proposes a novel approach for 4WS controller design, based on the concept of Artificial Flow Guidance (AFG), which relies on a spatially distributed motion reference through a two-dimensional vector field. This field provides high-level guidance while lower-level steering controllers to control axle centres motions relative to the flow. These flow vectors, computed in real-time via simple geometric construction, can be pre-computed globally to evaluate the guidance algorithm's efficacy. When controlling only the front axle, this same approach can function as an autonomous driving system. Relying solely on a spatial reference field and control targets' velocities enables the controller to work in a simple and robust fashion, without using a reference vehicle dynamics model or lengthy parameter tuning. The proposed approach's effectiveness is validated through co-simulation with MATLAB/Simulink and the CarMaker simulation platform. AFG control performance is found to be at least comparable to that of more complex 4WS controllers using methods such as MPC; in the cases considered, AFG provides superior path-tracking performance.

A tracking control method for articulated virtual rail train with N-unit based on the dynamic model

In this paper, an articulated virtual rail train running on an urban road with N-unit is introduced, and a new tracking control system is designed to realize the tracking control of the articulated virtual rail train. First, a dynamic model for the articulated virtual rail train with N-unit is derived with 11N degrees of freedom. Second, based on the dynamic model, a steering control system is designed, which includes the following sub-controllers: a unit 1 front-axle steering controller and a unit 1∼N rear-axle steering controller for approaching the virtual target path, a unit 2∼N front-axle steering controller for coordinating the movement of adjacent units, and a four-wheel-steering (4WS) controller for each unit. Finally, a numerical simulation model of the train with five units is built in MATLAB, and a cross-validation model is built in ADAMS software. The simulation and verification results show that the tracking errors are within 50 mm, and the lateral articulation forces are less than 2 kN, which indicates that the designed control system has a good tracking performance.

The Design and Test of the Chassis of a Triangular Crawler-Type Ratooning Rice Harvester

Due to the high rolling rate of a regular crawler paddy harvester and the absence of mature first season harvester products of ratooning rice, combined with the planting mode and harvest requirements of ratooning rice, a triangular crawler ratooning rice harvester is specifically designed. The structure and steering principle of the triangular crawler chassis are described. The hydraulic system is simulated and analyzed by AMESim2020 (Guangzhou, China) to verify the rationality of its design; RecurDynV9R4 (Guangzhou, China) is used to simulate and analyze the field straight/turning situation of differential steering chassis and rear-axle steering chassis. The results show that the rear axle steering chassis has a smaller turning radius and lower rolling loss rate and the change of track tension is more stable during steering. The field test is conducted to verify the reliability of the simulation results. The field test shows that the rolling loss rate of the rear axle steering chassis is reduced by 27.9% compared with the differential steering chassis. The machine’s operating speed is 2.8 km/h, the minimum turning radius is 780 mm, and the straight rolling rate is 26.8%. The operating performance is stable, and the operational process is smooth. Compared with the existing conventional harvester, the linear rolling rate of the first harvest of ratooning rice is reduced by 26.1%, and the test results are consistent with the RecurDyn simulation results. The results are reliable, providing a reference for the theoretical research of the chassis of the later ratoon rice harvester.

An adaptive tracking control method for the all-wheel-driving and active-steering articulated vehicle with n-units

To achieve the running control of the all-wheel-driving and active-steering articulated vehicles (AWDASAVs) with n-units, an adaptive tracking control method is proposed in this paper, which includes a real-time target trajectory generation and an adaptive tracking control system. Firstly, the AWDASAV kinematics model is derived, and then the front-axle trace as the target trajectory is computed for all rear-axle steering by using data compressing and filtering, coordinate transformation, and local spline differences, which has small data storage and high computational efficiency and makes it easier to use in AWDASAV. Secondly, an adaptive tracking control system composed of an adaptive active steering controller and a differential distribution controller is designed to achieve accurate trajectory tracking and coordinated movement for AWDASAV. Finally, the AWDASAV simulation model with five-units was built in ADAMS by code development for cross-validation simulation, and the simulations with two cases at various speeds are carried out to verify the simulation model and control method. To further investigate the proposed method, the influence of three parameters on the tracking control performance and comparison with different control methods are carried out. The results exhibit excellent tracking control performance.

Performance assessment of urban goods vehicles

Controlling greenhouse gas emissions is becoming increasingly more important. With road freight contributing to a significant amount of energy usage, finding ways to improve this sector will, in turn, lead to large reductions in carbon dioxide emissions, with one method to achieve this being to use larger vehicles. Currently, prescriptive legislation dictates the dimensions a vehicle can take. An alternative to this is to use ‘Performance-Based Standards (PBS)’. This involves determining a set of manoeuvres and performance metrics that a vehicle must perform and pass in order to be road-worthy, instead of saying a vehicle can be a certain size or a certain weight. Through innovation and optimisation, using this method will then allow larger vehicles that are safe for driving on the road to be built. The research conducted here involved creating a PBS framework based on low-speed manoeuvrability for rigid delivery vehicles as well as assessing the high-speed stability of articulated vehicles to determine whether they would be safe for use on urban roads. Additionally, design changes such as incorporating rear axle steering were considered to determine whether vehicles that had failed the proposed PBS framework could be made to pass.

Importance of Vehicle Body Elements and Rear Axle Elements for Describing Road Booming Noise

For investigating influences of vehicle components on the acoustic comfort at low frequencies, e.g., the booming noise behavior of a vehicle, building a whole car simulation model is useful. To reduce the model’s complexity and to save resources in the validation process, we first identify relevant components before building the model. Based on previous studies, we focus on the vehicle’s body and the rear axle. In this paper, we analyze which axle and body elements are crucial for describing road booming noise. For this purpose, we use impact measurements to examine noise transfer functions of the body and a vibro-acoustical modal analysis to identify coupled modes between the body’s structure and the interior cavity. For investigating relevant force paths from the rear axle to the body, we used a chassis test bench. We identify the main transmission paths of road booming noise and highlight which axle and body components have an influence on them. Mainly the rear axle in its upright direction in combination with a rigid body movement of the rear tailgate coupled with the first longitudinal mode of the airborne cavity causes road booming noise. Furthermore, the rear axle steering, the active roll stabilization and the trim elements of the vehicle’s body are essential to describe road booming noise. The results can be used to set priorities in the validation of individual axle and body components for future simulation models. We found that the ventilation openings, the front seats, the headliner, and the cockpit of a vehicle have little influence on its noise transfer functions from the rear axle connection points to the driver’s ear between 20 and 60 Hz.

Hierarchical Synchronization Control Strategy of Active Rear Axle Independent Steering System

The synchronization error of the left and right steering-wheel-angles and the disturbances rejection of the synchronization controller are of great significance for the active rear axle independent steering (ARIS) system under complex driving conditions and uncertain disturbances. In order to reduce synchronization error, a novel hierarchical synchronization control strategy based on virtual synchronization control and linear active disturbance rejection control (LADRC) is proposed. The upper controller adopts the virtual synchronization controller based on the dynamic model of the virtual rear axle steering mechanism to reduce the synchronization error between the rear wheel steering angles of the ARIS system; the lower controller is designed based on an LADRC algorithm to realize an accurate tracking control of the steering angle for each wheels. Experiments based on a prototype vehicle are conducted to prove that the proposed hierarchical synchronization control strategy for the ARIS system can improve the control accuracy significantly and has the properties of better disturbances rejection and stronger robustness.

Minimum-time optimal control for vehicles with active rear-axle steering, transfer case and variable parameters

When aiming to improve the performance of industrial sports cars at the limits of driving dynamics, the passive vehicle setup should be tuned under consideration of the actuator configuration and the control system capabilities. To objectively quantify the performance of given vehicle settings, minimum lap times can be determined using optimal control methods. The computed trajectories can be used to assess the benefits of certain actuators as well as to identify optimal vehicle setups and control strategies. This paper analyses the effect of rear-axle steering, longitudinal torque allocation via transfer case and selected vehicle parameters on lap time. The optimal roll moment distribution and longitudinal position of the centre of gravity are identified via concurrent optimisation. The optimal lap trajectories are generated by numerically solving a minimum-time optimal control problem using direct Hermite-Simpson collocation. To eliminate the problem of an unknown initial solution, the authors present an initialisation routine for vehicular optimal control problems. Moreover, a novel approach for the generation of smooth track curvature data is introduced.

A Review of Rear Axle Steering System Technology for Commercial Vehicles

A Review of Rear Axle Steering System Technology for Commercial Vehicles

Energy efficient cornering using over-actuation

This work deals with utilisation of active steering and propulsion on individual wheels in order to improve a vehicle's energy efficiency during a double lane change manoeuvre at moderate speeds. Through numerical optimisation, solutions have been found for how wheel steering angles and propulsion torques should be used in order to minimise the energy consumed by the vehicle travelling through the manoeuvre. The results show that, for the studied vehicle, the energy consumption due to cornering resistance can be reduced by approximately 10% compared to a standard vehicle configuration. Based on the optimisation study, simplified algorithms to control wheel steering angles and propulsion torques that results in more energy efficient cornering are proposed. These algorithms are evaluated in a simulation study that includes a path tracking driver model. Based on a combined rear axle steering and torque vectoring control an improvement of 6–8% of the energy consumption due to cornering was found. The results indicate that in order to improve energy efficiency for a vehicle driving in a non-safety-critical cornering situation the force distribution should be shifted towards the front wheels.

Development of control strategies of a multi-wheeled combat vehicle

This work develops a vehicle dynamics controller for vehicle stability, manoeuvrability and turning circle reduction for an 8 × 8 heavy combat vehicle utilising both torque vectoring and third and fourth axle steering. The proposed control scheme is composed of two distinct controllers, each with their own range of operation based on vehicle speed. A feedforward zero side slip (ZSS) controller actuates the third and fourth axle steering angles. It is used for manoeuvring at speeds of 30 kph and below and for turning circle reduction. A two degrees of freedom (DOF) linear parameter varying (LPV) H∞ controller that monitors steering wheel angle and yaw rate error and uses both the rear axle steering and torque vectoring to enhance vehicle stability and manoeuvrability at speeds above 40 kph. Gaussian distribution functions are used to switch from one controller to the other. The proposed control scheme is evaluated by running simulations using a validated computer simulation (TruckSim) full vehicle model in co-simulation with the controller and developed electric powertrain in Simulink. The proposed control system is able to greatly improve vehicle stability and manoeuvrability. A turning circle reduction of 30% is obtained using the ZSS feedforward method.

Unambiguous and Reliable Positioning in the vehicle in terms of Functional Safety and Cyber Security

Functional security and agile software development are two modern areas in product development, which initially have very opposite approaches. For example, formal tests are required by the relevant standards for the former, which must be documented very extensively. The agile software development, on the other hand, tries to come to its conclusion with as few documentation and flexible tests as possible. Also, the proof that testing and development are independent of each other for safety-critical projects is difficult in the context of the use of agile methods. However, taking the constraints of functional safety as given and taking advantage of the enormous flexibility of agile software development, e.g. With the use of Scrum, the Daily Team Meetings create new opportunities in product development. In contrast to previous positioning methods for linearly movable axles, a new developed approach for rear axle steering has not been used as an absolute value encoder, but a novel positioning concept has been researched and developed. Functional Safety first! A new safety concept must therefore be developed. The absolute value encoder, usually realized as an optical or magnetic bar-coded sensor, is used reliably but cost-effectively in a large number of systems. In order to save costs as well as space, the development of the new approach to the sensor will be dispensed with and the positioning will be realized via a new concept. The conventional concepts for position determination of axes is an absolute value encoder. However, this is not highly reliable and has no redundancy. With the new safety concept, the exact position of an axis can be determined and output with high accuracy by means of the various safety devices directly after switching on the system. As a result, the sensor system is hardly susceptible to errors. Here, a detailed error analysis has been carried out. Even after system crashes, there are enough detection points, which are constantly detected during normal operation and thus the plausibility check can be restored. The new explored approach allows the steering to work normally even in safe modes. However, the algorithms for protection have to take effect immediately if, for example, an expected index signal does not occur.

Electrohydraulic rear axle steering systems for agricultural vehicles

Electrohydraulic rear axle steering systems for agricultural vehicles

The non-proportionality of local stress paths in engineering applications

A scalar measure, which describes the non-proportionality of local stress paths in engineering applications, is introduced. For this purpose the moment of inertia approach by Meggiolaro is modified in a way that the stress time history is evaluated in a tresca-stress-space. This modification makes the non-proportionality factor invariant with respect to the coordinate system. An optimization procedure is implemented to derive a test set-up for new component tests with 2 load channels. The aim of the planned tests is to get a high non-proportionality at the potential crack initiation site. It is not possible to obtain a high non-proportionality factor at the failure location without selective weakening of the component (housing of a rear axle steering). Therefore specific areas of the structure are cut out and the optimization procedure is repeated. As a result of the optimization a test set-up with high local non-proportionality at the potential crack initiation site is achieved for the weakened structure. Another set-up with slightly less non-proportionality but with a very localized damage is derived. This set-up is preferred, because of the robustness in the physical test.

The effectiveness of rear axle steering on the yaw stability and responsiveness of a heavy truck

Rear axle steering (RAS) at low speed is available in heavy trucks to improve their manoeuverability and reduce tyre wear; by extending the functionality of the existing RAS to high speed turning and split-mu braking, considerable safety benefits and enhancement in driver comfort can be gained. In this study, a RAS System was developed and simulated in Matlab–Simulink which showed encouraging results. Furthermore, the developed system was implemented on a Volvo Truck and tested in a series of split-mu braking and ISO double lane change manoeuvers. The obtained results conform to the expectations.

Electro-hydraulic rear-axle steering for mobile cranes

Electro-hydraulic rear-axle steering for mobile cranes

Electronically controlled: Rear axle steering

Currently the technology of steering systems is experiencing major changes. In car applications beside the hydraulic rack and pinion steering, the fully electrically assisted steering systems are getting popular more and more. Also hydraulic steering systems superposed by additional electronic systems are gaining in the race of new developments. This tendency to electrification can also be observed in the commercial vehicle industry. In the following we want to highlight how ZF Lenksysteme, together with vehicle manufacturers, is leading into this new age of steering.

Performance and Safety Requirements for Auxiliary Steering Equipment Explained by Means of the Example of BMW's Active Rear-Axle Kinematics (ARK)

SUMMARY Since the end of 1991 BMW produces a new chassis control system for its 8 series coupe, called Active Rear-axle Kinematics (ARK). It is an electrohydraulic rear axle steering system with a speed-dependent transfer function for rear axle steering angle. It improves driving safety in severe steering maneuvers and reduces driver's stress in everyday driving. Its technology includes a comprehensive fail-safe concept which basically constitutes a dual channel design and monitors the proper system operation in a multi-stage comparison starting at the system inputs and ending at its output.