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Hydraulic Power Steering System Design in Road Vehicles: Analysis, Testing and Enhanced Functionality
Linköping University, Department of Management and Engineering. Linköping University, The Institute of Technology.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Demands for including more functions such as haptic guiding in power steering systems in road vehicles have increased with requirements on new active safety and comfort systems. Active safety systems, which have been proven to have a positive effect on overall vehicle safety, refer to systems that give the driver assistance in more and less critical situations to avoid accidents. Active safety features are going to play an increasingly important roll in future safety strategies; therefore, it is essential that sub systems in road vehicles, such as power steering systems, are adjusted to meet new demands.

The traditional Hydraulic Power Assisted Steering, HPAS, system, cannot meet these new demands, due to the control unit's pure hydro-mechanical solution. The Active Pinion concept presented in this thesis is a novel concept for controlling the steering wheel torque in future active safety and comfort applications. The concept, which can be seen as a modular add-on added to a traditional HPAS system, introduces an additional degree of freedom to the control unit. Different control modes used to meet the demands of new functionality applications are presented and tested in a hardware-in-the-loop test rig.

This thesis also covers various aspects of hydraulic power assisted steering systems in road vehicles. Power steering is viewed as a dynamic system and is investigated with linear and non-linear modeling techniques. The valve design in terms of area gradient is essential for the function of the HPAS system; therefore, a method involving optimization has been developed to determine the valve characteristic. The method uses static measurements as a base for calculation and optimization; the results are used in both linear and the non-linear models. With the help of the linear model, relevant transfer functions and the underlying control structure of the power steering system have been derived and analyzed. The non-linear model has been used in concept validation of the Active Pinion. Apart from concept validation and controller design of the active pinion, the models have been roven effective to explain dynamic phenomena related to HPAS systems, such as the chattering phenomena and hydraulic lag.

Place, publisher, year, edition, pages
Institutionen för ekonomisk och industriell utveckling , 2007. , 116 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1068
Keyword [en]
Hydraulic Power Steering, Active Safety, Comfort function, Shuttering, Linear modelling
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:liu:diva-8186ISBN: 978-91-85643-00-4 (print)OAI: oai:DiVA.org:liu-8186DiVA: diva2:23027
Public defence
2007-02-16, C3, Hus C, Linköpings Universitet, Linköping, 10:00 (English)
Opponent
Supervisors
Note
The printed version and the electronic version differ in that the electronic version contains two built in video films (see page 78 and page 89).Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2009-05-13
List of papers
1. Robust Design of a Power Steering System with Emphasis on Chattering Phenomena
Open this publication in new window or tab >>Robust Design of a Power Steering System with Emphasis on Chattering Phenomena
2007 (English)In: The 10th Scandinavian International Conference on Fluid Power, SICFP'07, Tampere, Finland, 21th–23th May, Tampere, Finland: Tampere University of Technology , 2007, 161-175 p.Conference paper, Published paper (Other academic)
Abstract [en]

This paper investigates the chattering effect occurring in power steering systems. Chattering is experienced as noise and vibration in steering systems and occurs when the steering system is activated by the driver or driven by the load, aligning torque. Chattering is a problem, which is a result of poor system layout with regards to system stability. The problem can reduce the performance of the system but is mainly a quality problem from the user´s point of view. In this paper, the phenomena is investigated with the help of a linear model of the system where the stability margin is analyzed for different characteristics of the valve.

Place, publisher, year, edition, pages
Tampere, Finland: Tampere University of Technology, 2007
Keyword
Power steering, chattering, linear model
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14251 (URN)
Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2009-05-13
2. Modeling and Validation of Power Steering Systems with Emphasis on Catch-Up Effect
Open this publication in new window or tab >>Modeling and Validation of Power Steering Systems with Emphasis on Catch-Up Effect
2005 (English)In: Proceedings of The 9th Scandinavian International Conference on Fluid Power, SICFP’05, (Eds. J-O Palmberg), CD publication, Link¨oping University, Link¨oping, Sweden, 1st–3rd June, 2005Conference paper, Published paper (Other academic)
Series
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14252 (URN)
Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2009-06-01
3. Modeling and Simulation of a Conventional Hydraulic Power Steering System for Passenger Cars
Open this publication in new window or tab >>Modeling and Simulation of a Conventional Hydraulic Power Steering System for Passenger Cars
2003 (English)In: Proceedings of The 8th Scandinavian International Conference on Fluid Power, SICFP’03, Tampere University of Technology, 7th-9th May, 2003, 635–650- p.Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14253 (URN)
Available from: 2007-03-15 Created: 2007-03-15
4. Active Pinion: A cost Effective Solution for Enabling Steering Intervention in Road Vehicles
Open this publication in new window or tab >>Active Pinion: A cost Effective Solution for Enabling Steering Intervention in Road Vehicles
2003 (English)In: The Bath Workshop on Power Transmission and Motion Control, PTMC’03, Bath, United Kingdom, 10th-12th, September, 2003Conference paper, Published paper (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14254 (URN)
Available from: 2007-03-15 Created: 2007-03-15
5. Increased Hydraulic Power Assisted Steering Functionality Using the Active Pinion Concept
Open this publication in new window or tab >>Increased Hydraulic Power Assisted Steering Functionality Using the Active Pinion Concept
2006 (English)In: Proceedings of 5th International Fluid Power Conference Aachen, IFK2006, Aachen, Germany, 20th-22nd March, 2006Conference paper, Published paper (Other academic)
Abstract [en]

The traditional way of assisting car drivers during steering is with the help of hydraulic power assisted steering (HPAS) systems, which were introduced in the 1960's. In these systems, the torque the driver applies to the steering wheel is used to open a spool valve, which then modulates the load pressure in a hydraulic piston in the steering gear, thus assisting the driver. Such systems are regarded as cost effective and robust, but at the same time associated with limited flexibility. Since the broad introduction of electric power assisted steering (EPAS) systems during past years, the possibility to freely control steering wheel torque has been achieved. Steering wheel torque control is utilized both by comfort and safety functions, such as park assist systems and lane keeping assist systems or the next generation of active yaw control functions. In this paper, a solution to the controllability problem is presented for conventional HPAS systems. The solution is based on a traditional hydraulic power steering unit with modification to the valve. Added to the valve is an extra pilot motor, which enables the valve to be actuated electrically without compromising the basic robust mechanical solution of a traditional hydraulic power steering unit. Control strategies for position control and offset torque control have been presented together with test results carried out in a hardware in the loop test rig. An important advantage of the proposed solution is its low electric energy consumption. The electric motor has to compensate for the tiny sealing friction in the hydraulic spool valve. In other respects it relies on the power gain capability of the hydraulic system. This concept is called Active Pinion.

Keyword
Hydraulic, Power Steering System, Lane Keeping Aid, Parking Pilot, Active Pinion
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14255 (URN)
Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2009-06-01
6. Parking System Demands on the Steering Actuator
Open this publication in new window or tab >>Parking System Demands on the Steering Actuator
2006 (English)In: Proceedings of ASME 2006 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, ESDA 2006, Torino, Italy, 4th-7th July, 2006Conference paper, Published paper (Other academic)
Abstract [en]

This paper describes how a hydraulic power steering system with increased flexibility, Active Pinion, can be applied as the actuator to an automatic parking system, Parking Pilot. The requirements on the actuator from the parking system and how the actuator's performance translates into parking maneuver performance is studied. The system have been installed in a test rig and in a demonstrator car.

Keyword
Parking Pilot, Hydraulic Power Steering, Active Pinion
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14256 (URN)
Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2009-06-01

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