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Increased Hydraulic Power Assisted Steering Functionality Using the Active Pinion Concept
Linköping University, Department of Management and Engineering. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Fluid and Mechanical Engineering Systems . Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Fluid and Mechanical Engineering Systems . Linköping University, The Institute of Technology.
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.

Place, publisher, year, edition, pages
2006.
Keyword [en]
Hydraulic, Power Steering System, Lane Keeping Aid, Parking Pilot, Active Pinion
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-14255OAI: oai:DiVA.org:liu-14255DiVA: diva2:23025
Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2009-06-01
In thesis
1. Hydraulic Power Steering System Design in Road Vehicles: Analysis, Testing and Enhanced Functionality
Open this publication in new window or tab >>Hydraulic Power Steering System Design in Road Vehicles: Analysis, Testing and Enhanced Functionality
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
Hydraulic Power Steering, Active Safety, Comfort function, Shuttering, Linear modelling
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-8186 (URN)978-91-85643-00-4 (ISBN)
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

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Rösth, MarcsPohl, JochenPalmberg, Jan-Ove

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