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Reducerat vridmotstånd i servoassisterade styrsystem
Luleå University of Technology, Department of Engineering Sciences and Mathematics.
2016 (Swedish)Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
Abstract [en]

In newer modern cars the steeringsystem is equipped with a servo that enhances the driver's input from the steering wheel down to the wheels. This is referred to as power-assisted steering. The reason why a modern car with the engine turned off or an older car with a lack of power-assisted steering, is so troublesome to maneuver is that the driver must overcome the friction that occurs between the tires and the surface underneath the tires which prevents the tires from rotating. A servo has been connected to the vehicle's steering system and assists the driver to overcome these forces and to create a more stable handling and an enhanced operation at a lower speed. Servos has in other words reduced the torque required at the steering wheel to rotate the tires. Although there is a reduced torque in the steering wheel provided by the servo, it´s for many individuals still not sufficiently reduced. Individuals with reduced or limited mobility in their hands or arms may experience difficulty in operating the steering wheel of a car. Especially challenging is it if the person obtains a car with an installed hand control for operating the acceleration and braking, leaving as the only alternative, to maneuver the steering wheel by one hand. By reducing the required torque, or effort, needed in the steering wheel, further it’s made possible for these people to independently use a car without any setbacks. Is it possible to reduce the needed effort at the steering wheel in all cars on the commercial market? The current commercial market consists, in majority, of the electric power-assisted steering systems(EPAS) and hydraulic power-assisted steering systems(HPAS). These two types of systems have been carefully studied and the challenges of reducing the needed effort has been analyzed. The studies and analyzes has been further developed to a result where the assisted steering systems, on the majority of the commercial market cars, can obtain a reduced effort at the steering wheel. How does the reduced effort procedure work? After identifying a torsion bar as the common denominator for the EPAS and HPAS systems the torsion bar could be studied further in its mechanical properties. The result of these studies gave support to theories of being able to machine the torsion bar in order to reduce the torque at the wheel. As a result of the driver's steering wheel movements a twist on the upper part of the torsion bar will accrue when the lower portion of the torsion bar, at first held stationary due to the friction between the tires and the vehicles underneath surface where it creates a displacement of the rods top end and bottom end. The displacement is entirely elastic and the factor that determines the amount of torque the servo will assist with. How the torsion bar interacts with in the different systems varies. In the EPAS systems the torsion bars displacement is interpreted by software and then translated to a control signal leading to an electrical motor. In HPAS systems however, the torsion bar is a major component in a hydraulic valve determining the systems hydraulic flow. By mechanically machining the torsion bar, it reduce its rotational resistance and the servo will with less effort be activated by the driver's steering wheel movements. Is intervention to weaken the torsion bar safe? The procedure is risky and complex but with the knowledge from this report, the help of the tools I developed, and the equipment and scientific results presented, it can be implemented with the OEMs safety margins still intact.

Place, publisher, year, edition, pages
2016. , 73 p.
National Category
Mechanical Engineering
URN: urn:nbn:se:ltu:diva-149OAI: diva2:971433
Subject / course
Student thesis, at least 15 credits
Educational program
Mechanical Engineering, bachelor's level
Available from: 2016-09-27 Created: 2016-09-16 Last updated: 2016-09-27Bibliographically approved

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