Products and solutions Sep 11, 2001 2:00 AM
TubPAS: Electromechanical steering assistance for cars of all sizes
Developed by Krupp Presta AG, TubPAS is an electromechanical power steering system which, unlike existing electrical systems, is also suitable for use in larger cars and offers advantages of price and functionality versus hydraulic power steering systems. Moreover, TubPAS consumes less fuel than hydraulic systems and is easier to install. Krupp Presta is part of the Powertrain business unit of ThyssenKrupp Automotive.
Use of existing electromechanical power steering systems is restricted to small cars, mainly because their drive units are mounted on the steering column. The steering power has to cover a relatively long distance and pass through several transmission stages before it reaches the wheels, suffering frictional and accuracy losses on the way. The drive units for these systems have to generate a correspondingly high level of energy. On bigger models, systems of this kind would require such heavy electric motors that they would weigh down the steering column and impede steering. Also, the electric systems used on today`s cars would not be able to provide enough energy.
On the TubPAS system, the drive unit is installed directly on the steering rack rather than on the steering column. As this allows the steering power to be transferred more directly to the wheels, even the power required for larger cars can be generated by compact units. With this development, Krupp Presta has significantly widened the scope for using electromechanical power steering systems and at the same time taken a first step toward "steer by wire" solutions.
The name TubPAS ("Tub" is short for tube, "PAS" stands for Power Assisted Steering) reflects the system`s space-saving design. The drive unit, in which a rotor with integrated ball screw unit translates the motion of the electric motor into an axial steering rack movement, is arranged concentrically around the steering rack. The data for the drive unit come from a sensor unit installed around the steering gear pinion. It measures steering torque and transmits it wirelessly to an ECU (Electronic Control Unit), which transfers the signal to the power electronics of the drive units. Wireless transmission of the torque signal helps keep friction in the system to a minimum, optimize efficiency and give the driver a good steering feel. To this end, Krupp Presta also selected a motor with rare earth magnets for the drive.
The entire power steering system consists of eight parts and is considerably easier to install than hydraulic systems. TubPAS consumes less fuel than conventional power steering systems because the electric motor only draws power when needed, whereas hydraulic pumps need powering all the time. As TubPAS is a programmable system, it offers additional functions. For example, TubPAS can be factory designed to provide sporting or comfortable steering characteristics. Moreover, TubPAS is capable of metering steering power infinitely in line with speed.
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