Abstract
Keywords
Electromechanical Power Steering (EPS); Gears; Sensors; Hybrid-ECU; Induction Motor
Abstract - ZF Lenksysteme has developed a new generation of high performance Electromechanical Power Steering Systems (EPS). The first members of this power steering family have been launched end of 2002 in the BMW Z4 and the Volkswagen Golf-Platform. Further projects are under development.
The main difference to known EPS-Systems and the challenge for the development team was:
- Full compatible with hydraulic steering systems in terms of on-center-feeling, steering characteristics, noise, vibration and kick-back-sensitivity
- High steering rackforces at high rack travelspeed with comfortable handwheel-torque
- To fulfill the high temperature underhood conditions in the cars engine compartment
- Requirement of waterproofness and wading capability
- High safety requirements
The EPS-System of ZF Lenksysteme is based on the following main features.
Integrated electric motor and control unit. The motor is an induction motor with patented winding scheme to reach high efficiency. The electronic control unit (ECU) is designed in microhybrid technology with multilayer LTCC-substrate for the logic circuit and DBC-sub-strate for the power stages. The substrates are mounted into a waterproof housing with integrated leadframes for internal and external connecting.
The torque sensor for sensing the drivers handwheel torque is based on a non-contacting magnetoresistive technology. In terms of safety the sensor is redundant and the signal transmission to the ECU is based on digital, redundant techniques.
The mechanical concept is based on a high performance rack and pinion steering gear. The motor torque will be transmitted via crossed helical gear to the separate pinion on the steering rack. The so called dual-pinion-system offers good conditions for variable packaging.
The whole system and all the components have been released after a wide range of car and bench tests. Especially durability and temperature tests have been under strong focus.
The software development and the test of the software was done according to latest safety requirements and specifications.
The result of the development efforts is a new generation of EPS-Systems, that fulfills the highest requirements in terms of comfort and performance for the driver.