Electro-hydraulic and electrical steering systems - Controller architecture

Most of today's vehicles are produced with servo controlled steering systems, where the pump is driven directly by the combustion engine. These systems will be replaced more and more by autonomous systems driven by their own electric motors. There are two different kinds of systems: Electro Hydraulic Power Steering (EHPS) where a pump driven by a DC motor builds up hydraulic pressure for steering assistance and Electric Power Steering (EPS) where a DC motor is attached directly to the steering mechanics. Both variants have the same principle, that the motor is only running when needed. Besides the reduced fuel consumption these systems show further advantages i.e. the possibility of electronic linkage with other systems and free programmable performance curves. Another big advantage of EPS is the total loss of hydraulic fluids for the steering system. Motorola currently is working on several production solutions for control units for EHPS as well as for EPS with the Electrical Control Unit (ECU) integrated or attached to the motor. Specific control concepts for different types of motors and ASICs have been designed in the Motorola design centre. The focus is on the failsafe and reliable operation and on the integration of the electronics with the system for a most favourable price. The circuit board layout and the packaging of the ECU have been adapted to the harsh environmental conditions and to the high EMC requirements. There are already existing serial production solutions for 12V supplies. With the introduction of 42V the use of EPS in vehicles with high axle loads will become of increasing interest.