Precise rotor position and speed for combined drive concepts
In hybrid drives, the engine speed sensing of the combustion engine and the rotor position sensing of the electric motor work closely together to enable a seamless transition between both drive sources. The engine speed sensor precisely captures the crankshaft speed and thus the operating state of the combustion engine.
This information is critical for optimally controlling start-stop operations, load changes, and ignition timing. In parallel, rotor position encoders in the electric motor deliver the exact rotor angle for field-oriented control. Only with this angle can the inverter precisely build up the magnetic fields and ensure fast, jerk-free starting.
In hybrid operation, both sensor signals are combined to precisely synchronize torque transfers between the electric motor and combustion engine. The result is high driving comfort, maximum efficiency, and harmonious power flow.
RWTH Aachen University is developing cost-efficient hybrid drives for vehicle segments where this technology has previously been considered too expensive. What makes it special: full hybrid functionality is achieved with a remarkably small number of components.
For this innovation, the “Mechatronics in Mobile Propulsion” team relies on our VarioCODER. The decisive factor was the flexible, modular, and variably mountable design of the rotor position encoder, which offers maximum design freedom particularly for large shaft diameters.
Different sensors are used in hybrid drives, depending on the architecture. For control of the electric machine, rotor position sensors detect the rotor position and speed sensors detect the speed. Current and voltage sensors provide further measured variables for controlling and monitoring the electric drive. Temperature sensors monitor windings, power electronics, and coolant, for example. Additional sensors are used on the combustion engine and in the transmission, for example for speed, pressure, or position. Which signals are required for clutch control and synchronization depends on the drive concept. The functional safety requirements are derived from the respective vehicle functions.
The rotor position of the electric machine in a hybrid drive can be detected with resolvers, magnetic encoders, or inductive rotor position sensors, for example. Which measuring principle is suitable depends, among other things, on motor design, installation space, speed, temperature, and electromagnetic interference fields. Angular accuracy, signal delay, and compatibility with the power electronics are equally important. The requirements for the electrical angle result from the control concept and the number of motor pole pairs. There is no universal accuracy specification for this. Inductive built-in sensors such as the VarioCODER enable compact, contactless detection of the rotor position.
Sensors in hybrid drives must work reliably under changing temperatures, vibrations, and electromagnetic interference. Depending on the installation location, requirements for resistance to oil, coolant, or other media may apply. Tight installation spaces often limit the available dimensions. For precise control and switching between operating modes, stable signals with suitable accuracy and low delay are important. Temperature limits and permissible loads must be defined for the specific installation location. For safety-relevant vehicle functions, additional requirements for diagnostics and fault control according to ISO 26262 apply.
