Transparent and Objective Development Process

New IAV methodology for rating electromechanical transmission actuation

High efficiency at low cost: these are the two most important demands on transmission actuation. A new IAV methodology provides information at an early stage of the development process on the key performance figures underlying individual solutions and permits an objective ranking of variants.

Electromechanical actuators are a major trend at the moment in transmission development because compared with their hydraulic or electrohydraulic counterparts, they promise significantly better efficiency. Energy is only used when gear-shifting actually takes place – thanks to “power on demand”, electromechanical actuators do not push up fuel consumption unnecessarily. And precisely this is so important to OEMs right now. If they want to meet the stringent CO2 requirements, the transmissions will need to make a contribution too. Added to this is the desire to minimize costs as well as new challenges from the start-stop function and increasing powertrain hybridization.

IAV has developed a new methodology for optimizing the layout of electromechanical actuators. The process starts by defining the demands on the transmission, such as type, number of gear speeds, available package and the question of whether any hybridization is wanted. The result of the process is a transmission-specific actuator system marked by benefits such as low energy consumption, favorable production costs and short gearshift times. “We start using the new methodology in the early design phase”, explains André Uhle, head of the Transmission Actuation Systems team at IAV. “To begin with, we find out which technical system can best meet our customer’s needs. In this phase, we can choose from various operating principles, such as a gear drum controller or spindle actuator system, and can also opt for either individual or central actuation.”

Library of transmission components

To design a new transmission actuator system, IAV’s experts set up a simulation model that breaks down the electromechanical actuating mechanism into its sub-functions of energy generation, torque/speed conversion and conversion of the direction of movement. “The subfunctions can be compiled from a component library, as in a modular system”, Uhle says. “Our library covers some 30 mechanical operating principles with all technically relevant parameters – this also includes an e-motor database with the key specifications of various manufacturers.”

A transient 1-D gearshift simulation makes it possible to estimate shifting times and energy consumption whereas predimensioning the motor elements delivers information on aspects like component stiffness, characteristic geometric data (such as diameter, length, pitch etc.), on gear ratio and on emotor characteristics. This provides the basis for determining all of the key characteristics of an actuator system at the concept stage: energy consumption, production costs, package requirement, weight and shifting time.

Ranking for the best solutions

The new methodology lets IAV’s experts compare various options and selectively vary the parameters until the optimum solution is found. “We vary the main system parameters, such as spindle pitch, gear ratio, as well as the characteristics of the e-motor within technically meaningful boundaries, leaving us with up to 500,000 variants for designing an actuator system”, Uhle reports. “Subsequent utility value analysis then gives us the basis for ranking potential solutions and for identifying the preferred option.”

The new methodology for designing transmission actuating systems has been in use at IAV for twelve months. “Before then, the approach in the concept phase heavily depended on the designer’s experience”, Uhle says. “We obviously still use this knowledge – but it’s now complemented by the results of simulation. This gives us a transparent and objective development process.”

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