Powering up

Hayley Everett

James Hayes discusses the recent GTR21 regulation relating to power rating for electrified vehicles.

Determination of Electrified Vehicle Power is the title of the Global Technical Regulation 21, or UNECE GTR21 for short. The GTR21 is a regulatory framework established under the UNECE WP.29, also known as the World Forum for Harmonisation of Vehicle Regulations, which is a working party within the United Nations Economic Commission for Europe (UNECE). WP.29 is responsible for developing and maintaining international vehicle regulations and standards to ensure the safety, environmental performance, and quality of vehicles and their components.

The aim of the GTR21 is to define a test procedure and system power rating that provide a reliable and repeatable way to command a vehicle to deliver maximum power in a laboratory setting and to give a comparable and valid basis for system power rating and as well as describe the measurements and calculations necessary to produce it.

Electrified vehicles and conventional vehicles are projected to coexist in the market for the foreseeable future. Many established regulations and procedures, such as WLTP, apply to both vehicle types and require a power rating as a critical metric. To ensure equitable treatment, it’s essential that the power rating for electrified vehicles is both qualitatively and quantitatively on par with the traditional engine-based power ratings that are standard for conventional vehicles.

The standardised test procedure for determining power aims to address a substantial challenge faced by manufacturers when conveying the power output of electrified vehicles to both the general public and regulatory authorities. It also provides a solution for determining system power rating for electrified vehicles for use with WLTP.

The GTR21 test procedure defines two alternatives for system power determination, Test procedure 1 (TP1) that determines vehicle system power rating via measured electrical power and ICE power, and Test procedure 2 (TP2) that determines vehicle system power rating via measured torque and speed at the axles or wheel hubs.

The test is conducted by having a fixed speed at which maximum power can be achieved and applying full accelerator pedal position for 10 seconds. The maximum power in a two second window defines the peak power and the last two seconds of the 10 second test represents the sustained power. The mean values of the second through fifth repetitions render the end results.

The GTR21 defines that hub dynamometer may be used for conducting the tests and particular for TP2 as it stipulates measurements of speed and torque at the wheel hubs, which is the core capability of a hub dynamometer.

The Swedish company Rototest pioneered vehicle power testing in the early nineties with its at the time revolutionary hub coupled dynamometer solution that would accurately measure the wheel hub output power of the vehicle. In the following three decades, Rototest has made itself a name for providing the automotive industry with advanced ViL-ready powertrain dynamometers that allow great flexibility in testing capability. Its dynamometers are used by OEMs, Tier-1s and research institutes globally, in countless applications and test scenarios. Adding GTR21 testing to the already extensive list of supported applications that today include ADAS testing, Vehicle-in-the-Loop, drive cycle etc is just another proof of the great testing flexibility their systems offer.

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