Prototyping an Integrated Electric Powertrain with REPS

At a testing facility of a leading global automotive supplier, engineers design and test prototypes of Integrated Electric Powertrain (IPT) systems for use in compact fuel cell powered cars. Based on stringent specifications provided by their customers, the engineers at this facility take to a challenging mission - designing the IPT from scratch in a burgeoning industry of electric and hybrid vehicle technology.

As with all prototyping, the need for a flexible yet robust testing facility is paramount. The customer needed to upgrade its three outdated dynamometer test cells in order to better accommodate the various testing involved in designing the IPTs. For Millbrook Revolutionary Engineering, this was no daunting task.

With years of experience in designing and building test cells from the ground up, Millbrook Revolutionary Engineering has an unmatched record for delivering high-quality testing products and services. At the forefront is the Revolutionary Engineering Pro System (REPS), a complete data acquisition and control system that is operator-friendly yet powerful enough to satisfy even the most advanced users. In order to evaluate the IPT design, REPS became an invaluable tool for the engineers at this automotive supplier testing facility

System Background

An IPT is an integrated system in that it combines an electric motor, a gearbox and a power electronic assembly. The electric motor, a permanent magnet motor, combined with the gearbox is capable of producing high torques at the wheel output. The power electronic assembly, which includes the power inverter, is responsible for all motor control, DC/AC voltage conversion, and current distribution across components.

Communication between REPS and the main control board is accomplished via CAN. Redundancy of the CAN signals is crucial; therefore two CAN buses are employed. In the event that the main CAN bus should fail, the IPT board switches automatically to the “backup” CAN bus.

Testing the Prototype

Throughout the design phase, the IPTs are rigorously tested for thermal performance, durability and efficiency. Test engineers use REPS to write the test profiles and run them in an automated manner, log data, and monitor test status.

Thermal Performance

One of the most significant tests undergoes is the thermal performance test. Its purpose is to study the temperature variations and performance of the motor assembly when different speeds and torques are applied.

Using REPS, engineers write thermal load test profiles to gradually ramp speeds and torques at the same time. Ramp rates are fully configurable in REPS and can be varied within a test profile. Torque commands as well as safety interlock signals required by the motor are sent from REPS to the motor control board via CAN.

Key Life

The key life test has two major goals: first, to determine the lifetime durability of the IPT, and second, to ensure the IPT can withstand driving patterns of 90th percentile drivers.

Based on information derived from proving grounds and putting the car under considerable amounts of stress, test profiles are developed to simulate lifetime stresses in a shorter amount of time for use in a test cell

Part of the key life test involves a high speed cycle to simulate drivers in the 90th percentile speed ranges. These are the drivers who typically exceed posted speed limits and accelerate and decelerate abruptly. Designers must be sure that the IPT can endure such driving behavior.

In the test cell, REPS allows test engineers to perform Road Load Simulation (RLS) and run test profiles that correlate to lifetime of the motor assembly.

Efficiency Map

To assess the efficiency of the IPT assembly, engineers use REPS to write an efficiency test profile.

Summary

In an IPT prototype development setting, dynamometer test cells need to provide engineers with the right tools in order to broaden their testing caabilities. When the customer found that their existing test cells were limiting them, they called on Millbrook Revolutionary Engineering to upgrade their facility with the REPS control and data acquisition system.

REPS demonstrated its versatility engineers to customize formulas and PIDs, and design test profiles for a variety of test requirements.

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