Electrification efforts at the world's major OEMs and parts suppliers are mainly directed at ensuring optimal range and performance. The powertrain, which represents the heart of the electric vehicle (EV)'s motive power, has a large impact on both metrics. More and more vehicle manufacturers and component suppliers are integrating the motor, inverter, and gearbox into an all-in-one e-drive system. This reduces the amount of wiring and driveshaft components, improves the use of internal space, reduces the vehicle's weight, and reduces the energy consumption caused by power transmission; all coveted design targets in the industry. This in turn improves the efficiency of the transmission from the e-drive to the axles, which can result in increased driving range. In addition, as EV motors continue to evolve, rotational speeds reaching beyond 20,000 rpm are becoming more and more common. The higher the speed, the greater the power density, and the smaller and lighter the motor can be made under the same power demand. This has already become a competitive focus for various automakers and motor manufacturers, as it not only improves the overall range of the vehicle but also reduces material usage.
Integrated e-drive systems and high-speed electric motors is irreversible.
It is now safe to say that the trend towards integrated e-drive systems and high-speed electric motors is irreversible. As a result, the complexity of test procedures for these products has increased, requiring more comprehensive and efficient test and verification methods. For example, due to the power output from the gearbox to the load on both sides of the axle, the test bench structure for the integrated electric drive should ideally consist of a dual-axis e-drive test platform with low speed but high torque.
▲An integrated e-drive system
▲Dual-axis e-drive test platform schematic
Chroma's high-speed e-drive test
Constructing a test system for e-motors with speeds above 20,000 rpm is a challenge, as the design of the corresponding high-speed load dynamometer must be carefully considered. For example, because any deviation from the center is more likely to cause damage to the mechanism at high speeds, a universal joint with a larger allowable eccentricity must be designed in the shaft coupling. In addition, the frictional heat generated by the high-speed rotation requires using specialized bearings made of high-quality materials to avoid damage.
▲Chroma's high-speed e-drive test platform
E-drive test system architecture
Early-stage design verification testing of electric powertrains is ideally done with a test system composed of a load power meter, data collector, and battery simulator. Such a test system allows for the validation of the electric powertrain before the real-vehicle test phase. It includes crucial test items such as drive system efficiency, locked-rotor torque performance, power supply characteristics, and durability and reliability. The test platform's battery simulator enables programmable control of different charge and discharge curves. This facilitates the simulation of battery reactions within the powertrain and helps to test the powertrain's performance under dynamic real-world driving conditions. During the R&D phase, it assists engineers in adjusting the integration control strategy of the motor and motor driver. Furthermore, prior to the whole vehicle validation stage, it allows for a comprehensive understanding of the overall drive control performance under a wide range of real-world operating conditions, thereby saving significant costs associated with road testing and troubleshooting.
Let us take the important scenario of uphill starting as an example. EVs usually only have one or two fixed gear ratios. When facing underground passages or garage ramps with slopes steeper than 10%, they may not be able to meet the requirements for uphill starting. Insufficient torque during the hill start can cause the vehicle to slide, and excessive starting torque can cause accidents due to sudden acceleration. This is why it's important to test the capability of the motor control unit (MCU) to output stall detection when torque is applied under a maximum current supply. This test can be conducted multiple times according to different load requirements. Based on the test results, the starting control strategy of the MCU can be adjusted to ensure that the EV can meet the requirements of different road conditions, including uphill starting, and thereby prevent accidents from occurring.
Automakers will be especially interested in energy consumption testing through a whole vehicle simulation test. To achieve this, the e-drive test system can be combined with simulated vehicle models. By conducting energy consumption tests under NEDC (New European Driving Cycle) and WLTC (Worldwide Harmonized Light Vehicles Test Cycle) conditions, the energy consumption of the simulated whole vehicle can be fully verified. Furthermore, by feeding the system with more vehicle and environmental data such as vehicle weight, tire parameters, drag coefficient, transmission system parameters, etc., the user can confirm whether the motor or MCU will overheat or fail when climbing hills or when the accelerator is pushed to its limit, as well as in other simulated real-world scenarios.
This solution enables test personnel to address problems before entering the whole-vehicle testing phase, which effectively reduces development costs and improves testing efficiency. The risk of failure during on-road verification is also significantly reduced, strengthening personnel safety.
▲E-drive system test lab setup
Chroma 1210 E-Propulsion Test System
The Chroma 1210 E-Propulsion Test System is a complete solution that combines a dynamometer, battery simulator, and measurement and control instruments. Designed to meet customer needs, the system can be customized with additional equipment such as constant temperature and humidity control, liquid cooling, and other relevant tools. This versatile test solution is suitable for powertrains of electric passenger and commercial vehicles as well as hydrogen fuel cell hybrid vehicles. It provides simulation testing for electric drive systems and fully covers testing of electric motors, motor control units, and powertrain systems.
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