This paper introduces the new energy vehicle technical requirements on electric drive system, GEELY electric drive system technology status & planning and standard system, it’s aimed to discuss the electric drive system technical requirements and development direction in the future.
With the reduction of subsidies, the cost reduction becomes the primary task of the electric drive system. Highly integrated design is the development trend of electrical drive system. The cancel of three-phase cables and high-voltage connectors, the integrated design of housing, and the shared bearing design are the main solutions of the integrated design. In order to get more driving space, the layout space of the powertrain assembly is compressed. High speed, large speed ratio and small center distance configuration are become the trending requests of products. From the trend of nearly three years, we can see, that the highest speed of motor is increased from 12000rpm to 16,000rpm, and the speed ratio is changed from 7-9 to 10-13, also the center distance is compressed from 205mm to 185mm.
The Geely electric drive system has changed from the split design to the integrated design. We start the independent research and development work of the integrated electric drive system (EDS project). Geely will develop the 400V electric drive platform independently, which is based on the EDS project. Improvements to the motor cooling system and the solutions to increase the voltage will be the primary means, which can improve the e-motor performance. The EDS system, which is developed by Geely, integrates five modules and functions: E-motor, Reducer, Motor Control Unit (MCU), Vehicle Control Unit (VCU) and transmission control unit (TCU). The e-motor adopts Hair-PIN winding technology. The reducer has parking function. The control unit (EDU) is highly integrated. The drive module uses high-power module, named HP-drive, supplied by Infineon. Basic software is developed based on AUTOSAR software architecture. The application software of EDU is developed based on SPM and the software of existing independent MCU and VCU. Functional safety and network management are developed based on the vehicle requirements, and the functional safety level reaches ASIL-C.
The stator windings of EDS’ motor adopt the multi-layer Hair-PIN process, which can greatly improve the fill factor and shorten the height of the end winding, and then reduce the copper losses and improve the heat dissipation capacity of the motor. The power density can reach 12.9 kW/L at 340Vdc voltage (US DOE2020 target is 5.7 kW/L, china 2020 target is 4.0 kW/L), it is much higher than the U.S.Drive’s statistical technical average level of the leading enterprises. Meanwhile, the continuous output ability of the motor is about 15% higher than that of the circular line motor at the same space. On the other hand, the rigidity of the motor stator assembly and the NVH performance can be improved by using the tight Hair-PIN winding.
The rotor of EDS motor is designed with double layer V type that has higher reluctance magnetic torque, which can greatly reduce the rare-earth magnet usage and cost of the motor.
Integrated EDU Controller: to create the integrated EDU development platform which is based on Aurix297 chip microcontroller. This platform has the characteristics of integration, compatibility and openness. The platform can support the dual motor controller development, and take into consideration of the software and hardware design reservation of domain controller. The platform can update fast to fit the Aurix3XX series microcontroller and the higher requirement from automatic drive, for example the requirement of functional safety with ASIL D. The platform can adapt the challenge of the domain controller implementation on a large scale in 2020.
Simultaneously, Geely has built a standard system from vehicle to components based on the vehicle attributes. The NVH standard requires the whole process of component development and decomposes the directions into the the electromagnetic scheme, structural design, software and powertrain design at the beginning. The NVH target need to complete in the B-simple. Through the analysis of the big data of Cao Cao program, the user’s road spectrum is corrected. With EDS as the object, the endurance test condition is adjusted. The vibration standard acceleration is increased from 3g to 6g. The endurance test bench of e-motor and controller are combined. The time of verification cycle and the cost of development are reduced to 70%.