Coaxial Multi-Motor Drive System for High Power Density
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Solution Overview
Problem
Existing coaxial driving systems with multiple electric motors face challenges in achieving high power density, system efficiency, and compact integration while maintaining high performance, due to limitations in torque, power output, and flux weakening at high speeds, as well as difficulties in packaging and balancing the vehicle.
Innovation Solution
A coaxial propulsion system with multiple electric motors sharing a common shaft, where the motors can operate simultaneously or individually, utilizing a combination of motor types such as permanent-magnet synchronous, asynchronous, and switched reluctance motors, with shared cooling and optimized efficiency maps to select the most efficient motor for specific speed and torque requirements, and integrated with a differential and speed reducer for enhanced efficiency and regenerative braking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If two or more electric motors are used to achieve high torque and power output, then the power and torque performance is improved, but the system volume and weight increase
Solution Approach 1:
The patent combines two or more electric motors into a single integrated housing with a shared common shaft, merging multiple motor units into one compact assembly. This reduces the overall system volume compared to separate motor installations while maintaining the combined power output capability.
Solution Approach 2:
The patent employs a nested configuration where multiple motor stators and rotors are arranged concentrically around a shared common shaft. The motors are nested within each other in a compact radial arrangement, maximizing space utilization and minimizing the overall footprint of the multi-motor system.
2Power
If two or more electric motors are stacked closely at the same location, then the power density is improved, but the packaging difficulty and vehicle balance are worsened
Solution Approach 1:
The patent merges multiple motor units into a single integrated housing assembly, simplifying the packaging process. The unified structure with shared mounting points and common shaft eliminates the need for separate mounting procedures for each motor, thereby reducing packaging complexity despite high power density.
Solution Approach 2:
The common shaft serves multiple functions by being the output shaft for all motors simultaneously, while also serving as the rotational axis for each individual motor. This multi-functionality reduces the number of components and simplifies the overall packaging arrangement.
3Loss of energy
If permanent-magnet synchronous motors are used, then the efficiency is improved, but the flux weakening requirement at high speeds causes system efficiency loss
Solution Approach 1:
The patent changes the motor type parameter from permanent-magnet synchronous motors to asynchronous motors, which do not require flux weakening control at high speeds. This parameter change eliminates the associated efficiency losses while maintaining high-speed operational capability.
4Power
If two or more electric motors are used, then the torque and power output are improved, but the coordination control complexity increases
Solution Approach 1:
The patent combines multiple motors onto a single common shaft, which mechanically couples them and simplifies control coordination. The shared shaft ensures synchronized rotation, reducing the control complexity compared to independently controlled motors on separate shafts.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables high torque and power output while reducing size, weight, and cost, maintaining high performance and efficiency across various speeds without flux weakening losses, and allows for optimal motor selection and efficient energy recovery through regenerative braking.
Implementation Method 1
electric motor is used to directly or indirectly drive a vehicle... permanent-magnet synchronous motors or asynchronous motors
Implementation Method 2
The main shaft is provided with a bearing at each of two ends, and is provided with a bearing in a middle portion
Implementation Method 3
the electric motors share a cooling system
Data Source
Figure 1~2
Figure 3~4
AI summary
The disclosure discloses a coaxial propulsion system with multiple electric motors (121), comprising a housing (111), two or more electric motors being provided in the housing (111), characterized in that: The electric motors share one common shaft. Electric motor is a permanent-magnet synchronous motor, an asynchronous motor or a switched reluctance motor, and of different efficiency maps. The disclosure can improve the power density and system efficiency of propulsion system while maintaining high performance output, to enhance the integration level, and reduce size, weight and cost.