Coaxial Axial-Flux Propulsion Unit for Torque Split and Speed Range
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Solution Overview
Problem
Existing motor vehicle drive systems, particularly those with dual-motor units, face inefficiencies due to high-performance electrical machines that are not optimized for everyday driving cycles, leading to limitations in power density and maximum speed, and require larger radial installation spaces which negatively impact torque and speed capabilities.
Innovation Solution
A drive device featuring three axial flux machines, where two machines are connected to output shafts to provide efficient torque distribution and a third machine acts as a boost electric motor connected to the differential gear, enabling higher maximum speeds and efficient operation with smaller rotor dimensions, and using freewheels or switching elements to bypass the differential gear for enhanced performance scaling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high-performance electrical machines are used to provide sufficient torque and power, then power density is improved, but radial installation space increases and maximum speed is limited
Solution Approach 1:
The drive device is segmented into three separate axial flux machines arranged coaxially, where two machines handle efficient everyday driving operations and the third machine provides boost power during high-power requirements. This segmentation allows each machine to be optimized for specific operating conditions without requiring any single machine to be oversized, thereby reducing the radial installation space while maintaining high power density.
2Power
If high-performance electrical machines are used to provide sufficient torque and power, then power density is improved, but maximum speed is limited
Solution Approach 1:
The system dynamically switches between different operational configurations: during everyday driving, two axial flux machines operate independently to provide efficient torque distribution; during high-power requirements, the third axial flux machine is engaged to provide additional boost power. This dynamic operation allows the system to achieve high maximum speeds when needed while maintaining efficient operation during normal driving, resolving the contradiction between power density and maximum speed capability.
3Productivity
If dual-motor units are used to enable torque distribution, then driving performance is improved, but efficiency decreases due to non-optimized machines for everyday driving cycles
Solution Approach 1:
Each of the three axial flux machines is locally optimized for specific operational requirements. Two machines are configured for efficient everyday driving operations with characteristics optimized for continuous operation, while the third machine is configured for high-power boost operations. This local quality differentiation allows each component to operate in its optimal efficiency range, improving overall system efficiency while maintaining high driving performance.
4Force
If larger radial dimensions are used in electrical machines, then torque capability is improved, but speed capability deteriorates
Solution Approach 1:
The system transitions from relying on a single machine with compromised dimensions to using three axial flux machines arranged coaxially in the axial dimension. This dimensional change allows the system to achieve high torque capability through combined output of multiple machines with smaller radial dimensions, while maintaining speed capability. The coaxial arrangement enables torque scaling without sacrificing speed performance.
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 achieves particularly efficient operation with high power density, allowing for scalable and efficient torque distribution, higher maximum speeds, and optimized performance for both everyday driving and high-power requirements without oversizing the electric machines.
Implementation Method 1
three axial flux machines arranged coaxially to one another and coaxially to the output shafts and coaxially to the differential gear, namely a first axial flux machine, a second axial flux machine, and a third axial flux machine. Each axial flux machine has a respective stator and at least two rotors, which can be driven by means of the respective stator and are thus rotatable about a respective machine axis of rotation relative to the respective stator
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a drive device (10) for a motor vehicle, having a first drive shaft (12), via which a first vehicle wheel (14) of a vehicle axle of the motor vehicle can be driven, having a second drive shaft (16) arranged coaxially to the first drive shaft (12), via which a second vehicle wheel (18) of the vehicle axle of the motor vehicle can be driven, having a differential gear (20), via which the drive shafts (12, 16) can be driven, and having three axial flux machines (32a-c) arranged coaxially to each other and coaxially to the drive shafts, namely a first axial flux machine (32a), by means of which the first drive shaft (12) can be driven bypassing the differential gear (20), a second axial flux machine (32b), by means of which the second drive shaft (16) can be driven bypassing the differential gear (20), and a third axial flow machine (32c) arranged in the axial direction of the axial flow machines (32a-c) between the first axial flow machine (32a) and the second axial flow machine (32b), by means of which the drive shafts (12, 16) can be driven via the differential gear (20).