Two-Motor Planetary Driveline for Compact Two-Speed EV Shifting
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Solution Overview
Problem
Multi-speed electric driveline systems face challenges such as space inefficiencies, increased geartrain losses, and motor degradation due to multi-stage planetary gear reductions and single motor setups, which affect packaging and efficiency in electric vehicles.
Innovation Solution
A compact electric driveline system using two electric machines with a planetary gearset and friction clutches to achieve two-speed functionality with reduced drag, along with a separate electric machine for a lubricant pump and heat exchanger for efficient cooling, and axle disconnect clutches for granular traction control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a multi-stage planetary gear reduction is used, then gear ratio range is increased, but space efficiency decreases and geartrain losses increase
Solution Approach 1:
The transmission is divided into two independent single-stage planetary gearsets instead of one multi-stage reduction. Each gearset provides a gear ratio, and their combination achieves the overall ratio range without requiring physical stacking of multiple stages, thus reducing transmission space while maintaining adaptability.
Solution Approach 2:
Instead of achieving gear ratio multiplication through serial stacking in one dimension (multi-stage), the patent uses parallel arrangement of two single-stage planetary gearsets. This dimensional reorganization reduces the axial length and overall volume of the transmission while preserving the required gear ratio range through selective clutch engagement.
2Adaptability or versatility
If a multi-stage planetary gear reduction is used, then gear ratio range is increased, but geartrain losses increase
Solution Approach 1:
By segmenting the gear reduction into two separate single-stage planetary gearsets with independent clutch control, the system can selectively engage only the necessary gearset for current operating conditions. This reduces the number of meshing stages actively transmitting power, thereby minimizing cumulative geartrain losses while maintaining the ability to achieve various gear ratios.
Solution Approach 2:
The transmission employs dynamic clutch control to selectively engage or disengage specific planetary gearsets based on real-time operating conditions. This dynamic reconfiguration allows the system to optimize the active power transmission path, minimizing energy losses by avoiding unnecessary gear meshing stages while maintaining the required gear ratio range.
3Device complexity
If a single motor is used, then device complexity is reduced, but reliability decreases due to motor degradation
Solution Approach 1:
The driveline is segmented into two independent motor units, each capable of providing propulsion. This segmentation creates redundancy where one motor can continue operating if the other degrades or fails, significantly improving reliability while maintaining manageable system complexity through modular architecture.
Solution Approach 2:
The system can dynamically change operational parameters by redistributing power demands between the two motors based on their individual health states and performance capabilities. This allows continuous adaptation to motor degradation conditions, maintaining reliable operation across varying motor performance levels.
4Temperature
If independent coolant loops are used for motor and transmission cooling, then cooling effectiveness is improved, but device complexity increases
Solution Approach 1:
The patent merges the previously separate coolant loops for motors and transmission into a single integrated cooling circuit. This consolidation maintains effective cooling of all components while reducing system complexity by eliminating redundant pumps, reservoirs, and control systems, achieving both cooling effectiveness and simplified architecture.
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
The system achieves efficient and smooth shifting between gear ratios with reduced losses, improved motor operation, and enhanced cooling efficiency, while allowing for adaptable traction modes, thereby increasing vehicle efficiency and reducing the likelihood of driveline inoperability.
Implementation Method 1
a planetary gearset with a first gearset component that is rotationally coupled to a first electric machine and a second electric machine
Implementation Method 2
a first friction clutch that is coupled to a third gearset component in the planetary gearset and configured to selectively brake the third gearset component
Implementation Method 3
a heat exchanger that is coupled to a transmission housing or a vehicle frame. The heat exchanger is configured to transfer heat from a lubricant in the transmission to a coolant that is circulated through the heat exchanger
Implementation Method 4
A third electric machine is additionally included in the driveline system. The third electric machine is mechanically coupled to a lubricant pump
Data Source
AI summary
Methods and systems for an electric driveline are provided. In one example, the electric driveline system includes a transmission with a planetary gearset, with a first gearset component rotationally coupled to a first electric machine and a second electric machine, and a first output interface and a second output interface rotationally coupled to a first axle and a second axle, respectively, and a second gearset component in the planetary gearset. The driveline system further includes a first friction clutch configured to selectively brake a third gearset component and a second friction clutch configured to selectively couple the first gearset component to an output shaft.