EV Drivetrain Recirculation Gear Layout for High Torque
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Solution Overview
Problem
Heavy-duty electric vehicles face challenges with high reduction ratios in their drivetrains, leading to heavy and bulky gears that increase weight and compromise ground clearance due to high load requirements.
Innovation Solution
A compact and lightweight drivetrain design featuring a motor shaft, output shaft, main shaft, pinions, gearwheels, a clutch system, and a recirculation shaft, allowing for two speed configurations that distribute load between the main and recirculation shafts, reducing the load on gearwheels and pinions, and incorporating a differential with a carrier and needle roller bearings for improved compactness and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a high reduction ratio is used to achieve high vehicle loading capacity, then the torque necessary to start the vehicle is provided, but the gears become heavy and bulky, increasing weight and compromising ground clearance
Solution Approach 1:
The drivetrain is divided into two independent power transmission paths: a direct path (main shaft to output shaft) and a recirculating path (main shaft to gearwheels to recirculation shaft back to main shaft). This segmentation allows the torque to be distributed across multiple gear meshes, reducing the load and weight of individual gears while maintaining the high reduction ratio needed for high torque output.
2Force
If a high reduction ratio is used to provide necessary torque, then vehicle loading capacity is increased, but the gears must be designed to withstand high loads making them bulky and affecting ground clearance
Solution Approach 1:
The power transmission is segmented into multiple paths with multiple gear stages. The recirculating path adds intermediate gear meshes that distribute the torque load, allowing each gear to be smaller in volume while the overall system achieves the required high reduction ratio for high torque multiplication.
Solution Approach 2:
The recirculation shaft acts as an intermediary element that introduces additional gear meshes into the power transmission path. These intermediate gears (gearwheels meshing with the recirculation shaft) distribute the torque load, reducing the size and volume of individual gears while maintaining the overall high reduction ratio.
3Force
If standard parallel axis drivetrain with high reduction ratio is used, then high vehicle loading capacity is achieved, but additional weight is added and ground clearance problems occur
Solution Approach 1:
The drivetrain is segmented into two parallel power transmission paths that work simultaneously or alternatively. This segmentation distributes the torque load across multiple gear meshes, reducing the weight of individual components and the overall drivetrain weight while maintaining the high reduction ratio necessary for high vehicle loading capacity.
Solution Approach 2:
The clutch system enables dynamic switching between the direct power transmission path and the recirculating path, or between different combinations of these paths. This dynamic capability allows the drivetrain to optimize weight distribution and component loading based on operating conditions, reducing overall drivetrain weight while maintaining high torque capability.
Data Source
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Figure 2
AI summary
A drivetrain (14) comprises a main shaft (28), driven by an electric motor (12), and a wheel output shaft (36A, 36B). Two gearwheels (46, 48), mounted around the output shaft to rotate freely, are meshing with respective main pinions (32, 34) integral with the main shaft. A clutch system (52) car engage either one of the gearwheel with the output shaft. To reduce the load applied to the gearwheels, the drivetrain comprises a recirculation shaft (34), freely rotating relative to a housing (60) of the drivetrain, and two recirculation pinion (56, 58), integral with the recirculation shaft, each meshing with a respective gearwheel. When the clutch system engages one of the gearwheel with the output shaft, the recirculation shaft is driven by the main shaft through the other gearwheel meshing with the respective main and recirculation pinions, and the output shaft is driven both by the main and recirculation shafts, through the engaged gearwheel meshing with the respective main and recirculation pinions.