Centralized Electric Four-Wheel Drive Torque Distribution
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Solution Overview
Problem
Conventional four-wheel drive systems, particularly full-time electric four-wheel drive systems, face challenges in actively distributing drive torque between axles and wheels, leading to issues such as wheel slippage, reduced maneuverability, and poor driving stability on uneven surfaces due to the 'different speed-same torque' characteristic of traditional differentials.
Innovation Solution
A centralized full-time electric four-wheel drive system that utilizes a dual rotor motor with controlled output torque distribution between axles and wheels, incorporating a center differential and bevel gear differentials to achieve active torque distribution, allowing for unequal power output between axles and wheels, thereby addressing the limitations of traditional systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional differential is used in four-wheel drive system, then the structure is simple and easy to manufacture, but the drive torque cannot be actively distributed between wheels and axles, causing wheel slippage and reduced maneuverability
Solution Approach 1:
The patent segments the single centralized power source into multiple independent power sources (front axle motor and rear axle motor), allowing each axle to receive and independently control drive torque. This segmentation enables active torque distribution between axles and wheels, resolving the contradiction by sacrificing some manufacturing simplicity for significantly improved adaptability in torque control.
Solution Approach 2:
The patent implements dynamic torque distribution by independently controlling the output torque of each power source based on real-time wheel speed, adhesion conditions, and vehicle state. The control system continuously adjusts torque allocation to optimize maneuverability and prevent slippage, transforming the static torque distribution of traditional systems into a dynamic, adaptive system.
2Adaptability or versatility
If distributed drive with hub motor is used, then the torque distribution is improved, but the unsprung weight increases and reliability decreases
Solution Approach 1:
The patent merges the advantages of centralized drive (lower unsprung weight, better reliability) with the torque distribution capabilities of distributed drive. By placing motors on the drive axles rather than in wheel hubs, the system achieves active torque distribution while keeping the motor mass on the sprung mass, thus improving adaptability without compromising reliability.
Solution Approach 2:
The patent introduces a torque distribution mechanism (planetary gear sets and clutches) as an intermediary between the power sources and wheels. This intermediary enables flexible torque distribution while isolating the power sources from direct wheel contact, reducing the impact of wheel-side failures on overall system reliability.
3Device complexity
If single centralized power source is used, then the structure is compact and simple, but the four-wheel drive capability is limited without transfer case or coupling device
Solution Approach 1:
The patent segments the power transmission path by introducing independent power sources for front and rear axles, eliminating the need for complex transfer cases and coupling devices. Each axle has its own motor that can independently deliver torque, simplifying the overall drivetrain architecture while maintaining four-wheel drive capability.
Solution Approach 2:
The patent makes each power source universal by enabling it to operate independently or in coordination with the other. The front axle motor and rear axle motor can function as separate power sources or work together to provide four-wheel drive, eliminating the need for dedicated torque transfer mechanisms while maintaining versatility.
4Ease of operation
If electromagnetic multi-plate clutch is used for torque distribution, then the torque transfer is achieved, but the response speed is limited and energy loss increases
Solution Approach 1:
The patent replaces the electromagnetic multi-plate clutch system with a direct mechanical torque distribution mechanism using planetary gear sets and clutches that engage/disengage based on wheel speed differences. This mechanical system responds faster than electromagnetic clutches and reduces energy loss by eliminating the need for continuous electromagnetic engagement and disengagement.
Data Source
AI summary
A centralized full-time electric four-wheel drive system, including: a housing; a central differential; a main drive unit, whose power output gear meshes with the ring gear of the central differential; a dual-rotor motor having a first and a second output gear at either end; a rear-axle differential; a first planetary gearset (PG), whose sun gear and ring gear connect to the carrier of the central differential and the housing respectively; a second PG with common carrier of the first PG, whose sun gear connects to the sun gear of the central differential and ring gear meshes with the first output gear; a third PG, whose sun gear and ring gear connect to the semi-axle of the rear-axle differential and the housing respectively; a forth PG with common carrier of the third PG, whose sun gear connects to the rear-axle differential cage and ring gear meshes with the second output gear.