Electrically-Variable Transmission Torque Allocation
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Solution Overview
Problem
Existing hybrid powertrains are not well-suited for high-performance vehicles, particularly in all-wheel drive configurations, as they prioritize efficiency over performance and handling, and are limited in their ability to allocate torque between axles and couple torque with battery state of charge.
Innovation Solution
An electrically-variable transmission system that includes a transaxle housing with gear carriers and pinions connecting opposing axle portions, along with internal combustion and electric machines, allowing for the distribution of rotational power to all wheels and enabling torque allocation between axles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If hybrid powertrains prioritize efficiency and fuel economy, then fuel consumption is reduced, but vehicle performance and handling deteriorate
Solution Approach 1:
The powertrain is segmented into multiple independent power sources: an internal combustion engine connected to a first axle, and a separate electric machine connected to a second axle. This segmentation allows each power source to operate independently, enabling the engine to optimize for fuel efficiency while the electric machine provides performance enhancement without compromising overall fuel economy.
Solution Approach 2:
The system dynamically allocates power between the two axles based on driving conditions. The electric machine can independently drive the second axle to provide performance bursts when needed, while the engine continues to operate in its efficient range. This dynamic power distribution resolves the contradiction by adapting performance output to actual driving requirements rather than maintaining constant high-performance capability.
2Weight of moving object
If hybrid powertrains are designed for two-wheel drive, then weight and fuel consumption are reduced, but all-wheel drive performance capability is lost
Solution Approach 1:
Instead of using a single heavy power source that must be duplicated for all-wheel drive, the system segments power delivery across two axles with the engine driving one axle and an electric machine driving the other. This approach provides all-wheel drive capability while avoiding the weight penalty of duplicating the entire engine system.
Solution Approach 2:
The electric machine serves multiple functions: it can independently drive the second axle for all-wheel drive operation, it can recover braking energy, and it can provide torque assistance. This multi-functionality allows the system to achieve all-wheel drive capability without adding dedicated components for each function, thereby controlling overall weight.
3Adaptability or versatility
If a separate electric machine is added to the second axle for all-wheel drive, then all-wheel drive capability is achieved, but device complexity increases
Solution Approach 1:
The electric machine is designed to perform multiple functions within a single component: it provides propulsion to the second axle, enables all-wheel drive operation, handles energy recovery during braking, and provides torque vectoring capability. By consolidating these functions into one machine rather than using separate systems for each function, the overall device complexity is managed while achieving all-wheel drive capability.
4Adaptability or versatility
If torque allocation between axles is decoupled from battery state of charge, then power distribution flexibility is improved, but energy management efficiency deteriorates
Solution Approach 1:
The control system continuously monitors battery state of charge and uses this information to dynamically adjust torque allocation between the engine and electric machine. When battery charge is high, the system can allocate more torque to the electric machine for enhanced performance. When battery charge is low, the system prioritizes engine torque and regenerative braking to recharge the battery. This feedback mechanism maintains energy management efficiency while preserving torque allocation flexibility.
Data Source
AI summary
A transaxle (200) operatively connects a first associated rotational connection and a second associated rotational connection with an associated vehicle axle. An electrically-variable transmission includes an engine (108), a first electric machine (110) operatively connected to the engine, second and third electric machines (130 and 132), a first transaxle (126) operatively connecting the engine and second electric machine to an associated vehicle axle (104A), and a second transaxle (128) operatively connecting the first and third electric machines to another associated vehicle axle (104B). A method (300, 400, 500) is also included.