Dual Electric Machine Power Recirculation for Full-Charge Braking
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Solution Overview
Problem
When a vehicle's electric energy storage device is fully charged or in a condition where it cannot accept additional charge, operating the electric machine as a generator to provide regenerative braking is not desirable, leading to increased friction brake usage, which can be less effective on extended negative grades.
Innovation Solution
Operate a first electric machine in motor mode and a second electric machine in generator mode, with the generator's power being consumed by the motor, adjusting gear ratios to manage braking and efficiency, thereby providing vehicle braking without charging the energy storage device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the electric machine operates as a generator to provide regenerative braking, then vehicle braking is provided and kinetic energy is converted to electrical energy, but the energy storage device may become overcharged when its state of charge is already high
Solution Approach 1:
The patent introduces a power recirculation intermediary system where the generator's output is redirected to a motor instead of the energy storage device. This intermediary pathway allows kinetic energy to be converted to electrical energy and then back to mechanical energy for dissipation, preventing overcharging while maintaining regenerative braking functionality.
Solution Approach 2:
The system dynamically changes the operational parameters of the electric machines based on the energy storage device's state of charge. When the storage device is full, the controller switches from charging mode to power recirculation mode, changing the generator's output destination and the motor's function from propulsion to power absorption.
2Ease of operation
If friction foundation brakes are used for extended duration on negative grades, then vehicle braking is provided, but brake effectiveness decreases due to wear and heat
Solution Approach 1:
The patent replaces the mechanical friction braking system with an electric braking system using generator-motor power recirculation. This substitution eliminates direct friction contact while providing equivalent braking force, preventing wear and heat buildup associated with extended friction brake usage on downhill grades.
3Productivity
If the electric machine operates as a generator with high efficiency, then more electrical energy is produced, but this increases the risk of overcharging the energy storage device
Solution Approach 1:
The motor serves as an intermediary that absorbs excess electrical energy from the generator without charging the storage device. This allows the generator to operate at high efficiency and produce maximum electrical energy while the motor converts it back to mechanical energy for dissipation, decoupling energy generation from storage device charging.
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
Reduces friction brake wear and provides effective braking by utilizing electric machines efficiently, maintaining a net zero power exchange with the energy storage device, even when it is fully charged.
Implementation Method 1
The electric machine may also operate as a generator to convert a vehicle's kinetic energy into electrical energy
Implementation Method 2
A vehicle may include an electric machine that may provide propulsive force to propel the vehicle
Data Source
AI summary
Methods and systems for operating a driveline that includes two electric machines are described. In one example, one electric machine is operated in a generator mode and the other electric machine is operated in a motor mode so that electric power that is generated by the electric machine that is operated in the generator mode is consumed by the electric machine that is operated in the motor mode.