Regenerative Braking Torque Control for Electric Vehicle Thermal Management
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Solution Overview
Problem
Existing electric powered vehicles face challenges in maintaining sufficient motive power performance during flat-road and uphill travel following downhill travel due to motor generator temperature increases from regenerative power generation, leading to limited output torque and poor fuel efficiency.
Innovation Solution
An electric powered vehicle with a motor generator, power conversion unit, and regeneration control portion that limits regenerative power generation during downhill travel based on road gradient and motor temperature, adjusting torque command values to prevent excessive heat generation and ensure sufficient torque for subsequent travel conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If regenerative power generation is performed during downhill travel, then energy recovery is improved, but motor generator temperature increases excessively
Solution Approach 1:
The regenerative braking control device dynamically adjusts the regenerative braking force based on real-time motor temperature measurements. When the motor temperature exceeds a predetermined threshold, the control device reduces or stops regenerative braking to prevent excessive temperature increase, while allowing full regenerative braking when temperature is within acceptable ranges.
Solution Approach 2:
The system changes the operational parameters of regenerative braking based on temperature conditions. The control device monitors motor temperature and adjusts the regenerative braking force parameter accordingly, switching between different braking modes (full regeneration, reduced regeneration, or mechanical braking only) based on temperature thresholds.
2Force
If regenerative braking force is increased on downhill roads, then braking performance is improved, but wheel lock occurs causing skid
Solution Approach 1:
The control device continuously monitors wheel speed and vehicle state to detect downhill conditions and adjusts regenerative braking force accordingly. When downhill travel is detected, the system reduces regenerative braking force to prevent wheel lock, and uses feedback from wheel speed sensors to maintain optimal braking force that prevents skidding while maximizing energy recovery.
3Temperature
If motor generator size is increased to handle temperature increases, then thermal capacity is improved, but device complexity and cost increase
Solution Approach 1:
The control device performs preliminary temperature monitoring and proactive temperature management by detecting temperature trends before excessive heating occurs. The system anticipates temperature increases during downhill regenerative braking and adjusts braking force in advance to keep motor temperature within safe operating limits, preventing the need for oversized cooling systems.
4Use of energy by moving object
If continuous regenerative power generation is performed during downhill travel, then energy recovery is improved, but output torque is limited during subsequent uphill travel
Solution Approach 1:
The control device implements periodic temperature monitoring and adjusts regenerative braking in a cyclical manner based on temperature thresholds. During downhill travel, the system alternates between regenerative braking phases and mechanical braking phases, allowing the motor temperature to remain within acceptable ranges while still recovering significant energy, thereby preserving output torque capability for subsequent uphill travel.
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
This solution effectively suppresses motor generator temperature increases during downhill travel, securing output torque for flat-road and uphill travel, improving fuel efficiency by avoiding low gear shifts and simplifying cooling requirements.
Implementation Method 1
a motor generator (MG) having both the functions of an electric motor and an electric generator is generally employed as an electric motor for the vehicle
Implementation Method 2
a power conversion unit configured to perform bidirectional electric power conversion between a chargeable power supply and the motor generator
Data Source
AI summary
A regeneration control portion sets a torque command value (in general, a negative value) of a motor generator at a time of regenerative braking. A braking cooperative control portion calculates a total braking force (power) required for the entire vehicle based on a brake depression force BK of a driver and also controls the shares of the output of the total braking force between a hydraulic brake and the motor generator. An MG-ECU drives and controls the motor generator so that a regenerative torque is generated according to a torque command value. The regeneration control portion puts a limitation such that the absolute value of the regenerative torque is smaller at a time of downhill travel than at a time of flat-road travel, for the same brake operation.