Regenerative Braking Torque Limits for Hybrid Vehicle Drivability
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Solution Overview
Problem
Hybrid vehicles with electric motors experience unacceptable drivability due to uncontrolled transient characteristics of regenerative braking, particularly in vehicles without transmission or clutch, leading to excessive negative torque application that impairs drivability and power generation efficiency.
Innovation Solution
A method and system for scheduling regenerative braking torque by sensing the accelerator pedal position, determining the motor/generator speed, and using an algorithm to set a torque limit, which includes rate limiting decreases in torque below zero Nm, thereby controlling the regenerative braking command to balance power generation and drivability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If regenerative braking torque is not limited, then power generation efficiency is improved, but drivability deteriorates due to excessive negative torque application
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the regenerative braking torque limit based on motor speed. The torque limit is not fixed but varies with operating conditions, specifically transitioning from a higher limit at higher speeds to a lower limit at lower speeds. This resolves the contradiction by optimizing power generation at high speeds while preventing excessive torque and maintaining drivability at low speeds.
Solution Approach 2:
The patent implements dynamics by making the torque limit adaptive rather than static. The control system continuously monitors motor speed and adjusts the torque limit accordingly, creating a dynamic control strategy that responds to changing operating conditions. This allows the system to maximize regenerative braking effectiveness when appropriate while maintaining smooth drivability characteristics.
2Speed
If electric motor provides fast transient response for regenerative braking, then acceleration response is improved, but drivability deteriorates due to uncontrolled transient characteristics
Solution Approach 1:
The patent applies preliminary anti-action by preemptively limiting the regenerative braking torque before excessive negative torque can be applied. The torque limit is established based on motor speed conditions, preventing the harmful transient effect before it occurs. This approach maintains the fast response capability of the electric motor while pre-comparing the torque request against the speed-dependent limit to avoid drivability issues.
3Loss of energy
If torque limit is set high for maximum power recovery, then energy storage efficiency is improved, but drivability deteriorates due to abrupt deceleration
Solution Approach 1:
The patent resolves this contradiction through parameter changes by making the torque limit a function of motor speed. At high speeds, the torque limit is set higher to maximize energy recovery. As speed decreases, the torque limit is reduced to prevent abrupt deceleration and maintain smooth drivability. This speed-dependent parameter adjustment optimizes both energy storage efficiency and drivability across the operating range.
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
The solution effectively limits excessive negative torque during regenerative braking, enhancing drivability and power storage efficiency by setting a desirable torque limit range, ensuring smooth deceleration and maintaining power generation capabilities.
Implementation Method 1
converting kinetic energy from regenerative braking into electrical energy and storing the electrical energy in an energy storage device
Data Source
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AI summary
A method is provided for scheduling regenerative braking torque, comprising: sensing a position of an accelerator pedal; generating a torque request value in response to the sensed accelerator pedal position; determining a speed of operation of a motor/generator; determining a torque limit in response to the torque request value and the determined speed of the motor/generator; generating a regenerative braking command in response to the torque limit; and outputting the regenerative braking command to the motor/generator.