Electric Machine Torque Compensation for Creep Speed Stability
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Solution Overview
Problem
Electrified vehicles face challenges in maintaining desired driveline speed during vehicle creep conditions due to variations in road grade and vehicle mass, which can lead to disturbances in torque output and inefficiencies in energy conservation.
Innovation Solution
A method and system that control the torque output of an electric machine by estimating road grade and vehicle mass, calculating torque compensation values, and adjusting the torque output to compensate for these variations, using a combination of feed-forward and feedback torques to maintain optimal speed and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the electric machine is spun down to zero speed to conserve energy, then energy conservation is improved, but the ability to quickly provide torque output when the brake pedal is released deteriorates
Solution Approach 1:
The control system performs preliminary action by maintaining the electric machine at a predetermined minimum speed rather than spinning it down to zero. This preliminary maintenance of rotational speed ensures that the electric machine can immediately provide required torque output when the brake pedal is released, eliminating the delay that would occur if the machine needed to spin up from zero speed while still conserving energy through reduced idle speed operation.
2Speed
If the electric machine maintains a predetermined minimum speed during creep conditions, then torque response capability is improved, but energy consumption increases
Solution Approach 1:
The system applies dynamics by making the electric machine speed adaptive rather than fixed. The control system continuously monitors vehicle creep conditions and adjusts the minimum speed threshold dynamically based on actual torque requirements, road grade, and vehicle mass. This dynamic adjustment allows the system to maintain sufficient torque response capability while minimizing energy consumption by reducing the minimum speed when full performance is not required.
Solution Approach 2:
The control system changes the operational parameter of electric machine speed from a fixed zero-state to a variable minimum speed state. By implementing a predetermined minimum speed threshold that can be adjusted based on vehicle conditions, the system optimizes the balance between torque response capability and energy consumption, ensuring the machine operates efficiently across different creep conditions without unnecessary energy waste.
3Stability of the object's composition
If torque output is adjusted to compensate for road grade and mass variations, then driveline speed stability is improved, but control system complexity increases
Solution Approach 1:
The control system implements feedback by continuously monitoring actual driveline speed and comparing it to the desired speed during vehicle creep conditions. Based on this feedback, the system adjusts the torque output of the electric machine to compensate for road grade and mass variations. This feedback mechanism maintains driveline speed stability without requiring overly complex control algorithms, as it uses standard closed-loop control principles already common in vehicle systems.
Solution Approach 2:
The system applies preliminary action by pre-calculating or pre-determining the minimum speed threshold and torque compensation strategies before actual creep conditions occur. By having predetermined control parameters and compensation values ready, the system can quickly respond to varying road grades and masses without requiring complex real-time calculations, thus maintaining driveline speed stability while keeping control system complexity manageable.
Data Source
AI summary
A method according to an exemplary aspect of the present disclosure includes, among other things, controlling a torque output of an electric machine of an electrified vehicle during a vehicle creep condition, the torque output calculated based at least on a road grade estimate and a vehicle mass estimate.