Feedforward Wheel Torque Limiting for EV Startup Oscillation
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Solution Overview
Problem
Existing methods for mitigating powertrain oscillations in electric vehicles, particularly during startup, are inadequate as they fail to effectively manage oscillations caused by low battery state of charge and temperature, leading to noise, vibration, and harshness issues.
Innovation Solution
Implementing a feedforward torque limit control strategy that dynamically adjusts wheel torque based on the instantaneous discharge power limit and minimum threshold vehicle speed, ensuring the torque remains within the battery's capabilities, even at low speeds, to prevent drastic torque changes and oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If discharge power throttling is commanded at the rechargeable battery during vehicle startup, then the battery is protected from excessive discharge, but significant powertrain oscillations occur
Solution Approach 1:
The controller proactively determines a feedforward torque limit based on battery state of charge and temperature before oscillations occur. This preliminary action prevents the need for reactive discharge power throttling, thereby avoiding powertrain oscillations while still protecting the battery.
Solution Approach 2:
The torque limit is dynamically adjusted based on real-time battery conditions (state of charge and temperature). This dynamic adjustment allows the system to optimize between battery protection and smooth torque delivery, preventing oscillations while maintaining battery safety.
2Reliability
If wheel torque is limited by disturbance rejection control strategies, then traction loss is managed, but powertrain oscillations during startup are not addressed
Solution Approach 1:
Instead of waiting for disturbances to occur, the controller proactively establishes a feedforward torque limit based on battery conditions before vehicle startup. This preliminary torque limitation prevents powertrain oscillations during startup while maintaining adequate traction management.
Solution Approach 2:
The system continuously monitors battery state of charge and temperature, using this feedback to dynamically adjust the torque limit. This closed-loop feedback ensures both traction management and prevention of startup oscillations across varying operating conditions.
3Speed
If large wheel torque is requested at low vehicle speed, then vehicle acceleration is improved, but battery discharge limits are exceeded causing oscillations
Solution Approach 1:
The torque limit is dynamically adjusted based on vehicle speed and battery conditions. At low speeds, the limit prevents excessive torque requests that would cause oscillations, while still allowing adequate acceleration. As speed increases, the limit is adjusted to maintain smooth operation.
Solution Approach 2:
The system changes the torque parameter based on operating conditions (speed, battery SOC, temperature). By dynamically modifying this key parameter, the system achieves both acceptable vehicle acceleration and prevention of powertrain oscillations across different operating regimes.
Data Source
AI summary
Methods and systems are provided for limiting requested wheel torque during startup of a vehicle having an electrified powertrain. In one example, a method may include, responsive to a discharge power currently available being less than or equal to a threshold discharge power, operating the vehicle while requesting the wheel torque at a feedforward torque limit, the feedforward torque limit being based on the discharge power and a threshold vehicle speed. In this way, large shifts in wheel torque may be avoided upon startup of the vehicle, thereby reducing noise, vibration, and harshness at the electrified powertrain.