Hybrid Vehicle Torque Rate Limiting for NVH Reduction
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Solution Overview
Problem
Hybrid electric vehicles face challenges in managing torque supplied by traction motors and engines, particularly in maintaining efficient operation during rapid changes in driver demand, which can impact vehicle drivability and lead to noise, vibration, and harshness (NVH) issues.
Innovation Solution
A system and method that control the engine and electric machine torque by selecting an operating point based on efficiency and current engine speed, with the electric machine providing responsive torque to driver demand while limiting the rate of change of electric machine torque based on the rate of change of driver demand torque, using lookup tables to adjust the rate limit dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the electric machine torque is quickly adjusted to compensate for transients in driver demand, then the system responsiveness and powertrain efficiency are improved, but the vehicle drivability and NVH performance deteriorate
Solution Approach 1:
The patent applies dynamics by making the rate limit adaptive rather than fixed. The controller dynamically adjusts the rate limit based on operating conditions such as vehicle speed, engine operating point, and battery state of charge. This allows the system to respond quickly when conditions permit while limiting rapid changes when they would harm drivability, resolving the contradiction between speed and ease of operation.
Solution Approach 2:
The patent changes the parameter of rate limiting from a static value to a dynamically adjusted value based on multiple operating parameters. By monitoring vehicle speed, engine torque, battery charge state, and other parameters, the system adjusts the rate limit to optimize both responsiveness and drivability under different conditions, resolving the contradiction through parameter adaptation.
2Speed
If the electric machine torque is quickly adjusted to compensate for transients in driver demand, then the system responsiveness is improved, but the noise, vibration, and harshness (NVH) performance deteriorates
Solution Approach 1:
The system dynamically adjusts the rate limit based on real-time operating conditions. When vehicle speed is high or the engine is already operating near optimal points, the rate limit is relaxed to allow faster torque changes. When conditions are sensitive to rapid changes, the rate limit is tightened to reduce NVH, thus resolving the contradiction between response speed and NVH performance.
Solution Approach 2:
The patent modifies the rate limit parameter based on multiple inputs including vehicle speed, engine operating point, and battery state of charge. This parameter adaptation allows the system to permit rapid torque changes when they won't cause NVH issues while limiting them when they would, resolving the contradiction between speed and harmful factors.
3Use of energy by moving object
If the engine is operated at the most efficient operating point to maximize powertrain efficiency, then the energy management is improved, but the ability to quickly respond to driver demand changes deteriorates
Solution Approach 1:
The electric machine acts as an intermediary between the engine and the driver demand. It absorbs or provides torque to compensate for the difference between the engine's efficient operating point and the actual driver demand, allowing the engine to stay at its optimal efficiency point while the electric machine handles rapid torque adjustments, thus resolving the contradiction between energy efficiency and response speed.
Solution Approach 2:
The system dynamically adjusts the rate limit based on the operating point and battery state of charge. When the battery has sufficient charge and the engine is at an efficient operating point, the system allows faster electric machine torque changes to maintain efficiency while responding to demand. When the battery is low or the engine is already at a limit, the rate limit is adjusted to prevent compromising efficiency, resolving the contradiction through adaptive parameter changes.
Data Source
AI summary
A system and method for controlling a hybrid vehicle having an engine and a traction motor include operating the engine at an operating point selected based on system efficiency, operating the electric machine to provide an electric machine torque responsive to a difference between a driver demand torque and the engine torque associated with the operating point, and limiting a rate of change of the electric machine torque in response to a rate of change of the driver demand torque. The electric machine torque rate limit may vary continuously responsive to the rate of change of driver demand torque and whether the driver demand torque is increasing or decreasing.