Engine Torque Estimation for Low-Temperature ISG Starts
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Solution Overview
Problem
At low ambient temperatures, open loop engine torque estimates are inaccurate, leading to excessive ISG torque output, which can prevent engine starting as the engine speed is reduced to zero, making it difficult to initiate combustion.
Innovation Solution
Estimating engine torque based on engine speed and air flow, and adjusting the electric machine torque accordingly, with a fraction of the estimated torque at low temperatures to prevent engine rotation stoppage and facilitate combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If open loop engine torque estimates are used at low temperatures, then engine torque control is simplified, but the accuracy of torque estimation deteriorates leading to excessive ISG torque output
Solution Approach 1:
The patent applies parameter changes by switching between different torque estimation methods based on engine temperature. At low temperatures, a simplified open-loop estimation is used, while at higher temperatures, a more accurate closed-loop estimation based on actual engine torque is employed. This resolves the contradiction by adapting the estimation accuracy to the operating conditions.
Solution Approach 2:
The patent implements dynamics by dynamically adjusting the torque estimation approach based on real-time temperature conditions. The system transitions from a static simplified estimation to a dynamic adaptive estimation that incorporates actual engine torque feedback when temperature conditions permit, thereby improving accuracy without permanently increasing system complexity.
2Speed
If ISG torque is increased to compensate for high estimated engine torque, then engine speed control is improved, but the engine speed is reduced to zero preventing engine starting
Solution Approach 1:
The patent applies feedback by using actual engine torque measurements to adjust ISG torque output. Instead of relying solely on open-loop estimates that may be inaccurate at low temperatures, the system incorporates feedback from actual engine torque sensors to dynamically adjust the compensating torque, preventing over-compensation that would stop engine rotation.
Solution Approach 2:
The patent implements preliminary anti-action by anticipating the potential harm of excessive ISG torque compensation before it occurs. The system monitors temperature conditions and adjusts the torque estimation approach in advance to prevent the scenario where excessive compensation would reduce engine speed to zero and prevent starting.
3Reliability
If accurate engine torque estimation is achieved at low temperatures, then engine starting reliability is improved, but the complexity of torque control increases
Solution Approach 1:
The patent resolves this contradiction by changing the control parameter approach based on temperature. At low temperatures, the system uses a simplified estimation with appropriate safety margins, while at higher temperatures, it transitions to a more complex but accurate closed-loop estimation. This conditional parameter change improves starting reliability without permanently increasing system complexity.
Data Source
AI summary
A method and system for operating a vehicle that includes an integrated starter/generator and a driveline disconnect clutch is described. In one example, the method estimates engine torque as a function of engine temperature during cold engine starts so that if an estimate of engine torque is in error, the integrated starter/generator may still successfully start the engine.