Hybrid Vehicle Torque Control During Engine Start Faults
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Solution Overview
Problem
In hybrid electric vehicles, engine start faults during transmission downshifts in electric mode can lead to incomplete torque transitions, affecting fuel economy and drivability due to saturated electric machine output torque beyond its constant torque knee point.
Innovation Solution
A controller is implemented to monitor electric machine rotational speed and, upon detecting an engine start fault and saturated output torque, cancels the transmission ratio change, reverses to a previous ratio, and initiates an engine start to ensure smooth powertrain operation in hybrid mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the transmission ratio change is executed during engine start in electric mode, then the transmission downshift can be completed, but the engine start fault causes incomplete torque transitions and affects fuel economy
Solution Approach 1:
The controller detects engine start fault conditions before completing the transmission ratio change and applies preliminary counter-action by canceling the transmission downshift request. This prevents the harmful effect of incomplete torque transitions by stopping the transmission ratio change when engine start fault is detected, thereby maintaining reliable torque delivery while preserving the option to retry the downshift after engine start succeeds
2Productivity
If the transmission ratio change is executed during engine start, then the transmission downshift can be completed, but the electric machine output torque becomes saturated beyond its constant torque knee point
Solution Approach 1:
The controller continuously monitors electric machine rotational speed and compares it against the constant torque knee point threshold. When the electric machine speed exceeds this threshold during transmission downshift, the controller detects torque saturation through feedback and cancels the transmission ratio change request, preventing power loss while maintaining system reliability
Solution Approach 2:
The system dynamically adjusts transmission ratio change execution based on real-time electric machine operating conditions. The controller evaluates whether the electric machine is operating within its constant torque region or beyond the knee point, and dynamically cancels or allows transmission downshift accordingly, optimizing both power delivery and transmission shift completion
3Reliability
If the transmission ratio change is canceled due to engine start fault, then torque transition reliability is maintained, but the transmission downshift is delayed
Solution Approach 1:
The controller prepares for potential transmission downshift cancellation by monitoring engine start status in advance. When engine start fault is detected, the controller has already evaluated the situation and can immediately cancel the transmission ratio change without delay. This preliminary monitoring and evaluation mechanism ensures reliable torque transitions while minimizing time loss through rapid fault detection and response
Data Source
AI summary
A vehicle includes a powertrain having an electric machine operatively coupled to a transmission and selectively coupled to an engine, and a controller. The controller, while operating the powertrain in an electric mode and in response to an accelerator pedal position initiating a transmission ratio change that results in a request to operate the powertrain in a hybrid mode and an engine start fault, outputs a cancellation request to cancel the transmission ratio change.