Hybrid Motor Speed Mapping for Engine Power Demand
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Solution Overview
Problem
In hybrid electric vehicles, converting driver torque demand to power demand is challenging at zero or near-zero vehicle speeds, leading to potential excess engine power production and battery overcharging, which can cause vehicle shutdown or degrade acceleration performance.
Innovation Solution
A controller and method that maps motor speed properly using a modified non-zero speed to determine power demand, avoiding excess power production and ensuring optimal system efficiency and performance by introducing a hysteresis feature near zero motor speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If motor speed is mapped to zero or near-zero values at low vehicle speeds, then the control algorithm computes power demand based on actual motor speed, but this leads to excess engine power production and battery overcharging
Solution Approach 1:
The patent modifies the motor speed parameter itself by introducing a minimum threshold speed value. When the actual motor speed falls below this threshold, the controller uses the threshold value instead of the actual speed for power demand calculations. This parameter modification prevents the computation of excessively low power demands that would otherwise cause the engine to produce more power than needed, thereby resolving the contradiction between measurement accuracy and power production control.
Solution Approach 2:
The patent introduces an intermediary control layer between the motor speed measurement and the power demand calculation. This intermediary is the speed mapping function with threshold enforcement, which acts as a mediator to translate the actual motor speed into a controlled speed value for computation purposes. This intermediary prevents direct transmission of zero or near-zero speed values that would lead to problematic power demand calculations, thus resolving the contradiction without sacrificing essential measurement information.
2Power
If motor speed is mapped to non-zero values to prevent excess power production, then engine power is better controlled, but this may degrade acceleration performance when vehicle is rolling backward
Solution Approach 1:
The patent implements a dynamic threshold enforcement mechanism that adapts to the current operating state of the vehicle. The controller evaluates whether the vehicle is in a rollback condition and adjusts the speed mapping accordingly. When rollback is detected, the system allows different speed mapping behavior compared to normal operation, thereby dynamically optimizing both engine power control and acceleration performance based on real-time vehicle state.
Solution Approach 2:
The patent incorporates feedback from vehicle state sensors to determine whether the vehicle is rolling backward. This feedback mechanism allows the controller to distinguish between normal low-speed operation and rollback conditions, and to adjust the motor speed mapping strategy accordingly. The feedback loop ensures that acceleration performance is maintained during rollback while still preventing excess power production during normal operation, resolving the contradiction through state-dependent control.
3Device complexity
If standard motor speed mapping is used without modification, then the control algorithm is simpler, but this causes battery overcharging and vehicle shutdown
Solution Approach 1:
The patent applies preliminary action by pre-defining threshold values for motor speed before the power demand calculation is performed. This threshold enforcement is built into the speed mapping function that is called during normal control operations. By preparing and enforcing these thresholds in advance, the system prevents battery overcharging conditions without requiring complex real-time decision-making or additional control logic, thus maintaining algorithm simplicity while improving reliability.
Data Source
AI summary
A controller and a control method is disclosed for determining a power demand for an engine in a hybrid electric vehicle powertrain. In computing engine power demand, a modified motor speed is used at zero and near-zero actual motor speeds to satisfy a driver demand for vehicle traction wheel torque.