Predictive Regenerative Braking Downshift Control
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Solution Overview
Problem
Regenerative braking efficiency in hybrid and electric vehicles decreases at lower speeds, as the automatic transmission downshift timing is not optimally synchronized with brake application, limiting the electric machine's ability to deliver maximum power and thus affecting fuel economy.
Innovation Solution
The timing of the first regenerative braking downshift in the automatic transmission is adjusted based on predicted brake torque rate and brake pedal input rate, using predictive road grade, vehicle speed, and driver history data to determine the optimal downshift torque and timing, ensuring the electric machine operates in its constant power region for maximum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the transmission downshifts earlier during regenerative braking, then the electric machine speed increases and regenerative braking efficiency improves, but the vehicle may experience unnecessary downshifts or operate outside optimal torque ranges
Solution Approach 1:
The controller predicts future brake pedal input rates using road grade information and driver history before the actual braking event occurs. This preliminary prediction allows the transmission to downshift at the optimal moment, ensuring the electric machine is ready to operate in its constant power region when regenerative braking begins, thereby maximizing energy recovery while maintaining stable motor operation.
Solution Approach 2:
The system continuously monitors actual brake pedal input rates and compares them with predicted values. This feedback mechanism allows the controller to adjust downshift timing in real-time, ensuring that downshifts occur only when they will improve regenerative braking efficiency without causing the electric machine to operate outside its optimal torque range.
2Reliability
If the transmission downshift timing is delayed, then the electric machine operates more stably, but regenerative braking efficiency decreases due to lower electric machine speed
Solution Approach 1:
The controller performs preliminary downshifts based on predicted brake pedal input rates before the actual braking event. By using road grade information and driver history to predict future braking behavior, the system ensures the transmission is already in the optimal gear when regenerative braking begins, allowing the electric machine to immediately operate in its constant power region at high speed and high efficiency.
Solution Approach 2:
The downshift timing is made dynamic and adaptive rather than fixed. The controller continuously adjusts downshift timing based on real-time comparisons between actual and predicted brake pedal input rates, allowing the system to optimize for both electric machine stability and regenerative braking efficiency under varying driving conditions.
3Measurement precision
If predictive algorithms use more data parameters, then downshift timing accuracy improves, but system complexity increases
Solution Approach 1:
The controller leverages existing multi-functional data sources already present in modern vehicles, including road grade information from navigation systems, driver history from telematics, and real-time brake pedal position sensors. By universally utilizing these existing data streams for multiple purposes (route planning, driver behavior analysis, and regenerative braking optimization), the system achieves high downshift timing accuracy without adding dedicated hardware complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances regenerative braking efficiency and fuel economy by ensuring the electric machine operates in its optimal power delivery region, capturing more regenerative energy and improving overall vehicle performance.
Implementation Method 1
kinetic energy of the vehicle is converted to electricity for charging a high voltage battery using an electric machine as a brake and a generator
Data Source
AI summary
A vehicle may include an engine selectively coupled to a motor and a transmission. The vehicle may include a controller configured to, in response to actuation of a brake pedal, command the transmission to downshift during a regenerative braking event based on a regenerative braking downshift torque. The regenerative braking downshift torque may be determined from a predicted brake pedal input rate. The predicted brake pedal input rate may be based on road grade, vehicle headway range and a driver history. The predicted brake pedal input rate may be classified as Low, Medium, or High. The regenerative braking downshift torque may also be determined from a predicted brake torque rate that is based on a predicted deceleration rate of the vehicle, a vehicle speed prediction and a road grade prediction within a future time interval that begins upon actuation of the brake pedal.