Hybrid Powertrain Shift Hunting Control via Electric Torque Assist
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Solution Overview
Problem
Automatic transmissions in hybrid electric vehicles experience shift hunting when driving on grades, leading to excessive upshifting and downshifting, which causes difficulty in maintaining constant speed and reduces fuel efficiency.
Innovation Solution
The powertrain method involves using an electric machine to increase wheel torque when ascending a grade, allowing the transmission to remain in a higher gear by combining engine and electric motor torque, thereby preventing cyclic shifts and maintaining desired vehicle speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the transmission follows the calibrated shift schedule on grades, then the vehicle can maintain speed on level ground, but shift hunting occurs causing excessive upshifting and downshifting
Solution Approach 1:
The control system predicts future gear shift requirements based on current vehicle state and grade conditions, executing preliminary adjustments to prevent shift hunting before it occurs. The system calculates predicted vehicle speed and gear shift timing in advance, allowing proactive rather than reactive gear management.
Solution Approach 2:
The shift schedule is made dynamic by continuously adjusting gear selection based on real-time vehicle conditions including actual speed, grade slope, and accelerator pedal position. Rather than following a fixed calibration, the system adapts gear shifts dynamically to match actual driving conditions, preventing the cyclic upshift-downshift behavior characteristic of shift hunting.
2Speed
If the transmission downshifts to maintain speed on grades, then vehicle speed can be maintained, but fuel economy deteriorates due to remaining in lower gear
Solution Approach 1:
The system predicts when speed maintenance will be needed on grades and prepares the transmission in advance. By calculating the vehicle's momentum and the grade's impact on speed, the system can maintain higher gears longer while still preventing speed loss, thereby improving fuel economy without sacrificing speed maintenance capability.
Solution Approach 2:
The control system modifies the shift schedule parameters specifically for grade conditions, adjusting the thresholds for upshifts and downshifts based on detected grade slope. This allows the transmission to operate in higher gears during grade climbing than would be permitted by the standard calibration, reducing fuel consumption while maintaining adequate speed control.
3Use of energy by moving object
If the transmission upshifts close to tractive effort crossovers, then fuel economy improves, but the transmission becomes perceived as unresponsive when inhibiting upshifts to prevent shift hunting
Solution Approach 1:
The system continuously monitors vehicle speed, grade conditions, and accelerator pedal position to detect the onset of shift hunting. When shift hunting is detected or predicted, the system provides feedback to the transmission control to inhibit further upshifts that would trigger the hunting cycle. This feedback mechanism maintains perceived responsiveness by preventing the cyclic behavior that drivers find unsettling.
Solution Approach 2:
The system predicts potential shift hunting conditions before they occur and takes preliminary action to prevent upshifts that would trigger the hunting cycle. By anticipating the problem rather than reacting to it, the system maintains smooth, responsive operation while preserving fuel economy benefits from higher gear operation.
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 prevents shift hunting, enhances fuel economy by maintaining operation in higher gears, and provides a responsive driving experience by adapting to increased road load without unnecessary gear changes.
Implementation Method 1
an electric machine for transmitting power to at least some of the vehicle wheels
Data Source
AI summary
In a powertrain for a motor vehicle that includes an engine, a transmission driveably connected to the engine and wheels of the vehicle, an electric machine for transmitting power to at least some of the vehicle wheels, a method for controlling the powertrain includes operating the engine and transmission to produce a wheel torque at a desired vehicle speed with the transmission operating in a desired gear in response to a demanded wheel torque, increasing the demanded wheel torque due to the vehicle ascending a grade, determining a magnitude of wheel torque able to be produced in the desired gear, using the electric motor to provide a second wheel torque in combination with wheel torque whose magnitude is equal to or greater than the wheel torque being produced in the desired gear, and continuing to operate the transmission in the desired gear.