Virtual Gear Selection for CVT Shift Simulation
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Solution Overview
Problem
Hybrid electric vehicles with continuously variable transmissions lack the ability to simulate the gear ratio shifting experience of step-ratio transmissions, leading to driver expectations not being met in terms of engine speed and torque changes during upshifts and downshifts.
Innovation Solution
A method and system that allow a hybrid-electric vehicle to simulate a step-ratio transmission by selecting virtual gears based on accelerator pedal position and vehicle speed, controlling engine and traction motor speeds to provide noticeable changes in torque and engine speed, mimicking the behavior of a manual transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a continuously variable transmission is used to eliminate shift shock, then ride comfort is improved, but the driver cannot experience the expected engine speed and torque changes during gear shifts
Solution Approach 1:
The system creates virtual gear ratios that copy the characteristic engine speed and torque changes of traditional step-ratio transmissions. The controller calculates and displays virtual gear values that mimic conventional transmission behavior, allowing drivers to experience expected shift characteristics without actual mechanical gear changes.
Solution Approach 2:
The system changes the parameter representation by introducing virtual gear ratios as a new parameter. Instead of relying on physical gear ratio changes, the system uses virtual gear parameters that are calculated based on engine speed, vehicle speed, and acceleration rate to simulate traditional transmission behavior.
2Ease of operation
If virtual gear ratios are simulated in a continuously variable transmission, then driver expectations are met, but the system complexity increases
Solution Approach 1:
The existing controller in the hybrid electric vehicle is enhanced to perform multiple functions: it continues to manage the continuously variable transmission while also calculating virtual gear ratios, processing shift requests, and coordinating engine and motor speeds. This multi-functionality avoids adding separate dedicated systems for virtual gear simulation.
Solution Approach 2:
The system replaces complex mechanical gear shifting mechanisms with electronic control and software calculations. Instead of physical gear changes, the system uses electronic control to adjust engine and motor speeds, substituting mechanical complexity with electronic control logic.
3Object-affected harmful factors
If the transmission does not provide discrete gear ratios, then shift shock is eliminated, but torque multiplication effects are lost
Solution Approach 1:
The system merges the functions of the engine and electric motor to achieve torque multiplication effects. By coordinating the operation of both power sources, the system can simulate the torque multiplication that would normally occur during downshifts in traditional transmissions, combining their outputs to deliver enhanced torque when needed.
Solution Approach 2:
The system uses parameter changes in engine and motor speeds to simulate torque multiplication. When a downshift is requested, the controller adjusts the operating parameters of the engine and motor to create the characteristic torque increase associated with gear downshifts, even though no actual gear change occurs.
Data Source
AI summary
A method of operating a vehicle having a continuously variable transmission to simulate a step-ratio transmission. The method includes increasing an output torque based on a modified accelerator pedal position in response to a corresponding virtual gear selection. An initial virtual gear is determined or selected from a predetermined finite number of available virtual gears based on an accelerator pedal position, a vehicle speed, and whether an upshift or downshift has been requested. The engine speed and engine torque are controlled to meet driver expectations of increased or decreased engine speed or vehicle output torque.