CVT Discrete Ratio Control for Hybrid Manual Shifting
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Solution Overview
Problem
In hybrid vehicles with electronic continuously-variable transmissions, manual shifting can be challenging when the engine is off, as engine speed is not proportional to vehicle speed, leading to issues in selecting the initial gear during all-electric driving states.
Innovation Solution
A controller operates the continuously variable transmission at one of a predetermined number of discrete ratios of engine speed to vehicle speed, allowing for a change in engine speed by a predetermined amount upon manual shifting, either increasing or decreasing, based on the engine's on or off state, to simulate a step-gear shift experience.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the continuously variable transmission operates in continuous ratio mode, then the transmission is smooth and efficient, but manual shifting does not provide the expected discrete engine speed changes
Solution Approach 1:
The system dynamically switches between continuous ratio mode and discrete ratio mode based on driver input. When manual shifting is requested, the controller temporarily imposes discrete ratio constraints on the CVT, creating a dynamic control mode that adapts to driver expectations while maintaining the underlying continuous variable transmission capability.
Solution Approach 2:
The controller changes the operational parameters of the CVT by selecting from a predetermined set of discrete ratios when manual shifting is requested. This parameter change imposes specific engine speed to vehicle speed ratio constraints, transforming the continuous ratio behavior into discrete step-like transitions that provide the expected manual shifting experience.
2Adaptability or versatility
If the engine speed is not proportional to vehicle speed in hybrid configurations, then the powertrain is flexible and efficient, but selecting initial gear during all-electric driving becomes challenging
Solution Approach 1:
The system pre-establishes a set of predetermined discrete ratios that represent valid engine speed to vehicle speed relationships. When the driver requests manual shifting during all-electric driving, the controller selects from these pre-defined ratios, providing immediate and appropriate gear selection without requiring real-time calculation or driver knowledge of complex powertrain dynamics.
Solution Approach 2:
The predetermined discrete ratios act as an intermediary between the driver's shifting request and the complex hybrid powertrain dynamics. This intermediary layer translates simple driver intent into appropriate engine speed changes, bridging the gap between all-electric driving mode and manual shifting expectations without exposing the driver to the underlying complexity.
3Ease of operation
If the transmission uses virtual gears to simulate step-gear shift, then the shifting feel is improved, but the engine speed change may not meet driver expectations
Solution Approach 1:
The controller segments the continuous ratio range into predetermined discrete ratios, each representing a specific engine speed to vehicle speed relationship. This segmentation ensures that when manual shifting occurs, the engine speed changes by at least a predetermined amount, providing both the step-gear feel and the precise engine speed changes that drivers expect from manual shifting.
Data Source
AI summary
A vehicle includes an engine, a continuously variable transmission, and a controller. The controller, responsive to a request to manually shift the continuously variable transmission and the engine being on, operates the continuously variable transmission atone of a predetermined number of discrete ratios such that a speed of the engine changes by at least a predetermined amount.