Automatic Transmission Skip Downshift Controller
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Solution Overview
Problem
Existing automatic transmission systems face challenges in performing skip downshifts efficiently, leading to potential shock during gear engagement due to rapid rotation speed increases, especially in hybrid vehicles where the input shaft inertia is higher.
Innovation Solution
A controller for an automatic transmission that disengages multiple engagement elements to quickly increase the input shaft rotation speed, forming an intermediate gear stage with a lower transmission ratio, and then engages the necessary elements to complete the skip downshift, thereby moderating the rotation speed increase and reducing shock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the increase rate of the rotation speed of the input shaft is increased to shorten the skip downshift time, then the shifting time is reduced, but shock occurs when the engagement elements are engaged to complete the shifting
Solution Approach 1:
The skip downshift process is segmented into multiple phases: first disengaging engagement elements to enter neutral state, then forming an intermediate gear stage with a lower transmission ratio than the post-shifting gear stage, and finally completing the shift to the target gear stage. This segmentation allows the rotation speed increase to be controlled in stages, reducing shock while maintaining short overall shifting time.
Solution Approach 2:
An intermediate gear stage is introduced as a mediator between the pre-shifting and post-shifting gear stages. This intermediate stage has a transmission ratio that is lower than the post-shifting gear stage, allowing the input shaft rotation speed to be increased to an intermediate synchronized rotation speed before the final engagement. This intermediary state prevents direct high-speed engagement that would cause shock.
2Speed
If the engagement elements are disengaged to quickly increase the input shaft rotation speed, then the shifting speed is improved, but the engagement elements experience higher stress during the subsequent engagement
Solution Approach 1:
The engagement elements are prepared in advance by disengaging them before the rotation speed increase begins. This preliminary disengagement allows the input shaft rotation speed to be increased without the constraint of engaged elements, and the elements are re-engaged only when the rotation speed reaches the appropriate synchronized level, reducing stress during engagement.
Solution Approach 2:
The transmission ratio parameter is changed in stages through the intermediate gear stage. By first establishing an intermediate gear stage with a lower transmission ratio than the final gear stage, the system allows the input shaft rotation speed to increase to an intermediate synchronized rotation speed, thereby reducing the stress parameter during the final engagement of the post-shifting gear stage.
3Productivity
If a skip downshift shifts two or more gear stages through a single operation, then the productivity of the transmission system is improved, but the control complexity increases
Solution Approach 1:
The control process is segmented into distinct sequential steps: disengaging engagement elements, forming an intermediate gear stage, and completing the final engagement. This segmentation of the control process makes the complex skip downshift operation more manageable and controllable, reducing control complexity while maintaining high shifting efficiency.
Solution Approach 2:
The engagement elements are temporarily discarded (disengaged) to allow rapid rotation speed increase, then recovered (re-engaged) in a controlled manner after the intermediate gear stage is formed. This temporary discarding and recovering of engagement elements enables the skip downshift to achieve high productivity while the controlled recovery process manages the complexity of the operation.
Data Source
AI summary
When starting a skip downshift, a controller for an automatic transmission disengages two or more engagement elements that are in an engaged state. The disengaging two or more engagement elements includes setting a first engagement element, which is one of the two or more engagement elements that are disengaged and is used to form an intermediate gear stage having a lower transmission ratio than a post-shifting gear stage, to an engagement preparation state that maintains a state immediately before the engaged state. Subsequently, the controller engages a second engagement element, which is used to form both the intermediate gear stage and the post-shifting gear stage, and temporarily increases engagement pressure of the first engagement element. The controller disengages the first engagement element and engages a third engagement element, which is used to form the post-shifting gear stage, to form the post-shifting gear stage.