Automatic Transmission Controller Downshift Logic
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Solution Overview
Problem
Existing automatic transmission systems in manual mode experience discomfort due to immediate auto upshifts following downshifts, causing busy shifting sensations for drivers.
Innovation Solution
A speed change control device that includes a controller for automatic transmissions, which upshifts gears when the input shaft rotation speed exceeds a predetermined high speed, determines if a downshift request exists, calculates the post-downshift rotation speed, and performs a downshift to a gear position where the input shaft rotation speed is below a set limit, preventing immediate auto upshifts and reducing gear position changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If auto upshift function is maintained to prevent excessive engine rotation speed, then engine protection is improved, but driver comfort deteriorates due to immediate upshifts following downshifts
Solution Approach 1:
The controller performs preliminary calculation of the input shaft rotation speed after downshift before actually executing the downshift. By predicting the post-downshift rotation speed in advance and comparing it with the rotation speed limit value, the system prevents downshifts that would lead to immediate auto upshifts, thus avoiding shift busyness while maintaining engine protection.
Solution Approach 2:
The system uses feedback from the calculated input shaft rotation speed to control the downshift operation. The controller continuously monitors the relationship between current gear position, input shaft rotation speed, and the calculated post-downshift rotation speed, adjusting downshift execution based on whether the calculated speed exceeds the rotation speed limit value.
2Speed
If downshift is executed immediately upon driver request in manual mode, then responsiveness to driver input is improved, but shift busyness increases causing driver discomfort
Solution Approach 1:
Before executing the downshift, the controller performs preliminary calculation of the input shaft rotation speed that would result from the downshift. This preliminary action allows the system to predict whether the downshift would cause immediate auto upshift and prevent it in advance, maintaining responsiveness while avoiding shift busyness.
Solution Approach 2:
The system applies preliminary anti-action by preventing the downshift when the calculated input shaft rotation speed after downshift would exceed the rotation speed limit value. This preemptive prevention stops the harmful sequence of immediate downshift followed by immediate auto upshift before it can occur.
Data Source
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AI summary
A speed change control device for an automatic transmission according to this invention determines whether or not a request to downshift a gear position of the transmission exists during traveling in a manual speed change mode (S1, S2), and calculates an input shaft rotation speed of the transmission following a downshift based on the downshift request (S4). When it is determined that the calculated rotation speed is higher than a rotation speed limit value (S5), the speed change control device performs a downshift to a gear position at which the input shaft rotation speed of the transmission is lower than the calculated rotation speed (S6, S8).