Automatic Transmission Downshift Control Using Anticipated Speed
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Solution Overview
Problem
Automatic transmissions in manual mode often refuse downshifts during strong braking, failing to account for vehicle deceleration and resulting in delayed gear changes, which are unsatisfactory for sporty driving.
Innovation Solution
The calculation of predicted engine speed is modified to include anticipated speed based on vehicle deceleration, actual speed, and current gear, allowing downshifts at higher engine speeds by using an anticipated speed value that is lower than the actual instantaneous speed, thus authorizing gear changes prohibited by the static threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the static downgrade authorization threshold is used to control downshifts in manual mode, then the transmission control is simple and reliable, but the driver cannot downshift at high engine speeds during strong deceleration, resulting in poor sporty driving performance
Solution Approach 1:
The system calculates an anticipated engine speed that is lower than the actual instantaneous speed, representing a future state after deceleration. This preliminary calculation allows the control system to authorize downshifts in advance based on the anticipated speed being below the threshold, rather than waiting for the actual speed to drop. The offset between actual and anticipated speed creates a time buffer that compensates for the gear change latency.
Solution Approach 2:
The patent transitions from a static threshold comparison (actual speed vs. fixed threshold) to a dynamic assessment that incorporates vehicle deceleration rate. The anticipated speed is calculated by applying an offset to the actual speed, where the offset magnitude depends on the deceleration rate. This dynamic approach allows the system to adapt to varying driving conditions and driver intentions in real-time.
2Speed
If gear changes are executed immediately when the threshold is met, then the response is fast, but the engine speed after downshift may exceed the maximum threshold, causing unacceptable noise and vibration
Solution Approach 1:
The system performs a preliminary check using the anticipated engine speed (which is lower than actual speed) to authorize downshifts in advance. By the time the actual gear change executes, the vehicle deceleration has reduced the engine speed, so the final speed after downshift falls within the acceptable range, avoiding noise and vibration issues.
Solution Approach 2:
The patent applies a counteracting offset to the actual speed to generate a lower anticipated speed value. This preliminary anti-action compensates for the speed increase that would otherwise occur during downshift, allowing the system to authorize changes that would normally be prohibited by the static threshold.
3Reliability
If the system waits for actual speed to drop below the threshold before authorizing downshift, then the engine speed remains within acceptable limits, but the gear change latency causes poor driving experience during strong braking
Solution Approach 1:
The control system authorizes downshifts in advance by comparing the anticipated engine speed (actual speed minus offset) with the maximum authorized speed. This preliminary authorization based on predicted future state allows the gear change to begin earlier, reducing the perceived latency while ensuring that the final engine speed after downshift will be within acceptable limits.
Data Source
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Figure 2
AI summary
Method for controlling downshifts of an automatic transmission in manual mode, in which the downshift is permitted by comparing a predicted engine speed in gear n‑1, which is calculated as a function of the speed of the vehicle in this gear, against a permitted engine speed threshold, in which method the downshift is authorized if the predicted engine speed is below the authorization threshold and is forbidden if not, characterized in that, during sharp decelerations, the actual value of the speed is replaced in the calculation of predicted engine speed in gear n‑1 by an anticipated value that is a function of: - the deceleration of the vehicle, - the actual speed, and - the current gear.