Automatic Transmission Downshift Control on Deceleration Slopes
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Solution Overview
Problem
Existing speed change control apparatuses for automatic transmissions fail to consider road gradients and reacceleration during downshifting, leading to engine over-revolution and delayed downshifting, which hinders the ability to maintain high engine speeds during deceleration.
Innovation Solution
A speed change control apparatus that selectively switches between automatic and manual modes, using a deceleration detector, gradient acquiring unit, and state transition determining unit to set high-speed downshift allowable revolution numbers based on deceleration rate and road gradient, allowing downshifting only when the engine revolution reaches or falls below this threshold and canceling it upon reacceleration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If downshifting is prohibited in high engine revolution range to suppress engine over-revolution, then engine over-revolution is suppressed, but downshifting execution is delayed causing driver dissatisfaction
Solution Approach 1:
The patent dynamically adjusts the downshift allowable revolution number based on detected deceleration rate and road gradient. During high deceleration on downhill roads, the system raises the allowable revolution threshold, enabling earlier downshifting. This dynamic adjustment resolves the contradiction by adapting the restriction level to actual driving conditions, allowing timely downshifting while preventing engine over-revolution only when necessary.
Solution Approach 2:
The system changes the parameter of downshift allowable revolution number according to deceleration rate and road gradient conditions. By calculating these parameters in real-time and adjusting the threshold accordingly, the system enables downshifting at higher revolutions during high deceleration events, eliminating the time delay while maintaining engine protection under normal conditions.
2Speed
If vehicle decelerates at high rate during downshifting, then downshifting speed increases, but engine revolution number decreases excessively causing difficulty in maintaining desired high engine speed
Solution Approach 1:
The system performs preliminary assessment of deceleration rate and road gradient before permitting downshifting. By detecting these conditions in advance and setting appropriate allowable revolution thresholds, the system prevents excessive engine speed drops that would occur during high-rate deceleration, thereby maintaining desired engine speeds while still enabling rapid downshifting when appropriate.
3Loss of time
If downshift allowable revolution number is set high to enable early downshifting, then downshifting timing is advanced, but engine over-revolution occurs during normal deceleration
Solution Approach 1:
The patent applies different downshift allowable revolution thresholds for different deceleration conditions. During normal deceleration, a conservative threshold prevents engine over-revolution. During high deceleration events on downhill roads, a higher threshold enables timely downshifting. This localized quality adjustment resolves the contradiction by applying appropriate restriction levels to specific operational contexts.
Data Source
AI summary
A speed change control apparatus includes a shifting operation unit, a speed change controller, a deceleration detector, a gradient acquiring unit, and an allowable revolution number setting unit. The speed change controller changes the speed ratio of the automatic transmission on the basis of a shifting operation received by the shifting operation unit. In a case where the shifting operation unit receives a downshift request during deceleration of the vehicle, the allowable revolution number setting unit sets high-speed downshift allowable revolution number on the basis of the deceleration rate of the vehicle detected by the deceleration detector and the road-surface gradient acquired by the allowable revolution number setting unit. The speed change controller executes downshifting in a case where: the shifting operation unit receives the downshift request during the deceleration of the vehicle; and engine revolution number becomes equal to or smaller than the high-speed downshift allowable revolution number.