Automatic Transmission Downshift Control via Engine Output Synchronization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing automatic transmission systems face challenges in smoothly downshifting due to delays in friction element engagement/disengagement, leading to gear shift shocks and inefficiencies in engine brake application, particularly when downshifting on steep slopes, as the timing for throttle valve opening and engine output increase control is often misaligned with the hydraulic pressure and vehicle operational states.
Innovation Solution
A control device and method for automatic transmissions that includes a hydraulic pressure control system, a downshift control mechanism, and an engine output increase control system, which performs a preliminary output increase followed by a main output increase during downshifts, allowing for precise control of throttle opening degrees in two stages to synchronize engine output with gear shifts, reducing shift shocks and improving deceleration performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the throttle valve is closed to apply engine brake during downshift, then the engine brake force is improved, but the gear shift time is prolonged and shift shock occurs
Solution Approach 1:
The control device preliminarily increases engine output by controlling the throttle valve before the downshift is completed, preparing the engine rotational speed in advance. This preliminary action ensures that when the friction elements engage/disengage, the engine speed is already close to the target, reducing the actual gear shift time and minimizing shift shock while maintaining sufficient engine brake force.
Solution Approach 2:
The system dynamically adjusts the throttle valve opening degree based on real-time detection of hydraulic pressure and gear shift progress. During downshift, the throttle opening is controlled to increase engine output at appropriate rates, making the engine brake application dynamic and adaptive rather than static, thereby optimizing both brake force and shift speed.
2Loss of time
If the throttle valve opening degree is controlled to increase engine output, then the gear shift time is shortened, but the shift shock is increased
Solution Approach 1:
The system performs preliminary engine output increase before the main downshift engagement, gradually raising engine rotational speed in advance. This preliminary action reduces the speed differential that would otherwise cause shock during the actual gear engagement, allowing faster shifts without increasing shock.
Solution Approach 2:
The throttle valve control is implemented in periodic stages: first a preliminary increase phase, then a main increase phase, and finally a stabilization phase. This periodic control of engine output ensures smooth transitions and prevents abrupt changes that would cause shift shock, while still achieving short gear shift times.
3Device complexity
If timer-based control is used for engine output increase, then the control logic is simplified, but the synchronization with hydraulic pressure and vehicle state is inaccurate
Solution Approach 1:
The control device continuously detects hydraulic pressure in the hydraulic control circuit and vehicle operational states, using this feedback to dynamically adjust the throttle valve opening degree. This feedback mechanism ensures precise synchronization of engine output increase with the actual gear shift process and hydraulic pressure changes, achieving accurate control without overly complex logic.
Data Source
AI summary
A hydraulic pressure of each corresponding one of a plurality of friction elements of a gear shift mechanism of the automatic transmission is controlled to downshift the gear shift mechanism from a current gear stage to a next gear stage, at which an engine brake is operated, upon receiving a driver's demand for deceleration. An engine output of the engine is increased by increasing a throttle opening degree of the engine in at least two steps in an absence of a driver's operation on an accelerator of the vehicle at the time of the downshifting of the gear shift mechanism from the current gear stage to the next gear stage.