Transmission Downshift Control Using Measured Output Torque
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing automatic transmission systems fail to effectively detect and prevent neutral and tie-up states during coasting downshifts, leading to shift shocks and unpredictable drive torque, as they rely primarily on speed measurements and open-loop pressure adjustments that are not adaptable to varying clutch friction torques and hydraulic system variability.
Innovation Solution
A closed-loop control method that computes changes in output torque and input speed to adjust off-going and on-coming clutch pressures, using direct torque measurements to maintain output torque within predetermined limits and fully engage the on-coming element, while adjusting clutch pressures based on turbine speed dips to prevent tie-up states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If open-loop pressure control is used for off-going and on-coming clutches, then the control system is simple, but the system cannot adapt to varying clutch friction torques and hydraulic variability causing neutral or tie-up states
Solution Approach 1:
The patent implements closed-loop feedback control by measuring output torque with a torque sensor and using this measurement to dynamically adjust clutch control pressures. The controller continuously monitors actual output torque and modifies off-going and on-coming clutch pressures in real-time to maintain torque within acceptable ranges, preventing neutral and tie-up states during coasting downshifts.
Solution Approach 2:
The system dynamically changes control parameters (clutch pressures) based on measured output torque. The controller adjusts pressure profiles adaptively during the downshift event, modifying timing and magnitude of pressure changes to account for varying clutch friction characteristics and hydraulic system variability under different operating conditions.
2Difficulty of detecting and measuring
If speed sensors are used to detect tie-up state, then detection is possible, but the neutral state cannot be detected or corrected
Solution Approach 1:
The patent replaces speed-based mechanical sensing with direct torque measurement using a torque sensor. This substitution allows the system to directly measure the physical quantity (torque) that defines neutral and tie-up states, providing explicit detection of both conditions that speed sensors cannot distinguish.
Solution Approach 2:
The torque sensor acts as an intermediary that provides direct information about the torque state during downshift. By measuring output torque directly, the sensor serves as a mediator between the clutch engagement process and the controller, enabling precise detection and correction of both neutral and tie-up states through torque-based feedback.
3Reliability
If adaptive open-loop pressure adjustments are made, then tie-up state detection is improved, but the system cannot control the amount of dropped drive torque during coasting downshift
Solution Approach 1:
The closed-loop torque feedback control enables the system to not only detect tie-up states but also precisely control the amount of drive torque during coasting downshift. The controller uses measured output torque to continuously adjust clutch pressures, maintaining torque within a target range and preventing excessive torque drop that would cause shift shocks.
Data Source
AI summary
A downshift control method during a coasting drive condition includes computing changes in output torque and input speed from initial output torque and initial input speed; reducing offgoing element pressure, provided a change in input speed exceeds a reference input speed change; using closed loop control based on output torque and a change in measured output torque to adjust oncoming element pressure such that output torque remains between predetermined maximum and minimum torques; and fully engaging the oncoming element.