Transmission Latch Valve Torque-Aware De-Latch Control
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Solution Overview
Problem
The existing automatic transmission control systems face challenges in smoothly transitioning between clutch states during shifts, leading to issues like engine flare or tie-up, due to the slow de-latch state transition of the latch valve, which affects the coordination of torque capacity between shift elements and engine torque.
Innovation Solution
A latch valve design with a spool that moves between latched and de-latched positions, controlled by a controller that commands pressure changes based on transmission input torque, including a rapid de-latch procedure at high torque, direct de-latch at moderate torque, and undershoot avoidance at low torque, to ensure smooth clutch release and prevent torque disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the latch valve transitions slowly from latched to de-latched state, then the system maintains stability, but the shift smoothness deteriorates causing engine flare or tie-up
Solution Approach 1:
The controller commands the control pressure to decrease below the latch pressure before the spool actually transitions to the de-latched position. This preliminary pressure reduction ensures that when the spool does transition, the clutch apply pressure is already reduced, preventing sudden torque changes and ensuring smooth shifts.
Solution Approach 2:
The system uses feedback from the spool position and pressure sensors to dynamically adjust the control pressure commands. The controller monitors the de-latch transition progress and adjusts the control pressure in real-time to maintain optimal clutch apply pressure throughout the transition, preventing both engine flare and tie-up conditions.
2Speed
If the controller reduces control pressure quickly to enable rapid de-latch, then shift speed improves, but clutch slip occurs causing torque disturbance
Solution Approach 1:
The controller proactively reduces control pressure below latch pressure before the spool transition begins, pre-positioning the clutch apply pressure at an appropriate level. This preliminary action prevents clutch slip during the transition by ensuring pressure is already reduced when the spool moves, eliminating torque disturbances while maintaining rapid transition speed.
Solution Approach 2:
The system dynamically changes the control pressure parameter from above latch pressure (latched state) to below latch pressure (de-latched state) in a controlled manner. By adjusting the control pressure to specific target values based on the transition phase, the system maintains reliable clutch torque control throughout the rapid de-latch transition, preventing both slip and tie-up conditions.
3Stability of the object's composition
If the latch pressure is set high to ensure reliable latching, then the latched state stability improves, but the de-latch transition time increases
Solution Approach 1:
The controller commands control pressure reduction before the spool transition begins, preparing the system for rapid de-latching. This preliminary pressure reduction creates a larger pressure differential that accelerates spool movement while maintaining latched state stability during normal operation, thereby reducing de-latch transition time without compromising latching reliability.
Solution Approach 2:
The system dynamically adjusts control pressure based on the desired state. During normal operation, high latch pressure ensures stable latching. During de-latch transitions, the controller dynamically reduces control pressure below latch pressure to accelerate spool movement. This dynamic parameter adjustment maintains stability when needed while enabling rapid transitions when required.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables rapid and controlled transitions of the latch valve, improving shift smoothness and preventing torque disturbances, thus enhancing the coordination of torque capacity during transmission shifts.
Implementation Method 1
pressure between the second and third lands bias the spool toward the latched position
Implementation Method 2
The latch valve may also include a return spring biasing the spool toward the de-latched position
Implementation Method 3
Fluid from the circuit may be routed to a piston apply chamber of a clutch causing the piston to exert a force related to the fluid pressure
Data Source
AI summary
A transmission includes a latch valve with latched and de-latched states. In the de-latched state, the latch valve directs a control pressure to a clutch apply circuit. In the latched state, which is entered in response to a control pressure higher than a latch pressure, the latch valve directs a line pressure to the clutch apply circuit. A controller manages the transition from latched to de-latched differently depending upon the transmission input torque and gear state. At high transmission input torque, the controller first reduces the control pressure to rapidly accelerate a spool in the latch valve, and then increases the control pressure to prevent clutch slip. At low torque, the controller reduced the pressure to an intermediate value during the transition and then reduces it again. At moderate torques, the controller reduces the pressure directly to a target pressure in a single step.