Transmission Park Valve End-Cap Mechanism
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Solution Overview
Problem
Existing hydraulic control systems for automatic transmissions face issues with reliably engaging and disengaging the parking pawl, particularly in conditions where the transmission may override driver selection, leading to unintended vehicle movement.
Innovation Solution
A valve system with a spool and end-cap mechanism, supported by springs and check valves, is used to control fluid pressure and mechanically link the spool to the parking pawl, ensuring engagement and disengagement based on fluid pressure changes and relative pressures in clutch apply circuits, preventing hydraulic lock conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional hydraulic control system is used to engage the parking pawl, then the system can control fluid pressure to engage/disengage the pawl, but the system may experience hydraulic lock conditions that prevent reliable engagement
Solution Approach 1:
The hydraulic control system is segmented into multiple independent chambers (first chamber, second chamber, third chamber) with separate fluid pathways. This segmentation prevents hydraulic lock by providing alternative fluid flow paths through check valves, allowing pressure equalization if one pathway becomes blocked.
Solution Approach 2:
Check valves are introduced as intermediary components between the chambers and clutch apply circuits. These check valves mediate fluid flow by allowing pressure equalization in one direction while preventing backflow, thereby preventing hydraulic lock conditions and ensuring reliable parking pawl engagement.
2Reliability
If the parking pawl is engaged using a simple hydraulic system, then the system structure can be simplified, but the system cannot reliably prevent unintended vehicle movement under all conditions
Solution Approach 1:
The system uses dynamic pressure control in multiple chambers to reliably engage and hold the parking pawl. Fluid pressure dynamically adjusts based on operational conditions, ensuring the pawl remains engaged without unintended vehicle movement while maintaining system reliability.
Solution Approach 2:
The hydraulic system incorporates feedback mechanisms through check valves and pressure-dependent spool positioning. The system automatically responds to pressure changes and operational conditions, ensuring reliable parking pawl engagement and preventing unintended vehicle movement without requiring complex external control systems.
3Ease of operation
If the end-cap is held in neutral position by a spring, then the system can maintain a default position, but the spring deformation requires additional chamber volume changes that complicate the hydraulic circuit
Solution Approach 1:
The hydraulic system is divided into multiple chambers with independent fluid pathways. The first chamber controls end-cap position through spring deformation, while the second and third chambers provide separate fluid supply and venting pathways. This segmentation allows the spring mechanism to operate without requiring complex volume changes in a single chamber.
Solution Approach 2:
Check valves serve as intermediaries that decouple the spring mechanism from complex hydraulic volume changes. The check valves allow pressure equalization and fluid flow control without requiring the end-cap chamber to undergo complex volume changes during spool positioning.
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 system effectively engages and disengages the parking pawl reliably, preventing unintended vehicle movement by using fluid pressure and mechanical linkage to control the pawl's position, ensuring it remains engaged without power consumption when parked.
Implementation Method 1
The spring deforms in response to fluid pressure in the first chamber such that the end-cap slides with respect to the bore from the neutral position
Implementation Method 2
The spring may be, for example, a Belleville spring
Implementation Method 3
The spring may deform in response to fluid pressure in the second chamber such that the end-cap slides with respect to the bore from the neutral position
Implementation Method 4
The spring may be, for example, a Belleville spring
Implementation Method 5
A first check valve may alternately fluidly connect the first chamber to a first clutch apply circuit and an out-of-park circuit based on relative pressure between the first clutch apply circuit and the out-of-park circuit
Implementation Method 6
The spool and the bore may define a third chamber continuously fluidly connected to the pressure source such that pressure in the third chamber biases the spool toward the park position
Implementation Method 7
The spring may deform in response to fluid pressure in the fourth chamber such that the end-cap slides with respect to the bore from the neutral position permitting the spool to move from the intermediate position toward the park position
Data Source
AI summary
A park valve includes a slidable end-cap. Under normal circumstances, the end-cap is held in a nominal position by a spring, such as a Belleville spring. The park valve performs a multi-plexing function in which an out-of-park circuit is connected to line pressure when the valve is in an out-of-park position and is vented when the valve is in a park position. In an intermediate position, a hydraulic lock condition may potentially occur. When engaging park, the hydraulic lock condition is prevented by the slidable end-cap.