Transmission Park Valve Spool Segmentation
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Solution Overview
Problem
Existing hydraulic control systems for automatic transmissions face issues with reliable engagement and disengagement of the parking pawl, particularly in scenarios where the transmission may override driver selection, leading to unintended vehicle movement or power consumption during extended unattended periods.
Innovation Solution
The system incorporates a park valve with first and second spools, a compression spring, a pin, and a solenoid, which allows for precise control of the parking pawl engagement and disengagement through hydraulic circuits and line pressure management, ensuring the pawl remains engaged without power consumption and can be reliably disengaged when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the parking pawl is engaged using a simple hydraulic control system, then the engagement mechanism is simple, but the reliability of engagement and disengagement is insufficient
Solution Approach 1:
The hydraulic control system is segmented into multiple independent spools (first spool for park engagement, second spool for line pressure control) with separate control circuits. This segmentation allows each spool to perform its specific function reliably without interfering with the other, improving overall system reliability while maintaining manageable complexity through functional decomposition
Solution Approach 2:
A pin mechanism acts as an intermediary between the solenoid and the first spool. The pin translates the solenoid's linear motion into precise spool positioning, ensuring reliable engagement and disengagement of the parking pawl. This intermediary component bridges the electrical control signal and the hydraulic action, enhancing reliability through controlled mechanical interaction
2Reliability
If the parking pawl remains engaged during extended unattended periods, then the vehicle remains secured, but power is consumed to maintain engagement
Solution Approach 1:
The first spool is designed with a spring bias that automatically maintains park engagement without requiring continuous electrical power. Once engaged, the hydraulic system's mechanical spring forces hold the spool in position, making the system self-sustaining during unattended periods. The solenoid only consumes power during transition phases, not during extended park maintenance
Solution Approach 2:
The solenoid operates periodically only during engagement and disengagement transitions rather than continuously. The hydraulic system uses stored energy in springs and fluid pressure to maintain state between transitions, creating a periodic control pattern that reduces overall power consumption while maintaining vehicle security
3Speed
If the parking pawl is disengaged quickly, then the response time is fast, but sudden jerks occur during gear ratio transitions
Solution Approach 1:
The second spool is activated in advance to prepare the line pressure circuit before the first spool completes its disengagement motion. By pre-adjusting hydraulic pressure conditions, the system smooths the transition process and prevents sudden jerks while maintaining fast overall disengagement response. This preliminary action coordinates pressure management with mechanical motion
Solution Approach 2:
The hydraulic control system dynamically adjusts line pressure during the disengagement process through coordinated spool motion. The second spool modulates pressure in response to the first spool's position, creating a dynamic pressure profile that enables fast disengagement while suppressing harmful vibrations and jerks through real-time pressure optimization
4Reliability
If the transmission overrides driver selection to engage park, then vehicle safety is improved, but driver control is reduced
Solution Approach 1:
The hydraulic control system incorporates feedback mechanisms through pressure sensors and spool position detection that monitor actual park engagement conditions. When override conditions are detected (such as unintended vehicle movement), the system provides feedback to the control logic to activate the solenoid and adjust spool position, restoring safe park engagement while logging the event for driver awareness
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
This solution provides secure and power-efficient engagement and disengagement of the parking pawl, preventing unintended vehicle movement and reducing power consumption, while allowing for smooth transitions between gear ratios without sudden jerks.
Implementation Method 1
The solenoid pulls the pin away from the first spool
Implementation Method 2
The compression spring separates the first spool from the second spool, biasing the first spool toward the first position and biasing the second spool toward the fourth position
Implementation Method 3
The line pressure circuit biases the first spool toward the first position. The first and second hydraulic circuits bias the second spool toward the third position
Data Source
AI summary
A transmission includes a hydraulically actuated park valve with two spools in a common housing. One of the spools engages and disengages the park mechanism in response to manipulation of line pressure and engagement of specified shift elements. A pin selectively engages this spool to hold it in position. The valve is designed such that friction holds the spool in position in the absence of hydraulic pressure or electric power. The second spool controls an out-of-park circuit such that the park mechanism remains disengaged when desired. The two spools are separated by a compression spring.