Park Mechanism Spring Biasing for Reliable Engagement
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Solution Overview
Problem
Existing park mechanisms in automatic transmissions face challenges in reliably engaging and disengaging the park position, especially when the vehicle is in motion, which can lead to high stresses on system components and potential failures, particularly in park-by-wire systems where hydraulic pressure can fail.
Innovation Solution
A park mechanism comprising a housing, a park gear, a pawl, a rod, a cam, and springs, where the pawl is biased to engage the park gear by a spring and an actuator, ensuring engagement without hydraulic pressure, and a cam mechanism that holds the pawl in place, allowing disengagement when the rod moves to the no-park position, preventing vehicle movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If hydraulic pressure is used to engage the park mechanism, then the engagement force is sufficient, but the system reliability decreases when hydraulic pressure fails
Solution Approach 1:
The patent replaces the hydraulic actuation system with a purely mechanical spring-loaded pawl mechanism. The spring provides continuous engagement force on the pawl, which mechanically engages with the park gear teeth. This eliminates hydraulic pressure dependency while maintaining sufficient engagement force through the spring's mechanical properties.
Solution Approach 2:
The spring mechanism is self-actuating and requires no external energy source or control system. The spring automatically maintains the pawl in the engaged position through its stored elastic energy, and the mechanical linkage automatically disengages the pawl when the output shaft rotates, providing fail-safe operation without hydraulic pressure or electronic controls.
2Reliability
If the park mechanism is mechanically linked to the shift selector, then the engagement is reliable, but the device complexity increases
Solution Approach 1:
The patent extracts and eliminates the complex mechanical linkage between the shift selector and park mechanism. Instead of using a mechanical connection, the invention uses a simple rod that responds to output shaft rotation to automatically control the cam and pawl engagement, simplifying the overall system architecture while maintaining reliable park engagement.
Solution Approach 2:
The rod serves multiple functions: it transmits the disengagement command from the shift selector, controls the cam position, and thereby controls the pawl engagement state. This multi-functional component replaces what would otherwise require multiple separate mechanical linkages, reducing system complexity.
3Reliability
If the pawl is biased by spring and actuator, then the engagement is secure without hydraulic pressure, but the device complexity increases
Solution Approach 1:
The patent merges the spring biasing mechanism with the actuator into a single integrated assembly. The spring is positioned to directly bias the pawl toward the engaged position, while the actuator simply needs to overcome this spring force to disengage the pawl. This integration reduces the number of separate components and simplifies the overall actuation system.
Solution Approach 2:
The spring provides a continuous counteracting force that balances the engagement requirements. By pre-loading the spring to provide the necessary engagement force, the actuator only needs to apply force in the opposite direction to disengage, rather than needing to generate the full engagement force itself. This reduces actuator complexity and size.
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 mechanism effectively prevents vehicle movement by engaging the park gear even without hydraulic pressure, reducing stress on components and ensuring safe parking, while allowing disengagement for vehicle movement, thus enhancing reliability and safety.
Implementation Method 1
A spring reacts against the housing biasing the cam toward the extended position and biasing the rod toward the park position. The spring may be a coil spring with the rod extending through the spring.
Implementation Method 2
The cam is supported to slide axially with respect to the rod between an extended position and a retracted position. Whenever the rod is in the park position with the cam in the extended position, the cam holds the pawl in the engaged position.
Data Source
AI summary
A park-by-wire system uses a single spring to bias the system towards park and to permit a ratcheting feature which delays the engagement of park until vehicle speed drops below a threshold. A cam slides with respect to a rod. A stop on the rod limits travel in one direction. The spring biases the cam toward the stop but compresses as necessary to allow the cam to move during ratcheting operation. The spring reacts against the housing. Acting through the cam and the stop, the spring biases the rod toward the park position. The design limits the number of components that move during ratcheting operation. Specifically, the rod and actuator do not oscillate during ratcheting operation.