Speed-Responsive Mechanical Range Lock for Transfer Case
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Solution Overview
Problem
Existing motor vehicle transfer cases lack a reliable mechanical failsafe mechanism to prevent inadvertent shifting out of desired speed range configurations at high rotational speeds, which can lead to undesirable mode changes during operation.
Innovation Solution
Incorporating a shift sleeve lock that automatically engages at predetermined rotational speeds, using a centrifugal force-responsive mechanism to block axial movement of the shift sleeve, thereby maintaining the transfer case in a desired speed range configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical failsafe mechanism is added to prevent inadvertent shifting at high speeds, then reliability is improved, but device complexity increases
Solution Approach 1:
The lockout mechanism uses dynamic centrifugal force that varies with rotational speed to automatically engage at high speeds and disengage at low speeds. The weights are positioned such that centrifugal force overcomes spring bias at high speed to lock the shift sleeve, while at low speed the spring can overcome centrifugal force to allow shifting. This dynamic response provides automatic speed-dependent protection without complex control systems.
Solution Approach 2:
The mechanism uses the transfer case's own rotational speed to trigger the lockout condition. The centrifugal force generated by the rotating weights directly responds to the operating condition (high speed) and automatically engages the lockout without requiring external sensors, electronic controls, or additional power sources. The system serves itself by using its operational parameter (rotational speed) to activate the protective function.
2Reliability
If electronic sensors and electronic locks are used to prevent mode shifts, then reliability is improved, but cost increases
Solution Approach 1:
The patent replaces electronic sensors, electronic control units, and electronic locks with a purely mechanical centrifugal lockout mechanism. The mechanical weights, springs, and cam-based locking system provide the same protective function as electronic systems but eliminate the need for expensive electronics, sensors, and associated wiring. This mechanical substitution reduces cost while maintaining the reliability function.
3Ease of operation
If the shift sleeve is allowed to move freely at all speeds, then ease of operation is improved, but reliability deteriorates due to inadvertent shifting at high speeds
Solution Approach 1:
The mechanism dynamically adjusts the restrictiveness of shift sleeve movement based on rotational speed. At low speeds, the spring bias allows free movement for normal shifting operations. At high speeds, centrifugal force automatically engages the lockout to prevent inadvertent shifting. This dynamic behavior provides both ease of operation when needed and protection when required.
Solution Approach 2:
The effective stiffness of the locking mechanism changes with rotational speed parameter. At low speed, the spring provides a soft bias that allows movement. At high speed, the centrifugal force parameter changes the balance of forces, causing the cam to engage and effectively increase the stiffness to infinity (complete lockout). This parameter-dependent behavior automatically provides appropriate operation restrictions based on operating conditions.
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 effectively prevents unintended mode shifts at high speeds, ensuring the transfer case remains in the intended configuration, enhancing operational reliability and safety without requiring costly sensors or electronic locks.
Implementation Method 1
a shift sleeve lock automatically engageable with the shift sleeve responsive to the transfer case exceeding a predetermined rotational speed, to prevent axial movement of the shift sleeve above that speed
Data Source
AI summary
A transfer case for a motor vehicle. An input is rotatable about an axis to receive torque, an output is rotatable about the axis to transmit torque, and a planetary gear set is rotatable about the axis and operatively coupled between the input and the output. A shift sleeve circumscribes and is axially slidably carried along the axis, and a shift sleeve lock is automatically engageable with the shift sleeve responsive to the transfer case exceeding a predetermined rotational speed, to prevent axial movement of the shift sleeve above that speed. A related method is also provided.