PTU Disconnect Assembly Split-Spline Design
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Solution Overview
Problem
Existing vehicle power transfer units (PTUs) lack efficient mechanisms for disconnecting and reconnecting shafts to optimize torque transmission in four-wheel drive and all-wheel drive configurations, leading to increased fuel mileage and reduced emissions, but require longer shift distances and higher forces.
Innovation Solution
A PTU disconnect assembly featuring a split-spline design with a collar and cam assembly that reduces shift distances by half, allowing for quicker and easier disconnection and reconnection of shafts, utilizing a rotary cam and cam follower to move the collar between connected and disconnected states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional PTU disconnect mechanism is used, then shaft disconnection is achieved, but shift distance is long and required force is high
Solution Approach 1:
The spline connection is segmented into multiple sections along the axial direction, allowing the collar to disconnect by moving only a portion of the total spline engagement distance. The first and second splines are positioned at different axial locations, enabling staged disengagement that reduces the required shift distance and time.
Solution Approach 2:
The collar is designed to be movable along the axial direction, transitioning dynamically between connected and disconnected positions. This dynamic positioning allows the collar to engage or disengage splines selectively, reducing the time and force required compared to static connection mechanisms.
2Device complexity
If a conventional PTU disconnect mechanism is used, then shaft disconnection is achieved, but the structure is complex and packaging space is large
Solution Approach 1:
The collar integrates multiple functions into a single component: it simultaneously engages with both the first spline on the first shaft and the second spline on the second shaft, and provides both connection and disconnection capabilities. This merging reduces the number of separate parts and simplifies the overall mechanism structure.
Solution Approach 2:
The collar serves multiple purposes: transmitting torque when engaged, enabling disconnection when moved axially, and providing a unified interface for both shaft connections. This multi-functionality eliminates the need for separate disconnect mechanisms, reducing device complexity and packaging requirements.
3Reliability
If splines are continuously engaged, then torque transmission is continuous, but fuel mileage increases and emissions increase
Solution Approach 1:
The spline engagement is made dynamic rather than continuous. The collar can be moved axially to disengage splines when torque transmission is not needed, allowing the drivetrain to operate in a disconnected state that reduces energy loss and improves fuel efficiency, while maintaining the capability for continuous transmission when required.
Data Source
AI summary
A vehicle power transfer unit (PTU) disconnect assembly can include a first shaft, a second shaft, and a collar assembly. The first shaft has a first split-spline at its exterior surface. The second shaft is telescoped over the first shaft and has a set of splines at its exterior surface. A helical gear is carried by the second shaft. The collar assembly is situated around both of the first and second shafts. The collar assembly has a second split-spline at its interior surface.