Power Transfer Unit Axial Offset Absorption
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Solution Overview
Problem
Power transfer units in four-wheel-drive vehicles face challenges in designing compact structures that absorb axial offsets between shafts without causing eccentric or precessional motion, which can lead to vibration and increased load on oil seals.
Innovation Solution
A power transfer unit design featuring a casing with multiple shafts and bearings that absorb offset through bevel and pinion gears, preventing eccentric motion and allowing for a more compact installation by ensuring firm support and alignment of shafts within the unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If shafts are elongated to meet design requirements and absorb offsets, then the power transfer unit can accommodate shaft misalignment, but shaft eccentric motion and precessional motion occur causing vibration and increased load on oil seals
Solution Approach 1:
The power transfer unit is divided into modular components: a casing containing a differential mechanism, an input shaft assembly, and an output shaft assembly. This segmentation allows each module to be optimized independently for handling offset while maintaining overall stability.
Solution Approach 2:
The differential mechanism acts as an intermediary between the input and output shafts, accommodating axial offsets through its internal gear geometry while preventing direct transmission of eccentric motion between shafts.
2Volume of moving object
If the power transfer unit is installed in a relatively small space among other devices, then space utilization is improved, but the design freedom is restricted and shaft support becomes more difficult
Solution Approach 1:
The bearing support structures are merged with the casing walls, eliminating the need for separate support brackets or mounting structures. This integration reduces the overall unit volume while simplifying the shaft support system.
Solution Approach 2:
Bearings are positioned at different axial locations along the shafts rather than concentrating support at single points. This distributed support arrangement fits within compact spaces while maintaining shaft stability.
3Reliability
If bearings are positioned to support long shafts, then shaft support is improved, but the unit size increases and installation freedom is reduced
Solution Approach 1:
The casing incorporates localized bearing mounting features at specific positions along its length, providing shaft support only where structurally necessary rather than along the entire shaft length. This minimizes the unit's overall length while ensuring adequate support.
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 design effectively absorbs large axial offsets, reduces the likelihood of shaft motion-induced vibrations, and allows for a more compact and stable power transfer unit installation, enhancing the freedom of design in constrained spaces.
Implementation Method 1
the second shaft comprising a bevel gear; and a third shaft being rotatably supported by the casing and extending in a direction distinct from the first shaft and the second shaft, the third shaft comprising an internal end including a pinion gear in mesh with the bevel gear
Implementation Method 2
a first shaft being rotatably supported by a first bearing sitting on the first side of the casing and a second bearing sitting on the second side of the casing
Data Source
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AI summary
A power transfer unit for extracting torque from a transmission of an automobile is comprised of: a casing having a first side having a coupling portion for combining with the transmission and a second side opposed to the first side; a first shaft being rotatably supported by a first bearing sitting on the first side of the casing and a second bearing sitting on the second side of the casing, penetrating the casing from the coupling portion to the second side, and combining with the transmission to receive the torque; a second shaft being rotatably supported by a third bearing sitting on the first side of the casing and a fourth bearing sitting on the second side of the casing and gearing with the first shaft to rotate in parallel with the first shaft, the second shaft comprising a bevel gear; and a third shaft being rotatably supported by the casing and extending in a direction distinct from the first shaft and the second shaft, the third shaft comprising an internal end including a pinion gear in mesh with the bevel gear and an external end led out of the casing, wherein the first bearing is disposed closer to the coupling portion than the bevel gear is.