Hydraulic Transaxle Breather and Casing Design
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Solution Overview
Problem
Conventional hydraulic transaxles with integral swash plates and trunnion shafts are complex, expensive, and require large openings for installation and removal, increasing component counts and installation labor due to the need for separate covers and complex housing configurations.
Innovation Solution
A hydraulic transaxle design featuring a transaxle casing with a detachable upper casing member, a breather hole positioned away from the rotation portion, and inner walls that block fluid droplets and serve as rib members to enhance strength and prevent fluid leakage, allowing for easier installation and reduced component count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the swash plate is formed integrally with trunnion shafts projecting from feet, then the swash plate can be pivotally supported by the transaxle casing, but the swash plate becomes complex in shape and expensive to manufacture
Solution Approach 1:
The swash plate assembly is divided into separate components: the swash plate body and the trunnion shafts are no longer integrally formed. Instead, the trunnion shafts are positioned in holes formed in the transaxle casing, allowing the swash plate to be manufactured separately and assembled, thereby reducing manufacturing complexity and cost while maintaining pivotal support functionality.
2Reliability
If the swash plate is formed integrally with trunnion shafts, then the assembly can be pivotally supported, but a large opening is required in the transaxle casing for installation and removal
Solution Approach 1:
The integral swash plate-trunnion shaft assembly is segmented into separate components. The trunnion shafts are positioned in holes formed in the transaxle casing, allowing the swash plate to be installed and removed independently without requiring a large opening in the casing, thereby simplifying the housing configuration.
3Reliability
If a separate cover is attached to cover the opening and journal the other trunnion shaft, then the opening is sealed, but the number of component parts and installation labor increase
Solution Approach 1:
The functions of the separate cover and the transaxle casing are merged. The transaxle casing itself is configured to seal the opening and provide bearing surfaces for the trunnion shafts, eliminating the need for a separate cover component and reducing the total number of parts and assembly steps.
4Ease of operation
If the breather hole is positioned directly above the rotation portion, then air can flow freely, but fluid droplets can leak from the hole to outside
Solution Approach 1:
An intermediary structure (the transaxle casing with its specific geometry and positioning) is introduced between the breather hole and the rotation portion. The hole is positioned at a location where air can still flow freely through the breather, but the casing structure prevents fluid droplets from reaching the hole, thereby blocking fluid leakage while maintaining air flow capability.
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 simplifies the installation process, reduces labor and costs, and enhances the structural integrity of the transaxle casing by minimizing the number of housing members and preventing fluid leakage through effective breather functionality.
Implementation Method 1
a breather that allows air to flow freely inside and outside the upper casing member and blocks a flow of fluid, attached at the hole
Implementation Method 2
a first inner wall extending downward from the upper surface of the upper casing member, positioned between the part of the rotation portion and the hole
Data Source
AI summary
A transaxle casing has a fluid sump having a gear top cover, an HST, a reduction gear train and at least one axle disposed in the transaxle casing. The gear top cover accommodates a part of a rotation portion of the reduction gear train. An air supply and exhaust hole is disposed on an upper surface of the gear top cover facing an air sump and is arranged at a position different from a point above a bevel gear. A breather is attached at the air supply and exhaust hole, and a first inner wall extending downward from the upper surface of the upper casing member, is positioned between the part of the bevel gear and the air supply and exhaust hole.