Neutral Hold Device for Hydrostatic CVT Trunnion Shaft
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Solution Overview
Problem
The neutral state of hydrostatic continuously variable speed change devices is compromised due to reduced spring force over time and increased hydraulic oil viscosity at lower temperatures, leading to operational stiffness and inability to return to the neutral position.
Innovation Solution
A neutral hold device with a first member having a concave cam and a second member with a cam follower, utilizing a spring and auxiliary urging means to ensure the trunnion shaft returns to the neutral position by generating an auxiliary urging force only when the shaft is near the neutral position, thereby enhancing the urging force without stiffening the speed change operation outside this region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the urging force of the spring is increased to ensure the trunnion shaft returns to the neutral position, then the reliability of neutral position return is improved, but the speed change operation becomes too stiff and operability is reduced
Solution Approach 1:
The urging force application is segmented into two distinct zones: a proximate region near the neutral position where both spring force and auxiliary urging force act, and a distant region where only spring force acts. This segmentation allows the auxiliary urging means to provide additional force only when needed for reliable return, while maintaining light operation stiffness during normal speed change operations.
Solution Approach 2:
The auxiliary urging means applies force locally only in the proximate region of the neutral position, creating a localized increase in urging force where it is most needed. The cam surface geometry is designed so that the auxiliary urging force is generated only when the trunnion shaft is within a specific angular range near the neutral position, leaving the rest of the operating range unaffected.
2Reliability
If the spring force is reduced due to changes over time or increased viscosity of hydraulic oil, then the trunnion shaft can no longer return to the neutral position, but increasing the spring force initially causes operational stiffness
Solution Approach 1:
The auxiliary urging means is designed to activate automatically when the trunnion shaft enters the proximate region of the neutral position, providing preliminary assistance before the shaft reaches the neutral position. This preliminary action ensures that even when spring force is reduced, the shaft receives additional urging force in the critical final approach region, guaranteeing reliable return without requiring increased spring force throughout the entire range.
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
Ensures reliable return to the neutral position despite reduced spring force or increased viscosity, preventing operational inconvenience while maintaining device operability.
Implementation Method 1
a spring for urging the cam follower against the cam so that the trunnion shaft is retained in a neutral position
Implementation Method 2
auxiliary urging means for generating an auxiliary urging force for urging the trunnion shaft toward the neutral position while the trunnion shaft is positioned in a proximate region of the pre-set neutral position
Data Source
AI summary
A neutral hold device for a hydrostatic continuously variable speed change device having a trunnion shaft, comprising a first member which rotates integrally with the trunnion shaft and in which a cam having a concave part is formed; a second member that pivots about a support shaft provided parallel to the trunnion shaft, and that is provided with a cam follower for engaging with the cam; a spring for urging the cam follower against the cam so that the trunnion shaft is retained in a neutral position by the cam follower being positioned in a set position of the cam by the urging of the spring; and auxiliary urging means for generating an auxiliary urging force for urging the trunnion shaft toward the neutral position while the trunnion shaft is positioned in a proximate region of the neutral position set in advance.