Oscillating Hydraulic Control Mechanism for Tractor Stepless Transmission
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Solution Overview
Problem
Existing hydrostatic transmission (HST) control mechanisms for tractors face challenges in minimizing the servo unit size, facilitating easy attachment and detachment, and absorbing differential movement between the actuator and trunnion shaft, while avoiding interference with the vehicle body frame and maintaining stability under eccentric loading.
Innovation Solution
A control mechanism with a piston rod, piston, cylinder case, spring, and proportional pressure control valves, where the pivot shaft supports the cylinder case oscillatably, and the spring is aligned coaxially with the piston rod to reduce radial size and facilitate easy attachment, and a mounting part allows for detachment and adjustment of the manipulation lever.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the actuator is disposed at a low position under the step to ensure sufficient vertical gap for connection work, then the facility for connecting and disconnecting the actuator is improved, but the distance between the actuator and the trunnion shaft becomes large, causing large differential movement that requires complex absorption configurations
Solution Approach 1:
A link mechanism is introduced as an intermediary component between the actuator and the trunnion shaft. The link connects the piston rod of the actuator to the arm that rotates on the trunnion shaft, mediating the differential movement between the linear actuator motion and the circular arm rotation. This intermediary structure absorbs the differential movement without requiring complex configurations at the actuator itself.
2Volume of moving object
If the HST is minimized for arrangement in the casing serving as the vehicle body frame, then the compactness and simplicity of the vehicle body frame is improved, but the actuator cannot be easily separated for external attachment on the outside of the casing
Solution Approach 1:
The control mechanism is divided into separate functional segments: the HST unit housed within the casing, and the actuator unit that can be independently attached or detached. The link mechanism serves as a flexible connection segment that bridges these separated components, allowing the actuator to be positioned externally while maintaining functional integration with the minimized HST in the casing.
3Length of stationary object
If a link or arm is used to connect the trunnion shaft to the actuator disposed at low position, then the large vertical gap is bridged, but the structure complexity increases and assembly becomes more difficult
Solution Approach 1:
The link mechanism is designed with dynamic characteristics that allow it to adapt to the differential movement between the linear actuator and the rotating arm. The link can change its orientation and angle during operation, dynamically adjusting to accommodate the large vertical gap and the different motion types without requiring a rigid, complex fixed structure.
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 solution effectively downsizes the servo unit, enhances assemblability, and simplifies attachment and detachment, while maintaining stability and preventing interference with the vehicle body frame, thus improving the overall efficiency and maintenance of the HST system.
Implementation Method 1
a spring adapted to bias the manipulation lever in a neutral direction coaxially with the piston rod
Implementation Method 2
a piston provided on the piston rod coaxially with the piston rod; a cylinder case provided with a cylinder adapted to house the piston rod and the piston such that the piston rod and the piston are displaceable in an axial direction, the piston and the cylinder forming a first fluid chamber to be supplied with a hydraulic fluid for withdrawing the piston rod from the cylinder
Data Source
AI summary
A control mechanism for a stepless transmission is a control mechanism connected to a manipulation lever in a stepless transmission and disposed outside a housing of the transmission. The control mechanism includes: a) a piston rod connected to the manipulation lever; b) a piston provided on the piston rod coaxially with the piston rod; c) a cylinder case provided with a cylinder adapted to house the piston rod and the piston such that the piston rod and the piston are displaceable in an axial direction, the piston and the cylinder forming a first fluid chamber to be supplied with a hydraulic fluid for withdrawing the piston rod from the cylinder and a second fluid chamber to be supplied with the hydraulic fluid for introducing the piston rod into the cylinder; d) a spring adapted to bias the manipulation lever in a neutral direction coaxially with the piston rod; e) a proportional pressure control valve adapted to selectively supply the hydraulic fluid to the first fluid chamber or the second fluid chamber, the proportional pressure control valves being mounted to the cylinder case; and f) a pivot shaft adapted to support the cylinder case oscillatably with respect to the housing.