Hydraulic Stepless Speed Changer Torque Stability
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Solution Overview
Problem
Existing work vehicles with hydraulic stepless speed changing apparatuses face instability during slope travel due to sudden torque release when switching between speed changing operations, leading to unstable braking functions.
Innovation Solution
Incorporating a return oil passage with an unload valve and a throttle valve connected to a hydraulic tank, allowing gradual release of high-pressure oil and maintaining torque in the hydraulic stepless speed changing apparatus, enabling smooth gear switchover operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a bypass passage is established between high-pressure side circuit and low-pressure side circuit during braking operation, then the torque of the hydrostatic stepless speed changing apparatus is released, but the torque is released all at one time causing sudden release of braking function and vehicle instability
Solution Approach 1:
A throttle valve is introduced as an intermediary component in the bypass passage to mediate the torque release process. The throttle valve restricts and controls the flow of high-pressure work oil from the high-pressure side circuit to the hydraulic tank, preventing sudden torque release while still enabling the speed changing operation to proceed smoothly.
Solution Approach 2:
The throttle valve creates a gradual, controlled release of torque over time rather than an instantaneous release. By restricting the flow rate of hydraulic oil, the system transitions from a sudden torque release to a progressive, periodic action that maintains vehicle stability during the speed changing operation.
2Ease of operation
If the unload valve is switched to unloading condition during braking, then the drive torque is released for smooth gear switching, but the braking function is suddenly released causing vehicle instability
Solution Approach 1:
The throttle valve serves as an intermediary between the unload valve and the hydraulic tank, controlling the rate at which high-pressure oil is discharged. This intermediary component ensures that while the unload valve switches to the unloading condition for smooth gear switching, the actual torque release is gradual rather than sudden, maintaining braking function stability.
Solution Approach 2:
The throttle valve changes the flow rate parameter of the hydraulic oil in the bypass passage. By restricting the flow, the system transforms the parameter of torque release from instantaneous to gradual, allowing the unload valve to function for gear switching while preventing sudden loss of braking 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
This solution ensures stable operation by preventing sudden torque release, maintaining resistance against inadvertent movement, and simplifying the switching process between speed changing operations, enhancing the reliability and stability of the work vehicle.
Implementation Method 1
the throttle valve functions to restrict sudden transport of the high-pressure work oil guided from the high-pressure side circuit to the hydraulic tank
Implementation Method 2
the unload valve is released to guide high-pressure work oil from the high-pressure side circuit to the hydraulic tank via the return oil passage, thus releasing a high-pressure condition
Data Source
AI summary
A work vehicle includes a hydraulic stepless speed changing apparatus and a gear type speed changing apparatus operable to receive output from the hydraulic stepless speed changing apparatus to convert it into a plurality of stages of speed. A return oil passage connected to a high-pressure side circuit of the hydraulic stepless speed changing apparatus is connected to a hydraulic tank. The return oil passage incorporates an unload valve and a throttle valve, between which an operably coupling mechanism is provided. This operably coupling mechanism switches over the unload valve to an unload condition in response to an operational displacement of a brake operating member for operating a brake to its braking side.