Work Machine Anti-Stall Bleed Circuit Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing work machines with hydrostatic transmission (HST) systems face limitations in their anti-stall features, particularly when significant loads are applied, leading to engine stall risks due to the complexity and cost of existing solutions, which often involve increasing oil escape rates that can result in malfunction or have limited effectiveness.
Innovation Solution
A work machine design incorporating a bleed circuit with a throttle to quickly reduce pilot oil flow to the swash plate positioning circuit, along with additional bleed circuits for the bucket and work implement, to alleviate engine load by dropping pilot pressure and preventing engine stall without increasing system complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amount of escape of oil from the flushing relief valve is increased to improve anti-stall feature, then the control pressure drops faster, but the flushing valve may malfunction due to excessive oil introduction
Solution Approach 1:
The invention extracts the harmful effect of excessive oil escape from the flushing relief valve by introducing a separate bypass circuit that allows controlled oil drainage independent of the flushing valve, thereby preventing flushing valve malfunction while maintaining anti-stall functionality
Solution Approach 2:
The bypass circuit acts as an intermediary mechanism between the charge pump and the flushing valve, providing an alternative path for oil drainage that mediates the conflict between needing fast pressure drop and preventing flushing valve overload
2Reliability
If the amount of escape of oil from the charge relief valve is increased to improve anti-stall feature, then the control pressure drops faster, but there is a limit to how much this can be increased
Solution Approach 1:
The invention segments the oil drainage function into two independent paths: one through the charge relief valve and another through the bypass circuit, allowing each to operate within optimal limits without compromising the other
Solution Approach 2:
The bypass circuit provides additional oil escape capacity beyond what the charge relief valve can provide alone, enabling faster pressure drop without overloading any single component
3Reliability
If a controller is added to detect engine rotational speed and control the swash plate positioning to prevent stall, then the anti-stall feature is improved, but the construction complexity and cost increase greatly
Solution Approach 1:
The system uses the engine's own rotational speed variations to automatically trigger the anti-stall response through the bypass circuit, eliminating the need for external sensors and controllers while maintaining effective stall prevention
Solution Approach 2:
The bypass circuit provides passive feedback based on charge pump discharge pressure, which naturally increases when engine speed drops, automatically opening the bypass to reduce HST pump displacement and prevent stall without active control
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 improves the anti-stall feature by quickly reducing engine load through controlled pressure drops, preventing engine stall during high-load conditions while maintaining a simple and cost-effective system arrangement.
Implementation Method 1
a bleed circuit configured to drain, via a throttle, a portion of the pilot oil supplied to the swash plate positioning circuit
Implementation Method 2
a swash plate positioning circuit configured to effect positioning of a swash plate of the HST pump with pilot oil supplied from the pilot pump
Data Source
AI summary
Disclosed is a work machine having a traveling apparatus and a work implement driven by an engine. A hydraulic system mounted on the work machine includes an HST pump comprising a swash plate, variable displacement pump driven by the engine, an HST motor connected in a closed circuit to the HST pump and a pair of speed-changing oil passageways, the HST motor being driven by an amount of oil supplied by the HST pump, thereby to drive the traveling apparatus, a main pump driven by the engine, the main pump supplying pressure oil to the work implement, a pilot pump driven by the engine, a swash plate positioning circuit configured to effect positioning of a swash plate of the HST pump with pilot oil supplied from the pilot pump, and a bleed circuit configured to drain, via a throttle, a portion of the pilot oil supplied to the swash plate positioning circuit.