Electro-Hydrostatic Actuator Pressure Control for Traction Stability
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Solution Overview
Problem
Electro-hydrostatic systems in work machines, such as hydraulic excavators, lack the responsiveness of conventional load-sense hydraulic systems due to rapid pressure changes, leading to potential loss of traction and other operational drawbacks.
Innovation Solution
An electro-hydrostatic system with a controller that sets a reduced pressure limit and delays consumer motion by restricting pressure until a command to stop is given, mimicking the responsiveness of conventional load-sense systems by monitoring pressure parameters and adjusting the maximum pressure limit accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If electro-hydrostatic systems use rapid pressure changes for quick response, then system responsiveness is improved, but loss of traction and over-actuation occur
Solution Approach 1:
The controller pre-establishes a reduced pressure limit threshold before external load contact occurs. When the actuator approaches an external load, this pre-set limit prevents excessive pressure buildup, mimicking the delayed response of conventional load-sense systems and preventing loss of traction while maintaining electro-hydrostatic system advantages
Solution Approach 2:
The controller continuously monitors pressure parameters in the hydraulic circuit and compares them against the reduced pressure limit. When the pressure exceeds this limit, the controller detects the external load condition and adjusts pump operation accordingly, creating a feedback loop that prevents over-actuation while maintaining system responsiveness
2Speed
If electro-hydrostatic systems operate without pressure limiting, then actuator speed is improved, but over-actuation and loss of control occur
Solution Approach 1:
The controller applies a reduced pressure limit that is lower than the maximum system pressure capability but sufficient for normal operation. This partial limitation prevents excessive pressure buildup during external load contact while allowing full actuator speed and performance during normal conditions, achieving a balance between speed and control precision
3Reliability
If conventional load-sense systems use delayed response to external loads, then traction stability is improved, but productivity is reduced
Solution Approach 1:
The patent replaces the mechanical hydraulic feedback mechanism of conventional load-sense systems with an electronic control system that monitors pressure parameters and adjusts pump operation. This substitution achieves the desired delayed response effect through software control rather than mechanical means, preventing traction loss while minimizing the impact on operational efficiency
Data Source
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AI summary
In conventional load-sense systems, there is a delay between a hydraulic function being impeded by an external force and further motion of the function. This is typically due to cavitation on the low pressure side of the pump. Electro-hydraulic systems, however, typically respond very quickly because the low pressure side of the pump may be pressurized because the low-pressure side of the actuator may feed directly to the pump rather than going to tank. Thus, an operator cannot as easily rely on feedback for when a function has encountered an external load. This may result in loss of vehicle traction or other drawbacks. Therefore, provided is a system and method for mimicking a load-sense system's responsiveness using an electro-hydrostatic system via an induced passive or active time-delay.