Mechanical Feedback Displacement Control for Hydraulic Pumps
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Solution Overview
Problem
Conventional electrical displacement control (EDC) mechanisms for hydraulic pumps face issues such as slow off-stroke rates, high initial current requirements, and limited valve opening during on-stroke response, leading to potential overshooting to the 'fail to max' condition, especially during engine startups with limited electrical power.
Innovation Solution
A mechanical feedback control mechanism for hydraulic pumps using a movable displacement control member with a control valve assembly that includes a biasing member and a valve actuator, allowing for precise positioning of the control actuator, and a failsafe state that ensures fluid venting to prevent overshooting, while maintaining fast response times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional electrical displacement control (EDC) is used with fail to max default state, then safety is improved, but off-stroke rate becomes slow and overshooting occurs
Solution Approach 1:
The patent employs a mechanical feedback control mechanism where the control valve member receives feedback from the control actuator position to automatically adjust fluid flow. The feedback spring and control valve create a closed-loop system that prevents overshooting to fail-to-max condition while maintaining fast response rates, eliminating the need for electronic rate slowing.
Solution Approach 2:
The patent replaces the conventional electrical displacement control (EDC) system with a mechanical feedback control system. The control valve member, feedback spring, and biasing member work together as a mechanical system to control the control actuator position, substituting electronic control with a purely mechanical approach that inherently prevents overshooting.
2Reliability
If conventional EDC valve timing is adjusted to minimize overshooting, then reliability is improved, but valve opening during on-stroking is limited and response time increases
Solution Approach 1:
The mechanical feedback control system continuously monitors the control actuator position and automatically adjusts the control valve member to maintain precise positioning. The feedback spring provides continuous positional feedback, enabling the system to respond rapidly to position deviations without the need for conservative timing adjustments, thus maintaining fast on-stroke response while preventing overshooting.
3Ease of operation
If conventional EDC is used during engine startup with limited electrical power, then system operation is maintained, but high initial current is required and response is slow
Solution Approach 1:
The patent replaces the electrical displacement control system with a mechanical feedback control system that uses spring forces and fluid pressure instead of electrical actuators. During engine startup with limited electrical power, the mechanical system requires minimal electrical input (only for the solenoid to initiate movement), while the feedback spring and biasing member provide the primary control forces, dramatically reducing initial current requirements.
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 mechanical feedback control mechanism enables fast and precise displacement control with reduced current requirements, preventing overshooting and ensuring rapid response during transient conditions, even in the event of electrical failures.
Implementation Method 1
The control assembly further includes a biasing member, such as a spring, which may be operably coupled to the first and/or second valve parts, in which the biasing member is configured to selectively position the first and second valve parts to open or close a vent flow passage
Implementation Method 2
a control valve member that is movable within a fluid flow path of the control assembly to control a flow of fluid to or from the control actuator
Data Source
AI summary
A variable displacement hydraulic pump including a control actuator configured to interact with a movable displacement control member to control the displacement of the pump; and a displacement control valve assembly configured to provide mechanical feedback control of positioning of the control actuator and thereby the displacement control member. The displacement control valve assembly includes a control valve member that is movable within a fluid flow path of the control valve assembly to control a flow of fluid to or from the control actuator. The control valve assembly includes a first valve part, a second valve part, and a biasing member configured to selectively position respective one or more portions of the first and second valve parts relative to each other to open or close a vent flow passage in response to an operating state of the pump. When in a normal operating state of the pump, the biasing member is configured to position the first and second valve parts relative to each other such that the vent flow passage is closed, and the control valve member moves in the fluid flow path to control the flow of fluid to or from the control actuator. When in a failsafe state of the pump, the biasing member is configured to position the first and second valve parts relative to each other such that the vent flow passage is opened, thereby enabling fluid from the control actuator to escape via the vent flow passage.