Meterless Hydraulic System with Restricted Pilot Makeup Control
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Solution Overview
Problem
Conventional hydraulic systems face inefficiencies due to fluid restriction for speed control, while meterless systems suffer from instabilities, pump overspeeding, and pressure spikes during transitional operations.
Innovation Solution
A hydraulic system with a primary pump, actuator, and closed-loop passages, incorporating a charge circuit, makeup valve, and restricted pilot passages to control fluid flow and pressure, reducing instabilities and overspeeding through selective fluid direction and regeneration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If fluid restriction is used to control actuator speed in conventional hydraulic systems, then actuator speed control is achieved, but flow losses increase and overall system efficiency decreases
Solution Approach 1:
The patent removes the metering valve (fluid restriction device) from the system entirely. Instead of restricting flow through a valve, the system uses a pump with variable displacement to precisely control the flow rate delivered to the actuator, eliminating throttling losses and improving overall system efficiency while maintaining speed control capability
Solution Approach 2:
The system changes the control parameter from flow restriction (valve opening degree) to pump displacement. By varying the pump's displacement parameter, the system directly controls the flow rate to the actuator without creating pressure drops or flow losses associated with restrictive valves
2Device complexity
If meterless hydraulic system operates in transitional modes, then system simplicity is maintained, but instabilities and pressure spikes occur
Solution Approach 1:
The system incorporates a feedback mechanism where a portion of the actuator rod-end pressure is fed back to the pump control. This feedback loop allows the pump displacement to be automatically adjusted based on actual load conditions, stabilizing system operation during transitional modes between resistive and overrunning conditions without requiring complex additional control devices
Solution Approach 2:
The pump serves multiple functions: it acts as both the primary power source for driving the actuator and the control element for stabilizing system pressure. The same pump that delivers power also responds to feedback signals to adjust its displacement, providing both power delivery and stability control in a single component
3Loss of energy
If meterless system operates in overrunning mode, then energy efficiency is improved, but pump overspeeding occurs
Solution Approach 1:
The feedback connection from actuator rod-end pressure to pump control prevents pump overspeeding during overrunning mode. When the actuator operates in overrunning condition, the rod-end pressure increases and feeds back to the pump control, automatically reducing pump displacement to match the load requirements, thereby preventing overspeeding while maintaining energy efficiency
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
Enhances hydraulic efficiency by minimizing energy wastage, stabilizing actuator movement, and preventing pump overspeeding, while maintaining system simplicity and reducing the need for metering valves.
Implementation Method 1
at least one restricted pilot passage configured to direct pilot fluid to the makeup valve to move the makeup valve and allow the charge fluid into the first and second passages
Data Source
AI summary
A hydraulic system is disclosed. The hydraulic system may have a primary pump, a hydraulic actuator, and first and second passages fluidly connecting the primary pump to the hydraulic actuator in a closed-loop manner. The hydraulic system may also have a charge circuit, a makeup valve movable to selectively allow charge fluid from the charge circuit to enter the first or second passages, and at least one restricted pilot passage configured to direct pilot fluid to the makeup valve to move the makeup valve and allow the charge fluid into the first and second passages.