Logic-Controlled Flow Compensation for Single-Rod Hydrostatic Actuators
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Solution Overview
Problem
Hydrostatic actuators face malfunctions due to differential fluid flows across the piston, leading to uneven pressure and potential circuit failure, as existing solutions like valve-compensated and pump-compensated circuits do not adequately address flow imbalances.
Innovation Solution
A hydrostatic actuator system with a reversible hydraulic pump, main fluid lines, and a hydraulic charging circuit, along with a charge control system that monitors pressure differentials and connects the charging circuit to the rod or cap side of the cylinder based on pressure thresholds to equalize flows, using either hydraulic or electronic signal processing to control compensation flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a hydrostatic actuator uses a single-rod hydraulic cylinder with differential piston areas, then the actuator can provide different forces on extension and retraction, but the differential areas cause unequal fluid flows into and out of the cylinder, leading to pressure imbalances and circuit malfunction
Solution Approach 1:
A charge circuit is introduced as an intermediary component between the hydraulic cylinder and the reservoir. This charge circuit selectively supplies or receives fluid based on pressure differentials, acting as a mediator to balance the unequal flows caused by differential piston areas. The charge circuit connects to the rod side when cap side pressure exceeds rod side pressure, and vice versa, thereby equalizing flows at the pump ports and preventing circuit malfunction
Solution Approach 2:
The system dynamically changes the pressure parameters by selectively connecting the charge circuit to different cylinder sides based on real-time pressure differentials. When the weighted cap side pressure exceeds rod side pressure, the charge circuit connects to the rod side to increase its flow; when rod side pressure exceeds weighted cap side pressure, the charge circuit connects to the cap side to increase its flow. This dynamic parameter adjustment equalizes the flows and maintains circuit reliability
2Ease of operation
If the pump displacement is reversed to pump fluid through the opposite ports to retract the cylinder, then the flow direction changes, but the opposite situation occurs where higher flow is forced into the pump input, increasing pressure and causing malfunction
Solution Approach 1:
The charge circuit serves as a pressure-regulating intermediary that prevents excessive pressure buildup in the pump input during retraction. By selectively connecting to the cap side when rod side pressure exceeds weighted cap side pressure, the charge circuit provides an additional flow path that equalizes the pump input flow and prevents dangerous pressure increases, enabling safe bidirectional operation
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 system effectively stabilizes fluid flows across the piston, preventing pressure imbalances and ensuring continuous operation without critical performance regions, reducing costs and improving reliability.
Implementation Method 1
a hydraulic charging circuit for supplying/releasing charging fluid to and from the first and second main fluid lines to compensate for differential flow on opposing sides of the hydraulic cylinder
Implementation Method 2
monitor a weighted pressure differential across a piston of the hydraulic cylinder
Data Source
AI summary
A single-rod hydrostatic actuator or pump-controlled actuator, comprises a hydrostatic pump connected in a closed circuit to a single-rod hydraulic cylinder where the cylinder velocity is directly controlled by the pump flow, without the need of intermediary valves. Due to the absence of throttling losses, the efficiency of hydrostatic actuators is considerably superior to the efficiency of conventional valve-controlled circuits. However, because of the differential areas at the cap and rod sides of the cylinder, the flows coming into and out of the cylinder do not match. Several attempts have been made to this date to produce a stable, robust and reliable circuit that can be used in everyday applications but no circuit has ever been conceived to reach the high standards of reliability and robustness required by industry. The current invention solves the problem of the differential flows with a design that is reliable, oscillation-free and robust. The present conception is based on the correction of a misstated theory concerning the modus operandi of hydrostatic actuators. The resulting design can be translated into different embodiments using electronic or hydraulic technologies and uses only logical combinations of the pressure readings at the cap and rod-sides of the circuit.