Electro-Hydraulic Actuator Flow Restrictor for Low-Noise Retraction
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Solution Overview
Problem
Conventional electro-hydraulic actuators (EHAs) experience excessive vibration and noise when retracting under high compressive loads, particularly in applications like bariatric hospital beds, due to insufficient fluid flow to maintain the extend side check valve open, leading to unstable oscillation and resonating sounds above 70 dB.
Innovation Solution
Incorporating a fixed orifice restrictor in the fluid line between the extend side fluid chamber and the check valve to reduce pressure closing the check valve, ensuring the spool remains open and stabilizes fluid flow back to the tank, thereby minimizing noise and vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the pump flow is reduced by up to 70% when lowering a bariatric bed frame via PWM control, then energy consumption is reduced, but the pump cannot provide enough flow to keep the extend side pilot operated check valve open, resulting in unstable oscillating spool and excessive vibration with resonating sound greater than 70 dB
Solution Approach 1:
A flow restrictor is introduced as an intermediary component in the fluid line between the extend side fluid chamber and the check valve assembly. This flow restrictor mediates the fluid flow to maintain sufficient pressure to keep the check valve open, preventing spool oscillation and excessive noise while allowing reduced pump flow operation.
Solution Approach 2:
The flow restrictor changes the pressure parameters in the fluid line by creating a controlled pressure drop. This parameter change ensures that sufficient pressure is maintained at the check valve to keep it open during low-flow PWM operation, eliminating the instability and noise associated with valve closure.
2Force
If a high compressive load is applied to the actuator as it retracts, then the actuator can support heavier loads, but the pump may not be able to provide enough flow to keep the extend side pilot operated check valve open, leading to unstable oscillating spool and excessive vibration
Solution Approach 1:
The flow restrictor serves as a mediator that maintains the pressure differential needed to keep the check valve open under high compressive loads. By controlling the fluid flow through the restrictor, the system can handle heavy loads without experiencing valve closure and subsequent spool oscillation.
3Productivity
If the check valve is allowed to close under reduced flow conditions, then the system can operate with lower pump flow, but this results in unstable oscillating spool and resonating sound greater than 70 dB
Solution Approach 1:
The flow restrictor is positioned as an intermediary element that prevents the check valve from closing during reduced flow operation. By maintaining sufficient pressure through the restrictor, the system achieves both efficient low-flow operation and stable valve behavior without oscillation or noise.
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 reduces noise and vibration, allowing for smooth operation of bariatric hospital beds by maintaining the check valve in an open position, even under high compressive loads, resulting in minimal to no sound or excessive vibration during raising and lowering.
Implementation Method 1
adding a fixed orifice restrictor in a fluid line between the extend side fluid chamber and a check valve, thereby reducing the pressure closing the extend side check valve
Implementation Method 2
The pressure of hydraulic fluid pumped into or out of the fluid chambers moves the piston within the barrel
Implementation Method 3
an electric motor that drives a hydraulic pump to move fluid between a reservoir and a hydraulic actuator
Data Source
AI summary
An electro-hydraulic actuator (EHA) comprising a pump, an electric motor drivingly coupled to the pump, and a piston-cylinder assembly having a piston and rod assembly axially movable within a cylinder. The cylinder has a piston-side cylinder chamber and a rod-side cylinder chamber that are each in fluid communication with the pump to effect movement of the piston and rod in response to fluid flow between the cylinder and the pump. The EHA further includes a check valve assembly arranged in a fluid line between the pump and the piston-side cylinder chamber and a flow restrictor in the fluid line between the piston-side cylinder chamber and the check valve assembly.