Hydraulic Pump Unload Control for Work Machine Surge Pressure
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Solution Overview
Problem
Existing hydraulic drive apparatuses in work machines experience surge pressure issues when the control valve is opened, leading to increased load torque on the engine and reduced hydraulic fluid flow rate, which affects the response at startup.
Innovation Solution
A hydraulic drive apparatus with a pump pressure detector, actuator holding pressure detector, unload valve, and target pressure calculation part that calculates a target pressure based on the actuator holding pressure to control the pump pressure, preventing sudden increases and ensuring reliable actuator operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the control valve is opened to increase the discharge amount of the hydraulic pump, then the hydraulic actuator can be actuated, but the pump pressure suddenly increases causing surge pressure that reduces engine speed and hydraulic fluid flow rate
Solution Approach 1:
The system performs preliminary action by detecting the opening of the control valve before the hydraulic actuator actually moves, and in advance reduces the pump discharge amount in response to this detection. This preliminary reduction of discharge amount prevents the pump pressure from suddenly increasing to surge pressure levels, while still allowing the hydraulic actuator to be actuated when needed.
2Stress or pressure
If the relief valve is used to restrict pump pressure, then the upper limit of circuit pressure is fixed, but energy loss occurs in the relief valve
Solution Approach 1:
The invention substitutes the purely mechanical relief valve system with a control system that uses sensors to detect control valve opening and electronically controls the hydraulic pump's discharge amount. This substitution eliminates the need for the relief valve to restrict pump pressure, thereby eliminating the energy loss that occurred when hydraulic fluid bypassed through the relief valve.
3Loss of energy
If the variable displacement hydraulic pump is used to adjust capacity, then energy loss in the relief valve is reduced, but surge pressure cannot be effectively reduced
Solution Approach 1:
The system implements feedback by using a sensor to detect the opening state of the control valve and feeding this information back to the controller, which then adjusts the pump discharge amount in response. This closed-loop feedback control enables effective reduction of surge pressure by dynamically adjusting the discharge amount based on actual operating conditions, something that simple capacity adjustment of a variable displacement pump cannot achieve.
Data Source
AI summary
Provided is a hydraulic drive apparatus of a work machine capable of reducing a surge pressure. The hydraulic drive apparatus includes a control valve interposed between the hydraulic pump and a hydraulic actuator, an operation device moving the control valve in response to an actuator operation, an unload valve, an unload operation valve changing a pilot pressure of the unload valve in response to an input of an unload operation command, a target pressure calculation part, and an unload operation command part. The target pressure calculation part calculates a target pressure that increases with an increase in the holding pressure of the hydraulic actuator. The unload operation command part inputs an unload operation command to the unload operation valve to make the pump pressure of the hydraulic pump follow the target pressure.