Hydraulic Pump Unload Control for Work Machine Surge Pressure
Find Innovative SolutionsGenerate Solutions
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 that includes a hydraulic pump, a hydraulic actuator, a control valve, a pump pressure detector, an actuator holding pressure detector, an unload valve, an unload operation valve, a target pressure calculation part, and an unload operation command part, which calculates and adjusts the target pressure to ensure the pump pressure follows the actuator holding pressure, preventing sudden increases and thus reducing surge pressure.
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 opens the unload valve to prevent surge pressure from occurring. This proactive measure allows the system to prepare for pressure changes before they happen, ensuring smooth operation without affecting the actuator's response capability.
Solution Approach 2:
The unload valve acts as an intermediary between the hydraulic pump and the hydraulic actuator. It provides an alternative path for hydraulic fluid to return to the tank, mediating the pressure surge that would otherwise directly affect the actuator operation and engine performance.
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 system dynamically controls the unload valve opening degree based on real-time detection of control valve opening and hydraulic actuator motion state. This dynamic adjustment allows the system to optimize the balance between pressure control and energy efficiency, opening the unload valve only when necessary to prevent surge pressure rather than maintaining a fixed pressure restriction.
Solution Approach 2:
The system changes the operational parameters of the unload valve (opening degree, timing) based on detected system conditions. By adjusting these parameters dynamically, the system achieves effective surge pressure prevention while minimizing energy loss compared to a fixed relief valve setting.
3Loss of energy
If a variable displacement type 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 control by detecting both the control valve opening state and the hydraulic actuator motion state, then using this information to control the unload valve. This feedback mechanism enables the system to respond to actual system conditions and prevent surge pressure effectively, something that simple capacity adjustment of the hydraulic pump cannot achieve.
Solution Approach 2:
The system replaces the mechanical capacity adjustment mechanism with a controlled valve system. Instead of relying solely on mechanical pump capacity changes, the system uses the unload valve controlled by detection mechanisms to prevent surge pressure, achieving better control effectiveness.
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 ensures reliable startup of the hydraulic actuator and effectively restrains surge pressure, maintaining engine speed and hydraulic fluid flow rate by controlling the pump pressure based on the calculated target pressure.
Implementation Method 1
The unload valve is formed of a pilot-operated selector valve having a pilot port and provided in an unload line, configured to be opened at an opening degree corresponding to a pilot pressure to be input to the pilot port to thereby allow the hydraulic fluid to flow through the unload line at a flow rate corresponding to the opening degree
Implementation Method 2
configured to be opened at an opening degree corresponding to a pilot pressure to be input to the pilot port
Implementation Method 3
The hydraulic pump discharges hydraulic fluid. The hydraulic actuator is coupled to the movable element and operated to actuate the movable element by supply of hydraulic fluid discharged by the hydraulic pump
Data Source
Figure 1
Figure 2
Figure 3
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 (30) interposed between the hydraulic pump (10) and a hydraulic actuator (20), an operation device (40) moving the control valve (30) in response to an actuator operation, an unload valve (50), an unload operation valve (56) changing a pilot pressure of the unload valve (50) in response to an input of an unload operation command, a target pressure calculation part (70), and an unload operation command part (70). The target pressure calculation part (70) calculates a target pressure that increases with an increase in the holding pressure of the hydraulic actuator (20). The unload operation command part (70) inputs an unload operation command to the unload operation valve (56) to make the pump pressure of the hydraulic pump (10) follow the target pressure.