Wheel Loader Hydraulic Control for Accurate Load Weighing
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Solution Overview
Problem
Existing load weight measurement devices in construction machines face accuracy issues due to fluctuations in cylinder pressure caused by rapid operational actions of the working device, particularly when hydraulic cylinders reach their stroke ends, leading to reduced calculation accuracy.
Innovation Solution
A construction machine equipped with a hydraulic pump, directional control valves, pilot hydraulic pumps, solenoid valves, pressure and attitude sensors, and a controller that limits command current output to solenoid valves when the working device's attitude meets certain conditions to prevent pressure confinement in hydraulic cylinders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the working device is rapidly operated or operated until the hydraulic cylinder rod reaches the stroke end, then the operational efficiency is improved, but the cylinder pressure fluctuates and becomes confined, reducing load weight measurement accuracy
Solution Approach 1:
The controller performs preliminary detection of cylinder pressure and piston position before the relief state occurs. When the piston is detected to be at or near the stroke end (first position) and pressure exceeds the threshold, the controller preemptively limits the command current to the solenoid valve, preventing the pressure confinement from occurring in the first place. This allows rapid operation to continue while avoiding measurement errors.
Solution Approach 2:
The system continuously monitors cylinder pressure via the pressure sensor and piston position via the attitude sensor, creating a feedback loop. When the feedback indicates that the piston is at the stroke end and pressure is high, the controller automatically adjusts the solenoid valve command current to prevent pressure confinement, thereby maintaining measurement accuracy during rapid operations.
2Speed
If the rod of the hydraulic cylinder reaches the stroke end and relief state occurs, then rapid pressure oil flow into the cylinder happens, but the remarkable volume of pressure is confined making accurate load weight measurement difficult
Solution Approach 1:
The controller detects when the piston is at or near the stroke end using the attitude sensor before the rapid pressure oil flow and relief state occur. By preemptively limiting the command current to the solenoid valve at this detected position, the system prevents the pressure confinement that would otherwise occur during rapid pressure oil flow, maintaining measurement accuracy.
Solution Approach 2:
The attitude sensor provides continuous feedback on piston position. When feedback indicates the piston has reached the first position (stroke end), the controller responds by limiting the solenoid valve command current, preventing pressure confinement even during high-speed pressure oil flow operations.
3Adaptability or versatility
If the working device is operated until the hydraulic cylinder rod reaches the stroke end, then the working range is maximized, but pressure confinement occurs reducing measurement accuracy
Solution Approach 1:
The system uses the attitude sensor to detect when the piston is at or near the stroke end (first position) before pressure confinement occurs. The controller then preemptively limits the command current to the solenoid valve, preventing measurement errors while allowing the working device to operate through its full range including stroke end positions.
Solution Approach 2:
Continuous feedback from the attitude sensor on piston position enables the controller to automatically adjust solenoid valve command current when the piston reaches the stroke end, preventing pressure confinement and maintaining measurement accuracy across the entire working range of the hydraulic cylinder.
Data Source
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AI summary
Provided is a construction machine capable of improving the accuracy of load weight measurement without reducing the operational efficiency of a working device. A wheel loader 1 as a construction machine comprises a hydraulically driven working device 2 and a controller 5,5A for measuring the weight of a load, wherein the wheel loader 1 includes a changeover switch 121 as a changeover device for switching whether to measure the weight of the load, and in a case where an attitude of the working device 2 satisfies a predetermined load measurement condition, the changeover switch 121 is valid, and pistons 222, 242 are positioned in a first area provided on one end side or in a second area provided on the other end side, the controller 5, 5A limits the command current to be output to lift arm solenoid proportional valves 45 and the bucket solenoid proportional valves 46.