Hydraulic Pilot Pressure Control During Gravity-Driven Cylinder Motion
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Solution Overview
Problem
In work machines with hydraulic systems, when operations like boom lowering or arm crowding are performed, there is a risk that the delivery pressure of the hydraulic pump becomes lower than the pilot primary pressure, especially when the weight and center of gravity of the work device are altered, such as by replacing the bucket with a heavier one.
Innovation Solution
The work machine incorporates a system with a main circuit, a pilot circuit, a bypass cut valve, and meter-out restrictors, where a controller adjusts the opening areas of these components based on pressure sensors and operation signals to maintain a stable pilot primary pressure during gravity-directed operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bypass sequence valve is controlled to maintain delivery pressure equal to or higher than pilot primary pressure, then the pilot primary pressure can be maintained under normal conditions, but the delivery pressure becomes insufficient when the work device weight increases or operates in gravity direction
Solution Approach 1:
The bypass sequence valve is replaced with a bypass cut valve whose opening area is dynamically adjusted by a solenoid valve based on real-time pressure feedback. This dynamic control allows the system to adapt to changing load conditions and gravity-directed operations, maintaining adequate delivery pressure while ensuring stable pilot primary pressure.
Solution Approach 2:
A pressure sensor detects the delivery pressure and feeds this information back to the control unit, which then adjusts the bypass cut valve opening area accordingly. This closed-loop feedback mechanism ensures that the delivery pressure remains sufficient even when the work device operates in gravity direction or when weight increases.
2Stress or pressure
If the bypass cut valve opening area is increased to maintain delivery pressure, then the delivery pressure is sufficient, but the pilot primary pressure becomes unstable during gravity-directed operations
Solution Approach 1:
The control unit receives feedback from the pressure sensor monitoring delivery pressure and adjusts the bypass cut valve opening area to maintain adequate delivery pressure. Simultaneously, the meter-out restrictor opening area is adjusted based on operation signals to stabilize the pilot primary pressure during gravity-directed operations.
Solution Approach 2:
The system dynamically changes the opening area parameters of both the bypass cut valve and meter-out restrictor based on operational conditions. The bypass cut valve opening area is adjusted to maintain delivery pressure, while the meter-out restrictor opening area is adjusted to stabilize pilot primary pressure during gravity-directed operations.
3Reliability
If the meter-out restrictor opening area is reduced to stabilize pilot primary pressure, then the pilot primary pressure remains stable, but the cylinder speed decreases
Solution Approach 1:
The meter-out restrictor opening area is dynamically adjusted based on operation signals from the operation device. During gravity-directed operations, the opening area is reduced to stabilize pilot primary pressure. During normal operations, the opening area is increased to maintain adequate cylinder speed.
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
This configuration ensures a stable pilot primary pressure during operations that involve the gravity direction, preventing a decrease in cylinder speed and maintaining system stability even with changes in the work device's specifications.
Implementation Method 1
a pressure sensor that senses the pressure of the hydraulic operating fluid on a delivery side of the hydraulic pump
Implementation Method 2
a first pressure reducing valve that is provided in the pilot circuit and reduces a pressure of the hydraulic operating fluid delivered from the hydraulic pump to generate a pilot primary pressure
Implementation Method 3
a second pressure reducing valve that is provided in the pilot circuit and reduces the pilot primary pressure to generate a pilot secondary pressure acting on a pilot pressure receiving section of the cylinder control valve
Implementation Method 4
a third pressure reducing valve that is provided in the pilot circuit and reduces the pilot primary pressure to generate a pilot secondary pressure acting on a pilot pressure receiving section of the bypass cut valve
Implementation Method 5
a check valve that is provided in the regeneration passage, permits a flow of the hydraulic operating fluid from the meter-out passage to the meter-in passage, and prohibits a flow of the hydraulic operating fluid from the meter-in passage to the meter-out passage
Implementation Method 6
a meter-out restrictor that is provided in the meter-out passage
Data Source
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AI summary
A work machine includes: a cylinder control valve that controls a flow of a hydraulic operating fluid from a hydraulic pump to a hydraulic cylinder; a first pressure reducing valve that reduces the pressure of the hydraulic operating fluid delivered from the hydraulic pump to generate a pilot primary pressure; a second pressure reducing valve that generates a secondary pressure acting on a pressure receiving section of the cylinder control valve; a bypass cut valve; a third pressure reducing valve that generates a secondary pressure acting on a pressure receiving section of the bypass cut valve; a regeneration passage that connects a meter-in passage and a meter-out passage to each other; a meter-out restrictor; and a controller. The controller controls the third pressure reducing valve such that the opening area of the bypass cut valve becomes smaller, when the pressure of the hydraulic pump sensed by the pressure sensor becomes lower, and reduces the opening area of the meter-out restrictor as the operation amount of an operation of operating a work device in the gravity direction becomes larger.