Hydraulic Pump Control Path for Smooth Steering Turn-Back
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Solution Overview
Problem
Hydraulic drive devices with variable displacement pumps experience a momentary catch or heavy steering when turning the steering wheel back due to fluctuations in differential pressure, leading to insufficient power steering cylinder operation.
Innovation Solution
A hydraulic drive device with a variable displacement pump, displacement control valve, power steering cylinder, power steering valve, loading cylinder, and a loading valve, where the loading valve's spool has a groove forming a communication passage between the second hydraulic oil passage and the pilot line at the neutral position, ensuring a desired pilot pressure is generated and maintaining pump displacement to secure flow rate and discharge pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the displacement control valve controls the variable displacement pump to reduce pump displacement when LS differential pressure reaches or exceeds the set pressure during steering wheel turn-back, then the pump displacement is reduced to match the loading device demand, but the flow rate of hydraulic oil decreases and discharge pressure drops, causing insufficient power to the power steering cylinder and heavy steering
Solution Approach 1:
The hydraulic system is segmented into two independent control paths: one for the power steering device (via the first hydraulic oil passage) and one for the loading device (via the second hydraulic oil passage). This segmentation allows the displacement control valve to respond to loading device demands without affecting power steering oil supply, resolving the contradiction between pump displacement control efficiency and power steering cylinder power maintenance.
Solution Approach 2:
A communication passage is introduced as an intermediary path connecting the second hydraulic oil passage (loading device path) to the first hydraulic oil passage (power steering path). This intermediary allows hydraulic oil to flow from the loading device path to the power steering path when needed, ensuring power steering cylinder power is maintained even when pump displacement is reduced for loading device operation.
2Ease of operation
If the power steering valve temporarily becomes neutral state when steering wheel is turned back, then the pilot pressure is not generated in the power steering device, but the LS differential pressure reaches or exceeds the set pressure causing the displacement control valve to reduce pump displacement
Solution Approach 1:
The communication passage is pre-configured in the loading valve spool to enable automatic oil flow redirection. When the power steering valve temporarily enters neutral state during steering wheel turn-back, the communication passage proactively provides an alternative path for hydraulic oil to reach the power steering cylinder, preventing power loss before it occurs.
Solution Approach 2:
The system uses differential pressure feedback from the loading device path to control pump displacement. However, the communication passage ensures that power steering requirements are also considered in this feedback loop, as any pressure drop in the loading path can trigger oil flow through the communication passage to maintain power steering pressure, resolving the reliability issue during transient neutral states.
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 prevents the driver from feeling a catch when turning the steering wheel by maintaining adequate power to the power steering cylinder, ensuring smooth operation by controlling the variable displacement pump based on differential pressure.
Implementation Method 1
a variable displacement pump 3 that discharges hydraulic oil
Implementation Method 2
the displacement control valve controls the variable displacement pump to increase displacement of the variable displacement pump when differential pressure between discharge pressure of the hydraulic oil discharged from the variable displacement pump and pilot pressure generated in the pilot line is smaller than a predetermined set pressure
Implementation Method 3
a power steering cylinder 5 that is driven by the hydraulic oil discharged from the variable displacement pump
Implementation Method 4
a loading cylinder 7, 8 that is driven by the hydraulic oil discharged from the variable displacement pump
Implementation Method 5
a pilot line 18 that connects the loading valve 29, 38 and the displacement control valve 4
Data Source
AI summary
A hydraulic drive device for an industrial vehicle includes a variable displacement pump, a displacement control valve, a power steering cylinder, a power steering valve, a loading cylinder, a loading valve, a hydraulic oil passage, and a pilot line. The displacement control valve controls the variable displacement pump to increase displacement of the variable displacement pump when differential pressure between discharge pressure of hydraulic oil discharged from the variable displacement pump and pilot pressure generated in the pilot line is smaller than a predetermined set pressure. A spool of the loading valve is provided with a groove portion that forms a communication passage that makes communication between the hydraulic oil passage and the pilot line at a neutral position of the loading valve when the power steering valve is located in a neutral position.