Hydraulic Excavator Pump Control for Charge Pressure Drops
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In work machines, such as hydraulic excavators, the pressure in the hydraulic working fluid flow path can drop below the charge flow path pressure during excavation, leading to cavitation and accelerated aging of the closed-circuit pump due to insufficient fluid supply.
Innovation Solution
A work machine with a closed-circuit and open-circuit pump system, controlled by a controller, adjusts the delivery capacity of both pumps to maintain optimal fluid flow, using an excess fluid discharging device to prevent negative pressures and cavitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the charge circuit adds hydraulic working fluid to the hydraulic working fluid flow path when pressure drops, then the fluid level is maintained, but negative pressure and cavitation occur when the added fluid amount is insufficient
Solution Approach 1:
The excess fluid discharging device discharges excess hydraulic working fluid from the closed circuit to the charge flow path in advance, before the pressure drop occurs. This preliminary action ensures that sufficient fluid is available in the charge flow path when the charge pump needs to add fluid, preventing negative pressure and cavitation in the closed-circuit pump.
Solution Approach 2:
The charge flow path serves as an intermediary reservoir that stores hydraulic working fluid discharged from the closed circuit. When the closed-circuit pump needs fluid, the charge pump can supply it from this intermediary path, ensuring continuous fluid supply and preventing cavitation.
2Productivity
If the closed-circuit pump operates at high delivery capacity during excavation, then productivity is improved, but fluid shortage and negative pressure occur when the bucket hits hard soil
Solution Approach 1:
The system discharges excess fluid to the charge flow path in advance, creating a fluid reserve before the high-demand excavation operation begins. This ensures that when the bucket hits hard soil and fluid demand spikes, the charge pump has sufficient fluid available to maintain positive pressure and prevent cavitation.
Solution Approach 2:
The excess fluid discharging device operates continuously or periodically to maintain the charge flow path fluid level, ensuring uninterrupted fluid supply to the closed-circuit pump even during high-demand excavation operations. This continuous action prevents fluid shortage and cavitation.
3Quantity of substance
If the charge pump delivers fluid to the closed circuit, then fluid shortfall is compensated, but the pressure in the charge flow path drops below the closed circuit pressure
Solution Approach 1:
The excess fluid discharging device pre-charges the charge flow path with hydraulic working fluid from the closed circuit, establishing a pressure head in advance. This preliminary pressurization ensures that when the charge pump delivers fluid to compensate for shortages, the charge flow path pressure remains sufficient to prevent reverse flow and maintain system pressure balance.
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 system inhibits the deterioration of the closed-circuit pump by ensuring adequate fluid supply, preventing cavitation and maintaining operational efficiency during excavation.
Implementation Method 1
an excess fluid discharging device that discharges an excess hydraulic working fluid of the closed circuit to the charge flow path
Implementation Method 2
a closed-circuit pump that is connected to the hydraulic actuator in a closed circuit, and supplies and discharges a hydraulic working fluid to and from the hydraulic actuator
Implementation Method 3
an open-circuit pump that is connected to the hydraulic actuator in an open circuit, and supplies the hydraulic working fluid to the hydraulic actuator
Implementation Method 4
a charge pump that delivers the hydraulic working fluid to the charge flow path
Data Source
AI summary
A work machine includes: a hydraulic actuator; a closed-circuit pump that is connected to the hydraulic actuator in a closed circuit, and supplies and discharges a hydraulic working fluid to and from the hydraulic actuator; an open-circuit pump that is connected to the hydraulic actuator in an open circuit, and supplies the hydraulic working fluid to the hydraulic actuator; a charge pump; a charge flow path that introduces the hydraulic working fluid delivered from the charge pump to the closed circuit; an excess fluid discharging device that discharges an excess hydraulic working fluid of the closed circuit to the charge flow path; and a controller that controls a delivery capacity of the closed-circuit pump and a delivery capacity of the open-circuit pump. The controller increases the delivery capacity of the open-circuit pump, or reduces the delivery capacity of the closed-circuit pump when a state of a pressure of the charge flow path has transited to be lower than a predetermined pressure threshold from equal to or higher than the predetermined pressure threshold, or when a state of the work device has transited to a state of performing the excavation work from a state of not-performing the excavation work.