Closed-Circuit Pump Switching Valve Control for Oil Film Protection
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Solution Overview
Problem
In construction machines with hydraulic closed circuits, maintaining zero pump delivery volume during no-operation or traveling leads to high load on pumps, increasing engine load and reducing reliability due to potential oil film breakage in variable displacement swash plate hydraulic pumps, especially in large machines.
Innovation Solution
A construction machine with a bidirectionally tiltable hydraulic pump, a charge pump, check valves, and a controller that opens a switching valve to maintain a minimum delivery volume when the pump tilting angle is zero for an extended period, ensuring piston displacement and preventing oil film breakage by introducing hydraulic fluid to the sliding portions and controlling delivery pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the pump delivery volume is controlled to zero during no-operation or traveling, then energy saving is achieved, but the reliability of the hydraulic pump decreases due to oil film breakage
Solution Approach 1:
The control device periodically opens the switching valve to establish communication between the delivery port and charge line at predetermined intervals during no-operation or traveling states. This periodic action prevents continuous zero-delivery conditions that cause oil film breakage, while still maintaining overall energy efficiency by keeping the pump in a low-power state most of the time.
Solution Approach 2:
The switching valve acts as an intermediary mechanism that periodically connects the delivery port to the charge line. This intermediary connection allows hydraulic fluid to flow through the pump, maintaining the oil film without requiring continuous high-power operation, thus resolving the contradiction between energy saving and reliability.
2Loss of energy
If the pump delivery volume is maintained at zero for extended periods, then fuel consumption is reduced, but piston abrasion increases due to centrifugal force pressing pistons against cylinder walls
Solution Approach 1:
The control device implements periodic opening of the switching valve during idle periods, creating intermittent fluid flow that prevents piston abrasion without requiring continuous operation. This periodic intervention maintains the protective oil film while minimizing overall fuel consumption by keeping the pump in zero-delivery mode most of the time.
Solution Approach 2:
The control device predicts or detects upcoming operation requests and opens the switching valve in advance before the piston makes contact with the cylinder wall. This preliminary action prevents abrasion by establishing fluid flow before damage occurs, while still maintaining energy efficiency by closing the valve again after the preventive action.
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
Prevents oil film breakage, improves pump reliability, and reduces fuel consumption by maintaining an oil film between pistons and cylinders, ensuring high operational efficiency and durability of the hydraulic pump.
Implementation Method 1
a check valve that is provided in a hydraulic line connecting the charge line and the closed circuit pump to each other and permits hydraulic operating fluid to flow from the charge line into the closed circuit pump
Implementation Method 2
a switching valve that is provided in a hydraulic line connecting one of delivery ports of the closed circuit pump and the charge line to each other and is opened and closed according to a control signal from the controller
Implementation Method 3
in a case where a state in which the delivery volume of the closed circuit pump is kept to zero continues for a predetermined time period or more, open the switching valve and keep the delivery volume of the closed circuit pump to a predetermined delivery volume or more
Implementation Method 4
In the state in which the tilting angle is zero, the piston in the pump is little displaced with respect to the cylinder and is pressed against a cylinder wall surface by the centrifugal force of the piston itself
Data Source
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AI summary
Provided is a construction machine configured such that a hydraulic actuator is driven by a hydraulic pump for a closed circuit, by which oil film breakage of the hydraulic pump for a closed circuit is prevented to improve the reliability and a high operation rate can be obtained. The construction machine includes a switching valve that is provided in a branch hydraulic line connecting one of suction/delivery ports of a closed circuit pump and a charge line to each other and is opened and closed according to a control signal from a controller. The controller is configured to, in a case where a state in which a delivery volume of the closed circuit pump is kept to zero continues for a predetermined time period or more, open the switching valve and keep the delivery volume of the closed circuit pump to a predetermined delivery volume or more, the predetermined delivery volume being greater than zero.