Construction Machine Hydraulic Circuit With Variable Bypass Flow Control
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Solution Overview
Problem
In hydraulic circuits for construction machines, existing technologies face challenges in controlling the flow rate from a fixed-volume hydraulic pump to a center bypass oil path, leading to increased energy loss and reduced operability during combined operations of work machine actuators and traveling motors.
Innovation Solution
A hydraulic circuit configuration that includes a variable-volume pump, a fixed-volume pump, and a negative control throttle, with a direction-switching valve that controls the flow rate by distributing hydraulic oil between the fixed-volume pump and the center bypass oil path based on a negative control signal, allowing for precise control of the flow rate according to the required flow rate of the actuator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the bleed-off opening area of the direction-switching valve is set small to reduce flow rate to the center bypass, then energy loss is reduced, but the pressure in the center bypass flow path abnormally rises causing increased energy loss and deteriorated operability
Solution Approach 1:
The patent applies dynamics by making the bleed-off opening area variable rather than fixed. The direction-switching valve's bleed-off opening area is dynamically adjusted based on operating conditions (traveling vs. work machine operations), allowing the system to adapt flow rates to match actual demands and prevent abnormal pressure buildup while minimizing energy loss.
Solution Approach 2:
The patent changes the parameter of bleed-off opening area based on operational mode. During traveling operations, a larger bleed-off area is provided to prevent pressure buildup, while during work machine operations, a smaller area is used to reduce energy loss. This parameter adjustment resolves the contradiction between energy efficiency and operability.
2Reliability
If the discharge flow rate of the variable-volume piston pump is reduced to prevent engine stall, then engine stability is improved, but the movement speed of the actuator becomes significantly slower causing deterioration of operability
Solution Approach 1:
The patent segments the hydraulic system into two independent pump systems: a variable-volume piston pump for work machine actuators and a fixed-volume hydraulic pump for traveling motors. This segmentation allows each pump to operate independently according to its specific demands, enabling the variable-volume pump to reduce discharge flow rate for engine stability while the fixed-volume pump maintains adequate flow for actuator movement speed.
Solution Approach 2:
The patent introduces a fixed-volume hydraulic pump as an intermediary component that supplies hydraulic oil to the traveling motor independently. This intermediary system prevents the need to reduce the variable-volume pump's discharge flow rate for engine protection, as the fixed-volume pump compensates for flow demands during traveling operations.
3Device complexity
If hydraulic oil from the fixed-volume hydraulic pump is joined to the center bypass flow path, then flow rate control is simplified, but the flow rate cannot be controlled according to the required flow rate of the actuator causing energy loss
Solution Approach 1:
The patent applies dynamics by providing different bleed-off opening areas based on operational mode. During traveling operations, the bleed-off opening area is set to allow free flow to the center bypass, simplifying control. During work machine operations, the bleed-off opening area is restricted to control flow rate and minimize energy loss, while still allowing the fixed-volume pump to join its output to the center bypass flow path.
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 enables efficient control of the flow rate from the fixed-volume pump to the center bypass oil path, reducing energy loss and improving the operability of construction machine actuators by matching the flow rate with the required demands, preventing engine stalls and ensuring smooth operation.
Implementation Method 1
detect an oil pressure upstream of the negative control throttle as a negative control signal, and to control the variable-volume pump based on the negative control signal
Implementation Method 2
a direction-switching valve including a first oil path extending from the fixed-volume pump to the oil tank and a second oil path extending from the fixed-volume pump to the center bypass oil path
Data Source
AI summary
Provided is a hydraulic circuit, for a construction machine, which drives an actuator by merging pressure oil from a fixed-volume pump into a center bypass oil path from a variable-volume pump to an oil tank, wherein the flow rate of flow from the fixed-volume pump to the center bypass oil path can be controlled in accordance with a requested flow rate of the actuator. A distribution direction-switching valve, which has a first oil path from a fixed-volume pump to an oil tank and a second oil path from the fixed-volume pump to a first center bypass oil path, has a first signal reception unit which causes a spool to slide in a direction in which the first oil path is formed, and a second signal reception unit which causes a spool to slide in a direction in which the second oil path is formed, and determines a distribution ratio of pressure oil flowing to the first oil path and the second oil path in accordance with the difference in size of the signals received by the first signal reception unit and the second signal reception unit, the first signal reception unit receiving a signal based on a negative control signal.