Center Bypass Valve Control for Low-Speed Hydraulic Operation
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Solution Overview
Problem
The hydraulic drive control system for construction machines like hydraulic excavators, when operating at reduced engine rotational speeds, results in a decreased lever operation range for hydraulic actuators, leading to deteriorated operability during slow-speed operations such as crane works.
Innovation Solution
A hydraulic control system with a variable displacement pump, center bypass directional flow control valves, and a controller that adjusts the center bypass control valve to maintain a wider lever operation range by calculating and controlling the combined opening area of the directional flow control valves based on operation amounts and engine rotational speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the rotational speed of the prime mover is lowered below rated rotational speed to enable slow speed operation, then energy consumption is reduced and slow speed operation becomes possible, but the lever operation range in which the rate of flow supplied to the hydraulic actuator is variable shrinks, deteriorating operability
Solution Approach 1:
A center bypass control valve is introduced as an intermediary component in the center bypass line between the hydraulic pump and the hydraulic fluid tank. This valve mediates the flow distribution by allowing excess hydraulic fluid to bypass through the center bypass line when the main directional control valves are in the neutral position, thereby maintaining a wider lever operation range for variable flow supply to hydraulic actuators even at reduced engine rotational speeds.
2Loss of energy
If the delivery rate of the hydraulic pump is reduced to match lower engine rotational speed, then energy efficiency improves, but the lever operation amount increases when hydraulic fluid starts flowing into the load holding side, reducing the variable flow range
Solution Approach 1:
The center bypass control valve dynamically adjusts the opening area of the center bypass passage based on the operational state. When the engine operates at reduced rotational speed, the control valve opens the center bypass passage to allow hydraulic fluid to flow through the bypass line, thereby compensating for the reduced delivery rate and maintaining an adequate lever operation range for variable flow control to the hydraulic actuators.
Data Source
AI summary
A construction machine is provided. If the rotational speed of a prime mover is set lower than a rated rotational speed and the delivery rate of a hydraulic pump is lowered, the construction machine can prevent deterioration of the operability in slow speed operation works by keeping wide a lever operation range in which the rate of flow supplied to a hydraulic actuator is variable. A center bypass control valve (2) is arranged downstream of a plurality of directional flow control valves (1, 20, 21) in a center bypass line (12), and if an engine rotational speed (N) detected by a rotational speed sensor (19) is lower than a rated rotational speed (Nmax), a controller (10) calculates a combined opening area obtained by combining opening areas of the plurality of directional flow control valves in the center bypass line based on operation pilot pressures (Pp1, Pp3 to Pp6) detected by pressure sensors (7, 25, 26, 28, 29) and controls the center bypass control valve such that an opening area of the center bypass control valve becomes smaller than the combined opening area.