Hydraulic Control Circuit With Variable Bypass Opening at Engine Start
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Solution Overview
Problem
In hydraulic control circuits for construction machines, it takes time for the pressure of the pump oil passage to reach the required pressure after engine start-up, leading to poor operational responsiveness of hydraulic actuators due to the initial maximal opening area of the bypass valve controlled by a spring, which results in a low rotational speed and small pump discharge initially.
Innovation Solution
A hydraulic control circuit that includes a controller to set the opening area of the bypass valve to a first opening area once the required pressure is reached and to a second, smaller opening area until the pressure is achieved, utilizing an electromagnetic proportional pressure reducing valve and a proportional solenoid to adjust the bypass valve's opening area based on engine start-up and operational signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the bypass valve opening area is maximized at initial position by bypass valve spring, then energy saving is achieved when operation implement is in neutral, but the time for pump oil passage pressure to reach required pressure increases during engine start-up
Solution Approach 1:
The bypass valve opening area is made dynamically adjustable through a proportional solenoid that receives different control signals based on operational state. During engine start-up, the solenoid restricts the opening area to build pressure quickly; during neutral operation, the solenoid allows full opening for energy saving. This dynamic adjustment resolves the contradiction between rapid pressure buildup and energy efficiency.
Solution Approach 2:
The opening area parameter of the bypass valve is changed based on operational conditions. A controller adjusts the proportional solenoid signal to modify the bypass valve opening area: reduced opening area during engine start-up to minimize pressure loss and accelerate pressure buildup, and maximized opening area during neutral operation to enable energy-saving bypass flow.
2Loss of time
If the bypass valve opening area is small during engine start-up, then the pressure buildup time is reduced, but energy consumption increases
Solution Approach 1:
The bypass valve operates in periodic modes corresponding to different operational states. During engine start-up period, the valve maintains a restricted opening area to prioritize pressure buildup. Once the required pressure is achieved and the system transitions to neutral operation, the valve switches to full opening mode for energy saving. This periodic adjustment based on operational phase resolves the energy-time contradiction.
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 shortens the time for the pump oil passage to reach the required pressure, enhancing the operational responsiveness of hydraulic actuators by maintaining pressure at a predetermined level and reducing energy consumption.
Implementation Method 1
a proportional solenoid that causes the bypass valve spool to move against an urging force of the bypass valve spring
Implementation Method 2
a bypass valve spring that urges the bypass valve spool to an initial position
Data Source
AI summary
To provide a hydraulic control circuit for a construction machine capable of shortening a time duration from the start of an engine until the pressure of a pump oil passage reaches a required pressure. A hydraulic control circuit for a construction machine includes a hydraulic pump that is driven by an engine; a hydraulic actuator that is operated by hydraulic oil discharged from the hydraulic pump; a hydraulic pilot type control valve that controls an amount and a direction of supply of the hydraulic oil to the hydraulic actuator from the hydraulic pump; a pump oil passage that connects the hydraulic pump and a pump port of the hydraulic pilot type control valve; a bypass oil passage that branches from the pump oil passage and extends to a hydraulic oil tank; a bypass valve that is disposed in the bypass oil passage and controls an amount of the hydraulic oil returning to the hydraulic oil tank through the bypass oil passage; and a pilot oil passage that branches from the pump oil passage and extends to a pilot port of the hydraulic pilot type control valve; an electromagnetic proportional pressure reducing valve that is disposed in the pilot oil passage and controls a pressure acting on the pilot port; a controller that controls an operation of the bypass valve and the electromagnetic proportional pressure reducing valve; and an operation implement for outputting an operation signal to the controller in response to an operation applied from an operator. The controller sets the opening area A of the bypass valve to a second opening area A1 in a state where an operation signal is not output from the operation implement after the engine has been started and the pressure of the pump oil passage has reached a required pressure P0, and sets the opening area A of the bypass valve to a second opening area A2 which is smaller than the first opening area A1 during a time duration from the start of the engine until the pressure of the pump oil passage reaches the required pressure P0.