Excavator Hydraulic Circuit for Low-Pressure Engine Starting
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Solution Overview
Problem
Shovels equipped with unified bleed-off valves often fail to start the engine due to the unified bleed-off valve being closed during start-up, causing the hydraulic oil discharge to be shut off, which prevents the starter motor from rotating the engine's rotation shaft.
Innovation Solution
The hydraulic circuit is configured to maintain a discharge pressure equal to or less than a predetermined pressure during engine start-up, ensuring the unified bleed-off valve is open, allowing hydraulic oil to flow to the hydraulic oil tank and preventing excessive pressure buildup, thus enabling reliable engine starting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the unified bleed-off valve is closed during engine start-up to control hydraulic oil flow, then hydraulic system pressure control is improved, but the engine cannot start because the starter motor cannot rotate the engine's rotation shaft
Solution Approach 1:
The unified bleed-off valve is divided into two independent control paths: an electronic control path for normal operation and a mechanical control path for engine starting. This segmentation allows the valve to serve two different functions independently - electronic control for hydraulic pressure management during operation, and mechanical control for ensuring engine starting capability, thereby resolving the contradiction between pressure control and starting reliability.
Solution Approach 2:
The mechanical control path is designed to automatically open the unified bleed-off valve during engine starting before electronic control is activated. This preliminary mechanical action ensures that hydraulic oil can be discharged to the tank, reducing engine load on the starter motor, and enabling reliable engine starting before electronic pressure control takes over.
2Measurement precision
If electronic control of the unified bleed-off valve is used, then hydraulic pressure control precision is improved, but system reliability deteriorates when electronic control malfunctions
Solution Approach 1:
A mechanical control path acts as an intermediary backup system when electronic control malfunctions. This mechanical path includes a spring-loaded mechanism that automatically opens the unified bleed-off valve, serving as a mediator between the electronic control system and the hydraulic system. When electronic control fails, the mechanical intermediary ensures the valve can still open to discharge hydraulic oil, maintaining system reliability while preserving electronic pressure control precision during normal operation.
Solution Approach 2:
The unified bleed-off valve is designed to change its control parameter from electronic signal-based control to mechanical spring-force-based control when switching between normal operation and starting modes. During normal operation, electronic control provides precise pressure regulation. During starting or failure conditions, the mechanical control path changes the control parameter to spring force, which automatically opens the valve to reduce engine load, thereby maintaining reliability across different operational states.
3Stress or pressure
If the unified bleed-off valve remains closed during engine start-up, then hydraulic oil discharge is controlled, but excessive pressure buildup prevents the starter motor from rotating the engine
Solution Approach 1:
The mechanical control path is activated preliminarily during engine starting to open the unified bleed-off valve before electronic control engages. This preliminary action discharges hydraulic oil to the tank, preventing excessive pressure buildup that would otherwise create excessive engine load on the starter motor, thereby enabling successful engine starting.
Solution Approach 2:
The mechanical control path extracts the critical function of opening the unified bleed-off valve during engine starting from the electronic control system. By taking out this specific function and implementing it through a dedicated mechanical path, the system ensures that hydraulic oil can be discharged to reduce engine load on the starter motor, while the electronic control system retains responsibility for precise pressure control during normal operation.
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 allows the shovel to reliably start the engine even if electronic control of the unified bleed-off valve is malfunctioning, by ensuring the hydraulic oil can be discharged to the tank, reducing engine load and allowing the starter motor to rotate the engine effectively.
Implementation Method 1
the hydraulic circuit is configured so that a discharge pressure of the hydraulic pump becomes equal to or less than a predetermined pressure during start-up of the engine
Data Source
AI summary
A shovel includes a lower traveling body, an upper turning body turnably mounted on the lower traveling body, an engine provided in the upper turning body, a hydraulic pump and a hydraulic oil tank provided in the upper turning body, a plurality of hydraulic actuators driven by the hydraulic pump, and a hydraulic circuit connected to the hydraulic pump, wherein the hydraulic circuit includes a plurality of control valves configured to control flows of hydraulic oil between the hydraulic pump and the plurality of hydraulic actuators, and a unified bleed-off valve configured to collectively control bleed-off flowrates of the plurality of control valves, wherein the hydraulic circuit is configured so that a discharge pressure of the hydraulic pump becomes equal to or less than a predetermined pressure during start-up of the engine.