Unloading Valve Control for Industrial Vehicle Hydraulic Stall Prevention
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Solution Overview
Problem
Industrial vehicles, such as forklifts, experience engine stalls due to insufficient engine torque when the hydraulic pump load increases, particularly when an electromagnetic valve is used to control hydraulic oil supply and drainage, and existing configurations are inadequate in preventing such stalls.
Innovation Solution
The implementation of a pressure compensation circuit with an unloading valve, controlled by a vehicle control device, which manages the open/closed state to regulate hydraulic oil pressure, ensuring the unloading valve enters a closed state during initial load application to maintain pressure and then opens to prevent rapid pressure rises, thereby preventing engine stalls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the hydraulic pump load increases to operate the hydraulic operation device, then the hydraulic operation function is improved, but the engine torque becomes insufficient causing engine stalls
Solution Approach 1:
The unloading valve is opened in advance before the hydraulic operation device is activated, allowing the hydraulic pump to discharge oil at a reduced initial load. This preliminary action prevents the engine from stalling when the hydraulic load is applied, as the engine can start operating the hydraulic pump without immediate full load.
Solution Approach 2:
The unloading valve dynamically switches between open and closed states based on the operational phase. It is opened during engine startup or low-load conditions to reduce hydraulic pump load, and closed during normal operation to maintain proper hydraulic pressure. This dynamic adjustment resolves the contradiction between providing sufficient hydraulic power and preventing engine stall.
2Reliability
If the unloading valve is opened to reduce hydraulic pump load, then engine stall is prevented, but hydraulic pressure cannot be maintained
Solution Approach 1:
The unloading valve transitions from an open state during engine startup to a closed state during normal operation. When opened, it allows hydraulic oil to bypass the pump, reducing load and preventing stall. When closed, it maintains proper hydraulic pressure for operation. This dynamic state change resolves the contradiction between preventing stall and maintaining pressure.
Solution Approach 2:
The unloading valve operates periodically - opened during startup phase to prevent stall, then closed during operational phase to maintain pressure. This periodic switching between open and closed states allows the system to sequentially achieve both objectives of stall prevention and pressure maintenance.
3Productivity
If the unloading valve is closed to maintain hydraulic pressure, then hydraulic operation efficiency is improved, but rapid pressure increases may occur causing engine stalls
Solution Approach 1:
The unloading valve is opened in advance before hydraulic operations commence, allowing the hydraulic system to build pressure gradually without sudden spikes. This preliminary opening prevents rapid pressure increases that would cause engine stalls, while still allowing the system to become operational.
Solution Approach 2:
The unloading valve acts as a cushioning mechanism by being opened beforehand to absorb potential pressure spikes. When the valve is open, it provides a pressure relief path that cushions against rapid pressure increases, protecting the engine from stalls while the hydraulic system prepares for 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 solution effectively suppresses rapid pressure increases in the hydraulic mechanism, preventing engine stalls by maintaining sufficient torque during cargo handling operations and efficiently managing hydraulic pressure to ensure stable engine operation.
Implementation Method 1
an unloading valve that connects the supply passage and the drainage passage to each other
Implementation Method 2
a relief valve that is connected to the supply passage and operated by pressure of the hydraulic oil flowing through the supply passage
Implementation Method 3
a hydraulic pump driven by the engine
Data Source
AI summary
An industrial vehicle includes an engine, a hydraulic pump, a hydraulic operation device, a supply passage, a drainage passage, an unloading valve that connects the supply passage and the drainage passage to each other, and a controller that controls open/closed state of the unloading valve. If an on-load period at the time of application of load on the engine is less than a first predetermined time, the controller performs open/close control of causing the unloading valve to enter the closed state to set an on-load state, thereby increasing pressure of hydraulic oil passing through the supply passage and then causing the unloading valve to enter the open state.