Wheel Loader Hydraulic Unloading to Prevent Engine Stall
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Solution Overview
Problem
Work vehicles with electric operation levers face engine stalling due to excessive load when operating loading work devices, particularly in systems without load switching valves, leading to increased component count and vehicle size.
Innovation Solution
A work vehicle equipped with a hydraulic actuator, directional control valves, solenoid control valves, and a controller that detects discharge pressure and engine rotational speed to switch the directional control valves to a neutral position, unloading hydraulic oil to the tank when excessive load is detected, preventing engine stalling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a load switching valve is added to prevent engine stalling, then engine stalling is prevented, but the number of components increases and vehicle size increases
Solution Approach 1:
The directional control valve is designed to perform multiple functions: it controls hydraulic oil flow to the actuator during normal operation and also serves as an unload path to the tank when engine stalling is detected. This eliminates the need for a separate load switching valve, reducing component count while maintaining engine protection capability.
Solution Approach 2:
The patent combines the functions of the directional control valve and the load switching valve into a single component. The directional control valve is modified to include an unload path that can direct hydraulic oil back to the tank, merging two previously separate functions into one valve assembly, thereby reducing the number of components.
2Reliability
If a load switching valve is added to prevent engine stalling, then engine stalling is prevented, but the vehicle body size increases
Solution Approach 1:
The directional control valve is designed to perform multiple functions: it controls hydraulic oil flow to the actuator during normal operation and also serves as an unload path to the tank when engine stalling is detected. This eliminates the need for a separate load switching valve, reducing component count while maintaining engine protection capability.
Solution Approach 2:
The patent combines the functions of the directional control valve and the load switching valve into a single component. The directional control valve is modified to include an unload path that can direct hydraulic oil back to the tank, merging two previously separate functions into one valve assembly, thereby reducing the number of components.
3Use of energy by moving object
If the engine output torque is reduced to match minimum requirements, then fuel consumption is reduced, but the engine is more prone to stalling under load
Solution Approach 1:
The control unit continuously monitors engine rotational speed and compares it to a predetermined threshold. When the engine speed drops below the threshold indicating excessive load, the control unit automatically activates the unload path in the directional control valve to reduce hydraulic system pressure and load on the engine, allowing it to maintain stable operation at lower power settings.
Solution Approach 2:
The hydraulic system dynamically adjusts its load on the engine based on real-time engine performance conditions. The directional control valve can switch between providing full hydraulic pressure to the actuator and providing an unload path to the tank, enabling the system to adapt to varying engine capacity and prevent stalling while maintaining fuel efficiency.
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
Prevents engine stalling in work vehicles with electric operation levers by efficiently managing hydraulic load, reducing the need for additional components and maintaining vehicle functionality.
Implementation Method 1
a pressure sensor configured to detect a discharge pressure of the hydraulic pump
Implementation Method 2
a rotational speed sensor configured to detect a rotational speed of the engine
Implementation Method 3
a solenoid control valve configured to supply the directional control valve with a control pressure for controlling and switching the directional control valve
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Provided is a work vehicle which can prevent an engine from stalling regardless of type of a system mounted on a vehicle body. In a wheel loader 1 equipped with a loading work device 11 operated by an electric operation lever 19, first and second directional control valves 5, 6 include neutral positions 5N, 6N for causing hydraulic oil discharged from a hydraulic pump 12 to return to a hydraulic oil tank 10, respectively, and in the case where a discharge pressure P of the hydraulic pump 12 is a main relief pressure Pr or more and an engine rotational speed N is less than a low idle rotational speed NL, a controller 2, 2A restricts the output of control signals to first and second solenoid control valves 3, 4 so as to cause the first and second directional control valves 5, 6 to be switched to the neutral positions 5N, 6N, respectively.