Hydraulic Pump Merging Control for Smoother Vehicle Unloading
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Solution Overview
Problem
Existing hydraulic drive systems for work vehicles, such as wheel loaders, experience significant impact on operators due to sharp changes in pressure oil flow rate when unloading, which current technologies fail to mitigate effectively.
Innovation Solution
A hydraulic drive device featuring a main pump and a sub-pump with a merging directional valve, a relief valve having a pressure override characteristic, and a controller that manages the flow passages to gradually reduce pressure oil flow, thereby minimizing operator impact during unloading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the unload valve is operated to release pressure oil from the first pump to the tank, then the pressure oil is supplied to the lift cylinders only from the second pump and the impact and collision sound are reduced, but the flow rate of pressure oil reduces sharply and a large impact is still imparted to the operator
Solution Approach 1:
A flow control valve is introduced as an intermediary component between the main pump and the actuator. This valve gradually reduces the flow rate of pressure oil during unloading operations, preventing sharp flow rate changes while still enabling the unload valve to release pressure oil from the sub-pump. The flow control valve mediates between maintaining productivity and reducing impact on the operator.
Solution Approach 2:
The system dynamically adjusts the flow rate of pressure oil from the main pump by controlling the flow control valve in response to system pressure conditions. During unloading, the flow rate is gradually reduced rather than abruptly cut off, creating a dynamic transition that prevents sharp flow rate changes while maintaining system functionality.
2Object-affected harmful factors
If the flow rate of pressure oil is reduced sharply when the unload valve is operated, then the pressure oil is supplied only from the second pump, but it is still probable that a large impact is imparted to the operator
Solution Approach 1:
The flow control valve is activated in advance of complete unloading to gradually reduce the flow rate from the main pump. This preliminary action prepares the system for unloading by smoothly transitioning the flow rate before the unload valve fully engages, preventing sudden impact on the operator while minimizing the time required for the transition.
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
The solution reduces the impact on operators by moderating the flow rate change during unloading, enhancing operator comfort and reducing fatigue, while also allowing for cost-effective production using a gear pump as the sub-pump.
Implementation Method 1
the relief valve has a pressure override characteristic having a tendency that the relief pressure increases from a cracking pressure to a set pressure as a relief flow rate increases
Implementation Method 2
a sub-flow passage for making pressure oil of the sub-pump merge with the main flow passage and supplying the pressure oil to the actuator
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
This hydraulic drive device for a work vehicle includes a main pump (1) of a variable displacement type or a fixed displacement type discharging pressure oil, a main flow passage (F1) for supplying pressure oil of the main pump to an actuator, a sub-pump (5) of a fixed displacement type discharging pressure oil, a sub-flow passage (F2) for making pressure oil of the sub-pump merge with the main flow passage and supplying the pressure oil to the actuator (2), a merging directional valve (6A) for connecting or cutting off the main flow passage and the sub-flow passage, a controller (30) for controlling operation of the merging directional valve, and a relief valve (7A) arranged in the sub-flow passage, in which the relief valve has a pressure override characteristic having a tendency that the relief pressure increases from a cracking pressure to a set pressure as a relief flow rate increases.