Hydraulic Pump Merging Control for Smoother Work Vehicle Lifting
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Solution Overview
Problem
Existing hydraulic drive systems for work vehicles, such as wheel loaders, still impart significant impact to operators due to sharp changes in pressure oil flow rates when unloading, despite measures to reduce fatigue and collision sounds.
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 that gradually reduces pressure oil flow, and a controller to manage the directional valve operation, ensuring a moderate change in flow rate during arm raising motions.
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 collision sound and impact on the operator are reduced, but the flow rate of pressure oil supplied to the lift cylinders reduces sharply causing large impact to the operator
Solution Approach 1:
A flow rate control valve is introduced as an intermediary component between the main pump and the actuator. This valve gradually adjusts the flow rate of pressure oil during the unloading process, preventing sharp flow rate changes while still enabling the unload valve to release pressure oil from the first pump. The flow rate control valve acts as a mediator that smooths the transition, reducing both collision sounds and impact on the operator simultaneously.
Solution Approach 2:
The system dynamically adjusts the flow rate of pressure oil during operation. The flow rate control valve is configured to gradually change the flow rate based on operational conditions, particularly during unloading phases. This dynamic adjustment ensures that the flow rate decreases progressively rather than abruptly, maintaining smooth operation while achieving the unloading function.
2Reliability
If the flow rate of pressure oil is reduced sharply when the unload valve is operated, then the unloading function is achieved, but a large impact is imparted to the operator operating the actuator
Solution Approach 1:
The flow rate control valve serves as an intermediary that decouples the unloading function from sharp flow rate changes. It allows the unload valve to perform its function of releasing pressure oil while independently controlling the flow rate transition to be gradual, thereby eliminating the harmful impact on the operator without compromising unloading reliability.
Solution Approach 2:
The flow rate control valve is positioned upstream in the hydraulic circuit to cushion the flow rate changes before the pressure oil reaches the actuator. By预先 (in advance) controlling the flow rate during the unloading process, the system prevents sudden flow rate reductions from reaching the operator, thus cushioning the harmful effects before they occur.
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 reduces the impact on operators by gradually reducing the pressure oil flow rate, enhancing the operability and usability of the hydraulic drive system while maintaining energy efficiency and cost-effectiveness.
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
Data Source
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.