Variable Displacement Hydraulic Pump Control for Partial-Load Efficiency
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Solution Overview
Problem
In hydraulic systems of the electrical positive control type, energy is wasted when the operating amount of the operation device is less than the maximum, due to excessive discharge flow rate of the pump relative to the meter-in opening area of the control valve.
Innovation Solution
A hydraulic system configuration that includes a variable displacement pump, a control valve with a meter-in opening area that increases in proportion to the operation signal, an unloading valve to define an unloading flow rate, and a controller that adjusts the regulator to ensure the discharge flow rate is the sum of the control valve required flow rate and the unloading flow rate, preventing excessive pump discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the discharge flow rate of the pump is increased in proportion to the operating amount of the operation device, then the hydraulic actuator can respond quickly to operation commands, but energy is wasted when the operating amount is less than maximum
Solution Approach 1:
The patent applies dynamics by making the pump discharge flow rate dynamically adjustable based on actual system needs. The controller continuously monitors the meter-in opening area of the control valve and adjusts the pump's discharge flow rate accordingly, transitioning from a static linear relationship to a dynamic adaptive relationship that matches actual hydraulic demand.
Solution Approach 2:
The patent implements feedback control where the controller receives information about the meter-in opening area from the control valve and uses this feedback to adjust the pump's discharge flow rate. This closed-loop feedback mechanism ensures the pump supplies exactly the flow needed by the actuator, eliminating the energy waste inherent in open-loop proportional control.
2Quantity of substance
If the meter-in opening area of the control valve is increased, then the flow rate to the hydraulic actuator increases, but the pressure difference across the meter-in opening decreases
Solution Approach 1:
The patent applies parameter changes by simultaneously adjusting multiple parameters: when the meter-in opening area increases, the controller also increases the pump's discharge flow rate and adjusts the regulator to maintain appropriate pressure. This coordinated parameter adjustment ensures both sufficient flow rate and adequate pressure difference are maintained throughout operation.
3Reliability
If the pump discharge flow rate is excessively high relative to the meter-in opening area, then the hydraulic actuator has sufficient flow available, but energy consumption increases due to the mismatch
Solution Approach 1:
The patent applies partial action by having the pump supply only the portion of flow that is actually needed by the hydraulic actuator, rather than always supplying maximum or excessive flow. The controller calculates the required flow based on the meter-in opening area and regulates the pump to provide precisely this amount, eliminating the excessive flow that causes energy waste.
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 suppresses wasteful energy consumption by maintaining a constant pressure difference across the meter-in opening, allowing for efficient energy use even at partial operation, and enables pressure management similar to load-sensing systems without additional mechanical complexity.
Implementation Method 1
a variable displacement pump that supplies hydraulic oil to at least one hydraulic actuator
Implementation Method 2
the control valve changing a meter-in opening area thereof, such that an increase rate of the meter-in opening area increases
Implementation Method 3
an unloading valve that defines an unloading flow rate, at which the hydraulic oil discharged from the pump is released to a tank
Implementation Method 4
the pressure difference between the upstream-side pressure and the downstream-side pressure of the meter-in opening can be kept constant
Data Source
AI summary
A hydraulic system includes: an operation device that outputs an operation signal corresponding to an operating amount of an operating unit; a variable displacement pump that supplies hydraulic oil to a hydraulic actuator; a control valve interposed between the actuator and pump, the control valve changing a meter-in opening area thereof, so an increase rate of the opening area increases in accordance with increase in the operation signal; a regulator that adjusts a tilting angle of the pump; an unloading valve that defines an unloading flow rate, at which the hydraulic oil is released to a tank; and a controller that, when the operation device is operated, determines a control valve required flow rate so rate is proportional to the meter-in opening area of the control valve, and controls the regulator so a discharge flow rate of the pump is a sum of the control valve and unloading flow rates.