Hydraulic Drive Pressure Compensation for Stable Flow Division
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional hydraulic drive systems for construction machines face issues with energy efficiency due to meter-in loss and unstable pressure control, leading to unpleasant shocks and bleed-off losses, especially when transitioning between composite and single actions.
Innovation Solution
A hydraulic drive system with a variable displacement pump, directional control valves, and pressure compensating valves that adjust pressures to match the highest load pressure, along with a controller that calculates and controls the set pressure of an unloading valve based on meter-in pressure losses to minimize bleed-off and maximize energy efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If load sensing control with differential pressure across meter-in openings is used for pump flow rate control, then flow rate control is achieved, but meter-in loss increases reducing energy efficiency
Solution Approach 1:
The invention changes the pressure parameter relationship by controlling the pump delivery pressure to be equal to the highest actuator load pressure without adding the conventional LS differential pressure. This eliminates the additional pressure drop across meter-in openings, reducing meter-in loss and improving energy efficiency while maintaining adequate flow rate control capability.
2Loss of energy
If the set pressure of the unloading valve is set high to prevent bleed-off loss, then energy efficiency improves, but sudden changes in demanded flow rate cause pump pressure to exceed set pressure causing unstable control and shocks
Solution Approach 1:
The invention dynamically adjusts the unloading valve set pressure based on the highest actuator load pressure rather than using a fixed high pressure setting. The controller continuously monitors actuator load pressures and sets the unloading valve pressure accordingly, allowing the system to adapt to changing flow rate demands and maintain stability while minimizing bleed-off losses.
Solution Approach 2:
The system uses feedback from pressure sensors monitoring actuator load pressures to control the unloading valve set pressure. The controller receives pressure signals, calculates the highest load pressure, and adjusts the unloading valve pressure setting to match this highest pressure plus a small differential, ensuring stable control response to sudden flow rate changes while minimizing energy loss.
3Stability of the object's composition
If pressure compensating valves control differential pressure to maintain flow dividing control, then flow distribution is stable, but differential pressure becomes a source of energy loss
Solution Approach 1:
The invention changes the pressure differential parameter to be equal to or close to zero by controlling pump delivery pressure to match the highest actuator load pressure. Pressure compensating valves maintain flow dividing control stability with this minimal differential pressure, eliminating the conventional LS differential pressure and its associated energy losses while preserving adequate flow distribution stability.
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 system achieves stable flow dividing control, reduces meter-in loss, and enhances energy efficiency by minimizing bleed-off losses and preventing sudden changes in actuator speed, thereby improving operability.
Implementation Method 1
a variable displacement hydraulic pump that delivers hydraulic fluid to a plurality of actuators
Implementation Method 2
a plurality of pressure compensating valves provided in downstream sides of the plurality of meter-in orifices and a controller that controls the delivery flow rate of the hydraulic pump in response to a lever input of an operation lever device and adjusts the plurality of meter-in orifices in response to the lever input
Implementation Method 3
an unloading valve that discharges the hydraulic fluid of a hydraulic fluid supply line of the hydraulic pump to a tank when a pressure of the hydraulic fluid supply line increases and exceeds a set pressure
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Even where the differential pressure across a directional control valve associated with each actuator is very small, flow dividing control of the plurality of directional control valves can be performed stable, and even where a demanded flow rate suddenly changes at the time of transition from composite action to single action or the like, a sudden change of the flow rate of hydraulic fluid to be supplied to each actuator is prevented to implement superior combined operability. Further, the meter-in loss of the directional control valves can be reduced to implement a high energy efficiency. To this end, a plurality of pressure compensating valves 7a, 7b and 7c for controlling such that the pressure in the downstream side of the meter-in opening of a plurality of directional control valves 6a, 6b and 6c becomes equal to the highest load pressure are individually arranged in the downstream side of meter-in openings of the plurality of directional control valves 6a, 6b and 6c, and demanded flow rates for the directional control valves 6a, 6b and 6c are calculated from input amounts of operation levers. Besides, the meter-in pressure loss of a predetermined directional control valve is calculated from the demanded flow rates for and meter-in opening areas of the directional control valves 6a, 6b and 6c, and the set pressure of the unloading valve 15 is controlled using the value of the meter-in pressure loss.