Variable Displacement Pump Control via Virtual Pressure
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Solution Overview
Problem
Existing methods for controlling variable displacement pumps in construction machines, such as hydraulic excavators, face inefficiencies due to constant pump discharge flow rates and neglect of engine horse power, leading to potential engine stall and suboptimal utilization of the pump.
Innovation Solution
A method involving closed-center-type directional control valves that detect real discharge flow rates and operation amounts to determine virtual discharge pressures, allowing for dynamic adjustment of pump control based on actual flow rates and bleed-off characteristics, thereby optimizing pump utilization and preventing engine stall.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pump discharge flow rate is limited by engine horse power calculation, then the risk of engine stall is reduced, but the effective utilization of the variable displacement pump is limited
Solution Approach 1:
The invention dynamically adjusts the pump discharge flow rate based on real-time operating conditions. The controller continuously monitors engine horse power availability and actuator flow rate requirements, then adjusts the pump discharge flow rate accordingly. This dynamic adjustment allows the system to maximize pump utilization when engine capacity permits while preventing engine stall when horse power is insufficient, resolving the contradiction between reliability and productivity.
2Productivity
If the pump discharge flow rate is kept constant, then the pump operates efficiently, but the system cannot adapt to varying engine load conditions
Solution Approach 1:
The invention changes the operating parameters of the pump based on engine load conditions. Specifically, the controller adjusts the pump discharge flow rate parameter according to the available engine horse power and actual actuator flow rate requirements. This parameter adjustment allows the system to maintain optimal pump efficiency across varying engine load conditions while adapting to different operational demands, resolving the contradiction between productivity and adaptability.
3Productivity
If the commanded pump discharge pressure is calculated without considering engine horse power, then the pump can be effectively utilized, but engine stall may occur
Solution Approach 1:
The invention implements a feedback control mechanism where the controller continuously monitors engine horse power availability and uses this information to adjust the commanded pump discharge pressure. The system calculates the available horse power based on engine operating conditions and feeds this information back to the pressure control algorithm. This feedback loop ensures that pump utilization is maximized within the constraints of available engine power, preventing engine stall while maintaining effective pump operation.
Data Source
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AI summary
A method for controlling a variable displacement pump by calculation by a controller using a closed-center-type directional control valve, the method allowing effective utilization of the variable displacement pump while avoiding the risk of engine stall is provided. [Means for Resolution] The method includes the steps of: determining a first virtual discharge pressure from the real discharge flow rate of the variable displacement pump based on a characteristic curve defining the relation between discharge pressure and discharge flow rate of the variable displacement pump; determining a virtual bleed-off flow rate based on a virtual bleed-off area of the closed-center-type directional control valves determined according to the operation amount of the directional control valves, and determining a second virtual discharge pressure of the variable displacement pump based on a value obtained by subtracting the actuator flow rate and the virtual bleed-off flow rate from the virtual discharge flow rate of the variable displacement pump; and controlling the variable displacement pump based on a smaller value of the first virtual discharge pressure and the second virtual discharge pressure.