Hydraulic Actuator Flow Limiting for Low-Speed Pump Pressure Control
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Solution Overview
Problem
Existing hydraulic systems in working machines face issues where the delivery flow rate of the pump may be insufficient, leading to hydraulic actuators being controlled based on the prime mover's rotation speed, resulting in inadequate pressure supply.
Innovation Solution
A working machine with a controller that limits the maximum flow rate of hydraulic fluid supplied to hydraulic actuators based on the prime mover's actual rotation speed, using a variable displacement hydraulic pump and control valves, ensuring the flow rate does not exceed the pump's delivery capacity, and incorporating a load sensing system to maintain constant differential pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the prime mover's rotation speed is insufficient, then the delivery flow rate of the pump decreases, but the supply flow rate required by hydraulic actuators remains high, resulting in inadequate pressure supply
Solution Approach 1:
The control valve is designed with dynamic flow rate characteristics that adapt to the prime mover's rotation speed. The valve's flow rate characteristic changes based on the rotation speed signal, allowing the system to maintain appropriate pressure while preventing excessive flow rate demands that the pump cannot satisfy.
Solution Approach 2:
The controller receives feedback about the prime mover's actual rotation speed and uses this information to adjust the control valve's characteristics. This feedback mechanism ensures that the control valve's flow rate capacity matches the pump's actual delivery capability at each rotation speed, preventing pressure insufficiency.
2Speed
If the control valve allows high flow rate, then the hydraulic actuators can operate quickly, but the pump cannot supply sufficient flow rate at low rotation speeds, causing loss of pressure control
Solution Approach 1:
The control valve's flow rate characteristic is made dynamic rather than fixed. Based on the prime mover's rotation speed, the controller adjusts the valve's characteristics to allow higher flow rates when the pump can supply them (high rotation speed) and restricts flow rate when the pump capacity is limited (low rotation speed), thus maintaining pressure control while enabling fast actuator operation when possible.
Solution Approach 2:
The control valve's flow rate parameter is changed based on the rotation speed condition. The controller modifies the valve's flow rate characteristic parameter according to the actual rotation speed, allowing the system to optimize between actuator speed and pressure maintenance depending on the prime mover's capability at each moment.
3Reliability
If the minimum delivery flow rate of the regulator is mechanically set to a value more than zero, then the pump always delivers some flow, but this causes unnecessary energy consumption and heat generation when actuators do not require flow
Solution Approach 1:
Instead of continuous minimum flow delivery, the system uses periodic or demand-based flow delivery controlled by the control valve. The valve opens only when actuators require hydraulic fluid, allowing the pump to deliver flow intermittently rather than continuously, thus reducing energy consumption and heat generation during idle periods while maintaining reliability when needed.
Data Source
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AI summary
A working machine (1) includes a prime mover (5) to produce power, a variable displacement hydraulic pump (P) to be actuated by power produced by the prime mover (5) to deliver hydraulic fluid, a hydraulic actuator (26) to be actuated by hydraulic fluid delivered by the hydraulic pump (P), a control valve (30) to adjust hydraulic fluid to actuate the hydraulic actuator (26), and a controller (11) configured or programmed to control the control valve (30). The controller (11) is configured or programmed to, based on an actual rotation speed of the prime mover (5), control the control valve (30) to limit a maximum flow rate (MF) of hydraulic fluid supplied from the control valve (30) to the hydraulic actuator (26) such that the maximum flow rate (MF) does not exceed a limit flow rate (LF), and the limit flow rate (LF) corresponding to a rotation speed (R) of the prime mover (5) is equal to or less than a maximum delivery flow rate of the hydraulic pump (P) corresponding to the rotation speed (R).