Hydraulic Pump Control for Load Sag Prevention
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Solution Overview
Problem
In hydraulic systems with variable displacement pumps, initiating a load-lifting movement from standstill often results in load sagging due to the delay in activating the variable displacement pump, especially in forestry cranes and hydraulic excavators, leading to operational difficulties and safety risks.
Innovation Solution
The method involves opening the third connection earlier than the first connection to initiate a flow to the hydraulic consumer, allowing the variable displacement pump to be activated under reduced pressure, and then opening the first connection with a time delay to ensure the delivery pressure exceeds the load pressure without hydraulic medium removal, using a proportional directional spool valve to manage pressure signals and flow rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the variable displacement pump is activated immediately when initiating a lifting movement, then the load can be lifted without sagging, but the hydraulic consumer initially removes hydraulic medium causing the load to sag
Solution Approach 1:
The control device activates the variable displacement pump in advance before the hydraulic consumer actually needs the hydraulic medium for lifting. By detecting the opening of the proportional directional spool valve, the system pre-activates the pump to build up pressure and deliver hydraulic medium, eliminating the delay and preventing load sagging during the transition from standby to lifting mode.
2Reliability
If the delivery pressure of the variable displacement pump is increased to overcome load pressure immediately, then lifting can start without sagging, but energy consumption and mechanical stress increase
Solution Approach 1:
The pump is activated in advance at a controlled rate, building up delivery pressure gradually before the hydraulic consumer requires full lifting pressure. This preliminary activation at moderate pressure levels reduces peak energy consumption and mechanical stress while still ensuring the load is supported when lifting begins.
Solution Approach 2:
The control device dynamically adjusts the delivery pressure of the variable displacement pump based on the actual needs of the hydraulic consumer. By modulating the pump's displacement and delivery pressure in real-time according to the lifting phase, the system optimizes energy efficiency while maintaining load stability throughout the operation.
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 approach prevents load sagging during initiation, enables immediate regulation of the lifting movement, and reduces energy consumption and mechanical stress by optimizing pressure levels and flow rates, allowing for precise and safe operation.
Implementation Method 1
hydraulic controls with at least one load-holding valve... variable displacement pump as a pressure source... load-moving hydraulic consumers... hydraulic medium is removed from the hydraulic consumer
Implementation Method 2
proportional directional spool valve to manage pressure signals and flow rates... opening the third connection earlier than the first connection to initiate a flow... control device regulates the variable displacement pump
Data Source
Figure 1~2
Figure 3~6
Figure 7~9
AI summary
In a method for hydraulically lifting a load with a hydraulic consumer (1) by adjusting a proportional directional control valve (4), wherein the control (H) comprises a load pressure signal circuit (6) led via the proportional directional control valve (4) to a control device (3) of a variable displacement pump (2), a third connection (18, 19; 18', 19') in the load pressure signal circuit (6) from the variable displacement pump (2) to the hydraulic consumer (1) is opened prior to the opening of a first connection (21, 9) from the variable displacement pump (2) to the hydraulic consumer (1) and to the opening of a second connection (11, 16) in the load pressure signal circuit (6) from the hydraulic consumer (1) to the control device (3), and the pressure signal for the control device (3) is increased by raising the pressure of the variable displacement pump (2) to at least approximately the pressure level of the load pressure in the hydraulic consumer (1). In the control system, the third connection is provided either in the proportional directional control valve (4) or in a separate valve (32).