Hydraulic Pump Power Control to Prevent Engine Lug
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Solution Overview
Problem
Construction machines with hydraulically controlled implements often experience engine lug due to excessive hydraulic power demand, leading to reduced productivity, increased emissions, and inefficient fuel combustion, as existing control systems may be complex and costly.
Innovation Solution
A hydraulic control system that detects engine speed and determines a desired power value, selecting the lower of an allowable power value from a map relating to engine speed to adjust the variable displacement pump's piston displacement, ensuring the pump delivers only the necessary power to prevent engine lug.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the displacement of the variable displacement hydraulic pump is increased to meet high hydraulic power demand, then the hydraulic flow and power output increase, but the engine rotational speed decreases causing engine lug
Solution Approach 1:
The control system proactively determines the allowable pump power value based on current engine speed before the engine lugs. By using a map that relates engine speed to allowable power, the system predicts and prevents engine lug condition before it occurs, rather than reacting after speed drops. This preliminary action allows the system to maintain hydraulic power output while keeping engine speed within acceptable ranges.
Solution Approach 2:
The control system continuously monitors engine speed and compares it against the map data to determine allowable pump power. This feedback loop ensures that the pump displacement is adjusted in real-time based on actual engine operating conditions, preventing engine lug while maximizing hydraulic power output. The system uses sensor inputs to continuously update the allowable power value and adjusts pump displacement accordingly.
2Speed
If the operator reduces hydraulic power request to prevent engine stall, then engine speed is maintained, but machine productivity decreases due to overcompensation
Solution Approach 1:
The control system provides continuous feedback on engine speed and automatically adjusts pump displacement to maintain optimal operating conditions. This eliminates the need for operator intervention and overcompensation, as the system precisely controls hydraulic power delivery based on real-time engine speed data and the predefined map, ensuring maximum productivity without engine lug.
Solution Approach 2:
The control system autonomously manages the conflict between hydraulic power demand and engine speed by automatically adjusting pump displacement. The system serves itself by using sensor inputs and the stored map data to independently determine allowable power values and adjust pump operation, eliminating the need for operator overcompensation and maintaining maximum machine productivity.
3Reliability
If multiple sensors and complex control methodology are used to accurately control engine speed, then engine lug is effectively controlled with minimum oscillation, but system complexity and cost increase
Solution Approach 1:
The control system extracts and utilizes only the essential engine speed parameter from available sensor inputs. Rather than processing multiple complex sensor signals and operating parameters, the system focuses on the single critical parameter of engine speed and uses it directly with the stored map data to determine allowable pump power. This extraction approach simplifies the control methodology while maintaining reliable engine speed control.
Solution Approach 2:
The system uses a pre-stored map (lookup table) that copies the relationship between engine speed and allowable power values. This pre-computed map serves as a simplified model of the engine-hydraulic system characteristics, eliminating the need for complex real-time calculations and multiple sensors. The map acts as a pre-processed reference that provides accurate control values with minimal system complexity.
Data Source
AI summary
A method of controlling a hydraulic system having a variable displacement pump operatively coupled to an engine. The method includes detecting a speed of the engine, and determining a desired power value of the pump. The method also includes identifying an allowable power value that may be expended by the pump at the detected speed. The method also includes selecting a pump power value. The selected pump power value is the lower of the allowable power value and the desired power value. The method further includes adjusting the pump to deliver the selected pump power value.