Hydraulic Pump Control to Prevent Engine Lugging in Construction Machines
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Solution Overview
Problem
Existing construction machines with hydraulic drive systems experience engine lugging down due to rapid increases in demanded torque when operators work the control lever at high speeds, especially in hydraulic closed circuits without restrictor elements, leading to engine speed drops or stalls.
Innovation Solution
A construction machine equipped with a variable displacement hydraulic pump, pressure sensors, and a controller that estimates demanded torque based on actuator velocity and pressure, limits velocity to prevent excessive torque changes, ensuring the engine operates within safe torque limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the control lever is operated at high speed to increase actuator velocity, then productivity is improved, but the demanded torque change rate increases causing engine lugging down
Solution Approach 1:
The controller predicts future demanded torque based on current actuator velocity and acceleration before the engine actually experiences the torque change. By anticipating the torque demand and preparing accordingly, the system prevents engine lugging down before it occurs, allowing high-speed operation without compromising engine stability
Solution Approach 2:
The system dynamically adjusts the control strategy based on real-time engine state and hydraulic circuit conditions. The controller continuously monitors engine speed, torque demand, and actuator velocity to adaptively manage the hydraulic pump delivery flow rate, enabling the system to maintain both high productivity and engine reliability under varying operational conditions
2Speed
If the hydraulic pump delivery flow rate is increased to meet high velocity demands, then actuator speed is improved, but torque demand on the engine rises sharply causing lugging down
Solution Approach 1:
The controller predicts future torque demand by calculating the rate of change of actuator velocity and the mechanical advantage of the hydraulic circuit. This preliminary torque prediction allows the system to prepare for upcoming power demands and smooth out torque fluctuations before they reach the engine, enabling high actuator speeds without sharp torque spikes
Solution Approach 2:
The system continuously monitors actual engine speed and torque demand, comparing these measurements against predicted values. Based on this feedback, the controller adjusts the hydraulic pump delivery flow rate in real-time to maintain actuator velocity while preventing excessive torque demands that would cause engine lugging down
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 solution effectively suppresses engine lugging down across various operational conditions and actuator load states, maintaining stable engine performance by controlling delivery flow rates and limiting demanded velocities.
Implementation Method 1
a pressure sensor configured to detect a load pressure on the first hydraulic actuator
Implementation Method 2
a variable displacement first hydraulic pump driven by the engine; a first hydraulic actuator driven by pressure liquid delivered from the first hydraulic pump
Data Source
Figure 1
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AI summary
An object of the present invention is to provide a construction machine capable of suppressing lugging down of an engine irrespective of contents of operation of an operator and the load state of a hydraulic actuator. A controller 50 includes: a demanded torque estimating section 50c configured to estimate demanded torque as torque demanded from an engine 9 by the first hydraulic pump on the basis of a demanded velocity of a first hydraulic actuator 1 and a load pressure on the first hydraulic actuator; a demanded velocity limiting section 50d configured to, in a case in which a demanded torque change rate as a change rate of the demanded torque exceeds a predetermined change rate, limit the demanded velocity such that the demanded torque change rate becomes equal to or lower than the predetermined change rate; and a command calculating section 50e configured to calculate a delivery flow rate of the first hydraulic pump on the basis of the demanded velocity of the first hydraulic actuator, the demanded velocity being limited by the demanded velocity limiting section.