Travel Motor Speed-Stage Control to Prevent Engine Stall
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Solution Overview
Problem
Existing working machines, such as skid steer loaders and compact track loaders, face challenges in preventing engine stall and efficiently managing speed transitions, as current control systems struggle to optimize pilot pressure and rotation speed stages effectively.
Innovation Solution
A working machine system with a prime mover, a traveling pump, a traveling motor, a traveling switching valve, and a controller that adjusts pilot pressure based on the set rotation speed stage, using different control lines and gain settings for PI or PID control to manage speed transitions and prevent engine stall.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pressure control valve is controlled to rapidly decrease the traveling primary pressure when a traveling load exceeding a predetermined level is applied, then the engine stall is prevented, but the decrease in engine revolving speed cannot be minimized effectively under all operating conditions
Solution Approach 1:
The patent applies dynamics by making the control characteristics changeable based on operating conditions. The controller switches between a first control characteristic (for low engine speeds) and a second control characteristic (for high engine speeds), allowing the pressure control valve to be controlled dynamically according to the actual engine revolving speed and load conditions, thereby preventing engine stall while maintaining speed stability
Solution Approach 2:
The patent changes the control parameters (control characteristics) based on the engine revolving speed. When the engine revolving speed is equal to or lower than a predetermined value, the first control characteristic is used; when it exceeds the predetermined value, the second control characteristic is used. This parameter change approach optimizes the balance between preventing engine stall and maintaining engine speed stability
2Device complexity
If a single control characteristic is used for pressure control, then the control system is simple, but it cannot optimize performance across different engine speed ranges and load conditions
Solution Approach 1:
The patent implements a dynamic control system that automatically selects between first and second control characteristics based on the engine revolving speed. This dynamic approach improves speed transition efficiency and overall productivity without significantly increasing device complexity, as the controller simply switches between pre-defined control characteristics based on speed thresholds
3Speed
If the rotation speed stage of the traveling motor is shifted rapidly, then the response speed is improved, but gear-shifting shocks occur
Solution Approach 1:
The patent applies beforehand cushioning by controlling the pressure control valve to adjust the traveling primary pressure in advance during speed stage transitions. When the traveling motor shifts from a high-speed stage to a low-speed stage, the controller increases the traveling primary pressure to cushion the shock, thereby reducing gear-shifting shocks while maintaining rapid response
Data Source
AI summary
A working machine includes a prime mover, a traveling pump driven by a power of the prime mover to deliver operation fluid, a traveling motor rotated by the operation fluid delivered from the traveling pump to have a rotation speed stage shiftable between a first speed stage and a second speed stage higher than the first speed stage, a traveling switching valve shiftable between a first state where the rotation speed stage of the traveling motor is set to the first speed stage and a second state where the rotation speed stage of the traveling motor is set to the second speed stage, an actuation valve configured to change a pilot pressure of a pilot fluid to control a flow of operation fluid delivered from the traveling pump, and a controller configured to control the pilot pressure of the pilot fluid output from the actuation valve so that a value of the pilot pressure differs depending on whether the set rotation speed stage of the traveling motor is the first speed stage or the second speed stage.