Hydraulic Traction Drive Control for Engine Stall Prevention
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Solution Overview
Problem
Outdoor power equipment units face challenges in efficiently managing varying load conditions, leading to engine overload and potential stall, especially when operating with inexperienced operators, as existing control systems fail to account for all load situations and additional engine drains from components beyond the traction drive and work implement.
Innovation Solution
A control system with an electronic controller that monitors prime mover load, work implement load, and temperature inputs to automatically adjust the ground speed of the traction drive system, reducing engine load by modifying the traction drive pump displacement and potentially shutting off the cooling fan when necessary, without requiring operator intervention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the operator manually slows down the mower when engine lug is detected, then the engine load is reduced to prevent stall, but the productivity and quality of operation deteriorate due to slow response time and operator skill requirements
Solution Approach 1:
The control system automatically detects engine load conditions and adjusts traction drive pump displacement without operator intervention. The system serves itself by monitoring engine parameters and making real-time adjustments to prevent engine stall, eliminating the need for operator skill and rapid manual response.
Solution Approach 2:
The control system continuously monitors engine load indicators and uses this feedback to automatically adjust the traction drive pump displacement. When engine load exceeds predetermined thresholds, the system reduces pump displacement to reduce load, creating a closed-loop control system that maintains reliable operation.
2Speed
If the operator pushes further down on the traction pedal when engine lug occurs, then the ground speed increases, but the engine load increases further causing engine stall
Solution Approach 1:
The control system monitors engine load in real-time and provides feedback control. When engine load approaches dangerous levels, the system automatically reduces traction drive pump displacement to prevent stall, overriding any operator input that would increase load. This feedback mechanism prevents the counterproductive action of pressing the pedal harder during engine lug.
Solution Approach 2:
The control system takes preliminary action by detecting approaching engine stall conditions and automatically reducing pump displacement before the operator can press the pedal harder. This preemptive anti-action prevents the scenario where increased pedal pressure would cause engine stall.
3Speed
If the available engine horsepower is fully utilized to maintain ground speed, then the vehicle speed is maintained, but the quality of cut deteriorates when encountering longer and thicker grass
Solution Approach 1:
The control system dynamically adjusts the traction drive pump displacement based on real-time engine load conditions. When encountering longer and thicker grass that increases implement load, the system automatically reduces ground speed to maintain the quality of cut, allowing the engine to operate within its power capabilities while adapting to changing conditions.
4Speed
If a less experienced operator reacts to engine lug by pressing the traction pedal harder, then the ground speed increases, but the engine load increases causing complete stoppage
Solution Approach 1:
The control system automatically protects against inexperienced operator actions by monitoring engine load and automatically reducing pump displacement when stall conditions are detected. This self-service protection eliminates the need for operator expertise and prevents complete stoppage even when operators press the pedal harder during engine lug.
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 solution enhances engine horsepower utilization, prevents engine stalls, and maintains the quality of operation by automatically adjusting to extreme load conditions, ensuring safe and efficient operation even under varying demands.
Implementation Method 1
The traction drive systems of outdoor power equipment units often comprise one or more hydraulic pumps that are driven by the prime mover. The pressurized hydraulic fluid from such pumps is supplied to one or more hydraulic motors that rotate the traction drive members.
Implementation Method 2
A fan drive system driven by the prime mover is provided for powering a cooling fan that cools one fluid in at least one cooling system carried on the frame.
Data Source
AI summary
An outdoor power equipment unit comprises a self-propelled mower having a hydraulic traction drive system. When engine load exceeds a predetermined percentage of full load, a controller automatically reduces the stroke of a variable displacement pump in the traction drive system to reduce the ground speed of the mower without the operator having to change the position of the traction pedal. This reduces engine load to enhance continued good cutting performance. At any time, the controller can take the same actions to reduce ground speed if an excessively high temperature in a fluid used in a cooling system on the mower is detected, or if excessive loads on the mower decks of the mower are detected, or both.