Dual Hydrostatic Pump De-stroking Linkage for Engine Speed Control
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Solution Overview
Problem
Zero turning radius (ZTR) mowers struggle to maintain optimal cutting blade rotation speeds in adverse mowing conditions, such as heavy or dense grass, leading to poor cut quality due to engine strain and lack of automatic speed reduction.
Innovation Solution
A dual hydrostatic pump system with an infinitely variable linkage and engine speed sensor that automatically reduces travel speed by adjusting the stroke range of the pump input, maintaining cutting blade rotation within an optimal range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the operator pushes both control handles or sticks all the way forward to maintain high travel speed, then productivity is improved, but the engine speed drops below optimal range causing poor cut quality
Solution Approach 1:
An engine speed sensor continuously monitors engine RPM and provides feedback to a control system. When the sensor detects that engine speed has dropped below the optimal range (below 2000-2500 rpm), the control system automatically adjusts the hydrostatic pump to reduce travel speed, thereby maintaining engine speed and cut quality without requiring operator intervention.
Solution Approach 2:
The mower system automatically monitors its own engine speed and self-adjusts its travel speed when adverse conditions are detected. The system serves itself by detecting low engine speed and automatically reducing pump stroke to maintain optimal operating parameters, eliminating the need for operator awareness or manual control adjustments.
2Manufacturing precision
If the operator pulls back on both control handles or sticks to maintain optimal engine speed, then cut quality is improved, but productivity decreases due to reduced travel speed
Solution Approach 1:
The engine speed sensor continuously monitors engine RPM and provides feedback to the control system. When optimal engine speed is maintained, the system allows maximum travel speed. When engine speed drops below optimal, the system automatically reduces travel speed, eliminating the need for operators to manually reduce speed and maintain suboptimal productivity.
Solution Approach 2:
The patent replaces manual mechanical control (operator pulling back on control handles) with an automated electronic control system. The electronic system uses sensor feedback and automated pump control to maintain engine speed, substituting the operator's mechanical action with an automated system that optimizes both cut quality and productivity.
3Reliability
If mechanical or electrical controls limit control handle travel to a preset speed, then engine speed is maintained within range, but the system cannot automatically adapt to adverse mowing conditions
Solution Approach 1:
The engine speed sensor provides real-time feedback about actual engine operating conditions. This feedback enables the system to detect when adverse conditions (tall, wet, dense grass) are causing engine strain and automatically adjust travel speed accordingly, providing both reliability and adaptability.
Solution Approach 2:
The system dynamically adjusts travel speed based on real-time engine speed feedback rather than using a fixed preset speed limit. The hydrostatic pump's variable stroke capability allows continuous adjustment of travel speed to match actual mowing conditions, providing dynamic adaptability rather than static limitation.
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 system ensures cutting blades rotate within an optimal range even when the engine is straining, improving cut quality by automatically adjusting speed in heavy grass conditions without affecting operator control ranges.
Implementation Method 1
a dual hydrostatic pump that provides hydraulic fluid independently to a pair of motors on drive wheels
Implementation Method 2
Pump arms on the right and left sides of the dual hydrostatic pump each define a stroke between a neutral position, a full forward position, and a full rearward position
Data Source
AI summary
A zero turning radius mower has a dual hydrostatic pump with right and left pump arms. A linkage between the pump arms and a pair of control levers destrokes both sides of the pump simultaneously if engine speed drops below a specified value. The linkage allows each pump arm to have a first stroke range if the engine powering the pump is above the specified value, and a second smaller stroke range if the engine powering the pump is below the specified value.