CVT Transmission for Zero Turn Radius Lawn Mowers
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Solution Overview
Problem
Riding lawnmowers face challenges in achieving a tight or zero turn radius due to high costs and inefficiencies of zero turn mowers, and standard mowers have limited turning capabilities and stability issues on slopes, requiring a transmission that can vary ground speed while maintaining constant engine RPM.
Innovation Solution
A continuously variable transmission (CVT) system using pulley-based technology with Fixed Center Distance (FCD) and Adjustable Center Distance (ACD) systems to coordinate rear wheel speeds with front steering wheels, allowing for efficient and cost-effective tight or zero turn radius capabilities, including forward and reverse speed control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a zero turn mower system is used to achieve tight turning radius, then the turning capability is improved, but the cost and complexity of the system increases significantly
Solution Approach 1:
The transmission system is divided into two independent stages: first stage CVT for ground speed control and second stage dual CVTs for differential wheel speed control. This segmentation allows each stage to perform a specific function, achieving zero turn capability without requiring a completely complex zero turn mower system.
Solution Approach 2:
The first stage CVT serves multiple functions: it controls ground speed and also provides the foundation for differential wheel speed control in the second stage. This multi-functionality reduces the need for separate dedicated components for each function, thereby reducing overall system complexity.
2Ease of operation
If hydrostatic transmission is used to achieve variable ground speed, then the ease of operation is improved, but the energy efficiency deteriorates
Solution Approach 1:
The patent replaces hydrostatic transmission with a mechanically-based CVT system using variable diameter pulleys and belts. This mechanical substitution maintains the ease of continuous ground speed control while improving energy efficiency by eliminating the inherent inefficiencies of hydrostatic systems.
Solution Approach 2:
The CVT system uses the engine's own rotational motion to directly drive the variable diameter pulleys, which in turn control the belt speed and thus the ground speed. This self-service mechanism eliminates the need for additional hydraulic pumps and fluid systems, reducing energy losses.
3Stability of the object's composition
If the engine is positioned in the front of the mower, then the stability on slopes is improved, but the turning radius increases
Solution Approach 1:
The system dynamically adjusts the speed of each rear wheel independently through the second stage dual CVTs. This dynamic speed adjustment allows the mower to achieve zero turn radius even with the engine positioned in the front, as the differential wheel speeds compensate for the engine position rather than requiring rear-engine configuration.
4Device complexity
If a standard riding mower with mechanical steering is used, then the device complexity is reduced, but the turning radius and maneuverability are limited
Solution Approach 1:
The patent introduces a belt-driven intermediary system between the engine and the rear wheels. The variable diameter pulleys and belts act as intermediaries that translate engine rotation into variable ground speed and differential wheel speeds, achieving superior maneuverability without complex mechanical steering linkages.
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 CVT system provides a cost-effective and efficient means to achieve tight or zero turn radius, improving maneuverability and stability on various terrains while maintaining engine RPM consistency, enhancing cutting performance and user experience.
Implementation Method 1
The system includes two stages: the first stage controlling the primary ground speed, and the second stage having dual CVTs (e.g., left and right) that input into dual gear reducers (left and right)
Implementation Method 2
The second pulley is spring loaded allowing the two sheave halves to move in and out and when the diameter of the first pulley changes the spring pressure of the second pulley, it forces the pitch diameter of the second pulley to change in accordance with the first
Implementation Method 3
A belt goes from pulley A (which is mounted on the engine shaft) to pulley B of B/C (a double pulley with B being the variable speed pulley and C being a fixed pulley)
Data Source
AI summary
A continuously variable transmission (CVT) system, which turns the rear wheels of a lawn mower or similar vehicle at different speeds in a coordinated method with the front steering wheels in order to achieve the best turning radius (including a tight or zero turn radius, if desired) under most conditions. The system comprises two stages: the first stage comprising a Fixed Center Distance CVT pulley system, and the second stage comprising dual CVTs (e.g., left and right) that input into dual gear reducers (left and right), which are mechanically connected to the rear wheels. The second stage dual CVTs (left and right) are synchronized with the steering wheel, thus achieving different rear wheel speeds and/or directions based on the steering wheel position.