Pneumatically Actuated CVT Sheave Control
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Solution Overview
Problem
Mechanically controlled continuously variable transmissions (CVTs) face limitations in control options, power efficiency, noise, vibrations, and high fuel consumption, especially at high rotational speeds, and require additional heavy and costly components for pneumatic or hydraulic control systems, which can lead to vehicle inoperability if control is lost.
Innovation Solution
A CVT system featuring a pneumatically actuated piston that selectively exerts force on a sheave, allowing for adjustable gear ratios based on engine RPM, torque, and vehicle speed, using pressurized air to assist centrifugal weights in controlling the gear ratio, thereby enhancing control and efficiency without the need for additional heavy components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a pneumatic or hydraulic system is added to control the CVT gear ratio, then control options and adaptability are improved, but device complexity and weight increase due to additional pumps and reservoirs
Solution Approach 1:
The patent combines the pneumatic control system with the existing CVT pulley structure by integrating the piston directly into the pulley assembly. The piston is positioned within the pulley's internal geometry, merging two separate systems (pneumatic control and mechanical transmission) into a unified structure, thereby improving adaptability without proportionally increasing device complexity
Solution Approach 2:
The pulley structure serves multiple functions: it maintains the belt engagement function while simultaneously housing the pneumatic piston that controls the gear ratio. This multi-functionality allows the same component to provide both mechanical transmission and pneumatic control, reducing the need for separate dedicated control components
2Measurement precision
If a fully controlled pneumatic or hydraulic system is implemented, then gear ratio control precision is improved, but reliability decreases as any loss of control could result in vehicle inoperability
Solution Approach 1:
The CVT system maintains its ability to operate without external pneumatic control through the inherent mechanical properties of the centrifugal weights and springs. The piston provides assistive control when needed, but the system can revert to passive mechanical operation, ensuring self-sufficiency and reliability even if pneumatic control is lost
Solution Approach 2:
The system design incorporates redundant mechanical elements (centrifugal weights and springs) that provide a backup control mechanism. This ensures that if the pneumatic system fails, the mechanical components can maintain basic CVT operation, cushioning against complete system failure
3Device complexity
If mechanical control with centrifugal weights is used, then device complexity is reduced, but power efficiency deteriorates due to frictional losses from the belted construction
Solution Approach 1:
The patent introduces a pneumatic piston to assist the mechanical centrifugal weight control system. The pneumatic force acts on the pulley to supplement the mechanical control, potentially reducing the frictional losses inherent in purely mechanical belted CVT systems by providing an additional non-contact control mechanism
4Productivity
If the engine operates at high rotational speeds to maintain vehicle speed, then productivity is improved, but harmful factors increase including noise, vibrations, and fuel consumption
Solution Approach 1:
The CVT system with pneumatic assistance enables dynamic adjustment of gear ratios to optimize engine operating conditions. By continuously varying the gear ratio based on vehicle speed and load requirements, the system can maintain the vehicle at desired speeds while allowing the engine to operate at more efficient rotational speeds, reducing noise, vibrations, and fuel consumption
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 provides a robust, reliable, and versatile CVT that optimizes gear ratios for improved fuel efficiency, reduces noise and vibrations, and allows for independent gear ratio control, simulating a multi-gear transmission while minimizing the size and energy consumption of the pneumatic compressor.
Implementation Method 1
at least one piston selectively exerts force on the second sheave, the fluid is pressurized air and the at least one piston is actuated pneumatically
Implementation Method 2
centrifugal weights (usually on the driving side) acting against the force of a spring to provide the desired gear ratios
Implementation Method 3
centrifugal weights (usually on the driving side) acting against the force of a spring
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A CVT pulley includes a shaft having disposed thereon, a first and second sheave, and a spider. A spring biases the sheaves away from one another. The axially moveable second sheave is disposed axially between the axially fixed spider and the first sheave. A plurality of centrifugal weights, connected to either the spider or the second sheave, have a portion that moves radially outward with rotation of the shaft. The axial distance between the spider and the second sheave depends at least in part on the radial position of the portion which depends on the rotational speed. At least one cylinder is adapted to receive fluid. At least one piston, rotatable with the shaft, is adapted to move in the at least one cylinder in response to fluid being received therein, thereby selectively exerting force on one of the sheaves towards the other. CVTs and vehicles are also disclosed.