CVT Driving Pulley Ball Spline Backlash Reduction
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Solution Overview
Problem
Conventional snowmobile drive trains with continuously variable transmissions (CVT) experience significant friction and stiction due to the sliding mechanism connecting the fixed and movable sheaves, limiting responsiveness to engine speed and torque changes, while traditional splines can introduce backlash, potentially leading to premature wear.
Innovation Solution
A centrifugally actuated driving pulley with a ball spline assembly connects the movable sheave to the fixed sheave, featuring angularly offset and ogival cross-section grooves to minimize backlash and friction, utilizing a damper assembly to reduce vibrations and enhance axial movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a sliding mechanism with plastic sliders is used to connect the fixed and movable sheaves, then the desired type of connection is achieved, but significant friction and stiction are created between the sheaves
Solution Approach 1:
The patent replaces the sliding mechanism with plastic sliders with a ball spline mechanism. The ball spline uses ball bearings to facilitate axial movement between the fixed and movable sheaves, eliminating the high friction and stiction characteristic of plastic slider sliding contact while maintaining the rotational connection and axial mobility requirements.
Solution Approach 2:
The patent changes the fundamental mechanism type from sliding friction-based connection to ball-bearing-based rolling contact. This parameter change in the connection mechanism fundamentally alters the friction characteristics, reducing both static and kinetic friction to enable more responsive axial movement of the movable sheave.
2Stability of the object's composition
If traditional splines are used to connect the fixed and movable sheaves, then rotational fixation is achieved, but backlash is introduced which can lead to premature wear
Solution Approach 1:
The patent replaces the traditional spline teeth engagement mechanism with a ball spline mechanism using ball bearings. This substitution eliminates the backlash inherent in toothed spline connections while maintaining the rotational fixation between sheaves, as the ball bearings provide continuous contact without the clearance gaps present in traditional splines.
Solution Approach 2:
The ball bearings act as intermediary elements between the fixed and movable sheaves, providing both rotational connection and axial movement capability. This intermediary mechanism eliminates direct metal-to-metal spline tooth contact that causes backlash, replacing it with ball-bearing-mediated contact that maintains stability while reducing wear.
3Reliability
If the grooves in the ball spline assembly are angularly offset with ogival cross-section, then backlash is minimized, but manufacturing complexity increases
Solution Approach 1:
The patent employs asymmetric ogival cross-section grooves that are angularly offset from each other in the ball spline assembly. This asymmetric geometry is specifically designed to minimize backlash by creating interference-fit conditions that eliminate clearance between mating surfaces, though it does increase manufacturing complexity compared to symmetric cylindrical grooves.
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 solution reduces friction and stiction, improves responsiveness, and minimizes backlash, thereby enhancing the performance and longevity of the driving pulley in CVT systems.
Implementation Method 1
a plurality of ball bearings disposed radially between the first and second shafts, each one of the plurality of ball bearings being disposed in one of the plurality of first grooves and in a corresponding one of the plurality of second grooves
Implementation Method 2
The driving pulley includes a centrifugal actuation system through which the drive ratio of the CVT is varied progressively as a function of the engine speed
Implementation Method 3
A spring biases the movable sheave and the second shaft axially away from the fixed sheave
Data Source
AI summary
A centrifugally actuated driving pulley for a continuously variable transmission (CVT) has a movable sheave that is connected to the fixed sheave via a ball spline assembly. Also disclosed is a driving pulley for a CVT having a movable sheave that is connected to the fixed sheave via a ball spline assembly, where at least some of the outer grooves receiving the ball bearings of the ball spline assembly are angularly offset from at least some of the corresponding inner grooves receiving the ball bearings of the ball spline assembly. Also disclosed is a driving pulley for a CVT having a movable sheave that is connected to the fixed sheave via a ball spline assembly, where at least some of the outer and inner grooves receiving the ball bearings of the ball spline assembly have a generally ogival cross-section. A CVT and a vehicle having a CVT are also disclosed.