Toroidal CVT Piston Clearance Structure for Interference-Free Sealing
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Solution Overview
Problem
In toroidal continuously variable transmissions, assembly errors and elastic deformations lead to interference between the piston main body portion and the cylinder, causing an imbalance in sealing pressure.
Innovation Solution
A toroidal continuously variable transmission design with a trunnion having a shaft portion and a main body portion, where a gap is formed between the outer peripheral surface of the shaft portion and the inner peripheral surface of the piston, allowing for radial movement and reducing interference and sealing pressure imbalance, and including lubricating oil passages for effective lubrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the piston is rigidly fixed to the trunnion, then the structural strength is improved, but interference between the piston and cylinder occurs due to elastic deformation or assembly errors
Solution Approach 1:
The connection between the piston and trunnion is segmented into two functional zones: the boss portion is rigidly fixed to the trunnion for strength, while the piston main body portion is made movable relative to the trunnion through a clearance fit. This segmentation allows different parts to serve different functions - the fixed boss provides structural integrity while the movable main body accommodates deformation and assembly errors without interfering with the cylinder.
Solution Approach 2:
The piston main body portion is designed to be dynamically movable relative to the trunnion rather than rigidly fixed. This dynamic capability allows the piston to adjust its position radially when the trunnion elastically deforms or when assembly errors occur, preventing interference with the cylinder while maintaining the rigid connection at the boss portion for structural strength.
2Reliability
If the piston is made movable relative to the trunnion, then interference with the cylinder is prevented, but sealing pressure imbalance occurs due to radial movement
Solution Approach 1:
The piston is segmented into the boss portion (rigidly fixed) and the piston main body portion (movable). The sealing surfaces are located on the piston main body portion, which can move radially to prevent interference while the rigid boss portion maintains overall structural stability. This segmentation allows controlled radial movement that prevents interference without causing severe sealing pressure imbalance.
Solution Approach 2:
The clearance between the piston outer peripheral surface and the trunnion inner peripheral surface is carefully controlled within a specific range (0.01-0.05 times the piston diameter). This parameter optimization allows sufficient radial movement to prevent interference with the cylinder while limiting the movement to minimize sealing pressure imbalance, achieving a balance between the two conflicting requirements.
3Reliability
If a gap is formed between the piston and trunnion, then radial movement is enabled to prevent interference, but device complexity increases
Solution Approach 1:
The complex rigid fixation structure is extracted and replaced with a simpler clearance fit between the piston and trunnion. Instead of using complex joints, bearings, or adjustment mechanisms to allow radial movement, the invention simply provides a controlled gap that enables the piston main body portion to move radially relative to the trunnion, significantly reducing structural complexity while achieving the desired reliability.
Solution Approach 2:
Instead of making the piston rigidly fixed and providing clearance between the piston and cylinder (which would complicate the cylinder structure), the invention inverts the approach by providing clearance between the piston and trunnion. This allows the piston to move relative to the trunnion to prevent interference with the cylinder, simplifying the overall device structure while maintaining reliability.
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
Prevents interference between the piston and cylinder, reduces sealing pressure imbalance, and allows for smooth operation even with assembly errors or elastic deformations, enhancing the transmission's reliability and efficiency.
Implementation Method 1
even if the trunnion elastically deforms by receiving a load from the power roller
Implementation Method 2
including lubricating oil passages for effective lubrication
Data Source
AI summary
A toroidal continuously variable transmission includes: input and output discs; a power roller sandwiched between the input disc and the output disc so as to be tiltable; a trunnion supporting the power roller and configured to be tiltable about a tilt axis of the power roller and reciprocatable in a direction along the tilt axis; a piston attached to a shaft portion of the trunnion so as to be externally fitted to the shaft portion; and a cylinder forming a pressure chamber which makes the piston reciprocate in the direction along the tilt axis. An inside gap is formed between an outer peripheral surface of the shaft portion of the trunnion and an inner peripheral surface of the piston.