Integrated Hydraulic Clutch Piston for Compact CVT Design
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Solution Overview
Problem
Existing power transfer devices with hydraulic friction clutches increase the axial length and size of the device, leading to a larger oil pump and inefficiencies in low return control for continuously variable transmissions.
Innovation Solution
A power transfer device with a hydraulic clutch that decouples the continuously variable transmission and axles using a movable sheave and piston, allowing for compact design and reduced oil pump size by integrating the piston as both a hydraulic actuator and clutch component, and utilizing a return spring to restrict movement and eliminate inertia-related torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a hydraulic friction clutch is provided between the output shaft of the continuously variable transmission and the axles to decouple them, then the hydraulic pressure required to change the groove width of the pulley is reduced, but the axial length of the power transfer device increases
Solution Approach 1:
The invention merges the clutch drum and piston into a single integrated component. The piston forms part of the clutch drum structure, eliminating the need for a separate clutch drum. This integration reduces the axial length of the power transfer device while maintaining the decoupling function between the continuously variable transmission and axles, thereby reducing the hydraulic pressure required for pulley groove width change without increasing axial length.
Solution Approach 2:
The piston serves multiple functions: it acts as both a hydraulic actuator for controlling the pulley groove width and as a structural component of the clutch drum. This multi-functionality eliminates the need for a dedicated clutch drum, reducing the overall axial length of the device while achieving both the decoupling function and the hydraulic actuation function.
2Productivity
If the groove width of the pulley is changed to execute low return control, then the speed ratio can be brought closer to the lowest speed side before the vehicle is stopped, but a relatively high hydraulic pressure is required which increases the size of the oil pump
Solution Approach 1:
By integrating the piston with the clutch drum structure, the invention reduces the overall hydraulic pressure required to achieve the desired pulley groove width change. This pressure reduction allows for a smaller oil pump while maintaining the low return control performance that brings the speed ratio closer to the lowest speed side before vehicle stop.
Solution Approach 2:
The integrated piston-clutch drum assembly acts as an intermediary mechanism that reduces the hydraulic pressure transmission requirements. By combining the clutch function with the hydraulic actuation, it mediates between the high-pressure requirement for low return control and the oil pump size constraint, enabling efficient pressure utilization.
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 enables efficient belt return control, suppresses the increase in oil pump size, and maintains a compact design by decoupling the transmission and axles, thus addressing the size and efficiency issues in low return control.
Implementation Method 1
an oil pump that generates a hydraulic pressure to be supplied to the first and second hydraulic actuators
Implementation Method 2
a return spring that restricts movement and eliminates inertia-related torque
Data Source
AI summary
A power transfer device includes a hydraulic clutch capable of coupling and decoupling a secondary shaft of a CVT and axles to and from each other. A secondary pulley of the CVT includes a movable sheave movably supported by the secondary shaft, and a secondary piston that rotates together with the secondary shaft and that constitutes a second hydraulic actuator together with the movable sheave. The secondary piston of the second hydraulic actuator is used to define an engagement oil chamber of the hydraulic clutch.