CVT Ratio Control with Torque Release Mechanism
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Solution Overview
Problem
Conventional continuously variable transmissions (CVTs) lack a user-operable control mechanism similar to manual transmissions, making it difficult for drivers to manage creep torque and initial speed mismatches during vehicle launch and low-speed maneuvers, especially in vehicles without a launch device like torque converters.
Innovation Solution
A user-operable ratio control system coupled with a torque release device, allowing manual adjustment of the variator ratio through a foot pedal or lever, which operatively connects to the movable torque transfer part, enabling control over the CVT ratio and decoupling from the torque transfer part to emulate clutch functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a user operable ratio control part is directly linked to the movable torque transfer part, then the user can directly control the variator ratio, but the force required becomes too large to be comfortably provided by the user
Solution Approach 1:
A control cable or linkage acts as an intermediary between the user-operable ratio control part and the movable torque transfer part. This intermediary transmits the user's input force through a mechanical advantage system, allowing the user to control the variator ratio without directly applying the large forces needed to move the torque transfer part against the variator's internal forces.
Solution Approach 2:
The system uses a dynamic control mechanism where the ratio control part can move through a range of positions, and this movement is translated through the control linkage to adjust the torque transfer part position. The system dynamically responds to user input while managing the force requirements through the mechanical advantage of the linkage system.
2Measurement precision
If the torque transfer part position is precisely controlled for geared neutral, then the transmission can achieve stationary output with running engine, but minor deviations cause large creep torque at low wheel speed
Solution Approach 1:
The system incorporates feedback from the movable torque transfer part position to the control mechanism. This feedback allows the control system to detect deviations from the geared neutral position and make corrective adjustments, maintaining precise positioning and preventing creep torque generation even when subjected to external disturbances or user input variations.
Solution Approach 2:
The control system is designed to anticipate and prevent creep torque by maintaining the torque transfer part in the precise geared neutral position before any disruptive forces are applied. The system prepares for potential deviations by continuously monitoring and adjusting the position, cushioning against the harmful effects of position drift before they manifest as creep torque.
3Adaptability or versatility
If a torque release device is added to decouple the ratio control part from the torque transfer part, then clutch functionality is emulated, but the device complexity increases
Solution Approach 1:
The torque release device is integrated with the existing ratio control mechanism, combining the functions of ratio control and torque release/disengagement into a unified system. This integration allows the same control linkage and cable system to perform both ratio adjustment and complete decoupling functions, emulating clutch behavior without requiring entirely separate control systems.
Solution Approach 2:
The control linkage and cable system serves multiple functions: it transmits user input for ratio control, enables complete decoupling for clutch-like functionality, and can be integrated with the torque release device. This multi-functionality reduces the need for separate dedicated mechanisms for each function, managing the complexity increase while achieving versatile control capabilities.
Data Source
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AI summary
The invention relates to an arrangement for controlling a variator in a continuously variable transmission such as a vehicle transmission. The arrangement comprises a user operable ratio control part such as a lever (50) and a device for operatively coupling the ratio control part to a movable torque transfer part of the variator such as its rollers (18). The coupling device is, in the particular embodiment described, a hydro-mechanical arrangement. By moving the user operable ratio control part (50), the user exercises control over the variator ratio. In accordance with the invention the arrangement further comprises a torque release device such as a valve (60) which is operable by the user to decouple the ratio control part from the movable torque transfer part. By doing so, the torque release device offers functionality which is in some ways analogous to that of a clutch in a conventional stepped ratio vehicle transmission.