Variable Torque Limiting Clutch for CVT Torque Spike Protection

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Solution Overview

Problem

Steel belt continuously variable transmissions (CVTs) face damage from torque spikes in strenuous applications like trucks and off-road vehicles due to slip at the belt/sheave interface, which existing over-clamping methods attempt to prevent but result in inefficiency and heat generation.

Innovation Solution

An adjustable variable torque limiting (VTL) clutch is integrated between the driven sheave and drivetrain, hydraulically connected to manipulate both the sheave member and clutch, allowing selective torque coupling and uncoupling to manage torque spikes without over-clamping, ensuring slip occurs at the clutch rather than the belt/sheave interface.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If over-clamping is applied to prevent slip during torque spikes, then the CVT is protected from damage, but drivetrain inefficiency increases due to friction losses

Engineering Contradiction:

Improveprotection from torque spike damageVSAvoidfriction losses

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The system segments the torque management function by introducing a separate clutch assembly between the driven sheave and drivetrain. This clutch can independently engage to limit torque transmission during spikes, protecting the CVT without requiring continuous over-clamping of the belt, thus reducing friction losses during normal operation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The clutch assembly acts as an intermediary component between the driven sheave and drivetrain. It mediates torque transmission by selectively engaging to limit torque spikes, allowing the belt/sheave interface to operate at optimal clamping forces without the need for excessive clamping to protect against spikes.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If over-clamping is used to handle large torque spikes in strenuous applications, then slip is prevented, but drivetrain efficiency deteriorates

Engineering Contradiction:

Improveprevention of slipVSAvoiddrivetrain efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The clutch assembly provides dynamic torque management by engaging only when torque spikes occur. This allows the system to adapt clamping forces to actual operating conditions, preventing slip during spikes while maintaining optimal (lower) clamping forces during normal operation to preserve drivetrain efficiency.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the torque transmission parameter dynamically through clutch engagement. During normal operation, the clutch disengaged allowing efficient power transmission. During torque spikes, the clutch engages to limit torque, preventing slip without requiring permanent over-clamping that would reduce efficiency.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If a dedicated hydraulic control system is added for the clutch, then torque limiting control is improved, but device complexity increases

Engineering Contradiction:

Improvetorque limiting controlVSAvoidhydraulic control system

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system merges the hydraulic control function by using the existing hydraulic passages in the driven sheave to also control the clutch assembly. This integration eliminates the need for a separate dedicated hydraulic control system, reducing overall device complexity while maintaining reliable torque limiting control.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The hydraulic system is designed with multi-functionality, where the same hydraulic passages serve dual purposes: controlling the movable sheave member for CVT ratio adjustment and controlling the clutch assembly for torque limiting. This universal approach reduces system complexity while achieving both functions reliably.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

This solution protects the CVT from torque spikes by limiting torque transmission to below the driven sheave's capacity, preventing slip and associated damage while maintaining efficiency by reducing friction losses and eliminating the need for dedicated hydraulic control systems.

Implementation Method 1

The hydraulic system is configured to manipulate both the movable sheave member of the driven sheave and the VTL clutch with shared hydraulic pressure

Methodology Applied

Scientific EffectHydraulic pressure: Pressure Increase

Implementation Method 2

The VTL clutch is coupled between the driven sheave and the drivetrain to selectively couple torque between the driven sheave and the drivetrain

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS11543006B2Variable torque limiting clutch for a steel belt continuously variable transmission

Publication Date: 2023.01.03 TEAM IND INC

AI summary

A driven sheave and variable torque limiting clutch assembly for a CVT that includes a drive sheave, a driven sheave, a VTL clutch and a hydraulic system is provided. The driven sheave is operationally coupled to a drive sheave via belt of the CVT. The driven sheave includes a fixed sheave member and a movable sheave member. The driven sheave is operationally coupled to a drivetrain. The VTL clutch is coupled between the driven sheave and the drivetrain to selectively couple torque between the driven sheave and the drivetrain. The hydraulic system is configured to manipulate both the movable sheave member of the driven sheave and the VTL clutch with shared hydraulic pressure.