CVT Speed Ratio Drift Control via Dynamic Command Adjustment

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Solution Overview

Problem

Continuously variable transmissions (CVTs) face challenges in maintaining desired speed ratios due to conditions like cold temperatures, wheel slip, or reduced hydraulic pressure, leading to speed ratio drift, which can result in loss of propulsion, reduced torque capacity, and decreased reliability and fuel efficiency.

Innovation Solution

A method that measures and adjusts the commanded speed ratio to match the measured speed ratio when drift occurs, allowing for reduced further drift and improving launch performance, torque capacity, drivability, reliability, and fuel economy by setting the commanded speed ratio to a value different from the desired speed ratio if the measured speed ratio exceeds a threshold.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If hydraulic pressure is increased to maintain desired speed ratio, then speed ratio control is improved, but system complexity and power requirements increase

Engineering Contradiction:

Improvespeed ratio controlVSAvoidhydraulic power

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

The control system dynamically adjusts the commanded speed ratio parameter based on detected drift conditions, changing the operational parameters of the CVT to match actual performance rather than relying on fixed desired ratios that may become unachievable under certain conditions

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If commanded speed ratio is adjusted to match measured speed ratio, then speed ratio drift is reduced, but precision of maintaining desired ratio decreases

Engineering Contradiction:

Improvespeed ratio stabilityVSAvoidspeed ratio accuracy

Core Design Contradiction:

Stability of the object's compositionVSMeasurement precision

Solution Approach 1:

The system continuously monitors the measured speed ratio and uses this feedback to detect drift conditions, comparing actual performance against commanded values and adjusting the commanded ratio accordingly to maintain stability

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

Instead of trying to force the measured speed ratio to match the desired commanded ratio through increased hydraulic pressure, the system inverts the approach by adjusting the commanded ratio to match the measured ratio, accepting actual performance as the new target

Inventive Principle:

Principle #13The other way round (Inversion)

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 approach effectively reduces and eliminates speed ratio drift, enhancing launch performance, torque capacity, drivability, reliability, and fuel efficiency by dynamically adjusting the commanded speed ratio to match the measured speed ratio under conditions of pressure limitations or other adverse conditions.

Implementation Method 1

The clamping forces for the variator pulleys are provided using hydraulic actuators and the clamping force generated by those hydraulic actuators depends upon the hydraulic pressure of fluid provided to the actuators

Methodology Applied

Scientific EffectHydraulic pressure: Pressure Increase

Data Source

PatentUS10690245B2Method and system for controlling a continuously variable transmission for a vehicle propulsion system

Publication Date: 2020.06.23 GM GLOBAL TECHNOLOGY OPERATIONS LLC

AI summary

A control system and method for controlling a continuously variable transmission in a vehicle propulsion system includes measuring a speed ratio of the continuously variable transmission, determining whether the measured speed ratio is drifting away from a commanded speed ratio, and adjusting the commanded speed ratio to a value that is different than a desired speed ratio if the measured speed ratio is drifting away from the commanded speed ratio.