Powertrain Controller Prevents Shift Hunting in CVT

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Solution Overview

Problem

Continuously variable transmissions experience shift hunting, leading to increased fuel consumption, operator discomfort, and transmission wear when operating near shift points, especially in drivetrains without flexible or fluid couplings, which can cause damage from asynchronous shifts.

Innovation Solution

A powertrain system with a controller that operates the engine at a first substantially constant speed and adjusts to a second constant speed based on detected shift conditions, utilizing a variator and multiple gearsets to prevent shift hunting by managing engine speed and transmission ratios.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If the transmission delays the shift point to prevent shift hunting, then shift hunting is reduced, but asynchronous shifts occur causing shocks and potential damage to the driveline

Engineering Contradiction:

Improveshift stabilityVSAvoidshocks and forces to driveline

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The system changes engine speed parameters dynamically - operating at a first constant speed during normal conditions and switching to a second different constant speed when shift conditions are detected. This parameter change prevents the transmission from operating in the unstable band around the shift point, thereby preventing shift hunting while avoiding asynchronous shifts that cause shocks.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If the transmission operates in a band around the shift point, then it can maintain optimal performance, but shift hunting occurs increasing fuel consumption and transmission wear

Engineering Contradiction:

Improvetransmission performanceVSAvoidfuel consumption

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The controller continuously monitors transmission operation and detects shift conditions based on feedback from the system. When shift conditions are detected, the controller adjusts engine speed to a different constant speed, creating a feedback loop that prevents the transmission from operating in the shift hunting band, thereby reducing fuel consumption while maintaining performance.

Inventive Principle:

Principle #23Feedback

3Productivity

If the transmission operates in a band around the shift point, then it can maintain optimal performance, but operator discomfort or irritation occurs due to shift hunting

Engineering Contradiction:

Improvetransmission performanceVSAvoidoperator discomfort

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

By changing engine speed parameters to a second constant speed when shift conditions are detected, the system eliminates the oscillating shifts that cause operator discomfort while maintaining transmission performance through controlled operation outside the unstable shift band.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS8568271B2System and method to prevent shift hunting in a powertrain

Publication Date: 2013.10.29 CATERPILLAR INC

AI summary

A method for preventing shift hunting in a powertrain including an engine and a transmission having a variator, a first gearset, and a second gearset is disclosed. The method includes operating the engine at a first substantially constant speed, detecting a shift condition, and operating the engine at a second substantially constant speed as a function of detecting the shift condition. The second speed is different than the first speed.