Parallel Path Transmission Anti-Hunt Control via Lock-Out Timer

Solution Overview

Problem

Parallel path variable transmissions experience inefficient and annoying gear train oscillations due to repetitive shifts, which can decrease the useful life of the drive train and engine, and existing hysteresis algorithms are impractical for these systems.

Innovation Solution

A method that shifts the transmission at synchronous points and sets a lock-out timer to prevent subsequent shifts until expiration, with the option to override the timer if the output ratio trends back toward the prior synchronous point and passes a predetermined threshold, thereby controlling oscillations without relying on hysteresis limits.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If automatic gear ratio selection is implemented based on engine speed, then operator convenience is improved, but gear train oscillations occur causing reduced reliability and increased wear

Engineering Contradiction:

Improveautomatic gear selectionVSAvoiddrive train oscillation

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The controller predicts future engine speed based on current acceleration trends and proactively selects gear ratios that will maintain optimal operation, preventing oscillations before they occur by anticipating the system's future state rather than reactively responding to current conditions

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system continuously monitors engine speed, acceleration, and deceleration rates, using this feedback to dynamically adjust gear ratio selection and prevent oscillations by responding to actual system behavior rather than relying on fixed shift points

Inventive Principle:

Principle #23Feedback

2Reliability

If hysteresis algorithm is used to prevent oscillations, then drive train reliability is improved, but it is ineffective for parallel path variable transmissions where shift points must be singular

Engineering Contradiction:

Improveoscillation controlVSAvoidcompatibility with parallel path transmission

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The controller predicts future engine speed based on current acceleration trends and proactively selects gear ratios that will maintain optimal operation, preventing oscillations before they occur by anticipating the system's future state rather than reactively responding to current conditions

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system transitions from static hysteresis-based shift points to dynamic, predictive gear selection that adapts to real-time acceleration and deceleration rates, allowing the control strategy to flexibly respond to varying operating conditions without requiring multiple fixed shift points

Inventive Principle:

Principle #15Dynamics

3Productivity

If frequent shifts are allowed to maintain optimal engine speed, then productivity is improved, but drive train wear increases reducing useful life

Engineering Contradiction:

Improveoperational efficiencyVSAvoiddrive train life

Core Design Contradiction:

ProductivityVSDuration of action of stationary object

Solution Approach 1:

The controller predicts future engine speed based on current acceleration trends and proactively selects gear ratios that will maintain optimal operation, preventing oscillations before they occur by anticipating the system's future state rather than reactively responding to current conditions

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system continuously monitors engine speed, acceleration, and deceleration rates, using this feedback to dynamically adjust gear ratio selection and prevent oscillations by responding to actual system behavior rather than relying on fixed shift points

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS7660657B2Anti-hunt system and method for parallel path variable transmission

Publication Date: 2010.02.09 CATERPILLAR INC

AI summary

A system and method for largely controlling transmission gear ratio oscillation is disclosed. When shifts are executed substantially at synchronous points rendering hysteretic anti-hunting schemes impractical, the disclosed techniques in any combination thereof may allow for oscillation control via an overridable lock-out timer. For oscillation control during incline navigation and other similar loading scenarios, the transmission may be selectively locked if certain operational criteria are met.