Free-Piston Engine Transient Control via Reference Signal Shifting

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Solution Overview

Problem

Free-piston engines face challenges in controlling piston movement during transient events, leading to irregular trajectories and tracking errors, which complicates engine operation and increases the risk of misfire, especially when switching between motoring and firing modes.

Innovation Solution

A control algorithm that detects combustion events and applies a reference shift to the control signal to realign it with the actual piston trajectory, using a 'virtual' crankshaft methodology that compares actual and reference trajectories to adjust the piston movement, similar to mechanical crankshaft control in conventional engines.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a free-piston engine operates during transient events such as switching between motoring and firing modes, then the engine can change operational modes flexibly, but the piston trajectory becomes irregular and tracking errors increase

Engineering Contradiction:

Improveoperational mode switching capabilityVSAvoidpiston trajectory control stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The control system dynamically adjusts the reference trajectory based on detected combustion events. When a combustion event is detected, the system shifts the reference trajectory in real-time to account for the transient period, allowing the controller to adapt to changing operational conditions while maintaining reliable piston trajectory control throughout the transient event

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system continuously monitors piston position and detects combustion events, then uses this feedback to determine when to apply reference trajectory shifts. This closed-loop feedback mechanism enables the controller to respond to actual engine conditions and maintain accurate trajectory control during mode transitions

Inventive Principle:

Principle #23Feedback

2Use of energy by moving object

If calibration-based control methodology is used for normal operation, then the engine operates efficiently at desired conditions, but transient events create irregular piston trajectory that cannot be efficiently regulated

Engineering Contradiction:

Improveengine operational efficiencyVSAvoidtransient event response capability

Core Design Contradiction:

Use of energy by moving objectVSAdaptability or versatility

Solution Approach 1:

The control system transitions from static calibration-based control to dynamic adaptive control during transient events. The controller detects combustion events and dynamically shifts the reference trajectory in real-time, enabling the system to maintain efficiency during normal operation while gaining the adaptability needed to handle transient events effectively

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes control parameters dynamically by applying reference trajectory shifts when combustion events are detected. This parameter adjustment allows the control system to adapt to transient conditions while preserving the efficiency benefits of calibration-based control during steady-state operation

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If no crankshaft and flywheel assembly is used, then the number of moving parts is reduced and frictional losses are reduced, but the engine cannot directly mechanically control piston movement

Engineering Contradiction:

Improvefrictional losses from moving partsVSAvoidpiston movement control capability

Core Design Contradiction:

Loss of energyVSEase of operation

Solution Approach 1:

The patent replaces the mechanical crankshaft-flywheel control system with an electronic control system that uses sensors, processors, and actuators. The electronic controller detects combustion events and adjusts piston trajectory through electronic signals to a control device, substituting mechanical control with electronic control while maintaining the ability to regulate piston movement

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The control system introduces an electronic intermediary (the controller) between the combustion event and the piston movement regulation. This intermediary detects combustion events and mediates the control response by applying reference trajectory shifts, enabling precise piston control without direct mechanical coupling

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS10202897B2Systems and methods for transient control of a free-piston engine

Publication Date: 2019.02.12 REGENTS OF THE UNIVERSITY OF MINNESOTA

AI summary

A free-piston (“FP”) engine is a type of internal combustion engine with no crankshaft, so that its piston trajectory is no longer constrained by the mechanical linkage. FP engines have a high potential in terms of energy saving given their simple structure, high modularity and high efficiency, among other attributes. One of the technical barriers that affect FP engine technology is a lack of precise piston trajectory control. For example, the presence of a transient period after a single combustion event can prevent the engine from continuous firing. The present subject matter provides a control scheme that can utilize a reference and control signal shifting technique to modify the tracking error and the control signal to reduce the transient period.