Marine Engine Speed Offset for Panic Shift Stalling Prevention
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Solution Overview
Problem
Existing marine propulsion systems face challenges in smoothly transitioning engine speed when helm demand changes, leading to speed discontinuities and potential engine stalling during rapid throttle adjustments, particularly in panic shift scenarios.
Innovation Solution
A method that calculates an engine speed offset based on the difference in helm demand and time since the demand change, temporarily elevating the engine speed to prevent stalling by maintaining a higher throttle valve position, which allows for a larger air volume in the intake plenum, and filters this offset as the helm demand stabilizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the engine speed is rapidly decreased in response to a decrease in helm demand, then the engine speed responds quickly to the helm demand change, but speed discontinuities and engine stalling occur during rapid throttle adjustments
Solution Approach 1:
The system detects a rapid decrease in helm demand (panic shift condition) before the engine speed can drop to stalling levels. It preemptively maintains a higher throttle valve position and applies an engine speed offset to keep the engine speed elevated, preventing the air volume in the intake plenum from dropping too low and causing stall
Solution Approach 2:
The system changes the engine speed setpoint parameter dynamically by applying an offset based on the detected panic shift condition. The offset is calculated based on the difference between current and previous helm demands, and the engine speed is maintained at an elevated level rather than following the normal reduction trajectory
2Reliability
If the throttle valve position is maintained at a higher position during rapid throttle changes, then a larger air volume is maintained in the intake plenum preventing engine stalling, but the engine speed does not decrease quickly enough to match the reduced helm demand
Solution Approach 1:
The system preemptively maintains higher throttle valve position and engine speed when a panic shift condition is detected, before the engine would naturally slow down. This preliminary action ensures adequate air volume is already present in the intake plenum to handle the subsequent rapid throttle closure without causing stall
Solution Approach 2:
The system creates a cushion of additional air volume in the intake plenum by maintaining higher throttle position and engine speed beforehand. This cushion of air volume acts as a buffer that prevents the engine from stalling when the throttle is rapidly closed, even though it temporarily delays the engine speed reduction
3Productivity
If a feed forward signal is used to predict and move the throttle valve to the predicted position, then the engine speed control is improved without waiting for slower responding PID controller, but speed discontinuities may occur during rapid helm demand changes
Solution Approach 1:
The system modifies the feed forward signal calculation by incorporating an engine speed offset when a panic shift condition is detected. This parameter change ensures that the throttle valve is commanded to a position that maintains adequate air volume, preventing the speed discontinuities and stalling that would otherwise occur with standard feed forward control
Solution Approach 2:
The system uses feedback from the helm demand signal to detect rapid decreases (panic shift conditions). This feedback triggers a special control mode where the feed forward signal is adjusted to maintain higher engine speed, creating a closed-loop response that prevents speed discontinuities while preserving the fast response benefits of feed forward control
Data Source
AI summary
The speed of a marine propulsion system's engine is temporarily elevated in response to a decrease in helm demand. A controller receives a command to decrease the helm demand from a first helm demand to a second helm demand and compares a demand difference between the second helm demand and the first helm demand to a threshold demand delta. In response to the demand difference exceeding the threshold demand delta, the controller tabulates a time since the demand difference exceeded the threshold demand delta and determines an engine speed offset based upon the second helm demand and the time. The controller determines a non-elevated engine speed setpoint corresponding to the second helm demand and calculates an elevated engine speed setpoint based on the non-elevated engine speed setpoint and the engine speed offset. Engine speed is then decreased to the elevated engine speed setpoint.