Common Rail Fuel Injection Controller Dynamics
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Solution Overview
Problem
In common rail fuel injection systems, the differential term in feedback control can cause unintended behavior in fuel pressure due to temporal deviations, leading to increased particulate matters and nitrogen oxides in exhaust gas and abnormal noise, especially when the target pressure changes rapidly.
Innovation Solution
A controller that restricts the reflection of the differential term in the control amount when the pressure deviation increases with target pressure, using adjustment processing to prevent unintended increases or decreases in fuel pressure, thereby maintaining stable fuel injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the differential term is used in feedback control to improve following performance, then the actual pressure can track target pressure changes more accurately, but temporal deviation causes the differential term to generate unintended behavior when target pressure changes rapidly
Solution Approach 1:
The control system dynamically adjusts the differential term based on the state of actual pressure relative to target pressure. When actual pressure is lower than target pressure, the differential term is restricted or set to zero. When actual pressure equals or exceeds target pressure, the differential term is calculated normally. This dynamic adjustment resolves the contradiction by adapting the control strategy to real-time conditions, preventing unintended behavior during rapid pressure changes while maintaining accurate tracking during normal operation.
2Loss of time
If the differential term is calculated based on pressure deviation fluctuation, then phase lag is improved in cyclic fluctuation cases, but the influence of differential term increases when pressure deviation rapidly changes
Solution Approach 1:
The harmful influence of the differential term is extracted and removed by setting it to zero or restricting it under specific conditions where it causes unintended behavior (when actual pressure is lower than target pressure). This allows the system to eliminate the harmful phase advance effect while preserving the beneficial phase lag compensation during normal cyclic operations, thus resolving the contradiction between phase lag improvement and prevention of unintended behavior.
3Manufacturing precision
If feedback control is performed to conform actual pressure to target pressure, then fuel injection accuracy is improved, but temporal deviation between control output and pressure reflection causes control reliability to decrease
Solution Approach 1:
The system applies preliminary anti-action by restricting the differential term before it can cause unintended behavior. By monitoring the relationship between actual and target pressure, the system preemptively prevents the differential term from generating harmful effects during the temporal deviation period, thus maintaining control reliability while preserving fuel injection accuracy.
Data Source
AI summary
In a common rail fuel injection system, a fuel pump pressure-feeds fuel to a common rail, which accumulates the fuel at high pressure corresponding to fuel injection pressure. An electronic control unit (ECU) drives and controls a suction control valve provided in the fuel pump to regulate a pressure-feeding amount of the fuel and to perform fuel pressure feedback control. The ECU calculates a differential term of a control amount of the suction control valve based on a pressure deviation of the fuel pressure in the common rail with respect to target pressure. The ECU sets the differential term at zero when the fuel pressure is higher than the target pressure and the differential term of the control amount is a value for pressure-feeding the fuel.