Diesel Exhaust Fluid Delivery Pressure Control via Segmented Valve and Pump Loops
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Solution Overview
Problem
The complexity of DEF delivery systems increases with the addition of a backflow valve, transforming the system from a single-input, single-output control system to a multiple-input, single-output system, making it challenging to manage pressure and mass flow balance effectively, and complicating failure detection.
Innovation Solution
A dual-variable control strategy is implemented, where the system operates under two different control schemes based on mass flow rates, using a PID controller to manage the backflow valve and pump independently, ensuring stable pressure and mass flow delivery by controlling the backflow valve at low flow rates and adjusting pump speed at high flow rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a backflow valve is added to increase delivery capability, then the total delivery of the system is improved, but the control mechanism complexity increases
Solution Approach 1:
The control mechanism is segmented into two independent control loops: an inner loop controlling the backflow valve and an outer loop controlling the pump. This segmentation allows each controller to operate independently with its own control window, reducing the overall control complexity while maintaining the ability to deliver increased fluid volumes through coordinated operation of both components.
2Productivity
If a backflow valve is added to affect mass flow balance, then the delivery capability is improved, but failure detection becomes more difficult
Solution Approach 1:
The control system is divided into separate control windows for the backflow valve and pump, allowing failure detection to be performed independently for each component. The controller can isolate and diagnose issues with either the backflow valve or pump separately, making failure detection easier despite the added complexity of the backflow valve.
3Measurement precision
If pressure is controlled by varying both pump speed and backflow valve, then accurate dosage is achieved, but the control variables cannot be easily decoupled
Solution Approach 1:
The control system segments the pressure control function into two distinct control windows: one for the backflow valve and one for the pump. Each control window operates independently with its own PID controller, allowing accurate pressure control to be achieved while keeping the control variables decoupled and manageable.
Data Source
AI summary
A diesel exhaust fluid delivery system and a dual-variable control strategy for adjusting the delivery pressure and the mass flow rate of the fluid passing through the system. The method for operating the system using two operating modes: low flow rate and high flow rate. While operating in the low flow rate operating mode, the speed of a DEF pump remains constant and DEF delivery to the exhaust system is adjusted by controlling a backflow valve. While operating in the high flow rate operating mode, the backflow valve is closed and the speed of the pump is adjusted to regulate DEF delivery to the exhaust system.