Common Rail Fuel Pump Control via Segmented Metering Valves
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Solution Overview
Problem
Common rail fuel pumps face inefficiencies due to high-pressure fuel leakages and uneven distribution of pumping duty among pump elements, leading to reduced efficiency and potential fatigue failure, and there is a need for accurate control of rail pressure to maintain injection pressure.
Innovation Solution
A control method for a fuel pump assembly with multiple pump elements, where each element has a dedicated metering valve and is driven by a cam with multiple lobes, uses a PI controller to adjust the control valve based on measured and demanded rail pressure, incorporating proportional and integral terms to maintain rail pressure and diagnose faults by comparing integral terms across cam lobes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single inlet metering valve is used to meter fuel entering all pump elements, then the pumping duty is distributed equally among pump elements, but the frequency of pumping strokes for each element is maximum leading to potential fatigue failure
Solution Approach 1:
The patent divides the single inlet metering valve into multiple separate metering valves, with each pump element having its own dedicated metering valve. This segmentation allows independent control of each pump element's pumping duty, enabling reduced frequency of pumping strokes for specific elements to prevent fatigue failure while maintaining overall system productivity.
2Adaptability or versatility
If each pump element is provided with its own dedicated metering valve, then the pumping duty can be independently controlled, but the device complexity increases
Solution Approach 1:
The system segments the fuel metering function into separate valves for each pump element, enabling independent control of pumping duty for each element. This allows flexible adaptation to varying operational requirements while managing complexity through modular design.
Solution Approach 2:
Each dedicated metering valve serves multiple functions: it controls fuel metering for its associated pump element, enables independent pumping duty adjustment, and facilitates fault isolation. This multi-functionality justifies the increased complexity by providing versatile control capabilities.
3Ease of manufacture
If pump elements operate with clearances between components, then assembly is simplified, but high-pressure fuel leakages occur during pumping stroke reducing pump efficiency
Solution Approach 1:
The patent implements feedback control by monitoring rail pressure and using this information to adjust the metering valve timing and duration. This feedback mechanism compensates for fuel leakages through clearance gaps, maintaining pump efficiency without requiring tighter tolerances or more complex sealing arrangements.
Solution Approach 2:
The system dynamically changes operational parameters (metering valve timing, duration, and pumping frequency) based on detected conditions to compensate for fuel leakages. By adjusting these parameters in response to pressure deviations, the system maintains efficiency despite the presence of clearance-based leakages.
4Reliability
If rail pressure is not controlled accurately, then the control system is simpler, but injection pressure cannot be maintained
Solution Approach 1:
The patent employs feedback control where rail pressure is continuously monitored and used to adjust metering valve operation. This closed-loop system maintains accurate rail pressure and injection pressure stability, justifying the added complexity through improved reliability and control precision.
Data Source
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AI summary
A method and apparatus for controlling a fuel pump assembly comprising a plurality of pump elements (10) for delivering fuel at high pressure to a rail volume, each of the pump elements (10) comprising a plunger (12) which is driven by an associated cam to perform at least one pumping event per engine revolution and a control valve (20) for controlling fuel flow into and/or out of the pump chamber (14). Each pumping event corresponds to an associated cam lobe of the associated cam. The method comprises, for each pumping event of each pump element, controlling the control valve (20) of said pump element (10) in response to an output control signal (52a-52f, 114) derived from at least one previous pumping event. The output control signal (52a-52f, 114) is derived by measuring fuel pressure within the rail volume to derive a measured rail pressure value (42); and comparing the measured rail pressure value (42) with a demanded rail pressure value (46) to derive a rail pressure error (102). A proportional and integral calculation is performed on the rail pressure error (102) to derive a proportional term (104) for the rail pressure error (102) and an integral term (110) for the rail pressure error (102). The proportional term (104) and the integral term (110) are combined to derive the output control signal (52a-52f, 114). Monitoring of the integral term (110) for each pumping event of each pump element provides a means for identifying and diagnosing a fault condition within the fuel pump assembly or associated fuel system.