Fuel Rail Pressure Control via Leak Rate Compensation
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Solution Overview
Problem
Conventional fuel supply systems for Diesel engines face challenges in controlling rail pressure effectively, leading to inefficient fuel injection and increased pollutant emissions due to the complex relationship between fuel injection timing, engine operating conditions, and internal leaks, requiring labor-intensive experimental analysis for system tuning.
Innovation Solution
A method for controlling rail pressure by establishing relationships between rail pressure and injector leak rates, estimating fuel drain rates, and adjusting pump operation to maintain desired intake flow rates, using a controller with feed-forward and feedback units to compensate for variations in engine load and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional experimental analysis and tuning of the complete fuel supply system is used, then appropriate fuel rail pressure can be maintained in all operating conditions, but considerable amounts of labour are required and the process must be redone whenever components are replaced
Solution Approach 1:
The patent segments the fuel supply system into separate components (injector, pump, rail) and establishes independent characteristic relationships for each. The injector leak rate is determined as a function of rail pressure alone, while the pump delivery rate is determined as a function of pump speed and rail pressure. This segmentation allows each component to be analyzed and tuned independently, eliminating the need for complete system re-tuning when individual components are replaced.
Solution Approach 2:
The patent performs preliminary characterization of each component by establishing their characteristic relationships before actual operation. The injector leak rate characteristics and pump delivery rate characteristics are determined in advance through separate experiments and stored in the control unit. During operation, the control unit simply retrieves and applies these pre-determined characteristics, eliminating the need for time-consuming experimental analysis during system assembly or component replacement.
2Manufacturing precision
If the pump is controlled to deliver a specific fuel drain rate, then fuel injection timing can be optimized, but the pump cannot be straightforwardly controlled due to internal leakage rates depending on pressures and temperature
Solution Approach 1:
The patent implements a feedback control mechanism where the control unit continuously monitors the actual rail pressure and compares it with the desired rail pressure. Based on this comparison and the pre-determined pump characteristics, the control unit adjusts the pump speed to achieve the desired fuel delivery rate. This feedback loop compensates for variations in internal leakage rates caused by pressure and temperature changes, enabling precise control of fuel injection timing without requiring direct control of the pump's internal parameters.
Data Source
AI summary
Methods, a fuel supply system, and a computer readable medium embodying a computer program product are provided for controlling rail pressure in a fuel supply system comprising a fuel pump, an injector and a rail connecting the injector to the pump. At least one of the methods includes, but is not limited to establishing a relationship between said rail pressure and a leak rate of the injector, estimating a fuel drain rate from said rail based on a fuel injection rate, the rail pressure and said rail pressure/leak rate relationship, estimating a desired intake flow rate of said pump based on said fuel drain rate, and controlling the pump to operate at said desired intake flow rate.