Detecting Passive Pressure Limiting Valve Opening in Common Rail Systems
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Solution Overview
Problem
In common rail fuel injection systems, the passive pressure limiting valve can unintentionally open due to factors like cable breakage or a stuck suction throttle, leading to increased rail pressure and reduced engine efficiency, with existing methods being ineffective in such cases.
Innovation Solution
A method that detects the opening of the pressure limiting valve by comparing rail pressure with a second limit value and recognizing a strongly negative pressure gradient, without requiring hardware changes or additional sensors, using existing signals to recommend power reduction or emergency stop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the rail pressure is allowed to increase to a high level (e.g., 1950 bar) during load reduction, then the pumping volume increases and rail pressure rises, but the pressure limiting valve opens unintentionally causing rail pressure to drop to a low level (e.g., 800 bar) and engine efficiency decreases
Solution Approach 1:
The control method applies preliminary action by proactively increasing the PWM signal value before the rail pressure reaches the dangerous opening level of the pressure limiting valve. When load reduction is detected and rail pressure exceeds a first threshold (e.g., 1800 bar), the PWM signal is temporarily increased to a higher value (e.g., 80% instead of 40%) to preemptively prevent the pressure from reaching the valve opening threshold, thereby avoiding the harmful pressure drop and maintaining engine efficiency
2Speed
If the PWM signal is temporarily increased to suppress unintentional opening of the pressure limiting valve, then the dynamics of the control member are increased, but the method becomes ineffective when failures occur such as cable breakage or suction throttle plug not being correctly locked in position
Solution Approach 1:
The control method implements feedback by continuously monitoring the actual rail pressure and comparing it with the desired pressure level. When the rail pressure fails to reach the desired level despite the increased PWM signal (indicating a failure such as cable breakage or stuck throttle), the system detects this discrepancy and can trigger appropriate failure responses. This feedback mechanism ensures the system not only responds quickly but also detects when the quick response mechanism is ineffective due to component failures
3Stability of the object's composition
If the rail pressure control has a comparatively long reaction time, then the control system is stable, but the rail pressure can increase to such an extent that the pressure limiting valve opens, causing efficiency loss and murky exhaust gases
Solution Approach 1:
The control method applies dynamics by making the PWM signal value adjustable and responsive to changing operating conditions. Instead of using a fixed PWM value, the system dynamically increases the PWM signal to a higher value when load reduction is detected and rail pressure approaches the critical threshold. This dynamic adjustment allows the control system to maintain stability under normal conditions while responding quickly to prevent efficiency loss when needed
Data Source
AI summary
In a method for detecting the opening of a passive pressure limiting valve for releasing fuel from a common rail fuel injection system to a tank with a fuel supply including a throttle wherein, based on a stationary rail pressure present during manual operation, a load reduction is detected when the rail pressure exceeds a first limit value and, as a result, a PWM signal for controlling the suction throttle is temporarily increased, the opening of the pressure limiting valve is recognized if, as a result, the rail pressure exceeds a second limit value and increases still further.