Diesel Engine EGR Valve Control for Turbocharger Overspeed Prevention
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Solution Overview
Problem
In diesel engines with turbocharging and EGR systems, the rotational speed of the turbocharger often exceeds allowable limits during engine acceleration due to rapid increases in exhaust gas flow, leading to potential turbocharger failure.
Innovation Solution
A diesel engine control system that includes a fuel injection amount detection unit, boost pressure detection unit, and engine operation state detection unit, which determines whether to close or open the EGR valve based on both the fuel injection amount and boost pressure, ensuring the rotational speed of the turbocharger remains within safe limits by confining the exhaust gas flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the EGR valve is closed to increase exhaust gas flow to the turbocharger during engine acceleration, then the boost pressure rises more quickly and engine acceleration performance is improved, but the rotational speed of the turbocharger rapidly exceeds the allowable speed and the turbocharger breaks down
Solution Approach 1:
The EGR valve opening degree is dynamically adjusted based on the rotational speed of the turbocharger. When the rotational speed is below the allowable speed, the EGR valve is closed to maximize exhaust gas flow and boost pressure rise. When the rotational speed approaches the allowable limit, the EGR valve opening degree is increased to reduce exhaust gas flow and prevent overspeeding. This dynamic control strategy allows the system to adapt to changing operating conditions and resolve the contradiction between acceleration performance and turbocharger reliability.
Solution Approach 2:
The control system uses feedback from the rotational speed detection unit to continuously monitor the turbocharger's rotational speed and adjust the EGR valve opening degree accordingly. The feedback mechanism compares the actual rotational speed with the allowable speed and modifies the EGR valve position to maintain safe operating conditions while optimizing acceleration performance. This closed-loop control ensures that the turbocharger operates within safe limits while still achieving rapid boost pressure rise.
2Speed
If the EGR valve is closed regardless of turbocharger rotational speed during acceleration, then engine acceleration performance is improved, but the exhaust gas amount rapidly increases causing the turbocharger rotational speed to exceed allowable limits
Solution Approach 1:
The control system transitions from a static on/off control strategy to a dynamic continuous control strategy. The EGR valve opening degree is continuously adjusted based on the real-time rotational speed of the turbocharger, allowing for precise control of exhaust gas flow. This dynamic control enables the system to optimize acceleration performance while preventing turbocharger overspeeding by finely tuning the EGR valve position according to current operating conditions.
Solution Approach 2:
The control system changes the control parameter from a binary state (EGR valve fully closed or fully open) to a continuous parameter (EGR valve opening degree). By varying the opening degree of the EGR valve as a continuous parameter based on turbocharger rotational speed, the system achieves more precise control over exhaust gas flow rate. This parameter change allows for gradual adjustment of exhaust gas flow to match the turbocharger's capacity, preventing overspeeding while maintaining acceleration performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach prevents the turbocharger's rotational speed from exceeding safe limits during engine acceleration, thereby preventing damage and improving fuel efficiency while reducing NOx generation.
Implementation Method 1
a turbine provided in an exhaust passage is driven by energy of exhaust gas, an intake air is compressed by a compressor coupled to the turbine
Implementation Method 2
an EGR valve is closed, a part of exhaust gas discharged from the cylinder is made not to flow into an EGR passage
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An EGR control unit (34S), in accelerating an engine, closes an EGR valve (19) to stop EGR, in a case where an increased amount (ΔQ) of a fuel injection amount (Q) detected by a fuel injection detection unit (31S) is larger than a preset first threshold value (ΔQc), a boost pressure (Pb) detected by a boost pressure detection unit (32S) is lower than a preset second threshold value (Pbc), and an engine operation state detected by an engine operation state detection unit (33S) is outside a preset high rotation and high load operation state region (Ra). As a result of this, an exhaust gas amount flowing into a turbocharger (16) can be confined within a proper range in accelerating the engine in a diesel engine (10), which avoids a rotational speed (Nt) of the turbocharger (16) from rising exceeding an allowable rotational speed (Nta) in accelerating the engine to prevent trouble of the turbocharger (16).