Engine Exhaust Gas Recirculation System Torque Management
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Solution Overview
Problem
Existing engine systems face challenges in maintaining engine torque across all driving regions without using a rich air-fuel ratio, particularly in high-speed and high-load regions, which can lead to decreased fuel efficiency and increased emissions of incomplete combustion products.
Innovation Solution
An engine system that recirculates exhaust gas using a turbocharger and an electric supercharger, with a controller managing the flow of recirculated gas and external air to maintain torque without rich air-fuel ratios, incorporating an EGR cooler and a three-way valve to optimize gas flow and compression in various driving conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a rich air-fuel ratio is used in high-speed and high-load region, then engine torque is maintained and exhaust temperature is reduced, but fuel efficiency deteriorates and emissions of incomplete combustion products increase
Solution Approach 1:
The system dynamically changes the air-fuel ratio parameter based on operating conditions. In high-speed and high-load regions, it transitions from theoretical air-fuel ratio to rich air-fuel ratio combustion only when necessary to maintain torque, while using exhaust gas recirculation to reduce exhaust temperature. This parameter change strategy allows the engine to maintain performance while minimizing fuel efficiency deterioration and emissions.
2Power
If exhaust gas recirculation is applied in low-load region, then torque can be maintained, but the differential pressure between upstream and downstream of EGR valve is minimal making it difficult to supply exhaust gas
Solution Approach 1:
The patent introduces a low-pressure EGR apparatus as an intermediary system that bypasses the traditional high-pressure EGR valve. This low-pressure EGR system recirculates exhaust gas after it has passed through the turbine and catalyst, where the pressure differential is more favorable. The low-pressure EGR apparatus includes an EGR cooler and connects to the intake line upstream of the compressor, enabling effective exhaust gas recirculation in low-load regions where conventional EGR systems struggle.
3Object-generated harmful factors
If theoretical air-fuel ratio combustion is applied in all driving regions, then emissions are reduced, but output and torque of the engine are lost in high-speed and high-load region
Solution Approach 1:
The system dynamically adjusts the air-fuel ratio based on real-time operating conditions rather than maintaining a fixed theoretical ratio. The controller monitors engine speed, load, and other parameters to determine when rich air-fuel ratio combustion is necessary to maintain torque. This dynamic approach allows the engine to operate at theoretical air-fuel ratio in most conditions to minimize emissions, while temporarily switching to rich combustion only when power demands require it.
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 system effectively maintains engine torque across all driving regions while improving fuel efficiency and reducing emissions by optimizing the recirculation of exhaust gas and external air, even in low-load and high-speed conditions where air supply is challenging.
Implementation Method 1
a turbine disposed in the exhaust line
Implementation Method 2
a compressor in the intake line and rotated with the turbine to compress external air
Implementation Method 3
an EGR cooler disposed in the first recirculation line and configured to cool exhaust gas flowing through the first recirculation line
Data Source
AI summary
An engine system includes an engine with a combustion chamber, an intake line in which external air flows, and an exhaust line in which exhaust gas flows. A compressor is disposed in the intake line and rotated with a turbine to compress external air. A first recirculation line is branched off from the exhaust line and merged into the intake line. An EGR cooler cools exhaust gas flowing through the first recirculation line. A second recirculation line is branched off from the first recirculation line. A bypass line is branched off from the first recirculation line between an electric supercharger and the EGR cooler. A three-way valve is disposed where the bypass and first recirculation lines join. An intake valve is disposed in the intake line between where the first recirculation line and intake valve join and where the bypass line and intake valve join.