Exhaust Cam Angle Control for Low-Speed Drivability
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Solution Overview
Problem
In vehicle engines, the recirculation of exhaust gas to reduce NOx emissions can lead to deteriorated ignition ability and increased fuel consumption, particularly in low-speed driving ranges, due to valve overlap periods causing combustion instability and backfire phenomena.
Innovation Solution
An apparatus and method that control the exhaust cam angle based on current engine speed and air inflow amount, using databases to select target angles that minimize valve overlap, thereby improving drivability in low-speed ranges by preventing premature ignition and reducing fuel consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the exhaust cam is retarded to increase EGR rate, then NOx reduction is improved, but fuel consumption increases and drivability deteriorates in low-speed range
Solution Approach 1:
The exhaust cam angle is made dynamically adjustable based on driving conditions. The control unit selectively applies cam angle retardation only when necessary (high-speed, high-load conditions), while maintaining optimal cam timing for low-speed conditions, thus dynamically optimizing the balance between NOx reduction and fuel efficiency
Solution Approach 2:
The invention changes the exhaust cam angle parameter selectively based on engine operating conditions. By monitoring vehicle speed, acceleration, and load, the control unit adjusts the cam angle to achieve EGR only when it doesn't negatively impact fuel consumption or drivability
2Productivity
If the exhaust cam is retarded to improve volumetric efficiency, then combustion stability is improved, but valve overlap causes backfire and combustion instability in low-speed range
Solution Approach 1:
The exhaust cam timing is dynamically adjusted based on real-time driving conditions. During low-speed operation, the cam angle is maintained without excessive retardation to prevent valve overlap and combustion instability, while allowing cam retardation during high-speed operation when volumetric efficiency benefits are more significant
3Object-generated harmful factors
If EGR rate is increased to reduce NOx, then emission performance is improved, but ignition ability deteriorates
Solution Approach 1:
The invention selectively changes the exhaust cam angle parameter to achieve EGR only under conditions where ignition ability is sufficient to handle the increased exhaust gas concentration. The control unit monitors engine operating parameters to determine when EGR can be applied without compromising ignition reliability
Data Source
AI summary
An apparatus and a method for controlling a valve includes a first database which stores a plurality of first exhaust cam angles and outputs a first exhaust cam angles corresponding to a current engine speed and inflow air amount. A second database stores a plurality of second exhaust cam angles and outputs a second exhaust cam angles corresponding to the engine speed and inflow air amount. A target angle decision unit selects the exhaust cam angles outputted from the first and second databases as a target angle for controlling an operation of an exhaust valve, in accordance with a current gear stage of a vehicle. A camshaft control unit controls rotational motion of a camshaft coupled to the exhaust cam so that the exhaust cam reaches the target angle, in which the plurality of first exhaust cam angles are in a range in which the exhaust cam is not retarded.