Variable Intake Valve Cam Profile for Internal EGR
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Solution Overview
Problem
Diesel engines face challenges in reducing noxious emissions, particularly NOX, due to limitations in existing exhaust-gas recirculation systems, including low pressure differences in long-route EGR systems which hinder sufficient flowrate of exhaust gases under certain operating conditions.
Innovation Solution
A diesel engine with an electronically controlled hydraulic system for variable actuation of intake valves, featuring cams with a main lobe for induction strokes and an additional lobe for additional opening during expansion and exhaust strokes, with a boot-shaped profile that varies lift as the crank angle changes, allowing for internal EGR combined with external long-route EGR to control emissions effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a long-route EGR system is used to recirculate exhaust gases, then exhaust gas treatment is improved, but the pressure difference is low which hinders sufficient flowrate of exhaust gases
Solution Approach 1:
The EGR system is segmented into two independent pathways: internal EGR through the additional cam lobe during exhaust stroke, and external long-route EGR through the duct downstream of treatment devices. This segmentation allows each pathway to operate independently, with the internal pathway compensating for insufficient flowrate in the external pathway while maintaining the benefits of treated exhaust gas recirculation.
Solution Approach 2:
The cam profile parameters are specifically designed with an additional lobe that provides controlled valve lift during the exhaust stroke. By adjusting the lift amount, duration, and timing of this additional lobe, the system optimizes the pressure difference and flowrate for internal EGR, compensating for the low pressure difference in the external long-route system while maintaining effective emissions control.
2Object-generated harmful factors
If internal EGR is implemented using an additional cam lobe, then exhaust-gas recirculation is improved, but the system complexity increases
Solution Approach 1:
The camshaft serves multiple functions: the main lobe controls intake valve opening during the induction stroke for normal air intake, while the additional lobe enables internal EGR during the exhaust stroke. This multi-functionality allows the same mechanical component to handle both normal valve operation and emissions control, avoiding the need for separate actuators or complex electronic control systems.
Solution Approach 2:
The cam profile itself provides the EGR function through its geometric design. The additional lobe's shape, position, and lift characteristics are predetermined during manufacturing, allowing the system to automatically regulate internal EGR flow based on engine operating conditions without requiring active control mechanisms. The system self-regulates through the passive mechanical design of the cam profile.
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 configuration enables precise control of diesel engine operations to drastically reduce noxious emissions, particularly NOX, by optimizing exhaust-gas recirculation and valve lift profiles across various engine conditions.
Implementation Method 1
at least one intake valve for each cylinder is controlled by the respective tappet, against the action of the aforesaid elastic means, via hydraulic means including a pressurized fluid chamber
Implementation Method 2
the pressurized fluid chamber is designed to be connected, by means of a passage controlled by a solenoid valve, with an exhaust channel, so that, when said solenoid valve is open, the intake valve is uncoupled from the respective tappet
Implementation Method 3
the cam for controlling said intake valve with variable actuation has a main lobe for causing opening of the valve during the induction stroke for intake of fuel into the engine cylinder and an auxiliary lobe for causing an additional opening of the intake valve during the expansion and exhaust strokes
Implementation Method 4
during the exhaust stroke part of the exhaust gases passes from the cylinder into the intake duct, through the open intake valve
Data Source
AI summary
A supercharged diesel engine is equipped with an electronically controlled hydraulic system for variable actuation of the intake valves of the engine. The cam that controls each intake valve has an additional lobe for causing an additional opening of the intake valve, during the exhaust stroke, so as to provide an exhaust-gas recirculation directly inside the engine. Said additional lobe is shaped in such a way as to give rise to a profile of the additional lift of the valve as the crank angle varies with a boot conformation, including an initial stretch with a gentler slope extending from a point of zero lift corresponding to the expansion stroke in the engine cylinder. The engine is moreover equipped with a duct for exhaust-gas recirculation of the long-route type, which picks up the gases from a point of the exhaust duct set downstream of the catalytic converter and of the particulate trap.