Variable Valve Actuation Control Valve Cavitation Prevention
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Solution Overview
Problem
The existing system for variable actuation of engine valves in internal-combustion engines experiences issues with cavitation and noise due to pressure imbalances during the late-valve-opening and multilift modes, particularly at low engine RPM and high temperatures, where the pressure in the pressurized fluid volume drops below the environment pressure, leading to reverse fluid flow and vibrations.
Innovation Solution
The electronic control unit is programmed to manage the control valve such that it re-establishes communication between the pressurized fluid volume and the lower-pressure environment before the pressure significantly drops, ensuring a minimal pressure differential and preventing cavitation and hammer effects by switching off the solenoid current earlier in the engine valve's closing cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the solenoid valve is kept closed during the entire cam lift cycle to maintain full valve lift, then the valve opening duration is improved, but pressure drops below environment pressure causing cavitation and reverse fluid flow
Solution Approach 1:
The solenoid valve is switched off in advance (before the cam lift cycle ends) to prevent pressure from dropping below environment pressure. This preliminary action maintains positive pressure differential throughout the valve operation, preventing cavitation and reverse flow while still achieving the desired valve timing and duration.
Solution Approach 2:
The control system anticipates the pressure drop issue and counteracts it by closing the solenoid valve earlier than the conventional end of cam lift. This preliminary anti-action prevents the harmful pressure differential from developing in the first place, eliminating cavitation and fluid hammer effects.
2Reliability
If the solenoid valve is switched off earlier to prevent cavitation, then fluid flow stability is improved, but the valve closing timing is advanced
Solution Approach 1:
The solenoid valve switching-off timing is precisely calculated and set in advance to occur just before pressure would drop below environment pressure. This preliminary action maintains fluid flow stability while minimizing the impact on valve opening duration, as the valve remains fully open throughout the cam lift cycle.
3Reliability
If the control valve maintains communication between pressurized fluid volume and lower-pressure environment, then cavitation is prevented, but energy loss increases due to continuous pressure maintenance
Solution Approach 1:
Instead of maintaining continuous communication between the pressurized fluid volume and environment, the solenoid valve is periodically switched on and off based on the cam lift cycle phase. The valve is closed during the main lift phase to maintain pressure, and opened briefly at the end to equalize pressure, creating a periodic control pattern that balances cavitation prevention with energy efficiency.
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 effectively eliminates cavitation and noise issues by maintaining a stable pressure differential, reducing the risk of reverse fluid flow and associated vibrations, and ensures reliable operation across various engine conditions.
Implementation Method 1
a solenoid valve (24) having a body in which is defined a passage which, when the solenoid valve is in its initial state, connects the volume of pressurized fluid (C) to the environment at lower pressure (23)
Implementation Method 2
The master piston (16) is able to transmit a thrust to the stem (8) of the valve (7) so as to cause opening of the latter against the action of the elastic means (9), by means of pressurized fluid (preferably oil coming from the engine-lubrication circuit) present in a volume of pressurized fluid (C)
Implementation Method 3
Opening of each intake valve (7) is controlled, in the way that will be described in what follows, by a camshaft (11), which is rotatably mounted about an axis (12) within supports of the cylinder head (1) and comprises a plurality of cams (14) for actuation of the intake valves (7)
Data Source
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AI summary
A system for variable actuation of an engine valve of an internalcombustion engine comprises a master piston (16) driven directly or indirectly by a cam (14) of a camshaft (11). A slave piston (21) is driven by said master piston (16) by means of a volume of pressurized fluid (C) interposed between the master piston (16) and the slave piston (21). The slave piston (21) causes the engine valve (7) to open, against the action of a spring (9). An electrically operated control valve (24) controls a communication between the volume of pressurized fluid (C) and an environment at lower pressure (23), with which a fluid accumulator (270) is in communication. An electronic control unit (25) is programmed for controlling the electrically operated control valve (24), so as to actuate the engine valve (7), depending upon the operating conditions, according to one or more different valve modes, including a late-valve-opening (LVO) mode and/or a multilift (ML) valve mode. When one of these valve modes is actuated, the control valve (24) opens the aforesaid communication in advance with respect to the end of the lift cycle of the cam (14), and not after closing of the engine valve (7), in such a way as to prevent or reduce a decrease in pressure in the volume of pressurized fluid (C) after closing of the engine valve (7).