Four Stroke Engine Exhaust Valve Linkage Design
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Solution Overview
Problem
Conventional four-stroke internal combustion engines suffer from low energy recovery from exhaust gases due to the slow opening speed of poppet valves, resulting in significant irreversible pressure losses and reduced available energy for turbines.
Innovation Solution
Synchronizing the camshaft with the crankshaft to rotate at the same speed, and utilizing a linkage arrangement to prevent valve motion during the compression stroke, allowing for a quicker opening of the exhaust valve and reducing throttling losses, thereby enhancing energy recovery from exhaust gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a camshaft controlled poppet valve is used, then the valve is robust and durable, but the opening speed is slow due to the valve being at rest when it starts to open
Solution Approach 1:
The valve is given a preliminary motion before the actual opening phase. The camshaft profile is designed to first accelerate the valve from rest, then maintain it in an open position. This preliminary acceleration phase prepares the valve for rapid opening, reducing the throttling period during blowdown while maintaining the robust camshaft-controlled actuation mechanism.
2Power
If the exhaust arrangement opens before the piston reaches BDC, then power is maintained, but irreversible pressure losses increase due to throttling
Solution Approach 1:
The camshaft rotation speed is changed from the conventional half crankshaft speed to the same speed as the crankshaft. This parameter change doubles the angular velocity of the camshaft, which directly increases the valve opening speed. The faster opening reduces the duration of throttling, thereby reducing irreversible pressure losses while maintaining the necessary blowdown timing for power preservation.
3Ease of operation
If the camshaft rotates at half the crankshaft speed, then the valve timing is conventional, but the valve opening speed is reduced
Solution Approach 1:
The camshaft rotation speed is dynamically adjusted to match the crankshaft speed instead of being fixed at half speed. This dynamic change in operational parameters allows the system to achieve faster valve opening speeds while maintaining proper valve timing control through the modified camshaft profile designed for the new rotation regime.
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 significantly reduces irreversible throttling losses, allowing a larger portion of blowdown energy to be transferred to the turbine, increasing the recovery of energy from exhaust gases and improving engine efficiency, including increased brake thermal efficiency and open/closed cycle efficiency.
Implementation Method 1
a camshaft controlled poppet valve has a drawback in that it is at rest when it starts to open, which entails a slow initial opening speed of the poppet valve. Thus, the poppet valve throttles an outflow of exhaust gases through the exhaust arrangement during at least an initial portion of the blowdown, which reduces the available energy in the exhaust gases
Implementation Method 2
The brake power of an ICE is the power available at an output shaft/crankshaft of the ICE. The exhaust arrangement of the ICE has to be opened before the piston reaches its BDC during the power stroke. From the discussion above it follows that low loss of the exhaust gases from the cylinder to a turbine is problematic to achieve
Data Source
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AI summary
Herein a four stroke internal combustion engine (2) comprising at least one cylinder arrangement (4), a crankshaft (20), a camshaft (25), and a turbine (8), is disclosed. The camshaft (25) is synchronised with the crankshaft (20) to rotate at a same rotational speed as the crankshaft (20). A linkage arrangement (40) is configured to prevent the motion of the valve head (30) every alternate rotation of the camshaft (25), such that the exhaust opening (28) remains closed during a compression stroke of the piston (10). Also a method for controlling a four stroke internal combustion engine (2) is disclosed.