Exhaust Valve Actuation for Engine Braking Retarding Power
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Solution Overview
Problem
Existing engine braking systems for large tractor-trailer trucks, particularly turbocharged engines, face challenges in achieving effective retarding power due to high exhaust manifold pressure and low engine air flow rate, which can lead to increased in-cylinder component temperatures and reduced braking efficiency.
Innovation Solution
A control system that commands the exhaust valve to open and close multiple times during each engine cycle, using an exhaust back pressure valve and a counter-preload device to manage valve spring preload, enhancing exhaust manifold gas temperature and air flow rate to increase retarding power without violating design constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the exhaust back pressure valve is closed to increase exhaust manifold pressure for engine braking, then retarding power is improved, but engine air flow rate decreases and in-cylinder component temperatures increase
Solution Approach 1:
The exhaust valve is commanded to open and close multiple times during each engine cycle, creating periodic action. This allows the exhaust manifold pressure to be periodically released, maintaining higher average air flow rate through the engine while still achieving high peak pressures for retarding power when the valve is closed
2Power
If the exhaust back pressure valve is closed to increase exhaust manifold pressure for engine braking, then retarding power is improved, but in-cylinder component temperatures increase
Solution Approach 1:
The periodic opening and closing of the exhaust valve creates cycles of high pressure (for retarding power) followed by pressure release (which reduces temperature buildup). This periodic action allows the system to achieve high retarding power while preventing excessive temperature increases in in-cylinder components
3Object-generated harmful factors
If the exhaust valve is held constantly open during the entire engine cycle, then compression-release effect is generated, but retarding power is reduced
Solution Approach 1:
Instead of holding the exhaust valve constantly open, the system uses periodic opening and closing actions during each engine cycle. This creates the compression-release effect during specific phases while maintaining high exhaust manifold pressure during other phases, thereby achieving both the compression-release effect and high retarding power
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 enhances engine retarding power by increasing air flow rate and exhaust manifold temperature, potentially doubling retarding power while maintaining system efficiency and avoiding excessive temperature increases.
Implementation Method 1
when the pressure within the exhaust manifold is greater than the pressure in the cylinder
Implementation Method 2
selectively restricting exhaust gas from flowing from the exhaust manifold to ambient
Implementation Method 3
using an exhaust back pressure valve and a counter-preload device to manage valve spring preload
Data Source
AI summary
A control system and method for engine braking for a includes an engine braking control and at least one exhaust valve actuator responsive to demands from the braking control for causing the exhaust valve to open. The braking control is configured to command the exhaust valve actuator to substantially open and substantially close the exhaust valve at least twice during each engine cycle, a first event and a second event, when the pressure within the exhaust manifold is greater than the pressure in the cylinder. The braking control can also command the exhaust valve actuator to substantially open and substantially close during a third event between the first and second events.