Switching Tappet and Roller Finger Follower for Engine Braking
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Solution Overview
Problem
Existing compression release engine braking systems for internal combustion engines are sensitive, expensive, and difficult to implement and maintain, with a need for improved control and cost-effectiveness, especially for certain types of valvetrains.
Innovation Solution
The implementation of a switching tappet and roller finger follower systems that selectively cooperate with inner and outer cam lobes for exhaust and compression release during respective strokes, allowing for controlled compression release braking and the option to shift the exhaust brake event to a power stroke, with a default position for compression release, enabling braking during gas release on the power stroke and lower power starting during compression stroke release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a compression release engine brake is implemented, then engine braking function is provided, but the system becomes sensitive and difficult to implement and maintain
Solution Approach 1:
The valve train is segmented into multiple components: a camshaft with separate compression release cam lobes and exhaust cam lobes, a follower assembly with roller and finger, and a switching mechanism. This segmentation allows independent control of compression release and exhaust functions, simplifying implementation and maintenance of the braking system.
Solution Approach 2:
The follower assembly serves multiple functions: it acts as a standard exhaust valve follower during normal operation and as a compression release brake actuator when the camshaft is rotated. The same physical components perform both routine valve actuation and braking functions, reducing system complexity.
2Reliability
If a compression release engine brake is implemented, then engine braking function is provided, but the system cost increases
Solution Approach 1:
The camshaft, follower assembly, and associated valve train components serve dual purposes: normal exhaust valve actuation and compression release braking. By making these components multi-functional rather than adding separate dedicated braking components, the system cost is reduced while maintaining reliable engine braking function.
Solution Approach 2:
The compression release braking function is merged with the existing exhaust valve actuation system. The same camshaft lobes, follower assemblies, and valve stems that control exhaust flow during normal operation are used to provide compression release braking, eliminating the need for separate braking components and reducing overall system cost.
3Adaptability or versatility
If camshaft is rotated to shift exhaust brake event to power stroke, then braking function is achieved, but control complexity increases
Solution Approach 1:
The camshaft is made rotatable relative to the crankshaft, allowing dynamic adjustment of the compression release event timing. This enables the system to shift the braking event between different strokes (exhaust or power stroke) by simply rotating the camshaft to different angular positions, providing adaptability without complex control mechanisms.
Solution Approach 2:
The primary control parameter is the camshaft rotation angle. By changing this single parameter, the system can shift the timing and stroke of the compression release braking event. This simple parameter change approach provides versatile braking control without increasing device complexity.
Data Source
AI summary
A system includes an engine with a plurality of pistons housed in respective ones of a plurality of cylinders, an air intake system provides air to the plurality of cylinders through respective ones of a plurality of intake valves, an exhaust system to release exhaust gas from the plurality of cylinders through one of a plurality of exhaust valves, and a controller coupled to a sensor to control a switching tappet for compression release braking. Alternatively to a tappet, the system includes a roller finger follower controlling an opening and closing timing of exhaust valves, the roller finger follower has an inner roller follower arm adjacent an outer sliding follower, and a controller that in response to an engine braking request locks the inner roller follower arm with the outer sliding follower to contact a second cam lobe and open the exhaust valve during a compression stroke of the cylinder.