Variable Compression Ratio Mechanism Fail-Safe Control
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Solution Overview
Problem
Existing variable compression ratio mechanisms in internal combustion engines face challenges in controlling compression ratio when the drive mechanism fails, leading to potential over-compression issues due to increased complexity with hydraulic circuits or high load on actuators in electric motor-based systems, affecting fuel efficiency and causing abnormal combustion.
Innovation Solution
A control apparatus that includes a fuel cut mechanism, failure detection, and control operations to manage in-cylinder pressure by adjusting throttle valve opening, intake valve timing, and exhaust valve timing during a failure, reducing the compression ratio and preventing excessive increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hydraulic circuit for abnormal condition is added to guide working oil between hydraulic chambers, then the compression ratio can be controlled to vary only to a lower compression ratio side when the hydraulic drive mechanism is abnormal, but the configuration becomes complex and cannot handle abnormalities in the drive mechanism itself
Solution Approach 1:
The patent extracts the fail-safe function from the hydraulic drive mechanism itself and implements it through a separate, simpler hydraulic circuit that operates independently. This circuit uses a hydraulic motor connected to a rack and pinion mechanism to move the cylinder vertically, providing compression ratio control without requiring complex integration with the main hydraulic drive system.
Solution Approach 2:
The patent segments the compression ratio control system into two independent parts: the normal hydraulic drive mechanism for regular operation, and a separate fail-safe hydraulic circuit for abnormal conditions. This segmentation allows each subsystem to be optimized independently, reducing overall system complexity while maintaining reliability.
2Reliability
If a helical torsion coil spring is provided to apply biasing force toward the lower compression ratio side, then the variable compression ratio mechanism returns to low compression ratio state when the electric motor is failed, but the load of driving is large under normal condition requiring a large-sized actuator
Solution Approach 1:
The patent replaces the mechanical spring-based biasing system with a hydraulic-based fail-safe mechanism. Instead of using a helical torsion coil spring that requires large actuator size, the invention uses a hydraulic motor with rack and pinion mechanism to provide the necessary force for moving the cylinder, thereby reducing actuator size while maintaining the fail-safe function.
3Device complexity
If the compression ratio is not controlled when the drive mechanism fails, then the mechanism remains simple, but the compression ratio becomes higher than intended causing abnormal combustion
Solution Approach 1:
The patent introduces a hydraulic motor as an intermediary component that mediates between the failure condition of the main drive mechanism and the compression ratio control requirement. This hydraulic motor acts as a backup actuator that can independently control the rack position, preventing abnormal combustion while maintaining relative simplicity of the overall system.
Data Source
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AI summary
An internal combustion engine (1) that has a variable-compression-ratio mechanism (2) has variable valve mechanisms (7, 8) for an intake valve (4) and an exhaust valve (5), respectively. If a malfunction in the variable-compression-ratio mechanism (2), which controls a mechanical compression ratio via an electric motor (31), is detected from the amplitude of variations in an actual compression ratio, then if the fuel supply to the engine is cut, a throttle valve (14) is opened wider than would be the case if the variable-compression-ratio mechanism (2) were not malfunctioning, thereby reducing in-cylinder negative pressure during the intake stroke. Also, the timing with which the intake valve is closed is advanced and the timing with which the exhaust valve is opened is retarded, increasing the in-cylinder positive pressure during the compression and power strokes. This prevents the variable-compression-ratio mechanism (2) from increasing the compression ratio when control is lost.