Variable Compression Ratio Engine Secondary Piston Mechanism
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Solution Overview
Problem
Internal combustion engines face limitations in achieving optimal fuel efficiency and power output due to fixed compression ratios, particularly at varying engine speeds and loads, where elevated compression ratios improve efficiency at low loads but reduce power at high loads, and vice versa.
Innovation Solution
A variable compression ratio (VCR) internal combustion engine design featuring a secondary piston mechanism, including electro-mechanical, hydraulic, or pneumatic actuators, that adjusts the combustion chamber volume to dynamically change the compression ratio, enabling operation according to the Miller cycle and optimizing fuel efficiency and power output across different engine conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed compression ratio is used in the engine, then the engine structure is simple and reliable, but the fuel efficiency and power output cannot be optimized across varying engine speeds and loads
Solution Approach 1:
The patent applies the dynamics principle by introducing a variable compression ratio mechanism that allows the compression ratio to change dynamically based on engine operating conditions. The secondary piston can adjust the combustion chamber volume in real-time, transforming the fixed compression ratio system into an adaptive one that optimizes fuel efficiency at low loads while maintaining power output at high loads
Solution Approach 2:
The patent segments the piston function into two independent components: a primary piston for power generation and a secondary piston for compression ratio control. This segmentation allows the secondary piston to independently adjust the combustion chamber volume without interfering with the primary piston's combustion function, enabling flexible compression ratio variation while maintaining engine reliability
2Use of energy by moving object
If an elevated compression ratio is used at low engine speeds, then fuel efficiency is improved, but power output is reduced
Solution Approach 1:
The variable compression ratio mechanism enables dynamic adjustment of the compression ratio based on engine speed and load conditions. At low engine speeds, the system increases the compression ratio to improve fuel efficiency by more complete combustion. At high engine speeds, the system reduces the compression ratio to prevent excessive cylinder pressures that would limit power output, thus optimizing the trade-off between fuel efficiency and power across the operating range
3Power
If a reduced compression ratio is used at high engine speeds, then power output is improved, but fuel efficiency deteriorates
Solution Approach 1:
The system dynamically reduces the compression ratio at high engine speeds to maintain acceptable cylinder pressures and prevent knock, allowing the engine to produce maximum power output. Although a lower compression ratio typically reduces fuel efficiency, the ability to maintain higher engine speeds and optimize combustion timing compensates for this, achieving an overall improvement in fuel efficiency compared to a fixed compression ratio system operating throughout the entire speed range
4Productivity
If a variable compression ratio mechanism is added to the engine, then fuel efficiency and power optimization are improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The secondary piston is nested within the combustion chamber space, utilizing the existing cylinder volume. The secondary piston moves within the cavity formed by the cylinder head and primary piston, effectively using the available space without requiring additional external components. This nesting approach minimizes the increase in device complexity while enabling variable compression ratio functionality
Solution Approach 2:
The patent introduces a mechanism including an actuator and transmission components (such as a worm gear system) that serves as an intermediary between the control system and the secondary piston. This intermediary mechanism translates small actuator movements into precise secondary piston positioning, enabling accurate compression ratio control while using compact, manufacturable components
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
The VCR engine enhances fuel efficiency at low engine speeds and increases power at high engine speeds by dynamically adjusting the compression ratio, overcoming the limitations of fixed compression ratio engines and improving thermal efficiency and reducing emissions.
Implementation Method 1
The mechanism can include an electro-mechanical actuator having a stepper motor operatively connected to a worm wheel in mesh with a worm screw
Implementation Method 2
the mechanism can include a hydraulic actuator driven by the oil pressurized by the fluid pump
Implementation Method 3
the mechanism can include a pneumatic actuator driven by the vacuum pump
Implementation Method 4
The secondary piston shaft can include a check-valve arranged inside the gas passage such that the check-valve is configured to relieve pressure from inside the combustion chamber into the blow-off orifice above a predetermined combustion pressure value
Data Source
AI summary
A variable compression ratio (VCR) internal combustion engine includes an engine block defining a cylinder and a cylinder head mounted to the engine block and defining at least a part of a combustion chamber. The engine also includes a reciprocating primary piston arranged inside the cylinder and configured to compress a mixture of air and fuel and a crankshaft arranged in the engine block and rotated by an application of a combustion force to the primary piston. The engine additionally includes a secondary piston mounted in the cylinder head, movably with respect to the combustion chamber and a mechanism configured to shift the secondary piston in the cylinder head and thereby vary a volume of the combustion chamber and a compression ratio of the engine. A vehicle employing such an engine is also disclosed.