Noncircular Crankshaft Geometry for Extended Minimum Combustion Volume

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Solution Overview

Problem

Existing crankshaft systems for piston engines have circular rod journal trajectories, leading to low output torque and inefficient fuel use due to minimum combustion chamber volume being at TDC, which limits torque production and requires advanced ignition timing, and prior modifications like cycloid or hypocycloid mechanisms fail to maintain constant combustion volume from 0° TDC to 14° ATDC or beyond.

Innovation Solution

A novel crankshaft system with a noncircular crankpin trajectory, where the minimum combustion chamber volume is extended beyond TDC and kept constant using a gear system with a ring or sun gear constraint, allowing for both advanced and retarded ignition, and maintaining combustion volume variation within 0.2% from 0° ATDC to a specific angle, thereby enhancing torque and fuel efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a circular rod journal trajectory is used, then the structure is simple, but the minimum combustion chamber volume is located at TDC position resulting in low output torque

Engineering Contradiction:

Improvecrankshaft structureVSAvoidoutput torque

Core Design Contradiction:

Device complexityVSPower

Solution Approach 1:

The patent applies asymmetry by changing the circular rod journal trajectory to a noncircular trajectory (specifically hypocycloid or epicycloid). This asymmetric path allows the minimum combustion chamber volume to be extended beyond TDC position, enabling the combustion pressure to act on the crankshaft at angles where torque multiplication is more effective, thereby increasing output torque while maintaining reasonable structural complexity through standardized gear mechanisms.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent employs curved geometric paths (hypocycloid and epicycloid trajectories) instead of a simple circular path for the rod journal. These curved trajectories are generated through gear mechanisms that convert the circular motion of the crankshaft into noncircular motion of the piston, allowing optimization of the combustion chamber volume profile throughout the expansion stroke to improve torque production.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Stress or pressure

If ignition is advanced before TDC, then peak combustion pressure is achieved, but the peak combustion chamber volume is far from minimum volume at low speed resulting in low combustion pressure

Engineering Contradiction:

Improvecombustion pressureVSAvoidignition timing

Core Design Contradiction:

Stress or pressureVSLoss of time

Solution Approach 1:

The patent changes the temporal parameter of combustion by extending the minimum combustion chamber volume position to occur after TDC (up to 14° ATDC or beyond). This parameter change allows the combustion event to be better synchronized with the expansion stroke, enabling both advanced and retarded ignition strategies to achieve peak combustion pressure at optimal volumes, thereby improving combustion efficiency and reducing timing losses.

Inventive Principle:

Principle #35Parameter changes

3Shape

If cycloid, trochoid, hypocycloid or epicycloids mechanisms are introduced to modify combustion chamber volume, then the trajectory is modified, but the combustion chamber volume is not constant from 0° TDC to 14° ATDC

Engineering Contradiction:

Improvecrankpin trajectoryVSAvoidcombustion volume consistency

Core Design Contradiction:

ShapeVSReliability

Solution Approach 1:

The patent applies dynamics by using rotating gear mechanisms (planet gears, sun gears, or ring gears) that dynamically adjust the rod journal trajectory throughout the crankshaft rotation. These mechanisms continuously modify the combustion chamber volume profile, creating an extended minimum volume region from TDC to 14° ATDC or beyond, thereby achieving both trajectory modification and volume consistency through dynamic mechanical action.

Inventive Principle:

Principle #15Dynamics

4Power

If minimum combustion chamber volume is extended to 14° ATDC or beyond, then output torque is increased, but the device complexity increases with gear systems

Engineering Contradiction:

Improveoutput torqueVSAvoidcrankshaft system

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

The patent achieves universality by designing gear mechanisms (planet gears, sun gears, or ring gears) that serve multiple functions: they generate the noncircular rod journal trajectory, control the combustion chamber volume profile, and can be integrated with the existing crankshaft structure. This multi-functionality allows torque enhancement through extended minimum volume while minimizing additional complexity by using standardized gear components that perform multiple roles in the system.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS11473654B2Reciprocating engine with extended minimum combustion chamber volume

Publication Date: 2022.10.18 YUAN DEFANG

AI summary

A crankshaft system is provided. The crankshaft has a main journal, a rod journal rotates around the main journal, a planet gear is attached to the rod journal and can rotate around the rod journal, the rotation of the planet gear is constrained by a constraining gear, the teeth number of the constraining gear is integer k times of the teeth number of the planet gear, a crankpin is mounted on the planet gear, one end of a connecting rod of a piston is attached to the crankpin, the constraining gear is a ring gear or a sun gear, the trajectory of the crankpin is noncircular. The combustion chamber volume keeps constant from 0° ATDC to 14° ATDC, or the minimum combustion chamber volume extends from TDC to 14° ATDC or after 14° ATDC.