Carburetor Arcuate Cam Surface Eliminates Choke Reaction Torque
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In small internal combustion engines, the reaction torque from the choke lever can override the governor's control of the throttle lever, especially at varying throttle valve positions and engine speeds, leading to inconsistent engine performance.
Innovation Solution
The carburetor design incorporates an arcuate segment on the cam surface with a constant radius, allowing the throttle valve to move at least 15 degrees while engaging the follower surface, which aligns the reaction force with the throttle lever's axis, thereby eliminating reaction torque and preventing override of the governor's control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional cam surface without an arcuate segment is used, then the carburetor structure is simpler, but the reaction torque from the choke lever overrides the governor's control of the throttle lever, leading to inconsistent engine performance
Solution Approach 1:
The cam surface incorporates an arcuate segment with a constant radius of curvature, creating a curved engagement path between the cam surface and follower surface. This curvature allows the reaction force to remain aligned with the throttle lever's axis of rotation throughout the throttle valve's movement range, eliminating reaction torque and ensuring consistent governor control without adding complex mechanisms
2Measurement precision
If the throttle valve moves more than 15 degrees during cam surface engagement, then the governor's control precision is improved, but the reaction torque becomes more significant and can override governor control
Solution Approach 1:
The arcuate segment provides a curved engagement path that maintains force alignment over an extended throttle valve movement range of at least 15 degrees. The constant radius of curvature ensures that the reaction force vector consistently passes through the throttle lever's axis, eliminating reaction torque even as the throttle valve moves through a wide range of positions, thus enabling precise control without force interference
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A carburetor (10; 118; 122; 126; 262) configured for use with an internal combustion engine includes a body (14; 14a; 14b; 130; 130a) defining a passageway (18; 18a; 18b; 134; 134a) therein, a throttle lever (30; 30a; 30b; 146; 146a) including a cam surface (90; 90a; 90b; 230; 230a), and a throttle valve (26; 26a; 26b; 142; 142a) positioned in the passageway and responsive to movement of the throttle lever. The throttle valve (26; 26a; 26b; 142; 142a) is configured to rotate about a first axis from a wide-open first position to a second position at least 50 degrees from the first position. The carburetor also includes a choke lever (46; 46a; 46b; 162; 162a) including a follower surface (94; 94a; 94b; 236; 236a) configured to be engaged by the cam surface and a choke valve (42; 42a; 42b; 158; 158a) positioned in the passageway and responsive to movement of the choke lever. One of the cam surface (90; 90a; 90b) and the follower surface (94; 94a; 94b; 236; 236a) includes an arcuate segment (98; 98a; 98b; 238; 238a) having a constant radius centered on a second axis. The arcuate segment is sufficiently long such that the throttle valve is configured to move at least 15 degrees while the other of the cam surface and the follower surface engages the arcuate segment.