Straight Bevel Gear Tooth Geometry for Outboard Motor Efficiency
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Solution Overview
Problem
Conventional outboard motors with Gleason type spiral bevel gears experience lower power transmission efficiency due to friction, leading to degraded engine performance and increased manufacturing costs, particularly for low-power motors.
Innovation Solution
A power transmission device using straight bevel gears with a clutch mechanism, where the forward and reverse driven bevel gears have different tooth width shapes, reducing friction and manufacturing costs while maintaining tooth strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If Gleason type spiral bevel gears are used, then the gear case size can be reduced, but power transmission efficiency deteriorates due to friction
Solution Approach 1:
The invention changes the geometric parameters of the gear teeth by using straight bevel gears instead of spiral bevel gears, and specifically designs the tooth width to be smaller at the large diameter end and larger at the small diameter end. This parameter change reduces the contact area and friction between mating teeth, thereby improving power transmission efficiency while maintaining compact gear case dimensions.
2Volume of stationary object
If Gleason type spiral bevel gears are used, then gear case size is reduced, but manufacturing cost increases due to specialized facilities
Solution Approach 1:
The invention adopts straight bevel gears which can be manufactured using conventional machining methods without requiring specialized spiral gear manufacturing facilities. This substitution with a simpler, more commonly manufactured gear type significantly reduces manufacturing costs while still achieving the desired compact gear case size through optimized tooth geometry.
3Loss of energy
If straight bevel gears are used, then manufacturing cost and power loss are reduced, but tooth strength may be insufficient
Solution Approach 1:
The invention applies local quality by making the tooth width variable along the cone height, with smaller width at the large diameter end and larger width at the small diameter end. This non-uniform distribution concentrates the load-bearing capacity where it is most needed, enhancing tooth strength and preventing breakage while maintaining the low-friction advantages of straight bevel gears.
Solution Approach 2:
The invention introduces asymmetry in the tooth geometry by designing different tooth widths at different locations along the gear cone. The tooth width is intentionally made asymmetric, being narrower at the large diameter end and wider at the small diameter end, which optimizes both strength distribution and friction reduction.
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 use of straight bevel gears improves mechanical efficiency and reduces manufacturing costs, while the unique tooth shapes enhance tooth strength and durability, preventing degradation in power transmission.
Implementation Method 1
a bevel gear with teeth having a Gleason type spiral tooth shape has lower efficiency of power transmission than a bevel gear with teeth having a straight tooth shape, due to power loss resulting from friction between the teeth
Data Source
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AI summary
An outboard motor provided with an engine (11) includes a power transmission device (30). The power transmission device (30) includes a drive shaft (21) which is driven by the engine (11) and a propeller shaft (23) which is driven by the drive shaft (21) through a bevel gear mechanism. The bevel gear mechanism includes a drive bevel gear (22) which is mounted to the drive shaft (21) and a forward driven bevel gear (24) and a reverse driven bevel gear (25) which are mounted around the propeller shaft (23) so as to face each other and engage with the drive bevel gear (22). The forward driven bevel gear (24) and reverse driven bevel gear (25) always engage with the drive bevel gear (22) and are selectively connected to or disconnected from the propeller shaft (23) via a clutch mechanism (27), a driven bevel gear including the forward driven bevel gear (24) and reverse driven bevel gear (25) and the drive bevel gear (22) are configured as straight bevel gears, and the forward driven bevel gear (24) and the reverse driven bevel gear (25) in the driven bevel gear are formed to be different in shapes in a tooth width direction at a side of each tooth thereof.