In this reversing bevel arrangement, one input pinion keeps two identical opposed bevel gears turning freely in opposite directions on the output shaft. A sliding double clutch locks the shaft to the left gear, neither gear, or the right gear to select forward, neutral or reverse.
Reversing Bevel Gears with Double-clutch Interactive Calculator
Enter tooth counts, input rpm and input torque. Choose +1 for the left clutch, 0 for neutral or −1 for the right clutch to compare ideal output speed and lossless torque.
Equation Used
- The two driven bevels are identical and rotate freely at equal magnitude in opposite directions.
- The clutch state is +1 left, 0 neutral or -1 right.
- Torque follows the ideal reduction ratio during steady, lossless transmission.
- Real engagement dynamics, efficiency and component ratings are excluded.
The companion diagram follows the same inputs and clutch state. Its circles indicate rotating components; they are not bevel-gear tooth profiles.
How the reversing drive works
The input pinion engages two identical bevel gears facing one another on the output shaft. The gears turn freely in opposite directions until the sliding clutch couples one of them to the shaft.
Moving the clutch left selects one direction. Moving it right selects the other. At the center, neither gear is coupled to the output. The input can keep turning in the same direction throughout, although the conditions for changing gear depend on the actual clutch and machine.
Comparing a reversing drive
Opposed bevel gears provide two rotation directions from one input pinion. Marine transmission patents below describe examples of this principle, with different clutch arrangements. The diagram here shows the basic selection principle rather than one specific gearbox.
Try increasing the driven-gear tooth count: output speed falls and ideal output torque rises. Increasing pinion tooth count has the opposite effect. The two driven gears share one tooth-count input because they are identical in this example.
Ideal reduction, speed and torque
The reduction ratio is Zd/Zp. With clutch state s = +1 left, 0 neutral or −1 right, ideal output speed is nout = s ninZp/Zd. The signs identify the two output directions.
While engaged, ideal output torque magnitude is TinZd/Zp. The calculator writes this as |s|TinZd/Zp so the neutral result is zero. This assumes steady transmission without losses, not the torque during a shift or a component capacity.
The reduction remains visible in neutral as a tooth-count ratio. Zero displayed output speed is a neutral-state assumption; inertia or external loading can still move a disconnected shaft.
Worked example
At 1200 rpm, 25 N·m, 16 pinion teeth and 40 driven teeth, the reduction is 2.5:1. Left engagement gives +480 rpm and 62.5 N·m ideal torque. Right engagement gives −480 rpm with the same torque magnitude.
Neutral displays zero output rpm and zero transmitted torque, while both free bevel gears continue rotating. It does not represent a brake or a locked output shaft.
Reading the results and animation
These inputs establish an ideal tooth-count ratio. Gear dimensions, tooth contact, losses, strength and clutch capacity need additional geometry, materials and load data. The torque result is not a permissible working load.
Playback is slowed for viewing. The circles and connecting lines show component relationships and opposite rotation, not a three-dimensional bevel mesh. Their sizes do not change with tooth count, and the clutch block is an engagement symbol rather than a shaped dog clutch.
The state control changes the connection instantly. Real synchronization, impact, drag and braking are outside the calculation. Use the identified transmission documentation for shifting and service limits.
Reversing-drive questions
Why do the two driven bevel gears rotate oppositely?
They engage the input pinion from opposite sides. With identical driven gears, their speed magnitudes are equal and their rotation directions are opposite.
What do the clutch-state numbers mean?
Choose +1 to couple the left gear to the output, 0 for neutral, or −1 to couple the right gear. Positive and negative output rpm identify the two directions; they are labels, not a universal clockwise convention.
Does neutral stop the gears or hold the output?
No. The two free gears continue turning with the input. Neutral leaves neither coupled to the output shaft. The calculator displays zero output speed and transmitted torque in this state, but does not model coasting, drag or braking.
Is the displayed torque a gear or clutch rating?
No. It is input torque multiplied by the ideal reduction ratio, assuming lossless steady transmission. It does not establish tooth strength, clutch capacity or engagement loads.
Does this calculator determine when the clutch can be shifted?
No. The state control changes an ideal connection instantly. It does not calculate synchronization, engagement time, impact or operating limits; those depend on the actual transmission.
Primary references
- WO1993005317A1, Transmission device, especially for boat motors — two freely mounted bevel gears selectively lockable to a shaft by clutch means.
- US20150375841A1, Transmission for Marine Propulsion — facing forward and reverse bevel gears and forward-neutral-reverse clutch selection.
- KHK, Calculation of Gear Dimensions — bevel-gear pitch cones and angular-velocity ratio from tooth counts.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
