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Reduction drive

Partner: Ben Bashor

Reduction drive (also with a transformation of the direction of rotation)

A reduction drive, also known as a reduction gear, is a mechanical device to shift rotational speed. A planetary reduction drive is a small scale version using ball bearings in an epicyclic arrangement instead of toothed gears.

Reduction drives are used in engines of all kinds to increase the amount of torque per revolution of a shaft: the gearbox of any car is a ubiquitous example of a reduction drive. Common household uses are washing machines, food blenders and window-winders. Reduction drives are also used to decrease the rotational speed of an input shaft to an appropriate output speed. Reduction drives can be a gear train design or belt driven.

Planetary reduction drives are typically attached between the shaft of the variable capacitor and the tuning knob of any radio, to allow fine adjustments of the tuning capacitor with smooth movements of the knob. Planetary drives are used in this situation to avoid "backlash", which makes tuning easier. If the capacitor drive has backlash, when one attempts to tune in a station, the tuning knob will feel sloppy and it will be hard to perform small adjustments. Gear-drives can be made to have no backlash by using split gears and spring tension but the shaft bearings have to be very precise.

Reduction gear in light aircraft

Piston-engined light aircraft may have direct-drive to the propeller or may use a reduction drive. The advantages of direct-drive are simplicity, lightness and reliability, but a direct-drive engine may never achieve full output, as the propeller might exceed its maximum permissible rpm. For instance, a direct-drive aero engine (such as the Jabiru 2200) has a nominal maximum output of 64 kW (85 bhp) at 3,300 RPM, but if the propeller cannot exceed 2,600 rpm, the maximum output would be only about 70 bhp. By contrast, a Rotax 912 has an engine capacity of only 56% of the Jabiru 2200, but its reduction gear (of 1 : 2.273 or 1 : 2.43) allows the full output of 80 bhp to be exploited. The Midwest twin-rotor wankel engine has an eccentric shaft that spins up to 7,800 rpm, so a 2.96:1 reduction gear is used.

Aero-engine reduction gears are typically of the gear type, but smaller two-stroke engines such as the Rotax 582 use belt drive with toothed belts, which is a cheap and lightweight option with built-in damping of power surges.

Reduction Drives on Marine Vessels

Most of the world’s ships are powered by diesel engines which can be split into three categories, low speed (<400 rpm), medium (400-1200 rpm) and high (1200+ rpm). Low speed diesels operate at speeds that are already within the optimum range for propeller speeds and so can directly transmit from the engine to the propeller. For medium and high speed diesels, the rotational speed of the crankshaft in the engine must be reduced in order to reach the optimum speed for use by a propeller.

This(1) is done by making the engine turn a high speed pinion against a gear, turning the high rotational speed from the engine to lower speed for the propeller. The amount of reduction is based off of the number of teeth on each gear. For example, a pinion with 25 teeth turning a gear with 100 gear(2) must turn 4 times for the larger gear to turn once, reducing the speed by a factor of 4. This is the simplest setup and a large variety are used in the industry. The three arrangements most used are double reduction, two pinion nested; double reduction, two-pinion articulated and double reduction, two-pinion, locked train. On the Training Ship Golden Bear, the reduction gear aboard the ship has a ratio of 3.6714:1, so when the the two Enterprise R5 V-16 Diesel Engines operate at 514 rpms the propeller will turn at 140 rpms.(3) Reduction Drives are not only used on engines, if a piece of auxiliary machinery would benefit from having shaft turning speeds reduced then a reduction drive may be attached to it.

The gears used in a reduction gearbox are usually double helical gears. Helical gears are used because of the distributed load on the gear teeth increases the decreases the amount of maintenance that needs to be performed and increases the lifetime of the gear, both important qualities in a marine environment. The double helical gear set can also be called a herringbone gear and consists two oppositely angled sets of teeth.(4) A single set of helical teeth will produce axial thrust along due to the angular nature of the teeth but by adding a second set opposed to the first set the axial thrust created by both sets cancels each other out.

When installing reduction gears on ships the alignment of the gear is critical. Correct alignment helps ensure a a uniform distribution of load upon each pinion and gear. The gears are designed so that this occurs under operating conditions whilst aboard the ship. When manufactured, the gears are assembled in the shop so as to obtain uniform load distribution and tooth contact. These gears must then undergo transportation to the ship upon which they will operate. There, it is required that these gears achieve proper alignment when first operated under load. Some shipbuilders will have the gears shipped and lowered into the ship as a complete assembly, some others will have the gears dismantled, shipped, reassembled in their shops and lowered as a complete assembly into the ship while finally others will have the gears dismantled, shipped and reassembled in the ship. (5) These are the most common methods to achieve proper alignment and each of them work based upon the assumption that proper alignment was correctly achieved at the manufacturer.

Because of the involvement in the process of aligning reduction drives, there are two main sources of responsibility to achieve proper alignment. That of the shipbuilder and that of the gear manufacturer. The shipbuilder must provide a foundation that is sufficiently strong and rigid so that the gear mounting surface does not deflect greatly under operating conditions, a shaft alignment drawing that details the positions of line bearing and the method for aligning the forward piece of line shafting to the the reduction gear coupling and the location of stern tube being such that the normal wear down of the stern tube will not induce significant movement of the reduction gear coupling from its proper alignment. (Sources?)

The gear manufacturer is then responsible for ensuring basic gear alignment, such that the final assembly measurements are taken carefully and recorded for the reduction drive to be installed correctly, proper tooth contact in the factory, where the manufacturer accurately and precisely assembles the gears and pinions, and denoting all steps performed, making measurements of parts at the different steps and final assembly then forwarding this data to the shipbuilder so that they may assure the degree of accuracy required by the gear designer in the resulting shipboard assembly. (6)

Thrust bearings do not commonly appear on reduction drives on ships because axial loading is handled by a thrust bearing separate from the reduction drive assembly. But on smaller reduction drives attached to auxiliary machinery or if the design of the ship demands it, one can find thrust bearings as a part of the assembly.

In order to ensure a reduction drive's smooth working and long lifetime, it is vital to have lubricating oil. A reduction drive that is ran with oil free of impurities like water, dirt, grit and flakes of metal, requires little care in comparison to other type of engine room machinery. In order to ensure that the lube oil in the reduction gears stay this way a lube oil purifier will be installed with the drive.

Peer Review by Gage Sturgeon

1- These two paragraphs have the same subject and should be combined to form one paragraph with the same topic.

2- This is a word error that needs to be changed from gear to teeth.

3- This is specific information about the Golden Bear itself and belongs in the Wikipedia article about itself.

4- Again this is information that doesn't belong in this article and the hyperlink should suffice for explaining it.

5- This sentence is fluffed and needs to be shortened since you are explaining things that are implied.

6- Run on sentence that is extremely complex and hard to understand.

Common grammatical errors:

Comma splices

Run ons that cause a lot of awkward sentences.

Subject-verb agreement

Areas missing sources.

Citations"

(2)- It is a technical and research bulletin from SNAME. It can be trusted since it is a government organization and the information is meant to show information for learning purposes.

(3)- It is a book that is self published by the company that creates the reduction gears. It is trustworthy only since it talks about data in a non biased way.

(4)- It is a training manual published by the Naval Education and Training Professional Development and Technology Center. It is trustworthy since it is backed by the NAVY and meant to train individuals.

All resources are relatively old and could be outdated! — Preceding unsigned comment added by GageSturgeon2 (talk • contribs) 00:09, 18 April 2018 (UTC)

== Other Uses of Reduction Drives == (What?)