What is Reduction Gearbox? | What is Reducing Gearbox? | What is Speed Reducer

A gear reducer is a part of the vehicle that changes speed. A speed reducer or reducing gearbox is used to reduce the input velocity of a motor while increasing the torque produced by the input. The reducing gearbox or reduction gearbox has teeth on the pinions and wheels that mesh with each other to transfer power from the driver shaft to the driven shaft to reduce speed. This article deeply explains different aspects of the reduction gearbox.

What is a Reduction Gearbox?

A reduction gearbox is a mechanical device used to reduce the output speed of the motor. It increases the output torque of the shaft by reducing the output speed. The reduction gearbox converts the revolution of the drive motor’s output shaft to the speed required to run the propeller.

The reducing gearbox is also known as a speed reducer, reduction drive, or torque multiplier. It links the driver motor to the driven load. The speed reducer or reduction gearbox has a simple construction, like a gear train between the machinery and the motor.

reduction gearbox

The reduction gearboxes are most commonly used on different types of engines to improve the torque per revolution of the shaft. A gearbox in any car is a common example of a reduction drive.

The output-to-input gear ratio slows the motion of the output shaft, increases the delivery torque, and decreases shaft rpm.

Few types of speed reducers behave like gear trains between different components, but in spite of the complexity, the slow-motion is possible because the input section has a fewer number of teeth than the output section, slowing the movement of the output gear, increasing the torque and reduces the rpm. You can also use these gears to monitor the input velocity, output speed, and torque.

Construction of Reduction Gearbox

A reducer gearbox is installed to achieve equal or greater output torque but with lower input velocity to meet lower output speed requirements. The reduction gearbox has multiple rotating gears that work in conjunction with the wheels.

As the high-velocity input motion of the wheel function transfers to the rotary gears, the gears change the incoming motion or torque. The number of gears in a reduction gearbox varies according to the output speed requirements. The reduction gearbox is also referred to as reduction gear assembly.

construction of reduction gear, reducing gear

In the case of speed reducer, increasing the torque through the gear ratio increases the output torque of the rotary system and reduces wasted efficiency.

In some cases, the speed reducer increases torque by reducing the speed, while some applications install it to reduce torque and increase speed. In this case, the wind turbine generator applies gear reduction to convert the relatively low velocity of the turbine blades to a high speed of the generator coil that can generate electricity. These applications use gear reduction that is designed opposite of those in cases that reduce speed and improve torque.

How to choose a good reduction gearbox is another big problem. There are multiple types of reduction gearboxes, including but not limited to the planetary worm, right angle, and parallel shaft gears.

A parallel shaft reduction gear uses a pinion gear with a certain number of teeth in the mesh and drives another gear with many teeth.

Read Also: Different types of Engines

Types of Reduction Gearbox

The reduction gearbox has the following major types:

  1. Single Reduction Gearbox
  2. Double Reduction Gearbox

1) Single Reduction Gearbox

This gearbox has only one set of gears. It has ports for the propeller shaft and motor shaft to enter the assembly. A small gear is a pinion driven by the drive motor shaft.

Single Reduction Gearbox

As the pinion receives power from the drive motor, it further drives the large gear. This large gear is directly coupled to the propeller shaft. As the large gear receives motion by the small gear, it rotates the propeller shaft. A single gear assembly typically has a gear that has two times more size than the pinion.

2) Double Reduction Gearbox

This type of speed reducer is used in very high-speed conditions. In this gearbox, the pinion installs on the input shaft. This pinion is connected to the middle part known as the first gear.

Double Reduction Gearbox

The first gear further connects to another shaft with the low-speed pinion. The pinion gear is fixed to the second deceleration section, which is directly linked to the drive shaft. This design helps to reduce speed up to a 20:1 ratio.

There are some other types of the speed reducer that are given below:

3)  Magnetic Speed Reducer

A magnetic reduction gearbox or magnetic speed reducer has the capacity to beneficially replace the traditional speed reducer. This gearbox ensures proper speed and torque control by utilizing a magnetic attraction force instead of physical contact between rotating parts.

These types of speed reducers are not very common because of their high weight, low torques, and complex design.

The magnetic gear doesn’t need lubrication. Therefore, it has a low maintenance cost. The absence of lubrication also means that the device can operate at very high temperatures (actual temperature range is -200°C to 350°C).

4) Parallel Shaft Reduction Gearbox

This speed reducer contains multiple gear assemblies, which increases the reduction capacity of the system. The overall gear reduction ratio is determined by increasing the ratio of individual gear in each gear assembly. If the gearbox contains 7:1, 6:1 and 5:1 sections, the overall ratio is 210:1 (7 x 6 x 5 = 210).

In this example, if the speed of electric motor speed is 3,550 rpm, the gear reducer reduces this speed by a factor of 210 to 16.9 rpm. If the torque of this electric motor is 2 lb-in, it increases by a factor of 210 to 420 lb-in (before the waste of efficiency).

If the pinion and carrier have the same number of teeth, there will be no reduction, and the gear ratio will be 1:1.

The gear of the parallel shaft reduction gearbox works as idler gear, and its main function is to change the direction of rotation, not increase torque or decrease speed.

5) Planetary Gearbox

The planetary gearbox depends on the number of teeth on the sun gear and ring gear. Therefore, calculating the gear ratio of this gearbox is not much insightful. The planetary gear acts like idler gear and doesn’t affect the gear ratio.

planetary gearbox
Planetary Gearbox 

The planetary gear ratio is equal to the total number of teeth on the sun and ring divided by the number of sun gear teeth.

Read Also: Working of Planetary Gearbox

6) Right-Angle Worm Reduction Gearbox

The gear ratio of this gearbox depends on the threads of the worm and the number of teeth on the mating worm wheel. If the worm has 3 threads and the attached worm wheel has 48 teeth, the output gear ratio is 16:1 (48/3 = 16/1).

A speed reducer plays a vital role when rotating systems such as electric motors and engines can’t deliver sufficient torque or speed properly. Right-angle worm, parallel shaft, and planetary gears are types of reduction gearboxes used to apply the gear reduction.

7) Helical gearbox

In this gearbox, the gears are generally locked up at 90 degrees—these gears are most commonly installed in overlapping or parallel positions. The overlapping gearbox has low load capacity than the parallel gearbox. This type of reduction gearbox generates less noise than the spur gearbox.

The helical gearboxes are best suitable for systems that need high torque power and high speed. The helical gearboxes require very low repair or maintenance. In this way, they lower the consumer cost by an excellent performance.

Read Also: Function of Gearbox in IC Engine

Reduction gearbox ratio or Gear reduction ratio formula

Divide the number of teeth on a large gear by the number of teeth on a small gear to calculate ” reduction gear” or gear ratio. Let’s explain it with an example.

Consider a 60-tooth large gear is meshing with a 10-tooth pinion gear. An electric motor or engine uses to run the pinion gear. In this case, the resulted gear ratio is 6:1 (60/10 = 6/1).

If the engine speed is 3550 rpm, the gearbox lessens this speed by a factor of 6 to 591.66 rpm (3550/6). If the engine torque is 15 lb. in, the reducer gearbox increases that torque up to five times (75 lb. in) before subtracting the transmission efficiency loss.

The parallel shaft gearbox contains many sets of gear, which increases gear reduction. In the parallel shaft gearbox, the overall gear reduction ratio is determined by increasing the ratio of individual gear in each gear assembly. If the gearbox contains 5:1, 4:1 and 3:1 sets, the overall ratio is 60:1 (5 x 4 x 3 = 60).

In the example above, an engine or electric motor uses to drive the small gear. If the motor has 3400 rpm speed, the gearbox reduces it by a factor of 60 to 56.6 rpm (3400/60). The torque increases from 8 lb.in to 480 lb.in.

If the pinion has the same number of teeth as its corresponding gear, there is no delay, and the gear ratio is 1:1. The gear ratio of a planetary gear depends on the number of teeth on the sun gear and ring gear.

What are the Selection Criteria for Choosing a Reduction Gearbox?

Follow the following important tips while selecting a reduction gearbox:

  • Torque: The main function of a reduction gearbox or speed reducer is to increase the torque of the driver engine, allowing the receiving gear or shaft to rotate according to the new torque. Therefore, the manufacturers of the gearboxes specify the minimum and maximum torque (usually represents in N.m) that each of their components can deliver. The torque density depends on the speed reducer. For example, planetary reduction gearboxes have a high density of torque.
  • Reduction Gearbox Type: You must choose the best suitable type of speed reducer according to the nature of your application. The input and output shafts of these gearboxes may be orthogonal, coaxial, or parallel shafts. These types vary according to the application.
  • Reduction ratio or Gear ratio: Another purpose of using a reduction gear is to reduce engine speed. Therefore, you must consider the reduction ratio while selecting a gearbox for your system. This reduction ratio helps to determine the output velocity according to the input speed of the engine. The manufacturer also provides this information in the product manual. This information shows as revolutions per minute (RPM).
  • Service Life: The service life of the gearbox that you must keep in mind while selecting it. You must select a gearbox that has long service life and require minimum maintenance.

FAQ Section

What is a Speed reducer?

A speed reducer or reducing gearbox is used to reduce the input velocity of a motor while increasing the torque produced by the input.

What are reduction gearboxes used for?

A reduction gearbox uses to transform the revolutions of the main motor output shaft into the speed required to run the propeller. It has meshing teeth on pinions and wheels that convey motion from a drive shaft to a driven shaft and decrease speed.

What are the applications of gearbox?

The gearboxes have the following major applications:

  • Wind and Tidal Energy
  • Hydro Power
  • Turbo
  • Power Generation
  • Rail Vehicles
  • Cement
  • Mining
  • Oil and Gas
Read More
  1. Different types of Engines
  2. Different types of IC Engines
  3. Types of External Combustion Engines
  4. Working of Planetary Gearbox

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