# Compound Gear Train | Gear arrangement, working, Gear Transmission Ratio

From TypeAndList
Published Date: 2019-07-15
Modified Date: 2019-07-15

Compound gear train is a type of gear train which is used to transmit motion and power from one shaft to another shaft. Compound gear train consists of one or more compound gear (intermediate gears) with input (driving) and output (driven) gears. Compound gear is use in compound gear train which is a difference between simple gear train and compound gear train. Compound gear has two or more rigidly fixed gears of different size and has different number of teeth on the same shaft with same axis of rotation and same angular velocity. These gears are different in size and have different number of teeth, which is used to achieve speed up or slow down the final output.

Contents

## 1. Gear train

Gear train is a combination or arrangement of gears and used for transmitting motion and power from one shaft to another shaft. Gear trains are used to achieve large and different velocity ratio in small area or space. Gear trains are use for increasing or reducing speed of driven (output) shaft. Examples of gear trains use in machines are lathe machine, milling machine, in watch and many others. Different types of gear trains are as follow.

### 1.1. Types of gear train

Simple gear train

In simple gear train multiple gears are used to obtain different velocity ratio. Only one gear is mounted on each shaft and these shafts are rigidly fixed or not movable.

Compound gear train

Compound gear is use in compound gear train which is a difference between simple gear train and compound gear train. Compound gear has two or more rigidly fixed gears of different in size and has different number of teeth on the same shaft with same axis of rotation and same angular velocity.

Reverted gear train

Reverted gear trains are a special type of gear trains. In which driving gear shaft axis and driven gear shaft axis are in a line.

Epicyclic gear train

In epicyclic gear trains, the shaft axes are not fixed means the shaft axis is movable. There is a relative motion between the gears axis.

## 2. Compound gear

Compound gear has two or more rigidly fixed gears of different in size and has different number of teeth on the same shaft with same axis of rotation and same angular velocity. These gears may be located together with no axial distance between two or more gears as shown in figure 1 or have some axial distance between two or more gears as shown in figure 2, which is depend upon application or design requirement.

## 3. Gear arrangement in compound gear train

Compound gear train arrangement is divided into three parts that are driving gear, intermediate gears and driven gear. Driving gear is fixed to the input power shaft, which has rotary motion. Driving gear is a primary source of motion and power. Driving gear is mesh with intermediate gears, from driving gear this power and motion is transfer to the intermediate gears. Intermediate gears consist of one or more compound gear. One of the last gear or may be more than one gear of intermediate gears mesh with driven gear. Driven gear is last gear of gear train, which is fixed to the output shaft. Arrangement of compound gear train is shown in figure 3, which consist of driving and driven gears and intermediate gears consist of one compound gear.

## 4. Working of compound gear train

A compound gear train is shown in figure 4, which consist of one driving gear, intermediate gears consist of two compound gears and one driven gear. As shown in figure 4, driving gear 1 is rotate in clockwise direction which is mesh with gear 2. Gear 2 is smaller in size and has lesser number of teeth than gear 1; hence rotational speed of gear 2 is increase than gear 1. Gear 2 and 3 are compound gear, due to this both are rotate in anticlockwise direction and at same rotational speed. Gear 3 is mesh with gear 4, which is smaller in size and has lesser number of teeth than gear 3 hence rotational speed of gear 4 is increased. Gear 4 and 5 are compound gear due to this both gear rotate in clockwise direction and at same rotational speed. Gear 5 is mesh with driven gear 6, which is rotate in anticlockwise direction. Gear 6 is bigger in size and has more number of teeth than gear 5 and hence reduction in rotational speed of gear 6.

A compound gear train is shown in figure 5, which consist of one driving gear, intermediate gear consist of one compound gear and two driven gear. As shown in figure 5, driving gear 1 is rotate in clockwise direction which is mesh with gear 2. Gear 2 is bigger in size and has more number of teeth than gear 1, hence reduction in rotational speed and increase in torque of gear 2 than gear 1. Gear 2, 3 and 4 are compound gear, hence these gears are rotate in anticlockwise direction and at same rotational speed. Gear 3 and 4 mesh with gear 5 and 6 respectively, gear 5 is smaller in size and has less number of teeth than gear 3 and gear 6 is bigger in size than gear 4 and has more number of teeth. These are two output driven gears with two different rotational speeds.

Like these two different compound gear trains, there are various possibilities of gears arrangement in compound gear train as per need and application.

## 5. Gear transmission ratio of compound gear train

A compound gear train is shown in figure 6 consist of one driving gear, one intermediate compound gear and driven gear. There are four gears in this compound gear train and notation of their speed and number of teeth is as per following.

N1 = Speed of gear 1
N2 = Speed of gear 2
N3 = Speed of gear 3
N4 = Speed of gear 4

T1 = Number of teeth on gear 1
T2 = Number of teeth on gear 2
T3 = Number of teeth on gear 3
T4 = Number of teeth on gear 4

Gear 1 is driving gear, gear 2 and 3 is compound gear and gear 4 is driven gear.

N2/N1 = T1/T2

N4/N3 = T3/T4

Multiplying,

(N2/N1)*(N4/N3) = (T1/T2)*(T3/T4)

N4/N1 = (T1/T2)*(T3/T4)

Train value (N4/N1) = (Product of number of teeth on driving gears) / (Product of number of teeth on driven gears)

## 6. Applications of compound gear train

• It is used in automobile
• It is used in clock and watch.
• It used in lathe machine.
• It is used in Compound gear box.

## 7. Advantages of compound gear train

• Small gear ratio is required for large speed reduction
• It can obtain higher and lower velocity ratio.
• Less space required compare to simple gear train.