What is the gear ratio

Very often a term such as a gear ratio is used to describe the movement of a particular mechanism. What is it and what is its essence, let's try to figure it out now.

Each mechanism is characterized by the presence of an input and output shaft and, accordingly, input and output parameters, which, in particular, include the interrelated speed and angular velocity. The motor is always connected at the beginning of each device and transmits motion to the input shaft. This shaft is also called the master, since it then transfers the movement to the mechanism as a whole and the output (driven) shaft in particular. In this case, the angular velocity of the shaft at the output changes either its value, or the direction, or both. Therefore, in order to determine the relationship or change in the characteristics of the rotation of the driven and driving shafts, the concept of interest was introduced.

Thus, it can be argued that the gear ratio for any mechanical device can be found by dividing the final angular velocity by the initial one. Given the existing direct relationship between the characteristics of the motion of the shaft, the desired ratio is similarly found through the known values of the rotational speeds of the shafts. Since the same values are divided, the found parameter will not have a dimension.

The transmission ratio is determined not only for elementary transmissions, but also for more complex devices. These include, in particular, gearboxes, multi-stage gearboxes. Here you have your own peculiarities of calculations. On the last devices we will dwell in more detail.

The gear ratio will depend on the number of stages. If its composition includes only one transmission, then it is enough simply to calculate the desired value for it as for a simple device in order to achieve its goal. If there are several stages, the total gear ratio can be determined by multiplying the gear ratios of all stages or by dividing the angular velocity of the shaft at the input to the reducer by the angular velocity at its output. You can also use the knowledge of torque. To do this, you need to find the ratio at the output and the input. If it is greater than one, then the reducer is called raising, if less - lowering. Whichever method you choose for your calculations, in all cases the same numerical value should be obtained. You can check the correctness of your calculations using all the methods listed.

The gear ratio is also determined in various ways. In addition to the above, you can also use the knowledge of the number of teeth on the drive and driven wheels. For this it is sufficient to find the ratio of the last value and the first. Sometimes in the literature, the gear ratio is calculated in this way , but it is noted that it can not be less than unity. However, recently these concepts have merged together, and in many modern textbooks at the rate of "Machine parts" in a similar way it is calculated precisely the ratio, and not just the number. This seems to be correct, since they actually reflect the same thing: how input and output parameters of the transmission change, although initially it did not matter whether the output parameter was divided into output or vice versa.

Many use the gear ratio to solve the inverse problem. For example, if we know this characteristic of the mechanism and its input angular velocity, then to find the output it will suffice to multiply the named parameters by one another.

I hope that the information you have read has allowed filling in some gaps in your knowledge, and you can use it when performing various engineering calculations.