There are various types of bearings, each with their own strengths. Do you know what kinds of machines use what kinds of bearings?
In this part, we will introduce the bearings used in cars, as “Part I” of our introduction of the applications of bearings.
1. How are bearings used in a car?
In order to increase a car’s performance by, for example, decreasing the CO2 (carbon dioxide) emissions that cause global warming, or reducing the number of breakdowns, bearings becomes more and more important.
In this part, we will explain how bearings are used in the transmission and differential gear that transfer power from the engine to the wheels.
Fig. 1: The system that transfers driving force from the engine to the wheels
2. Bearings used in the transmission
Sometimes we want to drive faster, or we need a large amount of driving force such as when driving uphill. It is necessary to achieve a driving force appropriate for the driving circumstances.
The transmission is a device that converts the power from the engine into driving force and transmits it to the wheels. Inside, many different types of bearings are working together, each utilizing their own strength, and inside the individual parts of a car there are also a great many bearings in use.
Transmissions can be classified into two broad categories: manual and automatic. In cars with manual transmissions, a gear stick used to operate it is installed next to the driver’s seat.
Fig. 2: The gear stick used to operate a manual transmission
The driver operates the gear stick manually, in order to convert the power from the engine into a force appropriate for the situation in which the driver is driving.
The manual transmission consists of shafts and gears. These parts are supported by bearings, and we would now like to introduce those bearings.
Fig. 3: The structure of a manual transmission
Fig. 4: How a manual transmission works
Bearings that support shafts
A bearing, of a type to match the magnitude of the power from the engine, is used, and it supports both the rotation of the shafts and the force being applied by the gears.
Table 1: Bearings that support shafts
|Radial load||Axial load||Type of bearing|
|Small||Small||Deep groove ball bearing|
|Big||Small||Cylindrical roller bearing|
|Big||Big||Tapered roller bearing|
We explained about radial and axial loads in Part 4, so please check there as well if you haven’t already.
Fig. 5: Deep groove ball bearings for supporting shafts
Bearings that support gears
In a manual transmission, gears remain in rotation and interlocking with each other at all times.
In order to convey the appropriate driving force to the wheels for the speed we want to travel, we use the gear stick to select the gear (A) that best fits that driving force. The selected gear (A) is connected to the shaft, and rotates the shaft the same number of times.
In order to transmit a different driving force to the wheels for the changed situation, we use the gear stick to disconnect the connected gear (A) from the shaft and select the gear (B) that best fits that driving force. The selected gear (B) is connected to the shaft, and rotates the shaft with the same number of rotations.
In this case, the gear that is disconnected from the shaft (A) rotates independently of the shaft.
Just as the gear and the shaft have a different number of rotations, the needle roller bearing (a combination of needle rollers and cages) is mounted between the gear and the shaft, and rotates between the inside surface of the gear and the outside surface of the shaft.
Fig. 6: The numbers of rotations of gears and shafts used to increase or decrease speed
Fig. 7: A bearing (combination of needle rollers and cages) for supporting a gear
3. Bearings used in differential gears
When a car turns left or right, the wheels on the inside rotate slower than the wheels on the outside.
The differential gear is a device that converts the driving power from the transmission into even greater driving power and allows for different numbers of rotations for the left and right wheels.
Fig. 8: Wheel rotation when a car turns
At the differential gear, gears attached to the pinion shaft (the shaft connected to the transmission) and the shaft on the wheel end interlock at a right angle. Bearings support both the rotation of the shafts and the force being applied by the gears.
Fig. 9: The layout of a differential gear
Fig. 10: The structure of a differential gear
Tapered roller bearings that support shafts
The combined tapered roller bearings simultaneously support both the radial and the axial load (in both directions), and by maintaining the correct interlocking of gears transmit a large amount of driving force to the wheels on both sides.
JTEKT provides the best low-friction torque tapered roller bearings in the world, which allow for an extremely small loss of driving force during rotation. On top of this, we are also making compact bearings a reality, greatly contributing to a decrease in CO2 emissions from cars.
Fig. 11: Low-friction torque tapered roller bearings
In this part we explained about the bearings that are used in devices that transmit power from the engine to the wheels, but there are a great many bearings used in the other parts of cars. By utilizing the strengths of each of the bearings, we increase the driving performance and safety of automobiles.
In order to achieve safer and more comfortable driving, there is a greater and greater demand for bearings with both high functionality and high reliability.
Do you know what kinds of machines, apart from cars, use what kinds of bearings?
Part 1 we explained how a bearing is a component that supports rotating shafts.
For this reason, it’s safe to say with certainty that bearings are used in any machine that has a shaft.
In this part, we will continue on where the last part left off, and talk about the applications of bearings.
Specifically, we will now introduce the bearings used in machines in three fields: “generate energy”, “creation of materials” and “machining.”
1. Bearings that create energy: wind turbine generators
Electric power generators create the energy that we need in our day-to-day lives. In recent years there has been a greater interest in using to use green energy that does not emit CO2 (carbon dioxide), one of the gases that cause global warming. In particular, wind turbine generators have been popping up all over the world.
Maintenance inspections are difficult when such turbines are located in high located at a high altitude, and so there is increased demand for bearings that have a high degree of reliability (they hardly ever break) and a long lifespan.
There are a lot of bearings that are used in wind turbine generators, but here we would like to introduce the “main shaft bearings” that receive force from the wind and convey rotation to the generator.
Fig. 1: High-altitude wind turbine generators
Fig. 2: The structure of a wind turbine generator
Main shaft bearings
In a wind turbine generator the force of the wind spins the main shaft, and that rotation is transmitted to the generator to generate electricity.
The main shaft bearings support not only the weight of the blades and the rotational part but also the force of the wind, whose force and direction change in an irregular manner.
For this reason, we mainly use spherical roller bearings, which are able to support a large amount of force and have an excellent aligning capability.
■ What is “aligning capability”?
This refers to the ability of the inner ring, rolling elements, and cage to continue to rotate, aligning themselves if they have become misaligned.
We also described the aligning capability of spherical roller bearings in Part 4: “What Are the Differences Between Bearings? The various types and special features of bearings,” so please check that out if you haven’t already (or if you need a refresher).
Furthermore, because they are able to support a large amount of force, we use large spherical roller bearings, with an outside diameter of 1 meter or more, for the main shaft.
Fig. 3: A large-scale spherical roller bearing for the main shaft of a wind turbine generator
2. Bearings that create materials: steel rolling mills
As a representative example of a machine that creates materials for things, we will now introduce the rolling mill, which turns steel materials into the shape needed to serve their purpose.
Fig. 4: Typical examples of steel shapes
In a steel rolling mill, a steel sheet is passed through to rotating rolls, and force is applied to stretch it out. There is an old saying that goes “strike while the iron is hot.” This saying is true: steel materials are usually rolled at a very high temperature. Here, bearings, under high-temperature conditions, support an exceedingly large amount of force to rotate the rolls.
Fig. 5: The structure of a steel rolling mill
Bearings used in work rolls
In work rolls, we use four-row tapered roller bearings, in order to support the exceedingly large radial load and bi-directional axial load that are generated during rolling.
Fig. 6: A four-row tapered roller bearing for use in a work roll
Bearings used in backup rolls
Work rolls, when rolling, can become warped easily due to the heavy load, but the backup roll protects against that warping. In backup rolls, we use four-row cylindrical roller bearings to support the exceedingly large radial load and double-row tapered roller bearings to support the axial load.
Fig. 7: Bearings for use in backup rolls
In 1943 JTEKT created the first steel rolling mill bearing in Japanese history, and ever since has been providing a large number of bearings for use not only in rolling mills but throughout the entire steel industry.
3. Bearings for machining: machining centers (machine tools)
Lastly, let’s take a look at the mechanical devices used in machining.
Mechanical devices used in transforming (“machining”) products and components into the optimal shape are called machine tools.
In particular, recent years have seen a rapid rise in the prevalence of machining centers that are used in machining and are controlled by computer.
Thanks to machining centers, minute and precise machining that cannot be performed by hand is made possible, and the time needed for machining is reduced dramatically.
Fig. 8: A machine tool used in a machining center
In the spindles attached to machining centers, we need to use bearings with a low temperature increase, so as not to cause warping of the product due to heat generation, or decreased precision of the machining.
Fig. 9: The structure of a machining center and its spindle
In spindles, we use angular contact ball bearings, which can simultaneously support a radial load and an axial load during machining.
Fig. 10: Angular contact ball bearings used in a spindle
JTEKT was the first in the world to produce ceramic bearings.
These ceramic bearings do not heat up much, even when rotating at high speed, and thus guard against the dimensional warping of the machined products.
In addition, they allow for the supply of only the necessary amount of lubricating oil, which is the cause of this heat generation, to the required areas, and to promptly discharge it.
Conclusion: Bearings support our daily lives
From machines that generate energy, to machines that create materials, to machining tools–we don’t often witness these products directly in our day-to-day lives. But, as we have introduced in this column, a great many bearings are used for machines in the industry. These bearings not only support the force and the rotation, but they support our daily lives. Furthermore, the functionality that is demanded of bearings is increasing all the time, with bearings suited for different applications being highly sought after.