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Gear unit types and their application - gear drives and chain gears
In this article, various gear unit types are presented and their areas of application explained. Gear units are indispensable components in many machines and vehicles. They enable the transmission of torque and speed between the input shaft and output shaft, which ensures optimum power transmission.
Types of gear drives
Gear drives are a commonly used form of power transmission in mechanical systems. Gear drives are a commonly used form of power transmission in mechanical systems.
All types of gear units listed have in common that their main task is to convert engine speeds and torques, i.e. to effect a change of engine speeds and torques between input and output by means of the design and the components used.
- spur gear
- bevel gear
- worm gear
spur gear
Spur gears are a form of rolling gears and are a popular means of implementing the above tasks in one application due to their simple design. The axes on which the spur gears are mounted (with external or internal toothing) are aligned parallel to each other. The toothing of the spur gears included is developed as straight or helical toothing. In this case, spur gears can consist of an input shaft and one or several output shafts. These are referred to as single-stage or multi-stage spur gears.
Spur gears typically enable a gear ratio of i ≤ 6, which can however be further increased by a multi-stage design. Furthermore, spur gears are characterised by their cost-effective manufacture, high robustness and high efficiency.
Application example
In this application, a workpiece is transferred from one conveyor to the subsequent process by turning the workpiece by 180° onto another conveyor.
- 1) First, the arm turns the workpiece by 90°.
- 2) Then the rods turn the gripping device by the next 90°.
Click here to learn more about this application and view it as an animation.
Bevel gear
Like spur gears, classic bevel gears belong to the group of rolling gears. Bevel gears consist of a larger bevel gear wheel called a crown wheel and a smaller bevel gear wheel called a pinion. In simple bevel gears, the conical tips of the crown wheel and pinion converge in one intersection point. Their main characteristics are that the axes on which the gears are mounted are not arranged in parallel, but at an angle to one another (often 90°). This makes it possible to achieve a deflection of the transmitted force using bevel gears.
AThis property is different if the crown wheel is designed as a flat wheel, i.e. its partial cone angle is close to 90°. In this case, due to the different peripheral speeds, a 90° deflection could no longer be achieved when using a bevel gear wheel as a pinion. FIf this deflection is still desired, crown wheels can be used in combination with simple spur wheels.
In some cases, it may be necessary to transfer and deflect rotational movements between axes that do not have a common intersection point. HScrew bevel gears (also referred to as "hypoid gears") can be used for this purpose. In hypoid gears, the rolling behaviour of the pinion changes from a rolling movement to a screw movement in which the tooth flanks slide against each other.
Worm gear
Worm gears consist of a worm and a worm wheel and belong to the group of screw gears. Worm gears are characterised by high gear ratios of up to i ≤ 40 and, under certain conditions, have a self-locking function, which can be used for various applications.
However, due to the high sliding friction between the worm and worm wheel, worm gears have a lower efficiency than other transmission types. The high sliding friction also means that suitable material pairings and efficient lubrication should be ensured when selecting the components.
Application example
The worm gear and worm wheel are powered by the motor and the reel at the shaft end winds the wire.
Click here to learn more about this application.
Toothed belt and chain gears
A chain gear or toothed belt gear consists of two or more gear wheels or toothed belt pulleysthat are connected to each other by means of a circumferential chain or toothed belt. The movement of a gear wheel (input wheel) sets the chain or the toothed belt and thus also the other gear wheel (output wheel) into motion.
The principle of the chain gear enables power transmission over longer distances and offers the possibility to vary speeds and torques depending on the size ratios of the gear wheels.
For example:
- Conveyor systems: Chain gears are used in industrial applications to transport materials over longer distances.
- Machine tools: Chain gears can be used in machine tools to enable precise movement or positioning of workpieces or tools.
Application example
A motor-driven conveyor system that uses a system of rollers, drive wheels and toothed belts.
- The rollers are driven by chain gears - i.e. by toothed belts and toothed belt pulleys.
- The rollers are each equipped with an O-ring for good contact with the sides and corners of the glass circuit board.
Click here to learn more about this application.
Gear wheel types
In order to understand the different types of gear units, it is important to consider the different gear wheel types. Below, we discuss the different gear wheel types and their special features.
- Spur gear wheels
- Gear racks
- Bevel gear wheels
- Worm shafts
Compensating couplings are indispensable in many cases. They ensure an even transfer of power between the gear wheels and compensate for any tolerances – this significantly increases the service life of all components.
Spur gear wheels
Spur gear wheels are the most widely used form of gear wheels where the toothing is located on the circumference of the cylindrical gear wheel.
Externally toothed spur gear wheels
Externally toothed spur gear wheels have externally aligned circumferential toothing. In the case of two interlocking, externally toothed spur gear wheels, the direction of rotation changes when the rotational movement is transferred from the driving gear wheel to the driven gear wheel.
Internally toothed spur gear wheels
For internally toothed spur gear wheels, also called hollow gear wheels, the circumferential toothing is aligned internally.
When combining an internally toothed spur gear wheel with an externally toothed spur gear wheel, the direction of rotation of the driven gear wheel does not change in contrast to the combination of two externally toothed spur gear wheels.
The special design can also achieve a space-saving arrangement of the gear wheels by reducing the axial spacing. Another special feature of the internal toothing is the concave design of the tooth flanks, which increases the contact surface, thus reducing wear when combined with convex toothing.
Gear racks
Gear racks can be considered a special form of the spur gear wheels, which have a width of any size. They consist of a rack to which a toothing without curvature is attached. Gear racks translate the rotational movement of an externally toothed spur gear into a linear movement.
The reverse case is also possible: Gear racks translate their linear movement into a rotational movement of an externally toothed spur gear wheel.
Application example
For lifting and lowering several lifters with one air cylinder.
In this application, only one drive is needed to move several lifters simultaneously in one continuous operation (up and down).
- 1) The space-saving air cylinder unit (yellow, on the far right of the image) performs a linear movement and moves the gear rack forwards and backwards.
- 2) The linear movement of the gear rack (pinion) moves the front spur gear wheels.
- 3) The front spur gear wheels perform a rotational movement and transfer the force to the rear spur gear wheels by means of axles.
- 4) The rear spur gear wheels engage in the rear gear racks of the lifters. They translate their rotational movement back into a linear motion.
Click here to learn more about this application and view it as an animation.
Bevel gear wheels
Bevel gear wheels have a conical design, in which the toothing is located on the outer side of the cone (outer surface).
The toothing of bevel gear wheels can be designed as straight or spiral toothing.
Worm shafts
Worm shafts (short "worms") occur together with worm wheels in worm gears. The worm shaft has a helical thread that engages in the toothing of the worm wheel.
Worm gears are characterised by high gear ratios and can have a self-locking function under certain conditions, which can be used for various applications. However, due to the high sliding friction between the worm and the worm wheel, worm gears have a lower efficiency than other gear unit types.
The worm shaft is a modification of the helical toothing, in which one or more spiral teeth (gears) are introduced into the shaft.
Toothing types
The toothing type has a major influence on the efficiency of the gear unit and the forces occurring during operation in later application. Depending on the application, different forms of toothing may be the means of choice.
- Straight toothing
- Helical toothing
- Double helical toothing
Straight toothing
The straight toothing is the simplest type of toothing options, in which the teeth in the case of spur gear wheels are arranged parallel to the axis of rotation of the gear wheel. This form of toothing is inexpensive in production and represents a widespread toothing variant.
In the case of straight toothing, up to 3 teeth are simultaneously engaged with a counter wheel, which distributes the load over several teeth. BWith straight toothed gear wheels, the entire width of the tooth flank engages at once when the drive forces are transferred, making the noise development and wear higher than with helical toothing.
Helical toothing
In the case of helical toothing (e.g. helical spur gear wheel), the teeth are at an angle to the axis of rotation of the gear wheel. This increases the contact ratio, i.e. the ratio of the contact length to the pitch of the gear wheel. This has a positive effect on the smooth running and wear resistance, allowing higher speeds to be achieved.
Compared to straight toothing, this design is more expensive in production and the axial forces occurring during operation must be absorbed.
A special form of helical toothing is the curved gearing. In addition to the angular arrangement, the individual teeth describe an curved course along the middle of the tooth, which is accompanied by a further increase in the contact ratio and the associated advantages.
Double helical toothing
In the case of double helical toothing (also called herringbone toothing or double helix toothing), the circumference of the gear wheel is divided into a left-hand and a right-hand half.
This complex design is comparatively expensive in terms of manufacturing costs, but combines the advantages of the toothing variants mentioned above, which enables a high level of smooth running and wear resistance.
