Bevel gear

Bevel gear is a gear design. They are used to transmit rotary motion and torque. A characteristic feature is the angle to one another the driving and driven shafts whose axes have a common intersection. The power is transmitted through bevel gears. In axial offset is also called Kegelradschraubgetrieben (equivalent hypoid gears ).

Kegelradschraubgetrieben at the sliding portion during rotation is higher than Kegelradwälzgetrieben. This means that the teeth roll and slide off. The slide comes about by relative movements of the contact surfaces of the bevel gear and pinion gear. This rolling or sliding motion at Hypoidkegelradgetrieben favors higher gear ratios and correspondingly better efficiencies at start compared to the worm gear.

Construction and application

A bevel gear pair consisting of a bevel gear ( crown often ) and a bevel pinion. The axes are often shifted 90 °, other angles are possible. Areas of this angle gear are where high reduction ratios, torques and movements are required. Most of the drive is via the bevel pinion, left and right directions of rotation are possible.

The gear ratio is the ratio of the number of teeth z2 of the bevel gear by the number of teeth z1 of the bevel pinion. A self-locking with worm gears does not occur. Bevel gear are used as power transmission in presses, rolling mills, machine tools, and in automation, wherever movements and forces are transmitted at an angle.

Types of bevel gears

The basic forms differ in the reference surface:

• Straight teeth: the edge lines of the Planradverzahnung are straight lines that pass through the Planradmitte.
• Helical teeth: the edge lines are straight lines. They form a circle around the Planradmitte.
• Curved teeth: the edge lines form curves. The edge lines can be, for example, circular arcs, involute or cycloidal.

Straight bevel gears are

The Geradzahnkegelrad as a machine element is mentioned in 1780, the first patents were issued in 1876 to William Gleason. Geradzahnkegelräder despite the narrowing of the usage in another array for use. The limits of their use, the circumferential speed, the noise and the transmitted power. The limit of the peripheral speed is generally referred to at 8 m / sec. The noise and the transmitted power are related to the degree of overlap closely related. In contrast to the spiral and hypoid bevel gears degree of overlap results in Geradzahnkegelrädern only from the pure profile contact ratio. This moves - depending on the gear ratio - 1 to 1.7 for large numbers of teeth. The original Geradzahnkegelrad the longitudinal direction of the tooth was straight. This dental course meant that at least resultant deflections of the axes, the tooth bearing immediately inside, outside, on the tooth header or footer focused. In this way, the noise is significantly increased and reduced, the tooth load to a minimum.

The geometrical arrangement of the tools formed of längsballige tooth. The magnitude of the crowning can be varied by the use of tools with different pressure angles. When designing a Geradzahnkegelradsatzes must, because it is a abgewälzte teeth on the gear ratio, the minimum number of teeth and pressure angle are taken into consideration. For the possible undercut the minimum number of teeth and the pressure angle is responsible.

As the engagement angle for this toothing 14 ° 30 ', 17 ° 30', 20 °, 22 ° 30 ' and 25 ° normal.

Bevel gears

The Schrägzahnkegelrad as designed and manufactured with a difference the Geradzahnkegelrad: The edge lines tangent to a circle around the Planradmitte. Otherwise, the forward statement made for the Geradzahnkegelrad also has its accuracy.

In Geradzahn - spur gears occurs as a resultant of the tangential force on a component as a radial load, which is determined in their resulting position only by the pressure angle. In addition to this radial force which thus acts perpendicularly to the axis, there is no force which is parallel to the axis, ie axially directed. If this spur gear has an additional Zahnschrägungswinkel and one speaks of a helical gear or a helical gear, causes this Zahnschrägungswinkel addition to the radial force by a component in the axial direction. If these conditions transferred to a bevel gear, as a result of the torque to be transmitted a component in the radial direction - that is, perpendicular to the axis - and a component in the axial direction. In the calculation to determine the radial and axial force of the pressure angle of the teeth, the angular function of the cone angle and hence the transmission ratio is one. Since the two basic input or output values ​​for this calculation are the same for both directions of rotation, and the magnitude and direction of these forces remains constant.

Spiral bevel gears ( spiral and hypoid )

The Spiral

The Geradzahnkegelrädern was mentioned that the overall degree of overlap of the teeth consists only of the profile contact ratio in the transverse section. For the straight-toothed bevel gear of the transverse section is equal to the normal section. At this point, it should be noted again that the noise behavior of a bevel gear may be related to the size of the contact ratio. For spiral bevel gears, the overall degree of overlap of the profile contact ratio and the overlap ratio is composed. Since with increase in the mean spiral angle increases, the overlap ratio, so can be significantly altered by changing the helix angle at constant pressure angle of the total contact ratio.

The scope of Spiral bevel gears is a place where Straight bevel gears and helical gears, bevel gears can no longer meet the demands made. At Geradzahnkegelrädern three factors mentioned, which limit the use of this type of wheels. It was the peripheral speed, the sound and the transmittable power.

When considering the noise behavior you stay at the helix angle, which, as already mentioned, the size of the total contact ratio influences prevail. Noise tests on spur gears have shown that an increase of the total contact ratio of 1 to about 2.5, a continuous drop in the noise level was recorded. Of interest is the finding that a further enlargement of the contact ratio did not yield any more noise reduction than 2.5 out to about 3 or 4. With certain restrictions, conditions of coverage on bevel gears can be transferred.

Next, when the transmitted power is treated, it is found that these can be influenced by the change in the total contact ratio. The strength calculation of bevel gear the size of the contact ratio is included in the bill. From this we can say that for the same wheel dimensions and the same torque to be transmitted by changing the helix angle, the specific load can be reduced with respect to the Zahnfußbiegespannung. Thus it can be stated in summary that the advantage of spiral bevel gears towards the Geradzahn and helical tooth bevel gears is characterized by larger achievable peripheral speed, better noise performance and higher power to be transmitted.

Due to the advantages listed here Spiralkegelradsatzes of the scope of such bevel gears is very large, of course. The drive axles of automobiles and other vehicles would be unthinkable in today's speeds without these spiral bevel gears. The machine tool manufacturer, serves mainly this machine element, as the cutting speed in the mechanical fabrication and hence the spindle speed in recent years have been significantly increased. In the field of stationary gear that are added to the general engineering, the spiral bevel gear is used predominantly.

The hypoid

Hypoid gears are a form of spiral bevel gears. The basic difference consists in that the pinion and Tellerradachsen not converge on one point, that is, the pinion shaft is offset from the wheel axis in height. This offset is called the pinion offset. The pinion offset should not exceed a limit of 20% of the outer cone distance for passenger car and light truck axle transmission 40% and for trucks, tractors, buses and rail vehicles.

Needs to determine the position of the axial offset are made for this purpose a clear definition. As shown in Figure A, you should consider a hypoid gear in such a way that when you look at the Tellerradverzahnung the pinion is rotated to the right and you hereby determines if the pinion is offset above or below the middle.

The advantages of Hypoidkegelradsatzes can be put together as follows:

• Through the pinion offset the pinion gets a larger spiral angle as the ring gear. The resulting from the larger spiral angle larger end module has an enlargement of the pitch circle diameter of the hypoid pinion result. This can in turn be a higher load capacity of a hypoid gear demonstrate to a spiral bevel gear. Thus, the surface pressure reduced to the teeth.

• Due to the mentioned in the first point increase in the spiral angle of the pinion the degree of overlap of the teeth is increased. Thus, with the same dimensions higher ratios can be realized than with spiral gears.

• Due to the axial offset can / must in most cases constructive nor an additional bearing for the pinion to be provided. Thereby, the Abdrängungswerte are mutually substantially improved as the relative motion of the pinion and crown wheel of the.

Hypoid gears are mainly used in addition to the general engineering in the automotive industry. It should not go unmentioned that enters through the pinion offset an additional sliding of teeth in dental longitudinal direction. This additional longitudinal sliding is not a disadvantage, however, a high-pressure oil to be used for lubrication,

Manufacture of bevel gears

The various materials that are used for the production of bevel gears comprise a plurality of iron, non-ferrous material and non-metallic materials.

The choice of material depends on various factors and operating conditions:

• Type of service
• Peripheral speed
• Degree of accuracy required
• A process for preparing
• Desired size and weight of the drive
• Allowable stress
• Shock resistance
• Wear resistance

The following materials are suitable:

Applications

The bevel gear has many different applications such as locomotives, marine applications, automobiles, printing presses, automation, mechanical engineering, steel mills, conveyor systems, or test benches. Wherever force and motion may be transmitted at an angle, a high efficiency with cycle operation is necessary, and maintenance applications are desired

Bevel gears in the differential gear, that is, two shafts rotating at different speeds, as they occur in the cornering of a vehicle. Bevel gears are used as a primary mechanism for hand drills. While the handle of the drill is turned in a vertical direction, the bevel gears of the chuck to rotate horizontally. The bevel gears in a hand drilling machine have the added advantage of increasing the speed of the chuck, and this makes it possible to drill a number of different materials.

Spiral bevel gears are important components for rotating drive systems. These components are required, if something is to be operated at a high speed, high load and a large number of load changes. That is, for example, used to redirect the shaft of a horizontal gas turbine engine for the vertical rotor. Even with rotary tables of machine tools is this application.

Hypoid gears are very often found in robotics and automation. Even as precursors in robotic arms with robotic transmissions. Hypoid bevel gears often have single-stage high gear and low weight.

Lubrication

To prevent friction and heat as well as to provide protection against corrosion, different types of lubrication on bevel gear units can be selected:

Requirements for the construction

In slowly rotating Kegelradwälzgetrieben usually sufficient radial bearings. In Kegelradschraubgetrieben ( hypoid ) are additionally formed axial forces or movements that need to be collected with thrust bearings. The bevel gear pairs are usually made ​​of hardened steel. High loads and low wear are desired. In order to improve the noise behavior and to keep the wear of the tooth flanks as low as possible, the bevel gear has to be calculated via software programs, optimizes the contact area ratio and the contact pattern can be set.

Further, the stiffness or flexure of the bevel gears must be considered. The storage (possibly elastic and balancing angle ) must be adapted to the circumstances.