Mechanical design. Design a pair of helical gears.

The calculation formula is available in the mechanical design manual.

There are a variety of failure modes of gear transmission, but for a specific gear transmission working under hail conditions, usually only one failure mode is the main failure mode, theoretically the corresponding design criteria and calculation methods should be selected for its main failure mode to determine its transmission size, so as to ensure that the transmission does not fail during the whole working life. However, there are no effective and mature calculation methods and complete design data for failure modes such as tooth surface wear and plastic deformation.

At present, when designing the gear transmission working under general working conditions, it is usually only calculated according to the two criteria of ensuring the contact fatigue strength of the tooth surface and the bending fatigue strength of the tooth root. For the gear transmission that is prone to gluing failure at high speed and heavy load, the anti-gluing ability of the tooth surface should also be calculated. As for the ability to resist other failures, the corresponding countermeasures are taken in the design only according to the cause of the failure, and no precise calculation is made.

In general, the design criteria for gear transmission are:

1) For closed soft tooth surface gear transmission, the main failure mode is tooth surface pitting, so the design and calculation are carried out according to the contact fatigue strength of the tooth surface, and then checked according to the bending fatigue strength of the tooth root.

2) For the closed hard tooth surface gear transmission, the tooth surface has a strong pitting ability, and the main failure mode is the bending fatigue fracture of the tooth root, so the design and calculation are carried out according to the bending fatigue strength of the tooth root, and then checked according to the contact fatigue strength of the tooth surface.

3) Split gear transmission, the main failure mode is tooth surface wear and tooth root bending fatigue breakage, so first according to the tooth root bending fatigue strength for design calculation, and then consider the influence of wear, Wang Fanfan will be the strength calculation to obtain the gear modulus appropriately increased.

The problem of mechanical design of the gear transmission given by the subject should be considered in this way, because the width of the gear is to be reduced under the condition that other parameters remain unchanged, that is, it can be solved by the relationship of proportion. Namely.

sqrt(bmin)×σh =sqrt(b)×[h]bmin=(σh/[σh]×sqrt(b))^2=(400/500×sqrt(80))^2= mm

According to the contact strength h] condition, so the bmin should be taken 51mm.

Of course, choose the envy of the slant or the herringbone.

Because of helical gear transmission.

When the contact line on the tooth surface moves along the meshing plane, that is, it enters the meshing from the top of the tooth, the contact line changes from short to long, and then from long to short, and the upper tooth is not completely detached, and the next tooth has entered the meshing, so that the load on each tooth changes from small to large, and then from large to small, so that the meshing process is smooth, and the impact, vibration and noise are eliminated.

And because the teeth are spiral-shaped, the contact line of the stool on the tooth surface in the meshing area is larger than that of the straight teeth. It can be seen that in terms of force and transmission, helical gears are better than straight gears.

I hope this brother can solve your doubts.

First, the nature is different.

1. Helical gear transmission: a common part often used in mechanical transmission, the gear is made of high-quality high-strength alloy steel.

2. Spur gear transmission: a classification method of gears.

Second, the advantages are different.

1. Advantages of helical gear transmission:

1) Good meshing performance: the meshing process between the helical cylindrical gear teeth is an excessive process, and the force on the tooth surface is gradually increased from small to large, and then from large to small; Helical cylindrical gears are suitable for high-speed, heavy-duty occasions.

2) Large degree of coexistence: The increase of coincidence degree improves the bearing capacity of the gear. This prolongs the service life of the gears. The degree of coincidence is mainly determined by the engagement time, while the long engagement time and large contact area of helical gears reduce stress. Stable power transmission and economic growth.

3) Compact structure: the smaller the minimum number of teeth, the more compact the structure.

2. Advantages of spur gear transmission: strong bearing capacity and durability.

Third, the disadvantages are different.

1. Disadvantages of helical gear transmission: it is more troublesome to manufacture and uneconomical.

2. Disadvantages of spur gear transmission: when the gear is large in modulus, tooth punching and other reasons, it is not convenient to measure the diameter of the tooth top circle. It is easy to cause impact and noise, and the transmission stability is poor.

In the design of mechanical transmissions, what are the transmission components, can the use of spur cylindrical gears be considered? Where should helical cylindrical gears be used? What is the difference between these two types of gears when checking the flexural strength and contact strength?

Why does the center distance a of the transmission have an effect on the contact strength of the gear teeth? Please analyze how it is affected.

The constant gears in the transmission are helical cylindrical gears. Straight-toothed cylindrical gears are only used in low and reverse gears. Needle roller bearings or bushings for constant gear are often meshed with the spindle.

The third, fourth or fifth gear is kept and the middle of the spindle is positioned and centered, so the main sleeve.

The third, fourth or fifth gear is not driven by the spindle and can rotate or not rotate independently, so as to avoid the restraint of the spindle rotation. At the same time, the internal and external rotation of the needle roller bearing or bushing reduces wear on the inner diameter of the gear and the outer surface of the spindle journal. When the transmission is in fourth, fifth or third gear, that is, when the main shaft gear is engaged with the main shaft, the engaged gear bearing or bushing is not rotating, and the other needle roller bearings or bushings are rotating.

When the vehicle slides downhill and the engine is turned off, the clutch is engaged, and the transmission is in neutral position, the first shaft driving gear and the second shaft driven gear and the pagoda gear, the constant gear and the like are all in a stationary state, only the second shaft rotates due to the drive of the rear transmission, and the needle roller bearing or bushing rotates with the rotation of the second shaft at this time, so once the vehicle has this situation for a long time, it is very unfavorable to the needle roller bearing or bushing.

Advantages of helical gearing:

1. Good meshing performance. The contact line of the helical gear tooth is a straight line inclined to the gear axis, and the gear tooth begins to mesh and disengage from the meshing gradually, so the transmission is stable and the noise is small, and this meshing mode also reduces the influence of manufacturing error on the transmission.

2. The degree of overlap is large. It can reduce the load of each pair of gear teeth, so as to improve the bearing capacity of the gear, prolong the service life of the gear, and make the transmission stable.

3. The minimum number of teeth of the helical standard gear without undercutting is less than that of the spur gear, so a more compact mechanism can be obtained by using helical gear transmission.

Disadvantages of helical gearing:

Helical gear transmission generates axial thrust when it moves, causing damage to the axial structure.

Middle bull gear: number of teeth: 123; Modulus: 2; pressure angle 20°; Common Normal: , spanning 14 teeth. Spring code.

Diameter of tooth top circle: 250; Tooth root round straight barrage diameter: 241.

Peripheral pinion: Number of teeth: 82;Modulus: 2; pressure angle 20°; Common Normal: , spanning 10 teeth.

Diameter of tooth top circle: 168; Root circle diameter: 159.

The above large and small pinions are all standard spur gears. backlash; coincidence degree; slip rate; Tooth ratio.

The maximum number of pinion teeth is 51, and the number of teeth of the large gear is 154

You should have a gear ratio requirement.