Number of teeth Z
Closed gear transmission generally has a higher speed, in order to improve the stability of the transmission and reduce the impact vibration, the number of teeth is better, the number of teeth of the pinion can be taken as z1=20~40. Open (semi-open) gear transmission, because the gear teeth are mainly worn and failed, in order to make the gear not too small, so the pinion should not choose too many teeth, generally can take z1 = 17 ~ 20.
Helix angle
β > 0 is left-handed;
β < 0 is right-handed
Pitch
pn=ptcosβ (subscripts n and t represent normal and end face marks, respectively)
modulus
The modulus refers to the ratio of the tooth pitch p between the ipsilateral tooth profiles of the adjacent two teeth to the pi π (m=p/π), in millimeters. Modulus is one of the most basic parameters of modular gear teeth, and the modulus of straight teeth, helical teeth and bevel tooth gears can refer to the standard module series table (GB/T 1357-1987).
mn=mtcosβ
m=p/ π
The indexing circle of the gear is the basis for designing and calculating the size of each part of the gear, and the circumference of the gear indexing circle = πd = z p
Modulus m is a basic parameter that determines the size of a gear. If the gear module with the same number of teeth is large, its size is also large.
Pressure angle
α rb=rcosα=1/2mzcosα
At the tangent point P of the two gear pitch circles, the acute angle between the common normal of the two tooth profile curves (that is, the force direction of the tooth profile) and the common tangent line of the two segments (that is, the instantaneous direction of motion at point P) is called the pressure angle, also known as the meshing angle. For a single gear is the tooth shape angle. The pressure angle of standard gears is generally 20". In some cases, α=14.5°, 15°, 22.50° and 25° are also used.
Indexing circle diameter
d=m*z
Center distance
a=1/2*m(z1+z2)
Correct engagement conditions
m1=m2,α1=α2,β1=β2
To save the gear from root cutting, for a standard ruler cylindrical gear α=20o, z1≥17 should be taken. Z2=u·z1。
Tooth top height coefficient and top clearance coefficient
—h*a 、C*
When two gears mesh, it is always the tooth top of one gear that enters the tooth root of the other gear, and in order to prevent thermal expansion and have the space to store lubricating oil, the root height is required to be greater than the tooth top height. For this purpose, a crown height coefficient and a top clearance coefficient are introduced.
Normal teeth: h*a =1; C*=0.25 short teeth: h*a=0.8; C*=0.3
