2.2. Reduction unit kinematical and capacity calculations.

Rotational frequency of drive shafts:

• high speed shaft;

• low speed shaft .

Angular speeds of drive shafts:

• inlet ;

• outlet .

The following ratios between torques on the shafts are used for transmission calculation

, hence,.

Drive shaft torque, at :

• –it’s direction matches the direction of the shaft rotation, i.e. it’s a torque of moving forces

• –Its direction is oppose to shaft rotation, i.e. it’s a torque of resisting forces

Results of design work are to be outlined in Table 4

Table4.

Reduction unit characteristics

Characteristics	Shaft 1	Shaft 2
Rotational frequency, r/min
Angular speed, R/s
Torque, Newton per meter

2.3. Toothed gear drive calculation

Gear drives are mechanisms transmitting a movement with the assistance of gears. The gears are parts (cylinders) having evenly located teeth (cogs) and gashes (Fig. 2).

Pinion- is a smaller of two interacting gears,

and wheel – is a larger of the two interacting gears.

а)	б)	в)	г)
Fig. 2. Basic types of cylindrical gears. External gears: spur (а); helical (б); double helical (в). internal gear (г)

2.3.1. Assessment of permissible stresses

Hardness of gear wheels should be selected subject to application and conditions of transmission operation. In our coursework we use carbon and alloyed steels subjected to heat treatment, allowing to ensure required hardness under given thickness of the part blank .

Table 5.

Options of gear hardness

Option	wheel		pinion
	hardness	GOST 8479-70	hardness	GOST   8479-70
1	212…248 НВ	S490 (655)	248…293 НВ	S640 (785)
2	223…262 НВ	S540 (685)	262…311 НВ	S685(835)
3	235…277 НВ	S590 (735)	277…321 НВ	S735 (880)
4	248…293 НВ	S640 (785)	293…331 НВ	S785 (930)
5	235…277 НВ	S590 (735)	277…321 НВ	S735 (880)
Note: GOST 8479-70 define forging features; symbols: S – type of strength; number in three digits – yield stress value in MPa; in brackets tensile strength value in MPa is given

In the coursework the gear hardness option is defined by its benchmark data. (Table1).

The selection of hardness of pinion and wheel should be carried out as per the following rule: maximum limit of wheel hardness should comply with minimum limit of pinion hardness.

Permissible stresses are assessed for the following conditions:

• continuous operation under constant load;

• helical gear;

• part blank- forging;

• heat treatment of gear wheels – improvement (hardening with further high temperature tempering).

Permissible stresses for surface load durability

CHIPPING

This type of calculation exclude fatigue chipping of teeth surfaces, the main reason for teeth surface rapture.

Permissible surface stresses for transacting gears are calculated as follows:

, МPs

где , ;

–average hardness value;

–safety ratio for homogeneous material structure.