机械设计18_锥齿轮.ppt

1、04,Gears IV Helical, Bevel Gears,04 - 2,Helical, Bevel and Worm Gears,Parallel Helical Gears,Worm Gearset,04 - 3,Straight Bevel Gears: Terminology,Pitch: measured at the large end of the tooth,04 - 4,Straight Bevel Gears: Virtual Teeth Number,The figure shows the profile of the teeth at the back con

2、e.,The profile of the teeth at the back cone resemble that of a spur gear having a pitch radius equal to the back-cone radius, rb.,04 - 5,Straight Bevel Gears: Standard,Bevel gears are inherently not interchangeable, since tooth form is closely tied to the method used for producing the gears, and a

3、different value of addendum is used for different gear ratio.,See AGAMA for tooth profiles for standard straight bevel gears.,04 - 6,Straight Bevel Gears: Gear Ratio,04 - 7,Force Analysis: Bevel Gearing,Power and Torque,Force,SI System,US System,04 - 8,Parallel Helical Gears: Helix Angle,Helix Angle

4、,Spur gears are merely helical gears with a zero helix angle,y is not standardized, but commonly range from 15 to 30.,Lower values give low thrust load.,Higher values give smoother motion,04 - 9,Helical Gears: Right and Left Helix,Right & Left Handed Helical Gears,Notes,For a pair of meshed parallel

5、 helical gears: G = 0, and y1 = y2 , i.e., one must be right handed and the other one must be left handed.,For a pair of meshed helical gears, y1+y2 = G, the acute angle between the two axes of rotation.,04 - 10,Parallel Helical Gears: Rack,Spur Rack,Helical Rack,04 - 11,Parallel Helical Gears: Pitc

6、hes,Diametral Pitch,Circular Pitch,04 - 12,Parallel Helical Gears: Pressure Angles,The transverse pressure angle, ft, is the angle between the common tangent plane and the projection of contact force on the plane of rotation.,Transverse Pressure Angle,Normal Pressure Angle,Normal pressure angle fn,

7、is the angle between the contact force and the common tangent plane of the pitch cylinders,Basically, it is the pressure angle viewed from the axis of rotation.,Relation,04 - 13,Force Analysis: Helical Gearing,Power and Torque,Force,SI System,US System,SI System,US System,04 - 14,Helical Gears: Dire

8、ction of Axial Force,Driver,Right Helix,Left Helix,Driven,04 - 15,Helical Gearing Force Analysis: An Example,A 1 hp electric motor runs at 1800 rev/min in the clockwise direction, as viewed from the positive x axis. Keyed to the motor shaft is an 18-tooth helical pinion having normal pressure angle

9、of 20, a helix angle of 30, and a normal diametral pitch of 12 teeth/in. The hand of the helix is shown in the figure. Make a three-dimensional sketch of the motor shaft and pinion, and show the forces acting on the pinion and the bearing reactions at A and B. The thrust should be taken out at A.,04 - 16,Solution I: Free Body Diagram,Free Body Diagram,(Right Helix),(Left Helix),04 - 17,Solution II: Geari