Question Set 136

· What are Bevel Gears and what are its types?

Bevel gears are the type of gears in which the two shafts happen to intersect. The gear faces which are tooth bearing are conical in shape. They are generally mounted on shafts which are 90 degrees apart but they can be made to work at other angles as well. The bevel gears are classified into the following types on the basis of pitch surfaces and shaft angles:
> Mitre Gears: These types of gears are similar to each other ie. they have the same pitch angles and contain the same number of teeth. The shaft axes intersect at 90 degrees angle.
> Angular bevel gears: When two bevel gears connect at any angle apart from 90 degrees.
> Crown bevel gears: When the two shaft axes intersect at an angle greater than 90 and one of the bevel gears have a pitch angle of 90 degrees they are known as crown bevel gears.
> Internal bevel gears: In these type of gears the teeth on the gears is cut on the inside area of the pitch cone.

· What are the different values that need to be determined in order to design a cylinder for an ICE?

The following values are needed to be determined:
> Thickness of the cylinder wall: The cylinder walls in an engine is made witness to gas pressure and the side thrust of a piston. This results in two types of stresses: longitudinal and circumferential stress. Both the types of stresses are perpendicular to each other and hence it is aimed to reduce the resulting stress as much as possible.
> Length and bore of the cylinder: The length of the cylinder and the length of the stroke is calculated on the basis of the formula: length of cylinder L = 1.15 times the length of the stroke (l). L = 1.15(l)
> Cylinder flange and studs: The cylinders are always cast integral as a part of the upper crankcase or in some cases attached to it by means of nuts and bolts. The flange is integral to a cylinder and henceforth its thickness should be greater than that of the cylinder wall. The thickness of flange should generally be between 1.2t-1.4t where t is the cylinder thickness.
The stud diameter is calculated by equating gas load ( due to max pressure ) to the grand total of all the resisting forces of the studs.

· What are considerations taken into account while creating a piston head?

The piston head is designed on the basis of the following considerations:
> The crown should have enough strength to absorb the explosion pressure inside the engine cylinder.
> The head must always dissipate the heat of the explosion as quickly as possible to the engine walls. The thickness of the head is calculated on the basis of another formula which takes into consideration the heat flowing through the head, the conductivity factor of the material. The temperature at the center and edges of the head.
> The thickness of the piston head is calculated on the basis of the Grashoff`s formula which takes into consideration the maximum gas pressure of an explosion , the permissible bending and the outside diameter of the piston.