509076 J.K Essay Example

A multi-plate friction clutch is designed to transmit 75 kW from an engine rotating at 2000 RPM. Inner and outer diameter of the plates are 100 mm and 150 mm. Pressure is uniform at 150 KN/m² and =0.25. Calculate the torque, end thrust and number of plates required.

Given ‘N’ = 2000rpm

Power =75kW=75000W

W = end thrust (N)

P = pressure = 150kN/m²

r1 =outer radius =0.15/2 = 0.075m

r2 = inner radius = 0.1/2 =0.05m

T = torque =358.1Nm

= coefficient of friction=0.25

W = is end thrust= 1472.6N

r₁ =outer radius = 0.075m

r₂ = inner radius = 0.05m

n = number of driven plates

From task 3A, the outside diameter of the plates is increased to 200mm. Determine the torque, end thrust and number of plates required.

= angular velocity (rad/s)

Where ‘N’ = 2000rpm

From

W = end thrust (N)

P = pressure = 150kN/m²

=outer radius = 0.1m

= inner radius = 0.05m

T = torque =358.1Nm

W = end thrust 3534.3N

=outer radius = 0.1m

= inner radius = 0.05m

n = number of driven plates

Rounding up we n=6 pairs

Compare the answers you have obtained from tasks 3A and 3D. You must critically evaluate the answers you have obtained.

From the calculation it can be seen that increasing the clutch radius increased the thrust required to be applied to be able to transmit the required power. On the other hand in the clutch with a smaller outer radius the thrust is much lower but there is need to have higher number of plates in order to generate the required torque. For the higher radius clutch increased thrust means that there is need to use a bigger and stronger springs. Also the plates with larger radius will have high velocity at the outer surfaces of the plates even though in both clutches the speed of rotation is at 2000rpm. This means that in the first clutch there will be high relative velocities between the plates at the time of engagement of the plate. With high relative velocities it will mean that with high radius there will be increased wear of the clutches and thus there will be reduced efficiency. It will also mean that there will be need to replace the plate much frequent than in the case where we have smaller radius. With the increased thrust force it means that high stress is the driven shaft. In order for increased stress to be sustained by the shaft it will require a larger diameter driven shaft assuming in both cases the same material is to be used.

On the other hand for the smaller radius clutch it is seen that the number of plates almost three times those in the larger radius clutches. This increased number means that there is need to have extra space to accommodate them, which in turn translate to have a longer driven shat as well as the casing. The increased shaft length plus the number of plates will increase the amount of moment of inner of the system and thus increased loss of energy in friction. Will also mean that it will take longer to have the maximum speed to be attained in the driven shaft because of the increase in the moment of inertia. Initially reducing the radius of the disc is a step on ensuring there is maximum toque transmission and the maximum speed is reached within the shortest time possible. This is achieved by increasing the number of plates but beyond a certain number of plates it is no longer beneficial to have more plates. In order to increase the number of plates without the number becoming a burden , it is important to have the plates be close to each other, to make them to be as thin as possible and also the material should the of relatively low density. In this way we will have the clutch being compact enough to fit in the available space and not adding unnecessary weight to the assembly.

Explain where slider crank mechanisms are used in engineering applications.

Slider crank mechanism consist an arm attached that is attached at right angle to a rotating shaft enabling the reception of a reciprocating motion. This mechanism is used in the conversion of circular motion to reciprocating motion or in obtaining the reverse result. We may have the arm being a bent portion of a shaft, or it may be a separate arm or a disk that is attached to it. The connecting rod also known as conrod is attached to the end of the crank where the end of the rod attached to the crank will usually move in a circle describing motion while the end display linear motion after being constrained.

Crack mechanisms are very important as they are used in most combustion engine in changing reciprocating movement to rotary movement. An assembly consisting of a piston, the connecting rod (conrod) and crankshaft is thought of as being a classic engineering application of slider crank mechanism. Generally the slider crank transmits motion that is generated through linear displacement of the piston caused by combustion and in the cylinder resulting to rotational motion in the shaft. The slider crank mechanism has many applications with engine application being the dorminant. The application of the mechanism in generating power can be traced to the steam engine that came up in late 18^th century and has further developed to be the sole mechanism that is being used in modern internal combustion engine. A single piston model can be thought of as being the functional, example of this mechanism.

The standby single acting involves the use of a piston-wrist-pin conrod resembling an automotive engine is an example of the slider crank mechanism. With this engine there is provision of a clear visual kinematics for the slider mechanism.

Quick-Return Mechanisms Quick-return is another form of slider crank mechanism. In this mechanism there is a fast stroke in one direction while the other direction consist of much slow when the being driven by an rotational actuator that has a constant speed. This are commonly found in machine tools where it necessary to slow cutting stroke and fast return stroke. The two different quick-return mechanisms as shown in the two kinematic diagrams below with a showing an offset slider-crank linkage while b is a crank-shaper linkage.

Scotch Yoke Mechanism

This is a common mechanism that is capable of converting rotational motion to linear motion or the other way round. As can be seen from the figure below a pin that is on a rotating link has engagement in a slot of a sliding yoke. As for the input and output movement, the sotch yoke describes a slider-crank with the slider motion being sinusoidal.

Devices in package

From the figure it can be seen that the mechanism consists of a rotating will which is powered by an electric motor. Through the linkages the motion is transformed to a reciprocating motion where the package placed at the table can be pushed to the conveyor belt which will in turn move it to a desired location.

Another application of the slider crank mechanism is the backhoe. The mechanism it can be seen consists of three sliding movement which finally results to rotational movement in the backhoe even though a full circle rotation is not experienced.