INTRODUCTION
As a mechanical engineering student one should be able to follow the steps in engineering design process.
We are asked to design a friction clutch for a one ton truck. The issue of transporting load has become one of the biggest problem in this country. A solution to this is a friction clutch of a one ton truck that will carry the load to different parts of the country. This will make life so much easier because people do not have to carry their loads on small vehicles. The one ton truck needs a clutch that will be suitable for it to engage and disengages the engage when the truck starts moving.
FUNCTIONS OF A CLUTCH
-It transmits the torque from the engine to the drive train. -It smoothly delivers the power from the engine to enable smooth truck’s movement.
-Its performance is very quiet and it reduces vibration that that is drive related. -It also protects the drive train whenever it is given an inappropriate use.
HOW DOES THE FRICTION CLUTCH WORK?
The way the clutch works it is quite interesting. When the pedal of the clutch is pressed, a hydraulic pistol pushes on the release fork which presses the throw-out bearing against the middle of the diaphragm spring. The clutch disc is then disconnected from rotating the flywheel that is attached to the engine. When the pedal is released then the disc will start to engage contact with the flywheel and it starts to transmit the torque from the engine to the rest of the drive train.
The speed of the torque that is transmitted is at a lower rate at the beginning and the engine under load cannot start. The transmitting system provides a connecting and disconnecting of the engine to the rest of the transmission system.
SAFETY CONSIDERATIONS
This process of engaging and disengaging the engine should cause no harm to the passengers, it should be smooth and cause no shock to the passengers. As the clutch permits gradual taking of load when it is operated well, it prevents some jerky motion of the truck and strain in other part of the truck is avoided as well as strain from the passengers.
RESEARCH ON DIFFERENT TYPES OF FRICTION CLUTCHES
Single plate clutch – It has only two members, one mounted on the driving shaft and the other on the driven shaft. The shafts are parallel and are concentric with each other .One shaft is fixed in its housing and the other is splined causing it to move axially.
When the effective radius of contact is increased the torque also increases. It has the following components flywheel, pressure plate, clutch covers, a clutch plate, release levers, clutch shaft, and withdraw fork and bearing. The single plate clutch is very easy to operate and it is very much easier to change the gear. This clutch does not suffer from binding cones.
It generates low heat, there is no need of cooling the medium. It is used in big cars meaning that it can be suitable for the one ton truck. The only disadvantage is that the torque transmission capacity is less. Multi plate clutch – is a clutch in which the multiple clutch plate are used to make frictional contact with the flywheel of the engine in order to transmit power between the engine shaft and transmission on the automobile vehicle.
They contains more than three discs. This type of a clutch is mostly used in heavy duty commercial, racing a cars and military vehicles. Its advantage is that it can be operated on both dry and wet conditions. When it is operated in wet (using oil) the engagement is smooth and it reduces the temperature and prolongs its life.
But the dry clutch is used without oil and the driving plates lined on each side with a frictional material. It has an inner drum which is coupled to the gearbox shaft that has a number of plates splined as its outer periphery. The other drum is connected to the flywheel and carries a number of plate splined at its inner circumference and the plate can revolve together with the drum but can slide axially. The spring keeps the inner and outer plates pressed together making it possible for the member to transmit power to the driven member. Wet and dry clutch – wet clutches operate in the present of oil while the dry clutch operates without the presence of oil.
In a wet clutch the sound level is less because the oil prevents the friction sound of the between the plates. It has a long life as compared to the dry clutch and its maintenance is cheaper. The dust is removed by the oil filters and its tear and wear is much less as compared to the dry clutch. In a dry clutch the sound level is more because there is no oil to reduce the friction sound in between the plates. This clutch is expected to have a low life expectancy and it keeps on wearing out resulting in a high cost of maintenance.
Cone clutch – is a device that engages and disengages power transmission for the driving to the driven shaft. It uses two conical surfaces to transmit torque. The torque transferred is much more higher compared to the one at the plate. Its operation is very fast and the gear is changed at a faster rate. These type of clutches are normally used for racing cars. Internal and external clutch SPECIFICATIONS The weight of the clutch must not exceed 454 kg because it might cause some problems on how it operates.
Size – the pressure plate has 10 splines on the hub and has 6 holes with diameter 30 mm on the pitch circle of 170mm radius. And it has 30 holes with the radius of 2mm connected to support links. The cost of the clutch is reasonable, this ensures that the cost of the truck will not be too expensive just because of a clutch. Many companies and people who are in need of this truck will be able to afford it and it will save them money because the servicing of the clutch will not be too often.
Materials used – the pressure plate is made of a grey cast iron. A ceramic is used to make the clutch disc because it has high thermal conductivity and high diffusivity. Torque = 106 Nm Power =50 kW
POSSIBLE SOLUTIONS
The cone clutch might work for the ton truck since it has a high torque and the gears can be changed quicker. The only problem about the cone clutch is that it is not used for cars with heavy load but can only be used for racing cars.
If this clutch is placed on the truck it will damage the clutch in a short period of time. A wet clutch may also solve the problem because it has less wear and tear and the maintenance is cost is low. Another solution is the dry clutch since it does not use oil, the user does not have to buy the oil for it to function. The dry clutch also have some disadvantages, the friction of the plates will make a large amount of sound and the person driving the truck may not enjoy the ride. And the clutch takes a little time to wear resulting in high maintenance. For the single plate clutch, its changing gear is fast, it generates low heat and the diaphragm spring is less affected by the centrifugal forces.
CHOSEN DECISION
The clutch that was chosen to be designed in the final design is the single plate clutch. This type is very suitable to the one ton truck because it can handle the pressure of having a heavy load.
COMPONENTS OF THE SINGLE PLATE CLUTCH
Flywheel – it is the driving member of the connected to the pressure plate of the clutch shaft and is in the same position as the bearings. Clutch plate – it is the driven member of the single plate clutch and its surfaces has frictional materials.
It has a central hub consisting of splines limit the axial travel along the gear box driving shaft. Pressure plate – it presses the clutch plate onto the flywheel between the cutch cover assembly and the pressure plate. The pressure plates are fitted with the pressure springs. Clutch cover – this one is the driving member of the clutch assembly bolted to the flywheel.
The clutch plate revolves together with the flywheel but in the process of disengaging the flywheel and the pressure plates rotate freely. With drawl fork and bearing – The fork carries with drawl bearings and are pivoted on a ball mounted in the clutch. Release levers – are pivoted on pins to the clutch covers and their outer ends are positioned on the pressure plate lugs and their ends are projecting towards clutch shaft. Clutch shaft – it is found inside the gear box and it is splined to the hub of the clutch plate which is sliding it.
One end is supported by the spigot bush and the other end carries one of the constant mesh gear. The single plate clutch is always engaged in position and to disengage it, the pedal is pressed
ADVANTAGES OF A SINGLE PLATE CLUTCH
This type of clutch responds very well and at a faster rate. The diaphragm is less affected by the centrifugal forces and it can withstand high rotational speeds. As the diaphragm acts as both release levers and clamping spring some extra parts like levers, eyebolts and struts are eliminated in the diaphragm spring because the friction wear of these wear does not occur. Despite the fact that it consists of only single plate, the changing gear is very easy to deal with than any other clutch and pedal movements are very less, in this case the driver of the truck will have less work to move the pedal.
Lastly, it is more reliable as it does experience binding cones.
DISADVANTAGES OF A SINGLE PLATE CLUTCH
It an old type of a clutch, it is not used in small vehicles and the torque transmission is less.
STRESS ANALYSIS SEE FIGURE
1 The outer diameter(Do) =200mm The inner diameter(Di) =180mm Torque = (Power*60)/(2*pi*N) = ((50*10^3)(60))/(2*pi*4500) = 106 Nm The ratio of the radii Di/Do = 180/200 = 0.9 n=number of contact surfaces =2 W=force W = T/(n*u*R) =106/(2*0.4*0.095) =1395N
