4. bearing & clutch

CHAPTER – 4 : BEARING & CLUTCH

FRICTION IN PIVOT & COLLAR : For transmission of power pulleys, gears, couplings etc. are mounted on rotating shaft. During transmission of power, rotating shaft is subjected to axial thrust. A bearing surface for thrust bearing has to be provided to take this thrust & to maintain alignment of shaft in its correct axial position. Using various types of thrust bearings, the axial thrust on the shaft is taken up & elements of machine become safe.

The bearing surface provided at the end of shaft to take axial thrust is known as pivot. When a collar is provided along with the length of shaft to bear the axial thrust is known as collar.

The relative motion between the contact surface of a thrust bearing is resisted by the friction between the contacting surface & it's results into loss of power. In modern practice ball & roller thrust bearings are used during power transmitted with heavy load.

In case when the bearings are new & have a perfect fit between contact surface, the load is well distributed over the entire area of contact. So the intensity of pressure distributed over the area of contact is constant i.e. p (contact pressure) = constant. This assumption is considered as uniform pressure theory.

When the bearing become old, the bearing surface gets worn out & hence the contact pressure no remains constant. The wear of the surface at different points of contact depends upon the intensity of pressure & velocity of rubbing at the point of contact. Under this condition, for uniform wear, it is assumed that p.r = constant. This assumption is considered as uniform wear theory.

Theory of Machine (1MEB25) Prepared By : Prof. Jignesh Dangi














CLUTCH : A clutch is a device used to transmit the rotary motion of one shaft to another when desired. The axes of the two shafts are coincident. For run machinery, need some energy input which is supplied from some source, known as prime movers coupled to the machines. When the prime movers are coupled permanently with the machines, the power is continuously transmitted to the machines. To stop the machine, the prime mover is also required to stop in such cases. Many time it is necessary to change the speed of machine frequently, where it is required to stop prime mover becomes inconvenient. e.g. in automobiles, where vehicle has to be stopped or change the gear, it is required that the driven shaft should stop but the engine should run continuously. Again the vehicle is to start from rest or kept running after gear is changed. This is achieved by using clutch mounted between engine shaft and gear box input shaft & it is operated with the lever by driver. Advantages of clutch as below.

1) It can be easily engaged or disengaged without stopping engine.2) To restart the prime mover/engine with no load.3) To protect the prime mover/engine from overload.4) It enables the driver to pick up & accelerate gradually without any major shock.

SINGLE PLAT CLUTCH : This is shown in the below diagram. The operation is as follows.• The flywheel A is bolted to a flange on the drive shaft B. • The plate C is fixed to a boss which is free to slide axially along the driven shaft D to

which it is splined. It therefore rotates with shaft D.



• Two rings G of special friction material are riveted or bonded to A and E or alternatively to plate C.

• The presser plate E is bushed internally so that it revolves freely on the driven shaft D & it is integral with the with drawl sleeve F.

• A number of springs are arranged around the clutch ( Shown as S) so as to press the two friction surfaces together.

• The Clutch operates by moving the with drawl sleeve to the right. This compresses the Springs S and removes the pressure between the friction surfaces. Hence the driving shaft keeps rotating but the driven shaft does not rotate.

• Fig. Show, by compression of spring S on pressure plate E which keep the clutch in engaged position. So driving shaft will rotate driven shaft in such engaged position.

Fig. 4.1

MULTI PLATE CLUTCH : Fig. Shows the multi plate clutch. The operation is as follows.• There are more than one driving plates C1 as well as driven plates C having more than

two contacting surfaces which increase capacity of clutch to transmit torque.• Flywheel B is fixed with driving shaft G & the outer casing A is attached to flywheel face

with the help of bolts. • Friction plat C1 which can slide axially in the groove & rotate along with the casing.



The friction plat C is positioned between two friction plates C1.• The pressure plate E is integral with the sleeve J having a groove F to accommodate

the end of the operating lever.• Helical compression spring S is placed between the casing A & pressure plate E with

initial axial compression pressure giving on pressure plate E which keep the friction plate C & C1 in contact with each other.

• Because of friction force between driving plates C1 & driven plates C, the power is transmitted to driven shaft H.

• When the force is applied on the lever which fitted in groove F, the sleeve J move away along with the pressure plate E on the right hand side creating gaps between the plates C & C1, leaving the contact between them. As a result power is not transmitted to the driven shaft H. So driving shaft G is only rotate & driven shaft H is not rotate.

Fig. 4.2

CONE CLUTCH : As shown in fig. the contact surfaces are in the form of cones, it is known as cone clutch. The operation is as follows.

• Here the member A having internal conical surface which fitted on driving shaft C & the member B having external conical surface which fitted on driving shaft D.

• Friction lining E is fitted on both conical surfaces A & B.• In the engaged position, the friction surface E of two cones A & B are in complete

contact due to spring pressure that keeps one cone pressed against the other all time.• When the clutch is engaged, the torque is transmitted from the driving shaft C to the

driven shaft D through the friction cones. • For disengaging the clutch, the cone B is pulled back through a lever system against

the force of the spring.• Cone clutch has large torque capacity for smaller axial force compared to plate clutch.



Fig. 4.3

EQUATIONS :

DescriptionAssumption

Uniform Pressure Uniform WearFlat pivot/Foot step

bearingT = 2 u W R

3T = 1 u W R

2 Flat collar bearing (single/multiple)

T = 2 u W (R13 -R 2

3 ) 3 (R1

2-R22)

T = 1 u W (R1+R2) 2

No. of collar in multiple collar bearing

n = Wp ll (R1

2-R22)

Power lost in friction P = 2 ll N T/60000 Kw

NOTE If assumption not given in example, take equation of uniform pressure to calculate power lost in friction.

Single plate clutch

T = 2 u W (R13 -R 2

3 ) 3 (R1

2-R22)

Where, W = p ll (R12-R2

2)

T = 1 u W (R1+R2) 2

Where, W = 2 ll p R2(R1-R2)

Multi plate clutch

T = 2 u W (R13 -R 2

3 ) ne

3 (R12-R2

2)

Where, W = p ll (R12-R2

2)

T = 1 u W (R1+R2) ne

2

Where, W = 2 ll p R2(R1-R2)Power transmission P = 2 ll N T/60000 Kw

NOTE If assumption not given in example, take equation of uniform wear to calculate power transmission in clutch.

TYPES OF BEARINGS : 1) Ball bearing : Ball bearings, as shown in fig, are the most common type by far. They are found in everything from skate boards to washing machines to PC hard drives. These bearings are capable of taking both radial and thrust loads, and are usually found in



applications where the load is light to medium and is constant in nature (ie not shock loading). The bearing shown here has the outer ring cut away revealing the balls and ball retainer. 2) Roller Bearing : Roller bearings like the one shown in fig. are normally used in heavy duty applications such as conveyer belt rollers, where they must hold heavy radial loads. In these bearings the roller is a cylinder, so the contact between the inner and outer race is not a point (like the ball bearing above) but a line. This spreads the load out over a larger area, allowing the roller bearing to handle much greater loads than a ball bearing. However, this type of bearing cannot handle thrust loads to any significant degree. A variation of this bearing design is called the needle bearing. The needle roller bearing uses cylindrical rollers like those above but with a very small diameter. This allows the bearing to fit into tight places such as gear boxes that rotate at higher speeds.

(a) Ball bearing (b) Roller bearing.

Fig. 4.4

3) Thrust ball bearing : Ball thrust bearings like the one shown to the left are mostly used for low-speed non precision applications. They cannot take much radial load and are usually



found in lazy susan turntables and low precision farm equipment.

Fig. 4.5

4) Thrust roller bearing : Roller thrust bearings like the one illustrated to the left can support very large thrust loads. They are often found in gear sets like car transmissions between gear sprockets, and between the housing and the rotating shafts. The helical gears used in most transmissions have angled teeth, this can causes a high thrust load that must be supported by this type of bearing.

Fig. 4.6

5) Taper roller bearing : Tapered roller bearings are designed to support large radial and large thrust loads. These loads can take the form of constant loads or shock loads. Tapered roller bearings are used in many car hubs, where they are usually mounted in pairs facing opposite directions. This gives them the ability to take thrust loads in both directions. The cutaway taper roller on the left shows the specially designed tapered rollers and demonstrates their angular mounting which gives their dual load ability.



Fig. 4.7

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4. bearing & clutch