multiplat- or multiple disc clutch

MULTIPLAT- OR MULTIPLE DISC CLUTCH

A multiplate clutch is used when large amount of torque is to be transmitted. In a multiplate clutch, the number of frictional linings and the metal plates are increased which increases the capacity of the clutch to transmit torque, as shown in Fig.7.5. The multiplate clutch works in the same way as the single plate clutch by operating the clutch pedal. They are extensively used in motor cars, machine tools, etc.

1. Torque Transmitted on Multiplate Clutch

Let

n1 = Number of discs on the driving shaft, and

n2 = Number of discs on the driven shaft.

⸫ Number of pair of contact surfaces, n = n1 + n2 − 1.

Then, total frictional torque acting on the clutch is given by

Example 7.9 

A multiplate clutch has three pairs of contact surfaces. The outer and inner radii of the contact surfaces are 100 mm and 50 mm respectively. The axial spring force is limited to 1 kN. Assuming uniform wear, find the power transmitted at 1500 rpm. Take μ = 0.35. 

[A.U., Nov/Dec 2006]

 0.05 m; W = 1 kN = 1000 N;

Given data: 

n = 3; r1 = 100 mm = 0.1 m; r2 = 50 mm = 0.05 m; W = 1 kN = 1000 N; N = 1500 rpm; μ = 0.35

Solution: 

For uniform wear, torque transmitted is given by

Example 7.10 

A multiplate clutch consisting of 6 plates, each plate of external diameter 150 mm and internal diameter 100 mm, is to transmit 7.5 kW at 900 rpm. Assuming μ = 0.1, determine the pressure on each effective pair of surfaces in contact.

Given data: 

np = 6; d1 = 150 mm or r1 = 75 mm = 0.075 m; d2 = 100 mm or r2 = 50 mm = 0.05 m; P = 7.5 kW = 7.5 × 103 W; N = 900 rpm; μ = 0.1

Solution:

As given, number of plates, np = 6

⸫ Number of pair of surfaces in contact, n = np – 1 = 6 – 1 = 5

Example 7.11 

A multiplate clutch has three discs on the driving shaft and two on the driven shaft. The external and internal radii of the contact surfaces are 100 mm and 50 mm. Assuming uniform wear and coefficient of friction as 0.25, find the maximum axial intensity of pressure between the discs for transmitting 25 kW at 1600 rpm.

Given data: 

n1 = 3; n2 = 2; r1 = 100 mm = 10.1 m; r2 = 10.1 mm = 0.05 m; μ = 0.25;

P = 25 kW = 25 × 103 W; N = 1600 rpm

Solution: 

Number of pairs of contact surfaces, n = n1 + n2 - 1 = 3 + 2 - 1 = 4

Torque transmitted for uniform wear is given by

We also know that the axial force on each friction surface,

Example 7.12

A multiple friction clutch is required to transmit 75 kW at 1500 rpm. The plates are alternately of steel and phosphor bronze and they run in oil. The coefficient is 0.2 and the axial pressure with which they are pressed together is 2600 N. The inner and outer diameters of the disc are 150 mm and 250 mm. Calculate the number of plates required, Assume uniform intensity of pressure.

 [A.U., Apr/May 2011]

Given data: 

d1 = 250 mm or r1 = 125 mm = 0.125 m; d2 = 150 mm or r2 = 75 mm = 0.075 m; P = 75 kW = 75 × 103 W; N = 1500 rpm; W = 2600 N; μ = 0.2

Solution: 

For uniform pressure, the torque transmitted by the clutch is given by

Hence, there will be 10 plates, in which 5 plates on the driving shaft and 5 plates on the driven shaft. Ans.

Example 7.13 

A power of 60 kW is transmitted by a multiplate clutch at 1500 rpm. Axial intensity of pressure is not to exceed 0.15 N/mm2. The coefficient of friction for the friction surfaces is 0.15. The external radius of friction surface is 120 mm. Also the external radius is equal to 1.25 times the internal radius. Find the number of plates needed to transmit the required power. Assume uniform wear. 

[A.U., Nov/Dec 2011]

Given data: 

P = 60 kW = 60 × 103 W; N = 1500 rpm; μ = 0.15; pmax = 0.15 N/mm2 = 0.15 × 106 N/m2; r1 = 120 mm = 0.120 m; r1 = 1.25 r2

Solution: Given that r1 = 1.25 r2

Assuming uniform wear, the axial force exerted is given by

Torque transmitted by a multiplate disc clutch, for uniform wear, is given by

Now equating equations (i) and (ii), we get

Hence, there will be 12 total plates, in which driving and driven shafts having six plates each. Ans.