Friction Clutches MCQ Quiz - Objective Question with Answer for Friction Clutches - Download Free PDF

Concept:

For a single plate clutch with both sides effective and assuming uniform wear, torque transmitted is:

\( T = 2 \times \mu \times W \times \frac{R_o + R_i}{2} \)

Given:

\( W = 1000~N \), \( R_i = 0.10~m \), \( R_o = 0.15~m \), \( \mu = 0.5 \)

Calculation:

\( T = 2 \times 0.5 \times 1000 \times \frac{0.15 + 0.10}{2} = 1000 \times 0.125 = 125~\text{N·m} \)

Concept:

In the case of a new clutch, the intensity of pressure is approximately uniform, but in an old clutch, the uniform wear theory is more approximate.

Considering uniform pressure:

When the friction lining is new, uniform pressure theory is applicable. Therefore,

p = constant

wear ∝ pr

wear ∝ r

The wear at the outer radius will be more.

When the friction lining is new, the wear varies directly to the radius.

When the pressure is uniformly distributed over the entire area of the friction face: (r1 and r2 = External and internal radii of friction faces)

\(P = \frac{W}{{\pi [r_1^2 - r_2^2]}}\)

Torque transmitted by the clutch:

T = μ W R

\({R_m} = \frac{2}{3}\left[ {\frac{{R_1^3 - R_2^3}}{{R_1^2 - R_1^2}}} \right]\)

The uniform pressure theory is applicable only when the friction lining is new. When the lining is put into service, wear occurs.

Considering Uniform axial wear:

The basic principle in designing machine parts that are subjected to wear due to sliding friction is that normal wear is proportional to the work of friction. The work of friction is proportional to the product of normal pressure ( p) and the sliding velocity (V). Therefore,

Normal wear ∝ Work of friction ∝ p.V

p.V = K (a constant) or p = K/V

It may be noted that when the friction surface is new, there is a uniform pressure distribution over the entire contact surface. This pressure will wear most rapidly where the sliding velocity is maximum and this will reduce the pressure between the friction surfaces.

It is assumed that the wear is uniformly distributed over the entire surface area of the friction disk.

wear ∝ pr = constant

Let p be the normal intensity of pressure at a distance r from the axis of the clutch. Since the intensity of pressure varies inversely with the distance, therefore

p.r = C ⇒ p = C/r

Pressure distribution in the uniform wear theory is inversely proportional to the radius.

\(C = \frac{W}{{2\pi [r_1 - r_2]}}\)

T = μ W R

\({R_m} = \frac{{{R_1} + {R_2}}}{2}\)

Explanation:

Cone angle:

• The term "cone angle" refers to the angle formed by the lines projecting from the observer's eye to the object being viewed in a perspective drawing. It helps in visualizing how objects diminish in size as they recede into the distance.
• The cone angle is applicable for any shape of objects in perspective views because it defines the field of view and the extent of visual distortion due to perspective.

Perspective Views:

• In perspective drawing, objects appear smaller as they get further away from the observer, mimicking how the human eye perceives depth and distance.

Concept:

Number of pair in contact, N = n1 + n2 – 1

where n1 is the number of discs on driving shaft and n2 is the number of discs on the driven shaft.

Calculation:

Given:

n1 = 6, n2 = 5

Explanation:

Centrifugal Clutch

• A centrifugal clutch is a type of automatic clutch that uses centrifugal force to engage the clutch mechanism.
• It is commonly used in small engine-driven devices such as go-karts, mopeds, and small motorcycles.
• The clutch engages more firmly as the engine speed increases, allowing for a smooth and automatic transfer of power.
• In a centrifugal clutch, the clutch shoes are connected to the engine shaft and are free to move radially.
• As the engine speed increases, the centrifugal force acting on the clutch shoes also increases.
• When the centrifugal force is sufficient to overcome the spring force holding the shoes inwards, the shoes move outward and make contact with the inner surface of the clutch drum.
• This contact transmits the engine's power to the output shaft, engaging the clutch.
• As the engine speed increases, the centrifugal force acting on the clutch shoes also increases.
• This increased centrifugal force causes the clutch shoes to move outward and make contact with the inner surface of the clutch drum.
• The contact force between the clutch shoes and the drum increases due to this centrifugal force, leading to the engagement of the clutch.
• This process continues as the engine speed increases, ensuring a firm and secure engagement of the clutch.

Advantages:

• Automatic engagement and disengagement based on engine speed, providing a smooth and seamless operation.
• Simple design with fewer components, making it easier to maintain and repair.
• Provides a gradual engagement, reducing the chances of stalling the engine.

Disadvantages:

• Limited torque capacity, making it unsuitable for high-power applications.
• The engagement can be less precise compared to manual clutches, leading to potential slippage.

Applications:

• Centrifugal clutches are commonly used in small, low-power applications such as go-karts, lawnmowers, chainsaws, and small motorcycles.
• They are also used in various industrial machines where automatic engagement and disengagement are beneficial.

Explanation:

Clutch:

A clutch is a mechanical device that is used to connect or disconnect the source of power from the remaining part of the power transmission system at the will of the operator. The clutch design took the help of two theories which are mentioned as follows.

Explanation:

• The Clutch is used to connect and disconnect transmission of power from the engine flywheel to the gearbox drive shaft.
• The Clutch consists of driven and driving shafts.
• A clutch cover is mounted on the flywheel by a set of screws. 
• A pressure plate presses the clutch plate against the flywheel by the pressure of springs. 
• A pressure plate acts as a driven member of a clutch.
• The clutch plate hub is splined on the gearbox drive shaft.
• The clutch plate rotates along with the flywheel and power is transmitted to the drive shaft.
• When the clutch pedal is pressed, the release bearing pushes the thrust plate through the linkages.

Concept:

A cone clutch consists of inner and outer conical surfaces.

• The outer cone is keyed to the driving shaft, while the inner cone is free to slide axially on the driven shaft due to splines as shown in the figure.
• They are simple in construction and are easy to disengage. However, the driving and driven shafts must be perfectly coaxial for efficient functioning of the clutch.
• Cone clutches are friction clutches. 

• To avoid self-engagement in the cone clutch, its semi-cone angle is always kept greater than the angle of static friction.

Concept:

Number of pair in contact, N = n1 + n2 – 1

where n1 is the number of discs on driving shaft and n2 is the number of discs on the driven shaft.

Calculation:

Given:

n₁ = 6, n₂ = 5

Explanation:

Single and multiple-plate clutch:

As the number of contacting surfaces increases, more amount of heat will be generated.

Multiplate clutch has more contacting surfaces as compared to single plate clutch resulting in more amount of heat generation. Thus, a large amount of heat generation requires cooling to maintain functionality therefore multi-plate clutches are considered as wet clutch while single plate clutches are considered as dry clutches.

Explanation:

Let us consider a disc clutch,

r_o is the outer radius of the disc

r_i is the inner radius of the disc

P is the intensity of pressure

F = normal force on the disc

Normal reaction on the strip is given by \(dF = P\left( {2\pi x\;dx} \right)\)

The total force is given by \(\mathop \smallint \nolimits_{{r_i}}^{{r_o}} P\left( {2\pi x\;dx} \right) = 2\pi P\left( {\frac{{r_0^2 - r_i^2}}{2}} \right) = \;\pi P\left( {r_0^2 - r_i^2} \right)\)

Frictional force developed on the disc is given by \(d{F_f} = \mu \;P\left( {2\pi x\;dx} \right)\)

Frictional torque developed on the disc is given by \(d{F_f} \times x = \mu \;P\left( {2\pi {x^2}\;dx} \right)\)

Total Frictional Torque \({T_f} = \;\mathop \smallint \nolimits_{{r_i}}^{{r_o}} \mu P\left( {2\pi {x^2}\;dx} \right) = \mu P\;2\pi \left( {\frac{{r_0^3 - r_i^3}}{3}} \right)\)

Mean radius of the clutch is given by \({R_m} = \frac{2}{3}\left( {\frac{{r_0^3 - r_i^3}}{{r_0^2 - r_i^2}}} \right)\)

When Uniform wear theory is used

P.r = C (constant)

P₁r_i = P₂r_o = C

\(F = 2\pi C\left( {{r_o} - {r_i}} \right)\)

\({T_f} = \mu C\pi \left( {r_o^2 - r_i^2} \right)\)

and Mean radius \({R_m} = \frac{{{r_0}\; + \;{r_i}}}{2}\)

Concept:

Multiple disc clutch:

• A multiple-disc clutch, used when a large torque is to be transmitted.
• The inside discs usually made of steel are fastened to the driven shaft to permit axial motion except for the last disc.
• The outside discs usually made of bronze are held by bolts and are fastened to the housing which is keyed to the driving shaft.
• The multiple disc clutches are extensively used in motor cars, machine tools etc.​

Number of disks = number of pairs of contacting surface + 1

∴ Number of pairs of contacting surface = Number of disks - 1

Number of pairs of contact surfaces (n) = n­1 + n2 – 1

where n­1 = Number of discs on the driving shaft, n2 = Number of discs on the driven shaft.

Calculation:

Given:

n₁ = 3, n₂ = 4

n = n­1 + n2 – 1 

n = 3 + 4 - 1 = 6

∴ Number of pairs of contact surfaces for friction clutch is 6

Explanation:

Explanation:

Flat pivot bearing:

Frictional torque transmitted (Uniform Pressure Theory), \(T =\frac{2}{3}\mu WR\)

Frictional torque transmitted (Uniform Wear Theory), \(T =\frac{1}{2}\mu WR\)

Conical pivot bearing:

Frictional torque transmitted (Uniform Pressure Theory), \(T=\frac{2}{3}\mu WR.\csc α \)

Frictional torque transmitted (Uniform Wear Theory), \(T=\frac{1}{2}\mu WR.\csc α \)

where, W = Axial load, R = Bearing radius, α = Semi angle of cone

From the above expressions, We can conclude that the frictional torque transmitted in a conical or flat pivot bearing assuming uniform pressure in comparison to the assumption of uniform wear is more.

Additional Information

Concept:

According to the Uniform wear theory, it is assumed that the wear is uniformly distributed over the entire surface area of the friction disk. This theory is used for worn out clutches.

Uniform Pressure theory is applicable only when the friction lining is new. When the lining is put into service, wear occurs. Therefore a major portion of the life of friction lining comes under the uniform wear criterion.

There are two phases of wear mechanism in the friction lining. They are as follows

1. When friction lining is new, uniform pressure theory is applicable that means

P = constant

Wear ∝ Pr, ∴ wear ∝ r

Therefore wear will be more at the outer radius at the start and since the pressure of the plate is rigid, this wear will release the pressure at the outer edge.

2. Once the pressure at the outer radius is released there will be no wear at the outer edge. The wear will now take place at the inner edge due to the contact of the pressure plate. This will again release the pressure and wear will stop at the inner edge. This process of wear at the outer and inner edge will be continued alternatively till the pressure is adjusted in such a manner that the product of ‘‘Pr’’ again becomes constant.