Design of Clutch

DESIGN OF CLUTCH

The design of the clutch is based on two theory named as uniform pressure theory and uniform wear theory. 

Following things has to be considered while designing...

• Power: What amount of power is to be transmitted by the clutch, for a given power, the torque is to be calculated by the power torque relation.                                                                                 [ Power = Torque* Angular Velocity]

• Size: How much space is available for installation of the clutch. 

(a) For a given torque, sufficient space is available for installation of the clutch, a single plate clutch is used. Cars, Trucks, Buses, Loaders etc... heavy and big machine are equipped with a single plate clutch.
(b) For a given torque, the size of the clutch plate is more but space for the installation is less, a multi-plate clutch is to be used instead of single plate clutch. Motorcycle, bike, scooter, mopeds etc... are equipped with multi-plate clutch for power transmission. 

In the case of space limitation, a multi-plate clutch is used instead of single plate clutch. for the design of multi-clutch first, decide the diameter of the clutch plate and by using mathematical relation, find the torque transmitted by a single plate of the multi-plate clutch (T1)

Torque (T) = Power/Angular Velocity
Torque transmitted by a single plate of the multi-plate clutch (T1)
Number of the plate in multi-plate clutch = T/T1

METHOD OF ANALYSIS

 Uniform Pressure

The torque that can be transmitted by a clutch is a function of its geometry and the magnitude of the actuating force applied as well the condition of contact prevailing between the members. The applied force can keep the members together with a uniform pressure all over its contact area and the consequent analysis is based on uniform pressure condition

Uniform wear

However, as time progresses some wear takes place between the contacting members and this may alter or vary the contact pressure appropriately and uniform pressure condition may no longer prevail. Hence the analysis here is based on uniform wear condition

Torque transmitted by Uniform Pressure

The differential equation for axial load

                                    ......1

   

Differential equation for frictional force

                                             ......2

Differential equation of Torque

                   ........3

Integrating above torque equation, we can get, Torque transmitted by Uniform Pressure

         

Torque transmitted by Uniform Wear

_{C is wearing constant = intensity of pressure*radius    [ C=p*r]}

 

Integrating above torque equation, we can get, Torque transmitted by Uniform Wear

Cone clutch

The torque transmitted by the cone clutch is given by the following equation

is the semi-cone angle.




For more reading click below link
Introduction to clutch    https://learnmachinedesign.blogspot.com/2016/08/single-plate-and-multi-plate-clutch.html

Friction clutch https://learnmachinedesign.blogspot.com/2016/07/friction-clutch.html

Single plate and Multi-plate clutch

Single plate clutch

An axial clutch is one in which the mating frictional members are moved in a direction parallel to the shaft. 

Single Plate and Multi-plate clutch come under the axial clutches. The flywheel is mounted on the driving Shaft by means of key and friction plate is mounted to driven shaft by means of splines. The splines are made on the driven shaft to provide axial movement for engagement and disengagement. Actuating spring keeps friction plate and flywheel are in contact and power/motion is transmitted from driver shaft to driven shaft. When the power of motion is to be interrupted the driven disc is moved axially creating a gap between the members by means of the fork is inserted into the collar on the driven shaft.

Figure 1 Schematic of single plate clutch 

A single disc or plate clutch, as shown in Fig 1 consists of a clutch plate whose both sides are faced with a frictional material. It is mounted on the hub which is free to move axially along the splines of the driven shaft. The pressure plate is mounted inside the clutch body which is bolted to the flywheel. Both the pressure plate and the flywheel rotate with the engine crankshaft or the driving shaft. The pressure plate pushes the clutch plate towards the flywheel by a set of strong springs which are arranged radially inside the body. The three levers (also known as release levers or fingers) are carried on pivots suspended from the case of the body. These are arranged in such a manner so that the pressure plate moves away from the flywheel by the inward movement of a thrust bearing. The bearing is mounted upon a forked shaft and moves forward when the clutch pedal is pressed.

When the clutch pedal is pressed down, its linkage forces the thrust release bearing to move in towards the flywheel and pressing the longer ends of the levers inward. The levers are forced to turn on their suspended pivot and the pressure plate moves away from the flywheel by the knife edges, thereby compressing the clutch springs. This action removes the pressure from the clutch plate and thus moves back from the flywheel and the driven shaft becomes stationary. On the other hand, when the foot is taken off from the clutch pedal, the thrust bearing moves back by the levers. This allows the springs to extend and thus the pressure plate pushes the clutch plate back towards the flywheel.

Figure 2 Exploded view of Single plate clutch

The axial pressure exerted by the spring provides a frictional force in the circumferential direction

when the relative motion between the driving and driven members tends to take place. If the torque

due to this frictional force exceeds the torque to be transmitted, then no slipping takes place and the

power is transmitted from the driving shaft to the driven shaft.

Multi-plate Clutch

A multi-plate clutch, as shown in figure 3, consists of two sets of plates A and B. plates of set A are usually made of hardened steel, while those of set B are made of bronze. Plates of set A  are connected to driven shaft by means of splines. There are through bolts are passed through the holes in the plates of set B which is bolted to the drum keyed to the driving shaft. A clearance fit between the bolt and the holes in the plates allow disks of set B to move in axial direction. the axial force p, which is required to hold the plates together, is provided by means of springs. 

when the driving shaft rotates, the drum, along with bolts and plates of set B, also rotate. Power is transmitted from the plates of set B to those of set A by means of friction.   

 Figure 3 Multi-plate clutch

METHOD OF ANALYSIS

 Uniform Pressure

The torque that can be transmitted by a clutch is a function of its geometry and the magnitude of the actuating force applied as well the condition of contact prevailing between the members. The applied force can keep the members together with a uniform pressure all over its contact area and the consequent analysis is based on uniform pressure condition

Uniform wear

However as the time progresses some wear takes place between the contacting members and this may alter or vary the contact pressure appropriately and uniform pressure condition may no longer prevail. Hence the analysis here is based on uniform wear condition

Design of Clutch --  https://learnmachinedesign.blogspot.com/2018/12/design-of-clutch.html

Friction Clutch

Introduction

The power is transmitted by friction surfaces between driver and driven shaft. The frictional contact is made by engaging two discs having friction surface made of metal, woven, or ceramic material. The engagement of two friction surface is made by helical compressive spring.

The friction-clutch design, besides allowing for the main requirements (minimum clutch weight, simplicity, of construction, high reliability, and others), should ensure the following:

• Reliable transfer of engine torque to the transmission in all service conditions.
• Smooth starting of the automobile from rest and complete engagement of the clutch.
• Proper disengagement, i.e. complete disconnection of the engine form the transmission with guaranteed clearance between friction surfaces.
• Minimum moment of inertia of driven elements of the clutch, which permits smoother shifting of gears and reduces the wear of the friction surfaces in the synchronizer.
• Necessary heat rejection from friction surfaces.
• Safeguards the transmission against dynamic loads.
• Convenience and ease of control, which are estimated by the effort to be applied to the pedal and pedal movement on disengaging the clutch.

Clutch Frictional Material

Clutch friction linings are subjected to severe rubbing so that generation of heat in relatively short periods takes place. Therefore, the lining material should have a combination of the following properties to withstand the operating conditions.

• Relatively high coefficient of friction under entire operating conditions.
• Maintenance of friction properties during entire working life.
• Relatively high energy absorption for short periods.
• Withstanding high pressure plate compressive loads.
• Withstanding high impacts of centrifugal force during gear changing.
• Adequate shear strength to transmit engine torque.
• High level of endurance in cyclic working without effecting friction properties.
• Good compatibility with cast iron facings over the entire range of operating tempera­ture.
• A high degree of tolerance against interface contamination without affecting its friction take-up and grip characteristics.

Positive Clutch

Introduction

A clutch is a mechanical component is used to transfer power from driver shaft to driven shaft at will of operator. Clutch is very popular in automobile industry to starting of the engine from rest and disconnecting the transmission for shifting gears.

Classification

The clutches are classified as follows 

1. Positive clutches
2. Friction clutches

Positive clutches

Positive clutch transmit power by rigid connection between driver and driven shaft by means of providing jaws on it. These type of clutch is suitable for the applications where quick and simple engagement and disengagement are required. For engagement, driver and driven shaft must be unloaded condition and stationary or relatively slow synchronize speed.

Positive drive means no slip.

In Positive clutches there is no slipping during engagement.

In the absence of slip, there is no relative motion between driver and driven surfaces results no heat generation during engagement and disengagement.

Points to remember

1. Positive clutch is small in size as compare to friction clutch for same power transmitting capacity.
2. In-capable of slipping.
3. The engaging clutch surfaces interlock to produce rigid joint they are suitable for situations requiring simple and rapid disconnection.
4. The engaging surfaces are usually of jaw type.
5. The jaws may be square jaw type or spiral jaw type.
6. Designed empirically by considering compressive strength of the material used.

Advantages of Positive clutches

1. Simple in design
2. No slip occur during power transmission
3. No heat generated during operation
4. Compact in size and low cost.
5. Life is more at slow speed

Disadvantages of Positive clutches 

1. Engagement is possible at very slow synchronize speed or stationary condition.
2. Life is reduce at higher speed engagement

 Types of Positive clutches

Application of Positive Clutches

Positive cluches are suitable for slow speed apllication where higher torque is required.

• Rolling Mill
• Power press