Clutches

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  Mechanical Design

  • P.R.N. Childs, T.H.C. Childs(Authors)
  • 2003(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  10.2 Clutches The function of a clutch is to permit the connec-tion and disconnection of two shafts, either when both are stationary or when there is a difference in the relative rotational speeds of the shafts. Clutch connection can be achieved by a number of tech-niques from direct mechanical friction, electro-magnetic coupling, hydraulic or pneumatic means or by some combination.There are various types of Clutches as outlined in Figure 10.3.The devices considered here are of the friction type. Clutches must be designed principally to sat-isfy four requirements: 1. The necessary actuation force should not be excessive. 2. The coefficient of friction should be constant. 3. The energy converted to heat must be dissi-pated. 4. Wear must be limited to provide reasonable clutch life. Alternatively the objective in clutch design can be stated as maximization of a maintainable friction coefficient and minimization of wear. Correct clutch design and selection are critical because a clutch that is too small for an applica-tion will slip and overheat and a clutch that is too large will have a high inertia and may overload the drive. Positive contact Clutches have teeth or serrations, which provide mechanical interference between mating components. Figure 10.4 shows a square jaw and Figure 10.5 shows a multiple serration posi-tive contact clutch. This principle can be com-bined with frictional surfaces as in an automotive Chapter 10 195 synchromesh clutch. As helical gears cannot be shifted in and out of mesh easily, the pragmatic approach is to keep the gears engaged in mesh and allow the gear to rotate freely on the shaft when no power is required but provide positive location of the gear on the shaft when necessary (see also Chapter 6, Section 6.3.1). Friction Clutches consist of two surfaces, or two sets of surfaces, which can be forced into frictional contact.A frictional clutch allows gradual engage-ment between two shafts.

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  Mechanotechnics N6 Student's Book

  TVET FIRST

  • Sparrow Consulting(Author)
  • 2021(Publication Date)
  • Macmillan

    (Publisher)

  The result is the ability to start and stop the driven shaft without impacting the driving shaft. Clutches are also used to control the transmission of power or motion in amount or over time. In Figure 1.2, the clutch transmits the engine’s power to the transmission for the vehicle to pull away and during driving (a). It disconnects the engine power when stopping the vehicle or changing gears (b). Figure 1.2: Engaged and disengaged clutch in a vehicle (a) When pulling away and driving (b) During gear changes and stopping power: the ability to supply a machine with a form of energy coaxial: having a common axis torque: rotating force 3 Clutches TVET FIRST A clutch consists of four main components (see Figure 1.1): • Flywheel. • Clutch plate. • Pressure plate. • Release bearing. The flywheel is mounted on the engine shaft. It is the driving member of the clutch. The pressure plate is bolted to the flywheel, and they rotate together. The pressure plate acts as a spring-loaded clamp and clamps the clutch plate to the flywheel. The release bearing is behind the pressure plate. It can move axially along the driven shaft or transmission shaft of the vehicle. It is used to load the spring, which causes the clamping action of the pressure plate. The clutch plate or friction plate is located between the flywheel and pressure plate. The clutch plate is mounted on a guide that moves along splines cut into the input shaft. flywheel clutch cover diaphragm spring release bearing clutch plate pressure plate clutch fork Figure 1.3: Clutch components The clutch pedal is connected to the clutch fork with a clutch cable or hydraulic system (see Figure 1.3). This causes the fork to pivot. The clutch fork is attached to the release bearing. It controls its direction of motion along the shaft. To engage the clutch: • The release bearing applies an axial force to a coil spring or diaphragm spring in the clutch cover. This pushes the pressure plate onto the clutch plate.

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  Fundamentals of Machine Design: Volume 2

  • Ajeet Singh(Author)
  • 2017(Publication Date)
  • Cambridge University Press

    (Publisher)

  Outcomes Learn definition, function, and types of Clutches Difference between positive drive and friction clutch Friction materials and their coefficient of friction Variation of bearing pressure with radius Torque transmission capacity with uniform pressure and uniform wear theories Maximum torque transmission capacity Design of single plate clutch Time for clutch engagement Heat generated during clutching Multi-plate and cone Clutches Design of a cone clutch Centrifugal clutch; its construction, working, and design 18.1 Definition and Function A clutch is a device, which can be used to connect or disconnect the incoming power from a driver shaft to a driven shaft at same speed or less than driver speed, whenever desired without stopping the driver shaft. It is used invariably in an automobile, shown in picture on right side, where engine rotates continuously, while the wheels rotate at reduced speeds from zero to maximum. The power comes from C H A P T E R 18 Clutches Fundamentals of Machine Design, Volume II 682 engine to clutch at speed N . Speed after the clutch can have any value between zero to N and then to gear box to allow different speed to get high torque at starting as shown pin Figure 18.1. In top gear, there is no reduction. Universal couplings help in transferring power at any angle. A permanent reduction of about 4–5 is provided in differential, to further reduce the speed of the propeller shaft and transfer power at right angles to the wheels. Engine Clutch Gear Box Universal coupling Propeller shaft Differential Axle Wheel Universal coupling Wheel Axle N N Figure 18.1 Location of a clutch in an automobile Main functions of a clutch are: • Connect or disconnect the power from a driver shaft to the driven shaft. The shafts should be collinear, that is, their axes should be in one straight line, otherwise its performance deteriorates. • Provide any speed between zero to maximum of the driver shaft speed.

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  Mechanical Design Engineering Handbook

  • Peter Childs, Peter R. N. Childs(Authors)
  • 2013(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  Chapter 13

  Clutches and Brakes

  Abstract

  A clutch is a device that permits the smooth, gradual connection of two shafts rotating at different speeds. A brake enables the controlled dissipation of energy to slow down, stop, or control the speed of a system. This chapter describes the basic principles of frictional Clutches and brakes and outlines design and selection procedures for disc Clutches as well as disc and drum brakes.

  Keywords

  Band; Brake; Clutch; Design; Disc; Drum; Friction; Long; Multiple; Power; Shoe; Short; Transmission

  Chapter Outline

  13.1 Introduction 13.2 Clutches 13.2.1 Design of Disc Clutches 13.3 Brakes 13.3.1 Disc Brakes 13.3.2 Drum Brakes 13.3.3 Short-Shoe External Drum Brakes 13.3.4 Long-Shoe External Drum Brakes 13.3.5 Long-Shoe Internal Drum Brakes 13.3.6 Band Brakes 13.4 Conclusions References Further Reading Nomenclature

  13.1 Introduction

  When a rotating machine is started it must be accelerated from rest to the desired speed. A clutch is a device used to connect or disconnect a driven component from a prime mover such as an engine or motor. A familiar application is the use of a clutch between an engine's crankshaft and the gearbox in automotive settings. The need for the clutch arises from the relatively high torque requirement to get a vehicle moving and the low torque output from an internal combustion engine at low levels of rotational speed. The disconnection of the engine from the drive enables the engine to speed up unloaded to about 1000 rpm, where it generates sufficient torque to drive the transmission. The clutch can then be engaged, allowing power to be transmitted to the gearbox, transmission shafts, and wheels. A brake is a device used to reduce or control the speed of a system or bring it to rest. Typical applications of a clutch and brake are illustrated in Figure 13.1

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  Light and Heavy Vehicle Technology

  • M.J. Nunney(Author)
  • 2016(Publication Date)
  • Newnes

    (Publisher)

  13 Friction Clutches 13.1 TYPES OF SINGLE-PLATE CLUTCH General requirements A clutch is a device used in engineering to engage smoothly two shafts in relative motion, one of which may be stationary, and to release them quickly or slowly at will. The purpose of fitting a clutch between the engine and gearbox of a motor vehicle is to satisfy the following requirements: 1 To connect a running engine smoothly and gradually to the remainder of the transmission system. 2 To permit gear changing when a vehicle is in motion. 3 To allow the engine to continue running when a vehicle is temporarily halted in gear with the clutch pedal depressed to disengage. A friction type of clutch is used in motor vehicles with manually operated gearboxes. Its functioning depends upon sufficient friction being developed between the contact surfaces of two or more members to transmit the desired torque without their slipping relative to each other. Their ability to slip before full engagement is, nevertheless, a decided advantage because it allows shock-free connection to be made between engine and gearbox. Heat is necessarily generated during any slip-ping of the clutch, but with fairly infrequent use there is usually sufficient time for it to cool. An important consideration in the design of Clutches is that the driven member connected to the gearbox should behave as little like a flywheel as possible. It should therefore be of lightweight construction and thus possess the minimum of inertia to ensure that it can be rapidly slowed down or speeded up, thereby assisting changing into higher or lower gears respect-ively. It was chiefly for this reason that the old-fashioned cone-type friction clutch (Figures 13.1a and b), although providing a powerful friction effect by its wedging action, was superseded by the plate-type friction clutch (Figure 13.1c).

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  Early Motorcycles

  Construction, Operation and Repair

  • Victor W. Page(Author)
  • 2012(Publication Date)
  • Dover Publications

    (Publisher)

  Theory of Friction Clutch Action. —Clutch forms that are applied to motorcycles are invariably of the friction type, as no progress has been made in utilizing the various hydraulic, pneumatic, or magnetic Clutches that have been offered at various times by over-sanguine inventors. The friction clutch has proven to be the most satisfactory, and has received wide practical application in its various forms. The important requirement of a clutch is that it will be capable of transmitting the maximum power of the motor without any loss due to slipping when fully engaged. A clutch should be operated easily and require but minimum exertion on the part of the operator. A clutch should be gradual in action, i. e., when it takes hold, the engine power should be transmitted to the driving member in a gradual and uniform manner or the resulting shock may result in serious injury to some part of the driving mechanism. It is also imperative that a clutch release at once when desired, and that there be no continued rotation of parts, which insures that the drive will be interrupted positively when the clutch is disengaged. In considering the design of a clutch, it is very desirable that this component be located in an accessible manner, which is a good feature, as it permits of easier removal for inspection, cleaning and repair. It is imperative that some form of adjustment be provided so a certain amount of wear will be compensated for, without replacing any expensive parts. A simple design with a minimum number of operating parts is more to be desired than a more complicated form which may have some minor advantages, but which is much more likely to cause trouble.

  To illustrate the transmission of power by frictional adhesion of various substances with each other, one can assume a simple clutch form consisting of two metal discs or plates in contact, the pressure keeping them together being due to the weight of one member bearing upon the other. If the discs are not heavy, it will be found easy to turn one upon the other, but if weights are added to the upper member a more decided resistance will be felt which will increase directly as the weight on the top disc and consequently the total pressure augments. It is possible to add enough weight so it will be difficult to move one plate without producing a corresponding movement of the other. If one of these plates is mounted on an engine shaft, and the other applied to the transmission member so that a certain amount of axial movement is possible, and the pressure maintaining contact was obtained by springs instead of weights, one would secure a combination capable of transmitting power, inasmuch as the spring pressure applied to one disc would force it against the other, and one shaft could not revolve without producing motion of the other.

  Types of Clutches.

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  Mechanical Science

  • W. C. Bolton(Author)
  • 2013(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  14.2 Friction Clutches A clutch is a device for connecting and disconnecting the drive between two coaxial shafts. Friction Clutches may be in the form of flat plates or conical surfaces. But whatever the form, the principle is the same. Connecting the two coaxial shafts involves bringing together two surfaces and holding them together. The requirement is that when one side of the clutch is made to rotate then the junction behaves as a solid coupling and transmits torque to the other shaft. 14.2.1 Plate Clutches Consider the forces occurring when two flat circular plates are in contact 354 Friction Clutches, bearings and belt drives 355 Fig. 14.1 Forces for flat surfaces pressed together. and pressed together by an axial force W , as illustrated in figure 14.1. For a ring segment of the surfaces in contact at radius r and thickness δ r , if the pressure exerted by one plate on the other is p then the axial force on the ring is the product of the pressure and the area over which it is acting and so axial force on ring = p 2 π r δ r Thus the total axial force on the two surfaces in contact is W = 2 π r 2 r 1 pr d r [1] The frictional force F is related to the normal reaction force R by F = µ R (equation [8], chapter 11). Thus the frictional force on the ring segment is frictional force = µ p 2 π r δ r This frictional force is tangential to the ring. Thus the moment of tangential force acting on the ring is moment of tangential force = ( µ p 2 π r δ r) r Hence the total torque T on the shaft is T = 2 πµ r 2 r 1 pr 2 d r [2] The integrals in equations [1] and [2] can be evaluated if some assumptions are made regarding the variation of the pressure p with radius r . Two cases 356 Mechanical Science are considered, one where it is assumed that the pressure is constant and does not vary with radius and one where it is assumed that there is uniform wear over the contact area.

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  Automotive Technician Training: Theory

  • Tom Denton, Hayley Pells(Authors)
  • 2021(Publication Date)
  • Routledge

    (Publisher)

  Diaphragm spring The diaphragm spring assembly is a cone-shaped diaphragm spring between the pressure plate and the cover. Its purpose is to clamp the pressure plate against the clutch disc. This spring is normally secured to the cover by rivets. When pressure is exerted on the centre of the spring, the outer diameter of the spring tends to straighten out. When pressure is released, the spring resumes its normal cone shape.

  Figure 9.25 Cone-shaped diaphragm spring

  Clutch release The centre portion of the spring is slit into a number of fingers that act as release levers. When the clutch is disengaged, these fingers are depressed by the release bearing. The diaphragm spring pivots over a fulcrum ring. This makes its outer rim move away from the flywheel. The retracting springs pull the pressure plate away from the clutch disc to disengage the clutch.

  Figure 9.26 Fingers

  As the clutch is engaged, the release bearing is moved away from the release fingers. As the spring pivots over the fulcrum ring, its outer rim forces the pressure plate tightly against the clutch disc. At this point, the clutch disc is clamped between the flywheel and pressure plate.

  Clutch assembly The individual parts of a pressure plate assembly are contained in the cover. Most covers are vented to allow heat to escape and air to enter. Other covers are designed to provide a fan action to force air circulation around the clutch assembly. The effectiveness of the clutch is affected by heat. Therefore, by allowing the assembly to cool, it works better.

  Create an information wall to illustrate the features of a key component or system

  9.1.5 Other types of clutch 2

  The simple definition of a clutch is something that engages or disengages drive. A number of different types of clutch are used for this purpose. Some of these are examined briefly over the following pages.

  Automatic transmissions use a torque converter, or fluid flywheel, to couple the engine and the gearbox. The torque converter is a fluid coupling in which one rotating part causes transmission fluid to rotate. This imparts a rotation to another part, which is connected to the gearbox.

  Figure 9.27 Automatic gearbox

  Torque converter

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