2What is Mechanical Engineering? 426What is Mechanical Engineering?Mechanical Engineering is the branch of engineering that focuses on the design, production, analysis, working and improvement of technical objects with moving parts.Main TopicsLinksGuidingTransmissionTransformation
3Linking in Technical Objects 427Linking in Technical ObjectsLinking is the mechanical function performed by any component that connects different parts of a technical object.
4Characteristics of Links You must know the main characteristics of linksChart on p. 428 in textbook.
5Links Direct OR Indirect Rigid OR Flexible Removable OR non-removable Complete OR Partial
6Degrees of Freedom of Movement 428Degrees of Freedom of MovementThe Degrees of Freedom are the set of independent movements that are possible for a given part in a technical object.E.g. A door can only rotate around the hinges – 1 degree freedomE.g. A manual transmission gear shift moves forward/back and left/right – 2 degrees of freedom
8431Guiding ControlsA Guiding Component or Control is a component whose mechanical function is to guide the motion of moving parts.
9431Types of GuidingTranslational Guiding ensures the straight translational motion of a moving part. E.g. a vertical window grooveRotational Guiding ensures the rotational motion of a moving part. E.g. a bicycle wheel hubHelical Guiding ensures the translation motion of a moving part while it rotates about the same axis. E.g. threaded shank in a vice
10Symbols for MotionYou must know the symbols for the 6 types of motion provided as a handout.
11Adhesion and Friction of Parts 433Adhesion and Friction of PartsAdhesion is the phenomenon by which two surfaces tend to remain in contact with each other without slipping.In mechanics, Friction is a force that resists the slipping of one part over another.Lubrication is the mechanical function performed by any component that reduces friction between two parts.
125 Factors affecting adhesion Nature of materials (eg: steel on asphalt vs. rubber on asphalt)Presence of a lubricant like oil or waxTemperature: the colder the temperature the less the adhesionSurfaces (rough vs. smooth)Mass of the object (a heavy object will have better adhesion, more friction)
13Motion Transmission Systems 435Motion Transmission SystemsMotion Transmission is the mechanical function of relaying a motion from one part to another without altering the nature of the motion.A Motion Transmission System is a set of components that perform the function of transmitting motion.
14445Some definitions:Driver component: receives the force required to activate the systemeg: crankset on a bikeDriven component: receives the motion and transfers it to another partEg: rear gears on a bikeIntermediate component: located between the driver and driven component – not all systems have this.Eg: the chain on a bike
15Characteristics of Motion in Transmission Systems 436Characteristics of Motion in Transmission SystemsThe most common rotational transmission systems are:Gear TrainsChain and Sprocket SystemsWorm and Worm Gear SystemsFriction Gear SystemsBelt and Pulley Systems
16Motion Transmission Systems See Figure on p. 437 for the main types
17Construction Considerations for Motion TRANSMISSION Systems 438Construction Considerations for Motion TRANSMISSION SystemsDepending on the need, a system may only rotate in one direction.That will affect the choice of system.
18438Gear TrainsThe direction of rotation changes from one wheel to the next.The system can be reversed.
20Gear Train FactorsGear teeth: all the gear teeth in a system must be identical – same shape, direction, size and be equally spaced. E.g. Straight or helicalGear type: the rotational axis of the gears can be positioned different ways (eg: car differentials)Gear size: the higher the number of teeth, the lower the speed of rotation – or bigger diameter slower speed.
23Chain and Sprocket Systems 439Chain and Sprocket SystemsThe direction of rotation of all sprockets on the same side of the chain is the same.A sprocket on the other side of the chain rotates in the opposite direction.It can be reversed.The smaller the sprocket the faster it turnsRequires frequent lubrication
24Worm and Worm Gear Systems 440Worm and Worm Gear SystemsThe direction of rotation depends on the direction of the threads on the worm screw shaft.It is not reversible.Worm must be the driver
25440Friction Gear SystemsThe direction alternates from one gear to the next.It is reversible.The smaller the diameter of the gear, the faster its rotation
26Friction Gear SystemsFriction gear systems are similar to gear trains except that motion is transferred by FRICTION and not by the GEAR TEETH.They are less efficient because of slippage.Factors that affect friction gear systems are: gear type (straight, bevel or spherical), gear size and choice of material.
27Belt and Pulley Systems 441Belt and Pulley SystemsSimilar to the chain and sprocket system.The chain is replaced by a belt.The sprocket is replaced by a pulley.The choice of the belt material and the tightness of the belt affect the friction and hence the efficiency of the system.The direction is the same for any pulley on the same side of the belt.It is reversible.The smaller the pulley, the faster its rotation
29Speed Changes in Motion Transmission Systems 442Speed Changes in Motion Transmission SystemsA Speed Change occurs in a motion transmission system when the driver does not turn at the same speed as the driven component(s).The speed change depends on the ratio of gears/threads of the driver compared to that of the driven component.
30Speed Changes in a Pulley or Sprocket Transmission System 442Speed Changes in a Pulley or Sprocket Transmission SystemTo increase the speed, the driven component should have a smaller diameter.To decrease the speed, the driven component should have a larger diameter.To keep the same speed, the two pulleys should have the same diameter.E.g. Driver Diameter = 15cmDriven Diameter cmSo the driven pulley is 3 times FASTER
32Speed Changes in Worm and Worm Gear Systems 442Speed Changes in Worm and Worm Gear SystemsThe larger the diameter of the worm gear, the greater the decrease in speed.To increase the speed, the driven component should have a smaller diameter.
34444TorqueTorque involves two forces of equal strength but applied in opposite directions which cause a component to rotate about an axis.Engine Torque increases the rotational speed of components in mechanical systems; provided by the engineResisting Torque slows or stops the rotation of components in mechanical systems; caused by friction, air resistance, gravitational force.
35Torque and Speed Change 445Torque and Speed ChangeIf engine torque = resisting torque, No speed changeIf engine torque > resisting torque, speed increasesIf engine torque < resisting torque, speed decreases
36Motion Transformation Systems The mechanical function of relaying motion from one part to another while CHANGING the type of motionEg: Rotational motion to translational motion
37Types of MOTION TRANSFORMATION Systems 446Types of MOTION TRANSFORMATION SystemsThe most common systems are:Rack and PinionsScrew Gear Type 1Screw Gear Type 2Cam and FollowersSlider-Crank systems
39Rack and Pinion Systems 447Rack and Pinion SystemsConverts rotational motion to translational motion or vice versaThe rack is the straight bar with teeth.The pinion is the gear part.It is used in many steering systems.The greater the number the teeth on the pinion, the slower its rotation
41Screw Gear Systems Converts rotation to translation 448Screw Gear SystemsConverts rotation to translationThe screw gear uses a threaded bolt to move another gear or itself.It is used in wrenches and car jacks.Not reversible
51Slider-crank System Converts rotation to translation or vice versa 449Slider-crank SystemConverts rotation to translation or vice versaUsed in car enginesThe slider is the piston.The crank attaches the piston to another wheel.Usually the slider is the driven component.
52450Check Up!Q. 1-13Depending on colour code, do the questions.