Gear Drives: Understanding Gears, Springs, and Their Functions

1. Gears, springs Flóra Hajdu B406 hajdfl@sze.hu

2. Content • Gears • Springs Hajdu Flóra

3. Geardrives • The function of a gear is to transmit motion from one machine part to another and wherenecessary to reduce or increase the revolutions of a shaft • Gears are the most durable and rugged of all mechanicaldrives - gears rather than belts or chains areused in automotive transmissions and most heavy-dutymachine drives. • may be grouped according to the position of the shafts that they connect • Spur gears connect parallel shafts • bevel gears connectshafts whose axes intersect • worm gears connect shaftwhose axes do not intersect. • A spur gear with a rack convertsrotary motion to reciprocating or linear motion. • Gear design is very complicated, dealing with problems as strength, wear, and material selection - Normally a gearsareselected from a catalog. • Most gearsare made of cast iron or steel, but brass, bronze, and plastic are used when factors such as wear or noise must beconsidered. Hajdu Flóra

4. Geardrives • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

5. Spurgears • Gears are used to transmit motion and power at constantangular velocity. • The specific form of the gear that best produces this constant angular velocity is the involute. involute is curve traced by a point on a tautstring unwinding from a circle (basecircle). • Every involute gear has only one base circle fromwhich all the involute surfaces of the gear teeth are generated. • This base circle is not a physical part of the gear andcannot be measured directly. • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

6. Spurgeardefinitions • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

7. Spurgeardefinitions • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

8. Spurgears – schematicsrepresentation • The teeth on a gear are not normally shown on the workingdrawings. Instead, they are represented by solid, and center lines (pitchcircle) • A sectional view is sufficient unlessa front view is required to show web or arm details. • For inch-size gears, diametral pitch is used instead ofmodule. The diametral pitch is a ratio of the number of teethto a unit length of pitch diameter. • Module is the term used on metric gears. It is the length ofpitch diameter per tooth measured in millimeters. • Straightspurgears Hajdu Flóra

9. Spurgears – schematicsrepresentation Hajdu Flóra

10. Gearpair – schematicsrepresentation Hajdu Flóra

11. Gearpair – schematicsrepresentation Hajdu Flóra

12. Rack and pinion • A rack is a straight bar having teeth that engage the teethon a spur gear. • In theory, it is a spur gear having an infinite pitch diameter -> all circular dimensions become linear. • The addendum, dedendum, and tooththickness are the same as those of the mating spur gear. • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

13. Rack – schematicsrepresentation Hajdu Flóra

14. Rack and pinion – schematicsrepresentation Hajdu Flóra

15. Bevelgears • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design • Bevel gears are used to transmit power between two shafts whose axes intersect. • The axes may intersect at any angle, but the most common is 90°. • The teeth are the same shape as spur gear teeth but taper toward the cone apex. • Cast iron is normally used for gears that are not subject to heavy duty. • Often a gear (largerdiameter) and pinion (smallerdiameter) are made of different materials for efficiency and durability. • The pinion is made of a stronger material - the teeth on the pinion come into contact more times than the teeth on the gear. • Common combinations are steel and cast iron, and steel and bronze. Hajdu Flóra

16. Bevelgear – schematicsrepresentation Hajdu Flóra

17. Bevelgearpair – schematicsrepresentation Hajdu Flóra

18. Worm and wormgears • Worm gears are used to transmit power between two shafts that are at right angles to each other and are nonintersecting. • The teeth on the worm are similar to the teeth on the rack, and the teeth on the worm gear are curved to conform with the teeth on the worm. • Thread terms (pitch,lead) are used on the worm • Since a single-thread worm in one revolution advances the worm gear only one tooth and space, a large reduction in velocity is obtained. • The ratio of worm gear speed to the worm speed is the ratio between the number of teeth on the worm gear and the number of threads on the worm. A worm gear with 33 teeth and a worm with a multiple thread of three has a ratio of 11: 1. • a single-thread worm has a low lead (or helix) angle, it is inefficient and consequently not used to transmit power - multi-thread worms are used. Hajdu Flóra

19. Worm and wormgears • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

20. Worm – schematicsrepresentation Hajdu Flóra

21. Wormgear – schematicsrepresentation Hajdu Flóra

22. Wormgear – schematicsrepresentation Hajdu Flóra

23. Gears– schematicsrepresentation • Helicalgear • Curvedgear • Herringbonegear Hajdu Flóra

24. Comparison of chain and geardrives • Advantages of chains • Shaft center distances for chain drives are relatively unrestricted, whereas with gears, the center distance must be such that the pitch surfaces of the gears are tangent -simpler, less costly, and more practical design. • Chains are easily installed. Assembly tolerances for chain drives are not as restricted as those for gears - Savings in the time of installation. • The ease of chain installation is a definite advantage when later changes in design, such as speed ratio, capacity, and centers, are anticipated. Hajdu Flóra

25. Comparison of chain and geardrives • Advantages of gears • When space limitations require the shortest possible distance between shaft centers, a gear drive is usually preferable to a chain drive • The maximum speed ratio for satisfactory operation of a gear drive is usually greater than that for a chain drive. • Gears can be operated at higher rotative speeds than chain drives. Hajdu Flóra

26. Springs • Role of springs • Flexiblecoupling • Energystorage • Forceortorquelimitation • Forceortorquemeasurement • Dampingvibrations • Sizebalancingclosingelement Hajdu Flóra

27. Springs • Springs may be classified into 3 groups according to their application. • Controlled Action Springs: have a well-defined function, or a constant range of action for each cycle of operation. Examples are valve, die, and switch springs. • Variable-Action Springs: have a changing range of action because of the variable conditions imposed upon them. Examples are suspension, clutch, and cushion springs. • Static Springsexert a comparatively constant pressure or tension between parts. Examples are packing or bearing pressure, antirattle, and seal springs. Hajdu Flóra

28. Springs The type or name of a spring is determined by characteristics such as function, shape of material, application, or design. • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

29. Spring characteristics • Deformation – force diagram Spring stiffness Hajdu Flóra

30. Spring nomenclature • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

31. Compressionsprings • A compression spring is an open-coiled helical spring that offers resistance to a compressive force • Compressionspingends • Plain open ends are produced by straight cutoff with no reduction of helix angle. The spring should be guided on a rod or in a hole to operate satisfactorily. • Ground open ends are produced by parallel grinding of open-end coil springs. Advantages of this type of end are improved stability and a larger number of total coils. • Plain closed ends are produced with a straight cutoff and with reduction of helix angle to obtain closed-end coils, resulting in a more stable spring. • Ground closed ends are produced by parallel grinding of closed-end coil springs, resulting in maximum stability. • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

32. Compressionsprings Hajdu Flóra

33. Compressionsprings nm=4,5 nö=6,5 nm=4 nö=6 Hajdu Flóra

34. Technicaldrawing of a compressionspring L0: rugó terheletlen hossza Ln: rugó hossza a megengedett legnagyobb próbaterhelés alatt L1, L2: megadott F1, F2 erőkhöz tartozó hossz Hajdu Flóra

35. Extensionsprings • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design • An extension spring is a close-coiled, helical spring that offers resistance to a pulling force. • It is made from round or square wire • The end of an extension spring is usually the most highly stressed part. Thus, proper considerationshould be given to its selection. • Different types of ends can be used on the same type of spring. Hajdu Flóra

36. Extensionsprings Hajdu Flóra

37. Torsion springs • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design • Springs exerting pressure along a path that is a circular arc, or in other words, providing a torque (turning action • usually a helical spring of round, square, or rectangular wire, loaded by torque. • The variation in ends used is almost limitless • A torsion bar spring is a relatively straight bar anchored at one end, on which a torque may be exerted at the other end, thus tending to twist or rotate it about its axis. Hajdu Flóra

38. Torsion springs Hajdu Flóra

39. Powersprings • A fiat coil spring, also known as a clock or motor spring, consists of a strip of tempered steel wound on an arbor and usually confined in a case or drum. Hajdu Flóra

40. Flatsprings • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design • Flat springs are made of flat material formed in such a manner as to apply force in the desired direction when deflected in the opposite direction. • A leaf spring is composed of a series of flat springs nested together and arranged to provide approximately uniform distribution of stress throughout its length. Springs may be used in multiple arrangements Hajdu Flóra

41. Flatsprings • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design • Flat springs are made of flat material formed in such a manner as to apply force in the desired direction when deflected in the opposite direction. • Bellevillespringsarewasher-shaped made intheform of a short, truntactedcone. May be assembled • in series toaccomodategreaterdeflections • In parallel toresistgreaterforces • Incombination of series and parallel Hajdu Flóra

42. Belevillesprings Hajdu Flóra

43. Rubbersprings • Application: vehicleindustry • Advantage • highdeformability • different shapes can be easily achieved, • highenergystorage. • Disadvantage: • the oxygen in the air causes the rubber to age rapidly, • it freezes in a cold environment, it becomes fragile, • Mineraloildissolves Hajdu Flóra

44. Rubbersprings Hajdu Flóra

45. Rubbersprings Hajdu Flóra

46. Air springs • Hydropneumaticsystem • The spherical spring element is separated by a diaphragm • the space between the membrane and the piston is filled with oil • Push rod is connectedwith a lever lever to the wheel. • By changing the oil charge, the chassis can be held at a constant height regardless of the load. • Automatic - the oil flow is controlled by the shift lever controlled by the wheel arm. • The constant oil pressure required to control the system is provided by an air-cushioned oil battery between the oil pump and the control pump. Hajdu Flóra

47. Spring clips • Spring clips perform multiple functions and eliminate the handling of several small parts -> reduce assembly costs. • generally self-retaining requiring only a flange, panel edge, or mounting hole to clip to. • light -duty fasteners and serve the same function as small bolts and nuts, self-tapping screws, clamps, spot welding, and formed retaining plates. • Dart-Type Spring Clips have hips to engage within panel or component holes. The top of arms of the fastener can be formed in any shape to perform unlimited fastening functions. • Stud Receiver Clips There are three basic types push-ons, tubular types, and self-threading fasteners. All are designed to make attachments to unthreaded studs, rivets, pins, or rods of metal or plastic. • Cable, Wire, and Tube Clips: These fasteners incorporate self-retaining elements for engaging panel holes or mounting on panel edges and flanges. Spring-clip cable, wire, and tubing fasteners are frontmounting devices, requiring no access to the back of the panel. • Spring Molding Clips Molding retaining clips are formed with legs that hold the clips to a panel and arms that positively engage the flanges of various sizes and shapesof trim molding and pull the molding tightly to the attaching panel • U-, 5-, and C-Shaped Spring Clips The fastening function is accomplished by using inward compressive spring force to secure assembly components or provide self-retrntion after installation. Hajdu Flóra

48. Spring clips • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

49. Summary • Geartypes • Gearassemblies • Spring types • Nextweek: Welded, soldered, glued and rivetedconnections

50. ThankYouforYourattention!