Mechanical Transmissions Chains Belts Gears

CONTENTS GEAR TYPES OF GEARS NOMENCLATURE APPLICATIONS OF GEARS VELOCITY RATIO GEAR TRAINS EXAMPLE PROBLEMS AND QUESTIONS

Gears – What are they? Gears are wheels with teeth. Gears mesh together and make things turn. Gears are used to transfer motion or power from one moving part to another.

Gears – The Purpose Sports cars go fast (have speed) but cannot pull any weight. Big trucks can pull heavy loads (have power), but cannot go fast. Gears cause this. Gears increase or decrease the power or speed, but you cannot generally speaking.

Gears are generally used for one of four different reasons: To reverse the direction of rotation To increase or decrease the speed of rotation To move rotational motion to a different axis

TYPES OF GEARS 1. According to the position of axes of the shafts. Parallel 1.Spur Gear 2.Helical Gear 3.Rack and Pinion b. Intersecting Bevel Gear c. Non-intersecting and Non-parallel worm and worm gears

Types of Gears

SPUR GEAR Teeth is parallel to axis of rotation Transmit power from one shaft to another parallel shaft Spur Gears in any transmission system are employed for changing the speed and the torque and are fixed on shafts Gear ‘A’ is called the ‘driver’ because this is turned by a motor. As gear ‘A’ turns it meshes with gear ‘B’ and it begins to turn as well. Gear ‘B’ is called the ‘driven’ gear. Denti è parallelo all'asse di rotazione Potenza di trasmissione da un albero all'altro ad assi paralleli Utilizzato in cacciavite elettrico, oscillante sprinkler, sveglia windup, lavatrice e asciugatrice 11

Spur Gears Pinion Gear

External Set: Opposite Movement Spur Gears - Types External Set: Opposite Movement Internal Set: Movement in the same direction

Helical Gear The teeth on helical gears are cut at an angle to the face of the gear This gradual engagement makes helical gears operate much more smoothly and quietly than spur gears

Helical Gear… Helical Gears can be used for transmitting motion between parallel shafts as between perpendicular shafts. Helical gears used for transmission at an angle are called SPIRAL GEARS.

Herringbone gears are mostly used on heavy machinery. HERRING-BONE Gears are pairs of Helical Gears. These gears are used for large power transmission. Herringbone gears are mostly used on heavy machinery.

Rack and pinion Rack and pinion gears are used to convert rotation (From the pinion) into linear motion (of the rack) A perfect example of this is the steering system on many cars The rotary motion of pinion 1 (small gear) is transformed into linear motion of the rack 2. For transmitting large power worm & worm rack transmission is employed.

A ‘rack and pinion’ gears system looks quite unusual A ‘rack and pinion’ gears system looks quite unusual. However, it is still composed of two gears. The ‘pinion’ is the normal round gear and the ‘rack’ is straight or flat. The ‘rack’ has teeth cut in it and they mesh with the teeth of the pinion gear. The pinion rotates and moves the rack in a straight line - another way of describing this is to say ‘rotary motion’ changes to ‘linear motion’.

Bevel gears Bevel gears can be used to change the direction of drive in a gear system by 90 degrees. A good example is seen as the main mechanism for a hand drill. As the handle of the drill is turned in a vertical direction, the bevel gears change the rotation of the chuck to a horizontal rotation

Straight and Spiral Bevel Gears

WORM AND WORM GEAR Worm gears are used when large gear reductions are needed. It is common for worm gears to have reductions of 20:1, and even up to 300:1 or greater Many worm gears have an interesting property that no other gear set has: the worm can easily turn the gear, but the gear cannot turn the worm Worm gears are used widely in material handling and transportation machinery, machine tools, automobiles etc Ingranaggi a vite senza fine sono utilizzati quando riduttori di grandi dimensioni sono necessarie. E 'comune per ingranaggi a vite senza fine di avere una riduzione di 20:1, e addirittura fino a 300:1 o superiore Molti ingranaggi a vite senza fine hanno un interessante proprietà che non ha fissato altri attrezzi: il worm può facilmente girare la macchina, ma la marcia non si può girare la vite senza fine  Ingranaggi a vite senza fine sono ampiamente utilizzati nella movimentazione dei materiali e dei macchinari di trasporto, macchine utensili, automobili, ecc

Types of Gears “According to the position of axes of the shafts” Parallel Spur Gears Helical Gears Herringbone Gears B. Perpendicular Axis C. Planetary Intersecting Bevel Gears Non Intersecting Worm Gears Planetary Gears 22

Planetary Gears “suited for highly dynamic drives” With their weight advantage, planetary gearboxes are also well established for extremely high output torque and for mobile applications. The maximum ratio that can be achieved in a single stage is approximately i = 12. Larger ratios are then achieved by adding further downstream stages. Alongside the increased load capacity, it is also reduce noise emissions.

Nomenclature of Spur Gear Teeth Pitch circle gear diam. Clearance Fillet radius Base Circle = (tooth spacing)driven gear – (tooth thickness)driver , measured on the pitch circle. Backlash

NOMENCLATURE…. Face of a tooth: That part of the tooth surface lying outside the pitch surface. Flank of a tooth: The part of the tooth surface lying inside the pitch surface. Circular thickness (also called the tooth thickness): The thickness of the tooth measured on the pitch circle. It is the length of an arc and not the length of a straight line. Tooth space: pitch diameter The distance between adjacent teeth measured on the pitch circle. Backlash: The difference between the circle thickness of one gear and the tooth space of the mating gear. Circular pitch (Pc) : The width of a tooth and a space, measured on the pitch circle.

NOMENCLATURE OF SPUR GEARS