Gear trains. Prof Ahmed Kovacevic. Lecture 4. School of Engineering and Mathematical Sciences. Room C, Phone: , E-Mail: [email protected] uk. Gear 3 is idler. Used to change the direction of rotation or to connect two shafts at a distance. Simple “Compound”Gear Train. n n n n. TTTT/ /. (). R. n n n n. a combination is called gear train or train of toothed wheels. Since the speed ratio (or velocity ratio) of gear train is the ratio of the speed of the driver to.
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PDF | 4+ hours read | Gears are toothed cylindrical wheels used for transmitting mechanical power from one rotating shaft to another. Several. Gear Trains. Introduction: Sometimes, two or more gears are made to mesh with each other to transmit power from one shaft to another. Such a combination is. vice is needed, a gear train or one of its cousins, the belt or chain drive mechanism, will and gear trains of simple, compound, reverted, and epicyclic types.
It is also possible to determine a car's speed from the engine speed by multiplying the circumference of the tire by the engine speed and dividing by the combined gear ratio. The gears are represented by their pitch circles. The input gear in this gear train has 13 teeth and the idler gear has 21 teeth. This equation shows that the ratio of the circumference, the diameters and the radii of two meshing gears is equal to the ratio of their number of teeth,. Automobile drivetrains generally have two or more major areas where gearing is used.
Search inside document. Simple Gear Train - The simple gear train is used where there is a large distance to be covered between the input shaft and the output shaft. Darwin Lim. Jose Fernando Davila Vigo. Miguel Matias Reinero. Miry Lu D. Juanjo Acvdo. Velsami AmmasaiGounder. Roberto Barboza. Atanasius Hardito. More From Hendri Yoga Saputra.
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Pavan Kishore. Pcnhs Sal. Dedendum is the radial distance between the pitch circle and the dedendum circle. Addendum Circle: Addendum circle is the outer most profile circle of a gear.
Dedendum Circle: Dedendum circle is the inner most profile circle.
Clearance is the radial distance from top of the tooth to the bottom of the tooth space in the mating gear. Module m is the inverse of diametral pitch.
Full Depth: Full depth is sum of the addendum and the dedendum. Diametral Pitch: Diametral pitch p is the number of teeth per unit volume. Backlash is the tangential space between teeth of mating gears at pitch circles. Face Width: Face width is length of tooth parallel to axes. Pressure Angle: Pressure angle is the angle between the pressure line and common tangent to pitch circles. High pressure angle requires wider base and stronger teeth.
Pressure Line: Pressure line is the common normal at the point of contact of mating gears along which the driving tooth exerts force on the driven tooth. Circular Pitch: Circular pitch is the space in pitch circle used by each teeth. It is also called angle of obliquity. Pitch Angle: Pitch angle is the angle captured by a tooth. Gear Ratio: Gear ratio is numbers of teeth of larger gear to smaller gear. Path of Recess: Path of recess is the distance traveled along the pressure line by the contact point from the pitch point to the path of disengagement.
Path of Approach: Path of approach is the distance along the pressure line traveled by the contact point from the point of engagement to the pitch point.
Path of Contact: Patch of contact is the sum of path of approach and path of recess. Contact ratio is angle of angle of action and pitch angle.
Angle of Action: Angle of action is the angle turned by a gear during arc of contact. Arc of Contact: Arc of contact is the distance traveled by a point on either pitch circle of the two wheels during the period of contact of a pair of teeth. Arc of Approach: Arc of approach is the distance traveled by a point on either pitch circle of the two wheels from the point of engagement to the pitch.
Arc of Recess: Arc of recess is the distance traveled by a point on either pitch circle of the two wheels from the point to the point of disengagement.
Theory A compound gear is a number of gears fixed together. The motion of the input is transferred through the. The gear on the input shaft meshes with a larger gear on a counter-shaft or cluster gear. The gears that make up a compound gear usually differ in size and have a different number of teeth. This compound gear train has gears on three shafts.
The counter-shaft has a smaller gear formed on it. This is useful if there is a need to speed up or slow down the final output. Compound gear trains have two or more pairs of gears in mesh.
The output turns in the same direction as the input. Since two pairs of gears are involved. One of these two gears meshes with the driver and the other with the driven or follower attached to the next shaft as shown in Fig. But these gears are useful in bridging over the space between the driver and the driven. But whenever the distance between the driver and the driven or follower has to be bridged over by intermediate gears and at the same time a great or much less speed ratio is required.
For this reason it is called an idler gear. The same gear ratio is obtained for a sequence of idler gears and hence an idler gear is used to provide the same direction to rotate the driver and driven gear. If the driver gear moves in the clockwise direction, then the driven gear also moves in the clockwise direction with the help of the idler gear. In the photo, assuming the smallest gear is connected to the motor, it is called the drive gear or input gear.
The somewhat larger gear in the middle is called an idler gear. It is not connected directly to either the motor or the output shaft and only transmits power between the input and output gears. There is a third gear in the upper-right corner of the photo. Assuming that gear is connected to the machine's output shaft, it is the output or driven gear. The input gear in this gear train has 13 teeth and the idler gear has 21 teeth.
Considering only these gears, the gear ratio between the idler and the input gear can be calculated as if the idler gear was the output gear. At this ratio, it means the drive gear must make 1. Essentially, the larger gear turns slower. The third gear in the picture has 42 teeth.
For every 3. The idler gear serves to make both the drive gear and the driven gear rotate in the same direction, but confers no mechanical advantage. Belts can have teeth in them also and be coupled to gear-like pulleys. Special gears called sprockets can be coupled together with chains, as on bicycles and some motorcycles. Again, exact accounting of teeth and revolutions can be applied with these machines.
For example, a belt with teeth, called the timing belt , is used in some internal combustion engines to synchronize the movement of the camshaft with that of the crankshaft , so that the valves open and close at the top of each cylinder at exactly the right time relative to the movement of each piston. A chain, called a timing chain, is used on some automobiles for this purpose, while in others, the camshaft and crankshaft are coupled directly together through meshed gears.
Regardless of which form of drive is employed, the crankshaft-to-camshaft gear ratio is always 2: Automobile drivetrains generally have two or more major areas where gearing is used. Gearing is employed in the transmission , which contains a number of different sets of gears that can be changed to allow a wide range of vehicle speeds, and also in the differential , which contains the final drive to provide further speed reduction at the wheels.
In addition, the differential contains further gearing that splits torque equally between the two wheels while permitting them to have different speeds when travelling in a curved path. The transmission and final drive might be separate and connected by a driveshaft , or they might be combined into one unit called a transaxle.
The gear ratios in transmission and final drive are important because different gear ratios will change the characteristics of a vehicle's performance. A Chevrolet Corvette C5 Z06 with a six-speed manual transmission has the following gear ratios in the transmission:. In 1st gear, the engine makes 2. In 4th gear, the gear ratio of 1: The Corvette above has an axle ratio of 3. The differential ratio multiplies with the transmission ratio, so in 1st gear, the engine makes This means that for every complete revolution of the wheel, the car travels If the Corvette had larger tires, it would travel farther with each revolution of the wheel, which would be like a higher gear.
If the car had smaller tires, it would be like a lower gear. With the gear ratios of the transmission and differential and the size of the tires, it becomes possible to calculate the speed of the car for a particular gear at a particular engine RPM.
For example, it is possible to determine the distance the car will travel for one revolution of the engine by dividing the circumference of the tire by the combined gear ratio of the transmission and differential.
It is also possible to determine a car's speed from the engine speed by multiplying the circumference of the tire by the engine speed and dividing by the combined gear ratio. Note that the answer is in inches per minute, which can be converted to mph by dividing by A close-ratio transmission is a transmission in which there is a relatively little difference between the gear ratios of the gears. For example, a transmission with an engine shaft to drive shaft ratio of 4: This is because the close-ratio transmission has less of a progression between gears.
For the wide-ratio transmission, the first gear ratio is 4: For the close-ratio transmission, first gear has a 4: However, the difference between a close-ratio and wide-ratio transmission is subjective and relative.
Close-ratio transmissions are generally offered in sports cars , sport bikes , and especially in race vehicles, where the engine is tuned for maximum power in a narrow range of operating speeds, and the driver or rider can be expected to shift often to keep the engine in its power band.
Factory 4-speed or 5-speed transmission ratios generally have a greater difference between gear ratios and tend to be effective for ordinary driving and moderate performance use.
Wider gaps between ratios allow a higher 1st gear ratio for better manners in traffic, but cause engine speed to decrease more when shifting. Narrowing the gaps will increase acceleration at speed, and potentially improve top speed under certain conditions, but acceleration from a stopped position and operation in daily driving will suffer. Range is the torque multiplication difference between 1st and 4th gears; wider-ratio gear-sets have more, typically between 2.
This is the single most important determinant of low-speed acceleration from stopped.