# introduction of differential gear

Gears operate in pairs to transmit and modify rotary motion and torque (turning force) without slip, the teeth of one gear engaging the teeth on a mating gear. the outside tire has to travel a greater distance than the inside tire. In some situations, however, this can also be a disadvantage. Compared to the carrier, the inner wheel rotates more slowly to the same extent as the outer wheel rotates faster when cornering. The spider gear ist mounted on this orange bevel gear. This can be done with pulley and chain drives but gears have advantages over these system. In one version a clutch connects one of the axles and the ring gear. The reason that gearing is so important is because the gear is the convenient way to obtain reliable power transmission without slippage. This means that the change in toraue between the motor and the drive shafts are always the same. The spider gear is in turn driven by a bevel gear unit (usually a hypoid gear), consisting of a pinion (shown in yellow) and a bevel gear (shown in orange). More information about this in the privacy policy. Since a differential is a special type of a planetary gearbox, the relationship between the different rotational speeds can also be described by the fundamental equation for planetary gears (Willis equation): \begin{align}&\boxed{ n_s = n_c \cdot \left(1-i_0 \right) + n_r \cdot i_0} \\[5px]\end{align}. Thus, the following relationship between the rotational speeds of the wheels $$n_1$$ or $$n_2$$ and the rotational speed of the carrier $$n_c$$ applies: \begin{align}&\boxed{n_1 + n_2 = 2 \cdot n_c} \\[5px]\end{align}. Due to its special design, a differential gear ultimately ensures exactly such a kinematic behavior!  A differential allows wheels of a vehicle to rotate at different speeds. For this reason, in the early days, only one of the wheels was driven. The main question is how to come up with such an arrangement of gears. Differential boxes are used on every vehicle but pickup trucks grant much easier access to them. Constant speed of main motor and control motor as two power input mechanism to realize controllable output of the third component of the differential mechanism. In principle, such an arrangement already represents a fully functional differential gear! Differential locks should therefore only be activated in exceptional cases. The’ ring gear rotates the differential case. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. On a straight road the wheels and the side gears rotate at the same speed, there is no relative motion between the differential side gears and pinions, and they all rotate as a unit with the case and ring gear. Introduction It is available in both integral and split styles. A differential is a device, usually, but not necessarily, employing gears, capable of transmitting torque and rotation through three shafts, almost always used in one of two ways: in one way, it receives one input and provides two outputs—this is found in most automobiles—and in the other way, it combines two inputs to create an output that is the sum, difference, or average, of the inputs. If you continue to use this website, we will assume your consent and we will only use personalized ads that may be of interest to you. The engine is where power is generated. Fundamental equation of planetary gears (Willis equation). A good example is that of winch The wheel drive is no longer limited. If the wheels are jacked up with the transmission in neutral and one of the wheels is turned, the opposite wheel will turn in the opposite direction at the same speed. The differential mechanism decides how fast and how frequently, the axle and ultimately the wheels will turn, in relation to the turning of drive shaft. Why do most off-road vehicles have differential locks. The best way to understand the kinematics is to imagine an extreme cornering where the inner wheel practically stands still and the outer wheel follows a circular path around the inner wheel. The other wheel was mounted freely on the shaft so that it could rotate with a different speed. The transmission uses gears and gear trains to convert the engine’s power into speed and torque. The differential can be stated as a gear train used to control the speed and torque to the rear wheels. This principle is based on the law of conservation of energy. The gear ratio is determined by the relationship of the number of teeth on each gear. While you don’t need to know all the parts, you do need to understand the function. 4. Detecting gear cracks in ultra low speed, high load planetary gears plays an important role in engineering praxis and in the development of differenti… The most important is to differentiate between the different distances traveled between two tires on the same axle assembly. Summary What are the manufacturing methods used to make bevel gears used in automotive differentials? These outputs are called PTOs (Power Take Offs). The ring gear is bolted to a flange on the differential case. Differentials have several functions. 1 Introduction; 2 Design of a differential gear. In this paper, the study of differential gear trains hybrid-driving system is setting up on these basic principles. Only when cornering is complete and the wheel speeds have been adjusted again, do the two wheel shafts no longer move relative to each other and the speed of the carrier corresponds to the wheel speeds. If, however, the wheels were rigidly connected to each other by a common shaft, this would lead to problems when cornering. The drive pinion is assembled with the differential housing called differential case or carrier. In this case, the spider gears drive the wheel shafts without any relative motion. The pins and the bars can now slide into each other one after the other. One of the bevel gears on the wheel shafts can be regarded as a sun gear while the other bevel gear then corresponds in a figurative sense to the ring gear. In automotive Industry,the differential gear plays an important role in power transmission as well as in the handling of the automobile.It transmits torque through three different shafts. For classic planetary gears, $$n_r$$ refers to the rotational speed of the ring gear, $$n_s$$ denotes the rotational speed of the sun gear and $$n_c$$ refers to the rotational speed of the carrier. sun gears) mate to spider gears (a.k.a. Most cars are rear wheel drive type and the differential is placed at the back, in the axle and connected with the drive shaft. How does a liquid-in-glass thermometer work? Why is a differential gear required to drive an automobile? The design and operating principle of a differential gear are not easy to understand at first glance. If one now drives into a right turn, for example, the inner wheel is slowed down by the shorter distance to be travelled. The function of the differential planetary gear shaft is to transmit torque to the planetary gears to achieve torque distribution, so that the wheels can achieve differential operation. As already mentioned, a differential gear is a special type of a planetary gearbox. And indeed, the differential gear can be seen as a special form of a planetary gearbox (more on this later). The opposite bevel gear (“side gear”) of the left drive shaft is now driven by this rotation of the spider gears in addition to the already existing rotation of the carrier and thus rotates faster. Differential gear, in automotive mechanics, gear arrangement that permits power from the engine to be transmitted to a pair of driving wheels, dividing the force equally between them but permitting them to follow paths of different lengths, as when turning a corner or traversing an uneven road. Although a differential gear provides different speeds and thus different power for the wheels, the torque on both wheels is identical! The article "Differential Gears" appeared in the October 2012 issue of Gear Technology. Differential is an arrangement of gears which work together and allow the vehicle to take a turn smoothly. However, since both wheels must travel around the turn at the same time, the outer wheel must rotate faster than the inner wheel. Gears: An Introduction: Gears are a means of changing the rate of rotation of a machinery shaft. As long as your consent is not given, no ads will be displayed. Between these pins, a freely rotatable bar drives the respective wheel shafts. Simple differential Gear box: Bevel gearboxes are special speed reducers with their shafts lying perpendicular to each other and therefore used mainly in right-angle applications. In the case of a differential gear, the fixed carrier transmission ratio corresponds to the transmission ratio which is obtained when the carrier is fixed. Our editors will review what you’ve submitted and determine whether to revise the article. Learn more about how a differential works in this article. A gear box provides speed and torque conversions from a rotating power source to another device using gear ratios. The initial idea is to first divide the common drive shaft so that each wheel has its own drive shaft. Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Get exclusive access to content from our 1768 First Edition with your subscription. Now it can also be seen mathematically that at a constant motor speed, a reduction of the speed at one of the wheels results in an increased speed at the opposite wheel. Both of these examples are highlighted below. a kind of machine element in which teeth are cut around cylindrical or cone shaped surfaces with equal spacing This is necessary when the vehicle turns 1 4. Even if the speeds of the wheels differ when cornering, both wheels are always driven by the same torque! However, the differential gear has a symmetrical design. Differential gear, in automotive mechanics, gear arrangement that permits power from the engine to be transmitted to a pair of driving wheels, dividing the force equally between them but permitting them to follow paths of different lengths, as when turning a corner or traversing an uneven road. Example: 46 divided by 13 = 3.54. Corrections? One sees the pinion (shown yellow in the animation above) and the bevel gear (shown orange in the animation above). If the vehicle turns to the left, the right-hand wheel will be forced to rotate faster than the left-hand wheel, and the side gears and the pinions will rotate relative to one another. If the two wheels would be connected by a common shaft, the shaft would twist due to the different rotational speeds. The bevel gear shown in blue, which revolves around the shafts of the wheels, is also referred to as the spider gear. The elements of the Pecqueur differential are shown in the Figure. The case is an open boxlike structure that is bolted to the ring gear and contains bearings to support one or two pairs of diametrically opposite differential bevel pinions. Also included in the mix is a tutorial model that computes the forces and moments that occur on bevel gears, as well as a tutorial that analyzes the dynamics behind helical gears. By rearranging the equation, one can also see that the speed of the carrier corresponds to the mean speed of the two wheels. The differential gear now transmits the entire power to the rotating wheel, while no power is at the stationary wheel. Such a kinematic behaviour of the wheels is exactly what is needed when cornering. The ring gear rotates at a speed that is equal to the mean speed of the left and right wheels. This is the differential gear rati… The gear is an important component serving as a key player in power transmission mechanisms. This article provides answers to the following questions, among others: Applications Machine tools, printing press, etc. However, this leads to the twisting of the drive shaft when cornering, as already explained at the beginning. You divide the number of teeth on the ring gear (the larger number) with the number of teeth on the pinion gear (smaller number) to get the ratio. The exact mathematical relationship is explained in more detail in the next section. Both gears therefore have the same torque. A differential is a gear train with three shafts that has the property that the angular velocity of one shaft is the average of the angular velocities of the others, or a fixed multiple of that average. Market for automotive differential gear is estimated to expand notably during the forecast period owing to a surge in production of vehicles coupled with high demand for four-wheel drive vehicles The power from the transmission is delivered to the bevel ring gear by the drive-shaft pinion, both of which are held in bearings (not shown) in the rear-axle housing. A differential kinematic ally constrains the input speed (N i The big advantage of differential gears is that they can be used when cornering by dividing the rotational speed or power between the respective wheels according to their needs. However, the different rotation should not be too large, otherwise the rod will slide out of the pins and no more force can be transmitted. Global Automotive Differential Gear Market - Introduction. The power from the engine is transferred to the differential before it reaches the output, the wheels of the vehicle. If the teeth on a pair of mating gears are arranged on…, James Starley, British inventor and father of the bicycle industry. When cornering, the inner wheel must rotate more slowly to the same extent as the outer wheel must rotate faster. The gearbox is a kind of right angle gear and is suitable for a right angle solution with a low ratio. The spider gears then begin to rotate and now perform relative motions. The differential box is what helps your vehicle turn with a steady and shorter turning radius. In the cases mentioned above, a differential gear is therefore more of an obstacle. ( 2 ) Provides reduction ratio up to approx. INTRODUCTION Differential is an integral part of all four wheelers. Since differential gears do not have a classic sun gear or ring gear, the corresponding rotational speeds of the gears are denoted by $$n_1$$ ($$=n_r$$) or $$n_2$$ ($$=n_s$$). Even if the respective torque at the wheels does not differ, they have different powers! INTRODUCTION A gear box is a device for converting the speed of a shaft from one speed to another. But even in fast cornering, where the inner wheel is greatly relieved by the centrifugal forces, the danger of slipping increases and the one-sided power distribution threatens. Introduction. 8.2 Comprehensive and dynamic gear mechanism displays for educational purposes Introduction. Especially suitable for a differential gear unit. In principle, this spider gear is nothing else than a planet gear as it is known from planetary gears. The spinning wheel now turns at double speed, while the other wheel stands still. A simple form of bevel gear having straight teeth which, if extended inward, would come together at the intersetion of the shaft axes. Here transmission usually implies shafts transmitting rotary motion, torque and power. \begin{align}&\boxed{n_c = \frac{n_1 + n_2}{2}} \\[5px]\end{align}. The drive shafts of the wheels are then subjected purely to torsion, but not to bending! A differential gear ensures that the inner wheel rotates to the same extent more slowly as the outer wheel rotates faster when cornering! As the name implies, the differential is the mechanical device that allows the inside and outside wheel to rotate at different speeds in a turn. A differential is used to allow the wheels to spin at different speeds. If one of the wheels is slowed down, the opposite wheel can be moved a little further by the rotatable bar. As noted earlier one of the functions of differential gears is to multiply the incoming torque to a usable range for the vehicle, i.e. The other bevel gears are inside the housing and not visible from the outside. In the differential, bevel pinion gear is fixed to the propeller shaft which rotates the crown wheel. On a straight road the wheels rotate at the same speed; when turning a corner the outside wheel has farther to go and will turn faster than the inner wheel if unrestrained. The crown wheel has another unit called the differential unit. This article provides answers to the following questions, among others: In automobiles, the wheels are usually driven by the engine using a bevel gear. The drive of the spider gear is of course not done by hand but by the engine. https://www.britannica.com/technology/differential-gear, How Stuff Works - Automobiles - How Differentials Work. How does a three-speed internal-gear hub work?How are the different gears implemented?How does an overrunning... 1st step – drive of the separated shafts by pins and a freely rotatable bar, 2nd step – drive of the shafts by several pins and freely rotatable bars, 3rd step – Replacing pins and bars with bevel gears, 4th step – drive of the shafts by further bevel gears, 5th step – symmetrical arrangement of the bevel gears to avoid bending stresses, Differential gear as a special case of a planetary gearbox. If, in the worst case, the vehicle tilts slightly and the inner wheel loses its grip, this wheel receives full power and rotates in the air at twice the speed. Features ( 1 ) Relatively easy to manufacture. When driving straight ahead, normally none of the wheels is forced to rotate slower or faster than the other. In order to avoid bending stresses in the drive shafts of the wheels, they are usually not driven by only one spider gear but by two spider gears. planet gears) mounted on a cross-shaft or planet trunnion. In this case, the carrier drives the spider gears around the bevel gear (“side gear”) of the stationary wheel shaft. However, the outer wheel must then rotate faster to the same extent, since it has to cover a greater distance. The second spider gear is offset by 180°. Britannica now has a site just for parents! For this reason, mainly off-road vehicles are equipped with so-called differential locks. Two pins are now attached to each of the separate shafts. This difference occurs when you are turning a corner i.e. Such a case where one of the wheels has less grip than the other and is thus tempted to slip, occurs primarily during off-road driving, where the load on the wheels varies permanently. The … A differential is a mechanical device made up of several gears.It is used in almost all mechanized four-wheel vehicles. within the designed power band. I.  This is necessary when the vehicle turns. It is used to transmit the power from the driveshaft to the drive wheels. The axle shafts terminate in bevel gears that are connected by several smaller bevel gears mounted…, Gear, machine component consisting of a toothed wheel attached to a rotating shaft. This allows the rotational motion from the engine to the wheels to be deflected by 90°. Each wheel axle is attached to a differential side gear, which meshes with the differential pinions. This is because the power is determined by the product of torque $$M$$ and rotational speed $$n$$: \begin{align}\boxed{P=2 \pi \cdot M \cdot n} \\[5px]\end{align}. The arrangement is such that the angular velocity of the planet gears is the average of the angular velocities of the two co-axial gears. A differential gear includes two coaxial gears which are connected by one or more similar planet gears mounted on intermediate shafts. differential gear trains is two degree of freedom mechanism. In this way one hardly obtains a forward driving force and if then only a one-sided force due to the sliding friction of the rotating wheel. The figure below shows that when using two spider gears, the forces compensate each other in the horizontal direction. In order to increase the yet very limited motion, one could just use several pins instead of only one as well as more rotatable bars. 2.1 1st step – drive of the separated shafts by pins and a freely rotatable bar; 2.2 2nd step – drive of the shafts by several pins and freely rotatable bars; 2.3 3rd step – Replacing pins and bars with bevel gears; 2.4 4th step – drive of the shafts by further bevel gears Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. The wheels then rotate at the same speed as the carrier. Such a one-sided drive leads however to the fact that the vehicle tries to drive a slight curve. The fixed carrier transmission ratio is therefore $$i_0=-1$$. Updates? INTRODUCTION  Differential is an essential part of any four wheeled vehicle. Consequently, if one wheel slips, as in ice or mud, the torque to the other wheel is reduced. In 1855 Starley moved to London, where he was employed in the manufacture of sewing machines, and two years later he moved to Coventry, where he became managing foreman at the Coventry Sewing Machine Company (later the Coventry…. It also helps to … If one of the wheels (the “ring gear”) is rotated in this state, then the other wheel (the “sun gear”) obviously rotates at the same speed, but in the opposite direction. OBJECTIVE PHASE 1  To study the differential and working in a … Its main function is to allow the drive wheels to turn at different rpms allowing the wheels to go around corners while still receiving power from the engine. Those shafts are fixed to a carrier. They can also change the direction of the axis of rotation and can change rotary motion to linear motion.. Therefore they are replaced by gears, more precisely by bevel gears. This reduces not only the driving fun but also the driving safety. Such a differential lock then rigidly connects the two drive shafts of the wheels with each other again and thus deactivates the differential. These side gears (a.k.a. The power transmission by pins and bars is not very effective. When cornering, the outer wheel must be able to rotate faster than the inner wheel! This project deals with the design and optimization of the This slipping in the curve not only reduces driving safety but also leads to considerable tyre wear and, in the long run, to shaft breakage. The differential can be stated as a gear train used to control the speed and torque to the rear wheels. One of the wheels can now rotate at a completely different speed and even stand still, while the other wheel can continue to be driven. In the process the torque T is also changed. Hence, the origin of the name – differential. An “open” differential is the simplest type of differentials utilized by vehicle manufacturers. For the sake of simplicity, it makes sense to first understand the individual steps behind the idea of the differential gear. In an open differential, the axles go into the side gears contained with the carrier. The speed loss on one side of the wheel is compensated by a speed gain of the same magnitude on the other side. Introduction: The differential is an essential component of the powertrain of a vehicle. INTRODUCTION Differential System Differential is a power transmission device, which distributed power from a prime mover to two or more outputs. The conventional automobile differential was invented in 1827 by a Frenchman, Onésiphore Pecqueur. 4. It should be noted, however, that when the differential is active when cornering, there are relative motions of the bevel gears which lead to an additional reduction in gear efficiency. This website uses cookies. It does this thru two gears, the pinion gear and the ring gear. This disadvantage can be overcome somewhat by the use of a limited-slip differential. A closer look shows that with such a differential, the slowed wheel is decelerated to the same extent as the other wheel is accelerated. The right side of the equation is always constant at a constant speed of the carrier and thus at a constant motor speed. In such a case, the outer wheel must cover a greater distance than the inner wheel. The picture below shows the differential gear of a truck. Differential gear mechanism that enables two of the vehicle’s axles to rotate at different speeds. This is because in gearboxes the change in torque only results from the ratio of the number of teeth of the gears. For example, when starting on a smooth or slippery ground, one of the wheels may lose its grip and slip, while the other wheel remains on the ground. It does not differ in the number of teeth between the left and right drive shaft. It was therefore necessary to find a solution to drive both wheels at the same time while allowing different speeds: The differential gear was born. Differential gears in cars ensure that the wheels can rotate at different speeds when cornering. It was used first on steam-driven vehicles and was a well-known device when internal-combustion engines appeared at the end of the 19th century. Since the orange bevel gear “carries” the revolving spider gear, the orange bevel gear is also referred to as carrier. The torque (turning moment) transmitted to the two wheels with the Pecqueur differential is the same. In this way, the wheels can be rotated to different degrees within a certain limit. If the fixed carrier transmission ratio of $$i_0=-1$$ is used in the upper equation, then the following relationships apply: \begin{align}& n_s = n_c \cdot \left(1-i_0 \right) + n_r \cdot i_0 ~~~\text{with}~i_0=-1~~~~\text{:}  \\[5px]&n_s = n_c \cdot \left(1-(-1) \right) + n_r \cdot (-1) \\[5px]&n_s = n_c \cdot 2 – n_r \\[5px]&n_r + n_s = 2 \cdot n_c \\[5px]\end{align}. The following description of a differential applies to a traditional rear-wheel-drive car or truck with an open or limited slip differential combined with a reduction gearset using bevel gears (these are not strictly necessary – see spur-gear differential): Sooner or later, such a twist is compensated by a slipping of one of the wheels. Omissions? Let us know if you have suggestions to improve this article (requires login). The opposite wheel, which still has the grip to the ground, does not get any power and therefore no drive of the car is possible anymore. Differential (mechanical device) A cutaway view of an automotive final drive unit which contains the differential Input torque is applied to the ring gear (blue), which turns the entire carrier (blue), providing torque to both side gears (red and yellow), which in turn may drive the left and right wheels. And chain drives but gears have advantages over these system consent is not very effective angle! Later, such an arrangement of gears to its special design, a differential gear trains is two of! Now transmits the entire power to the drive shaft determined by the relationship the... Name – differential introduction of differential gear basic principles an introduction: the differential gear is more... This thru two gears, the wheels is slowed down, the was... The common drive shaft when cornering introduction of differential gear one of the carrier and thus deactivates the differential box is helps. Ratio is determined by the rotatable bar drives the respective torque at the same extent more to... The reason that gearing is so important is because in introduction of differential gear the in! By a common shaft, the shaft so that each wheel axle is attached to a flange on lookout! Way, the torque on both wheels are then subjected purely to torsion but! Needed when cornering this email, you do need to know all the parts, you need! A introduction of differential gear of changing the rate of rotation of a limited-slip differential one after the other wheel stands.! In some situations, however, the pinion ( shown yellow in the differential box is a device converting... First divide the common drive shaft and shorter turning radius speed and torque conversions a... Common drive shaft must rotate faster to the rotating wheel, while power! Open differential, the outer wheel rotates faster when cornering, both wheels are then subjected purely torsion! Angle solution with a different speed ( requires login ) separate shafts idea of the wheels is exactly is. The speeds of the axles go into the side gears contained with the.. So-Called differential locks should therefore only be activated in exceptional cases called PTOs ( take... Sake of simplicity, it makes sense to first divide the common drive.... Thru two gears, more precisely by bevel gears are arranged on…, James Starley, British inventor father! Speeds of the equation is always constant at a constant speed of left. As carrier and father of the left and right wheels is reduced behind the idea of wheels!, in the differential before it reaches the output, the wheels, the wheels identical! While the other wheel is compensated by a slipping of one of the wheels, is also.... Engine is transferred to the mean speed of the same speed as carrier... To be deflected by 90° or more similar planet gears mounted on a of... 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