How It Works | Locking Differential | Aussie Locker By Torq Masters Aussie Locker By Torq Masters How It Works General Information The Aussie Locker is a fully automatic and precision manufactured automatic differential locking device that does not require any manual operation to activate. It does not require any switches, external compressors, electrical cables, air lines, or pneumatic controls. The Aussie Locker relies on a simple and highly innovative mechanical design which makes use of two distinct sets of forces, "ground driven" forces acting on a wheel when cornering (forces the outside of the wheel to turn faster) and the engine driven forces through the drivetrain. The combination of these two sets of opposing forces and the unique Aussie Locker design allow the automatic locking and unlocking of the driving gears when a vehicle turns or requires differential action. How the Aussie Locker is different from a standard differential A standard differential is designed to perform two main traction related operations; Transmit engine power via the drive line to the wheels, Allow "differential action", i.e.

allow the wheels to travel at different speeds to allow cornering without drive train damage or tire damage.The traditional differential design allows for an infinitely variable rate of differentiation ranging from 50:50 where both wheels turn at the same speed (straight line driving) and a ratio of 100:0 where one wheel spins freely and the other is not driven at all (not what you want to face when off roading). The traditional differential also allows for all power to be transmitted to the "path of least resistance" which is fine on highways because both wheels have some degree of traction but off road you often require substantial power and in this case even a small difference in traction can result in wheel spin and the subsequent loss of traction. A limited slip (LSD) differential is simply a standard differential (also called open) with either a fixed bias or dynamic biasing mechanism which serves to only "partially" lock up" the two axles by way of clutch plates or special gear design. However, most require that both wheels still have some traction on the ground to operate and even when new will cause a wheel in the air to spin uncontrollably so as to be completely ineffective where off road traction is required.

The Aussie Locker overcomes the traction deficiency of the standard differential and a limited slip differential so as to ensure that 50:50 power split is achieved when driving irrespective of ground conditions, yet still allowing differential action when required. Simple explanation of the Aussie Locker operation The Aussie Locker mechanism allows a wheel to turn faster than the speed of the differential that is driving it (differentiation), but never allows a wheel to turn slower than the speed the differential and engine is turning it (traction). Therefore, a wheel cannot ever stop turning if the engine is driving it, but in a corner it can be forced to actually turn faster. Unlike a standard differential, the engine can never drive one wheel faster than the other. 100% positive locking The Aussie Locker is positive locking, meaning there is no slippage when locked. There is a mechanically solid engagement of all parts. In contrast a limited slip differential is not positive locking and does allow slippage and one wheel "spin up" i.e. the spinning of one wheel at twice the differential speed while the other wheel having traction remains motionless. With the "Aussie Locker" you get 100% of drive and traction to both wheels at all times.

Dynamic Locking Principle Unlike some other types of lockers, the Aussie Locker has a locking and unlocking principal that is dynamic. Dynamic in that the more power that is applied, the harder it locks so it doesn't need large bias forces operating on it to keep it locked. The bias spring forces are minuscule and can easily be compressed with two fingers. This results in a locker that is able to lock and unlock easily even when driving on extremely slippery surfaces like mud and wet grass. The locking mechanism is so sensitive that a wheel can be disengaged with one finger when a wheel is jacked up, off the ground. The "Aussie Locker" engineering philosophy is based on two sets of opposing forces but simplified over other automatic locker designs. Basically there are two forces acting on the two gear sets. One acting to unlock the cam and axle gears by the gear tooth design and effects of the ground driven forces acting on a wheel when cornering. The other is acting to lock the cam and axle gears due to the camming action of the cross shaft and axle gear due to the 4 dimensional spiral cut cam grove with bearing surfaces under the effects of engine power Depending on the situation, the locker can either uncouple the driving gears i.e.

if the differential force is acting on a wheel to turn it faster than the wheel is being driven by the differential and engine, then that side can freely disengage and unlock providing differential action. Load transfer and strength The Aussie Locker design uses a large number of very low profile teeth which collectively do all the ramping and the driving. Engine power is transferred through the flats of all 20 teeth at the same time rather than the original standard differential which has only 2 or 4 teeth driving at a time with all the force being transmitted between two points on the curved surface of the pinion and side gear teeth. The Aussie Locker Has 2-5 times greater surface area over which to transfer the engine power. This means that the Aussie Locker can handle engine power often found in modified off road vehicles with large tires. The design of the locker result in the gears being locked when driving vs. the slipping and sliding that occurs when traditional spider and side gears turn and mesh. Constant 4WDs Like all automatic lockers, the Aussie Locker cannot be used in front axles of constant 4Wheel Drive vehicles. Some vehicle manufacturers offer a part-time 4WD option and automatic lockers can be installed.

Some vehicle owners install part-time kits or use free wheeling hubs. High-strength, ultra-resistant alloy made in the USA The Aussie Locker is made from an hardened 9310 alloy steel from mills in the USA. search Differentials explained – Drivingfast.net Advertise Differentials explained Spinning wheels are most likely to result from cornering while on the gas, pulling away from a stand still or accelerating in a car with lots of power Now a little more depth… Differentials – an introduction Before understanding why a limited slip or locking differentials are important, first we’ll briefly need to touch on why we need a differential in the first place. In simple terms, a differential is a device which allows for the differences in wheel speed which naturally occurs when a car turns a corner. As you can see in Diagram 1, the inside and outside wheels of a car turn in different radius corners, and thus need to rotate at different speeds (with the outside wheels travelling faster). However at least two of the wheels will also need to be linked to allow the car to be two wheel drive. Consider a front wheel drive car with the two front wheels linked together with no flexibility, such as with a solid axle between them.

Diagram 1: Cornering with a front differential In this case a certain amount of tension would build up when cornering as the outside wheel tries to rotate quicker that the inside wheel (due to the bigger arc it must go through). Eventually this tension would relive itself with a wheel skipping over the surface, or with a drive shaft snapping. This situation is obviously not a good one, so differentials where invented (see Diagram 2). Diagram 2: A basic differential positioned between two driven wheels As you can see, a diff is essentially a combination of cogs which work together to turn the wheels. It looks complicated, but it uses simple mechanics to allow the two wheels to rotate at different rates. Diagram 3: A close up of a differential How a differential works: The drive from the engine rotates the large yellow crown wheel (1), which is attached to the smaller blue cogs (2). These planetary gears can rotate freely, but work together to turn the green side gears, which are connected to the half shafts (3). If one wheel needs to rotate faster than the other, the green cogs permit this to happen. Simple really!

Limited slip differentials Differentials work by allowing a flexible distribution of drive between the wheels on an axle, which allows for the different rates of rotation while cornering. However this flexibility is also the differential’s weakness, as it will always allow drive to ‘escape’ via the easiest route. So if you are turning a corner while hard on the gas in a powerful car, you can find that the inside wheel starts spinning (due to the weight transfer leading to less grip), and you lose the ability to put power down on the road via the outside wheel. This isn’t good, especially if you’re trying to put in a good time on the track, and this is why the limited slip differential ( LSD ) was invented. The differentials shown in the diagrams above are known as ‘open’ diffs which means they have no mechanism to prevent this drive loss. The first LSDs connected the two half shafts together with a clutch pack allowing a limited amount of clutch slip between each side of the axle. This allowed for the relatively small differences in rotation while cornering, but prevented violent wheel-spin from just one of the wheels which could lead to loss of drive.

Types of limited slip differential Today there are a variety of differentials which can reduce unwanted wheel-spin on one side of an axle, which is prevented using either viscous, mechanical, hydraulic and electronic systems. A simplified example of a clutch type LSD is illustrated in Diagram 4 below. Many race bred cars have LSDs fitted as standard, especially powerful front wheel drive cars which are more prone to wheel-spin while pulling out of a corner. Diagram 4: A clutch type LSD (limited slip diff) In Diagram 4 above, the simple open differential has been fitted with a clutch (1). This clutch prevents the two blue side gears from freely rotating independently which can help in the occasions when drive loss would be an issue, however there is enough flexibility in the system to allow small differences such as when cornering. Clutch packs such as these as usually held together by a spring, which automatically keeps the clutch tight even when it has worn down. The strength of the spring determines how aggressive the LSD becomes. Featured articles Snow & ice driving myths Myth 1: ABS is a bad thing in winter conditions Anti-lock braking system It is true that when ABS is operating in slippery conditions, your stopping distance is likely to be increased.

However, ABS prevents wheel lock-up and allows you […] 2.972 How A Differential Works CLASS/YEAR: 3 MAIN FUNCTIONAL REQUIREMENT(s): Distribute power from car transmission shaft to a pair of Left-Right wheels (1ST FUNCTIONAL REQUIREMENT) while allowing wheels to rotate at different speeds (SECOND FUNCTIONAL REQUIREMENT). DESIGN PARAMETER: Differential HISTORY: The differential was first invented in China, in the third century, A.D. GEOMETRY/STRUCTURE: Components In A Differential System Gear Teeth: The crown wheel and drive pinion teeth are helical, allowing for up-and-down movement in rough or uneven road conditions. EXPLANATION OF HOW IT WORKS/ IS USED: Why use a Differential?: When a car turns a corner, one wheel is on the "inside" of a turning arc, and the other wheel is on the "outside." Consequently, the outside wheel has to turn faster than the inside one in order to cover the greater distance in the same amount of time. Thus, because the two wheels are not driven with the same speed, a differential is necessary.

A car differential is placed halfway between the driving wheels, on either the front, rear, or both axes (depending on whether its a front-, rear-, or 4-wheel-drive car). In rear-wheel drive cars, the differential converts rotational motion of the transmission shaft which lies parallel to the cars motion to rotational motion of the half-shafts (on the ends of which are the wheels), which lie perpendicular to the cars motion. In Turns, Wheels Are at Different Speeds Location of Differential In Car How it works: Assuming the wheels do no slip and spin out of control, the following two examples of car motion describe how the differential works when the car is going forward and when it is turning. (see Limited Slip Differential section for wheel slipping). Differential When Car Travels In Straight Line (Wheels at Same Speed) When the car is traveling straight, both wheels travel at the same speed. Thus, the free-wheeling planet pinions do not spin at all. Instead, as the transmission shaft turns the crown wheel, the rotary motion is translated directly to the half-shafts, and both wheels spin with the angular velocity of the crown wheel (they have the same speed).

Differential When Car Turns A Corner (Wheels 2 On Outside of Turn) When the car is turning, the wheels must move at different speeds. In this situation, the planet pinions spin with respect to the crown wheel as they turn around the sun gears. This allows the speed of the crown gear to be delivered unevenly to the two wheels. DOMINANT PHYSICS: Differential (mechanical device) | BikeParts Wiki | Fandom powered by Wikia Edit A vehicle's wheels rotate at different speeds, mainly when turning corners. The differential is designed to drive a pair of wheels with equal torque while allowing them to rotate at different speeds. In vehicles without a differential, such as karts , both driving wheels are forced to rotate at the same speed, usually on a common axle driven by a simple chain-drive mechanism. When cornering, the inner wheel needs to travel a shorter distance than the outer wheel, so with no differential, the result is the inner wheel spinning and/or the outer wheel dragging, and this results in difficult and unpredictable handling, damage to tires and roads, and strain on (or possible failure of) the entire drivetrain .

History Edit There are many claims to the invention of the differential gear but it is likely that it was known, at least in some places, in ancient times. Some historical milestones of the differential include: 1827 – modern automotive differential patented by watchmaker Onésiphore Pecqueur (1792–1852) of the Conservatoire des Arts et Métiers in France for use on a steam cart . (Sources: Britannica Online and [1] ) 1832 – Richard Roberts of England patents 'gear of compensation', a differential for road locomotives . 1876 – James Starley of Coventry invents chain-drive differential for use on bicycles ; invention later used on automobiles by Karl Benz . 1897 – first use of differential on an Australian steam car by David Shearer . 1913 – Packard introduces the spiral-gear differential, which cuts gear noise. 1926 – Packard introduces the hypoid differential, which enables the propeller shaft and its hump in the interior of the car to be lowered.

1958 – Vernon Gleasman patents the Torsen dual-drive differential, a type of limited slip differential that relies solely on the action of gearing instead of a combination of clutches and gears. Note: The Antikythera mechanism ( 150 BC – 100 BC ), discovered on an ancient shipwreck near the Greek island of Antikythera , was once suggested to have employed a differential gear. This has since been disproved. Functional description File:Transmission diagram.JPG The following description of a differential applies to a "traditional" rear-wheel-drive car or truck with an "open" or limited slip differential: Torque is supplied from the engine, via the transmission , to a drive shaft (British term: 'propeller shaft', commonly and informally abbreviated to 'prop-shaft'), which runs to the final drive unit and contains the differential. A spiral bevel pinion gear takes its drive from the end of the propeller shaft, and is encased within the housing of the final drive unit. This meshes with the large spiral bevel ring gear, known as the crown wheel . The crown wheel and pinion may mesh in hypoid orientation, not shown.

The crown wheel gear is attached to the differential carrier or cage, which contains the 'sun' and 'planet' wheels or gears, which are a cluster of four opposed bevel gears in perpendicular plane, so each bevel gear meshes with two neighbours, and rotates counter to the third, that it faces and does not mesh with. The two sun wheel gears are aligned on the same axis as the crown wheel gear, and drive the axle half shafts connected to the vehicle's driven wheels . The other two planet gears are aligned on a perpendicular axis which changes orientation with the ring gear's rotation. In the two figures shown above, only one planet gear (green) is illustrated, however, most automotive applications contain two opposing planet gears. Other differential designs employ different numbers of planet gears, depending on durability requirements.

As the differential carrier rotates, the changing axis orientation of the planet gears imparts the motion of the ring gear to the motion of the sun gears by pushing on them rather than turning against them (that is, the same teeth stay in the same mesh or contact position), but because the planet gears are not restricted from turning against each other, within that motion, the sun gears can counter-rotate relative to the ring gear and to each other under the same force (in which case the same teeth do not stay in contact). Thus, for example, if the car is making a turn to the right, the main crown wheel may make 10 full rotations. During that time, the left wheel will make more rotations because it has further to travel, and the right wheel will make fewer rotations as it has less distance to travel. The sun gears (which drive the axle half-shafts) will rotate in opposite directions relative to the ring gear by, say, 2 full turns each (4 full turns relative to each other), resulting in the left wheel making 12 rotations, and the right wheel making 8 rotations. The rotation of the crown wheel gear is always the average of the rotations of the side sun gears.

This is why, if the driven roadwheels are lifted clear of the ground with the engine off, and the drive shaft is held (say leaving the transmission 'in gear', preventing the ring gear from turning inside the differential), manually rotating one driven roadwheel causes the opposite roadwheel to rotate in the opposite direction by the same amount. When the vehicle is traveling in a straight line, there will be no differential movement of the planetary system of gears other than the minute movements necessary to compensate for slight differences in wheel diameter, undulations in the road (which make for a longer or shorter wheel path), etc. Loss of traction Edit One undesirable side effect of a conventional differential is that it can reduce overall torque – the rotational force which propels the vehicle. The amount of torque required to propel the vehicle at any given moment depends on the load at that instant – how heavy the vehicle is, how much drag and friction there is, the gradient of the road, the vehicle's momentum, and so on. For the purpose of this article, we will refer to this amount of torque as the "threshold torque". The torque applied to each driving roadwheel is a result of the engine and transmission applying a twisting force against the resistance of the traction at that roadwheel.

Unless the load is exceptionally high, the engine and transmission can usually supply as much torque as necessary, so the limiting factor is usually the traction under each wheel. It is therefore convenient to define traction as the amount of torque that can be generated between the tire and the road surface, before the wheel starts to slip. If the total traction under all the driven wheels exceeds the threshold torque, the vehicle will be driven forward; if not, then one or more wheels will simply spin. To illustrate how a differential can limit overall torque, imagine a simple rear-wheel drive vehicle, with one rear roadwheel on asphalt with good grip, and the other on a patch of slippery ice. With the load, gradient, etc., the vehicle requires, say, Template:Convert of torque to move forward (i.e. the threshold torque). Let us further assume that the non-spinning traction on the ice equates to Template:Convert , and the asphalt to Template:Convert . If the two roadwheels were driven without a differential, each roadwheel would be supplied with an equal amount of torque, and would push against the road surface as hard as possible.

The roadwheel on ice would quickly reach the limit of traction (400 Nm), but would be unable to spin because the other roadwheel has good traction. The traction of the asphalt plus the small extra traction from the ice exceeds the threshold requirement, so the vehicle will be propelled forward. With a differential, however, as soon as the "ice wheel" reaches 400 Nm, it will start to spin, and then develop less traction ~300 Nm. The planetary gears inside the differential carrier will start to rotate because the "asphalt wheel" encounters greater resistance. Instead of driving the asphalt wheel with more force, the differential will still symmetrically split the total amount of available torque equally. ~300 Nm is sufficient to make the ice wheel to spin, but the equal amount of ~300 Nm is not enough to turn the asphalt wheel. Since the asphalt wheel remains stationary, the spinning ice wheel will rotate twice as fast as before. As the actual torque on both roadwheels is the same – the amount is determined by the lesser traction of the ice wheel. So both wheels will get 300 Nm each.

Since 600 Nm is less than the required threshold torque of 2000 Nm, the vehicle will not be able to utilise the output from the engine, and will not move. An observer will simply see one stationary roadwheel on one side of the vehicle, and one spinning roadwheel on the opposite side. It will not be obvious that both wheels are generating the same torque (i.e. both wheels are in fact pushing equally, despite the difference in rotational speed). This has led to a widely held misconception that a vehicle with a differential is really only "one-wheel-drive". In fact, a normal differential always allows the transmission of equal torque to both driven roadwheels; unless it is a specific type of differential, such as locking, torque-biasing, or limited slip type. A proposed way to distribute the power to the wheels, is to use the concept of gearless differential, of which a review has been reported by Provatidis [1] , but the various configurations seem to correspond either to the "sliding pins and cams" type, such as the ZF B-70 available for early VWs, or are a variation of the ball differential .

Traction-aiding devices File:ARB Air Locking Differential (RLH).JPG There are various devices for getting more usable traction from vehicles with differentials. One solution is the limited slip differential (LSD), the most well-known of which is the clutch-type LSD. With this differential, the side gears are coupled to the carrier via a multi-disc clutch which allows extra torque to be sent to the wheel with high resistance than available at the other driven roadwheel when the limit of friction is reached at that other wheel. Below the limit of friction more torque goes to the slower (inside) wheel. If there is no load on one wheel then no torque goes to the other so the LSD provides no torque except for spring loading, but some extra effect can be obtained by partially applying the vehicle's parking brake when one roadwheel is spinning, as this can provide some resistance there to increase the overall torque , and allow the other driven roadwheel to move the vehicle. This only works where the handbrake acts on the driven wheels, as in the traditional rear-wheel drive layout. Naturally, the handbrake should be released as soon as the vehicle is moving again.

A locking differential , such as ones using differential gears in normal use but using air or electrically controlled mechanical system, which when locked allow no difference in speed between the two wheels on the axle. They employ a mechanism for allowing the planetary gears to be locked relative to each other, causing both wheels to turn at the same speed regardless of which has more traction; this is equivalent to effectively bypassing the differential gears entirely. Other locking systems may not even use differential gears but instead drive one wheel or both depending on torque value and direction. A high-friction 'Automatic Torque Biasing' (ATB) differential, such as the Torsen differential, where the friction is between the gear teeth rather than at added clutches. This applies more torque to the driven roadwheel with highest resistance (grip or traction) than is available at the other driven roadwheel when the limit of friction is reached at that other wheel. When tested with the wheels off the ground, if one wheel is rotated with the differential case held, the other wheel will still rotate in the opposite direction as for an open differential but there with be some frictional losses and the torque will be distributed at other than 50/50.

Although marketed as being "torque-sensing", it functions the same as a limited slip differential. A very high-friction differential, such as the ZF "sliding pins and cams" type, so that there is locking from very high internal friction. When tested with the wheels off the ground with torque applied to one wheel it will lock, but it is still possible for the differential action to occur in use, albeit with considerable frictional losses, and with the road loads at each wheel in opposite directions rather than the same (acting with a "locking and releasing" action rather than a distributed torque). An additional function of the conventional electronic traction control systems usually use the anti-lock braking system (ABS) roadwheel speed sensors to detect a spinning roadwheel, and apply the brake to that wheel. This progressively raises the reaction torque at that roadwheel, and the differential compensates by transmitting more torque through the other roadwheel – the one with better traction. In Volkswagen Group vehicles, this specific function is called 'Electronic Differential Lock' (EDL). In a four-wheel drive vehicle, a viscous coupling unit can replace a centre differential entirely, or be used to limit slip in a conventional 'open' differential.

It works on the principle of allowing the two output shafts to counter-rotate relative to each other, by way of a system of slotted plates that operate within a viscous fluid, often silicone . The fluid allows slow relative movements of the shafts, such as those caused by cornering, but will strongly resist high-speed movements, such as those caused by a single wheel spinning. This system is similar to a limited slip differential. A four-wheel drive (4WD) vehicle will have at least two differentials (one in each axle for each pair of driven roadwheels), and possibly a centre differential to apportion torque between the front and rear axles. In some cases (e.g. Lancia Delta Integrale , Porsche 964 Carrera 4 of 1989 [2] ) the centre differential is an epicyclic differential (see below) to divide the torque asymmetrically, but at a fixed rate between the front and rear axle. Other methods utilise an 'Automatic Torque Biasing' (ATB) centre differential, such as a Torsen – which is what Audi use in their quattro cars (with longitudinal engines ).

4WD vehicles without a centre differential should not be driven on dry, paved roads in four-wheel drive mode, as small differences in rotational speed between the front and rear wheels cause a torque to be applied across the transmission . This phenomenon is known as "wind-up", and can cause considerable damage to the transmission or drive train. On loose surfaces these differences are absorbed by the tire slippage on the road surface. A transfer case may also incorporate a centre differential, allowing the drive shafts to spin at different speeds. This permits the four-wheel drive vehicle to drive on paved surfaces without experiencing "wind-up". Epicyclic differential File:Epicyclic gear ratios.png An epicyclic differential uses epicyclic gearing to split and apportion torque asymmetrically between the front and rear axles. An epicyclic differential is at the heart of the Toyota Prius automotive drive train, where it interconnects the engine, motor-generators, and the drive wheels (which have a second differential for splitting torque as usual). It has the advantage of being relatively compact along the length of its axis (that is, the sun gear shaft).

Epicyclic gears are also called planetary gears because the axes of the planet gears revolve around the common axis of the sun and ring gears that they mesh with and roll between. In the image, the yellow shaft carries the sun gear which is almost hidden. The blue gears are called planet gears and the pink gear is the ring gear or annulus. Spur-gear differential Edit This is another type of differential that was used in some early automobiles, more recently the Oldsmobile Toronado , as well as other non-automotive applications. It consists of spur gears only. A spur-gear differential has two equal-sized spur gears, one for each half-shaft, with a space between them. Instead of the Bevel gear , also known as a miter gear, assembly (the "spider") at the centre of the differential, there is a rotating carrier on the same axis as the two shafts. Torque from a prime mover or transmission , such as the drive shaft of a car, rotates this carrier. Mounted in this carrier are one or more pairs of identical pinions, generally longer than their diameters, and typically smaller than the spur gears on the individual half-shafts.

Each pinion pair rotates freely on pins supported by the carrier. Furthermore, the pinions pairs are displaced axially, such that they mesh only for the part of their length between the two spur gears, and rotate in opposite directions. The remaining length of a given pinion meshes with the nearer spur gear on its axle. Therefore, each pinion couples that spur gear to the other pinion, and in turn, the other spur gear, so that when the drive shaft rotates the carrier, its relationship to the gears for the individual wheel axles is the same as that in a miter-gear differential. Non-automotive applications Edit A differential gear train can also be used to allow a difference between two input axles. Mills often used such gears to apply torque in the required axis. It's also used in fine mechanical watches with a hand to show the amount of reserve power in the mainspring. The oldest known example of a differential was once thought to be in the Antikythera mechanism .

It was supposed to have used such a train to produce the difference between two inputs, one input related to the position of the sun on the zodiac , and the other input related to the position of the moon on the zodiac; the output of the differential gave a quantity related to the moon's phase . It has now been proven that the assumption of the existence of a differential gearing arrangement was incorrect. [2] In the first half of the twentieth century, mechanical analog computers , called differential analyzers , were constructed that used differential gear trains to perform addition and subtraction . The U.S. Navy Mk.1 gun fire control computer used about 160 differentials of the miter gear type. Differentials, usually flat but also spherical, are used in wristwatches to allow the power reserve to be indicated. Power from the mainspring is split via the differential to the time indications and the power reserve indicator. Differentials are also used in watchmaking to link two separate regulating systems with the aim of averaging out errors. Greubel Forsey use a spherical differential to link two double tourbillon systems in their Quadruple Differential Tourbillon. Active differentials Edit A relatively new technology is the electronically-controlled 'active differential'.

An electronic control unit (ECU) uses inputs from multiple sensors, including yaw rate, steering input angle, and lateral acceleration – and adjusts the distribution of torque to compensate for undesirable handling behaviours like understeer . Active differentials used to play a large role in the World Rally Championship , but in the 2006 season the FIA has limited the use of active differentials only to those drivers who have not competed in the World Rally Championship in the last five years. Fully integrated active differentials are used on the Ferrari F430 , Mitsubishi Lancer Evolution , and on the rear wheels in the Acura RL . A version manufactured by ZF is also being offered on the latest Audi S4 and Audi A4 [3] . The second constraint of the differential is passive – it is actuated by the friction kinematics chain through the ground. The difference in torque on the roadwheels and tires (caused by turns or bumpy ground) drives the second degree of freedom , (overcoming the torque of inner friction) to equalise the driving torque on the tires. The sensitivity of the differential depends on the inner friction through the second degree of freedom.

All of the differentials (so called “active” and “passive”) use clutches and brakes for restricting the second degree of freedom, so all suffer from the same disadvantage – decreased sensitivity to a dynamically changing environment. The sensitivity of the ECU controlled differential is also limited by the time delay caused by sensors and the response time of the actuators. See also Four-Wheel, Front-Wheel, All-Wheel Drive – Making ‘Sense’ out of Making ‘Traction’ – » What color is the sky? (required - to prevent spam) Four-Wheel, Front-Wheel, All-Wheel Drive – Making ‘Sense’ out of Making ‘Traction’ – If you understand why it’s better to have the inside lane when you race in a 440-yard dash, then you’ll certainly grasp this next concept. To refresh your memory, when you run against several other individuals on an oval track each of you starts in a separate lane. The person on the inside lane is actually running on a slightly smaller oval; with each of the runners on the outside lanes running on slightly larger oval paths. That’s where that cliché term of being on the “inside track” comes from. Okay, so what’s this got to do with cars?

Well, this “inside track” principle is what requires your automobile or truck to have a differential. Whenever you make a right or a left-hand turn in your vehicle, the wheels on the inside of the turn rotate fewer times (smaller arc) than the wheels that follow the turn on the outside. WHAT’S THE ‘DIFFERENCE”? When making a right-hand turn through an intersection, for example, the right-hand (inside) set of wheels might rotate 10 times to complete the arc — while the left-hand (outside) set of wheels rotate 11 times — resulting in “different” rotation speeds for the wheels.That brings in the natural term “differential” as the name of the mechanical device that allows wheel speeds to differ on front- or rear-drive systems. Now, what would happen if both sets of wheels were rotating on the exact same shaft? Clearly, the tires would wear more quickly (as every right or left turn would bring tire scuffing) — caused by the resistance of the tire rotation differential (e.g., on the intersection turn described above: 10 rotations of the inside wheel versus 11 rotations for the outside wheel).

To solve this ‘differential’ challenge, early automotive engineers invented a mechanical solution: the “differential.” It’s hard to have been a motorist and not heard the term “differential,” yet many have not had the opportunity to understand what this device does. Now you know why vehicles need to have the device to accommodate wheel speed/rotation differences, or perhaps this is just a reminder. Though the differential is an asset on turns — balancing the distribution of twisting power between the left and right-hand wheels (left and right-hand axles) — it also has a weakness when it comes to distributing power. DISTRIBUTION OF DRIVE POWER You’ll quickly relate to this next consideration if you’ve ever found yourself stuck in snow or mud. Since the nature of the differential is to split distribution of drive power (technically, the twisting force is called “torque”), if one wheel begins to lose traction it actually transfers a greater amount of torque to that very wheel that is slipping. So you can actually be sitting in the snow with a right (or left) drive wheel spinning uselessly with no traction, while the opposite-side wheel sits still and yet has traction!

Automobile engineers have created another technical feature to help in slippery-traction conditions and it’s called the “limited slip” differential. As its name implies, this device limits slipping by helping ensure equal power distribution to both left and right drive wheels. The limited-slip type differential is generally an optional feature and makes the drive wheels function more like they’re on a single axle (while still enabling them to rotate at different speeds when the vehicle rounds a corner). Now that you’re more familiar with the terms “differential” and “limited-slip”, let’s move to front-wheel drive, four-wheel drive and all-wheel drive. During this most of the past century and into the 21st Century, both automobiles and trucks have mostly been propelled by rear-wheel drive. While front-wheel drive systems have been offered on some models, the rear drive design has been “conventional.” More recently, emphasis on fuel economy (lighter weight/fewer parts) and economies of manufacturing have resulted in a proliferation of front-wheel drive vehicles.

FRONT ‘PULL’ OR REAR ‘PUSH’ Rather than having an engine up front, a transmission mid-way and a differential/rear axle assembly in the back, front-wheel drive consolidates all this hardware in the front of the car. Today, front-wheel drive has become dominant in newer cars, making rear-wheel drive more of the exception. In addition to the advantage of incorporating both the transmission and the differential up front along with the engine in a “transaxle” to simplify construction, this design offers a traction advantage. Since all of the weight of the power system hardware is directly over the driven wheels, this enhances traction in mud and snow. The front-wheel drive layout also takes up less space than the rear-wheel drive arrangement, enabling increased space for cargo and passengers. At this point then the concept of four-wheel drive seems pretty straight forward, right? How about this: If you purchase a four-wheel drive vehicle that is not equipped with either rear “limited-slip” or front and rear “locking” differentials, then you’re not really getting a true four-wheel drive to all ‘four’ wheels. What?

‘ALL-FOUR’ FOUR-WHEEL DRIVE Again if you’re driving on mud or snow, then even with available power going to the front and rear wheels — those front and rear differentials will still ultimately drive only one of the front wheels and one of the rear wheels (whichever wheels have less traction!). Of course, you’ll still be better off than with conventional two-wheel drive, as you’ll at least have drive power from both the front (pulling) and the back of the vehicle (pushing). When a four-wheel drive vehicle adds limited-slip or available locking differentials, only then does the system actually live up to engaging all four wheels at the same time. But wait! What about “all-wheel drive,” isn’t that the same thing as four-wheel drive? Nope. While most four-wheel drive systems allow shifting from two- to four-wheel drive (disengaging the front-wheel drive system), all-wheel drive is a bit of a hybrid “four-wheel drive.” An “all-wheel drive” system incorporates engineering that actually directs power to the wheel, or wheels, that have the mosttraction — so that you get optimum road grip at all times.

Instead of delivering power simultaneously to both the front and rear axles, if only the front wheels have traction, then the all-wheel drive design transfers the majority of power up front — where it’s needed most (or the rear, or a combination of both). PRACTICAL ALL-WHEEL DRIVE The important note about all-wheel drive is that it does not necessarily mean four-wheel drive, as it can engage either front wheels or rear wheels. The nature of the “all-wheel drive” system is really “best-wheel drive,” since it’s more of a thinking drive system. This is why you are seeing more new passenger cars and vans offering all-wheel drive systems. Four-wheel drive systems are generally heavier-duty than all-wheel drive systems, and are more suited for off-road driving where terrain requires the complete engineering of four-wheel drive. But whether your vehicle is front-wheel drive, four-wheel drive or all-wheel drive, when it comes to the differences at least you now have the ‘inside track’.

Understanding 4WD systems - CNN.com Understanding 4WD systems Vehicles can have Part Time 4WD, Full Time 4WD or Permanent 4WD Part Time 4WD: Don't drive for extended time on dry pavement with 4WD engaged Full Time 4WD offers both two-wheel drive mode and 4WD Maintenance is extremely critical for locking hubs on 4WD vehicles Next Article in Living » By Tom Torbjornsen ( AOL Autos ) -- With the explosive growth of the light truck segment as well as the impending onslaught of winter, I thought it would be fitting to write about four-wheel drive systems. There are a few different types available; and there are special maintenance practices that might cause some confusion. So let's get enlightened! Four-wheel drive systems can make driving safer on wet road conditions. 4WD systems can be classified as Part Time 4WD, Full Time 4WD, and Permanent 4WD. Part Time 4WD is the most basic of all 4WD systems. It gives the driver the choice of driving in two-wheel drive or 4WD. That sounds pretty good! However, the downside is that you shouldn't engage the 4WD on pavement unless it's very slippery.

That's because, with this system, when you engage 4WD you lock the front and rear wheels together through the transmission and transfer gearbox. This is great for straight-ahead traction and very slippery surfaces. However, on dry pavement it makes for odd cornering, and handling characteristics. Also you can harm the drive train components by driving in 4WD for extended periods of time on dry pavement. Consequently, you may find yourself having to stop the vehicle to engage or disengage, depending on the road conditions. AOL Autos: Top 5 SUVs So why choose this type of system? Two good reasons: • It's less costly to build and therefore to buy Don't Miss AOL Autos: 10 cars that sank detroit • It's very durable under heavy stress (generally more durable than the other 4WD systems, since it has fewer components) Full Time 4WD is the most commonly used system on the market. Full Time 4WD offers both two-wheel drive mode and 4WD, depending on road conditions (driver must engage and disengage the 4WD). In addition, the 4WD mode offers both a high and low mode for when the going really gets tough (driver shifts to high or low).

AOL Autos: Top 5 crossover vehicles Besides a transmission and transfer gearbox, a center differential couples the front and rear wheels. This differential allows the front and rear wheels to turn at different speeds as needed (unlike Part-Time 4WD system) for better handling. When the wheels start to spin due to slippery road conditions, the system reacts to wheel spin by progressively locking the front and rear wheels together to optimize traction. Although Full-Time 4WD requires the driver to engage it, once engaged it offers more "control" through the high and low mode selection (based on road conditions) and better cornering and handling on varying road conditions due to the differential. AOL Autos: Best luxury wagons Permanent 4WD is similar to Full-Time 4WD but it has no two-wheel drive mode. The vehicle is always in 4WD, so you don't have to determine whether conditions are right to engage it. AOL Autos: Cars with best Blue Book values We still have transmission, transfer gearbox and center differential coupling the front and rear wheels. The only difference is that torque (or power) is constantly being applied to all the wheels, giving maximum traction in all weather and road conditions.

Current systems have high and low modes for when the going gets tough; however, most importantly, the system does the thinking for you ... it automatically applies as much lock up (to all the wheels) as necessary for maximum traction. AOL Autos: Best-selling trucks and SUVs Next, a few definitions of common 4WD-drive terms that you may have heard of: Locking Differential - locks both wheels on the axle, forcing them to turn together to allow maximum traction Limited-Slip Differential - detects slippage in one wheel and sends torque to the other wheel that is not spinning. It operates is automatically. On-The-Fly-Shifting - allows the 4WD to be engaged while driving the vehicle (many systems require that you stop the vehicle in order to engage the 4WD). Manual Hubs - In order for 4WD to work, you must have a means of engaging the front wheel drive mechanism. This is done through the front hubs. On vehicles equipped with manual hubs, the operator must manually "lock in" the front wheels by turning a mechanical switch.

Automatic Hubs - Instead of manually "locking in" the front wheels in order to drive in 4WD, automatic hubs "lock in" the front wheels by a simple flip of an electrical switch in the comfort of your warm, cushy, SUV or pickup. Transfer Gearbox - an auxiliary gearbox attached to the transmission, which allows you to shift into a high and low range of 4WD for serious pulling or hauling. 4WD Maintenance Tips 4X4s have a transfer case, locking hubs, and front and rear differentials (some have an additional center-coupling differential). The maintenance of the transfer case is the same as on a standard transmission. Therefore, when checking the fluid, you are checking for (1) proper level, (2) the presence of moisture, (3) the presence of wear particles... either in the form of metal or friction material. A small amount of wear material is acceptable. However, excessive wear material can be an indication of a problem. One of three types of lubricants is used, depending on the carmaker. These lubricants are: ATF (Automatic Transmission Fluid), 30W motor oil, or 90W-gear oil.

The maintenance interval (which involves changing the lubricant) for transfer cases that use ATF and 30W motor oil is every 50,000 miles. For 90W gear oil the recommended interval is 80,000 miles. In regards to the locking hubs, maintenance is extremely critical. Locking hubs come in two forms: automatic and manual. Regardless of which one you have, they must be disassembled, cleaned and lubricated every two years or 24,000 miles. Snow, ice, water, salt, and mud usually find their way into these mechanized units, rendering them useless and costing the owner big bucks! By keeping up the maintenance on them you minimize expense and downtime. With respect to differential maintenance, there's not a whole lot to do except check the fluid level every oil change and visually inspect for any leakage. The technician should check the gear lubricant for proper level, color, and consistency. Low lubricant level indicates a leak; a milky color indicates moisture in the lubricant; and the presence of metal in the lubricant indicates mechanical wear. Check your owner's manual for the recommended fluid change intervals.

And check your owner's manual for specific operating instructions of your 4X4 system because the various systems function differently. There you have it, four wheeling made easy. Now go out and climb a mountain! Jeep Capability | 4x4 FAQ and Glossary | Jeep Four-Wheel Drive A drivetrain that utilizes a transfer case to distribute engine power between the front and rear axles in order to drive all four wheels. Full-time four-wheel-drive systems utilize a center differential or transfer case, which enables the front and rear driveshafts to turn at different speeds, thereby allowing engagement on dry pavement for normal driving conditions. A part-time system does not employ a center differential and, during normal driving conditions, must operate only in two-wheel drive. With a part-time system, the four-wheel-drive mode is to be used only when off-road or on wet or slippery surfaces. Front Axle Disconnect A mechanical or vacuum-operated component used primarily on four-wheel-drive models to connect and disconnect drive torque to the front axle. When shifting from four-wheel drive to two-wheel drive, this system disengages the front axle from the front driveline, so that the front wheels aren't turning the front driveline unnecessarily.

This reduces unnecessary front driveline wear, noise and fuel consumption. Ground Clearance The distance between the lowest point on the vehicle and the road surface. Maximum ground clearance is typically measured when a vehicle is devoid of passengers, cargo and fuel. Under normal conditions, the ground clearance is usually lower. The better the ground clearance, the less chance of sustaining undercarriage damage. Jeep® 4x4 vehicles feature optimized approach, departure and breakover angles to keep you clear of logs, rocks and uneven ground. Neutral When the shifter is in this position, the front and rear axles spin freely. Sometimes used for towing a Jeep® vehicle behind another vehicle (such as a motor home), so that uncoupling the driveshafts is not required. Also used in the process of shifting into 4 Low. Open-Center Differential Located in the transfer case on some full-time four-wheel-drive vehicles, this component works in the same way as an open differential in the axles, but is of a more compact design. This component employs a planetary gearset, with planetary gears that revolve around the sun gear and inside the ring gear.

Question: What mechanical device allows the wheels of a vehicle to turn at different speeds when cornering?
Answer: Differential