What is a gearbox demultiplier

IX International Student Scientific Conference Student Science Forum – 2017

A demultiplier is a transmission mechanism that is designed to increase torque. Many truck drivers also call it a splitter. But they are a little different, a little later on about that. This box is an auxiliary or transfer case, which has a lower range of gears. Usually, the demultiplier is used on cars, for operation in harsh conditions, when even for driving uphill with a large load, the usual number of gears is not enough. If the driver feels, that the engine works “hard” in the used gear and the revs would be prohibitive in a lower gear, switching the demultiplier to a lower gear makes the intermediate ratio, that is the gear is divided in half. [1]

The demultiplier extends the life of the transmission, due to the fact that it increases power evenly, by reducing the load. Simply put, the splitter increases the number of gears by 2 times, and thereby increases the vehicle’s traction force. It is turned on with a button on the lever, or a toggle switch, thus selecting the lower or higher range of gears.

As I said above, the demultiplier and the divider are slightly different. The splitter has a straight and upshift, and the demultiplier is just the opposite, straight and downshift. The demultiplier and divider can be installed together. If the box is a 4-speed, there will already be 16 gears, because as the splitter doubles the gears, so does the demultiplier. The direct transmission of the gearbox is the mode in which the engine revolutions are transmitted without increasing or decreasing, i.e. the torque is transmitted from the motor to the wheel axles directly. The efficiency in this case is very high, because the torque does not pass through the intermediate shaft.

The overdrive gear, as many know, is used to save fuel, also because of the low engine speed, in an overdrive gear, engine wear and noise emanating from the engine is reduced. The driveshaft rotates faster than the engine crankshaft when the overdrive gear is engaged.

In a downshift, the engine produces high revolutions at low speeds. Such a gear is needed to get higher torque, in cases where the engine is hard. For example, when a long steep uphill, or when driving off-road. In a lower gear, the motor will not overheat, when operating in harsh conditions. [2]

Figure 1 – Demultiplier Transmission (Shift Mechanism)

1, 5 – levers; 2 – shackle; 3 – box shaft; 4 – lock; 6 – damper;

The entire demultiplier mechanism consists of the shaft lever, fork shaft and fork. For shifting between rows, a pneumatic actuator of the shifting mechanism is used. The actuator itself consists of a valve block, pneumatic cylinder and connecting hoses. Compressed air is supplied to the block from the vehicle’s pneumatic system. When a downshift or reverse gear is engaged, compressed air enters the pneumatic cylinder and is thereby engaged. When the remaining gears are engaged, the compressed air supplied to the air cylinder activates a forward gear in the demultiplier.

The demultiplier, like all parts of the gearbox, is lubricated with oil, which is poured into the crankcase. A mixed lubrication system is used: pressure lubrication, splash lubrication, and oil mist lubrication. The demultiplier is lubricated by a pressurized oil pump. [3]

To operate the vehicle’s demultiplier and splitter, in most cases either automatic or semi-automatic shifting systems are used, without any additional shift levers of any kind. If higher gears are needed, an additional lever is used to operate the demultiplier, and a mandatory full stop of the vehicle is required to avoid unwanted, major transmission malfunctions. [4]

On demultiplier transmissions it is strictly forbidden:

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-shift from higher to lower range of gears at speeds greater than 30 km/h;

-Drive with gear lever in neutral;

-shift into reverse when driving, at an incomplete standstill.

In the demultiplier, gear shifting is automatic, i.e. the highest gear is engaged when the gearbox control lever is shifted from the fourth to fifth gear position, the lowest gear – when shifting from fifth to fourth gear.

When operating the gearbox with a divider, to shift, you must move the divider control toggle switch to the desired position, then after a short delay of the clutch (1 second) you must release the clutch pedal, and thus the gear will be automatically engaged.

Figure 2 – Scheme of switching gears by the divider

Summing up all written, we can say that the use of demultiplier and divider in gearboxes, both trucks and off-road vehicles, is simply necessary. Having experience in operating a truck, I can say that if the transmission worked in normal mode, the engine would simply overheat when transporting heavy loads, in fact, so would the box, and that would lead to the failure of these units. And repairing the engine and box would never be cheap, and it would take a lot of time, too. Therefore the splitter and demultiplier will save not only fuel, but will help to serve the engine and transmission for a long time, naturally, at correct operation of the car.

List of references

1. Demultiplier // ru.wikipedia.org URL: https://ru.wikipedia.org/wiki/Демультипликатор (accessed 12.03.2017).

2. Demultiplier gear arrangement // auto.today URL: https://auto.today/bok/5777-ustroystvo-peredach-demultiplikatora.html (date of reference: 12.03.2017).

3. gear shifting mechanism in demultiplier gearboxes // http://carspec.info URL: http://carspec.info/mnogovalnye-korobki-peredach (accessed 12.03.2017).

4. Splitter, demultiplier and continuously variable transmissions // http://www.chopper-bike.ru URL: http://www.chopper-bike.ru/view_invited_paper.php?id=228 (accessed 12.03.2017).

5. Features of the organization of service stations // Shakalov I.P., Prokhorova E.V. In the collection: Education, Science, Production Belgorod State Technological University. V.G. Shukhov. 2015. с. 1149-1151.

6. Application of additive technologies in mechanical engineering and manufacturing spare parts for cars // Matrenin A.V., Prokhorova E.V. In the collection: “The country lives while the factories work” Collection of scientific papers of the International scientific and technical conference. Editor in Chief Ovchinkin O.V. 2015. pp. 215-217.

7. The quick release of the main units and assemblies and repairability of vehicles // Prokhorova E.V., Sevryugina N.S. Bulletin of the Kharkov National Automobile and Road University. 2012. № 57. с. 97-103.

8. The solution of applied problems of optimization of stability of system “environment-man-technics”// Sevryugina N.S., Melikhova S.B., Volkov E.A. Modern Applied Science. 2015. Т. 9. № 3. с. 200-207.

What is a demultiplier?

Owners of trucks are often faced with a situation where when driving under load it becomes impossible to ensure optimal speed without overloading the engine. With passenger vehicles, such a problem does not arise as acutely. In such cases, it is considered appropriate to have an intermediate gear, the torque which is able to take the average value between each of the neighboring gears. It is clear that the designers could not but pay attention to this problem and therefore created a special mechanism, and at once in two variants. The first demultiplier helps to increase the torque at the expense of halving the number of gears. The second is a splitter which increases the number of upshifts.

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Synonyms are common in Russian: divider (a direct translation of the term “demultiplier”), additional gearbox , transfer case with a reduced gear.

Gearbox ZF 16S181 with open back crankcase, 3, 6 – 8 – planetary demultiplier

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What is a demultiplier and where is it used?

Most often demultipliers are installed on trucks, where you need more power at relatively low rpm. At the same time a sharp shift from one gear to another, especially if the vehicle is thoroughly loaded, causes a sharp drop in shock load on the gears while driving and breaking the transmission.

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Therefore, with the help of a lower gear it is possible to significantly reduce these same loads and get a very good effect of optimum operation of the vehicle.

The demultiplier can work both permanently (most trucks) and temporarily (in all-wheel drive passenger cars, this function is disabled simultaneously with the disengagement of all-wheel drive). In some types of modern vehicles, it works only with the lowest gears (usually first and second), until the moment when the car can reach a certain speed.

Depending on the manufacturer, model, and intended use, demultipliers can be:

In cars with increased cross-country capability and the ability to switch to all-wheel drive, to engage the demultiplier you may usually need to initially stop the car (if you are in motion, you will have to pull over to the curb to engage the demultiplier), and only then engage it.

In fact, is an integral part of the gearbox. Adjustable by manually or automatically shifting gears. On the lever (if shifting is manual) one can find a special flag signaling that the car is engaged in downshift.

In this simple way, the number of gears of the car actually doubles, which makes it possible to freely overcome even difficult climbs. They are ideally suited in cases when a trailer or a tow-bar is additionally hitched to the vehicle.

What is a demultiplier, its location

To begin with, let’s try to understand what a transmission demultiplier is, in what cases it is needed and where it is installed.

The demultiplier, which is sometimes called a reduction gearbox, is an additional unit of the box, which allows you to get double the number of gears. Its job is to create intermediate driving modes with half the intermediate increase in power, which, if used correctly and in a timely manner, extends the life of the entire transmission. Timely use should be understood as driving under load when none of the available gears provide optimum driving performance.

Simply put, the demultiplier reduces the load level on the transmission gears, doubling the total number of gears.

This additional transmission unit is located behind the gearbox, occupying basically little space and allowing increasing the traction of the vehicle when engaging any straight gear.

Let’s explain it on a concrete example. Let’s say your car is heavily loaded and you are driving on a section with a very gentle and long uphill slope. The fourth speed is unacceptable for you, as the car simply does not pull, and such mode is fraught with many troubles for the power unit. Everything seems to be normal at third speed, there is enough traction, but you are forced to move at less speed, than it would be possible, as increase in revolutions would lead to sharp growth of fuel consumption. But if there was one more gear between third and fourth, it would allow you to move in an optimal mode for the powertrain and transmission. That’s what the demultiplier is for: it offers this possibility. Activation of the device, as a rule, is carried out with the help of the button, located on the gearbox lever. Let’s note that it is possible to realize the possibility of doubling speeds by both increasing and decreasing the gear ratio. Devices of the first type are called demultipliers, the second – dividers. In principle, they have similar tasks, but the implementation mechanism is different.

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As a rule, the demultiplier is installed on vehicles designed for operation in severe conditions, when the usual number of gears in the gearbox is not enough. For example the driver feels that at the necessary driving speed the engine is running in 4th gear with an overload, and the RPM in 3rd gear is too high, the engine is “overkill”; by shifting the demultiplier (divider, additional gearbox) into a lower gear, the intermediate gear ratio in the transmission is obtained.

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How is a demultiplier constructed?

The splitter is a two-stage planetary type reducer, which has a small number of toothed gears. It is installed in front of the main box. The disadvantage of such a design solution is that at the input of the gearbox there is a certain increase in torque, as a result of which an increase in mass of the latter is required. Such a problem could be solved by installing the device behind the gearbox. However, this position is reserved for the demultiplier, which technically cannot be mounted at the front. The design of the demultiplier itself does not differ much from the splitter. At the same time its inclusion does not lead to an increase in the load on the basic box. The range of degrees for it is limited to 4. At higher values certain difficulties are observed.

More details about the principle of operation of the gearbox with a demultiplier and divider will be described in this video:

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For example, on some models of KAMAZ vehicles between the clutch and the gearbox a splitter (additional two-stage gearbox) with a direct and an overdrive gear is installed. When the vehicle is not loaded, the driving takes place in a high gear of the demultiplier, when operating with a heavy load (for example, towing a trailer or a semi-trailer, especially in adverse road conditions) the driver switches to a direct demultiplier gear. In this way, the vehicle has twice as many gears instead of five. With the demultiplier direct gear engaged, the total gear ratio of the gearbox is lower. For example, the ratio of the 5th gear with the demultiplier turned off (5th lowest) is between the ratios of the 4th and 5th gears with the demultiplier (highest).

On the gear lever of trucks with a divider is a switch (“checkbox”), connected by a flexible cable to the gas distributor. After the driver makes a shift on the lever, he presses the clutch pedal and the executive pneumatic actuator shifts the gear in the divider. Some transmissions have two dividers – one on the input (the divider proper, also called “half gears” in the jargon) and the other on the output (the demultiplier). The splitter is used in all gears, including reverse, for a slight change in gear ratio, and the demultiplier shifts the transmission between lower and higher gears, and is engaged by rocking the transmission lever fully to the left and right or by using an additional key on the side of the transmission lever.


This is the case with the Scania GRS905 and ZF 16S151 gearboxes, for example. Structurally it is a 4-speed manual transmission (four forward gears and one reverse gear), supplemented by a splitter and demultiplier. Acceleration and driving at low speeds is done with the demultiplier (on the lower row), which lowers the output shaft speed by 3.75 times (for GRS905 box). 16S151 allows engaging gears 1-4 or reverse (R), for GRS905 – gears 1-3, as well as “creeping” gear (very slow, C) or R. After acceleration to a certain speed the driver shifts to the upper range (the demultiplier is switched off, by brief movement of the lever from neutral to the right or by lifting the side key), the transmission ratio drops by 3.75 times and gears 1-4 become gears 5-8 – the 1st gear of the main gearbox after switching off the demultiplier gives the effect of 5th gear, 2nd gear becomes 6th and so on.

What is a planetary gearbox and how it works

The main transmission gears on the upper row are shifted with the same lever movements as on the lower row. The lever is moved from upshift to downshift by rocking the lever from neutral to the left or by dropping the side key, but at a speed of no more than 20-50 km/h so that no engine or transmission damage occurs because of the sharply increased gear ratio. The divider operated by the front key can be used in any gear, including reverse.

Off-road vehicles

On off-road vehicles, the transfer case has two gears, a higher gear (usually straight) and a lower gear (downshift), as well as a neutral. The downshift is blocked on vehicles with disconnected front drive axle (cannot be engaged with disconnected front axle).

In the car “Ural-377” (a variant of all-wheel drive “Ural-375” with wheel configuration 6×4 without a leading front axle) transfer case, of course, is absent, instead there was an additional gearbox with direct and downshift gears.

Foreign cars .

Some cars with all-wheel drive (developed on the basis of cars with front-wheel drive), such as the Toyota Sprinter Carib, Subaru cars with a manual transmission have an additional downshift first gear, which is engaged only when the rear axle is connected.

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Demultiplier as a part of a tracked machine’s steering mechanism

Some types of tracked planetary turning mechanisms which design includes two two-speed differential gears, allow realizing demultiplier function by simultaneous group (pair) switching of both gears from one mode of operation to another – from the high gear to the low gear. In this case, as in the case with the demultiplier, which is a part of the gearbox, there is an increase in torque at the output with a simultaneous decrease in speed. Such an option is only a consequence of the ability of such turning mechanisms to provide two gear ratios for maneuvering and formally is not a demultiplier, although it can be used like one.

Contrary to the widespread opinion that the vast majority of tracked vehicles have a demultiplier option in their steering mechanisms, in fact it was present only on relatively old vehicles: British Cavalier, Covenanter, Crusader tanks; Czech LT vz.38 tanks; the Hungarian Turan tank; the Japanese 三式中戦車 (Chi Nu) tank; Soviet tanks IS-1, IS-2, IS-3, T-44, T-54, T-55, T-62; Soviet armored fighting vehicles BMP-1, BMP-2; the Soviet tracked tractor AT-S. Also has such an option some less used on modern vehicles dual-flow mechanisms like on Panther tank: Panther itself, soviet AT-L caterpillar tractor, soviet MT-LB and MT-LBU caterpillar armored fighting vehicles.

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The step-up gearing

The overdrive gear used in the reducers of “divider” type allows selecting the sparing driving modes and is used mainly for long trips at high speeds (of course, for trucks). In addition to saving fuel, which in such cases can be significant, the use of the divider allows to reduce noise levels when working combination of the engine – transmission, reducing the load and wear of the power unit.

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When the splitter is engaged, the driveshaft begins to rotate at a higher speed than the engine’s crankshaft. The splitter doubles the number of gears on the vehicle, both forward and reverse. But if the machine has other gears (e.g. reduction gears), it will not be possible to use them simultaneously.

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The use of demultipliers in the automotive world

We have discussed what a demultiplier and splitter is, learned what a downshift and upshift are. Now we can safely move on to the use of the demultiplier in the automotive world.

It’s vital for trucks like Ural and KAMAZ (they use it on a regular basis), as well as for off-roaders (you can disable the multiplier when driving on an even surface). When driving on rough terrain or in adverse conditions, it saves fuel and significantly increases cruising speed.

Demultiplier serves to increase torque at low speed, which adds so to say “power” to your car.

Demultiplier is also used in agriculture – it is installed on tractors and caterpillars. This gives an opportunity to get additional “traction”.

Demultiplier is a necessary device, both for trucks and off-road vehicles. In this article, we looked at the specifics of the demultiplier and divider and where and in what situation you need to apply one or the other additional gearbox.

In fact, for a passenger car demultiplier is not something vitally necessary, but do not forget that cases are different and it is better to put something, at first glance unnecessary than “kill” your engine in attempts to drive out of the swamp, which can turn “dirt track” after a prolonged rain.

See also:

Which vehicles use multipliers and dividers

Heavy-duty trucks of domestic production (Ural, KrAZ, KamAZ) are equipped with multipliers as standard. This solution provides an opportunity to double the number of used gears if necessary, which is very important when transporting multi-ton cargo and driving on rough terrain. In this case, an optimal loading of the power train and transmission is achieved with a smoother increase in traction of the truck.

In essence, the auxiliary transmission enables each gear to be used in a double mode: a nominal mode and a lower/higher mode. The second mode is intermediate between the two adjacent gears.

Demultipliers are also often installed on off-road vehicles (UAZ, Toyota SUVs, Subaru). Since this category of vehicles is usually equipped with all-wheel drive, it is important to be able to disable both the downshift and all-wheel drive if, for example, you have to drive on a high-speed section of the highway on flat terrain.

Such an implementation optimizes fuel consumption and allows you to drive at cruising speed if necessary. However, the inclusion of all-wheel drive without stopping the vehicle is not possible (this rule has exceptions, but only on some off-road vehicles of the latest generations).

It is useful to include demultipliers also in the transmission of tracked vehicles for agricultural purposes. Additional reduction gear enables to increase the traction of agricultural machinery at critical moments, as well as to control the vehicle more adequately when overcoming various natural and man-made obstacles. Structurally, such demultipliers differ from their counterparts installed on wheeled vehicles, but the principle of operation remains the same. The use of the planetary turning mechanism in the caterpillar vehicles does not affect the operation of the reduction gear: both separate side of the drive gears and both tracks can be decelerated simultaneously.

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