What is OVERDRIVE mode and how to use it correctly

Given the great popularity of hydromechanical automatic transmissions, manufacturers manufacture this type of transmission in such a way as to achieve maximum user convenience and versatility. At the same time, there is also the task of reducing fuel consumption.

As you know, the most common today is a simple four-speed automatic. As a rule, these gearboxes have several standard and understandable operating modes, which greatly simplifies operation.

However, on many automatic transmissions, in addition to the basic ones, you can also find additional modes. In this article we will talk about what overdrive is on an automatic transmission, how overdrive on an automatic transmission is turned on and off, why this mode is needed and when it is used.

How to brake with a manual engine correctly

The deceleration mode of the engine and gearbox depends on the situation in which the car is located. More precisely, on the conditions of the road surface. For example, when driving on a flat road, engine braking will be different from driving down a mountain or on ice. Let's look at each mode in detail.

Rectilinear movement on a flat surface

These are the most ideal conditions. Drive along the highway in fifth gear. There is a turn or obstacle ahead. To apply engine braking, just release the gas pedal without pressing the clutch or changing gear.

The power unit remains in rigid coupling with the driving wheels of the vehicle. Since the fuel supply stopped when the gas pedal was released, the engine begins to “consume” energy. Torque is transmitted through the gearbox from the wheels to the crankshaft. Due to friction in the internal combustion engine and compression in the cylinders, this moment gradually fades away and the car begins to slow down smoothly. All this happens without the participation of brake mechanisms.

If at this moment you “squeeze” the clutch, the connection between the gearbox and the engine will be broken, the internal combustion engine will go into idle mode and the braking process will be interrupted. To continue it again, you need to smoothly move the clutch pedal until it “snaps” and release it. Don't forget about the speed of the car. If it is less than 20 km/h, the engine may stall. Therefore, it is recommended to use this maneuver at high speeds.

Let's go down the mountain

When descending a mountain, it is recommended to brake with a manual engine in lower gears. As mentioned above, if you do this in high gear, the efficiency will be low, the car will slow down smoothly and there is a chance that it will not fit into the turn. This is especially true on mountain serpentines.

To downshift:

1. Depress the clutch
2. Downshift
3. Use the gas pedal to raise the engine speed to 2500-3000 rpm. Smoothly release the clutch pedal. This way, you will “bring up” the engine speed to the speed of the input shaft of the manual transmission and there will be no impact on the clutch disc. You will protect the mechanism from damage
4. Release the gas pedal. You started to slow down with your engine.

A case from one's life. I had the opportunity to travel to the New World along the Crimean serpentines, where the descent was replaced by a sharp uphill through a sharp turn. I was driving in third gear, which was enough for me to use the brake pads minimally and slow down in time before the turn. Unfortunately, on such turns I often came across cars in a ditch - these were those who neglected the recommendations for effective braking with the gearbox and engine in mountainous areas and frequent use of the brakes.

We brake the internal combustion engine on ice or compacted snow

Engine braking on slippery roads in winter is an important skill that will protect you from skidding or drifting. It differs from the two modes described above. It is worth remembering that there is ice under the wheels, so the car’s behavior will be different.

Rules for how to properly slow down with a motor on ice:

1. Do not suddenly release the gas pedal. This will lead to wheel slip and loss of traction.
2. Do not release the clutch pedal sharply when switching to lower gears during engine braking. The car may skid. Because the wheels will sharply transmit torque to the motor, and since there is ice under them, their rotation speed will quickly drop. This is the equivalent of slamming on the brakes.

Which gear to choose and how to shift correctly

The VAZ 2110 shifts into reverse gear with a crunch.
In a VAZ 2112, when reverse gear is engaged, a crunching sound occurs in the same way when the gear is turned on. Well, it’s a very philosophical question. Let's think about it. We have six driving modes in a specific gear. Actually, now it is possible to systematize the gear selection algorithms (the value of the revolutions immediately before shifting, of course, conditional values, which may be different on your car):

And finally, I will answer the question of one of the readers: “Please describe the process of changing gears at speed, from low to high, and in what cases vice versa. If you can go into more detail, the order is of course clear: 1st - just to get going... then 2-3-4-5... But there are moments: you’re driving at 4 and there’s a traffic jam or a traffic light, you need to slow down, and then it’s green and traffic starts at a slow speed... is it necessary to switch to 3 or can you continue moving to 4, but slowly... and similar nuances...".

I usually focus on the situation and the flow speed in general. Let's say the cars ahead are accelerating, but it is clear that after 5-6 cars the flow is slowing down again. There is simply no point in accelerating and you can continue driving in the gear you were driving in, or you can turn it down and regulate the speed of the car by accelerating and braking the engine.

In my case, it all depends on my mood, the likelihood that someone will start squeezing in without warning and other factors, but most often I switch to low to keep the engine in good shape all the time, or in other words, in the zone of comfortable and powerful speeds.

Gear Modes

Let's take a closer look at how to use the transfer case on a Chevrolet Niva. It serves to switch to a lower gear and also blocks the center differential; this can be done at the same time. In order to engage a lower gear, you need to shift the lever to the right and up; to lock the lever, you need to pull it to the left all the way. The handle has the following designation:

• Low(L) - decrease;
• N-neutral;
• High(H) - normal, increased.

Low gear is engaged at a speed of no more than 5 kilometers per hour, or after a complete stop. In order to overcome a steep climb, or when driving where there is soft ground, so that the vehicle speed is minimal and at the same time stable, a lower gear must be engaged in advance. For example, if you are driving on a flat road in second or third gear, and a bad section of road appears in front of you, you need to stop and shift to a lower gear.

It is not recommended to turn on the center differential at high speed, since the car may skid strongly at the moment of switching. It is advisable to block where there is a slippery surface and the wheels begin to slip.

These include:

1. Switching the transfer case should only be done when the car is not moving.
2. You can also engage the differential while the vehicle is moving.
3. You can switch to a lower gear while the car is moving.
4. To ensure long-term and uninterrupted operation of the differential, it is necessary to periodically turn it on, especially in winter. This should be done once every 7 days.

Among domestic car enthusiasts, the Chevrolet Niva is a fairly popular SUV that appeals not only to fans of extreme driving, but also to fans of measured driving outside the city. Many people know that one of the features of a car of this brand is the presence of a transfer case in it.

Using this unit, you can enable downshifting, locking, or two functions at the same time, depending on the conditions. The question of how the Niva Chevrolet transfer case should be used correctly is of interest to many happy owners of such a vehicle and those who only intend to purchase it.

It should be immediately noted that you can engage both the lock and the transmission at the same time using the Chevrolet lever that changes gears. So, the lever shifts to the right, and then immediately up to engage a lower gear. To switch back to higher, the lever should simply be moved back.

Using a Niva Chevrolet transfer case, in addition to the above, neutral gear is also engaged, while the car will remain reliably in one place. The lock can be engaged at any time - in normal gear, in low gear - just switch the Chevrolet lever to the left.

This mechanism can operate in five modes:

• Neutral is on.
• The differential is unlocked when the "lowering" is turned off. In this case, the torque is distributed in a ratio of one to two.
• The differential is locked when overdrive is engaged. Here, torque distribution is carried out automatically, depending on the quality of wheel grip on the road.
• Downshift is engaged and the differential lock is disabled. The transfer of forces occurs in the same ratio as in the first case.
• The differential is locked and the gearbox is engaged. In this case, all axles are rigidly locked together, including the axle shafts. Torque is produced unevenly, depending on the type of road surface (dirt, sand, etc.). In this mode of operation, the best cross-country ability of the vehicle is achieved. But driving with a constantly engaged downshift and with locks will not work. This increases the load on the transfer case bearings. The Chevrolet Niva will soon require serious intervention in the transmission. Fuel consumption also increases significantly, which greatly eats up the tires.

Overdrive is... What is overdrive

Large English-Russian and Russian-English dictionary. 2001.

• rise in price
• step-up substation

See what “overdrive” is in other dictionaries:

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• Standard Vanguard - The Standard Vanguard model (“Standard Vanguard”, in Russian-language sources the incorrect “Standard Vanguard” is found) was produced by the Standard Motor Company in Coventry, England, from 1947 to 1963. Contents 1 Vanguard Phase I and IA 2 Vanguard... ... Wikipedia
• GOST R 51759-2001: Hydrodynamic transmissions for rolling stock of railway transport. General technical conditions - Terminology GOST R 51759 2001: Hydrodynamic transmissions for rolling stock of railway transport. General technical conditions original document: input traction power: Power equal to the difference between input power and power,... ... Dictionary-reference book of terms of normative and technical documentation
• MULTIPLIER - (Latin multiplicator, multiplying, increasing), in technology 1) a device for increasing the speed of rotation of a machine shaft (for example, an increasing gear drive). 2) A device for increasing fluid pressure (for example, in pumps and other hydraulic machines... ... Big Encyclopedic Dictionary

Why is low gear needed?

So, let's look at the example of an SUV. In this case, a reduction gear can significantly increase the vehicle's cross-country ability. In simple words, the presence of a downshift allows such a car to drive where cars with a conventional gearbox are not able to overcome the obstacle and continue driving.

Simply put, a low gear in the transmission allows the wheels to spin at a lower number of revolutions, while the engine operates in the standard speed range. This opportunity arises due to the fact that the transmissions of such cars use a transfer case (transfer case). In the transfer case, torque is distributed along the axles of the drive axles of the off-road vehicle.

To make it clearer, you need to pay attention to the following. Typically, the power unit produces maximum power at a certain number of revolutions

Also, at certain speeds, different from the speed of maximum power, the maximum torque is achieved, which is transmitted through the transmission to the drive wheels.

So, usually gearboxes are designed so that the engine delivers maximum torque and power fairly evenly at different speeds. The first gear allows you to move away, and in this gear the “emphasis” is on maximum torque, while in the 5th gear the car can move at high speed at maximum power speed.

For standard road conditions, such features of the gearbox are quite sufficient, but if it is necessary to overcome obstacles, difficulties arise. The fact is that, for example, when trying to drive uphill, and the surface is slippery or loose (snow, ice, mud, sand, softened soil), the torque in first gear is too high.

The result is that when you press the gas pedal, the car “buries” its wheels in snow or mud, slips and cannot continue moving. If you switch to second speed or higher, the engine will simply stall, since it does not have enough revolutions and power to overcome the difficult section.

It turns out that in a situation where you need high engine power (high speeds), but also need a smooth ride at low speeds and low wheel speeds, a conventional gearbox is powerless. It is with these features in mind that SUVs receive a transfer case with a low gear.

So, active low gear has a high gear ratio. This allows you to reduce the wheel speed and at the same time spin the engine to maximum power speed. As a result, the car is able to move at low speeds at maximum power speeds. This feature is indispensable on off-road terrain, when driving uphill, on steep descents, etc.

Winter driving on automatic

Installed modern car systems allow you to move from a place after a long period of inactivity in severe frosts. But this doesn't mean you need to rush. It would be better if you let the engine work without straining. Thus, when the oil mixture dilutes, the lubrication system is filled. As a result, the piston element will heat up. The manipulations will take no more than three minutes.

After starting the engine and pressing the brake pedal, you should move the automatic transmission to position D. This mode lasts about thirty seconds, then switches to reverse (R). Then you will have to wait a little, repeating these steps twice. The driver should lightly depress the gas pedal, initially holding the handbrake.

Proper movement on a snowy road requires maximum smoothness, without sudden acceleration and braking. A sufficient distance must be maintained between your car and the person driving in front. Don’t forget, when driving along a snowy road where there are often patches of ice, the activation of ABS will ensure that the vehicle moves in a straight line. At the same time, the braking distance will increase.

Purpose of double squeeze

Mechanisms such as synchronizers facilitate the process of gear shifting, making it smooth. At the same time, wear is reduced and the specific grinding noise characteristic of older models is also eliminated. If there are no synchronizers or they are broken, you cannot do without double squeezing.

So why is it really needed? The need is due to the equalization of engine speed by gears and shafts. Otherwise, these parts may jam at best. In practice, this happens as follows: moving at first speed, the engine speed is increased to three thousand revolutions. To switch to second, you need to release the gas, squeeze the clutch, go to neutral. Then wait until the speed drops and press the clutch again, switch to second. In this way, the shafts are equalized without damaging the gearbox. Then you can move on calmly.

In the case of re-gassing, the process is a reverse action. This implies reducing the gear without putting the gearbox to sleep. If you need to turn on the road, but it is impossible to do this in fourth gear, you must slow down and lower the gear. Otherwise, there is a risk of stalling. You can smoothly release the gas by squeezing the clutch and move to neutral. The next action will be to gain momentum. To do this, you will have to activate the gas pedal, in other words, make a shift. That's it, after that we managed to increase the speed. Synchronization with the shaft has occurred. You can now downshift and continue driving.

It is recommended to adhere to the throttle pause at neutral during the process. The main thing here is to catch the right clutch moment in time to prevent the car from stopping. Skills come with experience, of course. Therefore, there are no special skills or secrets here.

The question arises: why is this necessary when modern cars are equipped with synchronizers? If you remember that often the road is not perfectly smooth, there are always some obstacles.

Therefore, synchronizers may fail on the first bump or climb. This is where re-gassing comes to the rescue. For example, when going up, you realize that this transmission cannot pull you through. There are simply not enough revolutions, the throttle is overloaded. This allows you to switch to a lower gear without losing the necessary inertia.

How does overdrive work?

There is a button on the lever called “O/D (on|off)”, which controls the overdrive switching mode.

Pressing the OVERDRIVE (O/D) button provides the ability to enable or disable the automatic transmission shifting to fourth gear. To turn on overdrive, you just need to press a button, but no indication turns on. When the overdrive is turned off, when the button is pressed, it is indicated by a yellow indicator light with the inscription “O/D off” located on the instrument panel.

Subtleties of overdrive

What does overdrive on mean? This means that when accelerating, the transmission shifts sequentially from first to fourth gear, and then engages the torque converter lock-up. The last moment is accompanied by a slight push, which is perceived by some as a transition to fifth gear, although this is not true.

The reverse sequence results in a downshift during braking.

When overdrive is turned off, the ability to shift to a gear higher than third is blocked.

Why turn overdrive on and off?

Here is a clear example of how to use overdrive in the city. The car is moving on a long, gentle slope with heavy traffic and frequent changes in the speed of traffic flow - 40 - 60 km/h. If you turn on overdrive, you can feel a change in the operation of the gearbox. During acceleration, gears were shifted sequentially 1-2-3-4, sometimes the torque converter managed to lock up. The car moves at 60 km/h, with a minimum engine speed of less than 2 thousand. If the flow speed has sharply decreased, the brake is pressed, and the speed, accordingly, drops.

If at this moment the overall speed of the flow increases and there is a need to accelerate yourself, the car will not be able to respond quickly to this, since fourth gear will remain engaged, and the engine speed is clearly not enough for it. You can press the gas harder and the downshift will work. The result will be achieved and the gear will decrease and the engine speed will increase.

However, soon a similar situation will repeat itself again. Further, it is clear that such periodic switching becomes boring, travel comfort decreases, and the gearbox wears out when changing gears.

And if you now turn off overdrive, the result will be completely different. There are no switching speeds in this range. Driving has become more comfortable, the car responds more adequately to the gas pedal.

How does O/D work affect fuel consumption?

If overdrive is turned off, the gear is lower, and the speed is higher, then the car seems to be running at higher speeds. So it seems at first glance.

If you drive at high speed with overdrive turned off, then an increase in fuel consumption is quite possible.

If you use overdrive headlong, then measurements taken by specialists on various car models show that the difference, if it exists, is very unnoticeable. Therefore, I recommend taking up the practical use of overdrive and applying it in the right place at the right time.

How to use overdrive effectively

Manufacturers do not provide specific recommendations on this issue. Therefore, numerous recommendations are of a purely private nature. However, many drivers have developed them based on their own many years of experience, and they should be heeded. Having a minor problem, it is better to follow the advice of professionals. Over time, increased driving practice can produce its own changes, according to individual preferences and driving style. Some people prefer a quiet ride, without jerks or gear changes, while others pay more attention to fuel consumption. You can try everything, and then decide for yourself.

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It is reasonable to turn off overdrive when:

• long descents or ascents;
• “ragged”, periodically changing pace of traffic flow in urban environments;
• for more comfortable driving at speeds less than 50 km/h.

There is an opinion that you should turn off overdrive when overtaking while driving on the highway. However, many experts disagree with this for the following reasons:

• when overtaking, confusion is unacceptable, you should control the situation, and to work with overdrive you need to press a button, which means taking your hand off the steering wheel, which is no longer safe;
• If the car has a high speed, then turning off overdrive will cause a sharp increase in speed. However, there is no certainty that they will not reach the red zone.

In this case, the “brain” of the automatic transmission will think of everything itself and do what is needed in this situation. True, you also need to be able to use this technique, but that’s another story.

It is reasonable to turn on overdrive in the following situation:

• when driving on the highway;
• when driving for a long time at a constant speed;
• at high speeds, over 120 km/h.

How to use overdrive for beginners

Overdrive is a useful and necessary thing, but you need to know how to use it. Some professional drivers consider this small button to be absolutely indispensable. With experience comes the ability to predict the situation on the road; from the point of view of simple recommendations, you can turn on the required mode in time.

Conclusion!

If someone does not want to bother using this mode, we can advise not to do so. Overdrive, more of a service mode than a standard mode. Both the driver and his car will lose little if the “O/D on|off” button is never used.

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The automatic transmission has become no longer a luxury, but a common element of a large number of cars. The new switching method requires different skills and abilities from the driver. Not everyone knows about such a gearbox function as overdrive (o/d). Indeed, the developers of modern transmissions have left drivers with a lot to think about. Today you will learn everything about overdrive on an automatic transmission - what it is and how to use it.

Why do you need a gearbox with low gear?

Let's imagine a situation where, during a long climb in third gear, the engine does not have enough power to overcome an obstacle, and when switching to second gear, the number of revolutions is high. Then the downshifts come into effect. The car starts to move at high speeds, but at low speed. At the same time, engine power increases, and overcoming road obstacles becomes easier.

When the engine does not have enough power to overcome an obstacle, a reduced automatic transmission speed helps

A low-range gearbox increases torque at the wheels. The gear ratio of the secondary shaft increases, which in turn increases the speed of the axle. This property of the box is especially useful when overcoming small water obstacles, driving in icy or wet road conditions, especially on descents and ascents. And also when driving on “strong” off-road conditions, when in normal mode there is not enough power.

Downshift on SUVs Video

Turn on the "lower"

By starting a low-range gear, a large torque is transmitted to the wheel drive. As a result, difficult roads can be overcome without serious load on the engine.

This mode is not the only one on modern machines. The driver can also select other operating modes. You can save fuel while traveling on highways by switching the gearbox to high-speed operation. We often encounter the problem of traffic jams; in such a situation, it is logical to switch the gearbox to a mode not exceeding first gear. Typically this setting is used when driving at low speeds.

Why is low gear needed?

So, let's look at the example of an SUV. In this case, a reduction gear can significantly increase the vehicle's cross-country ability. In simple words, the presence of a downshift allows such a car to drive where cars with a conventional gearbox are not able to overcome the obstacle and continue driving.

Simply put, a low gear in the transmission allows the wheels to spin at a lower number of revolutions, while the engine operates in the standard speed range. This opportunity arises due to the fact that the transmissions of such cars use a transfer case (transfer case). In the transfer case, torque is distributed along the axles of the drive axles of the off-road vehicle.

To make it clearer, you need to pay attention to the following. Typically, the power unit produces maximum power at a certain number of revolutions

Also, at certain speeds, different from the speed of maximum power, the maximum torque is achieved, which is transmitted through the transmission to the drive wheels.

So, usually gearboxes are designed so that the engine delivers maximum torque and power fairly evenly at different speeds. The first gear allows you to move away, and in this gear the “emphasis” is on maximum torque, while in the 5th gear the car can move at high speed at maximum power speed.

For standard road conditions, such features of the gearbox are quite sufficient, but if it is necessary to overcome obstacles, difficulties arise. The fact is that, for example, when trying to drive uphill, and the surface is slippery or loose (snow, ice, mud, sand, softened soil), the torque in first gear is too high.

The result is that when you press the gas pedal, the car “buries” its wheels in snow or mud, slips and cannot continue moving. If you switch to second speed or higher, the engine will simply stall, since it does not have enough revolutions and power to overcome the difficult section.

It turns out that in a situation where you need high engine power (high speeds), but also need a smooth ride at low speeds and low wheel speeds, a conventional gearbox is powerless. It is with these features in mind that SUVs receive a transfer case with a low gear.

So, active low gear has a high gear ratio. This allows you to reduce the wheel speed and at the same time spin the engine to maximum power speed. As a result, the car is able to move at low speeds at maximum power speeds. This feature is indispensable on off-road terrain, when driving uphill, on steep descents, etc.

Demultiplier as part of the turning mechanism of a tracked vehicle [edit | edit code]

Some types of planetary turning mechanisms for tracked vehicles, the design of which includes two two-speed differential gearboxes, make it possible to implement the range-multiplier function through simultaneous group (paired) switching of both gearboxes from one operating mode to another - from high gear to low gear. In this case, as in the case of the range multiplier that is part of the gearbox, the output torque increases with a simultaneous decrease in rotation speed. This option is only a consequence of the ability of such turning mechanisms to provide two gear ratios for maneuvering and is not formally a range-multiplier, although it can be used like one.

Contrary to the widespread belief that there is a range option in the turning mechanisms of the vast majority of tracked vehicles, in fact it was present only on relatively old vehicles: British Cavalier, Covenanter, Crusader tanks; Czech tank LT vz.38; Hungarian Turan tank; Japanese tank 三式中戦車 (Chi-Nu); Soviet tanks IS-1, IS-2, IS-3, T-44, T-54, T-55, T-62; Soviet combat vehicles BMP-1, BMP-2; Soviet tracked tractor AT-S. Also, some little-used dual-flow turning mechanisms on modern vehicles, similar to those on the Panther tank, have a similar option: the Panther itself, the Soviet AT-L tracked tractor, the Soviet MT-LB and MT-LBu tracked combat vehicles.

First of all, let's say that the gears of any transmission are designed to regulate the speed of transmission of torque from the engine to the drive wheels. They are divided into direct ones, as well as those that increase torque and decrease it. Here we will talk in more detail about the latter type.

Low gear - operating principle

The low gear is part of the transmission and is mounted directly into the transfer case. It is there that the torque from the engine is distributed on the axis of the drive axles of the SUV.

Engines develop their full power at a given number of revolutions, and all torque is transmitted through the transmission to the drive wheels (each unit has its own speed threshold, at which it produces maximum torque). An ordinary gearbox is made so that the engine transmits all the power correctly and evenly at various speeds at which the car moves. For example, in first gear you can move away at a speed slightly higher than standard idle (for example, about 1000), and in fifth gear you can reach a high speed of several thousand. As a rule, engines develop their maximum power at just a few thousand revolutions. For some engines it is 2.5-3 thousand, for another it is under 6 thousand. It will not be possible to drive in first gear at such high speeds, so the engine power when driving will be far from maximum.

Consequently, it is no longer possible to drive onto a high obstacle - the engine will stall or the wheels will slip. The same is true when driving through mud, snow and other similar obstacles. In other situations, high engine power is required, but leisurely and careful driving is required - for example, on a rocky road with a cliff.

This is where downshifting comes in handy. And not only in these, but also in many others. What happens when you turn it on? Active low gear has a sufficiently high gear ratio, which allows the wheel speed to be reduced at maximum engine power. So it turns out that at low speeds the car operates at maximum power, which, with the proper approach, provides a huge advantage off-road, when climbing a steep slope and in other driving conditions.

Downgrade or accessible about complex

In our difficult age of nanotechnology and oil production in the Arctic, happy owners of “jeeps” are beginning to get used to turning on all-wheel drive with a beautiful button on the dashboard and rejoicing like children that they have a “real” SUV, but as soon as most of these monsters drive off-road from the asphalt, the owners begin remembering such an atavism as the lowering and swearing loudly at the overheated viscous coupling.

But you and I are real jeepers and we know that without lowering it’s not a jeep at all and life is bad without it, and that’s why when choosing a car we prefer, even if it’s from the last century and rotten like last year’s tomato, but still a real jeep. Not so long ago, in the process of building an iron horse, I had to delve into the question of what and why and with what it is eaten. Everyone talks smartly about some kind of Newtons, by the way, they like to mention them in test drives of any cars with such an air, as if the average car enthusiast is simply obliged to know how they affect the behavior of the car. Looking ahead, I will say that these numbers will not say anything if there is no understanding of what will ultimately reach the wheels. What got me the most was the arguments of more experienced comrades about which lowering of the transfer case is better: 4.16 or 4.9. For me personally, these are just numbers and there is no more meaning in them than in data on the population of Argentina. Strange numbers and clever words made my head spin and I wanted a button on the dashboard, instead of all this abstruse bullshit. But this is not our method, so I decided to figure out what kind of garbage this is and started studying the issue, in the process this article was born, since not a single sane source was found where the simple story was told, or rather, they were found, but they also wander into “abstruse distances” . I will try to explain everything as simply and clearly as possible. Let me make a reservation right away that in all calculations there will be many assumptions from the “let’s take one white horse in a vacuum” series, in particular we will not take into account friction losses, efficiency of units, etc., otherwise the formulas and calculations will be very long, whoever needs exact numbers will figure it out himself, we We will limit ourselves to a “general overview under ideal conditions.” So, take a deep breath and let's go!

We will assume that everyone knows the general principle of operation of the gearbox and there is no need to explain it, but if anyone is not in the know, then its task is to transmit the rotation of the engine, transforming it, depending on the selected gear, to the driveshaft, and then to the gearbox and wheels. But for driving without roads, it often turns out that “it would be necessary to lower it”; for this purpose they install a transfer case, that is, essentially another intermediate block of gears, which allows you to once again convert the rotation and lower the rotation speed. How it works? The simplest and most understandable example is a bicycle. Ever ridden a bike with a derailleur? Remember how it feels when the biggest gear is in front and the smallest in the back? It is very difficult to move a bicycle, but if it is moved, then for one revolution of the pedals it makes several revolutions of the wheel and flies like an arrow. What if it's the other way around? Yes, yes, you pedal in the soap, and the bike crawls like a turtle, but it crawls uphill and through mud and anywhere. Well, it’s the same with the lowering gear, only the engine works instead of you. In a lower gear, the load on the engine becomes noticeably less, and so does the speed, but it creeps anywhere and anyhow.

But on a bicycle everything is simple - two gears, on a car it’s also nothing complicated, but there are more gears and in almost every node the rotation is converted by one value or another. But let's take things in order. First, our engine spins a LARGE gear, which is called a flywheel. In the picture below, it's the big gear on the right.

Then this rotation is transmitted to the gearbox, then to the transfer case (if there is one), then through the driveshaft to the differential and then to the wheels.

Now mathematics and physics

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As soon as you start to understand the question, some scary numbers come up that the interlocutors operate with, and you, like a fool, don’t understand anything, but you’ve already realized that this much percentage reduction is cool, and if 1k is still a certain amount, “it’s a tractor” , and at the same time it can be lowered in bridges. All these conversations begin when the question of real off-roading arises, when the standard lowering is no longer enough to rotate the wheels from the tractor, which you, having seen enough of more experienced comrades, put on the car for some reason.

So, let’s try to figure it out together, using the Suzuki Jimny as an example.

Let me make a reservation right away: the numbers are approximate and taken from the Internet, I could be wrong. To begin with, we open the manual and find the following data:

— Gear ratios in the gearbox - Gear ratios in the transfer case - Gear ratios in the differentials

We also need torque on the internal combustion engine and wheel diameter. Specifically for a gym bike it looks like this:

— In standard differentials (gearboxes, call them whatever you want) it is 4.3 (although there are others) — Also from the book, the maximum torque of the Suzuki Jimny is 110 Nm at 4500 engine speeds.

The question remains of the wheel diameter. You can simply measure with a tape measure or calculate using the formula.

The standard Jimny wheel size is 205/70/15. This means that the wheel diameter is 2 profiles + rim diameter = 205mm x 70% x 2 + 15 x 25.2 = 665mm or approximately 26.4 inches.

Well, it seems like we’ve stocked up on all the initial data and are starting to calculate the scary numbers. Although no, before bothering your head with this garbage, you need to explain why it’s all. And this is necessary so that you can better understand the physics of vehicle movement and be able to calculate the optimal reduction under increased loads. After all, the manufacturer did not at all expect that its products would be stuffed glass deep into the swamp and, accordingly, if you want greater cross-country ability without damaging the units, then you should think about lowering the standard values.

To begin with, we have an engine that transmits rotation to the gearbox; at what frequency it rotates we can see on the tachometer. Then we delve into the performance characteristics of the gearbox and find out that in first gear the reduction is 2.962 (for the AT gearbox), that is, at the output after the gearbox, the driveshaft will make almost three times less revolutions, roughly speaking, for 1000 engine revolutions we will get 337 driveshaft revolutions shaft Next comes the transfer case with a reduced gear ratio of 2.145, that is, behind the transfer case we already have 157 revolutions, and then we go to the axles, to the main pair, which has a reduction of 4.3, with a total output at the wheels of 36.5 wheel revolutions per minute per thousand revolutions on the engine. The total reduction is: iob=2.962×2.145×4.3=37.32

We can also calculate the torque at the wheels - this characteristic is much more real than abstract horsepower or engine torque.

You can understand what torque is using a simple example. Let's take a stick and clamp one end of it in a vice. If you press on the other end of the stick, a torque (Mkr) will begin to act on it. It is equal to the force applied to the lever multiplied by the length of the force arm. In numbers, it looks like this: if you hang a 10-kilogram load on a lever one meter long, a torque of 10 kg*m will appear. In the generally accepted SI measurement system, this indicator (multiplied by the value of the acceleration of gravity - 9.81 m/s2) will be equal to 98.1 N*m. It follows from this that more torque can be obtained in two ways - by increasing the length of the lever or the weight of the load.

The motor produces torque Mdv. After conversion by the transmission, this moment is transmitted to each drive wheel of the car in the form of Mk and forces the wheel to rotate, i.e. it creates a shear force Fct = Mk/R at the point of contact of the wheel with the road, and this force is applied to the road through the wheel. The road surface prevents the wheel from rotating by a frictional force Fрт of the same magnitude, but applied to the wheel and directed in the opposite direction. To show that forces act on different objects, the points of application of forces in the figure are conditionally slightly spaced vertically:

This friction reaction force Fрт, multiplied by the number of driving wheels, moves the car. In relation to jimny, the accelerating force will be 4Fpt. Let's determine this value. The engine develops maximum torque Mdv=110 N.m at 4500 rpm. This means that in first gear in the gearbox with all our downshifts:

4Mk=Mdv.it=110×37.32 = 4105.2 N.m.

With standard size wheels, the traction force of all four wheels will be:

4Frt=Mdv.it/R=4105/0.332=12364 N=1236 kg.

That is, a little more than a ton. For comparison, for 1st gear without downshifting it will be only 557kg, and for third gear 437kg

Well, in general terms we figured it out. Of course, in real conditions, all these figures vary greatly depending on the relief, soil and other factors, but at least in general terms it became clear what and why. Again, if you want to lower the gear ratio in the transfer case or main pairs, now you can substitute your numbers to calculate what can come of it. In general, it is believed that for cars that conquer severe off-road conditions, the overall gear ratio should be from 50:1 to 80:1 with a manual transmission and from 40:1 to 70:1 with an automatic transmission.

So turn it down and go!

PS When writing the material, all sorts of different sources were used, in particular this one. I highly recommend it for those who want to delve deeper into the issue from the point of view of the physics of the process.

Source

Gear housings

Standardized cast gearbox housings are widely used in mass production. Most often, in heavy industry and mechanical engineering, housings are made of cast iron, less often of cast steel. When it is necessary to make the design as light as possible, light alloy bodies are used. The gearbox housing most often has attachment points - paws and/or ears, by which the gearboxes are moved and/or secured to the base. At the output of the shafts, seals are placed to prevent oil leakage. Structural elements are often placed on the gearbox housings to prevent an increase in pressure inside the gearbox resulting from the heating of the gearbox during operation.

In piece production, welded housings are widely used, allowing for individual design solutions.

Features of use

If the downshift does not engage, you should slow down the car, but it is best to make the connection before you start driving. When the clutch is depressed, the corresponding lever is moved to the required position. New cars have the ability to turn on electronically using a special button.

When using such a transmission, you cannot move on a hard surface, since the transmission will be subject to significant load at this time. To achieve maximum effect, you need to start at higher speeds.

It is important to monitor the clutch. Despite the fact that there is a decrease in the load on it several times, due to inexperience, damage can be caused by a sharp lowering after the engine reaches maximum speed

The low gear has a certain number. As it increases, the car begins to move more efficiently, regardless of the speed.

Extending the life of automation

First of all, the performance potential of the automatic transmission is determined by careful operation. An important factor that prolongs the durability of the mechanism is timely and high-quality maintenance.

The duration of a comfortable ride on an automatic transmission will be longer if you constantly monitor the oil level in the box. Using a dipstick from the engine will help sort this out. The main thing is to prevent leaks by changing the oil and filter. It is advisable to do this every 40–60 thousand km. Also, do not save money; it is better to use the original product.

In terms of operation, automation is many times more complex than mechanics. Moreover, such a transmission is more suitable for traveling around a metropolis. There’s just a nuance: the machine doesn’t like high overloads. Do not torture the system until it warms up. This is especially true in winter.

Once you change from a manual to an automatic, you can confidently say: you won’t change back.

Source

What are digital nomads like?

A prerequisite for digital nomadism is having a job that can be done from anywhere in the world with a stable and fast Internet connection. A digital nomad can be officially employed by one company, or be a freelancer with many clients, or even have his own business.

Our people go to the bakery by taxi

Banks and experts note changes in consumer standards

The main thing is that digital nomads are people who use technology to make a living while traveling. At the same time, they can either change host countries one after another, or lay low for some time in a place they like, if the visa regime allows.

Tuning – “How an ordinary Lada was turned into a sports car”

Off-road without reduction

SUV with reduction gear KIA Sorento

In recent years, the trend towards increasing the civility of SUVs and crossovers has acquired a scale that is depressing for experienced jeepers. Real SUVs are chasing comfort, which leads to an increase in their prices, and often to a decrease in cross-country ability and closer proximity to crossovers. Crossovers, in turn, are becoming more and more similar to asphalt machines. There are practically no frame SUVs left. Many people part with downshifts. Following the flagships, other SUVs are also becoming lighter. So the KIA Sorento has remained without a downshift since 2009. What can we say then about crossovers! The Porsche Cayenne S with a 6-speed Tiptronic S transmission has a reduction gear, but since 2010 the Porsche 958 Cayenne has received a new version of Tiptronic with 8 steps, but without a reduction gear. The designers of the Audi Q7 also abandoned downshifts. A general trend is visible, the paradox of which illustrates the “spiral” nature of development. Modern crossovers, or rather that part of them that has some claims to the title of SUV, are simply supplemented with 1-2 steps in the gearbox. The transmission of a quite “budget” Renault Duster is designed in such a way that it is better to start on the asphalt in second gear, and leave first for driving on questionable roads. Actually, their designers repeat the line of thought of the LuAZ developers. Only with other tasks. The buyer is inclined to pay more for comfort than for the capabilities of the car. This is probably a real change in the needs of the majority of motorists. And for true connoisseurs of free movement in different directions, there remain the indestructible simple cars of the last century and the off-road supercars of the new century.

https://youtube.com/watch?v=koKbdJUwEZ0

Application of reduction gear and differential lock

So, as we already understood, downshift is an additional gear that reduces the number of wheel revolutions at constant engine speeds. It is usually installed in the transfer case. Its presence makes the SUV more expensive, heavier and more complex. But on economy class cars it is not always installed; instead, the connection of the power take-off shaft to the rear axle gearbox occurs in the gearbox, in the downshift housing. Recently, there are fewer and fewer frame SUVs, and crossovers are moving closer to city cars. These cars often lack downshifts. Now there is a tendency that the priority is the presence of comfortable conditions in the car rather than its off-road qualities. Most manufacturers are switching to a monocoque body, and the frame structure remains a thing of the past. Real jeeps are still those SUVs that have a reduction gear and a differential lock, thanks to which they are not afraid of any obstacles.

Differential locking is necessary to increase cross-country ability. The differential itself is divided into interwheel and interaxle. Previously, cars did not have such technologies, so their absence had a negative impact on the safety of elements in the structure. The wheel differential allows the wheels to rotate at different speeds; this is necessary, for example, if the car is making a turn. But its presence can lead to the fact that when slipping, the engine power will go only to the wheel that is stuck, while the other will be stationary. When the differential is locked, the engine energy will be distributed equally between the wheels, and thus the car will be able to overcome the obstacle.

The center differential is similar in its principle of operation: it allows the front and rear axles to move at different speeds and along different trajectories. But in some situations this can significantly complicate control: if the front wheels are stuck, the rear ones will be inactive. Locking the center differential can successfully solve this problem. SUVs, known for their excellent cross-country ability, are usually equipped with three locks: rear, front and center differential.

What's the result?

As you can see, low gearing in a car that is positioned as an SUV is a necessity. In this case, the efficiency of the reduction gear itself will depend on the gear ratio.

Finally, we note that the driver must also be able to use downshifts correctly, since errors can lead to breakdowns of both the transmission itself and, in some cases, the car engine itself.

All-wheel drive device, types and types of all-wheel drive, diagram of the drive device on all-wheel drive cars. All-wheel drive boxes, features.

Gearbox differential: what is it, differential design, types of differentials. How does a gearbox differential work in a car transmission?

Which gear to choose and what is the correct shifting algorithm is a seemingly trivial question, but only for those who are used to driving a manual transmission and have been doing this for quite a long time. The note is intended for those who intuitively have switching skills. To gain basic knowledge, I recommend that you first read the note.