To what temperature does the gearbox heat up. General characteristics of gear oils

24.09.2019

14. APPLICATIONS

Appendix A. Gearbox

A.1 Transmission maintenance

The ZF service team is at your disposal for maintenance work on the gearbox and for problem solving.

Good maintenance means reliable transmission operation. It is particularly important that the necessary maintenance work be carried out correctly.

Danger for the environment!Lubricants and cleaning agents must not enter the ground, ground water or sewers. Ask the environmental authority in your area for safety data sheets for the respective products and follow them. Collect used oil in containers of sufficient size. Dispose of used oil, dirty filters, lubricants and cleaning agents in accordance with environmental regulations. Observe the manufacturer's instructions when handling lubricants and cleaning agents.

To fill the Ecomat gearbox, oils must be used according to the ZF Lubricant Specification TE-ML 14. The volume and brand of oils to be poured are indicated in the Chemmotological map.

Oil level control

Maintaining the correct oil level is critical. Too little oil leads to damage to the gearbox and incorrect operation, to partial or complete failure of the retarder, i.e. to reduced or no braking force. Too much oil leads to overheating of the gearbox.

Oil level control must be carried out together with maintenance in a service center with a frequency of 1/4 year. Checking the oil level must be carried out on a horizontally standing car and at the operating temperature of the gearbox. It is necessary to carry out a constant visual check for leaks in the gearbox. In exceptional cases, it is necessary to check on a "cold" gearbox (measurement of the approximate value). Then always check at operating temperature.

Control at operating temperature

The determining factor is level control at a transmission oil temperature of 80-90°C. To do this, put the vehicle in a horizontal position, switch the controller to the neutral position. In this case, the engine must run at idle speed.

CAREFULLY! The idling speed should be set between 500 and 700 min -1 .

The oil level should be in the warm range after about two minutes.

Reference value measurement

This is an oil level measurement done with the gear oil cold. Such control is carried out in the following exceptional cases:

When putting the gearbox into operation for the first time;

After a long idle time or when taking someone else's vehicle;

After the repair of the gearbox in the vehicle: for example, the removal of the oil sump, hydraulic control, heat exchanger for oil cooling, etc.;

After an oil or filter change.

The measurement of the reference value consists of two steps:

Control before starting the engine;

Control after starting the engine.

Then check at operating temperature.

Control before starting the engine

The oil level must be in the range indicated by "n motor. = 0" or higher.

NOTE!

If the level is higher, do not drain the oil.

Control after starting the engine

The engine should idle for 3 to 5 minutes (controller in neutral). Then measure the oil level. The oil level must be in the range indicated by 30 °C

Possibility of heating transmission oil

Gear oil during normal operation of the vehicle with retarder cycles can be heated to an operating temperature of 80-90 ° C in an oil bath provided to control the oil level.

If normal operation of the vehicle is not possible (winter season), then the transmission oil should be warmed up as follows:

Apply the parking brake.

Select gear ratio range "D".

Engage the brake mechanism of the service brake system.

If necessary, start the engine several times for 15 to 20 seconds at partial load at a speed of 1200 to 1500 min -1 .

Maximum allowable oil temperaturein front of the heat exchanger is 110°C (constant). After each warm-up phase, start the engine for 15 to 30 seconds with the gearbox in neutral at a speed of 1500 to 2000 rpm.

After reaching operating temperatureput the gearbox in neutral position and run the engine at idle for 2-3 minutes.

Then check the oil level according to paragraph 3.3.1.

Oil change interval

The oil change interval is determined according to the ZF lubricant specification TE-ML 14 and is indicated in the car's chemotology chart.

ATTENTION! The oil filter must be renewed at every oil change.

When changing from a mineral based oil to a partially synthetic oil, hydrocracked or synthetic ATF, it is recommended to have an unscheduled oil change in the middle of the oil change interval.

Oil drain

Drain the oil only at operating temperature and for at least 10 minutes after the engine has stopped.

The engine is at rest.

Unscrew the screw plug (1) (Fig. 14.1) of the oil drain hole and drain the oil.

Remove the filter cover (2).

Renew filter element, copper rings and O-rings.

Oil filling

Put on the filter cover 2 (Fig. 14.1) (screw tightening torque 25 Nm).

Screw in the oil drain plug (1) (tightening torque 50 Nm).

Pull out the oil level indicator (3) (Fig. 14.2).

Fill with oil.

Check oil level.

Rice. 14.1 Draining the oil.

Load cell setting control

The setting of the load cell must be checked after maintenance work on the gearbox or engine, during sudden shifts and at least every 3 months.

A prerequisite for the inspection is the correct setting of the motor. The control can be carried out by means of markings on the front side or on the top side of the housing.

For control it is necessary:

Turn off the engine;

Apply the parking brake;

Slowly depress the accelerator pedal to the actuation point (fuel pump full load stop), but no further than this point.

Rice. 14.3 Load cell setting control.

Maintain the position of the accelerator pedal (the marking of the load sensor lever must match the marking of the full load (high) on the housing).

Release the accelerator pedal to idle speed (the marking of the load sensor lever must match the marking of idling (low) on the housing).

ATTENTION!

Do not use stops on the load cell housing for adjustment.

Do not loosen the screws on the load cell body or the nut on the shaft.

Check ball heads for wear (too much play) and for grease.

A.2 Gearbox control Gearbox control features

The car is equipped with a controller. Depending on the configuration, a push-button switch or a joystick can be installed

Rice. 14.4 Controller (joystick) positions: R - reverse; N - neutral; D - automatic range of gear ratio change for forward movement (Drive);1, 2, 3 - limited ranges of gear ratio change for forward movement.

Engine startingonly allowed when the vehicle is at rest (brake on), the controller is in neutral ("N"). If the controller is not in the neutral position, the engine cannot be started.

CAREFULLY! Do not turn off/on the ignition while driving.

When shifting gearsyou must adhere to the following rules:

The controller must be in the neutral position.

The accelerator pedal must be in the idle position and n dvig.< 900 min -1 .

It is necessary to select the desired range of gear ratio change.

CAREFULLY! You cannot operate the controller and depress the accelerator pedal at the same time.

When operating a gearbox with the additional "gear release" function, the following rules must be observed when shifting gears:

The controller is in the neutral position.

The accelerator pedal is in the idle position and n dvig.< 900 мин -1 .

Select the desired gear ratio range and apply the brake. The system engages the appropriate gear only when the brake is applied.

For starting off, you needafter selecting the appropriate gear ratio range, wait approx. 1 to 2 seconds, release the brake and depress the accelerator pedal.

DANGER! On steep slopes, immediately depress the accelerator pedal after disengaging the brake. There is a danger of an accident due to the vehicle rolling backwards.

CAREFULLY! At temperatures below -15 ° C, do not move. Allow the engine to warm up at idle for approximately 5 minutes. Put the controller in neutral position.

Each gear ratio range corresponds to a certain range of gears. Gearshifts will only occur at specific shift points determined by the electronic automatic shifter. It makes no sense to manually intervene in the process of automatic gear shifting (sequential inclusion of gear ratio ranges).

DANGER! If the transmission is shifted to "N" while driving, the power flow between the engine and transmission is interrupted. This means loss of engine and retarder braking action. RISK OF ACCIDENT IS HIGH! The brake must be applied immediately. For safety reasons, in the event of a malfunction in the electronic automatic gearshift device or in the event of a power failure, the transmission is automatically shifted to the "neutral" position.

When driving on steep slopes, select the desired gear ratio range 1, 2 or 3 on the controller. In this way, the inclusion of higher gears is limited.

DANGER! In an extreme situation, to protect the engine, the mechanism that blocks the inclusion of higher gears is canceled. In this case, regardless of the selected gear ratio range, the gearbox can shift to the highest gear. RISK OF ACCIDENT IS HIGH! Follow the speed indicator!

When changing the direction of the vehicleBefore switching from forward to reverse or vice versa, the following conditions must be met:

The vehicle must be at rest.

The accelerator pedal must be in the idle position and n dvig.< 900 min -1 .

The controller must be in neutral position, if necessary, press the brake pedal.

Put the controller on D, 1,2,3 or R.

kick-down mode

Rice. 14.5 Kick-down mode.

To use the maximum engine power, higher switching points can be called up via the kick-down switch (fig. xxx) or CAN (for acceleration or on slopes). To do this, you must press the accelerator pedal beyond the point of full load (kick-down position).

Retarder Mode

The retarder is a hydrodynamic brake, gear-dependent and wear-free. It is advisable to use the retarder each time you brake. Thus, the working brake system is saved. The retarder can be activated using hand and/or foot controls.

Conditions for retarder mode (Retarder on/pressed):

Accelerator pedal in idle position.

The forward gear must be engaged.

Driving speed more than about 3 km/h

In this case, the system prevents higher gears from being engaged (upshift inhibit).

Rice. 14.6 Retarder mode.

CAREFULLY! If the accelerator pedal is depressed, the retarder is released. The action of the mechanism that blocks the inclusion of higher gears is terminated.

The retarder must be turned off when there is ice, when the oil temperature is above 150 °C. In the mode of operation of the retarder, a maximum oil temperature of 150 ° C is allowed (maximum 5 minutes).

ATTENTION! After each braking, the lever must be disengaged.

Stop, parking.

The vehicle can be stopped at any time, regardless of the position of the controller. The electronic automatic gear change device then shifts to the appropriate gear used for starting off.

For short stops it is necessary to apply the brake, the range of change of the gear ratio can remain on.

During long stops, it is necessary to put the controller in the neutral position and apply the brake.

The special version of the transmission "Neutral at Stop" (NBS) automatically shifts to "Neutral" if the following conditions are met:

The vehicle is at rest;

The parking brake is on;

The accelerator pedal is in the idle position.

As soon as one of the three conditions is not met, the shift to 1st gear is automatically performed immediately.

When parking, you must put the controller in the neutral position and apply the parking brake.

ATTENTION! Be sure to apply the parking brake when leaving the vehicle. When the engine is not running, there is no direct connection between the engine and the axle. The vehicle may roll away.

Towing

When towing a vehicle with a working gearbox, the following conditions must be met:

The controller must be in the neutral position.

The maximum duration of towing is 2 hours.

The maximum towing speed is 20 km/h. At ambient temperatures below -15 °C, the towing speed is 5 km/h.

If a gearbox failure is suspected, the cardan shaft between the gearbox and transfer case or the cardan shafts between the transfer case and drive axles must be flanged off.

As an exception, in dangerous situations, towing out of the immediate danger zone (eg intersection, tunnel, etc.) is also permitted without separating the drive chain.

Oil temperature limits

Oil temperature in front of the oil cooling heat exchanger in retarder mode, in exceptional cases, for a short time (maximum 5 minutes within an hour), a temperature of 150 ° C is allowed.

The oil temperature in front of the oil cooling heat exchanger in torque converter mode, the temperature limit for continuous operation is 110 °C, and in exceptional cases, for a short time (maximum 5 minutes within an hour), a temperature of 130 °C is allowed. During normal driving, the allowable temperature range is 90 -100°C.

The temperature of the oil in the oil bath of the gearbox must not exceed follow values even at high ambient temperatures: _

If the corresponding permissible oil temperature is exceeded, the following measures must be taken:

Partial load driving in low gear ratio range

Disable retarder.

If this does not lead to a decrease in oil temperature, then it is necessary to stop the car, put the controller in neutral position and move the engine to a higher speed.

If after a few seconds the temperature does not drop to the allowed range, then the possible causes are:

Too low or high oil level;

Faulty coolant circulation;

Transmission failure.

Checking the temperature of the gearbox is carried out by the diagnostic system of the electronic device for automatic gear shifting each time the on-board voltage is turned on, as well as during operation. An overheating of the oil in the gearbox is indicated by the ignition of a signal lamp on the block of control lamps of the electronic systems of the Kamaz 6560 car.

To protect the transmission in the event of a malfunctionthe following actions are provided:

Switching to the neutral position (in case of severe problems in the transmission voltage supply, for example, a short circuit);

Emergency vehicle operation mode.

For the emergency operation of the vehicle, special times and pressures are entered in the electronic automatic gearshift device to control the pressure. Besides:

The retarder does not work;

The Neutral at rest (NBS) function is not active;

The engine brake is not activated;

Torque converter lock-up clutch (WK) open;

Engine torque limitation to protect the gearbox (no engine control).

Transfer case

Engage high gear/neutral/low gear.

Gear shifting is carried out only on a stationary vehicle with a stationary input shaft. During the shift, it is necessary to interrupt the transmission of torque from the engine by engaging the clutch.

ATTENTION: switching mechanism - with cam clutches; to avoid damage, gear shifting must be carried out according to the rules.

Rice. 14.7. Pneumatic shifting: up and down gear 2 or 3 positions withlock, no spring.S- Conclusion - the highest gear;G- Conclusion - downshift;N- Output - neutral.

Enabling MOD lock

Rice. 14.8. Enabling MOD lock.

This transfer boxprovides a constant drive of the front axle through the center differential, that is, it is impossible to turn off the drive of the front axle. When slipping one or more wheels, it is recommended to turn on the differential lock. Blocking is carried out by means of an integrated working cylinder with a compressed air control pressure of 6.5-8 bar.

The differential lock can be engaged while driving,briefly engaging the clutch.

Avoid driving with the differential lock engaged on hard roads with good traction. Exception: steep ascents and descents.

To turn off the MOD lock while driving, you can not turn on the clutch.

After passing the section requiring differential lock, the lock should be turned off.

NOTE: slow turning off of the control lamp after turning off the front drive or blocking the MOD is not an error in the transfer case system. This is caused by a delay in the transmission in a certain position, which is eliminated when the dog clutch is disengaged after several load changes or steering wheel turns.

Turning on the PTO

The PTO N200 is switched on by means of a built-in working cylinder at a compressed air pressure of 6.5-8 bar. Before engaging the PTO, depress the clutch pedal and wait 5 seconds for the input shaft to stop. For the PTO to work on a stationary car, you need to set the neutral position of the transfer case. The indicator switch confirms that the box is off.

IMPORTANT: When switching on the PTO, the input shaft of the transfer case must be in a stationary state!

The clutch pedal should be released smoothly to avoid damage to the dog clutch if the PTO is not fully engaged (tooth-to-tooth engagement position)

Before disengaging, stop transmission of torque from the engine by disengaging the clutch.

When the vehicle is stopped, the PTO must be switched off!

Due to the slow pressure drop in the pneumatic system, the PTO is switched off by a pressure spring.

When the engine is started, the pressure rises again and the dog clutch engages itself.

If the transfer box input shaft is moving during this, the gear connections may be damaged.

Car towing

It is allowed to tow the car in any gear of the transfer case (high, neutral and low).

The driving speed must be chosen so that the permissible speed for the transfer case is not exceeded.

RULE: vehicle towing speedhigher or lowergear must not exceed 85% of the maximum permissible vehicle speed in the corresponding gear in normal mode.

Since in this case the cardan shaft connecting the transfer case to the gearbox comes into motion, the instructions of the gearbox manufacturer for towing the car must also be observed.

Vehicle towing speed neutral gear must not exceed 85% of the maximum permissible vehicle speed in top gear.

Towing a car with the front wheels raised is only allowed when the cardan shaft connecting the transfer case to the rear axle is disconnected.

In the event of a malfunction in the compressed air supply system, the neutral position in transfer boxes equipped with a pressure spring changeover mechanism can be switched on by screwing in the screw.

Rice. 14.9.

Instructions: Loosen locknut and screw inadjusting screw 1 to the stop.

ATTENTION: after each movement of the adjusting screws, it is necessary to adjust the switching mechanism, which must be carried out by qualified specialists

Conservation and storage

Optimal storage conditionsare achieved when the product is stored indoors, in a workshop or garage with moderate ventilation, relative humidity of not more than 60% and at a temperature of 15° to 20°C.

Before running in, the transfer boxes are filled with oil. Residual oil in the box can serve as temporary corrosion protection.

If the planned storage period exceeds 4 months, it is necessary to preserve the product as described below.

1. remove the breather and close the breather hole in the crankcase with a stopper;

2. fill the box with oil;

3. turn the box about its center so that the inner cavity is completely filled with oil;

4. During the cranking of the input shaft, turn on the higher / lower gear twice, drive the front axle or block the MOD, and also turn on the PTO;

5. store upright.

When stored in optimal conditions(storage indoors at a relative humidity of 60%) work according to paragraphs. 3-5 should be repeated every 6 months.

In more difficult conditionsin arctic or tropical climates, with a high salt content in the air (near the sea) pp. 3-5 should be repeated every 4 months.

ATTENTION: do not forget that before turning on the transfer case, you must install the breather in place!

The gearbox contains numerous moving parts which, when rubbing against each other, can release a large amount of heat energy. To cool the moving mechanisms of an automatic transmission, a special gear oil is used, which simultaneously cools and lubricates the moving parts. Problems in the lubrication system invariably lead to an increase in the operating temperature of the automatic transmission. In this case, the temperature of the coolant can reach 120 degrees or more, at which the lubricant loses its properties and increased wear on the gearbox begins.

Consequences of overheating automatic transmission

Automatic transmission overheating leads to failure, friction clutches and other moving elements. In some cases, even 10-20 minutes of operation of the gearbox in overheating mode is enough, which leads to serious breakdowns and the need for major repairs. That is why, at the first signs of overheating, as a rule, this is evidenced by the sensors built into the gearbox, it is necessary to turn off the car and transport it to the service on a tow truck. In this way, you can avoid significant problems caused by prolonged operation of the gearbox at elevated temperatures. During prolonged operation of the gearbox with an increased operating temperature, problems with the geometry of the hydraulic plate and the control unit may occur. It should be remembered that a control unit that has failed due to overheating cannot be repaired and therefore requires an expensive replacement. It is for this reason that the car owner needs to closely monitor the condition of the gearbox and, when the first messages about oil overheating in the automatic transmission appear, contact a specialized service center.

It also happens - with severe overheating, the torque converter turned blue, and the ventilation pipes melted

Causes of overheating

Let's describe automatic transmission overheating causes that need to be eliminated. The most common cause of transmission overheating is insufficient pressure in the cooling system. This happens due to insufficient oil level or problems with. The car owner needs to closely monitor the oil level in the gearbox and, if necessary, replace it.

Cooling problems can occur due to improper operation of the solenoids. The solenoids are located in the hydroblog and actually act as electrovalves in the lubrication and cooling system. If necessary, an appropriate signal is sent to the solenoid, the valve opens and oil flows to the moving elements, lubricating and cooling them.

Also, overheating of the gearbox can be caused by problems with the oil heat exchanger. This often happens when the heat exchanger is dirty, the cells of which are clogged with wear products, which does not allow the hot oil from the gearbox to be effectively cooled in the heat exchanger, which leads to an inevitable increase in temperature.

Signs of automatic transmission overheating - Video

How to eliminate automatic transmission overheating?

Gearbox repair for problems with overheating consists in diagnosing, which allows you to determine the cause of the temperature rise. An experienced craftsman will be able to quickly localize the problem and repair the gearbox as soon as possible. In most cases, to eliminate overheating of the automatic transmission, it is necessary to clean the valve body and the external heat exchanger. This work is a certain complexity, since it is required to dismantle the hydraulic unit and remove all the pipes that lead from the box to the heat exchanger. Cleaning can be carried out using modern technological means, which allows to ensure the maximum quality of the repair. All this eliminates the problem of overheating.

Cleaning the hydroblock in case of overheating

The automatic transmission has greatly simplified the process of driving. The standard automatic transmission is quite simple to operate and unpretentious to use. With proper care, it can work for a long time without any complaints. But if the driver does not follow the box, it may fail for a banal reason, for example, due to overheating. It can lead to tangible problems in the operation of the automatic transmission, which will require costly repairs or replacement of the unit.

Table of contents:

At what temperature should the automatic transmission operate

The automatic transmission contains ATF, which acts as a torque-transmitting link between the engine and the wheels. During the operation of the automatic transmission, the transmission fluid is heated, from which other elements of the gearbox can heat up. This can lead to final overheating if used improperly.

It is believed that the optimum ATF temperature for automatic transmission operation is between 65 and 100 degrees Celsius. If the temperature of the liquid in the box is exceeded, there is a high risk of damage to its components.

Please note: Specially for cooling the ATF fluid in modern cars, a radiator is used through which the fluid flows and cools.

What causes automatic transmission fluid overheating

As noted above, overheating of the ATF fluid in an automatic transmission can lead to a number of serious problems. Consider the most common of them:

As you can understand, automatic transmission fluid overheating is extremely dangerous and can lead to various problems.

How to detect automatic transmission overheating

An overheating automatic transmission is accompanied by the following symptoms:

The automatic transmission “kicks” when shifting gears - jolts and jerks are felt, which were not there before;
Transfers are switched at the raised turns;
Gear shifting is not always timely;
Some gears may not be included, for example, from the second box it will immediately jump to the fourth;
The overheating icon on the dashboard is on;
There is a smell of burnt ATF.

On some car models, it is possible to find out basic information about the operation of the nodes through the on-board computer. Among this information is often the temperature of the fluid in the gearbox. As noted above, if the temperature exceeds 100 degrees Celsius during operation, this indicates overheating.

Please note: On cars that do not have the automatic transmission fluid temperature control function by default, you can install a special diagnostic device, for example, ELM 327, which allows you to monitor the main parameters of the car, including the temperature in the automatic transmission.

Causes of automatic transmission overheating

Most often, automatic transmission overheating occurs for one of the following reasons:

Problems with automatic transmission fluid. If ATF does not change over 150-200 thousand kilometers (depending on the resource of the filled liquid), it begins to perform its functions worse. Over time, the additives in the liquid burn out, various debris appears in the liquid itself, and a precipitate forms. As a result, the circulation of such liquid becomes difficult;
Radiator problems. As noted above, automatic transmissions use a radiator to cool the ATF fluid. If it does not perform a function, for example, it is very dirty, this will lead to cooling difficulties, which will result in overheating of the box;
Many motorists know that it is not recommended to tow cars with automatic transmission, and it is also not recommended to act as a towing vehicle if your car has an automatic transmission. This is due to the fact that when towing a car, the automatic transmission may overheat and the wear of the box may increase;
Slip. Another problem that seriously harms the automatic transmission. If the car slips in place at high speeds, this leads to a strong heating of the box.

Please note: Many modern cars have protection against automatic transmission overheating, and the box turns off when it gets too hot.

As a rule, if the automatic transmission is in good condition and operates in optimal modes, it facilitates the process of driving a vehicle.

At the same time, even on new cars with an automatic transmission, the owner may encounter the fact that. Also, the gear oil in the machine may darken too quickly, etc.

Quite often, the cause of such failures is overheating of the automatic transmission. Next, we will look at how to understand that the automatic transmission is overheating, the reasons why the automatic transmission overheats, and what needs to be done in this case.

Read in this article

Overheating of the automatic box: consequences and signs

So, we note right away that a significant increase in the temperature of the transmission oil in the machine usually manifests itself in the form of certain malfunctions in the operation of the automatic transmission.

Ignoring such symptoms can lead to a reduction in the resource of the unit itself or breakdowns. In other words, in this case, the automatic transmission often fails, after which an expensive overhaul is required or.

We go further. The reasons for overheating of the automatic transmission can be different. First of all, in the unit itself there are a large number of loaded elements that interact with each other. As a result, a large amount of heat is generated, which is removed by the ATF transmission fluid.

It becomes clear that problems in the automatic transmission or gas turbine engine, a deviation from the norm of the oil level in the machine, a decrease in ATF pressure, and the loss of the properties of the transmission fluid itself lead to an increase in the temperature of the automatic transmission. In some cases, the oil in the gearbox is heated up to 120 degrees or more.

Such heating is critical, the oil loses its properties, the unit malfunctions, and the wear of the box increases significantly. The consequences of automatic transmission overheating are manifested in the form of a breakdown, as well as a number of other elements of the gearbox.

In practice, after a couple of tens of minutes, the operation of the automatic transmission in the maximum heating mode will be enough for the unit to fail. For this reason, it is important to promptly identify the symptoms of automatic transmission overheating. In cases where the automatic transmission overheats, signs of excessive heating can be determined independently. If the automatic transmission is very overheated, the transmission can transfer the unit to.

Check or A/T lights up on the dashboard, indicating problems with the automatic transmission. Various automatic transmission sensors detect an increase in temperature, a decrease in ATF pressure, etc. In such a situation, it is not uncommon when the torque converter literally turns blue from strong heating, the automatic transmission wiring is melted, the clutches burn and crumble.

In this case, when the automatic transmission has entered emergency mode, it is optimal to immediately stop using the car and deliver it to the service not on its own, so as not to worsen the situation further. Moreover, if it is supposed to tow without hanging the drive wheels, then you need to separately take into account all the rules and nuances of such towing a car with automatic transmission.

Please note that the machine does not always “fall” into an accident when overheated. Often the box works, the check does not light up, but the temperature approaches a critical point. In such a situation, after the machine reaches operating temperature, the driver usually feels obvious jerks, jerks when shifting, the machine slips, delays gear changes, etc. At the same time on a cold box it works fine.

You need to understand that in the future problems still cannot be avoided, since constant overheating, albeit not critical, significantly reduces the resource of friction clutches, solenoids, can cause deformations, etc. The transmission oil itself, under conditions of increased heating, also quickly loses its properties and becomes heavily contaminated. This means that the owner must constantly check the level and quality of the oil in the automatic transmission.

It is also important to note any changes in the operation of the unit and immediately carry out diagnostics, change the automatic transmission oil and filter in the automatic transmission in a timely manner, use high-quality fluids recommended by the transmission manufacturer itself.

Causes of automatic transmission overheating

If we talk about the reasons why the automatic transmission overheats, the following can be distinguished among the main ones:

Significant loads on the transmission and heavy operating conditions (trailer towing, frequent and long slippage in mud, snow, etc.)
Insufficient regular automatic transmission cooling or problems with the automatic transmission cooling radiator;
Reducing the oil pressure in the machine (dirty channels, filters, breakdown of the automatic transmission oil pump);
Low / high, malfunctions of the control system, problems with solenoids;

At the same time, problems associated with the automatic transmission oil cooler (automatic gearbox heat exchanger) are a common and common problem. The fact is that if the radiator is contaminated with deposits and natural wear products of the automatic transmission, the hot oil ceases to be effectively cooled in the radiator.

Also, failures are possible in the operation of other elements. For example, automatic transmission solenoids are valves that allow ATF to be directed through channels. If the solenoid does not fire in time, this leads to violations in the supply of the working fluid, which lubricates and cools the parts.

How to solve the problem of automatic transmission overheating

First of all, if the box overheats, it is necessary to start with automatic transmission diagnostics. An integrated approach usually allows you to quickly determine the cause and find out why the automatic transmission is heating up.

Often, to eliminate overheating of the machine, it is necessary to clean the valve body channels, change the transmission fluid and filters, and flush the automatic transmission oil cooler. For cleaning, you can use different methods, ranging from the use of flushing and ending with the disassembly of the unit.

Also an effective way to solve problems with overheating is to install an additional automatic transmission cooling radiator with a thermostat. Such a radiator allows you to quickly reach the operating temperature and further maintain the heating of the oil in the machine no higher than 70-90 degrees.

Taking into account the fact that many modern automatic transmissions can normally warm up to 100-110 degrees, experienced car owners install an automatic gearbox additional radiator not in case of urgent need, but in order to prevent and increase the life of the gearbox.

Types and principle of operation of automatic transmission sensors

The main purpose of the automatic transmission control system can be called the determination of the optimal moment at which a gear change should occur. To do this, many parameters must be taken into account. Modern designs are equipped with a dynamic control program that allows you to select the appropriate mode depending on the operating conditions and the current mode of the vehicle, determined by the sensors.

In an automatic transmission, the main ones are speed sensors (determining the speed on the input and output shafts of the gearbox), pressure and temperature sensors of the working fluid, and a selector position sensor (inhibitor). Each of them has its own design and purpose. Information from other vehicle sensors can also be used.

Selector position sensor

Selector lever position sensor

When changing the position of the gear selector, its new position is fixed by a special selector position sensor. The received data is transmitted to the electronic control unit (often it is separate for the automatic transmission, but at the same time it has a connection with the vehicle's engine ECU), which launches the corresponding programs. This activates the hydraulic system according to the selected driving mode ("P(N)", "D", "R" or "M"). In vehicle manuals, this sensor is often referred to as "inhibitor". As a rule, the sensor is located on the gearbox selector shaft, which, in turn, is located under the hood of the car. Sometimes, to obtain information, it is connected to the drive of the spool valve for selecting driving modes in the valve body.

The automatic transmission selector position sensor can be called "multifunctional", since the signal from it is also used to turn on the reverse lights, as well as to control the operation of the starter drive in the "P" and "N" modes. There are many designs of sensors that determine the position of the selector lever. The classic sensor circuit is based on a potentiometer that changes its resistance depending on the position of the selector lever. Structurally, it is a set of resistive plates along which a movable element (slider) moves, which is connected to the selector. Depending on the position of the slider, the resistance of the sensor will change, and hence the output voltage. All this is in a non-separable case. In the event of malfunctions, the selector position sensor can be cleaned by opening it by drilling out the rivets. However, it is quite difficult to set up an inhibitor for re-operation, so it is easier to simply replace a failed sensor.

Speed sensor

As a rule, two speed sensors are installed in an automatic transmission. One captures the rotational speed of the input (primary) shaft, the second measures the rotational speed of the output shaft (for a front-wheel drive gearbox, this is the speed of rotation of the differential gear). The automatic transmission ECU uses the readings from the first sensor to determine the current load on the engine and select the optimal gear. The data from the second sensor is used to control the operation of the gearbox: how correctly the commands of the control unit were executed and exactly the gear that was needed was switched on.

Hall sensor device and its signal form

Structurally, the speed sensor is a magnetic proximity sensor based on the Hall effect. The sensor consists of a permanent magnet and a Hall integrated circuit, located in a sealed housing. It detects the speed of the shafts and generates signals in the form of AC pulses. To ensure the operation of the sensor, a so-called “impulse wheel” is installed on the shaft, which has a fixed number of alternating protrusions and cavities (quite often this role is played by an ordinary gear). The principle of operation of the sensor is as follows: when a gear tooth or wheel protrusion passes through the sensor, the magnetic field created by it changes and, according to the Hall effect, an electrical signal is generated. Then it is converted and sent to the control unit. A low signal corresponds to a valley, and a high signal corresponds to a ledge.

The main malfunctions of such a sensor are case depressurization and contact oxidation. A characteristic feature is that this sensor cannot be “ringed out” with a multimeter.

Less commonly, inductive speed sensors can be used as speed sensors. The principle of their operation is as follows: when the gear tooth of the gearbox passes through the magnetic field of the sensor, a voltage appears in the sensor coil, which is transmitted to the control unit in the form of a signal. The latter, taking into account the number of gear teeth, calculates the current speed. Visually, an inductive sensor looks very similar to a Hall sensor, but has significant differences in signal shape (analogue) and operating conditions - it does not use a reference voltage, but generates it independently due to the properties of magnetic induction. This sensor can be called.

Fluid temperature sensor

Automatic transmission temperature sensor

The temperature level of the working fluid in the gearbox has a significant impact on the operation of the friction clutches. Therefore, to protect against overheating, an automatic transmission temperature sensor is provided in the system. It is a thermistor (thermistor) and consists of a housing and a sensitive element. The latter is made of a semiconductor that changes its resistance at different temperatures. The signal from the sensor is transmitted to the automatic transmission control unit. As a rule, it represents a linear dependence of voltage on temperature. Sensor readings can only be obtained using a special diagnostic scanner.

The temperature sensor can be installed in the transmission case, but most often it is built into the wiring harness inside the automatic transmission. If the permissible operating temperature is exceeded, the computer can forcibly reduce power, up to the transition of the gearbox to emergency mode.

Pressure meter

To determine the intensity of circulation of the working fluid in an automatic transmission, a pressure sensor may be provided in the system. There may be several (for different channels). The measurement is carried out by converting the pressure of the working fluid into electrical signals that are fed to the electronic transmission control unit.

There are two types of pressure sensors:

Discrete - fix deviations of operating modes from a given value. In normal operation, the sensor contacts are connected. If the pressure at the sensor installation site is lower than required, the sensor contacts open, and the automatic transmission control unit receives the corresponding signal and sends a command to increase the pressure.
Analog - convert the pressure level into an electrical signal of the appropriate value. The sensitive elements of such sensors are capable of changing resistance depending on the degree of deformation under pressure.

Auxiliary sensors for automatic transmission control

In addition to the main sensors related directly to the gearbox, its electronic control unit can also use information obtained from additional sources. As a rule, these are the following sensors:

Brake pedal sensor - its signal is used when the selector is locked in the "P" position.
Gas pedal position sensor - installed in the electronic accelerator pedal. It is necessary to determine the current driving mode request from the driver.
Throttle position sensor - located in the throttle body. The signal from this sensor indicates the current engine workload and influences the selection of the optimal gear.

The set of automatic transmission sensors ensures its correct operation and comfort during vehicle operation. In the event of sensor malfunctions, the balance of the system is disturbed, about which the on-board diagnostic system will immediately warn the driver (i.e., the corresponding “error” will light up on the instrument cluster). Ignoring malfunction signals can lead to serious problems in the main components of the car, therefore, if malfunctions are detected, it is recommended to immediately contact a specialized service.