In a planetary gear, all gears are constantly engaged. Different gear stages are achieved without breaking the thrust by driving or holding the sun wheel, planetary gears or planetary ring gear.
- 1 - parts set in motion;
- 2 - held parts.
Input signals
The electronic control unit receives information from:
- selector lever with multifunction position switch. The setting of the lever controls the activation of the reversing lights, the starter lock when in gear range, and the activation/deactivation of the speed control device;
- throttle potentiometer about its position. This node, known from injection, serves to calculate shift points;
- speed sensor in the gearbox to determine the speed of movement, as well as shift points. If this sensor is faulty, then a signal is taken from the Hall sensor;
- sensor on the number of revolutions at the input of the gearbox. It is also located on the gearbox and serves to determine the gear shift points;
- accelerator sensor in the throttle cable; it beeps when the gas pedal is fully depressed. This is followed by a shift to a higher gear or, if necessary, a downshift by one or two gear ratio ranges;
- brake light switch to release the electromagnetic lock of the selector lever. Selector lever moves from position «R» or «N» in one of the gear ratio ranges only with the brake pedal depressed;
- ATF temperature sensor in the gearbox. When the engine control unit receives a signal «fever», in some gear ratio ranges, a switch to a higher level occurs. This reduces the gap in the torque converter and lowers the temperature of the ATF - only then does it switch to the standard program.
Gear shift control
If you move the selector lever to the position «D», the pressurized ATF enters the so-called switching flaps in the box, which in turn hydraulically control the plate clutches and brakes. The control unit regulates the pressure using solenoid valves and thus determines the moment of upshifting or downshifting, as well as shift transitions. At the same time, there is communication with the ignition/injection control unit - when shifting to a higher gear, the ignition timing is slightly pushed back so that the shifting proceeds smoothly.
Signals from the control unit are then sent to the selector lever lock solenoid, the combined starter lock relay and to the reversing lights. If the Audi A4 is equipped with a speed control system, the control unit for automatic transmission only energizes it when the forward gear ratio range is engaged and a speed of 30 km/h is exceeded for the first time.
Self-diagnosis
The control unit of the electronic transmission can recognize the resulting defects and store them in the computer. Faults that occur are stored in a non-volatile memory. The storage device can be interrogated in the workshop. This is done with a reading device; unfortunately, there is no possibility for an amateur to interrogate a computer. If you suspect a malfunction in the gearbox control, then you can read the computer memory only in the Audi workshop.
Emergency run
4-speed automatic transmission
If the control unit has recognized a defect that has a significant negative impact on the functioning, or the control unit itself is faulty, the mode «emergency run». There are two emergency programs for this:
- If the selector lever is in position «D», «3» or «2», the gearbox hydraulically engages 3rd gear. The selected gear ratio range is enabled only in the positions of the selector lever «1» And «R».
- If the engine speed and speed signal is not received and the accelerator pedal is depressed for the first time exceeding the value of *, the transmission shifts to gear «N», i.e. no more drive. By switching off the ignition and restarting the engine, you can try to activate the transmission again.
Emergency run
Gearbox 5-NR-18
The gearbox has different emergency run modes depending on the nature of the fault:
- With a slight failure, the movement is carried out on a different gearshift program.
- If there is a defect in the mechanical part of the gearshift assembly, the gearbox remains engaged in the 4th gear while driving. Then, after turning off the engine, only the 3rd gear ratio range is switched on.
Checking the automatic transmission
The automatic transmission leaves little room for the amateur to take initiative. But a targeted check will help to localize the malfunction, which is not least of interest when buying a used car:
- If there is a malfunction, first of all check the ATF level in the gearbox.
- If the ATF smells burnt on the dipstick, then there is severe damage to the transmission. In this case, the brake bands or clutch plates may be defective.
- On a test drive, you can check the shift points.
- The way the gearshift process takes place gives information about the condition of the gearbox.
- Adjustment of the throttle cable with an integrated throttle shift mechanism is essential for perfect operation.
- The same applies to adjusting the selector lever cable.
Evaluation of the gear shift process
During a test drive, you can pay attention to the gear shifting process:
Switching to a higher gear: with a partially depressed gas pedal, the gear change is almost not felt; at full throttle or a hard press on the gas pedal, the transitions become more distinct, but a higher gear should always grab softly. A brief increase in engine speed when changing gear indicates a defect that should be examined more closely.
Downshifting: no gas (rolling) barely perceptible at very low speeds. A jolt when shifting into reverse at partial or full throttle is normal. Switching back without gas with the selector lever lasts one to two seconds. If the gas is simultaneously added to the forced shifting back with the selector lever, then the gear shift occurs without slowing down.
Advice: Vehicles with automatic transmission must not be towed more than 50 km, otherwise the transmission lubrication will be insufficient. For the same reason, the speed must not exceed 50 km/h. When towing, the selector lever must be in position «N». If in doubt, take a more convenient route and load the vehicle.
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