Transmission control unit or TCU is a device that controls modern electronic automatic transmission. TCU generally uses sensors from vehicles as well as data provided by machine control units (ECUs) to calculate how and when to change gears in the vehicle for optimal performance, fuel savings and shift quality.
Video Transmission control unit
Histori
Automatic electronic transmission has changed in the design of pure hydromechanical controls into electronic controls since the late 1980s. Since then, the development has been repeatable and the current design exists from several stages of development of automatic electronic transmission control. Transmission solenoids are key components for this control unit.
The evolution of modern automatic transmission and integration of electronic controls has enabled great progress in recent years. Modern automatic transmissions are now able to achieve better fuel economy, lower engine emissions, greater shift system reliability, increased shift shifts, improved shift speed, and better vehicle handling. The wide range of programmability offered by TCU enables modern automatic transmission to be used with precise transmission characteristics for each application.
In some applications, TCU and ECU are combined into one unit as a powertrain control module (PCM).
Maps Transmission control unit
Input parameters
Typical modern TCUs use signals from engine sensors, automatic transmission sensors and from other electronic controllers to determine when and how to shift them. The more modern designs share input or obtain information from inputs to the ECU, while older designs often have their own special inputs and sensors on machine components. The modern TCU is very complex in its design and makes calculations based on so many parameters that there is the possibility of unlimited shift behavior.
Vehicle speed sensor (VSS)
This sensor sends different frequency signals to TCU to determine the current speed of the vehicle. TCU uses this information to determine when tooth changes should be performed based on various operating parameters. TCU also uses the ratio between TSS and WSS used to determine when to change gears. If one of the TSS or WSS fails or malfunctions/becomes damaged, the ratio will be wrong which in return can cause problems such as false speedometer readings and transmission slips. To test these parts, check the resistance to verify it in the manufacturer's specifications.
Wheel speed sensor (WSS)
Modern automatic transmissions also have wheel speed sensor inputs to determine the actual vehicle speed to determine whether the vehicle will decrease or climb and also adjust the gear changes according to the speed of the road, and also whether to separate the torque converter at rest to increase fuel consumption and reduce load on the running gear.
Throttle position sensor (TPS)
TPS sensors along with vehicle speed sensors are the two main inputs for most TCUs. The older transmissions use this to determine the engine load, with the introduction of drive-by-wire technology, this is often the joint input between ECU and TCU. Input is used to determine the optimal timing and characteristics for tooth replacement in accordance with the load on the machine. The rate of change is used to determine whether the decrease falls precisely for overtaking, for example, the TPS value is also continuously monitored during the trip and the shift program is changed accordingly (economy, sport mode, etc.). TCU can also reference this information with vehicle speed sensors to determine vehicle acceleration and compare it to face value; if the actual value is much higher or lower (such as driving up or pulling the trailer) the transmission will change the pattern of gearshift that fit the situation.
Turbine speed sensor (TSS)
Known as the input speed sensor (ISS). This sensor sends different frequency signals to the TCU to determine the current rotational speed of the input shaft or torque converter. TCU uses the speed of the input shaft to determine the slippage of the torque converter and has the potential to determine the slip rate across the band and coupling. This information is important to set the converter application of the torque converter smoothly and effectively.
Temperature sensor temperature sensor (TFT)
This is also known as Transmission Oil Temperature. This sensor determines the temperature of the fluid in the transmission. It is often used for diagnostic purposes to check the ATF (Automatic Transmission Fluid) at the correct temperature. This primary usage has become a failsafe feature to decrease transmission if ATF gets very hot. In a more modern transmission, this input allows the TCU to modify the channel pressure and solenoid pressure according to the fluid viscosity change based on temperature to improve shift comfort, and also to determine the clutch setting of the converter torque lock.
Kick down
One of the most common inputs into the TCU is the kicking switch used to determine whether the accelerator pedal has passed the full throttle. Traditionally this is required on older transmissions with simple logic to ensure maximum acceleration. When enabled downshifts transmission to the lowest gear is allowed based on the current path speed to use the full power backup of the machine. It still exists in most transmissions although it is no longer necessary for use in many situations because TCU uses throttle position sensors, rate of change, and driver characteristics to determine if dental decay may be necessary, thus eliminating the traditional need for this. switch.
Brake light switch
This input is used to determine whether to activate a solenoid shift key to prevent the driver from selecting a driving range without feet on the brakes. In the more modern TCU, this input is also used to determine whether to lower the transmission to improve the braking effect if the transmission detects that the vehicle is down.
Traction Control System (TCS)
Many TCUs now have input from vehicle traction control systems. If TCS detects unfavorable road conditions, the signal is sent to TCU. TCU can modify the shift program with the initial upshifting, eliminating the clutch lock torque converter application, and also removes the first gear completely and pulls off in 2nd.
Redirecting
This simple on/off power switch detects the presence or absence of fluid pressure on certain hydraulic channels. They are used for diagnostic purposes and in some cases to control the application or release of hydraulic control elements.
Shipbuilding control module
If the vehicle is equipped with cruise control, the TCU may also have connections to the cruise control system. It can modify the shift behavior to take into account that the throttle is not operated by the driver to remove unexpected gearchanges when the cruise control is enabled. It is also used to inform the yacht control system about the position of the selector lever so that the control of the voyage can be disabled if the lever is shifted out of the driving distance.
Input from another controller
Various information is sent to TCU via a Controller Area Network communication or similar protocol (such as the Chrysler CCD bus, a local EIA-485 local area vehicle vehicle). In older vehicle designs, as well as in the aftermarket TCU sold to racing and hobby markets, the TCU receives only the signals required to control the transmission (engine speed, vehicle speed, throttle position or vacuum manifold, shift lever position).
Output parameters
Typical modern TCUs send signals for shifting solenoids, pressure control solenoids, torque converter locking solenoids and other electronic controllers.
Shift key
Many automatic transmissions lock the selector lever through the shiftlock solenoid to stop the selected driving range if the brake pedal is not pressed.
Moving solenoid
Modern electronic automatic transmission has an electric solenoid that is activated to change gear. Simple electronic control designs (such as Ford AOD-E, AXOD-E and E4OD) use solenoids to change the shifting points in the body of the existing valve, while more sophisticated designs (such as Chrysler Ultradrive and follow-up) use solenoid to control coupling indirectly, through a highly simplified valve body.
Solenoid pressure control
Modern electronic automatic transmission is fundamentally still hydraulic. This requires proper pressure control. The older automatic transmission design uses only one solenoid pressure control line that changes the pressure across the transmission. Newer automatic transmission designs often use a lot of pressure control solenoid, and sometimes allow the shift of the solenoid itself to provide precise pressure control during shifts by pressing the solenoid on and off. Pressure shift affects the quality of the shift (too high pressure will result in a rough shift, too low pressure will cause the clutch to overheat) and the shift speed.
Torque converter clutch solenoid (TCC)
Most automatic electronic transmissions use TCC solenoid to set the torque converter electronically. Once fully locked, the torque converter no longer uses torque multiplication and will rotate at the same speed as the engine. This provides a huge increase in fuel economy. The modern design provides a partial locking on the lower teeth to improve the fuel economy even further, but this can increase wear on the clutch component.
Output to ECU
Many TCUs deliver output to the ECU to slow the ignition timing, or reduce the fuel quantity, for several milliseconds to reduce the load on the transmission during heavy throttle. This allows automatic transmissions to shift seamlessly even on machines with large amounts of torque which would otherwise result in a more violent shift and possible damage to the gearbox.
Output to another controller
TCU provides information on transmission health, such as clutch wear and shear stress indicators, and can improve problem codes and set the malfunction indicator lights on the instrument cluster if serious problems are found. Output to the cruise control module is also often present to disable the shipping control if the neutral gear is selected, as in manual transmission.
References
Source of the article : Wikipedia
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