Older transmissions use this to determine engine load, with the introduction of drive-by-wire technology, this is often a shared input between the ECU and TCU. The TPS sensor along with the vehicle speed sensor are the two main inputs for most TCUs. To test these parts, check the resistance to make sure it's within manufacturer specs. If either the TSS or WSS fails or malfunctions/becomes faulty, the ratio will be wrong which in return can cause problems like false speedometer readings and transmission slipping. The TCU also uses a ratio between the TSS and WSS which is used to determine when to change gears. The TCU uses this information to determine when a gear change should take place based in the various operating parameters. This sensor sends a varying frequency signal to the TCU to determine the current speed of the vehicle. Modern TCUs are so complex in their design and make calculations based on so many parameters that there are an indefinite amount of possible shift behaviours More modern designs share inputs or obtain information from an input to the ECU, whereas older designs often have their own dedicated inputs and sensors on the engine components. The typical modern TCU uses signals from engine sensors, automatic transmission sensors and from other electronic controllers to determine when and how to shift. On some applications, the TCU and the ECU are combined into a single unit as a powertrain control module (PCM). The immense range of programmability offered by a TCU allows the modern automatic transmission to be used with appropriate transmission characteristics for each application. The modern automatic transmission is now able to achieve better fuel economy, reduced engine emissions, greater shift system reliability, improved shift feel, improved shift speed and improved vehicle handling. The evolution of modern automatic transmission and the integration of electronic controls have allowed great progress in recent years. Transmission solenoids are a key component to these control units. Since then, development has been iterative and today designs exist from several stages of electronic automatic transmission control development. 3.4 Torque converter clutch solenoid (TCC)Įlectronic automatic transmissions have been changing in design from purely hydromechanical controls to electronic controls since the late 1980s.2.5 Transmission fluid Temperature sensor (TFT).
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