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A transmission control unit or TCU is a device that controls modern electronic automatic transmissions. A TCU generally uses sensors from the vehicle as well as data provided by the engine control unit (ECU) to calculate how and when to change gears in the vehicle for optimum performance, fuel economy and shift quality.
An automatic transmission, also called auto, self-shifting transmission, n-speed automatic, or AT, is a type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually. Like other transmission systems on vehicles, it allows an internal combustion engine, best suited to run at a relatively high rotational speed, to provide a range of speed and torque outputs necessary for vehicular travel. The number of forward gear ratios is often expressed for manual transmissions as well.
An engine control unit (ECU), also commonly called an engine control module (ECM), is a type of electronic control unit that controls a series of actuators on an internal combustion engine to ensure optimal engine performance. It does this by reading values from a multitude of sensors within the engine bay, interpreting the data using multidimensional performance maps, and adjusting the engine actuators. Before ECUs, air-fuel mixture, ignition timing, and idle speed were mechanically set and dynamically controlled by mechanical and pneumatic means.
A gear or cogwheel is a rotating machine part having cut teeth, or in the case of a cogwheel, inserted teeth, which mesh with another toothed part to transmit torque. Geared devices can change the speed, torque, and direction of a power source. Gears almost always produce a change in torque, creating a mechanical advantage, through their gear ratio, and thus may be considered a simple machine. The teeth on the two meshing gears all have the same shape. Two or more meshing gears, working in a sequence, are called a gear train or a transmission. A gear can mesh with a linear toothed part, called a rack, producing translation instead of rotation.
Electronic automatic transmissions have been changing in design from purely hydromechanical controls to electronic controls since the late 1980s. Since then, development has been iterative and today designs exist from several stages of electronic automatic transmission control development. Transmission solenoids are a key component to these control units.
Hydraulic machines are machinery and tools that use liquid fluid power to do simple work, operated by the use of hydraulics, where a liquid is the powering medium. In heavy equipment and other types of machine, hydraulic fluid is transmitted throughout the machine to various hydraulic motors and hydraulic cylinders and becomes pressurised according to the resistance present. The fluid is controlled directly or automatically by control valves and distributed through hoses and tubes.
A transmission solenoid or cylinoid is an electro-hydraulic valve that controls fluid flow into and throughout an automatic transmission. Solenoids can be normally open or normally closed. They operate via a voltage or current supplied by the transmission computer or controller. Transmission solenoids are usually installed in a transmission valve body, transmission control unit, or transmission control module.
The evolution of the modern automatic transmission and the integration of electronic controls have allowed great progress in recent years. 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 immense range of programmability offered by a TCU allows the modern automatic transmission to be used with appropriate transmission characteristics for each application.
An internal combustion engine (ICE) is a heat engine where the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is applied typically to pistons, turbine blades, rotor or a nozzle. This force moves the component over a distance, transforming chemical energy into useful mechanical energy.
Emission standards are the legal requirements governing air pollutants released into the atmosphere. Emission standards set quantitative limits on the permissible amount of specific air pollutants that may be released from specific sources over specific timeframes. They are generally designed to achieve air quality standards and to protect human life.
Automobile handling and vehicle handling are descriptions of the way a wheeled vehicle responds and reacts to the inputs of a driver, as well as how it moves along a track or road. It is commonly judged by how a vehicle performs particularly during cornering, acceleration, and braking as well as on the vehicle's directional stability when moving in steady state condition.
On some applications, the TCU and the ECU are combined into a single unit as a powertrain control module (PCM).
A power-train control module, abbreviated PCM, is an automotive component, a control unit, used on motor vehicles. It is generally a combined control unit, consisting of the engine control unit (ECU) and the transmission control unit (TCU). On some cars, such as many Chryslers, there are multiple computers: the PCM, the Transmission Control Unit, and the Body Control Module, for a total of three separate computers as an example. These automotive computers are generally very reliable. The PCM commonly controls more than 100 factors in a car or truck. There are many hundreds of error codes that can occur, which indicates that some subsection of the car is experiencing a problem. When one of these errors occurs, usually it will turn on the "check engine" light on the dashboard. The PCM is one of potentially several on-board computers, or essentially the "brain" of the engine control system.
The typical modern TCU uses signals from engine sensors, automatic transmission sensors and from other electronic controllers to determine when and how to shift.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. 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
This sensor sends a varying frequency signal to the TCU to determine the current speed of the vehicle. The TCU uses this information to determine when a gear change should take place based in the various operating parameters. The TCU also uses a ratio between the TSS and WSS which is used to determine when to change gears. 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. To test these parts, check the resistance to make sure it's within manufacturer specs.
Modern automatic transmissions also have a wheel speed sensor input to determine the true speed of the vehicle to determine whether the vehicle is going downhill or uphill and also adapt gear changes according to road speeds, and also whether to decouple the torque converter at a standstill to improve fuel consumption and reduce load on running gear.
The TPS sensor along with the vehicle speed sensor are the two main inputs for most TCUs. 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 input is used to determine the optimum time and characteristics for a gear change according to load on the engine. The rate of change is used to determine whether a downshift is appropriate for overtaking, for example, the value of the TPS is also continually monitored during the journey and shift programmes are changed accordingly (economy, sport mode, etc.). The TCU can also reference this information with the vehicle speed sensor to determine vehicle acceleration and compare this with a nominal value; if the actual value is much higher or lower (such as driving uphill or towing a trailer) the transmission will change its gearshift patterns to suit the situation.
Electronic throttle control (ETC) is an automobile technology which electronically "connects" the accelerator pedal to the throttle, replacing a mechanical linkage. A typical ETC system consists of three major components: (i) an accelerator pedal module, (ii) a throttle valve that can be opened and closed by an electric motor, and (iii) a powertrain or engine control module. The ECM is a type of electronic control unit (ECU), which is an embedded system that employs software to determine the required throttle position by calculations from data measured by other sensors, including the accelerator pedal position sensors, engine speed sensor, vehicle speed sensor, and cruise control switches. The electric motor is then used to open the throttle valve to the desired angle via a closed-loop control algorithm within the ECM.
Known as an input speed sensor (ISS). This sensor sends a varying frequency signal to the TCU to determine the current rotational speed of the input shaft or torque converter. The TCU uses the input shaft speed to determine slippage across the torque converter and potentially to determine the rate of slippage across the bands and clutches. This information is vital to regulate the application of the torque converter lock-up clutch smoothly and effectively.
This may also be known as Transmission Oil Temperature. This sensor determines the fluid temperature inside the transmission. This is often used for diagnostic purposes to check ATF (Automatic Transmission Fluid) at the correct temperature. The main use of this has been as a failsafe feature to downshift the transmission if the ATF becomes extremely hot. On more modern transmissions this input allows the TCU to modify the line pressure and solenoid pressures according to the changing viscosity of the fluid based on temperature in order to improve shift comfort, and also to determine regulation of the torque converter lock-up clutch.
One of the most common inputs into a TCU is the kick down switch which is used to determine if the accelerator pedal has been depressed past full throttle.Traditionally this was required on older transmissions with a simple logic in order to ensure maximum acceleration. When activated the transmission downshifts into the lowest permissible gear based on current road speed to use the full power reserves of the engine. This is still present in most transmissions though is no longer necessary to use in most circumstances because the TCU uses the throttle position sensor, the rate of change, and driver characteristics to determine whether a downshift may be necessary, thus eliminating the traditional need for this switch.
This input is used to determine whether to activate the shift lock solenoid to prevent the driver selecting a driving range with no foot on the brake. In more modern TCUs this input is also used to determine whether to downshift the transmission to increase engine braking effect if the transmission detects that the vehicle is going downhill.
Many TCUs now have an input from the vehicle's traction control system. If the TCS detects unfavourable road conditions, a signal is sent to the TCU. The TCU can modify shift programmes by upshifting early, eliminating the torque converter lock-up clutch application, and also eliminating the first gear totally and pulling off in 2nd.
These simple on/off electric switches detect the presence or absence of fluid pressure in a particular hydraulic line. They are used for diagnostic purposes and in some cases for controlling the application or release of hydraulic control elements.
If the vehicle is fitted with cruise control the TCU may also have a connection to cruise control system. This can modify shift behaviour to take into account the throttle is not being operated by the driver to eliminate unexpected gearchanges when the cruise control is engaged. This is also used to inform the cruise control system about the position of the selector lever so that the cruise control can be deactivated if the lever is shifted out of a driving range.
A wide variety of information is delivered to the TCU via Controller Area Network communications or similar protocols (such as Chrysler's CCD bus, an early EIA-485-based vehicle local area network). In older vehicle designs, as well as in aftermarket TCUs sold into the racing and hobbyist markets, the TCU receives only the signals needed to control the transmission (engine speed, vehicle speed, throttle position or manifold vacuum, shift lever position).
The typical modern TCU sends out signals to shift solenoids, pressure control solenoids, torque converter lockup solenoids and to other electronic controllers.
Many automatic transmissions lock the selector lever via a shiftlock solenoid to stop a driving range being selected if the brake pedal is not depressed.
Modern electronic automatic transmissions have electrical solenoids which are activated to change gears. Simple electronic-control designs (such as Ford's AOD-E, AXOD-E and E4OD) use the solenoids to modify the shift points in an existing valve body, while more advanced designs (such as the Chrysler Ultradrive and its follow-ons) use the solenoids to control the clutches indirectly, by way of a greatly simplified valve body.
Modern electronic automatic transmissions are still fundamentally hydraulic. This requires precise pressure control. Older automatic transmission designs only use a single line pressure control solenoid which modifies pressure across the entire transmission. Newer automatic transmission designs often use many pressure control solenoids, and sometimes allow the shift solenoids themselves to provide precise pressure control during shifts by ramping the solenoid on and off. The shift pressure affects the shift quality (too high a pressure will result in rough shifting; too low a pressure will cause the clutches to overheat) and shift speed. :)
Most electronic automatic transmissions utilize a TCC solenoid to regulate the torque converter electronically. Once fully locked, the torque converter no longer applies torque multiplication and will spin at the same speed as the engine. This provides a major increase in fuel economy. Modern designs provide partial lockup in lower gears to improve fuel economy further, but this can increase wear on the clutch components.
Many TCUs provide an output to the ECU to retard the ignition timing, or reduce the fuel quantity, for a few milliseconds to reduce load on the transmission during heavy throttle. This allows automatic transmissions to shift smoothly even on engines with large amounts of torque which would otherwise result in a harder shift and possible damage to the gearbox.
The TCU provides information about the health of the transmission, such as clutch wear indicators and shift pressures, and can raise trouble codes and set the malfunction indicator lamp on the instrument cluster if a serious problem is found. An output to the cruise control module is also often present to deactivate the cruise control if a neutral gear is selected, just like on a manual transmission.
A transmission is a machine in a power transmission system, which provides controlled application of the power. Often the term transmission refers simply to the gearbox that uses gears and gear trains to provide speed and torque conversions from a rotating power source to another device.
A manual transmission, also known as a manual gearbox, a standard transmission or colloquially in some countries as a stick shift, is a type of transmission used in motor vehicle applications. It uses a driver-operated clutch, usually engaged and disengaged by a foot pedal or hand lever, for regulating torque transfer from the engine to the transmission; and a gear selector that can be operated by hand or foot.
A semi-automatic transmission is an automobile transmission that combines manual transmission and automatic transmission.
Manumatic, a portmanteau of the words manual and automatic, is a term referring to a class of automotive transmission.
Hydramatic is an automatic transmission developed by both General Motors' Cadillac and Oldsmobile divisions. Introduced in 1939 for the 1940 model year vehicles, the Hydramatic was the first mass-produced fully automatic transmission developed for passenger automobile use.
TorqueFlite is the trademarked name of Chrysler Corporation's automatic transmissions, starting with the three-speed unit introduced late in the 1956 model year as a successor to Chrysler's two-speed PowerFlite. In the 1990s, the TorqueFlite name was dropped in favor of alphanumeric designations, although the latest ZF-based transmissions with the 8-speed automatic has revived the name.
Dynaflow was the trademarked name for a type of automatic transmission developed and built by General Motors Buick Motor Division from late 1947 to mid-1963. The Dynaflow, which was introduced for the 1948 model year only as an option on Roadmaster models, received some severe early testing in the M18 Hellcat tank destroyer, which were built in Buick's Flint, Michigan assembly plant during World War II. It was also used in the 1951 Le Sabre concept car.
A direct-shift gearbox, commonly abbreviated to DSG, is an electronically controlled dual-clutch multiple-shaft gearbox in a transaxle design, with automatic clutch operation and with fully automatic or semi-manual gear selection. The first actual dual-clutch transmissions were derived from Porsche in-house development for their Model 962 racing cars in the 1980s.
The Turbo-Hydramatic 125 was the first in a line of automatic transmissions from General Motors designed for transverse engine application. Introduced in 1980, the line evolved into today's 4T40/45/65/80 line.
The AOD is a four-speed automatic transmission with overdrive. Introduced in 1980, it was Ford's first four-speed automatic overdrive transmission. The gearset design is based on the Ford "X" automatic transmissions used during the 1950s, 60s, and 70s. The AOD replaced many of Ford's older transmissions such as the C4, C5, and light duty applications of the FMX.
The Turboglide is a Chevrolet constant torque, continuously variable automatic transmission that made its debut as an optional transmission on Chevrolet V8 passenger cars for 1957. It consisted of a concurrently geared planetary gearbox with a 'switch pitch' dual-pitch torque converter stator. Turboglide utilized a die-cast aluminum transmission case, following Packard's Ultramatic of 1956. It was designed to help showcase the engineering features of the '57 Chevy, and was often ordered with the Rochester Ramjet Fuel Injection system on the 283 V8. Turboglide cost about $50 more than Powerglide, and was available in all 1957-1961 V8 engine models except the Corvette.
The Borg-Warner 35 transmission (BW-35) is an automatic transmission produced by the BorgWarner company. This article also applies to variations—the M-36 and M-37. When this article refers to "M-3x" it refers to all models. When model number specific it will use the exact model number.
Electronic Diesel Control is a diesel engine fuel injection control system for the precise metering and delivery of fuel into the combustion chamber of modern diesel engines used in trucks and cars.
Automotive electronics are electronic systems used in vehicles, including engine management, ignition, radio, carputers, telematics, in-car entertainment systems and others. Ignition, engine, and transmission electronics are also found in trucks, motorcycles, off-road vehicles, and other internal combustion-powered machinery such as forklifts, tractors, and excavators. Related elements for control of relevant electrical systems are found on hybrid vehicles and electric cars as well.
Synchronized down shift rev-matching system is a technology invented by Nissan for use on the Nissan 370Z. The technology was first used by Kamrul of Velocity In combination with the Engine Control Unit (ECU) and various sensors, the engine blips the throttle for the driver during both downshifts and upshifts to allow for better and smoother shifting, and improved handling.
A motorcycle transmission is a transmission created specifically for motorcycle applications. They may also be found in use on other light vehicles such as motor tricycles and quadbikes, go-karts offroad buggies, auto rickshaws, mowers and other utility vehicles, microcars, and even some superlight racing cars.
A quickshifter is a device that allows clutchless gearshift on a manual transmission, and is commonly used on motorcycles. It increases safety and comfort of the vehicle since it eliminates the need of adjusting the clutch or throttle before and after gearshift. Since they eliminate the need of adjusting clutch and throttle during gearshift, they are quicker(usually shift in less than 50 millisecond) and also used as performance enhancement on motorcycles.