Transmission Control Unit May Be Most Critical Of Powertrain Controllers

Transmission Control Unit May Be Most Critical Of Powertrain Controllers

Technology April 2020 Transmission Control Unit TCU Most Critical Powertrain Controllers

While the number of electronic control units in automobiles is increasing exponentially, the TCU continues to remain as one of the most important of them all

The powertrain of a vehicle consists of the engine and transmission, and the latter has been witnessing developments focussed towards enhancing driving experience as well as offering efficiency, in terms of fuel utilisation. The behaviour of the gears can be monitored and be made to perform in a desired manner with the help of an electronic intervention that comes in the form of the Transmission Control Unit (TCU).

A Transmission Control Unit (TCU) is generally found in vehicles that feature modern electronic automatic transmissions, where the information recorded by sensors as well as inputs from the engine control unit are used to perform the duty of changing gears appropriately in order to enable the balance between optimum performance, fuel economy and shift quality.

The basic function of a TCU is to evaluate relevant sensor signals and convert them into control commands for the mechanical transmission actuators, using the underlying software. TCUs consist of a microcontroller and integrated switching circuits that are optimised for specific applications. These TCUs also provide inputs for sensors and output stages for controlling the actuators across various automatic transmission systems. It is the modularity of the software architecture of TCUs that facilitates the use of multiple software-sharing models across transmission systems.


TCUs are applicable for automatic transmission systems alone, since their role is basically in the automatic shifting of gears according to the parameters set and the driving mode selected. Therefore, a TCU can be utilised in any form of automatic vehicle transmission, including Automated Manual Transmissions (AMT), Continuously Variable Transmissions (CVT), Double-Clutch Transmissions (DCT) as well as traditional Step-Automatic Transmissions (AT). The TCU leverages electronics to collect data and analyse the gearbox requirements, in addition to mechanical hydraulic actuators that control the shifting of gears appropriately. Component suppliers offer TCUs either integrated in the electronic module, attached to the transmission or as a standalone version based on the requirements in the end-application.

The role of TCUs in advanced transmissions like AT, CVT and DCT is critical, and has been in use since the development of these transmissions themselves. These advanced automatic transmission technologies have mostly been applied in vehicles that are part of a segment that is welcoming new technologies and one that enhances the overall efficiency and driving experience. This means the cost involved in a fine-tuned TCU will not add much to the overall cost of the vehicles in such segments. However, AMT is a technology that is more rudimental in nature, as it is the simplest form of automatic transmission. It is a manual transmission system, which makes use of electronics and actuators to shift from one gear to another.

This AMT technology has been receiving increased adoption in India owing to ease of driving, low-cost technology and fuel economy on par with manual transmissions. The traditional approach towards designing solutions for AMT control has been focussed towards controlling the clutching along with the gear shift, using only sensor-generated information. This method has enabled rapid development of the AMT technology, but with the presence of certain issues. AMTs have gear shifts that offer rough driving experience and are slow in responding to torque demands from the end user compared to other automatics. This prompted companies to conduct development of TCUs that carry out gear-shifting based on other data besides those solely generate by sensor information.


Current TCUs need to possess highly-accurate digital intelligence so as to identify the engine’s ideal operating point, in addition to having high-tech intelligence to enable complex operation of various kinds of automatic transmission systems. The processing power of modern TCUs is extremely high, with speeds higher than that of older computers. They are also being enabled with software-sharing capabilities so that they can be fitted on various types of automatic transmissions with limited tweaking requirements. It has increasingly been noted that TCUs are being developed in line with requirements for functional safety standards like ISO 26262, and even up to ASIL D standards.

Powertrain control provider Sedemac said it has also been capitalising on a model-based design approach for developing AMT ECU/TCU controllers. It has been carrying out this work in order to enhance the clutch and gear shift refinement control strategies further. Features such as torque and required timing can be synchronised using AMT controllers, thereby resulting in smooth gear shifts and reduced driver fatigue. This feature could increase the AMT adoption and their deployment in scooters will enable vehicles to have significantly higher fuel economy as compared to CVT. Such an approach also eliminates the duplication of electronic components. Therefore, the role of the TCU is essential in enabling any type of automatic transmission to perform better in terms of enhanced riding/driving dynamics, combined with optimum fuel economy.

The role played by a TCI is highly critical, especially since this controller has the capability of addressing the characteristics of both vehicle dynamics and fuel economy


Electric and hybrid electric vehicles generate buzz owing to the increased levels of adoption of such forms of mobility. EVs and certain types of hybrids have an electric motor that puts out power, which needs to be transferred to the axles and eventually the wheels. While the objectives of a TCU in an EV or hybrid are identical to those featured in vehicles with internal combustion engine, there are a few additional requirements that are essential.

The transmission in EVs need to be more robust than their ICE counterparts, since the complete amount of torque of the motor is available at the get-go itself. Additionally, since the electric motors powering these vehicles are quiet, there is a need for these transmissions to be much more silent in operation.The manner in which the gears are developed and the gearbox is designed addresses the decibel levels, the gear shifting also needs to be aligned to continue the silent performance of the transmission Furthermore, EVs and hybrids are not considered to be slow vehicles by any measure; therefore, the transmission needs to offer a thrilling feel to the driver by adding to the overall electric powertrain experience.

The software of TCUs has been, and continues to be developed to enable the requirements expected of vehicles energised by an electric source of power. The manner in which gears shift up and down, in order to be brisk and accurate, while maintaining appropriate acoustic levels becomes a matter of criticality for TCUs to adhere to EVs and hybrid electric vehicles.


TCU plays a significant role in the powertrain of a vehicle that is equipped with an automatic transmission, be it a two-wheeler, four-wheeler, commercial vehicle or off-highway vehicle. The source of energy for the powertrain also does not matter for the requirement of a TCU, as long as the vehicle features an automatic transmission system. The TCU is an integral part of the entire powertrain of a vehicle, as it affects the fuel economy, which is a major criterion for customers purchasing a vehicle. For those users focussed on driving dynamics and not so much around fuel efficiency, the TCU can be tuned to ensure a more responsive transmission responsive to driver inputs for an exhilarating driving experience.

The TCU can also enable balanced operation between the vehicle’s enhanced performance and optimum fuel economy, especially in vehicles equipped with different riding/driving modes. It can easily make adjustments to the transmission response in accordance with the type of mode selected by the driver, resulting in appropriate dynamics on the road. Therefore, the TCU may be one of a number of controllers present in a modern vehicle, but it definitely plays a substantial role in the powertrain performance of any vehicle that is equipped equipped with an automatic transmission system

(Inputs from, Bosch, Continental, Sedemac)

TEXT: Naveen Arul