The clutch position is controlled with a proportional electrohydraulic valve, which regulates the (oil) pressure in the concentric slave cylinder (CSC). The CSC is also equipped with a contactless position sensor which uses a Hall effect sensitive element.

The advantage of position measurement directly on the CSC is that dynamic and temperature-caused effects in the hydraulic line are included in the control loop, as opposed to measuring the position on a master cylinder. The disadvantage is that the CSC’s axial pulsation during engine running is also detected by the position sensor and superimposed over the travel signal. Suitable filtering compensates for this effect during processing of the raw signal in the transmission controller.

Quickshift AMT (Renault)

The first generation of Quickshift automated manual transmissions (AMT) were integrating an electrohydraulic actuation module on top of a manual transmission (MT). The clutch and gear positions were entirely regulated by the transmission control module (TCM), through fluid pressure. There are no electric motors in the system, for clutch and gear actuation, but only electronic controlled solenoid valves.

The clutch and gears actuation is performed using fluid under pressure. The fluid pump assembly (3) creates pressure in the hydraulic system, up to 30-40 bar. The hydraulic accumulator (1) has the role of storing the high pressure fluid. After several gear shifts or clutch actuation events, the pressure in the system (read by a pressure sensor) will decrease. The pressure is restored back at the nominal level by the electric pump.

When a gear shift is performed, the transmission control unit performs the following operations:

Automated Manual Transmission Selector Fork Diagram

• regulates the pressure in the CSC, through the actuator (2), in order to open the clutch
• increases pressure in the cylinder with piston for gear selection (8)
• increases pressure in the cylinder with piston for gear engagement (7)
• regulates the pressure in the CSC, through the actuator (2), in order to close the clutch

All the pressure regulation is done through electrohydraulic valves and managed by the TCU.

The first generation of Quickshift AMTs is using an electrohydraulic “add-on” module, supplied by Magneti Marelli. This module is mounted on top of an existing manual transmission and is replacing the external clutch and gear actuation mechanisms.

Easy-R AMT (Renault)

The new generation of automated manual transmission from Renault, Easy-R, uses electromechanical actuation instead of hydraulic technology, for “enhanced flexibility and swifter response”, while the number of components has been reduced by around 25 % in order to deliver “greater reliability and simplify servicing”.

The clutch actuation is performed by a single electric motor. The gear selection and gear engagement are, each, actuated by a electric motors. In terms of packaging, the clutch actuation module is integrated with the transmission control unit, while the gear actuators come together in a separate module.

Sensodrive AMT (Citroen)

The automated manual transmission from Citroen, Sensodrive, is similar with Easytronic (Opel) in terms of components and working principles. The clutch actuation is performed using one electric motor, the gear selection and engagement is using two electric motors.

Automated Manual Transmission Vs Automatic

In an AMT, when a gearshift is performed, both the engine and transmission electronic control modules are working together and exchange information. The gear change has to be performed even if the driver has the accelerator pedal pressed and the engine delivers torque.

In order to synchronize the engine output torque with the clutch and gear positions, the engine management system (EMS) must exchange torque and speed information with the transmission control module (TCM). All the information is exchanged on a communication bus called Controller Area Network (CAN).

The TCM also exchanges information with the body control unit (BCU) in order to display to the driver the driving mode and the engaged gear.

The current trend in the automotive industry is to use only electric motor actuation systems for clutch and gears. The main reason is that, as electronics and electric technology is developed, it has become possible to design and manufacture low price, reliable, high efficient electric actuators with the required level of performance (e.g. response time). These actuators can also deliver the required actuation force with minimum amount of electric power.

Gear actuation modules come also with a level of embedded diagnostic functions. If there is an issue with the electric motors or position sensors, the transmission control module is informed and takes the appropriate measures to guarantee the safety of the vehicle and the integrity of the components.

Driving modes

Nowadays, for a driver, is quite difficult to distinguish between an AMT, AT or DCT. If at a hardware level their are different in terms of layout and components, at the function (software) level, they all behave similarly.

In an AMT vehicle the driver has an accelerator pedal, a brake pedal, a program / gear selector lever and (optional) steering wheel paddle shifters. With the lever, the driver can select at least four modes:

• Automatic (also called Drive) (A, D)
• Manual (M or +/-)
• Neutral (N)
• Reverse (R)

In the Automatic mode (also called Drive mode), both the decision to shift gears and the actual gear shifting is performed by the transmission control module, without any intervention or input from the driver. The main criteria for a gear change is calculated function of the vehicle speed and engine load (accelerator pedal position).

In Manual mode, the driver can decide when to shift gears. By tipping “+” a upshift if requested and by tipping “-” a downshift is requested. In this mode, there are some protection functions active, which will shift the gears even if the driver didn’t requested it. For example, if the engine speed is too high, an upshift will be performed and, if the engine speed is too low (not enough engine torque), a downshift will be performed.

Most of the vehicles with AMT have a Snow mode. This mode is useful in driving conditions with low friction of the road. In this mode, for vehicle launch, the 2^nd gear is selected instead of the 1^st gear. This way, the traction force at the wheel is limited and wheel slip is avoided.

The main advantages of an automated manual transmission (AMT), compared with a manual transmission (MT), are:

• more comfortable driving (the gear shifting is done automatically)
• better fuel economy (the engine is kept in the most fuel efficient operating zone, through the gear ratio)
• wear diagnostic (the electronic controlled actuators can measure clutch wear and inform the driver)

The disadvantages is the higher price of the transmission which translates in slightly higher price of the vehicle.

6 Comments

Phill

How does the creep function work. Is it just slipping the clutch to allow low creep speed

Anthony Stark

Yes, it is slipping the clutch. Depending on how is calibrated it can slip at the beginning, to launch the vehicle and could fully engage later, which means that the vehicle is “idling in gear”. During the clutch slip control, the engine torque is also controlled to make sure that the engine is not stalled by the high load.

Geoff Lane

On my new 2021 Picanto it suggests creep is disengaged when brake is used (either foot brake or handbrake), so guessing when stationary and brake applied clutch fully disengaged, when brake released creep initiated until speed sufficient to fully engage.

Winston Poole

The 2020 model i10 has automated manual transmission , is it fully electrically actuated?
Thanks.

Mohammad

Really helpful thank you

Suresh Nabar

Hi! I have a Honda Civic 1.8SMT. I wish to change it to ATM. Please advice if it is possible and what would be the cost.

Even though close to 80% of heavy truck transmissions sold by Eaton are manual, there is still a demand for automatic transmissions. Eaton manufactures majority of the Class 8 manual transmissions for the United States and Canada with the exception of Mack whom use their own transmissions.

There are three types of transmissions found in semi-truck tractors, which are automated manual transmission, automatic transmission, and manual transmission. This article will mainly explore automated manual transmissions which are also referred to as automated mechanical transmissions. Allison TC10 automatic transmission is the only automatic transmission available for trucks today. TC10 transmissions are not yet adept to highway/over-the-road trucks therefore will not be covered in this article as we aim to determine the best semi-truck automatic transmission.

What is an automatic manual transmission?

An automatic manual transmission (AMT) is a combination of the traditional manual and automatic transmissions. An AMT is when a mechanical transmission is automated through the addition of actuators, computers, and sensors to the shift clutch and fork. People in the industry will commonly refer to AMT’s as an automatic transmission but it is important to make the distinction especially as torque converter hydraulic automatic transmissions are beginning to enter the market. The electronic parts which give AMT’s its name include the driver interface, gear shift actuator, sensors, clutch actuator, driver display (speeds) base gearbox, electronic control unit, and a clutch or torque converter.

The main supplies of automated manual transmissions are Daimler’s Detroit Diesel, Eaton, and Volvo. The AMT works by using a computer control system to automatically shift the gearbox of a manual transmission. This process is supported with actuators for the clutch and shift forks. There are different power modes for different types of driving conditions including maximum grade-ability and low speed maneuverability. AMTs have two pedals and a shift pad in place of the gearshift lever.

Automated Manual Transmission Smart

If you want to get an idea of which truck manufacturer uses which transmission supplier with which engine supplier, then refer to the table below:

Benefits and Downsides

There are benefits and challenges associated with AMT’s as there are with all types of truck transmissions.

Benefit #1: Better fuel efficiency

Manual transmissions are prone to human error because shifting the gear at the right time is important if the truck is to maintain the correct torque and speed for the corresponding driving situation. By preventing inefficient shifting by a trucker, the computer is able to override the manual shifting to produce more accurate gear positions. That is not to say that AMTs do not require skill to operate. In fact, the level of fuel economy benefits a truck operation gets out of an AMT will depend upon the capability of the driver and how well they are trained to handle electronic transmissions. However, it can be firmly said that the skill level and attention to detail required to operate an AMT is less than a manual transmission. The average improvement in fuel economy for fleets is estimated at 2%.
Another way fuel economy is improved with AMTs is through the coupling of electronic transmissions with other powertrain parts such as engines that use an electronic diesel fuel injection control system. Lower RPM with high torque allows the engine to consume less fuel. Down-speeding or low speed gearing with AMT’s has been analyzed by Cummins to cause a reduction in fuel economy from 7.10 MPG (AMT) to 6.92 MPG (manual) during a 330-mile highway haul which utilized the same route.

Benefit #2: Better Driver Recruitment, Training, and Safety

The people who make up the trucking industry benefit from the use of AMTs. In 2015, the American Transportation Research Institute ranked driver shortage as the 3rd biggest issue concerning the trucking industry. Perhaps, the career description is not as appealing to younger people and women so the familiarity of automatic transmissions can improve driver recruitment with these demographics. Existing drivers have also reported that less effort is required with AMTs compared to manual transmissions.

There are also some downsides to using an AMT in your truck(s).

Downside #1: Higher upfront cost and lower resale value

On average, an automated manual transmission costs $3,000 – $5,000 more than a manual transmission and when it’s time to sell they will net you a $1,000 to $1,500 loss.

Downside #2: Maintenance costs are higher

Electronically controlled transmissions are made up of more parts so when it comes to repairs, the cost is expected to be higher than its counterpart. However, AMTs do not place as great of a load on the clutches which means the clutch will have a longer life and reliability level.

It should be kept in mind that automated manual transmissions have only recently begun picking up steam in terms of their use which means most AMTs are still in their initial warranty coverage period. As a result, there is a lack of concrete data to accurately determine maintenance cost averages.

Downside #3: The need to Spec a truck in a more integrated way

Electronic transmissions will probably require you to assess the overall parts of your semi-truck tractor to ensure they are compatible for the best performance. Therefore, evaluate the powertrain as a whole and see how a AMT will fit in with the other parts such as the engine and axles.

Detroit Transmission

Daimler, the parent company of Detroit introduced its first automated manual transmission to be sold in North America. Detroit launched the production of its DT12 AMT in 2013.

The DT12 does come in a smaller variation but the one for the standard sleeper highway semi-truck, is approved for 120,000 GCWR (Gross Combined Weight Rating).

The ECOAST mode automatically disengages the transmission when traveling downhill. As a result, engine RPMs will drop, momentum will be maintained, and fuel economy will go up. It also has skip shift mode which essentially skips unnecessary gears which help improve acceleration to get to the cruise speed more efficiently. The Common Powertrain Controller improves communication and operation efficiency throughout the power-train. It is one of the lightest class 8 truck transmissions which is mainly due to its

It is one of the lightest class 8 truck transmissions which is mainly due to its aluminum housing and single countershaft. Detroit has also recently added a power take-off feature to their engines which is especially useful for owner-operators that haul different types of goods.

Eaton Transmission

Eaton has the largest market share in the heavy-duty truck transmission sector. It plays a similar role like Cummins does with its engines, being thatalmost every truck brand utilizes their product in their vehicles. However, Eaton transmissions are not featured in Mack trucks.

Eaton transmissions have been reported to perform well with Cummins’ engines.

Even though Eaton has made adjustments to its previous AMTs such as adding more aluminum, eliminating the external oil cooler, and reducing the number of hoses by 12 feet, the it is still a significant amount heavier than Volvo or Daimler transmissions.

Eaton’s Ultrashift PLUS series is available in 6 different models suitable for linehaul and vocational purposes. The Linehaul series for the UltraShift PLUS is built from the foundation of the Fuller 10-speed manual and utilizes an electronic clutch actuator to shift in a two-pedal method. It has no clutch pedals. The hill start aid will prevent your truck from rolling back. Skip shifting is featured to avoid unnecessary gears. Other features in the Eaton UltraShift Plus LSE are:

• Multiple operating modes including low, manual, and automatic
• Performs up with the highest torque capacity engines
• Engine overspeed protection
• Creep mode helps operator to curb, spread, and pave.

Volvo Transmission

Volvo manufactures its own transmissions for its own trucks under the I-Shift product line. Volvo does offer Eaton’s UltraShift PLUS. It may be of interest to you to know that Volvo is the parent company of Mack meaning they own the company. The I-Shift transmission is the same AMT used in

Mack Trucks but it is marketed under the name Mack mDRIVE which are paired with MP8 heavy-duty truck engines.

There are 4 types of I-Shift transmissions that vary based on software and mode. They are fuel economy basic, performance premium, comprehensive premium, and gentle-shift. The rock out and power launch features help truckers get their truck moving if it gets stuck in snow or mud.

Refer to this informative brochure for additional help regarding Volvo’s transmissions.

Factors to consider when evaluating the best semi-truck automatic transmission

Now we will discuss some key factors to consider when deciding which is the best semi-truck automatic transmission to buy.

• It should take little time to shift between gears
• Cost should be reasonable
• Power-take off operation should be included
• Good noise and handling
• No external cooler should be required
• Serviceable with reasonable maintenance costs
• Should not require special fluids
• Engine speed should be maintained at high levels when decelerating to maximize engine retardation.

Automated Manual Transmission Pdf File

Gear ratios will be covered in a future guide. For now, you should have enough basic information to be informed of the different automated manual transmission options and to have an idea of what specifications are relevant to you. Consult the respective AMT manufacturer’s websites for more information about their products.

Automated Manual Transmission Explained

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