Mercedes-Benz 9G-Tronic transmission

9G-Tronic is Mercedes-Benz's trademark name for its 9-speed automatic transmission for longitudinal engines. The transmission is suitable for rear-wheel drive, all-wheel drive, hybrid, and plug-in hybrid drives and has been gradually introduced in most model series, starting off with the W9A 700 converter-9-gear-automatic with maximum input torque as core model. The transmission was used in the E 350 BlueTEC in 2013 for the first time, and successively replaced both the 7-speed 7G-Tronic transmission and the 5-speed 5G-Tronic transmission. It includes versions for a maximum input torque of.
After the 5G- and 7G-Tronic, this is the 3rd generation of modern automatic transmissions, internally identified as NAG 3.
The Jatco 9AT transmission is based on the same globally patented gearset concept.

Key Data

Development and production

Development took place at the group's headquarters in Stuttgart-Untertuerkheim. Initially, the transmission was produced only at the Daimler plant not far away in Stuttgart-Hedelfingen. Since April 2016, the transmission has also been produced at Daimler's subsidiary Star Assembly in Sebeș, Romania.

Licensing to Jatco Ltd

In 2019, the Jatco Ltd, based in Fuji, Shizuoka, Japan, started licensed production for use in Nissan and Infiniti vehicles. In this version, input torque is limited to, allowing each of the gearsets 1, 2, and 4 to use only three planetary gears. Slightly modified gear dimensions give it a span of just under 9.1:1.

Specifications

Torque converter

One main focus was on increasing shift comfort, which is achieved on the one hand by measures in the control system and on the other hand by designing the torque converter accordingly. The hydrodynamic torque converter was largely taken over from the previous 7G-Tronic transmission.

Control system

The 9G-Tronic is fully electronically controlled. The shift elements are controlled via a new type of hydraulic direct control with electromagnetically actuated valves, which enables fast and smooth gear changes. Compared to the previous transmission, which had a hydraulic pilot control, leakage losses have been reduced by 80%.

Oil supply

The transmission is equipped with two oil pumps to ensure an energy-efficient supply of long-life synthetic fuel-economy low-friction oil: a mechanical rotary vane pump with chain drive, which is significantly smaller than its predecessor and located next to the main shaft, and a pump driven by a brushless electric DC motor. The mechanically driven pump is responsible for the basic supply of the transmission, with the flow rate depending on the speed of the drive motor. The additional pump is switched on by the electronic transmission control unit as required. This design enables the lubricating and cooling oil volume flow to be regulated as required and makes the 9G-Tronic start/stop-capable. When the drive motor is at a standstill, the transmission remains ready to start solely due to the supply from the electric auxiliary pump.
Filter elements for the two pumps are integrated in the plastic oil pan.

AMG SpeedShift 9G

AMG SpeedShift TCT 9G

The TCT 9G transmission is essentially the 9G-Tronic.

AMG SpeedShift MCT 9G

developed the MCT 9G transmission. It was first introduced in the Mercedes-AMG E 63 4Matic+.
The MCT transmission is essentially the 9G-Tronic with a start-off wet clutch replacing the torque converter. This saves weight and optimises the response to the accelerator pedal input. It is a computer-controlled double-clutching. The MCT acronym refers to this multiple-plate clutch. Its torque is rated at and it offers 4 drive modes: “C”, “S”, “S+” and “M” and boasts 0.1 second shifts in “M” and “S+” modes. MCT-equipped cars are also fitted with the new AMG Drive Unit as the central control unit for all driving dynamics functions and an innovative Race Start Function.
The driver can change gears either using the steering-wheel shift paddles or conventionally the selector lever. The new Race Start Function is a launch control system that enables maximum acceleration while ensuring optimum traction of the driven wheels.

Combined Parallel And Serially Coupled Gearset Concept For More Gears And Improved Cost-Effectiveness

Main Objectives

The main objectives in replacing the previous 7G-Tronic model were to improve fuel consumption by adding gears and increasing the gear span, while at the same time reducing manufacturing costs.
The wide gear span allows the engine speed level to be lowered, which is a decisive factor in improving energy efficiency and thus reducing fuel consumption by 6.5 %. In addition, the lower engine speed level improves the noise-vibration-harshness comfort and the exterior noise is reduced by up to 4 dB. A speed of 120 km/h is reached in the Mercedes-Benz E 350 BlueTEC in 9th gear at an engine speed of approx. 1350 rpm. Unsurpassed ratio span among longitudinal automatic transmissions for passenger cars.

Extent

As the design of the predecessor was significantly more complex than that of the direct competitor 6HP and even the new 8HP model from ZF with one more gear, the specification sheet also stipulate that at least one shift element must be omitted. This was achieved thanks to high-speed computer-aided design and has resulted in a globally patented gearset concept that requires the same installation space as the previous model and is also lighter. In the process, 85 billion gearset concepts were examined. Additionally, the unit brings the ability to shift in a non-sequential manner – going from gear 9 to gear 4 in extreme situations simply by changing one shift element.
After the 5G- and 7G-Tronic, this transmission is the 3rd generation in which in-line epicyclic gearing have been combined with parallel epicyclic gearing. The resulting progress is reflected in an even better ratio between the number of gears and the number of components used compared to all layouts previously used by Mercedes-Benz.

Gearset Concept: Quality

The ratios of the 9 gears are better distributed in all versions than in the direct competitors 8HP from ZF and much better than in the 10-speed transmissions from Ford/GM and Aisin/Toyota. The only noticeable weaknesses are the relatively small step between 5th and 6th gear and the too small one between 6th and 7th gear. These cannot be eliminated without affecting all other gears and thus impairing gear steps. On the other hand, these weaknesses are not overly significant.
All in all

the extra effort, reflected in the acceptable elasticity compared to the ZF 8HP is more than justified and
compared to the 10-speed gearboxes from Ford/GM and Aisin/Toyota, the absence of the 10th gear is more than compensated for by the significantly better distribution.

Maintenance

Compared to the predecessor gearboxes NAG 1 and NAG 2, the NAG 3 gearbox is much more highly integrated, meaning that repairs are only possible by replacing entire assemblies when servicing is required. This applies, for example, to the oil filters permanently integrated in the plastic oil pan. Another example is the fully integrated mechatronic module with sensors, control unit and electrohydraulic shift plate. This module must be replaced as a unit, even if, for example, only one sensor is defective.

Nomogram

This nomogram is a real geometric calculator exactly representing the rotational speeds of the transmission's 3x4 = 12 internal shafts for each of its 9 ratios, grouped according to their 4 permanent coupling on 3 joint ordinates and 5 independent ordinates. These ordinates are positioned on the abscissa in strict accordance with the proportions of the sun gears' teeth numbers relative to those of their rings. Consequently, the output ratios on the 3rd ordinate follows closely those of the actual transmission. This advantageous geometric construction sets us free from Robert Willis' famous and tedious formula, because all calculations are exclusively determined by lengths ratios, respectively teeth numbers on the abscissa for the 4 epicyclic ratios, and of rotational speeds on the 3rd ordinate for the 10 gear ratios.
This nomogram reflects the version from 2013.