The 9g Tronic gearbox is the first 9-speed automatic transmission complete with torque converter, but now, this system, which is designed for premium vehicles, is set to debut in the E 350 BlueTEC.
A classic automatic transmission’s drive element is a hydrodynamic torque converter. In the 9g Tronic transmission, the hydraulic circuit found in the torque converter has been improved, and the efficiency has also been raised to 92%. This is critical for fuel economy because there is a need to keep the losses brought about by physics when engine torque is being transferred to the input shaft transmission to a bare minimum. Put differently, the 9g-Tronic transmission a significant amount of engine power into tractive force. The first-generation 7g Tronic had 85% efficiency.
Key features of 9G Tronic Transmission
Twin turbine torsion damper and centrifugal pendulum
The torsion damper is not only one of the main features that enhance comfort but is also an important fuel-saving element in automatic transmission. It makes up for vibrations and eccentricities within the transmission. The law of physics states that the lower the road speed and rpm, and the lower the cylinder numbers, the more pronounced they can be. The result is that there is a conflict between fuel-efficient operation and comfort. But this is easily resolved by using a twin-turbine damper complete with a centrifugal pendulum. This can shift the center of gravity, depending on the vehicle’s rpm.
Additionally, the improved damping enables the reduction of slip in the torque converter clutch, which makes it more fuel-efficient.
The engineers have also integrated a return spring into the 9g Tronic torque converter clutch. Previously, the multi-disc lockup clutch was controlled only hydraulically. The return pressure spring enables activation even when the rpm is very low.
Oil supply using two pumps
The 9g Tronic contains two pumps to enable the efficient supply of 2nd-generation synthetic oil. The main pump, which is installed off-axis, is located adjacent to the main shaft. It’s also driven through a chain.
In an automatic transmission, for example, the 7g Tronic, the principal oil pump used to ring the transmission shaft, and it was directly driven. This way, the transmission shaft diameter made it nearly impossible to reduce the size of the pump to the appropriate size. This has caused the vane cell pump to be now put alongside the primary shaft. Also, its size is reduced to match requirements.
The mechanical principal pump, whose work is supplying oil to the electrohydraulically run automatic transmission system when the internal combustion engine is on, is supported by another electric secondary pump. The advantage of this design is that it enables the lubrication and coolant flow to be actively controlled on demand. It also implies that the 9g Tronic design can also be useful to a start/stop system.
When you switch off the engine, it leads to the actuation of the electric secondary pump, which not only ensures a defined basic structure but also guarantees that all the vital functions are maintained. When it’s time for the driver to re-start the engine, the delivery of oil by the auxiliary pump guarantees smooth acceleration. In some operating states with the engine on, the secondary pump also helps the primary pump. This can happen at very high temperatures or extremely low engine speeds. In such a case, oil flow is increased accordingly to ensure that the gears shift smoothly.
Shorter processing times and improved quality
A 9g Tronic transmission is characterized by shorter processing times per shaft and at the same time, the production quality is significantly improved. To cut down cycle times during the production process, engineers got rid of the normal guide sleeves when performing spot drilling. The machines make deep holes freehand while ensuring dimensional accuracy. Additionally, high working speeds are allowed by single-fluted cemented carbide drills that guarantee high working speeds.
In 7g Tronic plus automatic transmission, the speed was about 125 millimeters per second. This changes to a drilling speed of about 250 millimeters per minute. The immediate effect of this is that only three minutes are needed for the main shaft to be processed. This is about 63% less time compared to 7g Tronic plus production. Thanks to the improvements above, Mercedes-Benz engineers are implementing a project called “Green Project”.
Compact lightweight construction
The change of generation from 7g Tronic to 9g Tronic also saw development engineers focus more on the compact lightweight design area. Despite having two extra gears and the highest transferrable torque that just exceeds 1000 nm, the installation space required by the new automatic transmission is the same. Also, it is lighter by one Kilogram.
The 9g Tronic design also keeps the two-piece housing design. This means that the housing of the torque converter is made using lightweight aluminum alloy. On the other hand, the transmission housing uses a plastic oil pan that’s weight-optimized.
New drilling process
Creating a shaft like this is a huge challenge for production engineers. It has very specific requirements, especially when doing the 3 deep holes. For example, the drilled holes measuring 36.15 mm must adhere to the requirements of a thousandth millimeter. Additionally, machining must follow accurately defined geometrical specifications:
- Parallelism and distance of the holes viz-a-vis each other.
- The holes’ distance and parallelism versus the external haft surface,
- The need to avoid twisting completely during drilling
- The individual holes must have the correct depth
- The 3 drilled holes must have radial positioning to ensure free flow to transverse holes.
- The drilling must be free of any residues and especially microfine swarf should not be left in the holes.
The 9g Tronic gearbox certainly is a masterpiece. It has several components and features lots more new manufacturing processes which means increased complexity. The automatic gearbox is destined to perform well in the market compared to its predecessor, the 7g Tronic plus. It also has several advantages like reduced processing times, improved quality, and sturdier and lightweight construction.