Transmission - SN27.00-P-0000-01G
Model 118.3
Depending on the engine version, the new CLA-Class will be offered at market launch with three transmission variants.
6-speed manual transmission "FSG310" (transmission 711.6)
The 6-speed manual transmission was further developed to allow for its use in the new CLA-Class. It is offered in combination with the 1.4 l spark ignition engine M 282, 1.5 l diesel engine OM 608 and 2.0 l diesel engine OM 654.
Basic features of the 6-speed manual transmission include:
- 3-shaft spur gear system
- Drive shaft and both output shafts with fixed/floating bearing
- Multiple usage of gear pairs
- Four weight-optimized shift forks made from cast aluminum
- Material reductions in the housing and gear set
- Gear recognition for all gears
- Designed for torques up to 350 Nm
- Reduced transmission oil volume
- Reduced transmission weight
- Reduced drag losses
7-speed dual-clutch transmission "7F-DCT" (transmission 724.0)
The 7-speed dual-clutch transmission was further developed for use in the new CLA-Class. It is offered in the new CLA-Class in combination with the 2.0 l spark-ignition engine M 260.
Basic features of the 7-speed dual-clutch transmission include:
- Compact transmission housing
- "Wet" start-off clutch
- Park pawl via park by wire
- Fully integrated controller unit
- Electrohydraulic controller unit with electrically supported oil pump
- Start-stop suitable
- All-wheel drive 4MATIC suitable
The 7-speed dual-clutch transmission has been adapted to the installation space of the new A-Class. The dual clutch has been significantly improved with regard to the pulling-away and gearshift performance.
7-speed dual-clutch transmission "7DCT-300" (transmission 700.4)
This 7-speed dual-clutch transmission was also adapted for use in the new CLA-Class. It is offered in combination with the 1.4 l spark-ignition engine M 282 and the 1.5 l diesel engine OM 608.
Basic features of the 7-speed dual-clutch transmission include:
- Engine drag torque optimized gear set with fixed-loose bearing for output shafts
- Nested wet dual clutch
- Dip lubrication
- Electromechanical gear engagement via two selector drums
- Electrohydraulic clutch operation via pump actuators
- Software controlled clutch operation (facilitates different shift behavior)
- Electric oil pump for cooling the clutch
- Integrated transmission cooler
- Park pawl via park by wire
- Start-stop suitable
- Low dry weight of approx. 67 kg
8-speed dual-clutch transmission "8F DCT" (transmission 724.1)
The new 8-speed dual-clutch transmission sets new standards with regard to driving and gear shifting performance. At the same time, consumption and CO2 emissions are reduced further. With the expansion from 7 to 8 gears, it is possible to adapt the rotational speed of the drive gears more finely to the engine speed. This supports efficient and performance-oriented driving style. In addition, the steering axis inclination of Phi1/8 = 8.81 creates the prerequisites for being able to drive at defined vehicle speeds with a lower engine speed.
The 8-speed dual-clutch transmission 8F-DCT is used with the 2.0 l spark ignition engine M 260.
During the conception of the modular structure of the 8F DCT, the prerequisites for the combination were already created with an all-wheel drive or with a hybrid powertrain.
Transmission set-up
Essential features of the 8-speed dual-clutch transmission include:
- Fully integrated direct control
- Dry-sump lubrication
- Short start-off ratio and small gear step
- Rotational speed reduction in 8th gear
- Suitable for all-wheel drive
The weight of the 8F DCT was reduced compared to the 7F DCT by approx. 3.6 kg. The weight reduction was possible thanks to various lightweight construction measures, such as a plastic oil pan, a internal circuit with plastic cylinders, and a lightweight housing.
The gear ratio spread of Phi1/8 = 8.81 of the 8F DCT is on the tip of the dual-clutch transmissions with comparable torque capacity.
Dual clutch system
In the dual clutch system, the losses have been further reduced by the friction system of the dual clutch and the drive-off performance has been optimized. The control lever for reducing the dual clutch drag losses are the undulation of coating materials and viscosity reduction of the transmission oil.
Gear set
To be able to transmit torques up to 520 Nm, a high-performance gear set was developed in combination with the engines M260 and OM654. This gear set has been designed for a gear ratio spread of phi 1/8 = 8.81. The increments between the individual gears (differences in rotational speed) are small, which makes particularly comfortable shift operations possible.
The changeover from pre-compressed tapered roller bearings to a fixed/floating bearing and the reduction of the viscosity of the oil reduce the drag losses of the gear set to a minimum.
| Feature | Value | Unit |
|---|---|---|
| Maximum transferable torque | 1st gear: 300 | Nm |
| 2nd gear: 350 | ||
| 3rd - 4th gear: 400 | ||
| 5th - 8th gear: 450 | ||
| Maximum transferable output | 225 | kW |
| Maximum rpm | 7300 | 1 rpm |
| Number of forward/reverse gears | 8/1 | |
| Steering axis inclination | 8, 81 | phi |
| Shaft distance | 188 | mm |
| Length | 360 | mm |
| Weight | 82, 9 | kg |
| Filling capacity (Automatic Transmission Fluid) | 5, 5 | L |
8-speed dual-clutch transmission "8F DCT", cross section
Dry sump lubrication for 8-speed dual-clutch transmission "8F DCT"
The oil supply, lubrication, and cooling of the dual-clutch transmission takes place through a dry sump lubrication. During dry sump lubrication, the oil sump is pumped out, the oil level (A) is minimized and thus the churning losses are reduced. Cooling and lubrication occur through a lubricating spider which is mounted in the gear set chamber. Targeted lubrication of the toothing, a reduced oil filling capacity, and a reduced drag torque of the mechanical oil pump ensure efficient oil supply and lubrication. Additional efficiency measures include a mechanical oil pump with significantly reduced delivery volume and an electrically driven oil pump that is supported as required.
Oil filter system for 8-speed dual-clutch transmission "8F DCT"
The oil filter system in the "8F DCT" consists of:
- 1 Pressure oil filter
- 2 Suction oil filter
- 1 Dry sump oil filter
The oil from the gear set chamber runs through the dry sump oil filter and is delivered into the intake chamber via the electrical auxiliary oil pump (M42). The oil from the intake chamber is filtered through two suction oil filters. The primary suction oil filter sits in front of the mechanical oil pump, which generates the required oil pressure and flow volumes for the hydraulic procedures in the dual-clutch transmission. The secondary suction oil filter sits in front of the electrical auxiliary oil pump. Depending on the driving condition, it supplies the fully integrated transmission control electrohydraulic controller unit (Y3/14) with the filtered oil.
The waste heat of the transmission control, and the friction at the clutch plates and gear sets generate high transmission oil temperatures when driving. The waste heat is absorbed by the transmission oil. The transmission oil is filtered via a feed duct in the transmission housing over the pressure oil filter and delivered to the transmission oil heat exchanger. The transmission oil flows back through the return line to the oil pan.
Please find further information in the function description GF27.57-P-1101A "Detailed information on dual-clutch transmission oil supply".
Schematic diagram of dry sump lubrication