MPS6

Design and function

Note! Since the illustrations in this service information are used for different model years and/or model versions, some variation may occur. However, the essential information is always correct.

Transmission components










Input shafts




A. Inner input shaft
B. Outer input shaft





Inner input shaft:
A. 1st gear
B. 3rd gear
C. 5th gear

Outer input shaft:
D. 4th and 6th gear
E. 2nd gear
The split (divided) input shaft is the heart in the transmission. It consists of an outer hollow shaft which encloses an inner shaft.
The outer shaft powers the even gears, 2nd, 4th, and 6th.
The inner shaft powers the uneven gears, 1st, 3rd, 5th, as well as reverse gears.

Synchronization
The synchronizing units, interlock ball, springs and companion flange section make up a single unit. The synchronizing rings are made of brass. 1st, 2nd, 3rd and 4th gears have double synchronizing rings. 5th, 6th and back-up gears have a single synchronizing ring.
The synchronizing units for 1st, 2nd, 3rd and 4th gears are on the output shaft for 1st, 2nd, 3rd and 4th gears.
The synchronizing units for 5th, 6th gear and back-up gears are on the output shaft for 5th, 6th and back-up gears.

Wet double clutch









The transmission has two parallel wet clutches.
During shifting, they transfer the power from the engine to the split input shaft in the transmission.
A "wet" clutch is a clutch where the parts are immersed in oil to reduce friction and thus limit heat production. Each clutch has its own oil supply and cooling.
Wet disc clutches use hydraulic pressure to perform shifting. The oil acts inside the clutch piston. When the clutch is activated, the hydraulic pressure in the piston forces the coil springs to press the clutch disc against a fixed thrust plate.
The clutch disc has inner an tooth pattern which is adapted to engage the splines on the clutch drum. During rotation, the clutch drum engages and receives the power from the engine.
At declutch the oil pressure in the piston is reduced, which means that the pressure is reduced on the disc and the thrust plate.
Clutch 1 controls the uneven gears, 1st, 3rd, 5th, as well as reverse gear.
Clutch 2 controls the even gears, 2nd, 4th, and 6th gears. The clutches are independent of each other.
The double-clutch system has a damping device that connects the engine to the input side of the wet clutch system.
It is only during shifting that both clutches work at the same time.

Gearshift forks




1. Gearshift forks
There are 4 gearshift forks in the transmission. The Transmission control module (TCM) activates solenoids, which in turn activate hydraulics so that the gearshift forks mechanically engage the gears.

The gears' positions per gearshift fork are:
Gearshift fork 1 (uneven): R-N-5
Gearshift fork 2 (uneven): 3-N-1
Gearshift fork 3 (even): 2-N-4
Gearshift fork 4 (even): P-N-6
Both an even and an uneven gear can be activated at the same time and are then handled in parallel.
5th gear and N are blocked if R-gear is engaged, and N-gear and 1 are blocked if 3rd gear is engaged. Corresponding for even gears.
For more information about the Transmission control module (TCM), solenoids and sensors, see Design and function, transmission control module (TCM).

Oil pump




1. Oil pump
2. Oil filter
The oil pump supplies the hydraulics with oil and supplies the transmission's other components with oil for lubrication and cooling. The oil pump is driven by the engine.

Differential




The differential distributes power equally between the drive wheels, even if they are rotating at different speeds.
The differential consists of the differential housing, large and small side gears, shaft journals and thrust washers.
The differential has 4 gearwheels. The differential housing is completely sealed so that if a drive shaft is removed no dirt can penetrate and no oil can run out.

The hydraulic system









The transmission's hydraulic system consists of oil pump, wet double clutch, gearshift forks, hydraulic control system, and oil cooler.
The solenoids, that control the hydraulic valves, are located in the transmission's control system, which is installed on the transmission's leading edge. The solenoids are activated by the Transmission control module (TCM).
By controlling the hydraulic oil's pressure and flow the solenoids can control the transmission's cooling and lubrication of components, as well as control which clutch pressure and torque shall be used. Excess oil is lead back to the oil sump.
Gearshifting is performed by the oil sump building up a hydraulic pressure. The hydraulic valves, that are controlled by their respective solenoid, send the hydraulic pressure on to the clutch in question and gearshift fork, depending on which signals that come from the Transmission control module (TCM). The hydraulic pressure is built up at the clutch and then drops at the onset of shifting.
Information about how the Transmission control module (TCM) controls the solenoids is available in Design and Function, Transmission control module (TCM).

Oil chamber









The transmission has 3 oil chambers, one for the clutch, one for the hydraulic control system, as well as one for the mechanical parts in the transmission, such as shafts and gears.

Caution! The transmission oil differs from conventional ATF oil properties. Always use transmission oil that is specified for this transmission. Otherwise the function of the transmission will be damaged.

The oil level is checked using an overfilling plug (the transmission does not have conventional oil dipstick). For information on how oil level is checked, see INFORMATION/REPAIR/CLEANING CHECK AND ADJUSTING/Power transmission/Transmission.

Interface transmission - engine









The interface between the transmission and engine consists of a dog-clutch (claw clutch) and is unique to this transmission. The dog-clutch consists of 8 dogs (claws) that engage 8 dogs (claws) on the flywheel on the engine and are pre-loaded with a spring.
The interface is designed so that it can absorb small movements between engine and transmission.
Before the transmission is assembled with the engine, the first flywheel's first dog (claw), which is narrower, be fitted against the spring in the clutch housing with a special tool. The function of the first dog (claw) on the flywheel is to pre-load the spring on the clutch housing, the other 7 dogs transfer the engine's torque to the transmission.

Gear selector assembly




The gear selector assembly is positioned in the center console and is mechanically connected to the transmission by a cable which affects the gear valve.
In addition to positions P/R/N/D, a lever carrier with Geartronic also has a position for manual shifting (M). The manual gear positions can be selected at any time on the move.
For downshifting, the gear selector shall be moved to minus (-). For upshifting, the gear selector shall be moved to plus (+). At start, 3rd gear is the highest possible gear. The engine can only be started in position P or N.

Power flow

From 1st to 2nd gear




A. 1st gear.
B. Prepares transfer to 2nd gear.
C. Changes clutch.
D. 2nd gear.
Transfer from 1st gear to 2nd gear takes place in seven steps:

Step 1:
1st gear transmits full torque.
2nd gear is in neutral position.

Step 2:
1st gear transmits full torque.
2nd gear's control device is pressurized to synchronize and engage the gear.

Step 3:
1st gear transmits full torque.
2nd gear is fully engaged, the clutch prepares (is filled with hydraulic oil) to prepare power transmission.

Step 4:
1st gear transmits full torque but is reduced when 2nd gear's clutch increases the force.

Step 5:
1st gear's transfer force is reduced to zero when 2nd gear's clutch increases (takes over) the force.

Step 6:
1st gear does not transmit any power and its clutch is completely open.
2nd gear's clutch receives the engine's power, slipping is reduced to zero.

Step 7:
1st gear is disengaged.
2nd gear transmits full torque.
Other gearshifting takes place in the same way.

1st gear





2nd gear





3rd gear





4th gear





5th gear





6th gear





Reverse gear