Part I

8-Speed Automatic Gearbox 8HP

8-speed automatic gearbox 8HP
The new 8-speed automatic gearbox transfers more torque to the wheels and simultaneously increases efficiency. This 8-speed automatic gearbox is a planetary gear train with four single planetary gear sets.
The eight forward gears and the reverse gear are controlled hydraulically and electronically using a mechatronics module. The hydraulic shift unit and the electronic transmission control (EGS) have been combined to the mechatronics module.
The individual gear sets are connected by five shift elements, two multidisc brakes and three multidisc clutches. The planetary gear sets are aligned so that three shift elements are closed and only two are open for each gear. The considerable advantage is the reduction of drag.







Technical data
Power transmission in kilowatt 550 kW
Power transmission in Newton 900 Nm
metre
Torque converter NW270TTD
Maximum constant speed of the 7000 rpm
torque converter
Gearbox weight including oil in kg 99,0
Towing suitability 500 km at up to 80 km/h

Brief component description
The following components of the 8-speed automatic gearbox are described:
- Gear selector switch (GWS)
- Gear selector display
- Electronic transmission control (EGS)
- Gear sets
- Shift elements
- Torque converter
- Oil pump
- Parking lock
- Emergency release

Gear lever switch
In the Rolls-Royce, the selector lever for the automatic transmission is on the steering column.
The selector lever has an individual control unit, the so-called gear selector switch (GWS). The control unit is connected to the electronic transmission control (EGS) via the PT-CAN. A further connection is run via the PT-CAN2 for redundancy reasons.
The selector lever has a centre position. This is why the selector lever always returns to its initial position.







NOTICE: Separate functional description!

There is a separate functional description for the gear selector switch.

Gear selector display
The gear selector display is shown in the TFT display of the instrument panel (KOMBI). Faults are displayed by a bright, flashing gear selector diagram.







Electronic transmission control (EGS)
The electronic transmission control (EGS) processes signals from gearbox, engine and vehicle. The desired state of the gearbox is calculated in conjunction with stored data and from these signals, such as:
- Gear selection
- Converter lockup clutch strategy
- Specified setpoint value for activation of brakes and clutches

To implement the specified setpoint values, solenoid valves and pressure regulators are actuated using the power output stages and current regulator circuits. This controls the hydraulics of the automatic transmission.







The following sensors are in the gearbox:
- Turbine speed sensor
- Output speed sensor
- Position sensor to detect the parking lock position
- Gearbox oil temperature sensor
- Substrate temperature sensors

The processor of the electronic transmission control (EGS) has an internal memory of 2048 kilobit. The basic gearbox program occupies approx. 1536 kilobit. The approx. 512 kilobit remaining include the vehicle-specific application data. You can program the electronic transmission control (EGS). The main part of the programming process was performed by the Digital Engine Electronics (DME) programming. Adapting the functionality of the electronic transmission control (EGS) was implemented.

NOTICE: Reset adaptations!

Adaptations are performed automatically during the journey. After having performed repair work on the 8-speed automatic gearbox or replacing the 8-speed automatic gearbox, adaptations must be reset using the diagnosis system. Subsequently go for a test drive and engage all gears.
The valve body is located inside the mechatronics module. It includes valves and channels for hydraulic control. The valve body is divided into a lower section (valve body) and an upper section of the valve plate. They are separated by an intermediate plate. The following components are in the lower section:
- 14 hydraulic valves
- 7 electronic pressure control valves
- 1 solenoid valve
- 1 parking lock magnet to lock the parking lock

There are seven additional hydraulic valves in the upper section as well as inserts such as balls, screen filters and plate valves. The electronics module including the electronic transmission control (EGS) is fitted in the top valve body. The hydraulic lines on the upper section are the connection to the channels and connectors of the gearbox housing.







Gear sets
The eight forward gears and the reverse gear are generated by four single planetary gear sets. The two front gear sets have one single common sun gear. The others have one sun gear each.
The following information applies to planetary gear trains in general:
If two components of the same gear set (sun gear, planet spider or ring gear) are running at the same speed, this gear set is in block operation. The individual components are not moving with relation to each other but they rotate together around the centre axis.
If, for example, multidisc clutch E is closed, the sun gear and the ring gear of the gear set are rotating at the same speed. The planetary gears do not wear off. The planet spider also rotates with the same speed. The sun gears of the gear sets are supported on the transmission input shaft so they can rotate freely. The following rigid connections can be established in addition to those by the clutches:
- Planet spider 2 with transmission input shaft
- Planet spider 1 with ring gear 4
- Ring gear 2 with sun gear 3
- Ring gear 3 with sun gear 4
- Planet spider 4 with output shaft

One or more paths are created by shifting the shift elements and the mechanical connections of different components in the automatic transmission. These paths transmit the drive torque and transmission subsequently develops.







Shift elements
Brakes and clutches are described as shift elements that enable shifting and changing gears. The automatic transmission needs only five shift elements to change eight gears. The following shift elements are used:
- Two fixed multidisc brakes (brake A and B)
- Three rotating multidisc clutches (clutches C, D and E)

The multidisc clutches (C, D and E) transmit the drive torque to the planetary gear train. The multidisc brakes (A and B) support the torque against the gearbox housing.
Clutches and brakes are closed hydraulically. For this purpose, a piston is pressurized with oil to compress the disc sets. All shift elements, except multidisc brake B, are pressed back into their initial position by a disc spring as soon as the oil pressure drops. Multidisc brake B is opened hydraulically. The shift elements enable changing gears without traction interruption. For this reason, all gearshifts (from first to eighth gear and back) are performed as overlapping gear changes. During the shift process, the "transmitting" clutch remains actuated with a lower pressure value until the "receiving" clutch can transmit the torque.

Torque converter







A hydrodynamic torque converter is used in the 8-speed automatic gearbox. Its basic design with impeller, turbine wheel and stator remains unchanged. However, the three-way converter is a power-optimized development where the converter lockup clutch is actuated by an individual oil line. This provides the following advantages:
- The torque converter is optimally supplied and cooled even if the converter lockup clutch is closed
- Better activation of the converter lockup clutch is possible in all driving situations.

Line 1 is for oil supply.
Line 2 is for oil return.
Line 3 is for pressurized oil supply of the converter lockup clutch.
To decouple rotational vibrations from the engine to the gearbox, this type of torque converter can be combined with known damper systems:
- Turbine torsional vibration damper
- Dual damper system

The converter lockup clutch is for suppressing slip during torque transmission. It therefore contributes towards reduced consumption. The new three-way converter actuates the converter lockup clutch by a separate oil line. This means it is independent and disconnected from the turbine chamber. As before, the converter lockup clutch has a control range, i.e. an operating range in which a defined slip between gearbox input and output end is permitted. Mainly the transmission during opening or closing. This slip reduces rotational vibrations that are transferred from the engine to the gearbox. Improved control results from the possibility of considerably smaller mechanical slip in many operating ranges. An open converter lockup clutch was previously required for comfort reasons. Previously opening and closing the converter lockup clutch was performed by the pressure regulation of the gearbox. The direction of oil flow in the converter was influenced. Depending on the direction of oil flow, different pressure stages developed on both sides of the piston. This was how it was moved to either open or close. The improvement of the new gearbox is that independent activation results in improved control. This enables more operating ranges to be operated with a controlled instead of an open converter lockup clutch. Additionally, the flow of the converter can be optimized to suit the respective requirements at any time (e.g. cooling).

Oil pump
The main functions of the oil circuit correspond to those of its predecessor. The oil has the following task:
- Lubrication
- Controlling the shift elements
- Transmitting torque
- Cooling

It is a conventional recirculated compressed-air system with an oil pump that supplies a pressure control valve and itself is supplied from an oil sump. The pressure control valve (system pressure valve) sets the system pressure.
The system pressure is between 5.5 and 17.5 bar at a volumetric flow of 14.5 cm3 per minute.
A new type of oil pump is used. A double vane-type compressor is used in the 8-speed automatic gearbox. Double means that the shape of the pump body enables two supplies in one rotation of the pump. The double vane-type compressor is located in the gearbox behind the converter housing, above oil level. It is driven by a slightly faster rotating rolling tooth-type chain directly from the converter neck.
The oil pump takes in through a filter and supplies the oil to the system pressure valve. The required system pressure is set. Excess oil is returned to the intake port of the oil pump. Introduction into the intake port is in the direction of flow so that this has a charging effect. Cavitation and noise emission are therefore avoided and efficiency is improved.
The advantage of the double vane-type compressor is its small size compared to its delivery rate. The efficiency of the oil pump has improved by 10 - 30 % across the entire engine speed range compared to the toothed pump in the 6HP automatic transmission.

Parking lock
The 8-speed automatic gearbox is equipped with a parking lock to secure the vehicle against rolling away. The mechanism is identical to that of the predecessor. The parking brake blocks by using a locking pawl that engages in the gearing of the parking lock gear. The parking lock gear is located on the output shaft of the gearbox. The parking lock pawl is engaged by spring force. The parking lock is designed to ensure a secure position of the vehicle under the following preconditions:
- Uphill or downhill gradient of up to 32 %
- Speed below 2 km/h

The parking lock must not engage at speeds above 5 km/h. All models are equipped with electric gearshift via the gear selector switch (GWS). The parking lock is engaged by pressing a button or, under certain circumstances, also automatically.
The parking lock is actuated electrically. The notched disc in the gearbox is omitted. It is replaced by a parking disc, a parking lock cylinder, a solenoid valve and a parking lock magnet. A distinction is made between mechanically engaging the lock and associated electric activation. As mentioned above, the parking lock is engaged using spring force. Electric activation of the lock performed by:
- Activation via a button on the selector lever
- Switching the engine off while drive position is engaged
- If, when stationary, selector lever position R or D are engaged and neither the accelerator pedal nor the brake pedal are being operated, the seat belt of the driver's seat is released and the driver's door is opened.

The electronic transmission control (EGS) activates the solenoid valve and the parking lock magnets. The solenoid valve is located in the hydraulic shift unit. The parking lock magnet is located on the cylinder for the parking lock. Upon engaging the parking lock, the parking lock magnet for the parking lock cylinder is switched off. This results in releasing the mechanical lock and the piston. The solenoid valve in the shift unit is also switched off. The valve moves to rest position and the parking lock cylinder is bled. A pre-tensioned helical coiled spring on the parking disc pulls the piston towards the parking lock. The parking lock is engaged using the connecting rod attached to the parking disc.
It is engaged hydraulically. To engage, solenoid valve 2 actuates the parking lock valve so that the system pressure reaches the parking lock cylinder. This pushes the piston back against the spring force and the parking lock is released. The parking lock magnet is additionally actuated. It also locks the piston with a locking mechanism or keeps it in position N when the engine is at standstill. The parking lock is opened only under the following preconditions:
- Engine running
- Footbrake depressed
- Selector lever position in R, D or N

Emergency release
An emergency release is to be incorporated into the 8-speed automatic gearbox.
An additional Bowden cable enables manual release of the parking lock in certain situations, such as during power failures and when in emergency program.
Emergency release is currently located in front of the controller under the cupholder.
As of a later point in time the emergency release is only possible on the housing of the automatic transmission.

System overview







System functions
The following system functions are described:
- Generating gears
- Standstill decoupling
- Overlap control
- Driver type adaptation
- {LOW} mode (Rolls-Royce only)
- Driving situation evaluation

Generating gears
The following table shows the generation of individual gears. It shows which shift elements are closed and which are open as well as the resulting transmission.







Standstill decoupling
When the vehicle is at standstill and drive position D is engaged, the impeller rotates and the turbine wheel is at standstill. The vehicle drives off if the brake is not applied. Torque is transmitted. If the vehicle is held back by the brake, the driving power is transformed into heat by the inner friction of the gearbox oil in the converter. This driving power is generated by idle speed control of the engine that counteracts the resistance in the converter. For this reason, the 8HP automatic transmission is equipped with a so-called standstill decoupling, already used in the 6HP model. Standstill decoupling is realized by opening multidisc brake B. This reduces engine performance. If the vehicle is at standstill and the gear selector is in D, you can reduce fuel consumption.