Part II

8-Speed Automatic Gearbox 8HP

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 cup-holder.
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.
The following input dimensions are used for controlling the standstill decoupling:

Input dimension Explanation
Brake light switch Standstill decoupling is only active if the service brake is applied. Once the service brake is released, power transmission of multidisc brake B is closed immediately even before an accelerator pedal value is detected. In the vast majority of cases, the vehicle can be prevented from rolling backwards on gradients.
Accelerator pedal value If a defined accelerator pedal value is exceeded, standstill decoupling is deactivated.
Transmission output speed If a transmission output speed is detected, standstill decoupling is deactivated.
Engine speed The converter torque is calculated from the engine speed and the turbine speed (rpm differential) and the gearbox oil temperature.
Turbine speed The converter torque is calculated from the engine speed and the turbine speed (rpm differential) and the gearbox oil temperature.
Gearbox oil temperature The gearbox oil temperature is used to calculate the converter torque. In addition, standstill decoupling is only active within a gearbox oil temperature range of approx. 13 °C and 120 °C.
Slope angle of the vehicle The vehicle's slope angle is used to adapt re-engaging of the clutch to the slopes you drive off from.

To enable driving off free of deceleration and load alteration, multidisc brake B is not completely opened. A slight slip of approximately 20 % remains so that some torque is transmitted to the torque converter. If multidisc brake B was completely open, no torque would need to be transmitted to the converter (except the inner friction in the gearbox). Jerking could result when driving off. The following example shows the difference in the gearbox between a vehicle with/without standstill decoupling. Values are approximate because inner friction was not taken into account.







Overlap control
Gearshifts in the 8-speed automatic gearbox are performed as overlapping gearshifts. For this reason, freewheels are no longer used.
The adaptive transmission control unit makes driving with automatic transmission as pleasant as possible. The vehicle detects the driver's intentions and driving style as far as possible and adapts the shifting strategy accordingly. Additionally the vehicle condition and the driving situation are taken into account. There are different adaptation modes for the D driving program in the new 8-speed automatic gearbox.
The adaptive transmission control unit adapts optimally to individual driver's choices. The driver can concentrate on steering, accelerating and braking. Gear changes are actuated independently from the respective driving situation and the drivability.
The following driving situations are taken into account:
- Winter or summer
- With/without trailer
- At sea level or in mountainous environment

Driving speed and pedal sensor position are additionally detected. In the event of a kickdown the vehicle automatically changes to the gear that offers the best possible acceleration. The adaptive transmission control unit optimally supports the possibility to directly change down across several gears. Flexible shift points in combination with an optimally matching shifting process enable sporty and dynamic driving style, pleasant driving comfort and effective consumption values. In driving program D, driving situation evaluation enables an overlapping of individual or several adaptive functions, such as hill or trailer function. A basic map is selected for driving program D. Driving program D offers the driver comfort-oriented shift characteristics in conjunction with a relatively calm shift pattern.

Driver type adaptation
The following information is processed for adaptation purposes:
- Fast depressing of the accelerator pedal
- Rapid retraction of the accelerator pedal
- Corner assessment
- Brake evaluation
- Assessment when driving at a constant speed

Adaptation assesses the longitudinal and transverse dynamics from the following operating elements with relation to the driving speed:
- Accelerator pedal
- Brake
- Steering

These values result in the current driving condition and the driver's desired load. This is the basis to determine the driver's performance request and the current driving condition. The demand for higher dynamics is detected on the basis of these values. Driver type adaptation offers a temporary adaptation of the basic map. To be able to achieve consumption and comfort targets, the system selects defensive shift characteristics in driving situations without a specific performance request. The assumption applies that the vehicle should be in the highest possible gear and only shift down if power output is requested and the engine is already supplying full torque. Downshift threshold values are distributed across the range of the accelerator pedal so that fully depressing the pedal triggers a downshift of several gears. Due to the fact that smooth gear change setup is not ideal in every situation, the current driving situation is automatically determined and taken into account as a driving operation assessment.

Fast depressing of the accelerator pedal
This function can change the basic map depending on the speed with which the accelerator pedal is depressed.
For this reason, the determined accelerator pedal value is compared with threshold values that are saved in the control unit. This comparison leads to a temporary modification of the basic map.

Rapid retraction of the accelerator pedal
This function can change the basic map depending on the speed with which the foot is taken off the accelerator pedal. For this reason, the determined accelerator pedal speed value is compared with threshold values that are saved in the control unit. This comparison leads to delayed upshifts and it also avoids (multiple) upshifts.

Corner assessment
Corner assessment reacts on the lateral acceleration of the vehicle with an indirect adaptation of the driver type using the driver type scale. Evaluating lateral acceleration avoids unexpected gear change reactions. Gearshifts with high force transmission requirements in a transverse direction can influence the stability of the vehicle in a negative way. Lateral acceleration is calculated from the speed signals of the individual wheels, the yaw rate and the driving speed.

Brake evaluation
Brake evaluation supplies a driver type category. The process is identical to the evaluation of rapid retraction of the accelerator pedal. Deceleration is subsequently calculated and compared to a limit value graph within an adjustable time base. Depending on the determined driver type it selects a gearshift map.

Assessment when driving at a constant speed
Assessment when driving at a constant speed (not dynamic driving condition) is activated if the driver maintains the position of the accelerator pedal and does not change the driving speed. The vehicle immediately shifts up to the matching gear in driving program "D". This enables a tranquil, efficient driving style.

{LOW} mode (Rolls-Royce only)
{LOW} mode is activated and deactivated by pressing the {LOW} button on the selector lever.
{LOW} mode is recommended if the braking effect of the engine is to be increased, e.g. for a steep downhill gradient. In {LOW} mode the gears continue to shift automatically, but generally in lower gears than in selector lever position D. When the engine is stopped, {LOW} mode is automatically deactivated.
If {LOW} mode is active it is displayed beneath the gear selector display on the TFT display of the instrument panel (KOMBI).

Driving situation evaluation

Winter program
The winter program is activated/deactivated automatically. A defensive shift characteristics and shift stabilization are provided on the basis of the respective basic map (avoiding pendulum shifts). This enables the highest possible stability and driving safety on wintery, icy roadways. Stable gear positions support running gear interventions of automatic stability control (ASC) or dynamic stability control (DSC) in an optimum way. Downshift requests that result in tensile force and could lead to spinning wheels are suppressed. This exempts downshift requests explicitly requested by the driver. As long as the winter program is active, functions that influence the stability of the vehicle are only effective to an extent where instability is avoided or they are completely switched off.

Hill and trailer function
The hill and trailer function adapts the shift strategy to higher tractive power requirements. The corresponding tractive power reserves are built up and, depending on the engine performance available, engine speed level is increased. This excludes or limits the tendency for pendulum shifts and unnecessary frequent gear changes during driving. One driving resistance sensor constantly establishes deviations of the current driving resistance with relation to a reference value stored in the control unit. Vehicle parameters are, for example vehicle weight, gearbox, axle transmission ratio, rolling resistance and drag. The reduced performance of the engine in higher altitudes (approx. 1 % loss of filling per 100 meters) is adapted with hill adaptation. If possible, the loss of filling is compensated using the engine speed. The correction is calculated with a relation value from the determined air pressure and a reference value stored in the control unit.

Corner function
The corner function serves to support the dynamics driving experience. In addition, the corner function protects against gearshifts that would overstress the force application potential of the wheels. When cornering with a corresponding lateral acceleration, the driver gets the feeling that the performance of the engine is supplied sufficiently. Upshifts are partially suppressed with regard to driving safety and comfort. On a road with several corners (constant change of lateral acceleration) the corner function is not deactivated on straight stretches in-between. Upshift suppression remains on when going into the following corners. For comfort reasons, gears are not maintained at high engine speeds in long corners.

Braking downshift function
Depending on the performed braking action, downshifts are triggered at different speeds and only for as long as the driver is braking. For this reason, vehicle deceleration is determined by a change of the speed-proportional signal (wheel speed or gearbox output speed) or using the brake pressure in the wheel brake system. The optimum shift speed is determined depending on the following values for the individual downshifts from one or several stored characteristic curves:
- Speed when starting to brake
- Determined deceleration or read brake pressure

Control function for speed
Speed-controlled driving mode is supported by the shift strategy to achieve an efficient and smooth overall behavior. It ensures that the acceleration or tensile force (uphill driving) requested by cruise control is reached.

Additionally, there is no loss of comfort by increased gearshift activity or pendulum shifts. In line with the driving situation (constant-speed driving, acceleration, deceleration), cruise control selects the requested tensile force and the ideal gear. When cruise control is active Integrated Chassis Management (ICM) takes over the dynamic vehicle management task. Within certain limits the driver does not have to interact and the system actuates engine and service brake. For this purpose, Integrated Chassis Management (ICM) calculates the desired acceleration and transmits it. Digital Engine Electronics (DME) and Digital Engine Electronics 2 (DME2) determine the required engine torque on the basis of the current driveline transmission. This request is implemented within physical boundaries. It additionally provides a corresponding virtual accelerator pedal value. Amongst others, Integrated Chassis Management (ICM) detects the following operating conditions:
- Control function for driving at constant speeds
- Control function for the following operation
- Sensing any set speeds
- Corner control function
- Control function on downhill gradients

These operating conditions must be supported by the gearbox with individually adapted shift strategies. This corresponds to the features of the controller and also to subjective driver choices with relation to the shift characteristics. The gear selection mechanism uses suitable shift diagrams. The difference is that the torque or load request to the gearbox comes from the Integrated Chassis Management (ICM). Gear selection achieves that the selected speed is set without any loss of comfort (no increased shift activity or pendulum shifts). Similar to driver mode, the automatic transmission supports in the following driving situations:
- Normal operation with emphasis on comfortable shift characteristics and best-possible efficiency
- Uphill driving and trailer towing with the required tensile force reserves to avoid unnecessary shifting activity
- Downhill driving with downshifts that support deceleration
- Cornering detection with reduced shift activity to support the specific ACC control characteristics

Required gear determination
A special required gear determination is used in the 8-speed automatic gearbox. During downshifts it enables faster engagement of the matching gear for faster acceleration. For this purpose, the required gear is calculated from the speed with which the accelerator pedal is depressed. As soon as the driver starts depressing the accelerator pedal, speed is evaluated and the matching required gear is calculated for the downshift. The required gear is then directly engaged, possibly even by shifting down across several gears.

Characteristics curve of shift speeds
The electronic transmission control is equipped with three different shift speed levels.
The higher the level, the faster the gearshift. The corresponding shift speed levels are engaged depending on the selected driving programs and the speed at which the accelerator pedal is depressed.

Notes for Service department

Automatic transmission fluid
The 8-speed automatic gearbox is equipped with a life-time oil filling. During the entire running time the 8-speed automatic gearbox does not require an oil change.
The approved life-time oil type must be used after repairs on the gearbox or transmission oil cooler.

NOTICE: Do not mix with other automatic transmission fluids.

The life-time oil type must not be confused or mixed with other automatic transmission fluids. Using other oil types could result in a gearbox failure.
Use Shell L 12108 automatic transmission fluid.

General notes
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.