Automatic Transmission/Transaxle: Description and Operation

A5S 440 Z AUTOMATIC TRANSMISSION







The A5S 440 Z was developed to match the size and power output of the M62 V8 engine. It will first be installed in the 840i (9/96) and then be phased into production for the 740i/iL and 540i (1/97).

The transmission is similar in design to the A5S 560 Z, however its size and maximum torque rating is smaller to match the power output of the eight cylinder engine.



SYSTEM OVERVIEW
The A5S 440 Z transmission offers the following features and benefits:
- Maintenance free lifetime operation
- AGS adaptive shift and program control
- Gradual torque converter locking control
- Improved operating comfort and reliability
- Reduced vibration and noise characteristics
- Powertrain management control (CAN line)
- Expanded diagnostics through DIS
- Expanded failsafe functions


BASIC MECHANICAL OPERATION












Engine power enters the transmission through the four element, lock-up torque converter.
A single, high output oil pump supplies the pressurized oil for the all shifting requirements, lubrication, as well as the oil supply for the torque converter.

The primary mechanical drive components are:
- 3 Multi-plate drive clutches; A, B & C
- 3 multi-plate brake clutches; D, E & F
- 1 Free wheel (sprag type) one-way clutch
- 3 Planetary gear sets (wilson type); P1, P2 & P3

The ratio for each gear is produced by applying engine torque to a specific planetary gear, through the drive clutches, while holding other components of the gear sets with the brake clutches.

A single electro-hydraulic valve body controls the flow (or drain) of oil to (or from) the various clutches for the gear changes. The control of the drive components is similar to the A5S 560 Z transmission.

The sprag type free wheel is used to hold the planetary gear set for driving OFF, in low gear, with the gear selector lever in "D".

COMPONENTS

TORQUE CONVERTER







A new design torque converter is used on the new 440 Z transmission. It is smaller in diameter than the torque converter of the 560 Z transmission. It features a two sided friction plate, lock-up clutch which provides high power transmission with less application force.

The lock-up clutch is applied through a closed loop control in 4th or 5th gears. The control module uses the engine RPM and turbine shaft RPM to determine converter slippage as the lock-up clutch is applied.

The lock-up solenoid is a pressure regulator type valve that varies the duty cycle to lock and unlock the clutch. This avoids the abrupt lock-up feel associated with earlier type converter clutches (4HP22/24).

OIL PUMP







The crescent design oil pump is located behind the torque converter in the intermediate plate. It is driven directly by the engine through the converter shell and supplies the following:
- Main line oil pressure
- Torque converter feed pressure
- Lubrication oil pressure for the transmission

The oil pump incorporates the needle bearing converter support introduced on the A5S 560 Z.

ELECTRO/HYDRAULIC VALVE BODY







The large valve body assembly is made up of three smaller valve bodies mounted to a common channel plate. It is used to control the flow of oil and regulate the apply pressures to the clutches, torque converter, etc. As with previous transmissions it is located in the oil pan.

The valve body incorporates five pressure regulator valves (EDSs) and three magnetic valves (MVs). The AGS control module regulates the up/down shifting of the transmission through the control of these valves. The valves are individually replaceable.

SHIFT LOCK







As introduced in 1991, the shift lock feature prevents the unintentional movement of the shift lever from Park or Neutral.

The AGS module controls the operation of the shift lock solenoid. When KL 15 is switched ON, the shift lock is engaged until the brake pedal is depressed.

The shift lock solenoid's pin engages in the selector lever gate and prevents its movement.

IGNITION SWITCH INTERLOCK







Since 1993, an additional safety feature has been added known as the ignition switch interlock. The system is a cable that is connected between the selector lever and ignition switch housing. The ignition switch cannot be turned to the lock position for removal until the transmission has been shifted into park.

RANGE SELECTOR & PROGRAM SWITCH







The E38 and E31 will continue to use the "A" and "M" program switch for manual selection of the "M" program.

Manual selection of the extreme sport program is carried out by pulling the range selector lever into 4,3 or 2.

In the E39, the two position program switch is not used. The E39 manual program selection is limited to the extreme sport program by moving the shift lever to 4,3 or 2.

The extreme sport program is a manually selected aggressive program that raises the shift points above the automatically selected AGS sport program.

AGS (Adaptive Transmission Control)
The A5S 440 Z is equipped with the AGS 8.55, adaptive transmission control system. The accronym comes from the German name "Adaptive Getriebesteurung", meaning "Adaptive Gearbox Control".

The system automatically selects one of several different driving programs based on the driving style and road/environmental conditions. Advantages of the AGS shift control include:
- Shift program adapted to the driving style
- Improved safety - No unwanted UP/DOWN shifting while driving through curves.
- Automatic detection and selection of winter program for better traction.

AGS PROGRAM STRUCTURE
AGS as an electronic control logic for automatic transmissions was introduced with the 1994 model year E34s equipped with the M60 engine. Several changes have occurred to the control logic since its introduction due to customer feedback on ride comfort and shift quality. These changes are described in the following Service Information Bulletins:

- 24-04-96 May 96,
- 24-01-96 May 96

To understand AGS and its features as it applies to the A5S 440 Z a distinction has to be made between Pressure Adaptation and Adaptive Transmission Control. This applies to all vehicles equipped with the AGS control.

PRESSURE ADAPTATION







Pressure Adaptation has been a feature of the automatic transmission since the 4HP 22EH. The purpose of this pressure adaptation is to adjust the internal hydraulic pressures in the transmission continuously to maximize the shift comfort.

This adaptation is carried out automatically regardless of driving styles or driving habits.
Pressure adaption is essentially a separate function from the adaptive transmission control (AGS). This pressure adaptation value is stored in the control module and clearing the adaptation with the diagnostic tester clears this value ONLY.

It does not have any effect on the adaptive transmission control system.

ADAPTIVE TRANSMISSION CONTROL

The AGS can be broken down into two functional groups.
1. Driver controlled features,
2. System features that react automatically to the vehicle's operating conditions.

DRIVER CONTROLLED FEATURES OF AGS







The adaptive drive program is based primarily on throttle input. The AGS control module continuously monitors the throttle input for:
- The current pedal position
- The rate of change in pedal movement
- The number of acceleration requests
- The number of kickdown requests

Based on these inputs, the AGS will select one of three different driving programs as follows:
- Extreme Economy - shift points are at low speeds for a comfortable ride
- Economy - the shift points are raised for more engine performance
- Sport - The shift points are higher to take advantage of full engine performance (Pressing kickdown will result in the selection of the sport drive program).

This driving program selection is not adapted on a long term basis - nor is it stored in the control module memory when the ignition is switched off. It continually changes as the driver of the vehicle changes his driving habits.

AGS FEATURES THAT REACT TO OPERATING CONDITIONS







STOP AND GO - feature is activated by a defined sequence of shifts which are as follows:
- Upshift from first to second - followed by a downshift from second to first - followed by another upshift from first to second. This is then followed by the vehicle coming to a complete stop.

After this sequence, the transmission will stay in second gear. The AGS control has recognized stop and go driving and this function will prevent excessive shifting during the heavy traffic conditions. This second gear start will be canceled when:
- The vehicle speed exceeds 40 MPH
- The throttle pedal is pressed more than 90 %
- The range selector is moved to 'P', 'N' or 'R'

CURVE RECOGNITION - feature is activated when the AGS control module receives different wheel speed inputs from the left and right sides. During this condition, the AGS inhibits upshifts until the vehicle is traveling straight again. The purpose of this feature is to improve stability while the vehicle is cornering at higher speeds.

WINTER DRIVE PROGRAM - feature is activated when the AGS control module detects slippage at the rear wheels. In the winter program, the transmission will start in second gear and the shift points are lowered. The purpose of this program is to improve the drivability of the vehicle with slippery road conditions.

NON-AGS FUNCTIONS
The following features are part of the automatic transmission control system - but not AGS specific control features. They are carried over from earlier transmission control systems.

HILL RECOGNITION PROGRAM - the control module activates this feature when it receives a high engine load signal at slower road speeds. When the vehicle is traveling up hill the shift points are raised to prevent a "pendulum shift effect" of up and down shifting.

CRUISE CONTROL DRIVE - A special cruise control shift map is activated to prevent pendulum locking and unlocking of the torque converter while cruise control is activated.

MANUALLY SELECTED SPORT PROGRAM - feature is activated by moving the shift selector to '4', '3' or '2'. This activates the Extreme Sport shift program where the shift points are raised to provide maximum engine performance.

ENGINE WARM UP CYCLE - Depending on ambient temperature, the shift points are raised on a cold engine start up. This is designed to speed up the warn up cycle of the engine.

ELECTRO-HYDRAULIC CONTROL
SOLENOID VALVE OPERATION (output control)

Similar to the A5S 560 Z, the A5S 440 Z uses shift solenoid valves and pressure regulator valves for shift control as shown in the chart below.


Three solenoids MV1, MV2 and MV3 are strictly ON/OFF type valves used to control the hydraulic pressure flow in the valve body.

Three pressure regulator valves, EDS2, EDS3 and EDS5 are used for the so-called "Overlap Control" during shifting. The pressure regulator valves are used to apply pressure, to various clutches and brakes, during shifting, while at the same time pressure is draining from other clutches. This provides for smooth shifting because the delay time from one gear engagement to another is reduced.

Pressure regulator valve EDS1 is used to regulate the main line pressure used for shift control. Pressure regulator valve EDS4 is used for controlling the lock up clutch in the torque converter. All pressure regulator valves are controlled with a pulse modulated signal.







The chart shows the solenoid, EDS and clutch application chart for the ASS 440 Z transmission.

DIAGNOSIS/TROUBLESHOOTING







Starting with the 1996 model year, all electronic transmission control falls under the OBD II emission regulations. Any fault with the transmission that will effect tailpipe emissions must be recognized and stored in the OBD II memory. In addition to the transmission failure warning, the Check Engine Lamp must also illuminate when the criteria for OBD II recognition is satisfied.

Though, BMW system diagnosis and troubleshooting is performed using the DIS and MoDiC, this system can be readout by an independent Service Center using an OBD II compatible scantool.

Faults that fall under the OBD II criteria include:
- CAN line
- AGS power supply
- Transmission range selector switch
- Output speed sensor
- Turbine speed sensor
- Torque converter clutch
- Shift solenoid valves (MVs)
- Pressure regulator valves (EDSs)












All BMW Diagnosis and troubleshooting is carried out using the DIS or MoDiC with the most recent diagnostic software.

The following information is available on the diagnostic software:
- Control module identification
- Fault symptom troubleshooting
- Status displays
- Component activation
- Component testing procedures
- Special functions and information

SERVICE & REPAIRS







The A5S 440 Z transmission is factory filled with a semi-synthetic "lifetime" oil and requires no oil service or maintenance. This is the only oil type to be used in this transmission.

Oil: ESSO LT 7114 I

Capacity:
- with torque converter
= 9 liters
- without torque converter
= approx 6-7 liters

Operating temperature:
- normal = 90 °C
- max. = 130 °C

As with other ZF transmissions, checking the oil level requires the use of the DIS or MoDiC.







The level can only be checked when the oil temperature is in the range of 30 ° - 50 °C as displayed in "diagnostic requests (status pages)" of the DIS. At this temperature range, the oil level should be at the bottom edge of the fill/checking plug on the right rear side.







Only minor electrical/mechanical repairs can be carried out in the dealeship. The following are included in the repair scope:
- Oil leaks - Radial seals and gaskets.
- Mechanical faults - Torque converter, parking pawl, oil pan.
- Electrical faults - Solenoid valves, pressure regulator valves, wiring harness.
- Signal sensing - Turbine and output speed sensors, CAN Bus, temp sensor.