automatic transmission SSANGYONG MUSSO 1998 Workshop Service Manual

AUTOMATIC TRANSMISSION 5A-15
E23 POWER MODE

5A-16 AUTOMATIC TRANSMISSION
E23 NORMAL MODE

AUTOMATIC TRANSMISSION 5A-17
E23 LOW MODE

5A-18 AUTOMATIC TRANSMISSION
INTRODUCTION
The BTR Automotive Model 74 Four Speed Automatic Transmission is an electronically controlled overdrive four
speed unit with a lock-up torque converter. The lock-up torque converter results in lower engine speeds at cruise and
eliminates unnecessary slippage. These features benefit the customer through improved fuel economy and noise
reduction. Refer to table 1.1 for details of power, torque and configuration.
Of primary significance is the transmission control unit (TCU) which is a microprocessor based control system. The
TCU utilizes throttle position, rate of throttle opening, engine speed, transmission output speed, transmission sump
temperature, gear selector position and mode selector inputs, and in some applications a ‘kickdown’ switch to control
all shift feel and shift schedule aspects.
The TCU drives a single proportional solenoid multiplexed to three regulator valves to control all shift feel aspects.
The output pressure of this solenoid is controlled as a function of transmission sump temperature to maintain consistent
shift feel throughout the operating range.
Shift scheduling is highly flexible, and several independent schedules are programmed depending on the vehicle.
Typically the ‘NORMAL’ schedule is used to maximise fuel economy and driveability, and a ‘POWER’ schedule is used
to maximise performance. ‘WINTER’ schedule is used to facilitate starting at second gear.
Figure 1.1 details the differences between conventional and electronic transmission control systems.
Max Torque (Nm)
320Configuration
260 mm Torque Converter
Wide Ratio Gear Set
Splined Output for Transfer CaseMin Torque (Nm)
160 Model
M74 4WD
Transmission Table 1.1 - M74 Torque, Power and Configuration

AUTOMATIC TRANSMISSION 5A-19
Figure 1.1 - Conventional VS Electronic Transmission Control System

5A-20 AUTOMATIC TRANSMISSION
OPERATOR INTERFACES
There are three operator interfaces associated with the four speed transmission.
They are:
lThe gear select lever
lThe driving mode selector
lThe indicator light
These operator interfaces are described below.
GEAR SELECT LEVER OPERATION
The transmission uses a conventional selector lever. The selector lever can be moved from one position to another
within the staggered configuration of the selector lever gate to positively indicate the gear -selection as shown on
figure 2.1. For information about the gear selections available refer to table 2.1.
Figure 2.1 - Typical Gear Selector and Mode Switch

AUTOMATIC TRANSMISSION 5A-21
Downshift Type
RANGE ‘1’ (MANUAL ‘1’):
RANGE ‘2’ (MANUAL ‘2’):
RANGE ‘3’ (MANUAL ‘3’):
RANGE ‘D’ (DRIVE):
RANGE ‘N’ (NEUTRAL):
RANGE ‘R’ (REVERSE):
RANGE ‘P’ (PARK):Inhibited Above
First gear operation only with inhibited engagement as a function of vehicle
speed. Engine braking is applied with reduced throttle.
First and second gear operation with inhibited engagement of second gear, as
a function of vehicle speed. Engine braking is applied with reduced throttle.
First, second and third gear operation with an inhibited third gear engagement
at high vehicle speed. Refer to the vehicle owner’s manual.
Engine braking is applied with reduced throttle.
First, second, third and fourth gear operation. First to second (1-2), first to third
(1-3), second to third (2-3), second to fourth (2-4), third to fourth (3-4), fourth
to third (4-3), fourth to second (4-2), third to second (3-2), third to first (3-1)
and second to first (2-1), shifts are all available as a function of vehicle speed,
throttle position and the time rate of change of the throttle position (forced
downshift). Lockup clutch may be enabled in 3rd and 4th gears depending on
vehicle type. Refer to the owner’s manual.
Rear band applied only, with inhibited engagement as a function of vehicle
speed, engine speed and throttle position. The inhibitor switch allows the en-
gine to start.
Reverse gear operation, with inhibitor engagement as a function of vehicle
speed, engine speed and throttle position. The inhibitor switch enables reverse
lamp operation.
Rear band applied only, with inhibited engagement as a function of vehicle
speed, engine speed and throttle position. The transmission output shaft is
locked. The inhibitor switch allows the engine to start.
Table 2.1 - Gear Selections
DRIVING MODE SELECTOR
The driving mode selector consists of a mode selection switch and indicator light. The driving mode selector is
located on the centre console. See figure 2,1.
The schedules available to be selected vary with vehicle types. Typically the driver should have the option to select
between ‘NORMAL’ , ‘POWER’ or ‘WINTER’ modes.
When ‘NORMAL’ mode is selected upshifts will occur to maximise fuel economy and the indicator lights remain
extinguished. When ‘POWER’ mode is selected upshifts will occur to give maximum performance and the ‘POWER’
mode indicator light is switched on. When ‘WINTER’ mode is selected, starting at second gear is facilitated, the
‘WINTER’ mode indicator light is switched on and the ‘POWER’ mode indicator light is switched off.
Refer to the vehicle owner’s manual for specific modes for each vehicle type.

5A-22 AUTOMATIC TRANSMISSION
CONTROL SYSTEMS
GENERAL
There are two control systems associated with the transmission. The electronic control system monitors vehicle
parameters and adjusts the transmission performance. The hydraulic control system implements the electronic control
system commands.
ELECTRONIC CONTROL SYSTEM
The electronic control system is comprised of sensors, a TCU and seven solenoids. The TCU reads the inputs, and
under software control activates the outputs according to values stored in read only memory (ROM).
The TCU controls the hydraulic control system. This control is via the hydraulic valve body, which contains seven
electro-magnetic solenoids. Six of the seven solenoids are used to control the line pressure, operate the shift valves
and the torque converter lock-up clutch, and to turn on and off the two regulator valves (The two regulator valves
control the shift feel.).
The seventh solenoid is the proportional or variable pressure solenoid (VPS) which works with the two regulator
valves to control shift feel.
Figure 3.1 details a typical TCU control system schematic.
The individual component locations, operation and specifications which make up the electronic control subsystem
are covered in this section.
Figure 3.1 - Typical TCU Control System Schematic

AUTOMATIC TRANSMISSION 5A-23
Temperature (
° °° °
°C)
-20
0
20
100
135 (Overheat Mode Threshold)
Maximum
17,287
6,616
2,723
196
85Minimum
13,638
5,177
2,278
177
75Resistance (Ohms) Table 3.1 - Temperature / Resistance Characteristics
Figure 3.2 - Temperature / Resistance Characteristics

5A-24 AUTOMATIC TRANSMISSION
Transmission Control Unit(TCU)
The TCU is an in-vehicle micro-processor based transmission management system. It is usually mounted in the
vehicle cabin, under the instrument panel, under the seat, behind the side kick panels or under the floor in the
footwell on the passenger side. Different control units are supplied for different vehicle applications.
The TCU contains:
lProcessing logic circuits which include a central microcontroller and a back-up memory system.
lInput circuits.
lOutput circuits which control external devices such as the variable pressure solenoid (VPS), on/off solenoid
drivers, a diagnostics output and the driving mode indicator light.
The various items which make up the TCU are discussed below.
Processing Logic
Shift schedule and calibration information is stored in an erasable programmable read only memory (EEPROM).
Throttle input calibration constants and the diagnostics information are stored in electrically erasable programmable
read only memory (EEPROM) that retains the memory even when power to the TCU is disconnected.
In operation the software continuously monitors the input values and uses these, via the shift schedule, to determine
the required gear state, At the same time it monitors, via the solenoid outputs, the current gear state. Whenever the
input conditions change such that the required gear state is different to the current gear state, the TCU initiates a
gear shift to bring the two states back into line.
Once the TCU has determined the type of gear shift required the software accesses the shift logic, estimates the
engine torque output, adjusts the variable pressure solenoid ramp pressure then executes the shift.
The TCU continuously monitors every input and output circuit for short or open circuits and operating range. When
a failure or abnormal operation is detected the TCU records the condition code in the diagnostics memory and
implements a limp mode, The actual limp mode used depends upon the failure detected with the object to maintain
maximum driveability without damaging the transmission. In general input failures are handled by providing a default
value. Output failures, which are capable of damaging the transmission, result in full limp mode giving only third or
fourth gear and reverse. For further details of limp modes and memory retention refer to the Diagnostic Section.
The TCU is designed to operate at ambient temperatures between -40 and 85°C . It is also protected against
electrical noise and voltage spikes, however all the usual precautions should be observed, for example when arc
welding or jump starting.
TCU Inputs
To function correctly, the TCU requires engine speed, road speed, transmission sump temperature, throttle position
and gear position inputs to determine the variable pressure solenoid current ramp and on/off solenoid states. This
ensures the correct gear selection and shift feel for all driving conditions.
The inputs required by the TCU are as follows:
lEngine Speed
The engine speed signal is derived from the tachometer signal line, a dedicated sensor or a Controlled Area
Network (CAN).
lRoad Speed
4WD (Diesel) - The shaft speed signal is derived from the speedo sensor located on the transfer case. This signal
is transmitted directly to the TCU.
4WD (Gasoline) - The speedo sensor sends the shaft speed signal to the engine control module (ECM). The
information is then transferred to the TCU via the CAN.
lTransmission Sump Temperature
The transmission sump temperature sensor is a thermistor located in the solenoid wiring loom within the transmission.
This sensor is a typical NTC resistor with low temperatures producing a high resistance and high temperatures