SPECIFICATIONS OF THE 55-50 SN AUTOMATIC TRANSMISSION
Five speed compact automatic transmission with front wheel drive
The 55-50 SN automatic transmission has a five speed gearbox with a new epicyclic gear train added to the four speed automatic gearbox, maintaining the same overall length and the same distance between the axles. It is also more compact and has a greater capacity compared with the transmission fitted on conventional vehicles. The 55-50 SN weighs only six kilos more than the four speed automatic transmission.
55-50 SN
50-40 LE
Epicyclic gear train
4
3
Weight
About 90 kg
About 84 kg
Addition of new functions
Adoption of active speed sensor (NT - 6): Both the input and the output speed sensors have been replaced by active sensors.The accumulator has been abandoned (excluding C1) and the SLS adopted: the very new SLS (pressure control solenoid during gear changes) has been adopted to electrically regulate the pressure and avoid the use of the accumulator thereby producing a softer gear change. The gear change from second to third and from third to fourth is made "from clutch to clutch" thereby avoiding the use of the traditional clutch.Adoption of TIP gear change control (NT - 14): the TIP gear change control makes it possible to select the gear that the driver wishes to engage simply by operating the +/- gear lever.Addition of the slipping control (NT - 15) and modification of the lock-up clutch solenoid: by adding the slipping of the lock-up clutch, the operating area of the lock-up clutch has been extended, thereby improving fuel consumption. (A special fluid is required for the automatic transmission: JWS-3309). The lock-up clutch solenoid has been transformed into a linear type (SLU).Adoption of the N control (NT - 16): when the vehicle is stopped by braking, the automatic transmission is automatically positioned in neutral and not in "D", thereby improving fuel consumption.
Adoption of built in oil cooling device
The adoption of the integrated fluid cooling device offers the following advantages:
Reduction in the number of parts on the vehicle (thanks to the simplification of the cooling circuit).
Stabilization of the fluid level by adopting a differential unit supplied together with the automatic transmission fluid.
Possibility of controlling the temperature of the automatic transmission fluid.
Improved reliability, in terms of fluid leaks, thanks to the automatic transmission having no fluid circuit.
ELECTRONIC CONTROL SYSTEM (CONTROL MODULE FOR TRANSMISSION AND ELECTRONIC COMPONENTS)
Specifications
The C.A.E. fitted on this vehicle represents an important innovation from the user's point of view because of the major technological developments involved.In effect, in addition to the sophistication of the electronic control which governs the gear change strategies adapting to the style of the driver, there is the new TIP sequential alternative which allows the driver to use the vehicle in totally assisted conditions as found on conventional automatic transmissions and in manual gear change conditions with the TIP function where the intervention of the automatic function is limited to prevent incorrect or potentially damaging manoeuvres for the vehicle mechanics (the gearbox does not, for example, accept selections that would cause beyond rev conditions).The 5 speed Aisin type gearbox, with adaptive electronic control, with dual operating possibilities (Full Auto and Trip) is controlled by means of a double control grid for the gear lever positions.The electronic control mode adopted is the adaptive type, which means that the electronic management of the gear change is capable of analyzing the vehicle driving conditions and, after having compared them with the standard conditions memorized in its software, of selecting the operating programme (gear change law) that is best adapted to the current situation (see NCA [DF_5500]).The system manages the following three gear change laws:
Up hill: when driving uphill, the control unit compares the actual acceleration of the vehicle with the theoretical acceleration on a flat road, thereby determining the gradient of the road. It selects the change law and the most suitable ratio according to the gradient.
Down hill: when the control unit detects that the vehicle is accelerating with the throttle closed (descent) and is capable of estimating that by changing down a gear the vehicle will no longer be accelerating, it changes down a gear the first time the brake is operated.
Fast acceleration: depending on the speed with which the accelerator pedal is depressed, the control unit modifies the gear change and kick-down law.The CAE electronic control unit manages the operation of the automatic transmission through connection with:
the sensors/actuators fitted on the gearbox for acquiring the operating conditions and the operation of the clutches and brakes;
the injection/ignition control unit for the exchange of information relating to the engine;
the instrument panel for displaying the operating conditions.
ELECTRONIC COMPONENTS
Switch for starting in neutral (NSW)
The switch for starting in neutral indicates the automatic transmission ratio, at a given time, to the starter motor, the reversing light and the automatic transmission control unit.The switch for starting in neutral can only start the engine in "P" and in "N" (to prevent reckless driving).The switch for starting in neutral ensures that the reversing light comes on when reverse gear is engaged.The switch for starting in neutral can also be used to control the gear change.The switch for starting in neutral transmits information, making use of the circuit for the starter motor and the vehicle side reversing light directly, without going from the automatic transmission control unit.
The five gearbox solenoids are fitted directly on the valve casing. The solenoids can be in the ON or OFF position, depending on the control signal arriving from the automatic transmission control unit. The combined action of the five solenoids 1, 2, 3, 4, 5 (S1, S2, S3, S4, S5) makes it possible to change the gear ratios.
Input and output speed sensor (active sensors)
The output speed sensor detects the speed of the vehicle from the number of revs of the parking gear, whilst the input speed sensor detects the input speed for the automatic transmission from the number of revs of the drum C1: both then send a signal to the automatic transmission control unit.
Differences between active sensor and impulse sensor
Active sensor specifications:
this sensor has an integrated Hall circuit that manages the rectangular wave signal producing energy and transmitting the signal to the automatic transmission control unit exploiting the Hall effect. The automatic transmission control unit recognizes the signal in relation to the speed of the vehicle. The specifications of the output signal are fixed and do not therefore depend on the number of revs.
strong signal for noise
there may also be a low number of revs (10 rpm).
Impulse sensor specifications:
as a result of the rotation of the gear, a sinusoidal wave with an induction electro-motive force is produced, in relation to the speed of the vehicle, which is then sent to the automatic transmission control unit. The control unit converts the wave signal into an impulse signal and recognizes it in relation to the speed of the vehicle. The specifications of the output signal depend on the number of revs.
the minimum number of revs that can be detected is 50 rpm.
Oil temperature sensor
The oil temperature sensor is fitted directly on the valve casing which converts the temperature of the oil inside the automatic transmission into an electrical signal which is then sent to the automatic transmission control unit.
Linear pressure control solenoid (SLT)
The linear pressure control solenoid controls the throttle valve by means of a signal arriving from the automatic transmission control unit in addition to the linear pressure of the clutch and the brake to reduce the shock from the gear change.Direct control.
Lock-up clutch control solenoid (SLU)
The lock-up clutch control solenoid controls the linear pressure of the lock-clutch by means of the signal arriving from the automatic transmission control unit in addition to the hydraulic pressure of the lock-up clutch to reduce the shock from the gear change.Direct control:
Engine brake: Brake B3
Control of neutral (N): Brake B2.
Gearbox pressure control solenoid (SLS)
The gearbox pressure control solenoid operates through a signal arriving from the automatic transmission control unit.Direct control:
control of 2nd, 3rd, 4th speeds and neutral (N): brake B1
control of 5th speed and reverse gear: clutch C2
Transmission drive gear
The switch and sensor assembly, fitted on the automatic transmission, connects the switch for starting in neutral, the solenoids 1, 2, 3, 4, 5 (S1, S2, S3, S4, S5), the input speed sensor and the oil temperature sensor to three terminals.
Automatic transmission control unit control functions
Control of the gear change and the lock-up clutch.According to the gear change programmed, the control unit sends a signal to solenoids S1, S2, S3, S4 and S5, which are in the on/off position, to control the gear change in relation to the speed of the vehicle and the throttle valve opening.The 55-50SN version does not have different driving modes available for the driver to select. It is basically programmed for the "economy" mode, but the automatic gear change control unit can automatically change to different programmes depending on specific circumstances.
Adaptive control of gear change by the driver (Economy, Regular and Sports modes)
The Economy mode is used in normal driving conditions after having turned the ignition on and the driver's wishes are ascertained by using a logic that depends on the operation of the accelerator pedal. This makes it possible to change modes and move from Economy mode (low speed) to Regular mode (average speed) or Sports mode (high speed) according to the driver's wishes.
Uphill modes 1, 2
When the control unit detects that the vehicle is driving uphill from the engine torque and deceleration conditions, it alters the gear change strategy in relation to the gradient of the incline and avoids overloading the automatic transmission with gear changes.
Downhill mode
When the control unit detects that the vehicle is driving downhill, from the increased acceleration with the accelerator completely
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