Description And Operation

DESCRIPTION 

The Transmission Control Module (TCM) detects the conditions of the vehicle and performs calculations and processes the information that it receives from each sensor and switch.

It also sends control signals to each solenoid so that each type of control is implemented and optimized according to the vehicle's driving conditions.

OPERATION 

CONTROL ELEMENT				MAIN CONTROL CONTENT
Gear change point control	Automatic transmission control (D position)	Driving modes	Normal Mode	Selection mode during normal driving (without gear selection switches) Normal mode is selected using the drive selection It changes gear automatically according to the vehicle's speed and the measured pressure on the accelerator pedal.
			SPOT mode (with gear selection switches) - ABARTH	SPORT mode is selected using the drive selection It changes gear automatically according to the vehicle's speed and the measured pressure on the accelerator pedal. The lowest gear is selected in normal mode
			Active adaptive shift (AAS)	Unnecessary changes to a higher gear are suppressed for several seconds, maintaining the gear that matches the speed at which the accelerator pedal was released Depending on the force on the brake pedal, the gear is changed down to the optimal gear to reduce the vehicle's speed. On bends, changing to a higher gear is disabled in preparation for the acceleration after the bend. In high-altitude regions, the ideal gear for the environment is selected. The TCM estimates the gradient to select the appropriate gear for ascending and descending. In SPORT mode, the AAS system selects a lower gear with respect to normal mode maintains it for longer (with gear selection switches - selection paddles).
	Direct Control Mode			The direct control mode temporarily enables manual gear changes with the paddles (gear selection switches) even though the gear selection lever is at D When the system passes to direct mode, it automatically returns to the automatic transmission mode according to the driving conditions
	Manual Control Mode			When the M mode is selected, manual gear changes, performed by the driver using the paddles, have priority
Gear change pressure control	Line pressure control		Controls the line pressure with high accuracy and better control in response to the engine load and driving conditions
	Learning control		Learns the engine performance changes and deterioration of the transmission over time to optimize the clutch engagement pressure
Torque converter clutch control, slipping control			Gradually engaging and disengaging the TCC piston reduces "hiccups" during operation Implements the TCC control when the accelerator pedal is completely closed to improve fuel consumption and emissions Slip control, pulling the TCC when it is out of range increases the TCC's operating range and low speeds
Engine - transmission integration control			Controls the optimal engine output torque during gear changes Calculates the optimal clutch engagement pressure according to the engine output torque
On-board diagnostic system			Most of the transmission control includes self diagnosis functions. In the event of malfunction, the automatic transmission warning light turns on to warn the driver and a DTC is stored in the TCM When a malfunction is detected following a self-diagnosis test, the system is switched to prevent any hazardous situation while driving.

Gear change point control (automatic control)

When in the D position, the TCM implements the automatic gear change control according to the car speed and how much the accelerator pedal is pressed.

When SPORT mode is selected using the selection switch, a lower gear is selected with respect to normal mode, and the control is such that a greater drive force is guaranteed.

When performing automatic transmission control, the TCM determines the driving conditions based on each input signal and chooses the most appropriate driving mode for those particular conditions. Moreover, information such as torque variations and gear changes is exchanged via the PCM and CAN and control is carried out to obtain the optimal drive force based on the driving situation.

Determination of the driving range

If the D position signal is present at the input but the M position signal is not, the TCM performs control in automatic mode.

• For automatic control, NORMAL mode is usually selected, despite switching to the driving mode according to the driving conditions (without selection paddles).
  • AAS mode:  automatically controls the optimal gear change point in relation to the road conditions and the driver's actions;
  • High temperature mode:  when the transmission fluid reaches a high temperature, the engine torque is limited to eliminate the temperature rise and protect the transmission.
  • 5-6 gear change disable:  the TCM disables gear changes from 5th to 6th gear when it determines that the engine is cold based on the signal from the ECT sensor.
• NORMAL and SPORT modes can be selected by pressing the relative selector switch and the following modes are switched automatically according to the driving conditions combined with the NORMAL/SPORT mode (with steering wheel paddles):
  • AAS mode:  automatically controls the optimal gear change point in relation to the road conditions and the driver's actions;
  • High temperature mode:  when the transmission fluid reaches a high temperature, the engine torque is limited to eliminate the temperature rise and protect the transmission.
  • 5-6 gear change disable:  the TCM disables gear changes from 5th to 6th gear when it determines that the engine is cold based on the signal from the ECT sensor.

• Accelerator pedal suddenly fully pressed and then released:
  • When the accelerator pedal is pressed down to the end of its travel and released at a certain speed or faster, the change to a higher gear is disabled for specific time to improve the speed control and acceleration performance.
• Brake pedal pressed hard:
  • When deceleration occurs at a certain speed or faster, a lower gear is selected to facilitate subsequent acceleration;
  • During a gear change with the brake pedal firmly pressed, intermittent control (synchronized with the engine speed) is performed to minimize the gear change time;
• Cornering:
  • When turning a bend with a radius smaller than a specific value, changing to a higher gear is disabled to improve the vehicle's performance on the bend and when accelerating out of it;
• Uphill:
  • When climbing a certain gradient or greater, uphill mode control prevents unnecessary changes to a higher gear, maintaining the appropriate gear.
• Downhill:
  • When descending a certain gradient or greater with the brake pedal pressed, the gears are appropriately changed down according to the estimated gradient to use engine braking effectively. In this way, use of the brake pedal is reduced.
  NOTE:

  When SPORT mode is selected, the AAS system selects a lower gear with respect to that selected in NORMAL mode, and maintains it for a longer time.

Gear change point control (manual control) 

The TCM performs manual control when the M position is selected.

If the M position is selected, the driver's manual gear changes have priority. However, automatic gear changes could occur to a minimal degree to ensure safe driving and to protect the engine and transmission.

Gears can be selected by moving the gear lever forwards and backwards while driving in the M position.

When the gear lever is moved from the D to the M position while driving, the gear used while driving in the D position is maintained. In any case, while driving in D in 6th or 5th gear, if the lever is moved to the M position without pressing the accelerator pedal, the gear passes from 6th to 5th or from 5th to 4th respectively.

When changing to a lower gear using the selection lever without the accelerator pedal pressed and the selection lever in the M position, control is intermittent (synchronized with the engine rpm).

When the accelerator pedal fully pressed while driving in the M position, a kickdown gear change is performed to highlight the vehicle's acceleration performance, and if the engine reaches a high rpm with the pedal fully pressed, the gear is automatically changed up.

During the control in manual mode, for each driving speed, the engine braking force depends on the gear ratio. If the vehicle reaches a certain constant speed or lower, the gear is changed down automatically.

GEAR		CHANGE	GEAR CHANGE GEAR ENABLED/DISABLED
Gear change-up	1 time	1→2	Enabled driving at a certain speed or higher
		2→3
		3→4
		4→5
		5→6
	2 times consecutively	1→3
		1→3
		2→4
		3→5
		4→6
	3 times consecutively	1→4
		2→5
		3→6
	4 times consecutively	1→5
		2→6
Gear change-down	1 time	6→5	Enabled driving at a certain speed or lower
		5→4
		4→3
		3→2
		2→1
	2 times consecutively	6→4
		5→3
		4→2
		3→1
	3 times consecutively	6→3
		5→2
		4→1
	4 times consecutively	6→2
		5→1

The gear changes may be cancelled depending on the vehicle's speed. If a gear change-down is cancelled, the transmission warning light turns on to alert the driver.

If the engine reaches a high rpm speed, the following controls are performed to protect the engine:

• The throttle valve is reduced so that the engine speed does not reach the excess speed range and settles at a lower speed.
• If the high rpm condition continues, the engine speed is reduced, imposing a change to a lower gear.

• When the vehicle stops or the speed is very low, the selection lever is moved towards the + side and the gear changes to 2nd.
• On slippery surfaces such as snow-covered roads, forward acceleration and driving are aided. When in this mode and the selector is moved to gears other than 2nd, the 2nd gear mode is cancelled.
• Fully pressing the accelerator while in 2nd gear mode causes kickdown and 2nd gear mode is cancelled.

• When the steering wheel gear change switch is in operation with the selection lever in the D position the gear position may switch temporarily. When in direct mode, the D and M indicator lights turn on and the current gear is displayed. Direct mode may be cancelled in the following conditions:
  • A certain time has elapsed while driving at a constant speed
  • The vehicle is stopped or driven at a low speed
  • The gear change-up paddle is held pressed for a certain time or longer.

- Based on the output speed signals, the signals from the PCM (engine speed and how much the accelerator pedal is pressed) and the vehicle's speed, regular control of the TCC is obtained through controlling the TCC linear solenoid. Moreover, the amount of sliding and the slip control are obtained by adding the rpm signals.

• TCC control:  is performed using the TCC control solenoid. The solenoid is activated linearly in On and OFF, the converter's clutch operates and the pump and turbine impellers are connected. This allows the engine and automatic transmission to be coupled. The engine's output is connected directly to the automatic transmission, eliminating transmission losses and improving fuel consumption.
• Slip control:  is performed using the TCC control solenoid. The solenoid is activated linearly in On and OFF, the TCC piston inside the converter is actioned outside the TCC range. The TCC piston slides without being completely coupled, increasing the transmission efficiency and improving fuel consumption.

The TCC mechanism consists of a piston and a damper installed inside the torque converter.

TCC coupling - The TCM sends a signal to the TCC control solenoid while the TCC is being coupled. At the same time, the TCC coupling pressure is gradually increased. As a result, the pressure in the TCC piston slowly engages the TCC clutch, coupling the TCC gently.

TCC release - The TCM sends a signal to the TCC control solenoid while the TCC is being released. At the same time, the TCC coupling pressure is gradually drained. As a result, the TCC piston slowly releases the TCC clutch, releasing the TCC gently.

TCC slip control - Making the TCC piston slide when the TCC is in the OFF range, the slip control increases the TCC range at low vehicle speeds. This eliminates the increase in engine speed and increases the transmission efficiency and fuel economy. At the same time, sliding the TCC piston allows the engine vibrations to be absorbed by the torque converter.

- If any of the following conditions occurs, the torque converter clutch control is disabled:

• TCC control solenoid malfunction
• The transmission fluid temperature is equal to or lower than a specific value
• The output shaft speed is equal to or lower than a specific value
• Position other than D/M

Gear change pressure control (line pressure control) - The TCM guides the pressure control and regulates it according to how much the accelerator pedal is pressed, the vehicle's speed, the transmission fluid temperature and the gear change signal. As a result, the line pressure is precisely controlled according to the engine load conditions and the vehicle's driving conditions.

The TCM regulates the pressure control solenoid by increasing or decreasing the control current sent to the pressure regulator valve. In this way, it is possible to regulate the passage of fluid and therefore the line pressure.

Gear change pressure control (learning control) - The TCM optimizes the hydraulic pressure for engaging and disengaging the clutch by correcting the engagement pressure learning.

The TCM learns the engine's performance changes from the past gear changes and from the transmission wear over time and corrects the learning to ensure an optimal engagement pressure during the initial gear change.

Integration of transmission-engine control- The TCM controls the engine's output torque, reduces the torque fluctuations on the transmission output shaft during automatic gear changes and reduces the shocks that occur during gear changes.

During the automatic gear changes, the TCM sends torque reduction request signal via CAN and temporarily reduces the engine's output torque by delaying the ignition advance control. In this way, during gear changes the torque fluctuations on the transmission output shaft are reduced by engaging the clutch more gently.

Moreover, the TCM receives the engine's output torque from the PCM via C-CAN to determine the clutch engagement pressure based on the engine's output torque. As a result, the accuracy of the hydraulic control's pressure regulation is increased and the clutch engages gently.