Automatic Transmission/Transaxle: Description and Operation
GENERAL DESCRIPTION TRANSAXLEThe AF33-5 transaxle incorporates electronic controls that utilize the transaxle control module (TCM) to control shift points (through shift solenoid valves), torque converter clutch (TCC) apply and release (through the lock-up pressure control solenoid valve) and line pressure (through the line pressure control solenoid valve and the shift pressure control solenoid valve). Electrical signals from various sensors provide information to the TCM about vehicle speed, throttle position, engine coolant temperature, transaxle fluid temperature, gear range selector position, engine speed, converter turbine speed, engine load braking and operating mode. The TCM uses this information to determine the precise moment to upshift or downshift, apply or release the TCC and what fluid pressure is needed to apply the clutches. This type of control provides consistent and precise shift points and shift quality based on the operating conditions of the vehicle.
TRANSAXLE INPUTS
TRANSAXLE FLUID TEMPERATURE (TFT) SENSOR
The transaxle fluid temperature (TFT) is part of the transaxle wiring harness assembly (1). The TFT sensor is a resistor, or thermistor (2), which changes value based on temperature. The sensor has a negative-temperature coefficient. This means that as the temperature increases, the resistance decreases, and as the temperature decreases the resistance increases. The TCM supplies a 5-volt reference signal to the sensor and measures the voltage drop in the circuit. When the transaxle fluid is cold, the sensor resistance is high and the TCM detects high signal voltage. As the fluid temperature warms to a normal operating temperature, the resistance becomes less and the signal voltage decreases. The TCM uses this information to maintain shift quality and torque converter clutch apply quality over the operating temperature range.
TRANSAXLE OUTPUT SHAFT SPEED (OSS) SENSOR ASSEMBLY
The OSS sensor (1) is a 2 wire hall-effect sensor, located in the top of the transaxle case. This sensor is mounted in the case opposite the parking lock gear (2) that is splined to the underdrive planetary gear assembly shaft. The OSS sensor consists of a permanent magnet, a hall element, and integrated circuits. As the parking lock gear rotates, a square wave DC voltage signal is produced when the teeth on the gear pass by the hall element. Whenever the vehicle is moving, the OSS sensor produces a square wave DC voltage signal with a frequency proportional to vehicle speed. This signal is sent to the TCM. The TCM uses transaxle output speed to help determine line pressure, transaxle shift patterns, TCC apply pressure, gear ratios and TCC shudder for diagnostic purposes. The TCM also sends a vehicle speed signal to other controllers, based on the OSS signal.
TRANSAXLE INPUT SHAFT SPEED (ISS) SENSOR ASSEMBLY
The A/T ISS sensor operates identically to the A/T OSS sensor except it uses the stamped teeth on the forward and direct clutch housing and input shaft assembly (1) as the rotor (reluctor). Remember that the forward and direct clutch housing and input shaft assembly is driven at converter turbine speed. The TCM uses transaxle input speed to help determine line pressure, transaxle shift patterns, TCC apply pressure, gear ratios, and TCC slippage for diagnostic purposes.
TRANSAXLE RANGE SWITCH ASSEMBLY
The transaxle range switch assembly is a sliding contact switch attached to the manual shift shaft and detent lever assembly outside the transaxle case. The five inputs to the TCM from the transaxle range switch assembly indicate which position is selected by the transaxle selector lever. This information is used for engine controls as well as determining the transaxle shift patterns. The state of each input is available for display on the Scan tool. If the TCM detects an improper signal from the transaxle range switch assembly, a DTC will be activated.
TRANSAXLE OUTPUTS
SHIFT SOLENOID 1
The shift solenoid 1 valve is a normally open, ON/OFF type solenoid controlled by the TCM. When the shift solenoid I valve is energized (ON), S1 signal fluid is blocked from exhausting through the solenoid, thereby creating S1 signal fluid pressure. S1 signal fluid pressure acts on the Up shift valve and the MI shift valve.
When the shift solenoid I valve is de-energized (OFF), any existing S1 signal fluid pressure exhausts through the solenoid.
SHIFT SOLENOID 2
The shift solenoid 2 valve is a normally open, ON/OFF type solenoid controlled by the TCM. When the shift solenoid 2 valve is energized (ON), S2 signal fluid is blocked from exhausting through the solenoid, thereby creating S2 signal fluid pressure. S2 signal fluid pressure acts on the M2 shift valve, against spring force, to move the valve into the applied position.
When the shift solenoid 2 valve is de-energized (OFF), any existing S2 signal fluid pressure exhausts through the solenoid.
SHIFT SOLENOID 3 VALVE
The shift solenoid 3 valve is a normally closed, ON/OFF type solenoid controlled by the TCM. When the shift solenoid 3 valve is energized (ON), S3 signal fluid is allowed to exhaust through the solenoid, thereby exhausting any S3 signal fluid pressure present in the circuit.
When the shift solenoid 3 valve is de-energized (OFF), S3 signal fluid is blocked from exhausting through the solenoid, thereby creating S3 signal fluid pressure. S3 signal fluid pressure acts on the U2 shift valve, against spring force, to move it into the applied position.
SHIFT SOLENOID 4
The shift solenoid 4 valve is a normally open, ON/OFF type solenoid controlled by the TCM. When the shift solenoid 4 valve is energized (ON), S4 signal fluid is blocked from exhausting through the solenoid, thereby creating S4 signal fluid pressure. S4 signal fluid pressure acts on the U2 shift valve and the U1 shift valve.
When the shift solenoid 4 valve is de-energized (OFF), any existing S4 signal fluid pressure exhausts through the solenoid.
SHIFT SOLENOID 5
The shift solenoid 5 valve is a normally closed, ON/OFF type solenoid controlled by the TCM. When the reverse SS valve is energized (ON), S5 signal fluid is allowed to exhaust through the solenoid thereby exhausting any S5 signal fluid pressure present in the circuit.
When the shift solenoid 5 valve is de-energized (OFF), S5 signal fluid is blocked from exhausting through the solenoid, thereby creating S5 signal fluid pressure. S5 signal fluid pressure acts on the shift pressure relay valve, against spring force, to move it into the applied position.
LINE PC SOLENOID (SLT)
The line pressure control solenoid valve (normally high, 3-port linear pressure control solenoid) is a precision electronic pressure regulator that controls transaxle line pressure based on current flow through its coil windings. As Current flow is increased, the magnetic field produced by the coil moves the solenoid's plunger further away from the exhaust port. Opening the exhaust port decreases the output fluid pressure regulated by the line pressure control solenoid valve, which ultimately decreases line pressure. The TCM controls the line pressure control solenoid valve based on various inputs including throttle position, transaxle fluid temperature and gear state.
TCC LOCK UP PC SOLENOID (SLU)
The TCC lock up pressure control solenoid (SLU) is a normally low, 3-port linear pressure control solenoid used to control the apply and release of the forward and reverse clutches, and the torque converter clutch. The TCM operates the solenoid with a negative duty cycle at a fixed frequency of 32 Hz to control the rate of clutch apply/release. The solenoid's ability to ramp the clutch apply and release pressures results in a smoother clutch operation.
SHIFT PC SOLENOID (SLS)
The shift pressure control solenoid valve (normally high, 3-port linear pressure control solenoid) is a precision electronic pressure regulator that controls transaxle clutch apply pressure based on current flow through its coil windings. As current flow is increased, the magnetic field produced by the coil moves the solenoid's plunger further away from the exhaust port. Opening the exhaust port decreases the output fluid pressure regulated by the shift pressure control solenoid valve, which ultimately decreases clutch apply pressure. The TCM controls the shift pressure control solenoid valve based on various inputs including throttle position, transaxle fluid temperature and gear state.