Transmission Description
Transmission Description
The 5R55N has the following features:
^ Five forward speeds.
^ Electronic shift, pressure, and torque converter clutch controls.
^ Three compound planetary gear sets.
^ Three bands.
^ Four multi-plate clutches.
^ Three one-way clutches.
All hydraulic functions are directed by electronic solenoids to control:
^ Engagement feel.
^ Shift feel.
^ Shift scheduling.
^ Modulated torque converter clutch (TCC) applications.
^ Engine braking utilizing the coast clutch and band.
Transmission View
Upshifts
Transmission upshifting is controlled by the powertrain control module. The powertrain control module receives inputs from various engine or vehicle sensors and driver demands to control shift scheduling, shift feel and torque converter clutch (TCC) operation.
The PCM has an adaptive learn strategy to electronically control the transmission, which will automatically adjust the shift feel. When the battery has been disconnected, or a new battery installed certain transmission operating parameters may be lost. The Powertrain Control Module (PCM) must re-learn these parameters. During this learning process you may experience slightly firm shifts, delayed, or early shifts. This operation is considered normal and will not affect the function of the transmission. Normal operation will return once these parameters are stored by the PCM.
Downshifts
Under certain conditions the transmission will downshift automatically to a lower gear range (without moving the gearshift lever). There are three categories of automatic downshifts, coastdown, torque demand and forced or kickdown shifts.
Coastdown
The coastdown downshift occurs when the vehicle is coasting down to a stop.
Torque Demand
The torque demand downshift occurs (automatically) during part throttle acceleration when the demand for torque is greater than the engine can provide at that gear ratio. If applied, the transmission will disengage the TCC to provide added acceleration.
Kickdown
For maximum acceleration, the driver can force a downshift by pressing the accelerator pedal to the floor. A forced downshift into a lower gear is possible below calibrated speeds. Specifications for downshift speeds are subject to variations due to tire size and engine and transmission calibration requirements.
Range Selection
Depending on the vehicle options selected the transmission range selector may have different range positions.
The standard range selector has seven positions: P, R, N, D5, D4, 3 and 2.
J-Gate Range Selection
"P"
In the PARK position:
^ there is no power flow through the transmission.
^ the parking pawl locks the output shaft to the case.
^ the engine may be started.
^ the ignition key may be removed.
"R"
In the REVERSE position:
^ the vehicle may be operated in a rearward direction, at a reduced gear ratio.
^ backup lamps are illuminated.
"N"
In the NEUTRAL position:
^ there is no power flow through the transmission.
^ the output shaft is not held and is free to turn.
^ the engine may be started.
"D"
D is the normal position for most forward driving.
The D position provides:
^ automatic shift 1-5 and 5-1.
^ apply and release of the torque converter clutch.
^ maximum fuel economy during normal operation.
^ engine braking in 5th gear.
"D4"
The D4 position provides:
^ automatic shift 1-4 and 4-1.
^ apply and release of the torque converter clutch.
^ engine braking in 4th gear.
"D3"
The D3 position provides:
^ third gear start and hold.
^ the torque converter clutch may apply and release.
^ improved traction on slippery roads.
^ engine braking.
"D2"
The D2 position provides:
^ second gear start and hold.
^ the torque converter clutch may apply and release.
^ improved traction on slippery roads.
^ engine braking.
Disassembled Views
Bushings, Bearing and Thrust Washer Locator
Seals, Rings and Gaskets Locator
Torque Converter
The torque converter transmits and multiplies torque. The torque converter is a four-element device:
^ impeller assembly
^ turbine and damper assembly
^ reactor assembly
^ clutch
The standard torque converter components operate as follows:
^ Rotation of the converter housing and impeller set the fluid in motion.
^ The turbine reacts to the fluid motion from the impeller, transferring rotation to the geartrain through the input shaft.
^ The reactor redirects fluid going back into the impeller, allowing for torque multiplication.
^ The clutch and damper assembly dampens powertrain torsional vibration and provides a direct mechanical connection for improved efficiency.
^ Power is transmitted from the torque converter to the planetary gearsets and other components through the input shaft.
Geartrain
Power is transmitted from the torque converter to the planetary gearsets through the input shaft. Bands and clutches are used to hold and drive certain combinations of gearsets. This results in five forward ratios and one reverse ratio, which are transmitted to the output shaft and differential.
Planetary Gearset-Overdrive
The planetary gear overdrive carrier is driven by the input shaft.
^ The overdrive planetary gearset carrier drives the center shaft via the overdrive one-way clutch in 1st, 3rd, 4th, and reverse gears.
^ In 2nd, and 5th, the overdrive sun gear is held causing the pinion gears to rotate around the overdrive sun gear.
^ The pinion gears in turn drive the overdrive ring gear resulting in a 5th (overdrive) gear ratio of 0.75 to 1.
^ The overdrive planetary gearset is internally splined to the coast clutch for engine braking.
Planetary Gearset-Forward
The forward planetary gearset is splined to the output shaft.
^ The forward planetary gearset is driven by the forward ring gear when the forward clutch is applied.
^ The forward planetary gearset pinions drive the forward sun gear.
^ The forward sun gear is splined to the input shell.
^ The forward carrier is splined to the output shaft.
Planetary Gearset-Low/Reverse
The low/reverse planetary gearset is connected to the reverse brake drum by lugs from the low/reverse brake drum to the lugs of the low/reverse planetary gearset.
^ The low/reverse planetary gearset is driven by the forward sun gear, which is splined to the input shell.
^ The forward sun gear drives the pinions in the low/reverse planetary gearset.
^ The pinions of the low/reverse planetary gearset drive the output shaft ring gear and output shaft hub, which is splined to the output shaft.
^ The low/reverse planetary gearset can be held by the low one-way clutch in the low/reverse brake drum, or by the low/reverse band.
Input Shaft
^ The radial positioning of the input shaft is controlled by two bushings in the stator support.
^ Axial positioning of the input shaft is controlled by the splines in the converter turbine and the retaining ring in the overdrive planetary carrier.
Output Shaft
The output shaft is supported by a bearing in the case and by a bearing in the extension housing. End positioning is controlled by the parking pawl gear and by the reverse ring gear hub and snap ring.
Apply Components
Band-Overdrive
During 2nd and 5th gear operation, hydraulic pressure is applied to the overdrive servo.
^ This pressure causes the piston to move and apply force to the band.
^ This action causes the overdrive band to hold the overdrive drum.
^ This causes the overdrive sun gear to be held stationary through the adapter plate and the overdrive drum.
Band-Low/Reverse
During 2nd position, 1st position and reverse, hydraulic pressure is applied to the low/reverse servo.
^ This pressure causes the servo to move and apply force to the low/reverse band.
^ This action causes the low/reverse brake drum to be held.
^ This action causes the low/reverse planetary assembly to be held stationary.
Band-Intermediate
During 3rd position, hydraulic pressure is applied to the intermediate servo.
^ This pressure causes the servo to move and apply force to the intermediate band.
^ This action causes the direct clutch drum to be held.
^ The intermediate band holds the intermediate brake and direct clutch drum to the case in 3rd gear.
^ This causes the input shell and forward sun gear to be held stationary.
Clutches-Direct
The direct clutch is a multi-disc clutch made up of steel and friction plates.
^ The direct clutch is applied with hydraulic pressure and disengaged by return springs and the exhaust of the hydraulic pressure.
^ It is housed in the direct clutch drum.
^ During 4th, 5th, and reverse gear application, the direct clutch is applied transferring torque from the forward clutch cylinder to the direct clutch drum.
^ This action causes the forward sun gear to drive the pinions of the low/reverse planetary carrier.
Clutches-Forward
The forward clutch is a multi-disc clutch made up of steel and friction plates.
^ The forward clutch is applied with hydraulic pressure and disengaged by return springs and the exhaust of the hydraulic pressure.
^ The forward clutch is applied in all forward gears.
^ When applied, the forward clutch provides a direct mechanical coupling between the center shaft and the forward ring gear and hub.
Clutches-Coast
The coast clutch is a multi-disc clutch made up of steel and friction plates.
^ The coast clutch is applied with hydraulic pressure and disengaged by return springs and the exhaust of the hydraulic pressure.
^ The coast clutch is housed in the overdrive drum.
^ The coast clutch is applied when in 1st, 3rd, D4, and reverse positions.
^ When applied, the coast clutch locks the overdrive sun gear to the overdrive planetary carrier. This prevents the one-way clutch from overrunning when the vehicle is coasting.
This allows the use of engine compression to help slow the vehicle and provide engine braking.
One-Way Clutch-Direct
The direct one-way clutch is a sprag-type one-way clutch that is pressed into the center shaft.
^ The direct one-way clutch is driven by the ring gear of the overdrive planetary carrier.
^ The direct one-way clutch holds and drives the outer splines of the center shaft in 1st, 3rd, 4th and reverse gears.
^ The direct one-way clutch overruns during all coast operations and at all times in 2nd and 5th gear.
One-Way Clutch-Intermediate
The Intermediate One-Way Clutch is a sprag type one-way clutch.
^ The Intermediate One-Way Clutch connects the intermediate assembly to the input shell and sun gear assembly in third gear.
One-Way Clutch-Low/Reverse
The low/reverse one-way clutch is a sprag type one-way clutch.
^ The low/reverse one-way clutch holds the low/reverse drum and low/reverse planetary assembly to the case in 1st and 2nd gear.
^ In all other gears the low/reverse one-way clutch overruns.
Hydraulic System
Fluid Pump
^ The fluid pump provides the fluid pressure necessary to charge the torque converter, main control assembly, transmission cooling system, lubrication system and apply devices.
^ The fluid pump is a positive displacement, gear type pump.
The fluid pump is driven by the torque converter impeller hub.
Filter
^ All fluid drawn from the transmission fluid pan by the fluid pump passes through the fluid filter.
^ The transmission fluid filter and its accompanying seals are part of the fluid path from the sump (pan) to the fluid pump.
The transmission fluid filter has a bypass section, which allows fluid vented at the main regulator valve to be recirculated to the fluid pump, without passing through the transmission fluid filter.
Main Control
^ The main control valve body and related components are part of the pressure side of the hydraulic system.
^ The main control valve body consists of the solenoids, the valve body assembly and the separator plate.
^ These components combine to convert electrical signals into hydraulic actions.
All valves in the main control assembly are anodized aluminum and cannot be sanded, filed or dressed in any other way. If there is any damage to the valves that prevents or restricts their movement, install a new main control valve body.
Electronic System Description
The powertrain control module and its input/output network control the following transmission operations:
^ shift timing.
^ line pressure (shift feel).
^ torque converter clutch.
The transmission control is separate from the engine control strategy in the PCM, although some of the input signals are shared. When determining the best operating strategy for transmission operation, the PCM uses input information from certain engine-related and driver-demand related sensors and switches.
In addition, the PCM receives input signals from certain transmission-related sensors and switches. The PCM also uses these signals when determining transmission operating strategy.
Using all of these input signals, the PCM can determine when the time and conditions are right for a shift, or when to apply or release the torque converter clutch. It will also determine the pressure needed to optimize shift feel. To accomplish this the PCM uses three pressure control and four shift solenoids to control transmission operation.
The following provides a brief description of each of the sensors and actuators used to control transmission operation.
Powertrain Control Module
The operation of the transmission is controlled by the powertrain control module. Many input sensors provide information to the powertrain control module. The powertrain control module then controls the actuators, which determine transmission operation.
Air Conditioning (A/C) Clutch
An electromagnetic clutch is energized when the clutch cycling pressure switch closes. The switch is located on the suction accumulator/drier. The closing of the switch completes the circuit to the clutch and draws it into engagement with the compressor driveshaft. When the A/C is engaged, operating pressures are adjusted to compensate for additional load on the engine.
Brake Pedal Position (BPP) Switch
The brake pedal position (BPP) switch tells the powertrain control module (PCM) when the brakes are applied. The torque converter clutch disengages when the brakes are applied. The BPP switch closes when the brakes are applied and opens when they are released. The BPP is also used to disengage the brake shift interlock.
Engine Coolant Temperature (ECT) Sensor
The engine coolant temperature (ECT) sensor detects engine coolant temperature and supplies the information to the PCM. The ECT sensor is used to control torque converter clutch (TCC) operation.
Electronic Ignition (EI) System
The electronic ignition consists of a crankshaft position sensor, two four-tower ignition coils and the powertrain control module. The ignition control module operates by sending crankshaft position information from the crankshaft position sensor to the ignition control module. The ignition control module generates a profile ignition pickup (PIP) signal (engine rpm) and sends it to the PCM. The PCM uses PIP signal in the transmission strategy, wide-open throttle (WOT) shift control, torque converter clutch control and operating pressures.
Intake Air Temperature (IAT) Sensor
The intake air temperature (IAT) sensor provides the sequential fuel injection (SFI) system mixture temperature information. The IAT sensor is used both as a density corrector for air flow calculation and to proportion cold enrichment fuel flow. The IAT sensor is installed in the air cleaner outlet tube. The IAT sensor is also used in determining control pressures.
Mass Air Flow (MAF) Sensor
The mass air flow sensor measures the mass of air flowing into the engine. The MAF sensor output signal is used by the powertrain control module (PCM) to calculate injector pulse width. For transmission strategies, the MAF sensor is used to regulate electronic pressure control, shift and torque converter clutch scheduling.
Transmission Control Switch (TCS)
The transmission control switch (TCS) sends a signal to the powertrain control module (PCM) when the driver selects the D4 position, canceling operation of 5th (overdrive) gear.
The TCS is located within the range selector assembly (base shifter only).
The PCM uses this signal to control the shift solenoids to disengage/disable 5th gear operation and activates coast clutch. At the same time, the PCM changes the instrument panel indicator to display D4.
When the driver moves the range selector lever back to the D5 position, 5th gear operation is enabled, the coast clutch is released and the instrument panel indicator changes to display D5.
Throttle Position (TP) Sensor
The throttle position (TP) sensor is a potentiometer mounted on the throttle body. The TP sensor detects the position of the throttle plate and sends this information to the powertrain control module. The TP sensor is used for shift scheduling, electronic pressure control and torque converter clutch (TCC) control.
Digital Transmission Range (TR) Sensor
The digital transmission range (TR) sensor is located on the outside of the transmission at the manual lever. The digital TR sensor completes the start circuit in PARK, NEUTRAL, and the back-up lamp circuit in REVERSE. The digital TR sensor also opens and closes a set of four switches that are monitored by the powertrain control module to determine the position of the manual lever (P, R, N, D, 4, 3, 2).
Turbine Shaft Speed (TSS) Sensor
The turbine shaft speed (TSS) sensor is a magnetic pickup that sends the powertrain control module torque converter turbine speed information.
The TSS sensor is mounted externally on the case.
The PCM uses TSS information to help determine appropriate operating pressures and torque converter clutch (TCC) operation.
Output Shaft Speed (OSS) Sensor
The output shaft speed (OSS) sensor is a magnetic pickup, located at the park gear, that sends a signal to the powertrain control module to indicate transmission output shaft speed. The OSS is used for torque converter clutch control, speed scheduling and to determine electronic pressure control.
Intermediate Shaft Speed (ISS) Sensor
The intermediate shaft speed (ISS) sensor is a magnetic pickup that sends planetary sun gear speed information to the PCM. The ISS is mounted externally on the center of the case.
he PCM uses the ISS information to aid in determining pressure requirements.
Pressure Control Solenoids (PCA, PCB, PCC)
The pressure control (PC) solenoids are a variable force style (VFS) solenoid. The VFS type solenoid is an electro-hydraulic actuator combining a solenoid and a regulating valve.
The line pressure tap is used to verify output pressure from PC A or PC B by turning either one off while verifying the output from the other solenoid. The second pressure tap is used to verify the output from the PC C solenoid.
There are three PC solenoids located in the solenoid body assembly used to control line pressure, band and clutch application pressure within the transmission.
The powertrain control module varies the current to the PC solenoid.
The PCM has an adaptive learn strategy to electronically control the transmission, which will automatically adjust the shift feel. When the battery is disconnected or a new battery installed, certain transmission operating parameters can be lost. The Powertrain Control Module (PCM) must relearn these parameters. During this learning process, you may experience slightly firm shifts, delayed, or early shifts. This operation is considered normal and will not affect the function of the transmission. Normal operation will return once these parameters are stored by the PCM.
Torque Converter Clutch (TCC) Solenoid
The torque converter clutch (TCC) solenoid is a pulse width modulating type solenoid which is used to control the apply and release of the TCC.
Shift Solenoids- (SSA, SSB, SSC, SSD)
Four On/Off shift solenoids allow the powertrain control module to control shift scheduling.
^ The solenoids are three-way, normally open style.
^ The shift solenoids SSA, SSB, SSC, and SSD provide gear selection of 1st through 5th and reverse gears by directing PC pressures to the appropriate elements.
Coast braking and manual gears are also controlled by the shift solenoids.
Transmission Fluid Temperature (TFT) Sensor
^ The transmission fluid temperature (TFT) sensor is a thermistor-type sensor that varies a reference voltage signal. The resistance in the TFT varies with temperature. The powertrain control module (PCM) monitors the voltage signal across the TFT, and uses this information to determine the transmission fluid temperature.
^ The TFT is located on the solenoid body.
^ The PCM uses the TFT signal to help determine shift scheduling, torque converter clutch operation and pressure control requirements.
It sends a voltage signal to the powertrain control module. The voltage signal varies with transmission fluid temperature. The PCM uses this signal to determine whether a cold start shift schedule is necessary. The shift schedule is compensated when the transmission fluid temperature is cold. The PCM also inhibits torque converter clutch (TCC) operation at low transmission fluid temperatures and use to determine pressure control (PC) solenoid operations.
Reverse Pressure (RP) Switch
The reverse pressure (RP) switch is a simple open or closed switch that is used to detect the presence of pressure in the main control valve body. The switch is mounted on the main control valve body. When pressure is not present, the switch is opened and the voltage reading is high. When pressure is present, the switch is closed and the voltage reading will be near zero.