Part 2
Automatic Transmission ContinuedPLANETARY GEAR TRAINS
The planetary gear trains used on the 6HP26 transmission comprise a single web planetary gear train and a double web planetary gear train. These gear trains are known as Lepelletier type gear trains and together produce the six forward gears and the one reverse gear.
Single Web Planetary Gear Train
The single web planetary gear train comprises:
^ One sunwheel
^ Three planetary gears
^ One planetary gear carrier
^ One ring gear or annulus
Double Web Planetary Gear Train
The double planetary gear train comprises:
^ Two sunwheels
^ Three short planetary gears
^ Three long planetary gears
^ One planetary gear carrier
^ One ring gear or annulus
POWER FLOWS
Operation of the transmission is controlled by the TCM (transmission control module) which electrically activates various solenoids to control the transmission gear selection. The sequence of solenoid activation is based on programmed information in the module memory and physical transmission operating conditions such as vehicle speed, throttle position, engine load and selector lever position.
Powerflow Schematic
Engine torque is transferred, via operation of single or combinations of clutches to the two planetary gear trains. Both gear trains are controlled by reactionary inputs from brake clutches to produce the six forward gears and one reverse gear. The ratios are as follows:
The following table shows which solenoids are activated to produce the required torque output from the transmission.
The following table shows which clutches are operating for selected gear ratios to produce the required torque output from the transmission.
Shift Elements
The shift elements are three rotating multiplate clutches (A, B and E) and two fixed multiplate brakes (C and D). All shifts from 1st to 6th gears are power-on overlapping shifts. Overlapping shifts can be described as one of the clutches continuing to transmit drive at a lower main pressure until the next required clutch is able to accept the input torque.
The shift elements, clutches and brakes are actuated hydraulically. Fluid pressure is applied to the required clutch and/or brake, pressing the plates together and allowing drive to be transmitted through the plates. The purpose of the shift elements is to perform power-on shifts with no interruption to traction and smooth transition between gear ratios.
Power Flow 1st Gear
The gear selector lever and the manual selector valve spool are in the 'D' position. Engine torque is transmitted from the torque converter turbine shaft to the ring gear 1 of the single web planetary gear train and the outer plate carrier of clutch 'E'.
Ring gear 1 drives the planetary gears which rotate around sunwheel 1. This drives the planetary gear carrier 1 and also the outer plate carrier of clutch 'A' and the inner plate carrier of clutch 'B'.
When clutch 'A' is engaged, sunwheel 3 in the double web planetary gear train is driven and meshes with the short planetary gears.
The double web planetary gear train is locked against the transmission housing by brake 'D'. This allows ring gear 2 (output shaft) to be driven in the same direction as the engine via the long planetary gears.
NOTE: Refer to 'Shift Elements' illustration for key
Power Flow 2nd Gear
The gear selector lever and the manual selector spool valve are in the 'D' position. Engine torque is transmitted from the torque converter turbine shaft to the ring gear 1 of the single web planetary gear train and the outer plate carrier of clutch 'E'.
Ring gear 1 drives the planetary gears which rotate around sunwheel 1. This drives the planetary gear carrier 1 and also the outer plate carrier of clutch 'A' and the inner plate carrier of clutch 'B'.
When clutch 'A' is engaged, sunwheel 3 in the double web planetary gear train is driven and meshes with the short planetary gears.
Sunwheel 2 is locked to the transmission housing by brake clutch 'C'. The long planetary gears, which are also meshed with the short planetary gears, roll around the fixed sunwheel 2 and transmit drive to the double web planetary gear train carrier and ring gear 2 in the direction of engine rotation.
NOTE: Refer to 'Shift Elements' illustration for key
Power Flow 3rd Gear
The gear selector lever and the manual selector spool valve are in the 'D' position. Engine torque is transmitted from the torque converter turbine shaft to the ring gear 1 of the single web planetary gear train and the outer plate carrier of clutch 'E'.
Ring gear 1 drives the planetary gears which rotate around sunwheel 1. This drives the planetary gear carrier 1 and also the outer plate carrier of clutch 'A' and the inner plate carrier of clutch 'B'.
When clutch 'A' is engaged, sunwheel 3 in the double web planetary gear train is driven and meshes with the short planetary gears.
Sunwheel 2 is driven via clutch 'B' which is engaged. The long planetary gears, which are also meshed with the short planetary gears, cannot roll around the fixed sunwheel 2 and transmit drive to the locked double web planetary gear train carrier in the direction of engine rotation.
NOTE: Refer to 'Shift Elements' illustration for key
Power Flow 4th Gear
The gear selector lever and the manual selector spool valve are in the 'D' position. Engine torque is transmitted from the torque converter turbine shaft to ring gear 1 of the single web planetary gear train and the outer plate carrier of clutch 'E'.
Ring gear 1 drives the planetary gears which rotate around sunwheel 1. This drives the planetary gear carrier 1 and also the outer plate carrier of clutch 'A' and the inner plate carrier of clutch 'B'.
When clutch 'A' is engaged, sunwheel 3 in the double web planetary gear train is driven and meshes with the short planetary gears.
The double web planetary gear carrier is driven via clutch 'E' which is engaged. The long planetary gears, which are also meshed with the short planetary gears, and the double web planetary gear carrier, drive ring gear 2 in the direction of engine rotation.
NOTE: Refer to 'Shift Elements' illustration for key
Power Flow 5th Gear
The gear selector lever and the manual selector spool valve are in the 'D' position. Engine torque is transmitted from the torque converter turbine shaft to ring gear 1 of the single web planetary gear train and the outer plate carrier of clutch 'E'.
Ring gear 1 drives the planetary gears which rotate around sunwheel 1. This drives the planetary gear carrier 1 and also the outer plate carrier of clutch 'A' and the inner plate carrier of clutch 'B'.
When clutch 'A' is engaged, sunwheel 3 in the double web planetary gear train is driven and meshes with the short planetary gears.
The long planetary gears, which are also meshed with the short planetary gears, and the double web planetary gear carrier, drive ring gear 2 in the direction of engine rotation.
NOTE: Refer to 'Shift Elements' illustration for key
Power Flow 6th Gear
The gear selector lever and the manual selector spool valve are in the 'D' position. Engine torque is transmitted from the torque converter turbine shaft to ring gear 1 of the single web planetary gear train and the outer plate carrier of clutch 'E'.
Clutches 'A and 'B' are released, removing the effect of the single web planetary gear train. Clutch brake 'C' is applied which locks sunwheel 2 to the transmission housing.
Clutch 'E' is engaged and drives the double web planetary gear carrier. This causes the long planetary gears to rotate around the fixed sunwheel 2 and transmit drive to ring gear 2 which is driven in the direction of engine rotation.
NOTE: Refer to 'Shift Elements' illustration for key
Power Flow Reverse Gear
The gear selector lever and the manual selector spool valve are in the 'R' position. Engine torque is transmitted from the torque converter turbine shaft to ring gear 1 of the single web planetary gear train and the outer plate carrier of clutch 'E'.
Ring gear 1 drives the planetary gears of the single web planetary gear train which rotate around the fixed sunwheel 1. This transmits the drive to the single web planetary gear carrier, the outer plate carrier of clutch 'A' and the inner plate carrier of clutch 'B'.
With clutch 'B' applied, sunwheel 2 in the double web planetary gear train is driven and meshes with the long planetary gears.
The double web planetary gear carrier is locked to the transmission housing by brake clutch 'D'. This allows ring gear 2 to be driven in the opposite direction to engine rotation by the long planetary gears.
NOTE: Refer to 'Shift Elements' illustration for key
SELECTOR POSITION SWITCH
The Mechatronic valve block contains a position switch which is mechanically connected to the selector spool valve. The selector spool valve is connected by a selector shaft to the selector lever via a 'Bowden' selector cable.
The signals from the position switch are used by the TCM (transmission control module) to determine the P, R, N or D selection made by the driver.
CONTROL DIAGRAM
NOTE: A = Hardwired; D= High Speed CAN Bus
INSTRUMENT CLUSTER
The instrument cluster is connected to the TCM (transmission control module) via the CAN (controller area network) bus. Transmission status is transmitted by the TCM and displayed to the driver on one of two displays in the instrument cluster.
Malfunction Indicator Lamp (MIL)
The MIL (malfunction indicator lamp) is located in the lower left hand corner of the instrument cluster, below the fuel gauge. Transmission related faults which may affect the vehicle emissions output will illuminate the MIL (malfunction indicator lamp).
The MIL (malfunction indicator lamp) is illuminated by the ECM (engine control module) on receipt of a relevant fault message from the TCM (transmission control module) on the CAN (controller area network) bus. The nature of the fault can be diagnosed using an approved Land Rover diagnostic system which reads fault codes stored in the TCM (transmission control module) memory.
Transmission Status Display
The transmission status display is located on the right hand side of the instrument cluster, below the tachometer. The display shows the selector lever position and in the case of manual (CommandShift) mode, the selected gear. The selector lever position and gear selected displays are illuminated in a green color when active.
Additionally, the display also shows a low range symbol when low range is selected on. The low range symbol is illuminated in an amber color when active. when the transfer box is changing from low to high range, the low range symbol flashes until the range change is complete.
Message Center Display
The message center is located below the speedometer and the tachometer at the bottom of the instrument cluster. The message center is a LCD (liquid crystal display) to relay vehicle status information to the driver, refer to Information and Message Center for message details.
TRANSMISSION CONTROL MODULE (TCM)
The TCM (transmission control module) is an integral part of the Mechatronic valve block which is located at the bottom of the transmission, behind the fluid pan. The TCM (transmission control module) is the main controlling component of the transmission.
The TCM (transmission control module) processes signals from the transmission speed and temperature sensors, engine control module and other vehicle systems. From the received signal inputs and pre-programmed data, the module calculates the correct gear, torque converter clutch setting and optimum pressure settings for gear shift and lock-up clutch control.
The TCM (transmission control module) outputs signals to control the shift control solenoid valve and the Electronic Pressure Regulator Solenoids (EPRS) to control the hydraulic operation of the transmission.
The ECM (engine control module) supplies the engine management data on the high speed CAN (controller area network) bus system. The TCM (transmission control module) requires engine data to efficiently control the transmission operation, for example; flywheel torque, engine speed, accelerator pedal angle, engine temperature etc.
The steering angle sensor and the ABS (anti-lock brake system) module also supply data to the TCM (transmission control module) on the high speed CAN (controller area network) bus system. The TCM (transmission control module) uses data from these systems to suspend gear changes when the vehicle is cornering and/or the ABS (anti-lock brake system) module is controlling braking or traction control.
The selector lever is connected to the automatic transmission and the position switch in the transmission by a Bowden cable. Movement of the selector lever moves the position switch via the Bowden cable and the switch position informs the TCM (transmission control module) of the selected position. The sport/manual +/- CommandShift switch passes manual/sport selections to the TCM (transmission control module). An additional switch provides a selector lever in park position signal. Once the selector lever position is confirmed, the TCM (transmission control module) outputs appropriate information which is received by the instrument cluster to display the gear selection information in the message center.
The Mechatronic valve block also contains the speed and temperature sensors. These are integral with the Mechatronic valve block and cannot be serviced individually. The speed sensors measure the transmission input and output speeds and pass signals to the TCM (transmission control module). The fluid temperature sensor is also located in the valve block and measures the fluid temperature of the transmission fluid in the fluid pan.
The TCM (transmission control module) is connected to the starter relay coil. When the selector lever is in PARK or NEUTRAL, the module provides a ground for the coil allowing the starter relay to be energized and allow starter motor operation. If the selector lever is in any other position, the module will not provide the ground preventing starter motor operation.