Part 2
Transmission Description
Control Solenoid
A shift control SV (solenoid valve) is located in the valve block. The solenoid is controlled by the TCM (transmission control module) and converts electrical signals into hydraulic control signals to control clutch application.
The shift control solenoid is an open/closed, on/off solenoid which is controlled by the TCM (transmission control module) switching the solenoid to earth. The TCM (transmission control module) also supplies power to the solenoid. The TCM (transmission control module) energizes the solenoid in a programmed sequence for clutch application for gear ratio changes and shift control.
The resistance of the solenoid coil winding for solenoid is between 26 to 30.4 ohms at 20 °C (68 °F).
Sensors
Speed Sensors
The turbine speed sensor and the output shaft speed sensor are Hall effect type sensors located in the Mechatronic valve block and are not serviceable items. The TCM (transmission control module) monitors the signals from each sensor to determine the input (turbine) speed and the output shaft speed.
The turbine speed is monitored by the TCM (transmission control module) to calculate the slip of the torque converter clutch and internal clutch slip. This signal allows the TCM (transmission control module) to accurately control the slip timing during shifts and adjust clutch application or release pressure for overlap shift control.
The output shaft speed is monitored by the TCM (transmission control module) and compared to engine speed signals received on the CAN (controller area network) bus from the ECM (engine control module). Using a comparison of the two signals the TCM (transmission control module) calculates the transmission slip ratio for plausibility and maintains adaptive pressure control.
Temperature Sensor
The temperature sensor is also located in the Mechatronic valve block. The TCM (transmission control module) uses the temperature sensor signals to determine the temperature of the transmission fluid. These signals are used by the TCM (transmission control module) to control the transmission operation to promote faster warm-up in cold conditions or to assist with fluid cooling by controlling the transmission operation when high fluid temperatures are experienced. If the sensor fails, the TCM (transmission control module) will use a default value and a fault code will be stored in the TCM (transmission control module).
Damper
There is 1 damper located in the valve housing. The damper is used to regulate and dampen the regulated pressure supplied via EPRS 5. The damper is load dependent through modulation of the damper against return spring pressure.
The damper comprises a piston, a housing bore and a spring. The piston is subject to the pressure applied by the spring. The bore has a connecting port to the function to which it applies. Fluid pressure applied to the applicable component (i.e. a clutch) is also subjected to the full area of the piston, which moves against the opposing force applied by the spring. The movement of the piston creates an action similar to a shock absorber, momentarily delaying the build up of pressure in the circuit. This results in a more gradual application of clutches improving shift quality.
Spool Valves
The valve block contains 21 spool valves which control various functions of the transmission. The spool valves are of conventional design and are operated by fluid pressure.
Each spool valve is located in its spool bore and held in a default (unpressurized) position by a spring. The spool bore has a number of ports which allow fluid to flow to other valves and clutches to enable transmission operation. Each spool has a piston which is waisted to allow fluid to be diverted into the applicable ports when the valve is operated.
When fluid pressure moves a spool, 1 or more ports in the spool bore are covered or uncovered. Fluid is prevented from flowing or is allowed to flow around the applicable waisted area of the spool and into another uncovered port. The fluid is either passed through galleries to actuate another spool, operate a clutch or is returned to the fluid pan.
DRIVE CLUTCHES
Multiplate Drive or Brake Clutch - Typical
There are three drive clutches and two brake clutches used in the ZF 6HP28 transmission. Each clutch comprises one or more friction plates dependent on the output controlled. A typical clutch consists of a number of steel outer plates and inner plates with friction material bonded to each face.
On 3.0L diesel models, the uprated transmission includes additional clutch plates to enable the transmission to manage the additional power output from these engines.
The clutch plates are held apart mechanically by a diaphragm spring and hydraulically by dynamic pressure. The pressure is derived from a lubrication channel which supplies fluid to the bearings etc. The fluid is passed via a drilling in the output shaft into the chamber between the baffle plate and the piston. To prevent inadvertent clutch application due to pressure build up produced by centrifugal force, the fluid in the dynamic pressure equalization chamber overcomes any pressure in the piston chamber and holds the piston off the clutch plate assembly.
When clutch application is required, main pressure from the fluid pump is applied to the piston chamber from the supply port. This main pressure overcomes the low pressure fluid present in the dynamic pressure equalization chamber. The piston moves, against the pressure applied by the diaphragm spring, and compresses the clutch plate assembly. When the main pressure falls, the diaphragm spring pushes the piston away from the clutch plate assembly, disengaging the clutch.
PLANETARY GEAR TRAINS
The planetary gear trains used on the ZF 6HP28 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:
- Sunwheel
- Four planetary gears
- Planetary gear carrier (spider)
- Ring gear or annulus.
Torque Converter Input Shaft
The double planetary gear train comprises:
- Two sunwheels
- Three short planetary gears
- Three long planetary gears
- Planetary gear carrier
- Ring gear or annulus
TRANSMISSION CONTROL MODULE
The TCM (transmission control module) is an integral part of the Mechatronic valve block which is located at the bottom of the transmission, within 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, ECM (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.
CONTROL DIAGRAM
NOTE:
A = Hardwired; B = K bus; D = High speed CAN (controller area network) bus O = LIN (local interconnect network) bus.
OPERATION
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 TCM (transmission control module) memory and physical transmission operating conditions such as vehicle speed, throttle position, engine load and selector lever position.
Engine torque is transferred, via operation of single or combinations of clutches to the 2 planetary gear trains. Both gear trains are controlled by reactionary inputs from brake clutches to produce the 6 forward gears and 1 reverse gear. The ratios are as follows:
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 selector lever and the 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 selector lever and the 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 selector lever and the 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 therefore 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 selector lever and the 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 selector lever and the 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 selector lever and the 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 selector lever and the 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
Instrument Cluster
The instrument cluster is connected to the TCM (transmission control module) via the high speed CAN (controller area network) bus. Transmission status is transmitted by the TCM (transmission control module) and displayed to the driver in one of two displays in the instrument cluster. For additional information, refer to Instrument Cluster Description and Operation
Malfunction Indicator Lamp
The MIL (malfunction indicator lamp) is located in the tachometer of the instrument cluster. Transmission related faults which may affect the vehicle emissions 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 high speed CAN (controller area network). The nature of the fault can be diagnosed using Land Rover approved diagnostic equipment which reads the fault codes stored in the TCM (transmission control module) memory.
Transmission Status Display
The transmission status display is located in the tachometer of the instrument cluster. The display shows the selector lever position or the selected gear when in manual and sport modes.
The following table shows the displays and their descriptions.
Message Center
The message center is located in the center of the instrument cluster. The message center is a LCD (liquid crystal display) that relays vehicle status and operating information to the driver and can display messages relating to a number of vehicle systems. If a transmission fault occurs, the message GEARBOX FAULT is displayed in the message center. For additional information, refer to Information and Message Center Description and Operation
Transmission Control Module
The TCM (transmission control module) outputs signals to control the shift control solenoid valve and the EPRS to control the hydraulic operation of the transmission.
The TCM (transmission control module) processes signals from the transmission speed and temperature sensors, the selector lever, the ECM (engine control module) and other vehicle systems. From the received signal inputs and pre-programmed data, the TCM (transmission control module) calculates the correct gear, torque converter clutch setting and optimum pressure settings for gear shift and lock-up clutch control.
The ECM (engine control module) supplies the engine management data over the high speed CAN (controller area network) bus. 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. 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. 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.
Using the signal inputs and the memorized data, the TCM (transmission control module) control program computes the correct gear and torque converter lock-up clutch setting and the optimum pressure settings for gear shift and lock-up clutch control. Special output-side modules (power output stages, current regulator circuits), allow the TCM (transmission control module) to control the solenoid valves and pressure regulators and consequently precisely control the hydraulics of the automatic transmission. In addition, the amount and duration of engine interventions are supplied to the engine management by way of the CAN (controller area network) bus.
The TCM (transmission control module) determines the position of the selector lever using signals from:
- The selector switch in the transmission.
- The park lock and M/S (manual/sport) 'CommandShift' switches on the selector lever.
When the driver operates the steering wheel paddle switches the selections are sensed by the TCM (transmission control module), which then operates in the manual CommandShift mode. If the selector lever is in D, the CommandShift mode is temporary and will cancel after a time period or can be cancelled by pressing and holding the + paddle for approximately 2 seconds. If the selector lever is in the M/S position, the CommandShift mode is permanent and can only be cancelled by pressing and holding the + paddle for approximately 2 seconds or by moving the selector lever to the D position.
The TCM (transmission control module) transmits the position of the selector lever and the selected gear on the high speed CAN (controller area network) bus. This information is shown in the gear selector display in the instrument cluster.
Engine Stall
If the vehicle stalls it will coast down in gear, with the transmission providing drive to the engine. A restart can be attempted at this point and the engine may start and the driver can continue.
If the coast down speed reduces such that the speed of the engine is less than 600 rev/min, the transmission will go to neutral, D illumination will flash in the instrument cluster. The driver needs to select neutral or park and then press the brake pedal to restart the engine.
If the start/stop button is pressed when driving, the message ENGINE STOP BUTTON PRESSED is displayed in the message center but there will be no change to the ignition state. If the driver requires to switch off the engine, the start/stop button must be pressed for a second time. The engine will be stopped and will be back driven by the transmission as the vehicle coasts down.