Unit Repair
GENERAL DESCRIPTIONComponent Description:
This section provides information relating to the 'Powertrain' (formerly Hydra-Matic) 4L80E automatic transmissions fitted to the X-300 vehicle range.
The Powertrain in 4L8O-E is a four-speed, high torque capacity, electronically control led automatic transmission, which comprises a torque converter with lock-up direct drive clutch and three planetary gear sets. Five multiple disc clutches, one intermediate sprag clutch assembly, two roller clutch assemblies and two band assemblies provide the drive elements necessary for correct sequential gear engagement and operation.
The torque converter containing a pump, turbine (rotor), a stator assembly, and a clutch pressure plate splined to the turbine, acts as a fluid coupling for smooth torque transmission from the engine. The converter also supplies additional torque multiplication when necessary, and the torque converter clutch (TCC) pressure plate provides a mechanical direct drive or 'lock-up' above a certain speed in top gear for greater fuel economy.
Gear shift operations are controlled from the Transmission Control Module (TCM), which governs the electronically controlled valve body situated within the transmission.
Three planetary gear sets provide reverse and the four forward ratios, the changing of which is fully automatic in relation to load, vehicle speed and throttle opening. The tran-mission control module (TCM) receives and integrates various vehicle sensor input signals, and transmits operating signals to the solenoids located in the control valve assembly. These solenoids govern the transmission operating pressures, up-shift and down-shift gear selection patterns, and also the torque converter clutch operation from a pulse width modulated solenoid control.
The performance mode switch provides for selection of 'sport' or 'normal' mode as required by the driver. The switch input to TCM changes the gear shift pattern such that in 'sport' mode, shifts take place at higher engine speeds.
The 'kick-down' facility is activated by full downward travel of the accelerator pedal, providing a signal to TCM requesting greater acceleration hence downward gear shifts.
Gear Ranges
Selectable gear positions are: P - Park, R - Reverse, N - Neutral, D - Drive, 3, 2. The selected gear is displayed on a gear selection illumination module located above the selector mechanism.
P - Park position of the selector lever provides a mechanical locking of the output shaft of the transmission, and as such, must only be engaged when the vehicle is stationary. In addition, and for extra safety, the handbrake should also be applied. It is necessary to have the ignition on and the footbrake applied to move the selector lever from the Park position. For ignition key removal the selector lever must be in the Park position. The engine can be started in the Park position.
R - Reverse enables the vehicle to be operated in a rearwards direction. The engine cannot be started in the Reverse position.
N - Neutral position enables the engine to be started and operated without driving the vehicle. It also allows the vehicle to be moved manually for access, ie. for removal of the propeller shaft.
D - Drive position allows the automatic selection of all four forward gear ratios during normal driving conditions for maximum efficiency and fuel economy. On acceleration, down-shifts are obtained by depressing the accelerator pedal or by manual selection. The engine cannot be started in this position.
3 - Manual third position allows automatic operation of the three lower gear ratios but inhibits selection of the fourth ratio. This position is used for towing a trailer or negotiating hilly terrain when greater engine braking control is required. The engine cannot be started in this position.
2 - Manual second position allows automatic operation of the two lower gear ratios but inhibits selection of the third and fourth ratios. This position is used for heavy traffic congestion or negotiating hilly terrain when even greater engine braking control is required than is provided by manual third. This ratio may be selected at any vehicle speed - even if the transmission is in third or fourth ratio, the transmission will immediately down-shift to second gear provided the vehicle speed is below 137 km/ h (85 mile / h). The engine cannot be started in this position.
Note: With the performance mode switch in the 'normal' position, the vehicle will pull away in second gear. However, if more than 75 per cent of throttle is applied when the vehicle speed is between zero and 13 km / h (8 mile / h), then first gear will be selected. From 13 to 61 km/h (8 to 38 mile / h) first gear is obtainable by 'kick-down'. In 'sport' mode the vehicle pulls away in first gear and the transmission operates fully in all four forward gears.
Lubrication Circuits
Lubrication Flow:
Transmission oil passes from the transmi9sion unit, through the oil cooler and returns to the transmission unit via a connector in the case, into the valve body and into the lubrication pipe. The fluid is then routed to the rear of the transmission to lubricate the rear case, the rear extension housing bearing and the rear gearsets.
Lubrication fluid is also routed through the pump assembly and into the overrun clutch housing where it passes to the various apply components to cool and lubricate the transmission clutches and gear sets.
Cooler Circuit
With the torque converter clutch (TCC) released, transmission fluid returning from the torque converter is fed through the TCC shift valve into the cooler circuit, ie through the cooler feed pipe to the transmission cooler in the radiator and then back to the transmission unit lubrication circuits.
When the TCC is applied, ie the shift valve in the apply position, regulator converter fluid is passed through the valve and into the cooler circuit as described above.
TRANSMISSION COMPONENTS
Torque Converter
The torque converter is a three element (single stator) unit which acts as a fluid coupling to connect the engine power smoothly to the transmission gear train, and as a torque multiplier to provide extra power when pulling away from rest. The three elements of the converter are the pump (impeller), the turbine and the stator.
Planetary Gear Sets
Planetary Gear Sets:
Three planetary gear sets are used in this transmission: 'overdrive', 'reaction' and 'output'.
Each gear set comprises a center or sun gear, an annulus or internal gear, and a planetary carrier assembly which contains the smaller planet gears.
Direct drive in a planetary gear set is obtained when any two parts of a gear set rotate in the same direction at the same speed, thus driving the third component at the same speed. The planetary gears in this case act as wedges to drive the entire gear set as one unit and therefore the output speed of the transmission is the same as the input speed from the torque converter.
Conversely, a planetary gear set reverses the direction of power flow when a carrier assembly is held stationary and power is applied to the sun gear thus causing the planetary gears to act as idler gears to drive the internal gear in the opposite direction.
In first, second and third gears, the 'overdrive' roller clutch retains the 'overdrive' sun gear and carrier assembly to- gather, thereby driving the internal gear at the same speed.
In first gear, the 'output' internal gear drives the 'output' carrier planet gears clockwise, which causes the sun gear to rotate anti-clockwise. As the 'output' sun gear and the 'reaction' sun gear are common, the 'reaction' carrier planet gears rotate clockwise. The 'reaction' carrier, being held stationary by the 'LO' roller clutch, then causes the 'reaction' carrier planet gears to drive the 'reaction' internal gear and the output shaft, ie first gear.
Second gear is obtained when the 'output'/ 'reaction' sun gear is held stationary by the intermediate clutch and therefore when the 'output' carrier planet gears are driven clockwise by the rear internal gear, the planet gears rotate clockwise round the stationary sun gear. The 'output' carrier planet gears drive the 'output' carrier assembly and 'output' shaft clockwise, ie second gear.
Third gear is obtained when the direct clutch is applied; the power flow from the 'overdrive' planet gears and the forward clutch housing is then transferred to both the 'sun' gear and the 'output' internal gear. With the power flow through the 'overdrive' planetary gear set being a direct drive, and with both the sun gear and the internal gears of the 'output' planet gear set driving at converter turbine speed, the 'output' planetary gears act as wedges and drive the 'output' carrier assembly and output shaft together, ie direct drive, third gear.
In fourth gear, the 'overdrive' sun gear is held stationary by the fourth clutch being applied, then the 'overdrive' carrier being driven clockwise, the 'overdrive' planetary gears rotate clockwise also on their axes around the stationary sun gear. This causes the planetary gears to drive the 'overdrive' internal gear clockwise and so an 'overdrive' ratio is obtained through the 'overdrive' planetary gear set.
In reverse gear, the rear brake band is applied to hold the 'reaction' carrier stationary while the direct clutch is applied to supply clockwise power flow to the sun gear. Power flow from the 'overdrive' planetary gear set being a direct drive, the sun gear drives the 'reaction' planetary gears anti-clockwise which drives the 'reaction' internal gear ('output' carrier assembly) anti-clockwise, ie reverse gear.
Torque Converter Clutch
When a pre-determined speed is achieved in fourth gear, the torque converter clutch is enabled by the transmission control module through the pulse width modulated solenoid and a clutch plate provides a direct drive so reducing fuel consumption. Pulsing the solenoid causes the TCC valve to modulate pressure against the TCC. This pulsing or modulated pressure allows the TCC to slip slightly so providing a smooth apply and release of the TCC.
If the transmission fluid exceeds a temperature of 1250°C the TCC will also apply in second and third gears to reduce friction generated in the torque converter.
Pulse Width Modulated (PWM) Solenoid
This solenoid provides the gradual apply and release of the torque converter clutch for increased shift quality, see TCC.
Input And Output Speed Sensors (TISS) And (TOSS)
The two speed sensors are of the magnetic induction type, and are mounted on the left hand side of the transmission, the input sensor forward of the transmission centre, and the output sensor close to the rear extension housing. The induced voltage in the input sensor is generated from machined serrations on the forward clutch housing, and in the output speed sensor by serrations on the rear carrier assembly. The information from these two sensors is used by the transmission control module (TCM) to determine whether the engine is running, vehicle speed, the gear ratio, the TCC slip, and the turbine speed.
Shift Solenoids 'A' And 'B'
Both solenoids are attached to the valve body and are 'normally open exhaust valves'. The TCM activates the solenoid by grounding through an internal 'quad driver', activates the shift valve and so controls shift pattern.
For solenoid operation see Table 'ACTIVE COMPONENTS FOR EACH GEAR RATIO'. Solenoid 'A' is usually grey in colour, and solenoid 'B' is usually green.
Variable Force Solenoid/Motor (VFS)
The force motor is attached to the valve body and controls shift quality, dependant upon engine load, based on information received from the TCM.
Transmission Control Module (TCM)
This unit is an electronic module which controls gear shift points and shift quality. Using data received from various sensors, the TCM is 'updated' every 25 milliseconds, and adapts to changes in engine load, altitude, and other conditions. Electrical signals are then transmitted to the shift solenoids which activate the shift valves for precise shift control.
The TCM, located behind the passenger side fascia, has also a diagnostic capability such that it continually monitors the transmission's conditions and stores the performance data in its memory. This information can then be downloaded and read using the Jaguar Diagnostic System.
If a serious fault occurs, the TCM removes all electrical power from the three solenoid valves on the valve block and the transmission reverts to a mechanical default condition; this condition allows only mechanical selection of reverse and one forward (2nd - second) gear.
Pressure Switch Manifold (PSM)
This is a gear range sensing device used by the TCM to sense the gear range that has been selected by the driver. The PSM, located on the valve body, contains five normally open pressure switches which under the various fluid pressures fed from the manual valve, provide system signals to the PCM which determines the gear range that the transmission is operating in.
Transmission Temperature Sensor
The temperature of the transmission fluid is monitored by this sensor which relays information to the TCM. If the temperature rises above a certain figure, then the torque converter clutch is applied, see Torque Converter Clutch. This sensor is contained in the internal transmission harness.
Accumulators
The accumulators act as shock absorbers to cushion the engagement of the transmission clutches. The clutch 'apply' fluid pressure on one side of the accumulator piston acts against the accumulator spring pressure and the accumulator fluid pressure on the opposite side of the piston. This sequence is damped by controlling the exhaust rate of the accumulator fluid. There are accumulators for the second, third and fourth clutches.
OIL PUMP AND INTERNAL VALVES
The oil pump is mounted in the transmission assembly situated between the torque converter and the transmission gears casing. The pump is a constant mesh spur gear type and the drive gear, being keyed to the torque converter hub, is driven at engine speed whenever the engine is running. The oil pump contains valves for pressure regulation, torque converter clutch (TCC) enable and shift, converter limiting, and reverse boost.
Pressure Regulator Valve Train
A pressure regulating valve maintains the transmission fluid at a constant pressure, to ensure correct operation of the transmission, directing fluid into the converter limit valve, and the pump suction circuit to regulate the pump output.
Reverse Boost Valve
The boost valve is moved towards the pressure regulating valve when activated by torque signal fluid pressure from the variable force motor, the regulating valve is then moved against the fluid supply from the pump, and so boosts the line pressures in relation to engine torque. When reverse gear has been selected, the reverse fluid pressure forces the reverse boost valve to move towards the pressure regulator valve to boost the line pressure.
Torque Converter Clutch Enable Valve
To retain the TCC in a released condition, the TCC shift valve is held by regulated converter feed fluid which passes through the enable valve to the TCC enable circuit.
Torque Converter Clutch Shift Valve
The TCC shift valve, being held in the release position by spring force and TCC enable fluid, permits regulated converter feed fluid to pass through the valve and enter the TCC release circuit. To apply the TCC, enable fluid exhausts and the valve is shifted by signal fluid pressure
Converter Limiting Valve
This valve permits converter feed pressure from the pressure regulator valve to enter the regulated converter feed circuit. Excess converter feed pressure causes the limit valve to move against its spring pressure, and so the converter feed fluid is opened to exhaust.
VALVES IN THE VALVE BODY
The valve body contains: the accumulator valve, the actuator limit valve, the TCC apply valve, the manual valve, the 3 - 4 shift valve, the 2 - 3 shift valve, and the 1 - 2 shift valve.
Torque Signal Compensatory Valve
This valve is located in the accumulator housing, and torque signal fluid pressure is fed to it in each gear range. The spring in the valve dampens any pressure irregularities in the torque signal fluid pressure that are caused by the operation of the force motor.
Checkball Valves
There are 11 checkball valves, located in the valve block and transmission case, see Figs. 1 and 2. The function of each is described below.
(1) Overrun Clutch
Seats to direct D321 fluid through an orifice and into the overrun clutch, thereby helping to control the apply rate of the overrun clutch. When the overrun clutch releases, the exhausting fluid unseats and flows past the checkball and into the D321 circuit. This allows a faster exhaust of fluid and a quicker release of the overrun clutch.
(2) Second Accumulator
Seats to direct accumulator fluid through an orifice before entering the second gear accumulator circuit, helping to control the rate at which the second gear clutch fluid exhausts from the rear servo and the release rate of the intermediate clutch.
(3) Front Band Apply
Seats to direct Front Band Apply fluid through an orifice to help control the apply rate of the front band. When the band releases, the exhausting fluid unseats and flows past the checkball, thus allowing a faster release of the front band.
(4) Second Gear Clutch
Seats to direct 2-3 fluid through an orifice and into the second gear clutch (intermediate clutch circuit; this helps to control the apply rate of the intermediate clutch. When the clutch releases, the exhausting fluid unseats and flows past the checkball and into the 2-3 circuit, allowing a faster exhaust of fluid and a quicker release of the intermediate clutch.
(5) Third Accumulator
Seats to direct accumulator fluid through an orifice before entering the third accumulator circuit. This helps to control the rate at which the third clutch fluid exhausts from the accumulator and the release rate of the direct clutch.
(6) Fourth Accumulator
Seats to direct accumulator fluid through an orifice before entering the fourth accumulator circuit; this helps to control the rate at which the fourth clutch fluid exhausts from the accumulator and the release rate of the fourth clutch.
(7) Low / Reverse (Shuttle Valve)
Allows Low fluid to enter the Rear Band Apply circuit, when manual first has been selected (not selectable currently), or Reverse fluid, to enter the rear band apply circuit.
(8) Third Gear Clutch
Seats to direct accumulator fluid through an orifice and into the third clutch circuit; this helps to control the apply rate of the direct clutch in third gear. When the clutch releases, the exhausting fluid unseats and flows past the checkball and into the third clutch circuit, allowing a faster exhaust of fluid and a quicker release of the direct clutch.
(9) Reverse
Seats to direct reverse fluid through an orifice; this helps to control the apply rate of the direct clutch in reverse gear. When the clutch releases, the exhausting fluid unseats and flows past the checkball, allowing a faster exhaust of fluid and a quicker release of the fourth clutch.
(10) Fourth Clutch
Seats to direct reverse fluid through an orifice; this helps to control the rate at which the fourth clutch is applied. When the fourth clutch releases, the exhausting fourth clutch fluid unseats and flows past the checkball, allowing a faster exhaust of fluid and a quicker release of the fourth clutch.
(11) Third Clutch / Reverse (Shuttle Valve)
Allows either, third clutch fluid (when third gear has been selected), or Reverse fluid, to enter the third / reverse circuit.
Active Components For Each Gear Ratio
Active Components For Each Gear:
Note: This table is in two parts for convenience only: the upper table for Park, Neutral, Reverse and Drive for all automatic forward gears, and the lower table for Manual 3 and Manual 2 gear ranges.