Description - 1
Electronic Automatic Transmission (EAT)
DESCRIPTION
General
The Jatco 5-speed automatic transmission fitted to Freelander is controlled by an Automatic Transmission Control Unit (ATCU). The ATCU is located inside the engine E-box, and receives information from the following sources to calculate when to operate the solenoid valves contained within the gearbox to enable quick, smooth, quiet gear changes;
- The Engine Control Module (ECM) via the CAN-BUS,
- The instrument pack via the CAN-BUS,
- The cruise control ECU,
- The automatic transmission selector,
- The brake pedal switch,
- The automatic gearbox sensors.
Steptronic JATCO Automatic Gearbox
The JATCO five speed automatic gearbox is similar to conventional electronically controlled transmissions but provides the driver with an additional manual mode feature. Manual mode allows the driver to electronically select the five forward gear ratios and operate the gearbox as a semi-automatic manual gearbox.
Gearbox Casing
Refer to JATCO Automatic Gearbox illustration.
The gearbox casing contains the input shaft transmitting the power into the drive train. The drive train is made up of the planetary gear sets and clutches.
The clutches and brake bands control which elements of the planetary gear sets are engaged and their direction of rotation, to produce the P and N selections, five forward ratios and one reverse gear ratio. Power output is from the drivetrain through a reduction gear into a differential.
Gear Ratios
Valve Block and Solenoid Valves
Refer to JATCO Automatic Gearbox - Valve Block and Solenoids illustration.
The gearbox uses nine solenoid valves located on the valve block. The solenoid valves are energized/de-energized by the EAT ECU to control the gearbox fluid flow around the gearbox to supply clutches, brakes and brake band (gear change scheduling), fluid to the torque converter, lubrication and cooling.
Each solenoid valve is controlled separately by the EAT ECU. All nine solenoid valves can be classified into two types by their operating mode. Three of them are duty solenoid valves and the remaining six are on-off solenoid valves.
Each solenoid valve consists of an internal coil and needle valve. A voltage is passed through the coil of the solenoid to actuate the needle valve. The needle valve opens and closes the fluid pressure circuits. On-off solenoid valves close the fluid pressure circuits in response to current flow.
Duty solenoid valves repeatedly turn on and off in 50 Hz cycles. This opens and closes the fluid circuits allowing a higher level of control on the circuits. For example, smooth operation of the lock-up clutch in the torque converter to eliminate harsh engagement/ disengagement.
All of the solenoid valves are supplied with battery voltage and an earth path by the EAT ECU.
On/Off Solenoid Valves
The on/off solenoid valves are:
^ Shift solenoid valve A
^ Shift solenoid valve B
^ Shift solenoid valve C
^ Low clutch timing solenoid valve
^ Reduction timing solenoid valve
^ 2-4 brake timing solenoid valve.
The EAT ECU switches the on/off solenoid valves to open and close in response to vehicle speed and throttle opening.
Shift solenoid valves A, B and C are used to engage the different gear ratios within the gearbox. The position of these solenoid valves at any one time determines the gear selected.
Shift Solenoid Valve Activation
The reduction timing solenoid valve, low clutch timing solenoid valve and 2-4 timing solenoid valve are used by the EAT ECU to control the timing of the gear shift changes.
These solenoid valves carry out three main functions:
^ Shift timing control: For some shifts these three solenoid valves are used to assist line pressure control or 2-4 brake pressure control.
^ Line pressure cut back: When the gearbox takes up the drive there should be a high line pressure present. The EAT ECU controls the low clutch timing solenoid valve which is related to the vehicle speed in order to switch the fluid circuit of the line pressure to on or off therefore controlling cut back.
^ Reverse inhibition: If the vehicle exceeds 6 mph (10 km/h) and Reverse (R) is selected, the EAT ECU switches the low clutch timing solenoid valve on. This drains the gearbox fluid from the reverse clutch, therefore the clutch will be unable to engage.
Duty Solenoid Valves
The duty solenoid valves are:
^ Lock-up duty solenoid valve
^ Line pressure duty solenoid valve
^ 2-4 duty brake solenoid valve.
The lock-up duty solenoid valve is used by the EAT ECU to control the lock-up of the torque converter depending upon the vehicle speed and throttle position.
The EAT ECU will actuate the lock-up solenoid valve, which operates the lock-up control valve to direct fluid to either lock or unlock the torque converter.
The line pressure duty solenoid valve and 2-4 duty brake solenoid valve are used by the EAT ECU to control fluid line pressure in the gearbox.
The EAT ECU calculates the line pressure by using the engine speed, vehicle speed and throttle angle. The EAT ECU then actuates the solenoid valves accordingly to achieve the required line pressure.
The solenoid valves can fail in the following ways:
^ Open circuit
^ Short circuit to 12 or 5 volts
^ Short circuit to earth.
In the event of a solenoid valve failure any of the following symptoms may be observed:
^ Gearbox selects fourth gear only (shift solenoid valve failure)
^ Gearbox will not upshift to fourth gear (timing solenoid valve failure)
^ Increased fuel consumption and emissions (lock-up solenoid valve failure)
^ Gear shifts will have no torque reduction therefore gear changes will be very harsh (line pressure duty solenoid valve failure)
^ No pressure control will occur therefore gear changes from fifth gear will be very harsh (2-4 brake duty solenoid valve failure).
The EAT ECU operates the lock-up solenoid, which in turn supplies pilot pressure to the control valve. The control valve moves under the influence of the pilot pressure, blocking the release pressure feed to the lock-up clutch and redirecting it to the other side of the clutch mechanism.
With the release pressure removed, the lock-up clutch moves and engages with the torque converter, moving the lockup mechanism into the locked condition.
Smooth Lock-Up
Smooth lock-up occurs as the mechanism moves from the unlock to the locked condition. Torque converter release pressure is lowered gradually preventing a sudden lock-up clutch engagement, reducing lock-up shock.
The lock-up solenoid is a driven duty solenoid operating at 50Hz. The lock-up control valve has a pressure regulation device which reacts to torque converter release pressure and solenoid pilot pressure.
As the solenoid is operated, the pilot pressure is gradually applied to the control valve. This moves the valve, partially exposing the release pressure to a drain port.
The control valve is moved against an opposing spring by the increasing pilot pressure. The release pressure is decayed proportionally in response to the increasing pilot pressure allowing the clutch to smoothly engage with the torque converter.
Fluid Cooling
Fluid cooling is performed by a dedicated fluid cooler for the gearbox. On KV6 and Td4 cold climate models, a water cooled fluid cooler is located at the front of the gearbox. On Td4 hot climate models an air blast cooler, which replaces the water cooled cooler is located in the front LH wheel arch.
Fluid Cooler KV6
The fluid cooler is located on a bracket at the front of the gearbox. The cooler comprises cores which allow fluid to flow across from one side of the cooler to the other. Each core is surrounded by water jacket which allows engine coolant to flow around the cooler.
The cooler is connected to the gearbox by metal pipes and flexible hoses, and to the engine cooling system by coolant hoses.
The gearbox fluid flows from the gearbox to the upper connection on the fluid cooler. The fluid then flows through the cores in the cooler which are surrounded by engine coolant which cools the gearbox fluid. The fluid exits the fluid cooler via the lower connection and is returned to the gearbox.
The engine coolant flows from the engine oil cooler (on all except NAS and Gulf States models), or the cylinder block (on NAS and Gulf States models), to the lower coolant connection on the fluid cooler. The coolant exits the cooler via the upper connection and flows to the thermostat housing.
Sensors
The EAT ECU sets correct gear change scheduling using three speed signal inputs: intermediate speed, turbine speed and vehicle speed in conjunction with a throttle position signal from the ECM.
Intermediate Speed Sensor
The intermediate speed sensor is located within the gearbox. The EAT ECU uses this sensor to ensure correct gear engagement and to monitor the amount of slip within the gearbox.
The EAT ECU calculates the slip within the gearbox by comparing the difference between the inputs from the intermediate speed sensor and the turbine speed sensor.
The intermediate speed sensor detects the output gear rotation speed and sends an electrical output to pin 51 of the EAT ECU which also supplies an earth path for the sensor on ECU pin 20.
The sensor is an inductive sensor that produces a sinusoidal output at a frequency of 54 pulses per revolution of the output gear.
The intermediate speed sensor can fail in the following ways:
^ Sensor open circuit
^ Short circuit to 5 or 12 volts
^ Short circuit to earth.
The EAT ECU will detect sensor failure if the vehicle speed exceeds 25 mph (40 km/h) and the sensor output is equivalent to less than 600 rev/min for two seconds.
In the event of an intermediate speed sensor signal failure any of the following symptoms may be observed:
^ Upshift to 5th gear inoperative
^ Torque reduction request from the EAT ECU to the ECM inoperative.
A failure of the sensor will generate a 'P' code which can be retrieved using TestBook/T4 or any Keyword 2000 diagnostic tool.
Turbine Speed Sensor
The turbine speed sensor is located within the gearbox and is used by the EAT ECU to monitor the input shaft speed. The EAT ECU uses this sensor to ensure the correct gear ratio is selected and to ensure that there is not excessive slip within the gearbox drive train.
The turbine speed sensor detects the input shaft speed (turbine speed) and sends an electrical output to pin 24 of the EAT ECU which also supplies an earth path for the sensor on ECU pin 20.
The sensor is an inductive sensor that produces a sinusoidal output at a frequency of 36 pulses per revolution of the input shaft.
The turbine speed sensor can fail in the following ways:
^ Sensor open circuit
^ Short circuit to 12 or 5 volts
^ Short circuit to earth.
The EAT ECU will detect sensor failure if the vehicle speed exceeds 25 mph (40 km/h) and the engine speed is above 1300 rev/min, but the turbine speed is below 600 rev/min for two seconds.
In the event of a turbine speed sensor signal failure any of the following symptoms may be observed:
^ Upshift to 5th gear inoperative
^ Torque reduction request from the EAT ECU to the ECM inoperative.
A failure of the sensor will generate a 'P' code which can be retrieved using TestBook/T4 or any Keyword 2000 diagnostic tool.
Vehicle Speed Sensor
The vehicle speed sensor is located within the gearbox. The EAT ECU uses this sensor to monitor the rotational speed of the parking gear and calculate this reading into a vehicle speed. The EAT ECU also monitors the vehicle speed using a signal from the ABS ECU.
The vehicle speed sensor detects the parking gear rotation speed and sends an electrical output to pin 5 of the EAT ECU which also provides an earth path for the sensor.
The sensor is an inductive sensor that produces a sinusoidal output at a frequency of 18 pulses per revolution of the parking gear.
The EAT ECU uses the signal to calculate the following:
^ Amount of engine torque reduction required during gear changes
^ Notify the EAT ECU when the vehicle is stationary, for creep control.
The vehicle speed sensor can fail the following ways:
^ Sensor open circuit
^ Sensor short circuit to 12 or 5 volts
^ Sensor short circuit to earth.
The EAT ECU will detect sensor failure if the ABS ECU speed signal is more than 25 mph (40 km/h) but the vehicle speed sensor reading is less than 3 mph (5 km/h) for more than two seconds.
In the event of a vehicle speed sensor signal failure any of the following symptoms may be observed:
^ Upshift to 5th gear inoperative
^ Torque reduction request from the EAT ECU to the ECM inoperative.
If a failure of the vehicle speed sensor occurs and the ABS ECU speed signal is functional, the EAT ECU will control gear shifting using the ABS ECU signal.
If both the vehicle speed sensor and the ABS ECU speed signals fail, the EAT ECU will lock the gearbox in fourth gear (fail-safe mode) and inhibit torque converter lock-up control.