LR3/Disco 3
The shift control solenoid is an open/closed, on/off solenoid which is controlled by the TCM switching the solenoid to
earth. The TCM also supplies power to the solenoid. The TCM energises 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 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 to calculate the slip of the torque converter clutch and internal clutch slip. This
signal allows the TCM 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 and compared to engine speed signals received on the CAN bus from
the ECM. Using a comparison of the two signals the TCM 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 uses the temperature sensor signals to
determine the temperature of the transmission fluid. These signals are used by the TCM 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 will use a default value and a fault
code will be stored in the TCM.
Damper
There is one 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 twenty one 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 (unpressurised) 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, one 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
