Lexus RX300 (MCU15). Manual — part 49
CH
BO
CHASSIS — U140F AUTOMATIC TRANSAXLE
161ES15
Signals
from
Individual
Sensors
Engine &
ECT ECU
SL1
SL2
B
1
Accumulator
Solenoid Valve SL1 OFF
B
1
Brake ON
B
1
B
1
Control Valve
C
2
Accumulator
Solenoid Valve SL2 OFF
C
2
Clutch ON
C
2
C
2
Control Valve
#
#
169CH16
Input Shaft rpm
Time
Practical rpm Change Ratio
Target rpm
Change Ratio
Input Turbine
Speed Sensor
Engine
Engine &
ECT ECU
Clutch/Brake Pressure
Output Shaft T
orque
Time
Solenoid Drive Signal
SL2
Signals from Various Sensor
Engine rpm
Engine Torque Information
Fluid Temperature
SL1
69
2. Clutch Pressure Control
Clutch to Clutch Pressure Control
A direct clutch pressure control has been adopted for shifting from the 1st to 2nd gear, and from the 2nd
to 3rd gear. Actuates solenoid valves SL1 and SL2 in accordance with the signals from the engine &
ECT ECU, and guides this output pressure directly to control valves B
1
and C
2
in order to regulate the
line pressure that acts on the B
1
brake and C
2
clutch . As a result, compact B
1
and C
2
accumulators without
a back pressure chamber have been realized.
Clutch Pressure Optimal Control
Solenoid valves SL1 and SL2 are used for optimal control of clutch pressure. The engine & ECT ECU
monitors the signals from various types of sensors such as the input turbine speed sensor, allowing shift
solenoid valves SL1 and SL2 to minutely control the clutch pressure in accordance with engine output
and driving conditions. As a result, smooth shift characteristics have been realized.
CHASSIS — U140F AUTOMATIC TRANSAXLE
157CH19
Line Pressure
Except 4th
B
3
Brake ON
B
3
B
3
Orifice
Control Valve
B
3
Apply Fluid Pressure
B
3
Accumulator
#
70
3. Apply Orifice Control
The B
3
orifice control valve has been provided for the B
3
brake, which is applied when shifting from 4th
to 3rd. The B
3
orifice control valve is controlled by the amount of the line pressure in accordance with
shifting conditions, and the flow volume of the fluid that is supplied to the B
3
brake is controlled by varying
the size of the control valve’s apply orifice.
CH
BO
CHASSIS — U140F AUTOMATIC TRANSAXLE
169CH47
157CH17
Piston Fluid
Pressure Chamber
Piston
C
2
Clutch
Canceling Fluid
Pressure Chamber
C
2
Clutch
Clutch Fluid
Pressure
Centrifugal Fluid Pressure
C
3
Clutch
Shaft Side
Centrifugal Fluid Pressure
Applied to the Piston Fluid
Pressure Chamber
Fluid pressure
applied to piston
–
Centrifugal fluid pressure
applied to canceling fluid
pressure chamber
=
Target fluid pressure
(original clutch pressure)
Canceling Fluid
Pressure Chamber
(Lubrication Fluid)
Centrifugal Fluid
Pressure Applied
to Canceling Fluid
Pressure Chamber
Fluid Pressure
to Piston
Clutch
Target Fluid Pressure
Piston Fluid
Pressure
Chamber
71
4. Centrifugal Fluid Pressure Canceling Mechanism
A centrifugal fluid pressure canceling mechanism has been adopted in the C1, C2 and C3 clutches that
are applied when shifting from 2nd to 3rd and from 3rd to 4th. In the conventional clutch mechanism,
to prevent the generation of pressure by the centrifugal force that is applied to the fluid in the piston fluid
pressure chamber when the clutch is released, a check ball is provided to discharge the fluid. Therefore,
before the clutch can be subsequently applied, it took time for the fluid to fill the piston fluid pressure
chamber. During shifting, in addition to the pressure that is controlled by the valve body, the pressure that
acts on the fluid in the piston fluid pressure chamber also exerts influence, which is dependent upon rpm
fluctuations. In order to eliminate this influence, a canceling fluid pressure chamber is provided opposite
to the piston fluid pressure chamber. By utilizing the lubrication fluid such as that of the shaft, the same
amount of centrifugal force is applied, thus canceling the centrifugal force that is applied to the piston
itself. Accordingly, it is not necessary to discharge the fluid through the use of a check ball, and a highly
responsive and smooth shifting characteristic has been achieved.
CHASSIS — U140F AUTOMATIC TRANSAXLE
161ES26
Line Pressure
Primary Regulator
Fluid
Pressure
Current
Throttle Pressure
Pump
Solenoid Valve SLT
Solenoid Drive Signal
Input Turbine Speed Sensor
Fluid Temperature
Shift Position
Trans-
axle
Engine
Throttle Valve Opening
Intake Air Volume
Water Temperature
Engine rpm
Engine & ECT ECU
72
5. Line Pressure Optimal Control
The line pressure is controlled by using a solenoid valve SLT. Through the use of the solenoid valve SLT,
the line pressure is optimally controlled in accordance with the engine torque information, as well as with
the internal operating conditions of the torque converter and the transaxle. Accordingly, the line pressure
can be controlled minutely in accordance with the engine output, traveling condition, and the ATF tempera-
ture, thus realizing smooth shift characteristics and optimizing the workload on the oil pump.
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