Lexus RX300 (MCU15). Service 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.