Lexus ES300 (2002 year). Service manual - part 129

ENGINE – 1MZ-FE ENGINE

EG-21

211EG32

TWC

Main Muffler

6. Exhaust Pipe

General

 An ultra thin-wall, high-cell ceramic type TWC has been adopted. This TWC enables to improve exhaust

emissions by optimizing the cells density.

 2-way exhaust control system is provided to reduce noise and back pressure in the main muffler.

ENGINE – 1MZ-FE ENGINE

EG-22

208EG16

Control Valve Close

Exhaust
Gas

Control Valve Open

Low Engine Speed

Middle to High Engine Speed

2-Way Exhaust Control System

 

 A 2-way exhaust control system is used. This system reduces the back pressure by opening a variable

valve that is enclosed in the main muffler.

 The valve opens steplessly in accordance with the operating condition of the engine, thus enabling a

quieter operation at lower engine speeds, and reducing back pressure at higher engine speeds.

1) Construction

The control valve is enclosed in the main-muffler. When the exhaust gas pressure overcomes the spring
pressure, the control valve opens steplessly in accordance with the exhaust gas pressure.

2) Operation

a. When Control Valve is Closed (low engine speed)

Since the pressure in the main muffler is low, the control valve is closed. Hence exhaust gas does not
pass the bypass passage, and exhaust noise decreased by the main muffler.

b. When Control Valve is Open (middle to high engine speed)

The valve opens more as the engine speed and the back pressure in the muffler increase. This allows
a large volume of exhaust gas to pass the bypass passage, thereby substantially decreasing the back pres-
sure.

ENGINE – 1MZ-FE ENGINE

EG-41

211EG17

157EG23

Throttle Position Sensor

Camshaft Timing Oil Control Valve

VVT Sensor

Camshaft Timing Oil Control Valve

VVT Sensor

Engine Coolant Temp.
Sensor

ECM

Mass Air 
Flow Meter

Crankshaft Position Sensor

Crankshaft Position Sensor

Mass Air Flow Meter

Throttle Position Sensor

Engine Coolant Temp. Sensor

VVT Sensor

ECM

Target Valve Timing

Feedback

Correction

Actual Valve Timing

Camshaft Timing
Oil Control Valve

Duty Control

9. VVT-i (Variable Valve Timing-intelligent) System

General

The VVT-i system is designed to control the intake camshaft within a wide range of 60

 (of crankshaft

angle) to provide a valve timing that is optimally suited to the engine condition, thus realizing improved
torque in all the speed ranges and fuel economy, and reduction of exhaust emissions. The actual intake valve
timing is feedback by means of the camshaft position sensor for constant control to the target valve timing.

ENGINE – 1MZ-FE ENGINE

EG-42

211EG18

Engine Speed 
Throttle Opening Angle

ECM

VSV

Actuator

Intake Air Control Valves

Actuator

VSV

To Surge Tank

Vacuum Tank

10. ACIS (Acoustic Control Induction System)

General

The ACIS is realized by using a bulkhead to divide the intake manifold into 3 stages, with an intake air con-
trol valves in the bulkhead being opened and closed to vary the effective length and intake area of the intake
manifold in accordance with the engine speed and throttle valve opening angle. This increases the power
output in all ranges from low to high speed.

 System Diagram