Lexus RX300 (MCU15). Service manual — part 45

EG

ENGINE — 1MZ-FE ENGINE

EX

IN

EX

EX

IN

IN

TDC

BDC

Latest timing

To advance
side

EX

IN

Latest timing

187EG39

178EG21

To retard
side

187EG39

178EG22

53

Operation State

Range

Valve Timing

Objective

Effect

In Low to
Medium Speed
Range with
Heavy Load

4

Advancing the intake valve
close timing for volumetric ef-
ficiency improvement

Improved
torque in
low to me-
dium speed
range

In High Speed
Range with
Heavy Load

5

Retarding the intake valve
close timing for volumetric ef-
ficiency improvement

Improved
output

At Low
Temperatures

—

Eliminating overlap to prevent
blow back to the intake side for
reduction of fuel increase at
low temperatures, and stabiliz-
ing the idling rpm for decreas-
ing fast idle rotation

Stabilized
fast idle rpm
Better fuel
economy

Upon Starting/
Stopping the
Engine

—

Eliminating overlap to elimi-
nate blow back to the intake
side

Improved
startability

ENGINE — 1MZ-FE ENGINE

Intake Air Chamber

Throttle
Valves

Intake Air
Control Valve

Intake Air
Control Valve

157EG16

54

7. ACIS (Acoustic Control Induction System)

General

The ACIS improves the torque in the whole range, especially that in the low-speed range, by changing
the intake manifold length in three stages.
To suit the intake pulsations, this system controls the effective intake manifold length in three stages by
opening and closing the 2 intake air control valves that are provided in the intake air chamber and down-
stream of the throttle valves in accordance with the engine speed and the throttle opening angle.

" System Diagram A

Actuator

Throttle Valves

Intake Air
Control Valve

Actuator

VSV

Intake Air
Control Valve

VSV

To Throttle Body

Vacuum Tank

Engine Speed

Throttle Opening Angle

Engine
ECU

157EG15

Intake Air Control Valve

The intake air control valves, which are provided
in the intake air chamber and the lower reaches of
the throttle valves, open and close to change the
effective length of the intake manifold in three
stages.

EG

ENGINE — 1MZ-FE ENGINE

55

Operation

1) Heavy Load in the Low-Speed Range

To suit the longest cycle of the intake pulsations, the Engine ECU turns ON 2 VSVs so that the vacuum
acts on 2 actuators.
As a result, the 2 intake air control valves close, enabling the intake air chamber, throttle body, and
air cleaner hose to function as an intake manifold.

Throttle

V

alve

Engine Speed

Close

Close

: Effective Intake Manifold Length

170EG09

Close

Open

$

161ES49

!

High

2 VSVs ON

2) Heavy Load in the Mid-Speed Range

To suit the relatively long cycle of the intake pulsations, the Engine ECU turns ON the VSV of the
intake air chamber side and turns OFF the VSV of the throttle valve side, so that the vacuum acts on
the actuator of the intake air chamber side and the atmospheric air is drawn into the actuator of the throttle
valve side.
As a result, the intake air control valve in the intake air chamber closes, the intake air control valve
downstream of the throttle valve opens, enabling the intake air chamber to function as an intake manifold.

Throttle

V

alve

Engine Speed

Close

Open

: Effective Intake Manifold Length

170EG10

Close

Open

$

161ES50

!

High

VSV ON
(Intake Air Chamber Side)

: Effective Intake Air Chamber

ENGINE — 1MZ-FE ENGINE

56

3) During Idling, Light Load, and High-Speed Range

To suit the short cycle of intake pulsations, the engine ECU turns OFF the 2 VSVs, so that the atmospheric
air is drawn into the 2 actuators.
As a result, the 2 intake air control valves open, enabling the intake air chamber to function as a normal
intake air chamber.

Throttle

V

alve

Engine Speed

Open

Open

: Effective Intake Manifold Length

170EG11

Close

Open

$

161ES51

!

High

2 VSVs OFF

: Effective Intake Air Chamber

8. Fuel Pump Control

A fuel cut control is adopted to stop the fuel pump when the SRS airbag is deployed.
In this system, the airbag deployment signal from the airbag sensor assembly is detected by the engine
ECU, which turns OFF the circuit opening relay.
After the fuel cut control has been activated, turning the ignition switch from OFF to ON cancels the fuel
cut control, thus engine can be restarted.

179EG17

Front Airbag
Sensor
(RH and LH)

Airbag
Sensor
Assembly

Engine ECU

Circuit
Opening
Relay

Fuel Pump
Motor