Mazda X-5. Manual — part 16

MECHANICAL

01–10–15

01–10

Variable Valve Timing Mechanism
Function

• The variable valve timing mechanism continuously modifies the phases of the variable valve timing actuator

and the intake camshaft using hydraulic pressure controlled by the oil control valve (OCV) so that optimal valve
timing is obtained according to engine operation conditions.

• The oil control valve (OCV) operation is based on signals from the PCM according to engine operation

conditions and it controls hydraulic pressure to the variable valve timing actuator.

Operation and purpose according to driving condition
Idling range, light load range

• Due to a reduction in the amount of overlap, less combusted gas is returned to the intake port. This stabilizes

idle speed in the idling range, improving fuel economy, and also ensures engine stability in the light load range.

Medium load range

• Overlap amount has been increased and the EGR ratio inside the cylinder is higher. This reduces engine

friction loss (pumping loss), lowering the combustion temperature and reducing the amount of NOx the in
exhaust gas. The amount of hydrocarbon emission has also been reduced through reignition of non-combusted
gas.

Heavy load, low-middle speed range

• The intake valve is closed early, and high volumetric efficiency is obtained to improve low-middle speed torque.

Heavy load, high speed range

• Timing for intake valve closure is delayed and high volumetric efficiency is obtained to improve maximum

output.

When temperature is low

• The overlap amount has been minimized to prevent combusted gas from returning to the intake port and to

reduce the additional fuel injection amount. This improves fuel economy and stabilizes fast idle speed.

When engine is started or stopped

• Startability has been improved because the overlap amount has been minimized to prevent combusted gas

from returning to the intake port.

LOAD

ENGINE SPEED

IDLING RANGE

LIGHT LOAD RANGE

MEDIUM LOAD RANGE

HEAVY LOAD, LOW-MIDDLE
SPEED RANGE

HEAVY LOAD, HIGH SPEED RANGE

FULL LOAD PERFORMANCE

E5U110ZT5022

MECHANICAL

01–10–16

Construction

• The variable valve timing mechanism consists of a variable valve timing actuator, oil control valve (OCV), CKP

sensor, CMP sensor, and the PCM.

OIL CONTROL VALVE (OCV)

CKP SENSOR

CMP SENSOR

PCM

VARIABLE VALVE
TIMING ACTUATOR

ELECTRIC SIGNAL

HYDRAULIC PRESSURE

E5U110ZT5030

MECHANICAL

01–10–17

01–10

Hydraulic Pressure Flow Diagram

End Of Sie

OIL PAN

OIL PUMP

OIL
CONTROL
VALVE
(OCV)

OIL CONTROL
VALVE (OCV)
ADAPTER

CAMSHAFT

VARIABLE VALVE
TIMING
ACTUATOR

CYLINDER BLOCK

E5U110ZT5031

MECHANICAL

01–10–18

VARIABLE VALVE TIMING MECHANISM CONSTRUCTION/OPERATION [LF]

E5U011012111N05

Component and Function

Operation outline

• The variable valve timing actuator has two hydraulic chambers: a valve timing advance chamber and a valve

timing retard chamber. They are located between the integrated housing of the camshaft sprocket and the
camshaft integrated rotor. The oil pump supplies engine oil. to each chamber. Hydraulic pressure applied to
each chamber is controlled by the oil control valve (OCV) and the relative phases of the camshaft sprocket and
the camshaft are modified to obtain optimum valve timing according to engine operation conditions.

At engine start

• When the stopper pin in the variable valve timing actuator engages with the rotor, which is at the position of

maximum valve timing retard due to spring force, the camshaft sprocket and the camshaft rotate as one unit.
When the oil pump pressure rises and the stopper pin is disengaged, it becomes possible to modify the relative
angles of the camshaft sprocket and the camshaft.

Advancing valve timing

• When the spool valve in the oil control valve (OCV) moves to the left according to the PCM signal, hydraulic

pressure, from the oil pump, feeds into the valve timing advance passage and finally to the valve timing
advance chamber in the variable valve timing actuator. Then, the rotor integrated with the camshaft rotates in
the valve timing advance direction, against the housing driven by the crankshaft, and the valve timing is
advanced.

Variable valve timing actuator

• Continuously modifies the phases of the intake camshaft and crankshaft at the forward

end of the intake camshaft using hydraulic pressure from the oil control valve (OCV).

Oil control valve (OCV)

• Operated by current (duty signal) from the PCM. Switches the hydraulic oil passages

to the variable valve timing actuator.

CKP sensor

• Inputs engine revolution signal to the PCM.

CMP sensor

• Inputs cylinder identification signal to the PCM.

PCM

• Controls the oil control valve (OCV) so that optimum valve timing is obtained according

to engine operation conditions.

PCM

OIL CONTROL VALVE (OCV)

SPOOL VALVE

OIL PUMP

CAMSHAFT

VARIABLE VALVE TIMING ACTUATOR

ROTOR

HOUSING

OIL PAN

TO VALVE TIMING
ADVANCE CHAMBER

VALVE TIMING
ADVANCE
CHAMBER

FROM VALVE TIMING
RETARD CHAMBER

HYDRAULIC PRESSURE FLOW

E5U110ZT5032