Overhead camshafts (2)

Description 1036C

1.8 16v

Type

In ductile cast iron, each one turns on six mounts and is controlled directly by a toothed belt.

The camshaft oil seals take the form of oil sealing rings at the front.

2.4 20v

Type

The camshafts are made of spheroid cast iron, operated directly by a toothed belt.

The inlet side camshaft rotates on eight bearings and the exhaust side on on seven.

The camshaft oil seals take the form of oil sealing rings at the front.

1.9 JTD 16v

CAMSHAFTS

Cast iron, tempered and hardened on the cams.

1.8 16v

System specifications

An electronic, hydraulically-operated variable valve timing system has been adopted for the intake side camshaft.

The device allows the timing diagram (inlet stage) to be varied in accordance with the engine's load requirements; this parameter is processed by the control unit in accordance with the signals received from the air flow meter and rpm sensor, and sent as a command to the timing variator electromagnet.

2.4 20v

System specifications

An electronic, hydraulically-operated variable valve timing system has been adopted for the intake side camshaft.

Controlled directly by the fuel injection control unit, the purpose of the timing variator is to vary the timing of the inlet valves in accordance with the engine load and required rpm.

The control unit recognizes malfunctions in the phase transformer of the electrical circuit and prevents operation.

1.9 JTD 16v

CAMSHAFTS

The exhaust camshaft is driven directly by the toothed belt and transmits power to the inlet camshaft through a a pair of straight toothed gears.

The exhaust camshaft also drives the vacuum unit that is fitted on the gears side.

1.8 16v

Structure

The device consists of a main assembly fitted to the intake side camshaft, which alters the camshaft angle in relation to the drive pulley.

The system includes an actuation valve controlled by an electomagnet. Both are located on the intake manifold and connected hydraulically to the main assembly via ducts.

2.4 20v

Operation in closed stage (fc)

When the closed stage is required (idle speed and maximum power zone), the solenoid (1) is de-energized, so the slide valve (2), pushed by the return spring (3), remains raised, preventing the oil coming from the duct (A) from reaching the VVT.

In this case the timing of the inlet valves remains unchanged (closed).

1.9 JTD 16v

TAPPETS

There is a hydraulic tappet for each valve activated by a rocker arm, in turn, moved by the camshaft.

The rocker arms are designed to prevent serious damage to the other engine components if the timing belt breaks or comes off; in effect, on account of their special design the absorb the stresses caused through the contact between the valves and the pistons.

1.8 16v

Operation in closed stage

When the closed stage is required (idle speed and maximum power zone), the solenoid (1) is de-energized, so the slide valve (2), pushed by the return spring (3), remains raised, preventing the oil coming from the duct (A) from reaching the VVT.

In this case the timing of the inlet valves remains unchanged (closed).

2.4 20v

Operation in open stage (OS)

When operation in open stage is required (average speeds at high torque). The electromagnet (1) is energized, pushing the valve chest (2) downwards.

In this position, the oil coming from the duct (A) enters the chamber (B) of the piston, and from here, through a special hole, goes into the duct (C) in the piston.

The oil can only emerge from this duct through the top hole (in communication with the delivery pipe (D) to the variator). Since the valve chest (2) is lowered, the lower opening is not in contact with the exhaust duct (E).

The oil passes through the duct (D) and (F) and reaches the chamber (G), pushing in an axial direction towards the engine the piston (4), which comprises outer helical teeth, forcing it to rotate clockwise.

Its rotation is transmitted via a straight-teeth splined profile to the pinion (5) which, screwed onto the threaded end of the camshaft (6), transmits rotation to the camshaft, thus varying by 18° engine the timing of the inlet valves.

When the solenoid is de-energized, the valve chest (2) returns to its initial position, cutting off the flow of pressurized oil to the piston (4), but allowing oil to return to the discharge, thanks to the force of the return spring (7).

The duct (D) lubricates the camshaft journal in the various operating conditions.

The oil which leaks into the chamber (H) of the solenoid is discharged through the drain duct (E).

1.8 16v

Operation in open stage (OS)

When the open stage is required (medium rpm with high torque). The solenoid (1) is energized, thus pushing the slide valve (2) downwards.

In this position, the oil coming from the duct (A) enters the chamber (B) of the piston, and from here, through a special hole, goes into the duct (C) in the piston.

The oil can only emerge from this duct through the top hole (in communication with the delivery pipe (D) to the radiator), since the bottom hole, as the slide valve (2) has lowered, is not in communication with the discharge pipe (E).

The oil passes through the ducts (D) and (F) and reaches the chamber (G), pushing in an axial direction towards the engine the piston (4), which comprises outer helical teeth, forcing it to rotate clockwise.

Its rotation is transmitted via a straight-teeth splined profile to the pinion (5) which, screwed onto the threaded end of the camshaft (6), transmits rotation to the camshaft, thus varying by 25° engine the timing of the inlet valves.

When the solenoid is de-energized, the slide valve (2) returns to its initial position, cutting off the flow of pressurized oil to the piston (4), but allowing oil to return to the discharge, thanks to the force of the return spring (7).

The duct (D) lubricates the camshaft journal in the various operating conditions.

The oil which leaks into the chamber (H) of the solenoid is discharged through the drain duct (E).

2.4 20v

Type

The hydraulic tappets automatically cancel the valve clearance during engine operation, with the advantage of reducing:

• maintenance interventions
• engine noise.

1.8 16v

Type

The hydraulic tappets automatically cancel the valve clearance during engine operation, with the advantage of reducing:

• maintenance interventions
• engine noise.

2.4 20v

Operation in open stage

When the camshaft cam acts on the tappet (1) and consequently the piston (2), the oil trapped in the chamber (6), because the ball valve (4) closes, transmits the movement of the piston (2) directly to the sleeve (3) and so to the valve.

During this stage, because of the high pressure to which it is subjected, some of the oil in the chamber (6) leaks through the tiny gap between the piston (2) and sleeve (3).

1.8 16v

Operation in open stage

When the camshaft cam acts on the tappet (1) and consequently the piston (2), the oil trapped in the chamber (6), because the ball valve (4) closes, transmits the movement of the piston (2) directly to the sleeve (3) and so to the valve.

During this stage, because of the high pressure to which it is subjected, some of the oil in the chamber (6) leaks through the tiny gap between the piston (2) and sleeve (3).

2.4 20v

Operation in closed stage

In order for the tappet, thrust by the action of the spring (5), to follow the cam profile, a vacuum is created inside the chamber (6) which causes the opening of the ball valve (4) allowing the intake of oil.

The oil entering the chamber (6) replaces the oil which leaked out previously while the valve was open.

1.8 16v

Operation in closed stage

In order for the tappet, thrust by the action of the spring (5), to follow the cam profile, a vacuum is created inside the chamber (6) which causes the opening of the ball valve (4) allowing the intake of oil. The oil entering the chamber (6) replaces the oil which leaked out previously while the valve was open.