DESCRIPTION OF COMPONENTS

2.4 20V

CAMSHAFT

Specifications

The camshafts are made from spheroid cast iron, driven directly by the toothed belt.

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

There are oil seals for the camshafts at the front.

PHASE TRANSFORMER

Specifications

System details

An electronically controlled phase transformer with hydraulic implementation for the inlet side camshaft has been adopted.

Operated directly by the injection control unit, the phase transformer is designed to vary the timing of the inlet valves according to the engine speed and load conditions.

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

Operation

Operation in closed stage (fc)

When the closed stage is requested (idle speed and maximum power zone), the electro-magnet (1) is de-energized, therefore the valve body (2), thrust by the opposing spring (3), remains raised, not allowing the oil arriving from the ducts (A) to reach the phase transformer.

In this case, the valve timing remains unaltered (closed).

Operation in open stage (fa)

When the open stage is requested (average speeds at high torque). The electro-magnet (1) is energized, pushing the valve body (2) downwards.

In this position, the oil, coming from the ducts (A), enters the piston chamber (B) and from there the channel (C) via a special port.

From the above channel, the oil can only leave via the upper port (in contact with the oil supply duct (D) to the phase transformer). As the valve body (2) is lowered, the lower port is not in contact with the drainage duct (E).

On reaching the chamber (G) via the ducts (D) and (F), the oil, moving the piston (4) axially, towards the engine which, having helical teeth on the outside, is forced to rotate in a clockwise direction.

The rotation is transmitted, by means of a splined profile with straight teeth, to the pinion (5) which, bolted onto the threaded end of the camshaft (6), transmits the rotation to the shaft, altering the inlet valve timing by 18°.

When the electro-magnet is de-energized, the valve body (2) returns to its original position, interrupting the flow of oil under pressure to the piston (4), but allowing the oil to return to the drain, thanks to the thrust of the opposing spring (7).

The ducts (L) allow the lubrication of the camshaft bearing in all operating conditions.

The oil which reaches the electro-magnet chamber (H) is drained through the drainage duct (E).

TAPPETS

Specifications

Type

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

• maintenance operations
• engine noise.

Operation

Operation in open stage

When the camshaft cam acts on the tappet (1) and consequently on the piston (2), as a result of the closure of the ball valve (4), the oil in the chamber (6) transmits the movement of the piston (2) directly to the hose (3) and, as a result, to the valve.

During this stage, given the high pressure to which it is subjected, some of the oil in the chamber (6) flows through the minimal gap existing between the piston (2) and the hose (3).

Operation in closed stage

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

The oil introduced into the chamber (6) replaces that which escaped during the previous valve opening stage.

2.4 JTD 10V

CAMSHAFT

Specifications

Type

In cast iron, with induction-hardened cams, driven directly by toothed belt.

The camshaft is sealed at the front by an o-ring and at the rear by the vacuum pump gasket.

2.0 TB

CAMSHAFT

Specifications

Type

The camshafts are ductile cast iron, driven directly by a toothed belt.

The intake side camshaft turns on eight mounts while the exhaust side camshaft turns on seven mounts.

The camshaft oil seal function is performed by front o-rings.

PHASE TRANSFORMER

Specifications

System details

A variable valve timing system with electronic control and hydraulic acutation has been adopted for the timing side camshaft.

The variable valve timing system is driven directly by the injection system and performs the function of altering intake valve timing on the basis of engine load and speed requirements.

The control unit detects malfunctions in the variable valve timing system or electrical circuit and inhibits the drive.

Function

Operation in closed stage (fc)

When closed phase is required (idling and maximum power zone), electromagnet (1) is deactivated. Valve slide (2) then stays up under the pressure of counterspring (3), thus preventing fluid from channel (A) from reaching the variable valve timing system.

In this case, intake valve timing remains unchanged (closed).

Operation in open stage (fa)

When open phase is required (moderate speed at high torque). Electromagnet (1) is excited and presses valve slide (2) down.

In this position, fluid from channel (A) enters chamber (B) of the piston and then flows on through a hole into channel (C) inside the piston.

The fluid can leave this channel only through the upper hole (in communication with port (D) delivering fluid to the variable valve timing system). Because valve slide (2) is lowered, the lower hole is not in communication with exhaust port (E).

The oil flows through channels (D) and (F) into chamber (G), which moves piston (4) sideways toward the engine. Because the piston is fitted with external helical teeth, it is forced to turn clockwise.

Its rotation is transmittted via a splined curb toothed section to piston (5) which is tightened onto the threaded shank of camshaft (6) and transmits rotation to the shaft, thus altering intake valve timing by 18°.

When the electromagnetic is deactivated, valve slide (2) returns to its original position to cut off the flow of pressurised fluid to piston (4) but allowing fluid to return to the exhaust under the pressure of counterspring (7).

Channel (L) allows the camshaft journal to be lubricated under different operating conditions.

The fluid that leaks into electromagnet chamber (H) drains out through drainage port (E).

TAPPETS

Specifications

Type

The hydraulic tappets automatically cancel out valve play during engine operation. This offers the advantage of reducing:

• service requirements.
• engine noise

Operation

Operation in open stage

When the camshaft can operates tappet (1) and thus piston (2), the fluid trapped in chamber (6) transmits movement of piston (2) directly to sleeve (3) and hence to the valve due to closure of ball valve (4).

During this stage, because of the high pressure to which it is subject, part of the fluid in chamber (6) flows through the minimal gap between piston (2) and sleeve (3).

Operation in closed stage

As long as the tappet is pushed along the cam profile by spring (5), a depression builds up inside chamber (6) that opens ball valve (4) to allow fluid to enter.

The fluid taken into chamber (6) replaces the fluid that has leaked out during the previous valve opening stage.

2.4 JTD 20V

CAMSHAFTS

Specifications

Type

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

The exhaust camshaft also controls the vacuum unit fitted on the gears side.