FUNCINAMENTO DAS ELECTROVALVULAS DA SUSPENSÃO



FUNCINAMENTO DAS ELECTROVALVULAS DA SUSPENSÃO

The calculator of suspension decides to act on the suspension following the analysis of the information provided by the various sensors.

With this intention it can electrically order three electrovalves able to carry out the transformation of the electric signal into hydraulic action.

They are the unique means of action on the suspension.

[pic]

Two of these electrovalves - ordered simultaneously (but by separate circuits) are dedicated to hydractive, the last is being used for the SC-CAR:

- an electrovalve for regulator hydractive AV (train AV)

- an electrovalve for the regulator hydractive AR (train Ar)

- an electrovalve for regulator SC-CAR

Location spheres AV Activated (under seen ) Location spheres AR Activated (seen back)

[pic]

Principles of operation of the electrovalves

It functions in "all or nothing": They has two "stable" states according to whether it is or not fed electrically (it is not possible to proportion the opening of this valve).

Principal elements:

[pic] [pic]

- in blue: the mobile metal core carrying out the shunting of the liquid

- in orange: the spring maintaining in position the core in the absence of power supply

- in red: electrical coil (seen out of cut).

- 1 entry of the liquid (high pressure)

- 2 exit of the liquid in direction of the hydraulic element to feed

- 3 return of the liquid towards the tank (low pressure) the LHM under high pressure (resulting from the conjuctor/disjunctor) is represented in green.

Dismounted elements:

[pic]

"Closed" State (no power supply): In the absence of power supply the core is maintained by the spring resting against the hole (1), which is thus stopped. The tubes (2) and (3) communicate.

The liquid high pressure is blocked by the valve and does not reach the hydraulic element to command.

The connected hydraulic element returns from there the residual pressure (and its hydraulic escapes intern) towards the tank connected in (3)

[pic]

"Open" State (electrical power is supplied to the valve): The coil receives electrical current and them produces a magnetic field attracting the core (the spring is compressed) towards the hole (3) which is then closed. The tubes (2) and (1) communicate.

The liquid high pressure is transmitted to the element hydraulic to act in (2)

The return connected tank (3) is isolated from it.

[pic]

Electric drive of the electrovalve.

We saw in the preceding paragraph that the ordering of the electrovalve is electric. This chapter more precisely describes the implementation of the control signal.

General diagrams

[pic]

The electronics decides, starting from information collected sensors, if the electrovalve must be operated or not.

An electric signal is sent to the "relay" to complete or open of the electrovalve.

The "relay" is not a traditional electrostatic relay but a static relay: it acts like an electronic component without parts moving.

This static relay is the component VN05N from STMicroelectronics.

It is able (in more of its first function as a relay) to inform the command module of a possible malfunction:

- Short circuit (the exit of the component is directly connected to the mass)

- Open circuit (disconnected electromagnetic sluice gate)

- Overheating (put in automatic protection of the component)

The VN05N are physically located in the calculator of suspension:

[pic]

Electric diagrams

The electric diagram of the circuit of the electrovalve (in first approach) can be represented like the circuit below:

[pic]One could think that it is enough to actuate the relay and thus to close switch Ci to order the electrovalve above... It is a little bit more complicated!

[pic] At the time of the closing of the contact, the electrical power circulates and is on in the coil of electrovalve, creating a magnetic field to attracting the core.

Once the core attracted in its final position, the magnetic field of the coil is only used to maintain it in this position (and to move it either).

It is important that the time of release of the electrovalve - time between the beginning of the power supply and the effective passage in an open state must be the shortest possible to ensure a fast response to the ordering of the calculator: thus the coil absorbs - when the switch is firm - a current fort.

This current gives energy necessary to the fast displacement of the core in its final position. Once this position is reached, it is not necessary any more to provide such a large energy to maintain it in this position. (if this initial current were maintained there would be a risk of overheating of the coil and the possibly of burning).

The switch does not remain permanently closed after the initial period of displacement of the core, it opens and closed at a rate of 1000 times per second in "cutting out" the power provided to the coil by the control signal of the VN05N.

Time of the opening of the electromagnetic sluice gate

[pic]

beginning of the command: ~0,5 S core in position maintains:

=> 12v permanent => 12v "chopped" with 1000 Hz

Cut of a circuit comprising an inductive element (coil)

When the switch shuts off the current in the circuit, the coil is stored with energy.

This energy will not be able to remain stored by the coil and will be transformed into an electrical current circulating in the same direction that was circulating in the coil before the cut.

This current then will be dissipated while being transformed into spark on the level of the contacts of the switch (on a traditional switch)

[pic]

This spark uses a little bit (each time) the contacts of the switch (until destroying it in the long term...) It’s this phenomenon which causes the dysfunction of air-conditioning by the wear of the contacts of Neiman (spark to each cut of contact).

If the switch is not mechanical but electronic, this "residual current" can, in the best of the cases, overheat the component and, in worst of the cases, destroy it!.

In the case of the electrovalve, this phenomenon is all more tedious as, at the time of the "chopped" electric drive, there are 1000 cuts a second!!

The VN05N fortunately is resistant and is protected from overheating, which avoids its destruction. On the other hand, when it overheats, it completely shuts off the current during a few seconds (time to cool) then gives it (once cooled): We can inopportunely hear the electrovalve "claquer" with the stop.

It is to avoid these tedious phenomena that a diode is inserted in the circuit.

Recall on the operation of a diode

The diode is component bipolar (two ends), which has the principal following characteristic: it lets pass the current in a direction but blocks it in the other.

Its symbol is as follows:

[pic]

It is usually presented in this form:

[pic]

Illustration with a simple assembly: a pile and a bulb:

Feel passer by: the power is on, the bulb lights

[pic]

Feel blocking: the power is not on, the bulb remains extinct

[pic]

Contribution of a diode in the control circuit of the electrovalve gate

To prevent that the residual current - appearing at the time of the cut of the inductive circuit is not dangerous for the component of order, a diode is inserted in parallel of the reel (in the direction indicated)

Note: to facilitate the comprehension of the diagram, the VN05N is positioned between the coil and the mass: actually (on the vehicle) it is located between the +12v (battery) and coil (that does not change anything with the phenomenon).

[pic]Coil with Power On: the diode remains inactive since in the blocking direction (it is not used for nothing at this time)

[pic]Power Cut Of : the current resulting from the coil does not transform into spark on the level of the switch (or does not cause the overheating of the component), it goes this time Ci capacity to dissipate itself while circulating in the diode, which will be at this moment in the busy direction.

The current then will circulate between the coil and the diode until its disappearance supplements (very quickly: the various losses in wire and components involve a fast cancellation of this current).

Even if 1000 cuts a second take place, the command component not obstructed and can continue to function correctly.

A diode used like this is named "free wheel diode " (the current continues "to turn" on its impetus).

Effect of the "netting" of the free wheel diode

When this diode roasts, it leads any more current neither in a direction, nor in the other and one finds oneself in the case of a circuit without diode.

In practice, there are the VN05N which overheats and which shuts off by chance the current in the coil, which causes to close the electrovalve.

By the other hand, one also notes, when the diode is roasted, that the average tension at the boundaries of the coil is lower than its normal value and can be no more sufficient to maintain the coil in closed position: the electrovalve is closed again then mechanically, even in the presence of the "chopped" power supply.

For the hydractive, one finds oneself, in worst case, with a hydractive suspension in the hard mode almost permanently (except during the half second of initial power supply of the electrovalve...) or, in best of the cases, in hard mode by chance...

For the SC-CAR, the system:

- Does not function at all (except during the first phase of a half second); thus the car leans after first 1/2 second

- It will deactivate aleatory in the medium of a curve: not very probable in my opinion (except extreme case) because it is necessary (if it is supposed that the terminal voltage of the coil remains sufficient to maintain the core) that the VN05N overheat... what is not immediate!

Detection of the breakdown

It can be carried out in various ways (nonexhaustive list...):

- Listening of the noise of electrovalve (valid only for the hydractives EV)

At the stop, open the door, a electrovalve remains with power for 10 minutes, which is sufficient to cause the overheating of the VN05N and thus fermetures/ouverture inopportune (easily identifiable!)

- Test of the hardness of the suspension (valid only for the hydractives EV)

By comparing the clearance of the suspension in voluntarily firm mode (voluntarily disconnect the electrovalve) and in theoretically flexible mode (connected electrovalve) one can deduce from it that the electrovalve does not pass the suspension in flexible mode (and thus that the diode is roasted)

- Measurement of the average tension (with a simple voltmeter) at the boundaries of the electrovalve

This tension (in "chopped" mode) is about 2,7 v if the diode is not roasted; it can go down to 1,9v if not

- Use of a pile connected in each direction (disconnected electrovalve of the circuit of the car)

Measurement of the current in each direction: it is identical if the diode is roasted (different if not)

- Use of the electronic assembly below (to be connected in parallel of the electromagnetic sluice gate)

The led of the assembly ignites if the diode of the electromagnetic sluice gate is roasted when the electrovalve is ordered in "chopped"

[pic]

Breakdown service

In the case of the control circuit of the electrovalve, this diode is physically located in the moulding of the winding of the electrovalve and thus cannot - when it is roast- to be changed without changing the complete electrovalve.

[pic] [pic]

Nevertheless, considering the operation of this component, it is perfectly possible to add another diode (not roasted) outside the electromagnetic sluice gate (between wire or on the level of the calculator) which will play the same part exactly.

One can add besides this additional diode in "safety" even if the integrated diode is not roasted: in the worst case it is used for nothing, but in any event it does not harm!

Choice of the diode

Several possibilities exist (I do not know the reference of the diode of origin):

- a "simple" diode (sufficient "strapping man"): style 1N4007

- a Schottky diode of power: style 1N5822

principal advantage: the direct voltage drop is much weaker and thus there is less of return towards the order (there is always, even with the diode, a light return towards the order)

disadvantages:

* the average tension at the boundaries of the coil is slightly higher than its normal value (the initial diode should not be Schottky!); I do not think, nevertheless, that that gene really

* it is more expensive (~ 2€) -...

Addition of the diodes in the circuit

Still, there are several possibilities; here are two:

1) Directly in the calculator (an empty site is envisaged on the circuit on certain models of calculators)

Advantage: the three diodes are added to the same place without needing to go to seek wire under the car. Disadvantage: it is necessary to dismount the calculator (potentially with each netting of the new diode) and to know to weld onto printed circuit

Emplacements in the calculator:

[pic]

2) By manufacturing a small cable extension, which comes to fit between the wiring of origin and the electrovalve.

Advantage: no modification of the beam of origin or calculator/easier to change if it also roasts

Inconvenient: not so easy that that to put at the back, especially on the hydractive one (difficult of access)

Manufacture of the cable extension:

Socket (recoverable on Xantia: hydractive catch of origin or on the beam ABS)

[pic]

Catch male (recoverable on the beam ABS of Xantia or XM)

[pic]

It is important to locate wire well; with an ohmmeter for example (and of not proud with their position compared to the catch!)

[pic]

One can then weld wire between them to create the extension (addition of a retractable sheath thermo on the left before welding)

[pic]

Welding of the diode (to lay out well the "white feature" of the diode with dimensions +)

[pic]

After and retraction installation of the sheath

[pic]

Addition of black adhesive to finish

[pic]

Thanks to :

Alain for the photographs of the sites of the diodes on the calculator,

Billboquet5 and Tctrouge for the photographs of spheres AV and Ar,

The members of Acf for their invaluable councils and indications.

[pic]

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download