non hydractive spheres for hydractive xantia

[Mandrake]

I finally ordered 2 CX turbo spheres(500cc 75bars ) for the front and 2 Xantia non-turbo (400cc 40 bar) spheres for the back. I know not the best option, but for now anything should be better than the rock hard suspension that i have. At a later date i will try to further diagnose the system.

Ooh, err. What convinced you to buy CX front spheres ?

There is more than just the size and pressure of the spheres, there is the calibration of the centre bypass hole, and the strength of the leaf valves which critically affect the damping and handling. You're very unlikely to get an acceptable ride/handling combination from those spheres I'm afraid. Most likely it will be floaty and underdamped as CX front spheres have much larger center bypass holes than Xantia spheres due to different mechanical leverages - the CX has double wishbone suspension with a 3 to 1 leverage ratio on the arms while the Xantia has McPherson struts.

Also CX front sphere bypass holes are about 1.6mm from memory, while a Standard Xantia is about 1.1mm - this doesn't sound like much but its a huge difference in terms of damping.

I would have gone for Standard hydropneumatic Xantia spheres if you were abandoning getting the ECU/Electrovalves working...

[Mandrake]

In a hydractive 2 car which is in hard mode the flow between left and right sides is blocked off and this is a significant part of what cuts down body roll on a hydractive model when entering hard mode for cornering.

Standard spheres on a hydractive 2 model with hydractive disabled will indeed ride harder than a standard hydropneumatic model, there will be less body roll in cornering but driving straight ahead on undulating surfaces the car will tend to rock side to side with the surface of the road.

I don't think that's entirely correct Simon as within the Hydractive block there is a bypass to allow fluid to flow from side to side independent of the state of the electrovalve. The flow of fluid through this bypass is controlled by a small ball bearing that closes if the sideways flow become excessive, so in simple terms slight variations in road surface heights on each side when driving straight ahead shouldn't make much difference to the ability of the car to remain level.

The bypass only opens when there is a pressure imbalance between the side spheres and the height corrector. When the height corrector opens in the downwards direction the ball lifts off its seat naturally to allow pressure to flow back to the height corrector, and when the height corrector opens in the upwards direction a small rod pushes the ball off the seat in the other direction, however side to side flow is almost entirely eliminated - thats the whole point of the valve.

It's a while since I've seen the internal diagram of it (anyone got a copy ?) but I'm pretty certain that side to side flows (when the height corrector is not open) are almost entirely eliminated - even for small roll movements. (There is no noticeable hysteresis)

You can notice the operation of the valve if you disable the Hydractive system by removing the fuse, then attempt to rock the car side to side - it will be very stiff, but then cause the height corrector to open to raise or lower the car and whilst the car is raising or lowering you can rock the car sideways much more easily because the pressure imbalance to the height corrector is temporarily holding the bypass valve open, but as soon as the height corrector closes and the pressure imbalance disappears the valve closes again and side to side movement is again stiffened by blocking side to side flow. Clever valve

Of course in the soft mode there is a side to side flow path through the two damper valves, but even then its important that the ball valve works properly to block sideways flows otherwise the damper valves would be bypassed and would not provide damping of side to side (roll movement) in soft mode...

One of the improvements of the hydractive 2 system over hydropneumatic is that there is no damping of side to side flows in hydropneumatic - the only limitation is the diameter of the pipe, which makes a poor mans damper, but not a progressive one. Hydractive 2 has the very large pipe but then has proper damper valves that can provide progressive damping of sideways flows in soft mode, thus the damping of roll movements is very good with hydractive 2, giving good straight line roll axis stability in soft mode over uneven surfaces...

[DickieG]

The bypass only opens when there is a pressure imbalance between the side spheres and the height corrector. When the height corrector opens in the downwards direction the ball lifts off its seat naturally to allow pressure to flow back to the height corrector, and when the height corrector opens in the upwards direction a small rod pushes the ball off the seat in the other direction, however side to side flow is almost entirely eliminated - thats the whole point of the valve.

It's a while since I've seen the internal diagram of it (anyone got a copy ?) but I'm pretty certain that side to side flows (when the height corrector is not open) are almost entirely eliminated - even for small roll movements. (There is no noticeable hysteresis)

Of course in the soft mode there is a side to side flow path through the two damper valves, but even then its important that the ball valve works properly to block sideways flows otherwise the damper valves would be bypassed and would not provide damping of side to side (roll movement) in soft mode...

I've been having a read of my Citroen technical training manual that Citroen UK use to train their technicians and as far as I can work out the valve is open unless the car is cornering as the resulting crossflow of fluid pushes the ball against its seat and closes the valve. The height corrector works on the ball as you describe but the side ports will still remain open unless there is a sideways movement of fluid as when cornering. The bypass valve only bypasses the electrovalve, not the dampers within the Hydractive block.

The following technical guide http://citroen.tramontana.co.hu/technical-guide reads pretty similar to the manual that I have plus it has sectioned diagrams of the Hydractive blocks, page 27 describes these valves.

[Mandrake]

I've been having a read of my Citroën technical training manual that Citroën UK use to train their technicians and as far as I can work out the valve is open unless the car is cornering as the resulting crossflow of fluid pushes the ball against its seat and closes the valve. The height corrector works on the ball as you describe but the side ports will still remain open unless there is a sideways movement of fluid as when cornering.

Technically that's right, but it only takes the tiniest sideways flow for it to block. The functional diagrams in the article you link to aren't drawn to scale so make it appear that the ball has a long way to go to block one port or the other, but in practice its a very small distance. Any visible movement of the suspension arms (when you consider their piston diameter thus displaced oil) is going to be enough to trigger the valve to block.

The bypass valve only bypasses the electrovalve, not the dampers within the Hydractive block.

You're right, looks like I didn't remember that properly. I should have known better too, as I've dismantled a hydractive control block before and removed the damper valves... and the outside edge of the damper valves goes directly to the large diameter pipes with nothing in between. My bad.

The following technical guide http://Citroën.tramontana.co.hu/technical-guide reads pretty similar to the manual that I have plus it has sectioned diagrams of the Hydractive blocks, page 27 describes these valves.

I had a look and realised that I still have the full Hydractive 2 manual, and in fact its still sitting on my old home page

http://homepages.igrin.co.nz/simon/imag ... ive_II.pdf

Note: the forum seems to capitalise the C and put an accent above the e in Citroen, breaking the link (and all the other links to files hosted on my website from other threads) and I can't stop it from doing that... for the link to work citroen has to be manually edited to be in lower case with no accent above the e. (Any idea why this happens Jim ? )

I'm not sure if this is the same manual you're referring to but it is very detailed and is some sort of official manual. Page 22 has a to-scale drawing of the valve and its operation. Is this the same manual you have ?

[DickieG]

I'm not sure if this is the same manual you're referring to but it is very detailed and is some sort of official manual. Page 22 has a to-scale drawing of the valve and its operation. Is this the same manual you have ?

I think so, I obtained the manual many years ago then loaned it to an old forum member (Steve Braud) who published it on his own website, so if the copy you have came from the net it might well have originated from me

[xmexclusive]

As I understand the original Hydractive 2 the brake pressure switch was never used as the sole method of soft/hard switching.
According to the Citroen operating principles the switch is closed at rest.
It opens under a pressure in the brake circuit of 30 bars.
The suspension ECU then advises the change to firm state only when the vehicle speed exceeds 15mph.

I guess that Citroen found that the ECU microprocessor could be programmed to check for speed reduction just as quickly as it checked pressure and speed.
Just because the brake pressure sensor is an analogue device (always outputs its current reading).
A Microprocessor is digital and has to be programmed to read each sensor in turn.
The more important the sensor the more frequently it gets read.
When the sensor value changes there must be a variable delay until the micro clocks round to the next reading.

By todays standards we are talking about very slow and simple Microprocessors.
I remain amazed at the programming skills and effort that got these early micros to run ABS systems.

John

[Juliso35]

The most convenient point that I know of is the wire to the front electrovalve, which is part of the assembly that the hydroactive sphere attaches to.
You need to test with the plug still connected to the electrovalve, as unplugging it will stop the system from working.

With the valve activated you should see 4-6 volts on that wire.

Hi
According with this,....then if the reading is below 2V what could mean? A incorrect voltage may result in leaks?.
By the way... the described 100 ohm resistor test, if I undestarnd well.,,,this is a way to cheat the ECU and measure the EV voltage feeded? Of course with no buzzing (hum)???

[Mandrake]

Hi
According with this,....then if the reading is below 2V what could mean? A incorrect voltage may result in leaks?.
By the way... the described 100 ohm resistor test, if I undestarnd well.,,,this is a way to cheat the ECU and measure the EV voltage feeded? Of course with no buzzing (hum)???

It's a way to trick the ECU into activating the electrovalve supply voltage even if the electrovalves might have a faulty diode or other internal fault. As I described earlier in the thread if the ECU detects a fault with either electrovalve it will not supply power to either one, thus making it difficult to troubleshoot whether the electrovalves or ECU itself are faulty. (An electrovalve with a faulty diode will measure OK with an ohm meter but will still cause the ECU to shut down)

By replacing both electrovalves with a resistor the ECU will be satisfied thus allowing us to check output voltage from the ECU and check the functioning of the ECU separately. So are you saying you measure just below 2v ?

The normal voltage is around 3-4 volts, however it is not a DC voltage, it is a 12 volt peak to peak, 1Khz pulse width modulated square wave which averages to 3-4 volts, however if you measure it with a digital meter with a very low frequency response it may give an erroneous reading, as not all digital meters (especially cheap ones) will read a pulse width modulated signal in DC mode properly. (Some digital meters can't read much beyond a few hundred Hertz)

In that case you could try using a simple old fashioned analog volt meter as this will always give the correct reading for a pulse width modulated signal such as this.

[xmexclusive]

Edit note: see Simon's correction below to the errors in this post.
An electrovalve diode can be tested with a meter.
On a resistance check a good diode checks as dead short one way and virtually open circuit the other.
When the diode is installed across the electrovalve terminals the resistance must be checked on both polarities.
One way it will read the coil resistance where you should see around 100 ohms.
On the other polarity it should still read dead short as the current will go through the diode not the coil.
Very easy to condem a good electrovalve if you only test the wrong polarity and the diode is still good.
If the electrovalve reads around 100 ohms on both polarities then the built in diode is blown.
Time to fit an external diode to protect the VN05N in the ECU if it is still alive.

On the ECU output a common mode of partial failure of the VN05N's increases the off peiod of the output waveform.
This reduces the voltage measured by a meter and may well explain the low 2 volt reading seen here.
Looking at the ECU output signals on a scope tells all but is not an option for most of us.

John

[Mandrake]

An electrovalve diode can be tested with a meter.
On a resistance check a good diode checks as dead short one way and virtually open circuit the other.
When the diode is installed across the electrovalve terminals the resistance must be checked on both polarities.
One way it will read the coil resistance where you should see around 100 ohms.
On the other polarity it should still read dead short as the current will go through the diode not the coil.
Very easy to condem a good electrovalve if you only test the wrong polarity and the diode is still good.
If the electrovalve reads around 100 ohms on both polarities then the built in diode is blown.

Not wanting to be picky here, but that's incorrect.

The resistance of the electrovalve is 4.8 ohms as stated in the Hydractive 2 training manual I linked to earlier in the thread, not 100 ohms. Also, you cannot test the diode in the electrovalve with a standard multimeter in ohm meter mode because the 4.8 ohm coil resistance will swamp the diode - a multimeter will not pass enough current even in diode test mode to exceed 0.6 volts across 4.8 ohms, and therefore will not turn the diode on. Even with the diode intact it will simply measure 4.8 ohms both ways giving no indication whether the diode is ok.

The way to test the internal diode is as follows:

An 18 ohm 10 watt resistor and a 12 volt supply are required, along with a voltmeter. Connect the 18 ohm resistor in series with the electrovalve across the 12 volt supply and measure the voltage across the electrovalve, then reverse the battery polarity and measure again.

In the forward polarity the voltage will be about 2.4 volts, (diode reverse biased) and in the reverse direction it will be about 0.7 volts. A reverse reading of around 0.7 volts shows the diode is ok, if both polarities give 2.4 volts the diode is faulty.

Its important never to connect the electrovalve directly to 12 volts in the reverse polarity or the diode will be instantly destroyed.

Time to fit an external diode to protect the VN05N in the ECU if it is still alive.

I'd agree - there is no harm in fitting the external diodes as a preventative measure, and I've seen cases where the internal diode can become intermittent causing intermittent ride harshness.

On the ECU output a common mode of partial failure of the VN05N's increases the off peiod of the output waveform.
This reduces the voltage measured by a meter and may well explain the low 2 volt reading seen here.
Looking at the ECU output signals on a scope tells all but is not an option for most of us.

It's been a while since I've measured electrovalves but looking at the training material the "hold" voltage is a bit lower than I remember - the manual quotes 0.5 amps, and the coil resistance is 4.8 ohms, meaning the "normal" hold voltage is about 2.4 volts, although I'm sure when I measured mine it was more like 2.8 volts to 3 volts...

[aneesh84]

An electrovalve diode can be tested with a meter.
On a resistance check a good diode checks as dead short one way and virtually open circuit the other.
When the diode is installed across the electrovalve terminals the resistance must be checked on both polarities.
One way it will read the coil resistance where you should see around 100 ohms.
On the other polarity it should still read dead short as the current will go through the diode not the coil.
Very easy to condem a good electrovalve if you only test the wrong polarity and the diode is still good.
If the electrovalve reads around 100 ohms on both polarities then the built in diode is blown.

Not wanting to be picky here, but that's incorrect.

The resistance of the electrovalve is 4.8 ohms as stated in the Hydractive 2 training manual I linked to earlier in the thread, not 100 ohms. Also, you cannot test the diode in the electrovalve with a standard multimeter in ohm meter mode because the 4.8 ohm coil resistance will swamp the diode - a multimeter will not pass enough current even in diode test mode to exceed 0.6 volts across 4.8 ohms, and therefore will not turn the diode on. Even with the diode intact it will simply measure 4.8 ohms both ways giving no indication whether the diode is ok.

The way to test the internal diode is as follows:

An 18 ohm 10 watt resistor and a 12 volt supply are required, along with a voltmeter. Connect the 18 ohm resistor in series with the electrovalve across the 12 volt supply and measure the voltage across the electrovalve, then reverse the battery polarity and measure again.

In the forward polarity the voltage will be about 2.4 volts, (diode reverse biased) and in the reverse direction it will be about 0.7 volts. A reverse reading of around 0.7 volts shows the diode is ok, if both polarities give 2.4 volts the diode is faulty.

Its important never to connect the electrovalve directly to 12 volts in the reverse polarity or the diode will be instantly destroyed.

Time to fit an external diode to protect the VN05N in the ECU if it is still alive.

I'd agree - there is no harm in fitting the external diodes as a preventative measure, and I've seen cases where the internal diode can become intermittent causing intermittent ride harshness.

On the ECU output a common mode of partial failure of the VN05N's increases the off peiod of the output waveform.
This reduces the voltage measured by a meter and may well explain the low 2 volt reading seen here.
Looking at the ECU output signals on a scope tells all but is not an option for most of us.

It's been a while since I've measured electrovalves but looking at the training material the "hold" voltage is a bit lower than I remember - the manual quotes 0.5 amps, and the coil resistance is 4.8 ohms, meaning the "normal" hold voltage is about 2.4 volts, although I'm sure when I measured mine it was more like 2.8 volts to 3 volts...

Finally installed the spheres of Cx in the front and Xantia non turbo at the back. They were IFHS spheres that I received from AEP with the following part numbers SSCX75FG and SSXA40RX (75 bars 500cc and 40 bars 400 cc respectively). I must say I am very satisfied with the results. The car has that soft floating carpet feel. I would say, if you really abandon the hydractive system on a Xantia, this is the way to go. There is a slight roll though, but very much tolerable.

[DickieG]

Good to hear that you're pleased with the result

[aneesh84]

I finally ordered 2 CX turbo spheres(500cc 75bars ) for the front and 2 Xantia non-turbo (400cc 40 bar) spheres for the back. I know not the best option, but for now anything should be better than the rock hard suspension that i have. At a later date i will try to further diagnose the system.

Ooh, err. What convinced you to buy CX front spheres ?

There is more than just the size and pressure of the spheres, there is the calibration of the centre bypass hole, and the strength of the leaf valves which critically affect the damping and handling. You're very unlikely to get an acceptable ride/handling combination from those spheres I'm afraid. Most likely it will be floaty and underdamped as CX front spheres have much larger center bypass holes than Xantia spheres due to different mechanical leverages - the CX has double wishbone suspension with a 3 to 1 leverage ratio on the arms while the Xantia has McPherson struts.

Also CX front sphere bypass holes are about 1.6mm from memory, while a Standard Xantia is about 1.1mm - this doesn't sound like much but its a huge difference in terms of damping.

I would have gone for Standard hydropneumatic Xantia spheres if you were abandoning getting the ECU/Electrovalves working...

You are right, Initially the front cx spheres seemed very soft and comfortable, but today i took a little long drive along the country road which was bumpy. The car was smooth but softly rocking like a boat. After a while i seem to be getting a headache. Maybe I should go with a non-turbo xantia sphere: 400cc 70 bar 1.65 damper or maybe non hydractive turbo 400cc 55 bar 1.5 damper.

[Mandrake]

I would go with the latter - 400cc 55 bar, 1.5mm damper hole. Are you able to get them swapped or will you just have to buy another pair ?

75 bars is very high (36% softer than usual springing rate) and 1.65mm is quite large. (21% less damping than normal)

If you're unable to return the spheres for an exchange there is a simple modification you could try which I've used before - the centre bypass hole can be reduced in diameter to custom tune the damping.

The way I did it was to use solder (50/50 or 60/40) to block the hole, then drill out the solder using a smaller diameter precision drill bit. It takes a soldering iron with quite a high wattage (I used a portable gas soldering iron which is probably equivalent to about 100 watts) to solder the hole closed using a minimum of solder and a high enough temperature for it to flow across the centre flat surface around the hole. You don't want the solder flowing too far down into the hole, just blocking it at the surface in a layer about 0.5mm thick. After flowing some solder there I used a small file to file the solder flat and slightly above (0.5mm) the surface. You then just carefully drill the hole back out using a drill bit that is smaller than the original hole.

The solder is very soft and easy to drill, and can be reflowed and drilled out again easily to try different sizes. Because the spheres have a higher than normal gas pressure I would be inclined to make the hole size a bit smaller than normal - say 1.4mm. Every 0.1mm change in diameter makes quite a difference to damping as its the cross sectional area not diameter that matters so damping changes with the square of diameter. Just reducing the hole from 1.65mm to 1.4m is a 39% increase in damping and may be all that it takes to get rid of the floaty "rocking" behaviour without making the ride noticeably worse.

[DickieG]

I presently have 450cc 70 bar 1.65 damper hole sphere's on the front of my HDi, for general running around in my local area where the roads don't suffer subsidence so I don't encounter large undulations they give a very smooth ride, if however I travel further afield and I'm travelling at speed carrying a heavy load then they can feel a little under damped when travelling over deep/high irregularities in the road surface, but then my HDi does have a fully functional Hydractive system so uses the centre sphere, when I press the sport button it firms up the suspension sufficiently well to avoid any oscillation.

Bear in mind that these sphere's are standard specification for a non Hydractive Xantia using a 1.8 engine and as stated earlier in the thread using standard TD/2.0 sphere's with a 1.5 damper will apparently give a firmer ride than a non Hydractive Xantia so I can't help thinking that 1.65 damper hole sphere's will suit your purpose perfectly.