High-Pressure Hydraulics by Citro?n

[jeanlouis]

Berliet Stradair 20



In 1965 Berliet presents the Stradair, the first (and maybe the last) truck on air cushions.


Berliet Stradair prototype tests



The new pneumatic suspension is named "Airlam". For reassuring the driver, Berliet kept blades springs in case of pneumatic issues. It also hold the axles.
Notice the engine at the extreme front of the frame.


Mediatic presentation in May 1965 by the famous cascador of this age, Gil Delamare.


Inside, a comfort of saloon like the one of new Citroën truck presented at the same time (see above).








Reminding of the DS, the new (to) comfortable Berliet Stradair is not appreciated by everyone. In more at the starting, there is a lot of suspension problems.
The production is stopped in December1968.


In 1969, Berliet and Citroën associated present K serie trucks that replace the Stradair. The engine move to rear and the long bonnet is deleted. The cab topple over to front for the access to mechanical. Suspension is becoming classical again.

 

[jeanlouis]

1989 - Peugeot 405x4, a full-time four wheels drive







Peugeot 405x4 is available in GR, SR and MI 16 version, 107 ch and 160 ch. Only the rear axle has hydropneumatic suspension. The system is hydro-electric and only spheres are bought by the partner and rival Citroën. It is not very smart.
Twelve years later, Citroën will use this hydro-electric technology for the Hydractive 3 and 3+ suspension assembled on the C5.

 

[jeanlouis]

After centrifugal regulator for the automatic clutch (1960) and new hydraulics fluid LHM (1966), the DS reach at last its maturity. At the same age, a new 5 bearings engine 2175 cm3 more powerful is assembled on the DS 21. The old traction is now definitely forgetten. Below the hydraulics diagram of a model 1969.







From Citroën DS catalog 1969

 

[jeanlouis]

A special geometry of the front axle still increase safety of DS, GS, SM. Pivots and wheels are on the same axle. This drawing is possible because disk brakes are assembled on each side of the gear box (assembly in board). Starting the CX, first Citroën equiped with transversal engine, brakes are coming back inside the front wheels and the geometry of the axle become classic again.



Notice the only wheel central fixation of the DS until 1965.



GS



SM

 

[jeanlouis]

 

[jeanlouis]

My personal hydraulics Citroën


CX 25 GTI 1984, the only I have still today


DS 20 1970


GS 1220 Club 1974
GS X2 1976
GS X 1978
GSA Pallas 1982

3 cars, 3 different designs


DS, longitudinal engine behind the axle


GS, longitudinal engine in front of the axle


CX, transversal engine in front of the axle

 

[dargelos]

Wonderful drawings, I like them a lot.
Is there ever a problem with rubber ageing on the spare wheel?. It must get hot being stored close to the engine.

 

[jeanlouis]

I never had any problem with the rubber of the spare wheel. At this age, the front axle of Citroën models was very loaded, from 66 to 70 % of the total weight.

 

[jeanlouis]

Still 2 drawings for you Dargelos


SM : the position of units is nearly the same than the one of the DS.
Arms of the front axle were just returned to let the place to the famous V6 Maserati engine. Spare wheel is laying in the middle of the trunk


The BX inaugurated a new front suspension named "pseudo-Mac Pherson" by Citroën. It is the evolution of a traditional metallic Mac-Pherson (lower arm and force-leg) adapted to hydropneumatic. Spheres are tilted.

 

[dargelos]

These images must be the work of an expert draughtsman. Computers can't get cross sections to look this good.
Do you think that the spare wheel of the SM was initialy intended to be stored at the front like the DS?. To leave it lying casualy in the luggage space suggests that the design had to changed with no time to fit the wheel into a place of it's own.

 

[jeanlouis]

These images must be the work of an expert draughtsman. Computers can't get cross sections to look this good.
Do you think that the spare wheel of the SM was initialy intended to be stored at the front like the DS?. To leave it lying casualy in the luggage space suggests that the design had to changed with no time to fit the wheel into a place of it's own.

Indeed drawings are beautiful but most of the times they hide the reality.The photo below is showing the untidiness we find under the bonnet ot the SM. Unfortunately, whatever its form, it was impossible to put a spare wheel under it.



With the spare wheel disk we know today it would be possible to save some room for luggage.


Special feature of the Maserati engine, there is an intermediate shaft that drive camshafts 2 by 2 and all the auxiliaries : high pressure pump, air conditionning compressor, alternator. (at the left of the photo).
With a motorgroup assembled transversaly, in front of the axle, auxiliaries would be on the side of the car and it would be possible to put a spare wheel behind the mechanical like on the CX for example. It is neither a good location because it is heavy and very difficult to bring out.

 

[dargelos]

The top photograph shows why so many British mechanics were too scared to work on Citroens of the period. They were so different to the simple Austins and Rovers that they were used to.

So far you have shown us how hydraulic engineering can be used to allow pasengers to enjoy a more comfortable ride. But the same techniques can be used in reverse in give the passenger a highly uncomfortable ride, which is also an enjoyable one. The Tagada is a fairground ride which uses a pair of powerful actuators not as shock absorbers but as shock creators.

​

The operator triggers the actuators alternately to cause rocking and together to create jumping. Too much jumping is dangerous, there is enough power available to hurl the riders all the way out of the ride if the operator is not careful.
It really is fantastic good fun.

 

[jeanlouis]

Thank you Dargelos for sharing the Tagada that show us also how can be uncomfortable an hydropneumatic Citroën when spheres lost its gas nitrogene (azote). All the reputation of this damned machine is in this famous air cushion. More the volume of the gas is important, more it is comfortable. We saw it above with hydractive suspension of the XM for example.
Here is the different types of sphere :

DS


Black spheres until 1966 and green spheres starting 1967 allow to distinguish synthetic hydraulic fluid of the first models from LHM (green liquid)

Spheres are turned with machine and the 2 parts are screwed. They can be repaired by changing the rubber, the only piece that is sometimes used. This beautiful and expansive element has a volume of 700 cm3.

 

[jeanlouis]

GS



With the GS appeared in 1970, Citroën decide to produce hydropneumatic suspension in big serie. It is the class of Ford Escort, Fiat 128, Opel Kadett, Simca 1100, Renault 12, Peugeot 204 ... at last the famous model 6/7 CV that the constructor missed for years. To reduce the cost, spheres are swaged and cannot be repaired. This sphere type will be extended in 1974 to the last DS, CX, BX, XM, Xantia until 2002. Screwed spheres are kept for rear suspension of DS and CX estate. Volume : 400 cm3 on GS (light car) or 500 cm3 on DS and CX.

 

[jeanlouis]

BX (1982)



This new front suspension called pseudo Mac-Pherson by Citroën will be extended to XM and Xantia.

Rear suspension

 

[jeanlouis]

C5 (2001)






We can see above the difference between the old swaged sphere and the new flattened sphere of the C5, it also swaged. C5 inaugurated hydro-electric Hydractive 3 suspension. Apparently rubber issues seem solved, the constructor garantees for life its flat spheres. The volume is only 385 cm3 but, from Citroën, it is 30% more efficient than the old.

 

[jeanlouis]

[url=https://rapidgator.net/file/363b0cdedf8420003590deb7e922191b/DS_part_1.mp4.html]DS_part_1.mp4[/URL]
[url=https://rapidgator.net/file/d215ff26e620fc121a728c0ef70d51ba/DS_part_2.mp4.html]DS_part_2.mp4[/URL]

 

[dargelos]

Nice to see this here in colour, the copy on youtube is only black and white. Perhaps you have a connection with the company in order to obtain access to so much choice material?

 

[jeanlouis]

Thank you so much for your comments, Dargelos. The video about the DS is very bad quality because it come from a VHS transformed in DVD then converted in MP4 ! I found this VHS and some others with the number one of a classic models collection in news shopkeeper. They allways promoted their first number with various gifts. It was about 20 years ago.



As I am an old guy, I knew historic Citroën headquarters at Paris where they assembled cars and utilitaries until 1976, "quai de Javel" that became "quai André Citroën" in 1958. Most of drawings and technical doents I posted here come from there. I said I was mechanical trainee in a Citroën garage and I got all what I wanted. All was very easier at this age, I think. The constructor kept some offices at "quai de Javel" until 1982 then all was destroyed ! Starting 1973, the production was gradually transfered at Aulnay sous Bois near Paris (last DS then CX and many others), a manufactory also relocated today.

 

[jeanlouis]

SM 2, a Citroën SM version 2019

A french mechanical imagined then realized a SM evolution 48 years after its appearance. A lot of modifications (especially on the V6 Maserati engine) were necessary so that this prestigious coach could become a car for everyday.










Before - After : the passionate mechanical cleaned motor compartiment :thumbs up:

Aculators and pressure regulator move to the rear, near of the new LHM reservoir






I hope this advanced project will be success