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85-518: The purpose of this system is to provide a sensitive, dynamic and high-capacity suspension that offers superior ride quality on a variety of surfaces. A hydropneumatic system combines the advantages of hydraulic systems and pneumatic systems so that gas absorbs excessive force and liquid in hydraulics directly transfers force. The suspension system usually features both self-leveling and driver-variable ride height , to provide extra clearance in rough terrain. This type of suspension for automobiles

170-470: A synthetic ( liquide hydraulique synthétique , LHS). Both had the disadvantage of being hygroscopic . Disuse allows water to enter the hydraulic components, causing deterioration and requiring expensive maintenance. The difficulty with hygroscopic hydraulic fluid was exacerbated in the DS/ID due to the extreme rise and fall in the fluid level in the reservoir, which went from nearly full to nearly empty when

255-585: A France still deep in reconstruction after the devastation of World War II, and also building its identity in the post-colonial world, the DS was a symbol of French ingenuity. The DS was distributed to many territories throughout the world. It also posited the nation's relevance in the Space Age , during the global race for technology of the Cold War . Structuralist philosopher Roland Barthes , in an essay about

340-419: A car as early as 1902 by British Lanchester , volume production had not been applied until 1949, by USA small car manufacturer Crosley , but without success. The Citroën DS was the first successful fielding of disc brakes on a mass-produced car. Furthermore, at launch the DS featured innovative centerlock wheels which used a captive allen bolt as the central fastener whilst a hexagonal protrusion transferred

425-463: A dedicated brake accumulator on some models. On later cars fitted with Hydractive or Activa suspension, there may be as many as ten spheres. Spheres consist of a hollow metal ball, open to the bottom, with a flexible Desmopan rubber membrane, fixed at the 'equator' inside, separating top and bottom. The top is filled with nitrogen at high pressure, up to 75 bar , the bottom connects to the car's hydraulic fluid circuit. The high pressure pump, powered by

510-445: A filter assembly was fitted into the hydraulic reservoir. Cleaning the filters and changing the fluid at the recommended intervals removes most dust and wear particles from the system, ensuring the longevity of the system. Failure to keep the oil clean is the main cause of problems. It is also imperative to always use the correct fluid for the system; the two types of fluids and their associated system components are not interchangeable. If

595-500: A large, expensive executive car and a downward brand extension was attempted, but without result. Throughout the late 1950s and 1960s, Citroën developed many new vehicles for the very large, profitable market segments between the 2CV and the DS, occupied by vehicles like the Peugeot 403 , Renault 16 and Ford Cortina , but none made it into production. Either they had uneconomic build costs, or were ordinary "me too" cars, not up to

680-462: A less expensive variant, the Citroën ID , the DS was known for its aerodynamic, futuristic body design; unorthodox, quirky, and innovative technology, and set new standards in ride quality , handling , and braking, thanks to both being the first mass production car equipped with hydropneumatic suspension , as well as disc brakes . The 1967 series 3 also introduced directional headlights to

765-637: A mass-produced car. Italian sculptor and industrial designer Flaminio Bertoni and the French aeronautical engineer André Lefèbvre styled and engineered the car, and Paul Magès developed the hydropneumatic self-levelling suspension . Robert Opron designed the 1967 Series 3 facelift. Citroën built 1,455,746 examples in six countries, of which 1,330,755 were manufactured at Citroën's main Paris Quai de Javel (now Quai André-Citroën ) production plant. In combination with Citroën's proven front-wheel drive,

850-465: A rubber membrane. Citroën first introduced this system in 1954 on the rear suspension of the Traction Avant . The first four-wheel implementation was in the advanced DS in 1955. This type of suspension for automobiles was inspired by the pneumatic suspension used for aircraft landing gear, which was also partly filled with oil for lubrication and to prevent gas leakage, as patented in 1933 by

935-561: A separate front brake accumulator on power steering models. The old LHS and LHS2 (coloured red) cars used a different elastomer in the diaphragms and seals that is not compatible with green LHM. The orange LDS fluid in Hydractive cars is also incompatible with other fluids. The principles illustrated by the successful use of hydropneumatic suspension are now used in a broad range of applications, such as aircraft oleo struts and gas filled automobile shock absorbers , first patented in

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1020-804: A special need for a high level of ride quality to avoid further injury to the already-ill passengers. Early vehicles, like the Ford Model T , with its leaf spring , live axle suspension design, were both uncomfortable and handled poorly. Historically, weight was key to allowing cars such as the Rolls-Royce Silver Cloud and the Cadillac in the 1950s and the 1960s to have a more comfortable ride quality. However, there are various drawbacks to heavier cars, including poor fuel efficiency , acceleration, braking, cornering and additional stresses on components. Over time, technology has shifted

1105-426: A vehicle's effectiveness in insulating the occupants from undulations in the road surface such as bumps or corrugations. A vehicle with good ride quality provides comfort for the driver and the passengers. Good ride quality provides comfort for the people inside the car, minimises damage to cargo and can reduce driver fatigue on long journeys in uncomfortable vehicles, and also because road disruption can impact

1190-663: A wide market gap to the DS range all through the 1960s. In 1970, Citroën finally introduced a car to target the mid-range – the Citroën GS , which won the "European car of the Year" for 1971 and sold 2.5 million units. It combined a small 41 kW (55 hp) flat-4 air-cooled engine with Hydropneumatic suspension . The intended 79 kW (106 hp) Wankel rotary-engined version with more power did not reach full production. The DS maintained sales and remained competitive throughout its production run. Its peak production year

1275-446: Is a type of motor vehicle suspension system , designed by Paul Magès , invented by Citroën , and fitted to Citroën cars. The suspension was referred to as Suspension oléopneumatique in early literature, pointing to oil and air as its main components. The system was also used under licence by other car manufacturers, notably Rolls-Royce ( Silver Shadow ), Bmw 5-Series e34 Touring, Maserati ( Quattroporte II) and Peugeot . It

1360-488: Is hydrophobic, unlike standard brake fluid; therefore, water-vapour bubbles do not form in the system, as would be the case with standard brake fluid, creating a "spongy" brake feel. Use of mineral oil has thus spread beyond Citroën , Rolls-Royce , Peugeot , and Mercedes-Benz , to include Jaguar , Audi , and BMW . LHM, being a mineral oil, absorbs only an infinitesimal proportion of moisture, plus it contains corrosion inhibitors. The dust inhalation problem continued, so

1445-559: Is the simplest damper and one of the most efficient. Ride height correction (self leveling) is achieved by height corrector valves connected to the anti-roll bar, front and rear. When the car is too low, the height corrector valve opens to allow more fluid into the suspension cylinder (e.g., the car is loaded). When the car is too high (e.g. after unloading) fluid is returned to the system reservoir via low-pressure return lines. Height correctors act with some delay in order not to correct regular suspension movements. The rear brakes are powered from

1530-544: Is the stiffness of suspension components (e.g. springs , shock absorbers , anti-roll bars and bushings ). Other factors include suspension geometry, vehicle mass and weight distribution . Citro%C3%ABn DS The Citroën DS ( French pronunciation: [si.tʁɔ.ɛn de.ɛs] ) is a front mid-engined, front-wheel drive executive car manufactured and marketed by Citroën from 1955 to 1975, in fastback/sedan, wagon/estate, and convertible body configurations, across three series of one generation. Marketed with

1615-419: Is thus vital. A ruptured membrane means suspension loss at the attached wheel; however, ride height is unaffected. With no springing other than the (slight) flexibility of tyres, hitting a pothole with a flat sphere can bend the suspension parts or dent a wheel rim. In the case of main accumulator sphere failure, the high pressure pump is the only source of braking pressure for the front wheels. Some older cars had

1700-519: Is to provide a sensitive, dynamic and high-capacity suspension that offers superior ride quality on a variety of surfaces. The suspension system usually features both self-leveling and driver-variable ride height , to provide extra clearance in rough terrain. Hydropneumatic suspension has a number of natural advantages over steel springs, generally recognized in the auto industry. In a hydropneumatic system, gas absorbs excessive force, whereas liquid in hydraulics directly transfers force, which combines

1785-403: Is used as the trapped gas to be compressed, since it is unlikely to cause corrosion. The actuation of the nitrogen spring reservoir is performed through an incompressible hydraulic fluid inside a suspension cylinder. By adjusting the filled fluid volume within the cylinder, a leveling functionality is implemented. The nitrogen gas within the suspension sphere is separated from the hydraulic oil by

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1870-547: The 2+2 seating configuration meant the SM as actually produced could not seize the mantle from the DS. While the design funds invested would allow the DS to be replaced by two cars, a 'modern DS' and the smaller CX , it was left to the CX alone to provide Citroën's large family or executive car in the model range. The last DS came off the production line on 24 April 1975 – with Citroën building up approximately eight months of inventory of

1955-517: The Sport setting the car's suspension was always kept in its firmest mode. In the Auto setting, the suspension was switched from soft to firm mode temporarily when a speed-dependent threshold in accelerator pedal movement, brake pressure, steering wheel angle, or body movement was detected by one of several sensors. In Hydractive 2, the preset names were changed to Sport and Normal . In this new version

2040-541: The Sport setting would no longer keep the suspension system in firm mode, but instead lowered the thresholds significantly for any of the sensor readings also used in Normal mode, allowing for a similar level of body firmness during cornering and acceleration, without the sacrifice in ride quality the Sport mode in Hydractive 1 systems had caused. Whenever the Hydractive 1 or 2 computers received abnormal sensor information, often caused by malfunctioning electrical contacts,

2125-410: The 'break'/'Safari' (estate/station wagon) version of the DS, to continue sales until the autumn of 1975 when the estate/station wagon version of the CX would be introduced. The DS maintained its size and shape, with easily removable, unstressed body panels, but design changes occurred. During the 20-year production, improvements were made on an ongoing basis. The 1955 DS19 was 65% more expensive than

2210-524: The 10 days of the show, the DS took in 80,000 deposits; a record that stood for over 60 years, until it was eclipsed by the Tesla Model 3 which received 180,000 first day deposits in March 2016. The original list price for a 1959 ID19 was US$ 2,833 ($ 29,611 in 2023 dollars). Contemporary journalists said the DS pushed the envelope in the ride vs. handling compromise possible in a motor vehicle. To

2295-531: The 1960s at Heidelberg, Victoria , identified as the ID 19 "Parisienne." Australian market cars were fitted with options as standard equipment such as the "DSpecial DeLuxe" that were not available on domestic European models. Until 1965 UK cars were assembled at the manufacturer's Slough premises, to the west of London, using a combination of French-made knock down kits and locally sourced components, some of them machined on site. A French electrical system superseded

2380-500: The 1961 Ami . It was also designed by Flaminio Bertoni and aimed to combine Three-box styling with the chassis of the 2CV. The Ami was very successful in France, but less so on export markets. Many found the styling controversial, and the car noisy and underpowered. The Dyane was a modernised 2CV with a hatchback that competed with the 2CV inspired Renault 4 Hatchback . All these 2 cylinder models were very small, so there remained

2465-644: The 1985 cc engine replaced the original 1911 cc unit in September 1965 the manual-equipped DSes built in Slough were renamed DS19A . The Slough factory closed on 18 February 1966 and thereafter cars for the British market were imported fully assembled from the company's French plant. The British-built cars are distinguished by their leather seats, wooden (early ID19 models) or one-piece plastic (early DS19 models) dashboards, chromed number plate mount set into

2550-537: The 56 kW (75 hp) claimed for the DS19. Power outputs were further differentiated in 1961 when the DS19 acquired a Weber-32 twin bodied carburettor, and the increasing availability of higher octane fuel enabled the manufacturer to increase the compression ratio from 7.5:1 to 8.5:1. A new DS19 now came with a promised 62 kW (83 hp). The ID19 was also more traditional mechanically: it had no power steering and had conventional transmission and clutch instead of

2635-462: The Activa and Activa 2, the car leaned inwards by one degree in turns – Citroën acknowledged that this was somewhat of a marketing gimmick, and that a lean of zero degrees was optimal. An additional, perhaps unexpected, benefit of active suspension is that fuel consumption and tire wear is lowered overall. The negative camber designed into most suspensions in order to maximize the size of

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2720-552: The British one on the Slough cars in 1962, giving rise to a switch to "continental style" negative earthing. An intermediate model between the DS and the ID, called the DW , was introduced on the UK market in 1963 with a manual transmission and simpler foot-operated clutch while retaining the DS power unit, power steering and power braking; outside of the UK this model was known as the DS19M . When

2805-456: The Citroën brand name as an automotive innovator, building on the success of the Traction Avant , which had been the world's first mass-produced unitary body front-wheel-drive car in 1934. In fact, the DS caused such a huge sensation that Citroën was apprehensive that future models would not be of the same bold standard. No clean sheet new models were introduced from 1955 to 1970. The DS was

2890-469: The DS was used competitively in rally racing during almost its entire 20‑year production run, and achieved multiple major victories, as early as 1959, and as late as 1974. It placed third in the 1999 Car of the Century poll recognizing the world's most influential auto designs and was named the most beautiful car of all time by Classic & Sports Car magazine. The name DS and ID are puns in

2975-472: The DS's hydraulically controlled set-up. Initially, the basic ID19 was sold on the French market with a price saving of more than 25% against the DS, although the differential was reduced at the end of 1961 when the manufacturer withdrew the entry-level ID19 "Normale". A station wagon variant, the ID Break , was introduced in 1958. The ID was replaced by the D Spécial and D Super in 1970, but these retained

3060-653: The DS. The SM was not designed to be a practical 4-door saloon suitable as a large family car , the key market for vehicles of this type in Europe. Typically, manufacturers would introduce low-volume coupés based on parts shared with an existing saloon, not as unique models, a contemporary example being the Mercedes-Benz SLC (C107) . BMW follows a similar strategy of a mid-size sedan (5 series), large coupe (6 series), and large sedan (7 series) sharing common underpinnings. The SM's high price and limited utility of

3145-483: The French language. "DS" is pronounced exactly like déesse , lit.   ' goddess ' , whereas "ID" is pronounced as idée ('idea'). After 18 years of secret development as the successor to the Traction Avant , the DS 19 was introduced on 6 October 1955, at the Paris Motor Show . In the first 15 minutes of the show, 743 orders were taken, and orders for the first day totalled 12,000. During

3230-407: The Hydractive 3 suspension calculates the optimum vehicle height, using the following information: The 3+ Hydractive hydraulic suspension has 3 automatic modes: The BHI of the 3+ Hydractive suspension calculates the optimum vehicle height, using the following information: C5 I (2001–2004) C5 II (2004–2007) C6 (2005–2012) C5 III X7 (2007–2017) Ride quality Ride quality refers to

3315-558: The SC/MAC sphere, it often became known as the 'anti-sink' sphere, because of its ability to better maintain rear suspension height. The 2001 Citroën C5 has continued development of Hydractive suspension with Hydractive 3. Compared to earlier cars, the C5 stays at normal ride height even when the engine is turned off for an extended period, through the use of electronics. The C5 also uses orange synthetic hydraulic fluid named LDS fluid in place of

3400-527: The U.S. in 1934 by Cleveland Pneumatic Tool Co. Similar systems are also widely used on modern tanks and other large military vehicles. Hydractive Suspension is an automotive technology introduced by Citroën in 1990. The prototype debuted in 1988 on the Citroën Activa concept. It describes a development of the 1954 hydropneumatic suspension design using additional electronic sensors and driver control of suspension performance. The driver can make

3485-537: The United States, and little better in Canada. While promoted as a luxury car, it did not have the basic features that American buyers expected to find on such a vehicle, such as an automatic transmission , air conditioning , power windows , or a powerful engine. The DS was designed specifically to address the French market, with punitive tax horsepower taxation of large engines and very poor roads, and not for

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3570-451: The advantages of two technological principles : Suspension and springing technology is not generally well understood by consumers, leading to a public perception that hydropneumatics are merely "good for comfort". They also have advantages related to handling and control efficiency, solving a number of problems inherent in steel springs that suspension designers have previously struggled to eliminate. Although auto manufacturers understood

3655-446: The air, which caused corrosion in the system. Most hydraulic brake systems are sealed from the outside air by a rubber diaphragm in the reservoir filler cap, but the Citroën system had to be vented to allow the fluid level in the reservoir to rise and fall, thus it was not hermetically sealed. Consequently, each time the suspension would rise, the fluid level in the reservoir dropped, drawing in fresh moisture-laden air. The large surface of

3740-450: The application of the hydraulic system to the car's suspension system to provide a self-levelling system was an innovative move. This suspension allowed the car to achieve sharp handling combined with very high ride quality , frequently compared to a " magic carpet ". The hydropneumatic suspension used was pioneered the year before, on the rear of another car from Citroën, the top of range Traction Avant 15CV-H. The 1955 DS cemented

3825-407: The brake control or height corrector valves, also catching seeping fluid around the suspension push-rods. Height corrector, brake master valve and steering valve spools, and hydraulic pump pistons have extremely small clearances (1–3 micrometres) within their cylinders, permitting only a very low leakage rate. The metal and alloy parts of the system rarely fail, even after excessively high mileages, but

3910-577: The car it replaced, the Citroën Traction Avant . This affected potential sales in a country still recovering economically from World War II, so a cheaper submodel, the Citroën ID, was introduced in 1957. The ID shared the DS's body but was less powerful and luxurious. Although it shared the engine capacity of the DS engine (at this stage 1,911 cc), the ID provided a maximum power output of only 51 kW (69 hp) compared to

3995-412: The car's suspension system would be forced into its firm setting for the remainder of the ride. Starting with Xantia model year 1994 and XM model year 1995, all models featured an additional sphere and valve that together functioned as a pressure reservoir for rear brakes because of new hydraulic locks, letting the car retain normal ride height for several weeks without running the engine. Correctly called

4080-477: The car, but did not have the funds to put the prototype engine into production. The DS placed third in the 1999 Car of the Century competition, and fifth on the 2005 list of "100 Coolest Cars" by Automobile Magazine . It was also named the most beautiful car of all time by Classic & Sports Car magazine after a poll of 20 world-renowned car designers, including Giorgetto Giugiaro , Ian Callum , Roy Axe , Paul Bracq , and Leonardo Fioravanti . The DS

4165-456: The car, said that it looked as if it had "fallen from the sky". An American advertisement summarised this selling point: "It takes a special person to drive a special car". Because they were owned by the technologically aggressive tyre manufacturer Michelin , Citroën had designed their cars around the technologically superior radial tyre since 1948, and the DS was no exception. The car used double wishbone suspension with L-shaped arms at

4250-468: The cars, making them radically different from ordinary cars with common mechanicals. France was noted for the poor quality of its roads after World War II , but the hydropneumatic suspension as fitted to the Citroën ID/DS and later cars reportedly ensured a smooth and stable ride there. Hydropneumatic suspension offers no natural roll stiffness. There have been many improvements to the system over

4335-415: The company's high standard of innovation . As Citroën was owned by Michelin from 1934 to 1974 as a sort of research laboratory, such broad experimentation was possible. Michelin was getting a powerful advertisement for the capabilities of the radial tyre Michelin had invented, when such experimentation was successful. New models based on the small, utilitarian 2CV economy car were introduced, such as

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4420-501: The contact patch when turning leads to tire scrub, which wears out tires and increases fuel consumption. Citroën Hydractive (and later Hydractive 2) suspension was available on several models, including the XM and Xantia , which had a more advanced sub-model known as the Activa . The first Hydractive suspension systems (now known as Hydractive 1) had two user presets, Sport and Auto . In

4505-529: The curve outward and so it is possible to offer vehicles that are extremely comfortable and still handle very well or vehicles with excellent handling that are also reasonably comfortable. One technical solution for offering both excellent comfort and reduced or eliminating body roll is by using computer-controlled suspensions, such as hydraulic active suspension system (like Active Body Control ) or active anti-roll bars, but such systems are expensive because of their complexity. The main factor affecting ride quality

4590-468: The drive to a matching recess in the wheel. This made it possible to change the wheel very quickly in the event of a puncture and proved an advantage in motor racing . As with all French cars, the DS design was affected by the tax horsepower system, which effectively encouraged smaller engines. Unlike the Traction Avant predecessor, there was no top-of-range model with a powerful six-cylinder engine. Citroën had planned an air-cooled flat-6 engine for

4675-402: The driver's ability to control the vehicle. Suspension design is often a compromise between ride quality and car handling because cars with firm suspension can result in greater control of body movements and quicker reactions. Similarly, a lower center of gravity is more ideal for handling, but low ground clearance limits suspension travel and requires stiffer springs. Ambulances have

4760-454: The elastomer components (especially those exposed to the air) can harden and leak, typical failure points for the system. Spheres are not subject to mechanical wear, but suffer pressure loss, due to the pressurised nitrogen diffusing through the membrane. They can, however, be recharged, which is cheaper than replacing them. When Citroën designed their Hydractive 3 suspension they redesigned the spheres with new nylon membranes, which greatly slow

4845-405: The engine, pressurizes the hydraulic fluid (LHM – liquide hydraulique minéral) and an accumulator sphere maintains a reserve of hydraulic power. This part of the circuit is at between 150 and 180 bars. It powers the front brakes first, prioritised via a security valve, and depending on type of vehicle, can power the steering, clutch, gear selector, etc. Pressure flows from the hydraulic circuit to

4930-433: The entire event. In conventional cars, hydraulics are only used in brakes and power steering . In the DS they were also used for the suspension, clutch, and transmission. The cheaper 1957 ID19 did have manual steering and a simplified power braking system. An engine-driven pump pressurizes the closed system to 17.2 MPa (2,490 psi) At a time when few passenger vehicles had independent suspension on all wheels,

5015-401: The fluid in the reservoir readily absorbed moisture. Since the system recirculates fluid continually through the reservoir, all the fluid was repeatedly exposed to the air and its moisture content. To overcome these shortcomings of LHS, Citroën developed a new green fluid, LHM ( Liquide Hydraulique Minéral ). LHM is a mineral oil , quite close to automatic transmission fluid . Mineral oil

5100-518: The front and trailing-arms at the rear, with totally novel hydropneumatic spring and damper units . The car's advanced hydraulics included automatic self-levelling and driver adjustable ride-height , developed in-house by Paul Magès . This suspension allowed the DS to travel quickly on the poor road surfaces then common in France. In addition, the vehicle had power steering and a semi-automatic transmission (the transmission required no clutch pedal but gears still had to be shifted by hand, with

5185-661: The front bumper, and (on pre-1962 cars) Lucas -made electrics. These were all right hand drive cars. The DS was built and sold in South Africa from 1959 to 1975. The DS was sold in Japan, but the models were built in France and left hand drive . The DS was sold in North America from 1956 to 1972. Despite its popularity in Europe and regard for its design from the American motoring press, it did not sell well in

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5270-408: The front fenders. All models in the range changed nose design at the same time, including the ID and station wagon models. In late 1967, for the 1968 model year, the DS and ID was again restyled, by Robert Opron , who also styled the 1970 SM and 1974 CX. This version had a more streamlined headlamp design. This design had four headlights under a smooth glass canopy and the inner set swivelled with

5355-539: The green LHM mineral oil used in millions of hydropneumatic vehicles. A further improved Hydractive 3+ variation was for cars with top engines on the Citroën C5 and in 2005 was standard on the Citroën C6 . Hydractive 3+ systems contain additional spheres that can be engaged and disengaged via a Sport button, resulting in a firmer ride. The Hydractive 3 hydraulic suspension has 2 automatic modes: The BHI of

5440-476: The inherent advantages over steel springs, there were two problems. First, it was patented by the inventor, and second it had a perceived element of complexity, so automakers like Mercedes-Benz , British Leyland ( Hydrolastic , Hydragas ), and Lincoln sought to create simpler variants using a compressed air suspension . Citroën 's application of the system had the disadvantage that only garages equipped with special tools and knowledge were qualified to work on

5525-452: The lower specification position in the range. The D Super was available with the DS21 2175 cc engine and a 5-speed gearbox, and named the D Super 5. In September 1962, the DS was restyled with a more aerodynamically efficient nose, better ventilation, and other improvements. It retained the open two headlamp appearance, but was available with an optional set of driving lights mounted on

5610-511: The rate of deflation. These are recognisable by their grey colouring. Classic (non-saucer) green- (and grey-) coloured suspension spheres typically last between 60,000 and 100,000 km. Spheres originally had a threaded plug on top for recharging. Newer ('saucer') spheres do not have this plug, but it can be retrofitted, enabling them to be recharged with gas. The sphere membrane has an indefinite life unless run at low pressure, which leads to rupture. Timely recharging, approximately every 3 years,

5695-427: The rear suspension circuit. Because the pressure there is proportional to the load, so is the braking power. Citroën quickly realized that standard brake fluid was not ideally suited to high pressure hydraulics, and developed a special red-coloured hydraulic fluid named LHS ( Liquide Hydraulique Synthétique ), which they used from 1954 to 1967. The chief problem with LHS was that it absorbed moisture and dust from

5780-417: The same company. Other modifications followed, with design changes such as the 1960 "Double stage oleo-pneumatic shock absorber" patented by Peter Fullam John and Stephan Gyurik. Major milestones of the hydropneumatics design were: At the heart of the system, acting as pressure sink as well as suspension elements, are the so-called spheres, five or six in all; one per wheel and one main accumulator as well as

5865-406: The same design. Axles, wheel bearings, steering knuckles, and hydraulic components were either DS parts or modified DS parts. The SM had a different purpose than replacing the 15-year-old DS design, however – it was meant to launch Citroën into a completely new luxury grand touring market segment . Only fitted with a costly, exotic Maserati engine, the SM was faster and much more expensive than

5950-454: The seals. Using either fluid in the incorrect system would completely destroy the hydraulic seals very quickly. To help avoid this problem, Citroën added a bright green dye to the LHM fluid and also painted all hydraulic elements bright green. The earlier LHS parts were painted black. All models, including the station wagon and ID, were upgraded at the same time. The hydraulic fluid changed to

6035-498: The shift lever controlling a powered hydraulic shift mechanism in place of a mechanical linkage). It had a fibreglass roof which lowered the centre of gravity, and so reduced weight transfer . Inboard front disc brakes (as well as independent suspension) reduced unsprung weight. Different front and rear track widths reduced the unequal tyre loading, which is well known to promote understeer , typical of front-engined and front-wheel drive cars. Although disc brakes had been tried on

6120-536: The steering wheel. This allowed the driver to see "around" turns, especially valuable on twisting roads driven at high speed at night. The directional headlamps were linked to the wheels by cable. Behind each glass cover lens, the inboard high-beam headlamp swivels by up to 80° as the driver steers, throwing the beam along the driver's intended path rather than uselessly across the curved road. The outboard low-beam headlamps are self-leveling in response to pitching caused by acceleration and braking. Because this feature

6205-415: The suspension cylinders, pressurizing the bottom part of the spheres and suspension cylinders. Suspension works by means of a piston forcing LHM into the sphere, compressing the nitrogen in the upper part of the sphere; damping is provided by a two-way 'leaf valve' in the opening of the sphere. LHM has to squeeze back and forth through this valve which causes resistance and controls the suspension movements. It

6290-412: The suspension extended to maximum height and the six accumulators in the system filled with fluid. With every "inhalation" of fresh moisture- (and dust-) laden air, the fluid absorbed more water. For the 1967 model year, Citroën introduced a new mineral oil -based fluid LHM ( liquide hydraulique minéral ). This fluid was much less harsh on the system. LHM required completely different materials for

6375-416: The suspension stiffen (sport mode) or ride in outstanding comfort (soft mode). Sensors in the steering, brakes, suspension, throttle pedal and gearbox feed information on the car's speed, acceleration, and road conditions to an on-board computer, which in turn activates or deactivates an extra pair of suspension spheres on the circuit, to enable either a more smooth supple ride or tighter handling in corners. On

6460-464: The system is manufactured from steel tubing of small diameter, connected to valve control units by Lockheed type pipe unions with special seals made from Desmopan, a type of polyurethane thermoplastic compatible with the LHM fluid. The moving parts of the system, e.g. , suspension strut or steering ram, are sealed by contact seals between the cylinder and piston for tightness under pressure. The other plastic/rubber parts are return tubes from valves such as

6545-668: The technically superior LHM in all markets except the US and Canada, where the change did not take place until January 1969 due to local regulations. The DS was primarily manufactured at the Quai André-Citroën in the Javel neighborhood of Paris, with other manufacturing facilities in the United Kingdom, South Africa, the former Yugoslavia (mostly Break Ambulances), and Australia. Australia constructed their own D variant in

6630-542: The wrong type of fluid is used, the system must be drained and rinsed with Hydraflush (Total's Hydraurincage), before draining again and filling with the correct fluid. These procedures are clearly described in DIY manuals obtainable from automotive retailers. The latest Citroën cars with Hydractive 3 suspension have a new orange coloured LDS hydraulic fluid. This lasts longer and requires less frequent attention. It conforms to DIN 51524-3 for HVLP. The whole high pressure part of

6715-434: The years, including steel anti-roll bars , variable ride firmness ( Hydractive ), and active control of body roll ( Citroën Activa ). This system uses a belt- or camshaft-driven pump from the engine to pressurise a special hydraulic fluid , which then powers the brakes , suspension and power steering . It can also power any number of features such as the clutch , turning headlamps and even power windows . Nitrogen

6800-475: Was 1970. Certain design elements like the somewhat narrow cabin, column-mounted gearstick , and separate fenders began to seem a little old-fashioned in the 1970s. Citroën invested enormous resources to design and launch an entirely new vehicle in 1970, the SM , which was in effect a thoroughly modernized DS, with similar length, but greater width. The manual gearbox was a modified DS unit. The front disc brakes were

6885-425: Was also used on Berliet trucks and has been used on Mercedes-Benz cars, where it is known as Active Body Control . The Toyota Soarer UZZ32 "Limited" was fitted with a fully integrated four-wheel steering and a complex, computer-controlled hydraulic Toyota Active Control Suspension in 1991. Similar systems are also widely used on modern tanks and other large military vehicles. The purpose of this system

6970-426: Was inspired by the pneumatic suspension used for aircraft landing gear, which was also partly filled with oil for lubrication and to prevent gas leakage, as patented in 1933 by the same company. The principles illustrated by the successful use of hydropneumatic suspension are now used in a broad range of applications, such as aircraft oleo struts and gas filled automobile shock absorbers . Hydropneumatic suspension

7055-577: Was involved with DS competition again two years later, when a drunk driver in a Mini in Sydney Australia crashed into the DS that was leading the 1968 London–Sydney Marathon , 158 km (98 mi) from the finish line. Robert Neyret won the Rallye du Maroc in 1969 and 1970 in a DS 21. The DS was still competitive in the grueling 1974 London-Sahara-Munich World Cup Rally , where it won over 70 other cars, only 5 of which even completed

7140-452: Was not allowed in the US (see World Forum for Harmonization of Vehicle Regulations ), a version with four exposed headlights that did not swivel was manufactured for the US market. Although a directional headlight was previously seen on the 1948 Tucker 48 'Torpedo', Citroën was the first to mass-market adaptive headlights. The original hydropneumatic system used a vegetable oil ( liquide hydraulique végétal , LHV), but later switched to

7225-465: Was successful in motorsports like rallying , where sustained speeds on poor surfaces are paramount, and won the Monte Carlo Rally in 1959. In the 1000 Lakes Rally , Pauli Toivonen drove a DS19 to victory in 1962. In 1966, the DS won the Monte Carlo Rally again, with some controversy as the competitive BMC Mini -Cooper team was disqualified due to rule infractions. Ironically, Mini

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