Citroen C-Cactus Concept, 2007

 

 

 

 

• Citroen C-Cactus Concept, 2007

Citroën is unveiling C-Cactus at the 2007 Frankfurt Motor Show. This ingenious concept is a new take on vehicle design, centered on essential values. The Marque's ambitious aim is to market an ecological hatchback with cheerful, attractive styling, equipped with a hybrid HDi drivetrain and sold at the same price as an entry-level C4.

To square this complex equation, Citroën is exploring new forms of design. It has decided to abandon features that are not essential to comfort and to focus instead on technology, styling and equipment that are positive, ecological and valued by users.

Essential, intelligent and ecologically aware
C-Cactus is an ecological car. It includes a significant proportion of recycled or recyclable materials and, like the plant it is named after, it is low on consumption. Weighing just 1,306 kg and featuring a hybrid HDi drivetrain, C-Cactus consumes 3.4 l/100 km for CO2 emissions of 78 g/km.

At the same time, C-Cactus is no more expensive than a mid-range family car. Its low production cost can be attributed to the use of new materials and to a rational design process using a smaller number of parts. The cabin is made up of just over 200 parts, i.e. almost half the number used by a conventional hatchback of identical size.

An attractive and modern vehicle
C-Cactus is an essential car, with sharp styling and attractive features. Its curves give it a fun look and strong appeal, while the angles and rounded lines of the bodywork underline its dynamic character.

C-Cactus sets high standards of onboard comfort with a roomy interior that is worthy of a family car. It is 4.2 metres long and 1.8 metres wide with a wide range of equipment including air conditioning with automatic temperature control, a high-quality audio system, a panoramic glass sunroof, cruise control and a speed limiter.

The economic and ingenious solutions adopted for C-Cactus keep production costs down and make it possible to fit a diesel hybrid drivetrain, all for the price of an entry-level C4. To achieve this result, C-Cactus places the emphasis on equipment that is essential to passenger comfort. At the same time, it explores new design processes in order to show that economy and ecology need not be synonymous with a rough ride.

New avenues in design
C-Cactus is the result of an intelligent design process pursuing new objectives. By exploring new forms of expression and new technical solutions, Citroën's engineers cut the number of parts required to build the car.

To achieve this objective, the engineers:
    * simplified a number of parts and mechanisms to the extreme,
    * grouped several functions in a single part,
    * removed all parts that are non-essential to the running of the car or to the comfort and well-being of its occupants.

The dashboard has gone, and its usual functions are now grouped on the central console and the fixed hub of the steering wheel. The central console thus includes the active loudspeakers, gearbox controls and tactile screen giving access to the onboard computer, navigation system and air conditioning controls. The controls for the indicators, lights, wipers, horn and cruise control/speed limiter are on the fixed hub of the steering wheel, as are the tachometer and lights for the indicators, headlamps and warning signals.

Another example of simplification: the part used for the front bumper, which includes the headlamps and chevrons is the same as the part making up the lower part of the tailgate at the rear. This contributes to the assertive design of C-Cactus while bringing economies of scale in production.

The simplicity is also reflected in the design of the front end, which comprises just two parts: a fixed bonnet comprising the front wings, and a flap giving access to the vehicle maintenance functions (oil, windscreen washer, etc.).

Reflecting a similar approach, using the air conditioning makes it virtually unnecessary to open the windows. A simple sliding mechanism is therefore provided, since this is sufficient in normal use. Engineers were thus able to get rid of both the window frames and the opening mechanism.

A number of monoblock units are used for C-Cactus to reduce the overall number of parts. The door panels, for example, are made of two parts, compared with twelve in a conventional hatchback. The seats also comprise two parts: a highly comfortable, moulded, coloured, integral-skin foam part for the seat, and a solid monoblock frame to hold the foam in place and fix the seat to the floor rails. The ergonomics are excellent and - here again - the number of components is limited.

Advanced ecological features
To achieve real environmental impact, Citroën's objective has always been to market technologies and vehicles that are affordable to the greatest number. The objective with C-Cactus is to go one step further, by bringing out a car whose hybrid HDi drivetrain makes it truly ecological car, but that can be sold at the same price as an entry-level family car.

With its diesel hybrid drivetrain combining a 70 bhp DIN HDi diesel engine with a particulate filter and an electric motor providing additional power of 30 bhp DIN, C Cactus consumes just 3.4l/100 km with CO2 emission levels of 78 g/km over a combined cycle. In urban use, ZEV (Zero Emission Vehicle) mode provides silent, all-electric operation. On journeys involving successive acceleration and deceleration, the hybrid system limits fuel consumption by using both types of energy.

Other points also help to make C-Cactus a car that respects the environment.
The solutions adopted for the design of C-Cactus also contribute to bringing down fuel consumption and CO2 emissions. Using fewer parts makes the vehicle 15% lighter than a C4 Hybride HDi for a total weight of 1,306 kg.

The tyre width has also been kept down (205/45 R21) on C-Cactus, which adds to environmental performance.

Fewer parts also means smaller quantities of raw materials. In addition, a significant part of the materials used are recycled or recyclable. The windscreen and windows, for example, are made of recyclable glass. The tyres are also recyclable, as is the crude steel used for the door panels. This metal is unpainted and unvarnished but has been treated for corrosion.

The protective mats are made of recycled leather, taken from leather cut-offs that cannot be used by conventional tanneries. Many parts are made of cork, a natural material made from the bark of oak trees. The felt used for the door panels and fascia stowage compartments is made from wool. This material uses no chemical additives and is both recyclable and biodegradable.

The top speed of C-Cactus has deliberately been capped at 150 kph. This choice not only contributes to the car's good environmental performance, it also reflects Citroën's efforts to develop a green vehicle illustrating a new approach to the car, in which the motorist is in harmony with his/her surrounding environment.

Based on the bold but rational use of parts and materials, C-Cactus is an essential vehicle reflecting a new vision of the car focused on:
    * a new balance of priorities, and a design that pursues the essential without sacrificing comfort,
    * a design in which ecology and economy are synonymous not with dullness, but with expression and pleasure.

Through this attractive concept with its appealing offbeat styling, Citroën has developed a new take on the economical and ecological car. A vehicle at ease with its original and ingenious design. At the same time, this is a car that brings the occupants all the features essential for their comfort.

Looking for simplicity: intelligent, fun exterior design
C-Cactus has a unique personality: appealing, modern and offbeat, with its simple shapes and mix of round, curving lines. The original styling also reflects ingenious design choices. Throughout the design process, the focus was very much on simplicity. This led to the development of ingenious solutions that contribute to the attractive offbeat design of C-Cactus.

At the front, the headlamps of C-Cactus give the vehicle an appealing air with their rounded and slightly angular forms. They are underlined by two cylindrical air intakes cut out of the bumper, above an air intake grille of modern design which, while contributing to the vehicle's rounded forms, also adds a muscular energetic touch. The raised bonnet and two air intakes also contribute to the dynamic looks of C Cactus.

The vehicle's rounded forms are reflected in its profile. The dynamic design lines are accentuated by the forward flowing roof line and the asymmetric doors made of crude steel that has been treated for corrosion.

The doors feature an original cut-out since the fixed windows remove a number of the constraints that usually apply to design. Shaped to provide easy access to the interior, they give C-Cactus a curving, sleekly muscled appearance. The use of crude steel treated for corrosion, but without paint or varnish, contributes to savings in production costs while giving a strong, contemporary look.

The high waistline and 21-inch wheels also underline the strong character of C Cactus. The wheels were the focus of particular attention. Large-diameter wheels and low-profile tyres have become key styling features in vehicles of strong, contemporary design. Citroën worked with Michelin on the development of low-profile tyres with a large diameter and limited width. The low ground friction area limits fuel consumption and, at the same time, tyre production costs are kept under control since the manufacturing process requires only a small amount of rubber. For new and even more original styling, these specially designed tyres feature a green pattern on a white background printed inside a wide groove spanning the entire tread.

The same styling codes can be seen at the rear, where a combination of curves and taut lines illustrate the car's dynamic and appealing personality. The chevrons identify this car as a Citroën. The name "Cactus" appears in relief on the bottom of the tailgate, in a young, smooth, modern printface. The rear lights, which resemble the headlamps in shape, boast an innovative feature: cut-outs in the interior plastic that let the driver see through. This innovation considerably increases the driver's field of vision and may be particularly useful in manoeuvres, for example.

Fewer features for greater impact: a welcoming, attractive and cleverly designed interior
C-Cactus is also an original and ingenious car on the inside. The design cut-outs, choice of materials, patterns and colours give the cabin a minimalist, attractive and airy look.

The cabin materials reflect innovative choices. Their quality is immediately visible. Looking beyond their appearance, they are also economical and ecological. For example, cork is used for many decorative parts, as well as for the air vents and air conditioning panel. The floor features a pattern in recycled leather. The white lacquer finish of some parts and the visual effects created by the materials used contribute to the original design and perceived quality of the cabin.

Another key idea was to enhance the offbeat styling of C-Cactus by reducing the number of parts and the quantity of materials used for the decor.

Non-essential parts, such as the dashboard, are absent, while some of the parts that are usually hidden have been included in the decor. This is the case, for example, of the steering column, air conditioning ducts and the grid for fore-and-aft adjustment of the front seats. These features add a modern and original touch to the cabin. The refill for the scented air freshener is also visible. It contributes to the attractive appearance of the cabin, while enabling the driver to see how much is left.

The decor has not been put in. It has been created by removing material. This idea of decorating "in a vacuum" is reflected in the patterns present on the door panels and seat frames. The patterns cut-out in the door panels show the apple green felt inserted between panel and metal. The main role of this part is to soundproof the vehicle, but its colour and cut-outs make it an integral part of the décor. The same flower, plant and butterfly patterns - symbolising the environment, purity and well-being - are also found on several other cabin features. They are cut out, for example, in the white lacquer seat frame. These cut-outs show the coloured foam used for the seat cushions and give it a decorative quality.

Pertinent choices for an easy and enjoyable ride
C-Cactus boasts advanced equipment, optimised on-board space and modular design at an affordable price. Passengers have all the comfort essential to their well-being.

First, the ignition key of C-Cactus is a portable MP3 player with a touch screen. When it is plugged into the fixed hub of the steering wheel, it is recognised by the vehicle which can then be started. The fixed-hub steering wheel includes a wide variety of functions. In addition to the usual controls, it also includes the speedometer, which is of an unusual design. The figures, placed in relief around the hub, rotate according to speed and are positioned with respect to a fixed point.

A second touch screen on the central console includes a navigation system to guide the driver on the road. It also serves as an onboard computer. This equipment endows C-Cactus with high-tech advanced features while also keeping costs down, since functions are grouped together.

The central console features two powerful high-quality active loudspeakers that provide C-Cactus with an excellent sound system. Their ingenious layout limits both wiring and installation costs.

Generous interior space ensures passenger comfort. C-Cactus boasts the dimensions of a family car (4.2 metres long and 1.8 metres wide) with a generous and modular boot (between 500 and 1,100 litres). The rear seat, placed on a rail, slides up against the front seats. The floor pan, which is integral with the rear bench, also slides forward to reveal a subfloor. This reveals a virtually flat surface area to load bulky objects.

Another ingenious feature is a clip-on bag on the passenger side. This replaces the glovebox and can be used to carry objects outside the car.
For comfort and styling, C-Cactus features a panoramic glass sunroof that lets the light flood into the cabin.

Citroen C5 Airscape Concept, 2007

 

 

Citroen C5 Airscape Concept, 2007

The Citroen is unveiling C5 Airscape at the 2007 Frankfurt Motor Show. This exceptional concept car is a new take on the most beautiful of vehicles, the cabriolet.

C5 Airscape features powerful, dynamic exterior styling and an interior of exclusive design, made for driving pleasure and the comfort of three passengers. The original mechanism of the folding roof underlines the overall sophistication of design.

Styled for maximum appeal, C5 Airscape also delivers maximum performance. New-generation Snow Motion traction control provides a level of traction close to that of a four-wheel drive. Other useful features are provided by the UrbanHybrid system. This unit prevents noise and vibration when the engine stops and boosts engine torque when needed. At the same time, it shows real respect for the environment.

An expression of power and elegance
C5 Airscape is a car to turn heads. Its elegant proportions and sleek bodywork convey a sense of performance with a promise of power. The innovative folding top is an invitation to climb on board and take to the road. The interior layout, with its premium materials, delivers the highest standards of on-board comfort for the driver and all the passengers

Power and sophistication
A car of elegant lines, C5 Airscape conveys an impression of strength and sophistication, with its cleanly drawn body lines and ribbing at the top. The powerful look of the body is brought out by the raw, intense grey of the bodywork. This colour, whose intensity varies according to the light, gives C5 Airscape an elegant and precious look, consolidating its status as an executive vehicle.

Through its assertive front end, featuring large air intakes and long incisive headlamps, C5 Airscape makes a statement of performance. The headlamps - positioned on the bonnet with its two pronounced ribs - flank the large chrome chevrons stating Citroen's identity.

The profile of C5 Airscape reflects efforts to achieve optimal aerodynamic design. The roof line, particularly large windows and tapering chrome-plated door handles underline the flowing lines of the body, while the high waistline, clearly marked wheel arches and 19-inch wheels clearly identify C5 Airscape as a vehicle of status.

The powerful design of the front and rear ends highlight the on-road stance of C5 Airscape. The high-positioned rear lights extend the waistline and optimise the vehicle's dynamic looks. At the same time, a double chrome tail pipe underlines the car's luxurious design as does the concave rear window, which clearly identifies C5 Airscape as belonging to the family of large Citroen saloons.

The sophistication of C5 Airscape can also be seen in the original design of the folding roof, whose glazed upper part lets light flood into the cabin. Made entirely of carbon, this roof opens and folds away simply, without detracting from the looks of the concept car. It folds away automatically, without assistance, and without the driver having to open the upper part of the roof storage area in the boot. C5 Airscape reflects the purest traditions in vehicle design in that the metal-look roof with its textile lining resembles a roof made of canvas - the emblematic signature of executive cabriolets.

Leisure and sophistication
Fully upholstered in dark brown leather, the cabin of C5 Airscape conveys an appealing impression of sophistication. The particularly well designed seats suggest luxury and precision. The central section of the seats brings to mind the links of a watch strap, while the decorative stitching on the edges of the seats reinforces the taut, well-muscled look of the whole. To add the finishing touch to the executive design of the interior, the gear lever knob is set with leather and chrome. The chrome echoes the metal strip underlining the air conditioning controls and central console.

The design of the driving position on C5 Airscape was also dictated by the pursuit of driving pleasure. Refinement is the key word for the driver's surroundings, as reflected in the specific design of the instruments and their layout.

The driving position features a fixed-centred controls steering wheel that brings the main comfort functions and driving aids (navigation, radio, cruise control and speed limiter, on-board computer) within easy reach. Considered as points of contact, the pushbuttons feature an original covering resembling the texture of skin. They create a strong, fast-reacting sensory interface between the vehicle and the driver.

The sophisticated design of the instrument cluster on C5 Airscape reflects the requirements of optimised ergonomics and ensures that information is laid out legibly. The three dials feature annular needles, symbolising an advanced level of technology. The needles run around rather than across the dial for greater legibility and a more attractive design.

The air vents next to the dials underline this cabriolet's powerful character, as does the upper part of the instrument cluster, which takes the form of an air intake as on a competition car. The overall effect is enhanced by the clean, sculpted design of the dashboard. Its straight lines symbolise precision, while the soft curves symbolise dynamic performance. This configuration contributes to full driver control and exceptional driveability.

Driving sensations and improved respect for the environment
Styled for maximum appeal, C5 Airscape also delivers maximum performance. This concept vehicle is equipped with a V6 HDi engine associated with a particulate filter and able to run on biodiesel, along with an innovative Snow Motion traction control system for a performance close to that of a four-wheel drive, and UrbanHybrid technology for low fuel consumption and CO2 emissions. As a result, C5 Airscape boasts remarkable levels of performance that show real respect for the environment.

The technology serving the environment
Through its powerful engine, particulate filter and UrbanHybrid system, C5 Airscape illustrates Citroen's ability to reconcile vehicle performance with respect for the environment.

With its reversible alternator-starter and super-capacitors able to temporarily store large amounts of energy, the UrbanHybrid system delivers real benefits in terms of environmental protection, driving pleasure, acoustic comfort and vibration control.

In Drive mode, when this concept vehicle is travelling at under 6 kph and the driver's foot is on the brake pedal, the engine cuts out. For maximum driveability, it starts again instantly and automatically as soon as the driver releases the brake pedal. When the car is at a standstill, fuel consumption is zero and CO2 emissions are around 24 g over a combined cycle. Further, the onboard network (air conditioning, radio etc.) is powered by energy recovered during the deceleration and braking phases. This brings savings in fuel consumption and eliminates additional pollutant emissions.

Engine torque can be temporarily boosted, when overtaking for example, for a high-speed take-off.
When the car is at a standstill, the UrbanHybrid system prevents noise and vibration in the cabin, for the comfort of both passengers and passers-by.

Driveability and performance in all circumstances
The executive positioning of C5 Airscape is reflected by the presence of the 208 bhp 2.7 V6 HDi engine and particulate filter. Combining power and fuel economy, this engine develops 150 kW EEC (208 bhp DIN) at 4,000 rpm for torque of 440 Nm at 1,900 rpm. Right from the lowest speeds, it delivers smooth, gradual power with exceptional operating comfort. Driveability is further increased by a 6-speed automatic gearbox.

To deliver a high level of performance and improve active safety, C5 Airscape features Snow Motion, an innovative traction control system with extended functions. This system offers remarkable performance in terms of vehicle traction and "take-off" on surfaces with low grip, such as snow for example. The benefits, already significant with conventional tyres, are further increased when the concept car is shod with winter tyres. In this configuration, the performance of C5 Airscape is close to that of a four-wheel drive.

Taking the wheel of C5 Airscape is a total and continuous experience in driving pleasure. This is a car that brings leisure within easy reach.

Citroen C4 Picasso, 2007

 

Citroen C4 Picasso, 2007

The 5 seat C4 Picasso slips naturally into Citroën's compact MPV range between the established, best-selling Xsara Picasso and the award-winning seven seat version, which will now be known as the Grand C4 Picasso. With three compact MPVs and the full-size C8 people carrier, Citroën now boasts the broadest MPV range in its history.

The new 5 seat C4 Picasso benefits from the same forward thinking that shaped the design of the recently launched Grand C4 Picasso, with outstanding all-round visibility, a light and airy interior, leading cabin and boot space, incorporating a new version of Citroën's Modubox folding trolley, and the use of high quality materials. The easy-to-use and flexible interior lay-out combines with the uncluttered interior space and the highest levels of comfort to ensure that travelling is a pleasurable experience.

The interior of Citroën's newcomer is refreshingly light, with outstanding visibility provided by the huge windscreen, slim pillars and optional panoramic sunroof. Artificial lighting also plays a major role with the availability of various useful features, such as automatic welcome lights under the door mirrors, a portable torch in the boot and reading lights on the back of the front seats, all designed to make journeys easier.

The exterior dimensions (4.47m long, 1.83m wide and 1.66m tall) give the C4 Picasso an extremely spacious interior. This feeling of space is enjoyed by all passengers, with those in the front benefiting from the simple, uncluttered design of the dash, and those in the back from three individual, full-size seats and a flat floor. The innovative seating design, first seen in the Grand C4 Picasso, allows the rear seats to be quickly and easily folded flat into the floor.

When all 5 seats are in use, the new model leads the class with 500 litres of boot space underneath the luggage cover, extending to a maximum 1,734 litres once the rear seats are folded down. Helping to keep the boot tidy, the five seat C4 Picasso can also be equipped with a new version of Citroën's renowned Modubox. This innovative, removable trolley makes it easy to divide boot space and to transport objects outside of the vehicle.

The new 5 seat C4 Picasso provides a relaxing journey for all occupants. Suspension comfort can be further enhanced by the optional pneumatic rear suspension, while laminated acoustic side windows can be specified to make it even quieter inside. An automatic electronic parking brake and Hill Start Assist are fitted as standard and make everyday driving easier.

Thoughtful extras such as individual air flow controls for back seat passengers, an air quality sensor and a scented air freshener can all add to the pleasant onboard atmosphere. A high quality stereo system and folding video screens in the back of the front seats are also available to keep passengers entertained.

Developed on the same platform as the Grand C4 Picasso, which scored five stars in Euro NCAP tests, the new C4 Picasso meets the most stringent criteria for occupant protection, offering the likes of four Isofix seats, audible seatbelt warnings for all seats and seven airbags as standard.

Citroen DS 23 IE, 1973

Citroen DS 23 IE, 1973

The Citroën DS (also known as Déesse, or Goddess, after the punning initials in French) was an automobile produced by the French manufacturer Citroën between 1955 and 1975. Citroën sold nearly 1.5 million D-series during its 20 years of production.The DS is well-known for its futuristic, aerodynamic body design, and for its innovative technology (including its hydropneumatic self-leveling suspension system).

The DS advanced the achievable standards in terms of ride quality, roadholding, handling, and braking in an automobile. Automotive journalists of the time often noted that competitors took decades to adapt to the higher standards it set. The smooth, aerodynamic body lines gave the car a futuristic appearance. While it looked very unusual in 1955, public tastes appear to have caught up with the DS in the post-Ford Taurus/Audi 100 era.

Model history
After 18 years of development in secret as the successor to the venerable Traction Avant, the DS 19 was introduced on October 5, 1955 at the Paris Motor Show. The car's appearance and innovative engineering captured the imagination of the public and the automobile industry almost overnight. 743 orders were taken in the first 15 minutes of the show, and orders for the first day totalled 12,000.

Far from being just a fascinating technology in search of a purpose, contemporary journalists were effusive in noting how the DS dramatically pushed the envelope in the ride vs. handling compromise possible in a motor vehicle.

The high price tag, however, hurt general sales in a country still recovering from World War II 10 years earlier, and a submodel, the ID (another pun: in French, Idée, or Idea), was introduced in 1957 to appeal to more cost-conscious buyers. The ID shared the same body with the DS, but had more traditional features under the hood. It had no power steering (though this was added as an option later), and instead of the hydraulically controlled manual transmission and clutch, it had a conventional clutch and transmission. Interestingly, the first model series was called 11D, a clear reminder of the last model of the Traction Avant, the 11C. A station wagon variant, the ID Break, was introduced in 1958.
Outside of France, the car's radical and cosmopolitan design appealed to non-conformists. A United States advertisement summarised this selling point: "It takes a special person to drive a special car".

The DS managed to remain ahead of its time. It featured power disc brakes, a hydropneumatic suspension including an automatic levelling system and variable ground clearance, power steering and a semi-automatic transmission. A fiberglass roof reduced weight transfer. Inboard front brakes (as well as an independent suspension) reduced unsprung weight. Different front and rear track widths and tire sizes reduced the understeer typical of front-engined and front-wheel drive cars.

Despite the rather leisurely acceleration afforded by its small four-cylinder engine, the DS was successful in motorsports like rallying, where sustained speeds on poor surfaces are paramount.
The DS came in third in the 1999 Car of the Century competition, recognizing the the world's most influential auto designs. Winner and second place went to the Ford Model T and the Mini. It placed fifth on Automobile Magazine "100 Coolest Cars" listing in 2005.

Technical innovations
Hydraulic system
The hydraulic system of the DS 19 was a revolution. Previously hydraulics had been restricted to use in brakes and power steering; the DS used them for the suspension, clutch and transmission. The later ID19 had manual steering and a simplified power braking system.

Suspension
At a time when few passenger vehicles had caught up with the four-wheel independent suspension of the Traction Avant, the application of the hydraulic system to the car's suspension system to provide true self-levelling was a stunning move. This application - 'hydropneumatic suspension' - was pioneered the year before on the rear of the top of range Traction Avant 15CV-H.

Each wheel was connected not to a spring, but to a hydraulic suspension unit consisting of:

• a sphere of about 12 cm in diameter containing pressurised nitrogen
• a cylinder containing hydraulic fluid screwed to the suspension sphere
• a piston inside the cylinder connected by levers to the suspension itself
• a damper valve between the piston and the sphere

A membrane in the sphere prevented the nitrogen from escaping. The motion of the wheels translated to a motion of the piston, which acted on the oil in the nitrogen cushion and provided the spring effect. The damper valve took place of the shock absorber in conventional suspensions.

The hydraulic cylinder was fed with hydraulic fluid from the main pressure reservoir via a height corrector, a valve controlled by the mid-position of the anti-roll bar connected to the axle. If the suspension was too low, the height corrector introduced high-pressure fluid. If it was too high, it released fluid back to the fluid reservoir. In this manner, it maintained a constant height. A control in the cabin allowed the driver to select one of five heights:

• normal riding height.
• two slightly higher riding heights, for poor terrain.
• two extreme positions for changing wheels.

The DS did not have a jack for lifting the car off the ground. Instead, the hydraulic system enabled wheel changes with the aid of a simple adjustable stand.

Source and reserve of pressure
The central part of the hydraulic system was the high pressure reservoir, which maintained a pressure of between 130 and 150 bar in two accumulators. These accumulators were very similar in construction to the suspension spheres. One was dedicated to the brakes, and the other ran the other hydraulic systems. Thus in case of a hydraulic failure (a surprisingly infrequent occurrence), the first indication would be that the steering became heavy, followed by the gearbox not working; only later would the brakes fail.

Hydraulic fluid
The original hydropneumatic system used a vegetable oil (LHV or liquide hydraulique végétale) similar to that used in other cars at the time. Very soon, Citroën changed to using a synthetic fluid (LHS or liquide hydraulique synthétique). Both of these had the disadvantage that they are hygroscopic, as is the case with most brake fluids. Disuse allows water to enter the hydraulic components causing deterioration and expensive maintenance work. 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 the suspension "got up" and the 6 accumulators in the system filled with fluid. With every "inhalation" of fresh moisture- (and dust-) laden air, the fluid absorbed more water. In August 1967, Citroën introduced a new mineral oil-based fluid LHM, or liquide hydraulique minérale. This fluid was much less aggressive on the system and it remains in use to the present day.

Briefly illegal in the United States (US federal law requires motor vehicle brake fluid to be red - an exception had to be granted to Citroën), LHM has since been adopted by manufacturers like Rolls-Royce, Jaguar, BMW, and Audi under different labels, like "Total," "Pentosin," and others.

LHM required completely different materials for 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 former LHS parts were painted black.

Several different hydraulic pumps were used. The DS used a seven-cylinder axial piston pump driven off two belts and delivering 175 bar of pressure. The ID19, with its simpler hydraulic system, had a single cylinder pump.

Gearbox and clutch
The mechanical aspects of the gearbox and clutch were completely conventional and the same elements were used in the ID 19.

The gear change control consisted of:

• Hydraulic gear selector.
• Clutch control. This was the most complicated part. The speed of engagement of the clutch was controlled by:
• A centrifugal regulator, sensing engine rpm and driven off the camshaft by a belt
• The position of the butterfly valve in the carburettor (i.e. the position of the accelerator)
• The brake circuit: when the brake was pressed, the engine idle speed dropped to a rpm below the clutch engagement speed, thus preventing friction while stopped in gear at traffic lights. When the brake was released, the idle speed increased to the clutch dragging speed. The car would then "creep" much like automatic transmission cars. This drop in idle throttle position also caused the car to have more engine drag when the brakes were applied even before the car slowed to the idle speed in gear, preventing the engine from "pulling" against the brakes.

Impact on Citroën brand development
The 1955 DS in one stroke cemented the Citroën brand name as an automotive innovator. In fact, the DS caused such a huge sensation that Citroën was fearful future models would not be bold enough. Other than variations on the very basic 2 cylinder economy car Citroën 2CV, like the Citroën Ami, no new models were introduced from 1955 to 1970.

The DS was 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 market segments between the 2CV and the DS, occupied by vehicles like the Peugeot 403, Renault 16 and Ford Cortina. None made it to production. Either they had uneconomic build costs, or were ordinary "me too" cars, not up to the company's high standard of innovation. Because Citroën was owned by Michelin as a sort of research laboratory, such experimentation was possible. Citroën finally did introduce the clever Citroën GS in 1970, which sold a spectacular 2.5 million units.

DS in the US
While the DS was a hit in Europe, it seemed rather odd in the United States. Ostensibly a luxurious car, it did not have the basic features that buyers of that era expected to find on such a vehicle - fully automatic transmission, air conditioning, power windows and a reasonably powerful engine. The DS price point was similar to the contemporary Cadillac luxury car. Also, people at the time wanted only the newest models, which changed every year, like fashion, yet the DS appeared vaguely derivative of the 1950 Hudson Hornet step-down design.

Outdated US legislation also banned one of the car's more advanced features, aerodynamic headlamps, now common in US automobiles. Ultimately, 38,000 units were sold. The first year of the aerodynamic glass over the DS' headlights along with driving lights turned by the steering, was also the first year these features were outlawed in the US.

Design variations
The DS always maintained its size and shape, with easily removable, unstressed body panels, but certain design changes did occur.

A station wagon version was introduced in 1958. It was known by various names in different markets (Break in France, Safari and Familiale in the UK, Wagon in the US, and Citroën Australia used the terms Safari and Station-Wagon). It had a steel roof to support the standard roof rack.

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 the front fenders. In 1965 a luxury upgrade kit, the DS Pallas (after Greek goddess Pallas), was introduced. This included comfort features such as better noise insulation, leather upholstery and external trim embellishments.

In 1967, the DS and ID was again restyled. This version had a more streamlined headlamp design, giving the car a notably shark-like appearance. This design had four headlights under a smooth glass canopy, and the inner set swivelled with the steering wheel. This allowed the driver to see 'around' turns, especially valuable on twisting roads driven at high speed at night.

However, this feature was not allowed in the US at the time (see World Forum for Harmonization of Vehicle Regulations), so a version with four exposed headlights that did not swivel was made for the US market.
The station wagon edition, the Break (called the ID Safari on the UK market) and "Familiale", was also upgraded. The hydraulic fluid changed in all markets (except the US) to the technically superior LHM (Liquide Hydraulique Minérale).

Rarest and most collectible of all DS variants, a convertible was offered from 1958 until 1973. The convertibles were built in small series by French carrossier Henri Chapron, for the Citroën factory. In addition, Chapron also produced a few coupés, non-works convertibles and special sedans (DS Lorraine for instance).

DS engines
As with all French cars, the DS design was impacted by the tax horsepower system, which effectively mandated very small engines.

Unlike the Traction Avant predecessor, there was no top-of-range model with a powerful six cylinder engine. The DS was designed around an air cooled flat six based on the design of the 2 cylinder engine of the 2CV, similar to the motor in the Porsche 911. Technical issues forced this idea to be scrapped.

Thus, for such a modern car, the engine of the original DS 19 was also old-fashioned. It was derived from the engine of the 11CV Traction Avant (models 11B and 11C). It was an OHV four-cylinder engine with three main bearings and dry liners, and a bore of 78 mm and a stroke of 100 mm, giving a volumetric displacement of 1911 cc. The cylinder head had been reworked; the 11C had a reverse-flow cast iron cylinder head and generated 60 hp at 3800 rpm; by contrast, the DS 19 had an aluminium cross-flow head with hemispherical combustion chambers and generated 75 hp at 4500 rpm. Apart from these details, there was very little difference between the engines: even the locations of the cylinder head studs were the same, so that it was possible to put the cylinder head of a DS on a Traction Avant engine and run it.

Like the Traction Avant, the DS had the gearbox mounted in front of the engine, with the differential in between. Thus the DS is a really a mid engine front wheel drive car. It initially had a four-speed transmission and clutch, operated by a hydraulic controller. To change gears, the driver flicked a lever behind the steering wheel to the next position and eased-up on the accelerator pedal. The hydraulic controller disengaged the clutch, engaged the nominated gear, and re-engaged the clutch. Manual transmission control was a lower-cost option. The later and simpler ID19 also had the same gearbox and clutch, manually operated. In the 1970s a five-speed manual and 3-speed fully-automatic were introduced, in addition to the original four-speed unit.

The DS and ID powerplants evolved throughout its 20 year production life. The car was underpowered and faced constant mechanical changes to boost the performance of the four-cylinder engine. The initial 1911 cc 3 main bearing engine (carried forward from the Traction Avant) of the DS 19 was replaced in 1965 with the 1985 cc 5 bearing motor of the DS 19a (called DS20 from September 1969).

The DS 21 was also introduced for model year 1965. This was a 2175 cc, 5 main bearing engine. This engine received a substantial increase in power with the introduction of Bosch electronic fuel injection for 1970, making the DS one of the first mass-market cars to use electronic fuel injection.

Lastly, 1973 saw the introduction of the 2347 cc engine of the DS 23 in both carbureted and fuel injected forms. The DS 23 with electronic fuel injection was the most powerful production model, producing 141 horsepower.

IDs and their variants went through a similar evolution, generally lagging the DS by about one year. ID models never received the DS 23 engine or fuel injection. The DS was offered with a number of transmission options, including the "Hydraulique" 4-speed semi-automatic, 4-speed and 5-speed manuals and a 3-speed Borg-Warner full-automatic. The full-automatic transmissions were intended for the US market, but as Citroën withdrew from the US in 1972, the year of highest US sales, due to constrictive road rules, most automatic DSs, being the DS 23 EFI sedans with air conditioning, were sold in Australia.

Citroen SM Presidential, 1972

 

Citroen SM Presidential, 1972

The Citroën SM was a high performance coupé produced by the French manufacturer Citroën between 1970 and 1975. The SM placed third in the 1971 European Car of the Year contest, trailing its stablemate Citroën GS, and won the 1972 Motor Trend Car of the Year award in the US in 1972.

In 1961, Citroën began work on 'Project S' - a sports variant of the revolutionary Citroën DS. As was customary for the firm, many running concept vehicles were developed, increasingly complex and upmarket from the DS - eventually becoming a halo vehicle for the brand. Citroën purchased Maserati in 1968 with the intention of harnessing Maserati's high performance engine technology to produce a true Gran Turismo car, combining the sophisticated Citroën suspension with a Maserati V6 engine.

The result was the Citroën SM (Sport Maserati), first shown at the Geneva Motor Show in March1970. It finally went on sale in France in September of that year. All produced were left-hand-drive, although some RHD conversions were done in the UK.

The SM was Citroën's flagship vehicle, competing with other high performance GTs of the time from manufacturers such as Jaguar, Lotus and Porsche. It was also Citroën's way of demonstrating just how much power and performance could be accommodated in a front-wheel drive design.

The SM innovated a new type of variable assist power steering that has since spread throughout the vehicle population. It allowed great assistance to the motorist while parking, but little assistance at motorway speeds. The steering actually had the same "assist" at all speeds - the steering was hydraulically locked against steering movement of the wheels from the road ("feedback") up to the capacity of the unit. Hitting a chuckhole at high speed would not turn the steering wheel in the driver's hands! The hydraulic pressure to the power centering unit increased with speed, giving the impression of less and less power "assist." Enough pressure was admitted to the centering unit to return the wheels to the straight ahead position when the car was not moving. The centering pressure was regulated by a flyweight centrifugal governor driven by the pinion (secondary) shaft of the manual gearbox and by a proportioning valve connected to the pressure in the automatic gearbox, which pressure was proportional to the speed of the output shaft.

Contemporary automotive journalists were most effusive about the SM's dynamic qualities, which were unlike anything they had experienced prior. The SM provided a combination of comfort, sharp handling, and high performance not available in any other car at the time. Popular Science noted that the SM had the shortest stopping distance of any car they had tested. To this day this stopping distance remains outstanding.

Unfortunately, the SM did not find a sufficient customer base in the European GT market, but much of the SM's technology was carried forward to the successful Citroën CX, launched in 1974 - the DIRAVI steering being the most obvious example. The same basic engine in enlarged 3.0 L form (some in Italy had 2 litre) was used in Maserati's own Merak which, together with the Khamsin, used Citroën's high pressure hydraulics.

Styling
The look of the car was quite distinct. Designed in-house by Citroën's chief designer Robert Opron, the SM bore a vague family resemblance to the DS. Seen from above, the SM resembled a teardrop, with a much wider track at the front.

The SM was unusually aerodynamic for its era, with a very low drag coefficient. European critics marvelled at the resulting ability to travel for hours at 200 km/h (120 mph) in comfort. In addition, many of the details reflected Robert Opron's American background, notably the truncated 'fins' at the rear.

The SM combined many unusual features - lights that swivelled with the steering (except in the USA where such was illegal), unique self-centering and fully powered steering, self-leveling headlights (except in the USA where such was illegal), a wiper mechanism that was 'sensitive' to rain, and many other features that are now commonplace on the cars of today.

The SM's design was timeless; the car was even used in a 1999 television advertisement for British Petroleum of Spain, where 'a futuristic car was required'. It placed eleventh on Automobile Magazine's 2005 "100 Coolest Cars" listing.

In 1970, it was a car of the future and the fastest front-wheel drive car to be made. It was an example of the car as a symbol of optimism and progressive technology, similar to the SM's contemporary, the Concorde aircraft.

US exports
The main export market for the SM was the United States. In the US, the market for personal luxury cars was much larger than in Europe, with competitors like the Cadillac Eldorado, Lincoln Mark IV and Ford Thunderbird alongside a large selection of Italian, English, and German imports. Nevertheless, the unique design of the SM made quite a splash and won the Motor Trend magazine Car of the Year award in 1972: unheard of for a non-US vehicle at the time.

The SM's six headlight set up was illegal in the United States and consequently, US specification cars were fitted with four fixed round exposed lamps.

Despite initial success, US sales ceased suddenly - Citroën expected (but did not receive) an exemption for the 1974 model year 5 mph bumper regulation imposed by the NHTSA. The integral variable height suspension of the SM made compliance impossible. The law as written called for bumpers to be an exact height off the ground at all times, yet according to the laws of physics, cars dip at the nose on braking. Vehicles classified as trucks were always exempt and the entire law was eventually repealed in 1981. The final batch of 134 now illegal 1974 US model SMs were shipped to Japan.

The Engines
The SM was sold with three very similar, small, lightweight engines, all derived from the contemporary Maserati V8 fitted to the Quattroporte. Because of the V8 origin, this engine sported an unusual 90 degree angle between cylinder banks - a trait shared with the PRV V6.

The engines:

• 2.7 L V6 with Weber 42 DCNF carburettors, "C114-1" (170 bhp) (1970-1972)
• 2.7 L V6 with Bosch D-Jetronic injection, "C114-03" (178 bhp) (1973-1975 - Not available in the US)
• 3.0 L V6 with Weber 42 DCNF carburettors, "C114-11" (180 bhp) (1973-1975 - US only in 1973, rest of the world, automatic only in 1974 & 1975)

The size of the 2.7 L engine was limited by French puissance fiscale taxation, which effectively banned large displacement vehicles. The engine was also used in the Maserati Merak from 1973 to 1982 and the Ligier JS2 sports car. The final SMs were produced in the Ligier factory in Vichy.

5 speed manual and 3 speed Borg Warner fully automatic transmissions were fitted, but with the rest of the world outside North America only getting the fully automatic in 1974 & 1975.

The C114 is a relatively sturdy unit, provided certain modifications are performed to eliminate weak points leading to catastrophic damage:

• The sodium filled exhaust valves may break and drop into the cylinder. Solid valves are available.
• Primary distribution chain may wear out prematurely due to excessive vibration. A curved chain limiter should be fitted, eliminating vibration.
• Oil pump drive shaft is underdimensioned and may break. Maserati beefed up the shaft in later versions, and this should be retrofitted if not already present.

Citroen SM, 1972

 

 

Citroen SM, 1972

The Citroën SM was a high performance coupé produced by the French manufacturer Citroën between 1970 and 1975. The SM placed third in the 1971 European Car of the Year contest, trailing its stablemate Citroën GS, and won the 1972 Motor Trend Car of the Year award in the US in 1972.

In 1961, Citroën began work on 'Project S' - a sports variant of the revolutionary Citroën DS. As was customary for the firm, many running concept vehicles were developed, increasingly complex and upmarket from the DS - eventually becoming a halo vehicle for the brand. Citroën purchased Maserati in 1968 with the intention of harnessing Maserati's high performance engine technology to produce a true Gran Turismo car, combining the sophisticated Citroën suspension with a Maserati V6 engine.

The result was the Citroën SM (Sport Maserati), first shown at the Geneva Motor Show in March1970. It finally went on sale in France in September of that year. All produced were left-hand-drive, although some RHD conversions were done in the UK.

The SM was Citroën's flagship vehicle, competing with other high performance GTs of the time from manufacturers such as Jaguar, Lotus and Porsche. It was also Citroën's way of demonstrating just how much power and performance could be accommodated in a front-wheel drive design.

The SM innovated a new type of variable assist power steering that has since spread throughout the vehicle population. It allowed great assistance to the motorist while parking, but little assistance at motorway speeds. The steering actually had the same "assist" at all speeds - the steering was hydraulically locked against steering movement of the wheels from the road ("feedback") up to the capacity of the unit. Hitting a chuckhole at high speed would not turn the steering wheel in the driver's hands! The hydraulic pressure to the power centering unit increased with speed, giving the impression of less and less power "assist." Enough pressure was admitted to the centering unit to return the wheels to the straight ahead position when the car was not moving. The centering pressure was regulated by a flyweight centrifugal governor driven by the pinion (secondary) shaft of the manual gearbox and by a proportioning valve connected to the pressure in the automatic gearbox, which pressure was proportional to the speed of the output shaft.

Contemporary automotive journalists were most effusive about the SM's dynamic qualities, which were unlike anything they had experienced prior. The SM provided a combination of comfort, sharp handling, and high performance not available in any other car at the time. Popular Science noted that the SM had the shortest stopping distance of any car they had tested. To this day this stopping distance remains outstanding.

Unfortunately, the SM did not find a sufficient customer base in the European GT market, but much of the SM's technology was carried forward to the successful Citroën CX, launched in 1974 - the DIRAVI steering being the most obvious example. The same basic engine in enlarged 3.0 L form (some in Italy had 2 litre) was used in Maserati's own Merak which, together with the Khamsin, used Citroën's high pressure hydraulics.

Styling
The look of the car was quite distinct. Designed in-house by Citroën's chief designer Robert Opron, the SM bore a vague family resemblance to the DS. Seen from above, the SM resembled a teardrop, with a much wider track at the front.

The SM was unusually aerodynamic for its era, with a very low drag coefficient. European critics marvelled at the resulting ability to travel for hours at 200 km/h (120 mph) in comfort. In addition, many of the details reflected Robert Opron's American background, notably the truncated 'fins' at the rear.

The SM combined many unusual features - lights that swivelled with the steering (except in the USA where such was illegal), unique self-centering and fully powered steering, self-leveling headlights (except in the USA where such was illegal), a wiper mechanism that was 'sensitive' to rain, and many other features that are now commonplace on the cars of today.

The SM's design was timeless; the car was even used in a 1999 television advertisement for British Petroleum of Spain, where 'a futuristic car was required'. It placed eleventh on Automobile Magazine's 2005 "100 Coolest Cars" listing.

In 1970, it was a car of the future and the fastest front-wheel drive car to be made. It was an example of the car as a symbol of optimism and progressive technology, similar to the SM's contemporary, the Concorde aircraft.

US exports
The main export market for the SM was the United States. In the US, the market for personal luxury cars was much larger than in Europe, with competitors like the Cadillac Eldorado, Lincoln Mark IV and Ford Thunderbird alongside a large selection of Italian, English, and German imports. Nevertheless, the unique design of the SM made quite a splash and won the Motor Trend magazine Car of the Year award in 1972: unheard of for a non-US vehicle at the time.

The SM's six headlight set up was illegal in the United States and consequently, US specification cars were fitted with four fixed round exposed lamps.

Despite initial success, US sales ceased suddenly - Citroën expected (but did not receive) an exemption for the 1974 model year 5 mph bumper regulation imposed by the NHTSA. The integral variable height suspension of the SM made compliance impossible. The law as written called for bumpers to be an exact height off the ground at all times, yet according to the laws of physics, cars dip at the nose on braking. Vehicles classified as trucks were always exempt and the entire law was eventually repealed in 1981. The final batch of 134 now illegal 1974 US model SMs were shipped to Japan.

The Engines
The SM was sold with three very similar, small, lightweight engines, all derived from the contemporary Maserati V8 fitted to the Quattroporte. Because of the V8 origin, this engine sported an unusual 90 degree angle between cylinder banks - a trait shared with the PRV V6.

The engines - always mounted behind the front axle were:

•  2.7 L V6 with Weber 42 DCNF carburettors, "C114-1" (170 bhp) (1970-1972)
•  2.7 L V6 with Bosch D-Jetronic injection, "C114-03" (178 bhp) (1973-1975 - Not available in the US)
•  3.0 L V6 with Weber 42 DCNF carburettors, "C114-11" (180 bhp) (1973-1975 - US only in 1973, rest of the world, automatic only in 1974 & 1975)

The size of the 2.7 L engine was limited by French puissance fiscale taxation, which effectively banned large displacement vehicles. The engine was also used in the Maserati Merak from 1973 to 1982 and the Ligier JS2 sports car. The final SMs were produced in the Ligier factory in Vichy.

5 speed manual and 3 speed Borg Warner fully automatic transmissions were fitted, but with the rest of the world outside North America only getting the fully automatic in 1974 & 1975.

The C114 is a relatively sturdy unit, provided certain modifications are performed to eliminate weak points leading to catastrophic damage:

•  The sodium filled exhaust valves may break and drop into the cylinder. Solid valves are available.
•  Primary distribution chain may wear out prematurely due to excessive vibration. A curved chain limiter should be fitted, eliminating vibration.
•  Oil pump drive shaft is underdimensioned and may break. Maserati beefed up the shaft in later versions, and this should be retrofitted if not already present.

Citroen DS 21, 1972

 

 

Citroen DS 21, 1972

The Citroën DS (also known as Déesse, or Goddess, after the punning initials in French) was an automobile produced by the French manufacturer Citroën between 1955 and 1975. Citroën sold nearly 1.5 million D-series during its 20 years of production.The DS is well-known for its futuristic, aerodynamic body design, and for its innovative technology (including its hydropneumatic self-leveling suspension system).

The DS advanced the achievable standards in terms of ride quality, roadholding, handling, and braking in an automobile. Automotive journalists of the time often noted that competitors took decades to adapt to the higher standards it set. The smooth, aerodynamic body lines gave the car a futuristic appearance. While it looked very unusual in 1955, public tastes appear to have caught up with the DS in the post-Ford Taurus/Audi 100 era.

Model history
After 18 years of development in secret as the successor to the venerable Traction Avant, the DS 19 was introduced on October 5, 1955 at the Paris Motor Show. The car's appearance and innovative engineering captured the imagination of the public and the automobile industry almost overnight. 743 orders were taken in the first 15 minutes of the show, and orders for the first day totalled 12,000.

Far from being just a fascinating technology in search of a purpose, contemporary journalists were effusive in noting how the DS dramatically pushed the envelope in the ride vs. handling compromise possible in a motor vehicle.

The high price tag, however, hurt general sales in a country still recovering from World War II 10 years earlier, and a submodel, the ID (another pun: in French, Idée, or Idea), was introduced in 1957 to appeal to more cost-conscious buyers. The ID shared the same body with the DS, but had more traditional features under the hood. It had no power steering (though this was added as an option later), and instead of the hydraulically controlled manual transmission and clutch, it had a conventional clutch and transmission. Interestingly, the first model series was called 11D, a clear reminder of the last model of the Traction Avant, the 11C. A station wagon variant, the ID Break, was introduced in 1958.

Outside of France, the car's radical and cosmopolitan design appealed to non-conformists. A United States advertisement summarised this selling point: "It takes a special person to drive a special car".

Throughout its model lifetime, the DS managed to remain ahead of its time. It featured power disc brakes, a hydropneumatic suspension including an automatic levelling system and variable ground clearance, power steering and a semi-automatic transmission. A fiberglass roof reduced weight transfer. Inboard front brakes (as well as an independent suspension) reduced unsprung weight. Different front and rear track widths and tire sizes reduced the understeer typical of front-engined and front-wheel drive cars.

Despite the rather leisurely acceleration afforded by its small four-cylinder engine, the DS was successful in motorsports like rallying, where sustained speeds on poor surfaces are paramount.

The DS came in third in the 1999 Car of the Century competition, recognizing the the world's most influential auto designs. Winner and second place went to the Ford Model T and the Mini. It placed fifth on Automobile Magazine "100 Coolest Cars" listing in 2005.
History will remember the DS for many reasons, including the fact it was the first production car with front disc brakes.

Technical innovations
Hydraulic system
The hydraulic system of the DS 19 was a revolution. Previously hydraulics had been restricted to use in brakes and power steering; the DS used them for the suspension, clutch and transmission. The later ID19 had manual steering and a simplified power braking system.

Suspension
At a time when few passenger vehicles had caught up with the four-wheel independent suspension of the Traction Avant, the application of the hydraulic system to the car's suspension system to provide true self-levelling was a stunning move. This application - 'hydropneumatic suspension' - was pioneered the year before on the rear of the top of range Traction Avant 15CV-H.

At first it was often described as air/oil suspension, since both elements played a key role.

Each wheel was connected not to a spring, but to a hydraulic suspension unit consisting of:
    * a sphere of about 12 cm in diameter containing pressurised nitrogen
    * a cylinder containing hydraulic fluid screwed to the suspension sphere
    * a piston inside the cylinder connected by levers to the suspension itself
    * a damper valve between the piston and the sphere

A membrane in the sphere prevented the nitrogen from escaping. The motion of the wheels translated to a motion of the piston, which acted on the oil in the nitrogen cushion and provided the spring effect. The damper valve took place of the shock absorber in conventional suspensions.

The hydraulic cylinder was fed with hydraulic fluid from the main pressure reservoir via a height corrector, a valve controlled by the mid-position of the anti-roll bar connected to the axle. If the suspension was too low, the height corrector introduced high-pressure fluid. If it was too high, it released fluid back to the fluid reservoir. In this manner, it maintained a constant height. A control in the cabin allowed the driver to select one of five heights:
    * normal riding height.
    * two slightly higher riding heights, for poor terrain.
    * two extreme positions for changing wheels.

The DS did not have a jack for lifting the car off the ground. Instead, the hydraulic system enabled wheel changes with the aid of a simple adjustable stand.

Source and reserve of pressure
The central part of the hydraulic system was the high pressure reservoir, which maintained a pressure of between 130 and 150 bar in two accumulators. These accumulators were very similar in construction to the suspension spheres. One was dedicated to the brakes, and the other ran the other hydraulic systems. Thus in case of a hydraulic failure (a surprisingly infrequent occurrence), the first indication would be that the steering became heavy, followed by the gearbox not working; only later would the brakes fail.

Hydraulic fluid
The original hydropneumatic system used a vegetable oil (LHV or liquide hydraulique végétale) similar to that used in other cars at the time. Very soon, Citroën changed to using a synthetic fluid (LHS or liquide hydraulique synthétique). Both of these had the disadvantage that they are hygroscopic, as is the case with most brake fluids. Disuse allows water to enter the hydraulic components causing deterioration and expensive maintenance work. 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 the suspension "got up" and the 6 accumulators in the system filled with fluid. With every "inhalation" of fresh moisture- (and dust-) laden air, the fluid absorbed more water. In August 1967, Citroën introduced a new mineral oil-based fluid LHM, or liquide hydraulique minérale. This fluid was much less aggressive on the system and it remains in use to the present day.

Briefly illegal in the United States (US federal law requires motor vehicle brake fluid to be red - an exception had to be granted to Citroën), LHM has since been adopted by manufacturers like Rolls-Royce, Jaguar, BMW, and Audi under different labels, like "Total," "Pentosin," and others.

LHM required completely different materials for 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 former LHS parts were painted black.

Several different hydraulic pumps were used. The DS used a seven-cylinder axial piston pump driven off two belts and delivering 175 bar of pressure. The ID19, with its simpler hydraulic system, had a single cylinder pump.

Gearbox and clutch
The mechanical aspects of the gearbox and clutch were completely conventional and the same elements were used in the ID 19.

The gear change control consisted of:
    * Hydraulic gear selector.
    * Clutch control. This was the most complicated part. The speed of engagement of the clutch was controlled by:
    * A centrifugal regulator, sensing engine rpm and driven off the camshaft by a belt
    * The position of the butterfly valve in the carburettor (i.e. the position of the accelerator)
    * The brake circuit: when the brake was pressed, the engine idle speed dropped to a rpm below the clutch engagement speed, thus preventing friction while stopped in gear at traffic lights. When the brake was released, the idle speed increased to the clutch dragging speed. The car would then "creep" much like automatic transmission cars. This drop in idle throttle position also caused the car to have more engine drag when the brakes were applied even before the car slowed to the idle speed in gear, preventing the engine from "pulling" against the brakes.

Impact on Citroën brand development
The 1955 DS in one stroke cemented the Citroën brand name as an automotive innovator. In fact, the DS caused such a huge sensation that Citroën was fearful future models would not be bold enough. Other than variations on the very basic 2 cylinder economy car Citroën 2CV, like the Citroën Ami, no new models were introduced from 1955 to 1970.

The DS was 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 market segments between the 2CV and the DS, occupied by vehicles like the Peugeot 403, Renault 16 and Ford Cortina. None made it to production. Either they had uneconomic build costs, or were ordinary "me too" cars, not up to the company's high standard of innovation. Because Citroën was owned by Michelin as a sort of research laboratory, such experimentation was possible. Citroën finally did introduce the clever Citroën GS in 1970, which sold a spectacular 2.5 million units.

DS in the US
While the DS was a hit in Europe, it seemed rather odd in the United States. Ostensibly a luxurious car, it did not have the basic features that buyers of that era expected to find on such a vehicle - fully automatic transmission, air conditioning, power windows and a reasonably powerful engine. The DS price point was similar to the contemporary Cadillac luxury car. Also, people at the time wanted only the newest models, which changed every year, like fashion, yet the DS appeared vaguely derivative of the 1950 Hudson Hornet step-down design.

Outdated US legislation also banned one of the car's more advanced features, aerodynamic headlamps, now common in US automobiles. Ultimately, 38,000 units were sold. The first year of the aerodynamic glass over the DS' headlights along with driving lights turned by the steering, was also the first year these features were outlawed in the US.

Design variations
The DS always maintained its size and shape, with easily removable, unstressed body panels, but certain design changes did occur.

A station wagon version was introduced in 1958. It was known by various names in different markets (Break in France, Safari and Familiale in the UK, Wagon in the US, and Citroën Australia used the terms Safari and Station-Wagon). It had a steel roof to support the standard roof rack.

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 the front fenders. In 1965 a luxury upgrade kit, the DS Pallas (after Greek goddess Pallas), was introduced. This included comfort features such as better noise insulation, leather upholstery and external trim embellishments.

In 1967, the DS and ID was again restyled. This version had a more streamlined headlamp design, giving the car a notably shark-like appearance. This design had four headlights under a smooth glass canopy, and the inner set swivelled with the steering wheel. This allowed the driver to see 'around' turns, especially valuable on twisting roads driven at high speed at night.

However, this feature was not allowed in the US at the time (see World Forum for Harmonization of Vehicle Regulations), so a version with four exposed headlights that did not swivel was made for the US market.

The station wagon edition, the Break (called the ID Safari on the UK market) and "Familiale", was also upgraded. The hydraulic fluid changed in all markets (except the US) to the technically superior LHM (Liquide Hydraulique Minérale).

Rarest and most collectible of all DS variants, a convertible was offered from 1958 until 1973. The convertibles were built in small series by French carrossier Henri Chapron, for the Citroën factory. In addition, Chapron also produced a few coupés, non-works convertibles and special sedans (DS Lorraine for instance).

DS engines
As with all French cars, the DS design was impacted by the tax horsepower system, which effectively mandated very small engines.

Unlike the Traction Avant predecessor, there was no top-of-range model with a powerful six cylinder engine. The DS was designed around an air cooled flat six based on the design of the 2 cylinder engine of the 2CV, similar to the motor in the Porsche 911. Technical issues forced this idea to be scrapped.

Thus, for such a modern car, the engine of the original DS 19 was also old-fashioned. It was derived from the engine of the 11CV Traction Avant (models 11B and 11C). It was an OHV four-cylinder engine with three main bearings and dry liners, and a bore of 78 mm and a stroke of 100 mm, giving a volumetric displacement of 1911 cc. The cylinder head had been reworked; the 11C had a reverse-flow cast iron cylinder head and generated 60 hp at 3800 rpm; by contrast, the DS 19 had an aluminium cross-flow head with hemispherical combustion chambers and generated 75 hp at 4500 rpm. Apart from these details, there was very little difference between the engines: even the locations of the cylinder head studs were the same, so that it was possible to put the cylinder head of a DS on a Traction Avant engine and run it.

Like the Traction Avant, the DS had the gearbox mounted in front of the engine, with the differential in between. Thus the DS is a really a mid engine front wheel drive car. It initially had a four-speed transmission and clutch, operated by a hydraulic controller. To change gears, the driver flicked a lever behind the steering wheel to the next position and eased-up on the accelerator pedal. The hydraulic controller disengaged the clutch, engaged the nominated gear, and re-engaged the clutch. Manual transmission control was a lower-cost option. The later and simpler ID19 also had the same gearbox and clutch, manually operated. In the 1970s a five-speed manual and 3-speed fully-automatic were introduced, in addition to the original four-speed unit.

The DS and ID powerplants evolved throughout its 20 year production life. The car was underpowered and faced constant mechanical changes to boost the performance of the four-cylinder engine. The initial 1911 cc 3 main bearing engine (carried forward from the Traction Avant) of the DS 19 was replaced in 1965 with the 1985 cc 5 bearing motor of the DS 19a (called DS20 from September 1969).

The DS 21 was also introduced for model year 1965. This was a 2175 cc, 5 main bearing engine. This engine received a substantial increase in power with the introduction of Bosch electronic fuel injection for 1970, making the DS one of the first mass-market cars to use electronic fuel injection.

Lastly, 1973 saw the introduction of the 2347 cc engine of the DS 23 in both carbureted and fuel injected forms. The DS 23 with electronic fuel injection was the most powerful production model, producing 141 horsepower.

IDs and their variants went through a similar evolution, generally lagging the DS by about one year. ID models never received the DS 23 engine or fuel injection. The DS was offered with a number of transmission options, including the "Hydraulique" 4-speed semi-automatic, 4-speed and 5-speed manuals and a 3-speed Borg-Warner full-automatic. The full-automatic transmissions were intended for the US market, but as Citroën withdrew from the US in 1972, the year of highest US sales, due to constrictive road rules, most automatic DSs, being the DS 23 EFI sedans with air conditioning, were sold in Australia.