Back to the Future Part 5 – (Parts 1 – 4 are published in CITROËNVIE Magazine issues Spring 2010 through Winter 2011).
DS FEATURES – Automotive Pre-imminence
– by David Wooley
1955 DS 19 Citroën Automotive Design, was truly a revolutionary automobile. It included many industry firsts (!) modifications (*) or additions (@): Pressure-Reservoir (!): also called a fluid “accumulator”, a “nitrogen spring”, or simply a “sphere”. Seven or six spheres are used: the main pressure accumulator, the front brake accumulator, and the four suspension springs. The rear-brake accumulator was eliminated in 1961. A Pressure-Reservoir consists of a metal sphere filled with nitrogen gas under high pressure, separated from hydraulic fluid by a flexible rubber diaphragm. A steel washer is attached to the diaphragm so that when a sphere is removed from a vehicle, the diaphragm places the washer over the hydraulic fluid access hole, preventing the diaphragm from bursting. Spheres are refillable: the Nitrogen is re-pressurized after a few years, less expense than replacing “shocks”. The following is an extensive summary of DS features:
A. Three isolated and independent brake systems: front, rear and emergency/parking brake. (!)B. The DS 19 is the first high-volume family car with disc brakes. (!) (Crosley had 4 wheel disk brakes in 1949 that were discontinued because road-salts caused corrosion and brake failure. Jaguar raced a car with disc brakes in 1950.)
B. The front brakes are mounted at the transmission, not in the wheels, for better
cooling and less un-sprung weight. (!)
C. Huge, air rams cool the discs. (!) Overheating is near impossible.
D. The brakes are not muscle powered, nor muscle plus engine-dependent vacuum assisted. (!)
E. Brake accumulators are independent of the engine. (!) The central hydraulic system has 2470lbs hydraulic pressure available for fast, powerful brake response, plus a front accumulator volume sufficient to provide 40 emergency stops.
F. The high power brakes are functional even with the engine not running, or after a general hydraulic system failure. (!)
G. High-pressure hammering of the front brakes is eliminated, but the pressure released to the brake is not reduced. (!)
H. Rear brake pressure is dependent on static rear-axle hydraulic pressure, available from the self-leveling suspension. (!) Variable fluid volume for emergency stops is stored in the rear suspension spheres depending on the rear-load weight.
I. Front-to-rear brake effort distribution is dependent on changing rear-axle height, instantly responding to changes in road topography and attitude pitching, for effective power stopping on uneven surfaces. (!)
J. Forward weight transfers from a trailer, sensed by the brake computer, provide additional massive stopping power. (!)
K. The brake control is gas pedal height. (!) It moves ¼ inch providing very quick reaction time: no lifting of the foot.
L. The disc brake calipers compensate for brake pad wear, providing self- adjustment. (!)
M. Electrodes embedded in the brake pads activate a replacement warning light at 15% remaining pads. (@ 1965)
N. Disk brake pad-replacement is by opening the hood and removing a small lock nut and bolt (!), or safety pin. (* 1965)
O. In the unlikely event of a broken half axel, a Philips head screwdriver locks one inboard disk brake making a drive home possible with one powered front wheel. (! pre ’65) Caution: the speedometer speed reads twice the road speed.
P. In case of a brake or hydraulic failure, with warnings, a free pedal, self-adjusting, effective emergency brake, mechanically linked to the front discs is used. (!) It can be locked as a parking brake to hold on a 45degree slope.
Q Separate emergency/parking brake pads and calipers on the front discs.
A. Rising rate nitrogen springs. (!) The spring-rate raises in direct proportion to increases in the load as the suspension self levels. Steel springs are fixed rate with diminishing effectiveness near-unloaded or near-fully loaded. By selecting a lower ground clearance, the suspension geometry accesses softer spring rates for an incredibly smooth ride. Otherwise, the DS ride and handling characteristics remains constant regardless of changes in the load or topography.
B. Low frequency, high amplitude springs for comfort. (!) Steel springs tend to be bouncy high frequency, low amplitude.
C. The so-called ‘shock absorbers’, the integral spring dampeners, do not wear out and are never replaced. (!)
D. The spring dampeners are two-way restrictor valves that open in direct proportion to the size and rebound of the bump (!) The bigger the bump the greater the wheel movement: pitching and the sensation of hitting a bump are eliminated. Earlier lower top-speed DSs had less restrictive spring dampeners than later models allowing phenomenally smooth rides: driven at 60mph over a ploughed field, the rough direction, all have a smooth ride with no damage to the car.
E. Self-leveling suspension with driver selection: variable ground clearance of five positions from 3 to 11 inches. (!) For comparison the Hummer II has a ground clearance of 10.6 inches.
F. Increasing the load lowers the center of gravity of a DS, enhancing stability; the trunk floor is the bottom of the car.
G. Power jacking for tire changing. (!) A stand replaces the manual jack: raise car, install the jack-stand, and lower the suspension. The two wheels on that side of car clear the ground by about ½ foot, lifted by the two anti-roll bars.
H. Rigid-suspension-geometry based on tapered roller bearings, not rubber grommets, allows accurate steering. (The B11)
I. The axles are related by hydraulics but not inter-connected: front, forged leading side arms; rear, welded trailing arms.
J. Four wheel independent suspension with two torsion anti-roll bars, and a front axle hydraulic anti-roll function. (!)
K. 123 inch wheelbase is the longest compared to overall length. (!) Limousines use a long wheelbase for the same reasons, including to well suspend the passengers for comfort. The passengers ride between the wheels not over them.
L. Back tires are at the rear end of the car for collision safety and for stability. Rear suspension is forward of the wheels.
M. The front track is 4 feet, 11 1/16 inches, one of the widest in the industry compared to length for stability. Combined with “N” and self-correcting full power steering, it provides soft shoulder, or no-shoulder safe recovery. (!) One finger steering returns the car to the roadway after a front, or a front and rear tire drop-off. Front and rear climb the shoulder at the same time in full control, even at high speed. This design eliminates over-correction accidents and rollovers.
N. 8 inch narrower back-wheel track prevents parking lot accidents by offering a narrow rear to follow the front end.
O. Three point suspension with an extra rear wheel. Either rear wheel can be removed and the car safely driven.
P. Trailer-hitch pickup without manual jacking of the trailer tongue: lower, move, and raise the car or station wagon. (!)
Q. In case of hydraulic failure, rubber springs seamlessly engage at slower driving speeds. (!) Ground clearance is reduced.
R. Front-end and rear-end wheel alignments are not necessary except for collision repair. (!) The rear axles are “fixed”.
A. Fast, 2.7 turns lock-to-lock Servo-Feedback-sensitivity-to-the-driver steering, with a 36 foot wall-to-wall turning circle.
B. Steering is not muscle powered, nor muscle powered with fan-belt driven pump assist. (!)
C. A Pressure-Reservoir full powers the steering with 2470 lbs hydraulic pressure, independent of the engine. (!)
D. A spring-loaded cam lightly holds the steering wheel in the dead ahead position. (!) Combined with self-correcting steering: hands free driving. Pot holes, soft shoulders, and tire failure have no effect on hands free driving.
E. Center pinned front wheels transmit drag forces to the frame, not to the steering linkage. (!) A loss of either front tire even in a curve has little effect on the steering. Two blown-tire combinations front and rear have little effect.
F. The front wheel geometry becomes slightly non-parallel during turning, causing the inside wheel to grab the road harder, and at speed, slip first and squeal, thus providing an early warning of approaching loss of front-end adhesion.
G. Accurate rack-and-pinion steering gradually and seamlessly engages, with warnings, if hydraulic power is lost. (!)
H. Michelin “X” steel radial tires, nearly 16 inches in diameter. (!) Changed to “ASX” 15 inch asymmetric tread. (!1965)
Servo-Feedback controls for the driver:
A Servo-Feedback control-valve pushes back in direct proportion to the effort applied:
A. Sensitivity is felt to the power applied to the brakes and therefore the application of the brakes. (!)
B. Sensitivity to the road is felt through the steering wheel; a first for power steering (!), compare to blind power-assist.
C. Sensitivity to the throttle: the lower fuel economy position and the secondary carburetor barrel accesses are felt.
Servo-Feedback controls for the operation of the machinery. A servo control for machinery regulates the application of energy:
A. Self-leveling suspension: front and rear axle height-regulators operate independently in response to load changes. (!)
B. Spring rate modifications are made per axle by self-leveling based on increases and decreases in the load. (!)
C. Spring dampening modifications are made instantly per wheel based on the size of the bump. (!)
D. Engine idle-speed: low idle-speed with foot on brake opens the clutch. Foot off the brake causes a high idle-speed that begins to engage the clutch for low speed parking maneuvering or to prevent backwards drift on a hill.
E. A Servo-Feedback control checks that 2nd and 3rd gears are fully engaged before allowing the clutch computer to re-apply the engine. (!)
F. Servo-Feedback instructs the steering computer to maintain wheel positions in response to asymmetric road hazards (!)
Dashpots to reduce functionality speed:
A. Height control. (!) Dashpots eliminate immediate height regulation caused by slight road irregularity.
B. Gear selector. (!) A temperature-sensitive dashpot allows the synchromesh to operate without slamming the gears. Viscosity variations between hot and cold hydraulic fluid do not affect the timing.
C. Carburetor idling. A dashpot eliminates sudden engine starvation at low speed idle.
D. Self-leveling headlamps. (!) A dashpot eliminates responses to minor road undulations.
E. A short wire “floats” in a small chamber in the hydraulic line to the front brakes to modify rapid high-pressure brake application. This prevents high pressure brake hammering without reducing the applied brake pressure. (!)
F. A short wire “floats” in a small chamber of the hydraulic line between the two front suspension spheres to enhance anti-roll function. This increases the time-response of body rolling during hard cornering to resist rollovers. (!)
A. The self-correcting power steering computer functions in response to driver demands, or by road hazard activation. (!)
B. Height control regulation. (!) The driver selects the ground clearance; load variations activate height adjustment.
C. Power brakes. (!) Front brakes have a high-pressure source. The static rear axle load creates the rear brake-pressure.
D. The front-to-rear brake effort distribution constantly changes by variations of pitching and ground topography: a piston connected to the rear suspension hydraulics delegates foot pressure between the front and rear brake valves. (!)
E. The gear selector is driver activated. Semi-automatic function is obtained by light, fingertip command through a hydraulic computer to a simple, “manual type” gearbox and dry clutch activated by hydraulic pressures. (!)
F. Clutch management. The engine’s brake-activated low idle speed and the driver’s gear selection control the clutch. (!)
G. Pressure regulation. (!) The pressure-regulator/main accumulator maintains a hydraulic system pressure of about 2470lbs. The pressure-regulator diverts the hydraulic pump’s effort to relax when the spheres are adequately filled and driving needs are satisfied. The pump operates at high pressure about 10 seconds each two minutes, otherwise the fluid returns at low pressure to the storage tank. The accumulator acts a capacitor reducing the demands on the pump.
H. Priority valve. (!) The priority valve directs pressure to functions in sequence, first the pressure-regulator/main accumulator plus steering and transmission, then the front brake accumulator, third to the suspensions and rear brakes. The front brake accumulator remains fully charged at all time while the other systems slowly deplete when parked.
I. Security valves. (!) Security valves seal the separate systems from pressure/fluid theft should any hydraulic line or other portions of the hydraulic system fail. If a hydraulic line looses pressure or consumes too much fluid too fast, that line is isolated by seating a spring loaded ball valve. A large red warning light and associated function idiot lights warns the driver as that hydraulic function is gradually being replaced by a mechanical backup system.
A. Panorama view wrap-around windshield with a very narrow “A” columns for excellent forward, and front to side visibility. (!) With normal, two-eyed, parallax vision, the typical two front blind spots are eliminated.
B. Narrow “B” columns for better side visibility.
C. No wing vents for better side visibility.
D. Side dashboard vents provide face ventilation to replace the wing vents. (!) Vents have additional fan power.
E. Side-window defrosters are linked to the front windscreen defroster. (!) Defrosters have additional fan power.
F. Double sealed front and rear windshields with easy slide-down-and-out replacement. (!) Three bolts front or two bolts rear are extracted to remove the windshields.
G. Windows roll up along a soft rubber seal being thrust slightly sideways at the closed position to compress a perfect seal.
Very low center of gravity to prevent rollovers, plus lightweight construction where possible, for fuel economy and roadability:
A. Frameless doors.
B. Frameless side windows.
C. Composite body and frame construction (!) with well over 50 pieces of light weight nylon used in the body trim. (!)
a. Fiberglass or aluminum roof depending on model (!)
a. Fiberglass or aluminum roof depending on model (!)
b. Fiberglass or aluminum rear hood depending on year (!) replaced by steel. (* 1962)
c. Aluminum front hood, the largest aluminum panel used on a car. (!) It weighs 12lbs.
d. Aluminum or plastic fan shroud depending on model.
e. Nylon radiator fan. (!)
f. Nylon (!) or aluminum instrument panel and dashboard depending on year, partial replaced with steel (* 1965)
g. Nylon (!) or fiberglass headlamp buckets depending on year.
D. Massive, internally-reinforced aircraft type 8 inch hollow section, ladder frame, with no arches over the wheels. (!)
E. The rear seat bench weighs 4 lbs.
F. The two station wagons seat 7 or 8 passengers, have a ¾ ton plus payload with 75 lb capacity roof rack, and 80 cubic feet of storage with intermediate and back seats collapsed into a flat floor. The opened lower tailgate extends the floor to 8’ for longer loads. (!) Sedan specifications apply except for increased rear weight and rear brake capacities.
H. The opened upper tailgate shields standing persons and the rear of the station wagon from rain and allows full access.
I. Three point suspension with four wheels. (!) Positive weight distribution on the front axel, low center of gravity, with the hydraulic suspension permits three-wheel driving of the sedans.
J. The front wheels are 8 inches further apart than the back, enhancing stability with a low center of gravity. (!)
K. By selecting lesser ground clearances, the center of gravity can be lowered for increased comfort and enhanced safety.
A. In line four-cylinder, aluminum-head engine. Wet cylinder sleeves for in situ, from-the-top, piston replacement.
B. Overhead valves, valves float at 6000RPM to prevent over-revving. Maximum cruising speed is just under valve float.
L. Hemi-head, for more efficient combustion, with “V” valves operated by short push rods from an overhead camshaft.
M. Cross-flow head, for more efficient intake and exhaust.
N. Two-barrel carburetor provides very economical running, plus strong acceleration when needed.
O. Three massive main bearings for high speed cruising. Over square displacement and five main bearings. (* 1965)
P. The DS 23 was also available with an electronic fuel injection system, the first French car so equipped. (@ 1972)
A. Front-mounted transmission, for aerodynamic low hood profile, low center of gravity, and slight forward weigh bias.
B. Four speed “manual” gearbox with dry clutch disk and hydraulic slave cylinder, computer controlled and clutched. (!)
C. Fourth (1955) and fifth (@ 1970) gears have overdrive ratios for high-speed economic cruising.
D. Gear shifting and clutching are hydraulically powered independent of the engine, not muscle powered. (!)
E. Manual transmission and clutch option on lesser ID models. (1956)
F. Integral differential; the differential is in the transmission gear box.
G. The industries’ largest front wheel bearings and universal joints for strength, stamina, and reliability. (!)
H. Hex stub axles with integral, one securing lug. Unfortunately replaced with standard five lug system. (* 1965)
I. A Borg Warner 3 speed full automatic transmission (from an SM option) was later available. (@ 1970)
A. Removable body panels: 30 minutes to demount the entire body for body repair or panel replacement. (!) Rubber insulated mounts prevent rattles. Doors come off with the loosening of a lock nut and pulling a safety pin.
B. Door hinge positions are all-direction adjustable to assist door alignment such as after a collision.
C. Three front hood locks, two internal, plus one external safety latch under the hood.
D. Color-coded slip connections for wiring harnesses permit modular harness repair, and the detachment of the body.
E. Two front and two rear triangular frame members (in side view) extend the ladder frame; they progressively absorb energy from front, rear, or partial side collision. This concept was started with the B11. Development was finished prior to the front and rear crush system introduced by Benz in 1954.
Aerodynamics were created by Bertoni’s “rack of eye”; later improvements were perfected by wind tunnel. (!) Bertoni was the first to use clay models (full scale) for rapid visualization and design measurement. (!) The design and molds for his futuristic dashboard were created over a weekend. Bertoni’s job was to incorporate and encapsulate the engineers’ machinery into useful shapes:
A. Aerodynamic teardrop body shape.
B. Full body under panel.
C. Rear wheel fender skirts.
D. Aerodynamic wheel covers. (Most cars have propeller hub-caps to cool their wheel mounted brakes.)
E. Glass enclosed shoulder mounted quad headlamps. (@ 1965); 18% increased fuel economy at 55MPH, 22% at 95.
F. Three massive air rams under the front bumper feed air to the disc brakes and the radiator. (!)
G. No front radiator. A central air ram located under the front bumper feeds available high-pressure air to the radiator.
H. Self-clearing rear windshield. (!) Above 7 miles per hour, rain and snow does not hit the rear windshield.
I. The muffler and gas tank are located in ladder frame “steps”, out of the air stream; the tank above the under panel.
J. Aerodynamic cleanliness; the coefficient of friction of .37, reduced to .34 in 1965, was not surpassed for 27 years. (!)
Current sedans average about .35.
K. The center of aerodynamic pressure is to the rear of the center of gravity increasing dynamic stability and minimizing the effects of cross wind.
L. By selecting lower ground clearances, “ground effect” enhances aerodynamic cleanliness at high speeds.
A. Self-leveling high/low beam headlamps respond to major road undulations, and hard acceleration or braking. (! 1965)
B. Directional high beam spotlights that turn in advance of the curve. (! 1967) High speed night driving is now possible within one’s stopping distance on a curving road. (The first turning headlamp was a bumper mounted, after-market addition, sold in France in 1908, not the center mounted head lamp of the 1948 Tucker.)
C. Three position high-low beam switch: two low filaments, four high filaments, or all six. The third “on” position is located between the high and low switch positions for high speed nighttime cruising.
A. Soft rubber window and door seals: fewer pinches from accidentally slammed doors.
B. Soft rubber rear hood seal: no pinch from an accidentally slammed bonnet.
C. Overshot-spring rear hood supports both hold open and force shut the rear bonnet. (These hood springs are now imitated with nitrogen filled spring struts. Does anyone see the irony? )
D. Clean, obstruction-free passenger compartment for comfort and personal safety in case of collision.
E. Energy absorbing, collapsible glove box and dashboard. (!)
F. Single spoke steering wheel for better forward and instrument visibility. The left hand rests comfortably on the spoke.
G. Collapsible steering column: front-end accident protection for the driver.
H. Well-padded front-seat backs for rear passenger safety.
I. High ceiling for front and especially the rear passenger headroom, well padded for silence and safety.
J. Higher rear-seat elevation to increase forward viewing pleasure for the rear-seat passengers.
K. Flat floored passenger compartments, front and rear.
L. Two-inch floor mats and integral padding for comfort, to absorb road vibration, and to attenuate collision impacts (!)
M. Very deeply padded upright seats provide comfort and support; passengers are cradled during lateral accelerations.
N. Anti-whiplash rear-seat head-level padded trim.
O. Anti-whiplash devices for the front seats. (@ 1970?)
P. Three point seat belts and shoulder harness the front and rear passengers. Seat belts were offered before the requirement by US safety standards. (@ 1965?)
Q. Forward mounted spare tire, not in the bottom of the rear trunk, enhances front collision shock absorption. The trunk does not have to be emptied to change a tire. The spare tire is clean and fresh, not hung below the vehicle.
R. The jack stand and the tire tools stored in the spare tire, under the front hood for clean, easy access (!)
S. A slide rod is provided to avoid lifting a wheel to be demounted or changed. It also augments the lug-nut wrench handle if additional torque is needed to loosen the lug nut or lug nuts depending on year.
T. A childproof over-lock is provided to secure the parking brake lock.
U. Childproof door locks. (@ 1965?)
V. The DS is the introduction vehicle for the steel belted radial tire invented by Michelin. (!) The B11 in 1948 was the introduction vehicle for the radial tire, also invented by Michelin.
W. Fingertips from the steering wheel reach all essential controls: horn, turn signal, parking light/headlight, high-low beams, windshield washer and wiper, and gear selector are reached with out removing the hands from the steering. (!)
X. No self-canceling turn indicator. Only the driver knows when he is finished signaling his intentions to turn.
Y. Two position town and country horn.
Z. Optional Maserati air horn as the country horn. (@ 1965)
Other Notable Features:
AA. Nine passenger air-controls for individual comfort, including rear passenger compartment foot vent and heater.
BB. Optional electric powered rear passenger heater and rear window fan-defroster for severe climates. (@ 1964)
CC. Electric grid rear window defroster. (@ 1965)
DD. Optional headlamp windscreen washer and wiper for sever climates. (Sweden export models) (@ 1967?)
EE. Internal radiator; the air ram is bypassed during drifting snow. (!) A flap valve restricts air entrance in extreme cold.
FF. Roof mounted rear turn signals. (!)
GG. The average stopping distances are posted at the speedometer: higher stopping distances are exposed as the speed
HH. Red “Stop” light in center of idiot light cluster to indicate any critical failure. (!) Individual idiot lights define the
II. Manual crank to start engine with weak battery.
JJ. Secondary starter control at the battery for mechanics to turn the engine with the hood up.
KK. Curved front bumper for tighter parking and to reduce parking lot accidents. (!)
LL. Low bumper and a “soft” aluminum sloping hood absorbs impacts and slides pedestrians to the side. [See the new European automobile safety standards for pedestrians.]
MM. Steep sloping hood allows increased forward visibility: the road is visible 7 feet in front of the DS.
NN. Gas tank is located in the most protected part of the car, forward of the rear wheels, trunk, rear suspension and rear crush zone, isolated from the passenger compartment. (!) It is mounted within a step of the ladder frame.
NN. The sun visors extend to overlap in the middle of the windscreen (!) and pivot to the side windows.
OO. Rear visibility is provided with the rear trunk lid opened. (!)
PP. An electric master-switch under the hood can disable a locked car. Causal hot-wiring is impossible.
QQ. A hydraulic bypass valve is located under the hood. It too can disable a locked car for increased security. (!)
RR. Spring detent feedback informs the driver of the functional position of all controls including the gear selector.
SS. The industry’s first radiotelephone communication, on the Prestige model. (! 1958) The telephone connected the caller with a Paris telecommunication tower. The phone was located for the back seat passengers, along with a bar. (You’ve got to love the French)!