A British sports car concept featuring the Bluebird cartridge exchange instant recharging system




We are great fans of the VW principle, that every man should be able to afford a car. In fact that was Hitler's plan, where VW stands for "peoples car." Even a real baddie can have good moments. Prof. Porsche came up with a superbly simple design in the Beetle, that is unfortunately not suitable as an EV donor. The Metro above turned out to be just the ticket.



The rules for the Cannonball ZEV International Runs are simple, you must use production vehicle running gear - the car must be road legal. The ultimate prize is the Blue Bird World Cup. Our unique DC50 car began life as an Austin-Rover Metro. These cars used rubber cone and compressed gas suspension units with cross-axle liquid exchange known as Hydrolastic, or Hydragas suspension.


When servicing suspension bearings and joints using the rubber cone (hydrolastic) and hydragas system(s) it is necessary to de-pressurize the fluid to effect replacements. The UK team want their vehicle to be in tip-top condition so will be servicing the suspension roller bearings and spindles along with other brake and steering parts.




This is the basic suspension layout of the Metro, actually this is a picture Mini subframes. But they are very similar and of course the Metro was derived from the Mini design, an evolution rather than the Mini revolution. The Mini being the most popular car ever produced in the UK, with over 5,000,000 million cars sold worldwide. The Rover Metro's Hydragas suspension has sealed hydraulic displacers, one at each wheel connected on each side of the car by a reinforced plastic pipe. When a front wheel hits a bump, the upward force is transmitted to the fluid in the lower diaphragm. This in turn transmits the pressure to the gas in the upper diaphragm, which compresses to absorb the shock. At the same time, fluid is forced through the pipe to the rear unit. The result is that the floorpan stays level: the front end doesn't lift and the back end doesn't squat. At the same time, the redesigned geometry helps to prevent dive and lift on braking and acceleration, giving an impressively smooth, level ride.




There is usually quite a bit of confusion as to the difference between hydrolastic and hydragas systems, but it's fairly simple. Hydrolastic suspension has a rubber spring built into it - a sort of mini cone, when compared to the Mini dry cones, while hydragas uses a compressed gas spring. No rubber, which is sure to have made Dr Moulton cry. 


Both are suspension systems rather than just springs, in that they include a damping system to slow the action of the suspension. The operation of both systems is the same, operating in the same dimensional space. Thus, they are interchangeable.


The main objective of using fluids, is to hydraulically link the front to the rear, to provide a more level ride. The smoother the ride, the less energy the car will need to drive it along the tarmac.

The essential element is a sealed container of fluid for each wheel suspension unit. Hence there are four sealed containers to replace coil springs (for example). These are then linked fore and aft; the left front linked to the left rear, along with the right front linked to the right rear. 




In this diagram the left unit is uncompressed and the right compressed. 



There are two containers for each unit as seen in the diagram above, stacked on top of each other, with the nitrogen gas (spring) above the fluid filled chamber below.


The lower chamber is linked hydraulically to the fluid chamber at the opposite end of the car. In order to flow to another unit, the fluid has to flow through a valve assembly between the two containers, and then through a long pipe to the other unit.

The idea is that if the front wheel hits a bump, the compression of the suspension pushes the fluid to the rear unit. This causes the rear suspension to extend by the same amount that the front is compressed, keeping the car level despite the bump, so eliminating the fore/aft pitching that would occur if the bump affected the front suspension alone - as per most vehicles with "normal" (steel coil spring) suspension. The process is reversed when the rear wheel reaches the bump, again keeping the car level. This works for potholes as well as humps - useful today where the roads are so poorly maintained. Thomas Telford would be appalled.




The front hydragas unit is compressed by a bump, sending fluid to the rear which caused the swing arm to push down - so lifting the car by the same amount as the front wheel goes up - canceling out the bump. Some of you may have noticed the opportunity that such a system provides in terms of micro energy generation. This would not have occurred to Moulton or Issigonis, because of course their cars were petrol powered. Ours is electric with a battery store as a load leveler. See the example micro generators at the foot of this page - all of which are too large for this application.

It is the valve between the two containers that limits the rate at which any one suspension unit can compress or extend, and the diameter of the pipe that limits how quickly the transfer between either side's front and rear units can occur, providing the damping within the system. 


The next question is; what happens if both front and rear units are compressed at the same time, when they'd cancel each other out?  The answer is that the top containers of each unit have a spring inside them - rubber on the hydrolastic system and gas in the hydragas units. With the lower containers being squeezed by the suspension, and no way out of the upper containers (as in escape to the other end of the car) the fluid's only choice is to compress the spring, giving pretty much the same suspension action as if the spring itself was being compressed directly.


Why doesn't the fluid itself compress? That is because of a basic law of physics that says a fluid in incompressible. Of course we don't want it to compress, so it's made up or water (mostly) with some anti-freeze and anti-corrosion agents added. Coloring is added to help show up leaks or contaminated fluid easily.


The reason nitrogen gas is used, is because it is an "inert" gas - it is stable and does not react with most things, nor pressure or temperature. A compressed gas spring gives a rising-rate performance, too, just like a rubber spring.





LEFT - Front and RIGHT - Rear hydragas suspension diagrams showing the detail of the wishbones and swinging arm design. It all looks so simple and it is, but it took a lot of working out how to produce a suspension system using rubber (to begin with) and fluid.



Both systems are designed to be fit-and-forget parts or sealed units. History has shown that they have a working life in the region of 15 years and more before leakage and corrosion become issues. They provide an excellent quality of ride without compromising handling, and, providing the damping is set up correctly, don't "wallow" under cornering, braking and accelerating. The continued development of hydragas eventually led to fully cross-linked systems joining both the left and right sides together to make the most of the benefits.


Today, there are more modern systems that can outperform hydragas systems, but at greatly increased cost, and this level of performances was achieved over four decades ago, with relatively basic mechanical parts that lacked any kind of "active" or feedback control on them. Imagine how good they could be if they were active? We'll stay with what works for now, because the design outperforms most production cars today. There is no point re-inventing the wheel when there is more work to do on the EV drivetrain.






Dr Alex Moulton



Alexander Eric ("Alex") Moulton CBE, FREng (9 April 1920 – 9 December 2012) was an English engineer and inventor, specialising in suspension design.

Moulton was educated at Marlborough College and King's College, Cambridge. He was the great-grandson of the rubber pioneer Stephen Moulton, the founder of the family business George Spencer Moulton & Co. Ltd., in which he worked after World War II, specializing in rubber suspension systems for vehicles. His father, John Coney Moulton, was a naturalist working in the Far East.

During the war he had worked on engine design at the Bristol Aeroplane Company. In the late 1950s, after the acquisition of the family business by the Avon Rubber Company, Moulton started up a new company, Moulton Developments Limited, to design the suspension system for British Motor Corporation's new small car, the Mini, that was being designed by his friend Sir Alec Issigonis. 


The combination of conical rubber springs and small wheels was one of the many innovative developments that allowed Issigonis to achieve the Mini's small overall size. This was later refined into the hydrolastic and hydragas suspension systems used on later British Leyland cars such as the Austin Maxi, Austin Allegro and Rover Metro, and most recently on the MGF.



Sir Alex Moulton and his bicycle  


Alex Moulton with his most famous designs, the Moulton cycle with full rubber suspension and the Mini's rubber cone suspension.



Moulton also designed the Moulton Bicycle, again using rubber suspension and small wheels. Alex Moulton Bicycles is based in Bradford-on-Avon, Wiltshire, England.


Dr Moulton founded his own company, Moulton Developments Ltd, in 1956 and worked closely with the British Motor Corporation (BMC) for many years, developing automobile suspension systems. Famously, these included the rubber suspensions systems for the Mini and the Hydrolastic systems for the Austin 1100/1300 and other BMC and British Leyland models. Later, he was responsible for the Hydrogas system, which was developed for the Austin Allegro car and is still in use on the Rover 100 series and the MGF.


Alongside the development of suspension systems for cars, Dr Moulton designed his revolutionary Moulton Bicycle. He explained that this was: “… born out of a resolve to challenge and improve upon the classic bicycle …”  It is said that he holds the view that “… one is capable of pursuing two main avenues of research simultaneously, but no more”. We would agree with him.


The Moulton bicycle was the original full-suspension bicycle, highly efficient and designed with superior performance and comfort in mind. These bikes are lighter, safer and more comfortable, yet still go faster than most as well! The Moulton Bicycle is now a design classic, which has continued to be developed over many years, spawning a massive following of devotees and a wide range of models and variants.

Despite its early origins, the Alex Moulton Bicycle was a winner of the 2005 New Designer’s competition for the most iconic example of British ingenuity, nosing ahead of the ipod MP3 music player. James Dyson commented, “… good design is about how something works, not just how it looks, which is why I like the Moulton bike so much.”



Alex Moulton and Alex Issigonis


Dr Alex Moulton and Sir Alex Issigonis were great friends. They worked together on rubber and hydrolastic suspension - to give the UK some huge motoring successes. Sadly, the UK is backward in thinking forward on most fronts, thus surrendering a technological lead for lack of investment - the inability to predict the future such at to cater for the future is a major UK failing; part of the stiff upper lip attitude that sends pioneers elsewhere.





Sir Alexander Arnold Constantine Issigonis, CBE, FRS, RDI (18 November 1906 – 2 October 1988) was a Greek-British designer of cars, now remembered chiefly for the groundbreaking and influential development of the Mini, launched by the British Motor Corporation (BMC) in 1959. Sir Alex was just under 6ft tall with large expressive hands. He hated all things big - big cars, big organisations, big houses - and loved to shock his listeners.


Issigonis went into the motor industry as an engineer and designer working for Humber and competed successfully in motor racing during the 1930s and 1940s. Starting around 1930, he raced a supercharged "Ulster" Austin Seven, later fitting it with a front axle of his own design, leading to employment at Austin. This greatly modified machine was replaced with a radical special completed in 1939, constructed of plywood laminated in aluminium sheeting. The suspension was also of advanced design, with trailing arm front suspension attached to a steel cross-member, and swing axle rear, all with rubber springs made of catapult elastic. This car was remarkably light, weighing 587 lb, of which the engine contributed 252 lb. By the time the chassis had been completed (hard labour - it was all done by hand, no power tools), Issigonis had moved to Morris Motors Limited, but Austin supplied a "works" specification supercharged side-valve engine. Issigonis usually won, even when entered in the 1100cc class if there was no 750cc category. Most events entered were sprints, but he also raced at circuits.





Alec Issigonis at the drawing board. He was a practical engineer who had hand built a car in plywood and aluminium for some racing success, before he went on to work on rubber suspension and the Mini motor car.



At the end of 1956, following fuel rationing brought about by the Suez Crisis, Issigonis was ordered by Sir Leonard Lord to bring the smaller car, XC/9003, to production as quickly as possible. By early 1957, prototypes were running, and by mid-1957 the project was given an official drawing office project number (ADO15) so that the thousands of drawings required for production could be produced. 


In August 1959 the car was launched as the Morris Mini Minor and the Austin Seven, which soon became known as the Austin Mini. In later years, the car would become known simply as the Mini. Due to time pressures, the interconnected suspension system that Issigonis had planned for the car was replaced by an equally novel, but cruder, rubber cone system designed by Alex Moulton. 


The Mini went on to become the best selling British car in history with a production run of 5.3 million cars. This ground-breaking design, with its front wheel drive, transverse engine, sump gearbox, 10-inch wheels, and phenomenal space efficiency, was still being manufactured in 2000 and has been the inspiration for almost all small front-wheel drive cars produced since the early 1960s.



Many hydrolastic systems need an occasional top-up of the hydragas fluid to maintain the correct ride height, which in turn ensures the correct suspension characteristics. Failure to maintain the correct ride height results in accelerated & uneven tyre wear, poor handling dynamics & ride comfort. Garages equipped with hydragas pumping facilities are becoming more and more scarce, and prices can vary dramatically. This half litre bottle (500mls) of factory original / dealer fitted hydragas fluid should be enough for several top-ups. The cost is £6.75 + £2.90 postage & packing. Manufacturer (MG) Part Number: GZS1486. Interchange Part Number: S3SHHF5




A homemade evacuation and high-pressure system based on a bottle jack hydraulic pump. You'll need a vacuum pump to complete the system. It's far cheaper than buying one of the professional systems that cost around £400.





TURGO IMPULSE WHEEL - The Turgo wheel is a refined version of the Pelton. It was designed by Eric Crewdson in 1920. The maximum efficiency of an impulse wheel is achieved when the velocity of the runners at the center line of the nozzle is half the velocity of the incoming water. To achieve the highest velocities the ratio of the diameter of the wheel and the diameter to the center of the nozzle should be as small as possible. The wheel has a minimum ratio of 9:1, the Turgo has a minimum ratio of 4:1. The Turgo is half the size of the Pelton and operates at twice the speed. This makes the unit cheaper and reduces the amount of gearing necessary. The Turgo can have an efficiency of over 80% at the correct operating pressure.




Various micro generators that are commercially available using Pelton Wheels, or variations close in design to Francis Turbines. One obvious development that would be necessary for incorporation in a hydragas circuit, is dual flow: Simply put, another nozzle aimed at the generation wheel in the opposite direction such as to work with return pressure - and give generation on the up-stroke of the car's suspension, and the re-bound. Sounds promising. All you students out there looking for a masters degree project, give us a call. Our vehicle is at your disposal as a demonstration test bed from August 2014.
































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