Title: A seat to make cars safer
Pages: 32 - 35
Author: Richard Carr
Text: A seat to make cars safer
by Richard Carr
It is now recognised that the design of seating for cars can make a positive contribution to the safety of d rivers and passengers. A number of safety seats have been produced in recent years; the latest by an American designer who has spent a year at the Royal College of Art, on a Fulbright scholarship, developing the seat described in this article.
Almost everyone is now agreed that the simplest and most effective way to reduce the likelihood of injury in a road accident is to fit safety belts, especially to the front passenger seat - the most dangerous place of all. In Britain, the Ministry of Transport has recognised the value of safety belts by making them a compulsory fitting in all cars produced as from April next year; in America lap belts (de, belts without a shoulder harness) are already required by law in some states, and will become a standard fitting when the federal code on car safety comes into force in 1970; and in a few countries, safety belts are already required by law. In Sweden, for example, they are fitted in every Volvo made.
Although safety belts are thus an extremely important part of the passenger's equipment in a motor car, the seat itself also makes a big contribution to the passenger's safety, and in a number of different ways. It is extremely important, for example, that the occupant should be comfortable, and that the shape of the cushion and back of the seat (and their relation to each other) should be right for him. Similarly, in the case of the driver's seat, the height and angle of the seat, and its position vis a vis the dashboard, must relate ergonomically to the controls of the car and provide the driver with maximum visibility. The suspension of the seat must also be such that it damps down vibration, and so helps to keep driver fatigue to a minimum. Finally, the seat must be fixed to the floor in such a way that it will not break loose under impact. In the files of the Birmingham Accident Hospital, for example, there are a number of cases of people suffering injury in a road accident because, though they wore safety belts, their seats came away from the floor.
A lot of work has already been done to make a seat which meets all these requirements. The most notable example of this is the Cox safety seat (DESIGN 190/28-35 and 203/26) which is now available in two sizes, and can be fitted to a number of different cars. But despite the advanced design of some of its features, such as the built-in belt with its inertia reel and the filing cabinet type fitting of the seat to the sides of the car, the seat has a conventional construction, and in consequence suffers from bulk and weight. And on these two points alone, a considerable improvement has now been made in a research project undertaken in the research unit of the school of industrial design at the Royal College of Art.
Fulbright scholarship to the RCA
The seat project is the work of Joseph Koncelik, an American industrial designer who was trained at the Pratt Institute and Stanford University, and spent two years in the research studio (styling staff) of General Motors in Detroit, of which 18 months was spent on a project developing new concepts for passenger safety. The work in Detroit gave him a good introduction to car seating, since he investigated all types of seating to see how the problem of vibration could be overcome. In this way, he examined bench seats, single contoured seats and seats built up on aluminium castings, and upholstery based on foam, standard zig-zag springs, straps, torsion bars and rubber diaphragms. His next step was to develop a programme for research into automobile safety seating, for which he was given a Fulbright scholarship which took him to the RCA for one year, beginning in September 1965.
Mr Koncelik's programme had three main stages: first, a survey of automotive seat design as it exists in Britain today; second, the design of a seat based on the survey, and the building of a prototype; and third, tests and analysis of the prototype.
Surveying the field The first stage of the programme was completed by visiting a number of manufacturers of car seats and consulting whatever literature was available on the subject, most of which is kept by the Road Research Laboratory. Mr Koncelik also contacted leading research people in the field, and in particular J. Christopher Jones, who has carried out experimental comfort tests on a number of seats using subjects who have recorded their sensations during five hour spells in one seat. (In fact, Mr Jones' experiments have shown up weaknesses in some seats which were missed by tests carried out by the Consumers' Association, mainly because its subjects sat in the seats for three hours only, and it was only after three hours that real discomfort set in.) Then, having analysed his information, Mr Koncelik drew up a specification, based on the performance characteristics required, which led to the choice of materials and the configuration of the seat dimensions. At this stage it became apparent that his wish to have a seat that was both light and thin in cross section would be limited by the requirements of structural strength.
There was, in fact, a second set of compromises at this stage which involved the ergonomics of the seat. As Mr Koncelik puts it, "There are two ways of tackling the ergonomics of a project of this kind. The first is by starting from scratch, assuming no given criteria, using no particular vehicle, and then trying to achieve an optimum passenger seat for motor cars. To do this, the designer would have to prepare tests to deduce the optimum seated position of at least 85 per cent of the size range of people who would
A seat to make cars safer
This diagram shows a section through the seat. The hard lines inside the seat represent the diaphragms, and the grey area the foam rubber upholstery. The profile shape is based on an earlier version of the seat, and differs slightly from the seat shown in the photographs. Dimensions: seat depth 15 inches; seat width 23 inches; top of backrest above seat 26 inches (with headrest 34 inches); width of backrest at top 20 inches.
Diagram showing the interleaving rubber diaphragms for seat and back. The diaphragms are of comparatively low tension, and deflect about one inch along the centre line of the seat when loaded.
use his seat, and this would entail basic research into comfort, safety, fatigue and so on. The second method is to assume given criteria, choose a car with given dimensions, and start from there. I chose the second approach for three reasons: I wanted to achieve a working prototype, so the former method was immediately excluded because of the time limitations; the interior dimensions of actual cars offer 'real' parameters in which the ergonomic considerations are well delineated; and I have a personal aversion to projects that try to achieve 'ideal' solutions. And in the case of a car seat, the seat must be tuned to the car in which it is placed, and the comfort, feel, durability and type of safety options depend upon the size of the package and the amount of money the manufacturer is willing to spend on it.
Mr Koncelik chose the Austin 1800 for his package because it has good leg room front and rear, and space to spare for the additional structure of a safety seat. In fact, the 1800's own front seat is 24 inches wide, a dimension well outside the 17 inches minimum recommended for proper comfort, and the vertical dimension from the depressed contour of the seat cushion to the head liner is over 37 inches, which allows room for a headrest. In addition, the 1800 seat has an H point to heel hard dimension (de, the height of the passenger above the floor) of over 10 inches, which gives the designer latitude to use a spring system configuration. On the Koncelik seat, the other dimensional parameters of ergonomic importance adopted were that the deflection of the spring system should be no greater than 14 inches, and no less than 43 inch, to provide proper dynamic support; the trunk angle as measured off the vertical should be no more than 30ø; the peak of the lumbar support should be 5 inches up on the backrest from the base of the seated occupant's posterior; the length of the cushion should be no longer than 19 inches and no shorter than 15 inches; and the height of the backrest should depend on whether or not the belt is attached to the seat structure. If it is, the backrest should be high enough to prevent the belt causing spinal compression under impact.
Besides the major dimensional parameters, any movement of the occupant under impact conditions has to be kept to a maximum of 9 inches, as beyond this limit whiplash could develop which would be sufficient to injure or kill the occupant. Thus, the inertia reel and belt selected had to meet this requirement, and the fasteners and clips on the belt had to be designed so that, under strain, they would not ride upward and drive into the occupant's internal viscera - one of the dangers of lap belts.
Help from industry After the specifications had been drawn up, a drawing was made of the seat and detailed drawings of the frame were then prepared and submitted to Cox of Watford for comment. As a result of Cox's own experience of car seats, a number of modifications were suggested to eliminate several weaknesses. The frame itself was made in the RCA workshops. At the same time, Vitafoam was taken up on its offer to make two experimental interleaving rubber diaphragms, one for the back of the seat, the other for the cushion, and these were trimmed in pvc and cloth on Latex foam by Callow and Maddox Ltd. The seat was fitted with a safety belt, buckle and clip supplied by Kangol, and an inertia reel (built into the shoulder of the seat) supplied by Britax.
Basically, the Koncelik seat consists of a tubular steel frame which supports two rubber diaphragms, and a built-in safety harness. The frame itself is light yet strong, and the rubber diaphragms provide a flat springy material which cuts additional upholstery to a minimum, has a high, natural hysteresis loss (unlike steel springs, which can reverberate in much the same way as a tuning fork) and is very easy to trim. The springiness of the seat depends, in fact, on the thickness of the rubber used, and the rubber itself will never 'bottom' in the way that springs will flatten out and go dead when they are compressed beyond a certain limit. On the Koncelik seat, there is only sufficient tension to hold the diaphragms in place, and under normal loading there is only about a one inch deflection on the centre line along the seat cushion. Two things need further development on the seat: first, the length of the cushion, which Mr Koncelik believes is an inch too short; and second, the method of fixing the seat to the floor of the car, and adjusting its rake and movement fore and aft.
General view of the Koncelik seat installed in an Austin 1800 for tests at Silverstone. Although it is difficult to work out its cost on a mass production basis (it might be between £15 and £20, as against £6 retail for a standard car seat), the Koncelik seat could probably be produced in small quantities for between £20 and £30. This compares with a price of £33 for the Cox GT-3 Mark 1 safety seat.
The basic frame of the seat is made of 16 gauge, 1 1/16 inch diameter high tensile steel, and weighs 22 lb 14 oz. The complete seat with adjustors weighs just 34 lb.
The difficult problem of providing sufficient adjustment for passengers is made worse where the adjustment
mechanism has to bear the loads of the safety belts as transmitted through the seat frame. In elevation, there should
be a spread of at least 10 inches between the points at which the compression member and the tension member of
the structural frame join the adjustment mechanism, and this means that if a minimum of 6 inches fore and aft
adjustment is provided, the adjustor tracks will be quite long. However, in the Austin 1800, where the passenger is
higher off the floor than, say, in a sports car, a sophisticated adjustor which raises the seat as it moves forward, and
has a curved track which will tilt the back forwards to distribute the weight properly in the lower anthropometric
range, could be designed with a total fore and aft track of 3 inches. Mr Koncelik's seat, however, uses modified 1800
adjustors which do not meet his specification, though his drawings show the kind of adjustment mechanism that is
really needed. Its aim is to ensure that the eye points of all the occupants in the passenger seat are situated within
a kidney shape space about 2 inches across.
Testing the prototype
So far, the only really unresolved part of the project is its third stage -the testing and analysis of the prototype. Because only one has been built, it has been impossible to do crash testing to see how it (and the occupant) will stand up to rapid deceleration. Only two tests have been carried out, the first at Silverstone to measure subjective reactions based on Osgood's method (see the Measurement of Meaning*), and the second at the Consumers' Association's track in Essex to measure the vertical vibration input to the passenger from the seat suspension system as transmitted from the suspension and floor of the car. But much more extensive testing is required including crash testing to see how the frame and belt perform under stress, before a complete evaluation can be obtained. In the meantime, we can only echo the praise given by Mr Koncelik to the various manufacturers who have co-operated in this project. He says that he doubts if so much time and assistance would have been given (free) in the United States, and his experience confirms his belief that British manufacturers are wolf in the lead when it comes to know-how about car seats. Since Cox has taken the initiative by marketing its own safety seat, it is to be hoped that it or some other company will exploit the knowledge gained by Mr Koncelik's project, and make his own seat (or something like it) available for mass production.
*Measurement of Meaning, Charles E. Osgood and others, University of Illinois,1957,