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WHAT HOLDS BACK E BATTERY-ELECTRIC ?

30th June 1944, Page 26
30th June 1944
Page 26
Page 27
Page 26, 30th June 1944 — WHAT HOLDS BACK E BATTERY-ELECTRIC ?
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By W. J. Roberts

THE development of the battery-driven electric vehicle is intimately bound up with the history of the accumulator or battery. The limitations of the vehicle have always been fixed by the electrical and mechanical considerations inherent in the batteries available at the time.

Probably the earliest recorded event in which a batteryelectric machine participated was a reliability trial for motor vehicles organized as far back as 1904. Part of the route included Taddington Hill, on the Bakewell-Buxton Road in Derbyshire, and one of the cars that made easy work of the climb was electrically driven.

During the next few years many attempts were made to introduce and popularize the electric " motor brougham " for town use, doctors' visits, shopping, etc., and other short-distance work. These vehicles were moderately successful, and much unwarranted optimism prevailed regarding the future of electric transport.

The time was not ripe, however, for battery traction, and the accumulator industry at that period was not sufficiently well developed to sustain the effort, Then came the 1914-18 war and, in the years that followed, the rapid expansion of the petrol-vehicle industry pushed the electric into the background.

The history of accumulator development is probably known to most readers, but it is worth While to review the facts, as related to traction batteries. There are two main types of lead-acid accumulator, the Plante cell and the Faure cell, the active elements of both types being identical, viz., lead peroxide and chemically porous or " sponge" lead in a dilute solution of sulphuric acid.

In the Plante cell, the lead peroxide and sponge lead is produced by an electro-chemical process from metallic lead; the construction of this type of cell is of a rather massive nature and a large volume of electrolyte is required. It does not, therefore, naturally lend itself to applications in which lightness and compactness are the essential requirements.

The Faure type of cell was a later development of the Plante and, instead of the active materials being produced by electro-chernical means, they are applied in the form of a paste to lightly constructed " grids " or frames of antimonial lead, being subsequently " formed " into lead peroxide and sponge lead in the positive and negative plates respectively. It became obvious that the pasted type of cell held out great possibilities in connection with portable applications, such as traction uses, oa,s the capacity to weight ratio was much superior to that of the Plante type. Weight for weight, Faure cell possesses approximately three times the capacity of a Plante cell, but there was one disadvantage.

Early Troubles with the Pasted Positive Plates Owing to the tendency of the lead peroxide to soften, disintegrate, and fall out of the grids, it was found that the life of the pasted positive plate was short, and, for many years, this inherent defect was responsible for the batteryelectric vehicle failing to come up to expectations.

Modern battery-making technique has, fortunately, been able to overcome the trouble to a large extent, and it is now reasonable to expect a life of three to four years' normal service from a, modern traction battery.

During the period from 1920 to 1932 the petrol vehicle had developed rapidly and had practically captured the market for most forms .of road transport.. A distinct revival of interest in the electric vehicle then became evident for certain well-defined services, such as those which involved constant stopping and starting, a small total mileage, and which did not call for high road speeds.

As a result of this, modern electric vehicles have developed along two principal lines—the light delivery van and the lorry—in both of which spheres they have now become fairly well established.

Dealing with vehicle chassis design features, the problems encountered were numerous and varied, at the electric differs from its petrol counterpart in one or two vital considerations. To quote one instance; the petrol vehicle is designed for moderate weight-carrying capacity and for high torque at high speed, whereas the electric vehicle exerts a high torque at low road speeds.

Consequently, the whole transmission system of an electric vehicle requires to be designed to withstand stresses of a different nature to those of a petrol vehicle. Axle shafts, for example,need to be much stronger if they be transmitting power at -sloW speeds than they would need to he for high-speed transmission of the same power. In this connection, it may be noted, many makers fit a fuse in the motor leads in order to protect the drive assembly from damage by careless application of too heavy a starting

torque. This fuse is so arranged as' to " blow " at a current figure which would prove dangerous to the transmission line.

A good deal of experiment was also made during the early days with the object of deciding the most satisfactory layout for the motor and transmission system. Vehicles have been built and road testeclowitla various layouts, such as with motors in the wheels or bolted direct to the axles; mounted in the axle centre or above, the drive being taken through gears, and a system of shaft and chain -drive. The result of the experience gained has shown that the best position for the motor is up between the chassis sidemembers, where it is protected from wet, dirt and grit, being mounted at a slight angle and driving through a normal shaft with flexible couplings in a similar manner to the stRndard petrol vehicle.

Some of the Disadvantages of Front-wheel Drive Front-wheel drive has been suggested by many as being a desirable feature in battery-electric design, but several disadvantages present themselves, the first being the question of high torque at slow speeds. The use of constantvelocity joints of sufficient strength is open to question owing to the considerable increase in weight. They are by no means cheap (even for standard i.e. vehicles), and it may safely he assumed that the extra cost and liability to mechanical wear would preclude their use in electric vehicles.

Two other drawbacks, admittedly, not quite so serious, are the fact that the incorporation of a differential, together with two universal joints in a front axle, tends towards complication of the arrangement and involves redesigning. of the entire forward section.

Lastly, the use of a propeller shaft, with two half-axle shafts, provides a cushioned drive which it would be inadvisable to dispense with and which could not be obtained in any f.w.d. arrangement. The performance of a modern electric vehicle varies greatly according to the individual operating conditions, and only average figures can be given as examples. For the purpose of this article, the performance figures of three typical types of battery-electric vehicle are given. The first is a standard 10-cwt. utility van, the second a 40-cwt. machine with platform body, and the third a 7-cubic-yd. standard refuse collector. . It will be noted from the performance data relative to the 10-cwt. machine that alternative battery types are shown, :the standard and the oversize. The fitting of the oversize battery considerably increases the effective range of the vehicle,, but this is obtained at the cost of approximately 2 cwt. of pay-load--e.g., load with standard battery-10 cwt.; load with oversize battery, 8 cwt.

In any comparison of costs two important factors must be borne in Mind, as the electric vehicle competes with the i.e. vehicle only in certain specialized duties. It is specifically designed to do a particular job—that of making short trips involving numerous stops and starts.

Under such conditions of operation the electric has an outstanding advantage in that when it is stopped there is no question of current being consumed. On the other hand, when a petrol-driven van is used for stop-and-start duty, the driver invariably leaves the engine running, while he is making his call, The electric is ideally suited to repeated stopping and starting, for the reason that transmission shock is of little moment in so far as its effect upon the drive is concerned.

The Battery-electric has a Longer Useful Life For such a purpose the speed capacity of the i.c. vehicle cannot be usefully or economically employed, and it follows that the cost is proportionately higher. The other point is that the electric vehicle has a much longer life than its i.e.

counterpart. By reason of its construction the petrol vehicle, with its fast-running engine, its highly stressed transmission and gearbox, and its ancillary equipment, possesses a comparatively short useful life beyond which it does not pay to keep it in commission.

The average petrol vehicle will be found to show a considerable increase in maintenance cost and depreciation once it passes the 40,000 to 50,000-mile figure, whereas, the electric vehicle, having the minimum number of moving parts, continues to operate at a negligible figure for upkeep for many years.

In the following comparison of running costs between electric and petrol vehicles, the cost of current has been assumed at id. per unit " off peak " rate, and petrol at

'2s. lid. per gallon, these being current prices. The battery has been assumed to possess a life of three years; tyres are credited with 1,500 miles increased, life due to lower average speed and less " whip "; the electric vehicle chassis has been assumed as having a useful life of eight years, and the body and cab a life of only five years. It is considered that the foregoing are reasonable assumptions and, as such, are fair to the petrol vehicle. The two machines selected for comparison are 20-cwt. standard With any form of transport vehicle it is difficult to forecast the direction in which development will proceed, and the electric vehicle is no exception to this. At present, the most important consideration in limiting the application of electricity is the battery. Unless some revolutionary development in battery manufacture occurs there is no likelihood of the electric vehicle competing, to any great extent, with the established forms of medium and longdistance transport.

Possible Schemes Open for Future Development The possibility of alternative sources of electric power is one which must be considered as belonging to the distant future, as also must the idea of any established scheme of battery charging and changing by roadside battery stations. Neither of these is impossible, but the technical and commercial considerations involved are so great as to prevent any likelihood of a successful scheme being established. Rather is the development likely to be in the direction of lengthening of the mileage range with which must be coupled increased battery capacity, lighter vehicles, and the gradual improvement of battery-electric servicing facilities. Another reasonable assumption is the reintroduction of the petrol-electric vehicle in a modified form. Some promising experiments in this direction were made about three years ago; in this particular case two batteries were accommodated, one on each side of the chassis, and' a small engine-dynamo unit of nominal power housed under an orthodox bonnet.

The vehicle Was switched on alternate batteries for driving, and the engine unit, running at a fixed economical speed, was "'boosting " the other battery. It must be understood that no attempt was made to make the vehicle • independent of a charging station, the aim being more to extend the normal range of an initially fully charged battery. A range of about 190 miles was obtained on the initial trials, but, doubtless, this could be improved upon in time, The data regarding running costs are reproduced by courtesy of Morrison-Elcctricars, Ltd.

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