Popular Science Monthly/Volume 57/September 1900/Electric Automobiles
AS electricity has been so successful in the street railway, where it has superseded all other forms of motive power, it might naturally be supposed that it would do equally well in the automobile; but when the difference in the conditions is taken into consideration it will be found that such a conclusion is not justified. In the street railway systems the cars run continuously over the same route, and on that account the electric current required to operate the motors can be conveyed to them from a central power station by means of wires. With the automobile the case is very different; the vehicle has no fixed course, but is required to go everywhere, and the current must be supplied from a source carried by it. If primary batteries could be made so as to furnish electric currents at a low cost, then the electric carriage would be in the same position as those operated by steam or gasoline, and it could go wherever the proper chemicals to renew the battery could be obtained. But as there are no such primary batteries, the only way in which the current can be supplied is by the use of storage batteries, and these cannot give out any more energy than is put into them, and in practice cannot give quite as much. Thus if the capacity of the battery is sufficient to run the vehicle forty miles when this distance has been traversed the propelling power will be exhausted, and the batteries will have to be recharged before the carriage can go any further. If the recharging could be done in a few minutes, the storage battery would be as good as a primary battery that would generate electricity economically; but as it requires three or more hours, the electrical vehicle cannot be used for long runs, unless the user is willing to make long stops each time the battery has to be recharged. Even then an electric vehicle could not go everywhere, for it would be compelled to follow routes along which facilities for recharging the batteries could be found. From this fact it can be seen that the electric automobile carriage cannot cover the same field as the steam or the gasoline (in the present state of electrical development). Within the limits to which it is applicable, however, it can perform its work in the most satisfactory manner, and, in fact, no possible objection can be raised against it. Its operation is noiseless and vibration of the vehicle is impossible. There is no heat to inconvenience the passengers, no disagreeable smell, no escaping steam. Any desired speed can be obtained, although, of course, a heavy delivery wagon cannot be used also as a racer. The power can be made sufficient to propel any desired load up any grade, including grades far steeper than any to be encountered on streets or highways.
The only point in which the electric vehicle suffers in comparison with the others is in the weight. The capacity of a storage battery is proportional to its weight, and if it is made light, the power derived from it will be small or the time during which it is furnished will be short. To furnish one horse power for one hour requires about one hundred pounds of battery, so that if the average consumption of energy is at the rate of two horse power, one thousand pounds of battery
will keep the vehicle in motion for five hours. The weight of batteries used in automobiles ranges from four or five hundred to about two thousand pounds, and the distance traversed without recharging varies from twenty-five to ninety miles, so that the radius of action of electric vehicles can be said to vary from about twelve to forty-five miles from the charging station.
The general arrangement of an electric carriage can be understood from Fig. 1. The rectangle shown in broken lines at A represents the storage battery. The circle B under the seat represents the controlling switch. The motor is at C and imparts motion to the axle or wheels through the gearing contained in the casing D. When the carriage is stopped the controller B is turned into such a position that all electrical connections between the battery and the motor C are broken. To start the vehicle the controller B is turned so as to make the necessary electrical connections between the battery A and the motor C, and then the electric current passes from the battery through the controlling switch to the motor, and thence back to the controller and the battery. The heavy broken lines indicate the path of the current and the arrows show the direction. The velocity of the motor and the speed of the carriage are varied by varying the strength of the current, and this is effected by the movement of the controlling switch B. There are many ways in which the movement of this switch can vary the strength of the current, but an explanation of any one of them would be dry and rather technical; hence it is sufficient to say that whatever the arrangement of the connections of the controller with the other parts of the system, their relation is such that by the movement of the switch handle the speed of the motor is changed from zero to the maximum velocity.
|Fig. 2. Double Reduction.||Fig. 3. Single Reduction.|
In the majority of American vehicles the motion of the motor is transmitted to the wheels by means of spur gearing. In some cases a single motor is used, in others two; and in one or two designs that have come to public notice, four motors are employed, one for each wheel of the carriage. Fig. 2 illustrates what is commonly called a double reduction gear for single motor equipment. The outline A represents the motor, B being the shaft. Upon this shaft is mounted a small pinion which meshes into a larger wheel on the intermediate shaft C. This shaft carries a pinion which meshes into the wheel D mounted upon the axle of the vehicle.
Fig. 3 illustrates a single reduction double motor equipment, the motors being located at AA. In this arrangement the pinion on the end of the motor shaft meshes directly into a large gear secured to the carriage wheel, thus dispensing with the intermediate shaft C of the previous figure. The single reduction gear is the more simple in construction, but the motors run at a lower velocity, and on that account must be larger for the same capacity. With the double motor construction each wheel is driven independently and the axle C, in Fig. 3, remains stationary, as in any ordinary vehicle; but in a single motor equipment, arranged as in Fig. 2, the wheels are fastened to the axle and the latter rotates. When a carriage runs round a short curve the outer wheels will revolve faster than the inner ones, if free to move independently, as in Fig. 3. If they are rigidly attached to the axle, as in Fig. 2, one or the other will have to slide over the ground, and this is decidedly objectionable with rubber tires. To prevent this slipping of the wheels in rounding curves, the axles, in designs following the construction of Fig. 2, are made in two parts, and the gear D is arranged so as to drive the two halves, imparting to each one the proper velocity. Gear wheels of this kind are called compensating gears; they are made in many designs, but the most common form; s that illustrated in Fig. 1. In this drawing A is the gear D of Fig. 2, and BB
|Fig. 4. Compensating Gears.||Fig. 5. Single Motor Equipments.|
are bevel gears which are mounted upon studs C, which are virtually the spokes of wheel AA. Large bevel gears E and F are placed on either side of A E, being secured to G, which is one-half of the axle, and F and H, which is the other half. If the carriage is running in a straight lino, the two parts of the axle G and H will revolve at the same velocity and the gears BB will not revolve around the studs C, but in rounding a curve one of the halves of the axle will revolve faster than the other and then the gears B will rotate round the studs C. The compensating gear is not a feature peculiar to electric vehicles; it is used on all kinds of automobiles when the construction is such as to require it.
If a compensating gear is placed upon the axle the Latter, instead of. supporting its end of the vehicle, will itself have to he supported, for as it is cut in two at the center, it has no supporting strength. By placing the compensating gear on another shaft this difficulty can be overcome. Fig. 5 shows the construction used by the Columbia Company in its single motor equipment. In this arrangement the motor casing is made of sufficient length to reach from one side of the vehicle to the other. The armature and field magnets of the motor, which are the parts that develop the power, are located at A and the compensating gear is placed at B. The motor armature is mounted upon a hollow shaft, which is connected with the compensating gear. The shafts D
and C, upon which are mounted the pinions E and F. are turned by the side wheels of the compensating gear, and therefore will run at such velocities as the motion of the carriage wheels may require.
Fig. 6 shows a Columbia victoria provided with a single motor equipment
arranged in accordance with the diagram, Fig. 5. Fig 7 shows another Columbia vehicle in which a double motor equipment is employed. The position of the motor, with reference to the carriage wheel, in the single motor design, is shown in Fig. 8. The gear attached to the carriage wheel is used also as a brake wheel, a friction band being located so as to bear against the periphery, while the pinion on the end of the motor shaft meshes into teeth on the inner side of the rim. This single motor design is also used in the omnibus made by the Columbia Company, a number of which are now in regular service on Fifth avenue, New York. These omnibuses, which are illustrated in Fig. 9, seat eight passengers, and are able to carry as many as are willing to crowd into them. One feature of the electric motor
which fits it admirably for automobile service is the fact that for a short time it can put forth an effort far greater than its normal capacity, and it can do this at all times, without any special preparation. Owing to this feature it is practically impossible to stall the vehicle. If the wheels run into a rut or sink into a mud hole, the motor will be able to turn them around, and if they do not slip the carriage will be moved ahead.
The management of the vehicle is exceedingly simple and entirely free from care, the driver having nothing to tax his mind but the steering lever and the handle of the controlling switch. As the moving parts all have a rotatory motion and are perfectly balanced, there is no possibility of vibration, and there is an entire absence of heat or disagreeable odors.
Any one who has observed the action of a two-horse team will have noticed that, unless the pavement is very smooth, the tongue continually swings from side to side, and occasionally with a considerable amount of violence. It will be evident from this fact that if the front axle of an automobile were the same as that of a horse vehicle, the driver would have an unpleasant task, to say the least, in holding the steering lever in position, and should one of the wheels drop into a rut, the handle would be jerked violently out of his hand and the vehicle would sheer off to one side, possibly with serious results. To avoid this difficulty the front wheels of horseless carriages are arranged so as to swing round on a center close to the hub, if not actually within it. The most common construction is illustrated in Fig. 10, the first being a
view of the axle and wheels as seen from the front, and the second a view from above. On the left-hand side of Fig. 10, A is the axle proper, and BB are the portions upon which the wheels are placed. The central part A is held rigidly to the body of the vehicle or to the truck which carries it, and the ends BB are swung round the studs PP in a manner more clearly indicated on the right-hand side. Here the levers CC are shown, and these extend from the side of BB. The right-angle lever E is connected with the steering lever G by means of rod F, hence, when G is moved, rod D moves, and thus levers CC are rotated round the studs PP, and in that way the supporting studs BB which carry the wheels are turned. As the studs PP are not exactly in line with the plane passing through the center of the rim of the wheel, there is a slight tendency to jerk the steering handle round when
a wheel drops into a hole in the pavement, but the leverage of B being very short, this tendency is so small as to be hardly noticeable.
Fig. 10 illustrates the general principle upon which the front axle is designed, but the construction of the swivel joints P is far more elaborate, as can be seen from Fig. 11, which illustrates the actual design employed in the vehicles just described. Looking at Fig 9, it will be noticed that the front axle consists of two bars, one of which run
|Fig. 11. Front Axle.||Fig. 11. Front Axle Wheels.|
in a straight line from side to side, while the other is curved with the convex side upward. In Fig. 11 B is the end of the upper curved rod and C is the lower straight one. These two rods are secured into the casting A, which holds the part D upon which the wheel is carried, D being the part B at the left side of Fig. 10. The end E which is broken off in the drawing extends through the hub of the wheel and is provided with ball bearings so as to run without friction. The upper end F, of D, is arranged so as to be held by a ball bearing, as shown, against the end of J. By means of an adjusting screw I at the lower end, the parts are brought into proper position with reference to each other. The shaded portion H is the lever C at the right side of Fig. 10.
The left-hand end of Fig. 12 shows a design for front axle wheels which is one of the many modifications of the general arrangement just described. In this construction the wheel swings round the stud C, which is placed within the huh, and in a line, or nearly so, with the center of the rim. The rod A is the axle and F is the lover extending from the inner part of the wheel hub by means of which the steering is effected. The left-hand side of Fig. 12 is a view as seen from the front and the right-hand side shows the device as seen from above. In this last drawing it will be observed that as the lever F is attached to the inner portion of the wheel hub, if it is moved to one side or the other of axle A, by pulling or pushing on rod G, the wheel will be swung round. The advantage of designs of this type is that there is no strain whatever brought to bear upon the steering handle, and the
objection is that the wheel hub is made much larger and the whole construction is somewhat more complicated.
The arrangement of the front axle, so as to swing the wheels round a center close to the hub or within it, as described in the foregoing paragraphs, is used on all types of automobiles and is not a distinguishing feature of the electric carriage. In some of the lighter vehicles the front wheels are held in forks of a design substantially the same as that of the front wheel of the ordinary bicycle, the tops of the Fork-being connected with each other by means of a rod, as in the lower part of Fig. 10, so as to obtain simultaneous movement of the two wheels by the movement of a single steering handle.
In the majority of electric vehicles the power is applied to the rear axle, but some are made with the motors geared to the front axle. In a few of these designs the wheels and axle are made the same as in an ordinary carriage, so as to swing round a pivot or king bolt located at the center of the axle and reinforced by a fifth wheel. When this construction is used the steering, gear is made so as to hold the axle in position more firmly than in the other designs; but even with this assistance the driver has a harder task than with the independently swinging wheels. The advantage derived from swinging the whole axle is that the carriage can be turned round in a very small space, and on that account the construction is well adapted to cabs.
Several arrangements have been devised by means of which the power can be applied to the front wheels, while these may at the same time swing round independent centers. One of these constructions is illustrated in Fig. 13, the first drawing presenting the appearance when seen from above, the second being a view from the front. In the first diagram the motor is shown at A, and by means of pinion B and gear C, motion is transmitted to the axle, which is shown more clearly in the right-hand figure. On the ends of the axle are bevel gears FF,
and these mesh into other bevel gears which revolve round the vertical studs D. Through this train of gearing the bevel wheels E are driven, and these are attached to the hubs of the carriage wheels. From the first diagram of Fig. 13 it can be seen at once that the gears EE can swing round D in either direction without in any way interfering with the transmission of motion from gears FF. The levers HH are secured to the sleeves GG which swing round the studs DD, hence, by connecting these with the rod J and moving the latter to one side or the other by means of the steering handle, the wheels are turned in any direction desired.
While this construction renders the carriage as easy to steer as those in which the motors are connected with the rear axle, it sacrifices the advantage derived from applying the power to the front wheels, namely, the ability to turn round in a small space.
Another design for driving the front wheels which allows them to swing round independent pivots, is shown in Fig. 14, which is a coupé made by Krieger in France. The power is supplied by two motors, one being mounted on each swivel point. The construction can be understood by considering that in the lower part of Fig. 13 the motor would be secured to a suitable support at the end of the frame L, being held in such a position that the shaft would replace pivot D and a pinion mounted thereon would gear into wheel E. What the advantage of this construction may be, the writer is not able to point out; it certainly
shows, however, that there are many ways in which the object sought may be.
American manufacturers of electric vehicles, at least the great majority of them, resort to spur-gearing to transmit the motion of the motor to the driving wheels, but with the French designers the chain and sprocket appears to be in great favor. Fig. 15 shows a Jenatzy vehicle (French), in which the chain is used. This construction would not be received with favor by Americans, who as a rule desire to have the mechanical part of the apparatus hidden from view as much as possible. In the Jenatzy vehicle two chain gears are used, one on each side of the body, and from the engineering point of view this is the most desirable arrangement, as with it the driving wheels are independently operated and a compensating gear need not be placed upon the axle. The American designer, however, would in most cases be controlled more by the artistic appearance and would use a single chain which would be placed under the body of the carriage, and thus as much out of sight as possible.
Fig. 16 shows an English design of electric dog cart. The mechanism consists of a single motor which is connected with the axle by means of spur gearing, this being so arranged that several different speeds can be obtained for the vehicle with the same velocity for the motor. To obtain variable speeds by means of gearing it is necessary to introduce a considerable amount of complication, and in this country the opinion
of most designers appears to be that the gain effected thereby is not sufficient to compensate for the increased complication, and differential speed gearing is not often used.
A comparison of Figs 14 and 16 with 6 and 9 will clearly show that in so far as artistic effect is concerned, our manufacturers of electric vehicles have little to learn from Europeans, although the industry here is much younger than abroad. As to the operative merits, all that can be said is that the American carriages run so well and possess such endurance that it is probable that they are not second to any in these respects.