COUPLE GEAR TRACTOR SYSTEMS
There is no city in the country that has a more exacting standard set for the performance of its motor-driven fire apparatus than New York and it is safe to say that apparatus that will meet the severe requirements of this municipality will perform creditably in any city in this country or abroad. Owing to the character of the buildings and the towering heights to which they are erected the fire risk in New York is believed to be as great as any other city in the world. Among the various types of motor-driven fire apparatus that have given satisfactory service may be included the Couple-Gear electric and combination gas-electric forms. For over two and one-half years electrically-driven apparatus has been tested in a section of the city where calls have been numerous, and similar apparatus has been added to the department as a result of tests that have recently been completed satisfactorily.
The Couple-Gear system may be had in two or four-wheel drive, and the character of the driving motor installation is such that all wheels used on the motor vehicle become tractive as well as directive members. This system may be obtained in two types, either the gas-electric or the straight electric tractors. The two wheeled tractor depicted at Fig. 22, has the advantage that it may be attached readily to horse-drawn apparatus of conventional construction, and a steam fire engine is well adapted to such applications because the tractor portion can be easily substituted for the front end by joining the goose neck hanger irons supporting the boiler, steam engine and pumps directly to the chassis frame of the tractor. The two-wheeled form is almost invariably the straight electric drive, i.e., the current which energizes the motors is derived from a storage battery which must be charged periodically in order to keep it up to capacity. The four wheel form of tractors are intended to be used in connection with horse-drawn apparatus in much the same way as the three wheel tractor system previously described. The front portion of the horse-drawn conveyance is removed and the fifth wheel of the truck is attached to a suitable turn table attached to the chassis frame. The four wheel tractor forms generally supplied are shown at Fig. 23, that at A being the straight electric drive type, while the form outlined at B is the combination gas-electric tractor. The driving system consists of four Couple-Gear wheels in each case which are of exactly the same pattern though in the vehicle shown at A the energizing current is derived from a powerful storage battery carried in a large box hung underneath the frame between the front and rear axle. In the form shown at B the power is obtained from a gasoline engine, wheels form members of a very flexible variawhich drives a generator armature and thus makes the electricity used to propel the vehicle as it is needed. In the storage battery system it is possible for the battery to become depleted in time though with the combination system the power is really furnished by the gasoline engine and the generator and electric motors in the ble speed and power transmission system. All speed variations ranging from seven to fifteen miles per hour may be easily obtained by a controller system that is as easy to operate as on the simpler straight electric forms.
Copyright, 1914, by Victor W. Page, AH rights reserved.
The electric current generating set of the combination gas-electric machine is shown at Fig. 24, and the general appearance of the power plant and method of incorporating the engine and generator on a subframe to form a unit is very clearly indicated. The power producing element is a four-cycle, four-cylinder motor, having 5 1/4-inch bore and 6-inch stroke. A Stromberg carburetor is employed to supply the explosive mixture, a Bosch high tension Dual magneto system furnishes ignition. The weight of the complete engine and flywheel is about 800 pounds, while that of the generator is given at 765 pounds. The power plant unit which consists of the power-producing motor and generator of current is attached to the sub-frame, which member is suspended within the main frame from three points and the power plant is thereby relieved of any twisting strain while the wheels are accommodating themselves to uneven road surfaces. The frame is of open-end construction to make possible quick removal of the engine if necessary. The engine is a type patterned after the best automobile practice in design, but which is considerably heavier to make it a heavy duty engine instead of following proportions of the light or medium duty power plants so generally employed in conventional motor vehicle practice. The lighter forms of automobile motors will not prove satisfactory under the continuous duty imposed by generating service because the parts of the average automobile power plant are not of substantial enough proportions nor is the design of the water jacket liberal enough for carrying a continuous load at constant speeds.
The generator used in the Couple-Gear tractor is rated at 12.5 kilowatts and will deliver a current of 100 volts pressure at 680 revolutions per minute. It will furnish an ampere load 200 per cent, in excess of its normal rating with 100 per cent, rise in speed. The voltage at the maximum speed can be held as low as 40 volts if desired. The dynamo is a six-pole machine and is compound wound which method of winding is said to automatically assist the engine to hold or increase speed approximately at the same rate as the increase in power is demanded for vehicle propulsion. The generator is so wired with a rheostat connected to the field windings, that the operator may raise or lower the ratio of drive at will. The generator armature is directly connected to the engine crankshaft back of the flywheel by a flanged coupling and there is no opportunity for power loss between the gas engine and the electric generator armature.
The really distinctive feature of the CoupleGear system, and one that has contributed materially to its successful application is the method of incorporating the power transmitting motors in the wheels. Each wheel motor is of the direct current series wound railway type and the normal rating is 3 horse power capacity when drawing a current of S3 volts pressure. These motors have satisfactorily operated without any perceptible sparking at the commutator with current at 150 volts pressure. As one motor is enclosed in each of the four wheels and these have a momentary overload capacity of 200 per cent, the total available horse power at the four wheels is said to be 36 horse power. The motor is of the bi-polar pattern and on account of its compactness it is the pattern termed the “pancake” type. The back frame of the motor is a part of the inside support connected to the rigid axle that passes through the steering knuckle. The motor armature has a shaft running throuugh it which carries a small bevel pinion at each end. One pinion engages a circular bevel rack which is part of the outer disc of the wheel while the other pinion engages a similar rack which forms part of the inner disc. This construction has given the wheel its name, since a couple of forces is acting to turn the wheel around the motor and these forces are applied practically at the wheel rim, an evener or equalizer, which is a compound knuckle coupling, is located in the armature shaft and is said to allow the same amount of power to be transmitted to each pinion. It is believed that this has material bearing on the satisfactory operation _____ the wheel because it removes all sliding friction on the gear teeth and it insures the transmission of equal amounts of power to each side of the wheel to maintain a true balanced drive.
The construction of the Couple-Gear wheel may be readily ascertained by examining Fig. 25, which shows the wheel with motor in place though with the motor cover and one-half of the wheel or outer wheel disc, removed to enable one to understand readily the relation of the various parts of the power producing and transmission system. With the cover of the motor casing removed it is possible to understand clearly the method of installing the armature between the two pole pieces and also the method of attaching the wheel driving pinions to the armature shaft. A shaft projects from the motor cover that serves as a support for one of the disc members or sides comprising the wneels. The view at Fig. 20 shows a direct front view of the wheel with the tire-carrying rim removed, in order to show clearly the method by which each beveled pinion drives racks attached to each side wheel. The other disc member of the wheel has two circular hand holes covered by plates to give access to the wheel interior for oiling and inspection. The complete wheel is water-tight and continued immersion tests have failed to flood the interior.
By the use of this simple and direct bevel gearing, it is possible to obtain the great reduction of speed that is necessary between an electric motor armature and a traction member of large size in order that the motor may be compact and powerful, (a condition that involves high armature speed), and yet the wheels turn slowly enough so the vehicle speed will not he too high. The gear reduction is 25 to 1 and it is stated that tests of a wheel show that there is less than three per cent, power loss in the Couple-Gear drive. The effectiveness of the power transmission may be well understood when it is stated that whereas the drawbar pull required to move the gas-electric tractor on a good level road is about 150 pounds, the overload capacity of the generator and motors operating through the Couple-Gear system is sufficient to give a maximum drawbar pull of approximately 5,000 pounds, or thirty-three times that required to move the car on a level.
The control of the gasoline power plant is by a foot operated throttle and as the speed of the engine augments the current produced by the generator increases in proportion. The wheel motors are governed by a controller of the street railway type which makes it possible to vary the motor windings so that they will operate either in series, series-parallel or parallel, and a reverse lever located on the controller gives the same range of speed backward as forward and also operates an electric brake. The first point on the controller throws two motors in parallel and in scries with the other wo motors which are also in parallel; this series-parallel combination also being in scries with a starting resistance. The second and third points on the controller reduce the starting resistance while fourth point cuts out all resistance hut maintains the seriesparallel connection. The fourth notch or stop for the controller handle, is the first running point The fifth point connects all motors in parallel and the combination in series with the starting resistance. The sixth point cuts out a portion of the starting resistance and the seventh all of it, leaving all four motors in parallel on the full bus-bar voltage. This is the second running point. The eighth point, or extreme position of controller handle, which gives the highest speed, throws a shunt around the motor fields, thereby giving a greater speed.
All Couple-Gear tractors of the types shown at Fig. 23 are equipped with four wheel steer as well as drive. The steering wheel earned on a vertical steering column is connected to steering quadrants through a horizontal rod and worm gearing in such a manner that when the front wheels are deflected to the right the rear wheels are deflected at a corresponding angle to the left.
The advantages of this arrangement are, first, that it permits the car and trailer to turn in much narrower streets than would be possible if only two of the wheels were moved for steering and if anyone douhts the utility of the four wheel steer system the writer needs only to advise them to watch the control of a heavy tractor with a long hook and ladder or water tower attached and to see the way in which it can be turned around in close quarters or maneuvered into a fire house. Another advantage of having the wheels assume corresponding angles to the right and left is that the wheels always track and under unfavorable road conditions the rear wheels do not have to break a second track when the car travels around curves as is necessary when the usual system of front wheel steering and rear wheel drive is followed. The brakes provided are both mechanical and electrical. External contracting brakes are provided on all four wheels, these being arranged in pairs. The two on the rear wheels are connected to one foot operated lever and the two on the front members arc operated by another pedal. Electrical braking is accomplished by using the reversing drum of the main controller as an electrical brake control. In this system the wheel motors arc used as generators, they being connected by the reversing or braking drum to resistances and therefore as soon as the armatures of these motors, which become scries generators, arc rotated, as when descending long grades the resistance tends to stop the vehicle. The electrical brake is used only in cases of emergency or when descending long hills where they arc very useful in controlling the heavy vehicle and its trailer and thus save the friction linings of the mechanical brakes from rapid depreciation.
The record of the Couple-Gear straight electric propelled steam fire engine illustrated at Fig. 22, which is known as Engine 217, in service of the New York fire department, has been very impressive, and shows clearly the economy of this system of propulsion when compared to animal power. Before it was placed in active service it developed a speed exceeding 20 miles an hour, while a hill seven-eighths of a mile in length was negotiated in two minutes and thirty-five seconds. In the period ranging from April 24th, 1912, to the same date one year later the engine had responded to 319 alarms. Some of the runs were short and although no record was kept to show actual distances traversed, a mile run for each alarm was considered a fair average. The official figures of the fire department show a difference of $266, which represents clear saving between the cost of upkeep of the power tractor and the animals that were formerly employed in hauling this same engine, but these do not take into account the healthier and cleaner quarters made possible by the use of mechanical power, the increased speed in responding to alarms or any of the other advantages that would make mechanical power desirable even if it was as costly as the upkeep of an animal-drawn equipment.
Ed. Note: The next discussion will outline the principles of gasoline engine operation, and show the functions of all parts of the power plant, as well as their relation to each other.