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A New Petrol-Electric Bus.

16th January 1908
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Page 3, 16th January 1908 — A New Petrol-Electric Bus.
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The Stevens System of Transmission Embodied in a "Hanford" Chassis.

As announced in our last issue, the new petrol-electric bus which has been built for Thos. Tilling, Limited, by J. and E. Hall, Limited, of Dartford, and W. A. Stevens, Limited, of Maidstone, gave its first demonstration run on Thursday of last week. The vehicle left the Motor Club, in Coventry Street, about 11.30 a.m, on that day, and, after an excellent run, Dartford was reached a few minutes before 2 o'clock. The 14 passengers on the bus included several representatives of the technical Press. The party was at once conducted to the " North Pole " Hotel, where an excellent luncheon was served, Mr. H. J. Ward, one of the directors of J. and E. Hall, Limited, presiding. The subsequent tour through the works proved highly instructive and was much appreciated by the visitors. We have previously (see "THE COMMERCIM, MOTOR " for the 7th of November last) made reference to the many ingenious jigs and fixtures which are in constant use in these works, and some of these were seen in operation on the fine Herbert turret lathes and other modern machinery with which the works are equipped.

In the isste to which we have already referred, we gave a complete description of the " Hallford " chassis, including several illustrations of its excellent ph.p. engine and its effective air-brake arrangement. A further reference to this brake, illustrated by two " cards," was made in a more recent issue (the 2nd instant); it will not, therefore, be necessary to give any description of the engine in the present article. The rest of the chassis is entirely different from the standard one manufactured by this maker, owing to the fact that many modifications were necessary in order to adapt it for the incorporation of the new system of transmission. The latter is a combination of the patents of the S.B. and S. Syndicate, and W. A. Stevens, Limited, and consists of : a generator ; a series-parallel controller ; and two electric motors, which drive the back wrteels through the medium of propeller shafts and worm gearing.

The usual " Hallford " method of suspending the engine, at three points, from two cross members of the frame, is retained, as may be seen in our two line drawings showing the arrangement of the chassis in plan and in elevation. The shunt-wound, interpolar, continuous-current dynamo is directly coupled to the crankshaft through the medium of a flexible coupling of novel design : both the crankshaft and the armature shaft of the dynamo are flanged, and each is fitted with four projecting pins, or studs, which are turned up into the form of a sechon of a sphere; these pins project from the adjacent faces of the two flanges, which are about one inch apart. The space between the flanges is occupied by • a disc of soft rubber, through which the set of pins on the crankshaft flange transmits the drive to the other set of pins which are fitted on the flange of the armature shaft. Any slight errors in the alignment of the two shafts, due to whipping of the frame, are thus compensated, and a flexible drive is obtained for the dynamo. Immediately behind the generator (or dynamo), which is marked (F) in our photograph of the chassis, the controller (G) is mounted. This is, really, a doublepole, circular switch, which provides for four positive positions, viz. : neutral ; motors in series for reverse; motors in series for hill-climbing ahead; and motors in parallel for all normal running ahead. The controller is operated by a side lever which takes the place of the usual change-speed lever, and it is connected thereto by means of a rigid rod.

Behind the controller, the two motors (H, H,) are carried on two, stoutly-made bridge pieces. The motors are of the series-wound type and their armatures, commutators, and brushes, are completely enclosed. By means of the controller, these motors may be grouped either in series, or in parallel, according to the exigencies of the road surface. The series control is provided for hilly roads and starting in difficult places, but, for all ordinary running in London traffic, the parallel grouping of the motors will, perhaps, be found to give ample torque. The turning effort of the motors, when in parallel, is not so great as another system which we have tried, but, for the requirements of London motorbus service, it may prove quite sufficient. Each motor, drives one of the road wheels by means of worm gearing. The arrangement of the hack axle is quite novel and is the idea of Mr. Percy Frost Smith, the engineer to Thos. Tilling, Limited, the company which will operate this bus. The axle is of the "dead " type, provided with spherical portions which are enclosed within slipper blocks; these blocks, in turn, are allowed to slide vertically within the horn-plate brackets (L), according to the deflection of the bearing springs. On page 429 we reproduse a drawing which shows, in section, one end of the axle and its worm gearing. It will be seen that the worm-gear casings are securely bolted to flanges which ace integral with the axle, whilst the worm wheels are free to rotate on sleeves on the axle, which are mounted on Hoffmann ball bearings of that company's standard wheel-hub pattern. The centres, to which the worm wheels are bolted, are each provided with six claws which engage with similar claws on the wheel hub : the wheels may thus be removed without disturbing the worm gear, and the latter is free from any lateral strains which might, otherwise, be transmitted to them by the wheels. The worm

• shafts are also mounted on ball bearings which take both journal and axial ;loads. The worm gears were made by David Brown and Sons, of Hudders''field, and have a ratio of 12 to i : they constitute the only positive gear reduc

• tion in the transmission system. Spring-compensated torque rods (K,K,) anchor the axle, and keep its angular motion within the capacity of the bearing springs.

The worm shafts are driven by the motors through universally-jointed, 'telescopic, propeller shafts, and, at the forward ends of these (which, by the way, rotate at 1,200 revolutions per minute when the vehicle is running at 12 miles an hour), the pedal brake drums are mounted. A sectional view through the frame at that point, showing the means whereby the brake blocks, are operated, is given on the next page. It will be seen that there are two small, cast-iron shoes, acting at

diametrically-opposite points, on each brake drum. The blocks are drawn together through the medium of a series of bell-crank, and balancing, levers, and a long connecting rod which couples up the system of levers with the left-hand pedal (C). This arrangement, whilst giving perfect compensating action, is very sensitive and powerful ; the drums are so arranged that they may he cooled by water if necessary. In addition to the foot brakes, there is a pair of expanding blocks, acting within drums of large diameter, on each of the driving wheels, and these are operated by means of a side lever in the usual manner. The operation of the controlling levers of the bus is much the same as on any gear-driven vehicle. Two small levers are mounted on the steering wheel : the one on the left is for the partial control of the gas supply ; the one on the right controls a field resistance. The throttle lever only partly opens the throttle, so that, by the use of this lever alone, it is not possible to cause the engine to run faster than 350 or 400r.p.m. Higher engine speeds are not attainable until the controller lever is moved to the reverse, or to one of the forward-speed positions. The engine is governed so that its maximum speed, at any time, never exceeds t,o5or.p.m. By moving the right-hand, control lever, the resistance of the dynamo-field circuit may be altered, and, in that way, the running speed of the motors may be varied with in certain limits. The object of the resistance is to weaken the field of the generator, as occasion demands, and it is brought into operation when the bus is being started from rest, or on hills, when it is advisable to allow the engine to get away with it load. The accel

erator pedal (E) permits the engine speed to be controlled., by the right foot, at all speeds between the maximum allowed by the hand lever, and the highest speed allowed by the governor. Another pedal (D) is also operated by the right foot : when this pedal is depressed, a connecting rod from its lower end causes the generator circuit to be broken by means of a switch which is enclosed within the controller casing. This pedal is also caused to operate a small, vertical lever, or pawl, which engages with a notched quadrant ; the latter is keyed on the same shaft as the controller lever, and it will be obvious that no movement can be given to the controller lever until the pedal has been depressed, and the pawl has been withdrawn from engagement with the notched quadrant. The positions and shapes of the two right hand pedals render it impossible for both to be depressed at the same time. The accelerator must be released before the inter-locking pedal is depressed : there

fore, it is impossible to break the main circuit while the engine is running at a high speed. Each of the four positions of the controller is determined by the notches on the quadrant. The notch which corresponds to the neutral position is shallower than the others : this fact ensures that the main circuit shall never be closed while the controller is in the neutral position. By carefully following the circuits on the wiring diagram which is reproduced on page 428, it will be seen that the motor fields are always connected in series. The system of grouping is, briefly, as follows. The motor fields are always in series, but the direction in which the current posses through

them varies, whilst, with the armatures, the direction in which the current traverses remains constant, and the arrangement as to series, or paralleli is

varied according to requirement. . The electrical equipment has been manufactured by W. A. SteVens,

ted, of Victoria Works, Maidstone, and every precaution has been taken to ensure its protection •and cooling. The running of the dynamo and the motors is practically sparkless, and we are assured that the dynamo has been ;tested to the extent of a dead short circuit tween the poles, without giving any .%7.isible result at the brushes, and without injuring the machine in any Way. Such a result is, of course, only posSible when the brushes are adjusted to One particular point, but that position happens to be the one at which. the brushes are fixed before the dynamo leaves the Lest bed.

From the behaviour of the machine during its run from London to Dartford, and on the return journey, it is not possible to form any definite opinion of its capabilities. The system appears to be worked out on sound lines, and we shall watch its performance in London service with the greatest interest.

Tags

Organisations: Motor Club
Locations: Dartford, London

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