THE NEW PAGEFIELD MOTOR COACH CHASSIS.
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"You Don't Put Passenger Coaches on Freight Car Under-carriages,"—One Hears.
THE MOTOR COACH may be termed the latest development of the species motor vehicle, for, apart from • motor omnibuses, it has not been generally realized, until quite lately, that a special type of chassis is really required for this class of work. By comparison with the ordinary commercial vehicle, a char-a-bancs requires to be more powerfully engined so as to permit of higher average speeds up hill and down dale, as well as the negotiations of difficult country, which, in the case of the conveyance of merchandise, would have been avoided, but which, on account of the picturesque scenery to which it gives access, must be traversed. by the passenger coach. For the same reason it is essential that in designing the char-h-bancs chassis particular attention be devoted to the canstraction and efficiency of the brakes, and in addition the gearbox ratios have to be considered anew, from the aspect partly of the increased speed which is desirable and also on account of the possibly more difficult gradients which are likely to be encountered. It may be said at least that it is a sine qua non in the case of a ehar-abanes transmission that there' shall be four changes of speed provided for forward travelling.
The general outlines of the motor coach body demand a longer vehicle, than is usually customary for goods transport. The comfort of the majority of the passengers necessitates the bulk of the seating accommodation being within the wheelbase, which i n d cates another desirable feature for that type of chassis, namely, long wheelbase.The necessity for' silence in operation is more insistent in the case of passenger traffic, and this of late has generally been taken to connote worm drive for the rear axle. Last, but not least, it is necessary to keep in view the desirability of studying appearance. A motor coach must be handsome and pleasing to the eye, for it is a fact that, given the choice of two, and other things being equal, the prospective client will naturally take his seat in the one which appears to him to be better looking. The last-named characteristic, although not one which can be controlled to a peat extent by the chassis manufacturer, roust still be kept in view when deciding upon heights of frame, bonnet, etc., which should be in due proportion to the length of the wheelbase of the machine.
One of the latest firms to devote itself to the manufacture of motor coach chassis designed throughout with the object of meeting the requirements which we have laid down is Walker Brothers (Wigan), Ltd., makers of the Pagefield commercial vehicles, and we were particularly interested in examining an example of the latest practice of this company, which we did at Darlington, to note how far these desiderata had received consideration. The following few notes are written to some extent 'with the idea. of demonstrating its compliance with the points we have briefly enumerated above. As regards the engine, this is the well-known Dorman subsidy type, a fourcylinder unit of 120 mm. by 140 mm. bore and stroke respectively. At 1,000 revolutions per minute it develops 38-40 h.p. The engine itself is fairly well known. It is fitted to many of the best-known commercial vehicles, and has, for that reason, had frequent reference in these columns. It will not, ,herefore, be necessary to make more than passing mention of its more important details. The cylinders are designed on what is conveniently called the L-head type, the valves being situated along one side--the near side—and operated by a single camshaft. The exhaust manifold, which is freely provided with radiating fins, is also on that side of the cylinders, to which it is clamped in such a manner that it may easily be removed or replaced in ease of necessity. The inlet port is carried through between each pair of cylinders, for they are cast, in pairs, so that the induction pipe and carburetter are on the off side. It may be remembered that a particular feature of the construction of this engine is the combination of the inlet water • pipe and induction manifold in one, thus
conveniently providing means of maintaining the incoming mixture at an equitable temperature. An accessible centrifugal pump is mounted on the near side of the engine, its shaft being, prolonged to drive the magneto, which is located immediately behind it. A cast aluminium fan is. mounted in the customary position on a.
bracket which also serves as an oil filler pipe and air vent to the crankcase. The radiator is of the customary vertical gilled-tube type, and on the standard chassis a substantial radiator guard is provided. Particular attention has been paid in this engine Lo the important feature of lubrication. There is a gear type of oil pump situated in the sump, which collects oil therefrom through a gauze filter, delivering it through another to a continuous drilled. passage in the crankshaft, from which the oil passes to the surface of each of the main and crankshaft bearings. A by-pass from the system of piping leads to a small indicator of the plunger type, which is fixed on the dashboard in.full view of the driver. It is interesting to -note that pistons of the Zephyr type are fitted to these engines, it having been found that their addition adds considerably to the engine efficiency.
The clutch is an. old favourite on Pagefield chassisi It was used on the first machine of that type built in 1905, and has given such satisfaction that the firnt has never for one moment considered a change. Its principal feature is the adoption of three light coil springs evenly disposed on a pitch .circle on about two-thirds the diameter of the clutch centre' the particular advantage of this arrangement being that they
are readily adjusted. The gearbox provides, as we have claimed to be essential, four speeds forward and one reverse. It is what we are pleased to term three point suspended, from a couple of tubular cross-members of the main frame. The front support is a single clip about the middle of the cross-member. There are two special clips at the rear of the box, and the bolts securing them also serve as anchorage for the foot brake shoes. The gearbox itself, notwithstanding the ample provision in the way of gear changes, is remarkably compact, which is in great measure due to the ingenious utilization of the sliding pinions for a dual purpose. They either engage with their correspon cling gearwheels on the layshaft, or, entering internal kear rings which are integral with wheels on their own shafts, carry out the function which usually falls to the lot of claw or dog type clutches. Besides saving room in the box, this arrangement also has the advantage that it renders the operationef gear changing very facile. The substantial shafts of this component of the chassis are splined to receive the various gears. The idle wheels run on phosphor-bronze bushings, while the main bearings of the box are Hoffmann roller and Skofko double-row ball bearings, the latter being so disposed that they also accommodate the comparatively slight end thrusts which are occasionally developed in a gearbox.
The back axle is of the full floating type, the; load bearing portion being a substantial steel forging of what is familiarly known as the double-banjo typy. We particularly noticed the design of this forging, especially at the junction of the arms of the axle with the central hollow ring, and contrary to what has on occasion been the practice in the design of this type of axle, ample metal is left to obviate the somewhat unfortunate effects which otherwise occur as the result of vibration. The transmission gear itself ;s in• accordance with what we consider to be the best practice for char-h-bancs purposes, namely, the over head worm and-wheel. The latter' cOmplete with its differential gear will, after abstraction of the driving shafts, lift clear away from the axle, in case of need of inspection, adjustment, or, possibly, repair. The differential gear is of the bevel type with but two planetary pinions, it evidently having been considered wiser to dispense with the trouble which invariably occurs in connection with the manufacture of four star differentials by somewhat increasing the dimensions of the gears, so that ample strength is afforded on two pinions only. A good feature of the construction of this rear axle is the disposition of the substantial ball bearings, which have been brought as close as possible to the worm itself, thus affording it the maximum of support.
The method of seeming the road wheels to the axle is particularly important in this form of construction. In this case the axle tube is screwed at the end, and immediately behind the screwed portion provision is made for a. small key. A collar which, when everything is erected, bears against the wheel, is keywayed so as to engage with the same key. It is thus prevented from tending to turn with the wheel as the latter revolves. The nut which really secures the wheel in place bears against this non-revolving collar and thus also has no tendency to turn. Additional security, however, is afforded by forming the nut with a round collar at its base, cutting a slot in that collar, with which engages a setscrew which is itself screwed into the non-revolving washer. Finally, the setscrew is prevented from turning by a small split pin. It will be evident that a fairly complete chain or chapter of accidents must happen before either of the wheels ca.n come adrift, and it may well be said that the key which holds the main collar against movement is rightly so named. The wheels which are fitted as standard are of the disc type secured to steel hubs. The latter revolve on phosphor-bronze floating bushes, and we note with interest the unusually careful provision of means of lubrication. The discs of the wheels are relieved from the necessity of carrying any braking stresses by bolting the brake drums through them, to an enlarged flange of the hub.
As regards the general disposition of the various components it would appear that particular attention has been paid to the need for accessibility. The engine is bolted to a sub-frame and stands well out of the chassis. The lower part of the crankcase may easily be removed and access thus had to the connecting rods, gudgeon pins, pistons, etc. without any further dismantlement. We have already referred to the special advantage of the clutch. It need only be added that on lifting the floorboards of the7 driver's cab, the springs to this component are immediately available. The gearbox is placed in mid chassis, a short clutch shaft fitted with flexible diseuniversal joints intervening between clutch and box. The whole of the top of the gearbox is enclosed by a quickly removable lid which affords access for inspection. Further, the gearbox itself can quite easily be lowered away from the chassis by freeing the clamps which hold it to the tubular cross members. There is no need to disturb the body to perform this operation.
We have already referred to the accessibility which is an important feature of the rear axle. Flexible disc joints are not used for the propeller shaft, that at the front end being of the star type with phosphorbronze thimble bushes as bearings, the whole joint being enclosed, and ample provision made for lubrication. The rearmost joint is of the De Dion sliding block type, and the same comment as regards total enclosure and provision for lubrication also applies in this case.
We may now turn to what may be called minor or auxiliary details, such as the brakes, steering, etc. The former are all that could possibly be desired. One of our illustrations admirably portrays the location and substantial construction of the foot brake, which is of the locomotive type. Two arched levers embrace an unusually large drum behind the gearbox. To the centres of these levers are pivoted Ferodolined shoos. Below is the helicoid operating gear, which is operated by the usual pedal. The rear brakes are of the expanding type and are hand-controlled. In the design of these components, as in that of the major units of the chassis, the need for accessibility has again been kept in view. A nut, which is almost a hand wheel, is provided for the adjustment of the foot brake, and this is easily accessible from the oft side of the chassis, while similar adjustment is provided for the rear brake shoes. The steering gear is aE the worm and complete wheel type. Adjustment for the accuracy of engagement of the gear is arranged for and, in addition, when undue wear has taken place in one portion of the worm wheel, it may be revolved through a quarter of a circle, and a fresh set of teeth brought into engagement with the worm. The springing is on orthodox lines,. semi-elliptics, both for front and rear axles. The former are attached to the frame in dumb irons at the front, and shackled at the rear. The latter serve the dual pm', pose of absorbing road shocks and transmitting the torque and thrust reactions of the drive. The frame, as will be observed by reference to the illustrations, is remarkably well giesseted and stayed: the 'whole chassis, as a matter of fact, strikes one as having been specially designed to have the twin characteristics of speed andspower, while at the same time, as may be judged from the fact that the total weight is but 53 cwt., the need for keeping the moving load within reasonable limits has not been overlooked.
This is an important point, in view of the rapidly increasing use of the roads, the expense of repair, and the obligation which is, therefore, imposed upon all manufacturers to assist as much as possible towayds the solution of the road problem by producing reasonably light vehicles.
The following leading dimensions will no doubt be of intereist. The wheelbase is 14 ft. 6 ins., which leaves a distance of 11 ft. 7 ins, from the dashboard to the centre of the rear wheels. The overall length of the chassis is 22 ft. 6 ins., and the distance from the dashboard to the end of the frame is 17 ft. 4 ins. The track of the wheels is 6 ft. 9 ins., and the height of the frame, when the vehicle is loaded, 2 ft. 6 ins. The width of the frame is 3 ft. 3 ins., and the width overall 7 ft. 1i in. There is 12i ins, clearance under the front axle, and 10 ins, under the rear axle. Tyres, as standards, are 880 mm. by 120 min. single on the front, and 880 rum by 120 inni. on the rear.