A SUPER STEAMER!'
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ZEDESIGNED SENTINEL.
Entirely Remodelled, the Super-Sentinel has and Steering Gear. A New Tractor and T
Lures in Boiler, Engine Transmission, Brakes to be Included in the Maker's,Programme. OS . FAELY FIVE years of steady work having INbeen concentrated upon the design, testing, and proving of their new vehicle, the Sentinel *earn Waggon Works, Ltd., have not hesitated to christen it the Super-Sentinel. The new wagon was displayed to a party of guests invited to the works at Shrewsbury on Thursday last, and it was then put through its paces, acquitting itself most creditably.
Its predecessor, the 6-ton Sentinel, had secured for itself, in the course of the 16 years during which it has been in production, .a considerable measure of popularity. The makers have taken advantage of this in orderto lengthen the testing -stage in the development of the new wagon, otherwise the SuperSentinel could have been marketed a year ago.
So good, in fact, have the fundamental principles. of Sentinel design proved to be that there has been no temptatibli to depart from them. What has been_ done has been to take each component and to see how it could be improved, in order to secure the lowest passible running costs, the greatest ease of maintenance, and the longest possible life-20 years being regarded as a minimum. To this end some wearing parts have been cut right out and every other part has been improved. Two great advances , are made—in the boiler and in the transmission. The other details which have undergone important changes are the front axle, the steering gear, the ipringing, the engine, and the controls.
:The new wagon will handle " With ease loads of from 4 tons to 12 tons at the applicable legal speeds. It has aplatform length of 15 ft. 3 ins, on the short chassis, and of 17 ft. on the long chassis, whilst the standard platform widths are 7 ft. and 7 ft. 44ins. The wheelbases are 12 ft. 6+ ins. and 14 ft. 3+ ins., • according to chassis length.
To deal, now, with the improvements and modifications in detail We will begin with the boiler. The great change here is in the arrangement of the water tubes, which are given a much larger slope. This has been effeeted by pressing into the inner shell a number of " landings " spirally arranged, each tuba endbeing expanded in the spiral grooves thus formed. Our illustration showing the boiler partly in section clearly shows the arrangement. It will be seen that the tubes have a sharper inclination, permitting the water to circulate freely, Whilst this inclination and the: fact that the tubes are arranged longitudinally to the stoking hole, encourage dirt to fall off the tubes instead of lodging upon them. The old stoking shoot has been dispensed with,
• -and so the admission .of air 4,hrough it, tending .to impair the ?efficiency of the combustion, is ?"-prevented.The -upper -half of ?the stoking guide is retained,
but this does not project beyond the centre of the tubes, nor does 032
it enter the firebox. It will be of interest to note that a super-heater is employed.; and the heat has, with the new design, been raised by about 100 to 150 degrees Fahr: The engine has undergone complete redesigning whilst retaining all the original features. The first modification which one notices on inspecting the component is the inclusion of the differential in the crankcase. This gives the advantages of complete protection, and thorough lubrication, for it, and the provision of two driving shafts, each transmitting power through a chain to one of the rear wheels. Again, instead of a single camshaft running below
the cylinders, two camshafts enclosed in the crankcase are provided, one operating the steam valves and the other operating the exhaust. The cams are broader and better shaped, and; of course, the camshaft and gearing are thoroughly lubric,ated. The steam distribution is improved by this change, and higher economy is secured.
The valves have all been located at the front -end of the cylinders, where they are very accessible for regrinding the valve-stem bushes are longer, adjustment is provided for, and the feed pump is now driven by gear from, the valve-timing gear at about half engine speed, thus -vitt it a lly eliminating
cavitation, which occurs when a pump runs at high speed. The pump ram, again, has been increased in size.
The differential train is particularly interesting:
in fact, we cannot recall the employment in any road vehicle of anything precisely similar. Each crankpin houses a shaft, at• one end having a. pinion which meshes with a gearwheel secured to the inner end of the floating shafts which transmit the drive, and at the other end having a gearwheel which meshes with the gearwheel on the other crinkpia shaft. To makethe action of this differential train clear let us imagine the rear of the vehicle jacked up. If, now, one Of the road wheels Jae turned cloe'15.wise it will cause the nearer crankpin shaft to turn anticlockwise, this will cause the other crankpin shaft to turn clockwise, which will result in the, further floating shaft turning anti-eloc,kwise—in true differ:ential action. The floating shafts pass through the bored-out crankshaft and accommodate on their outer ends the chain sprockets, whereby the power
is transmitted through a pair of chains to' the chain wheels on the rear:Toa.d wheels.
This differential is very strong, and there is embodied in it a further feature. Each of the centre pair of gearwheels houses a cone clutch, which is held in engagement by a spring. A certain amount of resistanCe is arranged by the adjustment of the spring, and has to be overcome before any wheel of the differential can move independently of the crankshaft. By the choosing of clutches of correct diameter, and springs of . suitable strength, the differen tial is prevented from functioning until a difference of from 10 to 15 per cent. in load oceurs in the tractive effort at the rear road wheels. The effect of this is greatly to minimize any tendency to sideslip and the vehicle holds the road in a remarkable manner in consequence.
It will thus be seen that an
excellent piece of designing has been introduced into the crank shaft and differential gear of the Super-Sentinel, giving substantial 'advantages from Many points of view, not the least of which will be the'lengtbening of tyre life. It will be understood that the chain sprockets are carried on the ends of the crankshaft and that. they only rotate on the crankshaft § when the differential conies into operation. The crankshaft is equipped with balance weights to give smooth running. The exclusion of dust from the differential is a very great point.
The employment of two roller chains in place of a single chain enables lighter chains and sprockets to be used and the pitch to be finer. This, naturally, means a diminution, of noise as well as an improvement in the wearing qualities. The rear axle is a cylindrical forging and is a dead axle Carrying the rear road wheels on "journals of , extreme length. The wheels are bushed. With 12-in. by .41-in. husheq of phosphor .. bronze. .03
These bearings can be very easily attended to, whilst dust and grit are effectively excluded.
The brake supports are more satisfactory with a dead axle than with one that rotates, whilst the fitting of new tyres is greatly facilitated, for the wheels are not driven tightly on to tapers, as is necessary on rotating axles. The slacking off of the chain and the removing of the patent lock nut permit a wheel to be removed at once and easily.
T h e matter of
braking has been gone into very thoroughly. On each wheel is a large brake drum, one of the shoes being operated by hand and the other by foot. The foot brake, which should not act suddenly, or skidding may be induced, acts on the forward side of the drum, which position, again, gives it the advantage of exerting a much larger braking effort when the wagon is in rev rse. The hand-operated brake shoe acts on the rear half of the drum. and it is powerful enough to stop a wagon in either direction on the steepest hill. Oil cannot get on to the brake drums, so the brakes are always reliable. It must be remembered that the engine acts as a splendid brake.
Thefront axle has been taken forward and-given a horizontal bend to dear the boiler. The eyes in its end are solid with the axle, the lower end of the pivots being steadied by brackets bolted on in front This tends to greater safety,*for the pivot cannot escape under any conditions.
The steering gear consists of only three parts, -the worm, nut, and bell-crank lever, working immersed in an -oil bath mounted on the frame sidemember and the front cross-member.,T h esteerinA and connect. ing rods are-equipped with spring loaded ball joints, motor vehicle praciace being followed i n t It i s respect. The steering is quite irreversible, and the vehicle will turn in a remarkably small circle, a 25-ft. radius being ample for turning without reversing.
T h e vehicle is mounted on springs e34
which are of greater length and flexibilllty than hitherto, the springs being attached to the uncl-r side of the frame by means of dove-tailed guides and slippers, with .ample provision for lubrication. The recd-water tank is not altered, but it is now carried on two inverted channel-steel cross members instead of brackets. It has sufficient capacity fox journeys of 30 to 50 miles on good roads, and is suspended against four rubber buffers by two canvas
lined straps. The door for cleansing is of large area, and baffles are fitted to reduce the effects of wash. Being -rounded at the back children are prevented from riding upon it Two feed connections are provided, each having its own filter and shut-off valve, thus rendering cleaning easy. The blinkers are of very large capacity, enabling sufficient fuel for runs up to 200 niiles to be carried. Thus, with ample supplies of water and fuel, stops by the roadside are substantially reduced, and the average speed on a journey is kept at a high level:
Two further Super-Sentinel developments are the new tractor, which is claimed • to be an advance in tractor -'design, and the new six-wheeled tractorlorry. The former follows Sentinel lines', but the boiler is brought well back behind the front axle and the engine is mounted at the rear of th:i rear axle, the Chains, therefore, driving on their under run. This serves to bring the weight well over the driyinowheels. Such a machinu is of undoubted use over bad lands, as the load is pulled and riot carried, and the weight is more evenly distributed. The springing is par'ticularly good, and the vehicle is equipped with rubber tyres, the life of which is calculated 'at 15,000 miles on good roads. It will travel 50 miles on one tank of water, and will carry enough fuel for 100 miles. With a set of trailers a tractor can be kept-. more -constantly at work. We hope to be able to deal with this in a later issue and also with the new tractor-lorry-on six'wheels for 10-ton loads. A platform 24 ft. by 7 ft., with a low loading height, provides for exceptionally bulky loads. Perfect flexibility of movement at the junction of the tract-or and trailer portions is arranged;,, and ample. strength and stability have been given to all parts. The tractor for the tractor-lorry fo;.--. lows steam-wagon lines, not those of the tractor to which reference has just been made.
One of the most important of the ragny interesting features of the Sentinel wagon is the patent engine brake, .which should prove of particular use in connection with the heavy loads which the tractor-lorry will be called upon to carry.
This brake is not new, but has already proved its efficiency and reliability. When the pedal is pressed down the supply of steam to the engine is shut off, the main steam cock is then closed and the engine reversed and, if the pedal is now allowed to rise, the engine acts as an air compressor and forms apowerful bralge which will effectively hold the wagon without heating on the longest hills. As the wagon slows down the pressure on the pedal is increased, and a certain amount of the air is allowed to escape. so that the action is smooth and progressive.