AN ENTIRELY NEW SENTINEL SIX-WHEELER

15th November 1927, Page 127

15th November 1927

Page 127

Page 128

Page 127, 15th November 1927 — AN ENTIRELY NEW SENTINEL SIX-WHEELER

Noticed an error?
If you've noticed an error in this article please click here to report it so we can fix it.

An Exclusive Description of a Particularly Interesting New Vehicle Incorporating a Host of Ingenious Features.

SENTINEL steam vehicles, in the past, have held a very enviable position in the transport world. The latest product of this enterprising concern is certainly going to enhance still further the reputation maintained for so long by this Shrewsbury concern. It is claimed by the designers of .the new model that it is likely to set up some Dew heavy transport standards, for, with a reasonable wheel load, a very large carrying capacity is provided.

Special features have been incorporated, including such items as roller bearings throughout of stainless steel, steam braking oil each of the four wheels of the bogia (four shoes being located in each drum), and a new power unit with streamlined steam reducing eddies to a minimum, thereby increasing the power of the engine by

quite an appreciable amount. The engine, of course, is of the two-cylinder double-acting type and, with a two-speed gear with an incorporated differential, provides the equivalent of an eight cylinder petrol-engine torque. In the interests of lightness the crankcase is made entirely from aluminium, whilst oil circulation in the engine and gear units is maintained during the time that the crankshaft is revolving.

Turning to chassis components, compound rear springs are used and the four wheels of the bogie pivot abut one hollow. tapered axle.

Before going on to describe the vehicr6 in detail, it might be mentioned that extensive tests have been carried out in the Shrewsbury district over many hundreds of miles, when the load carried has in all cases been no less than 15 tons. In one particular test 15 tons were carried 19 miles, the fuel consumption being 1 cwt. of coal and 1 pint of oil. In another test, to show the accelerating powers of the vehicle, it was found possible to attain 6 m.p.h. from rest in 21 secs., 9 m.p.h. has been attained in a further 31 secs, whilst a further 5 secs, only was required to reach 12 m.p.h.

Ideas of braking have been revolutionized of late in order to cope with modern high-efficiency requirements. Suffice it to say that this new Sentinel, complete with 15 tons pay load, has been stopped dead from 12 m.p.h. in 22 ft. on a wet road without any sign of skidding whatever_ An ample steering lock is provided which will allow the vehicle to be turned in a 62-ft. circle.

Although the overall length is only 26 ft. 8 ins., with a mean wheelbase of 14 ft. (11 in., a platform area of over 140 sq. ft. is provided, the width being slightly more than 7 ft. The loading height ia 3 ft. log ins., whilst the frontwheel track is 5 ft. 3 ins., and the bogie track 5 ft. 91 ins. The tyre equipment is 160 MM. by 720 mm. front and 771 mm. by 160 mm. fitting on the bogie wheels.

Having given the foregoing general outline of the vehicle, attention can now be turned to a consideration of the new engine. In the first place, it might be mentioned that the unit actually gives an efficiency of 16 lb. of steam consumed per la.h.p.-hour, and is capable of a maximum of -90 b.h.p. The two doubleacting cylinders each have a bore and stroke of 6 ins. and 8 ins, respectively, the valves being of the ordinary mushroom spring-loaded type. The inlet and exhaust valves, headers, etc.,• have been streamlined in order, so far as possible, to eliminate loss due to steam eddy, resulting in a gain of about 15 b.h.p.

Following normal Sentinel practice, the engine suspension is effected by large-diameter truncated spheres held in brackets suspended from the main frame at the gear-shaft centre. At the front a twisted flat strip of steel is held at a point' below and between the two crosshead guides, allowing the complete flexing of the frame without distorting any part of the power unit. Both the cylinder and crosshead castings are of stiff section and are bolted together to form a perfectly rigid structure. The crosshead casting,* incidentally, has two Inspection covers, one on each side, in order that the gland nuts—two in numbeimay be conveniently got at. These nuts, by the way, are of the springleaded type and are arranged so that they can be turned by the fingers and automatically locked in position rotationally.

There are, of course, four valves to each cylinder, the exhausts, slightly larger than the inlets, being found underneath the cylinders, where they facilitate draining: Hollow push-rods are employed to operate the valves and they uermit lighter return springs 'to be used to the valves. The camshaft itself has three positions, and: in giving steam cut-offs of 89 per cent., 40 per cent. and 30 per cent, it adds materially to the driving flexibility and assists economical running. -Thus the camshaft, in conjunction with the new two-speed gearing, actually gives six forward speeds. The cut-off is operated by a lever, on the right-hand side of the driver, from which a rod emerges and moves both inlet and exhaust camshafts by means of two arms operating in a horizontal plane.

There is a continual oil circulation to and from the gearease, the effect of which is to keep the lubricant cool. The crankcase has a Capacity for 10 gallons of oil, which can be inserted through a convenient orifice on the side of the ease, • a gauge being in close proximity thereto and easily read while actually pouring in the lubricant. On the balance weights to the crankshaft scoops are formed, which, during

rotation, lift oil from the crankcase mid transfer it to the gearcase; the returning oil having to pass through a filter before it reaches the crankcase again, an arrangement which prevents any chippings from the gears reaching the internal parts of the engine.

The crankshaft itself is a webbed drop forging of 3 per cent, nickel-steel, and the connecting rods are the normal marine type of H-section drop forgings. The small ends of the connecting rods are fitted with phosphor-bronze bushes in such a way that there is no fear of them turning round and working loose. Each hollow piston is fitted 'with four rings and, like the crossheads, is fitted to the piston rod by a taper and nut fixing, thus preventing any slogger or wear.

There are several features which are mainly of interest to the user, and should he mentioned here as they are therefore important. In the first place, there are doors in the rear underside of the crankcase, which provide accessibility to the connecting-rod big-end bearings. Incidentally, these bearings can he adjusted to take up wear by the removal of shims without dismantling any part other.than the covers already mentioned. Indeed, the whole assembly lines can be withdrawn through the doors (after removing the piston heads, of course) ; the filters, too, can be taken :out for cleaning purposes through the aperture exposed by the removal of one of the covers, whilst the crankcase and gearease can very easily be drained by removing suitable plugs.

Another point of note is the fact that the end cover of the crankshaft can be removed by undoing a ring of nuts, when it allows the crankshaft itself to be withdrawn sideways after removing one roller bearing. All tappets are instantly adjustable and. by -virtue of a clean layout, spanners can conveniently be brought into effect on the adjusting nuts of the tappets. Again, all the valves are so arranged in staggered formation that they can be withdrawn for cleaning or replacement without dismantling, any other parts. The valve guides themselves are renewable and come out by undoing one nut.

Another interesting feature is a differential lock operated by a rod through a hollowshaft, locking the halves of the differential together by

internal sliding dog clutches. There is a handle protruding from underneath the chassis and fitted with a safety collar, the nut on the end of the shaft having to be removed together with, the collar before the lock can be brought into operation.

In order to keep down the unsprung weight to the lowest possible amount, chain drive has been adopted in preference to shaft. The two front wheels of the bogie are driven from the gear shaft the stub axles in a parallel plane to the central axle.

The main axle itself (i.e., the central one) is, of course, sprung. The suspension generally may be regarded as a floating component in order that full provision may be made for adjustment of both primary and secondary chains. Actually the ends of the master leaves of the semi-elliptic springs are turned over and form bearing surfaces, which. are in contact with channels attached to the main frame. Provision is made in these channels for lubrication, and keep-bolts are placed beneath Oa springs themselves to prevent the ends of the springs from jumping out of the channels. The forward end of the axle assembly is controlled by two adjustable radius rods and the rear wheels of the bogie are locked in grooves similar in disposition to the familiar rear wheel of a cycle. In this way movement (within limits) is provided in the spring attachment both for the flexing action of the spring and the fore and aft movement necessitated by the adjustment for chain tension. A subsidiary spring is mounted above the main swing and comes into operation only when the vehicle is excessively loaded.

The control includes steam braking on the four wheels, the power being applied through a special cylinder on two shoes in each of the four drums. An actuating pedal is so arranged that the resistance felt by the driver's foot is proportioned to the amount the brakes are being applied, and as the pedal resists sudden pressures the application is always silky. The shoes themselves are designed to work greased, so that escape of .oil from the axle cannot cause loss of efficiency. A steam pressure of 275 lb. per sq. in. has been adopted for the boiler in conjunction with 150 degrees Fehr, super heat.

Car-type controls have been adopted, and included in the up-to-date equipment are a V-shaped ventilated windscreen, electric lights working from a dynamo and armchair seats in the