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SENTINEL H.S.G. GAS CHAS S READY FOR PRODUCTION

11th November 1938, Page 146
11th November 1938
Page 146
Page 147
Page 148
Page 146, 11th November 1938 — SENTINEL H.S.G. GAS CHAS S READY FOR PRODUCTION
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REPRESENTING an event of historic importance in the commercialmotor world, and a centre of attraction at the Scottish Show, two new producer-gas vehicles have just been completed by the Sentinel Waggon Works (1936), Ltd., 72-74, Victoria Street, London, S.W.1. They are the first British vehicles, designed and built from the outset for operation on gas, and for quantity production, and this is the first description of them to be published.

Sentinel-H.S.G. is the make name, and the models on view at the Kelvin • Hall are both shown in chassis form. One is a 32-35-seater and the other a 5-tonner. The latter will be offered with two wheelbase lengths, the prices of the long and short chassis being provisionally fixed at £575 and £588 respectively.

In them are combined 35 years' vehicle building experience of the Sentinel company and 11 years' gasproducer experience of the H.S.G. concern. With regard to the latter, The Commercial Motor reported nearly six years ago (January 29, 1933) certain experimental work that was being carried out with a Ford van, equipped and modified to operate on solid fuel, and

D24 forecast a promising future for the plant used, later to be named the H.S.G. (High Speed Gas) , which was then in a relatively early stage of development. Some years after, an amalgamation was arranged with the Sentinel company and to-day the first Sentinel-H.S.G. vehicles appear. An examination at once reveals them to be good sound engineering jobs. It is obvious that every detail in their construction has been carefully thought out. Nowhere is there a sign of skimping or makeshift, everywhere indications of first-class design and thorough workmanship.

The passenger model has the producer at the rear, and an engine conventionally positioned at the front. The goods vehicle has its producer beside the driver in the place normally occupied by the power unit, whilst the engine is carried, with the cylinders horizontal, under the frame, in similar place and manner to the well-known Sentinel four-cylinder steamer. By this means there is no encroachment upon body space.

As the two chassis differ from each other so widely, we propose to describe them separately, starting with the passenger machine.

This has a wheelbase of 17 ft. 6 ins., is 27 ft. 3 ins. in overall length, and affords-23 It. of body. space. At the rear there is room for a seat on the ,off side of the producer and for a useful shelf above the tuyere-cooling radiator on its near side.

The power unit has six cylinders measuring 4/ ins. (117,5 mm.) by 51 ins. (133.3 rum.), " which gives a piston displacement of 529.5 cubic "ins. (8.67 litres). Its output at 2,400 r,p.in. is 90 b.h.p. and the compression ratio 8 to 1.

Overhead valves, operated by push rods are employed, the cylinders and crankcase form a single iron caSting, and the unit is mounted at three points on rubber.

Five-speed Gearbox.

Through a I5-in, clutch, it transmits power to a Clark unit-mounted fivespeed gearbox having helical-toothed fourth and third-speed gears. The ratios are 6.75, 9.99, 17.75, 30.11 and 53.19 to 1. Thence there is a Layrub two-piece shaft to a Kirkstall underslung-worm rear axle. The wheels are shod with 9-20 tyres. Braking is by the Dewandre triple-servo system, a large vacuum tank being included.

Having a maximum section of 10 ins. by 2-/ ins. by / in., the frame is a clean-looking structure with pronounced kick-ups, and a strong bridgebracing at the rear engine mounting. The supports for the producer are clearly seen in one of the accompanying pictures.

Features of this component are the water-cooled tuyere, which has its separate radia tor referred to earlier, and ingen ious clinker box.

Contained in a housing under the producer, from which it can be withdrawn, is a device, which forms as it were the floor of the producer and sup ports the burning fuel. There are no fire bars, but, in stead, a metal plate, hinged at the front and supported at the rear. On this, clinker accumulates, so that it needs to be lowered at intervals. This is an extremely simple operation. Carried out by moving a lever, at the side of the end cover.

The support for the clinker plate is a series of five shelves or steps on a hinged fitting. At starting, the plate rests on the top shelf ; when clinker accumulates, the fitting is swung back a little, allowing the plate to fall on to the next shelf, and so on.

There is no refractory lining to the producer as the dimensions of the fire are confined. Gas is drawn out, from the incandescent part, through a perforated plate, by a horizontal pipe approximately opposite to the horizontal tuyere. Water is fed to the fire from a drip-feed on the dash board. The tuyere-cooling system is thermosiphon.

From the producer a short pipe incorporating a bellows-type flexible connection leads direct to a centrifugal cleaner, which it enters tangentially at the top. From the centre of the top emerges the outlet pipe, the mouth of which is about half way down. A dust extractor, with quick-release fixing, is _ at the bottom.

Thence the pipe-line-3 ins, in diameter throughout—runs inside the frame, being kicked up over the axle, to a cooler, carried transversely underneath the frame. Gas travels to the other side through three 1*-in. pipes and back by three more. The end-castings of these cooling pipes have detachable covers to permit a cleaning brush to be passed through. Next it is conveyed to an oilwash cleaner, mounted outside the frame on the near side. This has an easily detachable sump. It requires attention only at intervals of 1,0001,500 miles. the dust box and clinker box normally need to be opened daily.

The Change-over Valves.

After passing under the bulkhead, the gas pipe forks, there being a throttle valve in each branch. These are interconnected, so that when either is open the other is shut, and operated by a small lever in the cab.

One branch goes to an electric motordriven suction blower and the other to the manifold. The blower is for starting, and for keeping the fire burning when the engine is switched off for some length of time. Discharge from the blower is by a burner above the roof, and ignition of the gas at the burner is ensured by an electric spark. A rheostat, giving five speeds, controls the motor. Integral in the manifold are two separate passages—a large one for gas and above it a smaller one for petrol. The latter is connected to a small Solex carburetter, the purpose of which is for moving the vehicle, if required, with-. Out lighting the fire. A screw-down valve puts one or other induction system out of action.

Between the fork and the manifold is incorporated an air valve, This is actually a twin valve, having in each of the two cylindrical chambers, seen in an accompanying sketch, a rotating barrel, with diametric aperture. One is for idling air and has an independent control, whilst the other is for main air, and is interconnected with the throttle, on the engine side of it. Within the barrel of the main valve is a further axially sliding valve, this, too, having a separate control.

The object is to admit air in a quantity proportional to the throttle open. ing, also to be able to adjust the proportion to suit varying conditions.

Throttle and air valves are operated by levers on a tubular shaft, fitted on the change-over-valve (from blower to engine) shaft, which runs across, from the control side, behind the engine.

Turning now to the goods chassis, this has a four-cylindered engine, with the same bore, stroke and compression ratio as the bigger unit, and a capacity of 352,9 cubic ins. (5.778 litres). It develops 70 b.h.p. at 2,400 r.p.m. The main casting is a solid-looking job and incorporates a sump on the under side, whilst the end cover, which replaces the normal sump, is a light-metal casting. Dry liners are used, and the overhead, push-rod-operated valves are of different sizes. (In. the " Six " they are the same, 2 ins.) The inlets are no less than 21 ins, in effective diameter and the exhausts n ins.

There is a 12-in, clutch, four-speed gearbox, one-piece Layrub shaft, and bevel axle.. Unit-mounted, the box gives ratios of 6.83, 11.8, 22.6, and 43.4 to 1, and the, axle is extremely sturdy, incorporating an outrigger pinion bearing and a crown-wheel excess-load anti:distortion pad.

Either 34 by 7 or 8.25-20 tyres are offered.

Lockheed-Girling brakes are used, application being via Dewandre servo gear. The alternative wheelbases are 11 ft. 6 ins. or 13 ft., and respective body spaces, 14 ft. 6 ins. or 17 ft, Straight for most of their length, but downswept forward of the engine, the frame side members have a maximum section of 74 ins. by 24 ins. by 7-32 in.

VA; The producer is slightly offset from the centre and its clinker box incorporates a different mechanism to achieve the same end. It is singularly ingenious, and we illustrate it by a drawing. The dropping of the arms supporting the clinker plate is controlled by a mechanism resembling the escape movement of a clock or watch.

Otherwise the gas plant is similar to that of the passenger machine, except for the arrangement and detail construction of the components and the fact that no separate radiator is necessary for the tuyere. The single radiator is placed behind the producer, with a fan behind it, where it is immediately over the front of the engine.

No possible criticism can be made.ol the horizontal positioning of the power unit on the score of inaccessibility,

because the valve gear, induction apparatus, and bearings can be reached more easily than with orthodox layout. The dynamo is also in an accessible position on the near side of the engine at the front.

Behind the near-side louvres in the front panel is the' gas cooler, and behind it again is the dust extractor. On the off side of the producer are the oil-wash cleaner, blower, etc.

All pipework on both models is well carried out. At first glance there seems to be rather a complexity of piping, but this is to some extent illusory, and actually the piping is quite simple and straightforward.

Readers will have observed that both engines are of large capacity; 3-4-litres are usual for a petrol 5-tonner and 6-7-litres for a 32-seater. By this means their performances should be equal to those of comparable petrol vehicles.

Producer gas has a lower calorific value than petrol, and despite the fact that it can be used with a higher compression ratio, the output is some 30 per cent less.

These new velficles surely command consideration. Apart from the advan tages of using home-produced fuel, there is the saving of cost. Comparable figures in pence per mile quoted

by the maker are 1.167 on petrol, 0.52 on oil, and 0.3 on producer gas, taking the cost of solid fuel as the high figure of 40s. per ton.

Furthermore, there is the attraction of the more flexible performance that is admittedly a gas characteristic, and finally it seems fitting that these vehicles should emanate from a works that has always devoted its activities to solid-fuel vehicles, and is now, virtually, doing no more than modifying its method of employing coal as a source of motive power.

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Organisations: US Federal Reserve
People: CHAS S READY
Locations: London

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