The Sheppee Superheated-steam Vehicle.
Page 5
Page 6
If you've noticed an error in this article please click here to report it so we can fix it.
The type of vehicle which is illustrated on this and the following page should be. of exceptional interest to all our readers in partly-developed countries ; it has been specially designed and constructed to meet the conditions prevailing in South Africa, which conditions are comparable with those existent in many other parts of the world. The vehicle was supplied to the Natal Government, and was one of the purchases made by the Hon. W. A. Deane, the Minister of Agriculture for Natal, when he made his tour of British motor manufacturers works, during May last, accompanied, in an advisory capacity, by a member of our Editorial staff.
Two interchangeable bodies were sent out with the chassis, one of them having a flat lorry platform, whilst the other was of the char-a-hancs type, with seating accommodation for from 18 to 20 passengers, and with a canopy for light luggage and a grid at the back for the stowage of mail packages. A noticeable point about the chassis is the high clearance of all the parts he
tween the wheels, none being nearer to the road surface than 18 in. This detail of design is a r»atter of great importance in motor vehicles which are intended for use on unmade roads or in undeveloped countries. The wheels arc of steel and of large diameter: there are two sets, One being fitted with detachable solid-rubber tires, whilst the other has wide wooden treads, the blocks forming which may easily be taken off and renewed, when required, by any lot-al earpenter. These wooden-tired wheels are intended for use when the lorry body is fitted, at which times the vehicle's speed is not expected to be very great.
One of our ihustrations shows a plan view of the chassis, and from this illustration it may be seen that all the working parts of the engine, differential gear, air-pump, etc., are eneased to reduce weer.
The steam generator is one of the lInsh type, the bottom coils of which are wire wound like the barrel of a large gun, the strength of the tube being thereby greatly reinforced. For this type of generator, the following advantages are claimed : 1, practically any kind of water may be used without doing any damage to its tubes; 2, oil in the water has no detrimental effect, and, consequently, condensed water may safely be. used ; 3, the generator cannot " burst " in the ordinary sense, and, if a tube should give out, there is no explosion; 4, practically any pressure of steam and any degree of seperheat may be obtained ; 5, it is easy to repair—a " burst ' tube may be replaced in half an hour ; 6, the burner used in connection with the generator is of simple construction and has no mechanical or working parts ; 7, the fuel consumed is paraffin which commodity can be obtained almost anywhere.
Other constructional points of note are that the vehicle has no changespeed gears, no delicate mechanism requiring constant adjustment, no glands or stuffing-boxes and no electrical devices.
The engine is one of the two-cylinder double-acting type. The steam chests of the cylinders are made separate from the tubular portion, which method of construction allows for the free and equal expansion of the cylinder walls. Mushroom-type valves are employed, and these have long stems with water-seal grooves in them, in order to prevent any escape of steam. The high degree of superheat which is sometimes employed in engines of this type has often caused trouble with the piston-rod gland packing, but Mr. Sheppee has overcome this objection by the fitting of a special form of packing, in which a cast-iron gland is free to " float " within a steel housing which is secured to the fm-out covers of the cylinders.
The two-thraw crenksithit is made of chronic-vanadium steel, and it is mounted in plain bearings of ample proportions. The drive from this shaft to the differential countershaft is transmitted through a single pair of plain spnr gears, and the differential gear, reducing gear and camshaft are all enclosed within the crankcase; the main bearings are oiled by a forced
m syste of rubrication. The differ ential gear and its shafts are mounted on ball bearings, and the outer ends of the shafts are flexibly coupled to two short chain-sprocket shafts from whick the drive is transmitted to the back wheels by means of enclosed roller chains.
The feed-water pump for the generator is operated by a steamdriven piston ; the steam distribution for this donkey-pump cylinder is controlled by a patented form of trip motion. The pump is mounted outside the off-side member of the frame, as is shown in one of the detailed photographs which are reproduced herewith. A sectional drawing, together with a full description of this donkey pump, was given in our issue of the 3rd December, 1908. Fitted immediately in front of the donkey pump are -the two forced-feed lubricators : these are connected to the donkey pump and are operated therefrom. One of these pumps delivers oil to the bearings of the crankshaft, camshaft, differential shafts and big-ends, whilst the other sends oil direct to the steam regulator. The latter lubricator is one of the double-plunger type, and is very simple in its construction. Its two plungers are operated from a single camshaft, and the return stroke of one of the plungers is effected by a rocking lever whiCh, in turn, is operated by the other piston during its delivery stroke. All the parts, including the suction valves, are contained within
the body ; the valves are mechanically operated, and no springs are employed.
Referring to the plan view of this chassis, it may be seen that the engine occupies a central position in the chassis, between the leading and driv
ing axles. The generator is placed under a bonnet in front. The fuel tank is slung underneath the frame at the rear of the chassis, whilst the main water tank is situated under the driver's seat. The condenser, as may be seen, is divided into three portions : Ime of these takes the form of a radiator, whilst, of the other two, one is mounted in front and the other behind the rear axle ; these are all connected in series, and included in the circuit is a feed-water heater.
.The temperature of the steam before it leaves the generator is indicated by the movement of a long finger over a horizontal quadrant; this finger is operated, through a multiplying lever, by an extremely-simple form of thermostat. The idea of automatic control, which was advocated by Serpollet, has been abandoned in the Sheppee machine, and the supplies of both fuel and water are regulated by hand ; the need for a large number ei delicate parts is thereby avoided. The dashboard and all the control gear are shown in one of our illustrations : referring to this view, the sight-feed glasses for the two forced-feed lubricators are shown at the extreme right of the dashboard ; to the left of these, at the bottom of the dashboard, is the relief valve ; the gauges fur indicating the steam pressure and the airpressure in the fuel tank occupy a position on the dashboard immediately in front of the steering pillar ; almost hidden by the steering pillar is the horizontal quadrant for the therm> stat, to which we have already referred; on the extreme left of thr driver's footboard, close to the dashboard, is the hand pump by which the initial air pressure in the fuel tank is created ; below the steering wheel is the lever by which the engine may bs reversed, and the point of cut-off for the steam valves varied ; a small star wheel is also shown on the steering column, and by means of this star wheel the steam valve for the donkey pump may be operated. The other two valves which are shown close to the water tank are the stop-valves for the water and fuel respectively.
When starting from all cold, it is necessary to force the first few charge& of water into the generator by means, of a hand pump, and, for this purpose, the pump plungers are connected up to a short lever that is pivoted at the side of the frame ; a removable extension is provided to this short lever, and, by its means, the pumps may be operated by hand. The extension maybe remove() as soon as tile steam pressure rises above 5 lb. or 10 lb. per sq. in.