Lubrication Systems for Commercial Vehicles.
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In our four previous articles, on the subject of the lubrication of commer-cial motor vehicles, we have already dealt exhaustively with a number of the different methods which are employed by manufacturers for the dent oiling of their engine bearings. We have, under classified headings, described the principal examples of (a) the combined gravity and mechanical feed systems ; (b) the combined me-chanical feed and " splash " designs ; and (c) the latest development of the splash system, in which a constant level is maintained in special troughs, which troughs are contained in the crank chamber of the engine. So far as engine lubrication is concerned, it now only remains for us to draw attention to the various makes of machine on which reliance is placed upon the widely-adopted forced-feed system, and to mention certain special arrangements which are peculiar to certain types of engines.
Numerous manufacturers have definitely standardised their most modern types of motors with the embodiment of a method of oiling which provides for the positive feed, in measured quantities, of oil to all the principal bearings. In such cases, the oil is collected in a sump at the bottom of the crank chamber, after it has filtered through a gauze, and it is then forced, by means of sonic suitable form of pump, up Into the various oil channels and conduits which lead to the drilled crankshaft The pump, which is most frequently employed is of the toothed-gear-wheel type, and a particularly-efficient form of this class of pump is the patented pattern made by the Albany Manufacturing Company, Limited, of Willesden. In some cases, however, a small reciprocating pump is employed, and reference is made to examples of this practice hereafter.
The Austin Motor Cornpany, Limited, John T. Thornycroft and Company, Limited, and The Maudslay Motor Company (1907), Limited, pin their faith to a gear-type pump and the usual drilled crank chamber and crankshaft. Tbornycroft has, however, on one of its most recent models, an arrangement for the squirting of oil, under pressure, direct on to the revolving connecting-rod big ends. A relief valve is fitted, which can be made to control the supply of oil to the bearings, and some provision of this nature is found on a great many systems of the type which we are now considering. When too much oil is passing to the bearings, suitable adjustment of such a relief valve opens a port which allows the oil to return direct to the base chamber. It is interesting to note that the Thornyeroft Company claims to be the first manufacturer co introduce into England the application of forced-feed lubrication to internal-combustion engines.
In the first article of the present series, we reproduce, as a representative example, a drawing • of the forced-feed systetn employed by Armstrong, Whitworth and Company, Limited, on its heavy commercial vehicles. The oil pressure is secured, on these models, by a small oscillating pump, which is placed in the crank chamber and which is driven by means of an eccentric sheave and strap from the induction camshaft. The gudgeon pins are oiled by a portion of the lubricant which finds its way up the hollow connecting rods from the drilled crank pins. A pressure gauge on the dashboard reveals the state of the oil circulation at all times.
We have already (page 5o5 ante) reproduced a drawing of the system employed on the Alldays' engines, and the methods, illustrated thereon, are typical of general practice in the direction of forced-feed lubrication. A substantiallydesigned relief valve, which is disposed at one side of the crank chamber, prevents the oil pressure from exceeding a predetermined limit. Any surplus oil, which might be pumped by the engine at high speeds, is passed through this valve directly back to the well or sump in the bottom of the crank case.
The recent Milnes-Daimler models have all been provided with small reciprocating pumps, driven direct off the camshaft, and, from this source, oil is driven in the usual way to the various ducts throughout the moving parts of the engine. The details of the drip-feed splash system, which was a feature of he earlier models, will be familiar to most of our readers.
The Arrol-Johnston machines are examples of consistent design in the matter of engine lubrication, and we are informed that the company has employed the forced-feed system, operated by a gear-wheel type of pump, for the past eleven years, and that it has never felt the necessity for a modification of the original scheme up to the present time. We had occasion to illustrate the well-arranged spring pump-drive from the camshaft in our first article on the present subject (p-age 459 ante). The
gudgeon pins on the Arrol-Johnston vertical engine are lubricated through the medium of small pipes, which run up the outside of the connecting rods, from the big ends to the crossheads.
The success of the Halley vehicles in the R.A.C. Commercial Vehicle Trials, was, in no small measure, due to the reliable, yet simple, forced oiling methods adopted on the chassis. A tell-tale pressure gauge is fitted on the dashboard, anti the pressure of io lb., at which the gear-wheel pump works, ensures a spraying effect inside the crank chamber as the oil exudes from the main and crank bearings.
We illustrate, by a diagram on this page, the latest form of automatic forced lubrication which has been employed on the Fiat utility models. The general arrangement of the system will be seen to be in accordance with customary practice, but a useful novelty is introduced by the inclusion of an overflow, hand-operated, regulating valve, which is fixed on the dashboard. The oil feeds are arranged in series, and a pressure gauge acts as a tell-tale for the circulation.
The Star Engineering Company, of Wolverhampton, employs various systems on the pleasure cars which it manufactures, but on its commercial vehicles, a special form of oil pump is used An eccentric-operated plunger, with two diameters, serves the double purpose of positively measuring the lubricant, and of subsequently forcing it through the one main pipe which has its various branches to all the bearings of the engine. We have already illustrated this appliance, as a special example of pump, on page 504 ante.
As a pioneer of positively-lubricated motor-vehicle mechanism, De DionBouton, I.imited, easily holds first place, and the ingenious methods adopted, for the ensuring of the proper and regular distribution of oil to all the moving parts of both its standard engines and its gearboxes, have been so frequently described that there is no need for a further detailed description of the whole system on the present ockasion. The latest model of four-cylinder De Dion engine embodies all the original ingenious features.
The Thames and the Argyll Companies have fitted their later models impartially with either a splash or a forced-feed arrangement, and customers are thus afforded a choice, which latitude, in our opinion, should not necessitate prolonged discussion as to the relative merits of the two types.
A novel arrangement is that adopted by the Critchley-Norris Motor Corn pany, of Bamber Bridge. Reference to the diagram, which we reproduce, will readily explain the system. An oil tank is in connection with the bottom member of a sight-feed lubricator, and with a small air pump which is driven off the engine camshaft. Air is pumped into this tank from the air pump, and o:1 is thus forced, by displacement, up into the bottom duct of a Wakefield sight-feed lubricator. Adjustable sight feeds allow the oil to rise—through glycerine—to the top member, which is also in connection with the air pressure from the pump. The oil is thus forced, in pre-determined amounts, through the various distributing feed pipes, to the principal moving parts of the engine in the usual way.
The crankshaft on the " Hallford " machine is carried in ball bearings. A small, gear-type, oil pump is driven by enclosed bevel gear, and it draws oil from a sump in the crank chamber, and delivers it, past a relief valve, to a hollow rod, which rod terminates in a strap encircling the crankshaft. The bore of this strap has an annular groove, round which the oil finds its way to the hollow crankshaft, and thence to the big ends of the connecting rods in the usual way. An important advantage, which accrues from the employment of ball bearings in the engine, is the possibility it affords of the entire enclosing of the ends of the crankshaft, so that no oil can escape. J. and E. Hall, Limited, looks for a consumption of one gallon for 300 miles on its threeton machines, and, it will be admitted, this is a very satisfactory result.
The regularity and freedom from breakdown of the Albion and Lacre vehicles owes not a little to the Murray patent mechanical lubricator, with which they are all fitted. We gave a fully-illustrated description of this appliance in our issue of 4th September, 1903. it will be remembered that it consists principally of a rotating distributor disc, which carries a springmounted plunger ; the motion of the pump is secured by the contact of this plunger successively with each of a ring of fixed cams.
Messrs, Durham, Churchill and Company, of Sheffield, use either the selfcontained lubricating system, as embodied in the Aster engines, or the Noakes' sight-feed lubricator. The tendency, on modern machines, is to run the gearbox snafts in ball bear ings, and this method simplifies the
lubrication to a great extent. As a general rule, it is only necessary to
partly fill boxes fitted in this way with vaseline or thick grease, which works its way into all the self-contained bear ings. Some makers—we may instance the Wolseley Company and J. and E. Hall, Limited, prefer to lubricate the ball bearings of their gearboxes with oil, and this should not require replenishing more frequently than once a month.
Where plain gun-metal bearings are employed, reliance is placed in the dis tributing effect of the rotation of the gear wheels, and frequently special pockets are cast in the gear casing, from which sumps the gear wheels take their supply of oil. Grooves in the bushes ensure sufficient distribution.
The gearboxes on the Arrol-Johnston
machines are provided with wells and suitable ducts; woollen strands are em
ployed to connect these ducts and wells, and so to ensure a constant supply of oil to all parts of the gearbox. The plain bearings on the Alldays' van are provided with automatic, spring-controlled grease lubricators.
Steering-gear joints, brake-gear joints, clutch centres and other minor movements are, as a rule, supplied with screw-down grease caps. Hubs are generally lubricated by the removal of the axle caps, the filling of the hubs with oil or grease, and the replacement of the caps. When plain bearings are used, they are usually of the floating variety, and are generously provided with grooves and holes into which the lubricant may find a way. We conclude this series of articles with a short description of two specially-prepared forms of bearings, and we reproduce drawings of both. With regard to the drawing of the " Thames " engine bearing, oil enters
through the duct (A), and an annular chamber (B) communicates, for a part
of the revolution, with a corresponding hole in the crankshaft. C is an additional trough, which catches the sprayed oil, and D is an oil thrower which prevents the lubricant from leaking out at the end of the case.
The second drawing is of a bearing on the Broom and Wade paraffin-driven
wagon, and it illustrates the care with which the surfaces are prepared to ensure a proper distribution of lubricant over the whole area of the bearing.