Live Axles for Commercial Vehicles.
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The Conclusion of Mr. G. W. Watson's Paper before the Institute of Automobile Engineers, and a Condensed Report of the Discussion which followed.
(Concluded from page 410 in our last issue.)
Lubrication of Wheel Bearings by Lzakage.
Massy makers go to a lot of trouble to prevent the oil passing from the central casing to the wheel bearings, and rely entirely upon grease lubrication for those pasts. This may have been a necessary precaution with old forms of axles, but it has been the experience of many makers that better results can be obtained by allowing leakage to occur, provided that steps are taken to catch such leakage and drain it away Irons the brakes and s,vheels, as shown in Figs. 2 and 10. This may not appear to be an economical -method, but it must be admitted that a little waste oil costs less than a pa:r of new wheel bushes, not to mention the possible loss of service and inconvenience to the user in the case of a wheel seizure when the vehicle is miles away from house-. There appears to be no reason why leaking oil should not be led to other working parts, such as brake earns, etc., and thus dispense with a Lumber of small greasers. An axl.e is more likely to receive proper attention in the way of lubrication if it. gives the driver no more trouble than putting an occasional pint or so of oil into the central casing.
Where it is not desirable to zellow leakage in this manner, substantial independent lubricators should be fitted on the AN hods. This is,. at best, a poor method, and the caps are in constant danger of being knocked off by contact with passing vehicles or road obst7uctions, or by working loose as a result of centrifugal force, and once a, cap is lost a driver rarely thinks of fitting a new one until a seized bearing draws his attention to the lack of lubrication. If lubricators are fitted, they should be kept filled with a very thin grease, whirls is the next best lubricant to heavy gear oil for the purpose.
Small but Important Considerations as to Lubricat ion.
Substantial weasel's, fitted in convenient hut safe positions, elesuld be provided for all other working parts, such as brake cams, etc. All passages to these bearings should he as large as possible and free from sharp turns, as in cold weather grease is liable to congeal into such a solid mass that it is impossible to force it along the passages. Greasers, too, should have screwed necks not less than in. in diameter,
otherwise they are easilY broken off. All thrust washers
should be provided with distribution paths. preferably in the form of eccentric grooves with the throw ni the eccentrics on the two sides arranged diametrically opposite, otherwise the washer AS ill be so weakened that it may split along the groove. Cross. or radial, grooves ace a source of danger because they invariably lead to breakage of the washer.
THE DISCUSSION.
Col. Crompton and "Unsprung Loads."
COLONEI R. E. CROMPTON, CM., opened the discussion :Of course the main objection to alive axle is the questien of unsprung load. There is a mass to be moved at. different speeds and in a manner which sets up motion of that part of the vehicle which results in harmonic motions of a very complicated nature. I have been studying this question, as most of you know, from the roadpoint of view for a very king time, mid I do not agree in the least with the author in saying that little is known about the damaging effect of unsprung weight. On the contrary, I cense hot from a discussion at the Institution of Civil Engineers on thisvery subjeet, namely the effect, with electric locomotives, of. unsprung weight. The electric locomotives suffer from that difficulty in most cases. The large electric locomotives have an armature of many tons geared direct on to the driving axles, and if you had heard Mr. Aspinall at the Institution of Civil Engineers last night discoursing on the fearful damage done to the rails by the unsprung weight of electric vehicles cm the Lancashire and Yorkshire, New York Central, and other lines, you would not lightly dismiss the question a unsprung weight. I am perfectly certain that unsprung. weight is a thing not to be nqgleeted. I for one prefer a light axle, although perhaps the man who has the repairing and upkeep may prefer a heavy one, but he has nothing to do with the roads, whereas I have.
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The question of lubrication is dealt with rather too easily by the author. He seems to consider that the leakage of oil is a good way of making certain that oil is passing through the channel that it should do and in the right direction. That may be all very well, but it is an exceedingly disagreeable thing for everybody else. It is very bad for the owners of rubber-tired vehicles which have to stand in oil patches in the road, and I think if there is an accursed thing it is the habit of certain vehicles of leaving oil deposits wherever they stop, and I think that a civilized community will put an end to that state of things very shortly. The people who have got over this difficulty arc the London General Omnibus Co. They have succeeded by their various forms of oil trays in preventing that nuisance to other users of the same "The Colonel" and "C.M."
I may not be up to date, hut I do not know exactly what the author means by the " CM." type of wheel. I have asked several people but they do not know. Does it mean " Commercial Motor " or " cast metal" or what ? I do know sense letters such as A.S.C., and MT., but I do not know what CM.'' means.
The "Tire People" and Unsprung Weight.
Mr. W. D, WILLI:01_8M%; : The question of unsprung weight, is one which I have had in mind, and I have attacked it from this point of view. My interests were rather at one time with chain-driven vehicles exclusively, and I thought if .1 could get the tire people to tell me that live-axle vehicles were heavier on tires than chain-driven vehicles' I had a very good point. I made certain inquiries, but unfortunately they did not carry me any further. They certainly told me that certain of the chain-driven vehicles were notoriously heavy on tires, but I hail to give it up. That rather goes to prove that unsprung weight is not quite so important as Col. Crompton would have us believe.
It is extremely important. that the tubular portion. of builtup axles should go well to the centre of the. axle and get a, good hold on the central porticos of it, to take the rod over the
flanges where they join up to the casting. Referring to axle materials, I think myself that oil-hardening steels for rear axle gears, particularly those of the double-Deduction type, if they do not do anything else they certainly quieten the axle. An axle of oil-hardening steel runs quieter. than an axle of case-hardening steel.
The question of splines is mentioned, and I certainly wish that a paper could be read on that matter. I think all manufacturers find a difficulty, particularly with gearboxes, in getting quietness, due to the trouble of not getting a correct lit en the splines when both gear and awle,are hardened.
The Stiffness of Cast Axle Casings.
Mr. 0. D. NORTH :—One of the advantages that I claim for the forged axle is that it is not so stiff as a cast axle. let other words it yields slightly all along its length, particularly in the centre. I do not go so far as to say that the weakness which has been pointed out at the junction of the extension of the banjo is an advantage, perhaps it is not, but I was rather surprised at the figures for the deflection, namely onesixth on a 4 in. radius. I believe that if you have wheel journals of certain diameter and material, and cut a shoulder where they join the spring side you will get fewer fractures if the material is forged, of ordinary design, than with a. casting of the ordinary pattern. If you are going to make a casting that will not fracture it must be stiff and that is a had point in an axle. Makers of ordinary carts have realized this.
Difficulties with Dies.
One of the disadvantages of the forged axle is the trouble of get hog it made, especially in there tithes. It is a. delightful thing when you have gut it, but our suppliers have just broken a die worth 2100, so I feel rather strongly on it. think the suggestion that we should make these banjoes as shallow as the extension is valuable. It never struck me before and I am very much obliged because the deeper the die is the more likely it is to fracture. It has occurred to ma that it may be possible instead of stamping this in a drop stamping, and the ordinary subsidy type requires the largest hammers in use in England, that it might be forced in a hydraulic press. While you are about it, it might be possible to forge the end pan solid. It sounds heavy I know, but I think you will find it is not at all had when you conic to draw it out. If there are any stampers or producers Of large hydraulic forgings present, I should be glad if they will criticise this. I do not think the axles will weigh„any more than the ordinary banjoforging with separate end pan. It gets rid of the beastly stud holes in the bottom and must give extra strength, and it makes an end pan which will stand striking a rock which an aluminium end pan will not. Nobody likes to put a east-steel one because it wilrbreak, and if it, can be lone in a hydraulic press.I believe cast-iron dies will be satisfactory, and the great trouble of die brea.kages Will be over.
Mr. North (of Wrigley's) on Axle Collars and Torque
Rods.
Axle collars have always given trouble trouble. This is what I should imagine would happen with that suggested by Mr. Watson. One day a collar seizes or begins to seize_ This end gets flat and the hardened washer cracks, or if it is soft it stretches. Nobody knows anything about it. It begins to revolve and perhaps runs for 1ODO miles or so until it wears right off the end of the axle. I have seen every conceivable design of thrust washer giving trouble one way or a nether, and I think you want a hardened nut or a good locking device which will pull a lorry up dead to a standstill I do not say it happens on every lorry sold, but every now and. then it, happens and these are the sort of troubles you have, or something very like them.
With regard to springs I think these are perfectly capable of taking the driving thrust and the torque. It is best to get rid of as many wearing parts as Possible. They cost less to run and less to make. The great thing is to have long springs and make the pointof attachment as low as possible.
Mr. F. G. Wootasan stated what he. thought were the snore correct definitions of the various classes of live-axle constructien.
'there is a reference to axle shafts and driving flanges. it is not desirable to make the axle drive and the driving flange in one piece, but it sometimes has to be. done to save the tremendous overhang. There is far too much overhang of the axle cap, and lampposts and walls suffer rather badly through this overhang.
The author mentions the omission of bushing to the differential wheels and pinions. If the surfaces are hardened and ground the practioe is sound. There are a few thousands running and giving no trouble. With regard to ball bearings, you can depart a good deal from the makers' lists, but if you want a no-trouble job, you must stick to the bearing makers' lists and the bearings will outlast the vehicle. There has been some talk about screwed adjustments as against positive adjustments. I prefer the screwed adjustment, as I always have a feeling that these small packing washers are very often lost. The question of torque and thrust is mentioned elsewhere. If you use the torque tube you will find it defeats the ease of dismounting the axle which you have already gained, by having the maximum mounted on the gear casing.
As to internal gear drive, I have had ROTOR correspondence with America lately, and that form of drive is in great favour for moderate size commercial vehicles. Here I think only the heavy Berna vehicle, and on the Continent the Mercedes, are fitted with this, but it is much lighter. I have had one laid out, and it is very much lighter than the &ruble reduction type. There is a good deal of sameness about these double reduction axles in America, for the reason that 90 per cent. of the wagon manufacturers there assemble from three maims axle makers.
Mr. Burford's Strong Preference for Ball Bearings.
Mr. IL G. Reasoste believe I was the first to introduce
into this country a vehicle having a load-carrying capacity of five tons mounted on ball bearings, and I believe the bail bearing to be the right bearing for the following reasons. First it is absolutely interchangeable; second, after the designer has finished and worked.ont his stresses and sizes, them is no possible chance of its being changed by the repairer through any tendency that may arise through reducing the shaft by scores, etc. You may get a broken hall race, but it is a standardized job and you can put it back and the machine i5 not altered from its original .design or conception. Further all the hall-hearing makers are very reliable, and I feel to-day, after some sixteen years experience, that ball bearings on heavy vehicles are quite the right kind for that class of work.
One speaker referred to the -question of back axles. I entirely agree: with him that the forged back -axles are the best form you can have and as regards the question of dies. Surely whether von spend 1;100 or .£,200 or even ,300 on a die, when it is once made properly you get very little. trouble. Enfortunately in November, the die from Which our axles are pressed out was broken. I sent to the drop forging company. and they told -me that my output was so small that they could
not afford to make a Letter die. If I was going to give them a bigger quantity they would put in a substantial die and it would never happen again. The trouble is that manufacturers are not in a position to .give drop-forging companies orders to justify the expense, which would be justified in the case of large orders.
Maacat SBILSON :—As this is a r6sume of back-axle design, I have taken it upon me to bring along a drawing of a design which is very uncommon in this country, but which I think is of great interest. It is the axle of the Jeffrey quad, in which the back axle is also the steering axle. I will leave. these drawings for you to look .at, but I would particularly point out that the differential in this case is a spiral-gear one. That is the first spiral-gear differential that I have seen, and I think it quite an interesting item of design. I am indebted to the English agents of this car for permitting nrre. to show you these drawings. There is one other thing which I would suggest Mr. Watson should publish in the paper, perhaps in the form of an appendix, so that the paper may be even more complete than it is, and that is the calculation of rear brakes. There is really very little useful information to the designer re that subject, and I think it would form a very useful aptiendix. In conclusion, Mr. Watson is rather severe on the Aar Office, and although I had nothing at all to do with these regulations, and when they were got out I never thought I ever should have anything to do with them, I think one is rather apt to look at the question from one's own point of view. The designer looks at it purely from the question of design. The War Office in this case were looking upon it from the point of view of store accommodation and handling, and I think that although they may have imposed certain restrictions on the designer they certainly had good cause to do so. Recently in obtaining particulars of frame dimensions and frame side members,
found that one maker who had supplied 330 vehicles of one type (subsidized type, not a subsidy type), had no less than 150 different frame drawings, that is, 150 dra;:;Tings for 330 frames, so I think the War Office were not quite as wide of the mark as perhaps it might appear.
The Author Replies to the Discussion.
Mr. WATSON in reply said :—Mr. Chairman, Ladies and GentlemenI have not been half so severely criticised as I expected. Colonel Crompton has been, I think, my severest critic on the question of unsprung weight. I quite agree unsprung weight should he limited as much as it possibly can, but I cannot agree that unsprung weight entirely should be allowed to govern design. The questions of safety of part must be kept in view. One may say why did we ever depart from chain drive, for instance. We probably only departed from that from the point of view of convenience of wheel change and silence of running, otherwise the chain drive certainly presented the best possible conditions for unsprung weight. Mr. Williamson told us that in his inquiries among tire makers he failed to get any definite views as to Whether unsprung weight had any effect upon tire wear. That also has been my own experience, and I believe I am right in thinking that the new regulations which may be issued in the near future by the Local Government Board will actually allow us greater axle weight than we have hitherto been allowed. The roads are being improved, largely due to the closer co-operation of road builders, and I believe even Colonel Crompton himself has advocated that we should have our axle weights increased to a certain extent, from the economical point of view, and I do not see myself that so long as we keep the unsprung weight down to a minimum consistent with safety that we are going off the right track.
Mr. Williamson rather supports my argument about the banjo centre having a good wide throat, and he refers to the fact that he was able to cut down the fhicknessof the thing very considerably. I believe it is possible with safety to cut down the thickness of that ring to about in. depth on something like 4-); in. or 41 in., providing the throat is easy, but if the throat has any counter bore in it, or is made with
sharp radius, then it, is positively dangerous, and I believe failures have occurred on one or two occasions due to that. I know that failures have occurred with axles where the throat has been cut down.
On the question of oil hardening gears, Mr. Williamson speaks of them as being quieter. That has also been my ex perience. I prefer oil hardening gears to case hardening gears at any time.
Mr. North holds the opinion that forged axles are more flexible than the built-up cast ones. Most certainly they are, and that is why I believe they are so much better and give so much better results. I have yet to hear of a forged. u44
axle giving trouble, although I know of many built-up ones which have given serious trouble. I think the safety of the forged axle is in its flexibility, whereas the cast casing has no flexibility, or so little that the whole structure of the axle is bound to suffer to a certain extent in the end due to increased vibration. Mr. NortIrs suggestion of the end part being stamped in one piece with the axle is certainly ingenious, but the point is, would it not interfere with one of the advantages of the built-up axle, that is, its removal complete which enables us to examine all the parts without lifting the top cover off a heavy car, which very often might mean haying to take the hoay off, and getting a crane or tackle to work. He also spoke of the high cost of deep centred forgings, hut the high cost and risk of damage of twist is due very largely to the greater pressure necessary to farce the metal into the deeper pockets, and that is one reason why
very strongly advocate giving a wide throat and compara
tively shallow centres. It makes a comparatively cheap stamping or even if you cannot make a stamping of it you can make a, steam-hammer forging and trepan the middle portion out on comparatively old-fashioned face-plate lathes and the rest with boring machines to finish the job off. I believe you can in that way produce axles comparing closely with stampings.
Mr. North also advocates long springs well down on to the axle. He considers they are best. So do I. I also think the springs should have as little camber as possible compatible with the general design of the machine. However, I did not propose to discuss springs in the paper. Mr. North also mentions underslung springs as having a tendency to roll. I well remember one of the earliest of the steam buses of modern times—I do not mean the earlier ones of the 19th century—running from Shepherd's Bush to Marble Arch or on sonic such route, which had underslung springs, and as the funnel passed up to the top along the side, when the bus rolled about in a manner most atrocious, old ladies clung hold of the funnel to steady themselves with rather unfortunate results. Mr. North also irientions the wear and tear on the cardan joints, if both brakes are on the hack axle, and I think it was Mr. North who stated that one can generally increase the -useful load on a machine without increaaing wear and tear on the chassis, in this way. I quite agree with, that because the wear on the differential gear arid all the transmission parts is reduced. The loads on them are reduced so much that one can increase the actual useful load carried without doing much harm. Mr. Woollard takes me to task for my definitions, but I am quite prepared' to accept any definitions put forward so long as they are generally accepted. I have heard so many versions of them that in order to make myself clear in this matter, I thought I would adopt my own definition just for the sake of argument. I enly put these forward not as being what should be accepted by everybody, but just to make it clear what I am driving at in the paper. I will adopt any others if they are. standardized by any authoritative body.
Mr. Woollard then touched upon any increased clearance that may he demanded. If any new regulations demand increased clearance we may have to use a double reduction type of axle with rack and pinion drive such as is used on the Burford vehicles. I like that type of axle very much, and had Mr. Burford usedithe same type of axle on his new type of vehicle I should most certainly have given greater attention to it. It has got rather an unfortunate reputation in the past due to the roaring arid shrieking that we had with the old exposed rack and pinion drive, but this has entirely been removed by reducing the diameter of the rack as Mr. Burford has done, and enclosing it and making it well lubricated and dust-proof. I have had a large experience of Mr. Burford's two-ton machines, and I must honestly say that I have never found an axle of that capacity that I liked so well.