THE NEED FOR EFFECTIVE BRAKES.
Page 16
Page 17
If you've noticed an error in this article please click here to report it so we can fix it.
The Coming of the Char-a-bancs Makes the Need Urgent for Better Systems of Braking.
This article is peculiarly authoritative, ris The author was responsible, during the war, for the brake efficiency of M.T. vehicles in unusually difficult country.
IT IS DOUBTFUL if any one part of the numerous units that constitute the modern mechanically propelled road vehicle has been subjected to so much criticism, and yet has continued merrily on in the error of its way, .. as the brake. gear. Quite naturally, the early brakes fitted to motorcars were constructed on the lines of those fitted to horse-drawn vehicles, and consisted.) of shoes made of wood or iron, which were caused to bear hard against the tyros of the wheels.
In those days designers were too busy to trouble much about brakes when the whole of their time.was needed to get the-'vehicle to move at all ; .nevertbeless, it was soon obvious that this system, whichttore chunks, out of the tyres, could' not continue in use ' with rubber at the price then reigning. The result was a. hurriedly-thought-out contrivance, consisting of a drum about the. size of a saucer and around it a piece of hoop-iron that, by an arrangement of levers, could be tightened on to the drum. This simple piece of mechanism served for the time being,tas it would hold the vehicle on a, hill of any steepness that it was likely to be able to climb.
As time werit,on, speeds became faster, cars were coaxed to climb to the to.: of mountains, and, with each degree of speed and•pow-er increase, the band brake was 'modified, bringing it to such a state that reasonable safetytwas still assured to the passenger. A little later, the internal-expanding shoe brake came along and gradually displaced the band brake, except in a few instances. 'Thanks to its neatness and compactness, it is by .far the Most popular form of brake to-day, but, mechanically, one of the most unsatisfactory pieces of mechanism on the car, on account of the inordinate amount of attention it needs if the vehicle is used to any extent in a really hilly district.
I write feelingly on this subject, having been responsible, during two years of the, war forpthetmaintenance of a large number of vehicles working in a hilly area, where once a fortnight was a quite normal rate for brake linings to need renewing.
About the time that. the internalexpanding shoe brake was accepted as thelast word in braking systems, the) commercial vehicle made its appearance. The history of the early days of the touring vehicle repeated itself. Designers, fully' occupiedwith the production of a vebiole that would carry its load, adopted the very natural -course of equipping their vehicles with en larged editions of the brakes fitted to touring -cars.
Under normal road' conditions, and with a good driver who uses hisbrains to save the brakes, ordinary internal expanding brakes as fitted to lorries give reasonable service. Occasionally, accidents do happen owing to the brakes :failing on some steep hills, but the driver, who is free from the re onsibility of human lives, is generally able to jump clear, 'and although the fr.lorry may be more or less.. badly damaged the disaster is regarded as a pure accident. The insurance company pays, and there the matter ends.
012
The Case of the Char-a-bancs.
With the advent of the char-h-bancs, however, this happy state of affairs.no longer holds. In place of a three-ton load of pig-iron, the driver may have 30 or 40 passengers behind him, for whose safety he and his employer are directly responsible, and human beings cannot be spilled into the road with impunity. Already one or two accidents involving loss of life have occurred and if manufacturers do not take all reasonable steps themselves to render their vehicles safe for public use, they are likely to find themselves hedged in on all sides by drastic regulations, and, when such regulations are drawn up, the authorities are not likely to err on the lenient side, or to withdraw them hastily; the. one quite natural object of Government officials being to cover themselves so that, whoever may be at fault, the public cannot lay the blame at their door.
This being the case, it is the obvious duty of manufacturers who cater for the char-a-bancs proprietor specially to consider his requirements and the safety of the passengers in the matter of brakes, remembering that human lives are at stake and that the risk of the thousandth chance cannot be tolerated in such cir Gums tanae,s.
The position of a char-habancs proprietor is unique: In the first place, he may have only one vehicle and no maintenance staff. He has probably developed from the horse-brake proprietor, and, consequently, relies for mechanical information entirely upon his drivers. His season only lasts for about five months in.the year, during which period it is of absolute-importance that the vehicles should be on the road every day that he can get a loan. The best touring ground, moreover, is usually in hilly districts, and, in some cases, the' drivers are not very experienced; or may even be scratch men who may have come straight from a 6 cwt. van to a 32-ria.ssenger char-a-bancs. Finally, the driver may be called upon to drive off into a hilly district quite unknown to him.
Under these conditions accidents can easily happen. Away from the restraining hand of the proprietor, and egged on by passengers to increase speed beyohd the scheduled limit, the driver suddenly finds himself on the top of a, steep downward slope ; at once he jams on the foot-brake, which, if on the eardan shaft, may be fierce enough to cause an axle' shaft or differential pinion to break, or, if on the back wheels, may be too slow in action to be effective. If this takes place about the end of the season, the side brake is probably on the verge of beine useless, and proves equally ineffective in stopping th7e vehicle. By this time the driver is too closely occupied in steering the vehicle to attempt to change clown to a lower speed and to use the engine as a brake, and so an accident happens.
Knowing the circumstances, the official view of such an accident would be that the driver was guilty of culpable neglige.nce in not seeing that his brakes were in order before starting. In this the official view might be quite wrong. It is possible, as far as the driver could ascertain, short of dismantling the whole brake gear, that it was in order. The wear that had taken place on one Or two previous hills may have been just enough to render the brakes sufficiently below their minimum stopping power to be ineffective in a sudden emergency, as by the very construction of the average brake gear there is but a very small margin of safety where a quick pall up is required on a steep hill. At the best, the brakes of the average char-a-banes a-re not more than twice the size of those fitted to a 30 cwt. touring car, yet they are expected to deal with from four to five times the weight.
The Engine as a Brake.
To put the blame for an accident on the driver on the ground that, knowing that his brakes were not in first-class order, he should havo changed into a lower gear is no answer to the problem. In the first place, it requires considerable skill to change down from, say, top speed to second speed with a vehicle travelling at or above its normal top speed, and it is not fair on the passengers that they should have to run the risk of the driver being sufficiently skilled, or being lucky enough to accomplish an operation which is difficult at the "best of times. Whilst every encouragement should be given to the driver to use his engine in low gear as a help to the brake on long hills, the process cannot be relied upon in an emergency, and, therefore, must be regarded as nonexistent as far as the ehar-h-bancs manufacturer is concerned.
Six Points for Manufacturers.
The natural way to slow up a vehicle is to apply the brakes, and, from my own experience of working vehicles in hilly country, I am of opinion that manufacturers of char-A-banes chassis should aim at the attainment of the six following objects in the design of their brakes.
(1) The brakes to be of such dimensions that either the hand-brake or the foot-brake will held the vehicle, fully loaded, on a gradient of, say, one in six. (2) The brakes should continue to function in an efficient manner for the whole char-a-ba,nes season without other adjustments than those that can be effected easily by the driver with a couple -of spanners. (3) When replacements are required, it should be possible to effect them in the shortest possible time, (4) The condition of the brakes should be capable of being readily seen.
(5) The brakes ahould be • capable of being held hard an for two or three miles on a:steep hill with a full load without damage due to overheating. Where two brakes are not sufficient for this requirement to be complied with, three should be fitted.
(6) Neither brake should be dependent for its action upon such comparatively delicate parts as differential pinions.
[In the second and final instalment of this article, to appear in the next issue, the author -deals with brake design with a view to efficiency and longevity of wearing surfaces.—En. C.M.]