ENSURING GREATER BRAKE EFFICIENCY.
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• A Suggestion for a Simple Appliance That Would Enable Brakes To Be Tested Under Actual Conditions of Weight and Wheel Alignment.
THE leading article which appeared in the issue of The Commercial Motor for April 26th, and the article on "Current Designs and Tendencies," which appeared in the issue for April 19th, covered the ground in relation to brakes and their adjustment to a certain extent, but there is much more that might be said on this very important subject with advantage, and it is with a view to add some of the missing links in the chain that I submit my views on this vitally important item in the equipment of a vehicle, particularly stipulating that they be not regarded as a criticism of what has already been said.
In the first place, I entirely agree with the Editor's views that, if some simple and inexpensive device could
be designed which would enable a garage engineer to test the power of retardation exerted by his brakes, it would be an advantage, especially where fleets such as those of bus undertakings are concerned. I, therefore, offer the suggestion here outlined as a basis for discussion. It is fundamentally necessary that the brakes be tested under the conditions that will prevail on the road. Hence the adjustment and test cannot be carried out with the wheels jacked up off the ground. 1, therefore, suggest that four plates of steel be let into the pavement at some part of the garage, flush with the ground, and at such a distance apart that they would be covered by the wheels of a vehicle to be tested.Chains of rollers should be laid on the steel surfaces, and these rollers would be surmounted by long plates of steel, having chequered surfaces for affording a grip to the tyres. The ends of the upper plates could be bent downwards so that they could be easily mounted by. a vehicle or removable ramps or small tapered blocks provided for the purpose. When the vehicle is in place, as shown in sketch, it should be anchored to a wall and the power necessary to move each of the sliding plates registered on a spring balance, the handle operating the bevel gear-driven screw which would endeavour to draw the plate away from the wheel with the brake applied.
By such a device the effect of each brake could be tested separately and under actual road conditions, namely, with the weight of the body on the axle and the wheel bushes in their normal alignment. The dynamometer could be portable, and all parts, excepting the plates let into the ground, could be removed when not in use.
With regard to the use of front-wheel brakes, it is curious that the pioneer work done by Hurst and Lloyd —or was it Lloyd and Plaister?—of Wood Green, N., B40 and of Allen Liversidge, should have led to nothing so far as those firms are concerned. They offered frontwheel brakes to the trade many years ago, but the trade turned them down. So far as my memory goes, these brakes were well made, and the design was much the same as brakes of the kind to-day, so that it is not easy to account for their unpopularity then as compared with their popularity now.
The matter of brake design might with advantage be considered from two entirely different points of view. There is the brake which is used for stopping a vehicle in traffic in the shortest possible space, and there is the brake which has to keep a vehicle under control on long and steep hills. In the former case, the generation of heat need hardly be considered, but in the latter instance heat and consequent expansion of drums have, I think, hardly received the consideration from designers that they should have. The experiment has been tried of driving a vehicle with a hand brake notched on for a long distance. At first the lower gears alone would drive the vehicle, but as the drums gradually heated and expanded, the higher gears could be used,-until the brakes became almost inoperative. The vehicle was then stopped, and, without altering the position of the hand lever, water from a hose was applied to the drums until they were of normal temperature. It was then found that the brakes wee gripping as firmly as when first applied. The expaTtsion of drums through heat may have been responsible for some of the fatal accidents that have occurred on long and steep hills.
I quite agree that we need some means whereby new linings could be fitted without keeping a vehicle off the road for a day, and that if more attention were given to this point by our designers such work could be done in an hour or two. A step in this direction is the marketing of brake linings, curved to shape, and with holes already bored and countersunk for rivets, for standard makes of vehicles.
The article referred to above, which appeared in the issue for April 19th, reviews most of the improved methods of applying brakes, such as the use of pressure derived from exhaust, vacuum, hydraulic power, etc., hut, for the rough conditions usually associated with the carrying of goods only, I am afraid that such devices will not endure the severe dose of neglect am]
unintelligent handling to which so many commercial motors are subjected. It would seem that the essential features necessary for brakes on vehicles other than those for carrying passengers are :—(1) Extreme simplicity-; (2) minimum of working parts; and (3) the ability for the driver to " feel " the pressure he is exerting on his brakes.
For heavy vehicles that have to descend long, steep hills I think that the present design is entirely wrong. The are described by a hand lever is necessarily limited to the convenient movements of the driver. The leverage obtained between hand lever and expander cam is limited by the necessary clearance that must exist between shoes and drum, so that when a driver has pulled his hand lever over to the extremity of its segment, he has no further power over his brake, and if this and his foot brake will not check the vehicle nothing but good luck will prevent disaster. In my opinion the perfect hand brake would be some modification of the Neate trailer brake or that used on the Yorkshire steam wagon, where, when the end of the segment is reached, the brake can be detained in that position whilst the driver moves his lever forward and takes a second or third pull. I do not for a moment suggest that the brakes mentioned here should be copied exactly as shown, but that some limitless brake should be designed having the same main characteristics, namely, the power to take more than one pull.
C. MI,.