Exhaust Brakes Do Not Cause Engine Wear"
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WTH continually rising maintenance costs, serious consideration was now being given in Britain to exhaust brakes as .standard equipment, stated a paper, "Exhaust Brake Design and Operation," by Mr. A. G. Stec and Mr. W. K. Cox read before the Instil-lite of Road Transport Engineers in London yesterday. They were certain that the time was not far distant when an exhaust brake would be a normal fitment on every heavy commercial chassis.
The efficiency of an exhaust brake was determined by the pressure created in the exhaust manifold. This was dependent on engine design, the main factors being the area of the underside of the exhaust valve and the tension of the exhaust-valve springs.
No Adverse Effects
In comparison with the average working pressure of the engine during the compression and power strokes, the additional load on the pistons during the exhaust stroke when the brake was in action did not have adverse effects on the engine. It had been proved that where engines had worn liners and pistons a saving of lubricating oil was effected.
A driver could not, in the authors' opinion, under present road conditions in this country be expected to operate an additional lever to work the exhaust brake; therefore some form of automatic control had had to be designed. An exhaust brake which was controlled from the main brake pedal would remain in action when the chassis brakes were brought into use and the vehicle was at a standstill, so that provision had had to be made for idling.
It had been found in practice that the slight by-pass in the valve plate caused by the working tolerance allowed sufficient air for idling, but did not in any way affect the manifold pressures obtained at the higher engine speeds.
300 Per Cent. Longer Life
In order to obtain some assessment of the saving in brake facings, an A.E.C. Regent Mark III had been selected and fitted with an Ashanco exhaust brake, and at the same time equipped all round with 1-in.-thick woven facings. The normal facing life on this class of vehicle, working stagecarriage services, was 21,000 to 22,000 miles and this bus had been rigidly retained on the same type of running.
After 15,000 service miles only + in. thickness of the facing had worn away. On this figure it appeared that an increased facing life up to 300 per cent. might be expected.
The question of wear on the engine and transmission through the use of exhaust brakes had been raised. Information which had so far been received from Continental operators c14 confirmed that no extra wear took place, and the possible wear which might occur by converting the exhaust stroke to a pressure stroke was more than offset by the reduction in engine revolutions when the vehicle was descending a gradient. After completing over 70.000 miles running, engines had been dismantled and after examination the writers were satisfied that no additional wear had been caused.
[At a meeting of the I.R.T.E. in Birmingham last month it was stated that an Australian report complained Of increased cylinder-bore wear caused by exhaust obturator brakes. A British operator said that exhaust brakes created extra sludging of lubricating oil and raised fuel consumption (The Commercial Motor, January II). The Clayton Dewandre Co., Ltd., later denied. that these criticisms could apply to the ClaytonOetiker exhaust brake (The Coinmercial Motor, February 8).] With regard to the transmission, careful checks had been made to see whether any additional, wear had been created, and it appeared that the 8-10 per cent. vehicle retardation normally obtained had not been found in any way detrimental.
Another trouble expected had been wear on the exhaust-valve butterfly spindle and bushes, but it had been found on mileages of over 80,000 that no wear at all took place.
The results of the authors' experience with the exhaust brake proved that, apart from considerable saving in brakefacing and drum wear, and the improvement in oil saving and engine life, it had a beneficial effect on tyre life. Not only did the lower heat generated in the brake equipment improve the overall brake efficiency by the elimination of fade, but the lower heat transmission to the tyres ensured that they ran at a more constant pressure.