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Smokeless Power : Non-skid Brakin, )sign Reliability
CHALLENGING Dr. F. Pischinger's views on diesel engine combustion, Mr. F. Zalud, director of research of the Automobile Research Institute, Prague, Czechoslovakia, quoted the results of experiments conducted by the Soviet Academy of Sciences and of tests in the Prague Institute, which proved, he claimed, that optimum • overall efficiency could be obtained without the use of masked inlet valves and inlet ports shaped to give a high rate of swirl. These features, said Mr. Zalud, reduced volumetric efficiency and they could be dispensed with (as a means of creating turbulence) if the shape of the cylinder-head components were matched to combustion requirements.
In support of the masked valve, Mr. D. G. Burton, chief engineer, diesel engines, C.A.V., Ltd., said that they were invaluable in a laboratory engine as they enabled turbulence to be varied for test purposes with the minimum complexity and cost and thus obviated major thodifications to the cylinder head in the experimental stage. Excessive swirl might affect performance more severely than zero swirl because it could create thermal problems, notably a very high nozzle tip temperature. In general, the author's observations could be applied to any type of engine having a multi-hole nozzle located centrally.
In reply to Mr. Zalud, Dr. Pischinger said be was satisfied with the practical results his company had obtained with masked valves and spiral-type inlet ports, but admitted that adequate swirl might be obtained some other way. The kinetics of combustion were too complicated to apply to practical laboratory work. Combustion had been studied as a three-dimensional problem as well as a phenomenon in a single plane.
It had been shown, said Dr. Pischinger, that the injected fuel should not attain too high a temperature too early in the combustion cycle, which was either detrimental to efficient burning or prevented burning entirely. The speed of compression was an important factor.
Smoke Meters The discussion on Dr. F. P. Malschaert's paper dealing with smoke meters was also controversial, particularly with regard to the inertia method of testing advocated by the author, in which the engine is accelerated in neutral for smoke measurement. Mr. W. Falkner, of Miinchen, said that repeated tests should be made with a Hartridge meter (which recorded all types of impurity) when the vehicle was being accelerated on the road in different gears. Inertia testing was unreliable, partly because the engine was not in a condition of thermal equilibrium.
Smoke testing with the vehicle operating at full load and a steady speed, or during moderate acceleration, was advocated by Dr. A. E. W. Austen, director and chief engineer, C.A.V., Ltd., who was also critical of the inertia method. In practice, there was no single method of smoke measurement that could be applied to engines of all sizes. An efficient smoke meter should be accurate to within I per cent.
Illustrating his comments with slides showing recent test results, Mr. J. D. Savage, British Petroleum Co., Ltd., emphasized that safeguards should be provided agai spurious results. A cold engine produced more smc than a hot engine and after an acceptable uniform temp ature had been established, the readings of three sticcessi tests could vary by more than 5 per cent.
Should makers aim at developing a simple fool-prc smoke meter that could be fitted to every vehicle or shot a method of testing with an existing type be sponsor which would be acceptable to the authorities? After aski these questions, Mr. C. L. Bailey, also of the Brit Petroleum Company, observed that fitting all vehicles w meters would not be generally approved and added ti stipulating a Hartridge smoke-limit reading of say 75, as Belgium, would not be appropriate to operating conditio in this country. It would be necessary to use one of t‘ ratings, depending on the size of the engine. In terms safety, the smaller engine could be allowed to operate at higher rating than the larger engine.
Co-operation—or Punishment Elaborating on the statements made in his paper, E Malschaert referred to medical evidence relating to t danger of lung cancer resulting from the presence • 3,4-benzpyrene in exhaust gas. Danger to health from tt cause could only be created, said Dr. Malschaert, if engine were consuming over twice the normal 'quantity fuel.
In the application of any smoke-density regulatio enforcement should not be punitive if the operator show( a willingness to co-operate in coping with the problet No weakness should be shown, however, in dealing wi the small number of persistent offenders. In reply to M Austen, Dr. Malschaert said that a meter latitude of on 1 per cent. was "over stringent "; the tests outlined hi been concerned only with maximum smoke readings. l defence of inertia testing, he pointed out that readin, were taken after the engine had been acclerated three tim in quick succession.
A variety of technical problems relating to brakir phenomena were reviewed by speakers during the discussic on the disc brake, vehicle 'dynamics under braking cond tions and vehicle vibrations caused by braking, papers c which were presented respectively by Dr. R. C. Parke by Mr. M. J. Odier and by Dr. D. Giacosa and Dr. 1 Cordiano. The majority of speakers favoured the di: brake in comparison with the drum type.
Adding to the information given in his paper whe making a summary, Dr. Parker said that the non-skid bral could not be fitted to existing types of vehicles (notabl the private car) because of lack of space, but it could anticipated that more sophisticated methods would developed. Skidding and consequent loss of control eaus a substantial proportion of accidents.
Opening the discussion, Mr. C. G. Tresidder, chi automotive engineer, Mobil Oil Co., Ltd., said that extensi tests had demonstrated the merits of using a lithium-ba grease for hub bearings (given that ample free space we provided in the hub cavity) when a large amount of he was dissipated from the disc through the bearings.
dvantages of the grease had been shown by tests of heavy tloon cars. It could be concluded that this type of grease as a satisfactory lubricant for the hubs of disc-braked e,hicles. In the case mentioned, the vehicle had covered 4,000 miles in two years without renewal of the grease. The need for a material with a higher coefficient of 'iction to cater for hand-brake operation was stressed by Ir. J. R. Botterill, of the Teves Company, Chefing Bremm, West Germany. At, the same time, it should be suitable ,r the service brake; the performance of the calliper was mited by the characteristics of available pad materials. In opposition to the. author, Mr. Botterill claimed that le disc brake was admirably suited for the application of self-energizing mechanism. The" hydraulic requirement" as reduced if disc brakes were employed. It was open doubt, however, whether the use of disc brakes reduced nsprung weight.
Braking Instability The serious loss of vehicle stability from rear-wheel ddding was mentioned by Mr. C. G. Giles, head of irface characteristics section of the Road Research aboratory, who pointed out that the application of an iti-skid device to the rear wheels would be a valuable rst step in increasing the safety of vehicles.
Replying to the speakers, Dr. Parker said that he had no dowledge of the use of lithium-base grease for hubs. In re field tests made by his company, hub-grease difficulties ad been more prevalent with drum-braked vehicles. laterials with a higher coefficient of friction were certainly !quired for hand brakes. The suggestion that self energiIlion should be applied to disc brakes was alarming acause it could reduce the consistency of operation. There ad been no case, in his experience, of a pad sticking to the isc on account of frost.
Referring to accidents on Ml, Mr. R. D. Lister, principal ientific officer, vehicle section, Road Research Laboraary, stated his conviction that many of the vehicles that ad left the carriageway had done so because of braking istability. A locked wheel provided 30 per cent. less raking effort than a wheel that was on the point of lockig. Braking a vehicle with one rear brake inoperative ',larked well with regard to stability. If the. rear wheels nly were working, the vehicle tended' to slew round trough an angle of 180 degrees if braked on a slippery )ad. Greater stability could be obtained by applying the
• oft brakes 0.5 sec. before the rear brakes by using restricn• orifices. Anti-locking devices improved the performace and stability of the braking' system.
Commenting on vehicle vibrations resulting from brakig, Mr. A. Goddard, director of engineering, Girling, td., described a type of brake shoe, the use of which had ired squeal and judder without modification of other amponents. The shoe was of the standard type but was iounted on struts arranged in a V, the facing load being iken by the upper ends of the V.
An example of bus tyres being worn out-of-round was escribed by Mr. V. E. Gough of the Dunlop Rubber Co., td. The tyre tread had worn uniformily, but braking nre varied considerably during rotation of the wheel. The trouble had been cured by permitting the shoes to float.
Analyses of stability based on fixed-control were criticized by Mr. C. G. Giles during the discussion on Dr. W. Karnm's paper on achieving maximum vehicle safety. Detailed observations of vehicles in three .speed. groups running on M1 had shown, said Mr. Giles, that very windy or very wet weather, or a combination of the two, had little effect on vehicle speed in any category. Although this indicated that many vehicles frequently operated above a dangerously critical speed, it proved that drivers continuously adjusted the steering to offset the effec-t of weather variables. An analysis of stability derived from tests of a vehicle having fixed control could, therefore, be very misleading. • Referring to Dr. Kamm's claims for front-wheel drive, Mr. Giles said it could be concluded from his comments that driving all the wheels would have advantages with regard to safety. In reply, Dr. Kamm .emphasized that a vehicle which had successfully passed a fixedcontrol test would be stable on the road and that this reduced the corrections the driver had to make. Four-wheel drive could not be recommended for normal road operations because it had" neutral "stability, in contrast to the positive stability offered by front-wheel drive.
Support was given by Dr, J. G. Giles of the Motor Industry Research Association for the claims of the slippertype hydraulic pump, mentioned in Mr. H. M. Clark's paper. Basing his statements on personal experience of a similar type of pump, Dr. Giles said that the principle had "a greater chance of universal application ". than any other type. An important feature of the unit described by Dr. Kamm Was the separate pumping action of the pistons. Referring to a comment by Dr. Giles in connection with viscosity, Dr. Kamm said that changes in viscosity in the normal range had tittle effect on performance or wear rates.
Design Reliability Upwards of 10 speakers took part in the discussion on design reliability, reviewed by Prof, C. Lipson and Mr. A. H. Krafve, and the associated subject of programme fatigue tests, various aspects of which were outlined by
Dr. E. Gassner and Mr. W. Schutz. Advocating the "before defect" method after summarizing the former paper, Prof. Lipson said that this involved "putting relia bility into the prodtict before the design stage. The reliability of seemingly identical parts, such as a crankshaft or an axle, could vary in the ratio 10 to 1, and if the component were contact loaded, the variation might be increased to 100 to I. It was essential to use statistical methods with the aid of an electronic computer to achieve optimum reliability and this was applicable to every type of machine including road vehicles, farm tractors and domestic washing machines. The ideal design was "just good enough," Over-designing wasted money. If he underdesigned, the designer would not keep his job very tong.
Mention was made by a number of speakers of acceleated road tests on abnormally rough surfaces as an alternative to programme fatigue tests, and in his reply Mr. Schutz said that such tests were lengthy and uneconomic and were not suitable for evaluating changes of design or of production methods. Whilst they could be used to determine whether a part was "good enough," they would not indicate if the part were "too good."