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Technical Paper

THE PHYSICAL CHARACTERISTICS OF ROAD AND FIELD DUST

1925-01-01
250010
In a study of the dust problem that has lasted more than 2 years, many observations, measurements and experiments were made to determine the nature and effect of dust and the best means for its elimination as a cause of engine wear. The results of these experiments, which seem to be of general interest, are reported and cover briefly such matters as the chemical composition of road dust, its particle size, specific gravity, and abrasive nature and the relative amounts of it to which an engine may be exposed under varied conditions. Curves are also submitted that show the average cylinder-wear on a number of test cars. The methods of testing air-cleaners are described, the principles underlying commercial air-cleaners are discussed and a list of what the author believes to be important elements of air-cleaners for passenger cars is given.
Technical Paper

BEST LOCATION FOR CARBURETER INTAKE1

1925-01-01
250007
Tests to determine the location under the hood of a motor vehicle where the air-intake of the carbureter will be exposed to the least dust were made by the agricultural engineering division of the University of California at Davis, Cal., and the results are given in the hope that they will serve a useful purpose. Of three types of dust-screen devised to catch the dust at different locations so that it could be photographed, and still would present little hindrance to passage of the air from point to point under the hood, the most effective was one of coarse hospital gauze stretched over frames set in transverse vertical positions on either side of and above the engine. The tests were made on two phaetons and a speed truck, run for less than 3 miles and following another car on a dusty road.
Technical Paper

FINAL REPORT ON THE 1924 CALIFORNIA AIR-CLEANER TESTS1

1925-01-01
250009
Rapid wearing out of the engines of farm tractors, trucks and automobiles led the University of California to undertake a study of the dust problem and the efficiency of air-cleaners in removing field and road dust from the air before it passes into the engine. Work was begun in 1922 and several reports have been made on the methods devised and the progress made during the last 2 years. Results to June, 1924, were given in the paper published in August, 1924. The present paper gives results of the studies to the end of 1924 and includes data from tests of 12 new makes or models of air-cleaner not previously tested or not fully tested. Of outstanding importance is the discovery that the quantity of dust inspired by any cleaner or carbureter is greatly reduced if the intake is placed high and faces away from the direction of motion of the vehicle.
Technical Paper

FOREIGN MATERIAL IN USED OIL: ITS EFFECT ON ENGINE DESIGN

1925-01-01
250004
Studies of samples of used engine-oil under the microscope show that the carbonaceous material is extremely finely divided and that the particles are held together loosely by oxidized oil. Dust particles in the oil can be distinguished from other foreign material by means of photographs taken with polarized light. Examination of a number of samples shows that the dust particles circulating with the oil are small in comparison with those drawn in through the carbureter intake, indicating that they have been pulverized on the cylinder-walls. The results of tests indicate that air-cleaners are of direct benefit, but the use of other devices to prevent dilution and to keep the oil free from foreign material is equally desirable. Oil-screens cannot be expected to remove any but the coarsest material, such as lint; hence they should be of fairly coarse mesh and of liberal area, in order to provide a free flow of oil at low temperatures. They should also be self-cleaning.
Technical Paper

MEASURING THE PERCENTAGE OF CRANKCASE-OIL DILUTION

1925-01-01
250003
Various methods of measuring the percentage of diluent in used crankcase-oils are summarized in this paper but the broader questions of deterioration of the oil due to other factors are not considered. The characteristics of viscometric methods and of steam, atmospheric and vacuum-distillation methods are discussed. It is pointed out that as dilution is not the only change the oil undergoes in service, methods based upon the assumption that oil is unchanged except by the presence of diluent may yield misleading results. Distillation methods seem best suited for this determination and those which are rational, in that the evaluation of the diluent is based on the change in the properties of the distillate as the distillation proceeds from diluent to oil, seem to promise the greatest accuracy over a wide range of diluents and oils.
Technical Paper

VOLTAGE REGULATION OF AUTOMOTIVE ELECTRICAL SYSTEMS

1925-01-01
250006
Progress made in the development of electrical equipment to serve adequately the needs of motorcoach service is reviewed. Electrical loads on motorcoaches are comparatively high, including the usual head, tail and dash lamps, body-marking and destination lamps and buzzer systems. As more and more electrical energy is used, the source of supply and its control become relatively more important. Not only does the electric generating system have to meet the demands of battery charging, but it should be able to carry the connected load with no battery in the circuit. This means that not only is sufficient energy necessary, but the voltage must be regulated in such a manner that the battery can be charged without endangering the life of the lamps because of excessive voltage, and no flicker in the light from the lamps must be perceptible. All these results must be attained under conditions of variable load, variable speed and the changeable temperatures encountered in service.
Technical Paper

MEASUREMENT OF ENGINE VIBRATION PHENOMENA

1925-01-01
250005
Smooth operation of motor cars becomes increasingly important as average driving-speeds become higher and as the public demands greater luxury and freedom from vibration. An analysis of vibration shows that it is caused by forces which can be calculated with considerable accuracy. Vibration itself is very complex, due to the inter-relation of forces, deflection and periodicity in the parts of the engine. In this paper a number of indicating and recording instruments devised for recording the actual resultant vibration and determining its exact character are described and their operation explained. Vibration due to unbalance of rotating parts, piston unbalance inherent in four-cylinder engines, bending of the crankshaft, centrifugal force, and torsional periods are discussed. Indicator-diagrams of the various kinds of vibration are shown. Unbalanced force and elastic reaction are the two general causes of vibration.
Technical Paper

THE PREVENTION OF SHIMMYING

1925-01-01
250016
Shimmying, although known for many years, did not become a serious problem until the arrival of the balloon tire and the four-wheel brake. Apparently, shimmying is of two kinds: the low-speed variety, which is merely a persistent front-wheel wabble without an abnormal bouncing of the axle, and the high-speed species, which is chiefly a persistent bouncing of the axle accompanied by wabbling of the wheels. The two most obvious effects are wheel wabble and axle bounce. As low air-pressure seemed to be the cause, the attention of the tire makers was first devoted to stiffening the body of the tire in various ways, but the results obtained were not satisfactory; and the conclusion was reached that the solution lay in making the car control the tire rather than attempting to control the car through the design of the tire. These considerations led to a search for mechanical means of control.
Technical Paper

WHEEL SHIMMYING: ITS CAUSES AND CURE1

1925-01-01
250015
Shimmying is an oscillating motion produced by repeated impacts or forces in the linkage of a mechanism that lacks stability or has become loose because of wear. Although previously existent in chassis in which the steering-gear was imperfect, it has become particularly noticeable since the introduction of low-pressure or balloon tires. But increasing the rigidity means increasing the unsprung weight, which, in turn, means greater impacts, hence, more shimmying. This is apparent in the effect produced by front-wheel brakes. Consequently, as the amount of looseness that can be removed is limited, the periodic forces that cause shimmying must be overcome.
Technical Paper

FRONT-WHEEL SHIMMYING1

1925-01-01
250017
Although wheel wabble, even with high-pressure tires, is of ancient origin and the general methods of controlling it have been well understood, its importance among present-day problems is due to the fact that the recognized specific for its treatment, namely, increasing the air-pressure in the tires, has been denied. Shimmying, as generally applied, includes wabble, or the sidewise vibration of the front wheels about the knuckle-pin, and tramping, or the bouncing of the wheels vertically, alternately on the two sides. In addition to discussing the advantages and disadvantages of the low-pressure tire, the author has enumerated the results of tests, some of which have been obtained from original research work by himself, others from the literature on the subject, with a view to determining whether shimmying is caused by defects in design, and what are the effects when certain modifications are introduced.
Technical Paper

EFFECTS OF BALLOON TIRES ON CAR DESIGN

1925-01-01
250018
Inasmuch as the use of low-pressure tires has become established, the conditions of car design affected by them are reviewed, particular reference being had to the members of the chassis included under the term unsprung weight, namely, the axles, the wheels and the tires. Referring to the principles that underlie basic design, the author first investigates the effect on the steering of such changes and compromises from the perfect structure as failure of the king-pin to coincide with the vertical load-plane, the inclination of the king-pin toward the wheel, or the wheel toward the king-pin, or both, and the giving of a toe-in to the front wheels. Further modifications have served to reduce the car shock, to add to the strength of all the parts by increasing the dimensions, to improve the spring-suspension, and to reduce the car weight per passenger.
Technical Paper

CALCULATION AND DESIGN OF COILED SPRINGS

1925-01-01
250012
In determining the characteristics of coiled wire springs, if all the component forces, including those .of torsion, transverse shear, tension, and compression, are considered, the calculation may be complicated and involved, but for practical purposes of design all can be ignored except torsion. The calculation then becomes simple. The underlying principles of the formulas that express the torsional characteristics of an ordinary helical spring are the same as those that govern torsion in a straight shaft; and the fact that the result would be the same if the shaft or wire were twisted in the opposite direction makes it clear why a coiled spring has the same stiffness in either compression or extension so long as all the coils remain open. In Begtrup's formula, as given in the handbooks, the only unknown factor is the modulus G, which is variously stated to be from 10,000,000 to 14,000,000 lb.
Technical Paper

SIX-WHEEL TRUCK CONSTRUCTION AND OPERATION

1925-01-01
250011
Benefits gained by distributing truck weights and loads among six wheels rather than four, include less liability to cause road destruction, greater carrying capacity and more economical operation. The author classifies the causes of road destruction under headings of excessive loads on tires, impacts between road and tires, traction effects of wheels, and braking effects and says that the remedy is to reduce load or to correct improper weight-distribution. Impacts probably contribute most destructive effects.
Technical Paper

HOW HARD DOES A CAR STEER?

1925-01-01
250014
Relative ease or difficulty of steering has in the past been largely a matter of psychology, of comparison rather than of measurement. One driver may find a car difficult to steer that another finds easy. Safety is the first essential, then comfort. Because the parts used in steering seldom break, present practice is considered safe, but the steering-ratio is very important. A low ratio that produces fast steering-effects may be entirely safe in the hands of a strong, safe, experienced driver, but absolutely unsafe in those of a weaker driver, even though he may be expert. Fatigue, however, will eventually affect the strong as well as the weak driver, so that comfort enters as well as safety.
Technical Paper

THE AUTOMOTIVE AIRBRAKE-WHY AND HOW

1925-01-01
250013
In an endeavor to find an engineering justification for the use of the airbrake on automotive vehicles, an investigation was first made as to what actually causes a car to stop when the brakes are applied; and it was ascertained that nothing that can take place within the car itself can directly influence the motion of the automobile as a unit, that its motion can be changed only by some force external to the car itself. Four such forces are normally present, namely, wind resistance, road resistence, gravity, and the adhesion of the road to the wheels. The first two are negligible. Grades have a measurable effect on the stopping distance, but the force that actually stops the car is the last named: the force that is applied from a point external to and in a direction opposite to that of the motion of the automobile.
Technical Paper

RECENT COOPERATIVE FUEL-RESEARCH PROGRESS

1925-01-01
250001
This report deals with further progress in the cooperative fuel-research. General factors underlying starting ability are discussed and experiments showing the effect of changes in spark character and of gas leakage are described. The probable mechanism of crankcase-oil dilution is treated, and further experiments with reference to this subject are explained. One experiment deals with operation with oil as a cooling medium to obtain high jacket-temperatures. Other experiments show the effect of change in piston clearance and in the number of piston-rings employed. Factors influencing the rate at which the diluent is eliminated from the diluted oil are shown to be of importance, and methods of examining these factors are stated.
Technical Paper

ANOTHER ASPECT OF CRANKCASE-OIL DILUTION

1925-01-01
250002
Wide differences of opinion are expressed by automobile builders regarding crankcase-oil dilution. The theories advanced in explanation of dilution fail to elucidate some important facts and must therefore be regarded as unsatisfactory. From a theoretical investigation, the author determines the conditions under which the vapors of various fuels condense during the compression stroke of the engine and, as a result of such analysis, presents the theory that “surface condensation,” or the aggregation of the liquid fuel-particles on the cylinder-walls, is chiefly responsible for crankcase-oil dilution. First, suggested explanations of the dilution are presented, references to previous experiments by several authorities are stated and these are discussed. The effect of jacket-water temperature is analyzed, and whether any condensation of fuel takes place during the compression stroke of a carbureter engine is debated.
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