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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.

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.

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Investigations indicate that detonation may be controlled by retarding the rate of combustion by chemicals added to the mixture, which serve to increase its specific heat and prevent excessive temperature, and by reducing the temperature of the walls of the combustion-chamber, so that the temperature of the charge previous to ignition will be lower and thus insure a normal rate of combustion. The present discussion is devoted to methods of controlling the temperature of the charge before and after the mixture enters the combustion-chamber, and before normal ignition occurs. Tests previously made on a poppet-valve engine and on a sleeve-valve engine revealed the impracticability of applying the laboratory methods used at that time to commercial practice and the need of eliminating some of the difficulties inherent in those methods of detonation control. The various changes made in the engine are described, including the specially designed spark-plugs.

Classes of service already provided by the street-car and the passenger automobile influence the expectations of the motorbus passenger regarding the quality of transportation service afforded by the motorbus. If an operator persuades people to ride in his motorbuses, it will be because they offer safety, economy, convenience and comfort to a greater degree than that offered by competitive transportation media. Since the public has demonstrated that, under favorable conditions, it will patronize the motorbus to an extent that yields a profit to the operators, the future success of this means of transportation lies wholly within the control of the motorbus builders and those who operate it. Of the factors that determine the degree of success attained, motorbus-body design bulks very large. Discussion of the subject is presented from the viewpoint of the passenger, as the motorbus approaches him, as he enters it and as he judges the quality of transportation it affords.

Balloon tires have caused the points at which the greatest trouble formerly occurred to be reversed; the greatest wear hitherto has occurred on the rear tires; now it occurs on the front. The carcasses of old tires were heavy and thick and carried a large part of the load; balloon tires are flexible and will support very little load. The air-pressure carries the load and gives greater cushioning effect. Four-ply tires have proved to be the most satisfactory and have none of the disadvantages of high-pressure tires. Balloon tires steer harder than high-pressure tires because of lower air-pressure, which necessitates a greater area of contact. Steering resistance is caused by the load on the tire and the increased area of contact. Many designers, in making the steering gear free to overcome steering resistance, make wheel-twitching possible. Shimmying may be classified as low-speed and high-speed, the latter occurring at speeds between 35 and 40 m.p.h. and being very violent.

An air-spring and a steel-spring combination has a characteristic load-curve that allows maximum flexibility in the general working-range of the axle yet has an increasing resistance to dissipate large shock-loads. By varying the compression volume in the air-spring, the load curve of the combination can be made more flexible or stiffer as occasion demands. Tests show that the steel-spring vibration alone had a duration of 5½ sec. with a period of 87.2 vibrations per min.; the combination, a 3-sec. duration with 60.0 vibrations per min. Field tests of front-axle movement were made, the test apparatus for these and other tests being illustrated and explained. The maximum axle-movement either above or below the normal line is increased when using air-springs, and the subsequent rebound shows more action on the underside of the normal line, the general tendency of the air-springs being to float the chassis on a slightly higher plane at the time of rebound.

Shimmying was noticeable before four-wheel brakes began to be used, but since that time the trouble has been greatly increased. Two kinds are distinguishable; (a) low-speed shimmying, a violent wabble of the front wheels about the king-pins without a bouncing of the front axle, and (b) high-speed shimmying, a severe bouncing of the front axle during which one hub is up while the other is down. This occurs at somewhat higher tire-pressures and at high car-speed. Believing that both forms are not correctible by changing the design of the tire and are only slightly affected by changes in the steering-gear, efforts were directed toward prevention rather than correction.

A bumper is a bar attached transversely in front of or behind a car body to prevent contact between an obstruction and the car body or to cushion the shock of collision between vehicles. The impact-bars have various sectional forms, from flat to round and from tubes to channels, and are composed of steel, wood or rubberized fabric. The attaching devices are sometimes yielding, sometimes rigid. The evolution of the bumper is shown in the records of the Patent Office. Early types had yielding attaching-parts and rigid impact-parts. These were followed by types having a rigid bar connected with the frame by only a spiral spring, by those having channel-steel impact-bars and others having round spring-steel extending from the frame-horns. A strip of rectangular spring-steel was then used by a Western blacksmith, and later a similar non-reinforced bumper appeared which was cut in two in the middle, the ends being overlapped and the overlapped parts clamped together.

In this investigation to determine strength and physical properties 12 motor-truck rear-wheels were tested, comprising two each of the following types: Class-B trucks, standard wood; Class-B truck, cast-steel; I-beam type; steel disc; aluminum; and rubber-cushion, each having a 34-in. diameter and a 12-in. tread. The wood, the I-beam and the cushion wheels each had 14 spokes; the aluminum and the steel-disc wheels had a solid web between the hub and the rim. All the wheels were tested without tires or brake-bands, were bushed to fit a 4-in. axle and the area of contact between the hub and the bushing was the same as that in service. Illustrations show the construction of the wheels. Requirements considered essential in a wheel were listed, and the tests were conducted to obtain data concerning them. One wheel of each type was subjected to a radial-compression test.

It is generally recognized that the dilution of crankcase-oil with water and unburned fuel tends to accelerate the wear of engine bearings, cylinders and pistons. The author traces the engineering development of a rectifying device and system designed to combat this problem. In this system, diluted oil that tends to work-up past the pistons, in company with the water vapor and unburned fuel that tend to work down into the crankcase, is drawn from the cylinder-walls and pistons by vacuum. This diluted oil is conducted into a still or rectifier where it is subjected to heat from the engine exhaust. The heating action is just sufficient to volatilize the fuel and water, the resulting vapor being returned to the intake-manifold and thence to the engine where it is burned. The lubricating oil that remains behind is conducted back into the crankcase. The system functions automatically.

This paper deals with progress in the Cooperative Fuel Research since the last report was presented to this Society. Previous tests had shown that the temperature of the jacket water exerted a major influence on the rate of dilution of crankcase oil. The reason for this influence was investigated and it was concluded that it was due to differences in the rate at which diluent was added to or eliminated from the oil-film upon the cylinder-walls, the temperature of this film being dependent upon the temperature of the jacket water. Experiments failed to show that changes in the temperature of the piston head or changes in the viscosity of the oil upon the cylinder-walls exerted a major influence upon the rate of dilution. These conditions were investigated as being probable consequences of a change in the temperature of the jacket water. Evidence is presented which demonstrates that under certain conditions the diluent may be eliminated from the oil at a fairly rapid rate.

A good air-cleaner is an essential part of automotive engine equipment. Many types of cleaner are on the market and the user must choose on the basis of the three essential requirements of maximum cleaning efficiency, minimum attention from the operator and minimum power-loss. With respect to these three essentials, the development of a laboratory method of testing air-cleaners starts with the premise that the test for efficiency should consist of feeding in a weighed quantity of dust, and an account be made for that which is not separated by the cleaner. The first method was to insert a white outing-flannel cloth in the airstream from the cleaner. The varied degrees of soiling of the cloths from different cleaners were a relative measure of their efficiency. This method was found unsatisfactory for several reasons. An attempt was made to use a dry centrifugal cleaner of predetermined efficiency, in series with the cleaner under test, to catch a portion of the dust escaping.

Trouble with the exhaust-valves of the Type-J air-cooled cylinder caused an investigation to be made of valve-cooling and of valve and guide wear. A temperature of 1300 deg. fahr. invariably caused fractures of the exhaust-valve stem at the junction of the stem and the neck. A file-hard tungsten-steel valve with a shallow hole and no filling eliminated breakage but scaling was apparent. The same valve, using a hard tungsten-steel guide, when tested with salt filling, gave improved cooling; the area of the hot zone was reduced in size and the stem remained dead-black. Scaling was reduced and the wear of the valve-stem and guide that appeared was overcome by substituting a roller tappet for the solid tappet previously used. Tests showed that extreme hardness is of advantage even for inlet-valves. Experiments with a Type-K air-cooled cylinder gave excellent results with a salt-cooled valve in spite of a very high head-temperature; with an unfilled valve the results were not so good.

References are made to published results of similar tests of air-cleaner devices conducted in 1922, and the scope of the 1924 tests is described. Road tests of air-cleaners were carried out and the tabulated data are presented. Efforts were made to find out how much dust the engine would draw in if the cleaner and connections were removed and to catch and weigh the dust the air-cleaner under test failed to catch. Dust was raised by a car running about 50 ft. ahead of the test-car and, to produce heavy dust-conditions, the road was dragged with a chain attached to the car and forming a loop behind it. The leading drivers maintained as nearly as possible a constant speed of 25 m.p.h. and chose the dustiest part of the road, following the same course on all the rounds.

Double-deck horse-drawn buses did not meet with much favor in the United States, but from the earliest days have been popular with persons of all classes in England, probably due in part to the British nation's love of outdoors and in part to the governmental policy of prohibiting the carrying of passengers in excess of the seating-capacity. Packed vehicles continued to be characteristic of transportation in this Country until public service regulation in the early days of the present century required that a reasonable number of seats should be provided. When the number of passengers was limited to the number of seats, at the time of the introduction of motorbuses on Fifth Avenue in New York City, the failure of the experiment was predicted, whereas subsequent service has proved it to be the cornerstone of success. London double-deck tramcars with 78 seats require about 3 sq. ft. of street space per passenger, while the latest type with 50 seats require about 4 sq. ft.

Shortage of the most desirable kinds of wood for automobile-body purposes has necessitated the substitution of second-choice woods having the essential required properties and the buying of stock for body parts in cut-up dimensions that conform in size with those now produced in the cutting-room. An investigation by the United States Forest Products Laboratory as to the species, kinds, grades, sizes and amounts used by the automotive industry shows that maple and elm comprise over one-half the total amount used and that ash and gum constitute one-half of the remainder. Although the quantity of ash used has not decreased, the increase in the production of medium and low-priced cars in the last few years bas caused a proportional increase in the demand for maple and elm.

The importance of the development of a light alloy for use in parts that are subjected to elevated temperatures has already been emphasized in many papers, among which that by S. D. Heron on Air-Cooled Cylinder Design and Development4 should be particularly mentioned. It was with this purpose in view that the foundry of the Engineering Division of the Air Service at McCook Field undertook a brief survey of the alloying, the casting, the heat-treatment, the physical properties and the metallography of an aluminum-copper-nickel-magnesium alloy of the Magnalite type as sand-cast under ordinary foundry conditions. It was found that the alloying involved no particular difficulty. The casting, however, showed the necessity for proper pouring temperatures, gating and placing of the chills and the risers. Several photographs are shown illustrating satisfactory and unsatisfactory methods of molding pistons and air-cooled cylinder-heads.

Operating costs and their relation to the age of the vehicle have been a subject of controversy for some time. One faction maintains that after a certain indefinite period it is economy to salvage or junk the equipment and replace the vehicles with later uptodate designs. The opposing faction believes that the costs depending on maintenance and operating efficiency can be kept fairly constant. Comparing a motor truck with a locomotive they cite the opinion of railroad officials that when proper running repairs are made locomotives can be maintained continuously in the same service and retain their original earning capacity for many years. When new locomotives are built it is usually for the purpose of replacing types that have become obsolete and the old ones are then relegated to some other branch of the service.

A brief summary of the history of motor rail-car equipment on the railroad represented by the author is given in his paper. Three gasoline-driven rail-cars were put into operation in 1910. The engine used for each car was a six-cylinder, 10 x 12-in., slow-speed, four-cycle reversible-type having overhead valves, an open crankcase and a 200-hp. rating, but experience has proved that the four-cycle reversible-type engine equipped with an air-operated starting-apparatus makes rather a complicated unit that is the cause of many difficulties. Details are given concerning these first three cars, their performance and the changes made in their equipment. In 1922, a two-car train consisting of a motorcoach and a trailer was installed. The coach is 28 ft. long, has a 12-ft. baggage-space, carries 30 passengers and weighs 28,000 lb.; the trailer is 32 ft. long, weighs 17,000 lb. and seats 36 passengers.