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Chassis Components of Proprietary Make
Page 88
Page 89
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The Specialists in the Manufacture of Chassis Parts are Constantly Enhancing the Efficiency of Their Products and the Industry Owes Much to Their Efforts in this Direction
MANUFACTURERS of commercial-vehicle chassis are much dependent upon the concerns which specialize in the production of parts and materials. The degree to which this applies, of course, varies.
The big company, making all the main components of its chassis, is less dependent than the concern which merely assembles proprietary units, but in every case the specialists in certain particular lines are in demand.
For purposes of reference a list of makers of proprietary chassis parts and materials (other than major components) is given on following pages.
The basis of every chassis being a frame, this unit claims precedence. Weight reduction is, perhaps, the most noteworthy form of recent development. Modern alloy steels of high quality are now being used where formerly members of heavier gauge, but inferior in respect of tensile strength, were employed. Pressings of scientific shape are used as cross-members, these being formed to give the maximum rigidity consistent with lightness, and being freely cut away. On chassis of transatlantic origin the "alligatorjaw " cross-member is widely used.
Methods of jointing vary, rivets and
fitted bolts both being used. Many modern frames incorporate both tubular and-channel-section members, this construction giving great strength against weaving and lozenging. Little progress has been made in welding in frame construction. It is customary for manufacturers to obtain frame pressings and, in some cases, complete frames, from engineering companies specializing in this form of steel work.
A large number of castings and forgings is incorporated in commercialvehicle chassis, numerous metals and alloys being employed. The concerns supplying parts of this nature are listed below, their names being followed by the metal in which they work. c88
During the past two years, metallurgical research has resulted in important improvements in their products. Bearing metals for heavy loading and high speeds, hard irons and bronzes, aluminium alloys for pistons with high heat conductivity and low expansion coefficients, and light alloys having other properties comparable with heavier metals, are all examples of the progress in this respect.
Greater precision in pyrometry and testing apparatus has advanced, in particular, the quality of road springs, and modern suspension systems are much superior to those of only a few years ago. Furthermore, methods of mounting springs, both at their centres and at their ends, have been improved and progressive-action springs are now commonly employed, so that vehicles can ride as smoothly when empty as when laden. Woodhead divided-back-plate springs are a noteworthy example of a modern development in this field.
The road tests conducted regularly by The Commercial Motor reveal, in no unmarked mariner, how braking
systems have advanced, even during the past twelve months. Drum and facing materials have played a big part, the latter now possessing frictional coefficients that are far less affected by rises in temperature than formerly.
A surprisingly large number of concerns is engaged in the production of facing material, and their united efforts are undoubtedly contributing to the safety on the road of goods and passenger vehicles.
A modern practice that deserves every encouragement is the use, when shoe refacing becomes necessary, of complete replacement units, comprising shoes to which the facings have been applied by the properly equipped specialist.
Servo brakes are more widely used than in the past and vacuum is the more popular system. Nevertheless, air is, in certain circumstances, much employed. For trolleybuses, for exexample, where there is no induction pipe to provide a constant supply of vacuum. The air system has the additional advantage that the cylinders may be smaller.
The Lockheed method of transmitting the braking force through liquid has gained favour, and interesting developments here are the methods adopted to guard against failure through overheating or leakage. Brake makers are showing their appreciation of the need for proportioning the braking force between the front and rear axles in accordance with the weight transference created by retardation.
For simplifying front-brake linkage arrangements, it is now common for the power cylinder to be mounted on the stub-axle swivel; examples are Dewandre and Westinghouse. A feature of the Feeny and Johnson brake is its lightness and quickness of action. The maker of the Theed brake has largely concentrated on conversion sets for models of popular chassis unequipped with power braking.
Among smaller chassis parts, bearings of various types must certainly be included. Two outstanding developments of the past few years are the leadbronze type, which has contributed in no small degree to the advancement of the high-speed oil engine, and the oilless bush for brake gear and the like. Modern ,Inethods of centrifugally casting white-metal bearings constitute a development, whilst the alloys used have been improved.
Mention should also be made of the growing popularity of the Silentbloc type of rubber bearing for oscillating angular motion.
In thm manufacture of all types of ball-and-roller bearing, more precise methods of grinding and measuring are being developed and these, combined with the use Of improved steel alloys and heat treatment, result in greater efficiency. Devices for retaining lubricant and excluding foreign matter can also be included.
In front-axle and steering-gear design one does not find among commercial vehicles the same revolutionary advances that have been taking place in
the private-car world. The explanation is, of course, that existing arrangements are adequate for the speeds at which the heavier machines habitually travel; Designers, however, have not been idle and we include an illustration of a David Brown worm-and-wheel steering box of the new "arc contact " type. This is an example. of the successful efforts that are being made to give lighter steering, and we write from personal experience when stating that, in respect of lightness, accuracy and freedom from interaction, modern steering gears are highly developed.
The Bluemel concern, well known as a maker of steering wheels, has recently introduced a device incorporating an extensible steering column, There seems to be scope for the employment
of this on light commercial vehicles, and it is an indication of the growing attention that is being paid to the comfort of the driver.
The silent running of the commercial vehicle is now a matter of greater importance than in the past, and in this connection it is worthy of note that the silencing of the exhaust gases is being more carefully studied. Two excellent examples of apparatus for this purpose are the Burgess and Bailey devices.
Two years ago we referred, in these pages, to apparatus for the simplification of chassis lubrication. The grouping of grease nipples has become an established practice and it is satisfactory to note that it has not been overdone, as early tendencies suggested might be the case, the length of tubing employed being kept down to the prac tical3le minimum consistent with the accessible positioning of the nipples. The use, however, of automatic lubricating devices has not advanced greatly, perhaps owing to the need for an excess of piping.