Valuable Research on Design Problems
Page 38
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NO one, who knows the facts can fail to be impressed by the extremely useful work which has been carried out for some years by the Research Department of the Institution of A uto mobile Engineers, which is ba.cked by a strong committee, the chairman of which, for this year, is Mr. W. A.. Tookey.
During a recent visit to the laboratories on the Great West Road, Brentford, we were received by the chairman and by Mr. J, Shearman of the member'ship' and publications subcommittee, and the recently appointed Director of Research, M.I.Mech.E.
The work of the Research Department is controlled by a. committee consisting of representatives from the I.A.E., affiliated members and Government Departments, and it is undertaken for the benefit of the motor and allied industries, dealing mainly with those problems which can best be investigated by co-operative means.
It will be realized that many concerns in the industry . have their own costly experimental departments. Consequently, endeavour is made to deal only with those investigations of a more general nature, which it would not pay to include in the purview of the individual laboratories.
Another extremely useful work undertaken is the abstracting and classifying of technical information from a large number of British and foreign publications, which are circulated to affiliated members in loose-leaf form, and to whom the originals can be loaned when desired. There is also an extensive library.
Not all the tasks undertaken' can be dealt with here, but a review of the main problems under investigation should be of interest.
• Valuing Oil De-aerating Devices •
In the chassis laboratory tests are being carried out with de-aerating devices for engine oil. Thecontinual circulation of aerated oil through a power unit may seriously damage highly loaded parts, due to the reduction in effective viscosity.
The principal object of the testing plant installed is to supply a sufficient quantity of such oil to enable the efficiency of the de-aerator to be determined over the range of conditions likely to be met in practice. The flow of oil and its temperature and pressure can 'be varied, and for inspection it is led through a glass tube.
The engine laboratory is engaged on research into the performance from producer gas, and in the studying of the power loss resulting from the use of this fuel in a converted petrol engine. The present equipment is a dry-type Government emergency producer using anthracite, and to simulate road conditions it is mounted on a " bumping " rig and cooled by air blast, the gas being passed through a filter packed with sisal. tow.
The engine is a six,cylindered, side-valve unit of 311 litres, of the type commonly used in vehicles up to 3 tons capacity. Orifice-type flow meters measure the gas and air, whilst gauges indicate the pressure drop across the orifices and the pressure and temperature at various points in the circuit.
Bpyond the air and gas throttles is a common pipe acting as a mixing chamber, conneeted to 'one branch of a T-piece mounted on the engine-intake manifold, the other branch carrying the normal petrol carburetter in an air-tight box, the air flow to which can also be measured. In addition; means for restoring losses of power are being examined. These have included raising the compression, increasing the calorific value of the mixture through introducing various quantities of petrol, and by steam injection in the producer.
Another interesting research is being made into the causes of the scuffing of piston rings, which can occur both under idling conditions and at high loads and temperatures. It is proposed to examine the relative merits of various surface finishes and treatments.
The general laboratory is dealing with a variety of tests, of which one of great importance concerns the overheating of tyres and brakes on buses. This trouble is sometimes found in vehicles operating under severe city-service conditions, especially in hilly districts. Excessive heat from the brake drums may reach the tyres and inner tubes.
Various design featieres and possible methods of reducing both brake-drum and rim temperatures are being studied. To do this, the wheels on one side are free to rotate while subjected to a continuous braking force applied through the normal mechanism, the load being measured by spring balance. The wheels at the other side are prevented from rotating by a torque arm and another spring balance, Temperature is measured by copper-constantan thermo-couples.
The starting performance of engines at low temperatures is being reviewed in a cold room, which gives controlled temperatures down to —25 degrees C. ( —13 degrees F.). The two engines used are mounted on test beds which can be run into the cold room on a ramp.
Two machines are in use for work on gear durability„the object being to study the effect of profile shape' and material on surface failure, using. a wide range of lubricants. Two pairs of gears are run as a closed train, an initial load being introduced by uncoupling the flanges of the divided shaft; twisting them relatively and bolting them together again.
• Proving Crankshaft Fatigue Strength • Three machines similar in principle but differing in detail design are being employed to ascertain the fatigue strength of typical full-size crankshafts under known alternating bending moments. The end throw of the crankshaft under test is provided with an extension shaft, the adjacent throw being bolted rigidly to a stiff platform. The end of the extension is then given a vertical reciprocating motion'by means of an eccentric and connecting rod, the amount. of eccentricity being adjustable. After a crank web in the first throw has been broken the whole shaft is moved forward so that the next throw is free for test.
• Another machine is employed for studying the durability and wear of small bearings of different materials under various conditions. It takes the form of a dummy singlecylindered engine with a built-up crankshaft having a. renew-. able crankpin, and is driven by an electric motor: The connecting rod has a solid-eyed bigLend into which the bearing under test is inserted. By using pistons of known weight, with the machine running at given speeds, alternating loads can be calculated.
A similar machine is equipped for the studying of the effect of aerated oil on the durability of various bearings.