Elaborate Equipment Designed to Test Proprietary Units Used in a Leading Swedish Make of Commercial Vehicle
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By L. J. COTTON, M.I.R.T.E.
Because of reflection or absorption of sound by surrounding objects, noise measurement is one of the most difficult laboratory tasks, and usually the noise level is shown on a scale calibrated in decibels or phons. Volvo has improved on the standard method by including a tape recording instrument, providing a permanent record of every experiment carried out either in the laboratory or on the road. Provided that all tests are made under identical conditions, the results are comparative.
Studying fuel-injection pump and injector characteristics is a task normally reserved for the specialist manufacturer. Volvo makes neither pumps nor injectors; these units are purchased from C.A.V. in Britain, and the Injector Co. of Sweden. Even so, the concern's equipment for studying fuel-injection phenomena is well in keeping with that used by the specialist companies.
Laboratory Tests The laboratory test-bench, made within the organization, is a glorified version of the standard fuel injection flow and phasing equipment, but includes a Phillips single-channel oscillograph. The Phillips oscillograph also figures in the engine-research and development bays, where it is used, for example, to study valve motion.
Another home-made apparatus is employed for measuring air swirl induced in the engine combustion chambers. This comprises an electrically driven compressor supplying air to an expansion chamber in the form of a 40-gallon drum. Air is conducted from the drum through the normal valve-porting to a cylinder sleeve equipped with an anemometer fitted in the bore to indicate the turbulence. The speed of the compressor and the volume of air are controlled, so that turbulence throughout the range of engine speed can be reproduced.
The largest apparatus in use at the time during my visit was a rig designed for testing radiator efficiency. This comprises a scaled version of the wind tunnel with the radiator tube-stack let in at the centre. Air is drawn from an external source and passed through the tunnel and radiator. The supply and temperature of water to the radiator are closely controlled, and thermometers introduced in the tunnel before and after the radiator stack, indicate the temperature drop.
Valve-spring resonance frequencies and damping characteristics are studied on a machine coupled to a stroboscope. The spring to be tested is placed between two pads, one of which is fixed and the other coupled to an eccentric which compresses the spring to represent cam movement.
The resistance to bending of frontaxle beams is measured by strain gauges in the laboratory. The beam is inverted from its normal position in the chassis and supported on a press at the spring pads. The swivels are then loaded hydraulically through the ram of the press. Wire straingauges are secured at all vulnerable points and the bending movement is related to the ram pressure.
The aim behind this research is to improve the life of the weakest part, therefore, the work can never be completed. There was a period when Volvo was "clutch conscious" and research work was initiated to improve the life of the springs and flexible centre-plate. The equipment used for the tests was a specially built fatigue-testing rig to determine stress and wear during operating conditions. These tests are now being continued with a complete chassis working on a dynamometer.
Apart from the makers of massproduction vehicles, few manufacturers, especially those relying upon proprietary-made components, could afford to investigate any potential weakness in a unit supplied from a specialist source.
Engine Research Engine development and research are carried out in the Gothenburg laboratories, where there are five test bays. These are equipped on a scale comparable with that of the Shell research laboratory at Thornton-leMoor.
The operative is partitioned from the test unit, which is housed on a bed in a sound-proofed bay. Sitting at a desk, he can observe the engine through a glass screen, but all controls and instruments are remotely connected to the desk and adjustment to the dynamometer or scale alongside the operative, can be made without his having to move from the desk. Scales for weighing fuel consumed during a trial are arranged alongside the operative.
Exhaust-smoke density is observed by means of a photo-electric cell. This, again, is equipment developed by Volvo, and is now being adopted other oil-engine research laboratories in Sweden and England. The smoke meter now in use gives readings reproduceable within a small percentage, and can be used for weeks without need for cleaning the glass windows.
Continental piston makers have shown great interest in a photographic device made by Volvo which records, on one plate, a complete picture of a piston's periphery. This is of special value in recording effects of running-in tests, determining piston clearance, its shape, and the nature of its bearing against the cylinder bore.
At the time of my visit to the laboratory, a new chassis-test dynamometer was being constructed to enable trials to be made up to speeds equivalent to 100 m.p.h., and for pulling forces of up to 2,600 lb. Au electronic device is to be incorporated which can be adjusted to give any desired load-speed characteristic, thus reproducing conditions of acceleration and braking on the road. This apparatus will be arranged for engine-cooling tests in complete vehicles with control of ambient temperature to correspond to arctic or tropical conditions.