Standardization and Construction of Buses
Page 70
If you've noticed an error in this article please click here to report it so we can fix it.
COMPLET1NG the papers read at the UITP XXXV1th International Congress in Tel Aviv (see The Commercial Motor, May 28) were two by the general manager and chief engineer respectively of ATAC, Rome. Signor C. Guzzanti, general manager of ATAC and chairman of a commission set up by U1TP, gave a report of progress made in studies on the standardization of buses, whilst Signor V. Puccinelli, chief engineer of ATAC, covered the use of lightweight *materials and plastics in bus construction.
The report of Signor Guzzanti dealt with five meetings of his committee held in 1963 and 1964 and, in addition, the work done through its representative on the ECE Working Party for the Construction of Vehicles. Under the heading of braking, Signor Guzzanti said that the U1TP had found itself faced with an accomplished fact as braking requirements had .already been agreed.
Proposals had been made that vehicles in service should require an efficiency 80 per cent that of new vehicles instead of 90 per cent, and also that for public transport vehicles provision should be made that braking would not involve standing passengers in any danger and that 50 per cent should be the maximum in the event of emergency.
Proposals Rejected
The proposals were rejected by the ECE Working Party and the commission is now carrying out its own studies on the question of braking with the object of drawing up standards which could be included in specifications laid down by the different transport undertakings. It is also examining whether it is preferable to have the control and transmission for the service brake to be entirely separate from the emergency brake and it has been decided to support a solution providing for the " possibility" of a single control but to "accept the most suitable solution ".
Other items in the report included motor vehicle noise and air pollution and the important narts were proposals concerning the standardization of vehicle sizes. For this, a modulus of 188 mm. had been agreed and this enabled all the dimensions of a vehicle to he established. Using the modulus principle, dimensions of standard buses could be as follows: Length (93 moduli), 10.97 in.; width (21 moduli), 2.48 rn.: unit comprising two Seals (12 moduli). 1.42 m.; surface provided for a standing passenger (4 by 3 moduli), 0.167 m.2, and surface provided for a seated passenger (4 by 6 moduli).
0.334 m.2.Another report proposed standardization of other characteristics rt28
and finally the specific power proposed for the engine was 12 b.h.p. per metric ton of gross weight.
The paper read by Signor Puccinelli covered the use of lightweight and plastics materials in bus construction most comprehensively. The author split his paper into two parts, the first dealing with reasons for use, characteristics of materials and their advantages and disadvantages and applications, whilst the second gave the results of a survey of public transport undertakings. discussion on the results and general conclusions.
Under reasons for use. Signor Puccinelli confined himself to reduction in weight as the sector of most interest, dealing fully with the considerations making light weight important. Plastics materials, it was said, were increasingly used and had proved of equal importance to light alloys, hut there was also the advantage that complex shapes for coachwork could be produced economically by using glass-fibre reinforced polyester resin. •
Technological characteristic's of light alloys and plastics were covered fully in the section of the paper dealing with them, compositions and strengths of various alloys being given together with
similar data for plastics .materials. In the next section, one of the advantages in the use of light alloys mentioned particularly was the stability of the vehicle in bends resulting from a lowering of the centre of gravity. This was of particular importance with double-deckers. Under disadvantages, Signor Puccinelli said that the purchase Price of a vehicle in light alloy would be higher than that of an equivalent vehicle in steel. But the ratio should tend to reduce because of the cost of raw materials becoming proportionately smaller than the cost of labour and by a reduction in production costs brought about by a more rational and extensive use of light alloys.
The need to combine parts made from steel with aluminium components raised the problem of corrosion by contacts resulting from electrochemieal differences between the materials, hut this could be avoided by surface protection with cadmium or zinc plating or the application
of thin films of synthetic material. It was also pointed out that large-scale use of light alloys may entail,. at the beginning, a considerable change in the traditional designs of coachwork.
Advantages of Plastics
Advantages of plastics materials given included resistance to chemical and atmospheric corrosion, low thermal conductivity, easier soundproofing, more freedom in design allowing complex shapes to be produced without specialized labour, a reduced time between design
and production and the elimination of serious damage in minor accidents.
The point was also raised that in the case of serious accident, passengers could be extricated from the body more easily as well as allowing easier and simpler repairs to be carried out. Also, the surface finish of a plastics component eliminated the need for varnishing and the plastics material needed practically
no maintenance. Drawbacks of reinforced plastics were stated as higher cost compared with steel, the need for a detailed knowledge of the actual resins used so that parts suitable for their taskT were obtained and the need for some effort on the part of management to ensure the success of the work.
Before' moving on to give the results of a survey of users of light alloys and plastics the author referred to a number of applications of these materials, including bodywork carried out by Park Royal Vehicles Ltd. and other British companies, but more fully dealt with were double-decker buses made by the Italian companies Aerfer and Viberti.
Replies to Questionnaire For the survey, 74 public transport undertakings in 19 countries replied to a questionnaire and the various replies were examined and analysed by the author. The "survey covered 18,762 vehicles in respect of light alloys and 11,190 in respect of plastics materials. The answers to the question asking if any peculiarities existed with regard to maintenance in the case of light alloys produced some interesting points. Of the undertakings replying to this question, 32-5 per cent reported no special problems with maintenance, whilst 41 per cent stated that maintenance presented some special difficulties. These included the need for thorough examination and maintenance of parts which oxidized rapidly and protection of the light alloys against corrosive acids and gases. It was quoted that repairs were easier in steel parts than in those of light alloy as it had been found that after a time the molecular structure of aluminium changed, whereby the light alloy became harder, making it difficult to straighten the part.
Two undertakings were said to have recommended strongly a large number of protective layers on the aluminium parts, especially those exposed to the atmosphere. These pointed out that a tendency to economize in this respect had the contrary effect as it led rapidly to the total loss of the protective efficiency.
Favourable comments in answer to the same question in regard to plastics included easy repair of damaged parts. longer life compared with metals, easier to clean and the ability to entrust repairs to semi-skilled workers.