CONFERENCES AT OLYMPIA
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Re'sume's of Papers Read and of the Discussions at Three Important Conferences, Municipal Passenger Transport, Road Policy and Road-transport Problems Generally Are the Subjects Covered
Problems of Municipal Passenger Transport A T the Conference, last Friday, of 11 the Municipal Tramways and Transport Association, Mr. R. Stuart Pilc.her, F.R.S.E., M.Inst.T., General Manager, Manchester Corporation Transport, submitted a paper prepared by a special committee of the Association and Mr. Pilcher's engineering assistant, Mr. C. B. Clapham, B.Sc.,
A.M.I.Mech.E., entitled " Some Modern Problems of the Municipal Passenger Transport Operator."
The notes were presented as a sequel to the papers delivered at the Exhibitions of 1931 and 1933, to induce members of the Association to discuss with the makers the problems of maintaining passenger vehicles in municipal service.
The members operate 6,500 buses and 900 trolleybuses almost • exclu sively for short-stage service. The engines have frequent periods of idle running and there is much low-gear work, the load factor is low, fuel consumption necessarily high, and wear greater than in other service.
Need for Longevity.
It is urged that for such vehicles makers should pay special attention to the wear of cylinders, valves, clutches and brakes, to brake heating and efficiency, accessibility and other factors exercising a major influence on the cost of maintaining a vehicle of the requisite reliability.
Municipalities use the oil engine for 27 per cent, of their aggregate -fleets, and the proportion is increasing. There is a marked improvement in the continuity of service from oil engines compared with three years ago. London Transport continues installing oil engines in new vehicles. The Board operates 850 oilers in a fleet of 5,500 and adds six to eight oilers per week. The fuel gives 9 m.p.g., compared with 5 m.p.g. on petrol. In 33 municipalities having considerable experience with four makes of sixcylindered oil engines, the return for -four-wheeled double-deckers on town service is 0.05 m.p.g. on oil and 4.93 m.p.g, on petrol.
Centrifuging of the fuel is desirable. One undertaking found that fuel pumps wear more rapidly at garages where the oil is not so treated. London Transport changes it sumpoil every 8,000 miles and records 250 B42 m.p.g. Municipalities generally change at 3,000 to 5,000 miles.
Maintenance, over a period of three years, shows a slight advantage to the oil engine. Smoky exhausts can be avoided if fuel pumps be kept adjusted to the correct maximum open ing and injectors carefully maintained_ The main troubles have been cylinder wear and failures of main and big-end bearings.
Some operators would like more experimental work done on the directinjection engine, which has advantages over the indirect type. It is cleaner, more economical, and less likely to stoppages in the lubricating system, but suffers from a tendency to smoky exhaust, a difficulty which must be eliminated.
In lighting, interior illumination should be judged on the actual light afforded to the seated passenger. The numbers and positions of lamps and the lighting load should now be known for any given seating capacity.
There is a general preference for double-pole wiring on trolleybuses, as being less liable to cause shorts, The modern tendency is to install low voltage lighting, using either a large battery or a motor-generator set. The Ministry insists on low-voltage lighting when all-metal bodies are Used. There is an urgent need for an effective fog lamp.
Brake Developments.
• The outstanding developments in brakingare the general adoption of the single wide shoe' and the single brake,dru,m, separate servo motors on the front axle; the increase of servoassisted hydraulic brakes, the use of non-metallic woven :shoe liners of. greater thickness, increased bearing surfaces on brake camshafts, and better means for lubrication. In some cases the coupling of hand and foot brakes, 'using the existing shoes on vehicles originally equipped with separate shoes, has reduced shoe wear by 50 per cent.
A difficulty with vacuum servos on oil engines is ,that at low speed the exhausters sometimes fail to maintain the vacuum unless the engine be raced, but a new type of exhauster has blades positive in their outward_ movement instead of -relying upon centrifugal force for thesealiag, and this gives a
vacuum of 15 ins, of mercury at 200 rpm. Using an automatic brake adjuster on the shoes, it was found that the pistons in the servos required such small movement that 50 per cent. of the bores coulil be blanked off in the main and auxiliary servos, thus per ■ mitting more brake applications.
Numerous fractures of the wheel rim or locking ring have been mentioned. These are dangerous to both gtaff and public.
The life obtained from cylinder liners remains at between -5,000 and 6,000 miles per .001 in. of wear. Stellite-faced exhaust valves remain in good condition after 90,000 miles.
In the discussion, Mr. Patmore said there was a growing need for a specification for. the lighting of vehicles, and suggested the formation of a committee of the two municipal associations and the Society of Motor Manufacturers and Traders.
Wear in Injector Pumps.
Mr. C. H. Stafford said that experience at Burnley showed that a considerable amount of wear took place in injector pumps, due to lack of proper lubrication facilities..
Mr. A. W. Reed referred to fog lighting, and said it had been found that the best lamp gave a flat-topped beam with a sharp cut-off and an absence of upward glare.
Mr. L. McKinnon said that in Glasgow 26 petrol buses used reclaimed lubricating oil. The lubricatingoil in the oil engines was changed every 5,000 miles, and in the petrol units every 10,000. The difference in the running between the reclaimed oil and the fresh was negligible.
Mr. C. Clarke said the practice in Birkenhead was to use 25 per cent
reclaimed oil with new oft Much trouble had been experienced with cracked aluminiumcrankcases. He thought the makers should use steel.
Mr. Lythgoe, of Middlesbrough, said he found the wear on the oil engine was only a quarter that on the petrol engine. It won all along the line, and after 84,000 miles did not need reboring, but only new piston rings. _ Mr. Craven, of Halifax, wanted better acceleration. Trolleybuses were giving particularly good results.