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. - Exanlination of .Past. and Present Bus-running •Schedules

11th March 1949, Page 11
11th March 1949
Page 11
Page 11, 11th March 1949 — . - Exanlination of .Past. and Present Bus-running •Schedules
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Which of the following most accurately describes the problem?

Sugge.sts the Question:

Why Not Constant-speed. Engines?

By j. V. Hewes

IT has long been appreciated, especially in aircraft engineering, that an unfluctuating load and constant speed of the engine crankshaft mean longer periods between major overhauls and a considerable measure of economy in running costs. The main reason

why aircraft engines have a less exacting time than commercial-vehicle engines is that, except for thc brief take-off periods at maximum throttle, they run at a constant speed and are not being continuously accelerated and decelerated With a road-vehicle engine, however, the speed may be changed from a tick-over to peak revoltitions every few hundred yards, and whilst there is no remedy for this, it may be of interest to speculate on a suggestion which would partly lessen the ill-effects.

To this end, I made an analysis of journey times given in the time tables of three well-known bus

companies over a period of 25 years. The routes were picked at random, but figures relating to all other routes regularly operated over the same period by the same three companies confirm the data here given.

In 1923 the route of the East Kent Road Car Co., Ltd., from Dover to Ramsgate via Sandwich, a distance

of 20 miles, took 105 mins.; five years later the running time was reduced to 75 mins., and to-day itis 70 mins. Between Canterbury and Margate, 17 miles, 75 mins. was scheduled in 1923, and 55 mins in November, 1928, a running time which applies to-day

In the early 'twenties, 3 hrs, was occupied by vehicles of Maidstone and District Motor Services, Ltd., in covering the 3,6 miles from Maidstone to Hastings, via Robertsbridge; by May, 1930, it was 2 hrs. 16 mins., and to-day it is 2 hrs. 11 mins From Ashford to Tenterden took 60 mins. in 1925; in the following year this was cut to 45 mins., which is the time allowed for the 12-mile run to-day

21 Minutes Saved in 25 Years The inland route of Southdown Motor Services, Ltd., between Brighton and Eastbourne, via Lewes, a distance of 25 miles, occupied 120 mins. in 1924, 100 mins. in 1930, and only one minute less than that to-day Between Worthing and Horsham, on what is part of the main London road, the 20-mile route required 105 minutes in 1924, 82 -mins. in 1930, and to-day the

schedule is 73 mins. _

If the route mileage of these six examples be added together, it will be found that a total of 130 is involved, which took 645 mins. to cover in-the period 1923-25, as against 475 mins:in 1948-49. But the most interesting of all the factors is that of the time saved during a quarter of a century Of this, 87 per cent. was saved before the end of 1930, and only 13 per cent, during

the following 18 years The reasons ' for the big difference in the respective periods are fairly plain if calculated on the basis of a theoretical annual improvement of 4 per cent.

Between 1923 and 1930 appreciable strides were made in improving riding comfort with developments of the pneumatic tyre; braking systems improved and acceleration was. vastly superior. No 'doubt the maximum , speed of the vehicles employed increased,

probably from an all-out 20 or 25-m.p.h. to the legal .

,

probably from an all-out 20 or 25-m.p.h. to the legal .

, maximum Of 30 -. . During the later period, from 1930 to 1949, the maximum speed of buses and coaches has continued to mount, despite the fact that the legal maximum speed has remained at 30 m.p.h The increased maximum speed of vehicles must, therefore, be regarded as purely incidental to raised compression ratios, higher permissible crankshaft revolutions and better acceleration, and not in the light of a definite objective. The proof may be found in one more example of a selected route: From Hastings to Rye the Fanning time allowed for the ordinary short-stage service is 45 mins., which is the same as that for the express coaches running from Margate to Bournemouth During the six or seven years when the maximum speeds of buses and coaches increased, a big saving in scheduled journey tithes was made possible by that improved performance, but since 1930 the saving that has been achieved is by rrieans other than an increase in the maximum speeds of the vehicles concerned.

Higher R.P.M. Unlikely As far as may be predicted, there seems to belittle likelihood of the legal limit of 30 m.p.h being raised. I, therefore, suggest that the engines of most commercial vehicles are practically certain to remain in their present stage of development in regard to their mak-in-aim crankshaft revolutions They may well become more flexible, power output at the bottom end of the scale may still increase and brakes may be improved still further On' the other hand, all the available evidence goes to confirm that' a more constant speed of engine operation is coming about Since' 1930 improvements in time schedules must have been obtained by running the vehicles for-a higher proportion of their travelling time at or near 30 m.p.h. Instead of merely touching 30 m.p.h. once in a while, modern buses and coaches must be able to attain and hold that speed in a quarter of the time and distance taken in 1923 and in about half the time they demanded

18 years ago

Has the time not now arrived for the testing of a constant-speed engine under road-operating conditions? Carefully chosen gear ratios and, particularly, an overdrive top are moves in the right direction The writer proved in a series of tests before the war that a 15 h.p. six-cylindered car, driven at a steady average of 4O m.p.h. on Brooklands track, consumed less fuel than when driven for the same time (not distance) in heavy traffic where 30 m.p.h. was never exceeded

Aircraft experience has proved that running engines at constant speed prolongs the life of the reciprocating parts The disadvantages would include added complication in the design of transmission systems and the possible waste of fuel 'when stationary Given the necessary driving technique, it might be possible to try out a bus fitted with a fluid coupling and preselective gears. The throttle would be set and locked; the gears would have to be used as much to help in braking on the over-run as aids to acceleration, and the vehicle: would have to be held stationary by the normal brakes against the pull of the fluid-coupling at the increased' ," tick,over " speed. Provided the thrOle setting was modest, there should be no elemeii. of danger

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Locations: Margate, Canterbury, London

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