ECONOMY WITHOUT TEARS
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By A. A. TOWNS1N,
A.M.I.Mech.E.
pERHAPS the most remarkable result of the road test recently carried out on a Dennis Loline was that the all-round fuel economy was the best recorded by any double-decker bus tested by this journal since the end of the Second World War. Highly creditable though this is in itself, it is even more noteworthy that neither passengers nor crew are made to suffer in the process. The degree of passenger comfort is well above average, whilst not only is the performance with the Gardner 6LW engine (the smaller of the two units standirdized) remarkably good in relation to the power/weight ratio, but the vehicle is exceptionally pleasant to drive. It is equally obvious that, although the Loline is somewhat lighter than most of its competitors, considerable attention has been given to durability and reduction of maintenance costs.
The Dennis Loline was first introduced in 1956 and in original form, subsequently designated Mk. I, very largely amounted to the Bristol Lodekka low-floor model built under licence, although the gearbox was of Dennis design. A version intended for forward-entrance bodies, the Mk. II, appeared in 1958. The present design (which remains unchanged after the recent temporary break in production) is the extensively redesigned Mk. III, having air suspension at the rear axle as standard equipment and being suitable for forwardor rear-entrance bodywork; it was introduced just over two years ago. Although the basic layout of the Bristol design is retained, the Loline Mk. III is almost entirely of Dennis origin so far as the mechanical units, other than the engine, are concerned. I understand that the only items to retain their common design with those of the Lodekka are some of the frame pressings and the rear axle casings.
As mentioned in The Commercial Motor of December 7, 1962, the versions of the Loline Mk. III now once again available comprise 18-ft.and 19-ft. 2-25-in.-wheelbase models with a choice of Gardner 6LW or 6LX engines and fouror five-speed gearboxes. The vehicle tested had the 6LW engine and five-speed gearbox. Although it had the longer wheelbase, capable of accommodating up to 74 seats in the 30-ft.-long bodywork, this vehicle was arranged as a 68-seater in the interests of comfort and circulating space. It was one of a fleet of 37 with forward-entrance bodywork by W. Alexander and Co. (Coachbuilders) Ltd., Falkirk, recently supplied to the Aldershot and District Traction Co. Ltd., who kindly agreed to lend it back to Dennis Bros. for the. test during the height of the preChristmas rush.
No. 447 was first licensed at the end of October, 1962, and had a mileage of 7,300 on the odometer at the beginning of the test. It had been taken straight' out of service and the Dennis engineers had no opportunity to carry out more than the most cursory inspection before installing the test equipment. The test results were particularly creditable for an " unseen " vehicle.
The kerb weight of the bus as prepared for testing was 12 tons 3 cwt. 2 qr., but with three members of the Dennis staff, myself and some loose equipment on board the weight came up to 12 tons 10 cwt., equivalent to a full complement of 68 seated passengers, driver and conductor, plus one standing passenger. The exceptional economy and good performance are undoubtedly the result of combining an engine well known for its thermal and mechanical efficiency with a transmission offering a particularly well-chosen set of .gear ratios. Dennis and Bristol are the only two British manufacturers to have Made a regular practice of producing double-decker buses with five-speed gearboxes; Aldershot and District received some Dennis Lance models so equipped a quarter of a century ago. It has continually surPrised me that more operators do not specify them and .this road test provided ample confirmation of the benefits to be obtained.
The Dennis V-series gearbox is of the all-indirect twoshaft layout. This eliminates the need for the transfer gearing often associated with a low-floor vehicle as the output shaft occupies the position of the laysbaft on a conventional gearbox. The propeller shaft is accordingly lowered and, in this case, moved to the right so as to leave the gangway clear. The unit is of the constant-mesh type, as it is considered by the Dennis engineers that synchromesh is not entirely satisfactory for a gearbox of this capacity, largely because of the size of effective synchromesh mechanism required, and the need to considerably lengthen gear lever travel if a heavy change is to be avoided.
Although the all-indirect layout means that the drive is always taken through gears, only one pair of gears is engaged at a time whenever the vehicle is travelling forwards, whereas two pairs of gears take the drive for the indirect ratios in a conventional gearbox. It also makes it possible to produce a more robust gearbox within the same space and particular care has been taken to make the entire unit capable of standing up to hard work for long periods without attention.
Similar remarks apply to the clutch, which on the Loline Mk. Ill is a Borg and Beck 16R6 single-plate unit. The bell housing is specially designed to give forced ventilation to cool the clutch plate, as it is considered that this has a marked effect on clutch life. The aim has been to produce a clutch and gearbox that will equal the modern diesel engine in terms of overhaul life. The prototype set has now completed 173,000 miles in service with Aldershot and District without attention.
Fifth speed, with an overall ratio of 4-25 to I. giving 26-9 m.p.h. per 1,000 engine r.p.m., gives the performance which might be associated with an overdrive ratio, including a maximum speed of 47 m.p.h., but is not too high to be regularly in use even on stage carriage service. It was found quite natural to engage fifth speed for 50 yards or so before braking during the six-stops-per-mile fuel con
sumption test, for example. My calculations indicate that the maximum gradient climbable in this ratio is about 1 in 52 and although it is difficult to confirm gradient performance of this order with precision, other readings taken with a Tapley meter on the vehicle tend to do so.
Fourth speed is slightly lower than the direct drive ratio., which would normally be expected to be used on a vehicle of this character, with an overall ratio of 6.31 to 1, giving 18-15 mph. per 1,000 engine r.p.m. This gives the comparatively limited maximum of 32 m.p.h., and the normal procedure for cruising at 30 m.p.h. is to accelerate in fourth gear to about that speed and then engage fifth. The hillclimbing and acceleration given by fourth are comparable with those usually given by the top gear of a more powerful bus with a four-speed gearbox, however, with a calculated gradient ability of 1 in 29-2.
The lover ratios give maxima of 8, 14 and 22 m.p.h. and it is worth recording at this point that the gradient ability figures quoted in the Dennis leaflet on the model were found to be decidedly conservative. They quote 1 in 11.7 for second gear, whereas my calculations based on 88 per cent
transmission efficiency and 25-1b./ton rolling resistance
suggest 1 in 10 or 224 lb./ton pull. The maximum Tapley meter reading recorded was 230 lb./ton. On this basis the maximum gradient climbable in first gear would seem to be about 1 in 5.6 rather than the 1 in 6.3 quoted by Dennis. Certainly the ease with which the vehicle restarted in first and reverse on a 1 in 7 gradient found on a side road just off the Hog's Back indicated an appreciable reserve of power.
The fuel consumption figures in the accompanying table speak very ably for themselves. Research among previous
road tests of double-deckers by The Commercial Motor
has revealed that only two of those carried out since 1946 had better non-stop figures, both being 26-ft.-long model's running in chassis form at gross weights of 10.15 and 11.15 tons respectively, the difference in consumption amounting to less than 8 per cent. Neither of these vehicles could equal the Loline's economy in stopping service, despite having the advantage of making only four stops per mile instead of six stops per mile as has been the standard practice for this journal's bus road tests in recent years. The Loline's figures under both two-stopsper-mile and six-stops-per-mite conditions have not, in fact, been equalled by any other double-decker tested by this journal, regardless of type or weight.
Time did not permit more than one pair of runs with the upper-deck load removed, nor for any no-load tests to be carried out. The non-stop tests were carried out
between Liphook and Petersfield on the A3 road, whilst the stopping tests were conducted over a stretch of the Guildford-Aldershot road on the outskirts of Guildford, neither route being flat. The Guildford-Aldershot-road stretch used forms part of Aldershot and District's Service 20, operated by Loline Mk. III models, and the half-load two-stops-per-mile figure of 13.65 m.p.g. is very close to the A. and D. fleet average for Lolines of 13-5 m.p.g., suggesting that this pair of runs was representative of actual conditions. The speeds quoted in the table exclude the 15 sec. spent at each stop.
Although making an efficient engine work fairly hard is often economical of fuel, it can be tiresomely noisy from the passenger's point of view. In the case of the 6LWengined Loline tested the noise level is barely higher than average and never becomes really objectionable. Liberal use of patterned aluminium sheet on the surfaces liable to be scuffed by passengers' feet on the Alexander body is undoubtedly practical, but the absence of any form of sound insulation in these areas allowed more noise to enter the passenger compartment than would otherwise do so. I had the impression that much could be done with a few shillings-worth of sound-absorbent material and some suitable adhesive, and this also applies to the driver's cab. The relatively low-pitched nature of the 6LW unit's characteristic sound is not unpleasant in nature and the gearing avoids the need for prolonged spells of maximum engine speed. The Gardner-designed flexible engine mounting is quite effective in insulating vibration.
The robust gearbox design has the beneficial side effect of keeping noise from this source down to a barely noticeable level, despite the use of straight-toothed gears. A slight, relatively high-pitched whine can be heard in fourth and fifth speeds, but this is also quite a pleasant sound, very reminiscent of earlier generations of Dennis overdrive gearboxes. The spur final drive gears in the rear . axle could also be heard faintly at times.
The standard of ride given by the air suspension at the rear axle was excellent. Forward-entrance buses can either be very harsh-riding at the extreme rear or prone To exaggerated rise and fall if softer conventional suspension is used. On this vehicle, however, it seemed natural to use the "drawing room" formed by the three long seats around the rear end of the lower saloon for off-duty moments when on the move during the test. The conventional suspension at the front gives a firmer ride but it was never found to be harsh, particularly well-judged damping being applied to both axles.
The brake tests produced good results, particularly as no preliminary adjustment had been done. The rear offside wheels tended to lock but the bus pulled up in a straight line. Tapley meter readings of between 66 and 74 per cent were obtained during the footbrake tests which revealed a normal amount of delay effect for a direct air-pressure actuated system. This could be detected in normal driving but was not sufficient to cause any difficulty in applying the degree of braking required. I found the handbrake to be among the most effective I have met on a vehicle of comparable weight, requiring very moderate effort.
Although the area round Guildford is quite hilly, no hill of length and -gradient suitable for brake Cade test or a timed climb which would allow the passage of a double-deck bus could be found within reasonable reach, and these tests were not carried out. More gentle but much longer climbs were made on several occasions, but the temperature gauge in the instrument panel showed that the engine was, if anything, slightly overcooled in
the comparatively cold weather during the test despite about three-quarters of the radiator being blanked off. The heating system was none the less most effective.
Thoroughly at Ease The Loline proved to be one of those vehicles in which a driver feels thoroughly at ease within a few yards of moving off, an important merit for a bus. Much of this is probably due to the comfortable driving position. The steering column is a good deal farther from the vertical than that on most double-deckers, and the pedals are arranged so that their movements seem natural for one's feet. Pressometer readings for full depression of clutch and .brake pedals were 60 lb. and 90 lb. respectively, but had a means of testing these not been available, my guess for the pedal pressures would have been appreciably less, as the muscular effort required seemed very moderate.
The steering was precise and quite light with just about the right degree of castor action at normal speeds and did not become as heavy when manceuvring as is sometimes the case on a vehicle of this weight. There was fully adequate " feel " without any noticeable kick-back, but it seemed a pity that there was appreciable steering column shake when the bus was travelling over normal main road surfaces. The relatively low centre of gravity undoubtedly helped in giving a sense of good stability and notably rollfree cornering. Steering demanded neither noticeable concentration on the straight nor excessive wheel-turning even on quite sharp corners.
The gearehange does much to support the idea that a good constant-mesh gearbox is well suited to a vehicle of this size. I was out of practice in the handling of a box of this type, not having driven anything so equipped for well over a year, but I. found the action light and positive, making it simple to time changes quite precisely so that the desired ratio engaged silently and without any difficulty. The ease of gear changing and well-chosen ratios helped to a remarkable degree in dispelling any impression of the bus being underpowered.
Taken overall, the Loline gives the driver the pleasant feeling that he is in undisputed command. Restarting on a moderate gradient is just as easy as with a private car, the handbrake releasing easily and smoothly and the clutch taking up the drive firmly but progressively, without any judder or hesitation. The accelerator pedal has the characteristic heaviness associated with the Gardner system of all-speed governing, but this is mitigated by the comfortable organ pedal used.
Viewed from the kerb, the bonnet line looks a little high because of the low waistline level of the lower deck. The vision from the driving seat is much better than might be expected and the bonnet is shaped so that the top edge of the nearside wing is just visible. The bottom corner of the wing is completely hidden, however, and a narrower bonnet would improve vision in this direction, which is frequently needed when pulling out from behind parked vehicles on urban bus work. The vision forward is very good, and the Alexander body on the test vehicle had commendably slender windscreen pillars. Vision forwards from the lower-deck seats is limited by the relative height of the bonnet, and an earlier trip in a similar vehicle as a passenger over a route unfamiliar to me showed this to be a definite if minor fault. The clearance over the cylinder head could not be reduced appreciably, but a narrower bonnet would permit a lower window line towards the left of the front bulkhead.
The forward entrance is neatly laid out, the gearbox being accommodated under the lower steps of the stairs so as to cause no intrusion on to the platform. This is level with the lower saloon floor and loading can easily be supervised from the driving seat. Although it is necessary for the driver to turn his head slightly more for this purpose than would be the case On a vehicle with entrance at the extreme front, his vision to the left at cross-roads is completely unobstructed.
The well-rounded " balloon " roof characteristic of Alexander double-decker bodies made the vision from the upper-deck seats of the test vehicle only slightly better than on a side-gangway low-bridge bus, and the front corner pillars were noticeably wide, as is generally the case when frameless front dome construction is used. The standard of finish throughout was good, however, the seats were comfortable, and there was no impression of interior trim being skimped to save weight or cost. The body weighs approximately 2 tons 15 cwt., a commendably low figure, yet only evident to the passenger in a slight springiness underfoot at certain points in the gangways.
Timed maintenance work could not be carried out within the period available for the test, but a visual check showed that the water and engine lubricating oil levels could be checked almost instantaneously with an external radiator filler cap and extended dipstick respectively. The bonnet opens easily and is supported by a strut to give good access to the engine, although it is necessary to climb up on top of the wing to reach most items. The only fault of any consequence on the vehicle as submitted for test was quickly remedied. Dennis Bros. has found the transmission system to be susceptible to vibration periods which vary in nature according to the type of engine fitted and, to a lesser degree, on individual chassis. The original system of torsional vibration dampers tended to interfere with the body layout and an interim solution to avoid this gave inadequate damping. A Dennisdesigned damper using spring-loaded friction discs, similar in principle to that used at the front of Gardner sixcylinder engine crankshafts, has recently been evolved and is being fitted to existing chassis as opportunity offers. This modification had not been carried out on the test vehicle as received and the effect inside the bus in fifth gear was reminiscent of wartime German bombers with desynchronized engine speeds. The new damper was fitted before the second day of testing and the roughness was almost completely eliminated. Had there been time to " tune" it correctly, the effect would no doubt have disappeared entirely. The Loline has the unusual virtue of pleasing both passengers and crew as well as being eConomical from the operator's point of view. Double-decker chassis of lower initial cost can be obtained but the extra money for this one seems likely to be more than fully repaid in the long run.