A Small Engine Gives Practical Benefits
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By John F. Moon,
ADVANTAGES in fuel economy that theoretically can be derived from the use of a relatively low-powered engine in a heavy goods vehicle are frequently offset by the disadvantages of greatly increased gear work, laborious hill-climbing and low average speeds. It can often happen also that, because the gears have to be used so frequently, there is no fuel saving at all.
An exception is the new Rowe Hillrnaster light six-wheeler, which, during a recent test, showed exceptional fuel economy for a vehicle running at almost 20 tons gross weight, whilst its acceleration was above average for the class. The power unit giving these benefits is the A.E.C. AV 470 oil engine, which, although having a cubic capacity of only 7.685 litres, has a gross power output of 125 b.h.p. (122 b.h.p. net) at 2,200 r.p.m.
This governed speed is slightly higher than is normally found with vehicles of this weight and was shown to be a great advantage in keeping up a reasonably high road speed without adversely affecting fuel economy.
The Rowe L/A/14 vehicle tested had the Eaton-Hendrickson tandem-drive bogie—the first use of this American design on a standard production vehicle in this country. The bogie is manufactured in Great Britain by A22 Eaton Axles, Ltd., Warrington.
Rubber forms the suspension medium, there being four load cushions which give lubrication-free suspension and deflect very little under full load, thereby providing an almost constant loading height.
The bogie has two Eaton 18800 single-speed hypoidbevel_ axles, driven through a Power Divider, which has a third differential with manually operated lock. The drive to the second axle is taken from the Power Divider through an open propeller shaft. The differential lock is springloaded so that it cannot be left engaged inadvertently and it principal purpose is to ensure traction at both axles when operating over slippery surfaces.
For normal road haulage in this country the complete double-drive bogie is an expensive luxury. but it would prove invaluable in a sixwheeled tipper working off the road, and there is a Rowe 13-ft.-wheelbase chassis suitable for this purpose.
Two variations of the basic Hendrickson bogie are offered in the Rowe specification. These retain the features of rubber suspension and walking beams, but make use of a trailing axle, the driving axle being either an Eaton 18800 single-speed unit with a ratio of 6.68 to I or an 18800 two-speed unit giving ratios of 6.5 and 8.87 to I.
As the performance of the test vehicle was shown to be entirely satisfactory with single-speed axles, it appears that the least expensive version of the bogie—that with the singlespeed axle--would be perfectly satisfactory for all the normal haulage in Great Britain. The two-speed unit
would, however, give a slightly higher maximum speed, faster hill climbing because of the greater spread of ratios, and an improved maximum-gradient performance. The single-speed axle, single-drive bogie costs £525 less than the double-drive unit.
The Rowe six-wheeler range was first announced in September. Basically it consists of three models: the 13-ft.wheelbase tipper, the 16-ft.-wheelbase general-haulage vehicle as tested, and an 18-ft. 1-in.-wheelbase model on which can be mounted a 24-ft.-long body.
Chassis weight has been carefully studied, with the result that the test vehicle, which had the heaviest possible specification, had a kerb weight of only 5 tons 14 cwt. The licensing weight of a chassis with a single-speed axle would be under 5.1 tons.
Despite the accent on weight saving, there is nothing flimsy about the chassis, and the frame, although having a maximum depth of only 81 in., is heavily boxed and flitchplated. Undoubtedly, weight has been saved by specifying the relatively small and light A.E.C. power unit as standard.
Alternatively the Meadows 6DC 500 150 b.h.p. six-cylindered unit or the Gardner 5LW 94 b.h.p. or 6LW 112 b.h.p. engines can be supplied. Further options include conventional twoor four-spring singleor double-drive bogies with worm axles, or a spiralbevel axle in the case of the singledrive bogie.
When the A.E.C. engine is fitted. a
14in. diameter single dry plate hydraulically operated clutch is employed. The standard gearbox is an A.E.C. five-speed synchromesh unit which has provision for fitting a power-take-off drive.
Girling two-leading-shoe hydraulic brakes at front and rear are operated
through a Clayton Dewandre air-pressure-actuation system. The hand brake is unusual for a vehicle of this size in being of the single-pull variety.
As offered for test, the L/A/14 chassis was fitted with the standard Jennings composite cab, which had a plastics roof panel with a large translucent section in it. The 22-ft. lightalloy platform body had been built by Alloy Transport Sections, Ltd., Birmingham. 19.
The test load consisted• of concrete blocks totalling 14 tons 1 cwt. To avoid the risk of this moving during braking tests, the blocks had been stacked up against the headboard, so that the centre of gravity of the load lay forward of the ideal position.
causing the front tyre loadings to be much higher than would be the case with an evenly distributed payload. With myself and Norman Snell,of M. G. Rowe (Motors) Doublebois, Ltd. aboard, the six-wheeler was tested at a gross weight of 19 tons 181cwt.
So -far as the front-axle 'loading is concerned, even with an evenly distributed load the standard 9.00-20 in. (12-ply) tyres would be overloaded, so the manufacturers are making provision for fitting either 10.00-20 in.. or Michelin Metallic equipment, and thus the same size of tyre will not be fitted to all wheels on future chassis.
collected the vehicle in the centre of London and drove it northwards to Luton. I had expected it to feel underpowered, but this illusion was immediately dispelled and I was pleasantly surprised at its liveliness when negotiating thick traffic on the way out of London.
Because of the high front-axle loading, the steering on tight. corners was inclined to be heavy, but this was of little account at normal speeds and on normal bends.
Rarely was it possible to get into top gear in London traffic, but the vehicle speed in fourth is just over 25 m.p.h. and this proved to be a suitable ratio for town working. Once on the open road heading towards Hatfield, top gear was used almost continuously and in this ratio the maximum speed, allowing for governor run-up, is in the region of 41 m.p.h.
Braking on Grease
Braking tests were conducted on a level stretch of the North Orbital Road, and previous rain and mud deposited from lorries working in the nearby sand tip had made the surface greasy. When making tests from 20 m.p.h. and 30 m.p.h. all the bogie wheels locked, and when braking from the higher speed the rear slewed sharply to the left, although correction at the steering wheel resulted in. the vehicle coming to rest safely.
In view of the adverse road conditions, the figures obtained are highly satisfactory, and it is safe to assume that on a completely dry surface the stopping distances would have been reduced by some 25 per cent. As it was, there was an average difference of .1g between the maximum deceleration shown by the Tapley meter and the average retardation indicated by the measured stopping distances.
Single-pull Hand Brake Because vehicles of this size are normally equipped with multi-pull hand brakes, hand-brake retardation figures are rarely obtained, but the Rowe six-wheeler, having a single-pull brake, was tested in this way and an average figure of 17 per cent, was recorded from 20 m.p.h. Although this does not commend the brake for emergency purposes, it is a reasonable figure.
For adequate power, however, a multi-pull unit should be employed, although the actual time taken to come to rest from initial application would not necessarily be less than was taken with the single-pull lever. A multipull brake is to be specified as optional on this chassis, with the further option of an air-pressure-assisted single-pull layout.
Acceleration tests were made along the same stretch of road and remarkably good figures were recorded from a standstill up to 30 m.p.h. For these tests the vehicle was started from rest in second .gear and the engine was run up to governor cut-out speed before making each change.
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Despite the relatively low torque output of the engine, the direct-drive times obtained between 10 m.p.h. and 30 m.p.h. were entirely satisfactory, although there were signs of transmission roughness between 17 m.p.h. and 19 m.p.h. and between 24 m.p.h. and 27 m.p.h. The vibration at these two periods appeared to originate from the region of the bogie and during subsequent testing it was noticed that
there was also a marked whine from the bogie gearing.
A calibrated one-gallon test tank was connected into the fuel system, and the fuel-consumption test was made over a six-mile undulating course between Barton and Cloph ill. This is not an easy route for a vehicle of this size. As an additional handicap, 1 had to shunt backwards and forwards several times to turn at a
sharp corner halfway thrOugh the test.
Nevertheless, the course was completed at an average speed of 23.5 m.p.h, although rarely was it possible to exceed 30 m.p.h., and the fuelconsumption rate was 10.7 m.p.g.—a particularly good figure.
On normal trunk running while carrying a full load, an average figure of at least 11 m.p.g. should be realized. An even better result would probably be obtained with a singledrive bogie, because of the lower frictional losses.
Fast Climb An ascent of Bison Hill, a 1-mile climb with an average gradient of .l in 104-, was made in an ambient tempera
ture of 40° F. The test lasted 5 minutes 50 seconds, which is an excellent time for a vehicle of 20 tons gross,and the use of bottom gear was necessary for 2 minutes. When taking the radiator temperatures before and after the climb, which indicated a rise of 30°F., it was noted that the engine was somewhat overcooled, because the highest temperature recorded was 120°F.
This excessive cooling would probably be a result of the vehicle being manufactured in Cornwall, where steep gradients are the rule rather than the exception, and it would certainly give an ample margin for prolonged gradient work. For greater efficiency, judicious blanking of the lower half of the radiator would bring the engine temperature up to a more satisfactory level for normal trunk running.
Alarming Fade Test To the horror of Mr. Snell, I then coasted the vehicle, down the gradient in neutral, using the foot brake to keep the speed down to 20 m.p.h. This lasted 2 minutes 43 seconds and on the lower slopes I engaged top gear for about 30 seconds and applied full throttle, driving the vehicle against the brakes to compensate for the reduced gradient at this point.
Mr. Snelrs fears were completely unfounded, because when a fullpressure stop was made from 20 m.p.h. at the bottom of the hill, the Tapley meter recorded .a slightly higher figure than had been obtained earlier in the day on a wet road. If there was any brake fade it was negligible, and the brakes did not even smoke.
Normally when a vehicle running at no more than half the weight of the Rowe is taken down this hill, varying degrees of brake fade are recorded, ranging from fair to dangerous.
Returning to the steepest part of Bison Hill, where the gradient is 1 in
6f, the vehicle was stopped. It was only just possible to prevent it from rolling backwards by using the hand brake, two hands being necessary to pull the lever back far enough. Bottom gear was then engaged and a full-throttle restart was made, although there was little power in hand once the clutch was fully engaged.
Operators who contemplate service which includes stops on gradients steeper than 1 in 6f would be well advised to specify the single-drive bogie with the two-speed axle, the low ratio of which should enable starts to be made on hills of up to 1 in 5.
Generally the Rowe handled well and was comfortable to drive. There was little engine noise apart from a slight whine from the timing gears, and the gear-change was first-rate, although the lever was directly mounted on the gearbox turret.
The vehicle rode well at all times, over good and indifferent surfaces, and the front suspension coped well with the overload. The rear end felt particularly steady. To improve the unladen ride the front suspension -is to be modified to include lower-rate spring and Aeon rubber helpers.
Clutch and brake pedals are light in operation and the brakes have adequate power to deal with all likely emergencies. The cab is generously glazed, so that all-round vision reaches a high standard, and there is plenty of room for a driver and passenger, the low engine cowl adding to the general air of spaciousness.
A slight point of criticism is that the instrument and switch panel is in the centre of the dashboard, with the speedometer failhest from the driver, and to reach the light switches entails a fair stretch.
Engine Accessible Because the chassis was being returned to Cornwall on the evening of the day that I made the tests, there was insufficient time to carry out my usual maintenance checks. Removal of the three-piece engine cowl showed that engine accessibility generally was good. The cowl sections themselves were particularly simple to remove, the top panel being held in place by two spring clips and each of the side panels having two knurled nuts.
Engine air is drawn through an AirMaze oil-bath cleaner above the cab floor to the left of the engine cowl and shrouded by a one-piece cowl secured by two clips.
So far as the rest of the chassis is concerned, lubrication points and filter locations follow conventional practice, with the added advantage, of course, that the Hendrickson bogie requires no lubrication.