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Husky six-wheeler for Kiwis
Page 79
Page 80
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HARSH CONDITIONS in many transport industries abroad demand more powerful and robust vehicles than those normally used in the UK. One company with considerable experience in this field is Fodens Ltd. of Sandbach. Cheshire, and I recently spent two days with one of its 6C6/22, 35-ton-gross combination weight six-wheeled loadcarrying prime movers destined for service in New Zealand.
The vehicle has an 18ft.-wheelbase and is powered by a Cummins NHK 220 sixcylinder diesel engine driving through a Foden 12-speed gearbox to double wormand-pinion rear axles. Designed for drawbartrailer operation, it is equipped for a towing eye. And a two-line braking system is incorporated, powered both through the main footbrake circuit and also via a hand reaction valve positioned on the side of the instrument panel. A non-tilting glass reinforced plastics cab is fitted and the rear bogie has a four-spring suspension.
I evaluated the machine in the difficult terrain between Congleton in Cheshire and Buxton in Derbyshire. The road I used— known as The Dumpers—twists and climbs for some 16 miles from the Cheshire plains into the foothills of the Derbyshire Peaks.
This route has many gradients of varying severity, each one situated so that it is virtually impossible to get a running approach to it. To comply with UK legal limits, it was possible only to load the vehicle to 22tons gross and although this was 13 tons below the designed gross combination weight of the machine, the severity of the country made up for the lack of payload. Many of the steeper gradients encountered were as severe as 1 in 6.5, but never was there any doubt in my mind that the Foden would negotiate them. In fact, the lower range of gears was never in use, the lowest ratio engaged throughout the climb being first direct drive.
The Foden transmission comprises a fourspeed constant-mesh main gearbox coupled to a three-speed air operated splitter giving an underdrive, a direct drive and an overdrive range of ratios. The splitter is an epicyclic unit, the change being effected by sliding dog clutches locking the epicyclic trains to the main shaft. An operating lever to the right of the steering wheel has three positions, and directs air pressure to a double-acting operating cylinder. This unit in turn moves the selector rod carrying the dog-clutch forks.
The method of operating the change speed is to select the required ratio while the transmission is still under load; this prevents a change taking place until the clutch is disengaged. The main gearbox and the epicyclic trains can be changed simultaneously where the ratios differ enough to make this exercise beneficial.
It is particularly useful that the underdrive ratio---engaged while the main box is in top gear—gives almost the same overall ratio as second gear engaged with the splitter in direct drive. When the going is tough, extremely smart changes can be made, using only the air control and the clutch pedal. Once the splitter unit is warm, changes can be made almost as quick as one can move the pedal. But because on the test vehicle the clutch adjustment was a fraction out, changes in the main gearbox were on the heavy side during the first day I had the vehicle. Slight shortening of the clutch rod eliminated this problem, making the vehicle much more pleasant to drive.
A useful piece of equipment for use in hilly terrain is the Jacobs engine brake. This device, by lifting the exhaust valves, converts the engine into a compressor when on overrun so offering resistance in a greater degree than when the valve gear is operating normally. Tests I carried out on this device proved that when operated while appropriate gears were engaged for any given speed, a retardation of 7.5 per cent was obtained.
On a vehicle of this class such retardation is ample for all normal braking requirements and only when I needed to stop quickly was it necessary to use the foundation, or wheel brakes. What this means in service is that lining life is considerably increased—when one does have to use the service braking system, drums are cool and in their most efficient condition.
Fuel consumption over the difficult route chosen was 5.6 mpg—with 22.5 mph average overall speed for this section a very good figure, indeed.
The brakes were subjected to full pressure testing, several stops being made from 20 and 30 mph. Although the maximum retardation obtained in all cases was adequate, delay in the air system caused the overall stopping distances to be a little disappointing. The figures recorded were 69.25f1 from 30 mph and 35.0ft from 20 mph.
The results obtained with the secondary system, which operates the front brakes via triple diaphragms and also applies a drum transmission brake via a mechanical linkage, were extremely acceptable giving a 35 per cent Tapley meter reading. • This brake is operated by a single-pull lever connected to the transmission brake and incorporating a pull-valve serving the front brake chambers.
On the road the Foden proved to be one of the most accurate heavy vehicles I have handled for a long time. Its steering was light and had just the right amount of selfcentring to make it possible to come out of a corner without having to wind off all the turns one had put on the wheel. The power assistance had no tendencies towards taking control of the vehicle away from the driver at any time, and even at very slow speeds still produced light and sensitive steering. The steering box is of the Burman recirculatoryball-type with hydraulic-ram power assistance. The wide range of gear ratios afforded by the 12-speed gearbox gives the vehicle the ability to operate in widely differing conditions. The direct drive range is ideal for cruising in urban conditions, the four ratios with the splitter in this condition being 1st, 4.65; 2nd, 2.48; 3rd, 1.49; and 4th, 1 to 1. Reverse gear in this ratio is 4.10 to 1. With the underdrive range engaged the overall ratios become 1st, 15.30; 2nd, 8.15; 3rd, 4.90; and 4th 3.29 to 1, while reverse is 13.45 to 1. Engaging the overdrive splitter gives the following range of ratios: 1st, 3.58; 2nd, 1.91; 3rd, 1.15; and top 0.77 to 1. Reverse in this range is 3.16 to 1. On an open road the powerful Cummins engine needed only the assistance of the four top ratios to keep it bowling along happily at 40 to 50 mph. The vehicle's maximum speed was 54 mph.
Among features which differentiate this machine from a similar type for service in the UK are an 8-ton-capacity front axle, and twin heavy-duty rear axles having a total capacity of 18 tons. The Cummins NHK 220 engine developing 212 bhp at 2,100 rpm and 585 lb.ft torque at 1,300 rpm is installed with an oil cooler and a large capacity radiator. Derating to allow for excessive altitude or ambient temperatures can be carried out as required.
Because of the need for the vehicle to operate away from places having adequate servicing facilities, the specification has been kept as simple as possible. Although, for instance, an air-assisted clutch would be desirable, and is of course available, Fodens has fitted a manual clutch to eliminate the possibility of failure while far removed from assistance.
The overseas-pattern cab has a doubleskinned roof incorporating a sun visor. Twin air scoops of ample dimensions should afford adequate ventilation in hot climates. These are augmented by swivelling quarterlights whiCh can be swung forward to form additional deflectors for fresh air.
A heavy steel bumper bar and steel wings are formed integrally with the cab. Extra robust mirror mountings are fitted and substantial towing eyes • 'protrude from the chassis frame through the front panel of the cab.
The vehicle I drove was mounted on slave wheels, the equipment for which it is designed being 10.00-20 16-ply rating on front tyres and 10.00-22.5 14-ply rating on the rear tyres. The body used on the test vehicle was also a slave unit, merely facilitating the carriage of a test load.
My overall impression of this vehicle was one of extreme solidity. Nothing about it made me feel that parts might carry away at the first sign of harsh treatment; it will in all probability get plenty of this during its working life.
The overall axle capacity of 26 tons and ample frictional area of the braking system, 51.4 sq.in. per ton—or 58.5 sq.in. per ton, if one includes the transmission brake— should provide for long and trouble-free life. Brakes are S-cam operated throughout via a Bendix Westinghouse pressure system. The vehicle has a 24Y lighting and starting system with a Sin.-diameter alternator, and a 50-gal fuel tank.