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RUDOLF DIESEL'S PR ESS LIV )N

26th May 1961, Page 58
26th May 1961
Page 58
Page 59
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Page 58, 26th May 1961 — RUDOLF DIESEL'S PR ESS LIV )N
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Which of the following most accurately describes the problem?

by John F. Moon,

A .M.I.R.T.E.

IT does not necessarily follow that the pioneer in a particular field is going to be able to maintain a profitable lead over his competitors once the idea has caught on." In the case of compression-ignition engines, however, the first builders of this type of power unit in the world have successfully managed to remain among the leaders of this field. I refer to M.A.N, Maschinenfabrik Augsburg-Niirnberg A.G., Germany, who built the world's first diesel engine in 1897 and whose activities are dealt with on pages 586-587.

All current M.A.N. commercial vehicles have diesel engines incorporating M.A.N.'s "M "-system and, having conducted the first road test of a M.A.N. lorry in Germany by a non-German journalist, 1 can write in fair praise about the success of this design: undoubtedly, the "M " engine— or " Whisper" engine as it is sometimes known—is the quietest medium-capacity high-speed four-stroke diesel at present in quantity production. At the same time, power and economy are particularly good also.

The vehicle tested was a nominal 9-tonner, with a 9.659litre "M " engine, the net power output of which is 172 b.h.p. at 2,200 r.p.m. Running at just over 131 tons gross weight, the test lorry gave 10.5 m.p.g. at 50 m.p.h. average speed, and 15.3 m.p.g. at 29 m.p.h. average speed, whilst acceleration from a standstill to 40 m.p.h. occupied less time than many 9-ton vehicles need to reach 30 m.p.h.

Particularly satisfying from the viewpoint of the occupants of the cab was the quiet running of the engine, and this cannot help but form a valuable contribution towards the reduction of driver fatigue, especially on long non-stop runs at near maximum speed, such as are possible on Autobahnen.

The version offered to me for test was a 770 LI model, a four-wheeler with a gross solo weight rating of 13 tons 16 cwt., but rated for 27 tons 12 cwt. when operating with semior drawbar trailers. There are several 770 types, all of which have the same ratings, but which vary in respect 104 of wheelbase and front-end layout. Four-wheel-drive chassis are made also. The test vehicle had a wheelbase of 15 ft. I in., and was a semi-forward-control model, this configuration having proved far and away more popular than the alternative forward-control layout since this model was introduced on the German home market last year.

Having vindicated itself under German conditions, the 770 is now available outside Germany, but so popular has this model been that currently there is a nine-month waiting list for it at home.

Because the 770 is very likely to be used with a trailer, the rather high engine output makes sense (in any case, German law demands 6 b.h.p. per ton gross weight). The model is, therefore, not to be compared directly with a typical British 14-ton-gross solo vehicle, the engine output of which would normally be in the region of 125 b.h.p. Despite its high power-to-weight ratio, though, the 770 was shown not to be heavy on fuel, presenting yet one more argument in favour of overrather than underpowering.

Apart from its combustion system, the basic theory of which is dealt with on pages 586-587, the " M " engine as used in road vehicles is conventional in design. All types have iron crankcase-and-cylinder-block castings, twoor three-bore cast-iron cylinder heads, steel-backed leadbronze-lined crankshaft bearings, and light-alloy pistons carrying four rings, the top ring being chromium-plated.

The D 2146 Ml unit employed in the 770 series has a gross S.A.E. rating of 184 b.h.p., and its dry weight is 1,650 lb. The overall length of the engine is approximately 481 in., the depth being 431 in.

In the 770 the engine is unit-mounted at four points with a Z.F. AK 6-55 six-speed constant-mesh gearbox. This box is conventional in all respects except with regard to the actual gear-change arrangements. For the forward ratios the lever has three pairs of gate positions, but these lie in a vertical plane, so that the lever has to be moved bodily upwards or downwards against spring pressure (instead of to left or right) at every other ratio change, then backwards or forwards.

This layout takes quite some time to get used to (to be quite honest, I never did get used to it), but the reason for its adoption is that transverse movement is eliminated, thus less space is needed between the driving seat and the engine cowl in a forward-control cab.

Unconventional also is the rear axle, although not to MAN: devotees, who have had 30 years in which to appreciate this unit, which is used in all M.A.N. goods vehicles and sonic passenger models. The axle consists of a dead 1-section beam, which acts as the load-carrying member, and at the back of which is mounted centrally the 2.625-to-1 spiral-bevel primary reduction gearing and the differential assembly. These gears are force lubricated.

Light half shafts take the drive to 2.385-to-I spur-gear secondary-reduction trains housed at the ends of the dead beam, these shafts being protected by thin steel tubes which are rubber sealed at each end. This type of axle assembly is claimed to be no heavier than a conventional rear axle, whilst the unit is shallow, giving good ground clearance.

The braking system also requires some explanation. At both axles leading-and-trailing-shoe brakes are employed, and the front brakes are hydraulic units, actuated by an airhydraulic system. The rear brakes are cam-operated with direct air actuation, plus mechanical linkage from the hand brake lever, which is designed to be used principally as a parking brake.

An air-pressure booster cylinder, is incorporated in the hand-brake linkage, and this is controlled by a trigger on the brake lever. When this trigger is depressed, the servo takes up the slack in the linkage, so speeding up brake application and dispensing with the need for a multipull mechanism. The hand-brake servo is spring-loaded also, so that if the air-pressure in the reservoir drops below about 60 p.s.i. the rear-wheel brakes are lightly applied automatically as a concrete warning to the driver that all is not well. (The normal air pressure is 100 p.s.i.)

In most other respects the 770 follows conventional chassis-design practice. The fairly light frame has pressedsteel channel-section side members of 1 in. nominal thickness, the maximum depth being 81 in. whilst the flange width is 3 in. Six cross-members are riveted in position, and the

spring-hanger brackets also are riveted in place. Semielliptic springs are employed at both axles, with helper leaves at the rear, and Z.F.-Gemmer cam-and-roller steering is used, no servo being offered.

Standard tyres are I0.00-20-in. " eHD reinforced," these being equivalent in load rating to 14-ply equipment. They are mounted on 7.50-20-in, disc wheels, but there is the option of Trilex three-piece detachable rims, these costing more than disc wheels but being popular overseas.

Of all-steel construction, the M.A.N. semi-forward control cab provides quiet and comfortable seating for driver and two passengers, with an acceptable range of all-round vision, although the ground-level forward visibility is nothing to write home about. The curved windscreen is in one piece, and in the doors there are hinged ventilator panels and wind-down windows. To the rear, vision is provided by a wide single light, plus twin exterior rear-view mirrors of sensible size.

The cab floor is rubber-covered, and the section of engine cowl that intrudes into the cab space is heavily quilted to reduce engine noise still further. Facia-panel fittings include a comprehensive set of instruments ahead of the steering column, a centrally located fuse box and a lidded glove locker on the passenger side. General stowage for odds and ends is limited, however, and under-seat space is taken up by the two batteries and the toolkit.

Control layout is good and the angle of the steering wheel unusual for a semi-forward-control design, being nearer than to be expected with a full-forward-control vehicle. s25 This angle is most pleasant, though, and has been achieved by using a universal joint in the column to bring the plane of the wheel near to horizontal.

Pendant clutch and brake pedals are uscd, the actions of which are good, but the accelerator pedal is rather a long way off the floor, resulting in a tiring foot angle except when using full throttle.

Complete with 16-ft. 5:in.-long drop-sided timber body and standard cab, the 770 tested had a kerb weight of 4 tons 19+ cwt. Of this the body accounted for nearly 11 cwt., and the actual chassis weight is quite reasonable by British standards. Test weights totalling 8 tons 13 cwt. had been placed in the body, so that with test gear, a member of the M.A.N. experimental department and myself aboard, the gross weight was cwt. above the makers' recommended figure. Distribution checks showed that less than 1+ tons of the payload was being carried by the front wheels, whilst the total rear-axle loading was 7+ cwt. above the British legal limit.

On getting into the cab I was somewhat startled to see, so early in the morning, two steering wheels and sets of pedals, but it turned out that this was not a driving-school model-the dummy set on the right-hand side had merely been fitted. as an installation check prior to offering righthand-drive on export models (this month), and the controls were not linked.

Because the fuel-test tank had only a small capacity, consumption tests had to be carried out over a I-kilometre section of the Munich-Berlin Autobahn. These were made

B26 at steady speeds, therefore, so the results recorded are slightly optimistic by the normal standard of tests conducted by The Commercial Motor, which are made from and to a stand-still. However, the 770 is geared for trunk haulage, and under British conditions it should have returned no less than 14 m.p.g. solo at a maximum speed in the region of 33 m.p.h.

an Autobahn, acceleration tests

were carried out on IGO the same piece of road, and these showed exceptional performance. F o r the standing start tests second, third, fourth and fifth gears 120 only were employed

pie() 2 '4130 .c

(the maximum speed 110 in fifth is 43 m.p.h., that in overdrive top being 52 m.p.h.), and the German driver was able to sweep through the gears. Direct-drive acceleration was particularly impressive, the take-up. from 10 m.p.h. being remarkably smooth. To get the speed down to 10. m.p.h. in this ratio, the exhaust brake was used to reduce the engine speed. this brake being a valuable optionalpiece of equipment controlled by a button on the cab floor, adjacent to the driver's left heel. • Retardation tests were not made on the Autobahn,. and stops carried out. from 20 and 30 m.p.h. revealed only average performance, my impression being . that system lag was somewhat excessive. No wheel locking occurred and the vehicle pulled up in a straight line. From 20 m.p.h. the retardation meter showed a maximum deceleration of 52 per cent., whilst from 30 m.p.h._ the figure was 50.5 per cent. Despite the air assistance, the handbrake performance was only passable, an average maximum figure of only 24 per cent. being obtained from 20 m.p.h.

A stop-start gradient test was carried out on the steepest, piece of road in the Munich -area, the gradient of which is only .1-in-8, however. I had expected Bavaria to be full of mountainous roads, but apparently they are all much to the south of the M.A,N. works. On this somewhat gentle slope a smooth second-gear restart was made with ease, the air-assisted hand brake having made it a light job to hold the vehicle on this gradient.

In view of the difficulty in finding a 'suitable slope for this test, I expected a longjaunt for the brake-fade and normal climbing. tests, and in this respect I was not disappointed—we had to drive 50 miles north. Even then, the hill proved to be onlya rise in the Autobahn, the general grade being 1 in 16.5 and the length 1.69 miles.

The ascent was made in an ambient temperature of 50° F. and before starting the climb the temperature of the engine coolant in the radiator header•tank was 151° F. The grade was scaled in the surprisingly short time of 3+ minutes, giving an average speed of 29 m.p.h. Much of the climb was made in fifth gear at about 35 m.p.h., but fourth gear was engaged for one minute, the speed being held at about 27 m.p.h. during this time.

A radiator blind is a standard fitting on IvI.A.N. yehicles, and before making the climb this was adjusted to cover. half the radiator block. Despite this, the coolant temperature rose by only 14°F. during the ascent, showing the cooling system, which is pressurized to 8.5 p.s.i. (high by British standards), to be adequate for trailer working in higher ambient temperatures, No exhaust smoking could be seen during this climb.

To check for fade resistance I coasted the 770 down this hill in neutral, the descent lasting about 44minutes, of which time it was necessary to keep the foot brake applied for only. 3-1minutes in order to keep

down to 20 m.p.h. A " crash " stop from 20 m.p.h. at the bottom of the hill produced a retardationmeter reading of 46 per cent., which compares fairly well with. the.maximum figure. obtained from. this speed with cold drums..

• Nevertheless, I Cannot help feeling that the total frictional area of the 770 is rather small for a vehicle _ Of this potential performance, being about 200 sq. in. below _that of a comparable British maximum-' capacity four-wheeler. The exhaust_ brake would undoubtedly be a help in prolonging lining life, however, and .for this reason alone: :ought really to be,a standard rather than an optional fitting..

The 770 is essentially a pleasant and comfortable vehicle to: drive, and the quietness of the. engine is most marked: except that when running on the governor, fan noise is quite distinat. At normal cruising speeds of about 40 m.p.h. the engine is turning over at little more than 1,500 r.p.m.—close to its maximum torque output and. optimum fuel-economy speed. Comprehensive cab lining, including a perforated plastics

roof lining, helps to cut down cab-interior noises. The driving position itself reaches a happy compromise, the driving seat being adjustable vertically and in a fore-andaft direction, besides having an .adjustable-spring, support to provide a range of adjustment to suit most drivers.

The 770 is nice to handle, the 211-in.-diameter 'steering wheel giving a " man-sized " feel. The steering is light at all times, without being vague, and castor action is good.

Maintenance tests were not carried out because of time limitations, but with respect to most of the chassis equipment, accessibility should be on a par with that of equivalent British vehicles. Engine accessibility, however, is not brilliant. Access to the forward part of the engine is given by an alligator-type bonnet, the range of opening of which is not great, further difficulty being created by the high line of the front wings. The rear of the engine can be reached only by removing the cab cowl. This is only to be expected, however, with a' "compromise" layout' such as semiforward-control, • • As tested, the 770 complete with standard cab and 16-ft.

5-in, drop-sided body costs £3,230 in Germany, whilst the chassis-cab variant Sells for £3,150. The standard 4 x 4 version is priced at £3,820-. Prices outside Germany vary according to the individual arrangements of dealers.

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People: John F. Moon
Locations: Munich

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