An Oiler with Petrol Pep
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Economy Coupled with Lively Acceleration in Cornmer TS3 Oil Engine. Ample Power for Hilly Work and Fast Hauls By John F. Moon,
A.M.I.R.T.E. PETROL-ENGINE performance coupled with oil-engine economy are given by the latest series of 5-ton and 7-ton goods chassis produced by Commer Cars, Ltd., Luton. The power unit which has these desirable qualities is the TS3 two-stroke oil engine which was first offered to the public in May of this year.
Since its introduction, the engine has been uprated to give 105 b.h.p., an increase of 15 b.h.p., and the torque output has been raised by 20 lb.-ft. This has necessitated the introduction of a larger gearbox and rear axle. The resulting combination gives a vehicle suitable for the haulage of 7-ton loads with double the fuel economy of an equivalent petrol-engined chassis but with a no less lively performance.
Apart from the increase in power output already noted, the TS3 engine is unchanged and the governed engine speed has not been increased, remaining at 2,400 r.p.m. Construction details of this engine include a three-cylindered opposed-piston layout, the pistons acting on a central crankshaft through dual rods and rocker arms.
A Roots-type Wade blower, mounted at the front of the engine and driven from the rear timing train through a spring-cushioned quill at 1.8 times engine speed, ensures complete scavenge of the exhaust system, the maximum operating pressure being 6 psi.
The engine, being almost cubeshaped, lends itself admirably to the under-cab position already used by Comrner in their petrol-engined 5-7ton chassis. It is mounted, in unit with the gearbox, at three points, with a Metalastik sandwich disposed centrally at the front, and two Metacone units, one each side of the clutch housing.
A 13-in.-diameter dry-plate clutch takes the drive to the new four-speed synchromesh gearbox. Baulk-type engagement is provided for the helical top, third and second helical gears, whilst first and reverse gears
have straight-cut teeth. A single propeller shaft is fitted to the shortwheelbase tipper chassis as tested, and this has Layrub joints at each end.
The new rear axle is a spiral-bevel unit, having a pressed-steel casing and offset differential to reduce the angle of the transmission line with the offset engine. The size of the final-drive gears has been increased to cope with the higher torque output of the oil engine and an increase in brake-shoe width has resulted in
62 sq. in. more frictional area. This has been found necessary because the reduced engine friction attendant on this design of power unit demands greater use of the brakes when descending long gradients.
The chassis for my test was equipped with a standard all-steel cab, Telehoist under-body, singleram tipping gear and a standard timber 6-cu.-yd. tipping body with drop sides and hinged tailboard. Iron weights were battened into the body, and with three persons in the cab, the gross vehicle weight was 11 tons 3i cwt., the front-axle load-, ing being 3 tons 6 cwt.
Tyres of 9.00-20-in. section (12 ply)
are fitted to all heavy-duty tipper chassis and the manufacturers recommend a maximum loading of 11 tons 3 cwt. Alternative tyre equipment is 825-20-in. (12 ply).
It was decided to try out the Power of the engine on Suceornbs Hill in Surrey, and this meant crossing the centre of London during the morning traffic. I was soon struck by the lively acceleration and good manceuvrability of the tipper in traffic and it did not take long to get clear of the built-up areas apd out into the suburbs.
At the bottom of Succumbs Hill, with an ambient temperature of 55° F., the instrument-panel temperature gauge, which is connected to the cooling system on the engine side of the thermostat, registered 180° F., and the radiator header tank was at a temperature of 157° F.
Top gear was engaged soon after starting, but low gear was necessary to scale the 1 in 4i gradient over the railway bridge, and after f min. in second gear, first gear was again resorted to for the last section of the hill which includes two sharp bends. The total time taken was 2 mm. 48 see., of which over 14 min. was spent in low gear and, at the top, the engine coolant temperature was 200° F,, whilst the water in the header tank, because of the high fan speed, had cooled to the extent of 1°F. —
The descent of the hill was made in top gear, the speed being kept down to 10 m.p.h. by the use of the foot brake. At the bottom of the hill, an emergency stop from 20 m.p.h. produced a Tapley meter reading of 54 per cent. A second climb was then made but this 'Tailed to produce any further temperature rises and the water in the header tank, which bad cooled off during the descent, remained at 150° F. During both these climbs, when in
low gear, the engine was running at full throttle and was at the governed speed for the majority of the time. Steeper gradients should be within the capacity of this unit and a modified cooling system has been designed for export .vehicles which may be operating in hot climates.
Greater use was made of the brakes when descending the hill for the second time and there was a strong smell of burnt facings by the time the bottom was reached. This time the Tapley gave a reading of 43 per cent. after an emergency stop and there was a slight increase in pedal travel, but the slight loss of effiCiency was not sufficient to cause undue anxiety.
At Godstone, on the A22 road to Eastbourne, the 16-gal. fuel tank was filled to overflowing, care being taken to remove all air from the tank, in preparation for the first leg of the fuel consumption run. The road south of God stone includes several sharp gradients and in East Grinstead, two halts were made because of traffic conditions.
Al Wych Cross, after 16 miles of running, third gear had been used for 3 min., in addition to the two halts which had required the use of the intermediate ratios. The average speed for the run was 26.4 m.p.h. and the 7i pints used indicated a consumption rate of 17.1 m.p.g.
The return run was made later in the day and a clearer road was available which allowed more continuous use of top gear. There were no stops and the consumption rate of 19.6 m.p.g. was obtained at an average speed of 27.8 m.p.h. The average figure of 18.35 m.p.g. for the two runs shows exceptional economy in view of the speed and road conditions, and when engaged on mainroad haulage it is probable that a slightly better figure will result. A slippery, wet road surface made mock of our attempts to obtain representative braking figures and it was decided to abandon the attempt in the hope of better conditions on the following day. These hopes were fulfilled and the short-distance trials were conducted near the Commer works at Luton.
The small brake pedal made it rather difficult to attach the solenoid switch of the brake-testing gear securely, but the problem was solved by tying it on with a piece of rag.
From 20 m.p.h. the average stopping distance was found to be 28 ft. and from 30 m.p.h. this distance was measured as 54 ft. Throughout all the tests, the rear wheels locked and it appeared that the front brakes were not taking their full share of the retarding effort.
Readings obtained with the Tapley meter showed that had better adhesion an all four wheels been available, these braking figures would have been better. There was little time delay in the system and full pedal pressure was used for all tests.
Acceleration figures showed an improvement upon those given by the petrol-engined version of this chassis. First gear was used for the • initial get-away during the standingstart tests because the works representative had found that this gave a faster acceleration rate. The engine pulled smoothly from 10 m.p.h. with direct-drive engaged and the acceleration to 30 m.p.h. was rapid as shown by the time of 30.75 sec.
The distinctive note of the TS3 engine is not at all obtrusive in the driver's cab and normal conversation was possible at all engine speeds, although the blower whine was discernible at high speeds. The synchyomesh engagement in the gearbox worked well but was a trifle stiff and slow in operation: a faster change being possible by double declutching.
The driving position permitted maximum visibility in all directions and although the steering was heavy at low road speeds the large steering wheel was easy to use, but a little too near the door for knuckle comfort.