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A NEW ATKINSON STE, FOR HILLY COUNTRY.

25th September 1923
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Page 16, 25th September 1923 — A NEW ATKINSON STE, FOR HILLY COUNTRY.
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The First Application of Epicyclic Gearing to Si Engine Provided. The Use of

Ion Chassis Design. Two Speeds and a Free :ngine when the Injector Fails.

THE .7c9mytEga4L moTog W fILLST THE need has always existed for

ample power an the., part. of heavy commercial goods vehicles--to enable them to be driven over roads in hilly districts and to take their loads over soft tracks or bad land—it is only lately that the general recognition by authorities of the advantage in relief ot traffic which can be afforded by a substantial increase in vehicular speed, has brought about a demand for higher speed capabilities to be utilized when and where the conditions are suitable.

Hitherto, therefore, it bas not been difficult to strike a working compromise between the call for speed on level roads and power reserve for hilly districts. But these two demands are now beginning to conflict, and it has to be pointed out that a vehicle suitably geared for the one set of conditions cannot be equally suitably geared for the other. In the case of the steam wagon the absence of the clutch, which forms part of the transmission system associated with the internal-combustion engine, and the fact that it is not a desirable component if its use can be avoided, originally operated against the employment of reduction gears, particularly of the "clash" type. However, reduction gearing is now gaining in vogue, and the adoption of an epicyclie two-speed gear on the 6-ton Atkinson steam wagon is quite a notable departure calling for special attention at our hands.

In the case of this popular make ef'vehicle the outstanding feature of the transmission is the driva by a single chain from the engine to the rear axle, than which nothing could be simpler nor more direct, the crankshaft and axle being disposed parallel to each other.

The standard Atkinson equipment has provided for 12 teeth on the crankshaft chain pinion, which would give the full legal speed on normal roads and , provide an ample reserve 'of power, but in the case of wagons going into Yorkshire and other hilly districts it has been the practice to supply 10-tooth pinions, which, whilst giving ample power for the hills, naturally limited the speed an the level. Latterly, with the call for more speed in districts with easy gradients and good roads,. such as in Liverpool and Manchester, 11-tooth pinions have been supplied.

By the adoption of an epicyclic reduction gear, giving two speeds with a relation of 2.8 to 1, the makers can now adopt a 13-tooth pinion as the standard, so that on top gear and with 42-in, road wheels and 33 teeth in the chain wheel the engine speed will be 200 revolutions per minute at a road speed of 8 m.p.h. and 300 r.p.m. at a road speed of 12 mrp.h. Thus, in future all Atkinson wagons will he supplied with or without the epieyelic gear' according to the country in which they are required to operate.

By the use of the *cyclic gear instead of clash gears great advaraages have been secured. In the first place, the gear is foolproof. The driver has one lever to operate, and one of the three working positions gives a free engine.

Perhaps at this point a description of the gear may with advantage be given, the references being to the lettering on the part sectional side and end elevations of the engine crankcase, chain pinion, and reduction gear. The crankshaft (A) carried in the main bearing (B) of the engine crankcase (U) carries an arm (D) made in halves,and bolted firmly to the crankshaft. The drive is transanitted by splines itE) cut from the solid shaft, which engage with corresponding grooves in the arm (D). Carried by the arm .(I)) and arranged so as to revolve in gunmetal bushes (F) are two planetary pinions (0). These pinions•have teeth cut in their rims, as at I and P. The teeth (I) engage with teeth cut in the rim of a sun wheel (J) carried by, and concentric with, the crankshaft (A). On the face of the sun wheel (J) deg teeth are cut, as shown at K. Carried by the sun wheel (J) and attached thereto by means of bolts (N) is a brake drum (L), to which a dust cover is attached.

Carried by, and concentric with, the crankshaft (A) is a direct-drive clutch (M), which is driven by, and is free to slide upon, splines (N) cut solid from the crankshaft. On the face of the clutch (M) are formed dog teeth (0), which are suitably shaped so as to engage with the dog teeth K, when the clufea is moved forward by the arm (P). A helical steel spring is provided at Q to facilitate the engagement of the teeth (K and 0).

Carried by, and concentric with, the crankshaft (A) is the chain pinion (R), which transmits the drive from the engine to the rear axle. Teeth formed on the chain pinion engage with teeth (12) on the planetary system. A packing gland is provided to prevent escape of oil. The brake band (8), with suitable operating mechanism (T) and bearing on the brake drum (L) is provided. The spring (U) attached to the brake band acts as an anchorage for the band.

The modus operandi is as'follows:::-To bring the top gear into use the direct-drive clutch (M) is moved forward by the arm (P) until the dog teeth (0 and K) engage. As the clutch is attached to the crank shaft by means of the splines (N), the sun wheel (3) will be driven at the same speed as the crankshaft (A), and, as the chain pinion (R) is directly coupled through the pinions (0), the whole gear will be revolved in its entirety, there being no relative movement between the chain pinion (R) and the crankshaft (A).

To bring the low gear into operation the* directdrive clutch (M) is disengaged through the arm (P), and the brake band (8) is tightened on to the drum (L), thereby holding the sun wheel (J) stationary. The arm (D) is now driving, and the pinions (0) revolve about their own axes and roll upon the sun wheel (J), thereby driving the chain pinion (R) in the same direction as the crankshaft (A) at a reduced speed.

The free engine is provided by the fact that when the direct-drive clutch (M) is disengaged, and before the brake band (8) is tightened upon the drum (L), the planetary gears (G) are free to roll about the chain pinion (R), so that the crankshaft (A) may revolve and the chain pinion (R) remain stationary.

This free-engine position is very useful. Thus. should the injector fail, the driver can put his engine into neutral and use his water pump for replenishment of the boiler. When a wagon is waiting in a queue, such a failure might entail the driver withdrawing from the queue and drawing his fire and putting matters right, a waste of time thus being incurred.

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