USING A NEW PRINCIPLE IN FINAL DRIVES.
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Some Details of a New Range of American-built Chassis in which the Rear Axles Float and Have a Relay Action.
APRINCIPLE of most unusual interest is embodied in a new range of chassis produced by the Commerce Motor Co., of Ypsilanti, Michigan. Tbe range will eventually include models of capacities from 1 ton to 5 tons, but the only example actually built up to the present is a 34-to/men
The actual idea of the relay drive is comparatively simple, although the carrying out of the drive presents certain engineering difficulties.
The relay action can easily be understood if we take as an example one of those dog-operated mill wheels which are to be seen in some parts of the Continent. In these, the mill wheel, instead of being turned by water, as is usual, is turned by a dog which runs in the interior. In starting the wheel, or whenever there is extra resistance to its movement, the dog will climb higher up the inside until eventually the energy thus built up overcomes the resistance.
In the Commerce design the final drive is by spur gears meshing with internally toothed rings. The dead axle carrying the wheels passes through the gaps in D-shaped forgings and is keyed at each end to the centres of circular-ribbed castings, which, at their lower parts, are permitted to swivel on the ends of the live axle, through. which the torque is conveyed.
The centres of the two axles are T ins, apart, in the case of the fll-ton model, and the bosses in the ribbed castings are provided with phosphorbronze bushes, as. of course, considerable movement is liable to occur between these ribbed castings and the driving axle.
The D-shaped forgings are bolted to the casing of the live axle and carry at their upper portions the road springs, so that the weight of the chassis and the load upon it is transmitted first to the live axle and then through the ribbed castings to the dead axle, and so to the wheels.
It will thus be seen that whilst the Jive-axle housing is prevented from rotating and is tied to the chassis, both by the springs and by the radius rods, the dead axle is virtually floating, and it can move through the arc of a circle of which the live axle forms the centre.
Now we will study what happens when a vehicle with this form of drive Starts away. When the power is first applied through the live axle the chassis and its load begin to move forward and upward until the rolling resistance of the wheels is overcome, and the greater this resistance the more will the chassis move forward and upward in relation to the rear wheels.
In carrying out tests with this vehicle, lengths of 10-in. by 10-in.
timber were placed in front of the rear wheels, with the vehicle at rest, and when the clutch was engaged the wheels simply rolled over the timber after the chassis had moved forward and upward for a sufficient distance. This test was repeated in both directions with the engine running at a comparatively slow speed and without slipping the clutch.
It is said that with this form of final drive a vehicle can pull itself out of soft ground with the wheels sunk
almost to the axle, and that gradients of 40 per cent. can be ascended with
full load, but this, of course, depends upon engine power and gearing, as the relay action of such a drive as this can only provide extra energy for a short distance.
Another way of looking at the problem is to consider a wheel as being split at the top and flattened out into a see-saw. If a person were at one end of the see-saw and then walked up it until just past the fulcrum point, the see-saw would tip over. The weight of the person being lifted to the height of the fulcrum by walking up the plank would represent so much energy—in other words, stored work—which is, of course, partially expended when the see-saw is tipped over.
Reverting to the vehicle, with this at rest the driving pinions are immediately, below the dead axle, but when travelling forward on the level and on ordinary surfaces the pinions are slightly advanced—in other words, the dead axle has lagged behind slightly.
Directly a hill is encountered, however, this lagging is accentuated and the pinion is well in front of the dead axle. The actual effect is to lengthen and shorten the wheelbase by a small amount, according to whether the vehicle be travelling forward or backward.
It is claimed that the drive helps to maintain the momentum of the truck when it is under way, but this, to our mind, is not feasible. It is only. when resistances are momentarily increased that the action would appear to give any particular benefit. The permitted movement of the dead axle is 60 degrees to either side of the live axle.
In climbing around the internal racks the driving pinions can move, the truck backward or forward 61 ins., and at the same time the entire rear of the vehicle is raised 3ft ins., and this without necessitating movement of the rear -wheels, although these, of course, must be held securely, as their power of surmounting obstacles is increased to the maximum.
One point against the design is that the live-axle casing is rather close to the ground, but this is somewhat balanced by the fact that immediately an obstacle is encountered by the wheels the live axle is automatically raised until the moment of the weight lifted overbalances the moment of the traction , resistance. • The pinions adjust themselves to every road irregularity, automatically conserving and expending power according to requirements. Actually, when the vehicle is in motion and an object is encountered, the wheels slow down, but the momentum of the vehicle causes the chassis and its load to move in the manner explained until the wheels are overbalanced and move forward, so climbing over the obstruction.