A DIFFERENTIAL STEERED CHASSIS.
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A Résumé of Recently Published Patents.
In the majority of cases lour-wheel driven chassis are so constructed that a portion of the power at least has to be transmitted through the steering pivots
of the vehicle, and therein lies the weakness of the type. It is a failing which is
always evident, to a greater or less degree, although in later designs it is less so, but mainly at the expense of increased complication and consequent greater cost of production. In an alternative con struction, not yet adopted to any extent commercially, the steering pivots them selves are eliminated from the •chassis, by the simple process of differentiating between the proportion of the driving torque which is transmitted to the pairs of wheels on the opposite sides of the chassis, and so controlling the direction. By increasing the proportion of power, for example, which is transmitted to the offside wheels, and correspondingly de creasing that which goes to the nearside wheels, the vehicle would be forced to turn to the near side, and if the propor tion of power transmitted to the two sidea was varied in a contrary manner the reverse effect would result. Such an arrangement is described, 14 Schneider and Cie., in specification No.
142,034. The chassis is a chain-driven one, and the cross-shaft, with -which is.
incorporated, as usual, the differential gear, is disposed midway along the frame.. It carries two pairs of sprocket pinions, instead of Only one, and they are situated two together. at each end of the shaft. Sprocket wheels of the usual type are bolted to all four road wheels, which run on solid dead axles. The arrangement will be understood if reference be made to oar itlurtration, which is reprOduced from the patent specification, and it will at the same time be gathered that, in the ordinary way, without any artificial nia.nipulation of the differential gear, all four wheels would be driven at the same speed, and the vehicle would proceed in a straight line in either a forward or reverse direction according to the position of the gears in the gearbox.
The differential gear, however, is subject to the control of a "super-differential," as it may be called, which is controlled directly' by the driver of the vehicle. On each of the two shafts of the main differential gear are mounted gearwheels: These are engaged, one directly and the other through the medium of an idler wheel which . acts as a reverser, to gears on the hubs of the sun wheels of the super-differential gear. In the ordinary way, when it is desired that the vehicle shall travel in a straight line, the super-differential gear la stationary, and as, owing to the intervention of the one idler reversing wheel in the train between the two differential gears, one sun wheel of the Super-differential gear is driven in the reverse direction to the other, the effect B42 of the connection•sbetween the two is merely to Oause the planetary Pinions to revolve idly on their spindles.
Motion of the -super-differential gear, however, will cause an alteration in the direction of movement of the chassis. If, for example, the super-differential gear is caused to revolve, as a whole' in the same direction as the wheels of the vehicle, it will carry with it the sun wheels, and also, of course, the gears on the hubs of those sun wheels. This will result in a retardation of the offside shaft of the main differential (see drawing) and an acceleration of the nearsklo one, so that the vehicle will turn to. the off side. . The control of the super-differential gear may be effected by means of an ordinary steering wheel, operated by hand, or it may be effected by gearing driven from the engine of the chasSis. •
It is interesting to note that there will be no need to "straighten up the steering..gear of a chassis in which this form of gear is embodied, as the vehicle proceeds in a straight line an soon as movement of the steering wheel ceases.
Detail Improvements.
Gear changing on a modern_ car is not lav any. means a difficult operation, but 'What .little obstacle does exist is due ma-idly to the fact that the dogs, or teeth; as the case may be, which -have to be engaged, are so nearly alike, spare to dog, or space to tooth, that precise similarity of speed of the two engaging members is necessary before that „,,engagement can take place. E. J. Wide provides, in No. 142,052, by the shortening of alternate dogs, or the diminution in the width of alternate teeth, for the more facile engagement of these parts, prior to the existence of that precise similarity of movement.
Ans..' automatic trailer brake, which takes effect whenever the tension in the drawbar connection is diminished, is the subject of No. 141,817, by V. Barningham. A spring is disposed so that it is always tending to put on the brake, but is prevented by a tie rodkor cable which is coupled to the draw-bar, and is taut
so long as the connecting link between tractor and trailer is also taut. liVhent
starting to move, the cable operating the brake is tightened first, freeing the brake so that the tractor and trailer can pro= ceed. When the tractor is stopped, the tension in the drawbar is diminished, and the brake again takes effect, and if the trailer attempts to overrun the tractor, as when descending a hill, the same thing . happens, or, again, when the trailer becomes detached. The brake is so -fitted that reversion of motion of the trailer, as, for example, in the event of the trailer and tractor commencing to run back down a hill, the brake would act. Provision is made for the gear to be rendered inoperative in case of need, as when manoeuvring.
No. 141,782 is a modification and extension of the principle of the Rapson tyre, whereby a resilient wheel is constructed. The inner tube is carried well down in the body of the wheel, and the resilient member of the tyre is made practically solid, within the outer cover, but bears on its underside on to the inner pneumatic tube.
In the Suspension described in specification No. 122,412 by' O. A. janemian, the whole of the mechanism of the chassis, engine, gearbox, and transmisaion, are carried directlsr by the rear springs, which form, as it were, a bridge between the rear axle and the frame of the cats which practically carries cal, the body and the load.
No. 141,931, by G. H. Lanchester, describes a simplified electrically Operated change speed gear control.
In the springing device patented in specification No. 141,964 by Sisaire and Berwick, the springs are arranged, two pairs on each side of the chassis, and of those, two springs before and two behind the axle on each side', so that the movement of the axle is entirely vertical.
T. W. Paterson fits a petrol valve in the fuel supply system which is controlled by the pressure of the lubricating oil in the engine. A plunger is subject to that pressure, and when it drops the plunger also falls and cuts off the supply of fuel. The
specification is No 142,049.