The Meyers front drive (Fig. 141) is similar to the above types, in that the engine is placed forward of the front axle. The power of the motor is transmitted from the jackshaft, through side chains, to a shock absorbing bracket, carrying another sprocket attached to a short shaft, on the opposite end of which is a small gear, meshing with a large internal gear, bolted to the spokes of the wheels. The main frame is mounted upon semi-elleptic springs. The upper frame, which forms the pivoting member, has a detachable castor-like wheel and as the weight is to the rear of the unit, it is perfectly stable and can be driven from place to place. The vehicle is steered by means of a circular rack and pinion, upon a fifth wheel. The shock of starting is eliminated by a patented arrangement on the driving pinion. This pinion is mounted on an arm pivoted by the axle and is free to roll in the internal gear to a slight extent, its forward motion being limited by a positive stop and its rearward motion by the rod and spring shown.
In the types described above, the power is transmitted to the wheel by means of roller chains. In the Walter truck the power is transmitted by shafts and internal gears, along lines similar to the Latil front-drive trucks, built in France. The transmission of the Walter is mounted with the engine, to form a unit power plant, which is so located that the flywheel is just in front of the front axle, the entire engine overhanging the axle. From the sectional view of the transmission (Fig. 142), it will be noted that the differential and bevel driving gears are mounted at the front end of the secondary shaft, which is placed above the main shaft. From the differential, extends two universally jointed shafts to spur gear pinions on the steering knuckles, which mesh with internal gears bolted to the front wheels. There is no mechanism whatever back of the driver's seat, and the construction is very compact.
The layout is such that the front-drive unit does not have to be altered or changed in any way on vehicles, which drive the rear wheels also, the forward unit of the front drive being identical with the front unit of the four-wheel driven vehicle. The secondary shaft of the transmission is ex-tended back to another differential and bevel driving unit, mounted on a frame directly over the rear axle. This unit also has universal jointed shafts, extending to the rear steering knuckles and carrying spur pinions, which mesh with internal gears bolted to the rear wheels.
The rear axle is also used for steering in the four-wheel drive, but not in the front drive.
The conventional type of worm and gear-steering column is used, with a longitudinal cross-shaft, having a universal joint at its forward end. The rear end of this shaft carries a steering arm, which is connected with the usual linkage to the rear wheels, as shown in Fig. 143.
Fig. 143. Plan of the Walter-Four-Wheel Drive Chassis.
The Nash Quad and Duplex four-wheel drive trucks are also driven by means of internal gears and universal-jointed shafts. The wheel construction of the Nash Quad is shown in Fig. 144. The propeller shafts are driven from the secondary shaft of the transmission. The cross-shafts, which drive the wheels, are located above the axle, while the axle carries the weight only and has the driving gear and differential unit bolted to it. The driving pinion meshes with an internal gear, mounted in the wheel. The wheels are cast steel with integral rim, hubs and brake drums. The driving pinion is located above the steering knuckle and driven through a universal joint, the center of which is directly in line with the pivot center of the knuckle.
Fig. 144. Nash Quad Method of Driving Four Wheels.
The Duplex is also driven by means of internal gears in the wheels and universal joints mounted directly over the steering knuckles, and with drive shafts above the springs. However, the method of transmitting the power to the wheels is somewhat different from that described above. The transmission is of conventional design and built in a unit with the engine. Power is transmitted by shaft to a chain case, attached to the frame at approximately its center. This oiltight chain cane. Fig. 14.1. is the junction point, connecting the front and rear axle drive shafts, the driving sprocket, by means of a silent chain, delivering power to the sprocket, to which the fore and aft shafts are attached. The shaft, on which the driving sprocket is mounted, carries a brake drum, which forms the service brake, acting on all four wheels. Emergency brakes are on the rear wheels. The vehicle is steered by the front wheels only, in the usual manner.
Fig. 145. Duplex Four-Wheel Drive Chain Case.