The bevel-gear axle is almost universally used on pleasure cars. However, it is not very popular on commercial cars. being used only on the light vehicles of capacities up to 1,500 lbs. Its use is limited, owing to that it is very difficult to provide a higher reduction than four or five to one without sacrificing road clearance.
Fig. 119 depicts the G.M.C 1,500-lb. delivery car bevel drive rear axle, which is of the three-quarter floating type. The axle housing is divided into two halves having tubes riveted into it, which extend slightly beyond the wheel bearing. The differential is of the bevel-gear type and mounted on Hyatt roller bearings inside of the axle housing. Ball thrust bearings with ample adjustment are mounted on each side of the Hyatt roller bearings to take up the thrust load of the gears. The hub is provided with a Hyatt bearing, which is centered under the wheel and is retained by a threaded retaining member which has a funnel-shaped part formed integral to throw off the oil and prevent it from reaching the brakes. The hub is keyed to axle shaft, so that the weight is carried on the housing tube, while the shaft transmits the power. The spring seat swivels upon the brake spider, which also carries the ends of the truss rod. The axle housing has a bracket to support the brake shafts, so that the levers can be mounted close to the center of the axle. The brakes are of the internal and external type and operate on pressed steel brake drums bolted to the wheels. The propeller shaft is enclosed in the torque tube, which is bolted to the axle housing and carries the ball bearings for supporting the bevel pinion, while the pinion shaft and the propeller shafts have squared ends and are connected by a sleeve having a square hole fitting over the squared shaft ends.
The torque is taken by the torque tube through a large fork, which is hinged to a heavy cross member, while the spring is free at both ends. Radius rods, running from the brake spider diagonally to a point directly back of the torque tube fork, take up the thrust load.
Fig. 119. G.M.C. Delivery Car Bevel Gear Type Rear Axle.
The difficulty with the bevel-gear axle is overcome in the double reduction, internal gear and worm-gear axles. The double reduction and the internal gear type use two reductions, one by bevel gears and the other by spur gears, while in the worm-gear axle a large reduction can be obtained with a single pair of gears.
The advantages claimed for the double reduction are silent operation, enclosure of all working parts, while the differential bearings are relieved of thrust loads. By mounting one pair of gears above the other, approximately straight-line drive can be obtained.
The internal gear-drive axle possesses the advantages of silent operation and enclosed working parts. However, the differential bearings are subjected to thrust loads, since the spur gears are mounted in the wheel, and it is also difficult to obtain a straight-line drive. They possess an advantage in that this axle is divided into two units, the jack shaft which transmits the power and the dead rear axle which carries the weight. The jack shaft is similar to the chain drive jack shaft and may either be bolted to the front or rear of the dead axle.
The worm-gear axle is probably the most simple construction, since it has the least number of parts, can easily be arranged for straight-line drive, and possesses the features of silent operation, protection of parts subject to wear and a wide range of gear ratios can be provided without changing the distance between the worm and the wheel.
All types of shaft-driven axles can be made quite accessible so that maintenance can be held within reason. The double reduction and worm-gear axles are generally of the full floating type, in which the weight is carried on the axle tubes and the shafts are subject to only torsional stresses, as they only transmit power.
One of the first commercial car builders to use a shaft-drive axle was the Autocar Company, which equips all of its models with double-reduction axles. Extensive refinements have been made on this axle and it presents an excellent type of double reduction. This axle is shown in Fig. 120, and is what is termed a full-floating axle. The bevel gears are placed above the spur gears so that a straight drive can be obtained, while it also has an advantage in machining the bevel gears, since they are much smaller than they would be if they were used instead of spur gears for the final reduction. The spur gears are better able to take care of the torque of the second reduction and the differential bearings are relieved of the high thrust loads, which they would be required to carry if bevel gears were used.
The axle housing proper is cast in two halves joined together at the center. The spring seats are cast integral and the end of the housing is provided with a flange to which the brake spider is bolted. A reinforcing tube is placed into the housing, which extends a little beyond the spring seat, the end of which carries the wheel bearings. The bevel and spur driving gear and differential are mounted in a unit in the differential carrier and bolted to the housing proper. The drive shafts have splined ends and the wheel drive is taken through flanges bolted to the hub. Internal and external brakes are mounted on the brake drums inside of the wheel?