Leather and fabric universal joints have been used for some time because they present several features not obtainable with the mechanical type. The principle advantages are silent operation without wearing surfaces requiring no lubrication. Since there is no friction they are considered highly efficient in the transmission of power. However, this joint is not adapted to conditions when there is a great angularity between shafts since the flexibility of the disc is depended upon to compensate for this angular movement and also the elongation in the shaft. Experience generally with this type of joint has not been uniformly successful and extreme care is necessary in their design. Owing to its limitations in angular movement it is mostly used between the clutch and transmission when the angular movement is relatively small.
A typical joint of this type for use between clutch and transmission is shown in Fig. 09. It consists of several similar spiders usually three armed, fastened to the ends of the shafts to be connected and of a number of leather or fabric discs bolted between the spiders. The arms of the two spiders are staggered so that any arm of one of the spiders is located midway between two arms of the other spider. Three, four or five discs may be used and individual discs are often spaced by steel washers.
Fabric discs are usually rubberized. These are built up of layers of fabric with the warp of succeeding layers at slightly different angles. In fact the whole circle is divided into a number of parts equal to the number of layers in the discs and the angle thus arrived at is the angle between the warp of adjacent discs.
Fig. 99. Thermoid Fabric-Disc Type of Universal.
Propeller shafts were originally made of solid section, however, with the sudden increase in shaft-drive construction, especially where the transmission was in a unit with the motor, came a decided tendency to use either two shafts and three universal joints, or a large tubular shaft and two universal joints. The advantage of the tubular lies in its reduced weight and consequently the reduced whipping effect and pressure on the bearings. A large tubular shaft is shown in Fig. 94 and a divided shaft of solid section in Fig. 97.
These tubular shafts are made of 40 carbon seamless tubing and are attached to stub shaft which form the connections with the universal joints. The ends of these shafts are generally made a shrink fit into the tube and then welded. The manufacturer of the Ar-vac universal joint uses the shrink joint fit for shafts, but these have keyways cut into them so that the tube while being shrunk over the shaft can also be swaged into the keyways, thus strengthening the welded joints in the propeller shaft and permitting the driving strains to be taken by the swaged portion of the tube.
When two shafts are used a universal is generally attached to the transmission, while the other end of the shaft is mounted in an anti-friction bearing such as a ball or roller bearing. While this divided propeller shaft is not new, the use of a tubular shaft no doubt has an influence on the problem, and this center bearing is receiving considerable thought at present, which is evident through the number of designs in use at present.
The construction shown in Fig. 100 consists of a self-aligning ball bearing mounted in a housing which is bolted to a cross member of the frame. A shoulder on the shaft and the hub of the universal joint hold the bearing in position while its self-aligning feature and the end play allowed in the housing provides for frame deflexions and variations in shaft length.
On the Globe trucks a heavy duty Hyatt bearing is mounted on a stub shaft welded to the forward propeller shaft. This bearing is mounted in a bracket which is in the form of a hinge. This type of mounting may be so placed as to provide a straight-line drive from the transmission to the rear axle, since any deflexion on the side rails of the frame may be neglected, due to the hinged bracket providing the self-aligning feature. The slip joint is mounted as close to the bearing as possible, as shown in Fig. 101.
On several models of Diamond T-trucks four universals and three shafts are used, the center being supported by two roller bearings as illustrated in Fig. 102. Two slip joints are used, one immediately back of the transmission and the other back of the center shaft mounting. The bearings are Timken rollers and mounted in a dust-proof housing and provided with adjustment.
On the Bethlehem trucks the Barker floating bearing is used which permits the use of but two universal joints and a long shaft. This is depicted in Fig. 103 and is so mounted on the propeller shaft as to permit it to float between coil springs. This bearing has a free movement up and down with the propeller shaft in one of the slots of a pivoted arm. A coil spring on the shank of the bearing, which passes through the slot in the arm, slightly resists free movement of the shaft away from the arm, and another coil spring at the top of the arm acts similar in the opposite direction, the arm being pivoted at the lower end. This pivot arm is supported by a bracket attached to a cross member of the frame.
To secure the highest efficiency and absence from vibration, care should be observed to have the pins at opposite ends of the assembly parallel, as this will eliminate vibration which may become serious if the shaft whips as the velocity of thie front joint must be equalized by the rear joint, since the velocity varies during each quarter revolution. As the bearing pressures are necessarily high, proper means for lubrication must be provided. The assembly proper is usually provided with a housing to retain lubricant and means for inserting same.
Fig. 100. Lippard Stewart Propeller Shaft Mounting.
Fig. 101. Globe Propeller Shaft Mounting.
Fig. 102. Diamond T Center Bearing Mounting for Divided Propeller Shaft.
Fig. 103. Barker Propeller Shaft used on the Bethlehem Trucks.