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Q. What materials are used in multiple disc clutches?
A. The discs of multiple disc clutches designed to operate in an oil bath are usually thin stampings from saw steel sheets which are hardened and ground to a true surface. In some clutches the plates are all steel and in other forms the driving members are of steel while the driven plates are stamped from phosphor bronze sheets. In dry plate clutches the driven plates, which are faced with Raybestos or other suitable friction material, are steel stampings while the driving plates may be either steel stampings or cast iron plates. In some dry plate forms the driving members are cast iron while the driven plates are of bronze studded with cork inserts.
Q. What is a positive clutch?
A. The forms of clutches in which projecting members fit into depressions in the coacting part and which act as positive mechanical locks are termed “positive clutches."
Q. Are positive clutches ever used alone?
A. Positive clutches are always used in connection with a master clutch of the friction type because they would be much too harsh in action and impose considerable strain on the power plant and transmission parts if used alone.
Q. What types of band clutches have been used and how do they operate?
A. Band clutches have been made in two forms, the internal expanding and external constricting types. The former is seldom used at the present time because it is a very difficult type to balance properly and to keep in proper adjustment. The external band form outlined at Fig. 153 is used on the Haynes car and it consists of a metal clutch band adapted to constrict around a drive ring attached to the flywheel. The band is tightened by means of a constricting lever operated by a cam or inclined plane member pressed forward by a coil spring. In operation the external band, which is attached to the gearset drive shaft, clamps tightly around the drive ring while the internal band form spreads out against the internal periphery of a similar drive ring integral with the flywheel.
Q. What are the essential requirements of clutches and which type meets most of the requirements ?
A. A clutch must be simple to construct, apply and operate and it must be capable of transmitting the maximum engine power in a positive manner. It must release promptly and yet it should not engage too harshly. It should be of such form that any wear occurring will be automatically taken up and it should be easy to restore the frictional materials when these deteriorate. Practically all of these requirements are met by the friction clutch in any of its forms and the cone form owing to its simplicity and strength of parts is the most favored of all clutch types,
THE FRICTION TRANSMISSION
Why is change speed gearing necessary on gasoline automobiles ?
A. The gasoline engine develops power in direct proportion to its speed up to a certain point and it will slow down whenever an overload is applied. More power is needed to climb hills than is used to propel the car on the level and if the gasoline engine was directly attached to the rear wheel with a definite unvariable ratio it would not be possible to climb hills unless this reduction of speed between engine shaft and rear wheels was very low. When conditions were favorable, such as when the resistance to motion was slight, as on smooth level highways, the low reduction provided would be too slow and the car speed would be limited to that permitted by the gear ratio. At the other hand if the gear ratio was higher to permit more speed under favorable conditions it would be too high for hill climbing or propelling the car over rough road surfaces. In order to enable the power plant to develop its full power it is customary to provide some form of change speed gearing to permit of altering the ratio of drive between the engine and the rear wheels to suit road conditions. The usual ratio on the direct drive or highest speed varies from three to one to five to one in pleasure cars and may go as high as ten to one on heavy vehicles. This means that the engine crankshaft will make from three to ten turns while the rear wheels are revolving once. As a gasoline engine is not reversible it is customary to incorporate gearing that will permit of reversing the car motion in the change speed gear set.
Q. Why are electric and steam automobiles without change speed gearing?
A. It has been previously explained that steam engines or elec
tric motors, which derive their power from stored energy, are capable of operating at an overload and while their speed of rotation may be reduced it is possible to obtain the rated horse-power by admitting more steam to the cylinder or more current from the storage battery to the windings of the motor. Either the steam engine or the electric motor is capable of being reversed; by changing the direction of flow of the energizing agent in the case of the electric motor, by a simple shifting of valves in the steam engine. This flexibility of steam and electric power enables the manufacturer of these cars to dispense with change speed or reverse gearing.
Fig. 154.—The Lambert Friction Disc Combined Clutching and Speed
Q. What is the simplest method of obtaining speed reduction?
A. The simplest method of obtaining speed changes and one that will provide a large range of speed variations is by using friction discs or, as they are sometimes called, friction gearing.
Q. What is friction gearing?
A. Friction gearing in its simplest form consists of bringing two wheels into frictional contact with each other and holding them in
contact with sufficient pressure so the driving wheel will cause the member against which it bears to rotate as well. The simplest form of friction gear is the face friction drive.
Q. Describe parts of face friction gearing.
A. A typical face friction gear that has given good results in practice is shown at Fig. 154 and all parts are clearly depicted in the illustration. The engine drives an aluminum face driving member with its face at right angles to the engine crankshaft. The driven member is a fiber faced wheel carried by a cross shaft which extends across the frame and which is carried in suitable bearings attached to the frame sides. This countershaft carries the driving sprocket and is parallel to the face of the aluminum driving member. The fiber face driven wheel can be moved back and forth across the face of the driving member by suitable leverage connected with the control handle. The direction of countershaft rotation and its speed relative to the engine crankshaft is determined by the position of the fiber face driven wheel relative to the center of the driving member.
Q. How is clutching effect obtained?
A. The aluminum face driving member is capable of being brought into contact with the driven wheel or moved away from it at the will of the operator. The amount of pressure between the two members may be varied by a pedal. When the discs are brought into contact the drive is taken up and power is transmitted from one member to the other and as soon as the discs are separated the drive will be interrupted. The operator can control the amount of pressure and consequently the amount of drive to a nicety and consequently a gradual power application may be obtained.
Q. How is the car reversed?
A. The process of reversing is easily accomplished by pushing the fiber face driven wheel over to one side of center of the aluminum face driving member. As indicated in Fig. 154 the driven wheel is placed to the left of center, which is a position giving forward drive. If moved toward the right of center or toward the driving chain sprocket the countershaft will revolve in an opposite direction to the way it rotates when the driven disc is in forward drive