CHAPTER VIICLUTCHES
Clutches are essential in all gasoline cars, for the reason that the driving power of the motor must be frequently disconnected from the running gear.
These devices are designed to transmit motion from the engine to the transmission shaft, so that when the clutch is engaged the transmission shaft will turn with the engine shaft.
Clutch Requirements.—The first requisite of a clutch is its ability to firmly hold the two shafts together; the second is, that it may be engaged gradually, and not suddenly; third, that it must disconnect instantaneously; and, fourth, that the force required to hold the two parts of the clutch together must not produce an end thrust on either shaft.
These requirements must be met by a condition that the act of engaging the clutch will not necessitate a long movement of the foot pedal which sets the clutch. Other considerations must be taken into account, also, and that is facility for examiningand repairing, easy removal of worn or broken parts, and capability of adjustment as the contact surfaces wear.
Fig. 40. Cone Clutch.
Fig. 40. Cone Clutch.
It will be seen, therefore, that there are many elements necessary to provide a satisfactory clutch, well adapted for all purposes, and all these factors must be considered and understood by the boy who would be well informed.
Frictional Contact.—In any form of automobile clutches, there must be a frictional contact,which means wear, whatever may be the character of the material employed for the surfaces which are in engagement. As a result, clutches are now made which will permit the use of oil. Others dispense with it entirely.
Each type has its advantages. The cone clutches usually do not use a lubricant. This is described in the diagram, Fig. 40.
Cone Clutch.—In the drawing A represents the engine shaft, which has a fly wheel B, and C is the transmission shaft. The engine shaft has a short projecting stem D, which abuts the end of the transmission shaft C.
A hollow hub E is loosely journaled on the stem D, and is of sufficient length to extend over and have a bearing on the transmission shaft C, this latter being squared so it will turn with the hub, or it may be provided with a feather to work in a suitable groove in the hub, so that both will turn together, while permitting the hub to move longitudinally.
The inner end of the hub E has a web F, with a conical bearing surface G, which engages with an internal cone on the fly wheel.
Compression Spring in Clutches.—Within the hollow hub E is a compression spring H, one end of which rests against the inner end of the hub, and the outer end contacts against a collar I,which collar is screwed on the threaded end of the stem D, and by means of which the pressure of the spring may be regulated from time to time.
The normal action of the spring is to throw the cone surface G, into engagement, as shown in the diagram, and when the foot presses down the pedal J, the hub is moved back against the tension of the spring, and the clutch released.
It is obvious that if oil should find its way between the cone surfaces the grip would be materially lessened, and depending upon the kind of materials used.
Fig. 41. Multiple Disk Clutch.
Fig. 41. Multiple Disk Clutch.
The Multiple Disk Clutch.—A type of clutchwhich uses oil is shown in Fig. 41. The prominent feature of the multiple disk is the large area of contact surfaces available, and this, together with the comparative freedom from wear, owing to the lubricating material, makes it a favorite structure, especially on account of its gradual engagement which is not easily obtainable with a cone clutch.
In the drawing, the transmission shaft A has its ends reduced to receive thereon a set of disks B. The shaft is ribbed along the surface where the disks are located, and the disks B have cut-out portions C, for the ribs, so that, while the disks must turn with the shaft, they are free to move longitudinally.
The end of the engine shaft D, has a tubular housing E, to receive the end of the transmission shaft A. The inner end of this housing embraces the flange F, of a cylindrical shell G, this shell having within a series of disks H, secured to the shell so they will slide longitudinally, but turn therewith, and these disks alternate with the disks on the transmission shaft.
It will be observed that the flange F, of the shell G, has a tongue I, which slides within a groove J in the housing, so that the shell G, while turning with the shaft D, may be moved longitudinally on the shaft A, a limited distance.
The end of the shaft A, has a collar K, and between this collar and the end of the flange F, is an expansion spring L, so that the normal action of the spring is to push the web of the shell G, toward the disk head M, and thus force all the disks together and produce the friction of a very large surface.
In order to release the clutch, it is necessary to draw back the shell G. The mechanical action is merely shown, not the exact structural arrangement. An annular flange N is formed on the head of the shell, and a pair of hook-shaped bars O, pass through the wall of the case, their outer ends being actuated by the foot pedal, in any convenient manner.
Disadvantages of Multiple-Disk Clutches.—These clutches have also their weaknesses. Sometimes they will grip too quickly, if the lubricating oil is too thin, or if there is not enough of it; or, if it becomes very thick and gummy, the disks will not free themselves quickly, and the clutch will drag.
Care of Multiple-Disks.—When such is the case, it is better to take out all the lubricant, and thoroughly clean off the disks, and put in a fresh supply. If the case is kept properly closed, so that the oils will not be wasted, and no dust can enter, a light, thin oil, will last for a long time.
When the clutch slips, it is due to wear, or to insufficient spring pressure, and a new adjustment is necessary; and it is frequently the case that the rod between the clutch and pedal must be taken up, this being the case, usually, where there is any wear in the clutch itself.
The disks are, usually, wholly of metal. Among other materials, cork is used to face friction surfaces of different clutch designs, and a variety of materials are constantly added to the list, which have good wearing qualities.