CLUTCH CONSTRUCTION, TYPE AND CARE
The clutch used in automobile construction of the present day becomes a
necessary part of the equipment upon the adoption by manufacturers of
the progressive and selective types of sliding gear transmissions.
When the engine is started the clutch is “in,” that is, in contact
with the flywheel, and all parts of the clutch revolve with it at the
same speed. The shaft on which the clutch is mounted extends into the
transmission gear case, but as the transmission gears are in a neutral
position, the movement of the car is not affected.
When the car is to be started the clutch foot pedal (usually on the
left side of the steering column) is pressed down. This throws the part
attached to the drive shaft out of contact with the part attached to
the flywheel, and in its backward movement it comes into contact with
the clutch brake, as shown in Fig. 105, which stops it from revolving.
The hand gear control lever is shifted into the first speed slot or
position. The pressure on the foot pedal is then gradually released and
the clutch is carried in by spring tension, and the car moves off at
first speed.
=Second Speed.=--The clutch is thrown “out” after a brief lapse of
three to five seconds has been allowed for the brake to slow up
rotation in order that the gears to be meshed will be rotating at the
same speed. The hand control lever is now shifted into the second speed
slot, and the clutch pedals released.
=High Speed or Direct Drive.=--The clutch is thrown out and a few
seconds allowed for it to slow up. The hand control lever is shifted
into the high speed slot, which connects the drive or propeller shaft
directly to the clutch shaft and the car is driven at crank shaft speed
when the clutch is let in.
=Reverse.=--The clutch is employed in the same manner. However, the
motion of the car, the clutch and all gears must be at a stand still
before the gear control lever is shifted to the reverse speed slot, as
the gears in the transmission operate in the opposite direction.
[Illustration: Fig. 105. Cone Clutch and Brake]
OPERATION
A clutch always consists of two parts, one part which is attached to
the flywheel, and another part which operates on or against the part
formed by the flywheel.
While there are five to seven different types of clutches, but two
types are used by the majority of automobile manufacturers. The single
or multiple disc clutch is used almost exclusively in unit power plant
construction, while the cone type is used when the transmission is
carried in a separate unit.
Fig. 105 shows the cone clutch with its three adjusting springs and
clutch brake. The cone is shown in a lighter color than the flywheel.
It has a funnel-shaped surface with a slant or angle of from thirty to
thirty-eight degrees. The slanted surface is faced with leather and
fits into the rim of the flywheel which has been ground to the same
slant. The cone clutch is not attached to the flywheel but forms a
part and revolves with it when the faces are in contact. The cone is
carried on a separate short shaft which extends into the transmission
case. This shaft carries a steel plate or disc at the front end to
which the cone which slides on the shaft is anchored by studs extending
from the plate through the cone. The studs usually number three or
four and carry a two to three inch spring on the outer end back of the
cone. The cone is backed out of contact with the flywheel face, against
the tension of these springs, in a toggle leverage connected to the
foot pedal. The clutch brake shown in Fig. 105 is adjustable and makes
contact with the rim of the cone retarding the rotation when the cone
is drawn out of contact with the flywheel.
=Cone Clutch Care.=--The leather face of the cone should receive 5 to 7
drops of Neat’s foot oil every thirty days. A grease cup will be found
on the cone which provides lubrication for the shaft on which the cone
slides. This should be given a half turn every second day.
=Cone Clutch Adjustment.=--The three studs extending through the
cone, have a lock nut adjustment on the outer end, and the cone may
be adjusted up to make a stronger face contact by loosening the lock
nut and turning the inner nut to the right. This strengthens the
spring tension and causes the contact faces to set more firmly. This
adjustment, however, should take place only when clutch slipping is
noted. Only a little movement of the nuts is necessary, and all three
or four nuts should be taken up a like amount in order to prevent the
cone from running out of line or making uneven contact.
Fig. 106 shows the multiple disc clutch used almost exclusively in
connection with the unit power plant. This type of clutch consists of
a set of plates attached and driven by the flywheel, and another set
of plates or thin discs attached to the drive shaft. The drive shaft
plates operate between the flywheel plates. The contact is frictional
and the plates are held together by spring tension.
[Illustration: Fig. 106. Multi-Disc Unit Power Plant, Clutch and
Transmission]
BORG AND BECK CLUTCH
The new Borg and Beck Clutch is provided with a thrust bearing at the
inner end of the clutch sleeve, which does away with the friction
between the parts, and eliminates the need of a clutch brake.
The clutch is mounted in the customary way in a housing which contains
both the flywheel and the clutch.
[Illustration: Fig. 107. Borg and Beck Clutch]
Referring to the sectional view, Fig. 107, the action of the clutch
is clear if it is kept in mind that among the rotatable parts only
the driven group, comprising of the disk A and the shaft B, can stand
still when the flywheel is running. All the other rotatable parts are
anchored to the flywheel, and must revolve and drive with the latter.
The clutch brake was formerly mounted at the inner end of the clutch
shaft, and has been replaced by the thrust bearing shown at C.
When the clutch is disengaged there is no friction between the shaft
B, and the throw out sleeve D. The thrust bearing takes the rotating
drag of the clutch shaft, thereby eliminating the necessity for a brake
to check the spinning action. The friction and power action is readily
understood as, when the clutch is thrown in, all the rotating parts are
friction locked into a single combination and revolve as one with the
flywheel.
The power of the release clutch spring E, acting through the
throwout-collar F, and the bell crank pivot G, drives the thrust shoes
outwardly with a lever wedge toggle combination of powers against the
overhanging, inward beveled face to the thrust ring H, since the parts
on which they are mounted are backed against the cover wall or rigid
end of the clutch casing. It therefore follows that the full part
shafting effect of the thrust is communicated to the thrust ring H, and
the latter, in being driven hard toward the flywheel, sets up between
itself and the inner casing wall a friction grip sufficiently powerful
to stop the slippage of the asbestos rings upon the polished faces of
the discs, thus giving the drive to the car.
When the pedal is depressed to release the clutch, the retracing parts
telescope the coil of the spring E, until it occupies nearly a single
plane. The withdrawing parts also release the clutch shoes a sufficient
distance from the face of the thrust ring H to permit the latter,
together with its companion friction ring, to back away from the disc,
thus breaking the friction grip and permitting it to come to a stop,
while the flywheel and the parts of the clutch anchored to it are left
free to revolve idly.
The release disc A is so light that its spinning does not continue
except for a very short time and does not offer any clashing action
on the gears. The full thrust of the spring transmitted through the
powerful lever toggle action to the friction grip parts is always
sufficient to lock the driving flywheel parts, and the driven disc,
into a fixed nonslipping relation for a full driving action; but it
is still always within control of the driver, through the foot lever,
to let the clutch into engagement by degrees, and thus by a gradual
increase of the friction grip, gradually overcome the starting slippage.
=Adjustments.=--Taking up adjustments are provided by means of bolts
acting through adjustment slots in the cover. When the bolts are
loosened and shifted in their cover slots, they control and shift
with them an adjustment ring which brings all the shoes to new seats
against the nonslipping thrust ring and these seats being farther up
the inclines of the tapered ring, the ring is necessarily thrust much
farther toward the other friction parts, thus compensating the wear.
The adjustment for throw-out can be controlled by taking up the
friction grip adjustment, the latter being identical with the take up
adjustment just described, as these too are taken care of by the same
mechanical means to make the adjustment on the clutch.
=Disc Clutch Cleaning; Dry Plate.=--Dry plate clutches do not require
any oil, except that the grease cups (which provide lubrication for the
sleeve shaft and bearings) be filled weekly and given a half turn every
second day. The housing and plates should be cleaned whenever slipping
becomes noticeable. To do this remove the cover from the housing,
and the drain plug from the bottom, hold the clutch out, and squirt
kerosene over the plates with a dope gun. This will remove the grease
from the plates, and also any dirt or grit that may have lodged in the
bottom of the housing.
=Disc Clutch Cleaning; Wet Plate.=--The wet plate clutch is cleaned in
the same manner as the dry plate, except that the plug is first removed
from the bottom of the housing and the oil drained off before using the
kerosene. After the plates and housing have been cleaned, replace the
drain plug and fill the housing up to the clutch shaft with a heavy
cylinder oil.
CONE CLUTCH CLEANING
Cone clutches are always in perfect condition when leaving the factory
and should not require any further attention during the first season or
for eight to ten thousand miles of service.
After that it is usually necessary to replace the leather, or reline
the cone, which makes it as good and as serviceable as when it was new.
=New Clutch Leathers.=--New clutch leathers may be obtained from the
manufacturer, or from the service station, by giving the number and
model of the car. New clutch leathers obtained in this way are cut,
shaped, and have the ends cemented, and are ready to be slipped on
or off, over the cone and riveted into place. However, the leather
must first be soaked in water or Neat’s foot oil to make it soft and
pliable. This allows it to be driven or stretched over the cone. The
rivets must be counter-sunk to prevent the heads from extending above
the top surface of the leather, which would cause the clutch to “grab”
or jerk upon being engaged.
[Illustration: Fig. 108. Cone Clutch Leathers--Pattern--Cutting]
=Measuring and Cutting Clutch Leathers.=--Whenever possible it is
advisable to purchase clutch leathers cut and cemented, ready to
put on. But in case of emergency or when the proper size cannot
be obtained, a new leather may be cut from a piece of leather
three-sixteenth of an inch in thickness using the old leather as a
pattern. But in case the old leather is not available to serve as a
pattern, proceed in the following manner which is illustrated in Fig.
108, which shows how to make an exact pattern out of paper without
going into technicalities. Take a piece of heavy wrapping paper, forty
or fifty inches long and twenty inches wide, lay the cone on the left
hand edge about one inch from the bottom of the sheet, roll the cone
keeping the paper flat on the face until the starting edge meets the
sheet, hold the wrapped cone and draw a line around the inside of the
paper, letting the pencil rest against the edge of the large diameter
of the cone; repeat at the small end of the cone, then draw a line
parallel to the starting edge where it meets the sheet. This will give
you a pattern similar to that shown with the dotted lines in Fig. 108.
Now secure a piece of unstretchable leather (belting is preferable).
This belting or leather should be slightly longer than the pattern
you have just completed and sufficiently wide to embrace the curve;
about twelve to fifteen inches wide for the average clutch will be
sufficient, and about three-sixteenths of an inch thick.
Cut out the paper pattern and lay it on the leather belting as shown in
Fig. 108, and cut out with a sharp knife, leaving one-half inch over
at each end as a safety measure and for mitering the joints. Fit this
leather to the cone and cut the ends the exact size, miter the ends and
cement with a good leather cement. Be sure that you have the rough or
flesh side of the new facing on the outside; rivet it firmly in place
and smooth down the rough spots with a piece of coarse sand paper,
clean off all dirt, grease, and grit, especially the grit from the sand
paper, as this will grind and score the smooth surface of the flywheel
and cause clutch slipping. Paint the leather with Neat’s foot oil and
the clutch is ready to be assembled and adjusted.
=Cone Clutch Cleaning.=--Cone clutches usually do not require any
special care or cleaning unless oil or grease, other than (Neat’s
foot or castor) are applied accidentally or by mistake to the leather
face. If this happens the grease must be thoroughly cleaned off of the
leather face with kerosene or gasoline otherwise the clutch will not
hold. After the clutch leather has been washed allow it to dry for
twenty minutes and apply a thin coat of Neat’s foot oil evenly on the
leather face before reassembling the clutch.