Clutch

Phases of operation

One distinguishes three phases from operation for a device of clutch.

In coupled position : the clutch completely transmits the provided power (the car runs, the Moteur is related to the Gear box). It is generally the stable position of the device (absence of action of order).
In disconnected position : The transmission is stopped. Free wheel, or conveys stopped, the engine can continue to turn without involving the wheels. The situation is equivalent to the dead point.
transitional stage of slip : in particular during the clutch , the transmission of power is gradually restored. During this phase, the tree of entry and exit do not turn at same the vitesse ; there is then slip between the discs, therefore dissipation of energy, in the form of heat. This phase is to be limited in time, even if it is inevitable and makes it possible to gradually solidarize the engine and the gear box. The wear of the discs takes place during this phase.

It is the situation of slip which gives the conditions of dimensioning of the clutch. It determines the transmissible stall torque. Beyond, the slip is systematic. The same technological configuration is adopted besides on the systems torque limiters, which thus will patinate when the requested couple becomes too important.

Classification

The technological solutions adopted for this device are distinguished according to several criteria:

geometry of the surface of friction:

discs, the contact being effective according to a crown;
drum (in the case of certain centrifugal clutches);
conical (today abandoned except some applications to low power). Its interest lies in the fact that it is autobloquant: the conical assembly remains wedged in the absence of pressing effort. It is necessary to act to disconnect.

According to the number of discs (when they are discs)

single-plate;
two-plate with single order or separate control (double);
multidisk wet or dry.

One calls disc the element generally associated with the output shaft and gripped by two elements related to the driving shaft. It carries the trimmings of friction, and constitutes of this fact a wearing part. The number of surfaces of contact is always even; thus the pressing efforts do not induce constraints in the connection between the frame and the coupling system, and are in fact taken again by the clutch housing.

The number of discs announced in a clutch is thus the number of gripped discs provided with trimmings.

the lubrication of surfaces of contact can:

To function dry;
To function under oil bath.

According to the principle of order

Power-control;
Hydraulic Order ;
Electric drive controlled electronically;
Centrifuges (in this case the order voluntary but is not induced by the action on the accelerator).

the direction of the order

Ordering of clutch for the normally disconnected devices (case of small machines such Mower S and Cultivator), or of the centrifugal clutch machines (reduced Auto-cycle, model radiocontrolled);
Ordering of disengaging for the devices normally in catch.

Structure

Single-plate clutch

A clutch comprises several parts:

the driving wheel 2 , interdependent of the driving shaft 1 .
the clutch disk 3 which is solidarized in rotation with the tree of entry of the gear box 6 by Cannelure S.
the plate of pressure of the mechanism 4 , ensures the adherence of the clutch disk on the driving wheel in coupled position.
the springs of the mechanism (with diaphragm our case), 5 are resting against the Butée of clutch 7 .

When the ordering (hydraulic or with cable) of clutch is actuated, the thrust exerts a force on the diaphragm, the plates deviate then by releasing the disc from friction. The movement is less and less transmitted, making independent the gear box of the engine. That allows, for example, to remain motionless without fixing the engine, or to change gear.

The opposite operation consists in slackening the ordering of clutch gradually, to restore the connection engine/gear box. This operation is called “ to make patinate the embrayage ”.

Multidisk clutch

The multidisk clutches function according to the same principle, except that one uses a stacking of discs, one on two being in relation to the engine, one on two being in relation to the wheels. This stacking is maintained in pressure by springs.

A disc on two is notched on its circumference, enabling him to be interdependent of the bell of clutch, one on two is notched inside, enabling him to be interdependent of the nut of clutch.

The coupled position makes it possible to make interdependent the bell and nut of clutch.

This configuration much more compact radially than that with only one disc is that retained on the motor cycles. A multidisk clutch is often used when the coefficient of friction is decreased, for example at the time of a lubricated employment in zone. The addition of the discs increases the surface of friction and thus compensates for the coefficient.

Clutch electrorheologic

Recent progress in the electrorheology makes it possible to think of a new generation of clutch. Basing itself on the capacity of change enters the solid state and the liquid state of a electrorheologic Fluide. This type of clutch makes it possible to connect or isolate the couple from entry and that of exit very easily and quickly.

The principle of the clutch electrorheologic is very simple. When an electric field is applied, the fluid electrorheologic (ER) solidifies and connects the disc of entry and the disc of exit. When this field is removed, the fluid ER returns in a normal state (fluid). The disc of exit east thus isolated almost instantaneously from the disc of entry.

This type of clutch was manufactured and tested in laboratory. However, the current limits of the electrorheologic fluid (forced still weak threshold and uninsured stability) always prevent its marketing.

Dimensioning

The transmissible couple by a clutch depends on material constituting the Garniture S, on the number and dimensions of surfaces of Frottement between Disque S as of the force exerted by the Ressort S.

In general, one writes $C = N \ F \ NR \ R_ {eq}$ with $R_ {eq} = \ frac {2} {3}. \ frac {(R_e^3-R_i^3)}{(R_e^2-R_i^2)}$

with $N \$ the number (even or odd) of surfaces of friction

F \

the coefficient of friction between these surfaces

NR \

clamping force

R_e \

and

R_i \

rays external and interior of surfaces of frictions in the shape of bored discs

The performances, in particular the coefficient of friction, remain related to the temperature. This one rises quickly when the discs patinate. The unit must thus be able to be cooled.

The materials constituting the trimmings are synthetic products being formerly containing asbestos, which is prohibited today.

Particular case of the automatic box

There is no clutch with discs with a automatic gear box traditional: it is replaced by a hydraulic Torque converter. Indeed, the automated operation of a traditional clutch is rather delicate. This device is connected with a centrifugal clutch, the state of the coupling not depending in fact that on the number of revolutions of the engine. Passages speed with an automatic box themselves being obtained by actions on internal clutches with the box. The torque converter induces a variable slip, but also a substantial increase in the engine torque available.

Henceforth the manual gear boxes are more and more often Robot ized, which implies that the clutch is him also controlled by the electronics of the Calculateur.

See too

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