192 clutches and power-stop control – Clutches – Axially engaging
Reexamination Certificate
2000-04-28
2002-02-19
Bonck, Rodney H. (Department: 3681)
192 clutches and power-stop control
Clutches
Axially engaging
C192S070200, C192S083000, C192S10600R
Reexamination Certificate
active
06347695
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to clutches in general, and more particularly to improvements in friction clutches. Still more particularly, the invention relates to improvements in friction clutches of the type known as disc clutches wherein one or more motor- and/or engine-driven first discs can be moved into or from more or less pronounced frictional engagement (including no frictional engagement) with one or more second discs which can transmit torque to one or more driven components, e.g., to the input shaft of a transmission in the power train of a motor vehicle.
A disc clutch can be utilized as a so-called starter clutch in the power train of a motor vehicle, especially in a power train which employs an automatic transmission. A motor vehicle wherein the power train embodies an automatic transmission is disclosed, for example, in German patent application Serial No. 198 00 490. An automatic transmission can be of the type known as a multiple-speed (such as three-, four- or five-speed) transmission or an infinitely (continuously) variable transmission (e.g., the one known as CVT) A power train embodying a starter clutch and a CVT is also disclosed in commonly owned U.S. Pat. No. 5,667,448 granted Sep. 16, 1997 to Oswald FRIEDMANN for “POWER TRAIN”.
The disclosure of the commonly owned German priority patent application Serial No. 199 19 343.6-12 filed Apr. 28, 1999 as well as the disclosures of all U.S. and foreign patent applications and/or patents identified in the specification of the present application are incorporated herein by reference.
In many instances, a disc clutch comprises a first set of clutch discs (called friction driving discs) and a second set of clutch discs (often called driven plates) which alternate with the clutch discs of the first set. The means for engaging or disengaging the disc clutch often comprises a so-called apply piston which can be caused to move axially to thus urge the clutch discs of the two sets against each other with a variable force and to thus enable the driving discs to rotate the driven plates without any slip or with a selected slip.
As a rule, the starter disc clutch in the power train of a motor vehicle is operated in two stages. The first stage involves rapid axial displacement of the driving discs through a relatively large distance, e.g., to initiate the transmission of torque to the driven plates or discs. The second stage normally involves precision (minute or small) axial displacements of the driving discs to thus select the desired (optimum) extent of frictional engagement between the neighboring (alternating) driving and driven discs, i.e., to accurately select the magnitude of torque to be transmitted between the prime mover (such as an internal combustion engine) and the driven component(s) (such as the automatic transmission) in the power train of a motor vehicle.
If the output part (such as a camshaft or a crankshaft) of an engine transmits a torque which fluctuates within a certain range, such fluctuations entail corresponding variations of the force which the piston of the clutch engaging/disengaging assembly transmits to the interfitted (shuffled) driving and driven clutch discs. The force acts at right angles to the planes of the clutch discs, and any variations of such force normally entail an axial displacement of the driving and driven clutch discs (or of all but one clutch disc) relative to the two hubs, one for the driving discs and the other for the driven discs. One of the hubs has axially parallel internal splines mating with the external (peripheral) teeth of one of the two packages of clutch discs, and the other hub has axially parallel external splines mating with the internal teeth of the other package of clutch discs. The teeth of the clutch discs are, or should be, slidable along but should not rotate relative to the splines of the respective hubs. One of the hubs rotates with the output part of the en-engine, and the other hub is non-rotatably connected with the input element of the transmission.
Whenever the teeth of a clutch disc move along the neighboring splines of the respective hub, this invariably involves the generation of a certain amount of friction. The friction is not constant because its magnitude is a function of the forces acting in the circumferential direction of the clutch discs (i.e., of the magnitude of transitted torque) as well as of the so-called friction factor at the loci of frictional engagement between the teeth of a clutch disc and the splines of the respective hub.
Under ideal circumstances, any changes of pressure of oil or another pressurizable fluid which is employed to move the clutch engaging/disengaging piston axially should result in corresponding predictable axial displacements of the piston and hence in corresponding predictable changes (modulation) of frictional engagement between the driving and driven clutch discs. It has been ascertained that presently known disc clutches fail to satisfy such exacting requirements, and an important reason for such absence of predictability of the magnitude of transmitted torque is the unpredictability of the extent of frictional engagement between the (internal or external) teeth of the clutch discs on the one hand, and the (external or internal) splines of the respective hubs on the other hand. All the aforementioned second stage of operation of a conventional clutch disc normally involves are hysteresis losses rather than an accurate selection of a desired modulation of the torque being transmited between neighboring driving and driven clutch discs.
Conventional disc clutches exhibit certain additional drawbacks. For example, unpredictable frictional engagement between the teeth of the clutch discs and the splines of the respective hubs entails non-uniform wear upon such parts with the resultant generation of noise, escape of lubricant and/or the need for frequent inspection and replacement of parts.
OBJECTS OF THE INVENTION
An object of the present invention is to provide a disc clutch which is constructed and assembled in such a way that it can select the magnitude of transmitted torque with a degree of accuracy much higher than that achievable with presently known disc clutches.
Another object of the invention is to provide a disc clutch wherein the interfitted driving and driven clutch discs invariably respond to any and all desired or required changes in the action of the clutch engaging/disengaging arrangement.
A further object of the invention is to provide novel and improved discs for use in a clutch of the above outlined character.
An additional object of the invention is to provide a power train, particularly a power train for use in a motor vehicle, which embodies one or more disc clutches of the above outlined character.
Still another object of the invention is to provide a novel and improved method of transmitting torque between the internal combustion engine and the transmission (such as an automatic transmission) of a motor vehicle.
A further object of the invention is to provide the disc clutch with novel and improved means for shielding the piston of the clutch engaging/disengaging arrangement from corrosive and/or other undesirable influences of the fluid which is employed to shift the piston in its cylinder in order to change the magnitude of the torque which is to be transmitted by the clutch.
Another object of the invention is to provide a disc clutch wherein the exact magnitude of torque which is being transmitted between the two hubs is less dependent upon the magnitude of friction between the teeth of the clutch discs and the splines of the respective hubs than in heretofore known and utilized disc clutches.
An additional object of the invention is to provide novel and improved means for engaging and disengaging a disc clutch.
Still another object of the instant invention is to provide a disc clutch wherein the coolant for the clutch discs can be put to additional advantageous uses.
A further object of the invention is to provide novel and improved means for shielding the a
Friedmann Oswald
Kuhn Peter
Obrist Frank
Bonck Rodney H.
LuK Lamellen
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