Apparatus for damping torsional vibrations

Apparatus for damping torsional vibrations in the power train of a motor vehicle has two coaxial flywheels one of which is driven by the engine and the other of which can transmit torque to the input shaft of a transmission by way of a friction clutch. The flywheels are rotatable relative to each other against the resistance of a damper. Certain features of the apparatus reside in the dimensioning and distribution of its parts in the radial and axial directions of the flywheels to reduce the dimensions of the apparatus. The torque transmitting connection between at least one pair of neighboring rotary parts of the apparatus employs a slip clutch which yields when the applied torque exceeds a certain value. An intermittently or continuously active hysteresis device is utilized to operate in parallel with the energy storing springs of the damper.

BACKGROUND OF THE INVENTION
 The present invention relates to improvements in apparatus for damping
 torsional vibrations. More particularly, the invention relates to
 improvements in torsional vibration damping apparatus of the type wherein
 rotation of input and output members with each other is desirable (or at
 least acceptable) but angular movements of such members relative to each
 other (especially beyond a certain range of such angular movements) are
 undesirable or even damaging.
 It is known to utilize torsional vibration damping apparatus in the power
 trains of motor vehicles, e.g., between the rotary output component of an
 internal combustion engine (or another suitable prime mover) and the input
 component (e.g., a flywheel) of an automated or manually engageable and
 disengageable friction clutch which, in turn, serves to transmit variable
 torque to the rotary input component of a manually shiftable or automated
 or automatic variable-speed transmission.
 A drawback of many presently known torsional vibration damping apparatus is
 that they are bulky, complex and expensive. This creates serious problems
 in the power trains of numerous types of motor vehicles. Moreover, the
 assembly of conventional torsional vibration damping apparatus at the
 locale of use (such as an automobile assembly plant) is often a
 time-consuming procedure involving numerous welding, riveting,
 shape-altering, centering and/or other operations which contribute to the
 cost of the power plant and of the entire motor vehicle. Still further, it
 is normally necessary to establish and maintain supplies of large numbers
 of different spare parts.
 OBJECTS OF THE INVENTION
 An object of the invention is to provide a torsional vibration damping
 apparatus which is simpler, more compact and less expensive than, but just
 as reliable and versatile as, heretofore known apparatus.
 Another object of the invention is to provide a novel torsional vibration
 damping apparatus which can be utilized with particular advantage in the
 power trains of passenger cars and/or other types of motor vehicles.
 A further object of the invention is to provide a torsional vibration
 damping apparatus which can be utilized with particular advantage in the
 power trains of compact or miniature motor vehicles.
 An additional object of the invention is to provide a torsional vibration
 damping apparatus which can stand long periods of extensive use and wear,
 i.e., an apparatus whose useful life is longer (or even much longer) than
 that of presently known and utilized torsional vibration damping
 apparatus.
 Still another object of the invention is to provide a torsional vibration
 damping apparatus which is constructed and assembled in such a way that
 none of its parts must be immersed in a lubricant or another fluid medium
 in order to be capable of standing long periods of extensive use in the
 power train of a motor vehicle or elsewhere.
 A further object of the invention is to provide a highly effective
 torsional vibration damping apparatus which is superior to numerous
 heretofore known apparatus and which can be installed in existing power
 trains as a superior substitute for conventional torsional vibration
 damping apparatus.
 Another object of the invention is to provide a novel and improved modular
 torsional vibration damping apparatus.
 An additional object of the invention is to provide a torsional vibration
 damping apparatus which can be assembled, either to a large extent or even
 practically entirely, at the manufacturing plant in lieu of at the locale
 of ultimate use.
 Still another object of the invention is to provide novel and improved
 modules for use in the above outlined torsional vibration damping
 apparatus.
 A further object of the invention is to provide novel and improved damper
 means for use in the above outlined torsional vibration damping apparatus.
 Another object of the invention is to provide novel and improved methods of
 assembling torsional vibration damping apparatus for use in the power
 trains of motor vehicles.
 An additional object of the invention is to provide a power train which
 embodies the above outlined torsional vibration damping apparatus.
 Still another object of the invention is to provide novel and improved
 connections between various constituents of the improved torsional
 vibration damping apparatus, such as between the input and output members
 and the elements of a damper which operates between the input and output
 members.
 A further object of the invention is to provide the apparatus with novel
 and improved means for limiting the magnitude of torque which can be
 transmitted from a prime mover to a transmission or the like.
 Another object of the invention is to provide novel and improved input and
 output members for use in the above outlined torsional vibration damping
 apparatus.
 An additional object of the invention is to provide the apparatus with
 novel and improved means for centering its input and output members
 relative to each other.
 Still another object of the invention is to provide a novel and improved
 distribution of component parts which contributes to compactness of the
 improved apparatus as seen in the axial and/or in the radial direction of
 its rotary constituents.
 A further object of the invention is to design the various constituents of
 the apparatus in such a way that its fasteners and/or other removable or
 separable or exchangeable parts are readily accessible to standard tools.
 SUMMARY OF THE INVENTION
 The invention resides in the provision of an apparatus for damping
 torsional vibrations, particularly in the power trains of motor vehicles.
 The improved apparatus comprises rotary input and output members which are
 arranged to carry out rotary movements with and relative to each other,
 particularly about a common axis, and at least one damper which operates
 between and is arranged to oppose at least some (e.g., predetermined
 stages of) rotary movements of the input and output members relative to
 each other. The damper comprises at least one energy storing device, e.g.,
 a straight or arcuate coil spring or a set of interfitted coil springs.
 It is preferred to provide the input and output members with suitable
 flywheels or sets of flywheels. Thus, the input member can include or
 constitute a primary flywheel which can be driven by the output component
 (such as a camshaft or a crankshaft) of an internal combustion engine, and
 the output member can comprise or constitute a secondary flywheel which
 can serve to transmit torque to the input element of a transmission, e.g.,
 by way of a friction clutch. The damper of such apparatus is or can be
 arranged to oppose at least some rotary movements of the primary and
 secondary flywheels relative to each other.
 If the output member is to drive the input shaft of a transmission by way
 of a friction clutch, the secondary flywheel can be provided with an
 annular friction surface which faces away from the input member and the
 clutch can comprise a pressure plate, a clutch disc between the friction
 surface of the secondary flywheel and the pressure plate, and means (e.g.,
 a clutch spring which can constitute a diaphragm spring) for moving the
 pressure plate relative to the friction surface between a plurality of
 different axial positions in at least one of which the pressure plate
 causes the clutch disc to bear against the friction surface and to thus
 receive torque from the secondary flywheel, i.e., from the output member.
 The clutch disc can transmit torque to the input shaft of the
 transmission.
 The damper can comprise at least one rotary input element serving to
 receive torque from the primary flywheel, and a rotary output element
 which is rotatable relative to the at least one input element and can
 serve to transmit torque to the secondary flywheel. The at least one
 energy storing device of the damper is then interposed between portions of
 the at least one input element and of the output element to yieldably
 oppose rotation of the at least one input element and the output element
 relative to each other. Such apparatus can further comprise a first torque
 transmitting connection between the input member and the at least one
 input element of the damper and a second torque transmitting connection
 between the output element of the damper and the output member. The at
 least one energy storing device can be located at a first radial distance
 from the common axis of the input and output members, and each of the two
 connections can be located at a greater second radial distance from such
 axis.
 The just described embodiment of the improved apparatus can further
 comprise a frictional connection between at least one of the flywheels and
 (a) the at least one input element or (b) the output element.
 Alternatively, one can provide a form-locking connection between one of
 the flywheels and the at least one input element or between one of the
 flywheels and the output element of the damper.
 A first torque transmitting connection can be provided between the input
 member and the at least one input element, and a second torque
 transmitting connection can be provided between the output element and the
 output member. One of these connections can be installed at a first radial
 distance, and the other of these connections can be installed at a
 different second radial distance from the common axis of the input and
 output members.
 It is also possible to provide a frictional connection between one of the
 flywheels and the respective element of the damper, and a form-locking
 connection between the other flywheel and the other element of the damper;
 the form-locking connection can be disposed at a first radial distance,
 and the frictional connection can be disposed at a greater second radial
 distance from the common axis.
 The apparatus can further comprise means for limiting the magnitude of the
 torque which can be transmitted between the primary and secondary
 flywheels, and such torque limiting means can include a frictional
 connection between one of the flywheels and the respective (input or
 output) element of the damper.
 The torque transmitting connection between the rotary output component of
 the prime mover and the input member (such connection can include a set of
 externally threaded axially parallel fastening elements) can be placed
 nearer to the common axis than the energy storing device or devices of the
 damper, i.e., the torque transmitting connection can be disposed at a
 first radial distance from the common axis, and the spring or springs of
 the damper can be installed at a greater second radial distance from such
 axis.
 The apparatus can further comprise at least one radial bearing (such as a
 journal bearing or an antifriction bearing with one or more annuli of
 rolling elements between two races) to serve as a means for centering the
 flywheels relative to each other; such centering means can be located at a
 first radial distance from the common axis of the flywheels, and the
 aforementioned fastening means between the output component of the prime
 mover and the input member can be located at a greater second radial
 distance from the axis.
 One element (such as the input element) of the damper can comprise two
 annular parts or cheeks which are non-rotatably connected to each other,
 and the other element of the damper (such as the output element) can
 comprise a disc-shaped part (hereinafter called flange for short); at
 least a portion of the flange can be located between the two cheeks, as
 seen in the direction of the common axis of the input and output elements
 of the damper (such common axis preferably coincides with the common axis
 of the flywheels). A portion of at least one of the cheeks can form part
 of the centering means (such as the aforementioned radial bearing) which
 is installed between the two flywheels. For example, at least one of the
 cheeks or the flange can include a substantially cylindrical member (e.g.,
 a sleeve or a ring) which constitutes or can constitute the radially
 innermost portion of the at least one cheek or of the flange and forms
 part of the means for centering the flywheels relative to each other. Such
 substantially cylindrical portion can be said to constitute an axially
 extending portion of the bearing and to form part of the centering means.
 Such part of the centering means can constitute a separately produced part
 which is affixed to the input or output element of the damper.
 The means for centering the two flywheels relative to each other can form
 part of the input member or of the output member; such centering means can
 include an axially extending portion of the input or output member. Such
 part of the centering means can constitute a separately produced part
 which can be affixed to the primary flywheel or to the secondary flywheel.
 A suitable hysteresis device (hereinafter called hysteretic damping device)
 can be utilized to operate between the two flywheels, preferably in
 parallel with the at least one energy storing device of the damper. For
 example, the hysteretic damping device can include or constitute a
 friction generating device. In accordance with one presently preferred
 embodiment, the at least one energy storing device of the damper is
 located at a first radial distance from the common axis of the flywheels,
 and the hysteretic damping device can be located at a greater second
 radial distance from such axis.
 In accordance with another presently preferred embodiment, the connection
 between the primary flywheel and the input element of the damper can be
 disposed at a first radial distance from the common axis of the flywheels,
 the connection between the output element of the damper and the secondary
 flywheel is located at a second radial distance from the common axis, and
 the hysteretic damping device is located at a third radial distance from
 the common axis; the first radial distance can be greater or less than the
 second radial distance, and the third radial distance is preferably
 greater than one but less than the other of the first and second radial
 distances.
 Alternatively, the just discussed third radial distance (of the hysteretic
 damping device from the common axis) can be greater than the first as well
 as the second radial distance.
 If the hysteretic damping device comprises a friction generating device,
 the latter can be set up to generate a hysteresis which varies in response
 to rotation of the input and output members relative to each other.
 The radially outermost portion of the means for fastening the input member
 to the rotary output component of the prime mover can be placed at a
 predetermined distance from the common axis of the input and output
 members, and the radially innermost portion of the aforementioned flange
 of the damper can be located at a second radial distance from the common
 axis; such second radial distance preferably at least equals but can
 exceed the predetermined distance. The flange can be provided with at
 least one window for a portion of the at least one friction generating
 device of the damper; this window can be provided at (such as in or close
 to) the radially innermost portion of the flange, and the window can have
 an open side facing radially inwardly, i.e., toward the common axis of the
 flywheels.
 The radially innermost portion of at least one cheek of the damper can be
 disposed at a radial distance from the axis which at least equals but can
 exceed the aforementioned predetermined distance (of the radially
 outermost portion of the fastening means for the input member) from such
 axis.
 In lieu of (or in addition to) providing one or more windows for the energy
 storing device or devices in the flange, it is possible to provide such
 window or windows in at least one cheek of the damper.
 The flange of the damper can be provided with one or more openings radially
 outwardly of the energy storing device or devices; such opening or
 openings provide room for the passage of one or more fastener means
 serving to fixedly secure the two cheeks of the damper to each other. The
 opening or openings of the flange can extend circumferentially of the
 input and output elements of the damper.
 The primary flywheel can include a wall which extends radially of the
 common axis of the two flywheels; a radially outer portion of the flange
 can be placed next to and can be fixedly connected with such wall by
 suitable fastener means. Those portions of the wall and of the flange
 which are located radially inwardly of the fastener means can be spaced
 apart from each other to provide room for a portion of or for an entire
 hysteretic damping device. Distancing means can be interposed between the
 wall and the flange, at least in the region of the fastener means; such
 distancing means can comprise an annular mass.
 A multi-stage torque limiting connection can be installed between one of
 the input and output elements of the damper and one of the primary and
 secondary flywheels.
 The apparatus can comprise a module which includes the secondary flywheel,
 the pressure plate of the aforementioned friction clutch (which can be
 used to transmit torque from the secondary flywheel to the input shaft of
 the transmission in a power train), and a clutch disc which can be
 positioned between the secondary flywheel and the pressure plate and has a
 hub connectable with the input shaft of the transmission. The module can
 be mounted on the output element of the damper.
 If the improved apparatus comprises or cooperates with a friction clutch,
 that side of the secondary flywheel which faces away from the primary
 flywheel can be provided with the aforementioned friction surface which is
 or which can be located at a predetermined radial distance from the common
 axis of the flywheels. If such apparatus further comprises torque limiting
 means, the latter can be placed at or close to such predetermined distance
 from the common axis.
 The torque limiting means can operate between the input and output members
 of the improved apparatus and can include means for generating slip
 torque. Such torque generating means can include a resilient element which
 is arranged to store at least some energy in response to connection of the
 friction clutch with the secondary flywheel. The resilient element can
 comprise or constitute a diaphragm spring.
 One of the flywheels can be provided with at least one opening affording
 access to and manipulation of suitable fastening means serving to secure
 the output element of the damper to the other flywheel. Such fastening
 means can comprise one or more rivets. The other flywheel can constitute
 the secondary flywheel and is then normally provided with the
 aforementioned friction surface for engagement by the friction linings of
 the clutch disc which transmits torque to the input shaft of the
 transmission. The opening or openings of the one flywheel are or can be
 provided at such radial distance from the common axis of the flywheels
 that they overlap the friction surface of the secondary flywheel (as seen
 in the direction of the common axis of the flywheels).
 The distribution of various constituents of the improved torsional
 vibration damping apparatus in the radial direction of the common axis of
 the flywheels can be such that (a) the aforementioned radial bearing
 between the flywheels is located at a first radial distance from the
 common axis, (b) the means for fastening the input member (e.g., the
 primary flywheel) to the rotary output component of a prime mover is
 located at a greater second radial distance from the axis, (c) the at
 least one energy storing device of the damper is located at a greater
 third radial distance from the axis, (d) the torque limiting means an/or
 the hysteretic damping device is located at a greater fourth radial
 distance from the axis, and (e) at least one axial extension of the
 primary flywheel is located at a fifth radial distance greater than the
 fourth radial distance from the common axis.
 The radially outer portion of the primary flywheel can include at least one
 annular mass, particularly a mass having several layers of folded sheet
 material, especially a metallic sheet material. The aforementioned radial
 wall of the primary flywheel can be of one piece with the annular mass;
 this wall can be provided with one or more openings for fastening means
 which serves to secure the input member to the rotary output constituent
 or component of a prime mover. In lieu of being of one piece with the
 annular mass, the radial wall can constitute a separately produced part;
 the input member then further comprises means for securing the annular
 mass to the radially outer portion of the wall. The annular mass which
 constitutes or is carried by the radially outermost portion of the primary
 flywheel can support or can be made of one piece with a starter gear.
 Alternatively, or in addition to the starter gear, the annular mass at the
 radially outer portion of the primary flywheel can carry or can be made of
 one piece with suitable engine management indicia (for example, such
 indicia can be tracked by one or more speed monitoring and/or other
 sensors).
 If at least one of the two flywheels is movable axially relative to the
 other flywheel, the hysteretic damping device (which preferably operates
 in parallel with the energy storing device or devices of the damper) can
 include at least one resilient element (e.g., a diaphragm spring) which is
 arranged to bias the at least one flywheel axially toward the other
 flywheel.
 In lieu of forming part of the aforediscussed module (which includes at
 least some constituents of the friction clutch), the secondary flyweel can
 form part of a module which further includes the damper and is connectable
 with the primary flywheel. Such module can include or encompass one or
 more additional parts, such as the aforementioned friction clutch
 including the clutch disc which is insertable between a pressure plate of
 the friction clutch and the friction surface of the secondary flywheel.
 The friction clutch can be mounted on or otherwise carried by the
 secondary flywheel.
 The aforementioned hysteretic damping device can be designed in such a way
 that it comprises at least one friction ring which is surrounded by a
 portion of the input member or output member. Alternatively, the
 hysteretic damping device can comprise friction generating elements (e.g.,
 an annular array of such elements) confined by a suitable annular guide
 surface which surrounds and guides the friction generating elements and
 can have its center on the common axis of the flywheels.
 The means for limiting the magnitude of the torque which can be transmitted
 between the input and output members can comprise at least one resilient
 element (such as a diaphragm spring) which is stressed in the axial
 direction of the flywheels to assist the clutch spring (such clutch spring
 can constitute or include a second diaphragm spring). Suitable means can
 be provided for affixing the resilient element of the torque limiting
 means to the clutch housing.
 If the apparatus includes a module composed of or including the secondary
 flywheel, a friction clutch adjacent the friction surface of the secondary
 flywheel, and a clutch disc between the friction surface and the clutch,
 the housing of the clutch can be secured to the secondary flywheel or to
 the damper by fastener means which are accessible at one side of the
 secondary flywheel, namely the side located opposite the friction surface
 and confronting the primary flywheel. The fastener means can comprise
 external threads receivable in tapped bores of the clutch housing.
 Depending upon the interpretation of the term "friction clutch", the
 clutch disc can be considered as a component part of such clutch or as a
 discrete part.
 It is also possible to mount the fastener means for securing the clutch
 housing to the output member (e.g., to the secondary flywheel) in such a
 way that the constituents (e.g., bolts or screws or the like) are
 accessible for insertion or removal at the friction surface side of the
 secondary flywheel. The fastener means can be parallel to the common axis
 of the flywheels.
 At least one of the normally two cheeks forming part of the input element
 of the damper can be safely secured to the primary flywheel by two
 connecting means, namely a first connecting means located radially
 outwardly of the energy storing device or devices of the damper, and a
 second connecting means located radially inwardly of such energy storing
 device or devices. The first connecting means can comprise one or more
 rivets, and the second connecting means can further serve as the
 aforementioned means for securing the input member (e.g., the primary
 flywheel) to the rotary output component of the prime mover.
 In accordance with one presently preferred embodiment of the damper, the
 latter comprises several (particularly five) energy storing devices
 forming an annular array spacedly surrounding the common axis of the
 flywheels. Each such energy storing device can be located at or at least
 close to the same radial distance from the common axis.
 The torque limiting device of the improved apparatus can be installed to
 operate between the output element of the damper and the secondary
 flywheel. If a clutch is being utilized in such apparatus, it is
 attachable to and detachable from the secondary flywheel. The torque
 limiting means can comprise at least one resilient element (such as a
 diaphragm spring) which is stressed in the direction of the common axis of
 the flywheels in response to attachment of the friction clutch to the
 secondary flywheel, and which is caused or permitted to dissipate at least
 some energy in response to detachment of the clutch from the secondary
 flywheel.
 It has been found that, regardless of whether utilized individually or in
 any one of a number of different combinations with each other, the
 aforediscussed features contribute to simplicity, reliability, compactness
 (both in the direction of the common axis of the primary and secondary
 flywheels and in a direction at right angles to such axis) and numerous
 other advantages of the improved torsional vibration damping apparatus as
 well as of the power train which cooperates with or embodies such
 apparatus.
 The novel features which are considered as characteristic of the invention
 are set forth in particular in the appended claims. The improved torsional
 vibration damping apparatus itself, however, both as to its construction
 and the mode of assembling, installing and operating the same, together
 with numerous additional important and advantageous features and
 attributes thereof, will be best understood upon perusal of the following
 detailed description of certain presently preferred specific embodiments
 with reference to the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS
 FIGS. 1 and 2 illustrate a portion of a first torsional vibration damping
 apparatus 1 which is a so-called twin-mass flywheel including input and
 output members which are rotatable with as well as relative to each other
 about a common axis 5. The input member of the apparatus 1 comprises a
 first flywheel or primary flywheel 2, and the output member of the
 apparatus comprises a second or secondary flywheel 3. The primary flywheel
 2 is separably connected or connectable to the rotary output component
 (such as a camshaft or a crankshaft) of a prime mover, not shown, e.g., an
 internal combustion engine in a motor vehicle, by suitable fastener or
 fastening means 19. The illustrated fastening means comprises eight screws
 or bolts 19 which are parallel to the axis 5, which are located at the
 same radial distance from such axis, and which are equidistant from each
 other as seen in the circumferential direction of the primary flywheel 2.
 A portion of the output component of the prime mover is shown in FIG. 1 by
 dot-dash lines. The secondary flywheel 3 can transmit torque to the input
 shaft of a manual or automated transmission of the power train, for
 example, by way of a suitable friction clutch or the like; this will be
 described in greater detail with reference to FIG. 3. For example, the
 apparatus 1 can be utilized in lieu of the torsion damping apparatus which
 is disclosed in commonly owned U.S. Pat. No. 5,151,065 granted Sep. 29,
 1992 to Paul Maucher et al. for "TORSION DAMPING APATUS FOR USE WITH
 FRICTION CLUTCHES IN THE POWER TRAINS OF MOTOR VEHICLES". The disclosure
 of each and every patent and/or application identified in this
 specification is incorporated herein by reference.
 The means 4 for centering the flywheels 2, 3 so that they can rotate with
 and relative to each other about the common axis 5 comprises a suitable
 bearing 6, e.g., a combined radial and axial (thrust) bearing which
 comprises or can comprise one or more annuli of spherical or otherwise
 configurated rolling elements between two races (not shown).
 The apparatus 1 further comprises a damper 8 including an input element
 which can receive torque from the primary flywheel 2, an output element
 which can transmit torque to the secondary flywheel 3, and a set of five
 energy storing devices 7 in the form of elongated coil springs. The
 illustrated coil springs 7 are staight, equidistant from each other (as
 seen in the circumferential direction of the flywheels, and are disposed
 at the same radial distance from the axis 5. It is also possible to employ
 arcuate coil springs having centers of curvature on the axis 5.
 The secondary flywheel 3 is assumed to form part of a friction clutch,
 e.g., a friction clutch of the type shown at 151 in FIG. 3 or an analogous
 clutch. Therefore, the right-hand side of the flywheel 3 (as viewed in
 FIG. 2) is provided with a friction surface 9 which faces away from the
 primary flywheel 2 and is engaged by the friction linings of a clutch disc
 (see the friction linings 166 of the clutch disc 168 shown in FIG. 3) when
 the clutch is engaged. The friction surface 9 has the customary shape of
 one side of a washer and is provided on or close to the radially outer
 portion of the secondary flywheel 3. The radially outermost portion 10 of
 the flywheel 3 has axially parallel tapped bores 11 for the externally
 threaded shanks of fasteners in the form of bolts or screws serving to
 separably connect the flywheel 3 with the housing or casing (not shown) of
 the friction clutch (see the housing or casing 169 of the clutch 151 shown
 in FIG. 3).
 The radially outermost portion 10 of the flywheel 3 further carries axially
 parallel locating or centering pins 12 (only one shown in each of FIGS. 1
 and 2) portions of which are snugly received in suitable recesses, bores
 or holes of the clutch housing to facilitate and simplify predictable
 assembly of the flywheel 3 with the friction clutch.
 The illustrated flywheels 2 and 3 are solid masses made of a suitable
 metallic material; for example, these flywheels can constitute metallic
 castings. However, and as will be fully explained hereinafter in
 connection with the detailed description of several modified apparatus
 (for example, those shown in FIGS. 3, 5, 7 and 8), it is also possible to
 make at least one of the flywheels of a suitable sheet material (e.g.,
 metallic sheet stock) which is deformed to provide several suitably
 deformed layers extending in the direction of and/or at right angles to
 the common axis of the flywheels.
 The radially outer portion of the primary flywheel 2 carries a starter gear
 13 which can be welded, soldered or otherwise securely affixed thereto.
 Furthermore, the radially outermost portion of the flywheel 2 is provided
 with an axially parallel (annular) extension 14 which contributes to the
 mass of the primary flywheel and surrounds the radially outermost portion
 10 of the secondary flywheel 3.
 The radially innermost portion of the radially extending wall of the
 primary flywheel 2 carries an axially extending sleeve-like member 15
 which forms part of the centering means 4 and is surrounded by the inner
 race of the antifriction bearing 6. The outer race of this bearing is
 received in a cylindrical recess 16 provided in the radially innermost
 portion of the secondary flywheel 3. The member 15 is a separately
 produced part 17 having a radially outwardly extending collar 18 which
 overlies the exposed left-hand side of the radially extending wall of the
 flywheel 2 (as viewed in FIG. 2) and is affixed thereto by the
 aforementioned fasteners 19. In other words, such fasteners perform the
 dual function of securing the flywheel 2 to the output component of the
 prime mover and of securing the member 15 to the flywheel 2. However, it
 is equally within the purview of the invention to make the part 17 (or a
 similar part, e.g., without the sleeve 18) of one piece with the radially
 extending wall of the primary flywheel 2.
 The shanks of the fasteners 19 extend through registering holes of the
 collar 18 and the radially innermost portion of the radial wall of the
 flywheel 2, and the heads 19a of these fasteners bear against the inner
 side of the radial wall to thus clamp the sleeve 18 between the flywheel 2
 and the output component of the prime mover.
 In accordance with a further modification (not specifically shown), the
 separate part 17 can be dimensioned and configurated in such a way that
 the collar 18 is located at the right-hand side of the radial wall of the
 primary flywheel 2 (as viewed in FIG. 2) so that, when the fasteners 19
 are tightened, their heads 19a bear directly against the collar 18 and
 urge the latter against the adjacent side of the radially innermost
 portion of the radial wall of the flywheel 2. The utilization of the just
 described modified separately produced part (replacing the illustrated
 part 17) might necessitate certain changes in the configuration of the
 adjacent portion of the primary flywheel and/or in the configuration of
 certain other (neighboring) parts of the apparatus 1.
 The input element of the damper 8 is constituted by or includes a
 substantially radially extending disc-shaped or flange-like part 20
 (hereinafter called flange for short), and the output element 21 of the
 damper 8 comprises two annular parts 22, 23 (hereinafter called cheeks for
 short) which are disposed at opposite sides of the flange 20 (as seen in
 the direction of the common axis 5 of the flywheels 2 and 3). As can be
 seen in FIG. 2, the radially outermost portion of the flange 20 extends
 beyond the radially outermost portions of the cheeks 22, 23.
 The cheeks 22, 23 of the output element 21 of the damper 8 are maintained
 in the illustrated axially spaced-apart positions by suitable distancing
 elements 24. The illustrated distancing elements 24 are rivets having
 heads 27 abutting annular shoulders in axially parallel stepped bores 25
 of the secondary flywheel 3. That side of the flywheel 3 which faces away
 from the friction surface 9 is immediately adjacent the cheek 23 which has
 holes registering with bores 25 of the flywheel 3 and receiving portions
 of the shanks of the rivets 24. As can be seen in each of FIGS. 1 and 2,
 portions of the bores 25 are provided in the friction surface 9 of the
 secondary flywheel 3, and the remaining portions of such bores are
 provided in the flywheel 3 immediately radially outwardly of the friction
 surface 9.
 The left-hand side of the flywheel 3 (as viewed in FIG. 2) is provided with
 circumferentially extending grooves 28 which connect neighboring bores 25
 to each other and communicate with substantially radially inwardly
 extending channels 29 which are adjacent the cheek 23 and establish paths
 for the circulation of coolant (such as atmospheric air). The channels 29
 further communicate with inlet ports 30 which are provided in the flywheel
 3 to admit coolant into the channels. Additional coolant can enter the
 open radially inner ends of the channels 29. Cooling of the apparatus 1 in
 the region of the cheek 23 is desirable and advantageous because the
 secondary flywheel 3 is apt to be heated to an elevated temperature in
 response to repeated engagement and disengagement of the friction clutch
 as well as when the clutch is only partially engaged so that the
 aforementioned friction linings of the clutch disc slip along the friction
 surface 9. Additional ports 31 are provided in the radial wall of the
 primary flywheel 2 to afford access to the adjacent portions of the rivets
 24 as well as to admit additional coolant (atmospheric air) into the
 adjacent portions of the channels 29 or to permit the flow of heated air
 in the opposite direction. The directions of circulation of coolant in the
 apparatus 1 are shown in FIG. 2 by non-referenced arrows.
 The locations (32) where the radially outermost portion of the flange 20 is
 affixed to the primary flywheel 2 are adjacent the radially outermost
 portion of the radial wall of the primary flywheel. The means for
 connecting the flange 20 to the flywheel 2 comprises rivets 33 which are
 located radially outwardly of the rivets 24. The heads at the right-hand
 axial ends of the rivets 33 (as viewed in FIG. 2) are confined in
 complementary recesses 34 of the flange 20; this contributes to a
 reduction of the axial length of the apparatus 1.
 The sequence of steps involving the assembly of the apparatus 1 is
 preferably as follows: The first step involves the application of rivets
 33 at 32, i.e., the establishment of a rigid torque-transmitting
 connection between the primary flywheel 2 and the flange 20 of the damper
 8. The next step involves the establishment of rigid connections (at 28)
 between the cheek 23 and the secondary flywheel 3, i.e., the application
 of the rivets 24. Such operation is facilitated due to the provision of
 ports 31 in the primary flywheel 2.
 FIG. 1 shows that the aforementioned coolant-admitting ports 30 of the
 flywheel 3 are actually elongated straight tangentially extending openings
 in register with (i.e., at the same radial distance from the axis 5 as)
 the elongated straight coil springs 7 of the damper 8. It has been found
 that, under many circumstances, the utilization of a damper having five
 equidistant springs 7 is particularly advantageous, i.e., the
 energy-storing capacity of five coil springs is highly satisfactory for
 use in many types of power trains. Thus, by utilizing five coil springs 7,
 the maker of the apparatus 1 can ensure that the flywheels 2 and 3 can
 turn relative to each other through an angle which is sufficiently large
 to guarantee a highly satisfactory torsional damping action. In addition,
 the number (five) of the springs 7 is sufficiently small to ensure that
 the mounting of such springs in the elements 20, 21 of the damper 8 does
 not unduly affect the stability of the flange 20 and/or of the cheeks 22,
 23 even if these parts are not made of a material having a pronounced
 thickness or of a very expensive material which can stand pronounced
 deforming stresses when the apparatus 1 is called upon to transmit
 pronounced torques.
 FIG. 1 shows that those heads of the rivets 24 which are remote from the
 heads 27 extend into elongated arcuate slots 35 provided in the flange 20
 radially outwardly of the coil springs 7. These slots 35 extend along arcs
 (as seen in the circumferential direction of the flange 20) which equal or
 approximate the length of the ports 30. The extent of angular
 displacements of the flywheels 2 and 3 (i.e., of the input and output
 elements 20, 21) relative to each other is determined by the springs 7 as
 well as by the rivets 24. Thus, the flywheels 2, 3 can no longer turn
 relative to each other when the springs 7 are fully compressed so that the
 neighboring convolutions of each of these springs abut each other.
 Furthermore, the extent of angular displacement of the flywheels 2, 3
 relative to each other is limited by the selected length of the arcuate
 slots 35 (as seen in the circumferential direction of the flange 20, i.e.,
 each of the rivets 30 can be caused to move from the one end to the other
 end of the respective arcuate slot 35.
 The flange 20 is provided with tangentially extending cutouts or windows 36
 for portions of the coil springs 7. The radially inner portions of the
 windows 36 are open, i.e., such windows extend all the way into the
 radially innermost portion of the flange 20. Consequently, neighboring
 windows 36 are separated from each other by substantially radially
 extending arms or partitions 37. The radially innermost portion of the
 flange 20 extends close to the heads 19a of the fasteners 19, the same as
 the springs 7, i.e. (and as can be readily seen in each of FIGS. 1 and 2),
 each spring 7 is closely adjacent the nearest head 19a. This contributes
 to compactness of the apparatus 1 as seen in a direction radially of the
 axis 5.
 The cheeks 22, 23 of the output element 21 of the damper 8 are respectively
 provided with windows 38, 39 for those portions of the springs 7 which
 extend in the axial direction of the apparatus 1 beyond the respective
 sides of the flange 20. As can be seen in FIG. 1, the windows 38, 39 do
 not extend all the way to the radially innermost portions of the
 respective cheeks 22, 23; they are separated from such radially innermost
 portions by narrow circumferentially extending webs or strips 38a, 39a.
 The webs 38a, 39a contribute to the strength of the respective cheeks 22,
 23, i.e., relatively thin cheeks can stand the stresses which act upon the
 cheeks when the flywheels 2, 3 are caused to turn relative to each other
 whereby the flange 20 turns relative to the cheeks 22, 23 and/or vice
 versa. This causes the springs 7 to store energy or to store additional
 energy with attendant stressing of the parts 20, 22 and 23 in the
 circumferential direction of the flywheels.
 However, it is also possible to employ cheeks having windows 38, 39 which
 are open radially inwardly, i.e., toward the axis 5. Much depends upon the
 magnitude of the torque which is to be transmitted by the apparatus 1, on
 the thickness of the cheeks 22, 23 and/or upon the material of which the
 cheeks are made.
 The apparatus 1 further comprises a hysteretic damping device 40 which
 operates between the flywheels 2, 3 in parallel with the springs 7 of the
 damper 8. The illustrated hysteretic damping device 40 is a friction
 generating device which is disposed between the connecting means including
 the rivets 24 and the connecting means including the rivets 33, as seen in
 a direction radially of the axis 5. As seen in the direction of the axis
 5, the hysteretic damping device 40 is located between the flange 20 and
 the adjacent portion 41 of the aforementioned radially extending wall of
 the primary flywheel 2.
 The illustrated device 40 comprises a friction ring 44 surrounded by the
 adjacent ring-shaped portion 42 forming part of the primary flywheel 2 and
 having a narrow cylindrical surface 43 engaging the friction ring 44 to
 thus oppose rotation of the ring 44 and the primary flywheel relative to
 each other. The ring 44 can be replaced with an annulus of discrete
 radially onwardly extending tongues or shoes which bear upon the surface
 43. FIG. 2 clearly shows that the device 40 is actually recessed into that
 side of the primary flywheel 2 which faces toward the secondary flywheel
 3; this contributes to compactness of the apparatus 1 as measured in the
 direction of the common axis 5 of the two flywheels.
 The just mentioned shoes which can be utilized in lieu of the ring 44 can
 be located immediately adjacent each other, i.e., they can differ from the
 ring 44 only in that they are not of one piece with each other. However,
 it is also possible to replace the ring 44 with an annulus of discrete
 circumferentially spaced apart shoes which are separated from each other
 by relatively narrow or even wider gaps not unlike the teeth of a spur
 gear.
 An advantage of an annulus of discrete shoes (in lieu of the
 circumferentially complete ring 44) is that such shoes can bear upon the
 internal surface 43 of the primary flywheel 2 under the action of
 centrifugal force, i.e., with a force which varies in response to
 variations of the RPM of the flywheel 2. However, such desirable results
 can also be obtained by resorting to a split ring 44 or even by resorting
 to a circumferentially complete ring which is made of a material that
 permits at least some elastic radial expansion of the ring under the
 action of centrifugal force with attendant change in the frictional
 engagement between the one-piece ring 44 and the surface 43 in response to
 changes of the RPM of the flywheel 2.
 The illustrated one-piece ring 44 is acted upon by a resilient element 45,
 preferably a diaphragm spring, which reacts against the primary flywheel,
 as at 41, and bears upon the ring 44 to urge the latter against the flange
 20. In other words, the flywheel 2 and the flange 20 can turn relative to
 each other only by overcoming the frictional resistance of the ring 44
 which bears upon the flange under the action of the diaphragm spring 45
 and which also bears (or can bear) upon the internal surface 43 of the
 flywheel 2 under its own bias and/or under the action of centrifugal
 force.
 It is clear that the mounting of the ring 44 and spring 45 of the device 40
 can be such that the spring 45 reacts against the flange 20 and biases the
 ring 44 against the radial wall of the primary flywheel 2.
 In the apparatus 1 of FIGS. 1 and 2, the ring 44 of the hysteretic damping
 device 40 is coupled with play to the cheek 22. As can be best seen in
 FIG. 1, the radially outermost portion of the cheek 22 is provided with a
 set of projections 46 which are spaced apart from each other in the
 circumferential direction of the cheek and cooperate with suitable
 projections or protuberances 47 of the friction ring 44. The distances
 between neighboring protuberances 47 (as seen in the circumferential
 direction of the flywheel 2) and the widths of the projections 46 (again
 as measured in the circumferental direction of the flywheel 2) are
 selected in such a way that the parts 22, 44 can turn relative to each
 other through relatively small angles corresponding to the clearances 48.
 An advantage of such dimensioning and distribution of the projections 46
 and protuberances 47 is that the device 40 is ineffective when the
 flywheel 2 changes the direction of its rotation relative to the flywheel
 3 and/or vice versa. It can be said that the device 40 generates a delayed
 friction whenever one of the flywheels 2, 3 is caused to change the
 direction of rotation relative to the other flywheel.
 FIG. 1 shows that each of the two cheeks 22, 23 is provided with an annulus
 of projections 46. However, the projections 46 of the cheek 23 are not
 used; they are provided only because the two cheeks are identical in order
 to reduce the overall cost of the apparatus. The cheeks 22, 23 are mirror
 images of each other with reference to a plane which is perpendicular to
 the axis 5 and includes the flange 20.
 If the structure which is shown in FIG. 2 is assembled into a module at the
 manufacturing plant (in order to shorten the time which is required to
 install the apparatus 1 in a power train at the automobile assembly
 plant), it is preferred to install the fasteners 19 in the module in such
 a way that they cannot be lost or misplaced. This can be readily achieved
 by dimensioning and shaping the heads 19a in such a way that the shanks of
 the fasteners 19 can be inserted into and can pass through the holes
 provided therefor in the radially extending wall of the flywheel 2 but
 that the shanks cannot be withdrawn from such holes once the flywheels 2,
 3 and the elements 20, 21 of the damper 8 are properly connected to each
 other. FIGS. 1 and 2 show holes 49 which are provided in the radially
 inner portion of the secondary flywheel 3 in order to afford access to the
 heads 19a when the apparatus 1 is to be attached to the rotary output
 component of an engine in an automobile assembly plant.
 In the apparatus 1 of FIGS. 1 and 2, the cheeks 22, 23 of the output
 element 21 of the damper 8 are secured to the secondary flywheel 3, and
 the input element (flange) 20 of the damper is affixed to the primary
 flywheel 2. However, it will be readily appreciated that the mode of
 operation of the apparatus 1 is not changed if the functions of the flange
 20 and the cheeks 22, 23 are reversed, i.e., if the cheeks are affixed to
 the primary flywheel 2 to constitute the input element of the damper and
 the flange is affixed to the secondary flywheel 3 to constitute the output
 element of the thus modified damper.
 It is equally possible to modify the apparatus 1 by mounting the rivets 33
 radially inwardly of the rivets 24; such modification is preferably
 accompanied by the utilization of two cheeks at least one of which extends
 radially outwardly beyond the flange; the outer diameter of the flange in
 the thus modified apparatus can be reduced. The slots 35 are then provided
 in at least one of the cheeks radially outwardly of the flange in order to
 provide room for angular movements of the input element (including the
 modified cheeks) and the output element (including the modified flange)
 relative to each other.
 It is further possible to modify the apparatus 1 in such a way that the
 rivets 24 and 33 (or their equivalents) are installed at the same radial
 distance from the axis 5. It is then necessary to install the displaced
 rivets 24 and 33 in such a way that they alternate with each other as seen
 in the circumferential direction of the flywheels. Furthermore, it is then
 advisable to provide the cheeks and the flange with radially outwardly
 projecting arms, lugs or analogous extensions and to install the rivets
 24, 33 or their equivalents in the region of such extensions. The
 positions of the extensions on the cheeks on the one hand and on the
 flange on the other hand must be such that the thus modified input and
 output elements of the damper are capable of turning relative to each
 other through angles which are required to take advantage of the ability
 of the energy storing devices 7 to permit a desired angular displacement
 of the two flywheels relative to each other.
 FIGS. 1 and 2 show that the locations (at 10, 11 and 12) where the
 secondary flywheel 3 can be connected with the housing of a friction
 clutch (such as the friction clutch 151 of FIG. 3) are located radially
 outwardly of the connecting means including the rivets 28 and 33.
 An important advantage of the apparatus 1 is that its space requirements in
 the direction of the axis 5 as well as at right angles to such direction
 are surprisingly small. As concerns the savings in space in a direction
 radially of the axis 5, they are attributable to several of the
 aforedescribed features regarding the distribution of various constituents
 of the apparatus. Thus, the bearing 6 of the centering means 4 is located
 radially inwardly of the annulus of fasteners 19 which serve to secure the
 primary flywheel 2 to the output component of a prime mover. Furthermore,
 the diameter of the bearing 6 is relatively small, and the heads 19a of
 the fasteners 19 are closely or immediately adjacent the outer race of the
 bearing 6. The placing of the two sets of rivets 24, 33 radially outwardly
 of the springs 7 also contributes to appreciable savings in space (as seen
 radially of the axis 5). Still further, the location for the hysteretic
 damping device 40 is also selected in such a way that it necessitates
 little (if any) additional space in the direction of as well as at right
 angles to the axis 5. This is achieved in that the device 40 is mounted
 radially inwardly of the rivets 33 and radially outwardly of the rivets 24
 as well as in the aforementioned annular recess 42 of the primary flywheel
 2.
 Another advantage of the apparatus 1 is that the aforediscussed mounting of
 the device 40 with a large diameter renders it possible to generate a very
 pronounced frictional hysteresis without pronounced wear upon its
 component parts. The wear is low because the specific surface pressure and
 strain are relatively low due to the large diameter of the device 40. At
 any rate, such pressure and strain can be readily maintained within an
 acceptable range.
 Referring to FIG. 3, there is shown a portion of a modified torsional
 vibration damping apparatus 101 having an input member including a primary
 flywheel 102 and an output member including a secondary flywheel 103. The
 two flywheels are rotatable with and relative to each other about a common
 axis (indicated by a dot-dash line) and are centered relative to each
 other by a centering means 104 including a combined radial and axial
 (thrust) bearing 106 including a cylindrical sleeve 106a one end portion
 of which is connected with and surrounded by a radially outwardly
 extending collar 106b. The sleeve 106a centers the adjacent portions of
 the bearings 102, 103 relative to each other in the radial direction of
 the common axis, and the collar 106b serves as a means for preventing
 axial movements of the flywheels relative to one another.
 In FIG. 3, the collar 106b is of one piece with the sleeve 106a. However,
 it is equally possible to make the collar 106b as a separate part which is
 thereafter properly affixed to the sleeve 106a. In fact, it is equally
 possible to install the collar 106b (or an equivalent of this collar) at a
 location which is remote from the sleeve 106a, i.e., the centering means
 104 can include discrete radial and axial bearings.
 Still further, it is possible to install the 106a at a first radial
 distance and to install a discrete collar 106b at a different second
 radial distance from the common axis of the flywheels 102, 103. For
 example, the collar 106b can be installed between two parts one of which
 is affixed to the flywheel 102 and the other of which is affixed to the
 flywheel 103; these parts are designed to hold the collar 106b between
 them in such a way that the two flywheels are fixed in desired axial
 positions relative to each other.
 The means for yieldably opposing at least some angular movements of the
 flywheels 102, 103 relative to each other comprises a damper 108. The
 damper 108 of FIG. 3 is similar to the damper 8 of FIG. 2; it comprises an
 input element 120 constituted by a flange having a radially outer portion
 connected to the flywheel 102 by rivets 133 so that the parts 102, 120
 share all angular movements, and an output element 121 having two annular
 parts or cheeks 122, 123 nonrotatably affixed to the secondary flywheel
 103. Rivets 124, which extend through arcuate slots of the flange 120,
 serve to non-rotatably connect the cheeks 122, 123 to each other for
 limited angular movement relative to the input element (flange) 120. In
 contrast to the rivets 24 in the apparatus 1 of FIGS. 1-2 (these rivets
 secure the cheeks 22, 23 to each other and to the secondary flywheel 3),
 the rivets 124 merely connect the cheeks 122, 123 for joint rotation about
 the axis of the flywheels 102, 103, and a discrete fastener means 111a
 (e.g., one or more screws, bolts or bolts and nuts) is employed to
 non-rotatably affix the cheek 123 to the secondary flywheel 103 as well as
 to the housing 169 of the aforementioned friction clutch 151. Actually,
 the fastener means 111a serves to connect the secondary flywheel 102 and
 the cheek 123 with a module 150 which includes the friction clutch 151. It
 will be noted that the connecting means including the rivets 124 is
 located radially inwardly of the connecting means including the rivets 133
 as well as radially inwardly of the connecting means including the
 fastener means 111a. The radial distance of the rivets 133 from the common
 axis of the flywheels 102, 103 equals or approximates the radial distance
 of the fastener means 111a from such axis.
 The cheek 123 is provided with pocket-shaped recesses 139 for portions of
 energy storing devices 107 forming part of the damper 108 and constituted
 by coil springs only one of which can be seen in FIG. 3. The pockets 139
 extend in the axial direction as well as circumferentially of the
 flywheels 102, 103 and serve as retainers for or as a means for stressing
 the respective coil springs 107. In addition, the pockets 139 are
 preferably configurated in such a way that they contribute to rigidity and
 stability of the cheek 123. Such reinforcement or stiffening of the cheek
 123 enables the latter to actually carry the entire module 150. This
 module can be said to include the secondary flywheel 103, the friction
 clutch 151 and the clutch disc 168 (if the latter is considered a discrete
 component, i.e., not as a constituent of the friction clutch 151).
 The radially inner portion of the cheek 123 includes a tubular extension
 152 having a cylindrical internal surface 153 which surrounds the
 aforementioned sleeve 106a of the bearing 106 forming part of the
 centering means 104 for the flywheels 102 and 103. The extension 152 can
 be fixedly secured to or can slide relative to the sleeve 106a. The
 radially extending collar 106b of the bearing 106 is installed between a
 radially extending annular end face 154 of the sleeve-like extension 152
 of the cheek 123 and a radially extending portion 155 of the part 117
 corresponding to the part 17 in the apparatus 1 of FIGS. 1 and 2.
 The tubular extension 152 is a separately produced part 156 having a
 substantially L-shaped cross-sectional outline and including a radially
 outwardly extending annular washer-like portion 157 affixed to the
 radially innermost portion of the cheek 123 by rivets 158. The illustrated
 rivets 158 constitute suitably deformed parts of the washer-like portion
 157 and are reliably anchored in the adjacent portions of the cheek 123.
 The rivets 158 can be replaced by or utilized jointly with other types of
 connecting means; for example, the separately produced part 156 can be
 welded to the cheek 123.
 The primary flywheel 102 includes a radially extending wall 160 which can
 be made of a suitable metallic sheet material and the radially inner
 portion of which is connected to the separately produced part 117, e.g.,
 by the fasteners (one shown but not referenced) corresponding to the
 fasteners 19 of FIG. 2 and serving to connect the primary flywheel 102
 with the rotary output component of a prime mover. The radially outermost
 portion of the wall 160 is of one piece with an axially extending annular
 radially outermost portion 161 of the primary flywheel 102.
 The radially outer part of the wall 160 is offset relative to the radially
 inner part of such wall (as shown at 142) to provide room for a hysteretic
 damping device 140 which is or which can be identical with the device 40
 in the apparatus 1 of FIGS. 1 and 2.
 The annular radially outermost portion 161 of the primary flywheel 102
 surrounds the module 150. A portion of such module can extend axially
 beyond the open side of the annular portion 161, i.e., in a direction
 axially of the flywheel 102, away from the radial wall 160 and out of the
 annular portion 161.
 The inertia of the flywheel 102 can be increased by providing it with one
 or more auxiliary masses or flywheels. FIG. 3 shows a first auxiliary mass
 162 which surrounds the portion 161 of the flywheel 102 and includes two
 cylindrical or substantially cylindrical layers 162a, 162b the former of
 which surrounds the latter. The auxiliary mass 162 can constitute an
 originally cylindrical sheet metal blank which has undergone a suitable
 deforming treatment, namely a folding of one of its halves over the other
 half to thus form the layers 162a and 162b. The thus obtained auxiliary
 mass 162 is slipped onto the annular portion 161 and is reliably secured
 thereto, e.g., by welding or by deforming certain neighboring parts of the
 portion 161 and layers 162a, 162b to thus hold the three annular layers of
 the resulting multiple-layer part against axial and/or angular movement
 relative to each other. Such operations can be carried out in a suitable
 sheet metal forming and upsetting machine.
 In accordance with a feature of the invention which is embodied in the
 apparatus 101 of FIG. 3, the radially inner layer 162b of the auxiliary
 mass 162 is provided with suitably configurated, dimensioned and
 distributed engine management indicia 164 which can be monitored to
 generate signals serving to ensure proper timing of certain operations of
 the engine in the power train of a motor vehicle, e.g., to guarantee an
 optimum timing of fuel ignition and/or an optimum timing of fuel injection
 into the cylinders of the engine. The indicia 164 can be of one piece with
 the auxiliary mass 162, or they can be affixed to one of its layers 162a,
 162b.
 A second multiple-layer auxiliary mass 163 is affixed to the outer side of
 the radially outer portion of the radial wall 160 of the primary flywheel
 102. The mass 163 is a composite washer including two layers 163a, 163b
 which overlie each other as seen in the axial direction of the primary
 flywheel 102. This mass can also constitute a converted single-layer
 washer-like sheet metal blank which has undergone an appropriate deforming
 treatment. A narrower third layer 163c of the auxiliary mass 163 overlies
 a portion of the exposed side of the layer 163b. The intermediate layer
 163b fully overlaps the two outer layers 163a and 163c. It is clear that
 the number of layers in the auxiliary mass 162 and/or 163 can be increased
 or reduced without departing from the spirit of the invention.
 The radially outermost portions of the layers 163a, 163b together define a
 starter gear 113 which is of one piece with the auxiliary mass 163. It is
 often advisable to subject at least those portions of the layers 163a,
 163b which constitute and which are adjacent the starter gear 113 to a
 suitable hardening treatment. Alternatively, the entire auxiliary mass 162
 and/or 163 can be subjected to a suitable hardening treatment, e.g.,
 induction hardening.
 The means for connecting the auxiliary mass 163 to the primary flywheel 102
 includes the rivets 133 which further serve to affix the radially outer
 portion of the flange 120 to the radially extending wall 160 of the
 primary flywheel radially outwardly of the hysteretic damping device 140.
 However, it is also possible to connect the mass 163 to the flywheel 102
 by means other than the rivets 133.
 In contrast to the construction of the apparatus 1, that portion (103a) of
 the secondary flywheel 103 which is provided with the friction surface 109
 is not directly centered to the bearing 106 but rather by way of the cheek
 123 of the output element 12 of the damper 108.
 The separately produced part 156 can be omitted if the radially inner
 portion of the cheek 123 is provided with a cylindrical portion
 corresponding to the axial extension 152. Analogously, one can dispense
 with the separately produced part 117 of FIG. 3 if the radially innermost
 part 159 of the wall 160 of the primary flywheel 102 is made of one piece
 with the portion 115 which is surrounded by the cylindrical sleeve 106a of
 the bearing 106.
 FIG. 4 shows a portion of an apparatus which constitutes a slight
 modification of the apparatus 101 of FIG. 3. The construction of the
 module 150 and of the clutch 151 is practically identical to that of the
 similarly referenced parts in the apparatus 101 except that the housing
 169 of the clutch 151 shown in FIG. 4 is affixed to the portion 103a of
 the secondary flywheel 103 in a somewhat different way. Thus, and whereas
 the heads of the fasteners 111a shown in FIG. 3 are accessible at the
 periphery of the axially movable pressure plate 166, the heads of the
 fasteners 165 performing the same function in the apparatus employing the
 structure of FIG. 4 are accessible at that side of the portion 103a of the
 secondary flywheel which confronts the primary flywheel (not shown in FIG.
 4). As already mentioned hereinbefore, the module 150 of FIG. 4 comprises
 the portion 103a of the secondary flywheel, the clutch 151, and the clutch
 disc 168 with friction linings 167 located between the friction surface of
 the portion 103a and the pressure plate 166. The inner side of the housing
 169 in the friction clutch 151 of FIG. 4 tiltably supports the
 circumferentially complete radially outer portion of a clutch spring 170
 (such as a diaphragm spring) which serves to bias the friction linings 167
 of the clutch disc 168 against the portion 103a of the secondary flywheel
 when the clutch 151 is engaged. The clutch 151 is disengaged, either
 entirely or in part, by pushing the radially inwardly extending prongs of
 the clutch spring 170 axially in a direction toward the primary flywheel.
 In the damping apparatus 101 of FIG. 3, the cheek 123 forms part of the
 module 150 because the radially outermost portion of this cheek is affixed
 to the portion 103a of the secondary flywheel 103 by the fasteners 111a
 with heads accessible at the clutch side of the portion 103a.
 The fasteners 165 for the module 150 of FIG. 4 can further serve as a means
 for centering the clutch housing 169 relative to the portion 103a of the
 secondary flywheel. To this end, the fasteners 165 preferably constitute
 so-called dowel screws or close tolerance screws with smooth cylindrical
 shank portions in addition to the customary externally threaded shank
 portions. The cylindrical shank portions are preferably adjacent the heads
 of the fasteners 165 and are a close fit in the complementary holes or
 bores of the portion 103a.
 Alternatively, the fasteners 165 of the type shown in FIG. 4 can be
 replaced with standard screws; however, it is then advisable to employ one
 or more suitable dowel pins or other alignment pins (one shown in FIG. 4a,
 as at 165a) to ensure that the housing 169 is properly centered on the
 portion 103a of the secondary flywheel.
 The pressure plate 166 in the friction clutch 151 of FIG. 3 has suitably
 configurated recesses, grooves or sockets 166a for the heads of the
 fasteners 111a. This renders it possible to install such fasteners very
 close to the common axis of the flywheels 102 and 103, i.e., to render the
 apparatus 101 more compact as seen in the radial direction of the common
 axis. The pressure plate 166 in the friction clutch 151 of FIG. 4 has
 similar recesses 166b which render it possible to install the fasteners
 165 immediately radially outwardly of the friction linings 167 of the
 pressure plate 168.
 The torsional vibration damping apparatus 201 of FIG. 5 exhibits certain
 features of the apparatus 1 of FIGS. 1-2 as well as certain features of
 the apparatus 101 of FIG. 3. It comprises an antifriction ball or roller
 bearing 206 which forms part of the centering means 204 and has an inner
 race surrounding the cylindrical portion of the part 215 carried by the
 radially innermost portion of the radially extending wall of the primary
 flywheel 202. The rivets 224 perform the function of rivets 24 in the
 apparatus 1 and further serve to secure the portion 203a of the secondary
 flywheel 203 to the output element 221 of the damper operating between the
 input and output members of the apparatus 201 and including coil springs
 (one shown but not referenced) or other suitable energy storing devices.
 The portion 203a of the secondary flywheel 203 is an annular body which is
 provided with a friction surface 209 for the adjacent friction linings of
 the clutch disc forming part of or cooperating with the friction clutch
 251. The difference between the rivets 224 of the type utilized in the
 apparatus 201 and the rivets 124 in the apparatus 101 of FIG. 3 is that
 the rivets 124 merely connect the cheeks 122, 123 of the output element
 121 of the damper 108 to each other; on the other hand, the rivet 224
 which is shown in FIG. 5 connects the two cheeks of the output element 221
 to each other and additionally serves to connect the cheek 223 (i.e., the
 output element 221) to the portion 203a of the secondary flywheel 203.
 The construction of the friction clutch 251 of FIG. 5 is analogous to that
 of the friction clutch 151 in the apparatus 101 of FIG. 3 except that the
 housing 269 of the clutch 251 is not directly connected to the cheek 223
 of the output element 221 of the damper in the apparatus 201 but rather to
 a separately produced part 270 which is clamped to the cheek 223. The part
 270 includes a radially outermost portion 271 with axially parallel bores
 or holes for the fasteners 211a (only one shown in FIG. 5), and a radially
 inwardly extending portion 272 located between the portion 203a of the
 secondary flywheel 203 and the radially outermost portion 223a of the
 cheek 223. The rivets 224 urge the portion 223a against the portion 272 so
 that the latter is clamped between the portion 203a of the flywheel 203
 and the cheek 223 of the output element 221 of the damper in the apparatus
 201 of FIG. 5. A satisfactory frictional engagement between the portion
 272 on the one hand and the portions 223a, 203a on the other hand can be
 achieved by resorting to an appropriate configuration, dimensioning and
 mounting of the rivets 224 and/or by making at least the radially
 outermost portion 223a of the cheek 223 and/or the separately produced
 part 270 of a suitable elastically deformable material. This ensures that
 the form-locking connection between the housing 269 of the clutch 251 and
 the output element 221 of the damper exhibits the required frictional
 resistance to rotation of its constituents relative to each other. In
 other words, the just described frictional form-locking connection
 normally prevents rotation of the part 270 and the flywheel portion 203a
 relative to each other; however, such connection can yield when the
 magnitude of the torque to be transmitted from the flywheel portion 203a
 to the clutch housing 269 exceeds a maximum permissible value.
 The clutch spring 273 (such as a diaphragm spring corresponding to the
 spring 170 in the clutch 151 of FIG. 3) is designed and installed to
 ensure that the clutch 251 can readily transmit torque having a desired
 (predetermined) magnitude. When the clutch 251 is engaged, the spring 273
 causes the pressure plate 266 to urge the friction linings of the clutch
 disc (not referenced in FIG. 5) against the friction surface of the
 flywheel portion 203a and the latter urges the portion 272 of the part 270
 against the portion 223a of the cheek 223. In other words, the clutch
 spring 273 can influence the form-locking connection between the portion
 272 on the one hand and the portions 223, 203a on the other hand (at least
 when the friction clutch 251 is engaged). However, the influence of the
 bias of the spring 273 upon the aforementioned form-locking connection is
 greatly reduced (or is nil) when the clutch 251 is disengaged (in that the
 spring 273 permits the pressure plate 266 to reduce the force with which
 the friction linings of the clutch disc are urged against the friction
 surface of the flywheel portion 203a, or the spring 273 even permits the
 pressure plate 266 to become disengaged from the adjacent friction
 linings.
 It follows from the above that the form-locking connection is stronger when
 the clutch 251 is engaged than when the clutch is disengaged because the
 bias of the spring 273 upon the parts 203a, 272 and 223a is much more
 pronounced when the friction clutch is engaged. FIG. 5 shows the position
 of the diaphragm spring 273 by solid lines when the friction clutch 251 is
 engaged, and by dotted lines when the clutch is disengaged.
 The force-locking connection between the parts 223a, 272, 203a can be
 selected in such a way that it can respond to fluctuations of torque when
 the clutch 251 is disengaged and that it can also respond to fluctuations
 of torque exceeding, for example, the nominal engine torque; at such
 times, the friction clutch 251 and the part 270 (which is affixed to the
 clutch 251) can slip relative to the portion 203a of the secondary
 flywheel 203.
 FIG. 6 illustrates a modified design of the means for centering the primary
 and secondary flywheels relative to each other. The centering means 304 of
 FIG. 6 comprises an antifriction ball bearing 306 having an inner race
 which surrounds the axially extending cylindrical portion 315 of a
 separately produced part (corresponding to the part 17 in the apparatus 1
 of FIGS. 1-2) which is affixed to the innermost portion of the radial wall
 of the primary flywheel by fasteners 319. The outer race 306b of the
 bearing 306 is surrounded by an axially extending cylindrical portion 352
 forming part of a discrete constituent 356 having an L-shaped
 cross-sectional outline. The radially extending portion or part 355 of the
 constituent 356 is affixed to the cheek 323 of the output element of the
 damper in the apparatus including the structure of FIG. 6 in a manner as
 already described with reference to the apparatus 101 of FIG. 3, namely by
 rivets 358. However, such riveted connection can be replaced by or used
 jointly with other suitable connection or connections; for example, the
 portion 355 can be welded to the cheek 323.
 It will be noted that the radially extending portion 355 of the separately
 produced constituent 356 is adjacent that side of the cheek 323 which
 confronts the fasteners 319. The radially innermost part of the cheek 323
 includes projections 323a in the form of lugs extending radially inwardly
 beyond the constituent 356 and serving as a means for centering the outer
 race 306b of the bearing 306. In other words, the projections 323a serve
 to center the secondary flywheel (which is connected to the output element
 including the cheek 323) relative to the primary flywheel carrying the
 portion 315. Radial centering of the secondary flywheel is effected by the
 cylindrical portion 352.
 The torsional vibration damping apparatus 401 including the structure shown
 in FIG. 7 comprises coaxial primary and secondary flywheels 402, 403
 adapted to rotate relative to each other against the opposition of a
 damper and about a common axis determined by a centering means including a
 journal bearing 406 of a type similar to that shown (at 106) in the
 apparatus 101 of FIG. 3.
 The primary flywheel 402 forms part of or constitutes the input member of
 the apparatus and includes a radially extending wall 459 having a radially
 innermost portion 460 separably secured to the output component of a prime
 mover by axially parallel threaded fasteners 419. The radially outermost
 portion of the wall 460 is of one piece with an annular portion 461, and
 the junction between the parts 460, 461 of the primary flywheel 402
 carries a starter gear 413 which is welded, soldered or otherwise affixed
 thereto.
 The parts 460, 461 are preferably made of a suitable metallic sheet
 material, and the radially outer portion of the wall 460 carries two
 auxiliary masses or auxiliary flywheels 462, 463. The mass 463 is located
 at the outer side of the wall 460 (i.e., it confronts the prime mover when
 the apparatus 401 is in use), and the mass 462 is located opposite the
 mass 463, i.e., it confronts the secondary flywheel 403. Rivets 433 are
 utilized to securely affix the auxiliary masses 462, 463 to the wall 460
 of the primary flywheel 402. The basic constituent (460-461) as well as
 the auxiliary masses 462, 463 of the primary flywheel 402 can be made of a
 suitable metallic sheet material by resorting to blanks which can be
 folded and/or otherwise deformed in available machinery and at a
 reasonable cost. At least those blanks which are converted into the
 auxiliary masses 462, 463 can constitute suitably configurated flat pieces
 of metallic sheet material.
 The mass 462 has a substantially L-shaped cross-sectional outline with a
 twin-layer radially inwardly extending leg 462a and an annular outer leg
 462b adapted to carry the aforediscussed engine management (and/or other)
 indicia (shown at 464). The illustrated leg 462b consists of a single
 layer of metallic sheet material and is surrounded by the annular portion
 461.
 The input element or flange 420 of the damper 408 is adjacent the inner
 side of the wall 460 and is affixed to the latter as well as to the layers
 of the leg 462a by the aforementioned rivets 433. Due to the just
 described mode of utilizing the rivets 433 to connect the flange 420 to
 the legs 462a and to the wall 460, there is established between the parts
 460, 420 and radially inwardly of the layer 462 an annular space which
 receives the hysteretic damping device 440 in such a way that the latter
 does not or need not appreciably contribute to the dimensions of the
 apparatus 401 as seen in the direction of the common axis of the flywheels
 402 and 403. The device 440 can be similar to or identical with the device
 40 in the apparatus 1 of FIGS. 1-2 or with the device 140 in the apparatus
 101 of FIG. 3.
 The friction clutch 451 is affixed to the cheek 423 and to the secondary
 flywheel 403 in a manner as described with reference to FIG. 3 and is
 located radially inwardly of the annular leg 462b of the auxiliary mass
 462, i.e., radially inwardly of the annular portion 461 of the main
 section 460, 461 of the primary flywheel 402.
 It will be noted that the axial sectional views shown in FIGS. 3 to 7 are
 angularly offset relative to each other. The same holds true for at least
 some of the sectional views shown in FIGS. 8 through 17. The reason is
 that such selection of the sectional views ensures adequate or best
 possible illustration of various features which distinguish the
 illustrated embodiments from each other. Reference may be had, for
 example, to the sectional views of the cheeks 123, 223, 323, 423, of the
 portions 155, 255, 355, 455 as well as of certain other parts in the
 illustrated and already described embodiments. The clutch disc is also
 shown in different sectional views (compare the discs 168 and 568 of FIGS.
 3 and 8). For example, different axial sectional views are deemed to be
 necessary (i.e., axial sectional views which are offset relative to each
 other) in order to ensure that the Figures show the openings provided in
 the clutch disc (note the non-referenced opening in the clutch disc 168 of
 FIGS. 3 and 4) and/or in the clutch spring (such as 170 or 273) in order
 to afford access to the fasteners (such as 19, 319, 419, etc.) by
 resorting to standard tools and/or to specially designed tools. In this
 connection, reference may be had to published German patent applications
 Serial Nos. 41 17 579, 41 17 582 and 41 17 571 the disclosures of which
 are incorporated herein by reference.
 The torsional vibrations damping apparatus 501 of FIG. 8 comprises a damper
 508 which is, or which can be, at least substantially identical with the
 damper 8 in the apparatus 1 of FIGS. 1 and 2. Furthermore, the centering
 means 504 (including the bearing 506) between the primary and secondary
 flywheels 502, 503 of the apparatus 501 is identical with or at least very
 similar to the centering means 4 of the apparatus 1. Rivets 533 are
 provided to non-rotatably connect the primary flywheel 502 with the input
 element (flange) 520 of the damper 508, and rivets 524 are employed to
 establish a non-rotatable connection between the cheeks (including the
 cheek 523) of the output element of the damper 508 and the secondary
 flywheel 503. The primary flywheel 502 is a converted blank of sheet metal
 (in contrast to the primary flywheel 2 which is a casting or a forging and
 is normally subjected to at least some material removing secondary
 treatment upon completion of the casting or forging operation).
 The portion 503a of the secondary flywheel 503 (this portion constitutes
 the main portion or part of the flywheel 503) has a radially innermost
 portion which surrounds and carries the outer race of the bearing 506; the
 latter constitutes an antifriction bearing with an annulus of spherical or
 other suitable rolling elements. The inner race of the bearing 506
 surrounds a cylindrical sleeve of the annular portion 515 which is affixed
 to the primary flywheel 502, at least when the flywheel 502 is properly
 affixed to the output component of the prime mover.
 The radially extending wall 560 of the primary flywheel 502 carries an
 auxiliary mass 562 which is secured thereto by axially parallel rivets
 533; these rivets further serve to connect the wall 560 with the flange
 520 and to thus provide room for the hysteretic damping device (not
 referenced) radially inwardly of the radially extending twin-layer leg
 562a of the auxiliary mass 562. The annular portion 562b of the mass 562
 also comprises two layers, and this mass is also assumed to constitute a
 converted blank of metallic sheet material or any other suitable sheet
 material (preferably a suitably deformed originally round blank). The
 outer layer of the annular portion 562b is surrounded and can be contacted
 by the annular portion 561 which is of one piece with the wall 560 and
 carries a (non-referenced) starter gear. The wall 560 and the annular
 portion 561 constitute the two constituents of the main part 559 of the
 primary flywheel 502. The annular portion 561 can be utilized as a means
 for centering the auxiliary mass 562 relative to the main part 559.
 It is often preferred to design and to select the dimensions of the annular
 portion 561 in such a way that its stability exceeds that of the annular
 portion 562b of the auxiliary mass 562. This is particularly desirable
 when the portion 562b exhibits a tendency to undergo deformation under the
 action of centrifugal force.
 The friction clutch 551 which is mounted on the secondary flywheel 503 is a
 so-called self-adjusting clutch which is designed to automatically
 compensate for wear on those parts which are most likely or particularly
 likely to undergo at least some wear in response to repeated engagement
 and disengagement of the clutch, especially when the clutch is operated
 with slip which entails pronounced wear upon the friction linings 567 of
 the clutch disc 568. The friction linings 567 are located between the
 annular friction surface of the portion 503a of the secondary flywheel 503
 and the axially movable pressure plate of the clutch 551. The latter
 further comprises a suitable housing 569 which is rotated by the secondary
 flywheel 503, and a clutch spring 573 (e.g., a diaphragm spring which is
 tiltable relative to the housing 569 and is automatically shifted toward
 the friction linings 567 at necessary intervals in order to compensate for
 wear, at least upon the friction linings). An important advantage of a
 self-adjusting clutch is that the force which is required to disengage the
 clutch is at least substantially constant during the entire useful life of
 the clutch.
 Self-adjusting clutches which can be utilized in the apparatus 501 of FIG.
 8 are disclosed, for example, in commonly owned U.S. Pat. No. 5,450,934
 granted Sep. 19, 1995 to Paul Maucher for "FRICTION CLUTCH". Reference may
 also be had to published German patent applications Serial Nos. 42 39 291,
 43 06 505, 42 39 289 and 43 22 677.
 The manner in which the friction clutch 551 is attached to the portion 503a
 of the secondary flywheel 503 is analogous to that described in connection
 with the clutch 251 and portion 203a of the secondary flywheel 203 shown
 in FIG. 5. Thus, the force-locking connection is designed in such a way
 that the friction clutch 551 can slip relative to the portion 503a of the
 secondary flywheel 503 at least when the clutch is disengaged (so that the
 bias of the clutch spring 573 upon the portion 503a and the radially
 outermost portion 523a of the cheek 523 is less pronounced) and while the
 magnitude of transmitted torque undergoes abrupt and pronounced changes.
 The just described force-locking connection between the friction clutch 551
 and the portion 503a the secondary flywheel 503 can be said to constitute
 a torque limiting device (identified by reference character 574) which
 includes an annular diaphragm-like resilient element 570 acting not unlike
 a diaphragm spring. When not installed in the apparatus 501, the resilient
 element 570 assumes a frustoconical shape similar to that of an unstressed
 diaphragm spring. The imaginary apex of the cone is located to the left of
 the resilient element 570 (as viewed in FIG. 8), i.e., the cone tapers
 toward the radial wall 560 of the primary flywheel 502. The element 570 is
 stressed and deformed to assume the shape which is shown in FIG. 8 in
 response to the application of the rivets 524, i.e., in response to
 attachment of the output element (including the cheek 523) to the portion
 503a of the secondary flywheel 503. When properly installed, the resilient
 element reacts against the radially outer part of the portion 503a and
 bears against the radially outer portion 523a of the cheek 523. The
 location (annular surface) where an intermediate portion of the resilient
 element 570 reacts against the portion 503a of the secondary flywheel 503
 is shown at 503b. The radially outermost portion of the resilient element
 570 is affixed to the housing 569 of the friction clutch 551 by screws or
 the like.
 The bias of the properly installed resilient element 570 is or can be
 selected in such a way that the properly stressed element 570 generates an
 axial force force greater than the maximum disengaging force which is
 being applied during the useful life of the friction clutch 551. This
 ensures that the clutch housing 569 cannot be shifted in the axial
 direction of the flywheels 502, 503 under the bias of the resilient
 element 570. The slip torque of the torque limiting device 574 including
 the resilient element 570 can be reduced if the axial force furnished by
 the resilient element 570 equals or rather closely approximates the
 maximum disengaging force which is required to operate the friction clutch
 551.
 The part 270 in the apparatus 201 of FIG. 5 can also constitute or resemble
 a frustoconical diaphragm spring which is deformed (flattened) when
 properly mounted in the apparatus 201.
 The apparatus 601 of FIG. 9 comprises coaxial primary and secondary
 flywheels 602, 603 which are centered relative to each other by a device
 604 including an antifriction bearing similar to or identical with the
 bearing 6 of FIG. 2 or the bearing 506 of FIG. 8. The primary flywheel 502
 comprises a main part 659 including a radially extending wall and an
 annular radially outer portion 661. The main part 659 is a converted
 originally flat blank having a rather pronounced thickness (e.g., in the
 range of 4-7 mm) and preferably consists of a suitable metallic sheet
 material. The outer portion 661 has two closely adjacent annular layers
 661a, 661b which can or do actually contact each other. However, it is
 equally possible to design the outer portion 661 in such a way that its
 layers 661a, 661b are at least partially spaced apart from each other as
 seen in the radial direction of the flywheel 602; for example, such layers
 can define an annular space having a predetermined width as measured
 radially of the common axis of the flywheels 602 and 603. It has been
 found that the just described annular portion 661 can contribute
 significantly to the inertia of the main part 559 and of the entire
 primary flywheel 602.
 The main part 659 of the flywheel 602 carries an auxiliary mass 663 having
 a substantially L-shaped cross-sectional outline. The mass 663 has a
 twin-layer annular radially outermost portion 663b which surrounds and
 extends axially beyond the annular portion 661 of the main part 659. The
 radially extending portion 663a is outwardly adjacent the radially outer
 portion of the radial wall of the main part 659 and is secured to the
 radial wall by a set of rivets 633 (only one can be seen in FIG. 9). The
 annular portion 661 can serve as a means for centering the auxiliary mass
 663 on the main part 659. The illustrated mass 663 also constitutes a
 converted (originally plane) blank of a suitable metallic sheet material
 and is configurated in such a way that only its annular portion 663b
 comprises several (two) layers. It is clear that, if desired or necessary
 (namely to further increase the inertia of the primary flywheel 602), the
 radial portion 663a of the auxiliary mass 663 can comprise two or more
 layers and/or the annular portion 663b can comprise more than two layers.
 The starter gear 613 is installed in a seat 663c at the junction of the
 portions or legs 663a, 663b of the auxiliary mass 663.
 The rivets 633 serve to secure the auxiliary mass 663 to the main part 659
 of the primary flywheel 602 as well as to connect the primary flywheel
 with the cheeks 622, 623 of the input element 620 of the damper 608
 including the energy storing devices 607 (only one shown in FIG. 9). It
 will be noted that, in the apparatus 601, the cheeks 622, 623 form part of
 the input element 620 and the flange 621 forms part of or constitutes the
 output element of the damper 608. The flange 621 forms part of a
 frictional connection 674 which serves to normally transmit torque from
 the cheeks 622, 623 (via energy storing devices 607) to the secondary
 flywheel 603 of the apparatus 601.
 The cheek 623 is provided with several pockets or recesses 624 which are
 spaced apart from each other in the circumferential direction of the
 flywheels 602, 603. The recesses or pockets 624 extend axially away from a
 front surface 624a which abuts the cheek 622. The rivets 633 are adjacent
 the pockets 624, and such pockets can be said to constitute distancing
 elements which maintain the cheeks 622, 623 at a desired axial distance
 from each other. The pockets 624 extend through cutouts or windows 635
 which are provided in the flange 621 of the damper 608; this enables the
 pockets to contact the cheek 622 since the cheeks 622, 623 are installed
 at opposite sides of the flange 621 (output element) of the damper 608.
 The pockets or recesses 624 serve to cause the energy storing devices 607
 to store energy (or to store additional energy) when the flywheels 602,
 603 and the input and output elements of the damper 608 are caused to turn
 relative to each other. The cutouts or windows 635 further serve as a
 means for limiting the extent of angular displacement of the flywheels
 602, 603 relative to each other, i.e., each pocket 624 can move from
 abutment with the surface at one end to abutment with the surface at the
 other end of the respective window 635 (as seen in the circumferential
 direction of the flywheels 602 and 603). Thus, the means for limiting the
 extent of angular displacements of the flywheels 602, 603 relative to each
 other is clearly analogous to the corresponding means 24 and 35 in the
 apparatus 1 of FIGS. 1 and 2.
 The cheeks 622, 623 and the flange 621 are provided with at least partially
 overlapping cutouts for portions of the energy storing devices 607; the
 surfaces bounding such cutouts ensure that the devices 607 store
 additional energy or dissipate at least some energy when the cheeks 622,
 623 are caused to turn relative to the flange 621 and/or vice versa.
 The apparatus 601 further comprises a torque limiting device 674 which
 operates between the flange (output element) 621 of the damper 608 and the
 secondary flywheel 603. Furthermore, the device 674 serves to limit the
 magnitude of the torque which can be transmitted from the flange 621 to a
 friction clutch if such clutch is mounted on the secondary flywheel 603.
 The illustrated torque limiting device 674 is a multistage (in the
 apparatus 601 a two-stage) slip clutch. The two stages 674a and 674b are
 set up to operate in parallel with each other and the stage 674b is
 installed radially outwardly of the stage 674a.
 The stage 674a comprises an energy storing element 675 which constitutes a
 diaphragm spring and has a radially outermost portion abutting a cupped
 member 676 mounted on the secondary flywheel 603 in such a way that it
 cannot move relative to the flywheel 603 in the direction of the common
 axis of the two flywheels. Alternatively, the cupped member 676 can be
 affixed to the housing of a friction clutch while such clutch is being
 assembled with the secondary flywheel 603. It is desirable to ensure that
 the diaphragm spring 675 is held against rotation relative to the member
 676; this is achieved by providing the radially outermost portion of the
 element 675 with teeth 677 mating with complementary teeth on the adjacent
 portion of the cupped member 676. In other words, the first stage 674a
 comprises a form-locking connection 677 between the parts 675 and 676.
 The energy storing element 675 bears upon the radially outermost portion
 621a of the flange (output element) 621 of the damper 608 so that the
 flange 621 is frictionally held between the secondary flywheel 603 and the
 energy storing element 675. The just described parts 603, 621, 675 of the
 first stage 674a can directly abut each other; however, it is equally
 possible (and often desirable) to insert a friction lining or another
 friction generating device between at least two of these parts or to coat
 at least one side of at least one of the parts 603, 621, 675 with a layer
 of suitable friction generating material. For example, it is often
 advisable to phosphatize that side of the energy storing element 675 which
 abuts the flange 621, to phosphatize that side of the flange 621 which
 abuts the element 675 and/or to phosphatize that side of the flange 621
 which abuts the flywheel 603 and/or to phosphatize that side of the
 flywheel 603 which abuts the flange 621.
 The radially outer second stage 674b of the torque limiting device 674 also
 comprises an energy storing element 678 (such as a diaphragm spring) which
 is stressed axially of the flywheels 602, 603 between the portion 676a of
 the cupped member 676 and the portion 603a of the secondary flywheel. A
 friction generating lining is provided at each side of the energy storing
 element 678, i.e., adjacent the portion 676a of the cupped member 676 and
 adjacent the portion 603a of the secondary flywheel 603. However, such
 friction generating means are optional at least under certain
 circumstances; furthermore, they can be replaced by other types of
 friction generating means, such as a suitable friction generating coating
 on at least one of each pair of abutting surfaces in the stage 674b.
 Phosphatizing or the application of hard nickel coatings are but two of
 presently favored undertakings to ensure a desirable frictional engagement
 between the constituents of the stage 674b.
 A driving or motion transmitting connection 679 is provided between the
 stages 674a and 674b. The illustrated driving connection comprises mating
 gears including first teeth at the radially inner portion of the energy
 storing element 678 and second teeth at the radially outer portion of the
 flange 621. The two sets of teeth mesh with a certain amount of play in
 such a way that the radially inner stage 674a can act alone while the
 flywheels 602, 603 turn relative to each other through a selected angle.
 This selected angle is preferably not less than 10.degree. but can also
 greatly exceed 10.degree. (for example, it can equal or approximate or
 even exceed 20.degree.). However, it is also possible (and under certain
 circumstances desirable and advantageous) to select an angle which is less
 than 10.degree..
 FIG. 9 shows the cupped member 676 in that axial position in which the
 elements (such as diaphragm springs) 675 and 678 are caused to store
 desired or selected amounts of energy.
 The cupped member 676 can be installed in the apparatus 601 during
 attachment of a friction clutch (not shown in FIG. 9) to the secondary
 flywheel 603, and such operation involves attachment of the member 676 to
 the housing of the friction clutch. To this end, the member 676 can be
 designed and installed in such a way that it is movable in the axial
 direction of the flywheels 602, 603 prior to attachment of a friction
 clutch to the flywheel 603, i.e., such mounting of the friction clutch on
 the flywheel 603 automatically results in requisite axial positioning of
 the member 676. The energy storing elements 675 and 678 are free to move
 the member 676 in a direction to the left of the position shown in FIG. 9
 before the clutch is affixed to the secondary flywheel 603; such shifting
 of the member 676 to the left of the position which is shown in FIG. 9 is
 possible because the energy storing elements 675 and 678 store little or
 no energy prior to mounting of the friction clutch on the flywheel 603 but
 are caused to store energy by undergoing at least some stressing in the
 axial direction of the flywheels during attachment of the friction clutch.
 The unstressed energy storing elements 675 and 678 (which are assumed to
 constitute diaphragm springs) exhibit a conicity which is much more
 pronounced when they are permitted to dissipate stored energy or prior to
 undergoing axial stressing, such as in response to attachment of a
 friction clutch to the secondary flywheel 603. The imaginary apices of
 such conical energy storing elements 675, 678 are located to the right of
 their radially outermost portions, as viewed in FIG. 9. Such design and
 mounting of the elements 675, 678 ensure that, once the friction clutch is
 detached from the secondary flywheel 603, the latter can be turned
 relative to the primary flywheel 602 without any resistance or with a
 minimum of resistance. Such angular displacement of the secondary flywheel
 603 renders it possible to place its opening 649 into requisite positions
 of axial alignment with the fasteners 619, e.g., for the purpose of
 ensuring that the heads of the fasteners 619 can be reached and properly
 engaged by the working end of a suitable tool (not shown). This greatly
 simplifies the task of replacing a damaged apparatus 601 with a new one or
 of temporarily detaching the apparatus 601 from the output component of a
 prime mover for the purpose of inspection and/or maintenance and/or repair
 work.
 The slip torque of at least one of the stages 674a, 674b of the multistage
 torque limiting device 674 can be less than the nominal torque of the
 prime mover serving to rotate the primary flywheel 602. Nevertheless, the
 sum of torques which can be transmitted by the two stages can ensure a
 slip-free transmission of torque which is being supplied by the output
 component of the prime mover.
 The aforediscussed convenient turning of the secondary flywheel 603
 relative to the primary flywheel 602, particularly to gain access to the
 heads of the fasteners 619 by way of the openings 649, is especially
 important and desirable when the construction of the apparatus 601 is such
 that the heads of the fasteners 619 can be reached only from one axial end
 of the apparatus, such as in a direction from the right to the left as
 viewed in FIG. 9.
 The damper 608 of the apparatus 601 can also comprise five equidistant
 energy storing devices 607, such as coil springs. In addition to the
 previously discussed advantages of a damper employing five energy storing
 devices, such damper exhibits the advantage that the relatively small
 number of devices 607 can be installed close to the common axis of the
 flywheels 602, 603, i.e., close to the centering means 604. This renders
 it possible to reduce the diameter of the apparatus 601. It is presently
 preferred to install the centering means 604 radialy inwardly of the
 annulus of (preferably five) energy storing devices 607.
 The apparatus 701 of FIG. 10 comprises an input member including a primary
 flywheel 702, an output member including a secondary flywheel 703, a
 damper 708 which opposes angular movements of the flywheels 702, 703
 relative to each other and includes energy storing devices 707 in the form
 of coil springs, and a centering unit 704 including a bearing 706
 corresponding to or identical with the bearing 106 of FIG. 3 or the
 bearing 406 of FIG. 7. The bearing 706 can be replaced with an
 antifriction roller bearing corresponding to the bearing of the centering
 means 604 shown in FIG. 9, or the centering means 604 can utilize a
 bearing corresponding to the bearing 706.
 The bearing 706 comprises a first sleeve 706a and a second sleeve 706b
 which surrounds the sleeve 706a (these parts correspond to the components
 106a, 106b of the bearing 106 in the apparatus 101 of FIG. 3). The sleeve
 706 surrounds the axial extension 715 of the primary flywheel 702. For
 example, the sleeve 706a can be a press fit on the extension 715 or it can
 be fixedly secured to the extension 715 in any other suitable way (e.g.,
 by resorting to one or more threaded or other suitable fasteners). For
 example, the free end of the portion 715a can be calked or upset in a
 manner to ensure that the sleeve 706a is reliably maintained in a desired
 position. It is also possible to employ a prefabricated unit including the
 sleeves 706a, 706b, with the sleeve 706a already fitted into the sleeve
 706b at the bearing manufacturing plant. The just outlined procedure is
 desirable in many instances because, if the sleeves 706a, 706b are
 properly assembled at the bearing manufacturing plant, the axially
 extending part 715a of the portion 715 need not undergo a high-precision
 treatment such as grinding, turning or the like. It then suffices to
 produce or shape the portion 715a in a deep drawing machine and to subject
 (if necessary) the deep drawn part to a calibrating treatment.
 The construction of the damper 708 (which operates between the flywheels
 702 and 703) is analogous to that of the damper 108 of FIG. 3 or the
 damper which is shown in FIG. 5. A difference is that the radially outer
 portions of the cheeks 722, 723 are cupped radially outwardly of the
 energy storing devices 707 and abut each other, either entirely or in
 part. The abutting portions 722a, 723a of the cheeks 722 and 723 are
 affixed to the secondary flywheel 703 by rivets 724. The cheek 722 is
 provided with recesses or pockets 722b which are adjacent the rivets 724
 and extend axially of the apparatus 701 through openings 720a which are
 provided in the input element (flange) 720 of the damper 708. The output
 element 721 of the damper 708 includes the cheeks 722 and 723. The
 dimensions of the opening 720a and of the pockets 722b are selected in
 such a way that they permit the input and output elements 720, 721 of the
 damper 708 to perform the required angular movements relative to each
 other. Reference may be had to the description of cooperation between the
 rivets 24 and the corresponding openings 35 in the apparatus 1 of FIGS. 1
 and 2.
 The configuration of the main part 759 of the primary flywheel 702 is
 analogous to that of the primary part 659 of the primary flywheel 602 in
 the apparatus 601 of FIG. 9. The configuration of the annular portion 761
 is somewhat different from that of the annular portion 661 because the
 auxiliary mass 762 of the primary flywheel 702 is disposed in part within
 the annular portion 761. The axially extending annular portion 762a of the
 auxiliary mass 762 projects beyond the annular portion 761 and carries a
 starter gear 713. Such starter gear can be utilized jointly with or can be
 replaced by suitable engine management indicia 713a. Such indicia can form
 a separate ring which is utilized jointly with or in lieu of the starter
 gear 713.
 A hysteretic damping device 740 is installed to operate between the
 flywheels 702, 703, for example, in the same way as already described for
 the devices 40, 140 and 440.
 An energy storing resilient element 775 (shown in the form of a diaphragm
 spring) is installed between the flange 720 and the cheek 722 to establish
 a permanent basic friction or hysteresis that is effective during each
 stage of angular movement of the input and output elements 720 and 721 of
 the damper 708 relative to each other. The resilient element 775 is
 installed in such a way that it is stressed in the direction of the common
 axis of the flywheels 702 and 703. Since the secondary flywheel 703 has
 some freedom of axial movement, it can be acted upon by the energy storing
 diaphragm spring 775 to move toward the primary flywheel 702. The
 arrangement can be such that the flywheel 702 is biased or pulled toward
 the flywheel 702. The bias of the spring 775 is taken up by the radially
 outwardly extending collar 706b of the bearing 706. The spring 775 can be
 installed at another location, as long as it operates between two parts
 which can turn relative to each other. Furthermore, this spring can be
 utilized jointly with one or more additional springs to jointly generate
 and maintain a basic friction or hysteresis during each stage of angular
 movement of the input and output elements of the damper 708 relative to
 each other.
 FIG. 11 illustrates another centering unit 804 which employs a journal
 bearing (namely a bearing without spherical and/or other rolling elements
 between two races) adapted to be utilized in the apparatus 701 of FIG. 10
 as well as in other embodiments of the improved apparatus. The bearing 806
 is installed radially inwardly of the annular portion 815 (the latter
 forms part of or is affixed to the primary flywheel 802). The sleeve 852
 of FIG. 11 is carried by the secondary flywheel and is surrounded by the
 bearing 806.
 The apparatus 901 of FIG. 12 comprises a primary flywheel 902, a secondary
 flywheel 903, and a centering device 904 which is analogous to or
 identical with the centering device 4 of FIGS. 1-2, the device 304 of FIG.
 6 or the device 504 of FIG. 8 or the device 604 of FIG. 9. The damper 908
 and the torque limiting device 974 of the apparatus 901 are or can be
 identical with the units 608 and 674 in the apparatus 601 of FIG. 9. A
 difference between the cheek 922 of input element of the damper 908 and
 the cheek 622 of the apparatus 601 is that the cheek 922 comprises
 radially inwardly extending portions 922a which can be clamped between the
 heads 919a of the fasteners 919 and the radially inner portion of the
 radial wall 962 forming part of the primary flywheel 902. The wall 962 is
 made of a suitable metallic sheet material.
 That portion of the cheek 922 which extends radially outwardly beyond the
 energy storing devices 906 of the damper 908 is affixed to the wall 962 by
 rivets 933. Thus, the cheek 922 is fixedly secured to the wall 962
 radially inwardly of the energy storing devices 906 (as at 919a, 922a) as
 well as radially outwardly of the devices 906 (by the rivets 933). The
 intermediate portion of the cheek 922 (between the rivets 933 and the
 heads 919a, as seen radially of the common axis of the flywheels 902, 903)
 is spaced apart from the wall 962 so that the parts 922, 962 together form
 a box-shaped annular body which greatly enhances the stability of the
 corresponding part of the primary flywheel 902 and of the entire apparatus
 901 (as seen in the axial direction of the flywheels). Consequently, the
 axial stability or rigidity of the apparatus is quite acceptable even if
 the main part (including the wall 962) of the primary flywheel 902 is made
 of a relatively thin sheet material. The stability of the damper 908 and
 of the entire apparatus 901 can be further enhanced by providing the cheek
 922 and/or 923 with suitably configurated and dimensioned pockets (such as
 those in the cheek 123 of FIG. 3) for portions of the energy storing
 devices 906.
 The construction of the improved apparatus can be further simplified (with
 attendant reduction of its dimensions as seen in the axial and/or radial
 direction of the primary and secondary flywheels) by omitting one or more
 parts. For example, one of the two cheeks forming part of the input or
 output element of the damper can be omitted if the primary or the
 secondary flywheel is provided with means (such as pockets) for reception,
 retention and stressing of the energy storing devices of the damper. The
 means for receiving, retaining and stressing the energy storing devices of
 the damper can be provided directly in one of the flywheels or in a
 relatively simple part which is affixed to the flywheel.
 With specific reference to the apparatus 901 of FIG. 12, the cheek 922 can
 be omitted if the wall 962 of the primary flywheel 902 is provided with
 suitable pockets for portions of the energy storing devices 906. Such
 pockets can resemble the pockets 139 in the cheek 123 of the damper 108
 shown in FIG. 3. The pockets in the wall 962 can be formed during
 conversion of a sheet metal blank into the corresponding (main) part of
 the primary flywheel 902.
 FIGS. 13 and 14 illustrate certain features of a further torsional
 vibration damping apparatus 1001 which comprises a primary flywheel 1002
 and a coaxial secondary flywheel 1003. The main part 1059 of the primary
 flywheel 1002 is made of a metallic sheet material having a radially outer
 portion which carries a starter gear 1013. Such radially outer portion of
 the main part 1059 further supports an auxiliary mass 1062 which is
 secured thereto by rivets 1033. These rivets are of one piece with the
 radially extending wall of the main part 1059. The radially innermost
 portion of the radial wall of the main part 1059 is affixed to the rotary
 output component (not shown) of a prime mover by the externally threaded
 shanks of axially parallel fasteners 1019.
 The construction of the centering means 1004 (including the journal bearing
 1006) for the two flywheels is or can be identical to that of the
 centering means 104 or 704. An annular member 1080 is installed between
 the radially innermost portion 1059a of the radial wall of the main part
 1059 of the primary flywheel 1002 and the heads 1019a of the fasteners
 1019 to serve as a washer for the heads 1019a. This part 1080 extends
 radially inwardly beyond the fasteners 1019 and provides an annular
 support 1080a constituting an abutment (as seen axially of the flywheels
 1002, 1003) for the radially outwardly extending portion or collar 1006b
 of the bearing 1006. Furthermore, the radially innermost portion or part
 of the annular member 1080 further abuts an internal annular shoulder
 1015a of the portion 1015 which is affixed to the portion 1059a of the
 primary flywheel 1002 by the fasteners 1019 and is surrounded by the
 axially extending sleeve-like part of the bearing 1006. The shoulder 1015a
 can be omitted if the annular member 1080 is sufficiently stiff to ensure
 that its radially innermost portion 1080a can constitute a proper axial
 abutment for the collar 1006b without being propped by the annular portion
 1015.
 The annular member is practically flat in the regions of the heads 1019a of
 the fasteners 1019 and is provided with cutouts adjacent the heads 1019a.
 FIG. 13 shows that innermost portion 1080a is axially offset relative to
 the radially outer portion of the annular member 1080 so that the radially
 outer portion can abut the inner side of the portion 1059a.
 The part 1056 (corresponding to the part 156 in the apparatus 101 of FIG.
 3) is affixed to the cheek 1023, e.g., in the same way as described with
 reference to the parts 123, 156 in the apparatus 101 of FIG. 3. This part
 1056 is provided with openings 1082 which register with openings 1081
 provided in the cheek 1023 and serving to afford access to the heads 1019a
 by the working end of a suitable tool, not shown. As already discussed
 hereinbefore, the fasteners 1019 can be dimensioned, configurated and
 installed in the portion 1059a in such a way that they cannot be lost or
 misplaced but are ready for attachment of the flywheel 1002 to the output
 component of a prime mover as soon as the module shown in FIG. 13 reaches
 the automobile assembly plant.
 If the module further includes a friction clutch 1051 and a clutch disc
 1068 (see FIG. 13), the clutch disc 1068 is also provided with openings
 (one shown but not referenced in FIG. 13) which afford access to the
 openings 1082. The slots between and/or the configuration of the radially
 inwardly extending prongs 1073a of the diaphragm spring 1073 forming part
 of the clutch 1051 are also configurated in a manner to ensure that the
 working end of a tool can be advanced toward and into engagement with the
 heads 1019a of the fasteners 1019.
 The output element 1021 of the damper 1008 comprises two cheeks 1022, 1023
 which extend radially of the common axis of the flywheels 1002, 1003 and
 are axially spaced apart from each other to provide room for the flange
 1020 forming part of or constituting the input element of the damper 1008.
 The flange 1020 has radially inwardly extending arms 1037 which serve to
 stress the energy storing devices 1007 when the flywheels 1002, 1003 are
 caused to turn relative to each other.
 The cheeks 1022, 1023 are non-rotatably connected to each other by
 so-called pan head rivets 1033; this reduces the space requirements of the
 damper 1008 in the radial direction of the apparatus 1001. Furthermore,
 the cheeks 1022, 1023 are respectively provided with pockets or recesses
 1038, 1039 for portions of the energy storing devices 1007. Each pocket
 1036 is disposed between two neighboring arms 1037 of the flange 1020 (see
 FIG. 14) and is open radially inwardly toward the common axis of the two
 flywheels. The radially outer portion of the flange 1020 has outwardly
 bent axially parallel projections or arms 1083 which are affixed to the
 main part 1059 of the primary flywheel 1002. The connections between the
 main part 1059 and the arms 1083 can be established by providing the free
 ends of such arms with rivet heads 1084 which are anchored in the radially
 extending wall of the main part 1059. The manner in which the rivet heads
 1084 can be anchored in the main part 1059 is shown in FIG. 13a.
 The distribution and certain other features of the arms 1083 forming part
 of the flange 1020 are also shown in FIG. 14. Thus, the arms 1083 extend
 through elongated cutouts 1035 of the cheek 1022. When the energy storing
 devices 1007 of the damper 1008 are not stressed, the portions 1083a of
 the arms 1083 and the surfaces bounding the cutouts 1035 of the cheek 1022
 establish circumferentially extending clearances 1085 as seen in a
 clockwise direction and clearances 1086 as seen in a counterclockwise
 direction. The larger clearances are effective when the motor vehicle is
 called upon to pull a load, and the shorter clearances 1086 are effective
 when the motor vehicle is coasting.
 FIG. 14 further shows that the sets of rivets 1033 and 1083 alternate in
 the circumferential direction of the apparatus 1001. In other words, each
 rivet 1033 is located between two rivets 1083 and vice versa.
 The torque limiting unit 1074 operates between the cheeks 1022, 1023 of the
 output element 1021 of the damper 1008 and the portion 1003a of the
 secondary flywheel 1003. The unit 1074 comprises a radially inner part
 1003b of the portion 1003a; the part 1003b extends radially inwardly
 between the radially outermost portions of the cheeks 1022, 1023 and is
 located radially outwardly of the rivets 1033. The portion 1003a has an
 annular friction surface 1009 which is located radially outwardly of the
 rivets 1033 and surrounds a surface 1087 provided on the part 1003b. The
 surface 1087 is axially offset relative to the friction surface 1009,
 preferably through a distance corresponding to the thickness of the
 radially outermost portion 1023a of the cheek 1023. The axial offset 1088
 of the portion 1003a in the region of the radially innermost part of the
 friction surface 1009 defines an internal circular surface 1089. As can be
 seen in FIG. 13, the dimensions of the axial offset 1088 and of the
 radially outermost portion 1023a of the cheek 1023 are related to each
 other in such a way that the secondary flywheel 1003 is guided radially of
 the apparatus 1001 by the radially outermost portion 1023a and that the
 portion 1023a also serves as a means for selecting the axial position of
 the flywheel 1003. The periphery of the radially outermost portion 1023a
 of the cheek 1023 abuts the internal surface 1089.
 The torque limiting unit 1074 further comprises a resilient element 1075,
 shown in the form of a diaphragm spring, which serves to furnish the force
 necessary to establish a required frictional engagement between the parts
 which are to turn relative to each other only when the magnitude of the
 torque reaches or exceeds a predetermined maximum permissible value. The
 diaphragm spring 1075 is stressed between the cheek 1022 and the portion
 1003a of the secondary flywheel 1003. AS can be seen in FIG. 13, the
 spring 1075 reacts against the radially outer portion 1090 of the cheek
 1022 and bears upon the adjacent protuberances 1091 of the portion 1003a.
 The protuberances 1091 are located radially outwardly of the portion 1090
 of the cheek 1022. The properly stressed spring 1075 causes the surface
 1087 to bear upon the radially outer portion 1023a of the cheek 1023 so
 that the parts 1003b and 1023 are maintained in requisite frictional
 engagement with each other.
 A second frictional engagement is established between the diaphragm spring
 1075 and the protuberances 1091. It is preferred to establish a
 form-locking connection between the diaphragm spring 1075 and the cheek
 1022; this ensures that, if a slip is to take place in response to an
 undue increase of the applied torque, such slip will invariably entail an
 angular displacement of the portion 1003a and the diaphragm spring 1075
 relative to each other.
 FIG. 13 shows that the placing of the portion 1003a of the secondary
 flywheel between the cheeks 1022, 1023 of the output element 1021 of the
 damper 1008 contributes to compactness of the apparatus 1001 as seen in
 the axial direction of the flywheels. A reduction of the size of the
 apparatus 1001 in the radial direction of the flywheels 1002, 1003 is
 achieved by placing the rivets 1033 and the rivet heads 1084 at the same
 radial distance from the common axis of the flywheels. Additional savings
 in space, as seen radially of the flywheels, are achieved in that the
 energy storing devices 1007 are placed into immediate or close proximity
 of the fasteners 1019, and in that the bearing 1006 is installed radially
 inwardly of the annular array of the energy storing devices 1007.
 Furthermore, even the utilization of a journal bearing 1006, rather than a
 ball bearing, contributes to greater compactness of the apparatus 1001 as
 seen in the radial direction of the flywheels.
 An important feature of the apparatus 1101 a portion of which is
 illustrated in FIG. 15 is that the secondary flywheel 1103 and the damper
 1108 constitute a module which can be affixed to the primary flywheel 1102
 to thus achieve additional savings in time of assembling and installing
 the apparatus in the power train of a motor vehicle. The damper 1108
 comprises an input portion including or constituted by a flange 1120
 having a radially outer portion provided with tapped bores 1190 for the
 externally threaded shanks of screws 1191 or analogous fasteners having
 heads abutting the outer side of the radially extending wall of the
 primary flywheel 1102. Thus, the heads of the fasteners 1191 are readily
 accessible for engagement by a suitable tool.
 The module which is connected to the primary flywheel 1102 by the fasteners
 1191 can further comprise a friction clutch 1151 and a clutch disc 1168.
 The manner in which the clutch disc 1168 can be centered in such module is
 not specifically shown in FIG. 15.
 The module of FIG. 15 can be assembled with the bearing 1106 of the means
 for centering the flywheels 1102, 1103 relative to each other regardless
 of whether the module further includes the clutch 1151 and/or the clutch
 disc 1168. A fully assembled module is simply slipped onto the cylindrical
 part of the annular member 1115 which, in turn, is affixed to the primary
 flywheel 1102 in automatic response to the application of the fasteners
 1119, i.e., in response to attachment of the primary flywheel to the
 rotary output component of a prime mover. The mounting of the flange 1120
 on the primary flywheel 1102 (by means of the fasteners 1191) precedes
 attachment of the primary flywheel 1102 and annular portion 1115 to the
 output component of the prime mover.
 However, it is also possible to attach the primary flyweel 1102 and the
 annular portion 1115 to the output component of the prime mover prior to
 application of fasteners 1191 which serve to connect the primary flywheel
 with the module including the secondary flywheel 1103 and normally also
 the friction clutch 1151 and the clutch disc 1168. Such mode of assembling
 the apparatus of FIG. 15 exhibits the important advantage that the cheek
 or cheeks of the output element of the damper 1108 and/or the clutch disc
 1168 and/or the diaphragm spring and/or the housing of the clutch 1151
 need not be provided with openings for manipulation of the fasteners 1119.
 The apparatus of FIG. 15 further comprises a hysteresis device or
 hysteretic damping device 1140, preferably a device the operation of which
 is identical with or analogous to that of the previously described
 devices. The illustrated device 1140 comprises a friction ring 1144 as
 well as a resilient element 1145 shown in the form of a diaphragm spring
 which biases the friction ring 1144 in the axial direction of the
 flywheels. The device 1140 is to be mounted on the primary flywheel 1102
 prior to application of the fasteners 1191. When the fasteners 1191 are
 properly applied to connect the primary flywheel 1102 with the
 aforediscussed module including the secondary flywheel 1103, the diaphagm
 spring 1145 is automatically stressed by parts 1144a which then urge the
 radially inner portion of the diaphragm spring 1145 against the adjacent
 portion of the primary flywheel 1102.
 FIG. 16 shows a portion of a further apparatus 1201 having a hysteretic
 damping device 1240 which is mounted radially outwardly of the energy
 storing devices 1207 of the damper 1208 and axially between the cheeks
 1222, 1223 of the output element 1221 of the damper. However, and as fully
 described in connection with the apparatus 601 of FIG. 9, the cheeks can
 be installed in such a way that they constitute the output element of the
 damper.
 The device 1240 comprises a friction ring 1244 which can consist of an
 annulus of friction generating shoes and is in frictional engagement with
 the cheek 1223 on the one hand, and with a diaphragm spring 1245 (or an
 analogous energy storing element) on the other hand. The radially inner
 portion of the diaphragm spring 1245 abuts the cheek 1222 as seen in the
 axial direction of the primary and secondary flywheels 1202 and 1203.
 A further energy storing resilient element in the form of a diaphragm
 spring 1275 is installed between the input element (flange) 1220 of the
 damper 1208 and the cheek 1222. The purpose of the diaphragm spring 1275
 is to establish and maintain a continuous basic frictional engagement
 during each stage of angular movement of the flywheels 1202, 1203 and the
 input and output elements 1220, 1221 relative to each other.
 The function of the friction ring 1244 (or of the shoes which constitute
 this friction ring) is the same as that described in connection with the
 member 44 in the apparatus 1 of FIGS. 1 and 2. Thus, the hysteretic
 damping device 1240 operates with a certain amount of play which is
 effective whenever the flywheel 1202 changes the direction of its angular
 movement relative to the flywheel 1203 and/or vice versa.
 Referring now to FIG. 17, there is shown a torsional vibration damping
 apparatus 1301 the operation of which is analogous to that of the
 apparatus 101, 201, 401 or 501. This applies particularly to the operation
 of the damper 1308 and the hysteretic damping device 1340.
 The primary flywheel 1302 is made of metallic sheet material and is caused
 to remain coaxial with the secondary flywheel 1303 by a centering device
 or unit 1304 employing a journal bearing which contributes to a reduction
 of radial dimensions of the apparatus 1301.
 The damper 1308 comprises an output element 1321 including two axially
 spaced-apart cheeks 1322, 1323. The cheek 1323 can transmit torque to the
 portion 1303a of the secondary flywheel 1303 by way of a slip clutch 1374
 which constitutes a means for limiting the magnitude of the torque which
 the output element 1321 can transmit to the flywheel 1303. The mode of
 operation of the slip clutch 1374 is analogous to that of the slip clutch
 674 in the apparatus 601 of FIG. 9 or of the slip clutch 974 in the
 apparatus 901 of FIG. 12.
 More specifically, the slip clutch 1374 comprises a first stage 1374a and a
 second stage 1374b. Two resilient elements 1375 and 1378 of the slip
 clutch 1374 constitute diaphragm springs and correspond to the springs 675
 and 678 in the slip clutch 674 of FIG. 9. The diaphragm spring 1375 is in
 direct frictional engagement with the annular portion 1303a of the
 secondary flywheel 1303 and with a member 1376 corresponding to the member
 676 of the slip clutch 674. The member 1376 stresses the diaphragm spring
 1375 as well as the other diaphragm spring 1378, i.e., the function of the
 member 1376 is clearly the same as or analogous to that of the cupped
 member 674 in the slip clutch 674 of FIG. 9.
 An advantage of the apparatus 1301 of FIG. 17 is that its constituents can
 be assembled in a very simple, time-saving and hence efficient manner.
 Thus, the damper 1308 (including the input element or flange 1320, the
 output element 1321 including the cheeks 1322, 1323, and the energy
 storing devices 1307 can be assembled into a first module or partial
 module in a first series of steps. The assembly of such first module
 further involves the placing of the cupped member 1376 and at least one
 (1375) of the diaphragm springs 1375, 1378 axially between the cheek 1323
 and the flange 1320. The thus assembled first module can be assembled with
 the primary flywheel 1302; this involves affixing the radially outer
 portion of the flange 1320 to the adjacent radially extending portion of
 the flywheel 1302 by means of the rivets 1333. It is clear that the rivets
 1333 constitute but one form of fastener means which can be utilized to
 reliably secure the flange 1320 to the primary flywheel 1302.
 It is clear that the hysteretic damping device 1340 must be installed
 between the axially offset portion of the flange 1320 and the adjacent
 portion of the radial wall of the primary flywheel 1302 before the flange
 1320 is riveted to the primary flywheel. The part 1355 can be secured to
 the cheek 1323 before the making or application of the rivets 1333.
 The thus obtained larger module or subunit includes at least the primary
 flywheel 1302, the hysteretic damping device 1340 and the damper 1308, as
 well as the cupped member 1376 and at least the diaphragm spring 1375 of
 the torque limiting slip clutch 1374. The making of the apparatus 1301 of
 FIG. 17 further involves fixedly connecting the cupped member 1376 with
 the portion 1303a of the secondary flywheel 2303; this is achieved by
 employing the rivets 1350. The rivets 1350 can but need not be identical
 with or analogous to the rivets which are shown in FIG. 13a and serve to
 connect the part 1059 of the primary flywheel 1002 with the cheek 1022.
 The installation of the portion 1303a of the secondary flywheel 1303 in the
 apparatus 1301 of FIG. 17 must be preceded by insertion of the diaphragm
 spring 1378 and of friction rings (if any) to form part of the slip clutch
 1374.
 The next step involves assembly of the cupped part 1376 with the portion
 1303a of the secondary flywheel in such a way that the already inserted
 diaphragm springs 1375, 1378 of the slip clutch 1374 are caused to store
 adequate amounts of energy. These amounts of energy must suffice to ensure
 adequate operation of the two stages 1374a and 1374b of the slip clutch
 1374. FIG. 17 shows a suitable tool 1380 which engages one side of the
 member 1376, namely that side which faces away from the diaphragm springs
 1375 and 1378. The plant in which the apparatus 1301 is assembled is
 equipped with discrete tools 1380 or with sets of such tools each of which
 can enter into engagement with the member 1376 by way of one of several
 access openings or holes 1381 in the primary flywheel 1302. A set of
 several tools 1380 can reliably prop the member 1376 to ensure that the
 portion 1303a can cause the springs 1375, 1378 to undergo the necessary
 deformation. Additional tool or tools (not shown) can be utilized to prop
 the portion 1303a in requisite position during the application of the
 rivets 1350. The making of the rivets 1350 can involve the utilization of
 suitable rivet forming tools in the form of rams or the like; the exact
 nature of such tools forms no part of the present invention.
 It will be appreciated that the connection between the parts 1376 and 1303a
 can involve the utilization of fasteners other than the illustrated rivets
 1350. For example, the member 1376 can be provided with axially parallel
 extensions (not shown) passing through suitable holes in the portion 1303a
 to the right-hand side of the portion 1303a (as viewed in FIG. 17) and
 adapted to be bent over selected regions of the portion 1303a or to be
 otherwise affixed to the portion 1303a in order to ensure that the parts
 1376 and 1303a cooperate to maintain the diaphragm springs 1375, 1378
 under requisite stress, i.e., to ensure satisfactory operation of the
 stages 1374a and 1374b of the slip clutch 1374. If utilized, the just
 discussed extensions of the member 1376 can be caused to extend radially
 outwardly or in any other direction which is necessary to establish a
 reliable connection with the portion 1303a of the secondary flywheel 1303.
 Still further, it is possible to bond (e.g., weld by laser beams) the
 member 1376 to the portion 1303a; such bonding can be resorted to in
 addition to or in lieu of the utilization of the rivets 1350 or the like.
 The parts 1303a, 1376 can be directly or indirectly welded to each other,
 e.g., by employing connectors which are welded to such parts or which are
 welded to one of the parts 1303a, 1376 but otherwise affixed to the other
 part. For example, the connectors can include strips or the like made of
 metallic sheet material. All that counts is to ensure that the parts
 1303a, 1376 can cooperate to guarantee adequate stressing of the diaphragm
 springs 1375 and 1378.
 In accordance with still another procedure, the assembly of the apparatus
 1301 can involve mounting the slip clutch 1374 (including the cheek 1323)
 on the annular portion 1303a of the secondary flywheel 1303, securing the
 flange 1320 to the primary flywheel 1302 (including installing the
 hysteretic damping device 1340 and the cheek 1322)- The next step involves
 insertion of the energy storing devices 1307 and the application of rivets
 1385. Such mode of assembly is possible if the portion 1303a of the
 secondary flywheel is provided with openings 1386 (indicated by broken
 lines) to provide room for the application of the rivets 1385. Similar
 (properly aligned) openings 1387 are also provided or can be provided in
 the radially extending wall of the primary flywheel 1302. The openings
 1386, 1387 render it possible to provide the rivets 1385 with suitable
 heads 1385a, 1385b which hold the cheeks 1322, 1323 at a requisite axial
 distance from each other.
 Bolts and nuts can be utilized with advantage to establish certain
 connections in the apparatus of the present invention. For example, such
 types of fasteners can be utilized to secure the housing of a friction
 clutch to the secondary flywheel.
 Still further, it is possible to weld the nuts to one of the parts which
 are to be connected to each other and to cause the shanks of the bolts to
 pass through suitable openings in the other part and to mesh with the nuts
 in order to establish simple separable connections between a housing and a
 flywheel or between other types of parts.
 It is further clear that the hysteretic damping devices which are utilized
 in the torsional vibration damping apparatus of the present invention need
 not be designed to furnish a delayed damping action when the the direction
 of rotation of the primary and secondary flywheels relative to each other
 is reversed. Thus, the hysteretic damping device can remain effective
 during each and every stage of rotation of the flywheels with and relative
 to each other. For example, a hysteretic damping device can cooperate with
 at least one energy storing element which can effect an at least partial
 resetting of the friction generating element or elements of the hysteretic
 damping device in such a way that the damping action is not interrupted at
 any time including during reversal of the direction of rotation of the
 primary and secondary flywheels relative to each other.
 It is also possible to design the hysteretic damping device in such a way
 that its frictional damping action varies gradually or otherwise in
 response to changes in angular positions of the flywheels relative to each
 other. Thus, and when one of the flywheels is caused to turn relative to
 the other flywheel from a predetermined starting position, the frictional
 resistance offered by the hysteretic damping device increases in
 accordance with a selected pattern, e.g., gradually. This can be achieved,
 for example, by resorting to suitable ramps which are provided on or form
 part of the friction generating elements of the hysteretic damping device.
 Without further analysis, the foregoing will so fully reveal the gist of
 the present invention that others can, by applying current knowledge,
 readily adapt it for various applications without omitting features that,
 from the standpoint of prior art, fairly constitute essential
 characteristics of the generic and specific aspects of the above outlined
 contribution to the art of torsional vibration damping apparatus and,
 therefore, such adaptations should and are intended to be comprehended
 within the meaning and range of equivalence of the appended claims.