Damper unit for automotive power unit or the like

Abstract: A damper used to damp roll vibration of an automotive power unit includes housing (11) in which a disc (10) is immersed in a highly viscous liquid (12), and a linkage (17) which has universal (13, 14, 15, 16) joints formed at each end thereof. The linkage induces relative rotation between the housing and the disc. A resilient vibration attenuating arrangement is included in one or both of the universal joints for insulating the vehicle chassis from vibration which tends to be freely transmitted through the damper per se and cause cabin reverberation noise.

Description: The invention relates to a vibration damper of a viscous shear type. Description of the Prior Art JP-U-63-14036 discloses a damping arrangement wherein a circular plate or disc is mounted on a shaft of similar member which is rigidly connected to a power unit. The plate is disposed in a circular housing or casing in a manner to be immersed in a viscous fluid. The casing is connected to a vehicle chassis by way of a linkage which induces relative rotation between the circular disc and the circular housing. However, this arrangement has suffered from the drawback that the power unit is supported on the chassis by elastometric members in a manner to be simultaneously movable in a plurality of directions, the power unit does not just move in the roll direction but tends to move randomly in different directions in addition to the roll one. Accordingly, the actual device is required to include a linkage which has: 1. a connecting member which is made of flexible plate and which acts a spring link; or 2. at least one elastomeric bush between the casing and the chassis; or 3. a combination of a flexible link and elastomeric bushes. In the case a spring link is used, while the spring link is subject to tractive forces, there is no problem, however, when the link is subject to compressive forces, the link tends to flex and thus reduce the relative rotation between the housing and the disc. This of course reduces the effectiveness of the damper. In the case where one or more elastomeric bushes are used, when rolling motion of the engine occurs, the bushes distort in a manner which reduces the amount of relative rotation which is produced between the disc and the housing and thus again the damper is not used to its full potential. A combination of elastomeric bushes and a flexible connector increases the problem and markedly reduces the amount of relative rotation which is induced. DE-A-21 28 210 discloses a shock absorber to be used in the suspension system of a vehicle. This prior art shock absorber comprises a cylinder-piston-system having at is respective ends ball and ball seat-arrangements, respectively. US-A-2,354,428 discloses a vibration damper of the shear type having one ball seat provided with vibration insulation means. This vibration damper is used on a motor vehicle between the frame and running gear thereof to cushion a bound and rebound of the frame when the vehicle is traveling over an uneven road. EP-A-0 345 736, falling under Article 54(3) EPC, discloses a prior art vibration damper which has a construction as shown in Figures 1 to 12 of the drawings and as explained in detail in the corresponding parts of the description. It is the object of the invention to provide an arrangement which not only enables the maximum amount of relative rotation to be produced between a disc and a housing in a viscous shear type damper device but also attenuates annoying noise causing vibrations which tend to be transmitted through the damper from the power unit to the vehicle chassis. This object is achieved by the features as claimed in claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Figs 1 and 2 are front (sectional) and side elevations showing an embodiment as disclosed in EP-A- 0 345 736; Fig. 3 is a front elevation showing the disposition of a damper used to mount an engine and transmission (so called power unit on a vehicle chassis member; Figs. 4 and 5 are elevational views which show the freedom of movement permitted the damper unit is response to various motions of the engine; Fig. 6 is an elevational view showing a second embodiment wherein a damper according to the prior art (EP-A-0 345 736) used in combination with an elastomeric bush; Fig. 7 is a front elevational view showing a third embodiment of the prior art which features the provision of a ball seat which cooperates with one of the balls formed on the connection linkage; Figs. 8 and 9 are elevations showing various constructional variations of the connection linkage; Figs. 10 and 11 are views showing the construction which characterizes a fourth embodiment of the prior art; Fig. 12 is a sectional elevation showing a construction which characterizes a fifth embodiment of the prior art; Figs. 13 and 14 show an embodiment of the present invention; Fig. 15 is a cross-section of an elastomeric member which forms a part of one of the universal joints and which assist in attenuating vibrations which don't induce relative rotation between the disc and housing of the role damper; Figs. 16 to 19 show alternative elastomeric members which can be used in the universal joints in lieu of the one shown in Fig. 15; Fig. 20 is a graph showing in terms of load and flexure, the changes in spring constant which occur with the elastomeric member shown in Fig. 16; and Fig. 21 is a graph showing the force required to induce a change in spring constant of the member shown in Fig. 16. Fig. 3 shows a power unit damper A operatively connected between a power unit (viz., engine and transaxle combination) and a vehicle chassis. As shown the damper is connected between a center member 1 which is connected with the vehicle chassis via elastomeric bushes (no numeral) and a power unit 2 and disposed with respect to the center about which the power unit tends to roll (see curved double ended arrow). The power unit 2 is further operatively connected with a power unit mount 3 in a manner to support the power unit in the illustrated manner. It will be understood that other bushes and mounting device are used to support the engine. However, for the sake illustrative clarity these elements have been omitted. Figs. 1 and 2 show the construction of the damper A in detail. As will be noted in this embodiment the main body of the damper is supported on a bolt 4 which is detachably connected to a bracket 5 connected to the power unit 2. An annular disc 10 is disposed within casing 11 which is so constructed and arranged as to define an annular chamber 11a. This chamber is filled with a highly viscous silicon oil 12. The lower portion of the housing is formed with a ball seat 13 in which a spherical ball 14 is received. This ball 14 forms part of a link 17 which extends between the housing 11 and the center member 1. As best seen in Fig. 1, the lower end of the link 17 is formed with a second spherical ball member 16 which is received in a second ball seat 15b which is defined in connector 15. In this embodiment the connector 15 is formed of a rigid synthetic resin (e.g. Acetal) arranged to have first and second essentially cylindrical portions. The smaller diameter of the two portions is arranged to be disposed through an aperture formed in a bracket 6 which is, in this case, secured to the center member 1. The connector is also formed with first, second and third finger-like members 15c, 15c and 15d which are arranged to project through appropriately located apertures formed in a bracket 6 and/or engage suitable edge portions thereof in a manner which secures the connector in place prevents relative rotation with respect to the bracket 6. A radially extending slit 15a extends from outer periphery to the inner one. This slit permits sufficient flexibility to permit the ball member to be forced into the second ball seat 15b. When the connector 15 is disposed in place on the bracket 6, the connection which is established by the fingers prevents any flexure which may permit the slit to widen and allow the ball 16 to escape. In this figure C1, C2 and C3 respectively denote the center of motion of the damper, the upper ball 14 of the link 17 and the lower ball 16 of the same. Cr denotes the center of motion of the power unit 2. As will be appreciated in the normal or home position of the arrangement the three centers align with one another. In this embodiment the annular disc 10 is formed integrally with a stepped central boss portion 18. This plate and boss portion can be formed of aluminium, carbon steel, stainless steel or any suitable alloy. However, the material is not limited to these and any suitable other material can be used. The link 17 and the first and second ball members 14, 16 can be formed of aluminium, carbon steel, stainless steel, a suitable alloy or the like. In the first embodiment these elements are formed as a single integral unit. The disc 10 is arranged to extend from a large diameter portion 18a of the boss, while the steps defined between the large and small diameter portions are arranged receive O-ring seals 20. The first and second halves of the housing 11 are secured together by way of rivets 19 and arranged to cooperate with the large and small diameter portions of the boss in a manner to enclose the O-ring seals in the illustrated manner. These halves are also formed with annular flanges 11b which extend parallel to the periphery of the large diameter portion 18a and toward the surfaces of the disc 10. These flanges terminate at locations which are proximate the disc and thus enclose the silicon oil 12 in the annular chamber 11a. As the bearing surfaces 13 which define the ball seat are formed integrally in the members which define the casing 11, they preferably exhibit good heat resistance, sliding resistance and adequate mechanical strength. By way of example only, polyacetals may be used to form the same. The casing is formed with a slit 13a which has a width which is essentially the same as or slightly larger than the diameter of the center portion 17c of the link 17. The casing further is arranged to have an essentially inverted pear shape. The above construction is such that depending on the direction in which the center of motion Cr of the engine moves the relative movement shown in Figs. 4 and 5 is rendered possible. The operation of the above described device is such that, in the case that the power unit undergoes roll vibration in the direction indicated by the arrow in Fig. 3 the motion depicted in Fig. 4 is produced. Viz., under these circumstances, the center C3 remains in place while the center C1 is displaced through a distance 1. As a result the link 17 remains essentially stationary and the relative movement between centers C1 and C2 is such as to induce the disc to rotate through an angle ø with respect to the casing 11. Accordingly, the maximum relative movement between the disc 10 and housing 11 whereby the movement of the disc through the viscous fluid 12 attenuates the rolling the reduces the amount of vibration transmitted to the center member 1. However, as will be appreciated, there will be essentially no time when only the above described rolling vibration alone occurs. Viz., the power unit will tend to vibrate in a random number of directions simultaneously. However, with the construction according to the first embodiment, the movement shown in Fig. 5 is also rendered possible. Accordingly, even though the center C2 is displaced laterally with respect to the center C3 in a manner which brings the C3 center out of alignment with C1 and C2, essentially no effective reduction in the relative rotation between the disc 10 and the casing 11 occurs and therefore the loss of roll damping experienced with the earlier discussed prior art is not experienced. With the first embodiment the following effects are achieved. Firstly, as the link 17 is formed of a rigid inflexible material, and the universal type joints provided at each end thereof permit random displacement between the power unit 2 and the center member 1 the loss of roll damping depending on the direction in which the displacement occurs is obviated. As the ball 14 is seated in the ball seat provided in the casing 11 in a manner wherein essentially no relative displacement therebetween, it is not necessary to provide special ball seat members. This simplifies the construction and lowers the cost of the device. Space is further conserved and adequate structural strength provided to handle the forces transmitted between the power unit and the center member. The material in which the ball seat surfaces 13 are formed is selected so that the sliding resistance and friction which between the seat surfaces and the surfaces of the metallic spherical ball 14 is low and therefore tends to minimize frictional resistance. The centers C1, C2 and Cr are not subject to relative displacement relative to one another, no moments are applied to the casing 11 and the longevity of the same is assured. As the rotating parts of the device are not subject to twisting forces even under high roll vibration, the maximum roll damping effect is realized. Further, the absence of twisting forces prolongs the life of the O-rings and therefore assures that the device exhibits a long working life free of leakage and the like. The balls 14, 16 and and shaft which constitute the link 17 can be readily and economically formed of aluminium or the like rigid material. The disc 10 and center boss member 18 can be formed integrally in a manner which assures a permanent connection between the two parts, the changes of breakage are minimized along with an inherent compact configuration. The stepped configuration of the center boss portion 18 permits the O-rings to be disposed in locations which resiliently support the rotating element within the casing 11 in a manner wherein friction between casing and the rotating elements tends to be minimized. Even when the centers C1, C2 and Cr are moved out of alignment with center C3 the arrangement of the bracket 6 is prevented from being subject to twisting and bending forces. As the connector 15 is formed with the slit 15a is easy to snap the connector onto the ball 16 and then insert the same into the aperture formed in the bracket 6 and guide the finger like members 15c and 15d into place. Upon insertion into the bracket 6 expansion of the connector 15 in a manner which permits the ball 16 to come of engagement with the ball seat surfaces 15d is prevented. Fig. 6 shows a second embodiment of the prior art. In this arrangement the roll damper A is combined with the power unit mount 3 rather than being located at a separate site. In this arrangement the mount 3 is fixed to a suitable chassis member not shown. Fig. 7 shows a third embodiment of the prior art. In this arrangement a ball seat member 14 is additionally provided. This ball seat can be constructed and arranged in a manner disclosed hereinlater with reference to Figs. 16 to 19. Figs. 8 and 9 show alternative link constructions. As will be appreciated, the arrangement shown in Fig.8 is such that the upper ball 14 is detachably connected to the link 17. In the case of the arrangement shown in Fig. 9, the ends of a shaft which defines the main body of the link, are bent parallel and the balls rotatably disposed on the parallel portions. The ends of the shaft are formed with ball retaining heads such by a riveting type technique. Figs. 10 and 11 show a construction which characterizes a fourth embodiment of the prior art. As will be appreciated from the drawings, the disc 10 is formed with a plurality of arcuate ribs 10d while the inner surface of the casing halves are formed with correspondingly shaped corrugations 11d. This arrangement increases the surface area which is subject to viscous drag and increases the attenuation of roll vibration. The ribs 10d can be formed continuously to define circular ribs if so desired. Fig. 12 shows a fifth embodiment of the prior art. In this arrangement the two halves of the casing 11 are further formed with annular grooves 30, 31 in which seals can be disposed. In the illustrated embodiment only a single seal is disposed in groove 30 in a manner which prevents the leakage of the viscous liquid from the device by way of the interface defined between the two casing halves. If so desired the outer groove 31 can be left empty and used to collect any leakage that may occur with the passing of time. Figs.13 and 14 show an embodiment of the present invention. This embodiment features modified ball seat arrangements one of which is designed to attenuate vibrations of the nature which tend to cause reverberation noise in the vehicle cabin. In this arrangement the outboard ball joint features an essentially cylindrical shaped recess 40 which is formed in the casing 11 and a first elastomeric ball seat member 41 which is arranged to snugly fit into the recess. This ball seat 41 is formed with a spherical inner surface 41a which engaged the outboard ball 14 of the link and thus define a first universal joint. A rubber boot 45 is disposed about the outboard end of the link and arranged so that one end thereof is snugly received in the cylindrical shaped recess 40. The boot extends about the shaft portion on which the ball 14 is formed and thus excludes dust from the joint. The ball 16 formed on the inboard end of the link 17 is received in an elastomeric ball seat member 44 which is retained in a joint cover 42 fixed to the vehicle chassis or a member which is rigid therewith. In this embodiment the elastomeric member is arranged formed with a spherical inner surface 44a which engages the inboard ball 16 and a shaped external surface which is arranged to engage the inner surface 43 of the joint cover 42. The outer surface of the ball seat member has a radially extending projection which extends about the periphery thereof. As best seen in Fig. 15 this projection is defined in the middle of a concavity and is dimensioned to that the member ~ 44 must be distorted through a distance or clearance SC (in this case 0.5mm ~ 1.5mm) before the projection engages the inner surface of the joint cover. As will be appreciated until the projection or stopper 44c engages the inner surface of the joint cover 42, the elastomer from which the ball seat member 44 is formed primarily undergoes shear and thus offers relative little resistance to the distorting force (viz., is soft) . However, after the projection engages the inner wall, the shearing action is by enlarge replaced with compression and the resistance to distorting forces increases. After the projections are compressed the resistance to distortion increases rapidly. The operation of this embodiment is such during engine idling the very low frequency vibrations which are produced tend to effect the silicon oil 12 in a manner wherein the viscosity thereof increases. As a result, this vibration tends to be transmitted from the power unit to the vehicle chassis and result in the generation of reverberation noise in the vehicle cabin. However, with the instant embodiment, the second or inboard ball joint arrangement is such that, as shown in Fig. 20, in the idling range the initial spring constant k1 of the elastomeric ball seat member 44 is very small (k1 ≈ 0.5Kg/mm). When the projection 44c reaches and engages with the inner wall of the joint cover 42 the spring constant increases to a second low level k2 (e.g. k2 ≈ 3Kg/mm) which is suited to preventing the transmission of reverberation noise causing vibration which tends to be produced during vehicle acceleration. Viz., as shown in Fig. 21 when the force which is applied to the inboard ball joint exceeds F, the stopper clearance SC disappears and the spring constant increases from kl to k2. This latter mentioned spring constant k2 is maintained until the end of the zone in which acceleration related reverberation tends to be produced. Following the full compression of the projection 44c, the spring constant rapidly increases from the change over point, to a very high level. In this instant arrangement this tends to occur in response to large distortions in the order of 5mm. In this embodiment the maximum amount of permissible distortion is set at 5mm. When the power unit produces roll vibration (viz., the power unit exhibits a large relative displacement with respect the vehicle chassis) the elastomeric ball seat member 44 is distorted to the maximum permissible amount and the spring constant of the ball seat member 44 assumes a very high level. As a result the second ball joint exhibits an extremely small amount of play and very little loss in the roll vibration attenuating characteristics of the damper unit are observed. Of course the present invention is not limited to the arrangement shown in Fig. 15 and the arrangement illustrated in Fig. 16 can be alternatively used. The Fig. 16 arrangement is such that the spherical surface 44a can be formed with a plurality of recesses 44d. This arrangement reduces the amount of surface area in contact with the ball and thus reduces the amount of friction therebetween. Alternatively, as shown in Figs. 17 to 19 it is possible to arrange for a number of finger-like projections 44e to extend through the stopper clearance at predetermined intervals and engage the inner wall of the ball joint cover 42. Although the vibration damping arrangement has been disclosed in connection with the inboard or chassis side ball joint, it is within the scope of the present invention to provide the same at the outboard ball joint and/or on both if so desired. Simply by way of example the ball seat 13 shown in Fig.7 can be constructed to attenuate the transmission of the above mentioned reverberation noise generating type vibrations. As a further example, it is possible to arrange for an elastomeric grommet having suitably projections and/or recesses to be fitted about the synthetic resin connector 15 illustrated in Fig. 1, and use the grommet to attenuate the transmission of reverberation noise inducing vibrations from the power unit 2 to the vehicle chassis through the roll damper unit.

Claims: A vibration damper (B) of a viscous shear type comprising a disc (10) radially extended from a bolt / boss (18) which is connected via a bracket (5) to a first structure (2) wherein said disc (10) is arranged within an annular chamber formed in a housing (11) and filled with a viscous fluid (12) into which said disc (10) is immersed such that the disc (10) is movable relative to said housing (11); a rigid link (17) extending between said housing (11) and a second structure (1); a first universal joint (14) being arranged to connect a first end of said link (17) with said housing (11) ; a second universal joint (16) said second universal joint (16) operatively interconnecting a second end of said link (17) to said second structure (1); and vibration insulation means (41,44) for resiliently supporting said first and second universal joints (14,16) for attenuating vibration which tends to be transmitted between the first and second structures (1,2) without inducing relative movement between said disc (10) and said housing (11), wherein respective centers (C1,C2,C3) of motion of said disc (10), said first universal joint (14) and said second universal joint (16) are aligned in the vertical plane with each other in an initial position, and wherein said first universal joint (14) comprises: a first ball (14), being provided on said first end of said link (17); means defining a first ball seat (41) in which said first ball (14) is receivable, said first ball seat (41) comprising a resilient body which comprises said vibration insulation means; and a first casing in which said resilient body of said first ball seat (41) is disposed, said casing cooperating with said resilient body in a manner to define the maximum amount of distortion which can be induced in said resilient body, said casing being connected to said housing (11); and wherein said second universal joint (16) comprises: a second ball (16) being provided on said second end of said link (17); means defining a second ball seat (44) in which said second ball (16) is receivable, said second ball seat (44) comprising a resilient body which is disposed in a cavity defined in said vibration insulation means (41,44); and a second casing in which said resilient body of said second ball seat (44) is disposed, said casing cooperating with said resilient body in a manner to define the maximum amount of distortion which can be induced in said resilient body, said casing being connected to said second structure (1), wherein at least one of said resilient bodies of said first and second ball seats (41,44) exhibits: a first low spring constant (k1) in response to vibrations which induces distortion of the resilient body within a first predetermined range, and a second spring constant (k2) which is higher than the first spring constant (k1) in response to vibration which causes distortion of the resilient body in a second predetermined range. A vibration damper (B) as claimed in claim 1 wherein at least one of said resilient bodies of said first and second ball seats (41,44) exhibits a third spring constant (k3) which is higher than said second spring constant (k2) and which is induced in response to vibration which causes distortion greater than said second predetermined range and which proximates the maximum permissible amount of distortion.

Inventors: IDE TAKANOBU, IWAKURA MASARU, KOJIMA MASAMITSU, MOCHIMARU MASAMI, SHIMODA IKUO, IDE, TAKANOBU, IWAKURA, MASARU, KOJIMA, MASAMITSU, MOCHIMARU, MASAMI, SHIMODA, IKUO, IDE, TAKANOBU C/O OILES CORPORATION, IWAKURA, MASARU C/O OILES CORPORATION, KOJIMA, MASAMITSU C/O OILES CORPORATION, MOCHIMARU, MASAMI C/O OILES CORPORATION, SHIMODA, IKUO C/O OILES CORPORATION
Applicants: NISSAN MOTOR, OILES INDUSTRY CO LTD, NISSAN MOTOR CO., LTD., OILES CORPORATION
Application year: 1989
Main classification: F16F9
IPC codes: F16F9, B60K5