Strut mount and suspension mechanism using the same

A strut mount including: a first mounting member configured to be attached to a shock absorber; a second mounting member configured to be attached to a vehicle body; a main rubber elastic body elastically connecting the first and second mounting members to each other; a fluid-filled zone whose interior is filled with a non-compressible fluid such that a vibration damping effect is obtained based on a flow action of the fluid; and an orifice passage through which the fluid filled in the fluid-filled zone is induced to flow. A tuning frequency of the orifice passage is set to a frequency of a vibration transmitted during lockup of an automobile from a drive train of the automobile to the vehicle body via the shock absorber.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a strut mount configured to be mounted between a shock absorber and a vehicle body in an automotive suspension and to a suspension mechanism using the same. More particularly, the present invention pertains to a fluid-filled strut mount utilizing vibration damping effect based on the flow action of the fluid filling the interior and to a suspension mechanism using the same.

2. Description of the Related Art

Conventionally, vibration damping devices of various kinds have been used with the aim of realizing good ride comfort or the like for automobiles. By being disposed between the vibration source that constitutes the vibration transmission system and the component to be damped, the vibration damping devices are configured to prevent the vibration input from the vibration source from deteriorating the vibration state of the component to be damped. Such vibration damping devices include the one obtaining vibration damping effect through energy loss during elastic deformation of a rubber elastic body, the one obtaining vibration damping effect based on the flow action of the fluid, and the like.

One of the vibration sources which can be a problem in the automobiles is a power unit such as an internal combustion engine and motors. Accordingly, a countermeasure adopted in general is, for example, to dispose an engine mount serving as the vibration damping device such as disclosed in Japanese Unexamined Patent Publication No. JP-A-2010-078109 between the power unit which is the vibration source and the vehicle body which is the component to be damped, so as to prevent the vibration input from the power unit from being transmitted to the vehicle body. Besides, another one of the vibration sources which can be a problem in the automobiles is what is caused by the vibration of the wheel assembly due to depressions or ridges of the road surface, or the like. Accordingly, a countermeasure adopted in general is, for example, to dispose a suspension bushing serving as the vibration damping device such as disclosed in Japanese Unexamined Patent Publication No. JP-A-2014-145410 between the wheel assembly which is the vibration source and the vehicle body which is the component to be damped, so as to prevent the vibration input from the road surface from being transmitted to the vehicle body.

Meanwhile, for the automobiles in recent times, due to an increase in concerns about economical efficiency, reduction of the load on the environment or the like, enhanced fuel economy performance is highly required to the extent comparable to or greater than that for ride comfort or traveling performance. In order to meet the high requirement for such enhanced fuel economy performance, examined are measures such as downsizing of the engine by decreasing the number of cylinders, or performing lockup at a lower engine speed.

However, it has been revealed that when making an attempt to enhance fuel economy through decrease in the number of cylinders of the engine or reduction in the lockup engine speed, namely the engine speed at which lockup is performed, the vibration state of the vehicle body becomes deteriorated during lockup.

SUMMARY OF THE INVENTION

The present invention has been developed in view of the above-described matters as the background, and it is an object of the present invention to provide a strut mount with a novel structure which is able to realize an excellent vibration damping performance, and to provide a suspension mechanism using the same.

The above and/or optional objects of this invention may be attained according to at least one of the following modes of the invention. The following modes and/or elements employed in each mode of the invention may be adopted at any possible optional combinations.

The inventors examined the cause of deterioration of the vibration state of the vehicle body due to decrease in the number of cylinders or reduction in the lockup engine speed. Then, the inventors found out that the deterioration was caused by the vibration due to torque fluctuations during lockup being transmitted from the drive train such as a drive shaft to the vehicle body via a suspension as a transmission path. They guessed that in such a new vibration transmission path, during input of low-frequency vibration, resonance is produced in the vibration transmission system such as the suspension system and the drive train, for example. Accordingly, it is guessed that when the frequency of vibration due to torque fluctuations during lockup becomes lower due to decrease in the number of cylinders or reduction in the lockup engine speed, the vibration is amplified by the resonance and transmitted to the vehicle body so that the vibration state of the vehicle body becomes deteriorated. The inventors confirmed their guess through simulations and tests.

On the basis of such findings, the inventors considered that by reducing the transmission of the vibration on the vibration transmission path through which the vibration due to torque fluctuations during lockup is transmitted from the suspension to the vehicle body, it should be possible to improve the vibration state of the vehicle body and enhance vibration damping performance as well as quiet performance of the vehicle, and they achieved the present invention.

Specifically, a first mode of the present invention provides a strut mount comprising: a first mounting member configured to be attached to a shock absorber; a second mounting member configured to be attached to a vehicle body; a main rubber elastic body elastically connecting the first and second mounting members to each other; a fluid-filled zone whose interior is filled with a non-compressible fluid such that a vibration damping effect is obtained based on a flow action of the fluid; and an orifice passage through which the fluid filled in the fluid-filled zone is induced to flow, wherein a tuning frequency of the orifice passage is set to a frequency of a vibration transmitted during lockup of an automobile from a drive train of the automobile to the vehicle body via the shock absorber.

With the strut mount of construction according to the first mode, the vibration transmitted to the vehicle body via the shock absorber of the suspension during lockup will be decreased based on the flow action such as resonance action of the fluid flowing through the orifice passage. Thus, even if the number of cylinders of the engine is decreased or the lockup engine speed is reduced such that the frequency of vibration due to torque fluctuations during lockup becomes a low frequency for which resonance or the like of the suspension system or the drive train can be a problem, it is possible to prevent the vibration state of the vehicle body from being deteriorated during lockup.

Moreover, the strut mount is of fluid-filled type, and the orifice passage of the strut mount is tuned to the frequency of vibration transmitted to the vehicle body via the shock absorber during lockup. Therefore, with a simple structure utilizing the strut mount conventionally interposed between the shock absorber and the vehicle body, enhanced vibration damping performance during lockup can be realized.

A second mode of the present invention provides the strut mount according to the first mode, wherein the tuning frequency of the orifice passage is set not greater than 50 Hz.

According to the second mode, the tuning frequency of the orifice passage is set within the frequency range for which rigid body resonance or the like of the suspension system is likely to arise. This makes it possible to obtain excellent vibration damping performance in the frequency range for which amplification of vibration tends to be a problem due to resonance or the like of the suspension system or the drive train.

A third mode of the present invention provides the strut mount according to the first or second mode, wherein the fluid-filled zone includes a primary liquid chamber whose wall part is partially defined by the main rubber elastic body and an auxiliary liquid chamber whose wall part is partially defined by a flexible film, and the primary liquid chamber and the auxiliary liquid chamber are interconnected by the orifice passage.

According to the third mode, adopted is the structure in which the primary liquid chamber, which gives rise to internal pressure fluctuations during input of vibration, and the auxiliary liquid chamber, for which internal pressure fluctuations are less likely to arise due to deformation of the flexible film that permits changes in volume of the auxiliary liquid chamber, are interconnected by the orifice passage. Thus, vibration damping effect based on the flow action of the fluid can be advantageously obtained.

A fourth mode of the present invention provides the strut mount according to the third mode, wherein the flexible film has an annular shape such that the flexible film is allowed to be arranged axis-perpendicularly between the shock absorber and a coil spring that is placed externally about the shock absorber.

According to the fourth mode, the flexible film is arranged by utilizing the space between the shock absorber and the coil spring. This makes it possible to set the volume of the auxiliary liquid chamber with a large degree of freedom, thereby effectively attaining desired vibration damping performance.

A fifth mode of the present invention provides the strut mount according to any one of the first through fourth modes, wherein the strut mount is configured such that the vibration to be transmitted during lockup of the automobile from the drive train of the automobile to the vehicle body via the shock absorber is input across the first mounting member and the second mounting member in a generally axial direction, while a road surface vibration to be transmitted from a wheel assembly that is in contact with a road surface to the vehicle body via the shock absorber is also input across the first mounting member and the second mounting member in either one of a generally axis-perpendicular direction and a prizing direction, and a resonance frequency of the fluid with respect to the vibration input in either one of the generally axis-perpendicular direction and the prizing direction is set to a higher frequency than the tuning frequency of the orifice passage.

According to the fifth mode, the vibration damping effect will be exhibited with respect to not only the vibration transmitted during lockup from the drive train to the vehicle body via the shock absorber but also the vibration input from the wheel assembly that is in contact with a road surface. Moreover, the input vibrations from the road surface include the vibrations of frequencies roughly the same as that of the vibration transmitted from the drive train during lockup, as well as the vibrations of higher frequencies. Therefore, even if the resonance frequency of the fluid with respect to the vibration input from the road surface is set to a higher frequency than the tuning frequency of the orifice passage and the fluid flow with respect to the vibration input from the road surface is substantially blocked for the orifice passage due to antiresonance, the vibration damping effect can be efficiently obtained with respect to the vibration input from the road surface in the generally axis-perpendicular direction or the prizing direction.

A sixth mode of the present invention provides the strut mount according to the fifth mode, wherein the fluid-filled zone includes a primary liquid chamber whose wall part is partially defined by the main rubber elastic body and an auxiliary liquid chamber whose wall part is partially defined by a flexible film, and the primary liquid chamber and the auxiliary liquid chamber are interconnected by the orifice passage, the primary liquid chamber includes respective extended areas on opposite sides thereof in an axis-perpendicular direction and constricted areas interconnecting the extended areas in a circumferential direction, and the constricted areas are configured to allow a fluid flow therethrough between the extended areas due to the vibration input in either one of the generally axis-perpendicular direction and the prizing direction, and the resonance frequency of the fluid flowing through the constricted areas is set to a higher frequency than the tuning frequency of the orifice passage.

According to the sixth mode, it is possible to attain vibration damping effect with respect to the vibration input in the generally axis-perpendicular direction or the prizing direction based on the resonance action or the like of the fluid flowing between the extended areas through the constricted areas. Furthermore, since the extended areas and the constricted areas are provided in the primary liquid chamber, the vibration damping effect with respect to the vibration input in the generally axis-perpendicular direction or the prizing direction can be obtained with a compact and simple structure.

A seventh mode of the present invention provides the strut mount according to any one of the first through sixth modes, wherein the strut mount is configured to be mounted between the shock absorber and the vehicle body of the automobile that includes an engine having three cylinders or less.

According to the seventh mode, in automobiles equipped with an engine having three cylinders or less, in which the frequency of vibration transmitted during lockup from the drive train to the vehicle body is likely to be close to the frequency of rigid body resonance or the like of the suspension system, deterioration in the vibration state of the vehicle body during lockup can be avoided.

An eighth mode of the present invention provides a suspension mechanism comprising: a shock absorber and a suspension arm that are configured to connect a vehicle body and a wheel assembly; a strut mount according to claim1, the strut mount being configured to be interposed between the vehicle body and the shock absorber; and a suspension bushing configured to be interposed between the vehicle body and the suspension arm, wherein the suspension bushing includes a fluid-filled zone whose interior is filled with a non-compressible fluid, and an orifice passage through which the fluid filled in the fluid-filled zone is induced to flow, and a tuning frequency of the orifice passage is set to a frequency of a vibration transmitted during lockup of an automobile from a drive train of the automobile to the vehicle body via the suspension arm.

With the suspension mechanism constructed according to the eighth mode, the vibration due to torque fluctuations during lockup can be prevented from being transmitted not only by the strut mount from the shock absorber to the vehicle body, but also by the suspension bushing from the suspension arm to the vehicle body. This makes it possible to more advantageously avoid deterioration in the vibration state of the vehicle body during lockup, thereby achieving more enhanced vibration damping performance and quiet performance. Moreover, both the strut mount and the suspension bushing are of fluid-filled type and exhibit excellent vibration damping effect based on the flow action of the fluid. Thus, the vibration during lockup can be more effectively reduced.

According to the present invention, the vibration transmitted during lockup from the drive train to the vehicle body via the shock absorber of the suspension will be decreased based on the flow action such as resonance action of the fluid flowing through the orifice passage. Thus, even if the number of cylinders of the engine is decreased or the lockup engine speed is reduced such that the frequency of vibration due to torque fluctuations during lockup becomes a low frequency for which rigid body resonance or the like of the suspension system can be a problem, for example, it is possible to prevent the vibration state of the vehicle body from being deteriorated during lockup. Furthermore, with a simple structure utilizing the strut mount conventionally interposed between the shock absorber and the vehicle body, enhanced vibration damping performance during lockup can be realized.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described below in reference to the drawings.

FIGS. 1 and 2show a strut mount10according to a first embodiment of the present invention. The strut mount10has a structure in which a first mounting member12and a second mounting member14are elastically connected by a main rubber elastic body16. In the description hereinbelow, as a general rule, the up-down direction refers to the up-down direction inFIG. 1, which coincides with the mount axial direction. Besides, the front-rear direction refers to the left-right direction inFIG. 2, which coincides with the vehicle front-rear direction when mounted onto the vehicle. Meanwhile, the left-right direction refers to the up-down direction inFIG. 2, which coincides with the vehicle left-right direction when mounted onto the vehicle.

Described more specifically, the first mounting member12is a high rigidity component made of metal, synthetic resin or the like, and includes an inner tube member18having a small-diameter, approximately round tubular shape overall. The inner tube member18of the present embodiment has a roughly stepped round tubular shape whose upper part is made smaller in diameter than the lower part thereof. Moreover, at the lower end portion of the first mounting member12, integrally formed is an upper partition member20of flange shape extending radially outward in the axis-perpendicular direction. The upper partition member20has a roughly annular disk shape overall, and includes an annular mating slot22that opens onto the lower face and extends continuously about the entire circumference at the roughly center portion in the width direction, and screw holes24that open onto the lower face at several locations in the circumferential direction on the radially inside and outside of the mating slot22.

The second mounting member14is a high rigidity component the same as the first mounting member12, and includes an outer tube member26of large-diameter, tapered round tubular shape that is gradually constricted in diameter toward the top, and a mounting part28of flange shape integrally formed with its lower end portion so as to extend radially outward in the roughly axis-perpendicular direction. As shown inFIG. 2, the mounting part28has a roughly triangular plate shape overall viewed in the axial direction. Each side of the mounting part28curves so as to be convex radially outward, while its three corners are perforated by respective mounting bolts30whose axes each project upward.

Then, as shown inFIG. 1, the first mounting member12and the second mounting member14are disposed so as to be remote from each other on the roughly same center axis, and the main rubber elastic body16elastically connects the first mounting member12and the second mounting member14to each other. The main rubber elastic body16has an approximately round tubular shape overall with its inner peripheral portion bonded by vulcanization to the inner tube member18of the first mounting member12, and its lower face is overlapped and bonded by vulcanization to the upper face of the upper partition member20of the first mounting member12, while the upper part of its outer peripheral portion is bonded by vulcanization to the outer tube member26of the second mounting member14. The main rubber elastic body16of the present embodiment takes the form of an integrally vulcanization molded component including the first mounting member12and the second mounting member14. Also, a covering rubber32integrally formed with the main rubber elastic body16is overlapped and bonded by vulcanization to the lower face of the mounting part28of the second mounting member14, so that the head parts of the mounting bolts30are bonded to the covering rubber32in an embedded state.

Furthermore, the main rubber elastic body16includes a circular recess34. As shown inFIGS. 1 and 3, the circular recess34is a recess of groove form that opens onto the lower face of the main rubber elastic body16and extends in the circumferential direction, and is formed continuously about the entire circumference as shown inFIG. 3. Besides, with the circular recess34, as shown inFIGS. 1 and 4, the portions that are positioned on the opposite sides in the front-rear direction respectively constitute extended areas36whose up-down depth is large, while as shown inFIG. 1, the portions that are positioned on the opposite sides in the left-right direction respectively constitute constricted areas38whose up-down depth is small. Accordingly, the front/rear pair of extended areas36,36are connected in the circumferential direction via the left/right pair of constricted areas38,38.

Besides, a lower partition member40is attached to the upper partition member20of the first mounting member12. The lower partition member40is a rigid component made of metal or synthetic resin, and has a roughly annular disk shape overall. Moreover, the lower partition member40includes an annular mating protrusion42that corresponds to the mating slot22of the upper partition member20and projects upward at the roughly center portion in the width direction. The mating protrusion42includes a circumferential groove44that opens onto the upper face and extends for a prescribed length just short of once around the circumference in the circumferential direction, and the part opening upward is covered by a lid member46as a separate element from the lower partition member40. In addition, on the radially inside and outside of the mating protrusion42of the lower partition member40, there are formed a plurality of first screw insertion holes48that respectively correspond to the screw holes24of the upper partition member20.

Also, a flexible film50is disposed below the lower partition member40. The flexible film50is a thin-walled rubber film for which deformation in the thickness direction is readily permitted, and has an annular shape that is continuous about the entire circumference with a generally U-letter cross sectional shape that is convex downward. Furthermore, to the end part of the flexible film50positioned on the upper end thereof, an outer circumference fixing member52and an inner circumference fixing member54are bonded by vulcanization. The outer circumference fixing member52is a rigid component having a large-diameter, roughly annular disk shape, and is perforated in the up-down direction by a plurality of second screw insertion holes56at the locations corresponding to the first screw insertion holes48. Besides, the inner peripheral end of the outer circumference fixing member52is bonded by vulcanization to the outer peripheral end of the flexible film50continuously about the entire circumference. Meanwhile, the inner circumference fixing member54is a rigid component having a roughly annular disk shape whose diameter is smaller than that of the outer circumference fixing member52, and is perforated in the up-down direction by a plurality of second screw insertion holes56at the locations corresponding to the first screw insertion holes48. Besides, the outer peripheral end of the inner circumference fixing member54is bonded by vulcanization to the inner peripheral end of the flexible film50continuously about the entire circumference. Since the inner peripheral end of the outer circumference fixing member52and the outer peripheral end of the inner circumference fixing member54both project downward, bonding area to the flexible film50is largely obtained.

Then, the lower partition member40is overlapped with the upper partition member20of the first mounting member12from below and the mating protrusion42of the lower partition member40is inserted in the mating slot22of the upper partition member20. Meanwhile, the outer circumference fixing member52and the inner circumference fixing member54bonded to the flexible film50is overlapped with the lower face of the lower partition member40. Fixing screws58inserted into the first screw insertion holes48and the second screw insertion holes56are threaded onto the screw holes24, so that the upper partition member20, the lower partition member40, and the fixing members52,54are fixed to one another. While not shown explicitly in the drawings, the space between the overlapped upper partition member20and lower partition member40is fluid-tightly sealed by an O-ring or the like made of rubber that is arranged on the outer periphery and the inner periphery of the mating protrusion42, for example. Also, for example, by a seal projection that projects upward from the upper end face of the flexible film50being pressed against the lower face of the lower partition member40, the space formed between the lower partition member40and the flexible film50(an auxiliary liquid chamber64described later) is fluid-tightly isolated from the outside.

In this way, by the upper partition member20, the lower partition member40, and the flexible film50being fixed to one another, there is formed a fluid-filled zone60filled with a non-compressible fluid between the main rubber elastic body16and the flexible film50. The non-compressible fluid sealed in the fluid-filled zone60is not especially limited. For example, preferably employed are water, ethylene glycol, alkylene glycol, polyalkylene glycol, silicone oil, or liquid mixture of these or the like. Besides, it is desirable that the fluid sealed in the fluid-filled zone60be a low-viscosity fluid in order to advantageously obtain vibration damping effect by virtue of an orifice passage68or a constricted passage69to be described later, and a low-viscosity fluid having viscosity of 0.1 Pa·s or lower is preferably adopted.

Moreover, the fluid-filled zone60is bifurcated into upper and lower parts in the axial direction by the upper partition member20and the lower partition member40. Accordingly, above the upper partition member20, by the lower opening of the circular recess34being covered by the lid member46, there is formed a primary liquid chamber62whose wall part is partially defined by the main rubber elastic body16and which gives rise to internal pressure fluctuations during input of vibration. On the other hand, below the lower partition member40, by the upper opening of the flexible film50being covered by the lower partition member40, there is formed an auxiliary liquid chamber64whose wall part is partially defined by the flexible film50and which readily permits changes in volume due to deformation of the flexible film50.

Furthermore, the upper opening of the circumferential groove44formed in the mating protrusion42of the lower partition member40is covered by the lid member46. One lengthwise end of the circumferential groove44communicates with the primary liquid chamber62via an upper communication hole66that perforates the lid member46, while the other lengthwise end of the circumferential groove44communicates with the auxiliary liquid chamber64via a lower communication hole67(seeFIG. 3) that perforates the bottom wall of the circumferential groove44of the lower partition member40. With this arrangement, an orifice passage68that interconnects the primary liquid chamber62and the auxiliary liquid chamber64is provided.

With the orifice passage68, by adjusting the ratio (A/L) of the passage cross sectional area (A) to the passage length (L), the tuning frequency, which is the resonance frequency of the flowing fluid, is set within a frequency range of vibration due to the torque fluctuations that is transmitted during lockup of an automobile from the drive train to the vehicle via a shock absorber72to be described later. When vibration in the tuning frequency range of the orifice passage68is input across the first mounting member12and the second mounting member14, relative pressure fluctuations arise between the primary liquid chamber62and the auxiliary liquid chamber64. Then, fluid flow will take place between the primary liquid chamber62and the auxiliary liquid chamber64through the orifice passage68, such that vibration damping effect is configured to be obtained based on the flow action of the fluid such as resonance action of the fluid. In preferred practice, the orifice passage68is tuned to a low frequency from 1 Hz to 50 Hz including the resonance frequency of a suspension system described later, the drive train, or the like. In the present embodiment, on the assumption that the lockup engine speed, at which input vibration is required to be improved for the automobile that includes an engine having three cylinders, is from 1000 rpm to 1500 rpm, the orifice passage68is tuned to a frequency from 25 Hz to 37.5 Hz.

Also, by the lower openings of the constricted areas38,38of the primary liquid chamber62being covered by the lid member46, a constricted passage69that interconnects the extended areas36,36of the primary liquid chamber62is constituted by a portion of the primary liquid chamber62(the constricted areas38,38). With the constricted passage69as well, the same as the orifice passage68, the resonance frequency of the flowing fluid is tuned by adjusting the ratio (A′/L′) of the passage cross sectional area (A′) to the passage length (L′). Accordingly, the tuning frequency of the constricted passage69is set to a higher frequency than the tuning frequency of the orifice passage68. When vibration in the tuning frequency range of the constricted passage69is input across the first mounting member12and the second mounting member14, the orifice passage68substantially clogs due to antiresonance, while fluid flow actively takes place between the extended areas36,36of the primary liquid chamber62through the constricted passage69in a resonant state, thereby exhibiting vibration damping effect based on the flow action of the fluid. The tuning frequency of the constricted passage69is preferably set within the range of 20 Hz to 100 Hz, and in the present embodiment, set to a frequency on the order of 45 Hz to 100 Hz so as to match the frequency of vibration input from the road surface such as harshness.

The strut mount10of construction according to the present embodiment described above is provided to a suspension mechanism70of an automobile that includes an engine having three cylinders, as shown inFIGS. 5 and 6, and is interposed between a shock absorber72and a vehicle body74. Specifically, a stopper member75is overlapped with the inner tube member18of the first mounting member12from above, and the first mounting member12and the stopper member75is fixed to a piston rod76of the shock absorber72. The stopper member75is a high rigidity component made of metal or synthetic resin, and has a generally cup shape opening upward. To the upper end portion of the stopper member75, a flange-shaped stopper piece78is integrally formed so as to extend radially outward, and the outer peripheral end of the stopper piece78is covered by a cushioning rubber80. The inner peripheral end of the stopper member75is pinched in the up-down direction between upper and lower positioning nuts82,82, and the upper and lower positioning nuts82,82are threaded onto the piston rod76. By so doing, the stopper member75is positioned in the up-down direction with respect to the piston rod76.

On the other hand, the second mounting member14is fixed to the vehicle body74by the mounting bolts30. Specifically, the vehicle body74is overlapped with the mounting part28of the second mounting member14from above, while the mounting bolts30fixed to the second mounting member14is inserted into bolt holes86formed in the vehicle body74. By mounting nuts88being threaded onto the axes of the mounting bolts30projecting above the vehicle body74, the second mounting member14is configured to be attached to the vehicle body74. In this way, the first mounting member12is attached to the shock absorber72, and the second mounting member14is attached to the vehicle body74. By so doing, the upper end portion of the shock absorber72is attached to the vehicle body74via the strut mount10. The vehicle body74is perforated in the up-down direction by a circular hole in the portion to which the second mounting member14is mounted, and the rim of the opening of the circular hole is overlapped with the mounting part28of the second mounting member14.

Moreover, a spring support member90is overlapped with the mounting part28of the second mounting member14from below. The spring support member90includes a support part92having a generally annular disk shape and overlapped with the mounting part28of the second mounting member14from below, and an insertion part94extending downward from the inner peripheral end of the support part92and having a generally round tubular shape. The lower face of the support part92and the roughly entire face of the insertion part94are covered by a support rubber96.

With the lower face of the support part92covered by the support rubber96, overlapped is an upper end portion of a coil spring98that is placed externally about the shock absorber72, so that the upper end portion of the coil spring98is supported by the second mounting member14via the spring support member90. The spring support member90of the present embodiment is positioned with respect to the second mounting member14by being pressed by the coil spring98against the mounting part28of the second mounting member14. Besides, the annular flexible film50is arranged radially between the piston rod76of the shock absorber72and the coil spring98. With this arrangement, it is possible to set the up-down dimension of the flexible film50with a large degree of freedom, and a sufficient volume of the auxiliary liquid chamber64is obtained. In addition, an ample space for permitting deformation of the flexible film50is ensured, thereby sufficiently permitting changes in volume. The lower end portion of the coil spring98is supported by a cylinder of the shock absorber72, for example, and the coil spring98is configured to undergo extension/contraction in accordance with extension/contraction of the shock absorber72.

As described above, the first mounting member12of the strut mount10is attached to the shock absorber72while the second mounting member14is attached to the vehicle body74, so that the shock absorber72and the vehicle body74are linked in a vibration damped manner via the strut mount10.

The lower end portion of the shock absorber72is attached to a wheel assembly100, as shown inFIG. 6. The wheel assembly100has a structure in which a tire is mounted onto a wheel, and the lower end portion of the shock absorber72is attached to a steering knuckle102provided to the wheel. Furthermore, a suspension arm104is attached to the steering knuckle102of the wheel assembly100, and the suspension arm104is attached to the vehicle body74via a suspension bushing106at the opposite end from the steering knuckle102.

The suspension bushing106is, for example, a fluid-filled tubular vibration-damping device having a structure such as disclosed in Japanese Unexamined Patent Publication No. JP-A-2016-075347, and includes a fluid-filled zone whose interior is filled with a non-compressible fluid, and an orifice passage through which the non-compressible fluid flows. Besides, with the orifice passage of the suspension bushing106, the tuning frequency is set so as to match the vibration due to torque fluctuations during lockup. In the present embodiment, the tuning frequency of the orifice passage of the suspension bushing106is roughly the same as the tuning frequency of the orifice passage68of the strut mount10.

Furthermore, an axle attached to the steering knuckle102is configured to be rotated by a drive shaft110taken out of a differential of a power unit108, so that the wheel assembly100is configured to be rotated by the drive shaft110. The power unit108is elastically connected to the vehicle body74by an engine mount112. The specific structure of the engine mount112is not limited in particular, and any of various structures known in the art can be adopted such as a solid type, a fluid-filled type, an active type that decreases vibrations in an offset fashion owing to oscillation force of an electromagnetic actuator or the like, and a switching type whose vibration damping characteristics are switchable owing to a pneumatic actuator or the like.

Vibrations due to torque fluctuations arising during lockup of the drive train will be transmitted from the drive shaft110that constitutes the drive train to the steering knuckle102of the suspension mechanism70, and will be transmitted to the vehicle body74via the shock absorber72and the suspension arm104.

Here, the strut mount10is disposed between the shock absorber72and the vehicle body74, and vibrations due to torque fluctuations during lockup that are to be transmitted to the vehicle body74via the shock absorber72is input across the first mounting member12and the second mounting member14in the axial direction (up-down direction). Then, the vibrations due to torque fluctuations during lockup that are to be transmitted from the drive shaft110to the vehicle body74via the shock absorber72will be decreased owing to the vibration damping performance of the strut mount10. In particular, the strut mount10is fluid-filled type, and the orifice passage68is tuned to a frequency of vibration due to torque fluctuations during lockup. Thus, excellent vibration damping effect based on the flow action of the fluid will be exhibited with respect to the vibration due to torque fluctuations during lockup. Therefore, the vibration due to torque fluctuations during lockup is prevented from being transmitted from the suspension side to the vehicle body74via the shock absorber72, thereby improving vibration damping performance and quiet performance.

Moreover, the strut mount10of the present embodiment has a structure in which the primary liquid chamber62, which induces internal pressure fluctuations during input of vibration, and the auxiliary liquid chamber64, whose internal pressure is kept roughly constant owing to changes in volume, are interconnected by the orifice passage68. Therefore, during input of vibration, fluid flow through the orifice passage68will efficiently take place, thereby advantageously exhibiting vibration damping effect owing to the flow action of the fluid. In particular, since the vibration due to torque fluctuations during lockup is input to the strut mount10in the axial direction, internal pressure fluctuations in the primary liquid chamber62will be efficiently induced. This will produce relative pressure differential between the primary liquid chamber62and the auxiliary liquid chamber64, so that desired vibration damping effect can be advantageously obtained.

Meanwhile, the suspension bushing106is disposed between the suspension arm104and the vehicle body74. Accordingly, vibrations due to torque fluctuations during lockup that are to be transmitted from the drive shaft110to the vehicle body74via the suspension arm104will be decreased owing to the suspension bushing106. In particular, since the suspension bushing106is fluid-filled type and the orifice passage of the suspension bushing106is tuned to a frequency of vibration due to torque fluctuations during lockup, excellent vibration damping effect will be exhibited with respect to the vibration due to torque fluctuations during lockup. Therefore, the vibration due to torque fluctuations during lockup is prevented from being transmitted from the suspension side to the vehicle body74via the suspension arm104, thereby improving vibration damping performance and quiet performance.

Also, the orifice passage68of the strut mount10and the orifice passage of the suspension bushing106are both tuned to a low frequency on the order of 1 to 50 Hz, which is the frequency range of rigid body resonance of the suspension system (rigid body resonance of the shock absorber72or rigid body resonance of the suspension arm104), for example. This makes it possible to obtain vibration damping effect owing to the strut mount10and the suspension bushing106in the low frequency range for which amplification of vibration tends to be a problem due to rigid body resonance of the suspension system or the like.

Furthermore, even if the strut mount10and the suspension bushing106are implemented in an automobile that includes an engine having three cylinders or less, for which the frequency of vibration due to torque fluctuations during lockup is lower than that for an engine having four cylinders or more that has been generally adopted, it is possible to effectively decrease vibration due to torque fluctuations during lockup, since the orifice passages thereof are tuned to a low frequency. In particular, even if the lockup engine speed is reduced in addition to decreasing the number of cylinders such that the frequency of vibration due to torque fluctuations during lockup becomes lower to the frequency range for which vibration amplification due to rigid body resonance or the like of the suspension system or the drive train can be a problem, for example, it is possible to avoid deterioration in the vibration state owing to the vibration damping effect of the strut mount10and the suspension bushing106.

With respect to the vibration input due to torque fluctuations during lockup, the strut mount10and the suspension bushing106selectively exhibit either one of the vibration damping effect owing to high attenuating action based on the flow action of the fluid and the vibration damping effect owing to vibration insulating action (low dynamic spring behavior) based on the flow action of the fluid, depending on the tuning of the orifice passage. Whether the high attenuating action or the vibration insulating action is effective can be suitably selected in consideration of the resonance frequency of the vibration amplification system such as the suspension system and the drive train, the resonance frequency of the vehicle body74, and the like. As one example, in the case in which the differential between the resonance frequency of the suspension system, the drive train or the like and the resonance frequency of the vehicle body74is small, it is conceivable to tune such that the high attenuating action decreases the vibration amplification due to rigid body resonance of the suspension system and the drive train.

With a four-cycle engine, the frequency of vibration due to torque fluctuations during lockup can be easily calculated by using the number of cylinders of the engine and the engine speed during lockup, and specifically, can be calculated by multiplying the engine speed per second by one-half of the number of cylinders of the engine. As shown inFIG. 7, with a two-cylinder engine, the frequency of vibration due to torque fluctuations during lockup is 8.3 Hz for the engine speed 500 rpm during lockup, 16.7 Hz for 1000 rpm, and 25.0 Hz for 1500 rpm. With a three-cylinder engine, the aforementioned frequency is 12.5 Hz for the engine speed 500 rpm during lockup, 25.0 Hz for 1000 rpm, and 37.5 Hz for 1500 rpm. With a four-cylinder engine, the aforementioned frequency is 20.0 Hz for 500 rpm, 33.3 Hz for 1000 rpm, and 50.0 Hz for 1500 rpm. With a six-cylinder engine, the aforementioned frequency is 25.0 Hz for 500 rpm, 50.0 Hz for 1000 rpm, and 75.0 Hz for 1500 rpm.

In this way, if the number of cylinders is equal, the lower the engine speed during lockup is, the lower the frequency of vibration due to torque fluctuations becomes. Meanwhile, if the engine speed during lockup is equal, the smaller the number of cylinders is, the lower the frequency of vibration due to torque fluctuations becomes. In the range of 1000 rpm to 1500 rpm which can be adopted as the engine speed during lockup in order to realize enhanced fuel economy under the present circumstances, as shown inFIG. 7, with each of the two-cylinder, three-cylinder, and four-cylinder engines, the frequency of vibration due to torque fluctuations during lockup and the frequency of resonance mode of the suspension system and drive train are close to each other, so that amplification of vibration due to rigid body resonance of the suspension system or the drive train is likely to occur. Therefore, with respect to an automobile including a two-to four-cylinder engine and whose lockup engine speed is 1000 rpm to 1500 rpm, by applying the strut mount10and the suspension bushing106according to the present embodiment, the vibrations due to torque fluctuations during lockup can be effectively decreased. In particular, through application in an automobile that includes an engine having three cylinders or less, it is also possible to set the engine speed during lockup even lower, thereby enhancing fuel economy performance.

Moreover, as shown inFIG. 8, it was confirmed through tests and simulations that, with respect to the vibrations due to torque fluctuations during lockup, as the number of cylinders of the engine decreases, the ratio of vibration transmission via the path from the drive train to the suspension system becomes higher than that of transmission via the power train system as the path or that of transmission via other path. Therefore, with respect to the suspension mechanism70of the automobile that includes an engine having three cylinders or less, by applying the strut mount10and the suspension bushing106according to the present embodiment, the vibrations due to torque fluctuations during lockup can be more effectively decreased.

FIGS. 9 and 10show actual measurement data about an automobile including three-cylinder engine.FIG. 9shows the results of measuring the up-down vibrations of the strut mount on the suspension side during locked-up acceleration, and a plurality of peaks of vibration level which was thought to be rigid body resonance of the suspension system or the like were confirmed within the range for which the engine speed during lockup is 1000 rpm to 2000 rpm. Next,FIG. 10shows the ratio of contribution of vibration transmitted by each path so as to indicate which contribution is large in the floor vibrations (up-down vibrations, left-right vibrations, and front-rear vibrations) in the vehicle body74during locked-up acceleration. It was confirmed that the contribution of left and right strut mounts was large in the range of 1000 rpm to 2000 rpm. In particular, in the actual measurements inFIG. 10, in the range for which the engine speed is about 1370 rpm to 1600 rpm, the contribution of left and right strut mounts was as large as about 50% to 70%. Thus, it was confirmed that the vibrations due to torque fluctuations during lockup were input to the vehicle body74via the suspension system.

According to the actual measurements ofFIGS. 9 and 10, it was found that with an automobile including a three-cylinder engine, by adopting the strut mount10according to the present embodiment, it is possible to attain excellent vibration damping performance in the case in which the lockup engine speed is in the range of 1000 rpm to 2000 rpm. In particular, according toFIG. 10, it can be assumed that, by adopting the strut mount10, excellent vibration damping effect will be exhibited especially in the range of 1370 rpm to 1600 rpm. It should be appreciated that the actual measurements shown inFIGS. 9 and 10are not common to all automobiles including a three-cylinder engine, but are merely shown by way of example.

Also, with the strut mount10of the present embodiment, the primary liquid chamber62includes the front/rear pair of extended areas36,36and the left/right pair of constricted areas38,38, and the extended areas36,36are interconnected in the circumferential direction by the constricted areas38,38(constricted passages69,69) that is made tunnel-like by the lid member46. With this arrangement, when the wheel assembly100overrides depressions or ridges on the road surface or the like, with respect to the vibration input in the strut mount10in the generally axis-perpendicular direction (including the direction that inclines with respect to both of the axial direction and the axis-perpendicular direction) or in the prizing direction, relative internal pressure differential is produced within the front/rear pair of extended areas36,36, so as to allow a fluid flow through the constricted passages69,69between the extended areas36,36. As a result, the strut mount10will exhibit vibration damping effect based on the flow action of the fluid, and is able to obtain excellent vibration damping performance with respect to the vibration input from the wheel assembly100as well, which is in contact with a road surface.

In particular, the vibration input from the wheel assembly100that is in contact with a road surface when overriding depressions or ridges on the road surface or the like has a higher frequency than the vibration due to torque fluctuations during lockup does. Thus, the orifice passage68tuned to the frequency of vibration due to torque fluctuations during lockup substantially clogs due to antiresonance. On the other hand, with the constricted passages69,69, the resonance frequency of the flowing fluid is tuned to a higher frequency than the tuning frequency of the orifice passage68, and tuned to the vibration input from the road surface. Thus, desired vibration damping effect can be efficiently attained.

An embodiment of the present invention has been described in detail above, but the present invention is not limited to those specific descriptions. For example, while the preceding embodiment illustrated the strut mount10having the structure in which the vehicle body74is fixed by bolting to the second mounting member14, it is also possible to adopt the structure in which, for example, the vehicle body is overlapped with the second mounting member from above without being fixed thereto.

Besides, in the preceding embodiment, illustrated was the structure in which the primary liquid chamber62includes the front/rear pair of extended areas36,36and the left/right pair of constricted areas38,38, and a fluid flow will take place through the constricted areas38,38between the extended areas36,36so as to exhibit vibration damping effect based on the flow action of the fluid. However, such extended areas36,36and the constricted areas38,38are not essential. Specifically, with a strut mount120shown inFIG. 11, a circular recess122formed in the main rubber elastic body16has a cross sectional shape that is generally constant about the entire circumference. Accordingly, a primary liquid chamber124formed by the lower opening of the circular recess122being covered by the lid member46has a cross sectional shape that is generally constant about the entire circumference. With such strut mount120as well, the same as the preceding embodiment, with respect to the vibrations due to torque fluctuations during lockup, vibration damping effect will be attained based on the resonance action or the like of the fluid flowing through the orifice passage68between the primary liquid chamber124and the auxiliary liquid chamber64. Whereas the circular recess122inFIG. 11has a cross sectional shape that is equivalent to that of the extended area36in the preceding embodiment, no particular limitation is imposed as to the shapes of the circular recess and hence the primary liquid chamber. Moreover, the primary liquid chamber and the auxiliary liquid chamber need not have an annular shape that is continuous about the entire circumference, but may have a C-letter shape that extends just short of once around the circumference, or the like.

The preceding embodiment illustrated the strut mount10of dual-path type for which the vibration from the drive train is input substantially by the shock absorber72only. However, for example, the present invention can preferably be applied to a structure of single-path type like a strut mount130as shown inFIG. 12in a mounted state onto a vehicle, for which the vibration is input by both of the shock absorber72and the coil spring98. In the following description about the strut mount130shown inFIG. 12, components and parts that are substantially identical with those of the strut mount10in the preceding first embodiment will be assigned like symbols and not described in any detail, the same as the strut mount120shown inFIG. 11.

As shown inFIG. 12, with the strut mount130, the first mounting member12is attached to the piston rod76of the shock absorber72similar to the first embodiment, while a spring support fitting132for supporting the upper end portion of the coil spring98is attached to the first mounting member12.

Moreover, the spring support fitting132includes a tubular inner peripheral portion134, and the inner peripheral portion134is attached to the first mounting member12via an annular bearing136inserted into the inner tube member18. By so doing, when a rotational moment in the circumferential direction acts on an annular-plate shaped outer peripheral portion138for supporting the coil spring98, the spring support fitting132is allowed to rotate relative to the first mounting member12, so as to avoid torsion input in the circumferential direction with respect to the main rubber elastic body16. This will improve durability of the main rubber elastic body16.

With the bearing136, an upper part140is fixed to the first mounting member12, while a lower part142is attached rotatably relative to the upper part140via a rolling element144of ball form, so that the lower part142is rotatable with respect to the first mounting member12in the circumferential direction. In addition, the upper part140and the lower part142are relatively positioned in the up-down direction by a thin-walled connecting member146that is fitted externally thereon, and are retained so as not to be separated in the up-down direction. The inner peripheral portion134of the spring support fitting132is fixed to the lower part142of the bearing136.

With the strut mount130of structure as shown inFIG. 12, the vibrations in the up-down direction transmitted through the drive train due to torque fluctuations during lockup are input not only via the shock absorber72but also via the coil spring98. Then, in the strut mount130, the same as in the strut mount10of the first embodiment, vibration damping effect will be exhibited based on the flow action of the fluid. Accordingly, the vibration transmitted to the vehicle body74via the shock absorber72and the coil spring98will be decreased, thereby realizing good ride comfort or the like. As will be understood from this, the application range of the strut mount according to the present invention is not limited to application in the structure in which all the vibrations during lockup of the automobile is transmitted from the automotive drive train to the vehicle body via the shock absorber.

Furthermore, the preceding embodiment adopted the suspension bushing106of fluid-filled type, and illustrated the structure in which the tuning frequency of the orifice passage of the suspension bushing106was set to the frequency of vibration due to torque fluctuations during lockup. However, it would also be acceptable, for example, to tune the orifice passage of the suspension bushing to the frequency of vibration input from the road surface, or to adopt a solid-type bushing such as disclosed in Japanese Unexamined Patent Publication No. JP-A-2014-145410 or the like as the suspension bushing.