Cylindrical Anti-vibration device for motor mount

Abstract

Provided is a cylindrical anti-vibration device for a motor mount, the cylindrical anti-vibration device having a novel structure and being capable of ensuring durability while suppressing deterioration in a vibration state due to surging.　Specifically provided is a cylindrical anti-vibration device 10 for a motor mount, in which an inner shaft member 12 and an outer cylinder member 14 are connected by a plurality of rubber legs 16, wherein: four of the rubber legs 16, 16, 16, 16, which expand relative to each other in the circumferential direction toward the outer periphery, are configured from first rubber legs 16a, 16b that are positioned on two sides in a diagonal direction relative to the inner shaft member 12 and second rubber legs 16c, 16d that are positioned on two sides in the other diagonal direction; the distances D1 from the center axis C1 of the inner shaft member 12 to fixing surfaces of the first rubber legs 16a, 16b are configured to be shorter than distances D2 to fixing surfaces of the second rubber legs 16c, 16d; the center axis C1 of the inner shaft member 12 and the center axis C2 of the outer cylinder member 14 are misaligned relative to each other in the vertical direction; and the four rubber legs 16a, 16b, 16c, 16d all have different length dimensions.

Description

Cylindrical vibration isolation device for motor mount

[0001] The present invention relates to a cylindrical vibration isolation device for a motor mount used as a motor mount that connects an electric motor to a vehicle body in an electrically powered vehicle such as an electric vehicle (BEV) or a hybrid car in a vibration-damping manner.

[0002] Recently, with the trend toward electric vehicles, motor mounts that connect electric motors to vehicle bodies in a vibration-damping manner have been developed. As motor mounts, for example, a cylindrical vibration-damping device is used in which an inner shaft member and an outer cylindrical member are interconnected by a plurality of rubber legs extending radially, as disclosed in FIG. 5 of German Patent Application Publication No. 102018221375 (Patent Document 1).

[0003] DE 102018221375 A1

[0004] However, in motor mounts that provide vibration isolation for electric motors, which vibrate less than internal combustion engines, deterioration of vibration conditions in the high frequency range due to surging of the rubber feet is a common problem. In particular, when multiple rubber feet of approximately the same shape and size are used, as shown in Figure 5 of Patent Document 1, the resonant frequencies of the multiple rubber feet are approximately the same, which can lead to significant deterioration of vibration conditions at specific frequencies.

[0005] In Patent Document 1, a mass protrusion is formed on the rubber foot, and the mass damping action of the mass protrusion prevents the adverse effects on vibration caused by surging of the rubber foot. However, when a mass protrusion is provided on the rubber foot, strain concentrates on the base end of the mass protrusion when the rubber foot deforms during vibration input, making the mass protrusion and the rubber foot more susceptible to damage.

[0006] The problem to be solved by the present invention is to provide a cylindrical vibration isolation device for motor mounts with a novel structure that can prevent the vibration state from becoming significantly worse at specific frequencies due to surging while ensuring the durability of the rubber legs.

[0007] The following describes preferred embodiments for understanding the present invention, but the embodiments described below are merely examples and may be appropriately combined with one another. Multiple components described in each embodiment may be recognized and employed independently to the greatest extent possible, and may also be appropriately combined with any of the components described in other embodiments. Accordingly, the present invention is not limited to the embodiments described below, and various other embodiments may be realized.

[0008] The first aspect is a cylindrical vibration-damping device for a motor mount in which an inner shaft member and an outer cylindrical member are connected by a plurality of rubber legs extending between the radially opposing surfaces of the inner shaft member and the outer cylindrical member, and the plurality of rubber legs are four rubber legs that expand circumferentially toward the outer periphery in the vertical and horizontal directions, and the four rubber legs are composed of two first rubber legs located on both sides of the inner shaft member in a diagonal direction and two second rubber legs located on both sides of the inner shaft member in another diagonal direction, and the distance from the central axis of the inner shaft member to the fixing surface of the first rubber legs on the outer periphery is shorter than the distance from the central axis of the inner shaft member to the fixing surface of the second rubber legs on the outer periphery, and because the central axis of the inner shaft member and the central axis of the outer cylindrical member are offset from each other in the vertical direction, the length dimensions of the four rubber legs in the connection direction between the inner shaft member and the outer cylindrical member are all different.

[0009] In a cylindrical vibration isolation device for a motor mount constructed according to this aspect, the four rubber legs all have different lengths, which allows the four rubber legs to have different resonant frequencies in response to vibration input, thereby preventing significant deterioration of the vibration state at specific frequencies due to surging of the four rubber legs.

[0010] The first and second rubber legs have different lengths due to the difference in the distance from the central axis of the inner shaft member to the fixing surface of the rubber legs, and the central axis of the inner shaft member and the central axis of the outer cylindrical member are misaligned in the vertical direction, so that all four rubber legs have different lengths. This makes it possible to set different lengths for the four rubber legs without requiring the outer cylindrical member to have a larger diameter.

[0011] In the second aspect, in the cylindrical vibration-damping device for a motor mount described in the first aspect, the fixing surface of the first rubber leg on the outer surface of the inner shaft member is concave and opens toward the outer periphery.

[0012] According to the cylindrical vibration-damping device for a motor mount constructed in accordance with this embodiment, the fixing surface of the first rubber leg on the outer surface of the inner shaft member is concave, allowing the length of the first rubber leg to be set longer.

[0013] Furthermore, by forming the fixing surface of the first rubber leg on the outer peripheral surface of the inner shaft member in a concave shape, it is possible to design the shape of the portion of the outer peripheral surface of the inner shaft member outside the fixing surface of the first rubber leg with a large degree of freedom while ensuring a sufficient length of the first rubber leg, which makes it easier to design a surface that constitutes a stopper, for example, on the portion of the outer peripheral surface of the inner shaft member outside the fixing surface of the first rubber leg.

[0014] The third aspect is a cylindrical vibration-damping device for a motor mount described in the first or second aspect, in which the length dimension of the first rubber leg is greater than the length dimension of the second rubber leg.

[0015] With a cylindrical vibration-damping device for a motor mount constructed in accordance with this embodiment, the difference in length between the two first rubber legs located on both sides of a diagonal direction is reduced, and the difference in length between the two second rubber legs located on both sides of another diagonal direction is also reduced.As a result, for example, when an axial input is applied, unintended relative displacement such as vibration between the inner shaft member and the outer cylindrical member is less likely to occur, making it easier to stabilize the vibration state.

[0016] According to the present invention, it is possible to prevent the vibration state due to surging from becoming significantly worse at a specific frequency.

[0017] A front view showing a cylindrical vibration-damping device for a motor mount according to a first embodiment of the present invention. A cross-sectional view taken along line II-II of FIG. 1. A cross-sectional view taken along line III-III of FIG. 1. A cross-sectional view comparing the lengths of the rubber legs in the cylindrical vibration-damping device of FIG. 1. A graph showing the spring characteristics of a cylindrical vibration-damping device for a motor mount.

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] 1 to 3 show a motor mount 10 for a vehicle as a first embodiment of a cylindrical vibration-damping device for a motor mount according to the present invention. The motor mount 10 has a structure in which an inner axial member 12 and an outer tubular member 14 are interconnected by four rubber legs 16. In the following description, the vertical direction generally refers to the vertical direction in FIG. 1, the left-right direction generally refers to the left-right direction in FIG. 1, and the front-rear direction generally refers to the axial direction, i.e., the direction perpendicular to the plane of the paper in FIG. 1. Note that the vertical direction in the following description refers to the direction in which the main load is input to the motor mount 10 and does not necessarily correspond to the vertical direction of the vehicle when the motor mount 10 is mounted on the vehicle, as described below. Similarly, the left-right direction and front-rear direction in the following description do not necessarily correspond to the left-right direction and front-rear direction of the vehicle.

[0020] The inner shaft member 12 is a highly rigid member made of metal, fiber-reinforced synthetic resin, or the like, and is shaped like a rod that has a substantially uniform cross-sectional shape and extends linearly in the front-to-rear direction. The width dimension W of the inner shaft member 12 in the left-to-right direction is greater than the height dimension H in the up-to-down direction. The inner shaft member 12 is formed with bolt holes 18 that pass through in the axial direction. Because the inner shaft member 12 extends linearly and has a substantially uniform cross-sectional shape, it can be easily formed, for example, by extrusion processing.

[0021] The outer peripheral surface of the inner shaft member 12 is composed of a pair of horizontal surfaces 20 extending generally perpendicular to the up-down direction, a pair of vertical surfaces 22 extending generally perpendicular to the left-right direction, inner surfaces of a pair of recessed grooves 24 connecting the horizontal surfaces 20 and the vertical surfaces 22 on both sides in one diagonal radial direction, and a pair of inclined surfaces 26 connecting the horizontal surfaces 20 and the vertical surfaces 22 on both sides in the other diagonal radial direction. In this embodiment, the diagonal directions refer to the upper right, upper left, lower right, and lower left directions. One diagonal radial direction is the direction of extension of the II-II cross section in FIG. 1 , and the other diagonal radial direction is the direction of extension of the III-III cross section in FIG. 1 .

[0022] The inner surface of the recessed groove 24 has a groove bottom surface 28 that widens substantially perpendicular to one oblique radial direction, and groove side surfaces 30, 30 that extend from both widthwise ends of the groove bottom surface 28 toward the outer periphery of the inner shaft member 12 and widen perpendicular to the up-down or left-right direction. Therefore, the recessed groove 24 has an expanding shape in which the groove width dimension in the circumferential direction of the inner shaft member 12 increases toward the opening side. The recessed groove 24 extends linearly in the axial direction of the inner shaft member 12 with a substantially constant groove cross-sectional shape.

[0023] The inner shaft member 12 has a small oblique radial distance from the central axis C1 to the outer circumferential surface at the portions where the recessed grooves 24, 24 are formed. That is, the distance D1 from the central axis C1 of the inner shaft member 12 to the groove bottom surface 28 of the recessed groove 24 is shorter than the distance D2 from the central axis C1 to the inclined surface 26. In particular, in this embodiment, as can be seen from the drawings, this magnitude relationship is satisfied even when comparing the shortest distances from the central axis C1 to the corresponding surfaces.

[0024] The outer cylindrical member 14 is a highly rigid member formed of metal, fiber-reinforced synthetic resin, or the like, similar to the inner shaft member 12. The outer cylindrical member 14 has a thin-walled, large-diameter, and generally cylindrical shape, with an inner diameter dimension that is larger than the maximum outer diameter dimension of the inner shaft member 12. The inner diameter dimension of the outer cylindrical member 14 is generally constant around the entire circumference. The axial length of the outer cylindrical member 14 is shorter than that of the inner shaft member 12.

[0025] The inner shaft member 12 is inserted into the inner periphery of the outer cylindrical member 14. Since the inner shaft member 12 has a horizontally elongated flat shape and the inner diameter dimension of the outer cylindrical member 14 is substantially constant around the entire circumference, the distance between the vertical opposing surfaces of a horizontal surface 20 of the inner shaft member 12 and the inner periphery of the outer cylindrical member 14 is greater than the distance between the horizontal opposing surfaces of a vertical surface 22 of the inner shaft member 12 and the inner periphery of the outer cylindrical member 14.

[0026] The central axis C1 of the inner axial member 12 and the central axis C2 of the outer tubular member 14 are positioned approximately the same in the left-right direction, but are positioned differently in the up-down direction. That is, the central axis C1 of the inner axial member 12 is biased upward by a predetermined distance d with respect to the central axis C2 of the outer tubular member 14. As a result, the distance between the opposing surfaces of the inner axial member 12 and the outer tubular member 14 in the up-down direction is greater on the lower side than on the upper side.

[0027] Four rubber legs 16 are formed between the inner shaft member 12 and the outer cylindrical member 14. The inner peripheral end of each rubber leg 16 is vulcanization bonded to the inner shaft member 12, and the outer peripheral end is vulcanization bonded to the outer cylindrical member 14. The four rubber legs 16 are shaped to expand circumferentially toward the outer periphery and extend obliquely in the radial direction. The four rubber legs 16 are integrally connected at their inner peripheral ends fixed to the inner shaft member 12 by a tubular inner covering rubber 32 that covers the outer peripheral surface of the inner shaft member 12, and at their outer peripheral ends fixed to the outer cylindrical member 14 by a tubular outer covering rubber 34 that covers the inner peripheral surface of the outer cylindrical member 14. As shown in FIGS. 2 and 3, each rubber leg 16 has an axial end face that is curved and tapered so that it slopes inward in the axial direction toward the outer periphery, and the axial thickness dimension gradually decreases toward the outer periphery.

[0028] Between adjacent rubber legs 16, 16 in the circumferential direction, recessed holes 36 are formed, each penetrating in the axial direction. A stopper rubber 38 is disposed in each recessed hole 36, protruding from the outer tubular member 14 toward the inner axial member 12. The stopper rubber 38 is trapezoidal in axial view, narrowing in width in the circumferential direction toward its protruding tip. The protruding tip surface of the stopper rubber 38 is provided with irregularities for the purpose of reducing impact noise, and in this embodiment, three axially continuous peaks are provided, spaced apart from one another in the circumferential direction. The stopper rubber 38 is integrally formed with the outer covering rubber 34 and is provided integrally and continuously with the rubber legs 16.

[0029] The two rubber legs 16, 16 extending in one oblique radial direction are first rubber legs 16a, 16b fixed to the inner surfaces of the grooves 24, 24 of the inner shaft member 12, and the two rubber legs 16, 16 extending in the other oblique radial direction are second rubber legs 16c, 16d fixed to the inclined surfaces 26, 26 of the inner shaft member 12. In this embodiment, the groove bottom surface 28 and groove side surfaces 30, 30 constituting the inner surfaces of each groove 24 serve as the fixing surfaces for the first rubber legs 16a, 16b, and the inclined surfaces 26, 26 serve as the fixing surfaces for the second rubber legs 16c, 16d. Therefore, on the outer circumferential surface of the inner shaft member 12, the fixing surfaces for the first rubber legs 16a, 16b are concave and open toward the outer periphery, and the fixing surfaces for the second rubber legs 16c, 16d are flat.

[0030] 4, the lengths L1, L2 of the first rubber legs 16a, 16b are both longer than the lengths L3, L4 of the second rubber legs 16c, 16d. That is, the distance D1 between the fixing surfaces of the first rubber legs 16a, 16b on the inner shaft member 12 and the central axis C1 of the inner shaft member 12 is shorter than the distance D2 between the fixing surfaces of the second rubber legs 16c, 16d on the inner shaft member 12 and the central axis C1 of the inner shaft member 12, and the lengths L1, L2 of the first rubber legs 16a, 16b between the opposing inner shaft member 12 and the outer cylindrical member 14 are longer than the lengths L3, L4 of the second rubber legs 16c, 16d between the opposing inner shaft member 12 and the outer cylindrical member 14.

[0031] Furthermore, because the central axis C1 of the inner shaft member 12 is biased upward with respect to the central axis C2 of the outer cylindrical member 14, the length L1 of the lower first rubber leg 16a is longer than the length L2 of the upper first rubber leg 16b, and the length L3 of the lower second rubber leg 16c is longer than the length L4 of the upper second rubber leg 16d. Note that, because the central axis C1 of the inner shaft member 12 is biased upward with respect to the central axis C2 of the outer cylindrical member 14, the upper first rubber leg 16b is shorter and the lower second rubber leg 16c is longer, but the length L2 of the upper first rubber leg 16b is longer than the length L3 of the lower second rubber leg 16c.

[0032] As shown in Fig. 4, depending on the shape of the inner shaft member 12 and the relative positions of the inner shaft member 12 and the outer cylindrical member 14, the lengths of the four rubber legs 16a, 16b, 16c, and 16d are in the following order: length L1 of the first rubber leg 16a, length L2 of the first rubber leg 16b, length L3 of the second rubber leg 16c, and length L4 of the second rubber leg 16d (L1 > L2 > L3 > L4). Therefore, the lengths of the four rubber legs 16a, 16b, 16c, and 16d are all different from one another.

[0033] Since the four rubber legs 16a, 16b, 16c, and 16d have different lengths, the resonant frequencies (frequencies at which rubber surging occurs) of the rubber legs 16a, 16b, 16c, and 16d when they are bent and deformed are different from one another.

[0034] The motor mount 10 constructed as described above is attached to a vehicle by, for example, attaching the inner shaft member 12 to an electric motor (not shown) with bolts (not shown) inserted through the bolt holes 18, and attaching the outer tubular member 14 to the vehicle body (not shown) by press-fitting it into an attachment hole provided in the vehicle body. When the motor mount 10 is attached to the vehicle, the electric motor is connected to the vehicle body via the motor mount 10 in a vibration-damping manner.

[0035] When the motor mount 10 is installed on a vehicle, the shared support load of the electric motor is input in the vertical direction between the inner axial member 12 and the outer cylindrical member 14, displacing the inner axial member 12 downward relative to the outer cylindrical member 14. Even when such a shared support load is input, the central axis C1 of the inner axial member 12 is biased upward relative to the central axis C2 of the outer cylindrical member 14, the lower first rubber leg 16a is longer than the upper first rubber leg 16b, and the lower second rubber leg 16c is longer than the upper second rubber leg 16d.

[0036] When the motor mount 10 is mounted on a vehicle and vibration is input between the inner shaft member 12 and the outer cylindrical member 14, the relative displacement between the inner shaft member 12 and the outer cylindrical member 14 causes the four rubber legs 16a, 16b, 16c, and 16d to elastically deform, thereby providing a vibration-damping effect based on energy damping due to internal friction, etc., and vibration isolation.

[0037] Furthermore, when a large load is input between the inner shaft member 12 and the outer cylindrical member 14, the inner shaft member 12 and the outer cylindrical member 14 are displaced significantly relative to each other, causing the protruding tip surface of the stopper rubber 38 to indirectly abut against the inner shaft member 12 via the inner covering rubber 32. As a result, the inner shaft member 12 and the outer cylindrical member 14 abut against each other via the stopper rubber 38, thereby forming a stopper mechanism that limits the amount of relative displacement between the inner shaft member 12 and the outer cylindrical member 14. In this embodiment, four stopper rubbers 38, 38, 38, 38 are provided to protrude in four mutually different directions, and the amount of relative displacement between the inner shaft member 12 and the outer cylindrical member 14 can be limited in all radial directions by abutment via the stopper rubbers 38, 38, 38, 38. In this embodiment, since the central axis C1 of the inner shaft member 12 is located above the central axis C2 of the outer cylindrical member 14, the lower stopper rubber 38 has a larger vertical length dimension than the upper stopper rubber 38.

[0038] Incidentally, in the high-frequency range of around 1000 Hz to 1500 Hz, a problem with motor mounts arises when the bending elastic deformation of the rubber feet occurs in a resonant state, resulting in high dynamic springiness. If the four rubber feet indicated by the dashed lines in the graph of Figure 5 are identical in shape and size, all four rubber feet will resonate at roughly the same frequency, causing significant deterioration in vibration due to surging of the rubber feet.

[0039] Therefore, in the motor mount 10 of this embodiment, the four rubber feet 16a, 16b, 16c, and 16d have different lengths, and the frequencies at which high dynamic springiness occurs due to surging are different. Therefore, compared to the conventional structure shown by the dashed line in Figure 5, which experiences significant high dynamic springiness at a specific frequency, as shown by the solid line in the graph in Figure 5, the spring constant peaks are separated into multiple peaks that occur at different frequencies, and by dispersing the spring constant peaks, significant high dynamic springiness at a specific frequency is avoided. Therefore, deterioration of the vibration state due to rubber surging of the four rubber feet 16a, 16b, 16c, and 16d in the high frequency range is avoided, and better vibration-damping performance is achieved.

[0040] The distance D1 from the central axis C1 of the inner shaft member 12 to the fixing surfaces of the first rubber legs 16a, 16b is different from the distance D2 from the central axis C1 of the inner shaft member 12 to the fixing surfaces of the second rubber legs 16c, 16d, and the central axis C1 of the inner shaft member 12 is biased upward with respect to the central axis C2 of the outer cylindrical member 14. This allows the length dimensions of the four rubber legs 16a, 16b, 16c, 16d to be different from one another without increasing the outer diameter dimension of the outer cylindrical member 14.

[0041] The first rubber legs 16a, 16b are both longer than the second rubber legs 16c, 16d. This reduces the difference in length between the first rubber legs 16a, 16b located on one diagonal side of the inner shaft member 12, and also reduces the difference in length between the second rubber legs 16c, 16d located on the other diagonal side of the inner shaft member 12. This makes it less likely that unintended displacement, such as wobble, will occur between the inner shaft member 12 and the outer cylindrical member 14, making it easier to stabilize the vibration state.

[0042] In this embodiment, the distance D1 is made shorter than the distance D2 by forming grooves 24 in the fixing portions of the first rubber legs 16a, 16b in the inner shaft member 12. Therefore, the horizontal surfaces 20, 20 and vertical surfaces 22, 22 of the inner shaft member 12, which are the pressure-receiving surfaces of each stopper mechanism, can be provided with large circumferential width dimensions while ensuring a sufficient free length of the first rubber legs 16a, 16b, and the stopper mechanisms can be configured effectively.

[0043] In particular, in this embodiment, the inner shaft member 12 has a horizontally elongated, flat shape with a width greater than a height, which makes it easier to ensure a larger pressure-receiving surface for the stopper mechanism in the vertical direction, which is the main direction of load input, while ensuring the length of each rubber leg 16.

[0044] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the specific descriptions. For example, the central axis C1 of the inner axial member 12 may be biased downward relative to the central axis C2 of the outer tubular member 14. Furthermore, the central axis C1 of the inner axial member 12 may be offset from the central axis C2 of the outer tubular member 14 in the left-right direction in addition to the up-down direction.

[0045] The shape of the fixing surfaces of the first rubber legs 16a, 16b and the second rubber legs 16c, 16d on the inner shaft member 12 is not particularly limited as long as the distance D1 from the central axis C1 of the inner shaft member 12 to the fixing surfaces of the first rubber legs 16a, 16b is shorter than the distance D2 from the central axis C1 of the inner shaft member 12 to the fixing surfaces of the second rubber legs 16c, 16d. For example, the fixing surfaces of the first rubber legs 16a, 16b on the inner shaft member 12 may be flat, and the flat surface may be located closer to the central axis C1 of the inner shaft member 12 than the inclined surfaces 26, 26 that are the fixing surfaces of the second rubber legs 16c, 16d. Furthermore, for example, the fixing surfaces of the second rubber legs 16c, 16d on the inner shaft member 12 may be provided with convex portions that protrude outward, thereby making the free length of the second rubber legs 16c, 16d shorter than that of the first rubber legs 16a, 16b.

[0046] The inner shaft member does not necessarily have to have a constant cross-sectional shape along its entire axial length; the shape and size of the cross section may vary. For example, the inner shaft member may have a larger diameter at its axial middle portion than at its both ends. Alternatively, an inner shaft member having a large diameter at its axial middle portion can be constructed by fastening a synthetic resin (fiber-reinforced synthetic resin) ring member to the outer peripheral surface of an inner body that extends linearly with a constant cross-section at the axial middle portion. For example, by fastening a synthetic resin ring member having attachment surfaces for the first rubber legs 16a, 16b and the second rubber legs 16c, 16d to a metal inner body having an outer peripheral surface that is rotationally symmetrical about the central axis, the inner body can ensure the strength of the fastening portion to an electric motor, etc., while the synthetic resin ring member, which has a high degree of shape freedom, can easily and accurately realize a complex outer peripheral surface having the attachment surfaces for the first rubber legs 16a, 16b and the second rubber legs 16c, 16d.

[0047] When the cross-sectional shape of the inner shaft member changes in the axial direction, the distance D1 from the central axis of the inner shaft member to the fixing surfaces of the first rubber legs 16a and 16b needs only to be shorter than the distance D2 from the central axis of the inner shaft member to the fixing surfaces of the second rubber legs 16c and 16d in at least a portion of the axial direction. It is desirable that the distance D1 be shorter than the distance D2 over at least 50% of the axial length of the fixing surfaces of the rubber legs 16, and more preferably, the distance D1 be shorter than the distance D2 over the entire axial length. Furthermore, the distance D1 only needs to be shorter than the distance D2 over at least a portion of the circumferential direction of the inner shaft member, and it is not necessary for D1 to be less than D2 over the entire circumferential direction of the fixing surfaces. In other words, the distances D1 and D2 and the dimensions L1 to L4 do not need to satisfy the above-mentioned size relationship requirements throughout the entire axial direction, but preferably satisfy the size relationship requirements as an average value.

[0048] The difference between the distance D1 from the center axis C1 of the inner shaft member 12 to the outer peripheral surface in the oblique radial direction where the first rubber legs 16a, 16b are fixed and the distance D2 from the center axis C1 of the inner shaft member 12 to the outer peripheral surface in the oblique radial direction where the second rubber legs 16c, 16d are fixed does not necessarily have to be set over the entire axial length of the inner shaft member 12, as long as it is set at the fixed portions of the four rubber legs 16a, 16b, 16c, 16d. Therefore, for example, the inner shaft member 12 may have a rotationally symmetrical shape at both axial ends away from the fixed portions of the four rubber legs 16a, 16b, 16c, 16d.

[0049] By varying the inner diameter of the outer cylindrical member 14 in the circumferential direction, the lengths of the four rubber legs 16a, 16b, 16c, and 16d can be made to differ more greatly from one another.

[0050] The stopper mechanism is not essential to the motor mount 10, and the stopper rubber 38 can be omitted. The stopper rubber 38 can also be made to protrude from the inner shaft member 12 toward the outer cylindrical member 14. In this case, the stopper rubber 38 is formed integrally with the inner covering rubber 32.

[0051] REFERENCE SIGNS LIST 10 Motor mount (cylindrical vibration-damping device for motor mount, first embodiment) 12 Inner shaft member 14 Outer cylindrical member 16 Rubber legs 16a, 16b First rubber legs 16c, 16d Second rubber legs 18 Bolt hole 20 Horizontal surface 22 Vertical surface 24 Groove 26 Inclined surface (securing surface for second rubber leg) 28 Groove bottom surface (securing surface for first rubber leg) 30 Groove side surface (securing surface for first rubber leg) 32 Inner covering rubber 34 Outer covering rubber 36 Recessed hole 38 Stopper rubber W Left-right width dimension of inner shaft member H Vertical height dimension of inner shaft member D1 Distance from center axis of inner shaft member to bottom surface of groove D2 Distance from center axis of inner shaft member to inclined surface C1 Center axis of inner shaft member C2 Center axis of outer cylindrical member d Distance between C1 and C2 L1: Length of the first rubber leg 16a L2: Length of the first rubber leg 16b L3: Length of the second rubber leg 16c L4: Length of the second rubber leg 16d

Claims

1. A cylindrical vibration-damping device for a motor mount in which an inner shaft member and an outer cylindrical member are connected by a plurality of rubber legs extending between the radially opposing surfaces of the inner shaft member and the outer cylindrical member, the plurality of rubber legs being four rubber legs that expand circumferentially toward the outer periphery in the up-down and left-right directions, the four rubber legs being composed of two first rubber legs located on both sides in a diagonal direction to the inner shaft member and two second rubber legs located on both sides in another diagonal direction to the inner shaft member, the distance from the central axis of the inner shaft member to the fixing surface of the first rubber legs on the outer periphery is shorter than the distance from the central axis of the inner shaft member to the fixing surface of the second rubber legs on the outer periphery, and the central axis of the inner shaft member and the central axis of the outer cylindrical member are offset from each other in the up-down direction, so that the length dimensions of the four rubber legs in the connection direction between the inner shaft member and the outer cylindrical member are all different.

2. A cylindrical vibration isolator for a motor mount as described in claim 1, wherein the surface of the outer circumferential surface of the inner shaft member to which the first rubber leg is attached is formed into a concave shape that opens outward.

3. A cylindrical vibration isolator for a motor mount according to claim 1 or 2, wherein the length of said first rubber leg is greater than the length of said second rubber leg.

Images