Patent Description:
A torsion beam suspension used for rear wheels of a front-wheel drive vehicle is one type of automotive suspension, for example. The torsion beam suspension is in a structure where a trailing arm (trailing link) that supports each wheel on the left and right sides is connected by a torsion beam (torsion bar) arranged in the width direction of the vehicle, and an end of the trailing arm is integrally attached to a bush that is arranged obliquely to the front-rear direction of the vehicle.

A conventional bush structure is known to include an inner cylinder extending in the direction of the bush axis, an outer cylinder arranged radially outside the inner cylinder, and a main body rubber connecting the inner cylinder and the outer cylinder, where bores that penetrate the main body rubber in the direction of the bush axis are provided facing each other across the inner cylinder, and a convex portion that projects from the inner cylinder to the outer cylinder is provided at the center of the bore. Examples of the bush having such a bush structure include the one described in <CIT> (PTL <NUM>).

With the conventional bush structure, the relative relationship of the spring properties (spring property ratio) between a bore direction, which is a direction passing through the circumferential center of each of the oppositely arranged bores, and a solid direction, which is a direction passing through the circumferential center of each of the main body rubber portions that are oppositely arranged and sandwiched between the bores, is determined in the cross section of the bush. Therefore, the bush is generally arranged so that the front-rear direction of the vehicle, which has a heavy load on the bush, is substantially the solid direction. This is because that, in the solid direction, the spring property is hard and the displacement amount caused by input of load is small, so that the durability of the bush is maintained.

Under such circumstances, in order to improve the ride quality, for example, it may be desired to position the bush so that the front-rear direction of the vehicle, which has a heavy load on the bush, is moved to the bore direction side, for example, the front-rear direction of the vehicle is oriented substantially toward the center between the solid direction and the bore direction. As used herein, the bore direction refers to a direction that passes through a low-rigidity portion of an elastic body, where the elastic body is the main body rubber and the low-rigidity portion is formed by a space penetrating the main body rubber, and the solid direction refers to a direction that passes through a portion other than the low-rigidity portion of the elastic body, where the portion is formed by the main body rubber that is the elastic body.

Attention is also drawn to the disclosures of <CIT> and <CIT>.

However, for a bush where the bush axis is arranged obliquely to the front-rear direction of a vehicle, such as a torsion beam bush, the spring property is soft and the displacement amount caused by input of load is large in the bore direction in the case where the bush is positioned so that the front-rear direction of the vehicle is oriented substantially toward the center between the solid direction and the bore direction. This results in an increase in the displacement amount, that is, an increase in the pulling amount of the main body rubber portion, which makes it difficult to maintain the durability of the bush. Therefore, if it is attempted to maintain the durability of the bush while the bush is positioned so that the front-rear direction of the vehicle is oriented substantially toward the center between the solid direction and the bore direction, then the spring property ratio between the solid direction and the bore direction collapses.

As described above, for a torsion beam bush where the bush axis is arranged obliquely to the front-rear direction of a vehicle, it is difficult to maintain the durability of the torsion beam bush and keep the spring property ratio at the same time when the bore direction is tilted toward the side of the front-rear direction of the vehicle.

It could thus be helpful to provide a bush with which it is possible to maintain a predetermined spring property ratio between a low-rigidity portion and a portion other than the low-rigidity portion of an elastic body while maintaining the durability in the front-rear direction of a vehicle, in the state where the bush axis is arranged obliquely to the front-rear direction of the vehicle.

The bush of the present invention is provided as claimed in claim <NUM>.

The bush arrangement structure of the present disclosure is a structure where the bush of the present disclosure is arranged so that a front-rear direction of a vehicle passes through the convex portion.

According to the present disclosure, it is possible to provide a bush with which it is possible to maintain a predetermined spring property ratio between a low-rigidity portion and a portion other than the low-rigidity portion of an elastic body while maintaining the durability in the front-rear direction of a vehicle, in the state where the bush axis is arranged obliquely to the front-rear direction of the vehicle.

The following describes an embodiment of the present disclosure with reference to the drawings.

As illustrated in <FIG>, the bush (torsion beam bush) <NUM> of the present embodiment includes an inner cylinder <NUM> extending in the direction of a bush axis a, an outer cylinder <NUM> arranged radially outside the inner cylinder <NUM>, and a rubber portion <NUM>, which is an elastic body, connecting the inner cylinder <NUM> and the outer cylinder <NUM>, where the rubber portion <NUM> is provided with a bore <NUM> as a low-rigidity portion that extends a predetermined length in a circumferential direction and lowers rigidity in a radial direction, a convex portion 11a that projects from the inner cylinder <NUM> to the outer cylinder <NUM> is provided at a circumferential position corresponding to the bore <NUM> of the inner cylinder <NUM>, and the convex portion 11a is arranged to be shifted to one side in the circumferential direction with respect to a circumferential center of the bore <NUM>. In other words, the position of the circumferential center of the convex portion 11a is shifted from the position of the circumferential center of the low-rigidity portion. The position of the circumferential center of the bore <NUM>, which is the low-rigidity portion, and the position of the circumferential center of the convex portion 11a are shifted in the circumferential direction in a range of -<NUM>° to <NUM>° (excluding <NUM>°).

As illustrated in <FIG>, the bush <NUM> of the present embodiment is used in one type of automotive suspension, for example, a torsion beam suspension used in rear wheels of a front-wheel drive vehicle. In the torsion beam suspension, a trailing arm (trailing link) 15a that supports each wheel on the left and right sides (not illustrated in the figure) is connected by a torsion beam (torsion bar) 15b arranged in the width direction of the vehicle, and the trailing arm 15a is arranged on the vehicle body (not illustrated in the figure) with the bush axis a, which serves as a fulcrum of the trailing arm, being oblique to the front-rear direction of the vehicle. The bush <NUM> is mounted to an attaching member 15c fixed to the vehicle body. In the bush <NUM>, an end of the trailing arm 15a integrated with the torsion beam 15b is, for example, integrally attached to the outer cylinder <NUM> of the bush <NUM> (see <FIG>).

In the present embodiment, the inner cylinder <NUM> is formed in a cylindrical shape having an axial space 11b that penetrates in the direction of the bush axis a, the outer cylinder <NUM> is formed in an annular shape, the inner cylinder <NUM> and the outer cylinder <NUM> are formed by, for example, metal members, the rubber portion <NUM> is formed in an annular shape that fills the space between the inner cylinder <NUM> and the outer cylinder <NUM>, and the inner cylinder <NUM> and the outer cylinder <NUM> are arranged concentrically via the rubber portion <NUM>, as illustrated in <FIG>, <FIG>.

In the present embodiment, the bore <NUM> is formed as a through hole that penetrates the rubber portion <NUM> in the direction of the bush axis a (see <FIG>, <FIG>). In addition, the bore <NUM> is formed over a range (arc range) having a central angle of <NUM>° or more about the axis of the inner cylinder <NUM> (bush axis a) in the circumferential direction of the rubber portion <NUM>. For example, it is formed over a range (arc range) having a central angle of <NUM>° or more and <NUM>° or less and preferably <NUM>° or more and <NUM>° or less. Moreover, the bore <NUM> has a slit-shaped portion 14a extending in an arc shape along the circumferential direction and hole portions 14b at both ends in the circumferential direction (see <FIG>). When the bore <NUM> is formed over a range having a central angle of <NUM>° or more, the convex portion 11a can be freely arranged so that it is shifted from the slit-shaped portion 14a. Note that there is a part of the convex portion 11a on the radially inner side of the circumferential center of the bore <NUM> which is a low-rigidity portion. In other words, the convex portion 11a overlaps the circumferential center of the bore <NUM>, which is a low-rigidity portion, in the circumferential direction.

In the present embodiment, a pair of bores <NUM> are provided at positions that are axially symmetric with respect to the bush axis a with the inner cylinder <NUM> interposed therebetween, as illustrated in <FIG>. For example, the diameter direction passing through the vicinity of two hole portions 14b and 14b, which is a solid direction P1 passing only through the rubber portion <NUM>, the radial hardness of the bush <NUM> is higher than that in a bore direction P2 described later, leading to a hard portion. On the other hand, in the diameter direction passing through the two slit-shaped portions 14a and 14a, which is a bore direction P2 passing through the slit space, the radial hardness of the bush <NUM> is lower than that in the solid direction P1, leading to a soft portion.

In the present embodiment, the bore <NUM> is formed over a range having a central angle of <NUM>° or more about the axis of the inner cylinder <NUM> (bush axis a) in the circumferential direction of the rubber portion <NUM>, the pair of bores <NUM> and <NUM> are asymmetrically arranged with respect to both the axis of the solid direction P1 and the axis of the bore direction P2 (see <FIG>), and any spring property ratio (rigidity ratio) can be set between the solid direction P1 and the bore direction P2. In addition, because the bore <NUM> of the present embodiment is formed over a range (arc range) of <NUM>° or less, it is possible to guarantee the linearity of the spring property of the axis of the bore direction P2 for any displacement region.

As illustrated in <FIG>, the convex portion 11a of the inner cylinder <NUM> of the present embodiment is formed as an irregularly shaped projection of the inner cylinder <NUM>, where the projecting end is in the vicinity of the slit-shaped portion 14a, the substantially entire width in a radial direction of the rubber portion <NUM> corresponding to the slit-shaped portion 14a is set as the projection amount, and the projection range in the circumferential direction is shorter than the circumferential length of the slit-shaped portion 14a. Because the circumferential length of the convex portion 11a is shorter than the circumferential length of the slit-shaped portion 14a, the convex portion 11a can be arranged between the solid direction P1 and the bore direction P2 on one side in the circumferential direction with respect to the circumferential center of the bore <NUM>. For example, it can be arranged shifted to the solid direction P1 side, and only the rubber portion <NUM> with no convex portion 11a is in the bore direction P2.

With the above structure, the convex portion 11a of the inner cylinder <NUM> of the present embodiment, which is a projecting portion of the inner cylinder <NUM> formed of, for example, a metal member, reinforces the rubber portion <NUM> provided with the bore <NUM>, thereby increasing the tensile strength in the direction of the two convex portions 11a and 11a (see <FIG>). In addition, when the convex portion 11a is arranged shifted to the solid direction P1 side and does not extend to the bore direction P2, for example, only the rubber portion <NUM> with no convex portion 11a is in the bore direction P2 (see <FIG>). As a result, even if a convex portion 11a is formed in the inner cylinder <NUM>, the portion in the bore direction P2 is still a soft portion where the radial hardness of the bush <NUM> is low, thereby maintaining the softness.

In the present embodiment, the convex portion 11a is formed of a metal member, yet it is not limited to a metal member. For example, the convex portion 11a may be formed of a resin member and may be integrated with or separated from the inner cylinder <NUM>.

In the present embodiment, the low-rigidity portion is the bore <NUM> formed by penetrating the rubber portion <NUM> in the direction of the bush axis a, yet it is not limited to this. For example, the low-rigidity portion may be formed as a non-penetrating thin portion extending over a certain range that does not penetrate the rubber portion <NUM> in the direction of the bush axis a. Note that a low-rigidity portion can be easily formed by choosing the bore <NUM>.

In the present embodiment, the outer cylinder <NUM> may have an intermediate cylinder on the inner side, a rubber member may be provided between the inner cylinder <NUM> and the intermediate cylinder, and the intermediate cylinder may be press-fitted into the outer cylinder <NUM>. The outer cylinder <NUM> and the intermediate cylinder may both be formed of a metal member, or at least one of them may be formed of a resin member.

Next, a bush arrangement structure will be described. The following describes the case where the bush <NUM> of the present embodiment is used in a torsion beam suspension (see <FIG>), which is one type of automotive suspension. In other words, the following describes a bush arrangement structure in which the bush <NUM> of the present embodiment is arranged so that the front-rear direction of a vehicle passes through the convex portion 11a.

For the bush <NUM> of the present embodiment, the bush axis a is arranged obliquely to the front-rear direction of the vehicle (see <FIG>), the bush <NUM> is arranged so that the front-rear direction of the vehicle passes through the convex portion 11a, and the direction of the two convex portions 11a and 11a (see <FIG>), which is substantially the direction in the middle between the solid direction P1 and the bore direction P2 (the direction of approximately <NUM>° angle), is directed to the front-rear direction of the vehicle, that is, the horizontal direction (see <FIG>). As a result, in the bush <NUM> of the present embodiment, the positions of the bores <NUM> provided in the rubber portion <NUM> are unequally arranged with respect to the front-rear direction of the vehicle, and the two convex portions 11a and 11a are in the front-rear direction of the vehicle.

When the two convex portions 11a and 11a are in the front-rear direction of the vehicle, the durability of the rubber portion <NUM> does not deteriorate. The reason is as follows. For example, in the case where the rubber portion <NUM>, which is softer than the portion in the solid direction P1 and is provided with the bore <NUM>, has an input of force in the front-rear direction of the vehicle that is same to the input of force in the solid direction P1, the movement amount of the inner cylinder <NUM> and the outer cylinder <NUM> increases. Once the movement amount increases, the pulling amount of the rubber portion <NUM> increases, and the durability deteriorates. In the present embodiment, however, the two convex portions 11a and 11a serve as stoppers to suppress the deformation even when a force that is same to the force in the solid direction P1 is input in the front-rear direction of the vehicle, thereby preventing the movement amount of the inner cylinder <NUM> and the outer cylinder <NUM> from increasing.

As described above, according to the bush of the present disclosure and the bush arrangement structure of the present disclosure, the bush <NUM> of the present embodiment is arranged in the bush arrangement structure of the present embodiment so that the front-rear direction of a vehicle passes through the two convex portions 11a and 11a. In this way, even if the front-rear direction of the vehicle is arranged closer to the bore direction P2 in the bush <NUM> of the present embodiment, the spring property ratio (rigidity ratio) between the solid direction P1 and the bore direction P2 is maintained, the tensile strength in the front-rear direction of the vehicle is increased, the displacement amount caused by the input of force in the front-rear direction of the vehicle can be suppressed, the durability can be improved, and the softness in the bore direction P2 can be maintained.

Claim 1:
A bush (<NUM>) comprising an inner cylinder (<NUM>), an outer cylinder (<NUM>) arranged radially outside the inner cylinder (<NUM>), and an elastic body (<NUM>) connecting the inner cylinder (<NUM>) and the outer cylinder (<NUM>), wherein
the elastic body (<NUM>) in the form of a rubber portion (<NUM>) is provided with a low-rigidity portion (<NUM>) that extends a predetermined length in a circumferential direction and lowers rigidity in a radial direction,
a convex portion (11a) that projects from the inner cylinder (<NUM>) to the outer cylinder (<NUM>) is provided at a circumferential position corresponding to the low-rigidity portion (<NUM>) of the inner cylinder (<NUM>), and
the convex portion (11a) is arranged to be shifted to one side in the circumferential direction with respect to a circumferential center of the low-rigidity portion (<NUM>),
the low-rigidity portion (<NUM>) is a bore (<NUM>) formed by penetrating the elastic body (<NUM>) in a bush axial direction, characterized in that
the bore (<NUM>) has a slit-shaped portion (14a) extending in an arc shape along the circumferential direction and hole portions (14b) at both ends in the circumferential direction,
the convex portion (11a) is arranged on the radially inner side of the slit-shaped portion (14a), and
the convex portion (11a) of the inner cylinder (<NUM>) is formed as an irregularly shaped projection of the inner cylinder (<NUM>), where a projecting end is in a vicinity of the slit-shaped portion (14a), a substantially entire width in a radial direction of the rubber portion (<NUM>) corresponding to the slit-shaped portion (14a) is set as a projection amount, and a projection range in the circumferential direction is shorter than a circumferential length of the slit-shaped portion (14a).