Bush

Abstract

To provide a bush advantageous when changing a spring characteristic while saving costs with a simple constitution.SOLUTION: A bush 10A comprises a metallic inner cylinder 12, a metallic outer cylinder 14, and an elastic member 16 provided between the cylinders. A shape memory alloy 18 is provided on the elastic member 16. The elastic member 16 is provided between the inner cylinder 12 and the outer cylinder 14, and formed of various prior elastic materials such as rubber. The shape memory alloy 18 performs a shape recovery action by self-heating (Joule heat) due to energization, and changes a spring characteristic of the bush 10A.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a bush.

Background Art

[0002] As a vehicle suspension device, one in which a trailing arm supporting a wheel or a lower arm supporting a wheel is swingably connected to a vehicle body via a bush is known. The bush includes an inner cylinder, an outer cylinder, and an elastic member provided between them. For example, the inner cylinder is coupled to the trailing arm or the lower arm, and the outer cylinder is coupled to the vehicle body. Such a bush is designed to have a preset spring characteristic (elastic coefficient). The spring characteristic is the characteristic of the change amount of deflection with respect to a load. By the way, the bush has a tendency that the ride comfort improves as the deflection with respect to the load increases, or in other words, as the rigidity of the elastic member decreases, while the handling stability decreases. Also, the bush has a tendency that the handling stability improves as the deflection with respect to the load decreases, or in other words, as the rigidity of the elastic member increases, while the ride comfort decreases. Thus, the ride comfort and the handling stability are in a trade-off relationship. Therefore, Patent Document 1 discloses a technique for preferentially improving either the ride comfort or the handling stability by changing the spring characteristic of the bush by supplying hydraulic pressure from a hydraulic pressure source to a plurality of fluid chambers provided inside the elastic member.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the conventional technologies described above require the installation of a fluid chamber and a hydraulic power source, resulting in a complex configuration and increased costs. This invention has been made in view of the above circumstances, and aims to provide a bushing that is advantageous for changing spring characteristics while suppressing costs through a simple configuration. [Means for solving the problem]

[0005] To achieve the above objective, one embodiment of the present invention is a bush comprising an inner cylinder, an outer cylinder, and an elastic member provided between them, In a state deformed from a pre-stored shape The elastic member built-in , due to self-heating caused by the application of electricity The stored shape Shape recovery By doing so, the elastic member is compressed or extended between the inner cylinder or the outer cylinder, Shape memory alloy that changes the spring characteristics of the bush of Establish Ta It is characterized by the following: [Effects of the Invention]

[0006] According to one embodiment of the present invention, the spring characteristics of a bush can be easily and reliably controlled by switching between energizing and de-energizing the shape memory alloy. This eliminates the need for complex configurations such as providing a fluid chamber inside the elastic member and a hydraulic source to supply hydraulic pressure to the fluid chamber, as in the conventional method. This simple configuration is advantageous in changing the spring characteristics of a bush while suppressing the cost of the bush. [Brief explanation of the drawing]

[0007] [Figure 1] This is an explanatory diagram of a bush according to the first embodiment, where (A) is a plan view of the shape memory alloy before the shape recovery operation, (B) is a plan view of the shape memory alloy after the shape recovery operation, and (C) is a diagram showing the load-displacement characteristics of the bush. [Figure 2] (A) is a cross-sectional view of line XX in Figure 1(A), and (B) is a modified example of the cross-sectional view of line XX in Figure 1(A). [Figure 3]This is an explanatory diagram of a bush according to the second embodiment, where (A) is a plan view of the shape memory alloy before the shape recovery operation, (B) is a plan view of the shape memory alloy after the shape recovery operation, and (C) is a diagram showing the load-displacement characteristics of the bush. [Figure 4] This is an explanatory diagram of a bush according to the third embodiment, where (A) is a plan view of the shape memory alloy before the shape recovery operation, (B) is a plan view of the shape memory alloy after the shape recovery operation, (C) is a cross-sectional view of (B) along line CC, and (D) is a diagram showing the load-displacement characteristics of the bush. [Figure 5] This is an explanatory diagram of a bush according to the fourth embodiment, where (A) is a plan view of the shape memory alloy before the shape recovery operation, (B) is a plan view of the shape memory alloy after the shape recovery operation, and (C) is a diagram showing the load-displacement characteristics of the bush. [Figure 6] This is an explanatory diagram of a bush according to the fifth embodiment, where (A) is a plan view of the shape memory alloy before the shape recovery operation, and (B) is a plan view of the shape memory alloy after the shape recovery operation. [Figure 7] This is an explanatory diagram of a bush according to the sixth embodiment, where (A) is a plan view of the shape memory alloy before the shape recovery operation, and (B) is a plan view of the shape memory alloy after the shape recovery operation. [Modes for carrying out the invention]

[0008] (First Embodiment) Hereinafter, embodiments of the present invention will be described with reference to the drawings. This embodiment describes a case in which the bush of the present invention is applied to a vehicle suspension system that includes a bush that pivotably connects a lower arm supporting the vehicle's wheels to a suspension cross member (vehicle body).

[0009] As shown in Figure 1(A), the bush 10A comprises a metal inner cylinder 12, an outer cylinder 14, and an elastic member 16 provided between them, the elastic member 16 being made of a shape memory alloy 18. The inner cylinder 12 and the outer cylinder 14 are cylindrical in shape, and an elastic member 16 is provided between the inner cylinder 12 and the outer cylinder 14. The inner cylinder 12, the outer cylinder 14, and the elastic member 16 are arranged coaxially, and various conventionally known elastic materials such as rubber can be used as the elastic member 16. The inner cylinder 12 is connected to a suspension cross member (not shown) via fastening members such as bolts and nuts, and the outer cylinder 14 is connected to a lower arm (not shown). The inner circumferential surface of the elastic member 16 is vulcanized and bonded to the outer circumferential surface of the inner cylinder 12, and the outer circumferential surface of the elastic member 16 is vulcanized and bonded to the inner circumferential surface of the outer cylinder 14.

[0010] The shape memory alloy 18 undergoes a shape recovery operation through self-heating (Joule heating) caused by the application of electricity, thereby changing the spring characteristics of the bush 10A. In this embodiment, the shape memory alloy 18 is cylindrical, and its diameter expands or contracts during the shape recovery operation. The shape memory alloy 18 is located coaxially with the inner cylinder 12 and the outer cylinder 14, at a point midway between the inner cylinder 12 and the outer cylinder 14 in the radial direction of the elastic member 16. In this embodiment, the shape memory alloy 18 is formed into a cylindrical shape by weaving together wires made of shape memory alloy material in a mesh-like pattern. As shown in Figure 2(A), both ends of the shape memory alloy 18 in the axial direction are located on the same plane as the end faces of both ends of the elastic member 16 in the axial direction. Furthermore, both ends of the shape memory alloy 18 in the axial direction are connected to a current supply unit (not shown) via a cable (not shown), and the shape memory alloy 18 self-heats when a predetermined current is supplied to it from the current supply unit. The shape memory alloy 18 may be formed by processing a plate-shaped shape memory alloy material into a cylindrical shape. However, when the shape memory alloy 18 is formed by weaving a wire made of a shape memory alloy material into a mesh shape as in the present embodiment, compared with the case where a plate-shaped shape memory alloy material is formed into a cylindrical shape, the electrical resistance value of the shape memory alloy 18 can be made higher. Therefore, it is easier to self-heat by energization, and the shape recovery operation of the shape memory alloy 18 can be performed earlier during energization, which is advantageous in ensuring responsiveness.

[0011] In the present embodiment, the shape memory alloy 18 is incorporated into the elastic member 16 by being press-fitted into an intermediate position in the radial direction of the elastic member 16, and no gap is formed between the shape memory alloy 18 and the elastic member 16. Therefore, the shape memory alloy 18 and the elastic member 16 do not separate. Further, the elastic member 16 and the shape memory alloy 18 may be adhered using an adhesive. Also, in the present embodiment, the shape memory alloy 18 is incorporated into the elastic member 16 in a state where the diameter is reduced from the shape previously memorized in the shape memory alloy 18, that is, in a state deformed in the direction of diameter reduction. Then, the elastic member 16 incorporating the deformed shape memory alloy 18 is press-fitted between the inner cylinder 12 and the outer cylinder 14 to form the bush 10A.

[0012] Next, the operation and effect of the bush 10A will be described. As shown in FIG. (B), when current is supplied from the current supply unit to the shape memory alloy 18 and the temperature of the shape memory alloy 18 becomes equal to or higher than the shape recovery temperature inherent to the shape memory alloy 18 due to self-heating of the shape memory alloy 18, the shape memory alloy 18 executes a shape recovery operation of expanding from the diameter-reduced state to the memorized shape. Therefore, the first portion 16A located between the inner cylinder 12 and the shape memory alloy 18 of the elastic member 16 is extended and the rigidity of the first portion 16 decreases, while the second portion 16B located between the shape memory alloy 18 and the outer cylinder 14 of the elastic member 16 is compressed and the rigidity of the second portion 16B increases. In the case of the shape memory alloy 18 alone, once the shape recovery operation is performed due to self-heating caused by the application of electricity, the shape memory alloy 18 will not return to its original shape even if the electricity is stopped and it cools naturally. However, as shown in Figure 3(B), in this embodiment, a load is applied to the shape memory alloy 18 radially outward from the elastic member 16. Therefore, when the electricity is stopped and it cools naturally, this load causes the shape memory alloy 18 to return to its original shape.

[0013] Figure 1(C) shows the load-displacement characteristics that illustrate the spring properties of bush 10A. The solid line represents the case when the shape memory alloy 18 is not energized, and the dashed line represents the case when the shape memory alloy 18 is energized and performs shape recovery. When the shape memory alloy 18 is not energized, the load-displacement properties change almost linearly. In contrast, when the shape memory alloy 18 is energized, the inclination is greater in the low load region compared to the case when no energy is applied. This is because the preload of the first part 16A of the elastic member 16 is reduced, and the initial load decreases. Conversely, above a certain load, the inclination becomes smaller and is the same as in the case when no energy is applied (the dashed line overlaps with the solid line). This is because the rigidity of the first part 16A and the second part 16B balances out when a certain load is applied, and thereafter the first part 16A and the second part 16B receive the load as a single unit. In other words, in regions where the load applied to the bush 10A is low, the rigidity of the bush 10A decreases, which allows for greater displacement of the bush 10A, resulting in improved ride comfort compared to when the shape memory alloy 18 is not energized. Furthermore, in regions where the load applied to the bush 10A is high, the rigidity of the bush 10A increases, suppressing its displacement. As a result, the rigidity of the bush 10A is maintained, similar to the case when the shape memory alloy 18 is not energized, thereby ensuring steering stability. By switching between energizing and de-energizing the shape memory alloy 18 in this way, the spring characteristics of the bush 10A can be controlled to the desired characteristics.

[0014] Furthermore, the electrical control of the shape memory alloy 18 can be performed while taking into account the drive mode, which specifies whether to prioritize handling stability or ride comfort. Furthermore, it goes without saying that the current supply control to the shape memory alloy 18 can be performed while taking into account various information such as vehicle speed, ambient temperature, and bush temperature.

[0015] According to this embodiment, the elastic member 16 constituting the bush 10A is provided with a shape memory alloy 18 that performs a shape recovery operation by self-heating due to the application of electricity, thereby changing the spring characteristics of the bush 10A. Therefore, by switching between energizing and de-energizing the shape memory alloy 18, the spring characteristics of the bush 10A can be easily and reliably controlled. This eliminates the need for a complex configuration such as providing a fluid chamber inside the elastic member 16 and a hydraulic source to supply hydraulic pressure to the fluid chamber, as in the conventional method. This simple configuration is advantageous in changing the spring characteristics of the bush 10A while suppressing the cost of the bush 10A.

[0016] Furthermore, according to this embodiment, the shape memory alloy 18 is cylindrical and its diameter expands during the shape recovery operation. This is advantageous for easily and reliably controlling the spring characteristics of the bush 10A by switching between energizing and de-energizing the shape memory alloy 18.

[0017] Furthermore, according to this embodiment, since the shape memory alloy 18 is provided coaxially with the inner cylinder 12 and the outer cylinder 14, switching between non-energization and energization of the shape memory alloy 18 is advantageous for easily and reliably controlling the spring characteristics of the bush 10A, and is advantageous for uniformly controlling the spring characteristics in the circumferential direction of the bush 10A.

[0018] (Second Embodiment) Next, a second embodiment will be described with reference to Figure 3. In the following embodiments, parts and components similar to those in the first embodiment will be denoted by the same reference numerals, and their descriptions will be omitted. The descriptions will focus on the differences. In the bush 10B of the second embodiment, the arrangement structure of the shape memory alloy 20 on the elastic member 16 is the same as in the first embodiment, however, in the second embodiment, the shape memory alloy 20 is incorporated into the elastic member 16 in a state in which the diameter is expanded compared to the shape previously stored in the shape memory alloy 20.

[0019] Next, the effects and benefits of the bush 10B according to the second embodiment will be described. As shown in Figure 3(A), in the non-electric state, the shape memory alloy 20 is in a state where its diameter is larger than the original shape it was stored in. As shown in Figure 3(B), current is supplied to the shape memory alloy 20 from the current supply unit, and when the shape memory alloy 20 self-heats and its temperature rises above the shape recovery temperature specific to the shape memory alloy 20, the shape memory alloy 20 performs a shape recovery operation in which it shrinks from an expanded state and recovers to the stored shape. Therefore, the first portion 16A of the elastic member 16, located between the inner cylinder 12 and the shape memory alloy 20, is compressed, increasing the rigidity of the first portion 16A, while the second portion 16B of the elastic member 16, located between the shape memory alloy 20 and the outer cylinder 14, is stretched, decreasing the rigidity of the second portion 16B. In the case of the shape memory alloy 20 alone, once the shape recovery operation is performed due to self-heating caused by the application of electricity, the shape memory alloy 20 will not return to its original shape even if the power is stopped and it cools naturally. However, as shown in Figure 3(B), in this embodiment, a load is applied to the shape memory alloy 20 radially outward from the elastic member 16. Therefore, when the power is stopped and it cools naturally, this load causes the shape memory alloy 20 to return to its original shape.

[0020] Figure 3(C) shows the load-displacement characteristics that illustrate the spring properties of bush 10B. The solid line represents the case when the shape memory alloy 20 is not energized, and the dashed line represents the case when the shape memory alloy 20 is energized and performs shape recovery. When the shape memory alloy 20 is not energized, the load-displacement properties change almost linearly. In contrast, when the shape memory alloy 20 is energized, the inclination is greater in the low load region compared to the case when it is not energized. This is because the preload of the second portion 16B of the elastic member 16 is reduced, and the initial load is reduced. In contrast, above a certain load, the inclination is the same as when it is not energized. This is because the rigidity of the first portion 16A and the second portion 16B balances out when a certain load is applied, and thereafter the first portion 16A and the second portion 16B bear the load as a single unit. In other words, similar to the first embodiment, when the shape memory alloy 20 is energized, in regions where the load applied to the bush 10B is low, the rigidity of the bush 10B decreases, thereby ensuring a larger displacement, and thus improving ride comfort compared to when the shape memory alloy 20 is not energized. On the other hand, in regions where the load applied to the bush 10B is high, the rigidity of the bush 10B increases, which suppresses the displacement of the bush 10B. As a result, the rigidity of the bush 10B is maintained in the same way as when the shape memory alloy 20 is not energized, thereby ensuring steering stability. By switching between energizing and de-energizing the shape memory alloy 20 in this way, the spring characteristics of the bush 10B can be controlled to the desired characteristics, and therefore, the second embodiment also produces the same effects as the first embodiment.

[0021] (Third embodiment) Next, a third embodiment will be described with reference to Figure 4. The bush 10 of the third embodiment differs from the first and second embodiments in that, as shown in Figures 4(A) and (C), the cylindrical shape memory alloy 22 extends along the circumference of the outer surface of the inner cylinder 12. In detail, the inner surface of the shape memory alloy 22 is attached to the outer surface of the inner cylinder 12, and the outer surface of the shape memory alloy 22 is attached to the inner surface of the elastic member 16. In this embodiment, as shown in Figure 4(C), both ends of the shape memory alloy 22 in the axial direction are located inside the end faces of both ends of the elastic member 16 in the axial direction. However, as shown in Figure 2(A), both ends of the shape memory alloy 22 in the axial direction may be positioned on the same plane as the end faces of both ends of the elastic member 16 in the axial direction. However, positioning both ends of the shape memory alloy 22 in the axial direction inside the end faces of both ends of the elastic member 16 in the axial direction is more advantageous in suppressing the shape memory alloy 22 from falling off the elastic member 16. In the third embodiment, the shape memory alloy 22 is incorporated into the elastic member 16 in a state where its diameter is reduced compared to the shape previously stored in the shape memory alloy 22 when no current is applied.

[0022] Next, the effects and benefits of the bush 10C according to the third embodiment will be described. As shown in Figure 4(B), current is supplied to the shape memory alloy 22 from the current supply unit, and when the shape memory alloy 22 self-heats and its temperature rises above the shape recovery temperature specific to the shape memory alloy 22, the shape memory alloy 22 performs a shape recovery operation in which it expands from its contracted state and recovers to the stored shape. Therefore, the elastic member 16 is compressed, and the rigidity of the elastic member 16 increases. As shown in Figure 4(B), once the shape memory alloy 22 has recovered its shape due to self-heating caused by the energization, it will not return to its original shape even if the energization is stopped. In this embodiment, a load is applied to the shape memory alloy 22 from the elastic member 16 radially inward, so when the energization is stopped, this load causes the shape memory alloy 22 to return to its original shape.

[0023] Figure 4(D) shows the load-displacement characteristics that illustrate the spring properties of bush 10C. The solid line represents the case when the shape memory alloy 22 is not energized, and the dashed line represents the case when the shape memory alloy 22 is energized and performs shape recovery. When the shape memory alloy 22 is not energized, the load-displacement properties change almost linearly. In contrast, when the shape memory alloy 22 is energized, the load-displacement characteristics are shifted in a parallel direction upward along the vertical axis (load) compared to when it is not energized. This is because the preload of the elastic member 16 increases, and the rigidity of the bush 10C increases. In other words, when the shape memory alloy 22 is energized, the rigidity of the bush 10C increases, which suppresses the displacement of the bush 10C, thereby ensuring steering stability compared to when the shape memory alloy 22 is not energized. On the other hand, when the shape memory alloy 22 is not energized, the rigidity of the bush 10C is lower compared to when the shape memory alloy 22 is energized, which ensures displacement of the bush 10C and improves ride comfort. Therefore, according to the third embodiment, the spring characteristics of the bush 10C can be easily and reliably controlled to the desired characteristics by switching between non-energization and energization of the shape memory alloy 22. This is advantageous in changing the spring characteristics of the bush 10C while suppressing the cost of the bush 10C with a simple configuration.

[0024] (Fourth embodiment) Next, a fourth embodiment will be described with reference to Figure 5. In the fourth embodiment of the bush 10D, as shown in Figure 5(A), the cylindrical shape memory alloy 24 extends along the periphery of the inner surface of the outer cylinder 14, which is different from the third embodiment. More specifically, the inner surface of the shape memory alloy 24 is attached to the outer surface of the elastic body 16, and the outer surface of the shape memory alloy 22 is attached to the inner surface of the outer cylinder 14. Furthermore, in the fourth embodiment, the shape memory alloy 24 is incorporated into the elastic member 16 in a state where its diameter is expanded compared to the shape previously stored in the shape memory alloy 24 when no current is applied.

[0025] Next, the effects and benefits of the bush 10D according to the fourth embodiment will be described. As shown in Figure 5(B), current is supplied to the shape memory alloy 24 from the current supply unit, and when the shape memory alloy 24 self-heats and its temperature rises above the shape recovery temperature specific to the shape memory alloy 24, the shape memory alloy 24 performs a shape recovery operation in which it shrinks from an expanded state and recovers to the stored shape. Therefore, the elastic member 16 is compressed, and the rigidity of the elastic member 16 increases. As shown in Figure 5(B), once the shape memory alloy 24 has recovered its shape due to self-heating caused by the energization, it will not return to its original shape even if the energization is stopped. In this embodiment, a load is applied to the shape memory alloy 24 from the elastic member 16 radially outward, so when the energization is stopped, this load causes the shape memory alloy 24 to return to its original shape.

[0026] Figure 5(C) shows the load-displacement characteristics that illustrate the spring properties of bush 10D. The solid line represents the case when the shape memory alloy 24 is not energized, and the dashed line represents the case when the shape memory alloy 24 is energized and performs shape recovery. When the shape memory alloy 24 is not energized, the load-displacement properties change almost linearly. In contrast, when the shape memory alloy 24 is energized, the load-displacement characteristics are shifted in a parallel direction upward along the vertical axis (load) compared to when it is not energized. This is because the preload of the elastic member 16 increases, and the rigidity of the bush 10D increases. According to the fourth embodiment, when the shape memory alloy 24 is energized, the rigidity of the bush 10D increases, thereby suppressing the displacement of the bush 10D. This ensures greater steering stability compared to when the shape memory alloy 24 is not energized. On the other hand, when the shape memory alloy 24 is not energized, the rigidity of the bush 10D is lower compared to when the shape memory alloy 24 is energized, which ensures the displacement of the bush 10D and improves ride comfort. Therefore, according to the fourth embodiment, the spring characteristics of the bush 10D can be easily and reliably controlled to the desired characteristics by switching between non-energization and energization of the shape memory alloy 24. This is advantageous in changing the spring characteristics of the bush 10D while suppressing the cost of the bush 10D with a simple configuration.

[0027] (Fifth embodiment) Next, a fifth embodiment will be described with reference to Figure 6. As shown in Figure 6(A), the bush 10E of the fifth embodiment has a plurality of cavities 30 provided at intervals in the circumferential direction of the elastic member 16. Therefore, the elastic member 16 is provided with alternating hollow portions 30 and solid portions 32 along the circumferential direction. Furthermore, the shape memory alloy 26 is provided in the cavity 30, unlike in the first to fourth embodiments. The cavity 30 is provided at two locations opposite each other in the diametrical direction of the bush 10E, and has the same inner diameter. The shape memory alloy 26 is provided inside a pair of cavities 30 and has a cylindrical shape that extends along the inner surface of the cavities 30. The shape memory alloy 26 is formed in a cylindrical shape by weaving wires made of shape memory alloy material in a mesh-like manner, but as with the first embodiment, it may also be formed by processing a plate-shaped shape memory alloy material into a cylindrical shape. The shape memory alloy 26 is press-fitted into the cavity 30 of the elastic member 16 in a state where its diameter is reduced compared to the shape previously stored in the shape memory alloy 26 when no current is applied. Alternatively, the shape memory alloy 26 may be bonded to the inner surface of the cavity 30 using an adhesive.

[0028] Next, the effects and benefits of the bush 10E according to the fifth embodiment will be described. As shown in Figure 6(B), current is supplied to the shape memory alloy 26 from the current supply unit, and when the shape memory alloy 26 self-heats and its temperature rises above the shape recovery temperature specific to the shape memory alloy 26, the shape memory alloy 26 performs a shape recovery operation in which it expands from its reduced diameter state and recovers to the stored shape.

[0029] Therefore, as shown in Figure 6(B), when the shape memory alloy 26 undergoes shape recovery, the portion of the elastic member 16 located on the imaginary line connecting the pair of cavities 30 in the diametrical direction of the bush 10E is compressed, and the rigidity of this compressed portion of the elastic member 16 increases. In other words, when the shape memory alloy 26 is energized, the rigidity of the portion of the elastic member 16 located on the imaginary line connecting the pair of cavities 30 increases compared to when it is not energized. To put it another way, the preload of the elastic member 16 in the direction connecting the pair of cavities 30 increases, increasing the rigidity of the bush 10E, while the rigidity of other parts of the elastic member 16 remains almost unchanged. As shown in Figure 6(B), once the shape memory alloy 26 has recovered its shape due to self-heating caused by the energization, it will not return to its original shape even if the energization is stopped. In this embodiment, a load is applied to the shape memory alloy 26 from the elastic member 16 radially inward of the cavity 30, so when the energization is stopped, this load causes the shape memory alloy 26 to return to its original shape.

[0030] According to the fifth embodiment, by switching between energizing and de-energizing the shape memory alloy 26, the spring characteristics of the elastic member 16 in the diametrical direction of the bush 10E and in the direction connecting the pair of cavities 30 can be easily and reliably controlled to a desired characteristic. This is advantageous in changing the spring characteristics of the bush 10E while suppressing the cost of the bush 10E with a simple configuration. In the fifth embodiment, a case in which a pair of cavities 30 are provided was described, but the number and position of the cavities 30 are arbitrary. Furthermore, while the fifth embodiment described the case in which the energization and de-energization of the shape memory alloy 26 provided in a pair of cavities 30 are switched simultaneously, it is also possible to selectively perform the energization and de-energization control operation for each of the multiple shape memory alloys 26, as is optional.

[0031] (Sixth embodiment) Next, a sixth embodiment will be described with reference to Figure 7. As shown in Figure 7(A), the bush 10F of the sixth embodiment, like the fifth embodiment, has a plurality of cavities 30 spaced apart in the circumferential direction of the elastic member 16. Therefore, the elastic member 16 is provided with alternating hollow portions 30 and solid portions 32 along the circumferential direction. The shape memory alloy 28 is provided in the cavity 30. In the sixth embodiment, the cavity 30 is composed of two first slits 30A provided at two locations opposite each other in the diametrical direction of the bush 10F, and two second slits 30B provided at two locations opposite each other in the diametrical direction of the bush 10F, with a 90-degree phase difference from the first slits 30A. The first recessed portion 30A is composed of an elongated hole 3002 that extends in the diametrical direction of the bush 10F and penetrates in the axial direction of the bush 10F. The second trimmed portion 30B is formed by a trimmed body 3004 that extends in the circumferential direction of the bush 10F, and a pair of ends 3006 that protrude radially outward from both ends of the trimmed body 3004, penetrating the bush 10F in the axial direction. The shape memory alloy 28 comprises a first shape memory alloy 28A provided inside the first trimmed portion 30A and a second shape memory alloy 28B provided inside the second trimmed portion 30B. As shown in Figure 7(A), the first shape memory alloy 28A is positioned along the axial direction of the bush 10F over almost the entire length of the first cutout 30A, and the first shape memory alloy 28A is press-fitted into the first cutout 30A and incorporated in a compressed state compared to the shape previously stored in the first shape memory alloy 28A when not energized, so as to have a shape that is almost identical to the contour of the cross-sectional shape of the first cutout 30A. Similarly, the second shape memory alloy 28B is positioned along the axial direction of the bush 10F over almost the entire length of the second cutout 30B, and the second shape memory alloy 28B is press-fitted into the second cutout 30B in a compressed state compared to the shape previously stored in the second shape memory alloy 28B when not energized, so as to be substantially the same shape as the contour of the cross-sectional shape of the second cutout 30B. Furthermore, it is optional to bond the first and second shape memory alloys 26A and 26B to the inner surfaces of the first and second trim sections 30A and 30B using an adhesive. The first and second shape memory alloys 28A and 28B are formed by weaving together wires made of shape memory alloy material in a mesh-like structure. However, the first and second shape memory alloys 28A and 28B may also be formed from plate-shaped shape memory alloy material having contours corresponding to the cross-sectional shapes of the first and second trimmed sections 30A and 30B.

[0032] Next, the effects and benefits of the bush 10F according to the sixth embodiment will be described. As shown in Figure 7(B), current is supplied from the current supply unit to the first and second shape memory alloys 28A and 28B. When the temperature of the first and second shape memory alloys 28A and 28B rises above their respective shape recovery temperatures due to self-heating, the first and second shape memory alloys 28A and 28B perform a shape recovery operation in which they expand and recover to their stored shapes.

[0033] Therefore, as shown in Figure 7(B), the shape recovery operation of the first and second shape memory alloys 28A and 28B is performed, causing the first and second shape memory alloys 28A and 28B to expand inside the first and second trim sections 30A and 30B. As a result, the portion of the elastic member 16 located on the imaginary line connecting the pair of first slits 30A in the diametrical direction of the bush 10F is compressed, increasing the rigidity of this portion of the elastic member 16, and the portion of the elastic member 16 located on the imaginary line connecting the pair of second slits 30B in the diametrical direction of the bush 10F is compressed, increasing the rigidity of this portion of the elastic member 16. In other words, when the shape memory alloy 28 is energized compared to when it is not energized, the rigidity of the portion of the elastic member 16 located on the imaginary line connecting the pair of first slits 30A and the rigidity of the portion of the elastic member 16 located on the imaginary line connecting the pair of second slits 30B increase. To put it another way, the preload of the elastic member 16 increases in the direction connecting the pair of first slits 30A and the direction connecting the pair of second slits 30B, increasing the rigidity of the bush 10F, while the rigidity of the other portions of the elastic member 16 remains almost unchanged. As shown in Figure 7(B), once the shape recovery operation is performed by self-heating due to the application of current, the first and second shape memory alloys 26A and 26B will not return to their original shape even if the current is stopped. In this embodiment, a load is applied to the first and second shape memory alloys 26A and 26B from the elastic member 16 toward the inside of the first and second curb portions 30A and 30B, so when the current is stopped, the first and second shape memory alloys 26A and 26B return to their original shape due to this load.

[0034] According to the sixth embodiment, by switching between energizing and de-energizing the shape memory alloy 28, the spring characteristics of the elastic member 16 in the diametrical direction of the bush 10F and in the direction connecting opposing slits can be easily and reliably controlled. This is advantageous in changing the spring characteristics of the bush 10F to desired characteristics while suppressing the cost of the bush 10F with a simple configuration. In the sixth embodiment, the case in which the first and second trim sections 30A and 30B with the cross-sectional shape shown in Figure 7 are provided was described, but the cross-sectional shape, number, and position of the trim sections are arbitrary. Furthermore, while the sixth embodiment describes the case where the energization and de-energization of the first and second shape memory alloys 28A and 28B are switched simultaneously, it is optional to selectively perform the energization and de-energization control operation for each of the multiple shape memory alloys 28.

[0035] In this embodiment, the case described is one in which the bushings 10A-10F are applied to a suspension system in which the lower arm supporting the vehicle's wheel is pivotably connected to the suspension cross member (vehicle body). However, the bush of the present invention may be applied to a suspension system that pivotably connects a trailing arm supporting a wheel to the vehicle body, or to a roll rod that pivotably connects a vehicle's power plant to a suspension cross member, or it can be broadly applied to various conventionally known mechanisms that pivotably connect members used in various devices other than vehicles. [Explanation of Symbols]

[0036] 10A, 10B, 10C, 10D, 10E, 10F bushings 12 Inner cylinder 14 Outer cylinder 16 Elastic members 16A Part 1 16B 2nd part 18, 20, 22, 24, 26, 28 shape memory alloy 28A 1st shape memory alloy 28B 2nd shape memory alloy 30 Cavity 30A First Section 30B Second Section 3002 Long hole 3004 Suguri main body 3006 End 32 Middle School

Claims

1. A bush comprising an inner cylinder, an outer cylinder, and an elastic member provided between them, A shape memory alloy is provided that is incorporated into the elastic member in a deformed state from a pre-stored shape, and by self-heating due to the application of electricity, it recovers its shape to the stored shape, thereby compressing or extending the elastic member between the inner cylinder or the outer cylinder, and changing the spring characteristics of the bush. A bush characterized by the following features.

2. The shape memory alloy is cylindrical, and its diameter expands or contracts during the shape recovery operation. The bush according to feature 1.

3. The shape memory alloy is provided coaxially with the inner cylinder and the outer cylinder. The bush according to feature 1.

4. Multiple cavities are provided in the elastic member at intervals in the circumferential direction, The shape memory alloy is provided in the cavity, A bush according to claim 1 or 2, characterized in that it is a bush.

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