# Patent

## Title
Bush component force detection device

## Abstract

A bush component force detection device detects a component force acting on a cylindrical bush which is inserted into a hole provided in a frame of a vehicle to pivotally support a rod-like member inside thereof. The device includes: a cylindrical inner ring provided between a bush and a hole and mounted on an outer circumferential surface of the bush; a cylindrical outer ring disposed outwardly of the inner ring with a predetermined space from the inner ring and mounted on an inner circumferential surface of the hole; and a sensing unit that is a cylindrical member disposed in the space between the inner ring and the outer ring substantially concentrically to the rod-like member, the sensing unit having one end connected with the inner ring, the other end connected with the outer ring, and strain gauges disposed on an outer circumferential surface of the sensing unit.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority from Japanese Patent Application No. 2013-098597 filed on May 8, 2013, the entire contents of which are hereby incorporated by reference.
BACKGROUND
1. Technical Field
The present invention relates to a bush component force detection device that detects a component force acting on a bush which is provided in a connecting portion of a structural member of a vehicle.
2. Related Art
The suspension of a vehicle has an effect on riding comfort and driving stability of the vehicle, and so component forces of the suspension are measured and the riding comfort and driving stability of the vehicle are evaluated based on a result of the measurement, and the elasticity of the suspension is also adjusted. Therefore, the riding comfort and driving stability of a vehicle can be improved by accurately measuring dynamic change in each component force in portions of the suspension.
Various methods have been proposed to detect changes in component forces such as yaw, pitch, and roll which act on the portions of the suspension mechanism. For example, Japanese Unexamined Patent Application Publication No. 2011-85514 discloses a load measurement sensor which includes a plurality of strain gauges and is tightly fixed to a rod-like body such as a damper in the suspension mechanism of a vehicle.
Here, shafts, which serve as connecting portions between the frame of the vehicle and an arm member, are base points for allowing the arm member to be moved, and thus for the design and adjustment of the suspension mechanism, it is necessary to detect component forces in the connecting portions between the frame and the arm member with high accuracy.
However, even if a sensor is mounted on a damper, an arm member or the like as described above for measuring the behavior of each of the portions of the suspension, the behavior of each shaft (movable connecting portion of each member) may not be measured accurately. That is, in order to measure the behavior of each shaft of the suspension, calculation is performed based on a result of measurement made by a sensor which is mounted on an arm or a damper connected to the shaft to be measured, and thus the calculation gives only a predicted value. Particularly, when an elastic body such as rubber is used for a bush which serves as a bearing of the suspension, it is necessary to take spring characteristics and holes into consideration, and thus such a predicted value may be much different from an actual component force.
SUMMARY OF THE INVENTION
The present invention has been designed in consideration of the circumstances described above, and an object thereof is to provide a bush component force detection device capable of detecting a change in component forces for each axis in a suspension mechanism of a vehicle with high accuracy.
A first aspect of the present invention provides a bush component force detection device that detects a component force acting on a cylindrical bush which is inserted into a hole provided in a frame of a vehicle to pivotally support a rod-like member inside thereof, the bush component force detection device including: a cylindrical inner ring provided between a bush and a hole and mounted on an outer circumferential surface of the bush; a cylindrical outer ring disposed outwardly of the inner ring with a predetermined space from the inner ring and mounted on an inner circumferential surface of the hole; and a sensing unit that is a cylindrical member disposed in the space between the inner ring and the outer ring substantially concentrically to the rod-like member, the sensing unit having one end connected with the inner ring, the other end connected with the outer ring, and strain gauges disposed on an outer circumferential surface thereof.
The strain gauges are disposed on the outer circumferential surface of the sensing unit may detect a component force acting in a first radial direction, a component force acting in a second radial direction perpendicular to the first radial direction, a component force acting in an axial direction, a component force acting around an axis in the first radial direction, a component force acting around an axis in the second radial direction, and a component force acting around the axial direction.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic front view of a suspension device of a vehicle according to an implementation of the present invention;
FIG. 2 is a schematic plan view from above of the suspension device of FIG. 1;
FIG. 3 is a perspective view of a front bush according to the implementation;
FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 3;
FIG. 5 is a cross-sectional view taken along line V-V of FIG. 3;
FIG. 6 is an enlarged schematic cross-sectional view of part of FIG. 5;
FIG. 7 is a schematic perspective view of a sensing unit of the implementation;
FIGS. 8A to 8C are diagrams each illustrating a configuration of a bridge circuit of a force detection system in a six component force detection device; and
FIGS. 9A to 9C are diagrams each illustrating a configuration of a bridge circuit of a moment detection system in the six component force detection device.



DETAILED DESCRIPTION
FIGS. 1 to 9C illustrate an implementation of the present invention.
As illustrated in FIGS. 1 and 2, a vehicle body 1 of a vehicle equipped with a bush component force detection device of the implementation includes side members 2, upper members 3, strut towers 4, a cross member 5, and a suspension device 10.
Each of the side members 2 is a structural member that extends from a toe board (not illustrated) in a fore-and-aft direction of the vehicle, the toe board serving as a partition wall at the front of the cabin. The side members 2 are provided as a pair on the right and left sides of the engine compartment of the vehicle. The rear ends of the side members 2 on the right and left are connected to each other by a connecting member 21.
The upper members 3 are provided over the right and left side members 2, respectively in a direction outwardly of the vehicle. Each of the upper members 3 is a structural member that extends from the partition wall at the front of the cabin along the right and left edges of an engine hood in a fore-and-aft direction of the vehicle.
The strut towers 4 are provided between the outer ends of the side members 2 in a vehicle width direction and the inner ends of the upper members 3 in a vehicle width direction. The upper ends of the shock absorbers 41 described below are fixed to the strut towers 4.
The cross member 5 is a structural member that extends in a vehicle width direction and the both ends thereof are secured to the lower surfaces of the right and left side members 2 using a bolt or the like. Under the cross member 5, brackets 51 project downward which are connected to the respective lower arms 6 described below.
The suspension device 10 includes shock absorbers 41, lower arms 6, and support plates 7.
The shock absorbers 41 are each a hydraulic shock absorber that has a coil spring 42 on the outer circumferential surface. The upper end of each shock absorber 41 is rotatably mounted on corresponding one of the strut towers 4 and the lower end thereof is secured and fixed to the upper end of a front wheel suspension member (not illustrated) which rotatably supports a front wheel 11.
The lower arms 6 are suspension arms that are provided as a pair on the right and left sides in a vehicle width direction to support the lower ends of front wheel suspension members. Front bush mounts 61 are provided at the front side in the vehicular fore-and-aft direction of the inner ends of the right and left lower arms 6 in a vehicle width direction. Rear bush mounts 62 are provided at the rear side in the vehicular fore-and-aft direction of the inner ends of the right and left lower arms 6 in a vehicle width direction. Ball joints 63 are provided at the outer ends of the vehicle in a vehicle width direction.
Each of the front bush mounts 61 is a cylindrically shaped hole into which a front bush 100 is press-fitted and fixed and which has a central axis extending along the rocking central axis of a corresponding lower arm 6.
The front bush 100 is a rubber bush for vibration isolation, and includes an inner cylinder 110, a rubber 120, and an outer cylinder 130. The inner cylinder 110 and the outer cylinder 130 are substantially concentric cylindrical members, the inner cylinder 110 is inserted inside the outer cylinder 130, and the rubber 120 is provided between the inner cylinder 110 and the outer cylinder 130. In the rubber 120, bores 121 are formed as a pair on the right and left. The bores 121 are openings through in the axial direction of the inner cylinder 110. Each of the bores 121 is formed in an arc-shape in a plan view centered about the inner cylinder 110, and has different coefficients of elasticity in a radial direction (the x-axis direction) and in another radial direction (the y-axis direction) perpendicular to the x-axis. The axial lengths of the inner cylinder 110 and the outer cylinder 130 are approximately the same as the axial length of the inner circumferential surface of the front bush mount 61.
Each lower arm 6 is connected to the corresponding bracket 51 of the cross member 5 by a bolt (not illustrated) which is inserted into the inner cylinder 110 of the front bush 100 which is press-fitted into the front bush mount 61. The front bush 100 is provided with a front bush component force detection device 140 for detecting a component force acting on the front bush 100. The details of the front bush component force detection device 140 will be described below.
Each of the rear bush mount 62 is a portion into which a rear bush is press-fitted and fixed, and specifically is a cylindrically shaped hole having a central axis extending along the rocking central axis of the lower arm 6 in the vehicular fore-and-aft direction. The rear bush is a rubber bush for vibration isolation in a similar configuration to that of the front bush 100, and includes an inner cylinder, a rubber, and an outer cylinder. The inner cylinder and the outer cylinder are substantially concentric cylindrical members, the inner cylinder is inserted inside the outer cylinder, and the rubber is provided between the inner cylinder and the outer cylinder. The lower arm 6 is connected to a corresponding support plate 7 by a bolt which is inserted into the inner cylinder of the rear bush which is press-fitted into the rear bush mount 62.
The support plate 7 is a tabular member for supporting a lower portion of the lower arm 6 and is connected to a corresponding rear bush 200 by a bolt and secured to a portion near the rear end of the side member 2 by a bolt or the like, the rear bush 200 being press-fitted into the rear bush mount 62 of the lower arm 6 on each side.
Next, the front bush component force detection device 140 for detecting a component force will be described with reference to FIGS. 3 to 9C, the component force acting on the front bush 100 which is provided in the suspension device 10.
The front bush component force detection device 140 detects six component forces acting on the front bush 100 which connects the lower arm 6 and the cross member 5. The front bush component force detection device 140 includes a cylindrically shaped sensing unit 150, an inner ring 160 mounted on the outer circumferential surface of the outer cylinder 130 of the front bush 100, an outer ring 170 mounted on the inner circumferential surface of the front bush mount 61, a plurality of strain gauges provided on the sensing unit 150, and a bridge circuit including the gauges. The front bush component force detection device 140 is mounted on the outer surface of the front bush 100, and the front bush 100 along with the front bush component force detection device 140 is press-fitted into the front bush mount 61.
The sensing unit 150 is a cylindrical member which is formed to have a larger diameter than the front bush 100 and disposed substantially concentric to the front bush 100. The upper and lower ends of the sensing unit 150 are each provided with an insertion hole for a bolt, and formed to be slightly thicker than the middle portion. The middle portion is formed to have a certain thickness.
The inner ring 160 and the outer ring 170 are substantially concentric cylindrical members, a certain space is provided between the outer circumferential surface of the inner ring 160 and the inner circumferential surface of the outer ring 170, and the sensing unit 150 is disposed between the outer circumferential surface of the inner ring 160 and the inner circumferential surface of the outer ring 170. That is, the outer cylinder 130 of the front bush 100, the sensing unit 150, the inner ring 160, and the outer ring 170 are substantially concentric cylindrical members, and the inner ring 160 is disposed outwardly of the outer cylinder 130, the sensing unit 150 is disposed outwardly of the inner ring 160, the outer ring 170 is disposed outwardly of the sensing unit 150, and the inner circumferential surface of the front bush mount 61 is located outwardly of the outer ring 170. No space is provided between the outer cylinder 130 and the inner ring 160, and between the outer ring 170 and the inner circumferential surface of the front bush mount 61, but a certain space is provided between the inner ring 160 and the sensing unit 150, and between the sensing unit 150 and the outer ring 170. It is to be noted that the outer cylinder 130, the sensing unit 150, the inner ring 160, and the outer ring 170 are substantially concentric to each other, but may not be strictly concentric.
The inner ring 160 is a cylindrical member which is mounted on the outer circumferential surface of the outer cylinder 130 of the front bush 100, and formed to be substantially equal to the outer cylinder 130 in axial length. The inner circumferential surface of the inner ring 160 and the outer circumferential surface of the outer tube 130 are connected to each other with no space therebetween. It is to be noted that although the inner ring 160 and the outer cylinder 130 are separate members in the present implementation, without being limited to this, the inner ring 160 and the outer cylinder 130 may be integrally formed.
In the lower end of the inner ring 160, an inner ring flange 161 is formed which projects radially outward, and in the inner ring flange 161, a bolt insertion hole 162 through in the axial direction is formed. The lower surface of the sensing unit 150 is fixed to the upper surface of the inner ring flange 161 by a bolt which is inserted from below the inner ring flange 161.
The outer ring 170 is a cylindrical member which is provided radially outward of the inner ring 160 with a predetermined space between itself and the outer circumferential surface of the inner ring 160. When the front bush 100 is press-fitted in the front bush mount 61, the outer circumferential surface of the outer ring 170 is in contact with the inner circumferential surface of the front bush mount 61.
In the upper end of the outer ring 170, an outer ring flange 171 is formed which projects radially inward, and in the outer ring flange 171, a bolt insertion hole 172 through in the axial direction is formed. The upper surface of the sensing unit 150 is fixed to the lower surface of the outer ring flange 171 by a bolt which is inserted from above the outer ring flange 171. In this manner, the upper end of the sensing unit 150 is fixed to the outer ring flange 171 and the lower end thereof is fixed to the inner ring flange 161, and the sensing unit 150 is thereby disposed in the space formed between the outer ring 170 and the inner ring 160.
The front bush component force detection device 140 includes Fx detection system, Fy detection system, Fz detection system, Mx detection system, My detection system, and Mz detection system, each of which has a bridge circuit including strain gauges provided in the sensing unit 150.
Fx detection system detects a force Fx acting on the sensing unit 150 in a radial direction (hereinafter x-axis direction). Fy detection system detects a force Fy acting on the sensing unit 150 in a radial direction (hereinafter y-axis direction) perpendicular to the x-axis direction. Fz detection system detects a force Fz acting on the sensing unit 150 in an axial direction (hereinafter z-axis direction). Mx detection system detects a moment Mx acting on the sensing unit 150 around the x-axis. My detection system detects a moment My acting on the sensing unit 150 around the y-axis. Mz detection system detects a moment Mz acting on the sensing unit 150 around the z-axis.
Each of Fx detection system, Fy detection system, Fz detection system, Mx detection system, My detection system, and Mz detection system includes a bridge circuit having four strain gauges.
As illustrated in FIG. 7, Fx detection system includes strain gauges 151a, 151b, 151c, and 151d. The strain gauges 151a to 151d are strain gauges for a single axis, and are attached on the outer circumferential surface of the sensing unit 150 so that the direction of detection is parallel to the central axis direction of the sensing unit 150.
As illustrated in FIG. 8A, in the bridge circuit of Fx detection system, the strain gauges 151a to 151d are sequentially connected in a loop, and the positive electrode and negative electrode of a power supply are respectively connected to a point between the strain gauges 151b and 151c and a point between the strain gauges 151a and 151d, and thus the bridge circuit measures a potential difference across a point between the strain gauges 151a and 151b and a point between strain gauges 151c and 151d. 
As illustrated in FIG. 7, Fy detection system includes strain gauges 152a, 152b, 152c, and 152d. The strain gauges 152a to 152d are strain gauges for a single axis, and are attached on the outer circumferential surface of the sensing unit 150 so that the direction of detection is parallel to the central axis direction of the sensing unit 150 and the positions of the strain gauges 152a to 152d are 90 degrees shifted in phase around the central axis of the sensing unit 150 with respect to the attachment positions of the strain gauges 151a to 151d. 
As illustrated in FIG. 8B, in the bridge circuit of Fy detection system, the strain gauges 152a to 152d are sequentially connected in a loop, and the positive electrode and negative electrode of a power supply are respectively connected to a point between the strain gauges 152b and 152c and a point between the strain gauges 152a and 152d, and thus the bridge circuit measures a potential difference across a point between the strain gauges 152a and 152b and a point between strain gauges 152c and 152d. 
As illustrated in FIG. 7, Fz detection system includes strain gauges 153a, 153b, 153c, and 153d. The strain gauges 153a to 153d are strain gauges for a single axis, and are attached on the outer circumferential surface of the sensing unit 150 so that the direction of detection is parallel to the central axis direction of the sensing unit 150. The strain gauge 153a is disposed at the midpoint between the strain gauges 151a and 151b, and the strain gauges 153b to 153d are disposed at the positions 90 degrees, 180 degrees, and 270 degrees shifted in phase, respectively around the central axis of the sensing unit 150 with respect to the strain gauge 153a. 
As illustrated in FIG. 8C, in the bridge circuit of Fz detection system, the strain gauges 153a to 153d are sequentially connected in a loop, and the positive electrode and negative electrode of a power supply are respectively connected to a point between the strain gauges 153a and 153c and a point between the strain gauges 153b and 153d, and thus the bridge circuit measures a potential difference across a point between the strain gauges 153a and 153b and a point between strain gauges 153c and 153d. 
As illustrated in FIG. 7, Mx detection system includes strain gauges 154a, 154b, 154c, and 154d. The strain gauges 154a to 154d are strain gauges for a single axis, and are attached on the outer circumferential surface of the sensing unit 150 so that the direction of detection is parallel to the central axis direction of the sensing unit 150. The strain gauges 154a to 154d are disposed adjacent to the strain gauges 152a to 152d, respectively in the central axis direction of the sensing unit 150.
As illustrated in FIG. 9A, in the bridge circuit of Mx detection system, the strain gauges 154a to 154d are sequentially connected in a loop, and the positive electrode and negative electrode of a power supply are respectively connected to a point between the strain gauges 154a and 154c and a point between the strain gauges 154b and 154d, and thus the bridge circuit measures a potential difference across a point between the strain gauges 154a and 154b and a point between strain gauges 154c and 154d. 
As illustrated in FIG. 7, My detection system includes strain gauges 155a, 155b, 155c, and 155d. The strain gauges 155a to 155d are strain gauges for a single axis, and are attached on the outer circumferential surface of the sensing unit 150 so that the direction of detection is parallel to the central axis direction of the sensing unit 150. The strain gauges 155a to 155d are disposed adjacent to the strain gauges 151a to 151d, respectively in the central axis direction of the sensing unit 150.
As illustrated in FIG. 9B, in the bridge circuit of My detection system, the strain gauges 155a to 155d are sequentially connected in a loop, and the positive electrode and negative electrode of a power supply are respectively connected to a point between the strain gauges 155a and 155c and a point between the strain gauges 155b and 155d, and thus the bridge circuit measures a potential difference across a point between the strain gauges 155a and 155b and a point between strain gauges 155c and 155d. 
As illustrated in FIG. 7, Mz detection system includes strain gauges 156a, 156b, 156c, and 156d. The strain gauges 156a to 156d are shear strain gauges, and are attached on the outer circumferential surface of the sensing unit 150 so that the direction of detection is parallel to the circumferential direction of the sensing unit 150. The strain gauges 156a and 156b are disposed between the strain gauges 153a and 153b and between the strain gauges 153b and 153d, respectively. The strain gauges 156c and 156d are disposed symmetrically to the strain gauges 156a and 156b with respect to the central axis of the sensing unit 150.
As illustrated in FIG. 9C, in the bridge circuit of Mz detection system, the strain gauges 156a to 156d are sequentially connected in a loop, and the positive electrode and negative electrode of a power supply are respectively connected to a point between the strain gauges 156a, 156c and a point between the strain gauges 156b and 156d, and thus the bridge circuit measures a potential difference across a point between the strain gauges 156a and 156b and a point between strain gauges 156c and 156d. 
The rear bush 200 is also provided with a rear bush detection device for detecting component forces acting on the rear bush 200. Similarly to the front bush component force detection device 140, the rear bush detection device includes an inner ring, an outer ring, and a sensing unit. The rear bush detection device is capable of detecting component forces acting in radial directions (x-axis direction and y-axis direction), a component force acting in the axial direction (z-axis direction), a component force acting around the x-axis, a component force acting around the y-axis, and a component force acting around the z-axis, all the component forces acting on the rear bush 200.
As described above, the sensing unit 150 of the front bush component force detection device 140 is provided concentrically to the front bush 100 outwardly of the outer cylinder 130 of the front bush 100. For this reason, it is possible to directly detect a component force acting on the front bush 100, and thus the six component forces acting on the connecting portion between the lower arm 6 and the cross member 5 may be accurately detected. That is, each component force acting on the front bush 100 is not determined based on the component forces detected at positions away from the front bush 100, but is determined by direct detection using the front bush component force detection device 140 which is provided in the front bush 100 itself. Therefore, a complicated method of determination is not necessary, and accurate detection of the component forces is possible.
The upper end of the sensing unit 150 is fixed to the outer ring flange 171 and the lower end thereof is fixed to the inner ring flange 161, and thus the sensing unit 150 is disposed along the outer circumference of the front bush 100. Thus, a certain space is maintained between the sensing unit 150 and the inner ring 160, and between the sensing unit 150 and the outer ring 170. Therefore, even when the front bush 100 is deformed, the sensing unit 150 does not come into contact with the inner ring 160 nor the outer ring 170, and thus an accurate component force may be reliably detected.
Because the front component force detection device 140 is mounted on the front bush 100, together with the front bush 100, the front component force detection device 140 may be removed from the front bush mount 61. Thus, when the front bush component force detection device 140 is not used, the existing front bush 100 may be removed from the front bush mount 61, and a front bush 100 which is not provided with the front bush component force detection device 140 may be press-fitted into the front bush mount 61, and thus replacement work can be made easily.
In the suspension device 10 of a vehicle in the present implementation, the lower arm 6 and the cross member 5 are connected via the front bush 100, the lower arm 6 and the support plate 7 are connected via the rear bush 200, and the front bush 100 and the rear bush 200 are provided with respective component force detection devices for detecting a component force acting of the bush. However, without being limited to this, a bush may be used for a bearing member of a connecting portion of other structural members, and the bush may be provided with a component force detection device which is similar to the front bush component force detection device 140 in the front bush 100.
In the present implementation, a rubber bush is used for the front bush 100 and the rear bush 200. However, without being limited to this, a bush using, for example, urethane may be adopted.
In the present implementation, a plurality of strain gauges is attached on the outer circumferential surface of the sensing unit 150. However, without being limited to this, the plurality of strain gauges may be attached on the inner circumferential surface of the sensing unit 150.

## Claims

1. A bush component force detection device that detects a component force acting on a cylindrical bush which is inserted into a hole provided in a frame of a vehicle to pivotally support a rod-like member inside thereof, the bush component force detection device comprising:
a cylindrical inner ring provided between a bush and a hole and mounted on an outer circumferential surface of the bush;
a cylindrical outer ring disposed outwardly of the inner ring with a predetermined space from the inner ring and mounted on an inner circumferential surface of the hole; and
a sensing unit that is a cylindrical member disposed in the space between the inner ring and the outer ring substantially concentrically to the rod-like member, the sensing unit having one end connected with the inner ring, the other end connected with the outer ring, and strain gauges disposed on an outer circumferential surface of the sensing unit.

2. The bush component force detection device according to claim 1, wherein the strain gauges disposed on the outer circumferential surface of the sensing unit detect a component force acting in a first radial direction, a component force acting in a second radial direction perpendicular to the first radial direction, a component force acting in an axial direction, a component force acting around an axis in the first radial direction, a component force acting around an axis in the second radial direction, and a component force acting around the axial direction.