Load Sensor

Abstract

A detection unit (110) is provided with a plate-shaped piezoelectric element (111 to 113) which has a front surface (121) and a back surface (122) and which outputs an electric signal corresponding to the magnitude of a force applied along the electric axis. A sensor housing (130) has a first plate portion (131) positioned on the front surface side of the piezoelectric element and a second plate portion (132) positioned on the back surface side of the piezoelectric element, and accommodates the detection unit between the first plate portion and the second plate portion. The sensor housing includes support portions (133, 134) for supporting the first plate portion and the second plate portion. Some of a preload applied in advance to the first plate portion and the second plate portion along the vertical direction is applied to the support portion.

Description

[Technical field]

[0001] The present disclosure relates to a load sensor. [Background technology]

[0002] A force detection device including a first substrate, a second substrate arranged opposite the first substrate, and a circuit substrate provided between the first substrate and the second substrate has been proposed in, for example, Patent Document 1. A charge output element that outputs a signal in response to an external force is provided on the installation surface of the circuit substrate on the side of the second substrate. The charge output element is a piezoelectric body sandwiched between the second substrate and the circuit substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-196924 A Summary of the Invention

[0004] However, in the above conventional technology, a circuit board is disposed between the first board and the second board, and since each board has a certain thickness, it is difficult to reduce the size of the force detection device in the direction perpendicular to the installation surface of the circuit board, i.e., in the thickness direction of the charge output element.

[0005] In addition, when the force detection device is fixed to the measurement target, each board is fastened with a bolt in the thickness direction of the charge output element. In other words, a preload, which is a fastening load, is applied to the force detection device. As a result, the charge output element sandwiched between the second board and the circuit board receives the entire preload through each board, and the charge output element is destroyed. Therefore, in the conventional configuration, it is difficult to establish the mechanical strength of the charge output element, and the reliability of the force detection device is reduced.

[0006] In order to ensure the mechanical strength of the charge output element, it is conceivable to make the charge output element thicker, but making the charge output element thicker makes it even more difficult to reduce the size of the force detection device in the thickness direction of the charge output element.

[0007] In view of the above, an object of the present disclosure is to provide a load sensor that can be miniaturized in the thickness direction of a piezoelectric element while maintaining the mechanical strength of the piezoelectric element.

[0008] According to one aspect of the present disclosure, A load sensor used in a state where an axial force is applied to a load measuring component with a predetermined tightening torque, The load sensor includes a detection portion and a sensor housing.

[0009] The detection section is in the form of a plate having a front surface and a back surface, and includes a piezoelectric element that outputs an electrical signal corresponding to the magnitude of a force applied along an electrical axis.

[0010] The sensor housing is Located on the surface The piezoelectric element has a first plate portion and a second plate portion located on the back surface side of the piezoelectric element, and houses a detection portion between the first plate portion and the second plate portion.

[0011] The sensor housing is a support that supports the first plate portion and the second plate portion. Department Including piezoelectric element Along the thickness direction A part of the preload applied in advance between the first plate portion and the second plate portion is applied to the support portion. The detection unit includes a plurality of output electrodes for outputting electrical signals, and a plurality of ground electrodes. The piezoelectric element includes a pair of first piezoelectric elements arranged in parallel and outputting a first electrical signal corresponding to the magnitude of a force applied in one of the surface directions, a pair of second piezoelectric elements arranged in parallel and outputting a second electrical signal corresponding to the magnitude of a force applied in another direction perpendicular to the one of the surface directions, and a pair of third piezoelectric elements arranged in parallel and outputting a third electrical signal corresponding to the magnitude of a force applied in the thickness direction. The pair of first piezoelectric elements, the pair of second piezoelectric elements, and the pair of third piezoelectric elements are arranged in the thickness direction and in parallel. The multiple output electrodes are respectively disposed between a pair of first piezoelectric elements, between a pair of second piezoelectric elements, and between a pair of third piezoelectric elements, and are electrically connected to the pair of first piezoelectric elements, the pair of second piezoelectric elements, and the pair of third piezoelectric elements, respectively. Some of the multiple ground electrodes are arranged between adjacent elements in a pair of first piezoelectric elements, a pair of second piezoelectric elements, and a pair of third piezoelectric elements, thereby being shared between adjacent elements and being electrically connected to the adjacent elements. The plurality of ground electrodes are connected to a ground terminal that is common to the plurality of ground electrodes. The flexible substrate includes a plurality of wirings electrically connected to the detection portion, an insulating film covering the plurality of wirings, and a connection portion in which a plurality of signal terminals and a ground terminal respectively connected to the plurality of wirings are exposed from the upper surface of the insulating film. The piezoelectric element has an exterior surface. The sensor housing has an outer periphery that defines a space between the first plate portion and the second plate portion on the outer surface side of the piezoelectric element. The connection portion of the flexible substrate is disposed in the space at the outer periphery. The multiple output electrodes are connected to multiple signal terminals in space, respectively. The ground electrodes are connected to a ground terminal in space.

[0012] According to this, a part of the preload applied in advance in the vertical direction between the first plate portion and the second plate portion of the sensor housing is distributed not only to the piezoelectric element but also to the support portion of the sensor housing. Therefore, the preload applied to the piezoelectric element is reduced, so that the mechanical strength of the piezoelectric element can be ensured even if the thickness of the piezoelectric element in the vertical direction is reduced. In other words, the piezoelectric element can be made thinner. Therefore, the load sensor can be made smaller in size in the thickness direction of the piezoelectric element while maintaining the mechanical strength of the piezoelectric element. [Brief description of the drawings]

[0013] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: [Figure 1] FIG. 1 is a plan view of a load sensor according to a first embodiment; [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1; [Diagram 3] FIG. 3 is a cross-sectional view of the detection unit; [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. [Diagram 5] FIG. 5 is a diagram showing the relationship between frequency and response function. [Figure 6] FIG. 6 is a diagram showing the relationship between the thickness of the load sensor and the amount of deviation of the resonance frequency. [Figure 7] FIG. 7 is a plan view of a first piezoelectric element according to a second embodiment; [Figure 8] FIG. 8 is a plan view showing a modification of the second embodiment; [Figure 9] FIG. 9 is a plan view showing a modification of the second embodiment; [Figure 10] FIG. 10 is a plan view showing a modification of the second embodiment; [Figure 11] FIG. 11 is a plan view showing a modified example of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, a number of embodiments for carrying out the present disclosure will be described with reference to the drawings. In each embodiment, the same reference numerals may be used to designate parts corresponding to matters described in the preceding embodiment, and duplicated descriptions may be omitted. In each embodiment, when only a part of the configuration is described, other embodiments described previously may be applied to other parts of the configuration. In addition to combinations of parts that are specifically indicated as being possible in each embodiment, it is also possible to partially combine embodiments even if not indicated, as long as there is no particular problem with the combination.

[0015] (First embodiment) Hereinafter, a first embodiment will be described with reference to the drawings. The load sensor according to this embodiment is used, for example, to evaluate the influence of a transmission force based on vibration of an electric compressor on other components. The electric compressor is mounted on, for example, a vehicle.

[0016] As shown in FIGS. 1 to 4, the load sensor 100 includes a detection unit 110, a sensor housing 130, and a flexible substrate 150. The load sensor 100 includes a detection unit 110, a sensor housing 130, and a flexible substrate 150.

[0017] As shown in Fig. 3, the detection unit 110 detects a transmission force based on vibration of the electric compressor. The detection unit 110 includes a plurality of piezoelectric elements 111-113, a plurality of output electrodes 114-116, and a plurality of ground electrodes 117-120. Fig. 3 is a cross-sectional view at a position corresponding to the cross section II-II in Fig. 1.

[0018] Each of the piezoelectric elements 111-113 is an element for detecting forces in three axial directions. Each of the piezoelectric elements 111-113 is a piezoelectric crystal having an electrical axis, a mechanical axis, and an optical axis. Each of the piezoelectric elements 111-113 generates an electric charge when a force is applied in the direction of the electrical axis.

[0019] Each of the piezoelectric elements 111-113 is in the form of a plate having a front surface 121, a back surface 122, and an outer surface 123. One of the surface directions of the front surface 121 is defined as the X direction. The other direction perpendicular to the one surface direction of the front surface 121 is defined as the Y direction. The direction perpendicular to the front surface 121 is defined as the Z direction. The outer surface 123 corresponds to the outer circumferential surface of each of the piezoelectric elements 111-113 when the Z direction is taken as the axis.

[0020] Each of the piezoelectric elements 111 to 113 has a thickness of, for example, 0.5 mm or less in a direction perpendicular to the surface 121 of each of the piezoelectric elements 111 to 113. In this embodiment, the thickness of each of the piezoelectric elements 111 to 113 is 0.1 mm.

[0021] Each of the piezoelectric elements 111-113 outputs an electrical signal corresponding to the magnitude of a force applied along an electrical axis. Each of the piezoelectric elements 111-113 includes a pair of first piezoelectric elements 111, a pair of second piezoelectric elements 112, and a pair of third piezoelectric elements 113.

[0022] The pair of first piezoelectric elements 111 outputs a first electric signal corresponding to the magnitude of the force applied in the X direction. The pair of first piezoelectric elements 111 are arranged in parallel with a gap between them. The X direction corresponds to the shear direction. Therefore, a pair of first piezoelectric elements 111 for measuring the force in the shear direction is cut out from quartz crystal, and the shear direction of the pair of cut out first piezoelectric elements 111 is aligned with the X direction, which is the electrical axis.

[0023] The pair of second piezoelectric elements 112 outputs a second electric signal corresponding to the magnitude of the force applied in the Y direction. The pair of second piezoelectric elements 112 are arranged in parallel with a gap therebetween. The Y direction corresponds to the shear direction. Therefore, a pair of second piezoelectric elements 112 for measuring the force in the shear direction are cut out from quartz crystal, and the shear direction of the pair of cut out second piezoelectric elements 112 is aligned with the Y direction, which is the electrical axis.

[0024] For the pair of first piezoelectric elements 111 and the pair of second piezoelectric elements 112, piezoelectric quartz crystals for measuring the force in the shear direction are cut from quartz crystal, and the shear direction is aligned with the electrical axis. The electrical axis of the pair of first piezoelectric elements 111 is arranged along the X direction, which is the shear direction. The electrical axis of the pair of second piezoelectric elements 112 is arranged along the Y direction, which is the shear direction.

[0025] The electrical axis of one first piezoelectric element 111 is disposed in the opposite direction to the electrical axis of the other first piezoelectric element 111. Similarly, the electrical axis of one second piezoelectric element 112 is disposed in the opposite direction to the electrical axis of the other second piezoelectric element 112. The mechanical axes of the pair of first piezoelectric elements 111 and the mechanical axes of the pair of second piezoelectric elements 112 are each disposed along the vertical direction.

[0026] The pair of third piezoelectric elements 113 outputs a third electric signal corresponding to the magnitude of the force applied in the Z direction. The pair of third piezoelectric elements 113 are arranged in parallel with a gap between them. The Z direction corresponds to the compression direction. Therefore, a pair of third piezoelectric elements 113 for measuring the force in the compression direction is cut out from quartz crystal, and the compression direction of the pair of cut out third piezoelectric elements 113 is aligned with the Z direction, which is the electrical axis.

[0027] For the pair of third piezoelectric elements 113, a piezoelectric quartz crystal for measuring the force in the compression direction is cut from a crystal, and the compression direction is aligned with the electrical axis. The electrical axes of the pair of third piezoelectric elements 113 are arranged along the Z direction, which is the shear direction. The electrical axis of one third piezoelectric element 113 is arranged in the opposite direction to the electrical axis of the other third piezoelectric element 113. The mechanical axis of the pair of third piezoelectric elements 113 is arranged along the surface direction of the surface 121.

[0028] The pair of first piezoelectric elements 111, the pair of second piezoelectric elements 112, and the pair of third piezoelectric elements 113 are arranged in the vertical direction and in parallel with a gap therebetween. In this embodiment, the pair of third piezoelectric elements 113 is arranged between the pair of second piezoelectric elements 112 and the pair of first piezoelectric elements 111.

[0029] The output electrodes 114 to 116 are electrodes for outputting respective electrical signals. The output electrode 114 is disposed between a pair of first piezoelectric elements 111 and is electrically connected to the pair of first piezoelectric elements 111. In other words, the output electrode 114 is sandwiched between one first piezoelectric element 111 and the other first piezoelectric element 111.

[0030] Similarly, the output electrode 115 is sandwiched between one second piezoelectric element 112 and the other second piezoelectric element 112, and is electrically connected to the pair of second piezoelectric elements 112. The output electrode 116 is sandwiched between one third piezoelectric element 113 and the other third piezoelectric element 113, and is electrically connected to the pair of third piezoelectric elements 113. In this embodiment, the thickness of each of the output electrodes 114 to 116 is 0.05 mm.

[0031] Each of the ground electrodes 117-120 is an electrode connected to a pair of first piezoelectric elements 111, a pair of second piezoelectric elements 112, and a pair of third piezoelectric elements 113. In this embodiment, each of the ground electrodes 117-120 has a thickness of 0.05 mm.

[0032] Some of the ground electrodes 117 to 120, the ground electrodes 117 and 118, are disposed between adjacent elements in the pair of first piezoelectric elements 111, the pair of second piezoelectric elements 112, and the pair of third piezoelectric elements 113, and are thereby shared by adjacent elements. In addition, the ground electrodes 117 and 118 are electrically connected to the adjacent elements.

[0033] In this embodiment, the ground electrode 117 is sandwiched between the second piezoelectric element 112 and the third piezoelectric element 113 and is electrically connected to each of them. That is, the ground electrode 117 is an electrode common to Y and Z. Moreover, the ground electrode 118 is sandwiched between the third piezoelectric element 113 and the first piezoelectric element 111 and is electrically connected to each of them. That is, the ground electrode 118 is an electrode common to X and Z.

[0034] The ground electrode 119 is in contact with one of the second piezoelectric elements 112. The ground electrode 120 is in contact with the other of the first piezoelectric elements 111.

[0035] With the above configuration, the detection section 110 can be simplified by minimizing the stacking thickness and number of layers of the piezoelectric elements 111-113, the output electrodes 114-116, and the ground electrodes 117-120. Note that although the piezoelectric elements 111-113, the output electrodes 114-116, and the ground electrodes 117-120 are depicted as being separated from each other in Fig. 3, they are actually in contact with each other.

[0036] The sensor housing 130 is a case that contains the detection unit 110 and defines the external appearance of the load sensor. As shown in Fig. 1 and Fig. 2, the sensor housing 130 has a first plate portion 131, a second plate portion 132, an outer support portion 133, an inner support portion 134, an insulating resin 135, and an outer circumferential portion 136.

[0037] The first plate portion 131 is a portion arranged on the side of the front surface 121 of each of the piezoelectric elements 111 to 113. The second plate portion 132 is a portion arranged on the side of the rear surface 122 of each of the piezoelectric elements 111 to 113. The first plate portion 131 and the second plate portion 132 sandwich the detection portion 110. Note that the first plate portion 131 is omitted in FIG. 1.

[0038] The first plate portion 131 has a first through hole 137 that penetrates along the vertical direction. The second plate portion 132 has a second through hole 138 that penetrates along the vertical direction and is connected to the first through hole 137. In other words, the first plate portion 131 and the second plate portion 132 are ring-shaped.

[0039] The vertical length from the first plate portion 131 to the second plate portion 132 is the thickness of the load sensor 100. In this embodiment, the thickness of the load sensor 100 is, for example, 1.95 mm.

[0040] 1, the detection unit 110 has a third through hole 124 that penetrates in the vertical direction. That is, each of the piezoelectric elements 111-113, each of the output electrodes 114-116, and each of the ground electrodes 117-120 are ring-shaped. Therefore, as shown in FIG. 3, each of the piezoelectric elements 111-113 has an inner surface 125 that constitutes the third through hole 124. And, the third through hole 124 of each of the piezoelectric elements 111-113 is connected to the first through hole 137 of the first plate portion 131 and the second through hole 138 of the second plate portion 132.

[0041] 4, the outer support portion 133 is located on the side of the outer surface 123 of each of the piezoelectric elements 111-113, and supports the first plate portion 131 and the second plate portion 132. The outer support portion 133 is formed continuously along the outer surface 123, except for a portion of the outer surface 123 of each of the piezoelectric elements 111-113 that corresponds to the outer periphery 136.

[0042] The inner support portion 134 is located on the side of the inner surface 125 of each of the piezoelectric elements 111-113, and supports the first plate portion 131 and the second plate portion 132. The inner support portion 134 is formed continuously around the inner surface 125 of each of the piezoelectric elements 111-113.

[0043] The outer support portions 133 may be formed discontinuously along the outer side surfaces 123 of the piezoelectric elements 111-113. The inner support portions 134 may be formed discontinuously along the inner side surfaces 125 of the piezoelectric elements 111-113.

[0044] The insulating resin 135 is a component for electrically insulating the inner support portion 134 and the detection portion 110. As shown in Fig. 2 and Fig. 4, the insulating resin 135 is disposed between the inner support portion 134 of the sensor housing 130 and the inner side surfaces 125 of the piezoelectric elements 111 to 113. Note that the insulating resin 135 may also be disposed between the detection portion 110 and the outer support portion 133.

[0045] The outer peripheral portion 136 is a portion that protects the electrical connection portion between the detection portion 110 and the flexible substrate 150. The outer peripheral portion 136 is formed by a part of the outer support portion 133. The outer peripheral portion 136 forms a space 139 between the first plate portion 131 and the second plate portion 132 on the side of the outer surface 123 of each of the piezoelectric elements 111-113.

[0046] The portion of the outer support portion 133 that constitutes the outer periphery 136 is thicker than the other portions, in order to prevent the space 139 from being crushed by the load applied along the vertical direction.

[0047] Furthermore, the connection terminals 140-142 of the output electrodes 114-116 and the connection terminals 143-146 of the ground electrodes 117-120 are arranged in the space 139. The connection terminals 140-146 are arranged at intervals along the outer side surfaces 123 of the piezoelectric elements 111-113 so as not to overlap in the vertical direction. As a result, the connection terminals 140-146 are arranged in parallel on a plane, as shown in Fig. 1.

[0048] The sensor housing 130 is formed of a metal material such as stainless steel. For example, the first plate portion 131, the second plate portion 132, the outer support portion 133, and the inner support portion 134 are all prepared as separate bodies and then welded together to form the sensor housing 130. Alternatively, a metal plate may be cut to integrate the outer support portion 133 and the inner support portion 134 with the second plate portion 132, and then the first plate portion 131 may be welded to the integrated body.

[0049] The flexible substrate 150 is a wiring device that electrically connects the detection unit 110 to an external device. The flexible substrate 150 has a plurality of wirings 151 to 154, an insulating film 155, and a connection unit 156.

[0050] Each of the wirings 151-154 is electrically connected to the detection unit 110. Each of the wirings 151-154 includes three wirings 151-153 corresponding to three electric signals and one wiring 154 corresponding to a ground potential. An insulating film 155 covers each of the wirings 151-154.

[0051] The connection portion 156 is a portion where three signal terminals 157-159 connected to the wirings 151-154, respectively, and a ground terminal 160 connected to the wiring 154 are exposed from an upper surface 161 of the insulating film 155. The signal terminals 157-159 and the ground terminal 160 are arranged on the same plane.

[0052] An upper surface 161 of the insulating film 155 of the flexible substrate 150 faces the first plate portion 131 and is disposed on the same plane as one surface 147 of the second plate portion 132. One surface 147 of the second plate portion 132 is a surface on which the detection portion 110 is disposed. This allows the connection between the flexible substrate 150 and the detection portion 110 to be performed within the range of the space 139 of the outer periphery portion 136, thereby making it possible to thin the load sensor 100 in the vertical direction.

[0053] The ground terminal 160 is a terminal common to the ground electrodes 117 to 120. In this embodiment, the ground terminals 160 are provided in two places. Of course, the ground terminal 160 may be provided in one place. In this manner, the ground terminals 160 are consolidated into one terminal for each of the ground electrodes 117 to 120.

[0054] The connection portion 156 is disposed in a space 139 of the outer circumferential portion 136. The output electrodes 114-116 are connected to the signal terminals 157-159, respectively, in the space 139 via enamel wires 162. Similarly, the ground electrodes 117-120 are connected to a ground terminal 160 in the space 139 via enamel wires 162.

[0055] In this way, the load sensor 100 has a simple output structure in which a total of four wires are used for external output: three output wires 151-153 for each of the piezoelectric elements 111-113 and one ground wire 154. Since the connection part 156 is disposed in the space 139 of the sensor housing 130, the connection part 156 can be made thin in the vertical direction. Also, breakage of each enamel wire 162 between the detection part 110 and the flexible substrate 150 can be prevented. The above is the overall configuration of the load sensor 100 according to this embodiment.

[0056] Next, a load measuring method of the load sensor 100 will be described. The load sensor 100 is disposed between an electric compressor, which is a load measuring component, and a stay. In addition, bolts are passed through the through holes 124, 137, and 138 of the load sensor 100. Then, the electric compressor and the load sensor 100 are fastened together. Therefore, the load sensor 100 is sandwiched like a washer by the fastening torque of the bolts, and is used in a state in which an axial force (preload) corresponding to the fastening torque is applied. Each of the piezoelectric elements 111 to 113 detects a three-dimensional transmission force generated by vibration of the electric compressor as a load fluctuation.

[0057] The pair of first piezoelectric elements 111 are arranged along the X direction, which is the electrical axis of the piezoelectric element 111 in the shear direction. Therefore, when a force is applied in the X direction, the charge output is amplified by two times. On the other hand, the pair of first piezoelectric elements 111 are arranged along the Z direction, which is the mechanical axis of the piezoelectric element 111 in the compression direction. Therefore, when a force is applied in the Z direction, the charges generated in the pair of first piezoelectric elements 111 are cancelled out. As a result, the pair of first piezoelectric elements 111 output a first electrical signal corresponding to the magnitude of the force applied in the X direction.

[0058] Similar to the pair of first piezoelectric elements 111, the pair of second piezoelectric elements 112 outputs a second electric signal corresponding to the magnitude of the force applied in the Y direction.

[0059] The pair of third piezoelectric elements 113 are arranged such that their electrical axes are aligned along the Z direction, which is the compression direction. Therefore, when a force is applied in the Z direction, the charge output is amplified by two times. On the other hand, the pair of third piezoelectric elements 113 are arranged such that their mechanical axes are aligned along the shear direction. Therefore, when a force is applied in the shear direction, the charges generated in the pair of third piezoelectric elements 113 are offset. As a result, the pair of third piezoelectric elements 113 output a third electrical signal corresponding to the magnitude of the force applied in the Z direction.

[0060] Next, the effects obtained by the structure of the above-described load sensor 100 will be described. As described above, the load sensor 100 is fixed between the electric compressor and the stay, so that a preload, which is the bolt tightening force, is applied to the load sensor 100 in advance.

[0061] However, since the load sensor 100 includes the outer support portion 133 and the inner support portion 134, a part of the preload that is applied in advance between the first plate portion 131 and the second plate portion 132 of the sensor housing 130 along the vertical direction is applied to both the outer support portion 133 and the inner support portion 134. As a result, as shown in FIG. 4, a part of the preload is distributed not only to the detection portion 110 but also to both the outer support portion 133 and the inner support portion 134.

[0062] If the tightening force of the fastening bolt is F, then, for example, a preload of 0.6 F is applied to the outer support portion 133, a preload of 0.3 F is applied to the detection portion 110, and a preload of 0.1 F is applied to the inner support portion 134. In other words, the outer support portion 133 receives 60% of the tightening force, the detection portion 110 receives 30% of the tightening force, and the inner support portion 134 receives 10% of the tightening force.

[0063] In this way, the fastening force F is distributed to the outer support portion 133, the detection portion 110, and the inner support portion 134, so that the preload applied to each of the piezoelectric elements 111-113 is reduced. In other words, the preload acting on each of the piezoelectric elements 111-113 can be reduced to 1 / 3. The distribution ratio of the preload can be adjusted by the thickness of the outer support portion 133 and the thickness of the inner support portion 134 in the planar direction.

[0064] In this embodiment, a safety factor of 2.3 can be ensured for each of the piezoelectric elements 111-113. The load capacity of each of the piezoelectric elements 111-113 is 0.3 F×2.3=0.69 F. In the above example, the preload applied to the detection unit 110 is 0.3 F, which is sufficiently smaller than the load capacity. Therefore, even if the thickness of each of the piezoelectric elements 111-113 in the vertical direction is reduced, the mechanical strength of each of the piezoelectric elements 111-113 can be ensured. Therefore, the load sensor 100 can be miniaturized in the thickness direction of each of the piezoelectric elements 111-113 while maintaining the mechanical strength of each of the piezoelectric elements 111-113.

[0065] Furthermore, the inventors of the present disclosure investigated the response function of the load sensor 100 with respect to frequency when the thickness of the load sensor 100 in the vertical direction was changed. The results are shown in FIG.

[0066] The 0[dB] of the response function is 0[dB]=1[(m / s 2 5, when the thickness of the load sensor 100 is 0 mm, this corresponds to the case where the load sensor 100 is not disposed between the electric compressor and the stay.

[0067] As shown in Fig. 5, when the thickness of the load sensor 100 is increased, the waveform of the response function of the electric compressor deviates from the waveform of the response function when the thickness of the load sensor 100 is 0 mm. This is because, by sandwiching the load sensor 100 between the electric compressor and the stay, the load measurement position is moved away from the electric compressor, and the resonance frequency of the electric compressor changes according to the thickness of the load sensor 100. In addition, vibrations that differ from the actual phenomenon, i.e. load fluctuations, are generated, and it becomes impossible to measure the three-dimensional transmission force transmitted from the electric compressor to the stay in a state close to the actual phenomenon.

[0068] Therefore, the inventors of the present disclosure investigated the amount of shift in the peak frequency of each waveform when the thickness of the load sensor 100 is changed, based on the frequency of the peak of the waveform around 650 Hz when the thickness of the load sensor 100 is 0 mm. The results are shown in FIG.

[0069] As shown in Fig. 6, the greater the thickness of the load sensor 100, the greater the shift in the resonant frequency of the electric compressor. Since the thickness of the load sensor 100 according to this embodiment is 1.95 mm, it is possible to measure the transmission force with a resonant frequency change of 20 Hz or less. In other words, it is possible to measure the three-dimensional transmission force transmitted from the electric compressor to the stay in a state close to the actual phenomenon.

[0070] Alternatively, the inner support portion 134 may be subjected to a greater preload than the outer support portion 133. Alternatively, the inner support portion 134 and the outer support portion 133 may be subjected to the same magnitude of preload.

[0071] As a modified example, the sensor housing 130 may have only the outer support portion 133 of the outer support portion 133 and the inner support portion 134. Alternatively, the sensor housing 130 may have only the inner support portion 134 of the outer support portion 133 and the inner support portion 134. This makes it possible to distribute the preload applied to the load sensor 100 to the outer support portion 133 or the inner support portion 134.

[0072] In addition, the outer support portion 133 and the inner support portion 134 in this embodiment correspond to the support portion.

[0073] Second embodiment In this embodiment, differences from the first embodiment will be mainly described. As shown in Fig. 7, one first piezoelectric element 111 has two flat portions 126a and 126b. One flat portion 126a and the other flat portion 126b are offset by, for example, 45 degrees.

[0074] The flat portions 126a, 126b are formed on the outer side surfaces 123 of the pair of first piezoelectric elements 111. The flat portions 126a, 126b are flat surfaces along the vertical direction. The flat portions 126a, 126b are used for positioning the pair of first piezoelectric elements 111 in the rotation direction around an axis along the vertical direction.

[0075] Similarly, the other first piezoelectric element 111, the pair of second piezoelectric elements 112, and the pair of third piezoelectric elements 113 also have flat portions 126a, 126b. The output electrodes 114-116 and the ground electrodes 117-120 also have flat portions 126a, 126b similar to those of the piezoelectric elements 111-113. This makes it possible to improve the positioning accuracy of each of the piezoelectric elements 111-113 in the rotational direction.

[0076] As a modification, each of the piezoelectric elements 111 to 113 may have two flat portions 126a and 126c as shown in Fig. 8. One flat portion 126a and the other flat portion 126c are offset from each other by, for example, 90 degrees.

[0077] As a modification, each of the piezoelectric elements 111 to 113 may have two flat portions 126a and 126d as shown in Fig. 9. One flat portion 126a and the other flat portion 126d are offset from each other by, for example, 180 degrees.

[0078] As a modified example, as shown in FIG. 10, each of the piezoelectric elements 111 to 113 may have one flat portion 126a.

[0079] 11, each of the piezoelectric elements 111-113 may have two flat portions 126e, 126f on the inner side surface 125. Alternatively, each of the piezoelectric elements 111-113 may have one flat portion 126e on the inner side surface 125.

[0080] As a modified example, each of the piezoelectric elements 111-113 may have flat portions 126a-126e on both the outer side surface 123 and the inner side surface 125. For example, each of the piezoelectric elements 111-113 may have one flat portion 126a on the outer side surface 123 and one flat portion 126f on the inner side surface 125.

[0081] The present disclosure is not limited to the above-described embodiment, and various modifications can be made as follows without departing from the spirit and scope of the present disclosure.

[0082] For example, the load sensor 100 is not limited to detecting forces in three axial directions, but may be configured to detect forces in two axes or one axis.

[0083] In each of the above embodiments, the pair of third piezoelectric elements 113 is positioned between the pair of second piezoelectric elements 112 and the pair of first piezoelectric elements 111, but this is just one example of an arrangement. The pair of first piezoelectric elements 111, the pair of second piezoelectric elements 112, and the pair of third piezoelectric elements 113 may be arranged in any order in the vertical direction.

[0084] Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure.

Claims

1. A load sensor used in a state where an axial force is applied to a load measuring component with a predetermined tightening torque, A detection unit (110) having a plate-like shape with a front surface (121) and a back surface (122) and including piezoelectric elements (111-113) that output an electrical signal corresponding to the magnitude of a force applied along an electrical axis; a sensor housing (130) having a first plate portion (131) located on the front surface side of the piezoelectric element and a second plate portion (132) located on the back surface side of the piezoelectric element, and accommodating the detection portion between the first plate portion and the second plate portion; Including, The sensor housing includes a support portion (133, 134) that supports the first plate portion and the second plate portion, A part of a preload applied in advance between the first plate portion and the second plate portion along a thickness direction of the piezoelectric element is applied to the support portion, The detection unit includes a plurality of output electrodes (114 to 116) for outputting the electrical signal and a plurality of ground electrodes (117 to 120); The piezoelectric elements include a pair of first piezoelectric elements (111) arranged in parallel and outputting a first electric signal corresponding to the magnitude of a force applied in one direction of the surface direction, a pair of second piezoelectric elements (112) arranged in parallel and outputting a second electric signal corresponding to the magnitude of a force applied in another direction perpendicular to the one direction of the surface direction, and a pair of third piezoelectric elements (113) arranged in parallel and outputting a third electric signal corresponding to the magnitude of a force applied in the thickness direction, the pair of first piezoelectric elements, the pair of second piezoelectric elements, and the pair of third piezoelectric elements are arranged in the thickness direction and in parallel, the plurality of output electrodes are disposed between the pair of first piezoelectric elements, between the pair of second piezoelectric elements, and between the pair of third piezoelectric elements, respectively, and are electrically connected to the pair of first piezoelectric elements, the pair of second piezoelectric elements, and the pair of third piezoelectric elements, respectively; some of the ground electrodes (117, 118) are disposed between adjacent elements in the pair of first piezoelectric elements, the pair of second piezoelectric elements, and the pair of third piezoelectric elements, so as to be shared by the adjacent elements and to be electrically connected to the adjacent elements; The plurality of ground electrodes are connected to a ground terminal (160) common to the plurality of ground electrodes; The flexible substrate (150) includes a plurality of wirings (151-154) electrically connected to the detection unit, an insulating film (155) covering the plurality of wirings, and a connection portion (156) in which a plurality of signal terminals (157-159) respectively connected to the plurality of wirings and the ground terminal are exposed from an upper surface (161) of the insulating film, The piezoelectric element has an outer surface (123); the sensor housing has an outer peripheral portion (136) that defines a space (139) between the first plate portion and the second plate portion on the side of the outer surface of the piezoelectric element, the connection portion of the flexible substrate is disposed in the space at the outer periphery, the plurality of output electrodes are connected to the plurality of signal terminals in the space, The plurality of ground electrodes are connected to the ground terminal in the space.

2. The first plate portion has a first through hole (137) penetrating along the thickness direction, The second plate portion has a second through hole (138) that penetrates along the thickness direction and is connected to the first through hole, The detection portion has a third through hole (124) that penetrates along the thickness direction and is connected to the first through hole and the second through hole, 2. The load sensor according to claim 1, further comprising bolts which are passed through the first through hole, the second through hole and the third through hole and which apply an axial force to the load measuring component with a predetermined tightening torque.

3. The first plate portion has a first through hole (137) penetrating along the thickness direction, The second plate portion has a second through hole (138) that penetrates along the thickness direction and is connected to the first through hole, The detection portion has a third through hole (124) that penetrates along the thickness direction and is connected to the first through hole and the second through hole, The piezoelectric element has an outer surface (123) and an inner surface (125) that defines the third through hole, The sensor housing includes, as the support portion, one or both of an outer support portion (133) located on the outer surface side of the piezoelectric element and supporting the first plate portion and the second plate portion, and an inner support portion (134) located on the inner surface side of the piezoelectric element and supporting the first plate portion and the second plate portion, 3. The load sensor according to claim 1, wherein a portion of the preload applied in advance to the first plate portion and the second plate portion along the thickness direction is applied to either one or both of the outer support portion and the inner support portion.

4. The load sensor according to claim 1 or 2, wherein the piezoelectric element has a flat surface along the thickness direction and a flat portion (126a to 126f) for positioning in a rotational direction around an axis along the thickness direction.

5. The flexible substrate (150) includes a plurality of wirings (151 to 154) electrically connected to the detection unit and an insulating film (155) covering the plurality of wirings; The second plate portion has a surface (147) on which the detection portion is disposed, 3. The load sensor according to claim 1, wherein an upper surface (161) of the insulating film of the flexible substrate faces the first plate portion and is disposed on the same plane as the one surface of the second plate portion.

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