Obstacle detection device

Abstract

The invention comprises: an ultrasonic sensor, which is provided in a part of a vehicle at a predetermined height from a road surface, and is provided with a plurality of ultrasonic elements, which transmit detection waves toward the outside of the vehicle and receive reflected waves of the detection waves reflected by obstacles as received waves; and a control unit, which derives the distance to the obstacle, i.e., the obstacle distance, and the height of the obstacle, i.e., the obstacle height, based on the received waves and performs predetermined processing. Furthermore, when deriving the obstacle distance and the obstacle height, the control unit derives the obstacle distance and the obstacle height based on the intensity of the received waves received by the plurality of ultrasonic elements and the phase difference of the received waves received by the plurality of ultrasonic elements.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based on Japanese Patent Application No. 2019-219746 filed on December 4, 2019, the contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to an obstacle detection device using an ultrasonic sensor. Background Art

[0004] Conventionally, an obstacle detection device using an ultrasonic sensor has been proposed (for example, refer to Patent Document 1). Specifically, in this obstacle detection device, an ultrasonic sensor is provided at a position at a predetermined height of a vehicle.

[0005] Furthermore, if the ultrasonic sensor receives a receiving wave after sending the detection wave, the obstacle detection device determines the height of the obstacle based on the number of maximum peaks contained in the received wave. Specifically, when there are multiple maximum peaks contained in the received wave, the obstacle detection device determines the obstacle as a high obstacle (hereinafter, also referred to as a high obstacle) having a height above the position where the ultrasonic sensor is set. When there is only one maximum peak contained in the received wave, the obstacle detection device determines the obstacle as a low obstacle (hereinafter, also referred to as a low obstacle) having a height lower than the position where the ultrasonic sensor is set. In addition, a high obstacle is, for example, a wall, and a low obstacle is, for example, a curb or a roadblock.

[0006] Furthermore, when the ultrasonic sensor receives a reception wave after transmitting the detection wave, the obstacle detection device derives the obstacle distance to the obstacle based on the time from the transmission of the detection wave to the reception of the reception wave.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent No. 6340713 Summary of the invention

[0010] However, the inventors have studied the above obstacle detection device and confirmed that: when multiple low obstacles at different distances from the ultrasonic sensor are arranged close to each other, if the detection wave is reflected by each low obstacle, the received wave contains multiple maximum peaks. Therefore, the above obstacle detection device may mistakenly detect the presence of a high obstacle when multiple low obstacles are arranged close to each other.

[0011] An object of the present disclosure is to provide an obstacle detection device that can achieve improved detection accuracy.

[0012] According to one viewpoint of the present disclosure, an obstacle detection device detects obstacles existing around a vehicle, and comprises: an ultrasonic sensor, which is arranged in a portion of the vehicle at a predetermined height from the road surface, and is formed with a plurality of ultrasonic elements, the plurality of ultrasonic elements transmitting detection waves toward the outside of the vehicle, and receiving reflected waves of the detection waves reflected by obstacles as received waves; and a control unit, which performs predetermined processing by deriving the distance to the obstacle, i.e., the obstacle distance, and the height of the obstacle, i.e., the obstacle height, based on the received waves; when deriving the obstacle distance and the obstacle height, the control unit derives the obstacle distance and the obstacle height based on the intensity of the received waves received by the plurality of ultrasonic elements and the phase difference of the received waves received by the plurality of ultrasonic elements.

[0013] Here, when multiple ultrasonic elements receive received waves, when receiving reflected waves reflected from a high obstacle, reflected waves without a phase difference are also received, and when receiving reflected waves reflected from a low obstacle, only reflected waves with a phase difference are received. Therefore, by causing the control unit to derive the obstacle height based on the phase difference, even when multiple low obstacles at different distances from the ultrasonic sensor are close as obstacles, it is possible to suppress the obstacles from being erroneously detected as high obstacles. Therefore, it is possible to achieve improved detection accuracy.

[0014] In addition, the reference numerals in parentheses attached to each component etc. represent an example of the correspondence relationship between the component etc. and the specific component etc. described in the embodiment described later. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram showing the structure of an obstacle detection device.

[0016] Figure 2 It is a cross-sectional view showing the structure of an ultrasonic sensor.

[0017] Figure 3 This is a schematic diagram showing the connection between the ultrasonic sensor and the control unit.

[0018] Figure 4 This is a diagram showing the relationship among the number of ultrasonic elements, directivity angle, and sound pressure.

[0019] Figure 5 This is a schematic diagram showing a state where a detection wave is transmitted from an ultrasonic sensor.

[0020] Figure 6 This is a schematic diagram showing the propagation paths of the detection waves sent from the ultrasonic sensor and the reflected waves reflected by a high obstacle.

[0021] Figure 7 It is a diagram showing the relationship between the propagation distance of the reflected wave and the intensity of the received wave.

[0022] Figure 8 It is a diagram showing the relationship between the propagation distance of the reflected wave and the phase difference of the received wave.

[0023] Fig. 9 This is a schematic diagram showing the propagation paths of the detection waves sent from the ultrasonic sensor and the reflected waves reflected by low obstacles.

[0024] Fig.10 It is a schematic diagram showing the detailed propagation paths of the probe wave to be reflected by a low obstacle and the reflected wave that is reflected back.

[0025] Fig.11 It is a diagram showing the relationship between the propagation distance of the reflected wave and the intensity of the received wave.

[0026] Fig.12 It is a diagram showing the relationship between the propagation distance of the reflected wave and the phase difference of the received wave.

[0027] Fig.13 It is a flowchart which shows the process which the control part performs.

[0028] Fig.14 : is a diagram showing the relationship between the obstacle distance and the phase difference stored in the control unit according to the second embodiment.

[0029] Fig.15 This is a flowchart showing the processing executed by the control unit according to the fourth embodiment.

[0030] Fig.16 This is a schematic diagram showing the propagation paths of the detection waves transmitted from the ultrasonic sensor and the reflected waves reflected by a low obstacle according to the fifth embodiment.

[0031] Fig.17 This is a flowchart showing the processing executed by the control unit according to the fifth embodiment.

[0032] Fig.18 It is a diagram showing the relationship between the propagation distance of the reflected wave and the intensity of the received wave according to the fifth embodiment.

[0033] Fig.19 It is a diagram showing the relationship between the propagation distance of the reflected wave and the height of the road surface according to the fifth embodiment.

[0034] Fig. 20A It is a diagram showing the relationship between the propagation distance of the reflected wave and the intensity of the received wave according to the sixth embodiment.

[0035] Fig. 20B It is a diagram showing the relationship between the propagation distance of the reflected wave and the intensity of the received wave according to the sixth embodiment.

[0036] Fig. 20CIt is a diagram showing the relationship between the propagation distance of the reflected wave and the intensity of the received wave according to the sixth embodiment.

[0037] Fig.20D It is a diagram showing the relationship between the propagation distance of the reflected wave and the intensity of the received wave according to the sixth embodiment.

[0038] Fig.20E It is a diagram showing the relationship between the propagation distance of the reflected wave and the intensity of the received wave according to the sixth embodiment.

[0039] Fig.20F It is a diagram showing the relationship between the propagation distance of the reflected wave and the intensity of the received wave according to the sixth embodiment.

[0040] Fig.21 This is a schematic diagram showing a state where a detection wave is transmitted from the ultrasonic sensor according to the sixth embodiment.

[0041] Fig.22A This is a diagram showing the relationship between the sensor mounting height of the ultrasonic sensor according to the seventh embodiment and the phase difference when a reflected wave reflected by an obstacle is received.

[0042] Fig. 22B This is a diagram showing the relationship between the sensor mounting height of the ultrasonic sensor according to the seventh embodiment and the phase difference when a reflected wave reflected from a road surface is received.

[0043] Fig.23 It is a cross-sectional view showing the structure of an ultrasonic sensor according to an eighth embodiment.

[0044] Fig.24 It is a cross-sectional view showing the structure of an ultrasonic sensor according to a ninth embodiment.

[0045] Fig.25 This is a schematic diagram showing a propagation path of a reflected wave when the obstacle is a groove according to another embodiment.

[0046] Fig.26 is with Fig.25 The corresponding top view.

[0047] Fig. 27 It means existence Fig.25 Graph showing the relationship between the propagation distance of the reflected wave and the intensity of the received wave in the case of an obstacle shown.

[0048] Fig.28 It means existence Fig.25 Graph showing the relationship between the propagation distance of the reflected wave and the phase difference of the received wave in the case of an obstacle shown.

[0049] Fig.29This is a schematic diagram showing a propagation path of a reflected wave when the obstacle is a groove according to another embodiment.

[0050] Fig.30 is with Fig.29 The corresponding top view.

[0051] Fig.31 It means existence Fig.29 Graph showing the relationship between the propagation distance of the reflected wave and the intensity of the received wave in the case of an obstacle shown.

[0052] Fig.32 It means existence Fig.29 Graph showing the relationship between the propagation distance of the reflected wave and the phase difference of the received wave in the case of an obstacle shown. DETAILED DESCRIPTION

[0053] Hereinafter, embodiments of the present disclosure will be described based on the drawings. In addition, the same or equivalent parts among the following embodiments will be described with the same reference numerals.

[0054] (First Embodiment)

[0055] A first embodiment will be described with reference to the drawings. The obstacle detection device of this embodiment is mounted on a vehicle and is used to detect obstacles existing around the vehicle. Hereinafter, an example in which the obstacle detection device of this embodiment is used in a parking assist device will be described.

[0056] In this embodiment, if Figure 1 As shown, the obstacle detection device includes an ultrasonic sensor 10 provided on the vehicle 1 and a control unit 100 connected to the ultrasonic sensor 10. In addition, in the present embodiment, the vehicle 1 is, for example, a so-called four-wheeled vehicle, and has a body that is substantially rectangular when viewed from above and tires provided on the body. Figure 1 Although the ultrasonic sensors 10 are shown to be installed on the right and left sides of the vehicle, they are actually installed on the front and rear sides of the vehicle.

[0057] The ultrasonic sensor 10 is configured to send a detection wave along a directional axis, and the detection wave is an ultrasonic wave. In addition, the detection wave is sent from the ultrasonic sensor 10 with a specified width (i.e., a directional angle). In addition, the so-called directional axis refers to a virtual straight line extending along the detection wave sent from the ultrasonic sensor 10, which is a reference for the directional angle. In other words, the directional axis is an axis passing through the center of the detection wave. In addition, the ultrasonic sensor 10 is configured to receive a reception wave including a reflected wave that the detection wave is reflected back by obstacles existing in the surroundings, and output a detection signal based on the reception result. In addition, the action of receiving the reflected wave as a reception wave will be referred to as receiving the reflected wave below.

[0058] The structure of the ultrasonic sensor 10 of this embodiment will be described in detail below. Figure 2 As shown, the ultrasonic sensor 10 includes a transducer unit 20 , a support member 30 , a frame body 40 , and the like.

[0059] In the present embodiment, the transducer unit 20 is a MEMS type structured using a sensor substrate 24, and is set to have a structure having a plurality of ultrasonic elements 25. The sensor substrate 24 includes an SOI substrate formed by sequentially stacking a support substrate 21, an embedded insulating film 22, and a semiconductor layer 23. In addition, SOI is the abbreviation of Silicon on Insulator, and MEMS is the abbreviation of Micro Electro Mechanical Systems. In the following, the surface of the semiconductor layer 23 opposite to the embedded insulating film 22 is a surface 24a of the sensor substrate 24, and the surface of the support substrate 21 opposite to the embedded insulating film 22 is the other surface 24b of the sensor substrate 24.

[0060] A plurality of diaphragm portions 27 are formed on the sensor substrate 24 by forming recesses 26 from the other surface 24b side. In the present embodiment, the recesses 26 are formed on the sensor substrate 24 so that the diaphragm portions 27 are arranged two-dimensionally. In the present embodiment, the recesses 26 are formed so as to penetrate the embedded insulating film 22 and reach the semiconductor layer 23, and the diaphragm portion 27 is composed of the semiconductor layer 23. However, the recesses 26 may be formed so that the embedded insulating film 22 remains, and the diaphragm portion 27 may be formed of the embedded insulating film 22 and the semiconductor layer 23.

[0061] Moreover, a piezoelectric element 28 is formed on each diaphragm portion 27, which is formed by stacking a back electrode 28a, a piezoelectric film 28b, and a surface electrode 28c in this order. In this way, a plurality of ultrasonic elements 25 are formed on the sensor substrate 24 in this embodiment. That is, the ultrasonic element 25 of this embodiment is configured as a PMUT. PMUT is the abbreviation of Piezoelectric Micro-machined Ultrasonic Transducers.

[0062] In addition, in this embodiment, the back electrodes 28a of the piezoelectric elements 28 are integrated and a common ground potential is applied. In addition, the piezoelectric film 28b is composed of a piezoelectric ceramic that does not contain lead, such as scandium aluminum nitride (ScAIN) and aluminum nitride (AIN), or a piezoelectric ceramic that contains lead but has high versatility, such as lead zirconate titanate (PZT). Moreover, the piezoelectric film 28b is formed on the diaphragm portion 27 in a manner that becomes a planar shape equivalent to the diaphragm portion 27.

[0063] As described above, the diaphragm portion 27 is formed two-dimensionally, and therefore, each ultrasonic element 25 is arranged two-dimensionally. Figure 3 As shown, each ultrasonic element 25 is connected to the control unit 100 via a bonding wire 35, a connection terminal 36, etc., which will be described later. Figure 3 This is an example in which four ultrasonic elements 25 are formed in one direction of the surface direction of the sensor substrate 24 and four ultrasonic elements 25 are formed in a direction orthogonal to the one direction.

[0064] In this case, as for the ultrasonic element 25, Figure 2 and Figure 3 As shown in FIG. 1 , if the interval between the centers of adjacent ultrasonic elements 25 is set to interval d, it is preferred that the interval d be less than half the wavelength of the detection wave so that the azimuth is not binary with respect to a certain phase difference. In addition, the interval between the centers of adjacent ultrasonic elements 25 is, in other words, the interval between the centers of adjacent diaphragm portions 27.

[0065] In addition, if Figure 2 As shown, a pad portion 29 electrically connected to the back electrode 28 a and the front electrode 28 c is formed on one surface 24 a of the sensor substrate 24 .

[0066] In the case of such an ultrasonic element 25, if an AC voltage, i.e., a driving voltage, is applied to the piezoelectric element 28, the diaphragm portion 27 vibrates ultrasonically and transmits a detection wave. In addition, in the present embodiment, as described later, a driving voltage with equal phase is applied to each piezoelectric element 28 so that the directional axis of the detection wave is consistent with the normal direction of one surface 24a of the sensor substrate 24 (hereinafter also referred to as the normal direction of the sensor substrate 24). In addition, if the ultrasonic element 25 receives a receiving wave, the diaphragm portion 27 vibrates, and the piezoelectric element 28 generates an electric charge based on the vibration. Therefore, if the ultrasonic element 25 receives a receiving wave, a detection signal corresponding to the receiving wave is output.

[0067] The support member 30 is a member that fixes and supports the transducer unit 20. In the present embodiment, the support member 30 is composed of a multilayer substrate, a printed substrate, etc. Although not particularly shown, the support member 30 may also be mounted with various circuit components for signal processing.

[0068] In addition, the support member 30 of the present embodiment has a shape including a concave portion 31 and a convex portion 32 formed so as to surround the concave portion 31. Furthermore, the sensor substrate 24 is mounted on the concave portion 31 via a bonding member 33 so that the other surface 24b of the sensor substrate 24 faces the bottom surface of the concave portion 31. In addition, a silicone-based adhesive or the like is used for the bonding member 33.

[0069] A pad portion 34 is formed on the convex portion 32 of the support member 30 . The pad portion 34 is electrically connected to the pad portion 29 formed on the sensor substrate 24 via a bonding wire 35 .

[0070] Furthermore, a metal connection terminal 36 is arranged on the support member 30 so as to penetrate the convex portion 32 and the pad portion 34. Furthermore, the connection terminal 36 is mechanically connected to the support member 30 and electrically connected to the pad portion 34 by forming a bonding member 37 such as solder. Thus, each ultrasonic element 25 is connected to the connection terminal 36 via the pad portions 29 and 34. In addition, a solder resist 38 is arranged on the pad portion 34 between a portion connected to the bonding lead 35 and a portion connected to the bonding member 37.

[0071] The frame 40 is made of metal or the like, and is formed with a plurality of through holes 41 corresponding to the number of the connection terminals 36 provided on the support member 30. The support member 30 is arranged on the frame 40 via a bonding member 42 in such a manner that the connection terminals 36 pass through the through holes 41. In addition, an insulating member (not shown) for insulating the connection terminals 36 from the frame 40 is filled in the through holes 41. In addition, a silicone adhesive or the like is used for the bonding member 42, and an epoxy resin, sealing glass or the like is used for the insulating member.

[0072] The above is the structure of the ultrasonic sensor 10 of this embodiment. Figure 4 As shown, the ultrasonic sensor 10 can easily change the directional angle by changing the number of ultrasonic elements 25. Specifically, as far as the ultrasonic sensor 10 is concerned, the more the number of ultrasonic elements 25 is, the narrower the directional angle can be, and the fewer the number of ultrasonic elements 25 is, the wider the directional angle can be. In addition, as far as the ultrasonic sensor 10 is concerned, the more the number of ultrasonic elements 25 is increased, the higher the sound pressure can be, and obstacles far away can be detected.

[0073] Therefore, the ultrasonic sensor 10 preferably changes the number of ultrasonic elements 25 formed appropriately based on the mounting height, detection range, etc. In this case, many ultrasonic elements 25 may be formed in advance, and the directivity angle of the detection wave may be adjusted by controlling the number of ultrasonic elements 25 energized.

[0074] Moreover, when the ultrasonic sensor 10 is installed in the vehicle 1, the normal direction of the sensor substrate 24 is parallel to the horizontal direction. That is, when the pointing axis and the normal direction of the ultrasonic sensor 10 are consistent, the pointing axis is parallel to the horizontal direction. In addition, the so-called horizontal direction refers to a direction parallel to the horizontal plane. Moreover, the ultrasonic sensor 10 sends a detection wave toward the outside of the vehicle 1.

[0075] The control unit 100 has a storage unit such as a CPU, ROM, RAM, and non-volatile RAM (not shown), and includes, for example, an on-vehicle ECU. CPU is the abbreviation of Central Processing Unit, ROM is the abbreviation of Read Only Memory, RAM is the abbreviation of Random Access Memory, and ECU is the abbreviation of Electronic Control Unit.

[0076] Furthermore, the control unit 100 implements various control actions by having the CPU read out a program (i.e., each routine described later) from the ROM or non-volatile RAM and execute it. In addition, various data (e.g., initial values, lookup tables, mappings, etc.) used when executing the program are pre-stored in a storage unit such as the ROM or non-volatile RAM. In addition, a storage medium such as the ROM is a non-transitional physical storage medium.

[0077] Specifically, the control unit 100 is connected to the ultrasonic sensor 10. The control unit 100 controls the ultrasonic sensor 10 to transmit a detection wave from the ultrasonic sensor 10, and derives an obstacle distance L to the obstacle and an obstacle height h of the obstacle based on a reception wave received by the ultrasonic sensor 10 after transmitting the detection wave, and performs a predetermined process.

[0078] Below, refer to Figure 5 to Figure 12 The method for deriving the obstacle distance L and the obstacle height h executed by the control unit 100 of the present embodiment is described. In addition, the following description is made by taking the derivation method using the ultrasonic sensor 10 installed on the right side of the vehicle 1 as an example, and the derivation method using the ultrasonic sensor 10 installed on the left side, front, and rear of the vehicle 1 is the same. In addition, the following description is made of an example in which the obstacle 200 exists on the road surface 300 parallel to the horizontal plane. That is, in the present embodiment, if the distance along the horizontal direction between the ultrasonic sensor 10 (i.e., the vehicle 1) and the obstacle 200 is set to L, the obstacle distance L is equal to the distance L. In addition, the following description is made with the height from the road surface 300 to the ultrasonic sensor 10 (i.e., the installation height of the ultrasonic sensor 10) as the sensor installation height H. In addition, the sensor installation height H is a value adjusted when the ultrasonic sensor 10 is installed on the vehicle 1, and is a known value.

[0079] Moreover, hereinafter, among the reflected waves reflected by the obstacle 200 from the detection wave sent from the ultrasonic sensor 10, the reflected wave along the normal direction of the sensor substrate 24 of the ultrasonic sensor 10 is also referred to as a positive reflected wave, and the reflected wave in a direction inclined relative to the normal direction is also referred to as a multiple reflected wave. In addition, in the present embodiment, the ultrasonic sensor 10 is controlled so that the pointing axis is in the direction along the normal direction of the sensor substrate 24, and therefore, the positive reflected wave may also be referred to as a reflected wave along the pointing axis.

[0080] First, the control unit 100 causes the ultrasonic sensor 10 to transmit a detection wave. Figure 5 As shown, the detection wave is transmitted in such a manner that the directional axis D is parallel to the horizontal direction, and the directional angle is adjusted to, for example, approximately ±50°.

[0081] Furthermore, if the detection wave is reflected by the obstacle 200, the ultrasonic sensor 10 receives the reflected wave in the order of the propagation distances of the detection wave and the reflected wave from short to long. Figure 6 As shown, the propagation distance of the normal reflection wave to the ultrasonic sensor 10 is L. As a multi-reflection wave, for example, the propagation distance of the multi-reflection wave reflected by the boundary between the obstacle 200 and the road surface 300 to the ultrasonic sensor 10 is (H 2 +L 2 ) 1 / 2 .

[0082] Therefore, when the obstacle 200 is a high obstacle, L<(H 2 +L 2 ) 1 / 2 , so, if Figure 7 As shown in FIG. 1 , the ultrasonic sensor 10 receives the multiple reflected waves after receiving the regular reflected waves. Furthermore, when the received waves are regular reflected waves, as shown in FIG. Figure 8 As shown, the received waves received by each ultrasonic element 25 do not have a phase difference. Therefore, when the ultrasonic sensor 10 receives a received wave having an intensity greater than a predetermined threshold, the control unit 100 determines whether the received waves received by each ultrasonic element 25 have a phase difference. If there is no phase difference, it is determined that the obstacle 200 is a high obstacle. In other words, it is determined that the obstacle height h is greater than the sensor installation height H. In addition, if the obstacle 200 is a high obstacle, the obstacle distance L to the obstacle is derived based on the time from the transmission of the detection wave to the reception of the received wave.

[0083] also, Figure 7 The threshold in is set to a value to remove noise, etc., as described later Fig.11 The threshold of is the same. In addition, Figure 8As shown, when the ultrasonic sensor 10 receives multiple reflected waves, phase differences occur in the received waves received by the ultrasonic elements 25. This is the same as the multiple reflected waves at a low obstacle described later, so it will be described together later.

[0084] In the case where the obstacle 200 is a low obstacle, such as Fig. 9 As shown, the ultrasonic sensor 10 receives multiple reflected waves instead of regular reflected waves. In this case, the ultrasonic sensor 10 receives reflected waves in the multiple reflected waves in the order of the propagation paths of the detection waves and the reflected waves from short to long.

[0085] Here, if Fig.10 As shown, the propagation path in which the ultrasonic sensor 10 receives the reflected wave reflected by the boundary portion (hereinafter also referred to as the boundary portion) 201 between the obstacle 200 and the road surface 300 is set to the first propagation path R1. In addition, the angle between the first propagation path R1 and the road surface 300 is set to θ1. Similarly, the propagation path in which the ultrasonic sensor 10 receives the reflected wave reflected by the road surface 300 and then reflected by the upper end 202 of the obstacle 200 is set to the second propagation path R2. In addition, the angle between the propagation path to the point reflected by the road surface 300 in the second propagation path R2 and the road surface 300 is set to θ2. Moreover, the propagation path in which the ultrasonic sensor 10 receives the reflected wave reflected by the upper end 202 of the obstacle 200 and then reflected by the road surface 300 is set to the third propagation path R3. In addition, the distances of the second propagation path R2 and the third propagation path R3 are the same.

[0086] Furthermore, a virtual line whose angle between the point reflected by the road surface 300 in the second propagation path R2 and the second propagation path R2 is 90° is set as a reference line K. In addition, the reference line K can also be called a virtual line that divides the first propagation path R1, the second propagation path R2, and the third propagation path R3 into portions with equal distances and portions with different distances. Furthermore, the distance between the reference line K on the third propagation path R3 and the upper end 202 of the obstacle 200 is set as distance a. The distance between the reference line K on the second propagation path R2 and the upper end 202 of the obstacle 200 is set as distance b. The distance between the reference line K on the first propagation path R1 and the boundary portion 201 is set as distance c. Furthermore, a horizontal plane passing through the upper end 202 is set as a virtual horizontal plane 400.

[0087] In this case, the second propagation path R2 is the same distance as when total reflection occurs at the virtual point V1, and the third propagation path R3 is the same distance as when total reflection occurs at the virtual point V2. Moreover, the propagation distance of the reflected wave in the first propagation path R1 is expressed by the following formula 1, and the propagation distance of the reflected wave in the second propagation path R2 is expressed by the following formula 2. In addition, as described above, the propagation distance of the reflected wave in the third propagation path R3 is the same as the propagation distance of the reflected wave in the second propagation path R2.

[0088] [Formula 1]

[0089] The reflected wave of the first propagation path = (H 2 +L 2 ) 1 / 2

[0090] [Formula 2]

[0091] The reflected wave of the second propagation path = (H 2 +L 2 ) 1 / 2 -c+(a+b) / 2

[0092] In this case, the term {-c+(a+b) / 2} in the second propagation path R2 is a negative value. Therefore, the second propagation path R2 and the third propagation path R3 are shorter than the first propagation path R1. In addition, the distance of the propagation path of the reflected wave reflected between the upper end 202 of the obstacle 200 and the boundary 201 is the distance between the first propagation path R1 and the second and third propagation paths R2 and R3.

[0093] Therefore, if Fig.11 As shown in FIG. 1 , the ultrasonic sensor 10 first receives the reflected waves of the second propagation path R2 and the third propagation path R3, and finally receives the reflected wave of the first propagation path R1. Fig.12 As shown, when multiple reflected waves are received, since the multiple reflected waves are reflected waves from a direction tilted with respect to the normal direction of the sensor substrate 24 of the ultrasonic sensor 10 , phase differences occur in the received waves received by the respective ultrasonic elements 25 .

[0094] In this case, if the phase difference when the reflected wave in the first propagation path R1 is received is φ1, and the wavelength of the detection wave is λ, the phase difference φ1 is expressed by the following equation 3. Similarly, if the phase difference when the reflected wave in the second propagation path R2 or the third propagation path R3 is received is φ2, the phase difference φ2 is expressed by the following equation 4. In addition, in the present embodiment, the phase difference φ1 is equivalent to the first phase difference, and the phase difference φ2 is equivalent to the second phase difference. In addition, d in the following equations 3 and 4 is the interval between the centers of the adjacent ultrasonic elements 25.

[0095] [Formula 3]

[0096] φ1=2πd sinθ1 / λ

[0097] [Formula 4]

[0098] φ2=2πd sinθ2 / λ

[0099] Moreover, the angle between the reflected wave at the boundary portion 201 and the road surface 300 is θ1, so if the obstacle height h and the obstacle distance L are used, the angle θ1 is expressed by the following equation 5. In addition, the angle between the virtual horizontal plane 400 passing through the upper end 202 and the reflected wave at the upper end 202 in the second propagation path R2 is expressed by θ2, so the angle θ2 is expressed by the following equation 6.

[0100] [Formula 5]

[0101] θ1=tan -1 (H / L)

[0102] [Formula 6]

[0103] θ2=tan -1 {(Hh) / L}

[0104] Therefore, when the control unit 100 receives multiple reflected waves instead of regular reflected waves, the control unit 100 derives the obstacle height h and the obstacle distance L in the following manner. That is, the control unit 100 derives the obstacle height h and the obstacle distance L using the phase difference φ2, the phase difference φ1, and the above-mentioned equations 3 to 6, the phase difference φ2 being the phase difference at which the intensity of the received wave reaches a peak value after the multiple reflected waves reach or exceed a threshold value, and the phase difference φ1 being the phase difference at which the intensity of the received wave reaches a peak value again after the intensity of the received wave temporarily decreases.

[0105] Specifically, the control unit 100 uses the phase difference φ1 of the received wave to derive the angle θ1 based on the above formula 3. Then, the control unit 100 uses the derived angle θ1 and the known sensor installation height H to derive the obstacle distance L based on the above formula 5. Next, the control unit 100 uses the phase difference φ2 of the received wave to derive the angle θ2 based on the above formula 4. Then, the control unit 100 uses the derived angle θ2 and the obstacle distance L and the known sensor installation height H to derive the obstacle height h based on formula 6. Thus, the obstacle distance L and the obstacle height h are derived.

[0106] Then, the control unit 100 performs a predetermined process based on the derived obstacle distance L and obstacle height h.

[0107] The above is the structure of the obstacle detection device of this embodiment. Fig.13The processing performed by the control unit 100 in the obstacle detection device is described. In addition, an example of performing parking assist control using the obstacle detection device is described below. In addition, although not particularly shown in the figure, the control unit 100 is appropriately connected to each unit for performing parking assist control such as a brake unit, a powertrain unit, and a steering unit mounted on the vehicle 1.

[0108] Furthermore, when, for example, an automatic parking switch mounted on the vehicle 1 is operated by a passenger, the control unit 100 detects an obstacle and controls the brake unit, etc. to perform a predetermined parking assist control. The predetermined parking assist control refers to, for example, a process of detecting a parking space, a process of adjusting the angle of the vehicle direction to park the vehicle in the detected parking space, a process of parking the vehicle in the detected parking space, and the like.

[0109] First, the control unit 100 controls the ultrasonic sensor 10 to transmit a pulsed detection wave in step S101. Next, the control unit 100 determines in step S102 whether the reverberation period caused by the transmission of the detection wave has passed. Moreover, when the control unit 100 determines that the reverberation period has not passed (that is, step S102: No), the control unit 100 performs the processing of step S102 again. That is, the control unit 100 waits until the reverberation period has passed. In addition, the so-called reverberation period refers to the period during which the vibration of the ultrasonic element 25 remains due to the transmission of the detection wave.

[0110] When the control unit 100 determines that the reverberation period has passed (i.e., step S102: Yes), it determines in step S103 whether a reception wave exceeding the threshold value has been received. Furthermore, when the control unit 100 determines that a reception wave exceeding the threshold value has not been received (i.e., step S103: No), it determines in step S104 whether a predetermined period has passed. In addition, the predetermined period is set according to the desired detection range of the obstacle 200, etc. For example, when the detection range is 5m, the control unit 100 sets it to 30msec based on (5×2) / speed of sound.

[0111] When the control unit 100 determines that the predetermined period has not passed (i.e., step S104: No), the processing from step S103 is performed again. That is, when the control unit 100 has not received a reception wave exceeding the threshold, the processing from step S103 is repeated until a period in which a reception wave is likely to be received. On the other hand, when the control unit 100 determines that the predetermined period has passed (i.e., step S104: Yes), the processing ends.

[0112] When the control unit 100 determines that a received wave greater than the threshold value has been received (i.e., step S103: Yes), it determines in step S105 whether there is a phase difference between the received waves received by each ultrasonic element 25. That is, the control unit 100 determines whether the received received wave is a regular reflection wave or a multi-reflection wave. When the control unit 100 determines that there is no phase difference between the received received waves (i.e., step S105: No), the received wave is a regular reflection wave, so it is determined in step S106 that there is a high obstacle.

[0113] Then, in step S107, the control unit 100 derives the obstacle distance L. In this case, the control unit 100 derives the obstacle distance L based on the time from the transmission of the detection wave to the reception of the reception wave and the speed of sound. Then, in step S108, the control unit 100 determines that there is a high obstacle at the obstacle distance L and continues the vehicle control.

[0114] On the other hand, when the control unit 100 determines in step S105 that the received waves have a phase difference (ie, step S105 : Yes), since the received waves are multiply reflected waves, it determines in step S109 that a low obstacle exists.

[0115] In addition, if Figure 7 and Figure 8 As shown, the ultrasonic sensor 10 may also receive multiple reflected waves when the obstacle 200 is a high obstacle. However, in the case of a high obstacle, the ultrasonic sensor 10 receives the regular reflected wave before the multiple reflected waves. In addition, in the case of a high obstacle, if the control unit 100 determines in step S103 that a signal above the threshold of the received wave is received, it determines in step S105 that there is no phase difference, performs the processing from step S106, and ends the present processing. Therefore, only in the case of a low obstacle, it is determined in step S105 that there is a phase difference.

[0116] Then, the control unit 100 derives the obstacle distance L and the obstacle height h in step S110. In the present embodiment, as described above, the obstacle distance L and the obstacle height h are derived using the phase difference φ1 and the phase difference φ2 of the received waves and the above-mentioned equations 3 to 6.

[0117] Next, the control unit 100 determines in step S111 whether the obstacle height h is lower than the passable height of the vehicle 1. Then, if the control unit 100 determines that it is lower than the passable height (i.e., step S111: Yes), in step S112, it determines that there is a low obstacle at the obstacle distance L and continues to control the vehicle. The passable height is appropriately set according to the vehicle type, for example, 5 cm. In addition, as for the 5 cm obstacle, for example, a bump can be cited.

[0118] When the control unit 100 determines that the obstacle height is not passable (i.e., step S111: No), in step S113, the control unit 100 determines whether the obstacle height h is the height that the bottom surface of the vehicle body contacts. For example, in order to determine whether the obstacle height h is the height that the bottom surface of the vehicle body contacts, the control unit 100 determines whether the obstacle height h is the height that the bumper of the vehicle body contacts. In this case, the control unit 100 determines, for example, whether the obstacle height h is less than 20 cm.

[0119] When the control unit 100 determines that the height is such that the bottom surface of the vehicle body does not touch the height (i.e., step S113: Yes), the control unit 100 performs parking according to the parking method. For example, the control unit 100 determines whether to perform tandem parking in step S114. Then, when the control unit 100 determines that tandem parking is performed (i.e., step S114: Yes), in step S115, the control unit 100 performs a process for parking the vehicle 1 by making the vehicle 1 approach the obstacle 200 along the obstacle 200 and ends the process. In this case, the obstacle 200 is, for example, a curb.

[0120] On the other hand, when the control unit 100 determines that the tandem parking is not to be performed (i.e., step S114: No), that is, when it is determined that the parallel parking is to be performed, in step S116, the control unit 100 performs a process for parking the vehicle 1 by bringing the tires into contact with the obstacle 200 and ends the process. In this case, the obstacle 200 is, for example, a roadblock.

[0121] In addition, parallel parking refers to a parking method in which the vehicle is parked so that the parking vehicle and the vehicle are aligned in the vehicle width direction of the vehicle, and tandem parking refers to a parking method in which the parking vehicle and the vehicle are parked so that the vehicle is aligned in the front-rear direction of the vehicle.

[0122] When the control unit 100 determines that the obstacle height h is the height at which the bottom surface of the vehicle body contacts (ie, step S113 : No), the control unit 100 performs the same processing as step S108 and ends the processing.

[0123] In the present embodiment described above, the control unit 100 uses the phase differences φ1 and φ2 of the received waves received by the plurality of ultrasonic elements 25 to derive the obstacle distance L and the obstacle height h. Furthermore, when the obstacle 200 is a high obstacle, the received waves received by the plurality of ultrasonic elements 25 do not have a phase difference. Therefore, even when a plurality of low obstacles at different distances from the ultrasonic sensor 10 are close to the obstacle 200, the control unit 100 can suppress the obstacle 200 from being erroneously detected as a high obstacle.

[0124] Furthermore, when the obstacle 200 is a low obstacle, the control unit 100 performs vehicle control according to the obstacle height h, and thus can appropriately perform vehicle control.

[0125] Furthermore, the ultrasonic sensor 10 is a MEMS type structured using the sensor substrate 24. Therefore, mass production can be facilitated.

[0126] Furthermore, in each ultrasonic element 25 of the ultrasonic sensor 10, the interval d between the centers of adjacent ultrasonic elements 25 is less than half the wavelength of the detection wave. Therefore, it is possible to suppress the azimuth from being binarized with respect to a certain phase difference, and to suppress a reduction in the detection range.

[0127] In addition, the number of ultrasonic elements 25 or the number of ultrasonic elements 25 to which a driving voltage is applied is adjusted so as to achieve a predetermined directional angle in the ultrasonic sensor 10. Therefore, the ultrasonic sensor 10 that realizes a desired directional angle can be manufactured.

[0128] Furthermore, when a piezoelectric ceramic containing no lead, such as scandium aluminum nitride or aluminum nitride, is used as the piezoelectric film 28 b of the ultrasonic sensor 10 , it is possible to realize the ultrasonic sensor 10 with reduced influence on the environment.

[0129] (Second Embodiment)

[0130] The second embodiment is described. Compared with the first embodiment, the obstacle distance L and the obstacle height h from the low obstacle are derived by another method in this embodiment. As the rest is the same as the first embodiment, the description is omitted here.

[0131] In this embodiment, when the obstacle 200 is a low obstacle, the relationship between the obstacle distance L, the phase difference φ1, the phase difference φ2, and the obstacle height h is measured in advance to understand the relationship between them. Fig.14 As shown in FIG. 1 , the storage unit stores information related to the relationship between the obstacle distance L, the phase difference, and the obstacle height h. Fig.14 Only the reflected wave from the boundary 201, the reflected wave from the upper end 202 when the obstacle height h is 0.1m, and the reflected wave from the upper end 202 when the obstacle height h is 0.2m are shown. However, in fact, in more detail, information on the sensor installation height H is stored. In addition, Fig.14 These are the results when the sensor installation height H is 0.5m.

[0132] When deriving the obstacle distance L and the obstacle height h in step S110, the control unit 100 refers to the phase differences φ1 and φ2 of the received waves received by each ultrasonic element 25 and Fig.14 The obstacle distance L and obstacle height h are derived from the mapping.

[0133] Specifically, the phase difference φ1 is the phase difference when the reflected wave from the boundary 201 is received. Therefore, the control unit 100 uses the phase difference φ1 and the map to derive the obstacle distance L. In addition, the phase difference φ2 is the phase difference when the reflected wave reflected by the upper end 202 of the obstacle 200 is received. Therefore, the control unit 100 uses the phase difference φ2, the map, and the derived obstacle distance L to derive the obstacle height h.

[0134] As described above, even if the phase difference φ1, the phase difference φ2, and the mapping are used to derive the obstacle distance L and the obstacle height h, the same effect as the first embodiment can be obtained. In addition, the example of deriving the obstacle distance L using the phase difference φ1 and the mapping is described above. However, the control unit 100 can also derive the obstacle distance L using the above-mentioned formula 3 and formula 5 according to the phase difference φ1, and derive the obstacle height h using the obstacle distance L, the phase difference φ2, and the mapping. That is, the first embodiment and the second embodiment can also be appropriately combined to derive the obstacle distance L and the obstacle height h.

[0135] (Third Embodiment)

[0136] The third embodiment will be described. In this embodiment, the obstacle distance L to the low obstacle is derived by another method compared to the first embodiment. The rest is the same as the first embodiment, so the description is omitted here.

[0137] First, in the first embodiment described above, Fig.10 In the equations 7 to 9, the distance a, the distance b, and the distance c are expressed as follows.

[0138] [Formula 7]

[0139] a=b×cos2θ2

[0140] =h×cos2θ2 / sinθ2

[0141] [Formula 8]

[0142] b=h / sinθ2

[0143] [Formula 9]

[0144] c=b×cosθ2×cosθ1

[0145] =h×cosθ2×cosθ1 / sinθ2

[0146] =h×cosθ1 / tanθ2

[0147] Furthermore, the obstacle distance L is also expressed by the following formula 10.

[0148] [Formula 10]

[0149] L={(H 2 +L 2 ) 1 / 2 -c+a}×cosθ2

[0150] Therefore, in the processing of step S110, the control unit 100 of this embodiment uses the above equations 3 to 5 to derive angle θ1, angle θ2, and obstacle height h, then uses the above equations 7 to 9 to derive distance a, distance b, and distance c, and uses the above equation 10 to derive obstacle distance L.

[0151] As described above, even if the obstacle distance L is derived using the phase difference φ1, the phase difference φ2, the obstacle height h, the distance a, the distance b, and the distance c, the same effects as those of the first embodiment can be obtained.

[0152] (Fourth Embodiment)

[0153] The fourth embodiment is described below. Compared to the first embodiment, this embodiment derives the obstacle distance L by multiple methods, and performs a predetermined process based on the assumption that the obstacle 200 exists between the derived obstacle distances L. The rest is the same as the first embodiment, so the description is omitted here.

[0154] Reference Fig.15 The processing performed by the control unit 100 of this embodiment is described. Fig.15 As shown, when the control unit 100 determines in step S105 that there is a phase difference in the received wave (i.e., step S105: Yes), the obstacle distance L and the obstacle height h are derived in step S110. In this case, in this embodiment, the control unit 100 derives the obstacle distance L using equations 7 to 10 described in the third embodiment.

[0155] Next, in step S117, the control unit 100 uses the ToF (Time of flight) method of the propagation time from the transmission of the detection wave to the reception of the received wave with the phase difference φ1 and the speed of sound to derive the obstacle distance L. Specifically, the control unit 100 derives the obstacle distance L by (propagation time / 2)×speed of sound×cosθ1.

[0156] Then, in step S118 , the control unit 100 determines that the obstacle 200 exists between the obstacle distances L derived in steps S110 and S117 , and executes the processing from the subsequent step S111 .

[0157] As described above, in the present embodiment, when the obstacle 200 is a low obstacle, the control unit 100 uses the phase difference to derive the obstacle distance L in step S110, and derives the obstacle distance L by the ToF method in step S117. Then, the control unit 100 determines that the obstacle 200 exists between the two derived obstacle distances L, and performs control of the vehicle 1. Therefore, it is possible to further improve safety.

[0158] (Variation of the Fourth Embodiment)

[0159] A modification of the fourth embodiment is described. In the fourth embodiment, a method for deriving the obstacle distance L by the method described in the third embodiment in step S110 is described. However, step S110 may be a step of deriving the obstacle distance L using the phase difference, and the obstacle distance L may be derived by other methods. For example, the control unit 100 may derive the obstacle distance L by the method of the first embodiment, or may derive the obstacle distance L by the method of the second embodiment.

[0160] (Fifth Embodiment)

[0161] The fifth embodiment will be described. Compared with the first embodiment, the present embodiment takes into account the inclination of the road surface 300. The rest is the same as the first embodiment, so the description thereof will be omitted here.

[0162] First, if Fig.16 As shown, the road surface 300 may be inclined relative to the horizontal direction. In this case, the distance that the vehicle 1 actually travels to the obstacle 200 is the distance La along the inclined road surface 300. Therefore, in this embodiment, a corrected obstacle distance La is derived that also takes the inclination of the road surface 300 into consideration.

[0163] In addition, in this embodiment, if Fig.16 As shown, the distance between the virtual horizontal plane 401 passing through the ultrasonic sensor 10 and the portion of the road surface 300 where the obstacle 200 is arranged is set as the distance Ha. In addition, the distance from the ultrasonic sensor 10 to the obstacle 200 along the virtual horizontal plane 401 is set as the horizontal distance L. Moreover, the angle between the virtual horizontal plane 401 and the propagation path of the detection wave and the reflected wave reflected by the boundary portion 201 is set as the angle θ1. Moreover, the angle between the virtual road surface 402 assuming that the road surface 300 is a horizontal plane and the road surface 300 is set as the angle θ3.

[0164] In this case, the control unit 100 calculates the corrected obstacle distance La as follows. That is, the control unit 100 first uses the above-mentioned formula 3 to derive the angle θ1 from the phase difference φ1. In addition, the control unit 100 derives the distance (L) between the ultrasonic sensor 10 and the boundary portion 201 based on the propagation time and sound speed from the transmission of the detection wave to the reception of the received wave with the phase difference φ1. 2 +Ha 2 ) 1 / 2 .

[0165] Then, since Ha=L×tan θ1 is expressed, the control unit 100 derives the horizontal distance L from the obstacle 200 based on the derived angle θ1 and the distance from the boundary 201 .

[0166] The distance between the portion of the road surface 300 where the obstacle 200 is arranged and the virtual road surface 402 is expressed as H-Ha. Therefore, the angle θ3 is expressed by the following equation 11.

[0167] [Formula 11]

[0168] θ3=tan -1 {(H-Ha) / L}

[0169] The corrected obstacle distance La is also expressed as La=L / cosθ3. Therefore, the control unit 100 can derive the corrected obstacle distance La taking the inclination of the road surface 300 into consideration by deriving La=L / cosθ3.

[0170] Next, refer to Fig.17 The processing executed by the control unit 100 according to the present embodiment will be described.

[0171] When the control unit 100 determines in step S105 that there is a phase difference in the received waves (i.e., step S105: Yes), in step S119, the control unit 100 takes into account the inclination of the road surface 300 as described above and derives the corrected obstacle distance La. Then, the control unit 100 uses the derived corrected obstacle distance La and the above equation 7 to derive the obstacle height h.

[0172] As described above, in this embodiment, the inclination of the road surface 300 is also taken into account to derive the corrected obstacle distance La and the obstacle height h, so that the detection accuracy can be further improved. In addition, in this embodiment, since the inclination of the road surface 300 (i.e., the angle θ3) is derived, the inclination can also be applied to other devices in vehicle control (e.g., image detection), etc., thereby further achieving efficient vehicle control.

[0173] Here, when the road surface 300 is made of asphalt or the like and the reflected wave from the road surface 300 is random and strong, if the ultrasonic sensor 10 receives the reflected wave, Fig.18 As shown in FIG. 1 , the intensity of the received wave has a distribution with a random peak value. Therefore, for example, when the obstacle distance L is derived only from the time until the reflected wave is received, the possibility of false detection becomes high.

[0174] In contrast, in this embodiment, the inclination of the road surface 300 is derived together with the phase difference of the received wave. Therefore, by taking the inclination of the road surface 300 into consideration (i.e., differentiating the inclination of the road surface 300), as shown in FIG. Fig.19 As shown in FIG. 1 , the height (phase difference) of the road surface 300 has a peak at a low obstacle. Therefore, according to the present embodiment, even when the reflected wave of the road surface 300 is strong, false detection can be suppressed.

[0175] (Sixth Embodiment)

[0176] The sixth embodiment will be described. Compared with the first embodiment, the present embodiment changes the driving voltage applied to the ultrasonic sensor 10. The rest is the same as the first embodiment, so the description thereof will be omitted.

[0177] First, refer to Figures 20A to 20F The relationship between the intensity of the received wave and the obstacle height h is explained. Figures 20A to 20F These are simulation results when the sensor installation height H is set to 45 cm, the obstacle distance L is set to 75 cm, a 10 kHz driving voltage is applied to the sound source, and the sound source is set to a bass source to eliminate directivity.

[0178] like Figures 20A to 20F As shown in FIG. 1 , it can be confirmed that the lower the obstacle height h, the lower the intensity of the reflected wave reflected by the upper end 202 of the obstacle 200. That is, the lower the obstacle height h, the smaller the signal-to-noise ratio, i.e., the SN ratio, is, and the sensitivity is more likely to decrease.

[0179] Therefore, in this embodiment, the control unit 100 changes the directional axis D of the detection wave transmitted from the ultrasonic sensor 10 by controlling the phase of the driving voltage (ie, the AC voltage) applied to each ultrasonic element 25. Specifically, Fig.21 As shown, the control unit 100 transmits the detection wave so that the directional axis D is inclined toward the road surface 300 side with respect to the horizontal direction.

[0180] According to this, even when the obstacle 200 is a low obstacle, the intensity of the received wave can be enhanced, and the sensitivity can be improved.

[0181] (Seventh Embodiment)

[0182] The seventh embodiment is described below. Compared with the first embodiment, the present embodiment specifies the sensor mounting height H of the ultrasonic sensor 10. The rest is the same as the first embodiment, and thus the description thereof is omitted here.

[0183] First, if Fig.22A and Fig. 22B As shown in FIG. 1 , the lower the sensor installation height H is, the easier it is for the phase difference to become larger, thereby achieving improved sensitivity. However, in the conventional obstacle detection device that detects the obstacle distance L only based on the time of the reflected wave, the ultrasonic sensor 10 is installed at a height of more than 45 cm in consideration of the reflected wave from the road surface 300, which sometimes cannot exert sufficient sensitivity. In addition, Fig.22A This is the simulation result when receiving the reflected wave from obstacle 200 at an obstacle distance L of 3m. Fig. 22B These are simulation results when a reflected wave is received from the road surface 300 at a position 5 m away from the ultrasonic sensor 10 .

[0184] In contrast, in this embodiment, as described in the first embodiment, the obstacle distance L is derived using the phase difference of the received wave. Fig.22A In the case where a reflected wave reflected by obstacle 200 is received as shown in FIG. Fig. 22B Compared with the case where the reflected wave reflected by the road surface 300 is received, the phase difference becomes extremely large.

[0185] Therefore, in the present embodiment, the sensor installation height H can be configured at a sufficiently low position. Specifically, the sensor installation height H can be set to a height when installed at a portion of 20 cm that may be the portion closest to the road surface 300 in a general vehicle body. In addition, in order to achieve a more sufficient sensitivity than the ultrasonic sensor 10 in the conventional obstacle detection device, the sensor installation height H can be set to a position below 40 cm. That is, in the present embodiment, the sensor installation height H is set to be greater than 20 cm and less than 40 cm.

[0186] When the ultrasonic sensor 10 is installed at such a position, the control unit 100 may determine that the obstacle is a low obstacle when the phase difference is compared with a predetermined threshold and the phase difference is determined to be greater than the threshold (that is, it is not a reflected wave from the road surface 300).

[0187] As described above, in the present embodiment, the sensor mounting height H of the ultrasonic sensor 10 is set to be greater than or equal to 20 cm and less than or equal to 40 cm. Therefore, it is possible to further improve the sensitivity.

[0188] (Eighth Embodiment)

[0189] The eighth embodiment will be described. Compared with the first embodiment, this embodiment adds a temperature-sensitive resistor to the ultrasonic sensor 10. The rest is the same as the first embodiment, so the description is omitted here.

[0190] like Fig.23 As shown in FIG. 1 , the ultrasonic sensor 10 of the present embodiment has a temperature-sensitive resistor 50 whose resistance value changes according to the ambient temperature formed on one surface 24a of the sensor substrate 24. Furthermore, the control unit 100 is connected to the temperature-sensitive resistor 50, and the obstacle distance L and the obstacle height h are derived by taking into account the resistance value change (i.e., the detection result) of the temperature-sensitive resistor 50. That is, the control unit 100 also takes into account the ambient temperature to derive the obstacle distance L and the obstacle height h.

[0191] Specifically, if the speed of sound is set to v, the frequency of the detection wave is set to f, and the wavelength of the detection wave is set to λ, then v=fλ. Furthermore, if the temperature is set to T, the speed of sound v is expressed as v=331.5+0.6T. Therefore, when the control unit 100 derives the obstacle distance L from the high obstacle as the obstacle 200 in step S107, the obstacle distance L is derived by taking the temperature into consideration. In addition, when the control unit 100 derives the obstacle distance L and the obstacle height h from the low obstacle as the obstacle 200 in step S110, the obstacle distance L and the obstacle height h are calculated by taking the temperature into consideration by using the above-mentioned equations 3 to 6, thereby deriving the obstacle distance L and the obstacle height h.

[0192] According to this, the obstacle distance L and the obstacle height h are derived taking the temperature into consideration, so that the detection accuracy of the obstacle 200 can be further improved.

[0193] (Ninth Embodiment)

[0194] A ninth embodiment will be described. Compared to the first embodiment, the present embodiment changes the structure of the ultrasonic sensor 10. The rest is the same as the first embodiment, so the description thereof will be omitted.

[0195] In this embodiment, if Fig.24 As shown in the figure, the ultrasonic element 25 is formed by two-dimensionally arranging a plurality of piezoelectric elements 28 on a concave portion 31 formed on a support member 30. Specifically, in this embodiment, the back electrode 28a is directly formed on the concave portion 31 of the support member 30, and the sensor substrate 24 is not provided. In addition, the piezoelectric element 28 is formed in a block shape with a piezoelectric film 28b that is sufficiently thick compared to the first embodiment described above. In this embodiment, the ultrasonic element 25 is formed by such a piezoelectric element 28, and the transducer unit 20 is formed by arranging a plurality of such ultrasonic elements 25.

[0196] In addition, each ultrasonic element 25 has a back surface electrode 28 a and a front surface electrode 28 c electrically connected to a pad portion 34 formed on the support member 30 via a bonding wire 35 .

[0197] In this ultrasonic sensor 10, when an AC voltage, i.e., a driving voltage, is applied to each piezoelectric element 28, the piezoelectric element 28 vibrates ultrasonically to transmit a detection wave. In addition, when the ultrasonic element 25 receives a reception wave, the piezoelectric element 28 vibrates to generate electric charge in the piezoelectric element 28. Therefore, when the ultrasonic element 25 receives a reception wave, it outputs a detection signal corresponding to the reception wave.

[0198] As described above, even if the ultrasonic element 25 is formed of the block-shaped piezoelectric element 28 , the same effects as those of the first embodiment can be obtained.

[0199] (Other embodiments)

[0200] The present disclosure is described based on the implementation mode, but it should be understood that the present disclosure is not limited to the implementation mode and configuration. The present disclosure also includes various modifications and modifications within the equivalent scope. Moreover, various combinations and methods and other combinations and methods that make them contain only one element, contain more elements, or contain fewer elements also belong to the scope and scope of thought of the present disclosure.

[0201] For example, in each of the above-described embodiments, the interval d between adjacent ultrasonic elements 25 may be set to be equal to or larger than a half of the wavelength of the detection wave.

[0202] Furthermore, in the first to sixth and eighth embodiments described above, the sensor mounting height H of the ultrasonic sensor 10 may be set to 40 cm or more.

[0203] Furthermore, the above-mentioned embodiments may be appropriately combined. For example, the above-mentioned second embodiment may be applied to the above-mentioned third to ninth embodiments, and the obstacle distance L and the obstacle height h may be derived using mapping. The above-mentioned third embodiment may be applied to the above-mentioned fourth to ninth embodiments, and the obstacle distance L may be derived using distance a, distance b, and distance c. The above-mentioned fourth embodiment may be applied to the above-mentioned fifth to ninth embodiments, and the obstacle distance L may be derived using the phase difference and propagation time of the received wave, respectively, and it is determined that there is an obstacle 200 between the two derived obstacle distances L. The above-mentioned fifth embodiment may be applied to the above-mentioned sixth to ninth embodiments, and the corrected obstacle distance La may be derived by taking into account the inclination of the road surface 300. The above-mentioned sixth embodiment may be applied to the above-mentioned seventh to ninth embodiments, and the directional axis D of the detection wave transmitted from the ultrasonic sensor 10 may be tilted toward the road surface 300 side. The above-mentioned seventh embodiment may be combined with the above-mentioned eighth and ninth embodiments, and the sensor installation height H may be set to be greater than 20 cm and less than 45 cm. The above-mentioned eighth embodiment may be combined with the above-mentioned ninth embodiment, and the ultrasonic sensor 10 may be provided with a temperature-sensitive resistor 50. Furthermore, embodiments obtained by combining the above-mentioned embodiments may be further combined with each other, and the combination method may be appropriately changed.

[0204] In addition, in the above-mentioned embodiments, the case where the obstacle 200 has a convex structure protruding from the road surface 300 has been described. However, the above-mentioned embodiments can also be applied to the case where the obstacle 200 has a concave structure such as a groove.

[0205] For example, Fig.25 As shown in FIG. 2 , a groove with a concave structure is formed on the road surface 300 as an obstacle 200. In addition, here, the case where the depth of the groove is smaller than the width is described as an example. Fig.25 The length in the vertical direction of the paper, the width of the groove is set to Fig.25 The length of the paper in the left-right direction.

[0206] Furthermore, the upper corner of the groove on the vehicle side is set as point P1, the virtual line connecting the ultrasonic sensor 10 and the point P1 is set as virtual line K1, and the intersection of the virtual line K1 and the groove is set as point P2. In addition, the upper corner of the groove on the side opposite to the vehicle 1 is set as point P3, and the lower corner of the groove on the side opposite to the vehicle 1 is set as point P4. Furthermore, it is assumed that when the ultrasonic sensor 10 transmits the detection wave, the reflected wave from the road surface 300 is also received.

[0207] In this case, the ultrasonic sensor 10 receives the reflected wave in the order of the propagation paths of the detection wave and the reflected wave from short to long. Fig.26 and Fig. 27 As shown in FIG. 1 , the portion where the groove is formed receives the reflected waves reflected at points P1, P2, P3, and P4 in sequence. Fig. 27 In FIG. 1 , the solid line indicates the relationship between the propagation distance and the intensity of the received wave when the groove portion as the obstacle 200 is formed, and the dotted line indicates the relationship between the propagation distance and the intensity of the received wave when the obstacle 200 is not formed. The relationship between the propagation distance and the intensity of the received wave when the obstacle 200 is not formed here refers to the relationship when it is assumed that the reflected wave reflected at the virtual horizontal plane passing through the point P1 and the point P3 is received.

[0208] In the absence of the obstacle 200, the intensity of the received wave decreases as the distance increases. In this case, in the portion where the groove is formed, the reflected wave is blocked by the side wall of the groove, so the intensity of the received wave temporarily decreases sharply at the point P1. Fig.26 As shown in FIG. 1 , the ultrasonic sensor 10 also receives reflected waves from a portion at an equal distance where no groove is formed. Therefore, the intensity of the received wave does not become zero.

[0209] Thereafter, the intensity of the received wave becomes the same value as when there is no obstacle 200 at point P2, increases at the upper corner of point P3, and further increases at the lower corner of point P4 due to the influence of multiple reflected waves.

[0210] In addition, if Fig.28 As shown in FIG. 1 , when there is no obstacle 200, the phase difference of the received wave becomes smaller as the distance becomes longer. Fig.28 In FIG. 1 , the solid line indicates the relationship between the propagation distance and the phase difference of the received wave when a groove is formed as the obstacle 200. The dotted line indicates the relationship between the propagation distance and the phase difference of the received wave when a reflected wave reflected at a virtual horizontal plane passing through the points P1 and P3 is assumed to be received. The single-point chain line indicates the relationship between the propagation distance and the phase difference of the received wave when a reflected wave reflected at a virtual horizontal plane passing through the points P2 and P4 is assumed to be received.

[0211] In this case, at the portion where the groove is formed, the phase difference when the reflected waves from the points P1 and P2 are received is the same because the points P1 and P2 are located on the common virtual line K1. In addition, the phase difference when the reflected waves from the points P1 and P3 are received is consistent with the phase difference when the reflected waves reflected on the virtual horizontal plane passing through the points P1 and P3 are received (that is, the same as Fig.28Similarly, the phase difference when the reflected waves from the points P2 and P4 are received is consistent with the phase difference when the reflected waves reflected at the virtual horizontal plane passing through the points P2 and P4 are received (i.e., consistent with Fig.28 That is, when the groove is formed, the phase difference of the received wave is a waveform that increases sharply at the point P2 and the point P4.

[0212] In addition, for example, Fig.29 As shown in FIG. 1 , a groove portion whose depth is greater than its width is sometimes formed on the road surface 300 as an obstacle 200. In this case, Fig.25 Similarly, the upper corner of the groove on the vehicle side is set as point P1, the virtual line connecting the ultrasonic sensor 10 and the point P1 is set as virtual line K1, and the intersection of the virtual line K1 and the groove is set as point P2. In addition, the upper corner of the groove on the side opposite to the vehicle 1 is set as point P3, and the lower corner of the groove on the side opposite to the vehicle 1 is set as point P4. Fig.29 In the example of , since the depth is greater than the width, the point P2 is a point between the points P3 and P4. Furthermore, it is assumed that when the ultrasonic sensor 10 transmits the detection wave, the reflected wave from the road surface 300 is also received.

[0213] In this case, the ultrasonic sensor 10 receives the reflected wave in the order of the propagation paths of the detection wave and the reflected wave from short to long. Fig.30 and Fig.31 As shown in FIG. 1 , the portion where the groove is formed receives the reflected waves reflected at the points P1, P3, P2, and P4 in sequence. Fig.31 In FIG. 1 , the solid line indicates the relationship between the propagation distance and the intensity of the received wave when the groove portion as the obstacle 200 is formed, and the dotted line indicates the relationship between the propagation distance and the intensity of the received wave when the obstacle 200 is not formed. The relationship between the propagation distance and the intensity of the received wave when the obstacle 200 is not formed here refers to the relationship when it is assumed that the reflected wave reflected at the virtual horizontal plane passing through the point P1 and the point P3 is received.

[0214] In the absence of the obstacle 200, the intensity of the received wave decreases as the distance increases. In this case, in the portion where the groove is formed, the reflected wave is blocked by the side wall of the groove, so the intensity of the received wave temporarily decreases sharply at the point P1. Fig.30 As shown in FIG. 1 , the ultrasonic sensor 10 also receives reflected waves from a portion at an equal distance where no groove is formed. Therefore, the intensity of the received wave does not become zero.

[0215] After that, the intensity of the received wave increases at the upper corner of point T3, reaches the same value as when there is no obstacle 200 at point P2, and then further increases at the lower corner of point P4 due to the influence of multiple reflected waves.

[0216] In addition, if Fig.32 As shown in FIG. 1 , when there is no obstacle 200, the phase difference of the received wave becomes smaller as the distance becomes longer. Fig.32 In FIG. 1 , the solid line indicates the relationship between the propagation distance and the phase difference of the received wave when a groove is formed as the obstacle 200. The dotted line indicates the relationship between the propagation distance and the phase difference of the received wave when a reflected wave reflected at a virtual horizontal plane passing through the points P1 and P3 is assumed to be received. The single-point chain line indicates the relationship between the propagation distance and the phase difference of the received wave when a reflected wave reflected at a virtual horizontal plane passing through the point P4 and parallel to the virtual horizontal plane passing through the points P1 and P3 is assumed to be received.

[0217] In this case, at the portion where the groove is formed, the phase difference when the reflected waves from the points P1 and P2 are received is the same because the points P1 and P2 are located on the common virtual line K1. In addition, the phase difference when the reflected waves from the points P1 and P3 are received is consistent with the phase difference when the reflected waves reflected on the virtual horizontal plane passing through the points P1 and P3 are received (that is, the same as Fig.32 Likewise, the phase difference in the case of receiving the reflected wave from the point P4 is consistent with the phase difference in the case of assuming that the reflected wave is received at the virtual horizontal plane passing through the point P4 (i.e., consistent with Fig.32 That is, when the groove is formed, the phase difference of the received wave is a waveform that increases sharply at the point P2 and the point P4.

[0218] In this way, when the obstacle 200 is a concave structure, the phase difference also changes sharply. Moreover, the change mode of the phase difference changes sharply at the position P2 and the position P4 regardless of the relationship between the depth and width of the concave structure. Therefore, in this way, even if the obstacle 200 is a concave structure such as a groove, the above-mentioned embodiments can be applied.

[0219] In addition, when the obstacle 200 is a concave structure, as shown in FIG. Fig.28 and Fig.32 As shown, the phase difference of the received wave received by the ultrasonic sensor 10 becomes a waveform having a portion with a sharp increase due to the reflected wave received at the concave structure. On the other hand, when the obstacle 200 is a convex structure protruding from the road surface 300, the phase difference of the received wave received by the ultrasonic sensor 10 becomes a waveform having a portion with a sharp decrease due to the reflected wave received at the convex structure.

[0220] That is, the phase difference changes in opposite ways when the obstacle 200 is a convex structure and a concave structure. Therefore, the control unit 100 can easily determine whether the obstacle 200 is a convex structure or a concave structure by taking the phase difference change into consideration.

[0221] The control unit and method described in the present disclosure may also be implemented by a dedicated computer that is provided by a processor and a memory programmed in a manner to execute one or more functions embodied by a computer program. Alternatively, the control unit and method described in the present disclosure may also be implemented by a dedicated computer that is provided by a processor configured by utilizing one or more dedicated hardware logic circuits. Alternatively, the control unit and method described in the present disclosure may also be implemented by one or more dedicated computers that are configured by a combination of a processor and a memory programmed in a manner to execute one or more functions and a processor comprising one or more hardware logic circuits. In addition, the computer program may also be stored in a computer-readable non-transient tangible recording medium as instructions executed by a computer.

Claims

1. An obstacle detection device for detecting obstacles existing around a vehicle, characterized in that: have: an ultrasonic sensor disposed at a portion of the vehicle at a predetermined height from a road surface, the ultrasonic sensor having a plurality of ultrasonic elements, the plurality of ultrasonic elements transmitting detection waves toward an outer side of the vehicle and receiving reflected waves of the detection waves reflected by the obstacle as received waves; and a control unit configured to perform a predetermined process by deriving a distance to the obstacle, i.e., an obstacle distance, and a height of the obstacle, i.e., an obstacle height, based on the received waves, and in deriving the obstacle distance and the obstacle height, deriving the obstacle distance and the obstacle height based on the intensities of the received waves received by the plurality of ultrasonic elements and the phase differences of the received waves received by the plurality of ultrasonic elements; When the control unit derives the obstacle height, If it is determined that the received waves received by the plurality of ultrasonic elements have no phase difference, it is determined that the height of the obstacle is above the predetermined position, If it is determined that the received waves received by the plurality of ultrasonic elements have a phase difference, it is determined that the height of the obstacle is lower than the height of the predetermined position, When the control unit determines that the height of the obstacle is lower than the height of the specified position, the control unit sets the phase difference when receiving the reflected wave reflected from the boundary between the obstacle and the road surface as the received wave to be the first phase difference, sets the phase difference when receiving the reflected wave reflected from the upper end of the obstacle as the received wave to be the second phase difference, and uses the first phase difference and the second phase difference to derive the obstacle distance and the obstacle height.

2. The obstacle detection device according to claim 1, characterized in that: When deriving the obstacle distance, the control unit derives the obstacle distance based on the first phase difference and the second phase difference, and derives the obstacle distance based on the time from when the ultrasonic sensor sends the detection wave to when the receiving wave is received, and determines that the obstacle exists between the two derived obstacle distances, and performs the prescribed processing.

3. The obstacle detection device according to claim 1, characterized in that: The control unit derives the inclination of the road surface, and derives a corrected obstacle distance along the road surface as the obstacle distance taking the derived inclination of the road surface into consideration.

4. The obstacle detection device according to any one of claims 1 to 3, characterized in that: The control unit performs a predetermined process according to the height of the obstacle when the height of the obstacle is lower than the height of the predetermined position.

5. The obstacle detection device according to any one of claims 1 to 3, characterized in that: The ultrasonic sensor is provided at a position, which is the predetermined position, at a height of 20 cm to 40 cm from the road surface.

6. The obstacle detection device according to any one of claims 1 to 3, characterized in that: The ultrasonic sensor is formed by arranging a plurality of piezoelectric elements having a piezoelectric film to form the plurality of ultrasonic elements. The ultrasonic sensor transmits the detection wave by controlling a driving voltage applied to the piezoelectric element of the plurality of ultrasonic elements.

7. The obstacle detection device according to claim 6, characterized in that: Among the plurality of ultrasonic elements, a distance between centers of adjacent ultrasonic elements is less than half a wavelength of the detection wave.

8. The obstacle detection device according to claim 6, characterized in that: In the ultrasonic sensor, the number of the plurality of ultrasonic elements or the number of the ultrasonic elements to which the driving voltage is applied is adjusted so as to have a predetermined directivity angle.

9. The obstacle detection device according to claim 6, characterized in that: The ultrasonic sensor adjusts the phase of the driving voltage applied to the plurality of ultrasonic elements so as to have a directional axis along a predetermined direction.

10. The obstacle detection device according to claim 6, characterized in that: The ultrasonic sensor has a temperature-sensitive resistor whose resistance value changes according to temperature. The control unit derives the obstacle distance and the obstacle height by taking into account the detection result of the temperature sensitive resistor.

11. The obstacle detection device according to claim 6, characterized in that: The piezoelectric film is made of scandium aluminum nitride or aluminum nitride.

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