ULTRASOUND OBJECT DETECTION DEVICE

Abstract

Object detector that features: a receiving unit (220) designed to receive an oscillation signal corresponding to an oscillation of a microphone (11), wherein the microphone is designed to emit a transmitting wave, which is an ultrasonic wave, by being driven to oscillate on the basis of a drive signal while oscillating by receiving a reflected wave generated as a result of the transmitting wave being reflected by an object; a reduction identification unit (245) designed to identify, in a temporal change of an amplitude of the oscillation signal obtained by the acquisition unit, a reduction time (T3) of a first reduction from a value greater than a threshold (X) to the threshold or less after termination of the drive signal; a magnification estimation unit (140) designed to estimate a magnification reverberation time (T0) of the reflected wave based on the reduction time identified by the reduction identification unit, wherein the magnification reverberation time is before the reduction time and after a time of start of the drive signal; and a distance determination unit (150) designed to determine a distance to the object based on the magnification reverberation time estimated by the magnification estimation unit.

Description

Technical field

[0001] The invention relates to an ultrasonic object detector. State of the art

[0002] A transmit / receive ultrasonic object detector is known. In such an object detector, an oscillator that has emitted a transmit wave, which is an ultrasonic wave, receives a reflected wave. When the oscillator is driven to emit the transmit wave, a reverberation occurs in the oscillator after the drive signal has ceased. The energy of the reverberation is considerably greater than the energy of the reflected wave. Accordingly, a device is required to detect an object at a distance that is short enough for the reflected wave and the reverberation to overlap.

[0003] According to the technology disclosed in JP 2002 - 90 452 A, the presence of an object within a short distance is determined, for example, by multipath reflection based on the detection of second and subsequent reflected waves at the same perceivable distance as a result of overlap between a reverberation and a reflected wave, it is assumed that multiple reflected waves are coming from a single object.

[0004] JP S63-311192A discloses an object detector comprising: a acquisition unit designed to acquire an oscillation signal corresponding to the oscillation of a microphone, the microphone being designed to emit a transmitting wave, which is an ultrasonic wave, by being driven to oscillate based on a drive signal while oscillating by receiving a reflected wave generated as a result of the transmitting wave being reflected by an object; a decay identification unit designed to identify, in a temporal change in the amplitude of the oscillation signal acquired by the acquisition unit, a decay time of an initial reduction from a value greater than a threshold to the threshold or less after termination of the drive signal;a magnification estimation unit designed to estimate a magnification time of the reflected wave, wherein the magnification time is before the reduction time and after a time of start of the drive signal; and a distance determination unit designed to determine a distance to the object based on the magnification time estimated by the magnification estimation unit. Summary of the invention

[0005] According to studies by the inventors, the technology disclosed in JP 2002-90452A allows for distance measurement to an object only in cases where an object detector can receive multiple reflected waves through multipath reflection. An example of such a case is when a transmitted wave is reflected by a flat object with a large surface area, such as a wall. However, the object detector may not be able to receive multiple reflected waves through multipath reflection depending on the object's shape. For example, a transmitted wave may be reflected by an object shaped like a thin post, such as a traffic signpost.

[0006] It is an object of the invention to detect the distance to an object using a reflected wave when the reflected wave overlaps with reverberation. This object is achieved by an object detector with the features of claim 1. The dependent claims are directed to advantageous embodiments of the invention.

[0007] According to one aspect of the invention, an object detector comprises: a acquisition unit designed to acquire an oscillation signal corresponding to the oscillation of a microphone, wherein the microphone is designed to emit a transmitting wave, which is an ultrasonic wave, by being driven to oscillate based on a drive signal, while being caused to oscillate by receiving a reflected wave generated as a result of the transmitting wave being reflected by an object; a reduction identification unit designed to identify, in a temporal change in the amplitude of the oscillation signal acquired by the acquisition unit, a reduction time of a first reduction from a value greater than a threshold to the threshold or less after termination of the drive signal;a magnification estimation unit designed to estimate a reverberation magnification time of the reflected wave based on the reduction time identified by the reduction identification unit, wherein the magnification reverberation time is before the reduction time and after a time of start of the drive signal; and a distance determination unit designed to determine a distance to the object based on the magnification reverberation time estimated by the magnification estimation unit.

[0008] When the reverberation and the reflected wave overlap, the object detector estimates the amplification time of the reflected wave based on the time of the initial decrease from a value greater than the threshold to the threshold or less after the drive signal has ceased. The amplification time is the time before the decrease time and after the start of the drive signal. Thus, it is possible to determine the distance to the object using the reflected wave, even when the reverberation and the reflected wave overlap.

[0009] Note that the reference symbols in parentheses for the components each represent an example of a correspondence relationship between the respective components and specific components in the embodiment described later. Brief description of the drawings Fig. Figure 1 is a configuration diagram of a vehicle obstacle detector according to a first embodiment. Fig. Figure 2 is a configuration diagram of an ultrasonic sensor. Fig. Figure 3 is a flowchart of a process performed by a distance ECU. Fig. Figure 4 is a flowchart of a process carried out by a control unit of the ultrasonic sensor. Fig. Figure 5 is a graph representing the amplitude of an oscillation signal resulting from the reception of a normally reflected wave. Fig. Figure 6 is a graph representing the amplitude of the oscillation signal resulting from the reception of a reflected wave that overlaps with a reverberation. Fig. Figure 7 is a flowchart of a magnification point calculation process. Fig. Figure 8 is a graph that illustrates a relationship between a reflection amplitude model and a magnification reverberation time. Fig. Figure 9 is a diagram illustrating a method for calculating an early magnification time according to a second embodiment. Description of the embodiments: First embodiment

[0010] A first embodiment is described below. As it appears in Fig. Figure 1 shows a vehicle object detector according to the first embodiment, which is arranged in a vehicle, comprising an ultrasonic sensor 1, a vehicle speed sensor 2, an acceleration sensor 3, a control ECU 4 and a warning device 5.

[0011] The ultrasonic sensor 1 is, for example, located at the left end of a bumper of the front section of the vehicle, at the right end of the bumper of the front section of the vehicle, at the left end of a bumper of the rear section of the vehicle, or at the right end of the bumper of the rear section of the vehicle. The ultrasonic sensor 1 is capable of detecting an obstacle in an area surrounding the vehicle.

[0012] The ultrasonic sensor 1 includes a microphone 11, a transmitter circuit 12, a receiver circuit 13, a control unit 14 and a communication interface 15, as shown in Fig. 2 is shown.

[0013] Microphone 11 is driven by a control signal applied by the transmitter circuit 12, causing it to oscillate. The control signal is an electrical signal that changes at or near the resonant frequency of microphone 11. For example, the control signal could be a rectangular pulse signal.

[0014] The microphone 11 is activated by the control signal, causing it to oscillate and generate a transmission wave, which is an ultrasonic wave, and emit this wave into the vehicle's surroundings. Furthermore, the microphone 11 continues to oscillate for a period of time after the application of the control signal by the transmitter circuit 12 has ceased. This oscillation of the microphone 11, which occurs after the application of the control signal has ceased, is called reverberation.

[0015] If microphone 11 is driven during the transmission of the transmitting wave, a reverberation occurs in microphone 11 after the application of the drive signal has ceased. The energy of the reverberation is considerably greater than the energy of the reflected wave. In other words, the amplitude of the reverberation is considerably greater than the amplitude of the reflected wave. Accordingly, a device is needed to detect an object at a short distance, such that the reflected wave and the reverberation coincide.

[0016] Furthermore, the microphone 11 receives a reflected wave, which is an ultrasonic wave. This wave is generated when the transmitted wave is reflected by an object, such as a wall, causing an oscillation. When this oscillation occurs, the microphone 11 converts the reflected wave into an electrical signal and outputs this signal to the receiving circuit 13.

[0017] The microphone 11 can contain an oscillator and a drive circuit. In this case, the oscillator can be a piezoelectric oscillator with a sintered die containing piezoelectric ceramics, for example PZT or barium titanate. The drive circuit applies a voltage to the oscillator corresponding to the drive signal applied by the transmitter circuit 12, causing the oscillator to oscillate as described above.

[0018] The transmitter circuit 12 generates the above control signal in response to a transmit instruction signal from the control unit 14 and applies the control signal to the microphone 11. The microphone 11 is driven by the control signal, causing it to oscillate and thereby emit a transmission wave with the same frequency as that of the control signal into the vehicle's surroundings.

[0019] The receiving circuit 13 amplifies the electrical signal input from the microphone 11 and outputs an amplified signal (hereinafter referred to as the oscillation signal) to the control unit 14. The oscillation signal is a signal that corresponds to the oscillation of the microphone.

[0020] The control unit 14 is a microcomputer containing a CPU, RAM, ROM, and flash memory. The RAM, ROM, and flash memory are each non-volatile, computer-readable storage media.

[0021] The control unit 14 controls the operation of the microphone 11 via the transmitter circuit 12 based on a transmit command from the control ECU 4, causing the microphone 11 to emit the transmission wave. Furthermore, the control unit 14 calculates, for example, a distance to an object according to the oscillation signal received by the receiver circuit 13 and transmits the result of this calculation as acquisition information to the control ECU 4. The details of one of the processes of the control unit 14 are described later.

[0022] The communication interface 15 facilitates communication between the control unit 14 and the warning device 5. In particular, the communication interface 15 facilitates the transmission of the send command from the control ECU 4 to the control unit 14 and the transmission of the acquisition information from the control unit 14 to the control ECU 4.

[0023] The vehicle speed sensor 2 is a known sensor that outputs a vehicle speed pulse signal as a detection signal with a frequency corresponding to the rotational speed of the vehicle's wheels. The acceleration sensor 3 is a known sensor that outputs a detection signal corresponding to the acceleration of a vehicle body.

[0024] The control ECU 4 contains a communication interface 40 and a control unit 41, as shown in Fig. Figure 1 shows the communication interface 40, which is an interface circuit for communication with the communication interface 15 of the ultrasonic sensor 1.

[0025] The control unit 41 is a microcomputer containing a CPU, RAM, ROM, and flash memory. The RAM, ROM, and flash memory are each non-volatile, computer-readable storage media.

[0026] The warning device 5, which is controlled by the control ECU 4, warns a person inside the vehicle using either a picture or sound or tones, or both.

[0027] The following describes a process carried out by the control unit 14 of the ultrasonic sensor 1 and a process carried out by the control ECU 4. The control unit 41 executes a predetermined program, causing the control ECU 4 to repeatedly perform a process at regular intervals, which is described in Fig. Figure 3 shows that the control unit 14 of the ultrasonic sensor 1 executes a predetermined program, thereby causing the Fig. The process shown in section 4 is carried out.

[0028] In step 110 of the process in Fig. 3 The control ECU 4 transmits the send command to the ultrasonic sensor 1.

[0029] In step 210, the control unit 14 of the ultrasonic sensor 1 first determines whether the transmit command from the control ECU 4 has been received. If it has not been received, step 210 is repeated. If it has been received, the process proceeds to step 215. Thus, the control unit 14 repeats step 205 while no transmit command is being received. If the control unit 14 obtains the transmit command from the ultrasonic sensor 1 during the repetition of step 205, the process proceeds from step 210 to step 215.

[0030] In step 215, the control unit 14 outputs the transmit instruction signal to the transmitter circuit 12 for a predetermined duration. This causes the transmitter circuit 12 to generate the control signal and output the control signal to the microphone 11 for the predetermined duration. The microphone 11 is driven by the control signal, causing it to oscillate and emit a transmission wave at the same frequency as the control signal. The transmission wave encounters an object (e.g., an obstacle) in the vicinity of the vehicle, causing it to be reflected and generating the reflected wave. When the reflected wave reaches the microphone 11, the microphone 11 oscillates.

[0031] At this point, the receiving circuit 13 outputs an oscillation signal corresponding to the oscillation of the microphone 11 to the control unit 14. The oscillation signal corresponds to the oscillation of the microphone 11, which is driven by the control signal, wherein the oscillation of the microphone 11 corresponds to the reverberation caused after the termination of the control signal, and wherein the oscillation of the microphone is caused by the reception of the reflected wave.

[0032] As the process progresses from step 215 to step 220, the control unit 14 receives the oscillation signal from the receiving circuit 13 only during a predetermined waiting period since the output start point of the transmit instruction signal. A value obtained by multiplying half of this waiting period by the speed of sound corresponds to the maximum detectable distance of the ultrasonic sensor 1.

[0033] Subsequently, in step 225, the control unit 14 determines, based on the acquired oscillation signal, whether a normally reflected wave has been received. A normally reflected wave is one that is not masked by reverberation. To determine whether a normally reflected wave has been received, it is determined whether the amplitude of the oscillation signal acquired in the current iteration of step 220 has changed, during a detection period, from a value lower than a sensor output threshold X to a value greater than the sensor output threshold X, as described in Fig. 5 is shown.

[0034] A solid line in Fig. Figure 5 is a graph representing the amplitude of the oscillation signal resulting from the reception of the normally reflected wave by microphone 11. The solid line 61 represents an amplitude of the oscillation signal corresponding to the drive signal and the reverberation, and the solid line 62 represents an amplitude of the oscillation signal corresponding to the reflected wave. A sensor saturation value in Fig. 5 is a maximum amplitude value that can be detected by the control unit 14. Even if a voltage higher than the sensor saturation value is applied from the receiving circuit 13 to the control unit 14, the control unit 14 detects the sensor saturation value as a quantity corresponding to this voltage.

[0035] In this respect, the starting point of the recording time duration is a reference time Tr, which is reached after a predetermined reverberation time has elapsed since the output start point of the transmit instruction signal, as described in Fig. Figure 5 illustrates this. The endpoint of the acquisition time is a point in time reached after the waiting period described above has elapsed since the output start point of the transmit instruction signal. The reverberation time is the time from the output start point of the transmit instruction signal until a point in time at which reverberation is very unlikely to occur. The reverberation time can be predefined according to the characteristics of microphone 11 or can be modified by means of a learning process.

[0036] If the control unit 14 determines in step 225 that a normally reflected wave has been received, the process proceeds to step 230; otherwise, the process skips steps 230, 232, 235, 237 and 238 and proceeds to step 240.

[0037] In step 230, a detection distance D is calculated based on a time difference between the output start point of the transmit instruction signal and a magnification time Tu of the reflected wave 62. The detection distance D is added to the detection information. The magnification time Tu of the reflected wave 62 is the point in time at which the amplitude of the oscillation signal has changed during the detection time from a value less than the sensor output threshold X to a value equal to or greater than the sensor output threshold X. The detection distance D, which is a distance from the microphone 11 to an object, is calculated by multiplying half of the above time difference by the speed of sound.

[0038] Subsequently, in step 232, the control unit 14 identifies a maximum amplitude M of the reflected wave 62 and adds this maximum amplitude M to the acquisition information. The maximum amplitude of the reflected wave 62 is the maximum value of the oscillation signal amplitude at a time point after the magnification time Tu of the reflected wave.

[0039] Subsequently, in step 235, the control unit 14 identifies an amplitude maximum time Tm, that is, a time at which the maximum amplitude M of the reflected wave 62 is reached, and adds the amplitude maximum time Tm to the detection information.

[0040] Subsequently, in step 237, the control unit 14 calculates a zero-point time interval TD1 and adds it to the acquisition information. The zero-point time interval TD1 is a time interval from the point in time when the amplitude of the reflected wave 62 begins to increase from zero until the point in time when the amplitude of the reflected wave 62 falls back to zero, as described in Fig. Figure 5 is shown. The time at which the amplitude of the reflected wave 62 starts to increase or magnify from zero is a detection time of a most recent past amplitude of the oscillation signal before an amplitude of the oscillation signal corresponding to the reflected wave 62, which is detected by the control unit 14 for the first time as a value greater than zero.

[0041] Subsequently, in step 238, the control unit 14 calculates an increase time (or magnification time) T1 and a decrease time T2 and adds them to the acquisition information. The increase time T1 is the time interval from when the amplitude of the reflected wave 62 begins to increase until the amplitude reaches its maximum Tm. The decrease time T2 is the time interval from the amplitude reaches its maximum Tm until the amplitude of the reflected wave 62 has dropped to zero. Following step 238, the process of the control unit 14 proceeds to step 240.

[0042] Step 240 determines whether an early reduction time T3 is a time point after the reference time Tr mentioned above. The early reduction time T3, in a temporal change in the amplitude of the oscillation signal obtained after the drive signal has ceased being applied in the current iteration of step 220, is a time point of the first reduction from a value greater than the sensor output threshold X to the sensor output threshold or less.

[0043] It is assumed that the early attenuation time T3 is before the reference time Tr above if the reflected wave does not overlap with the reverberation, as in Fig. Figure 5 is shown. If, in contrast, the reflected wave overlaps with the reverberation, the early attenuation time T3 is a time after the reference time Tr above, as shown in Figure 5. Fig. Figure 6 is shown. Fig. 6 The control unit 14 detects a combined wave consisting of an oscillation 61 of the microphone 11 caused by the reverberation and an oscillation 64 of the microphone 11 caused by the reflected wave as an oscillation signal 65.

[0044] If in step 240 the early reduction time T3 is a time after the reference time Tr, the process of control unit 14 proceeds to step 245, otherwise the process skips step 245 and proceeds to step 250.

[0045] In step 245, the early reduction time point T3 is added to the data collection information. Following step 245, the process proceeds to step 250.

[0046] In step 250, the acquisition information is transmitted to the control ECU 4. If in step 225 it is determined that a normally reflected wave is received (for example, the one in Fig. (Case 5 shown), the acquisition information includes the acquisition distance D, the maximum amplitude M, the amplitude maximum time Tm, the zero-point time interval TD1, the increase time T1, and the decrease time T2. If the early decrease time T3 in step 240 is determined to be after the reference time Tr (for example, the one shown in Fig. (Case 6 shown), the recording information includes the early reduction time T3.

[0047] After the transmit command is sent in step 110, the control ECU 4 waits in step 115 for the receipt of the acquisition information from the ultrasonic sensor 1 for a predetermined period of time. When the control ECU 4 receives the acquisition information, the process proceeds to step 120.

[0048] If, in step 120, the acquisition information received in the current iteration of step 115 includes the acquisition distance D, the maximum amplitude M, the amplitude maximum time Tm, the zero point time interval TD1, the increase time T1 and the decrease time T2, this content is recorded in the frame of the control unit 41.

[0049] Subsequently, in step 125, a vehicle displacement is calculated. Specifically, a vehicle displacement since a time at which the detection distance D, the maximum amplitude M, the amplitude maximum time Tm, the zero-point time interval TD1, the increase time T1, and the decrease time T2 were recorded in the control ECU 4 as the most recent among the past opportunities to perform step 120, excluding the current iteration of step 120, is calculated based on the detection signal output by the vehicle speed sensor 2 and the acceleration sensor 3, respectively. The displacement includes a change in the vehicle's position and a change in its orientation.

[0050] Subsequently, in step 130, the control ECU 4 determines whether the reverberation and the reflected wave overlap. Determining whether the reverberation and the reflected wave overlap is equivalent to determining whether a later-described reverberation increase or reverberation magnification time can be assumed.

[0051] More precisely, if condition A and condition B are met, the control ECU 4 determines that the reverberation and the reflected wave overlap. If either condition A or condition B is not met, the control ECU 4 determines that the reverberation and the reflected wave do not overlap. If neither condition A nor condition B is met, the control ECU 4 determines that the reverberation and the reflected wave do not overlap.

[0052] Condition A is a condition that requires the early reduction time T3 to be recorded in the acquisition information received in the current iteration of step 115. Thus, with reference to step 240, condition A is equivalent to a condition that requires the early reduction time T3 to be after the reference time Tr.

[0053] Based on the location of an object identified at a point in the past and the vehicle's movement to and from that point in the past, it is determined whether condition B is met. In this context, the point in the past is defined as the most recent time at which the detection distance D, maximum amplitude M, amplitude maximum time Tm, zero-point time interval TD1, growth time T1, and decrease time T2 were recorded in the control ECU 4 as the most recent of all past opportunities to perform step 120, excluding the current iteration of step 120.

[0054] The following describes a case in which the ultrasonic sensor 1 is arranged to transmit the wave in a forward direction relative to the vehicle. It is assumed that the detection distance D to an object, as recorded by the microphone 11 at a specific time in the past, was 60 cm. Furthermore, the control ECU 4, in the most recent step (step 125), identified a forward travel distance of 40 cm for the vehicle since that time in the past.

[0055] In this case, the control ECU 4 determines in step 130 whether condition B is met by determining whether a value obtained by subtracting the forward travel distance from the recorded detection distance D is equal to or less than a target value (for example, 25 cm). In this example, the value obtained by subtracting the forward travel distance from the recorded detection distance D is 20 cm. Since this value is less than the target value, the control ECU 4 determines that condition B is met. As can be seen from the above, condition B is a condition that requires that the object detected in the past has moved closer and is at a predetermined distance or closer as the vehicle moves.

[0056] If the control ECU 4 determines that the reverberation and the reflected wave overlap, the process proceeds to step 140. If the control ECU 4 determines that the reverberation and the reflected wave do not overlap, the process skips steps 140 and 150 and proceeds to step 160.

[0057] In step 140, an amplification reverberation time T0 is calculated from the early reduction time T3. As described in Fig. As shown in Figure 6, the amplification reverberation time T0 is a time at which the amplitude of oscillation 64 increases from zero, or rather, when the oscillation 64, caused solely by the reflected wave, overlaps with the oscillation 61, caused by the reverberation. This amplification reverberation time T0 is therefore a time before the early reduction time T3 mentioned above and after the start of the drive signal.

[0058] For a calculation process of the magnification reverberation time T0, the control ECU 4 performs the following in Fig. The process described in section 7 is carried out. In step 410 of the process of Fig. 7. The control ECU 4 first reads the maximum amplitude M and the amplitude maximum time Tm of a most recent set from the RAM of the control unit 41, based on the sets from the detection distance D, the maximum amplitude M, the amplitude maximum time Tm, and the zero-point time interval TD1 recorded in the previous iteration of step 120. The most recent set is read because a reflected wave providing the maximum amplitude M and the amplitude maximum time Tm contained in the most recent set and the reflected wave currently overlapping with the reverberation are very likely to originate from the same object.

[0059] Subsequently, in step 420, the control ECU 4 determines an amplitude prediction curve S based on the maximum amplitude M and the amplitude maximum time Tm, which were read out in the current iteration of step 410, as described in Fig. 8 is shown.

[0060] The amplitude prediction curve S is a curve that represents a one-to-one relationship between time and amplitude. Assuming that the same single object can be present at several different distances from microphone 11, the amplitude prediction curve S represents possible relationships between the maximum amplitude M and the amplitude maximum time Tm of the waves reflected by that object.

[0061] t denotes the time elapsed from the moment a transmission wave was emitted by microphone 11 until the moment the transmission wave is reflected by the object and returns to microphone 11 as a reflected wave. y denotes the maximum amplitude of the reflected wave. In this case, the relationship y = A × t applies. -2× exp(-t × m × c / 2) between t and y. In this expression, c denotes the speed of sound, and m denotes an attenuation constant determined by temperature and humidity. The coefficient A is a positive number. The coefficient A is a constant value as long as the same object reflects the transmitted wave and the orientation of a reflective surface with respect to microphone 11 is the same. For example, in a case where the vehicle is moving straight ahead or backward while an object is stationary, the coefficient A is constant for that object. However, the values ​​of the coefficient A differ between different objects. This is because different objects have different reflectivities with respect to an ultrasonic wave, etc.

[0062] Determining the amplitude prediction curve S is similar to determining the value of the coefficient A. As described in Fig. As shown in Figure 8, determining the respective values ​​of the maximum amplitude M and the amplitude maximum time Tm allows the value of the coefficient A to enable the amplitude prediction curve S to pass through a point (M, Tm) in a time-amplitude space. More precisely, in the relational expression above, M is assigned to y and t is assigned to Tm, which means A = M × Tm 2 × exp(t × m × c / 2).

[0063] Note that the respective values ​​of the attenuation constant m and the speed of sound c are determined as follows. The control ECU 4 can calculate the attenuation constant m by identifying a current temperature and humidity using a known temperature and humidity sensor and inputting the temperature and humidity values ​​into an attenuation conversion table pre-recorded in the ROM of the control ECU 4. The attenuation conversion table contains the respective values ​​of the attenuation constant m for several temperature and humidity pairs. Alternatively, the control ECU 4 can calculate the attenuation constant m by identifying a current temperature using a known temperature sensor and inputting the temperature and a fixed humidity value (for example, 60%) into the aforementioned attenuation conversion table.

[0064] Furthermore, the control ECU 4 can calculate the speed of sound c by identifying a current temperature using a known temperature sensor and entering the temperature into a speed-of-sound conversion table that has been pre-programmed into the ROM of the control ECU 4. The speed-of-sound conversion table contains values ​​for the speed of sound c for several combinations.

[0065] Subsequently, in step 430, the control ECU 4 determines a reflection amplitude model R, which schematically represents a temporal change in the amplitude of the reflected wave that coincides with the reverberation. It is not necessary for the reflection amplitude model R to reproduce the temporal change in the amplitude of the reflected wave that coincides with the reverberation in detail. The reflection amplitude model R only needs to reproduce the temporal change of the reflected wave sufficiently to identify the later-described reverberation magnification time T0.

[0066] In particular, the reflection amplitude model R consists of the other two sides L1 and L2 of a triangle with a basis lying on a time axis with zero amplitude in the time-amplitude space, as described in Fig. 8 is shown. As it is in Fig. As shown in Figure 8, the reflection amplitude model R is determined such that the following conditions 1, 2 and 3 are satisfied; that is, condition 1 is that the position (T3, X) is traversed in the time-amplitude space, condition 2 is that a peak at which the amplitude is maximal lies on the amplitude prediction curve S, condition 3 is that a time difference TD0 between two points with zero amplitude is equal to the zero-point time interval TD1, and condition 4 is that a ratio between a time difference between one of the two points with zero amplitude (that is, magnification reverberation time T0) and a peak time and a time difference between the other point T4 and a peak time Tx is equal to T1 / T2.

[0067] In this context, the peak time Tx in condition 4 is a time at which a peak representing the maximum amplitude is reached. Furthermore, the two points T0 and T4 with zero amplitude are: T0, the time at which the amplitude of the reflection amplitude model R begins to increase from zero, and T2, the time at which the amplitude of the reflection amplitude model R has decreased to zero. The reflection amplitude model R that satisfies conditions 1, 2, 3, and 4 is uniquely determined.

[0068] Subsequently, in step 440, the control ECU 4 identifies the magnification reverberation time T0 based on the reflection amplitude model R, which was determined in the current iteration of step 430. As it is in Fig. As shown in Figure 8, a time point at which an earlier point from the two points with zero amplitude in the reflection amplitude model R lies in the time-amplitude space is identified as the magnification reverberation time T0. After step 440, the calculation process for the magnification reverberation time T0 is terminated.

[0069] In step 150, the distance from microphone 11 to the object is calculated based on the magnification reverberation time T0, which was calculated in step 140 of the current iteration. The distance is calculated by multiplying half the time elapsed between the time the transmit command was sent and time T0 by the speed of sound. Following step 150, the control ECU 4 proceeds to step 160.

[0070] The control ECU 4 issues a warning in step 160 based on the distance. Specifically, if the acquisition information received in the current iteration of step 115 includes the acquisition distance D, the maximum amplitude M, the amplitude maximum time Tm, and the zero-point time interval TD1, and steps 140 and 150 are skipped, the control ECU 4 issues a warning regarding the acquisition distance D. If the acquisition information received in the current iteration of step 115 includes the early decay time T3, and steps 140 and 150 are skipped, the control ECU 4 issues a warning regarding the distance identified in step 150.

[0071] More precisely, the control ECU 4 determines which of three distance ranges—short, medium, and long—corresponds to the reference distance. For example, the reference distance corresponds to a short distance if it is less than a first distance threshold, to a medium distance if it is not less than a first and a second distance threshold, and to a long distance if it is not less than a second distance threshold. The first and second distance thresholds can each be fixed values ​​or variable values ​​to provide hysteresis.

[0072] The control ECU 4 then issues a warning containing content corresponding to the identified distance range. For example, in a case where the warning device 5 is controlled to emit a warning tone at predetermined intervals, the length of the predetermined intervals differs between the short, medium, and long distances. More precisely, the length of the predetermined intervals for the medium distance is longer than the length for the short distance, and the length for the long distance is longer than the length for the medium distance. After step 160, an iteration of the process is performed in Fig. 3 completed.

[0073] As described above, in step 245, the control unit 14 of the ultrasonic sensor 1 identifies the early decay time T3 in the temporal change of the amplitude of the oscillation signal, which corresponds to the oscillation of the microphone 11. In step 140, the control ECU 4 then estimates the magnification reverberation time T0 of the reflected wave based on the early decay time T3, where the magnification reverberation time T0 is before the early decay time T3 and after the start of the drive signal. In step 150, the control ECU 4 then determines the distance to the object based on the estimated magnification reverberation time T0.

[0074] In a case where the reverberation and the reflected wave overlap, the control ECU 4 estimates the amplification time T0 of the reflected wave based on the decay time T3. The amplification time T0 is a point in time before the decay time and after the start of the control signal. Thus, in a case where the reverberation and the reflected wave overlap, it is possible to determine the distance to the object using the reflected wave.

[0075] In this regard, a procedure for calculating the reflection amplitude model R and the magnification reverberation time T0 is described in steps 430 and 440. The two sides L1 and L2, which define the reflection amplitude model R, are expressed by the following equations according to condition 3. Equation of side L1:y=−a×(t−T0−TD1) Equation of side L2: y=b×(t−T0)

[0076] In the equations, -a and b each represent a slope of side L1 and a slope of side L, respectively. Furthermore, according to condition 4... b=a×T2 / T2

[0077] In equations 1, 2 and 3, a, b, T0, y and t are unknown quantities and the quantities T0 and TD1 are known.

[0078] Based on equation 1, the intersection point between L1 and L2 is as follows. t=T0+TD1 / 2 y=a / 2×TD1

[0079] Since the intersection point lies on the amplitude prediction curve S according to condition 2, the following applies: b×(T0+T1−T0)=A×[exp{−m×c / 2×(T0+T1)}] / (T0+T1)2

[0080] Since side L1 passes through position (T3, X) according to condition 1, the following holds: X=−a×(T1−T0−TD1)

[0081] In equations 3, 6, and 7, a, b, and T0 are unknown quantities, while the other quantities are known. Therefore, it is possible to calculate the reverberation time T0 by solving equations 3, 6, and 7 for T0.

[0082] Furthermore, the control unit 14 causes the microphone 11 to emit a transmit wave (hereinafter referred to as the "past transmit wave") prior to the transmission of the transmit wave, which ultimately generates the oscillation 64 caused by the reflected wave superimposed with the reverberation, as described above. The past transmit wave is then reflected by the object, generating the reflected wave 62 mentioned above. The reflected wave 62 corresponds to a past reflected wave. When the microphone 11 receives and oscillates the reflected wave 62, the control unit 14 obtains an oscillation signal corresponding to the oscillation of the microphone 11 caused by the reflected wave 62. This oscillation signal corresponds to a past oscillation signal.

[0083] The maximum amplitude M and the amplitude maximum time Tm are then recorded in the control ECU 4, where the maximum amplitude M is the maximum amplitude value in a time-dependent change of the amplitude of the past oscillation signal, and the amplitude maximum time Tm is the time at which the amplitude reaches its maximum value in the time-dependent change of the amplitude of the past oscillation signal. The maximum amplitude M corresponds to a past maximum amplitude, and the amplitude maximum time Tm corresponds to a past maximum amplitude time. As can be seen from the above, it is possible to estimate the magnification reverberation time T0 with high accuracy using information regarding the amplitude of the reflected wave 62, which did not coincide with the reverberation in the past.

[0084] More precisely, the control unit 14 estimates the magnification time T0 as an earlier time with an increase in the above coefficient A.

[0085] Furthermore, the control ECU 4 determines whether the amplification reverberation time T0 is to be calculated, based on the location of an object identified at a point in the past and the vehicle's displacement since that point in the past. In other words, the control ECU 4 determines whether the reflected wave overlaps with the reverberation, based on the location of an object identified at a point in the past and the vehicle's displacement since that point in the past. This makes it possible to determine with high accuracy, based on the vehicle's past driving history, whether the reflected wave overlaps with a reverberation. Second embodiment

[0086] A second embodiment is described below. A vehicle object detector according to the second embodiment differs from the vehicle object detector according to the first embodiment only in the process content in step 140. In particular, in step 140, the control ECU 4 estimates a time point T3 that is a predetermined time Tb before the early reduction time T3, as described in Fig. Figure 9 illustrates this. The predetermined time Tb is a fixed, non-variable time. The predetermined time Tb is set in advance as a time essentially equal to the wavelength (duration) of the reflected wave that overlaps with the reverberation. The wavelength of the reflected wave is a quantity corresponding to the duration of the reflected wave. The remaining operations are the same as in the first embodiment.

[0087] This reduces the processing load for estimating the magnification reverberation time T0, even if the accuracy of the estimation of the magnification reverberation time T0 is lower than in the first embodiment.

[0088] With regard to the other functions, the vehicle object detector according to the second embodiment is able to achieve similar effects as in the first embodiment.

[0089] Note that in the first and second embodiments above, the control unit 14 of the ultrasonic sensor 1 serves as an acquisition unit by performing step 220 and as a reduction identification unit by performing step 245. Furthermore, the control ECU 4 serves as an acquisition information recording unit by performing step 120, as an estimation determination unit by performing step 130, as a magnification estimation unit by performing step 140, and as a distance determination unit by performing step 150.

[0090] Note that if the early reduction time T3 is later, the amplification reverberation time T0 is estimated as a later time in the second embodiment. Furthermore, the amplification reverberation time T0 can also be estimated as a later time in the calculation method for the amplification reverberation time T0, as in the first embodiment, if the early reduction time T3 is later. Other embodiments

[0091] Note that the invention is not limited to the embodiments described above and can be modified as needed. Furthermore, the embodiments described above are relevant to one another and can therefore be combined as needed, unless such combination is obviously impossible. Additionally, elements defining the embodiments described above are not strictly necessary unless they are specifically described as particularly necessary or as obviously necessary in principle. Furthermore, when numerical values ​​such as a number, a numerical value, a quantity, or a range of components of the embodiments are described in the embodiments described above, such numerical values ​​are not limited to specific values ​​as described unless it is explicitly stated that the specific values ​​are necessary or obviously limited to the specific values ​​in principle.In particular, when several exemplary values ​​of a quantity are given, any intermediate value between the values ​​may be used unless a specific description is separately given or the value is obviously impossible in principle. If a shape, positional relationship, etc., of a component, etc., is described in the above embodiments, the shape, positional relationship, etc., are not limited to a specific shape, positional relationship, etc., as described, unless expressly stated otherwise or they are limited in principle to the specific shape, positional relationship, etc. The invention may include the following modification examples of the above embodiments and any modification example within the equivalence range. Note that each of the following modification examples is independently and selectively usable or unusable in the above embodiments.In other words, any combination of the following modification examples can be used for the above embodiments. Modification example 1

[0092] The control ECU 4 can determine whether the reverberation and the reflected wave overlap, independently of the vehicle's displacement in step 130. Specifically, it determines that the reverberation and the reflected wave do not overlap if the most recent acquisition information includes the early decay time T3, and it determines that the reverberation and the reflected wave overlap if the acquisition information does not include the earlier decay time T3. Modification example 2

[0093] In the first embodiment, the reflection amplitude model R is defined by the two sides of equal length of an isosceles triangle with a base that lies on the time axis with zero amplitude in time-amplitude space. However, such a form of the reflection amplitude model R is not exhaustive or exclusive. The reflection amplitude model R can also take the form of a parabola that opens downwards. Modification example 2

[0094] In the second embodiment described above, the predetermined time Tb is a fixed time that is not variable. However, the predetermined time Tb can be a variable time. For example, the predetermined time Tb can be a quantity that increases with an increase in the coefficient A described in the first embodiment. Modification example 3

[0095] In the above embodiments, a single ultrasonic sensor 1 is connected to the control ECU 4. However, multiple ultrasonic sensors can be connected to the control ECU 4.

Claims

[1] Object detector which features: a receiving unit (220) designed to receive an oscillation signal corresponding to an oscillation of a microphone (11), wherein the microphone is designed to emit a transmitting wave, which is an ultrasonic wave, by being driven to oscillate on the basis of a drive signal while oscillating by receiving a reflected wave generated as a result of the transmitting wave being reflected by an object; a reduction identification unit (245) designed to identify, in a temporal change of an amplitude of the oscillation signal obtained by the acquisition unit, a reduction time (T3) of a first reduction from a value greater than a threshold (X) to the threshold or less after termination of the drive signal; a magnification estimation unit (140) designed to estimate a magnification reverberation time (T0) of the reflected wave based on the reduction time identified by the reduction identification unit, wherein the magnification reverberation time is before the reduction time and after a time of start of the drive signal; and a distance determination unit (150) designed to determine a distance to the object based on the magnification reverberation time estimated by the magnification estimation unit. [2] Object detector according to claim 1, wherein the magnification estimation unit is designed to estimate the magnification reverberation time as a later time if the reduction time is later. [3] Object detector according to claim 1 or 2, wherein the magnification estimation unit is designed to estimate a time point which is a fixed time earlier than the reduction time than the magnification reverberation time. [4] Object detector according to claim 1 or 2, further comprising a detection information recording unit (120), wherein if the microphone is caused to oscillate by receiving a past reflected wave generated by the object as a result of a reflection of a past transmitted wave, the acquisition unit is designed to acquire a past oscillation signal corresponding to an oscillation of the microphone caused by the past reflected wave, wherein the past transmitted wave is emitted by the microphone before the transmitted wave is emitted, The acquisition information recording unit is designed to record a past maximum amplitude and a past amplitude maximum time, wherein the past maximum amplitude is a maximum amplitude value in a time change of an amplitude of the past oscillation signal, and wherein the past amplitude maximum time is a time at which the amplitude reaches the maximum value in the time change of the amplitude of the past oscillation signal, and the magnification estimation unit is designed to To estimate the amplification time based on the past maximum amplitude recorded in the acquisition information recording unit, the past maximum amplitude time recorded in the acquisition information recording unit, the threshold, and the reduction time. [5] Object detector according to any one of claims 1 to 4, further comprising an estimation determination unit (130) designed to determine, on the basis of a location of an object identified at a time in the past and a displacement of a vehicle since that time in the past, whether the magnification estimation unit is to estimate the magnification reverberation time. [6] Object detector according to any one of claims 1 to 5, wherein the magnification estimation unit is designed to estimate the magnification reverberation time when the reduction time is after a reference time (Tr).

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