Driving assistance devices

Abstract

A driving assistance device (28) comprises: a sound wave control unit (30) which acquires information of a reflected wave from a distance measurement unit (17) which emits a sound wave (W) toward the driving direction of a vehicle (1) and receives a reflected wave of the sound wave reflected from an object; an information acquisition unit (32) which acquires temperature information around the vehicle; and a determination unit (38) which determines that a road surface in the driving direction of the vehicle is a frozen road surface by determining, based on the information of the reflected wave, that the distance measurement unit receives a reflected wave having a signal strength equal to or greater than a predetermined value from a predetermined distance or greater when the temperature based on the temperature information is less than a predetermined temperature.

Description

Technical Field

[0001] The present disclosure generally relates to a driving assistance device. Background Art

[0002] A known device or system detects objects that may serve as obstacles, such as another vehicle, a building (structure), a tree, and a pedestrian, existing around the vehicle by means of various sensors installed at the vehicle (the vehicle itself). This device performs brake assistance in order to avoid contact (collision) with the object. According to the aforementioned device, contact with the object can be avoided in various situations by estimating the road surface condition (road surface friction coefficient) by means of a sensor different from the sensor used to detect the object. Such a device is disclosed, for example, in JPH5-310110A and JP4966736B.

[0003] The road friction coefficient is the ratio of the friction force applied to the contact surface between the vehicle wheel and the road surface to the pressure applied vertically to the contact surface. Therefore, the road friction coefficient may not be estimated unless the wheel reaches the position where the road friction coefficient is to be estimated. For example, in the case where the road surface ahead of the vehicle in its driving direction is frozen, the road friction coefficient when the vehicle is being braked is smaller than the current road friction coefficient. The distance required for the vehicle to stop on the frozen road surface is therefore estimated to be shorter, which may cause control delays.

[0004] Therefore, there is a need for a driving assistance device that can acquire or estimate the road surface condition in the traveling direction of the vehicle in advance, for example, to reduce or limit control delay. Summary of the invention

[0005] According to one aspect of the present disclosure, a driving assistance device includes: a sound wave control unit that acquires information of a reflected wave from a distance measuring unit that emits a sound wave toward a traveling direction of a vehicle and receives a reflected wave of the sound wave reflected from an object; an information acquisition unit that acquires temperature information around the vehicle; and a determination unit that determines that a road surface in the traveling direction of the vehicle is a frozen road surface by determining, based on the information of the reflected wave, that the distance measuring unit receives a reflected wave including a signal strength equal to or greater than a predetermined value from a predetermined distance or more in a state where a temperature based on the temperature information is less than a predetermined temperature.

[0006] According to the aforementioned configuration, in the case where an object exists so as to reflect the sound waves emitted in the traveling direction of the vehicle in a state where the road surface is a frozen road surface with a temperature lower than a predetermined temperature, a part of the emitted sound waves is highly likely to be returned from the object after being reflected from the frozen road surface. That is, the distance measuring unit is highly likely to obtain a strong reflected wave from a farther position than the reflected wave obtained in the case where the road surface is a non-frozen road surface. The condition of the road surface at such a distance position in the traveling direction of the vehicle (i.e., the frozen road condition) can be obtained in advance by determining that the road surface in the traveling direction of the vehicle is a frozen road surface.

[0007] The determination unit includes a determination threshold for determining that the road surface in the traveling direction of the vehicle is a frozen road surface when the frequency of receiving the reflected wave including the signal strength equal to or greater than a predetermined value is equal to or greater than a predetermined number of times.

[0008] Therefore, the determination on the frozen road surface can be performed safely.

[0009] The determination threshold value changes according to the speed of the vehicle when the determination unit performs the determination.

[0010] In the case where the speed of the vehicle that is emitting the sound wave changes, the number of times the sound wave is received per unit time changes relative to the emitted sound wave. Therefore, the fluctuation of the determination accuracy according to the speed of the vehicle can be limited.

[0011] The determination unit determines whether a road surface in a traveling direction of the vehicle is a frozen road surface based on a graph indicating a relationship between a predetermined distance from the vehicle on a frozen road surface and a peak value indicating a signal intensity of a reflected wave.

[0012] Therefore, the accuracy of determination on a frozen road surface can be improved.

[0013] The driving assistance device also includes a control unit that starts to perform braking control at a position having a second braking distance that is longer than a first braking distance prescribed for a non-frozen road surface when the road surface in the direction of travel of the vehicle is a frozen road surface, so that contact between the vehicle traveling toward an object located in the direction of travel of the vehicle and the object can be avoided.

[0014] According to the aforementioned configuration, for example, in the case where it is determined that an object exists at a distant position on a frozen road surface in the traveling direction of the vehicle, braking control is started at a position of a second braking distance longer than a first braking distance prescribed for a non-frozen road surface, so that contact with the object can be avoided while the vehicle is being driven on the non-frozen road surface. Therefore, braking for contact avoidance with respect to the object can be achieved in consideration of slippage of the wheels of the vehicle on the frozen road surface.

[0015] The braking control is performed based on a required braking distance determined in advance according to the vehicle speed.

[0016] Therefore, the accuracy of control over the braking distance can be improved.

[0017] The sound wave control unit acquires information of the reflected wave from a distance measuring unit provided at the vehicle, the distance measuring unit being configured to emit the sound wave parallel to the traveling direction of the vehicle.

[0018] Therefore, the sound waves are limited to be mainly directed to the road surface to be excessively reflected from the road surface. Therefore, in the case of a non-frozen road surface, the acquisition of strong reflected waves from the road surface is limited so that the frozen road surface is erroneously determined. In addition, in the case of a non-frozen road surface, the road surface or a small object located on the road surface is limited to be erroneously detected as an obstacle, for example.

[0019] The driving assist device further includes a warning processing unit that performs a warning process when a road surface in a traveling direction of the vehicle is determined to be a frozen road surface.

[0020] The driver of the vehicle is thus safely alerted to frozen road surfaces, which increases safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The foregoing and additional features and characteristics of the present disclosure will become more apparent from the following detailed description considered with reference to the accompanying drawings, in which:

[0022] Figure 1 is a perspective view of a vehicle equipped with a driving assistance device according to an embodiment, with the interior of the vehicle partially seen through;

[0023] Figure 2 is a top view of a vehicle on which a driving assistance device according to an embodiment is installed;

[0024] Figure 3 is a block diagram of a configuration of a driving assistance system including a driving assistance device according to an embodiment;

[0025] Figure 4 is a block diagram of a configuration of a driving assistance device implemented at a CPU of the driving assistance device according to the embodiment;

[0026] Figure 5 is a schematic diagram illustrating a positional relationship between a vehicle on which a driving assistance device according to an embodiment is installed and a target object existing in a traveling direction of the vehicle, and a positional relationship between transmission and reception of ultrasonic waves;

[0027] Figure 6is a graph illustrating a reception tendency of reflected waves obtained when a vehicle equipped with a driving assistance device according to an embodiment approaches a target object on a non-frozen road surface (snowy road surface);

[0028] Figure 7 is a graph illustrating a reception tendency of reflected waves obtained when a vehicle equipped with the driving assistance device according to the embodiment approaches a target object in a state of a non-frozen road surface (non-frozen asphalt road surface);

[0029] Figure 8 is a graph illustrating a reception tendency of reflected waves obtained when a vehicle equipped with a driving assistance device according to an embodiment approaches a target object in a state of a frozen road surface;

[0030] Fig. 9 is a block diagram illustrating transmission and reception of ultrasonic waves according to whether a road surface is frozen and whether a target object exists;

[0031] Fig.10 is a graph illustrating a relationship between a determination threshold value as a basis for determining a frozen road surface and a vehicle speed in a driving assistance device according to an embodiment; and

[0032] Fig.11A and Fig. 11B Detailed Description of the Invention This is a flowchart for explaining frozen road surface determination and brake control processing performed by the driving assistance device according to the embodiment. DETAILED DESCRIPTION

[0033] The embodiments disclosed herein are explained with reference to the accompanying drawings. The configuration of the embodiment described below, as well as the operation, results, and effects produced by such configurations are examples. The embodiment can be implemented by other embodiments different from the following configurations, and at least one of the various effects based on the basic configuration and the derived effects can be obtained.

[0034] The vehicle 1 equipped with the driving assistance device may be a car including an internal combustion engine (engine) as a driving source (i.e., an internal combustion engine-type car), a car including an electric motor (motor) as a driving source (i.e., for example, an electric car and a fuel cell car), a car including both an engine and a motor as driving sources (i.e., a hybrid car), or a car including other driving sources. The vehicle 1 may include any type of transmission device and any type of device for driving the internal combustion engine and the electric motor (e.g., any type of device including systems and components). The system, number, and layout of the devices related to the driving of the wheels 3 of the vehicle 1, for example, may be appropriately adopted or specified.

[0035] As in Figure 1As shown in the figure, the vehicle body 2 constitutes the vehicle interior 2a where the passengers are located. In the vehicle interior 2a, the steering part 4, the acceleration operating part 5, the brake operating part 6 and the shift operating part 7 are arranged, for example, in a state opposite to the seat 2b for the driver as a passenger. The steering part 4 is, for example, a steering wheel (steering handle) protruding from the instrument panel 25. The acceleration operating part 5 is, for example, an accelerator pedal arranged near the driver's feet. The brake operating part 6 is, for example, a brake pedal arranged near the driver's feet. The shift operating part 7 is, for example, a shift lever protruding from the center console. The steering part 4, the acceleration operating part 5, the brake operating part 6 and the shift operating part 7 are, for example, not limited to the above.

[0036] In the vehicle interior 2a, for example, a display device 8 serving as a display output portion and an audio output device 9 serving as an audio output portion are provided. The display device 8 is, for example, a liquid crystal display (LCD) or an organic electroluminescent display (OLED). The audio output device 9 is, for example, a speaker. The display device 8 is, for example, covered by an operation input portion 10 that is transparent, such as a touch panel. The passenger can visually confirm the image displayed on the display screen of the display device 8 via the operation input portion 10. The passenger can perform operation input by, for example, touching, pressing or moving the operation input portion 10 with his finger at a position corresponding to the image displayed at the display screen of the display device 8. The display device 8, the audio output device 9 and the operation input portion 10 are, for example, provided at a monitor device 11 positioned at the vehicle width direction, that is, at the approximate center in the left-right direction of the instrument panel 25. The monitor device 11 may, for example, include an operation input portion, such as a switch, a dial, a joystick and a button. In addition, another audio output device may be provided at a position different from the position where the monitor device 11 is arranged in the vehicle interior 2a. Sound may be output by another audio output device different from the audio output device 9 at the monitor device 11. For example, the monitor device 11 may be shared with, for example, a navigation system and an audio system.

[0037] A display device 12 different from the display device 8 is provided in the vehicle interior 2a (see Figure 3 The display device 12 is disposed, for example, on an instrument panel portion 26 provided at an instrument panel 25 (see Figure 1) so as to be positioned approximately in the center of the instrument panel 25. The display device 12 is, for example, arranged between the speed display portion and the revolution (rotation speed) display portion. The size of the screen of the display device 12 is smaller than the size of the screen of the display device 8. The display device 12 can mainly display an image indicating information related to driving assistance of the vehicle 1. The amount of information displayed at the display device 12 can be less than the amount of information displayed at the display device 8. The display device 12 can be, for example, an LCD or an OLED. The aforementioned information related to driving assistance of the vehicle can be displayed, for example, at the display device 8 instead of being displayed at the display device 12.

[0038] As in Figure 1 and Figure 2 As shown in the figure, the vehicle 1 is, for example, a four-wheeled vehicle, and the four-wheeled vehicle includes left and right front wheels (3F) and left and right rear wheels (3R). The aforementioned four wheels (3F and 3R) are steerable. Figure 3 As shown in the figure, the vehicle 1 includes a steering system 13 that steers at least two wheels 3. The steering system 13 includes an actuator 13a and a torque sensor 13b. The steering system 13 is electrically controlled by, for example, an electronic control unit (ECU) 14 to operate the actuator 13a. The steering system 13 is, for example, an electric steering system or a steer-by-wire (SBW) system. The steering system 13 assists the steering force by applying a torque (i.e., an auxiliary torque) to the steering portion 4 via the actuator 13a, and steers the wheels 3 via the actuator 13a. In this case, the actuator 13a can steer a single wheel 3 or steer multiple wheels 3. The torque sensor 13b, for example, detects the torque applied to the steering portion 4 by the driver.

[0039] As in Figure 1 and Figure 2As shown in the figure, an imaging unit 15 is provided at the lower wall portion of the door 2h of the rear hatch located at the rear end portion 2e of the vehicle body 2. The imaging unit 15 is, for example, a digital camera incorporating an imaging element such as a charge coupled device (CCD) and a CMOS image sensor (CIS). The imaging unit 15 outputs moving picture data at a predetermined frame rate. The imaging unit 15 has a wide-angle lens or a fisheye lens, and the imaging unit 15 can, for example, shoot a range of 140° to 220° in the horizontal direction. The optical axis of the imaging unit 15 is set to be obliquely downward. Therefore, the imaging unit 15 continuously captures the rear image of the rear side of the vehicle body 2 - including the road surface where the vehicle 1 can move at the rear side of the vehicle 1 and the area where the vehicle 1 can be parked - and the imaging unit 15 outputs such an image as the captured image data. In another embodiment, a plurality of imaging units 15 may be provided. For example, one of the plurality of imaging units 15 may be arranged at the front side portion of the vehicle body 2, that is, at the front side portion in the front-rear direction of the vehicle, to obtain the front image of the vehicle 1. In addition, two of the plurality of imaging units 15 may be arranged, for example, at the right side rearview mirror and the left side rearview mirror, respectively, as the right end portion and the left end portion of the vehicle body 2 to obtain lateral images (right side image and left side image) of the vehicle 1. In the case where the imaging unit 15 is arranged at the rear end portion of the vehicle body 2, the rear image may be provided, for example, via the display device 8, so as to confirm the safety at the rear side of the vehicle 1 when the vehicle 1 is driven backward. In the case where the imaging unit 15 is arranged, for example, at the front end portion or the side end portion of the vehicle body 2, an image for confirming the safety in the corresponding direction may be provided. The ECU 14 may perform algorithm processing and image processing based on the image data captured by the plurality of imaging units 15 to generate an image with a wider viewing angle or generate a top view image used as a virtual image capturing the vehicle 1 from above.

[0040] As in Figure 1 and Figure 2As shown in the figure, a plurality of distance measuring units 16 and 17 are provided at the vehicle body 2. For example, four distance measuring units 16a to 16d and eight distance measuring units 17a to 17h are provided. Each of the distance measuring units 16 and 17 is, for example, a sonar (sonar sensor or ultrasonic detector) that emits ultrasonic waves used as an example of sound waves and captures reflected waves of the aforementioned ultrasonic waves. Based on the detection results of the distance measuring units 16 and 17, the ECU 14 detects, for example, whether an object, such as an obstacle, is located around the vehicle 1 and detects the distance to the object. Each of the distance measuring units 17 is used, for example, to detect an object at a relatively short distance. Compared with the distance measuring unit 17, each of the distance measuring units 16 is used, for example, to detect an object at a relatively long distance. In addition, the distance measuring unit 17 is used, for example, to detect objects located in front and behind the vehicle 1. The distance measuring unit 16 is used, for example, to detect an object located on the side of the vehicle 1.

[0041] According to the embodiment, each of the distance measuring units 17 can also be used as a sensor that acquires information for determining whether the road surface in the driving direction of the vehicle 1 is frozen (i.e., a frozen road surface). In the case of a frozen road surface, the irregularities (concave and convex surfaces) of the road surface are smoothed by being frozen compared to a non-frozen road surface, so that the reaction (echo performance) of the ultrasonic wave can be improved. Since the sound wave including the ultrasonic wave propagates through the air, the propagation loss decreases as the temperature decreases. According to the driving assistance device of the present embodiment, the determination of whether the road surface is frozen is performed on the basis of the aforementioned characteristics of the sound wave.

[0042] Figure 3 The configuration of a driving assistance system 100 including the driving assistance device 28 according to the embodiment is shown. Figure 3 1, in addition to the ECU 14, the monitor device 11, the steering system 13, and the distance measuring units 16, 17, the brake system 18, the steering angle sensor 19, the accelerator sensor 20, the drive system 21, the wheel speed sensor 22, and the gear position sensor 23 are electrically connected to each other via, for example, an in-vehicle network 24 used as an electrical communication line. The in-vehicle network 24 is configured as, for example, a controller area network (CAN). The ECU 14 sends a control signal via, for example, the in-vehicle network 24 to control the steering system 13, the brake system 18, and the drive system 21. The ECU 14 also receives, for example, detection results of the torque sensor 13b, the brake sensor 18b, the steering angle sensor 19, the distance measuring units 16, 17, the accelerator sensor 20, the gear position sensor 23, and the wheel speed sensor 22 via the in-vehicle network 24, and receives an operation signal of the operation input portion 10.

[0043] The ECU 14 includes, for example, a central processing unit (CPU) 14a, a read-only memory (ROM) 14b, a random access memory (RAM) 14c, a display control unit 14d, an audio control unit 14e, and a solid-state drive (SSD) (flash memory) 14f. The CPU 14a can perform various algorithmic processing and control, such as: image processing related to images displayed at the display devices 8 and 12; determination of whether the road surface in the driving direction of the vehicle 1 is frozen when performing driving assistance; contact avoidance control (e.g., braking control) according to the road surface condition; and warning output when a frozen road surface is found.

[0044] The CPU 14a, for example, reads a program installed and stored in a nonvolatile storage unit, such as the ROM 14b, and the CPU 14a performs algorithm processing based on such a program. The RAM 14c temporarily stores various data used for calculation at the CPU 14a. The display control unit 14d performs image processing mainly using the image data acquired by the imaging unit 15 among the algorithm processing performed by the ECU 14, and performs synthesis of the image data displayed at the display device 8. The audio control unit 14e mainly performs processing of audio data output from the audio output device 9 among the algorithm processing performed by the ECU 14. The SSD 14f, which is a rewritable nonvolatile storage unit, is configured to store data even when the power supply of the ECU 14 is cut off. The CPU 14a, the ROM 14b, and the RAM 14c, for example, can be integrated in the same installation package. The ECU 14 can be configured to use another algorithm logic processor or logic circuit, such as a digital signal processor (DSP), instead of the CPU 14a, for example. In addition, a hard disk drive (HDD) may be provided, for example, in place of the SSD 14 f , or the SSD 14 f and the HDD may be provided separately from the ECU 14 .

[0045] The brake system 18 is, for example, an anti-lock brake system (ABS) for limiting wheel locking during braking, an electronic stability controller (ESC) for limiting the slip of the vehicle 1 when the vehicle 1 turns, an electric (power) brake system for enhancing the braking force (performing brake assist), or a brake-by-wire (BBW). The brake system 18 applies the braking force to the wheel 3, that is, to the vehicle 1, via the actuator 18a. The brake system 18 can perform various controls based on a signal that detects wheel locking, free rotation and / or slip of the wheel 3 during braking, for example, based on the rotation difference between the right wheel and the left wheel 3. The brake sensor 18b detects, for example, the position of a movable component of the brake operating part 6. The brake sensor 18b can detect the position of a brake pedal as a movable component.

[0046] The steering angle sensor 19 detects, for example, the steering amount of the steering portion 4, such as a steering wheel. The steering angle sensor 19 is configured with, for example, a Hall element. The ECU 14 acquires the steering amount of the steering portion 4 performed by the driver of the vehicle 1 and the steering amount of each of the wheels 3 at the time of automatic steering from the steering angle sensor 19 to perform various controls. The steering angle sensor 19 detects the rotation angle of a rotating member included in the steering portion 4. The steering angle sensor 19 serves as an example of an angle sensor.

[0047] The throttle sensor 20 detects, for example, the position of a movable member of the accelerator operating portion 5. The throttle sensor 20 may detect the position of an accelerator pedal as a movable member. The throttle sensor 20 includes a displacement sensor.

[0048] The drive system 21 is, for example, an internal combustion engine system (engine system) or a motor system used as a drive source. The drive system 21 controls the fuel injection amount and the intake amount of the engine, or controls the output value of the motor, based on the requested operation amount (for example, the amount of depression of the accelerator pedal) of the driver (user) detected by the accelerator sensor 20. In addition, regardless of the operation performed by the user, the output values ​​of the engine and the motor can be controlled in cooperation with the steering system 13 and the braking system 18 according to the driving condition of the vehicle 1.

[0049] The wheel speed sensor 22 is provided at the corresponding wheel 3 so that each of the wheel speed sensors 22 detects the amount of rotation of each wheel 3 per unit time and the number of rotations (rotation speed) of each wheel 3. The wheel speed sensor 22 outputs the number of wheel speed pulses indicating the detected number of rotations as a detection value. The wheel speed sensor 22 may be configured with a Hall element, for example. The CPU 14a performs various controls by calculating the vehicle speed and the amount of movement of the vehicle 1 based on the detection value of the wheel speed sensor 22. In the case of calculating the vehicle speed of the vehicle 1 based on the detection value of the wheel speed sensor 22 located at the corresponding wheel 3, the CPU 14a determines the vehicle speed based on the speed of the wheel having the smallest detection value among the four wheels among the wheels 3, and the CPU 14a performs various controls. In the case where the detection value of one of the wheels 3 is greater than the detection values ​​of the other wheels 3, that is, in the case where one of the wheels 3 indicates a rotation number greater than the other wheels 3 by a predetermined number or more within a unit time period (unit time or unit distance), the CPU 14a regards the wheel 3 as slipping (that is, in a free-spinning state) and the CPU 14a performs various controls. The wheel speed sensor 22 may be provided at the brake system 18. In this case, the CPU 14a acquires the detection result of the wheel speed sensor 22 via the brake system 18.

[0050] The shift position sensor 23 detects, for example, the position of a movable member of the shift operating portion 7. The shift position sensor 23 may detect, for example, the position of a lever, an arm, or a button as a movable member. The shift position sensor 23 may include a displacement sensor, or the shift position sensor 23 may be configured as a switch.

[0051] The configuration, arrangement and electrical connection of the above-mentioned sensors and actuators may be appropriately specified or modified, for example.

[0052] Figure 4 1 is a block diagram illustrating a configuration of a driving assistance device 28 implemented at the CPU 14a of the driving assistance system 100 according to the embodiment. The CPU 14a includes modules that are implemented as the driving assistance device 28 by, for example, reading a program (driving assistance program) installed and stored at a storage unit such as the ROM 14b and executing such a program. The driving assistance device 28 implemented at the CPU 14a includes, for example, a sound wave control unit 30, an information acquisition unit 32, a vehicle speed calculation unit 34, a threshold value determination unit 36, a determination unit 38, a distance calculation unit 40, a deceleration start position calculation unit 42, a brake control unit 44, and a warning processing unit 46.

[0053] The sound wave control unit 30 includes a transmission wave control unit 30a and a reception wave control unit 30b. In the present embodiment, in order to determine whether the road surface in the driving direction of the vehicle 1 is frozen, the following distance measurement unit 17 can be used: the sound wave (ultrasonic wave) emission direction of the distance measurement unit 17 corresponds to the driving direction of the vehicle 1. The distance measurement unit 17 originally set to detect objects around the vehicle 1 is used, for example, to determine whether the road surface in the driving direction of the vehicle 1 is frozen, so that additional functions can be realized without increasing the cost of additional components. Figure 51 is a schematic diagram illustrating a method of determining whether a road surface is frozen by means of a distance measuring unit 17 (17a to 17d) provided at a rear portion of the vehicle 1 in a state where the vehicle 1 is driven backward on a road surface 48. As mentioned above, ultrasonic sonar is used for the distance measuring unit 17. The distance measuring unit 17 includes an ultrasonic transducer. The ultrasonic control unit 30a outputs a driving signal to oscillate the ultrasonic transducer of the distance measuring unit 17 at a constant period so that an ultrasonic wave W is emitted from the oscillation surface of the distance measuring unit 17. The ultrasonic wave W propagates through a medium (the medium is air in this embodiment) while expanding in a conical manner with respect to the ultrasonic transducer serving as a sound source. The distance measuring unit 17 receives a reflected wave of the emitted ultrasonic wave W by controlling the transmission wave control unit 30a, and the reflected wave is reflected in an overlapping manner and returns from a target object 50 located around the vehicle 1. The reception wave control unit 30b acquires the overlapping signal as a reception wave signal. The ultrasonic wave W attenuates as its propagation distance increases in a case where it propagates through the air under a normal environment. Therefore, the intensity of the received wave signal acquired by the received wave control unit 30b (i.e., the signal intensity of the reflected wave) decreases as the distance from the distance measurement unit 17 to the target object 50 that is reflecting the ultrasonic wave W increases. The aforementioned normal environment corresponds to an environment in which the reflection of the ultrasonic wave W is unlikely to occur at a portion other than the target object 50, i.e., a case where, for example, the road surface 48 on which the vehicle 1 is located is a non-hard flat surface. For example, according to a paved road surface (asphalt road surface), an unpaved road surface, and a snow road surface, each road surface is used as a general road surface on which fine concave and convex surfaces are formed so as to irregularly reflect the ultrasonic wave W or absorb the ultrasonic wave W. Therefore, the ultrasonic wave W is mainly reflected from the target object 50, so that the existence and the position of the target object 50 can be detected. At this time, the ultrasonic wave W propagated from the distance measurement unit 17 is, for example, specified to be emitted in approximately parallel to the traveling direction of the vehicle 1. Therefore, it is possible to obtain measurement by the ultrasonic wave W emitted from the distance measurement unit 17 to a distance in the traveling direction of the vehicle 1. The ultrasonic wave W is, for example, suppressed from being mainly guided to the road surface 48 and excessively reflected from the road surface 48 or a small object located on the road surface 48. The road surface 48 or such small objects located on the road surface 48 are thus restricted from being erroneously detected as obstacles, for example.

[0054] In the case where the road surface 48 in the traveling direction of the vehicle 1 is frozen, the distance measuring unit 17 can receive a strong reflected wave from a position at a relatively long distance relative to the vehicle 1 (the distance measuring unit 17). For example, in the state where the road surface 48 is frozen, the fine concave and convex surfaces on the road surface 48 are covered with snow, so that the road surface 48 is closer to a smooth and hard flat surface. Therefore, the ultrasonic wave W that strikes the frozen road surface 48 advances to the traveling direction of the vehicle 1 (i.e., behind the vehicle 1) without being irregularly reflected from the road surface 48, and strikes the target object 50 located in the traveling direction of the vehicle 1 (i.e., behind the vehicle 1). That is, the direct wave emitted from the distance measuring unit 17 and the indirect wave reflected from the frozen road surface 48 are both reflected from the target object 50, and the generated waves are received by the distance measuring unit 17. On the other hand, in the case where the road surface 48 is not frozen, the ultrasonic wave W that strikes the road surface 48 is irregularly reflected from the fine concave and convex surfaces on the road surface 48, so that the indirect wave toward the target object 50 is less than the indirect wave generated in the case where the road surface 48 is frozen. Therefore, when the road surface 48 is frozen, the signal intensity of the reflected wave from a position farther away from the distance measuring unit 7 is higher than when the road surface 48 is not frozen.

[0055] In the case where the road surface 48 is frozen, the ambient temperature of the road surface 48, that is, the ambient temperature of the vehicle 1, is lower than the ambient temperature in the case where the road surface 48 is not frozen. The propagation of sound waves (ultrasonic waves W) is generally affected by the following attenuation amount during its propagation: the attenuation amount is determined according to the temperature and humidity of the medium (which is air in this embodiment). In a low temperature environment (for example, a low temperature environment equal to or less than 10°C), the lower the temperature, the smaller the attenuation amount. Therefore, for example, in an environment (low temperature environment) in the case where the road surface 48 is frozen, the ultrasonic wave W (the reflected wave of the ultrasonic wave W) reflected from a position far away from the distance measuring unit 17 propagates with less attenuation. Specifically, compared with the case where the road surface 48 is not frozen, in the case where the road surface 48 may be frozen, the distance measuring unit 17 (receiving wave control unit 30b) can obtain a reflected wave with a higher signal strength from a farther position.

[0056] It is known that from between Figure 5The signal intensity of the reflected wave near the contact position P between the road surface 48 and the target object 50 is high. This is because the overlap of the ultrasonic wave W near the contact position P is, for example, greater than the overlap of the ultrasonic wave W at other parts (positions), such as a position of the target object 50 far from the contact position P (a position far from the road surface 48). In the case where the road surface 48 is frozen, the attenuation of the ultrasonic wave W during propagation is small, so that the signal intensity of the reflected wave from the vicinity of the contact position P is increased. In addition, the overlapping effect of the ultrasonic wave W (i.e., the indirect wave) reflected from the road surface 48 near the contact position P is increased, which further increases the signal intensity of the reflected wave from the vicinity of the contact position P.

[0057] Figures 6 to 8 The following are graphs: each of the graphs illustrates the relationship between the peak value (wave height value) indicating the intensity (signal intensity) of the reflected wave and the detection distance (distance from the target object 50) (i.e., the reception tendency of the reflected wave), which is based on the signal intensity acquired by the receiving wave control unit 30b according to the condition of the road surface 48. Each calibration point in the graph indicates the signal intensity (peak value) obtained when the reflected wave of the ultrasonic wave W emitted from the distance measurement unit 17 at a given time is received. For example, the emission of the ultrasonic wave W is performed five times per second. The range in which the target object 5 can be identified in a normal environment (i.e., an environment with a non-frozen road surface) - that is, the identification range - is, for example, within a range of 3000 mm from the distance measurement unit 17. As long as the target object 50 is within the range of 3000 mm from the distance measurement unit 17, the receiving wave control unit 30b can stably acquire the reflected wave of high signal intensity (high peak value), and the receiving wave control unit 30b recognizes whether the target object 50 exists and recognizes the distance from the target object 50. Even when an object is outside the above-mentioned recognition range of the distance measurement unit 17, data indicating the existence of the object can be obtained even if the accuracy of the distance to such an object decreases.

[0058] Figure 6 The figure shows the reception trend of the reflected wave acquired by the reception wave control unit 30b when the road surface 48 is an unfrozen asphalt road surface. The ambient temperature of the vehicle 1 is, for example, 10°C, at which the road surface is suppressed from freezing. Figure 6As shown in the figure, when the vehicle 1 (distance measuring unit 17) approaches the target object 50 and the relative distance between the vehicle 1 (distance measuring unit 17) and the target object 50 is equal to or less than 3000 mm, for example, a strong reflected wave reflected from the target object 50 can be received. Therefore, a signal with high intensity (high wave peak value) can be obtained. Specifically, the receiving wave control unit 30b can obtain the following information: the information is used to determine whether the target object 50 exists based on the signal strength, and is used to calculate the current position (i.e., relative distance) of the target object 50 based on the time period from the emission to the reception of the ultrasonic wave W and the sound speed when the relative distance is measured in an environment where the road surface 48 is suppressed from freezing. A plurality of distance measuring units 17 (17a to 17d) are arranged at the rear portion of the vehicle 1, so that each of the plurality of distance measuring units 17 transmits the ultrasonic wave W to the rear area of ​​the vehicle 1 and receives the ultrasonic wave W from the rear area of ​​the vehicle 1. Therefore, the detection results of at least two distance measuring units 17 are used to obtain triangulation. The position of the target object 50 can also be safely detected.

[0059] On the other hand, in the case where the relative distance between the vehicle 1 (distance measuring unit 17) and the target object 50 exceeds the recognition range of the distance measuring unit 17, that is, much more than 3000 mm from the distance measuring unit 17, the signal intensity of the reflected wave acquired by the receiving wave control unit 30b decreases due to attenuation during the propagation of the ultrasonic wave W. That is, the receiving wave control unit 30b can obtain the reception trend of the reflected wave, and the target object 50 entering the recognition range of the distance measuring unit 17 can be recognized based on the reception trend of the reflected wave.

[0060] Figure 7 is the reception trend of the reflected wave acquired by the reception wave control unit 30b when the road surface 48 is frozen. Figure 7 In the case where the road surface 48 is covered with snow or frost, or after rain, water generated by melting snow or frost, or rain water freezes on the asphalt road surface. For example, the state of an icy road surface is also included. The ambient temperature is equal to or less than 0°C at which the road surface is frozen, for example -10°C.

[0061] As in Figure 7 As shown in FIG. 4 , even in the case of frozen road surface 48, such as when road surface 48 is Figure 6In the case where the relative distance between the vehicle 1 (distance measuring unit 17) and the target object 50 is equal to or less than 3000 mm, such as when the vehicle 1 (distance measuring unit 17) approaches the target object 50, it is possible to receive a strong reflected wave reflected from the target object 50, so that a signal with a high intensity (high wave peak value) is obtained. That is, regardless of whether the road surface 48 is frozen or not, the receiving wave control unit 30b can obtain the following information: the information is used to determine whether the target object 50 exists according to the signal strength, and is used to calculate the current position (i.e., relative distance) of the target object 50 based on the time period from the emission to the reception of the ultrasonic wave W and the sound speed when measuring the relative distance. In this case, the position of the target object 50 can also be accurately detected by means of triangulation using a plurality of distance measuring units 17 (17a to 17d).

[0062] In the case where the target object 50 exists in the traveling direction of the vehicle 1 and the road surface 48 is frozen, the reduction in the attenuation amount of the ultrasonic wave W caused by the decrease in the medium temperature occurs simultaneously with the overlap of the indirect wave reflected from the target object 50 after being reflected from the frozen road surface. Therefore, the receiving wave control unit 30b can receive a strong reflected wave from the target object 50 located at a position far from the distance measuring unit 17, and initially can obtain only a low (weak) wave peak value that is indistinguishable from the noise of the road surface 48 from the target object 50. The receiving wave control unit 30b can obtain a reception tendency of a reflected wave including a high-intensity (high wave peak value) signal. For example, as Figure 7 As shown in FIG. 1 , a reflected wave with a high peak value is obtained at an area E where the detection distance is equal to or greater than 3000 mm, and the reflected wave with a high peak value cannot be detected according to Figure 6 Obtained. That is, when the distance measuring unit 17 receives a reflected wave having a signal strength equal to or greater than a predetermined value from a predetermined distance or greater distance based on the information of the reflected wave in a state where the temperature is less than a predetermined temperature, it is determined that the road surface in the driving direction of the vehicle 1 may be frozen. In this case, the signal strength of the reflected wave increases due to the overlap of waves (direct waves and indirect waves). Therefore, the reflected wave from a farther position is used as data indicating the following information: the information is used to determine whether the target object 50 exists based on the signal strength, and is used to calculate the current position (i.e., relative distance) of the target object 50 based on the time period from the emission to the reception of the ultrasonic wave W and the speed of sound when measuring the relative distance. The position of the target object 50 can be further accurately detected on the basis of triangulation using multiple distance measuring units 17 (17a to 17d).

[0063] Figure 8It is the reception trend of the reflected wave acquired by the reception wave control unit 30b when the road surface 48 is a snowy road surface and is not frozen. The road surface μ when the vehicle 1 is being driven is different between the snowy road surface and the frozen road surface. Specifically, the braking characteristics when the vehicle is driven at a lower speed are different between the snowy road surface and the frozen road surface, and therefore the snowy road surface and the frozen road surface must be distinguished from each other. In the case of a snowy road surface, the temperature around the vehicle 1 (the ambient temperature of the vehicle 1) is lower than 0°C, for example, -10°C, so that the snowy road surface is maintained. Figure 6 and Figure 7 In the same manner, when the relative distance between the vehicle 1 (distance measuring unit 17) and the target object 50 is, for example, equal to or less than 3000 mm, for example, when the vehicle 1 is approaching the target object 50, a strong reflected wave reflected from the target object 50 can be received and a signal with a high intensity (high wave peak value) can be obtained. That is, regardless of whether the road surface 48 is frozen or not, the receiving wave control unit 30b can obtain the following information: the information is used to determine whether the target object 50 exists based on the signal strength, and is used to calculate the current position (i.e., relative distance) of the target object 50 based on the time period from the emission to the reception of the ultrasonic wave W and the sound speed when measuring the relative distance. In this case, the position of the target object 50 can be further accurately detected on the basis of triangulation using a plurality of distance measuring units 17 (17a to 17d).

[0064] When the relative distance between the vehicle 1 (distance measuring unit 17) and the target object 50 reaches or exceeds, for example, 3000 mm, which is the identification range of the distance measuring unit 17, the signal strength of the reflected wave acquired by the receiving wave control unit 30b is reduced due to the attenuation during the propagation of the ultrasonic wave W. Snow includes properties for absorbing sound wave vibrations. In addition, snow crystals tend to form fine concave and convex surfaces on the surface of snowfall. Therefore, even under low ambient temperature conditions, reflection of the ultrasonic wave W is unlikely to occur at the road surface 48, reducing the possibility of indirect waves reaching the target object 50. Therefore, in the same manner as in Figure 6 In the same manner as the non-frozen asphalt road surface shown in the middle figure, for the snow road surface, the reception trend of the reflected wave in the case where the reflected wave signal strength at a long distance is low can be obtained.

[0065] exist Figures 6 to 8 In order to more effectively determine the frozen road surface, filtering can be applied to exclude or distinguish the range where the peak value is low and therefore difficult to distinguish from the noise, so as to confirm whether the reflected wave with a signal strength equal to or greater than a predetermined value is obtained from a predetermined distance or more.

[0066] Fig. 9is a table illustrating the transmission and reception of ultrasonic waves W according to different conditions. As an example, the conditions are based on whether the road surface 48 is frozen and whether the target object 50 exists. In the case where the road surface 48 is frozen and there is no target object 50 around the vehicle 1, the ultrasonic wave W emitted from the distance measurement unit 17 is reflected from the frozen road surface, but does not return to the distance measurement unit (vehicle 1) because there is no target object 50 (that is, the receiving wave control unit 30b is suppressed from acquiring the signal of the reflected wave). This state also occurs when the road surface 48 is a snowy road surface and there is no target object 50 around the vehicle 1. In this case, because the possibility of the vehicle 1 coming into contact with an obstacle, such as the target object 50, is, for example, low (or zero), it can be considered that the determination of whether the road surface 48 is frozen in the braking control of the vehicle 1 is not necessary.

[0067] When the road surface 48 is frozen and the target object 50 is located around the vehicle 1, the ultrasonic wave W emitted from the distance measurement unit 17 is reflected from the frozen road surface and returns to the distance measurement unit (vehicle 1). Fig. 9In the case of the above, the ultrasonic wave W emitted from the distance measurement unit 17 is reflected from the target object 50, and the generated reflected wave is further reflected from the frozen road surface (road surface 48) to be returned to the distance measurement unit 17. In another example, the ultrasonic wave W emitted from the distance measurement unit 17 is reflected from the frozen road surface (road surface 48) and the generated reflected wave is further reflected from the target object 50 to be returned to the distance measurement unit 17. That is, the distance measurement unit 17 can receive a strong reflected wave obtained by overlapping, for example, a direct wave suppressed from being reflected from the frozen road surface (road surface 48) with an indirect wave reflected from the frozen road surface (road surface 48) during the transmission and reception of the ultrasonic wave W. On the other hand, for example, in the case where the road surface 48 is not frozen, that is, the road surface 48 is a snowy road surface, and the target object 50 is located around the vehicle 1, the reflected wave reflected from the target object 50 and guided to the snowy road surface (road surface 48) in the ultrasonic wave W emitted from the distance measurement unit 17 is irregularly reflected from the snowy road surface or absorbed by the snowy road surface, and is therefore difficult to be returned to the distance measurement unit 17 (vehicle 1). In addition, even if a part of the ultrasonic wave W emitted from the distance measuring unit 17 is guided to the snow road surface (road surface 48), the above-mentioned part of the ultrasonic wave W is mainly irregularly reflected from the snow road surface or absorbed at the snow road surface, so that the indirect wave toward the target object 50 is extremely small. Therefore, the distance measuring unit 17 mainly receives the direct wave that is not reflected from the snow road surface. Compared with the frozen road surface, the signal intensity of the reflected wave is correspondingly reduced. The snow road surface includes a road friction coefficient that is lower than the road friction coefficient of the dry road surface, so that it is necessary to consider braking on the snow road surface. Whether the road surface 48 is a snow road surface or a dry road surface can be determined by, for example, performing image processing on the captured image data obtained by the imaging unit 15. In the case of a snow road surface, braking control can be performed, with the result that the determination process is different from the determination process performed on the frozen road surface according to the embodiment.

[0068] In the case of a non-frozen road surface with rainfall, the concave and convex surfaces on the asphalt road surface are suppressed from being covered by rainfall. Therefore, the ultrasonic wave W is irregularly reflected from the road surface, which causes Figure 6 In the case of an unpaved road, the ultrasonic wave W is also irregularly reflected from the road surface via the concave and convex surfaces on the road surface, which results in the same Figure 6 Even in this case, as long as the target object 50 is not located in the traveling direction of the vehicle 1, the received wave control unit 30b is suppressed from receiving a significant reflected wave.

[0069] As in Figure 4As shown in the figure, the information acquisition unit 32 acquires the ambient temperature information of the vehicle 1. For example, the information acquisition unit 32 acquires information from a temperature sensor for measuring the external temperature provided at the air conditioning device of the measuring vehicle 1, or acquires information from a temperature sensor (a sensor for correcting the speed of sound based on the temperature) provided at the distance measuring unit 16 or 17. In another embodiment, the external information center provides temperature information at the location where the vehicle 1 is located, for example, by means of a communication device, such as a network and a telephone line. The method for acquiring temperature information is not limited to the above. As long as the ambient temperature information of the vehicle 1 can be acquired, any method can be appropriately adopted. A dedicated temperature sensor for determining a frozen road surface can also be provided. In the case where the external temperature and the road surface temperature are different from each other, the road surface temperature can be estimated based on the acquired external temperature and past data, so that the estimated road surface temperature can be used as a determination condition (i.e., temperature threshold A) for determining whether the road surface is frozen, which can help to further accurately determine.

[0070] The vehicle speed calculation unit 34 calculates the vehicle speed of the vehicle 1 based on the detection result output from each of the wheel speed sensors 22. The threshold determination unit 36 ​​determines the following determination threshold (this determination threshold D will be explained later): This determination threshold is used to determine whether the road surface 48 is frozen on the basis of the vehicle speed of the vehicle 1 calculated by the vehicle speed calculation unit 34. The determination threshold can be experimentally determined in advance and stored in the ROM 14b, for example. The determination unit 38 determines whether the road surface 48 is frozen, for example, by referring to the reception trend of the reflected wave acquired by the receiving wave control unit 30b. As mentioned above, in the case where the road surface 48 is frozen, a signal with high intensity can be detected in the area E (see Figure 7 ) is received multiple times, wherein the detection distance is far from the distance measurement unit 17, and the area E is the same as the area E of the non-frozen road surface (see Figure 6 ) is located outside the recognition range of the distance measuring unit 17. That is, a plurality of peak values ​​of the reflected wave are calibrated at the area E. The determination unit 38, for example, compares the number of calibration points at the area E with the determination threshold (determination calibration point number) determined by the threshold determination unit 36. Then, in the case where the number of calibration points is greater than the determination threshold, that is, the frequency of the reflected wave having a received signal strength greater than a predetermined value is greater than a predetermined number of times, the determination unit 38 determines that the road surface in the traveling direction of the vehicle 1 is frozen.

[0071] In the case where the vehicle 1 is driven to move toward the target object 50, among the ultrasonic waves W emitted from the transmission wave control unit 30a at a predetermined time period, the number of reflected waves of the ultrasonic waves W reflected from the target object 50 received per unit time period changes according to the vehicle speed of the vehicle 1. For example, as in Fig.10As shown in the figure, the faster the speed, the Figure 6 and Figure 8 The smaller the number of reflected waves that can be received per unit time period (e.g., one second), the smaller the number of calibrated measurement points. Therefore, the relationship between the vehicle speed (e.g., vehicle speed based on kilometers) of the vehicle 1 on the frozen road surface and the number of receivable reflected waves (number of calibration points) is obtained in advance. When the vehicle speed is 5 km / h and the number of reflected waves received at the area E at this time is equal to or greater than five, the determination unit 38 determines that the road surface 48 is frozen. In this case, the threshold determination unit 36 ​​determines that the threshold value of the vehicle speed of 5 km / h is "5".

[0072] The distance calculation unit 40 calculates the distance from the distance measurement unit 17 (vehicle 1) to the target object 50 based on the time period from the transmission of the ultrasonic wave W by the distance measurement unit 17 to the reception of the ultrasonic wave by the distance measurement unit 17 after the transmitted ultrasonic wave W is reflected from the target object 50 and the sound speed at the time of the transmission and reception of the ultrasonic wave W (i.e., the sound speed depending on the temperature). As mentioned above, a plurality of (for example, four) distance measurement units 17 (17a to 17d) are provided at the rear end portion 2e of the vehicle 1. Each of the distance measurement units 17a to 17d is capable of transmitting the ultrasonic wave W and is capable of receiving the reflected wave of the ultrasonic wave W with respect to the target object 50 located in the rear of the vehicle 1. In this case, according to the position where the distance measurement unit 17 is arranged, the angle facing the same target object 50 is different in the plurality of distance measurement units 17, which results in different paths between the transmitted wave and the received wave among the plurality of distance measurement units 17. Therefore, the distance calculation unit 40 can use the results of the transmitted wave and the received wave of any two distance measurement units 17 to perform triangulation, which results in further accurate calculation.

[0073] In the case where the road surface 48 is determined to be a non-frozen road surface based on the determination result of the determination unit 38, the deceleration start position calculation unit 42 calculates the required braking distance of the non-frozen road surface under the condition that the vehicle 1 brakes on the non-frozen road surface at the current vehicle speed. In the same way, in the case where the road surface 48 is determined to be a frozen road surface based on the determination result of the determination unit 38, the deceleration start position calculation unit 42 calculates the required braking distance of the frozen road surface under the condition that the vehicle 1 brakes on the frozen road surface at the current vehicle speed. The deceleration start position calculation unit 42 calculates the following deceleration start position: braking (deceleration) should be started at this deceleration start position in order to stop the vehicle 1 without contacting the target object 50 by referring to the distance to the target object 50 calculated by the distance calculation unit 40. Each of the required braking distance of the non-frozen road surface and the required braking distance of the frozen road surface can be experimentally determined in advance according to the vehicle speed and stored in a storage unit such as the ROM 14b as a map, for example. The required braking distance of the non-frozen road surface can be further accurately specified according to climatic conditions, such as a dry road surface, a road surface with rain, and a road surface with snowfall, for example.

[0074] In the case where the rear end portion 2e of the vehicle 1 is considered to have reached the deceleration start position calculated by the deceleration start position calculation unit 42, the brake control unit 44 controls the brake system 18 so that a braking force based on the condition of the road surface 48 is automatically generated. For example, in the case where the road surface 48 is determined to be a frozen road surface, the brake control unit 44 serving as a control unit performs braking control from a second braking distance that is longer than a first braking distance with respect to a non-frozen road surface of the vehicle 1, so that contact between the vehicle 1 and the target object 50 can be avoided.

[0075] In the case where the determination unit 38 determines that the road surface 48 is frozen, the warning processing unit 46 performs warning processing, for example, by means of a warning message, such as "Caution, the road surface is frozen", a warning sound, and a warning light. The warning message and the warning light may be displayed, for example, on the display device 8 or the display device 12. The warning sound may be output, for example, via the audio output device 9. The warning processing unit 46 may output information or sound, for example, according to the proximity to the target object 50. In the case where the road surface 48 is not frozen, the warning related to the road surface condition may be omitted, so that only the approach warning to the target object 50 may be output.

[0076] Reference FIG. 11A to FIG. 11BThe flowchart in explains the operation of the driving assist device 28 including the aforementioned configuration. When the power supply of the vehicle 1 is turned on, each of the distance measuring units 17 is configured to constantly transmit ultrasonic waves W and receive reflected waves of the ultrasonic waves W, so as to detect (measure) whether the target object 50 is located around the vehicle 1 and detect (measure) the distance to the target object 50. The driving assist device 28 is operated to perform a determination whether the road surface 48 is frozen. The driving assist device 28 performs automatic braking control so as not to make contact with the target object 50.

[0077] First, the driving assistance device 28 continuously confirms whether the user makes a request for driving assistance start, for example, by means of the operation input part 10 (S100). In the case where no request is made (No in S100), the current operation is terminated. On the other hand, in the case where the user makes a request for driving assistance start, for example, by operating the operation input part 10 (Yes in S100), the determination unit 38 determines whether the reflected wave acquired by the receiving wave control unit 30b indicates that the road surface 48 is frozen based on a plurality of conditions (for example, the first condition to the fourth condition). In the case where the number of reflected wave data satisfying the above corresponding conditions is equal to or greater than a predetermined threshold value (fifth condition), the road surface 48 is determined to be a frozen road surface. In order to determine whether the road surface 48 is frozen, the determination unit 38, for example, first initializes the freezing determination counter value temporarily stored in the storage unit, such as the RAM 14c (S102). The driving assistance device 28 then determines whether the avoidance operation is being performed by the driver's operation on the brake operation part 6 (brake pedal) or by automatic braking performed by the brake system 18 itself by referring to the control state of the brake system 18 (S104). In a case where the avoidance operation is not performed (No in S104 ), the information acquisition unit 32 acquires the ambient temperature of the vehicle 1 from, for example, a temperature sensor provided at the air conditioning device or the distance measurement unit 17 ( S106 ).

[0078] In the case where the ambient temperature is lower than the temperature threshold A (e.g., 0° C.) serving as the first condition (Yes in S108), the determination unit 38 determines whether the signal intensity of the reflected wave of the ultrasonic wave W acquired by the received wave control unit 30 b is equal to or greater than a predetermined value (wave height threshold B) serving as the second condition (S110). Specifically, in the case where the ambient temperature is lower than 0° C., it is determined that the data of the reflected (received) wave (e.g., Figure 7The calibration point in the distance measurement unit 17 indicates that the road surface 48 is frozen and the first condition is considered to be satisfied. In the case where the peak value of the reflected wave obtained is equal to or greater than the wave height threshold value B (i.e., a strong reflected wave is returned), it is considered that the indirect wave reflected from the frozen road surface overlaps with the direct wave to obtain data of the strong reflected wave (calibration point). It is then determined that the reflected wave may indicate that the road surface 48 is frozen and the second condition is considered to be satisfied. The reflected wave attenuates as its propagation distance increases. That is, even for the reflected wave indicating the possibility of freezing, the peak value of the reflected wave reflected from a position farther from the distance measurement unit 17 is lower than the peak value of the reflected wave reflected from a position closer to the distance measurement unit 17. As mentioned above, the distance from the target object 50 used as the cause of the reflection is calculated based on the emission and reception time of the ultrasonic wave W and the speed of sound at the current temperature. Therefore, the wave height threshold value B used as the second condition can be changed according to the position of the target object 50 (i.e., the object as the cause of the reflection of the ultrasonic wave W). In this case, the relationship between the distance from the target object 50 on the frozen road surface and the wave peak value can be prepared in advance as a graph and stored at the ROM 14b, for example. The wave height threshold value B depending on the distance from the target object 50 can then be read at the determination in S110. In this case, even when the reflected wave (i.e., the wave peak value) from the target object 50 located at a distance of 6000 mm from the vehicle 1 is low, such a reflected wave can be determined as data indicating that the road surface 48 is frozen, which can contribute to the improvement of the determination accuracy.

[0079] In the case where the wave peak value is equal to or greater than the wave height threshold value B (Yes in S110), the determination unit 38 then compares the distance from the target object 50 with the distance threshold value C used as the third condition (S112). As mentioned above, when the distance from the distance measurement unit 17 to the target object 50 is short, a strong reflected wave equal to or greater than a predetermined value is returned regardless of whether the road surface 48 is frozen. In addition, in the case where the driving assistance device 28 according to the embodiment performs braking control for parking while performing backward driving at a low speed (e.g., 10 km / h or lower), the driving assistance device 28 is configured to pre-determine (detect) that the road surface 48 is frozen so as to start the braking operation (contact avoidance operation) in advance by foreseeing an increase in the braking distance on the frozen road surface. The reflected wave from a point at a predetermined distance or more away from the distance measurement unit 17 should therefore be used as data for frozen road surface determination. Therefore, the distance threshold value C is specified as 3000 mm as the third condition, for example, by referring to the required braking distance at a low speed when driving backward on a frozen road surface. In the case where the distance to the target object 50 is equal to or greater than the distance threshold value C (3000 mm) (Yes in S112), the determination unit 38 acquires the current speed of the vehicle 1 based on the detection value of each wheel speed sensor in the wheel speed sensor 22 (S114). The determination unit 38 determines whether the vehicle 1 is approaching the target object 50 by using the acquired vehicle speed as the fourth condition (S116). That is, in the case where the vehicle 1 is moving away from the target object 50, that is, the vehicle 1 is being driven forward, it is not necessary to perform a contact avoidance operation with respect to the target object 50. Therefore, the necessity of determining the road surface condition at the rear of the vehicle 1 is small. Whether the vehicle 1 is approaching the target object 50 or is moving away from the target object 50 can be determined, for example, on the basis of a comparison between the approaching speed of the target object 50 to the vehicle 1 and the speed of the vehicle 1 (own vehicle speed). In the case where the approaching speed is equal to or greater than the own vehicle speed (Yes in S116), it can be determined that the vehicle 1 is approaching the target object 50. That is, it can be determined that, in the case where the current temperature is less than the predetermined temperature (temperature threshold A), the reflected wave data includes a signal strength equal to or greater than a predetermined value (wave height threshold B) from a predetermined distance (distance threshold C) or a greater distance. In this case, the determination unit 38 determines that the reflected wave data acquired by the receiving wave control unit 30b indicates that the road surface 48 is frozen and updates the counter value for freezing determination (freezing determination counter value) by adding one (+1) (S118). On the other hand, in the case where the above-mentioned approach speed is lower than the own vehicle speed (No in S116), that is, the vehicle 1 is moving away from the target object 50, it is determined that the detection of the frozen road surface at the rear of the vehicle 1 is not necessary, and then the freezing determination counter value is initialized (S120).

[0080] Next, the determination unit 38 confirms whether a predetermined period of time has passed after the initialization of the freeze determination counter value (S122). Figure 7 As explained, in the case where a reflected wave having a signal strength equal to or greater than a predetermined value at a predetermined distance or greater is acquired a predetermined number of times, for example, in a state where the current temperature is lower than a predetermined temperature, the road surface 48 in the traveling direction of the vehicle 1 is determined to be frozen. Therefore, regardless of whether the reflected wave can be actually received, it is necessary to collect the reflected wave for a period of time. In the case where the predetermined period of time has not passed since the initialization of the freeze determination counter value (No in S122), the operation returns to S104, and the determination unit 38 determines whether the reflected wave data acquired by the received wave control unit 30b indicates that the road surface 48 is frozen, so as to repeat the process of updating or initializing the freeze determination counter value.

[0081] The distance from the target object 50 less than the distance threshold C (No in S112) corresponds to the acquired reflected wave data based on the reflected wave from the distance closer to the distance measuring unit 17. In this case, even in the case where the peak value is equal to or greater than the wave height threshold B and thus a strong reflected wave is acquired, it is impossible to distinguish whether such a strong reflected wave is caused by reflection from a frozen road surface. Therefore, the determination unit 38 is suppressed from performing the processing related to the freezing determination counter value, and the determination unit 38 stores the reflected wave data at the RAM 14c so that the operation moves to S122. In this case, the acquired reflected wave is used as an indication of the distance from the target object 50, for example. The peak value less than the wave height threshold B (No in S110) corresponds to a lower (weaker) reflected wave. In this case, even when the ambient temperature is less than the temperature threshold A, the road surface 48 is unlikely to be frozen, that is, the road surface 48 may be, for example, a snowy road surface. Therefore, the determination unit 38 is suppressed from performing the processing related to the freezing determination counter value, and the determination unit 38 stores the reflected wave data at the RAM 14c so that the operation moves to S122. In this case, the acquired reflected wave is used, for example, as an indication of the distance to the target object 50. In addition, in the case where the ambient temperature is equal to or greater than the temperature threshold value A in S108, it is unlikely that the road surface 48 is highly frozen. Therefore, in this case, the determination unit 38 is suppressed from performing the processing related to the freeze determination counter value, and the determination unit 38 stores the reflected wave data at the RAM 14c so as to move the operation to S122. In this case, the acquired reflected wave is also used, for example, as an indication of the distance to the target object 50. In the case where the vehicle 1 is currently performing the avoidance operation (Yes in S104), it is determined that Yes is that the necessity of specifying the condition of the road surface 48 is low. The determination unit 38 initializes the freeze determination counter value (S124) so ​​as to move the operation to S122. In this case, the acquired reflected wave is also used, for example, as an indication of the distance to the target object 50.

[0082] When a predetermined period of time has passed since the freezing determination counter value was initialized (Yes in S122), that is, the reflected wave collection for a specific period of time has been completed, a determination threshold D considered to be used for determining whether the road surface 48 is frozen is determined (S126). The determination threshold D can be determined by referring to Fig.10 The graph in is determined based on the vehicle speed of the vehicle 1 obtained in S114, because the number of reflected wave data that can be acquired changes according to the current speed of the vehicle. The determination unit 38 compares the freeze determination counter value updated in S118 with the determination threshold value D determined in S126 (S128). For example, in the case where the freeze determination counter value is equal to or greater than the determination threshold value D (Yes in S128), that is, when the calibration point equal to or greater than the determination threshold value D exists as in Figure 7 In the case where the freezing determination counter value is less than the determination threshold value D (No in S128), that is, the calibration point equal to or greater than the determination threshold value D does not exist as in Figure 6 In the case of the region E shown in FIG. 1 , the determination unit 38 determines that the road surface 48 is not frozen ( S134 ).

[0083] In the case where the road surface 48 is determined to be frozen (Yes in S136), the deceleration start position calculation unit 42 extends the braking distance (S138). For example, the deceleration start position calculation unit 42 extends the required braking distance for a non-frozen road surface at the same vehicle speed by 1.5 times the required braking distance for a frozen road surface. In the case where the road surface 48 is frozen, the deceleration start position calculation unit 42 calculates the deceleration start position (S140) that can avoid contact with the target object 50 and enable the vehicle to stop smoothly by referring to the current speed of the vehicle 1. In the case where the road surface 48 is determined to be non-frozen (No in S136), the operation in S138 is skipped, and the deceleration start position is calculated by using the braking distance when on a non-frozen road surface, that is, the normal braking distance in S140.

[0084] In the case where the current position of the vehicle 1 relative to the target object 50 reaches the deceleration start position calculated by the deceleration start position calculation unit 43 by referring to the distance to the target object 50 calculated by the distance calculation unit 40 (Yes in S142), the brake control unit 44 starts braking control (S144). For example, automatic braking is started by the brake system 18. In the case where the current position of the vehicle 1 relative to the target object 50 does not reach the deceleration start position, the operation is switched to S104 to repeatedly perform the processing related to obtaining the reflected wave and the processing related to the freezing determination counter value, so as to repeatedly perform the determination whether the road surface 48 is frozen.

[0085] According to the driving assistance device 28 of the present embodiment, the distance measurement unit 17 that detects whether the target object 50 exists and detects the distance to the target object 50 is also used to acquire (or estimate) whether the road surface 48 in the traveling direction of the vehicle 1 is frozen. Therefore, in the case where the road surface 48 in the traveling direction of the vehicle 1 is frozen, the deceleration start position is changed to a closer side portion specified in the case where the road surface 48 is not frozen by taking into account the slip on the frozen road surface, so that contact with the target object 50 can be safely avoided. In addition, the braking operation is also performed in advance, which can achieve smooth deceleration and stopping of the vehicle 1.

[0086] In the above-mentioned embodiment, whether the road surface 48 in the traveling direction of the vehicle 1 is frozen is determined in a state where the vehicle 1 is being driven backward at a relatively low speed. In another embodiment, whether the road surface 48 in the traveling direction of the vehicle 1 is frozen can be determined in a state where the vehicle 1 is being driven forward, which leads to the same or substantially the same effect. In this case, the distance measuring units 17e to 17h provided at the front portion of the vehicle 1 are utilized. Whether to determine whether the road surface 48 is frozen using the distance measuring units 17a to 17dh provided at the rear portion of the vehicle 1 or using the distance measuring units 17e to 17h provided at the front portion of the vehicle 1 can be determined by obtaining whether the vehicle 1 is being driven forward or backward through the gear position sensor 23 based on the position of the shift operation portion 7 (i.e., the reverse gear position or the forward gear position) obtained from the gear position sensor 23 when the driving assist device 28 obtains the driving assist start request.

[0087] In the above embodiment, in the case where the road surface 48 in the traveling direction of the vehicle 1 is determined to be frozen, the braking distance is extended so that the vehicle 1 brakes without coming into contact with the target object 50. In another embodiment, although the braking control is actually being performed due to the determination of a frozen road surface, the road surface μ can be acquired by the existing technology to adjust the braking force. In this case, further smooth braking can be achieved.

[0088] In the present embodiment, ultrasonic waves are used to determine whether the road surface 48 in the traveling direction of the vehicle 1 is frozen. Alternatively, audible sound may be used, which may lead to the same or substantially the same effect. In the present embodiment, where sound waves (such as ultrasonic waves) are used to determine whether the road surface 48 in the traveling direction of the vehicle 1 is frozen, the determination is suppressed from being affected by the brightness around the vehicle 1. Therefore, determination of whether the road surface is frozen, for example, at night or at a tunnel, can be performed with high accuracy, compared to determination based on a screen image, for example.

[0089] The driving assistance program executed by the CPU 14a according to the present embodiment can be set as a file that can be installed or executed and stored in a recording medium that can be read by a computer, such as a CD-ROM, a floppy disk (FD), a CD-R, and a digital versatile disk (DVD).

[0090] The driving assistance program may also be provided, for example, in the following manner: stored on a computer connected to a network such as the Internet, and downloaded via the network. In addition, the driving assistance program executed in the present embodiment may be provided or distributed, for example, via a network such as the Internet.

[0091] The embodiments are not limited to the above-described configurations and the embodiments may be changed or modified as appropriate.

Claims

1. A driving assistance device (28), comprising: A sound wave control unit (30), the sound wave control unit (30) acquiring information of reflected waves from a distance measurement unit (17), the distance measurement unit (17) emitting a sound wave (W) in the direction of travel of the vehicle (1) and receiving a reflected wave of the sound wave (W) reflected from an object; An information acquisition unit (32), wherein the information acquisition unit (32) acquires temperature information around the vehicle (1); as well as A determination unit (38) determines that the road surface (48) in the driving direction of the vehicle (1) is a frozen road surface by determining, based on the information of the reflected wave, that the distance measuring unit (17) receives a reflected wave including a signal strength equal to or greater than a predetermined value from a predetermined distance or greater, when the temperature based on the temperature information is less than a predetermined temperature.

2. The driving assistance device (28) according to claim 1, wherein: The determination unit (38) includes a determination threshold (D) for determining that the road surface (48) in the driving direction of the vehicle (1) is a frozen road surface when the frequency of receiving the reflected wave including the signal strength equal to or greater than the predetermined value is equal to or greater than a predetermined number of times.

3. The driving assistance device according to claim 2, wherein: The determination threshold value (D) is changed according to the speed of the vehicle (1) when the determination unit (38) performs determination.

4. The driving assistance device (28) according to claim 1, wherein: The determination unit (38) determines whether the road surface (48) in the traveling direction of the vehicle (1) is a frozen road surface based on a graph indicating a relationship between a predetermined distance from the vehicle (1) on the frozen road surface and a peak value indicating the signal strength of the reflected wave.

5. The driving assistance device (28) according to any one of claims 1 to 4, further comprising a control unit (44), which, when a road surface (48) in the driving direction of the vehicle (1) is a frozen road surface, starts to perform braking control at a position having a second braking distance longer than a first braking distance prescribed for a non-frozen road surface, so as to avoid contact between the vehicle (1) that is traveling toward an object located in the driving direction of the vehicle (1) and the object.

6. The driving assistance device (28) according to claim 5, wherein: The braking control is performed based on a required braking distance determined in advance according to the vehicle speed of the vehicle (1).

7. The driving assistance device (28) according to any one of claims 1 to 4, wherein: The sound wave control unit (30) acquires information of the reflected wave from the distance measurement unit (17) provided at the vehicle (1), and the distance measurement unit (17) is configured to emit a sound wave (W) parallel to the travel direction of the vehicle (1).

8. The driving assistance device (28) according to any one of claims 1 to 4, further comprising a warning processing unit (46) which performs warning processing when the road surface (48) in the driving direction of the vehicle (1) is determined to be a frozen road surface.

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