PREVIEW ROAD SURFACE DETECTOR, AND PREVIEW ROAD SURFACE DETECTION METHOD

A preview road surface detector is provided, which is capable of suppressing the crosstalk of received detection waves. A preview road surface detector, including: a distance sensor including a plurality of transmitters and at least one receiver installed on a vehicle body member and arranged in a direction intersecting a travel direction of a vehicle, the distance sensor detecting a value related to a distance between the vehicle body member and a measurement point on a road surface ahead of a vehicle, the measurement point corresponding to at least part of a road surface contact portion of a wheel; and a distance calculator that calculates a road surface distance as the distance from the vehicle body member to the measurement point, based on a detection value detected by the distance sensor, in which the transmitters transmit detection waves with a time difference between the adjacent transmitters.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese Patent Application No. 2022-153787 filed on Sep. 27, 2022. The entire contents of this application are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a preview road surface detector, and a preview road surface detection method.

Related Art

Recently, efforts to provide access to sustainable transport systems that also consider vulnerable participants in traffic, such as the elderly, people with disabilities, and children, have been intensified. In pursuit of this goal, research and development have been focusing on further improvement of traffic safety and convenience through development related to vehicle behavior stability.

In order to improve vehicle behavior stability, conventional active suspensions for vehicles such as automobiles are known, and one of such active suspensions includes: a road surface detector that detects road surface displacement ahead using an optical sensor; a vehicle speed detector that detects the speed of the vehicle; a vertical acceleration detector installed on the vehicle body at a position corresponding to the front wheels, the vertical acceleration detector detecting vertical acceleration of the vehicle body; and a storage that stores information on road surface displacement and vertical acceleration in a time series, in which, when it is determined that the detected road surface displacement is abnormal, vertical acceleration of a portion corresponding to the rear wheels of the vehicle body at the time of the vehicle having travelled a distance equivalent to the wheelbase is estimated from the vertical acceleration stored in the storage, based on the wheelbase and the vehicle speed, and then the actuator of the rear wheels is predictively controlled in accordance with the estimated vertical acceleration (refer to Patent Document 1).Patent Document 1: Japanese Unexamined Patent Application, Publication No. H05-96922

SUMMARY OF THE INVENTION

However, the problem with conventional technologies is the potential for crosstalk of laser waves or the like transmitted from a plurality of road surface sensors, and there is a need to more accurately recognize road surface conditions. Therefore, the present invention aims to solve the above-mentioned problems by providing a preview road surface detector that is capable of suppressing the crosstalk of received detection waves transmitted from a plurality of transmitters. Further, the present invention contributes to the energy efficiency.

(1) In order to solve the aforementioned problems, a preview road surface detector of the present invention includes: a distance sensor including a plurality of transmitters and at least one receiver installed on a vehicle body member and arranged in a direction intersecting a travel direction of a vehicle, the distance sensor detecting a value related to a distance between the vehicle body member and a measurement point on a road surface ahead of the vehicle, the measurement point corresponding to at least part of a road surface contact portion of a wheel; and a distance calculator that calculates a road surface distance as the distance from the vehicle body member to the measurement point, based on a detection value detected by the distance sensor, in which the transmitters transmit detection waves with a time difference between the adjacent transmitters.

With the preview road surface detector as such, a preview road surface detector capable of suppressing the crosstalk of received detection waves transmitted from a plurality of transmitters can be provided.

(2) In the preview road surface detector of the present invention, the detection waves are transmitted from the transmitters towards the road surface, and the detection waves are laser waves or millimeter waves.

With the preview road surface detector as such, accurate calculation of road surface distances becomes easier.

(3) In the preview road surface detector of the present invention, when at least one of the plurality of transmitters is a first transmitter, the first transmitter further includes a second transmitter arranged ahead or behind the first transmitter in the travel direction of the vehicle, and the first transmitter and the second transmitter transmit detection waves with a time difference.

With the preview road surface detector as such, when the amount of movement of the vehicle body in the pitch direction is estimated based on the detection values detected by the first and second transmitters, the crosstalk of transmitted detection waves can be suppressed. Crosstalk which may occur between detection waves originating from different positions in the front and rear of the vehicle can significantly impact malfunctions. Occurrence of such significant malfunctions can be suppressed.

(4) In the preview road surface detector of the present invention, one or more of the at least one receiver is arranged at an end in a vehicle width direction, and the transmitters are installed such that transmission directions thereof tilt towards the side of one or more of the at least one receiver.

With the preview road surface detector as such, the reception sensitivity in the case of receiving with fewer receivers can be enhanced, while suppressing the crosstalk of detection waves transmitted from transmitters with a small time difference in transmission, in particular, simultaneously transmitted detection waves.

(5) In the preview road surface detector of the present invention, the plurality of transmitters are divided into a plurality of groups, and the plurality of transmitters in each group simultaneously transmit detection waves.

With the preview road surface detector as such, the total transmission frequency per unit time across the plurality of transmitters can be increased, as compared to the situation where there is only one transmitter capable of simultaneous transmission.

(6) In the preview road surface detector of the present invention, the at least one receiver includes a plurality of receivers, and transmission directions of the plurality of transmitters that simultaneously transmit the detection waves tilt towards the sides of different receivers among the plurality of receivers.

With the preview road surface detector as such, the reception sensitivity in the case of receiving with fewer receivers can be enhanced, while suppressing the crosstalk of detection waves transmitted from transmitters with a small time difference, in particular, simultaneously transmitted detection waves.

(7) In order to solve the aforementioned problems, a preview road surface detection method of the present invention includes: a distance detecting step of detecting a value related to a distance between a vehicle body member and a measurement point on a road surface ahead of a vehicle, the measurement point corresponding to at least a central portion of a road surface contact portion of a wheel, the distance detected by way of a plurality of transmitters and at least one receiver installed on the vehicle body member and arranged in a direction intersecting a travel direction of the vehicle; and a distance calculating step of calculating a road surface distance, which is the distance from the vehicle body member to the measurement point, based on a detection value detected in the distance detecting step, in which in the distance detecting step, the transmitters transmit detection waves with a time difference between the adjacent transmitters.

With the preview road surface detection method as such, a preview road surface detection method can be provided, which is capable of suppressing the crosstalk of received detection waves transmitted from the plurality of transmitters.

Note that the above-described (1) to (7) can be arbitrarily combined as needed.

According to the present invention, a preview road surface detector can be provided, which is capable of suppressing the crosstalk of received detection waves transmitted from a plurality of transmitters.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described with reference to the accompanying drawings.FIG.1is a diagram illustrating an overview of a suspension system3of a vehicle to which a preview road surface detector1of the present embodiment is applied.

The suspension system3includes the preview road surface detector1, a preview control unit4, a suspension control unit5, a vehicle body member30, an active suspension D, and wheels W. Further, the preview road surface detector1is provided with a distance calculator12and a distance sensor11. The distance sensor11is provided with a transmitter11aor the like, and a receiver14. Note that the transmitter11aor the like, and the receiver14, are not illustrated inFIG.1, and are sequentially illustrated fromFIG.3onwards.

In the suspension system3, the suspension control unit5controls the active suspension D to stabilize the posture of the vehicle body member30. This control is performed based on, for example, the Skyhook theory.

When controlling the active suspension D, first, the preview road surface detector1acquires a road surface displacement L2ahead of the vehicle. Here, the road surface displacement L2refers to a distance between the road surface R currently in contact with the wheel W and the measurement point P, in the direction vertical to the road surface R. Note that the road surface R refers to the ground in contact with the wheel W. The measurement point P refers to a point on the ground where the distance sensor11measures the distance. The measurement point P is also a point on the road surface R that the wheel W is expected to overpass. The road surface displacement L2is also referred to as predictive information.

Next, the preview control unit4acquires the road surface displacement L2from the preview road surface detector1. Then, based on the value of the road surface displacement L2, the response delay of the active suspension D is compensated. In this manner, the suspension system3aims to improve the ride comfort of the vehicle.

Referring also toFIG.2, the suspension system3is described more specifically.FIG.2is a side view of the vehicle V, illustrating the installation mechanism of the distance sensor11. The vehicle V is provided with a vehicle body B and wheels W. The members constituting the vehicle body B include the vehicle body member30. Wheels W are provided on the lower side of the vehicle body member30.FIG.2illustrates a front wheel of the wheels W. The front wheels include a left-side wheel and a right-side wheel.FIG.2illustrates the left-side wheel among the left and right wheels.

The active suspension D, as well as the tire portion of the wheels W, absorbs unevenness of the road surface R. The suspension control unit5, as illustrated inFIG.1, controls the tire portion of the wheels W, as a vibration model. This vibration model is a parallel arrangement of a spring W1and a damper W2.

The active suspension D can control the damping force using a suspension spring D1and a hydraulic actuator. Alternatively, the active suspension D can be configured with the suspension spring D1and a variable damper D2arranged in parallel. The variable damper D2is a damper that controls the damping force and the thrust by way of an electromagnetic force. The active suspension D is provided between the vehicle body member30and the wheel W.

The suspension control unit5controls the variable damper D2as the control target.

Note that the active suspension D may be provided with an actuator. By the operation of the actuator, the preview control of the suspension can be carried out more smoothly. If an actuator is provided, it is preferable to have an actuator control unit for controlling the actuator. The actuator control unit can, for example, be provided as part of the suspension control unit5.

The preview road surface detector1is installed on the vehicle body member30. The preview road surface detector1is provided with a distance sensor11and a distance calculator12.

The distance sensor11measures a distance between the vehicle body member30and the measurement point P on the road surface R. The distance between the vehicle body member30and the measurement point P on the road surface R is referred to as a road surface distance L1. This measurement is performed using a technique such as ultrasound, laser light, or millimeter-wave radar.

The distance calculator12calculates the road surface displacement L2ahead of the wheel W, based on the measurement values of the distance sensor11. Specifically, the preview road surface detector1calculates the road surface displacement L2ahead of the wheel W by subtracting a vehicle height L3measured at the time from the road surface distance L1calculated by the distance calculator12. The vehicle height L3is a distance between the vehicle body member30and the road surface R at the road surface contact portion41.

In other words, ROAD SURFACE DISTANCE L1−VEHICLE HEIGHT L3=ROAD SURFACE DISPLACEMENT L2. Note that when calculating the road surface displacement L2, the vehicle height L3can also be obtained by referencing a value calculated by the suspension control unit5as a control variable.

(Time Required to Arrive)

The preview control unit4calculates the time required for the wheel W to arrive at the measurement point P in the road surface displacement L2, based on the vehicle speed at the time of measuring the road surface displacement L2and the distance from the tire contact point to the measurement point P in the road surface displacement L2in the travel direction of the vehicle V. This time required is referred to as “time required to arrive”. Note that the distance from the tire contact point to the measurement point P in the road surface displacement L2in the travel direction of the vehicle V can also be obtained by referencing information on the installation position of the distance sensor11.

The preview road surface detector1and the preview control unit4can periodically perform the aforementioned process for obtaining the road surface displacement L2. In this manner, predictive information on the road surface displacement L2can be obtained. Predictive information refers to information on the road surface condition ahead of the wheel W, which will be overpassed after a predetermined time, as described earlier. The road surface condition includes factors such as the road surface displacement L2and the unevenness of the road surface R.

The suspension control unit5controls the active suspension D, based on the predictive information on the road surface displacement L2. Therefore, the suspension control unit5can improve the ride comfort of the vehicle V.

(Installation of Preview Road Surface Detector)

The preview road surface detector1of the present embodiment includes the distance sensor11and the distance calculator12, as described above. Among these, the distance sensor11is installed on the vehicle body member30. On the other hand, the distance calculator12is implemented in the Electronic Control Unit (ECU) of the vehicle V.

(Installation of Distance Sensor)

Installation of the distance sensor11will be specifically described based onFIG.2. Note that an installation structure of the distance sensor11, as well as other structures of the vehicle V illustrated inFIG.2, is simplified for the convenience of explanation. Installation of the distance sensor11is not limited to the one described below.

Note that the travel direction of the vehicle V is referred to as ‘ahead’ direction, the reverse direction as ‘reverse’ direction, the upward vertical direction as ‘up’ direction, the downward vertical direction as ‘down’ direction, and the widthwise direction as ‘left’ and ‘right’ directions for the purpose of explanation. The installation structure of the vehicle sensors such as the distance sensor11is essentially bilaterally symmetrical. Therefore, the following description will primarily focus on one side (the left side) while omitting the description of the other side (the right side) as appropriate.

FIG.2is a side view of the vehicle V, illustrating the installation structure of the distance sensor11. Note that the outline of the vehicle V is indicated by the phantom line inFIG.2.

The vehicle V includes the vehicle body B as its main constituent. The vehicle body B includes, in addition to the vehicle body member30, the exterior member20and the distance sensor11, etc. The distance sensor11is fixed to the vehicle body member30.

The exterior member20is a member that forms the outer portion of the vehicle V. The exterior member20forms the outer shell of the vehicle V. On the other hand, the distance sensor11is a device that detects the road surface condition.

As long as the vehicle V is an automobile provided with the vehicle body member30, the exterior member20, and the distance sensor11as described above, the specific type and model of the vehicle are not limited in particular. The vehicle V can, for example, be a passenger car, bus, truck, utility vehicle, or the like.

Each member will be described below in more detail.

The vehicle body member30has the function of supporting the exterior member20. Moreover, the vehicle body member30is composed of members such as a front side frame31, an upper member32, a bumper beam extension33, and a bumper beam34. Note that the front side frame31, the upper member32, and the bumper beam34may be referred to as frame members.

The exterior member20includes an engine hood21, a front bumper22, and a front fender23. Note that the front bumper22may simply be referred to as “bumper”.

The engine hood21is a panel member that covers the upper surface of a portion ahead of the windshield. The front bumper22is located on the front side of the vehicle V and is composed of, for example, a panel member made of synthetic resin. In addition, the front bumper22includes a front portion22awhere an air intake and the like are provided, and a bottom portion22bthat extends rearward from the lower end of the front portion22a. The front fender23is a panel member that covers the area around the wheel W.

(Installation of Distance Sensor)

The distance sensor11is a sensor that detects the condition of the road surface R ahead of the vehicle V. The distance sensor11is fixed to the upper member32. The upper member32is a member that constitutes the vehicle body member30, as described above. The upper member32is arranged ahead of the wheel W.

More specifically, the distance sensor11is installed on the outer side surface of the upper member32in the vehicle width direction. The distance sensor11is located at the front end of the upper member32in the longitudinal direction.

(Configuration of Distance Sensor)

The distance sensor11of the present embodiment is configured to detect the road surface distance L1at the road surface R immediately ahead of the wheel W, as indicated with the arrow A1inFIG.2. The road surface distance L1is a distance between the vehicle body member30and the measurement point P on the road surface R. The distance sensor11can be appropriately selected from various types of sensors such as radar-based, camera-based, and laser-based sensors. The distance sensor11does not need to be composed of a single type of sensor. The distance sensor11can be configured by combining plural types of sensors, such as a camera-based sensor and a laser-based sensor, for example.

Next, detection of a distance by the distance sensor11will be described based onFIG.3.FIG.3Aillustrates an appearance of the distance sensor11when the wheel W is viewed from ahead of the vehicle V. The distance sensor11of the present embodiment is provided with five transmitters, from transmitter11ato transmitter11e. Each transmitter transmits a detection wave towards the road surface R. The transmitted detection wave is reflected on the road surface R and received by a receiver. The receiver will be explained later based on figures such asFIG.6.

The detection wave can be, for example, a laser wave or a millimeter wave. The method of detecting a distance by the transmitter and receiver is not limited in particular. Various approaches can be employed as the detection method, such as a method based on the principle of triangulation, a method that converts the reflected intensity of transmitted light into a distance, a method that calculates a distance based on the flight time of laser light, and so forth.

Detection of a distance will be specifically described. As illustrated inFIG.3A, the wheel W is in contact with a tire-road contact surface S1of the road surface R. Detection waves are transmitted from the five transmitters11ato11etowards the measurement surface S2of the road surface. The transmitters illustrated inFIG.3Aare referred to as, in order from the outer side to the inner side in the vehicle width direction, a first transmitter11a, a second transmitter11b, a third transmitter11c, a fourth transmitter11d, and a fifth transmitter11e. The detection waves transmitted from the respective transmitters are referred to as a first detection wave Ra, a second detection wave Rb, a third detection wave Rc, a fourth detection wave Rd, and a fifth detection wave Re.

InFIG.3A, the width of the part where the tire W contacts the road surface R is illustrated as a road surface contact width L4. In the configuration illustrated inFIG.3A, among the five transmitters, the fourth detection wave Rd transmitted from the fourth transmitter11dand the fifth detection wave Re transmitted from the fifth transmitter11eare transmitted towards the measurement surface S2, which is positioned on the inner side of the road surface contact width L4in the vehicle width direction. By arranging the transmitters in this manner, a road surface distance can be obtained over a wider range. This allows for monitoring a wider range of road surface conditions. As a result, the road surface conditions can be accurately recognized. This facilitates more appropriate control of the suspension, even when the vehicle V deviates in the lateral direction, that is, when turning left or right.

Note that the arrangement of the transmitters illustrated inFIG.3Ais exemplary, and the positions of the transmitters can be changed as appropriate. The receiver, which receives the detection waves transmitted from the transmitters and reflected on the road surface R, can be arranged at any arbitrary position as appropriate. For example, the receiver may be integrated with each transmitter and arranged with each transmitter. Alternatively, the receiver may be separate from the transmitters and arranged at a position different from the transmitters. The number of transmitters does not necessarily be the same as the number of receivers. The receiver may receive detection waves transmitted from the plurality of transmitters. This will be described in detail later.

In the preview road surface detector1of the present embodiment, the transmitters transmit detection waves with a time difference between adjacent transmitters. Description is provided based onFIG.3B.FIG.3Bis a diagram illustrating the transmission sequence of detection waves from each transmitter. As illustrated inFIG.3B, after the first transmitter11atransmits, the second transmitter11badjacent to the first transmitter11adoes not transmit. The third transmitter11c, which is not adjacent to the first transmitter11a, transmits after the first transmitter11a. The same pattern continues for the subsequent transmitters. After the third transmitter11ctransmits, the fourth transmitter11dadjacent to the third transmitter11cdoes not transmit. After the third transmitter11ctransmits, the fifth transmitter11e, which is not adjacent to the third transmitter11c, transmits. Thereafter, transmissions continue in the order as illustrated inFIG.3B. As described above, the transmitters do not transmit consecutively with adjacent transmitters. In this manner, the transmitters are adjusted to transmit with a time difference between adjacent transmitters.

The timing of transmissions as described above can be adjusted in the same manner, even if the number of transmitters changes. Description is provided based onFIGS.4A and4B.FIG.4Ais a diagram corresponding toFIG.3A, andFIG.4Bis a diagram corresponding toFIG.3B. The number of transmitters is different between the configurations illustrated inFIGS.3and4. The configuration illustrated inFIG.3has five transmitters. In contrast, the configuration illustrated inFIG.4has six transmitters. In the configuration illustrated inFIG.4, a sixth transmitter11fis further arranged on the inner side of the fifth transmitter11ein the vehicle width direction. A detection wave transmitted from the sixth transmitter11fis referred to as a sixth detection wave Rf.

As illustrated in the transmission sequence ofFIG.4B, even when the number of transmitters becomes six, the timing of transmissions is adjusted to ensure that the transmitters do not transmit consecutively with adjacent transmitters. As a result, the transmitters transmit with a time difference between adjacent transmitters.

(Transmission Frequency of Transmitters)

The transmission frequency of the transmitter is not limited in particular. The transmission frequency can, for example, be set to 1,000 Hz or higher. In other words, this frequency is 1 msec per cycle. Alternatively, the transmission frequency can be set to achieve a measurement cycle ranging from a minimum of 15 mm per cycle to a maximum of 30 mm per cycle. Here, the distance refers to a travel distance of the transmitters.

InFIGS.3and4, the plurality of transmitters are installed as arranged in a direction intersecting with the travel direction of the vehicle V. In other words, the plurality of transmitters are arranged in the width direction of the vehicle. The transmitters can also be arranged in a row along the travel direction of the vehicle V. Description is provided based onFIG.5.FIG.5is a view of the vicinity of the left front wheel of the vehicle V, as observed from above the vehicle V.

As illustrated inFIG.5, a first forward transmitter11F1is arranged ahead of the second transmitter11bin the travel direction. A first backward transmitter11B1is arranged behind the second transmitter11bin the travel direction.

In the configuration as illustrated inFIG.5, the second transmitter11band the first forward transmitter11F1transmit detection waves with a time difference. The second transmitter11band the first backward transmitter11B1transmit detection waves with a time difference. This can suppress the crosstalk of received detection waves.

Note that it is not necessary to provide both a forward transmitter and a backward transmitter as the transmitters in the longitudinal direction. Either the forward transmitter or the backward transmitter can be provided alone.

By arranging the transmitters in the longitudinal direction relative to the travel direction of the vehicle V, more accurate preview control can be achieved, for example, when the vehicle makes a turn. However, the crosstalk of detection waves, which may occur while receiving the detection waves, is likely to lead to significant malfunctions. In this regard, the preview road surface detector of the present embodiment can suppress the crosstalk of detection waves between transmitters arranged in the longitudinal direction. This is because those transmitters transmit detection waves with a time difference.

There are various manners of arranging the receivers. For example, as described earlier, the receiver can be arranged integrally with the transmitter. In contrast,FIGS.6to8illustrate the configurations where the receivers are arranged separately from the transmitters.FIGS.6to8respectively illustrate the different arrangements of the receivers and transmitters.

As an example of the receiver arrangement, one or more receivers are arranged at the ends in the width direction, and the transmitters can be installed such that transmission directions thereof inclined towards the sides of the one or more receivers. Specific description is provided below.

In the arrangement example illustrated inFIG.6, the transmitters and the receivers14are arranged within the sensor housing16. Within the sensor housing16, the five transmitters including the first transmitter11ato the fifth transmitter11eare arranged side by side in the vehicle width direction. The receiver14is arranged at one end in the vehicle width direction within the sensor housing16.

The transmission directions of the detection waves from the respective transmitters are not perpendicular to the road surface R. The transmission directions are inclined towards the direction of the receiver14. As a result, the detection waves reflected on the road surface R efficiently reach the receiver14. Therefore, even in the case of receiving with fewer receivers14, decrease in reception sensitivity can be suppressed.

Next, an arrangement example illustrated inFIG.7is described. The arrangement example illustrated inFIG.7is different from the arrangement example illustrated inFIG.6, and includes two receivers14within the sensor housing16. Specifically, a first receiver14ais arranged at one end of the sensor housing16in the vehicle width direction, and a second receiver14bis arranged at the other end of the sensor housing16in the vehicle width direction.

The first detection wave Ra transmitted from the first transmitter11a, the second detection wave Rb transmitted from the second transmitter11b, and the third detection wave Rc transmitted from the third transmitter11care received by the first receiver14a. In contrast, the fourth detection wave Rd transmitted from the fourth transmitter11dand the fifth detection wave Re transmitted from the fifth transmitter11eare received by the second receiver14b.

To ensure efficient reception, the transmission directions of the detection waves from the first transmitter11a, the second transmitter11b, and the third transmitter11care inclined towards the direction of the first receiver14a. In contrast, the transmission directions of the detection waves from the fourth transmitter11dand the fifth transmitter11eare inclined towards the direction of the second receiver14b. With this arrangement, even in the case of receiving with fewer receivers, the detection waves can be efficiently received while minimizing the load on each individual receiver.

The arrangement example illustrated inFIG.7can be used in the case where a plurality of transmitters simultaneously transmit detection waves, and the transmission directions of the transmitters are tilted towards different sides of respective receivers. For example, a case where the third transmitter (11c) and the fourth transmitter (11d) simultaneously transmit detection waves is considered. The transmission direction of the third transmitter (11c) is inclined towards the side of the first receiver (14a). In contrast, the transmission direction of the fourth transmitter11dis inclined towards the side of the second receiver14b. In this manner, the transmission directions of the simultaneously transmitted detection waves can be inclined towards different sides of the respective receivers. As a result, the crosstalk of detection waves transmitted from adjacent transmitters can be suppressed.

Note that even in the case of using fewer receivers, the transmission directions of the detection waves from the respective transmitters is not limited to the directions inclined towards the receiver14. As illustrated inFIG.8, even in the case of using one receiver, the transmission directions of the detection waves from the respective transmitters can be perpendicular to the road surface R. With such a configuration, the sensor housing16can be easily downsized. This is because the distance between the transmitters and the receiver14in the width direction of the vehicle can be reduced.

Grouping of transmitters is described below. Transmitters can be divided into a plurality of groups. The transmitters in each group simultaneously transmit detection waves. Specifically, the plurality of transmitters belonging to the same group simultaneously transmit detection waves. Description below is provided based onFIGS.9and10.FIGS.9and10both illustrate the transmission sequence of the transmitters. The number of transmitters is different between the transmission sequences illustrated inFIGS.9and10. The configuration illustrated inFIG.9has five transmitters. On the other hand, the configuration illustrated inFIG.10has six transmitters. In terms of the arrangement of transmitters, the transmission sequence illustrated inFIG.9corresponds to the arrangement inFIG.3A. On the other hand, the transmission sequence illustrated inFIG.10corresponds to the arrangement illustrated inFIG.4A.

In the transmission sequence shown inFIG.9, the first transmitter11a, the third transmitter11c, and the fifth transmitter11ebelong to the first group. The remaining second transmitter11band fourth transmitter11dbelong to the second group. The three transmitters belonging to the first group simultaneously transmit. Next, the two transmitters belonging to the second group simultaneously transmit. Thereafter, this process is sequentially repeated. This allows for increasing the transmission frequency while ensuring that adjacent transmitters do not simultaneously transmit.

As mentioned earlier, the transmission sequence illustrated inFIG.10has one more transmitter than the transmission sequence illustrated inFIG.9. Therefore, the sixth transmitter11fis added to the second group, in addition to the second transmitter11band the fourth transmitter11d. As a result, both the first group and the second group have three transmitters each.

Even if the number of transmitters increases, the transmission sequence can be similar to the transmission sequence described inFIG.9. Specifically, first, the three transmitters belonging to the first group simultaneously transmit. Next, the three transmitters belonging to the second group simultaneously transmit. Thereafter, this process is sequentially repeated. Even in the case of increasing the number of transmitters, this allows for increasing the transmission frequency while ensuring that adjacent transmitters do not simultaneously transmit.

Using the preview road surface detector1of the present embodiment, the following preview road surface detection method can also be executed. A preview road surface can be detected with a preview road surface detection method, including: a distance detecting step of detecting a value related to a distance between a vehicle body member30and a measurement point P on a road surface ahead of a vehicle V, the measurement point P corresponding to at least a central portion43of a road surface contact portion41of a wheel W, the distance detected by way of a plurality of transmitters and at least one receiver14installed on the vehicle body member30and arranged in a direction intersecting a travel direction of the vehicle V; and a distance calculating step of calculating a road surface distance L1, which is a distance from the vehicle body member30to the measurement point P, based on a detection value detected in the distance detecting step, in which, in the distance detecting step, the transmitters transmit detection waves with a time difference between the adjacent transmitters.

The embodiments of the present invention have been described above; however, the present invention is not limited to the aforementioned embodiments, and various modifications, alterations, and combinations are possible.

EXPLANATION OF REFERENCE NUMERALS