JP2014051195A - Road condition determination device and tire-side device for road condition determination device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a road condition determination device that highly precisely determines a road condition such as a wavy road surface, achieves low power consumption of a tire-side device and has a low device cost, and to provide a tire-side device for road condition determination device.SOLUTION: The road condition determination device includes: air pressure detection means that is disposed on a tire and detects (S2, S6, and S12) the air pressure of the tire at a set detection interval; road condition determination means that calculates (S7) an amplitude Pw and cycle T of a varying air pressure on the basis of the detected air pressure detection value P1, and determines (S10) a road condition; a wireless transmission part that is disposed on the tire and transmits a radio signal at a set wireless communication interval; a wireless receiving part that is disposed in a vehicle and receives the radio signal; and interval setting means that changes (S5) the detection interval and wireless communication interval to settings corresponding to the vehicle velocity V of the vehicle when the air pressure detection value P1 has changed to exceed a threshold ΔP.

Description

  The present invention relates to a road surface state determination device and a tire side device for a road surface state determination device mounted on a vehicle, and more particularly to an apparatus for determining a road surface state from a change in tire air pressure.

  In recent years, a technique for determining a road surface state on the side of a traveling vehicle has been proposed, and Patent Examples 1 and 2 disclose technical examples. The road surface condition detection device disclosed in Patent Literature 1 includes a piezoelectric element that is fixed to a tire and converts vibrations of the tire into an electric signal, and a communication unit that wirelessly transmits the electric signal to the vehicle side device. According to this configuration, the tire vibrates according to the road surface condition, and the road surface condition can be monitored by acquiring the road surface condition information by the vehicle side device. Moreover, it is said that introduction cost can be reduced compared with the structure which provides a road surface condition detection apparatus on the road side. Furthermore, it is described in the fifth embodiment that a road surface condition monitoring system can be configured by adding a piezoelectric element to an existing tire pressure monitoring system (TPMS) using a pressure sensor.

  The tire pressure monitoring device disclosed in Patent Document 2 is provided with wheel vibration detection means for each wheel, and the first tire pressure monitoring means for calculating the vehicle body speed and the wheel diameter is compared with vibration frequency spectrum data with reference spectrum data. Second tire pressure monitoring means, and the tire pressure is simultaneously monitored by both means. Thus, it is described that a decrease in tire air pressure can be accurately detected. The first tire pressure monitoring means extracts the change pattern of the vibration detection value on the front wheel side and the rear wheel side, and can determine the road surface condition. In contrast to the direct TPMS provided with the air pressure sensor, the technique of Patent Document 2 is an indirect TPMS not provided with the air pressure sensor.

JP 2010-125984 A JP 2006-162479 A

  Incidentally, Patent Document 1 describes that road surface condition information is acquired based on the frequency of an electric signal. Further, Patent Document 2 describes that road surface state information is acquired based on a change pattern of vibration detection values on the front wheel side and the rear wheel side, and examples include detection of road surface bumps (projections). Yes. An example of this type of road surface condition is a wavy road surface with repeated undulations. The wavy road surface often occurs naturally when a large number of vehicles come and go on the unpaved road. On wavy road surfaces, tire bounces and floats occur and the braking effectiveness varies, so it is preferable to control the traveling speed to be low. Therefore, it is considered that the running stability and safety of the vehicle can be improved by determining the road surface condition and applying the determination result to the brake control and the cruise control.

  In addition, when a vibration sensor or a pneumatic sensor is provided as a tire side device, the power source of the tire side device cannot connect a power supply cable or a signal cable supplied with power from the vehicle side to the tire side device. A wireless communication unit that transmits the detection signal is required. In the tire pressure monitoring system, the air pressure detection and the wireless communication can sufficiently detect a tire abnormality even at long intervals of the order of seconds. On the other hand, in the application of road surface condition determination, even shorter detection intervals and wireless communication intervals are required. Furthermore, if the detection interval is set to be constant, the pitch of the measurement points replaced with the position on the road surface increases when the vehicle speed increases, so the accuracy of road surface condition determination decreases. Therefore, it is preferable to shorten the detection interval and the wireless communication interval in response to an increase in the vehicle speed. However, as the detection interval and the wireless communication interval are shorter, the power consumption of the sensor and the wireless communication unit is increased, the battery is quickly consumed, and the battery is frequently replaced.

  Furthermore, in 5th Embodiment of patent document 1, since a piezoelectric element is provided with a pneumatic sensor, power consumption increases further and apparatus cost also rises. Therefore, if an air pressure sensor used for TPMS can be shared for road condition determination, there are significant advantages in both power consumption and device cost.

  The present invention has been made in view of the problems of the background art described above, and accurately determines a road surface state such as a wavy road surface, and the road surface state determination device has low power consumption and low device cost of the tire side device. It is another object of the present invention to provide a tire-side device for a road surface condition determination device.

  The road surface condition judging device of the present invention is provided on a tire equipped in a vehicle, and detects air pressure of the tire at a set detection interval, and the air pressure that fluctuates based on the detected air pressure detection value. The road surface state determining means for determining the road surface state of the road surface on which the vehicle is traveling based on the calculated amplitude and period, and the air pressure detection value and the air pressure are disposed on the tire. Of the data group consisting of the amplitude and the period of the road surface, and the road surface state, a radio transmission unit that converts the radio signal into a radio signal and transmits the radio signal at a set radio communication interval; A wireless receiver for receiving the transmitted wireless signal, and when the air pressure detection value changes beyond a threshold, the detection interval and the wireless communication interval correspond to the vehicle speed of the vehicle; And interval setting means for changing a constant, with a.

  Further, the interval setting means changes the setting to a detection interval and a wireless communication interval shorter than the initial detection interval and the initial wireless communication interval set at the time of starting the apparatus when the air pressure detection value changes beyond the threshold value. It is preferable to do.

  Further, the road surface condition determination means calculates at least one of an amplitude change amount and a period change amount in which the amplitude and the period of the air pressure have changed from the previous period when one cycle of the period in which the air pressure fluctuates has elapsed. When the calculated amplitude change amount and the periodic change amount are equal to or less than a predetermined amount, it is determined as a steady state, and in the steady state, the interval setting unit changes the setting in accordance with the vehicle speed of the vehicle. It is preferable to change the setting to a wireless communication interval longer than the communication interval or return the setting to the initial wireless communication cycle.

  Further, the road surface condition determining means calculates a single amplitude and a single cycle at which the air pressure varies, and based on the single amplitude and the single cycle of the air pressure, The undulation height and the undulation pitch length may be determined as the road surface state.

  Moreover, the tire side apparatus of this invention is applied to the road surface state determination apparatus of this invention, is mounted in the said tire, and consists of the said air pressure detection means, the said wireless transmission part, and the said space | interval setting means.

  Furthermore, it is preferable that the tire-side device is mounted on each of a plurality of tires of the vehicle, and is used alternately for road surface condition determination.

  The road surface state determination device of the present invention includes an air pressure detection unit, a road surface state determination unit, a wireless transmission unit, a wireless reception unit, and an interval setting unit. When the detected air pressure value changes beyond a threshold value, the detection interval and wireless Change the communication interval to a setting corresponding to the vehicle speed. Therefore, when the change in the air pressure detection value is less than the threshold value (that is, the road surface condition is good), the detection interval and the wireless communication interval are set longer than the time interval corresponding to the vehicle speed, and the tire side air pressure detection is performed. The power consumption of the means and the wireless transmitter can be reduced. Also, if the air pressure detection value changes beyond the threshold, the detection interval and wireless communication interval settings are changed to a time interval corresponding to the vehicle speed, so that data related to the determination of the road surface state can be acquired appropriately, and the determination of the road surface state can be performed. It can be performed with high accuracy.

  Further, in the aspect in which the interval setting means sets the initial detection interval and the initial wireless communication interval when the apparatus is started, the power consumption on the tire side can be significantly reduced until the air pressure detection value changes beyond the threshold value.

  Further, in the aspect in which the road surface state determining means determines the steady state, and the interval setting means changes the setting to a wireless communication interval longer than the wireless communication interval in which the setting is changed in accordance with the vehicle speed of the vehicle in the steady state, the steady state The wireless communication interval is lengthened while the detection interval corresponds to the vehicle speed. Here, the steady state in which the amplitude and the period of fluctuation of the air pressure are generally stable occurs when the vehicle travels on a wavy road surface that repeats the same undulating shape. Therefore, even while traveling on a wavy road surface, the power consumption required for the wireless communication on the tire side can be reduced while accurately determining the road surface state at the detection interval corresponding to the vehicle speed. In addition, when the wavy road surface changes to an irregular undulation shape, the wireless communication interval can be set to correspond to the vehicle speed, and the road surface state can be determined accurately without delay.

  Furthermore, in the aspect in which the road surface state determining means determines the undulation height and the undulation pitch length of the wavy road surface, the wavy road surface can be accurately determined. In addition, it is possible to improve the running stability and safety of the vehicle by applying the determination result of the wavy road surface to cruise control or brake control.

  Further, in the aspect of the tire-side device including the air pressure detection unit, the wireless transmission unit, and the interval setting unit, power consumption can be reduced by changing at least one of the detection interval and the wireless communication interval in the tire-side device.

  Further, in the aspect where the tire side device is mounted on each of the plurality of tires and is used for road surface condition determination in turn, the tire side device can be shared by making a slight change to the existing tire pressure monitoring system. Equipment cost is low. In addition, since a plurality of tire side devices are used alternately, the degree of consumption of the batteries contained in each of them is uniform, and maintenance for battery replacement is facilitated.

It is a block diagram explaining the road surface state determination apparatus of 1st Embodiment. It is a figure of the flowchart explaining operation | movement of the road surface state determination apparatus of 1st Embodiment. It is a wave form diagram of change of the air pressure detection value of a tire when vehicles are running on a dry asphalt road surface which is an example of a good road surface. It is a wave form diagram of a change of a tire air pressure detection value when a vehicle is traveling on a wavy road surface. It is a block diagram explaining the road surface state determination apparatus of 2nd Embodiment.

  A road surface condition determination apparatus 1 according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram illustrating a road surface state determination device 1 according to the first embodiment. The road surface state determination device 1 includes a tire-side device 3 mounted on any tire 2 of the vehicle and a vehicle-side device 4 mounted on the vehicle.

  The tire side device 3 is mounted inside the tire 2 and rotates together with the tire 2. As illustrated, the tire-side device 3 includes an air pressure sensor 31, a temperature sensor 32, a wireless communication unit 33, a control calculation unit 34, and the like. The tire side device 3 can be realized by adding some changes to the tire side device used in the existing tire pressure monitoring system. Examples of the location to be changed include, but are not limited to, a software function change of the control calculation unit 34, a detection interval of the air pressure sensor 31 and a change of the wireless communication interval of the wireless communication unit 33, and the like.

  The air pressure sensor 31 corresponds to a part of the air pressure detecting means, detects the air pressure inside the tire 2 in accordance with a detection command from the control calculation unit 34, and outputs a detection signal of the air pressure P0 after A / D conversion to the control calculation unit 34. To send. The temperature sensor 32 detects the air temperature inside the tire 2 in accordance with a detection command from the control calculation unit 34 and sends a detection signal of the air temperature T0 after A / D conversion to the control calculation unit 34.

  The wireless communication unit 33 corresponds to a wireless transmission unit of the present invention, and performs data transmission by wireless communication with the wireless communication unit 41 of the vehicle side device 4 in accordance with a communication control command from the control calculation unit 34. The wireless communication unit 33 converts the air pressure detection value P1 after temperature correction into a wireless signal and wirelessly transmits it. In addition, the wireless communication unit 33 receives a communication control command output from the road surface state determination ECU 42 and transmitted via the wireless communication unit 4 of the vehicle side device 4, and transmits data to the control calculation unit 34. That is, the wireless communication unit 33 has a bidirectional communication function. The wireless communication method between the two wireless communication units 33 and 41 is not particularly limited.

  The control calculation unit 34 is an electronic control unit (ECU) that incorporates a microcomputer and a storage unit and operates by software. The control calculation unit 34 receives detection signals of the air pressure P0 and the air temperature T0 after sending detection commands to the air pressure sensor 31 and the temperature sensor 32, and stores them in the storage unit. Then, the air pressure P0 is corrected by the air temperature T0, and the air pressure detection value P1 at the reference temperature is acquired. Therefore, the air pressure detection means of the present invention is configured by the combination of the air pressure sensor 31, the temperature sensor 32, and the temperature correction calculation function of the control calculation unit 34.

  The control calculation unit 34 further includes interval setting means of the present invention. That is, the control calculation unit 34 varies the setting of the detection interval for sending the detection command to the air pressure sensor 31 and the temperature sensor 32 based on the communication control command of the road surface state determination ECU 42. And the control calculating part 34 varies the setting of the radio | wireless communication interval of the radio | wireless communication part 33 based on the communication control command from road surface state determination ECU42. The control calculation unit 34 cooperates with the road surface state determination ECU 42 of the vehicle-side device 4 through the wireless communication units 33 and 41, thereby variably controlling the detection interval and the wireless communication interval. The detailed setting function as the interval setting means of the control calculation unit 34 will be described later with reference to the flowchart of FIG.

  When the wireless communication interval is set to the same length with respect to the air pressure detection interval, the wireless communication unit 33 wirelessly transmits each time the air pressure detection value P1 is acquired. In this case, a delay in data transmission due to wireless communication to the vehicle side device 4 can be reduced. Further, since the detection loss is reduced in the air pressure detecting means, the road surface condition can be detected efficiently. On the other hand, when the wireless communication interval is set longer than the air pressure detection interval, the wireless communication unit 33 can wirelessly transmit a plurality of air pressure detection values P1 stored in the storage unit of the control calculation unit 34 together. In this case, the power consumption required for wireless communication can be reduced.

  Further, the tire side device 3 incorporates a battery for power supply in a replaceable manner. A general button battery can be used as the power supply battery. The power source battery is a power source common to the air pressure sensor 31, the temperature sensor 32, the wireless communication unit 33, and the control calculation unit 34.

  The vehicle side device 4 is mounted on a vehicle and includes a wireless communication unit 41, a road surface state determination ECU 42, and the like. The vehicle side device 4 uses an in-vehicle battery that can be repeatedly charged as a power source, and unlike the tire side device 3, it is not necessary to consider battery replacement. The vehicle side device 4 can be realized by adding some changes to the vehicle side device used in the existing tire pressure monitoring system. The location to be changed can be exemplified by adding the function of the road surface condition determination ECU 42 to the air pressure monitoring ECU, and is not limited to this.

  The wireless communication unit 41 corresponds to a wireless reception unit of the present invention, and performs data transmission by wireless communication with the wireless communication unit 33 of the tire side device 3 in accordance with a communication control command from the road surface state determination ECU 42. The wireless communication unit 41 receives a wireless signal corresponding to the detected air pressure value P1 after temperature correction. In addition to this, the radio communication unit 41 also plays a role of transmitting a communication control signal from the road surface state determination ECU 42 to the control calculation unit 34 of the tire side device 3. That is, the wireless communication unit 41 has a bidirectional communication function.

  The road surface state determination ECU 42 is an electronic control device that incorporates a microcomputer and a storage unit and operates by software, and includes the road surface state determination unit of the present invention. As illustrated, the road surface condition determination ECU 42 is connected to the in-vehicle network 5 (for example, CAN) and cooperates with another on-vehicle electronic control unit (ECU). The road surface condition determination ECU 42 acquires information on the vehicle speed V via the in-vehicle network 5. Information on the vehicle speed V is wirelessly transmitted to the control calculation unit 34 via the two wireless communication units 41 and 33 and shared.

  First, the road surface condition determination ECU 42 calculates the amplitude Pw and the period T of the air pressure P (t) that varies with time based on the air pressure detection value P1 received by the wireless communication unit 33. The amplitude Pw is calculated from the maximum value and the minimum value of the air pressure P (t). The period T is calculated based on the detection interval of the maximum value and the minimum value of the air pressure P (t).

  In this embodiment, when it is determined that the road surface state is a wavy road surface, the power consumption of the road surface state determination device 1 can be suppressed. The wavy road surface here assumes a road surface state in which the undulating shape is repeated at a pitch of about 600 to 800 mm. The road surface condition determination ECU 42 calculates the amplitude Pw and the period T from the maximum value and the minimum value of the air pressure P (t) detected within the time of traveling on this repeated pitch. Therefore, when the interval setting means of the present invention changes the detection interval and the wireless communication interval according to the vehicle speed, even if the vehicle speed increases or decreases, the detection number of the air pressure detection value P1 obtained within the repeated pitch is not changed. Change the air pressure detection interval and wireless communication interval. The calculation range of the maximum value and the minimum value of the air pressure P (t) is not limited to this.

  Next, the road surface state determination ECU 42 determines the road surface state of the road surface on which the vehicle is traveling based on the amplitude Pw and the period T. By calculating the plurality of amplitudes Pw and the period T, it can be determined whether or not the road surface on which the vehicle is traveling is a wavy road surface that repeats the undulating shape.

  Incidentally, there is a causal relationship between the undulating height of the wavy road surface and the amplitude Pw of the air pressure P (t). If this causal relationship is obtained in advance through experiments, simulations, or the like, the road surface condition determination ECU 42 according to the first embodiment multiplies the amplitude Pw calculated from the air pressure P (t) by a preset coefficient to create a wave shape. The road undulation height can be determined. Further, the undulating pitch length of the wavy road surface can be determined by multiplying the cycle T calculated from the air pressure P (t) by the vehicle speed.

  The method for determining the undulation height and the undulation pitch length of the wavy road surface is not limited to this, and can be stored in the road surface state determination ECU 42 as a map in a list form, for example. The road surface condition determination ECU 42 may determine the undulation height and the undulation pitch length using this map.

  Next, operation | movement of the road surface state determination apparatus 1 of 1st Embodiment is demonstrated. FIG. 2 is a flowchart for explaining the operation of the road surface state determination apparatus 1 according to the first embodiment. First, when the ignition switch is turned on, the vehicle side device 4 is turned on and started. In step S <b> 1, the vehicle side device 4 transmits data to the tire side device 3 by wireless communication to the effect that it has started. In response to this, the interval setting means of the tire side device 3 sets an initial detection interval for detecting air pressure and an initial wireless communication interval for performing wireless communication. The initial detection interval and the initial wireless communication interval are determined to be on the order of seconds with the same length, and are the longest time intervals when the tire side device 3 operates.

  Steps S2 to S3 are operations when the vehicle is traveling on a good road surface with a small change in undulation height. In step S2, the air pressure detection means acquires the air pressure detection value P1 at the set detection interval. In step S2 immediately after the vehicle side device 4 is started, the initial detection interval is set at the longest time interval. In step S2 after returning from step S13, the detection interval and the wireless communication interval are set at the time interval set in step S13. The air pressure detection value P <b> 1 acquired by the air pressure detection means is wirelessly transmitted to the vehicle side device 4 by one data every time the wireless communication unit 33 performs wireless transmission.

  In step S3, the road surface state determination ECU 42 of the vehicle side device 4 determines whether or not the air pressure detection value P1 has changed beyond the threshold value ΔP. The threshold value ΔP of the present embodiment is a value that is necessary for determining the road surface condition, and is a so-called absolute value. When the detected air pressure detection value P1 exceeds the threshold value ΔP, it is determined that the road surface state has changed, and the process proceeds to step S4. If the detected air pressure detection value P1 is within the threshold value ΔP, it is determined that there is no change in the road surface condition, and the process returns to step S2. In addition, it is not limited to the aspect which makes threshold-value (DELTA) P an absolute value, For example, a predetermined variation | change_quantity can be used. When the predetermined change amount is used, it can be determined whether or not the difference between the average value of the air pressure detection values in the predetermined period until the previous time and the current air pressure detection value exceeds the threshold value ΔP.

  Steps S4 to S9 are operations performed when the air pressure detection value P1 fluctuates and the road surface state of the road surface on which the vehicle is traveling changes. In step S4, the road surface condition determination ECU 42 acquires information on the vehicle speed V, and shares the information on the vehicle speed V with the interval setting means. In the next step S5, the interval setting means changes the setting to the detection interval and radio communication interval corresponding to the vehicle speed V. Qualitatively, the detection interval and the wireless communication interval are set to be short as the vehicle speed V increases. Furthermore, quantitatively, it is preferable to change the setting to a detection interval and a wireless communication interval that are approximately inversely proportional to the vehicle speed V. Thereby, the pitch of the measurement points on the road surface can be kept substantially constant, and the accuracy of the road surface condition determination can be ensured.

  In step S6, the air pressure detection means acquires the air pressure detection value P1 at a detection interval set corresponding to the vehicle speed V. The acquired air pressure detection value P1 is transmitted to the vehicle side device 4 by wireless communication. In the next step S7, the road surface condition determination ECU 42 calculates the amplitude Pw and the period T from the acquired air pressure detection value P1. More specifically, the amplitude Pw is calculated from the maximum value and the minimum value of the air pressure detection value P1, and the period T is calculated based on the detection interval of the maximum value and the minimum value of the air pressure detection value P1. In step S8, the road surface condition determination ECU 42 compares the cycle T calculated this time with the cycle calculated last time. Specifically, the period change amount is calculated by subtracting the previously calculated period from the currently calculated period T, and the process proceeds to step S9.

  In step S9, the road surface condition determination ECU 42 determines whether or not the period change amount is equal to or less than a predetermined amount. When the periodic change amount is equal to or less than the predetermined amount, it can be determined that the road surface has a undulating shape that periodically changes, and the process proceeds to step S10. When the period change amount exceeds the predetermined amount, it is determined that the undulation shape is irregularly changed or a good road surface with less undulations, and the process returns to step S4. In the first step S9, since the cycle T calculated this time of the fluctuation of the air pressure P (t) and the cycle calculated last time are not aligned, the process returns to step S4 unconditionally.

  Note that the previously calculated cycle corresponds to the previous cycle of the present invention. In step S8, the cycle calculated this time is compared with the cycle calculated last time, but the present invention is not limited to this. For example, when the fluctuation of the air pressure P (t) continues repeatedly, there are a plurality of periods before the previous time, and the average value of the periods calculated in each period may be used as the “previous period”. Good. Further, not only the period T but also an amplitude change amount in which the amplitude Pw is changed may be used in combination. In this case, the road surface condition determination ECU 42 calculates the amplitude change amount by subtracting the previously calculated amplitude from the amplitude Pw calculated this time in step S8, and in step S9, at least one of the periodic change amount and the amplitude change amount has a predetermined amount. If so, the process returns to step S4.

  Steps S10 to S12 are operations when the vehicle is traveling on a wavy road surface. In step S10, the undulation height and the undulation pitch length of the wavy road surface are determined from the amplitude Pw and the period T calculated in step S7. In the next step S11, the interval setting means sets the wireless communication interval longer than the detection interval. The wireless communication interval at this time may be the same as or different from the initial wireless communication interval. Moreover, you may set a radio | wireless communication space | interval to the time interval which can determine the undulation height of a wavy road surface. Although the wireless communication interval becomes longer than the detection interval, in the present embodiment, since the air pressure detection value wirelessly communicated is one data, the latest air pressure detection value is transmitted to the road surface state determination ECU 42 by wireless communication. In addition, the air pressure detection value can be stored in the control calculation unit 34, and a plurality of air pressure detection values can be transmitted by wireless communication in one wireless communication.

  In the next step S12, the road surface condition determination ECU 42 determines whether or not the air pressure detection value P1 has changed beyond the threshold value ΔP. If there is a change, it is determined that the wavy road surface is in a steady state, or it is determined that the wavy road surface is finished and the air pressure detection value P1 exceeds the threshold value ΔP, and the process returns to step S7. When there is no change, it can be determined that the wavy road surface has ended and the vehicle has entered a good road surface with a small change in undulation height. After determining that the wavy road surface has ended, the process proceeds to step S13. In step S13, the detection interval is set to a time interval longer than the detection interval changed in step S5, and the process returns to step S2. The long detection interval at this time may be the same as or different from the initial detection interval.

  The above operation is summarized as follows. That is, while the vehicle is traveling on a good road surface with a small change in undulation height, steps S2 to S3 are repeatedly detected and wirelessly transmitted at long time intervals, and the road surface is undulated to generate a detected air pressure value P1. Proceeds to step S4. While the vehicle is traveling on an irregular undulating road surface, steps S4 to S9 are repeated for air pressure detection and wireless communication at short time intervals corresponding to the vehicle speed. And if it turns out that it is a wavy road surface where the same undulation shape is repeated, it will progress to Step S10. While traveling on a wavy road surface, steps S7 to S12 are repeated for air pressure detection and wireless communication at a detection interval corresponding to the vehicle speed and at a wireless communication interval longer than the wireless communication interval set at step S5. When the wavy road surface ends and the vehicle enters an irregular road surface, the process returns from step S9 to step S4. When the wavy road surface is over and the vehicle enters a good road surface with a small change in undulation height, the process returns from step S12 to step S2 via step S13.

  Next, an actual waveform in the road surface state determination device 1 of the first embodiment will be described as an example. FIG. 3 is a waveform diagram of changes in the tire air pressure detection value P1 when the vehicle is traveling on a dry asphalt road surface which is an example of a good road surface. FIG. 4 is a waveform diagram of changes in the tire air pressure detection value P1 when the vehicle is traveling on a wavy road surface. 3 and 4, the horizontal axis represents time, and the vertical axis represents the detected air pressure value P1.

  On the good road surface in FIG. 3, the air pressure detection value P <b> 1 is substantially constant with a slight change from time to time. Therefore, in steps S2 to S3 in the flowchart of FIG. 2, air pressure detection and wireless communication are repeated at long time intervals.

  On the other hand, in FIG. 4, the vehicle enters the wavy road surface at time t1, and thereafter, the air pressure detection value P1 changes in a sine wave shape. The air pressure detection value P1 increases beyond the threshold ΔP at time t2. Therefore, in the air pressure detection and the wireless communication, steps S2 to S3 are repeated at a long time interval until time t2, and steps S4 to S9 are repeated at a time interval corresponding to the vehicle speed after time t2. Furthermore, two periods T1 and T2 are calculated by time t3, and when they are approximately equal to each other (T1≈T2), it is determined that the road surface is a wavy road. Therefore, after time t3, air pressure detection and wireless communication are repeated at the detection interval set in steps S7 to S12 and the wireless communication interval longer than the wireless communication interval set in step S5.

  According to the road surface state determination device 1 of the first embodiment, when the change in the air pressure detection value P1 is less than the threshold value ΔP and the road surface state is good, the detection interval and the wireless communication interval are lengthened, and the tire side device 3 power consumption can be reduced. In particular, since the longest initial detection interval and initial wireless communication interval are set when the device is started, the power consumption of the tire side device 3 can be significantly reduced. When the air pressure detection value P1 changes beyond the threshold value ΔP, the setting of the detection interval and the wireless communication interval is changed according to the vehicle speed, so that data relating to the determination of the road surface state can be appropriately acquired, and the determination of the road surface state can be performed. It can be performed with high accuracy.

  Further, in a steady state where the vehicle travels on a wavy road surface and the air pressure detection value P1 changes periodically, the air pressure detection interval is set to a time interval according to the vehicle speed, and the wireless communication interval is set in step S5. Change longer than the wireless communication interval. Therefore, even while traveling on a wavy road surface, the power consumption required for wireless communication of the tire side device 3 can be reduced while accurately determining the road surface state at a detection interval corresponding to the vehicle speed. Further, when the shape changes to an irregular undulation shape, it is possible to accurately determine the road surface condition by setting the wireless communication interval corresponding to the vehicle speed without delay.

  Furthermore, since the road surface state determining means determines the undulation height and the undulation pitch length of the wavy road surface, the wavy road surface can be accurately determined. In addition, since the determination result of the wavy road surface can be provided to the cruise control ECU, the brake control ECU, and the like via the in-vehicle network 5, the running stability and safety of the vehicle can be improved.

  Next, the road surface state determination device 1A of the second embodiment will be described mainly with respect to differences from the first embodiment. FIG. 5 is a configuration diagram illustrating a road surface state determination device 1A according to the second embodiment. The road surface condition determination device 1A of the second embodiment is integrated into an existing tire pressure monitoring system.

  In the second embodiment, tire-side devices 3A to 3D are mounted on the four tires 2 of the vehicle, respectively. The four tire side devices 3 </ b> A to 3 </ b> D have the same configuration as the tire side device 3 of the first embodiment, and different ID codes for individual recognition are assigned to the wireless transmission units 33. Each of the tire side devices 3A to 3D is used in common for air pressure monitoring and road surface condition determination.

  On the other hand, the vehicle-side device 4A includes a wireless communication unit 45, an air pressure monitoring ECU 46, and the like. The wireless communication unit 45 is configured to perform 1: 4 simultaneous wireless transmission to the four tire side devices 3A to 3D and 1: 1 opposing wireless communication by specifying an ID code. In addition to the basic function of monitoring air pressure, the air pressure monitoring ECU 46 is added with the function of the road surface condition determination ECU 42 of the first embodiment. Further, the air pressure monitoring ECU 46 designates the tire side devices 3A to 3D used for road surface condition determination in turn. The replacement of the tire side devices 3A to 3D is performed, for example, at a time when the vehicle travels for a predetermined time.

  The road surface condition determination apparatus 1A of the second embodiment described above operates as part of a tire air pressure monitoring system. That is, when the ignition switch is turned on and the vehicle side device 4A is started, the air pressure monitoring ECU 46 acquires the air pressure detection value P1 from the four tire side devices 3A to 3D at a long time interval and monitors the air pressure. In parallel with this, the air pressure monitoring ECU 46 receives the air pressure detection value P1 from the specified specific tire-side device at variable detection intervals and wireless communication intervals, and uses it for road surface condition determination.

  According to the road surface condition determination device 1A of the second embodiment, the tire side devices 3A to 3D can be shared by only making a slight change to the existing tire pressure monitoring system, so the overall device cost is reduced. In addition, the four tire side devices 3A to 3D are used together for air pressure monitoring, and are used alternately for road surface condition determination, so that the degree of consumption of the built-in power supply battery is uniform, Maintenance of battery replacement is facilitated.

  In the first embodiment, the control calculation unit 34 of the tire side device 3 includes the interval setting unit, and the road surface state determination ECU 42 of the vehicle side device 4 includes the road surface state determination unit. However, the present invention is not limited to this. In other words, the distance setting means and the road surface condition determining means are functional means realized by software, and may be arranged on either the tire side or the vehicle side, or may be assigned functions on the tire side and the vehicle side. . Correspondingly, the type of data transmitted by wireless communication also changes.

  In the first embodiment, the road surface condition determination ECU 42 calculates the single amplitude Pw and the single period T in which the air pressure P (t) varies, but the present invention is not limited to this. That is, a road surface state other than the wavy road surface may be determined by using a frequency spectrum calculation by Fourier analysis or other calculation methods. Various other modifications and applications of the present invention are possible.

DESCRIPTION OF SYMBOLS 1, 1A: Road surface state determination apparatus 2: Tire 3, 3A-3D: Tire side apparatus 31: Air pressure sensor 32: Temperature sensor 33: Wireless communication part (wireless transmission part) 34: Control calculating part 4, 4A: Vehicle side apparatus 41: Radio communication unit (radio reception unit) 42: Road surface state determination ECU
45: Wireless communication unit (wireless reception unit) 46: Air pressure monitoring ECU
5: In-vehicle network ΔP: Threshold T, T1, T2: Period

Claims (6)

An air pressure detecting means disposed on a tire mounted on the vehicle and detecting the air pressure of the tire at a set detection interval;
Road surface state determination means for calculating the amplitude and period of the air pressure that varies based on the detected air pressure detection value, and determining the road surface state of the road surface on which the vehicle is traveling based on the calculated amplitude and period;
A wireless transmission unit that is disposed on the tire and transmits at least one wireless communication interval set by converting one or more of the data group consisting of the detected air pressure value, the amplitude and period of the air pressure, and the road surface condition into a wireless signal When,
A radio receiving unit disposed in the vehicle for receiving the radio signal transmitted from the radio transmitting unit;
A road surface condition determination device comprising: interval setting means for changing the detection interval and the wireless communication interval to a setting corresponding to the vehicle speed of the vehicle when the air pressure detection value changes beyond a threshold value.   The interval setting means changes the setting to a detection interval and a wireless communication interval shorter than an initial detection interval and an initial wireless communication interval set when the apparatus is started when the air pressure detection value changes beyond the threshold. Item 12. The road surface condition determination device according to Item 1. The road surface condition determining means calculates at least one of an amplitude change amount and a cycle change amount in which the amplitude and cycle of the air pressure have changed from the previous cycle when one cycle of the cycle in which the air pressure fluctuates has passed, When the amplitude change amount and the period change amount are equal to or less than a predetermined amount, the steady state is determined,
The interval setting means, in the steady state, changes the setting to a radio communication interval longer than the radio communication interval whose setting has been changed corresponding to the vehicle speed of the vehicle, or returns the setting to the initial radio communication cycle. The road surface condition determination apparatus according to 1 or 2.   The road surface state determination means calculates a single amplitude and a single period at which the air pressure varies, and a road surface state of a wavy road surface in which the undulation shape repeats based on the single amplitude and the single period of the air pressure. The road surface condition determination device according to any one of claims 1 to 3, wherein the undulation height and the undulation pitch length are determined as follows. Applied to the road surface condition determination device according to any one of claims 1 to 4,
A tire-side device for a road surface condition determination device that is mounted on the tire and includes the air pressure detection unit, the wireless transmission unit, and the interval setting unit.   The tire-side device for a road surface state determination device according to claim 5, which is mounted on each of the plurality of tires of the vehicle and used alternately for road surface state determination.

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