Traffic signal lamp countdown display method and traffic signal lamp countdown display system

Abstract

A traffic signal countdown display method and system capable of accurately and smoothly displaying a countdown display time. The method includes: a traffic signal information acquisition step in which a vehicle-mounted system receives a data packet containing traffic signal information at predetermined time intervals; a synchronized countdown time calculation step in which a synchronized countdown time obtained by synchronizing a system time of the vehicle-mounted system is calculated using a time stamp and a countdown time contained in the data packet; a countdown decrement rate adjustment step in which a countdown decrement rate of the vehicle-mounted system is adjusted according to a relationship between the synchronized countdown time and a predicted value of a countdown display time on the vehicle-mounted system side; and a countdown display time determination step in which, in a case where the data packet is received for the Nth time, a countdown display time on the vehicle-mounted system side after synchronization is determined according to a current countdown display time on the vehicle-mounted system side and the adjusted countdown decrement rate, N being a natural number equal to or greater than 2.

Description

TECHNICAL FIELD

[0001] The present application relates to a traffic signal countdown display method and a traffic signal countdown display system, in particular to a method and system for synchronously displaying the countdown time of a traffic signal in a display device in a vehicle. BACKGROUND

[0002] In the technical field of vehicle auxiliary driving, vehicle automatic driving, etc., there is a technology for recognizing the state information (for example, indicator light state information, countdown information, etc.) of a traffic signal and displaying the state information in a vehicle.

[0003] For example, in patent document 1, a time correction method for a traffic signal is disclosed, which corrects the countdown time of a traffic signal in integer level precision obtained by recognizing a target image including the traffic signal, and then uses the time stamp information in decimal level precision possessed by each target image to correct the recognized countdown time in integer level precision to the countdown time in decimal level precision.

[0004] Patent document 1: CN110309755A

[0005] However, the method of obtaining the state information of the traffic signal through image recognition has the problem that the recognition accuracy is greatly affected by the surrounding environment, for example, weather factors such as heavy fog and rainy weather will interfere with the recognition result, and the camera cannot be recognized when it is physically blocked.

[0006] In addition, there is currently a CV2X (Cellular Vehicle-to-Everything) technology for obtaining the information of the traffic signal through wireless communication. Compared with the image recognition technology in patent document 1, the CV2X technology solves the limitations of environmental influence, physical blocking, etc.

[0007] However, since the road side unit (RSU) may occur packet network delay, packet loss, etc. when transmitting data packets, it may cause the countdown displayed on the vehicle side to be non-smooth and uniform, for example, the countdown may be rolled back, discontinuous, jump, etc. Such non-smooth and uniform countdown display time affects the user experience. SUMMARY

[0008] In view of the above problems, the present application provides a traffic signal countdown display method and a traffic signal countdown display system which can improve the accuracy of the countdown display time and make it more smooth and uniform.

[0009] A traffic signal countdown display method characterized by comprising: a traffic signal information acquisition step in which a vehicle-mounted system receives a data packet containing traffic signal information at a predetermined time interval; a synchronized countdown time calculation step in which a synchronized countdown time obtained by synchronizing a system time of the vehicle-mounted system is calculated using a time stamp and a countdown time contained in the data packet; a countdown decrement rate adjustment step in which a countdown decrement rate of the vehicle-mounted system is adjusted based on a relationship between the synchronized countdown time and a predicted value of a countdown display time on the vehicle-mounted system side; and a countdown display time decision step in which, in a case where the data packet is received for the Nth time, a countdown display time on the vehicle-mounted system side after synchronization is decided based on a current countdown display time on the vehicle-mounted system side and the adjusted countdown decrement rate, where N is a natural number equal to or greater than 2.

[0010] According to the above-described traffic signal countdown display method, in deciding the countdown display time on the vehicle-mounted system side, both the synchronization information of the countdown time from the new data packet and the countdown display time currently displayed on the vehicle-mounted system side are taken into account to decide the countdown decrement rate of the countdown display, and thus, compared with a case where the countdown display time is decided without taking the countdown decrement rate into account or compared with a case where the countdown decrement rate is decided only based on the synchronization information of the countdown time from the new data packet, the variation of the countdown display time can be made more smooth and uniform while ensuring the accuracy of the countdown display time.

[0011] In the above-described traffic signal countdown display method, in a case where the data packet, i.e., a first data packet, is received for the first time at a first system time point of the vehicle-mounted system by the traffic signal information acquisition step, in the synchronized countdown time calculation step, a first time difference is calculated by subtracting a first time stamp in the first data packet from the first system time point, a first synchronized countdown time is obtained by subtracting the first time difference from a first countdown time in the first data packet, in the countdown decrement rate adjustment step, an initial value of the countdown decrement rate, i.e., an initial decrement rate, is set to be the same as a decrement rate of a standard time, and in the countdown display time decision step, the first synchronized countdown time is set as a first countdown display time on the vehicle-mounted system side.

[0012] In the traffic signal countdown display method described above, in a case where the traffic signal information acquisition step receives the data packet, which is the Nth data packet, at the Mth system time point of the vehicle-mounted system, where M is a natural number equal to or greater than 2, in the post-synchronization countdown time calculation step, a difference between the Mth system time point and the Nth time stamp in the Nth data packet is calculated to obtain an Mth time difference, the Nth countdown time in the Nth data packet is subtracted by the Mth time difference to obtain an Mth post-synchronization countdown time, in the countdown decrement rate adjustment step, a ratio of a predicted value of the Mth countdown display time on the vehicle-mounted system side at the Mth system time point to the Mth post-synchronization countdown time is calculated as a tentative decrement rate, in a case where a degree of change of the tentative decrement rate with respect to the current countdown decrement rate does not exceed a first threshold value set in advance, the tentative decrement rate is used as an adjusted countdown decrement rate of the vehicle-mounted system, and in the countdown display time determination step, the Nth-1 countdown display time on the vehicle-mounted system side is decremented at the adjusted countdown decrement rate to determine the Mth countdown display time on the vehicle-mounted system side.

[0013] According to the traffic signal countdown display method described above, the tentative decrement rate is used as the adjusted countdown decrement rate of the vehicle-mounted system only in a case where the degree of change of the tentative decrement rate with respect to the current countdown decrement rate is within a normal range. Thus, a large fluctuation in the countdown display rate caused by a tentative decrement rate with an excessively large degree of change is avoided, and the display of the countdown is made smoother and more uniform.

[0014] In the traffic signal countdown display method described above, the predicted value of the Mth countdown display time on the vehicle-mounted system side is a predicted value obtained by decrementing the current countdown display time at the current countdown decrement rate.

[0015] In the traffic signal countdown display method described above, an integer part of the countdown display time on the vehicle-mounted system side is used as the countdown display time actually displayed by the vehicle-mounted system.

[0016] In the traffic signal countdown display method described above, in the countdown decrement rate adjustment step, when the variation degree of the tentative decrement rate exceeds a first threshold value set in advance, the number of times of first variation excess is accumulated, and when the number of times of first variation excess does not reach a prescribed number of times, the current countdown decrement rate is maintained, in the countdown display time decision step, the current countdown display time on the vehicle-mounted system side is decremented in accordance with the current countdown decrement rate, thereby deciding the Mth countdown display time on the vehicle-mounted system side, and when the number of times of first variation excess reaches the prescribed number of times, the countdown decrement rate on the vehicle-mounted system side is restored to the initial decrement rate, in the countdown display time decision step, the Mth synchronized countdown time is decided as the Mth countdown display time on the vehicle-mounted system side.

[0017] According to the traffic signal countdown display method described above, by setting the number of times of first variation excess, even when the countdown in the received data packet occasionally jumps, the countdown display time does not immediately jump, thereby making it possible to suppress frequent jumping of the countdown display time or frequent variation of the countdown display speed, and thus making the variation of the countdown display time more smooth and uniform.

[0018] In the traffic signal countdown display method described above, the first threshold value is an upper limit value of a range in which the countdown decrement rate is allowed to vary due to delay or packet loss of data packet transmission, and when the variation degree of the tentative decrement rate is a ratio of the tentative decrement rate to the current countdown decrement rate, the first threshold value is set to a value equal to or greater than 0.7 and less than or equal to 0.9, or a value equal to or greater than 1.1 and less than or equal to 1.3.

[0019] In the traffic signal countdown display method described above, the first threshold value is an upper limit value of a range in which the countdown decrement rate is allowed to vary due to delay or packet loss of data packet transmission, and when the variation degree of the tentative decrement rate is a variation rate of the tentative decrement rate with respect to the current countdown decrement rate, the first threshold value is set to a value equal to or greater than 0.1 and less than or equal to 0.3.

[0020] If the variation degree of the countdown decrement rate exceeds the first threshold value, it can be considered that the variation of the countdown decrement rate is too large (i.e., the countdown is not continuous). By setting the first threshold value, it is possible to improve the smoothness and uniformity of the display and improve the experience of a user who observes the countdown display time.

[0021] In the traffic signal countdown display method described above, in the countdown decrement rate adjustment step, when the degree of change in the post-synchronization countdown time exceeds a second threshold value set in advance, the number of times of second change excesses is accumulated, and when the number of times of second change excesses does not reach a prescribed number of times, the current countdown decrement rate is maintained, and in the countdown display time decision step, the current countdown display time on the vehicle-mounted system side is decremented at the current countdown decrement rate, thereby deciding the Mth post-synchronization countdown display time on the vehicle-mounted system side, and when the number of times of second change excesses reaches the prescribed number of times, the countdown decrement rate of the vehicle-mounted system is restored to the initial decrement rate, and in the countdown display time decision step, the Mth post-synchronization countdown time is decided as the Mth countdown display time on the vehicle-mounted system side.

[0022] According to the traffic signal countdown display method described above, by setting the number of times of second change excesses, even when the countdown in the received data packet occasionally jumps, the countdown display time does not immediately jump, thereby making the frequent jumping of the countdown display time or the frequent change in the countdown speed less likely to occur, and making the change in the countdown display time more smooth and uniform.

[0023] In the traffic signal countdown display method described above, the second threshold value is an upper limit value of the range of change in the post-synchronization countdown time due to the delay or loss of data packets, and when the degree of change in the post-synchronization countdown time is the ratio of the post-synchronization countdown time to the current countdown display time, the second threshold value is set to a value equal to or greater than 0.7 and equal to or less than 0.9, or a value equal to or greater than 1.1 and equal to or less than 1.3.

[0024] In the traffic signal countdown display method described above, the second threshold value is an upper limit value of the range of change in the post-synchronization countdown time due to the delay or loss of data packets, and when the degree of change in the post-synchronization countdown time is the absolute value of the change rate of the post-synchronization countdown time with respect to the current countdown display time, the second threshold value is set to a value equal to or greater than 0.1 and equal to or less than 0.3.

[0025] If the degree of change in the countdown decrement rate exceeds the second threshold value, it can be considered that the change in the countdown decrement rate is too large (i.e., the countdown is discontinuous). By setting the second threshold value, the smoothness and uniformity of the display can be improved, and the experience of the user when observing the countdown display time can be improved.

[0026] In the traffic signal countdown display method described above, the prescribed number of times is set in advance to an integer greater than 0 and equal to or less than 5, based on the number of times of fault tolerance in which the countdown jumps.

[0027] A traffic signal countdown display system characterized by comprising: a traffic signal information acquisition unit that receives a data packet containing traffic signal information at a predetermined time interval; a synchronized countdown time calculation unit that calculates a synchronized countdown time obtained by synchronizing a system time of a vehicle-mounted system using a time stamp contained in the data packet and a countdown time; a countdown decrement rate adjustment unit that adjusts a countdown decrement rate of the vehicle-mounted system based on a relationship between the synchronized countdown time and a predicted value of a countdown display time on the vehicle-mounted system side; and a countdown display time decision unit that decides the countdown display time on the vehicle-mounted system side based on a current countdown display time on the vehicle-mounted system side and the adjusted countdown decrement rate in a case where the data packet is received for the Nth time, N being a natural number of 2 or more.

[0028] According to the above-described traffic signal countdown display system, when deciding the countdown display time on the vehicle-mounted system side, both the synchronization information of the countdown time from the new data packet and the countdown display time currently displayed on the vehicle-mounted system side are taken into account to decide the countdown decrement rate of the countdown display, and thus, compared with a case where the countdown display time is decided without taking the countdown decrement rate into account or a case where the countdown decrement rate is decided only based on the synchronization information of the countdown time from the new data packet, the variation of the countdown display time can be made more smooth and uniform while ensuring the accuracy of the countdown display time. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a diagram showing the configuration of the traffic signal countdown display system of the present application.

[0030] Figure 2 is a flowchart showing the traffic signal countdown display processing of the first embodiment.

[0031] Figure 3 is a flowchart showing the first countdown display time decision processing of the first embodiment.

[0032] Figure 4 is a flowchart showing the Mth countdown display time decision processing of the first embodiment in which the countdown decrement rate is not adjusted.

[0033] Figure 5 is a flowchart showing the Mth countdown display time decision processing of the first embodiment in which the countdown decrement rate is adjusted.

[0034] Figure 6 is a detailed flowchart showing the Mth countdown decrement rate adjustment step and the Mth countdown display time decision step of the first embodiment.

[0035] Figure 7is a detailed flowchart showing the Mth countdown decrement rate adjustment step and the Mth countdown display time decision step of the second embodiment. DETAILED DESCRIPTION

[0036] (First Embodiment)

[0037] Figure 1 is a diagram showing the configuration of the traffic signal countdown display system 1 of the present application. The traffic signal countdown display system 1 is included in a vehicle-mounted system, and the traffic signal countdown display function is one of a plurality of functions included in the vehicle-mounted system.

[0038] As shown in Figure 1 , the traffic signal countdown display system 1 includes an on board unit (OBU) 10 and a display unit 20. The on board unit 10 receives a data packet containing traffic signal information from a road side unit (RSU) 40 provided at a traffic signal 30 in a wireless communication manner, processes the traffic signal information in the data packet, and transmits the processed signal light information, countdown information, and the like to the display unit 20. The display unit 20 is, for example, a liquid crystal display, a head up display (HUD), or the like provided in a vehicle.

[0039] The on board unit 10 has a traffic signal information acquisition unit 11, a synchronized countdown time calculation unit 12, a countdown decrement rate adjustment unit 13, and a countdown display time decision unit 14.

[0040] The traffic signal information acquisition unit 11 receives a data packet containing traffic signal information from the road side unit 40 at a predetermined first time interval T1. The predetermined first time interval T1 is, for example, 0.5 seconds, 1 second, or the like. The communication manner between the traffic signal information acquisition unit 11 and the road side unit 40 is, for example, a wireless communication manner based on CV2X technology. The traffic signal information includes at least information of the countdown time COUNT_DOWN and the time stamp TIME_STAMP of the traffic signal, and can further include information of the current state of the signal light, the total duration of the traffic light, the signal light device ID, the position of the traffic signal, and the like.

[0041] The synchronized countdown time calculation unit 12 calculates a synchronized countdown time SYNC_TIME obtained by synchronizing the system time SYSTEM_TIME of the vehicle-mounted system using the time stamp TIME_STAMP and the countdown time COUNT_DOWN contained in the received data packet.

[0042] The countdown decrement rate adjusting unit 13 adjusts the countdown decrement rate RATE of the vehicle-mounted system based on the relationship between the synchronized countdown time SYNC_TIME and the predicted value of the countdown display time DISPLAY_TIME of the vehicle-mounted system. The countdown decrement rate RATE is a quantity indicating how fast the countdown display time DISPLAY_TIME of the vehicle-mounted system is decremented, and more specifically, is a quantity indicating how much the countdown display time DISPLAY_TIME of the vehicle-mounted system is decremented per unit time.

[0043] The initial value of the countdown decrement rate RATE (i.e., the initial decrement rate DEFAULT_RATE) is set to be the same as the decrement rate of the standard time, i.e., 1 second per second. That is, DEFAULT_RATE = 1.0.

[0044] When the unit time is set to 1 second and the countdown decrement rate RATE is less than 1, the decrement speed of the countdown display time of the vehicle-mounted system is slower than 1 second per second. For example, when the countdown decrement rate RATE is equal to 0.9, the countdown display time of the vehicle-mounted system is decreased by only 0.9 seconds for every 1 second of actual time.

[0045] The adjustment method of the countdown decrement rate will be described in detail later.

[0046] The countdown display time deciding unit 14 decides the next countdown display time DISPLAY_TIME of the vehicle-mounted system based on the synchronized countdown time SYNC_TIME calculated by the synchronized countdown time calculating unit 12, or based on the current countdown display time DISPLAY_TIME of the vehicle-mounted system and the adjusted countdown decrement rate RATE. The method of deciding the countdown display time will be described in detail later.

[0047] Figure 2 is a flowchart showing the traffic signal countdown display processing of the first embodiment.

[0048] In step S10, the traffic signal information obtaining unit 11 receives a data packet containing traffic signal information from the road-side unit 40 at a predetermined first time interval Tl.

[0049] In step S20, the traffic signal information obtaining unit 11 selects which kind of countdown display time deciding processing to perform based on the current countdown display situation and whether a new data packet containing traffic signal information has been received or not at a predetermined second time interval T2. The predetermined second time interval T2 is, for example, 0.1 seconds, 0.5 seconds, 1 second, etc.

[0050] In a case where the in-vehicle unit 10 is not performing countdown display and a new data packet is received (hereinafter referred to as a first case), the processing proceeds to step S30, and first countdown display time decision processing is executed. Details of the first countdown display time decision processing will be described later with reference to Figure 3 will be described.

[0051] In a case where the in-vehicle unit 10 is performing countdown display and a new data packet is not received (hereinafter referred to as a second case), the processing proceeds to step S40, and Mth countdown display time decision processing (M is a natural number equal to or greater than 2) that does not adjust the countdown decrement rate is executed. Details of the Mth countdown display time decision processing that does not adjust the countdown decrement rate will be described later with reference to Figure 4 will be described.

[0052] In a case where the in-vehicle unit 10 is performing countdown display and a new data packet is received (hereinafter referred to as a third case), the processing proceeds to step S50, and Mth countdown display time decision processing (M is a natural number equal to or greater than 2) that adjusts the countdown decrement rate is executed. Details of the Mth countdown display time decision processing that adjusts the countdown decrement rate will be described later with reference to Figure 5 will be described.

[0053] In the present embodiment, the in-vehicle unit 10 executes certain processing among steps S30, S40, and S50 at the second time interval T2, and M indicates the serial number of the system time on the in-vehicle system side and the serial number of each countdown display time decided by the processing of S30 to S50.

[0054] In step S60, the countdown display time decided by certain processing among steps S30, S40, and S50 is displayed by the display unit 20.

[0055] Figure 3 is a flowchart showing the first countdown display time decision processing of the first embodiment.

[0056] In the first case in Figure 2 , the data packet received at this time becomes a first received data packet (hereinafter referred to as a first data packet) for performing countdown display. Further, the system time point at which the traffic signal information acquisition unit 10 receives the first data packet is set as a first system time SYSTEM_TIME[1].

[0057] In step S301 (first synchronization-after countdown time calculation step), the synchronization-after countdown time calculation unit 12 calculates a first time difference DIFF_TIME[1] as a difference between the first system time point SYSTEM_TIME[1] and the first time stamp TIME_STAMP[1] in the first data packet.

[0058] DIFF TIME [1] = SYSTEM TIME [1] - TIME STAMP [1] (Formula 1)

[0059] Then, the first countdown time COUNT_DOWN[1] in the first data packet is subtracted by the first time difference DIFF_TIME[1] to obtain the first post-synchronization countdown time SYNC_TIME[1].

[0060] SYNC_TIME[1] = COUNT_DOWN[1] - DIFF_TIME[1] (Formula 2)

[0061] For the convenience of understanding, the following description is given in conjunction with a specific example.

[0062] In the specific example 1, it is assumed that the first time stamp TIME_STAMP[1] in the data packet received at the first system time SYSTEM_TIME[1] (SYSTEM_TIME[1] = 3.0 seconds) is 2.5 seconds, and the first countdown time COUNT_DOWN[1] in the data packet is 20 seconds. In this case, it is known from the above Formula 1 and Formula 2 that the first post-synchronization countdown time SYNC_TIME[1] is 19.5 seconds.

[0063] DIFF_TIME[1] = 3 seconds - 2.5 seconds = 0.5 seconds

[0064] SYNC_TIME[1] = 20 seconds - 0.5 seconds = 19.5 seconds

[0065] It should be noted that, for the convenience of description, the values of the system time and the time stamp assumed here are in a relatively simple numerical form. In fact, the values of the system time and the time stamp contain complete time information of hours, minutes and seconds, and the precision can be one hundredth of a second to ten thousandth of a second.

[0066] Next, in step S302 (first countdown decrement rate adjustment step), the countdown decrement rate adjustment unit 13 sets the countdown decrement rate to the initial decrement rate DEFAULT_RATE. That is, RATE = DEFAULT_RATE = 1.00.

[0067] Next, in step S303 (first countdown display time decision step), the countdown display time decision unit 14 takes the first post-synchronization countdown time SYNC_TIME[1] as the first countdown display time DISPLAY_TIME[1] on the vehicle-mounted system side.

[0068] In the above-mentioned specific example 1, when the first post-synchronization countdown time SYNC_TIME[1] calculated in step S301 is 19.5 seconds, the first countdown display time DISPLAY_TIME[1] is 19.5 seconds.

[0069] Generally, in order to keep the format consistent with the countdown time displayed by the traffic light, the integer part of the countdown display time on the vehicle system side is used as the actual countdown display time SHOW_TIME of the vehicle system.

[0070] In the above specific example 1, when the first countdown display time DISPLAY_TIME[1] is 19.5 seconds, the first countdown actual display time SHOW_TIME[1] of the vehicle system is 19 seconds.

[0071] In addition, Figure 3 In the process shown, the execution timing of step S302 is not limited thereto, and for example, it may be executed before step S301 or after step S303.

[0072] Figure 4 This is a flowchart showing the Mth countdown display time determination process without adjusting the countdown deceleration rate according to the first embodiment.

[0073] exist Figure 2 In the second case, since no new data packet is received at the Mth system time SYSTEM_TIME[M] (M is a natural number greater than or equal to 2), the countdown time calculation step after synchronization and the countdown deceleration rate adjustment step do not need to be performed. Figure 4 As shown, only the Mth countdown display time determination step S401 is executed without adjusting the countdown deceleration rate.

[0074] In step S401 , the M-th countdown display time DISPLAY_TIME[M] on the vehicle-mounted system side is obtained by decrementing the M-1th countdown display time DISPLAY_TIME[M-1] according to the current countdown decrement rate RATE.

[0075] DISPLAY_TIME[M]=DISPLAY_TIME[M-1]-T2*RATE (Formula 3)

[0076] In the above example 1, the second time interval T2 is set to 1 second. Assuming that no new data packet is received during the second system time SYSTEM_TIME[2] (SYSTEM_TIME[2] = 4.0 seconds), the second countdown display time DISPLAY_TIME[2] can be calculated as 18.5 seconds using the above formula 3.

[0077] DISPLAY_TIME[2] = 19.5 - 1 * 1.00 = 18.5

[0078] Further, it can be obtained that the second countdown actual display time SHOW_TIME[2] of the vehicle-mounted system at the second system time SYSTEM_TIME[2] is 18 seconds.

[0079] Figure 5 is a flowchart showing the Mth countdown display time decision process of adjusting the countdown decrement rate of the first embodiment.

[0080] In the third case in Figure 2 , since a new data packet is received at the Mth system time SYSTEM_TIME[M] (M is a natural number equal to or greater than 2), it is necessary to perform each step shown in Figure 5 including the synchronized countdown time calculation step and the countdown decrement rate adjustment step at this time. According to the order in which the data packets are received, the new data packet is referred to as the Nth data packet (i.e., the data packet received for the Nth time).

[0081] In step S501 (the Mth synchronized countdown time calculation step), the synchronized countdown time calculation unit 12 calculates the difference between the Mth system time SYSTEM_TIME[M] and the Nth time stamp TIME_STAMP[N] in the Nth data packet to obtain the Mth time difference DIFF_TIME[M].

[0082] DIFF_TIME[M] = SYSTEM_TIME[M] - TIME_STAMP[N] (Equation 4)

[0083] Then, the Nth countdown time COUNT_DOWN[N] in the Nth data packet is subtracted by the Mth time difference DIFF_TIME[M] to obtain the Mth synchronized countdown time SYNC_TIME[M].

[0084] SYNC_TIME[M] = COUNT_DOWN[N] - DIFF_TIME[M] (Equation 5)

[0085] In the above specific example 1, it is assumed that the second time stamp TIME_STAMP[2] in the second data packet (i.e., the data packet received for the second time) received at the third system time SYSTEM_TIME[3] (SYSTEM_TIME[3] = 5.0 seconds) is 4.6 seconds, and the second countdown time COUNT_DOWN[2] in the data packet is 19 seconds. In this case, it can be known from Equations 4 and 5 above that the third synchronized countdown time SYNC_TIME[3] is 18.6 seconds.

[0086] DIFF_TIME[3] = 5 seconds - 4.6 seconds = 0.4 seconds

[0087] SYNC_TIME[3] = 19 seconds - 0.4 seconds = 18.6 seconds

[0088] Next, in step S502 (Mth countdown decrement rate adjustment step), the countdown decrement rate adjustment unit 13 adjusts the Mth countdown decrement rate RATE[M] of the in-vehicle system in accordance with the relationship between the Mth post-synchronization countdown time SYNC_TIME[M] and the predicted value ESTIMATE_DISPLAY_TIME[M] of the Mth countdown display time on the in-vehicle system side.

[0089] where the predicted value ESTIMATE_DISPLAY_TIME[M] of the Mth countdown display time is obtained by decrementing the (M-1)th countdown display time DISPLAY_TIME[M-1] by the current countdown decrement rate RATE, as shown in Equation 6.

[0090] ESTIMATE_DISPLAY_TIME[M] = DISPLAY_TIME[M-1] - T2*RATE (Equation 6)

[0091] Figure 6 is a detailed flowchart of the Mth countdown decrement rate adjustment step and the Mth countdown display time determination step in Figure 5 Figure 6 Steps S5021 to S5027 in Figure 5 are detailed steps corresponding to the Mth countdown decrement rate adjustment step 502 in Figure 6 Figure 5 Steps S5031 to S5032 in

[0092] More specifically, in step S5021, the ratio of the predicted value ESTIMATE_DISPLAY_TIME[M] of the Mth countdown display time on the in-vehicle system side at the Mth system time point to the Mth post-synchronization countdown time SYNC_TIME[M] is calculated as a tentative decrement rate TMP_RATE.

[0093] TMP_RATE = ESTIMATE_DISPLAY_TIME[M] / SYNC_TIME[M] (Equation 7)

[0094] ​​Then, in step S5022, it is determined whether the change degree of the tentative decrement rate TMP_RATE with respect to the current countdown decrement rate RATE does not exceed a first threshold value.

[0095] When the change degree of the tentative decrement rate TMP_RATE with respect to the current countdown decrement rate RATE does not exceed the first threshold value, the process proceeds to step S5023, and the first change exceeding number is set to 0. The first change exceeding number indicates the number of times that the change degree of the countdown decrement rate RATE exceeds the first threshold value in succession.

[0096] The change degree of the tentative decrement rate can be a ratio RATIO_RATE of the tentative decrement rate to the current countdown decrement rate.

[0097] RATIO_RATE = TMP_RATE / RATE (Equation 8)

[0098] At this time, the first threshold value is preferably a value equal to or greater than 0.7 and equal to or less than 0.9, or a value equal to or greater than 1.1 and equal to or less than 1.3.

[0099] Further, the change degree of the tentative decrement rate can also be a change rate absolute value DELTA_RATE of the tentative decrement rate with respect to the current countdown decrement rate.

[0100] DELTA_RATE = | TMP_RATE / RATE - 1 | (Equation 9)

[0101] At this time, the first threshold value is preferably a value equal to or greater than 0.1 and equal to or less than 0.3.

[0102] The first threshold value is an upper limit value of the range of the change degree of the countdown decrement rate RATE that is allowed due to the delay or packet loss of the data packet transmission. If the change degree of the countdown decrement rate RATE exceeds this change degree, it can be considered that the change of the countdown decrement rate is too large (i.e., the countdown is discontinuous), and if the countdown decrement rate RATE is adjusted by the change degree that exceeds this threshold value, the smoothness of the display is reduced, which in turn affects the user's experience when observing the countdown display time.

[0103] Next, in step S5024, the tentative decrement rate TMP_RATE is set as the adjusted countdown decrement rate RATE of the in-vehicle system.

[0104] Next, in step S5031, the M-1th countdown display time DISPLAY_TIME[M-1] on the in-vehicle system side is decremented by the adjusted countdown decrement rate RATE, and thereby the Mth countdown display time DISPLAY_TIME[M] on the in-vehicle system side is determined.

[0105] DISPLAY TIME[M] = DISPLAY TIME[M - 1] - T2*RATE (Equation 10)

[0106] In the above embodiment 1, the third synchronization after countdown time SYNC_TIME[3] is calculated to be 18.6 seconds by the step S501. In the step S5021, the prediction value ESTIMATE_DISPLAY_TIME[3] of the Mth countdown display time is calculated to be 17.5 seconds and the temporary decrement rate TMP_RATE is calculated to be 0.941 by the Equations 6 and 7.

[0107] ESTIMATE_DISPLAY_TIME[3] = 18.5 - 1*1.00 = 17.5 seconds

[0108] TMP_RATE = 17.5 / 18.6 « 0.941

[0109] Next, in the step S5022, the ratio RATIO_RATE is calculated to be 0.941 by the Equation 8 or the change rate absolute value DELTA_RATE is calculated to be 0.059 by the Equation 9.

[0110] RATIO_RATE = 0.941 / 1 = 0.941

[0111] DELTA_RATE = |0.941 / 1 - 1| = 0.059

[0112] Since the calculated ratio RATIO_RATE or change rate absolute value DELTA_RATE does not exceed the first threshold value, the TMP_RATE = 0.941 is set as the adjusted countdown decrement rate RATE of the vehicle-mounted system in the step S5024.

[0113] Next, in the step S5031, the third countdown display time DISPLAY_TIME[3] is calculated to be 17.559 seconds by the Equation 10.

[0114] DISPLAY_TIME[3] = 18.5 - 1*0.941 = 17.559 seconds

[0115] Further, it can be obtained that the third countdown actual display time SHOW_TIME[3] of the vehicle-mounted system at the third system time SYSTEM_TIME[3] is 17 seconds.

[0116] On the other hand, as Figure 6As shown, in the judgment in step S5022, there is also a case where the degree of change of the tentative countdown rate TMP RATE with respect to the current countdown rate RATE exceeds the first threshold value.

[0117] When the degree of change of the tentative countdown rate TMP RATE exceeds the first threshold value in step S5022, proceed to step S5025, and accumulate (add 1) the first change exceeding number. Then, when the first change exceeding number does not reach the prescribed number of times (step S5026, No), maintain the current countdown rate RATE unchanged.

[0118] The prescribed number of times is set to an integer greater than 0 and less than or equal to 5 based on the number of fault tolerance times of the countdown jump. For example, in the case where the number of fault tolerance times is set to 3, it means that the countdown time after the jump is used to determine the countdown display time on the in-vehicle system side only when the degree of change of the countdown rate RATE exceeds the first threshold value continuously 3 times.

[0119] Next, proceed to step S5031, and decrease the (M-1)th countdown display time DISPLAY TIME [M-1] on the in-vehicle system side by the current countdown rate RATE, thereby determining the Mth countdown display time DISPLAY TIME [M] on the in-vehicle system side.

[0120] DISPLAY TIME [M] = DISPLAY TIME [M-1] - T2*RATE (Equation 10)

[0121] In the above-described specific example 1, assume that the third time stamp TIME STAMP [3] in the third data packet received at the fourth system time SYSTEM TIME [4] (SYSTEM TIME [4] = 6.0 seconds) is 5.2 seconds, and the third countdown time COUNT DOWN [3] in the data packet is 41 seconds. In specific example 1, assume that the third countdown time COUNT DOWN [3] jumps from the second countdown time COUNT DOWN [2] of 19 seconds to 41 seconds for ease of explanation. This case can occur based on human control by a traffic manager, and of course the specific reason for the countdown jump is not limited to this.

[0122] In this case, in step S501, the third synchronized countdown time SYNC TIME [4] is 40.2 seconds by Equations 4 and 5 described above.

[0123] DIFF TIME [4] = 6 seconds - 5.2 seconds = 0.8 seconds

[0124] SYNC_TIME[4] = 41 seconds - 0.8 seconds = 40.2 seconds

[0125] Next, in step S5021, the fourth countdown display time estimate value ESTIMATE_DISPLAY_TIME[4] is calculated to be 16.618 seconds and the provisional decrement rate TMP_RATE is calculated to be 0.413 by using the following equations 6 and 7.

[0126] ESTIMATE_DISPLAY_TIME[4] = 17.559 - 1 * 0.941 = 16.618 seconds

[0127] TMP_RATE = 16.618 / 40.2 = 0.413

[0128] Next, in step S5022, the ratio RATIO_RATE is calculated to be 0.439 by using the following equation 8 or the change rate absolute value DELTA_RATE is calculated to be 0.561 by using the following equation 9.

[0129] RATIO_RATE = 0.413 / 0.941 = 0.439

[0130] DELTA_RATE = | 0.413 / 0.941 - 1 | = 0.561

[0131] Since the calculated ratio RATIO_RATE or change rate absolute value DELTA_RATE exceeds the first threshold value (step S5022, No), the process proceeds to step S5025 in which the first change exceeding number is incremented by 1. The first change exceeding number at this time is 1.

[0132] In the specific example 1, the prescribed number in step S5026 is set to 3. Since the first change exceeding number at this time does not reach the prescribed number (1≠3), the current countdown decrement rate RATE is maintained.

[0133] Next, the process proceeds to step S5031 in which the fourth countdown display time DISPLAY_TIME[4] is calculated to be 16.618 seconds by using the following equation 10.

[0134] DISPLAY_TIME[4] = 17.559 - 1 * 0.941 = 16.618 seconds

[0135] Further, it is found that the fourth system time SYSTEM_TIME[4] is 16 seconds, which is the fourth countdown actual display time SHOW_TIME[4] of the in-vehicle system.

[0136] Next, assume that the fourth time stamp TIME STAMP[4] in the fourth data packet received at the next fifth system time SYSTEM TIME[5] (SYSTEM TIME[5] = 7.0 seconds) is 6.3 seconds, and the fourth countdown time COUNT DOWN[4] in the data packet is 40 seconds.

[0137] In this case, in step S501, the fifth synchronization after countdown time SYNC TIME[5] is 39.3 seconds by the above-described equations 4 and 5.

[0138] DIFF TIME[5] = 7 seconds - 6.3 seconds = 0.7 seconds

[0139] SYNC TIME[5] = 40 seconds - 0.7 seconds = 39.3 seconds

[0140] Next, in step S5021, the estimated value ESTIMATE DISPLAY TIME[5] of the fifth countdown display time is 15.677 seconds, and the temporary decrement rate TMP RATE is 0.399 by equations 6 and 7.

[0141] ESTIMATE DISPLAY TIME[5] = 16.618 - 1 * 0.941 = 15.677 seconds

[0142] TMP RATE = 15.677 / 39.3 « 0.399

[0143] Next, in step S5022, the ratio RATIO RATE is 0.424 by equation 8, or the absolute value of the change rate DELTA RATE is 0.576 by equation 9.

[0144] RATIO RATE = 0.399 / 0.941 = 0.424

[0145] DELTA RATE = | 0.399 / 0.941 - 1 | = 0.576

[0146] Since the calculated ratio RATIO RATE or the absolute value of the change rate DELTA RATE exceeds the first threshold (step S5022, No), the process proceeds to step S5025, in which the first change exceeding number is incremented by 1. The first change exceeding number at this time is 2.

[0147] Since the first change exceeding number at this time does not reach the prescribed number (2 « 3), the current countdown decrement rate RATE is maintained.

[0148] Next, proceeding to step S5031, the fifth countdown display time DISPLAY_TIME[5] is calculated as 15.677 seconds by formula 10.

[0149] DISPLAY_TIME[5] = 16.618 - 1 * 0.941 = 15.677 seconds

[0150] Further, it is found that the fifth countdown actual display time SHOW_TIME[5] of the in-vehicle system at the fifth system time SYSTEM_TIME[5] is 15 seconds.

[0151] The case where the first change exceeding number does not reach the prescribed number in step S5026 is explained above. On the other hand, as shown in step S5026, when the first change exceeding number reaches the prescribed number, proceeding to step S5027, the countdown decrement rate RATE of the in-vehicle system is restored to the initial decrement rate DEFAULT_RATE. Figure 6

[0152] Then, proceeding to step S5032, the Mth post-synchronization countdown time SYNC_TIME[M] is set as the Mth countdown display time DISPLAY_TIME[M] of the in-vehicle system side.

[0153] In the above-described specific example 1, it is assumed that the fifth time stamp TIME_STAMP[5] in the fifth data packet received at the sixth system time SYSTEM_TIME[6] (SYSTEM_TIME[6] = 8.0 seconds) is 7.2 seconds, and the fifth countdown time COUNT_DOWN[5] in the data packet is 39 seconds.

[0154] In this case, in step S501, the sixth post-synchronization countdown time SYNC_TIME[6] is found to be 38.2 seconds by the above-described formula 4 and formula 5.

[0155] DIFF_TIME[6] = 8 seconds - 7.2 seconds = 0.8 seconds

[0156] SYNC_TIME[6] = 39 seconds - 0.8 seconds = 38.2 seconds

[0157] Next, in step S5021, the estimate value ESTIMATE_DISPLAY_TIME[6] of the sixth countdown display time is calculated as 14.736 seconds, and the provisional decrement rate TMP_RATE is 0.386 by formula 6 and formula 7.

[0158] ESTIMATE_DISPLAY_TIME[6] = 15.677 - 1 * 0.941 = 14.736 seconds ​

[0159] TMP_RATE = 14.736 / 39.3 = 0.386

[0160] Next, in step S5022, the ratio RATIO_RATE is calculated to be 0.424 by Equation 8, or the absolute value DELTA_RATE of the change rate is calculated to be 0.576 by Equation 9.

[0161] RATIO_RATE = 0.386 / 0.941 = 0.410

[0162] DELTA_RATE = |0.386 / 0.941 - 1| = 0.590

[0163] Since the calculated ratio RATIO_RATE or the absolute value DELTA_RATE of the change rate exceeds the first threshold (step S5022, No), the process proceeds to step S5025, in which the first change exceeding number is incremented by 1. The first change exceeding number at this time is 3.

[0164] Since the first change exceeding number at this time has reached the prescribed number (3 = 3), the process proceeds to step S5027, in which the countdown decrement rate RATE of the in-vehicle system is restored to the initial decrement rate DEFAULT_RATE (RATE = 1.00).

[0165] Next, in step S5032, the sixth synchronization countdown time SYNC_TIME[6] is set as the sixth countdown display time DISPLAY_TIME[6] on the in-vehicle system side. That is, DISPLAY_TIME[6] = SYNC_TIME[6] = 38.2 seconds.

[0166] Further, it is found that the sixth countdown actual display time SHOW_TIME[6] of the in-vehicle system at the sixth system time SYSTEM_TIME[6] is 38 seconds.

[0167] According to the traffic signal countdown display system and the traffic signal countdown display method in the present embodiment, when deciding the Mth countdown display time DISPLAY_TIME[M] on the vehicle-mounted system side, the synchronization information SYNC_TIME of the countdown time in the new data packet and the (M-1)th countdown display time DISPLAY_TIME[M-1] currently displayed on the vehicle-mounted system side are taken into account to decide the countdown decrement rate RATE of the countdown display, compared with the case where the countdown display time is decided without considering the countdown decrement rate, or compared with the case where the countdown decrement rate is decided only according to the synchronization information of the countdown time in the new data packet, the variation of the countdown display time can be made more smooth and uniform while ensuring the accuracy of the countdown display time.

[0168] In addition, by setting the first change exceeding number, even in the case where the countdown COUNT_DOWN in the received data packet occasionally jumps, the countdown display time DISPLAY_TIME will not jump immediately, thereby the frequent jumping of the countdown display or the frequent change of the countdown display speed can be inhibited, so that the variation of the countdown display time is made more smooth and uniform.

[0169] (Second Embodiment)

[0170] The second embodiment is a variation of the above-mentioned first embodiment, and the only difference between the first embodiment and the second embodiment is that Figure 6 the processes of steps S5022, S5023, S5025 in Figure 7 will be described below.

[0171] Figure 7 is a detailed flowchart representing the Mth countdown decrement rate adjustment step and the Mth countdown display time decision step of the second embodiment. Among them, Figure 7 the steps S5022', S5023', S5025' in Figure 6 are different from the steps S5022, S5023, S5025 in

[0172] In step 5022', it is judged whether the change degree of the synchronization countdown time SYNC_TIME relative to the current countdown display time DISPLAY_TIME exceeds a second threshold value or not.

[0173] When the degree of change of the post-synchronization countdown time SYNC_TIME with respect to the current countdown display time DISPLAY_TIME does not exceed the second threshold value, the process proceeds to step S5023', and the second change exceeding number is set to 0. The second change exceeding number indicates the number of times that the degree of change of the post-synchronization countdown time SYNC_TIME exceeds the second threshold value consecutively.

[0174] The degree of change of the post-synchronization countdown time can be a ratio RATIO_TIME of the post-synchronization countdown time to the current countdown display time.

[0175] RATIO_TIME = SYNC_TIME / DISPLAY_TIME (Equation 11)

[0176] At this time, the second threshold value is preferably a value equal to or greater than 0.7 and equal to or less than 0.9, or a value equal to or greater than 1.1 and equal to or less than 1.3.

[0177] Further, the degree of change of the post-synchronization countdown time can also be a change rate absolute value DELTA_RATE of the post-synchronization countdown time with respect to the current countdown display time.

[0178] DELTA_RATIO_TIME = |SYNC_TIME / DISPLAY_TIME - 1| (Equation 12)

[0179] At this time, the second threshold value is preferably a value equal to or greater than 0.1 and equal to or less than 0.3.

[0180] The second threshold value is an upper limit value of the range in which the countdown decrement rate RATE is allowed to change due to the delay or packet loss of the data packet transmission. If the degree of change of the countdown decrement rate RATE exceeds this degree of change, it can be considered that the change of the countdown decrement rate is too large (i.e., the countdown is discontinuous), and if the countdown decrement rate RATE is adjusted with the degree of change exceeding this threshold value range, the smoothness of the display is reduced, which in turn affects the user's experience when observing the countdown display time.

[0181] On the other hand, as shown in FIG. 5B, in the judgment of step S5022', there is also a case where the degree of change of the post-synchronization countdown time SYNC_TIME with respect to the current countdown display time DISPLAY_TIME exceeds the second threshold value. Figure 7

[0182] When the degree of change of the post-synchronization countdown time SYNC_TIME exceeds the second threshold value in step S5022', the process proceeds to step S5025', and the second change exceeding number is incremented (by 1).

[0183] ​In the above embodiment 1, assume that the second time stamp TIME_STAMP[2] in the second data packet (i.e., the second received data packet) received at the third system time SYSTEM_TIME[3] (SYSTEM_TIME[3] = 5.0 seconds) is 4.6 seconds, and the second countdown time COUNT_DOWN[2] in the data packet is 19 seconds. The third synchronized countdown time SYNC_TIME[3] is calculated to be 18.6 seconds by the step S501.

[0184] In the step S5021, the estimated value ESTIMATE_DISPLAY_TIME[3] of the Mth countdown display time is calculated to be 17.5 seconds, and the temporary decrement rate TMP_RATE is calculated to be 0.941 by the equations 6 and 7.

[0185] ESTIMATE_DISPLAY_TIME[3] = 18.5 - 1 * 1.00 = 17.5 seconds

[0186] TMP_RATE = 17.5 / 18.6 « 0.941

[0187] Next, in the step S5022', the ratio RATIO_TIME is calculated to be 0.941 by the equation 11, or the absolute value DELTA_RATE of the change rate is calculated to be 0.059 by the equation 12.

[0188] RATIO_TIME = 18.6 / 18.5 = 1.005

[0189] DELTA_RATIO_TIME = | 18.6 / 18.5 - 1 | = 0.005

[0190] Since the calculated ratio RATIO_TIME or the absolute value DELTA_RATIO_TIME of the change rate does not exceed the second threshold value, the TMP_RATE = 0.941 is set as the adjusted countdown decrement rate RATE of the vehicle-mounted system in the step S5024.

[0191] Next, in the step S5031, the third countdown display time DISPLAY_TIME[3] is calculated to be 17.559 seconds by the equation 10.

[0192] DISPLAY_TIME[3] = 18.5 - 1 * 0.941 = 17.559 seconds

[0193] Further, it is found that the third countdown actual display time SHOW_TIME[3] of the vehicle-mounted system at the third system time SYSTEM_TIME[3] is 17 seconds.

[0194] In the above embodiment 1, assume that the third time stamp TIME_STAMP[3] in the third data packet received at the fourth system time SYSTEM_TIME[4] (SYSTEM_TIME[4] = 6.0 seconds) is 5.2 seconds, and the third countdown time COUNT_DOWN[3] in the data packet is 41 seconds.

[0195] In this case, in step S501, the third synchronized countdown time SYNC_TIME[4] is 40.2 seconds by the above equations 4 and 5.

[0196] Next, in step S5021, the estimated value ESTIMATE_DISPLAY_TIME[4] of the fourth countdown display time is 16.618 seconds, and the temporary decrement rate TMP_RATE is 0.413 by equations 6 and 7.

[0197] Next, in step S5022', the ratio RATIO_TIME is 2.289 by equation 11, or the absolute value DELTA_RATIO_TIME of the change rate is 1.289 by equation 12.

[0198] RATIO_TIME = 40.2 / 17.559 = 2.289

[0199] DELTA_RATIO_TIME = |40.2 / 17.559 - 1| = 1.289

[0200] Since the calculated ratio RATIO_TIME or the absolute value DELTA_RATIO_TIME of the change rate exceeds the second threshold (step S5022', NO), the process proceeds to step S5025', in which the second change exceeding number is incremented by 1. The second change exceeding number at this time is 1.

[0201] In embodiment 1, the prescribed number in step S5026 is set to 3. Since the second change exceeding number at this time does not reach the prescribed number (1≠3), the current countdown decrement rate RATE is maintained.

[0202] Next, the process proceeds to step S5031, in which the fourth countdown display time DISPLAY_TIME[4] is 16.618 seconds by equation 10.

[0203] DISPLAY_TIME[4] = 17.559 - 1*0.941 = 16.618 seconds

[0204] Further, it is found that the fourth countdown actual display time SHOW_TIME[4] of the fourth system time SYSTEM_TIME[4] of the in-vehicle system is 16 seconds.

[0205] Next, it is assumed that the fourth time stamp TIME_STAMP[4] in the fourth data packet received at the next fifth system time SYSTEM_TIME[5] (SYSTEM_TIME[5] = 7.0 seconds) is 6.3 seconds, and the fourth countdown time COUNT_DOWN[4] in the data packet is 40 seconds.

[0206] In this case, in step S501, the fifth synchronization countdown time SYNC_TIME[5] is found to be 39.3 seconds by the above-described equations 4 and 5.

[0207] Next, in step S5021, the estimated value ESTIMATE_DISPLAY_TIME[5] of the fifth countdown display time is found to be 15.677 seconds, and the temporary decrement rate TMP_RATE is found to be 0.399 by equations 6 and 7.

[0208] Next, in step S5022', the ratio RATIO_TIME is found to be 2.365 by equation 11, or the absolute value DELTA_RATIO_TIME of the change rate is found to be 1.365 by equation 12.

[0209] RATIO_TIME = 39.3 / 16.618 = 2.365

[0210] DELTA_RATIO_TIME = |39.3 / 16.618 - 1| = 1.365

[0211] Since the calculated ratio RATIO_TIME or the absolute value DELTA_RATIO_TIME of the change rate exceeds the second threshold value (step S5022', NO), the process proceeds to step S5025', in which the second change exceeding number is incremented by 1. The second change exceeding number at this time is 2.

[0212] Since the second change exceeding number at this time does not reach the prescribed number (2≠3), the current countdown decrement rate RATE is maintained.

[0213] Next, the process proceeds to step S5031, in which the fifth countdown display time DISPLAY_TIME[5] is found to be 15.677 seconds by equation 10.

[0214] DISPLAY_TIME[5] = 16.618 - 1*0.941 = 15.677 seconds

[0215] Further, it is found that the fifth countdown display time SHOW_TIME[5] of the fifth system time SYSTEM_TIME[5] of the on-vehicle system is 15 seconds.

[0216] Next, it is assumed that the fifth time stamp TIME_STAMP[5] in the fifth data packet received at the sixth system time SYSTEM_TIME[6] (SYSTEM_TIME[6] = 8.0 seconds) is 7.2 seconds, and the fifth countdown time COUNT_DOWN[5] in the data packet is 39 seconds.

[0217] In this case, in step S501, the sixth synchronized countdown time SYNC_TIME[6] is 38.2 seconds by the above-described equations 4 and 5.

[0218] Next, in step S5021, the estimated value ESTIMATE_DISPLAY_TIME[6] of the sixth countdown display time is 14.736 seconds, and the temporary decrement rate TMP_RATE is 0.386 by equations 6 and 7.

[0219] Next, in step S5022', the ratio RATIO_TIME is 2.547 by equation 11, or the absolute value DELTA_RATIO_TIME of the change rate is 1.547 by equation 12.

[0220] RATIO_TIME = 38.2 / 15 = 2.547

[0221] DELTA_RATIO_TIME = |38.2 / 15 - 1| = 1.547

[0222] Since the calculated ratio RATIO_TIME or the absolute value DELTA_RATIO_TIME of the change rate exceeds the second threshold (step S5022', NO), the process proceeds to step S5025', in which the second change exceeding number is incremented by 1. The second change exceeding number at this time is 3.

[0223] Since the second change exceeding number at this time reaches the prescribed number (3 = 3), the process proceeds to step S5027, in which the countdown decrement rate RATE of the on-vehicle system is restored to the initial decrement rate DEFAULT_RATE (RATE = 1.00).

[0224] Next, in step S5032, the sixth synchronized countdown time SYNC_TIME[6] is set as the sixth countdown display time DISPLAY_TIME[6] on the in-vehicle system side. That is, DISPLAY_TIME[6] = SYNC_TIME[6] = 38.2 seconds.

[0225] Further, it is found that the sixth system time SYSTEM_TIME[6] is 38 seconds as the sixth countdown actual display time SHOW_TIME[6] on the in-vehicle system side.

[0226] The above-described embodiments are merely examples of embodiments, and the present application is not limited to the above-described embodiments, and various changes, deletions, combinations, and the like can be made within the scope of the gist thereof.

Claims

1. A traffic signal countdown display method, characterized by, comprises: a traffic signal information acquisition step in which the vehicle-mounted system receives a data packet containing traffic signal information at predetermined time intervals; a synchronized countdown time calculation step in which a synchronized countdown time obtained by synchronizing the system time of the vehicle-mounted system is calculated using a time stamp contained in the data packet and a countdown time; a countdown decrement rate adjustment step in which the countdown decrement rate of the vehicle-mounted system is adjusted according to the relationship between the synchronized countdown time and a predicted value of the countdown display time on the vehicle-mounted system side; a countdown display time decision step in which, in the case where the data packet is received for the Nth time, the synchronized countdown display time on the vehicle-mounted system side is decided according to the current countdown display time on the vehicle-mounted system side and the adjusted countdown decrement rate, where N is a natural number of 2 or more, in the case where the data packet, which is a first data packet, is received for the first time by the traffic signal information acquisition step at a first system time point of the vehicle-mounted system, in the synchronized countdown time calculation step, a first time difference is calculated by subtracting a first time stamp in the first data packet from the first system time point, and a first synchronized countdown time is obtained by subtracting the first time difference from a first countdown time in the first data packet, in the countdown decrement rate adjustment step, an initial value of the countdown decrement rate, which is an initial decrement rate, is set to be the same as the decrement rate of a standard time, in the countdown display time decision step, the first synchronized countdown time is set as the first countdown display time on the vehicle-mounted system side, in the case where the data packet, which is an Nth data packet, is received for the Nth time by the traffic signal information acquisition step at an Mth system time point of the vehicle-mounted system, where M is a natural number of 2 or more, in the synchronized countdown time calculation step, an Mth time difference is calculated by subtracting an Nth time stamp in the Nth data packet from the Mth system time point, and an Mth synchronized countdown time is obtained by subtracting the Mth time difference from an Nth countdown time in the Nth data packet, in the countdown decrement rate adjustment step, a ratio of a predicted value of an Mth countdown display time on the vehicle-mounted system side at the Mth system time point to the Mth synchronized countdown time is calculated as a tentative decrement rate, and when the degree of change of the tentative decrement rate with respect to the current countdown decrement rate does not exceed a first threshold value set in advance, the tentative decrement rate is set as the adjusted countdown decrement rate of the vehicle-mounted system, in the countdown display time decision step, the current countdown display time on the vehicle-mounted system side is decremented at the adjusted countdown decrement rate, and thus the Mth countdown display time on the vehicle-mounted system side is decided.

2. The traffic signal countdown display method according to claim 1, wherein the predicted value of the Mth countdown display time on the vehicle-mounted system side is a predicted value obtained by decrementing the current countdown display time at the current countdown decrement rate. ​ ​ 3. The traffic signal countdown display method according to claim 1, wherein an integer part of the countdown display time on the in-vehicle system side is set as the actual countdown display time on the in-vehicle system side.

4. The traffic signal countdown display method according to claim 1, wherein in the countdown decrement rate adjustment step, when the degree of change in the provisional decrement rate exceeds a first threshold value set in advance, a first change exceeding count is incremented, and when the first change exceeding count does not reach a predetermined number of times, the current countdown decrement rate is maintained, and in the countdown display time decision step, the current countdown display time on the in-vehicle system side is decremented at the current countdown decrement rate, thereby deciding the Mth countdown display time on the in-vehicle system side, when the first change exceeding count reaches the predetermined number of times, the countdown decrement rate on the in-vehicle system side is restored to the initial decrement rate, and in the countdown display time decision step, the Mth synchronized countdown time is set as the Mth countdown display time on the in-vehicle system side.

5. The traffic signal countdown display method according to claim 1 or 4, wherein the first threshold value is an upper limit value of a range in which the countdown decrement rate is allowed to change due to delay or packet loss in data packet transmission, when the degree of change in the provisional decrement rate is a ratio of the provisional decrement rate to the current countdown decrement rate, the first threshold value is set to a value equal to or greater than 0.7 and equal to or less than 0.9, or a value equal to or greater than 1.1 and equal to or less than 1.

3.

6. The traffic signal countdown display method according to claim 1 or 4, wherein the first threshold value is an upper limit value of a range in which the countdown decrement rate is allowed to change due to delay or packet loss in data packet transmission, when the degree of change in the provisional decrement rate is an absolute value of a change rate of the provisional decrement rate with respect to the current countdown decrement rate, the first threshold value is set to a value equal to or greater than 0.1 and equal to or less than 0.

3.

7. The traffic signal countdown display method according to claim 1, wherein in the countdown decrement rate adjustment step, when the degree of change in the synchronized countdown time exceeds a second threshold value set in advance, a second change exceeding count is incremented, and when the second change exceeding count does not reach a predetermined number of times, the current countdown decrement rate is maintained, and in the countdown display time decision step, the current countdown display time on the in-vehicle system side is decremented at the current countdown decrement rate, thereby deciding the Mth countdown display time on the in-vehicle system side after synchronization, when the second change exceeding count reaches the predetermined number of times, the countdown decrement rate on the in-vehicle system side is restored to the initial decrement rate, and in the countdown display time decision step, the Mth synchronized countdown time is set as the Mth countdown display time on the in-vehicle system side.

8. The traffic signal countdown display method according to claim 7, wherein the second threshold value is an upper limit value of a range in which the post-synchronization countdown time is allowed to vary due to delay or packet loss of the data packet, in a case where the degree of variation of the post-synchronization countdown time is a ratio of the post-synchronization countdown time to the current countdown display time, the second threshold value is set to a value equal to or greater than 0.7 and equal to or less than 0.9, or a value equal to or greater than 1.1 and equal to or less than 1.

3.

9. The traffic signal countdown display method according to claim 7, characterized in that: the second threshold value is an upper limit value of a range in which the post-synchronization countdown time is allowed to vary due to delay or packet loss of the data packet, in a case where the degree of variation of the post-synchronization countdown time is an absolute value of a rate of change of the post-synchronization countdown time with respect to the current countdown display time, the second threshold value is set to a value equal to or greater than 0.1 and equal to or less than 0.

3.

10. The traffic signal countdown display method according to claim 4 or 7, characterized in that: the prescribed number of times is set in advance to an integer greater than 0 and equal to or less than 5, based on a number of times of fault tolerance in which the countdown jumps.

11. A traffic signal countdown display system, comprising: including: a traffic signal information acquisition unit that receives a data packet containing traffic signal information at predetermined time intervals; a post-synchronization countdown time calculation unit that calculates a post-synchronization countdown time obtained by synchronizing a system time of a vehicle-mounted system, using a time stamp contained in the data packet and a countdown time; a countdown decrement rate adjustment unit that adjusts a countdown decrement rate of the vehicle-mounted system, according to a relationship between the post-synchronization countdown time and a predicted value of the countdown display time on the vehicle-mounted system side; and a countdown display time decision unit that decides a countdown display time on the vehicle-mounted system side, according to the current countdown display time on the vehicle-mounted system side and the adjusted countdown decrement rate, in a case where the data packet is received for the Nth time, where N is a natural number equal to or greater than 2, in a case where the data packet, which is a first data packet, is received for the first time by the traffic signal information acquisition unit at a first system time point of the vehicle-mounted system, the post-synchronization countdown time calculation unit calculates a first time difference obtained by subtracting a first time stamp in the first data packet from a difference between the first system time point and the first countdown time in the first data packet, and calculates a first post-synchronization countdown time obtained by subtracting the first time difference from the first countdown time in the first data packet, the countdown decrement rate adjustment unit sets an initial value of the countdown decrement rate, which is an initial decrement rate, to be the same as a decrement rate of a standard time, the countdown display time decision unit decides the first post-synchronization countdown time as a first countdown display time on the vehicle-mounted system side, in a case where the data packet, which is an Nth data packet, is received for the Nth time by the traffic signal information acquisition unit at an Mth system time point of the vehicle-mounted system, where M is a natural number equal to or greater than 2, The post-synchronization countdown time calculation unit calculates a difference between the Mth system time point and an Nth time stamp in the Nth data packet to obtain an Mth time difference, and subtracts the Mth time difference from an Nth countdown time in the Nth data packet to obtain an Mth post-synchronization countdown time, The countdown decrement rate adjustment unit calculates a ratio of a predicted value of the Mth countdown display time on the vehicle-mounted system side at the Mth system time point to the Mth post-synchronization countdown time as a tentative decrement rate, and when a change degree of the tentative decrement rate with respect to a current countdown decrement rate does not exceed a first threshold value set in advance, the tentative decrement rate is used as an adjusted countdown decrement rate of the vehicle-mounted system, The countdown display time determination unit decrements a current countdown display time on the vehicle-mounted system side according to the adjusted countdown decrement rate, thereby determining the Mth countdown display time on the vehicle-mounted system side.

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