JP4831509B2 - Collision warning method in automobile - Google Patents

Description

  The present invention relates to a collision warning method for an automobile according to the superordinate concept of claim 1.

  Current road vehicles, especially commercial vehicles, are increasingly equipped with so-called cruise control systems to keep the speed constant. This system has the role of setting and maintaining a constant cruise speed that can be defined by the driver on a motorway or highway. This speed must also be maintained when the vehicle is traveling uphill or downhill. This allows the system to open the throttle valve appropriately or reduce the throttle opening, or (in the normal case) to operate the vehicle's continuous action brake (retarder).

In another refinement stage for the ACC (adaptive cruise control) or distance control system described above, the system can also detect and keep constant the distance to the preceding vehicle. Therefore, it is necessary to incorporate a sensor for detecting this interval. The sensor can be configured as a radar sensor or a laser sensor, for example. When the distance to the preceding vehicle is reduced to a predetermined target distance, and this is detected by the distance sensor, the vehicle distance is controlled to this target value by closing the throttle valve by ACC or further operating the service brake. The The predetermined target interval is, for example, 50 m for a truck. The vehicle speed can then be below the set cruise speed. Subsequently, when the preceding vehicle is accelerated again, the set cruise speed is controlled again. For safety and comfort reasons, ACC allows service brakes to be operated to a vehicle deceleration of approximately 2.5 m / s ² and thus far below the maximum possible 6-8 m / s ² deceleration. .

  If the preceding vehicle is suddenly decelerated strongly, or another vehicle suddenly enters the safety interval for the preceding vehicle from the adjacent lane, a dangerous condition occurs for ACC. In these cases, it is known to generate appropriate warnings (system limit warnings) to the driver to avoid accidents. When the above-described braking function of the ACC is not sufficient, the driver assists the ACC with additional driver braking so that a sufficient safety interval for the preceding vehicle can be maintained.

  However, if the danger of a rear-end collision is detected, the driver can be warned regardless of the ACC activation state (collision warning).

  From U.S. Pat. No. 5,931,547, a collision prevention system is known, and if the so-called collision time to an obstacle in front of his vehicle is less than a predetermined warning time, this system will inform the driver. An acoustic warning is issued. In this case, the hydraulic brake of the vehicle is automatically operated. At this time, the distance from the preceding vehicle is obtained by a laser distance sensor. For example, the automatic control is performed only when the braking pressure of the vehicle already existing by the driver braking is below a predetermined threshold, that is, the automatic braking is performed only when the driver does not sufficiently brake.

ここでΔｖは両方の車両の間の差速度である。ＴＴＣが閾値を下回ると、警告される。しかしこの方法は、特に小さい間隔又はほぼ零の相対速度の場合、実際の計算が非常に大きいＴＴＣを生じる、という欠点を持っている。それによりこの場合状況はＡＣＣにより危険なしと評価される。なぜならば、僅かな間隔のため危険な状況が存在しても、ＴＴＣが閾値より上に留まるからである。In this known system, the calculation of the collision time TTC or “time to collision” is performed by the following equation.

Here, Δv is the differential speed between both vehicles. A warning is issued if TTC falls below a threshold. However, this method has the disadvantage that the actual calculation results in a very large TTC, especially for small intervals or near zero relative velocities. In this case, the situation is then evaluated as dangerous by ACC. This is because the TTC stays above the threshold even if a dangerous situation exists due to the small interval.

  Furthermore, the known calculations according to the above formulas are considered appropriate even in the case of extremely dynamic driving situations, i.e. when the distance and relative speed of the vehicle always change significantly.

  From European Patent Application Publication No. 6827860, a distance control method for a vehicle and a device for carrying out this method are known, and when the target distance between its own vehicle and a preceding vehicle is exceeded, A warning is given to the person. The target interval is related to the traveling speed of the vehicle, the weather, and the traveling mode of the vehicle. The warning signal requires the driver to manually brake the vehicle in addition to ACC braking. The running response of the vehicle or its running mode is determined through the acceleration response and braking response so far.

  Finally, a braking control system is known from US Pat. No. 6,604,042, and automatic braking can be initiated when his vehicle approaches an object in front. Known systems further identify whether the driver is trying to overtake the preceding vehicle. In this case, the automatic braking started before the driver braking should be prevented. The known method further calculates the target deceleration of the own vehicle necessary to avoid a collision with the preceding vehicle. The calculated target deceleration is compared with the own vehicle deceleration threshold in a comparison circuit. When the calculated target deceleration is greater than or equal to a predetermined threshold and at the same time another condition is met, automatic braking of the vehicle is started.

  This known method does not include possible additional braking by the driver and does not take into account the driver reaction time. The necessary remaining time for the preceding vehicle is not taken into account as well. Furthermore, no collision warning signal unrelated to the control intervention is generated for the driver.

  The problem underlying the present invention is that in a car equipped with a distance sensor, which does not have the above disadvantages and possibly cannot maintain the remaining distance to the preceding vehicle after the end of ACC braking or after driver braking, It is to present a collision warning method that can generate a reliable warning signal for the driver.

  This problem is solved by the invention included in claim 1. The dependent claims contain appropriate developments.

  The method according to the invention has the particular advantage of taking into account the driver's reaction time to the generated warning signal. This reaction time is also taken into account when the driver is already braking. In this case, the driver reaction time, and thus the time from normal braking to the stronger or maximum braking required, is naturally less than the response time from unbraking to braking. This is because the driver's feet are already on the brake pedal.

  Another advantage of the method according to the invention is that the calculations performed are physically correct and can therefore be used in any situation. This avoids the risk of false alarms. Due to its simple mathematical construction, all the equations of the reference can be realized without any problems with limited computational power by a microcontroller with fixed-point arithmetic.

  The invention is explained in detail below with reference to the drawings.

  FIG. 1 schematically shows a vehicle “ego” and a preceding vehicle “vorne”. The distance between both vehicles is dx. Both stroke coordinates for the virtual 0 line are Xego and Xvorne. These stroke coordinates are defined as Xvorne-Xego = dx.

  As already described above, in principle, a collision warning can be issued to a vehicle having a sensor for detecting the periphery (for example, an ACC system distance sensor). This warning can be in the form of a sound, light or haptic signal.

  The distance and / or relative speed with respect to the preceding vehicle can be determined by the aforementioned sensor, for example, a radar sensor. The speed and acceleration or deceleration of the vehicle itself can be determined via wheel sensors as is well known. The speed and acceleration or deceleration of the preceding vehicle can also be obtained from the distance or relative speed obtained as described above. Such data is required for the later-described guidance of the collision warning.

  To realize the collision warning, in addition to the surrounding sensor device, it is needless to say that a controller having an appropriate algorithm (software) for calculating whether or not the collision warning is necessary in the current traffic situation is necessary. .

  It is common for dangerous traffic situations to occur because a slow target appears suddenly in front of its own vehicle, or the preceding vehicle is suddenly decelerated (or both problems occur simultaneously).

In addition to driver reaction time, it is useful to know if a vehicle decelerates during interval control or during driver intervention in order to form a warning criterion. Approximately, it can be assumed that the driver can decelerate at about 6-8 m / s ² during manual braking intervention, but the driver assistance system available in the European market is a longitudinal dynamic control. For this reason, it is usually up to 2.5 m / s ² . This relatively small value is justified by the fact that automatic full braking cannot be held responsible for safety reasons. This is because the following vehicle can no longer brake in a timely manner and may cause a rear-end collision. This cannot be taken for the following reasons. In other words, it is not possible to completely prevent the ACC command for full braking from being erroneously issued.

The criteria for collision warning, and in particular the vehicle deceleration a_ego_Bedarf for the following vehicle “ego”, is derived below so that it can maintain the remaining distance dx _Rest for the preceding vehicle: , It must be added to the ACC warning signal by the vehicle after the driver reaction time T _Reakt has elapsed.

  If the value of the deceleration a_ego_Bedarf calculated in this way is above the deceleration that can be achieved by ACC (this can be known by comparison), it will require the driver to assist ACC with additional braking. A system limit warning is issued.

  Moreover, when the value of the deceleration a_ego_Bedarf calculated in this way is above the assumed maximum deceleration to be generated by the driver, a general collision warning is generated regardless of the ACC.

  The reference or calculated required deceleration a_ego_Bedarf is based on the assumption that, according to FIG. 2, the driver has a reaction time T_Reakt and after this reaction time elapses, for example, the vehicle can be decelerated with a deceleration a_ego_Brems by full braking. Based on. The reaction time T_Reakt is a standard fitting parameter and is related to the situation. For example, when the driver already knows a dangerous situation and the foot is on the brake pedal, the reaction time is shortened.

  Assume that the preceding vehicle continues its current motion state throughout the entire calculation process. That is, the acceleration a_vorne of the previous vehicle remains constant during the calculation cycle. The calculation is performed for 50 ms, for example.

The next warning criterion is always extrapolating the motion status of the ego and preceding vehicles to the future based on the current motion status at each clock time of the warning algorithm, so that In order to avoid a rear-end collision with the vehicle, that is, to maintain the remaining distance dx _Rest , the deceleration a_ego_Bedarf that must occur after the reaction time T_Reakt has elapsed is calculated.

  If the value of a_ego_Bedarf calculated in this way is still above the vehicle deceleration that can be generated by the driver under normal conditions, ACC generates a general driver collision warning in addition to the system limit warning described above. I have to do it.

  The following calculation is the basis of the standard. A new criterion is calculated at each cycle time or cycle. The current time point (“0”) corresponds to the beginning of the time in the diagram shown in FIG.

Assume that the vehicle (“ego”) maintains the current deceleration in the future until the end of the reaction time “T_Reakt” (time “1”). At the end of the reaction time, the movement state of the own vehicle and the previous vehicle is calculated as follows.
General relationship according to Fig. 1 Interval: dx = X _borne -X _ego
Relative speed: dv = V _vorne -V _ego

ここでｄｘｏ＝時点０における間隔
ｖ＿ｏ＝時点０における速度
ａ＿ｏ＝時点０における減速度
ａ_{ｅｇｏ＿Ｒｅａｋｔ}＝時点“０”と“１”との間における自身の（一定な）減速度First, a general formula for the relative motion of both vehicles is established in relation to time (t). The next calculation of the interval dx (t) and the relative velocity dv (t) is valid during the reaction time (0 <t <T_Reakt) and therefore between the time points “0” and “1” in FIG.

Where dxo = interval at time 0 v_o = speed at time 0 a_o = deceleration at time 0 a _{ego_Reakt} = own (constant) deceleration between time “0” and “1”

As a special case of the above equation, if t = T_Reakt and thus at the end of the reaction time (time point “1”) in the previous calculation, the following equation is obtained:

  Now, after the reaction time T_Reakt has elapsed, the own vehicle deceleration a_ego_Bedarf is calculated which is sufficient to avoid a rear-end collision with the previous vehicle and to guarantee a slight remaining distance dx_Rest (for example 5 m).

ここでｄｘ_１，ｄｖ_１＝時点“１”における間隔又は相対速度
ａ_{ｅｇｏ＿Ｂｅｄａｒｆ}＝時点“１”と“２”との間における自身の車両の（一定の）減速度In that case, for the next time interval, a general formula for the vehicle motion or distance dx (t) and the differential speed dv (t) is established, and for (T_Reakt <t <T_Brems), ie “1” in FIG. An expression for the time interval between “and“ 2 ”is established.

Where dx ₁ , dv ₁ = interval or relative speed at time point “1” a _{ego_Bedarf} = (constant) deceleration of own vehicle between time points “1” and “2”

If t = T_Brems, and therefore at the end of the braking operation (time “2”) in time in the previous calculation, the following equation is obtained.

Now, as additional information, when the remaining distance is reached (time “2”) in the previous calculation, the remaining distance dx (t) of both vehicles becomes dx _Rest , and the relative speed dv (t) decreases completely, that is, 0. To be put into the previous calculation. Therefore, the following equation is obtained.
dx _{T_brems} = dx (t = T_Brems) = dx _rest
dv _{T Brems} = dv (t = T_Brems) = 0

By solving the equation dv (t = T_Brems) = 0 by T_Brems and putting the result into the equation dx (t = T_Brems), the following relationship can be found.

All elements of this formula are known. The values at time “1”, ie dx ₁ and dv _1, have already been calculated as described above. Therefore, the equation shown directly represents the deceleration (or acceleration in some cases) of the vehicle that is required to avoid a rear-end collision after the system or vehicle-specific reaction time resulting from the current kinematic situation. ing.

The value dx _Rest, ie the remaining distance for the preceding vehicle at the end of braking, is appropriately set to a value between 0 and 30 m.

  In order to generate a system limit warning and a driver-collision warning, two different cases are calculated simultaneously according to the above formula for a_ego_Bedarf.

  For a system limit warning, a reaction time T_Reakt at 0 is assumed and a_ego_Bedarf (T_Reakt = 0) is calculated. The value thus calculated is then compared to a predetermined deceleration that ACC can automatically generate, as described above. In order to obtain the required deceleration a_ego_Bedarf (T_Reakt = 0), if more braking is required than can be achieved by ACC, a system limit warning is issued requesting the driver to brake appropriately and appropriately.

  Due to the driver-collision warning, the above equation for a_ego_Bedarf with a reaction time T_Reakt (ie, actual driver reaction time) not equal to 0 is calculated. If the driver has not yet operated the brakes at the time of calculation, T_Reakt is conveniently set between 0.5 and 3 seconds. However, this calculation also applies to the special case where the driver is already actively braking at the time of the calculation. Again, the actual deceleration between points “0” and “1” (according to FIG. 2) can be used (approximately) as a_ego_Reakt. However, in this case, a shorter reaction time T_Reakt than in the normal case is issued for object determination and situation confirmation already performed by the driver. The shortened reaction time is caused in this case by the fact that the driver's foot is already on the brake pedal. Therefore, T_Reakt is conveniently set to a value of 0.1 to 2 seconds.

  In order to obtain the value a_ego_Bedarf (T_Reakt> 0) calculated in this way, a collision warning is issued if a greater vehicle deceleration that can occur during the maximum braking assumed by the driver is required. This warning is made regardless of whether ACC is used. When the driver converts the assumed maximum deceleration of the vehicle at the time of warning, the actual remaining interval is within the interval dx_Rest described above. If avoidance is still possible, in order to avoid a collision, the driver can adapt at the same time to conveniently bypass the preceding vehicle or obstacle.

  When the previous vehicle is faster than its own vehicle, the criteria cannot be applied correctly. However, in this case, unless the interval is too small, there is no fear of collision due to speed change.

  If the previous vehicle stops within the calculation time, the calculation must be extended appropriately to avoid defects. Therefore, the time interval until stopping must be calculated according to the current motion state (acceleration and speed) of the previous vehicle. After this point, the distance and relative speed remaining between the vehicles may be calculated based on the movement of the own vehicle. However, the simpler algorithm as described above is on the safer side of the result, i.e. it gives the driver an early warning, so the expansion of the calculation is in some circumstances to optimize the calculation time in the microcontroller. , Can not do.

  The above-mentioned collision warning and / or system limit warning can also be suitably used to start an automatic braking process by the vehicle's service brake at the same time. This has the advantage that braking is generally performed particularly fast. This is because the driver's reaction time is saved. On the other hand, braking is carried out immediately with the required high strength. The prerequisite for such automatic braking is, of course, that the vehicle is equipped with an ACC and an electrically drivable braking system. With such a system, the service brake can be driven regardless of the driver.

  As mentioned above, the deceleration of this automatic braking is advantageously limited to values well below the maximum possible deceleration. As a result, in the case of a false alarm that can occur in particular, a rear-end collision of a subsequent vehicle is prevented. Therefore, the determination of maximum braking is reserved for the driver.

  The system limit warning and / or the collision warning can be appropriately performed by sound and / or light and / or tactile sense.

  As described above, all the simple and extended criteria can be realized even in a limited calculation range in a microcomputer that performs fixed-point arithmetic (no opening, no solution of the equation). This allows the method according to the invention to be implemented inexpensively and in some cases can be undertaken by existing microcontrollers.

  The schematic diagram of two vehicles which drive | work forward and backward is shown.   Fig. 2 shows a vehicle braking diagram for explaining the induction of equations used in the method according to the invention for the vehicle deceleration to occur.

Explanation of symbols

dx distance between two vehicles ego own vehicle vorne preceding vehicle

Claims (7)

A collision warning method for an automobile, comprising a measuring device for detecting at least a distance (dx) with respect to a preceding vehicle of the automobile, and a distance signal is supplied to the evaluation device.
a) In the evaluation device, the vehicle deceleration (a_ego_Bedarf) that must be generated by the vehicle after the driver reaction time (T_Reakt) has elapsed is always calculated in order to be able to maintain the remaining distance (dx _Rest ) relative to the preceding vehicle. And
b) If the calculated deceleration (a_ego_Bedarf) value is above the assumed vehicle deceleration that can be generated by driver braking, a collision warning signal is issued,
c) If the value of the vehicle deceleration (a_ego_Bedarf) calculated under the condition that the driver reaction time is zero (T_Reakt = 0) is above the deceleration that can be achieved by the adaptive cruise control device (ACC), System limit warning signal is issued,
d) The following formula

Calculates the vehicle deceleration (a_ego_Bedarf), where dv ₁ = the relative speed of both vehicles at the end of the driver reaction time dx ₁ = the distance between both vehicles at the end of the driver reaction time dx _Rest = the end of braking A predetermined remaining interval of the preceding vehicle at a _{horn —} 0 = current deceleration of the preceding vehicle.

The method according to claim 1. 3. The method according to claim 1 or 2, characterized in that when the driver has not yet braked, the driver reaction time (T_Reakt) is set to 0.5-3 seconds. 3. The method according to claim 1, wherein when the driver is already braking, the driver reaction time (T_Reakt) is set to 0.1 to 2 seconds. 5. A method according to claim 1, wherein a system limit warning signal or a collision warning signal is used to initiate braking of the vehicle. 6. The vehicle having an adaptive cruise control device, wherein the vehicle deceleration calculated by the driver reaction time is limited to a value lower than an assumed vehicle deceleration that can be generated by driver braking. The method described. Method according to one of the preceding claims, characterized in that the system limit warning signal or the collision warning signal is a sound or light or tactile signal.

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