Method for controlling a vehicle-to-vehicle distance adjustment system

Abstract

A method for controlling a system for regulating the distance between a target vehicle (10) and a following vehicle (20), the regulating system being mounted on the following vehicle, is disclosed, the method comprising: implementing a control law (cmd) for regulating the distance, the control law calculating potential setpoint distances for a plurality of possible combinations of moving speeds of the following vehicle and the target vehicle; and, for a given combination of moving speeds of the following vehicle and the target vehicle in the plurality of possible combinations, determining a final setpoint distance from the potential setpoint distances previously calculated by the control law.

Description

Technical Field

[0001] The present invention relates to the field of driving assistance for motor vehicles. More particularly, the present invention relates to a method for controlling a vehicle-to-vehicle distance adjustment system. Background Art

[0002] The driving assistance features currently available in vehicles are designed to improve ride comfort and reduce road hazards. To this end, efforts have been made to develop features that maintain a predetermined setpoint distance, or safety distance, between two vehicles. Consequently, some vehicles may feature ACC (Adaptive Cruise Control) systems. This system, equipped in a vehicle known as a following vehicle, detects a vehicle ahead of it (known as a target vehicle). The following vehicle is equipped with a laser or camera to estimate the target vehicle's speed and distance, then controls the following vehicle's speed to maintain a safe distance. In many countries, road regulations require that following vehicles maintain a safe distance, particularly to avoid collisions when the preceding vehicle brakes or stops. The safety distance depends primarily on the following vehicle's speed. For example, under French road regulations, the safety distance corresponds to the distance covered by the following vehicle within a defined time interval of at least two seconds. In other words, regulations require that the following vehicle maintain a distance equivalent to two seconds of driving time between it and the target vehicle, as this time interval theoretically allows the user to maintain safety in the event of sudden braking.

[0003] For example, US Pat. No. 6,789,637 discloses a distance control mechanism for a motor vehicle. The device is adapted to observe a setpoint distance or setpoint time interval relative to a target vehicle (which is dependent on the driving speed). In determining the setpoint distance or setpoint time interval, the distance control takes into account a minimum distance or minimum time interval that can be specified by the driver. In response to low visibility conditions detected by sensors equipped with the vehicle, the distance control device is provided to increase the setpoint time interval determined for normal visibility. Thus, the control device implements a time interval that can be adjusted according to the visibility conditions in order to calculate the setpoint distance.

[0004] However, there are cases where controlling the safety distance behind the target vehicle according to the principles summarized above with reference to prior art documents is not sufficient to avoid a collision, especially when the braking ability of the following vehicle is impaired (e.g., due to severe wheel slippage of the vehicle).

[0005] Therefore, in these specific situations and at higher speeds, regulating the distance based on the time interval for implementing the ACC function does not provide sufficient guarantees in terms of the ability to avoid a possible collision, even if the ultimate goal of these assistance functions is to minimize road hazards. Summary of the Invention

[0006] Therefore, an object of the present invention is to provide a method for controlling and adjusting a safe distance from a target vehicle, which method at least partially overcomes the shortcomings of the prior art. Specifically, an object is to reduce the situation where a collision with a vehicle ahead cannot be avoided.

[0007] To this end, the present invention relates to a method for controlling a system for regulating the distance between a target vehicle and a following vehicle, the regulating system being mounted on the following vehicle, the method comprising:

[0008] A control law for regulating the distance is implemented that calculates at least the following potential setpoint distances for a plurality of possible combinations of travel speeds of the following vehicle and the target vehicle:

[0009] a first distance dTimegap calculated on the basis of a predetermined time interval tTimegapDist, this first distance corresponding to the distance covered by the following vehicle during said time interval according to its travel speed vEgo,

[0010] a second distance dSafetyDistStop calculated as a function of the respective driving speeds vEgo and vTarget of the following vehicle and the target vehicle, and as a function of predetermined deceleration values ​​aEgoSafetyDist and aTargetSafetyDist of said vehicles, said predetermined deceleration values ​​corresponding to the deceleration experienced by said vehicles during emergency braking,

[0011] a third distance dSafetyDistColl based on a predetermined collision speed from the preceding stationary vehicle, the predetermined collision speed being defined by a specified maximum speed vAccidentVelocity for such a collision, the third distance being calculated as a function of the travel speed vEgo of the following vehicle, the specified maximum speed vAccidentVelocity and a predetermined deceleration value aEgoSafetyDist of the following vehicle,

[0012] - a fourth distance corresponding to a minimum stationary distance of the following vehicle relative to the target vehicle,

[0013] And, for a given combination of the driving speeds of the following vehicle and the target vehicle among the plurality of possible combinations, determining a final setpoint distance from the potential setpoint distances previously calculated by the control law.

[0014] According to a preferred embodiment, determining the final setpoint distance comprises evaluating, for the given combination of driving speeds of the following vehicle and the target vehicle, a distance corresponding to a maximum of the first potential distance, the second potential distance, the third potential distance and the fourth potential distance.

[0015] According to one feature, the second potential distance is calculated using the following expression using the respective driving speed values ​​vEgo and vTarget of the following vehicle and the target vehicle and the predetermined deceleration values ​​aEgoSafetyDist and aTargetSafetyDist of the vehicles:

[0016]

[0017] The parameter tSystemTolerance corresponds to the delay time of the system.

[0018] According to another feature, the third potential distance is calculated using the following vehicle's travel speed value vEgo, the specified maximum speed value vAccidentVelocity for collision, and the following vehicle's predetermined deceleration value aEgoSafetyDist by the following expression:

[0019]

[0020] The parameter tSystemTolerance corresponds to the delay time of the system.

[0021] Preferably, the delay time of the system is defined by the time required to reach the required braking force and / or by the perception-reaction time of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Other characteristics and advantages of the invention will become more apparent on reading the following description given by way of illustrative and non-limiting example and with reference to the following single drawing:

[0023] [ Figure 1 ] schematically illustrates a distance adjustment system according to the present invention. DETAILED DESCRIPTION

[0024] Reference Figure 1 The distance control system according to the present invention is intended to control the vehicle in front (referred to as the target vehicle 20) by a predetermined distance (referred to as a safety distance) along with the following vehicle 10 equipped with the system. Typically, the following vehicle 10 is equipped with a measuring device, such as a radar-type device, which allows the distance and relative speed between the following vehicle and the target vehicle to be measured, and is also equipped with an on-board speed sensor capable of providing information about the vehicle's speed.

[0025] The control law of the system is then designed to provide acceleration setpoints and deceleration setpoints to be applied to the vehicles based on the measured relative distance, the speed of the following vehicle, and the relative speed of the following vehicle with respect to the target vehicle (depending on the setpoint safety distance) in order to control the longitudinal position of the following vehicle with respect to the target vehicle so that the distance between the following vehicle and the target vehicle remains substantially constant around the setpoint value.

[0026] This regulation is performed by acting on the engine torque and the brakes, depending on whether power or braking force must be applied to the system to respect the setpoint distance.

[0027] According to the invention, the control law cmd of the regulation system is based on the determination of a setpoint distance, which is selected from various definitions of the concept of safety distance according to a given combination of the driving speed vEgo of the following vehicle on the one hand and the driving speed vTarget of the target vehicle on the other hand, as will be explained below.

[0028] The first definition of the safety distance used by the control law is based on the concept of the distance covered by the following vehicle in a given time interval, denoted as tTimegapDist.

[0029] This safety distance, which is based on respecting a given time interval to the vehicle ahead, stems more specifically from regulatory requirements. Thus, in France and Germany in particular, road regulations stipulate that following vehicles must maintain a safety distance to avoid a collision when the vehicle ahead brakes or stops. The safety distance therefore corresponds to the distance covered by the following vehicle within a given time interval tTimegapDist, which is set to 2 seconds in France and 1.8 seconds in Germany, for example. Regulations therefore require that a minimum distance be maintained based on this given time interval. In other words, this safety distance (denoted dTimegap) is calculated based on this given time interval tTimegapDist multiplied by the speed of the following vehicle relative to the vehicle ahead:

[0030] dTimegap=vFgo.tTimegapDist

[0031] Therefore, the parameter tTimegapDist allows adjusting this safety distance.

[0032] The following table provides the safe distances based on a time interval set to 2 seconds for various speeds (in km / h) of the following vehicle and the target vehicle.

[0033] [Table 1]

[0034]

[0035] The second definition of safety distance used by the control law CMD of the present invention is based on the concept of vehicle stopping distance. This is the distance required for a vehicle to stop. This distance relative to the leading vehicle must be selected so that the following vehicle can stop behind it even if the leading vehicle brakes suddenly. This distance is related to the assumed braking performance of the following and target vehicles, but also takes into account system delays.

[0036] Therefore, to determine this stopping distance, the assumed braking capability of the following vehicle (denoted as aEgoSafetyDist) and the assumed braking capability of the target vehicle (denoted as aTargetSafetyDist) must be taken into account. Furthermore, the system's delay time (denoted as tSystemTolerance) must be taken into account, which depends, for example, on the time required to reach the required braking force and / or the system's perception-reaction time to an emergency braking situation.

[0037] As mentioned above, this definition of a safety distance based on the stopping distance is intended to prevent collisions in situations where the preceding vehicle brakes suddenly. In other words, if the following vehicle maintains a distance relative to the target vehicle corresponding to the stopping distance, then, at a guaranteed deceleration level, the following vehicle should be able to stop behind the target vehicle during sudden braking.

[0038] This safety distance (denoted dSafetyDistStop) is calculated as follows from the respective driving speeds vEgo and vTarget of the following and target vehicles and from the predetermined deceleration values ​​aEgoSafetyDist and aTargetSafetyDist of the vehicles, which thus correspond to the deceleration experienced by the vehicles during emergency braking:

[0039]

[0040] In order to provide a certain safety margin when determining the stopping distance, it is assumed that the braking capacity of the following vehicle is less than that of the target vehicle (for example, a difference of about 2 m / s). 2 ).in other words:

[0041] aEgoSafetyDist-aTargetSafetyDist≡2m / S 2 .

[0042] The following table provides the values ​​of the safety distance based on the stopping distance dSafetyDistStop, which are calculated for various combinations of the speeds of the following vehicle and the target vehicle (in km / h), where the input parameter aEgoSafetyDist = -3.7 m / s 2And aTargetSafetyDist=-5.7m / s 2 .

[0043] In addition, the system delay time tSystemTolerance is set to 0.4 seconds.

[0044] [Table 2]

[0045]

[0046] Therefore, by way of example, in the case where the speed of the following vehicle and the speed of the target vehicle are both equal to 50 km / h while maintaining a safety distance of approximately 14.7 m relative to the target vehicle, assuming that the target vehicle is moving at a speed of -5.7 m / s 2 If the following vehicle brakes at a deceleration level of -3.7 m / 2, the deceleration level of -3.7 m / 2 is sufficient to stop the following vehicle behind the target vehicle.

[0047] If the target's velocity is considered equal to zero, the first column of the table above also makes it possible to consider the case where there is a stationary object (whether a vehicle or a pedestrian) in front of the vehicle by providing the following values ​​for various velocities of the following vehicle at a deceleration level equal to -3.7 m / s. 2 The distance required to stop behind the stationary object.

[0048] The third definition of the safety distance used by the control law cmd of the present invention is based on the fact that a certain collision speed is guaranteed to be less than a specified speed when the vehicle ahead is stationary.

[0049] The collision speed is the impact speed of the vehicle upon hitting the obstacle. This safety distance, which is based on adherence to a certain collision speed, will make it possible to cope with mainly two different use cases. The first use case relates to the situation in which a target vehicle in front detects an obstacle in front of it and avoids it without reducing its speed. In this case, the following vehicle will therefore only be able to detect the obstacle after the leading vehicle has maneuvered to avoid the obstacle, or at most during this avoidance maneuver. The second use case relates to the situation in which a target vehicle in front of the following vehicle is involved in a pileup, which brings it to a standstill faster than in the event of emergency braking. However, the safety distance required for the following vehicle must make it possible to cope with these situations.

[0050] This definition of a safety distance based on a predefined collision speed includes taking into account the two parameters already defined in conjunction with the second definition of a safety distance based on stopping distance (as summarized above), namely the delay time tSystemTolerance of the system of the following vehicle and its assumed maximum braking capacity EgoSafetyDist. The safety distance is defined so that the collision speed of the following vehicle with the vehicle (or object) ahead is less than a specified maximum collision speed (denoted as vAccidentVelocity).

[0051] The safety distance (denoted as dSafetyDistColl) is calculated as follows based on the velocity vEgo of the following vehicle, the specified collision velocity vAccidentVelocity and the predetermined deceleration value aEgoSafetyDist of the following vehicle, while taking into account the delay time of the system:

[0052]

[0053] The following table provides the values ​​of the safety distance dSafetyDistColl based on the predefined collision speed. These values ​​are calculated for various combinations of the speeds of the following vehicle and the target vehicle (in km / h), where the input parameter is: aEgoSafetyDist = -3.7 m / s 2 , vAccidentVelocity=50km / h and tSystemTolerance=0.4s.

[0054] [Table 3]

[0055]

[0056] The fourth definition of a safety distance used by the control law cmd of the present invention is based on the concept of a minimum required standstill distance of the following vehicle relative to the target vehicle. More specifically, this minimum required standstill distance (denoted as dTargetDistMin) is chosen to give the vehicle driver a sense of security and ensure that he has enough space to maneuver around stationary objects in front of the vehicle when the vehicle approaches them, especially if the vehicle's autonomous driving mode is no longer enabled.

[0057] From a safety perspective, the minimum standstill distance of the following vehicle must be chosen to be greater than zero. By way of example, in the case where there is a vehicle ahead of the following vehicle, dTargetDistMin will be set equal to 3m, and in the case where there is an unidentified object ahead of the following vehicle or the following vehicle reaches the scene of an accident, dTargetDistMin will be set equal to 5m.

[0058] From a safety perspective, these values ​​are sufficient. Furthermore, human behavior in traffic jams is often quite different. Therefore, the stopping distance of a vehicle in a traffic jam relative to the vehicle ahead is much smaller than the values ​​set above.

[0059] The setpoint distance required by the control law for the regulation system is then the result of a choice between all these various definitions of safety distances (as summarized above), the choice depending on the speed of the following vehicle and the speed of the target vehicle.

[0060] More specifically, for each possible speed combination of the following vehicle and the target vehicle, the control law is designed to determine a set-point distance (denoted as d_cons) that corresponds to the maximum safety distance required according to the first, second, third and fourth definitions (as summarized above).

[0061] Therefore, for each combination of speeds of the following vehicle and the target vehicle, the setpoint distance d_cons required for the regulation system of the following vehicle is calculated as follows:

[0062] d_cons=max(dTimegap,dSafetyDistStop,dSafetyDistColl,dTargetDistMin)

[0063] The following table provides the values ​​of this setpoint distance, calculated for various combinations of speeds (in km / h) of the following vehicle and the target vehicle, based on the examples provided previously for each of the various safety distance definitions employed. Thus, the table contains the setpoint distances relative to the target vehicle that the following vehicle must adhere to.

[0064] [Table 4]

[0065]

[0066] Assuming that the distance to the target object or vehicle ahead is accurately detected by a measuring device on the following vehicle, it can be determined that there is no risk of collision if the adjusted distance is greater than a defined setpoint distance.

[0067] It can be seen that the maximum required setpoint distance is related to the following vehicle approaching a stationary target object. This is reflected in the first column of the table above, which defines the setpoint distance when the target's speed is zero. In this first column, the safety distance based on the stopping distance is based on the assumed braking ability of the following vehicle aEgoSafetyDist = -3.7 m / s 2The value of this assumed braking capacity is relatively low in order to avoid safety risks with respect to traffic behind the following vehicle. The required setpoint distance based on the calculated stopping distance decreases as the braking capacity of the following vehicle increases.

Claims

1. A method for controlling a system for adjusting a distance between a target vehicle (10) and a following vehicle (20), the system being mounted on the following vehicle, the method comprising: A control law (cmd) is implemented for regulating the distance, the control law calculating at least the following potential setpoint distances for a plurality of possible combinations of travel speeds of the following vehicle and the target vehicle: a first potential distance dTimegap calculated based on a predetermined time interval tTimegapDist, this first potential distance corresponding to the distance covered by the following vehicle during said time interval according to its driving speed value vEgo, a second potential distance dSafetyDistStop calculated from the respective driving speed values ​​vEgo and vTarget of the following vehicle and the target vehicle, and from predetermined deceleration values ​​aEgoSafetyDist and aTargetSafetyDist of said vehicles, said predetermined deceleration values ​​corresponding to the deceleration experienced by said vehicles during emergency braking, a third potential distance dSafetyDistColl based on a predetermined collision speed with the preceding stationary vehicle, the predetermined collision speed being defined by a specified maximum speed value vAccidentVelocity for such a collision, the third potential distance being calculated as a function of the driving speed value vEgo of the following vehicle, the specified maximum speed value vAccidentVelocity and a predetermined deceleration value aEgoSafetyDist of the following vehicle, a fourth potential distance corresponding to a minimum stationary distance of the following vehicle relative to the target vehicle, And, for a given combination of the driving speeds of the following vehicle and the target vehicle among the plurality of possible combinations, determining a final setpoint distance from the potential setpoint distances previously calculated by the control law.

2. The method according to claim 1, wherein Determining the final setpoint distance includes evaluating a distance corresponding to a maximum of the first potential distance, the second potential distance, the third potential distance, and the fourth potential distance for the given combination of travel speeds of the following vehicle and the target vehicle.

3. The method according to claim 1 or 2, wherein: The second potential distance dSafetyDistStop is calculated by the following expression using the respective driving speed values ​​vEgo and vTarget of the following vehicle and the target vehicle and the predetermined deceleration values ​​aEgoSafetyDist and aTargetSafetyDist of the vehicle: The parameter tSystemTolerance corresponds to the delay time of the system.

4. The method according to claim 1 or 2, wherein: The third potential distance dSafetyDistColl is calculated by the following expression using the traveling speed value vEgo of the following vehicle, the designated maximum speed value vAccidentVelocity of the collision, and the predetermined deceleration value aEgoSafetyDist of the following vehicle: The parameter tSystemTolerance corresponds to the delay time of the system.

5. The method according to claim 3, wherein The delay time of the system is defined by the time required to reach the required braking force and / or by the perception-reaction time of the system.

6. The method according to claim 4, wherein The delay time of the system is defined by the time required to reach the required braking force and / or by the perception-reaction time of the system.

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