Method and device for implementing a driver-independent brake force holding function in a motor vehicle when it is stationary on a roadway inclined in the longitudinal direction of the vehicle.

Abstract

Method for implementing a driver-independent brake force holding function in a motor vehicle (B2) when it is stationary on a road surface (100) inclined in the longitudinal direction of the vehicle, wherein the driver-independently maintained brake force is reduced when a release condition is met, in which - by means of a first distance sensor the uphill distance, which corresponds to the distance to the vehicle next to it in the uphill direction (A) is determined (103), - if a predetermined limit value is undershot due to the uphill distance (104), the braking force is reduced even before the release condition is met (105), so that the motor vehicle (B2) moves and - whereby the braking force is not reduced if the presence of a disturbance object (D1) is detected between the motor vehicle (B2) and the adjacent vehicle (A) in the uphill direction.

Description

State of the art

[0001] Functions for motor vehicles that brake the vehicle for a defined period of time are known from the state of the art.

[0002] As part of a well-known AVH function (AVH stands for "Automated Vehicle Hold," a vehicle detected as stationary on an uphill or downhill gradient is held stationary by braking interventions until a corresponding move-off request is detected. When this request is received, the braking system reduces the brake pressure and releases the vehicle for further travel. If unintended vehicle movement is detected while stationary, even though there is no move-off request, the vehicle is brought to a standstill by a driver-independent increase in brake pressure.

[0003] A well-known HHC function, where HHC stands for "Hill Hold Control," locks the brake pressure in the braking system at the moment of a standstill. After a period of approximately two seconds without the brake pedal being pressed, the pressure is automatically released. This function serves as a starting aid on uphill and downhill gradients, allowing the driver to move off without interacting with the handbrake.

[0004] The document FR 3 014 806 A1 discloses a method for carrying out a driver-independent brake force holding function in a motor vehicle when it is stationary on a roadway inclined in the longitudinal direction of the vehicle, wherein the driver-independently maintained brake force is reduced when a release condition is met, in which the uphill distance, which corresponds to the distance to the adjacent vehicle in the uphill direction, is determined by means of a first distance sensor, wherein if the uphill distance falls below a predetermined limit value, the brake force is reduced even before the release condition is met, so that the motor vehicle moves. Disclosure of the invention

[0005] The invention relates to a method for carrying out a driver-independent brake force holding function in a motor vehicle when it is stationary on a roadway inclined in the longitudinal direction of the vehicle, wherein the driver-independently maintained brake force is reduced when a predetermined release condition is met or fulfilled, wherein in the method - the uphill distance, which corresponds to the distance to the adjacent vehicle in the uphill direction, is determined by means of a first distance sensor, - if the uphill distance falls below a specified limit, the braking force is reduced before the release condition is met, so that the vehicle moves and - whereby the braking force is not reduced or a reduction in braking force is prevented if the presence of an interfering object is detected between the motor vehicle and the adjacent vehicle in the uphill direction.

[0006] This can prevent collisions caused by a sudden and unintentional rolling movement of the vehicle in front of or behind your own vehicle, while also preventing a collision with an obstructing object. This obstructing object is typically a pedestrian or cyclist who steps into the gap between the vehicle and the vehicle longitudinally adjacent to it.

[0007] An advantageous embodiment of the invention is characterized in that an interfering object is detected as being present when the uphill distance determined by the first distance sensor decreases, with the rate of decrease exceeding a predetermined threshold. The threshold is chosen to be so high that it cannot be reached simply by a neighboring vehicle rolling backward.

[0008] An advantageous embodiment of the invention is characterized in that an interfering object is detected as being present when several spatially parallel distance values ​​for the uphill distance are determined simultaneously by the first distance sensor system and their fluctuation range exceeds a predetermined threshold. This embodiment is based on the fact that a pedestrian or cyclist crossing in front of or behind a two-lane vehicle in its transverse direction is usually not detected by all distance sensors and therefore the fluctuation range of their output signals exceeds a limit value.

[0009] An advantageous embodiment of the invention is characterized in that the downhill distance, which corresponds to the distance to the adjacent vehicle in the downhill direction, is determined by means of a second distance sensor and, if the downhill distance falls below a predetermined limit, the reduced braking force is increased again and the motor vehicle is brought to a standstill. The braking force is immediately increased again and the motor vehicle is brought to a standstill again if the presence of an interfering object is detected between the motor vehicle and the adjacent vehicle in the downhill direction. By reducing the braking force of the own vehicle independently of the driver, the vehicle starts moving in order to avoid a collision caused by another vehicle. By increasing the braking force again, if necessary, a collision caused by the own vehicle is avoided due to the deliberately initiated rolling movement of the vehicle.

[0010] An advantageous embodiment of the invention is characterized in that the first and second distance sensors are an ultrasonic sensor, a video sensor or a radar sensor.

[0011] In particular, the embodiment is characterized in that the first and second distance sensors are distance sensors used within a parking assistance system or a parking system. This allows for a dual benefit of the distance sensor system.

[0012] An advantageous embodiment of the invention is characterized in that the brake force holding function maintains a braking force that holds the motor vehicle at a standstill when the road surface is inclined longitudinally and the vehicle is stationary, independent of the driver, and the predetermined release condition is a driver's desire to start moving, in particular an accelerator pedal actuation by the driver. This is particularly an AVH function or Automated Vehicle Hold function.

[0013] An advantageous embodiment of the invention is characterized in that the longitudinal inclination of the road is further determined while the motor vehicle is stationary, and the braking force maintained independently of the driver is dependent on the determined longitudinal inclination. The determination of the longitudinal inclination can also be used to determine whether the road is inclined uphill or downhill, or to determine which of the neighboring vehicles is traveling uphill and which is traveling downhill from the vehicle.

[0014] In particular, the longitudinal inclination of the road can be determined using a longitudinal acceleration sensor or GPS information. With GPS information, the current position of the vehicle is determined using GPS, and then the prevailing longitudinal inclination of the road at that location can be determined from a digital map.

[0015] An advantageous embodiment of the invention is characterized in that the brake force holding function maintains the brake pressure prevailing at the time the vehicle is stationary, and in that the predetermined release condition is the expiration of a time interval of a predetermined length after the driver has stopped applying the brake pedal. This is, in particular, a hill hold control function or HHC function.

[0016] The invention further encompasses a device containing means designed to carry out the methods according to the invention. This is, in particular, a control unit in which the program code for carrying out the methods according to the invention is stored.

[0017] The drawing includes the Fig. 1 to 3. Fig. 1 shows a possible collision scenario which is to be avoided with the present invention. Fig. 2 shows the avoidance of the Fig. 1 considered collision as well as the consideration of an interfering object by using the present invention. Fig. 3 shows the basic sequence of the method according to the invention.

[0018] The AVH and HHC functions considered in the state of the art only consider the vehicle itself. The surroundings are not monitored within these functions, and therefore these functions cannot react to changes in the vehicle's surroundings.

[0019] With the method according to the invention, brake force retention systems can continue to be used to their full extent and, in addition, potential rear-end collisions or impending collisions with pedestrians or cyclists can be responded to with minimal effort, so that damage to the own vehicle and to other vehicles as well as the consequences of collisions with pedestrians or cyclists can be avoided or reduced.

[0020] The invention is based on the use of an environment sensor or distance sensor, which detects the environment or the distance to neighboring vehicles at the front and rear. Distance sensors, which usually work on the basis of ultrasound, are already installed in many vehicle bumpers. These sensors can be used to estimate the distance to obstacles in front of or behind the vehicle. This information is displayed to the driver, for example, visually or acoustically. This distance can of course also be determined using optical or radar-based methods. Wheel speed or vehicle speed can be measured using wheel speed sensors, for example. This can be used to detect any unintentional vehicle movement, followed by a driver-independent build-up of brake pressure.

[0021] Furthermore, longitudinal acceleration sensors make it possible to determine the current longitudinal gradient of the road while stationary. This parameter allows the determination of the brake pressure required to keep the vehicle moving safely. It can also be used to determine the starting torque required for the vehicle to move off smoothly without rolling back.

[0022] If a pedestrian, cyclist or interfering object steps between two vehicles that are adjacent lengthwise, this can often be detected by the distance sensor. If the adjacent object is a two-lane motor vehicle, the distance values ​​determined simultaneously by the distance sensors on one side of the vehicle, i.e. the front or the rear, are generally very close to one another. Deviations of a few centimeters between the individual determined distance values ​​can arise because the vehicle's own bumper is curved and thus the distance sensors integrated into it are slightly shifted in the vehicle's lengthwise direction, because the bumper of the vehicle that is adjacent lengthwise is curved or because the individual sensors of the distance sensor system detect different components of the adjacent vehicle, such as the bumper, lights or trunk.

[0023] The distance to the neighboring vehicle is determined by weighting the individual measured distance values. This can be, for example, the shortest measured distance or an average of the two shortest measured distances.

[0024] If a pedestrian or cyclist enters the detection range of the distance sensor, the distances change at a very high speed. Such a rapid change in the detected distances cannot be caused by the simple rolling back of the adjacent vehicle. Furthermore, the determined distance values ​​in this case differ significantly from one another, at least temporarily, and thus exhibit a large range of fluctuation. This is not the case when a closed vehicle surface is detected using the distance sensor.

[0025] This makes it possible, after detecting very rapid distance changes by one or more distance sensors, to prevent a reduction in brake pressure and thus a rolling back movement or to carry out a rapid build-up of brake pressure.

[0026] In Fig. Figure 1 shows a scenario that is to be avoided with the present invention. Three vehicles A, B1 and C are considered, which stop one after the other on an incline at time t0. This is shown in the left column of Fig. 1. Vehicle B1 is assumed to be equipped with an AVH function, which is also active at time t0 and stops the vehicle. Vehicle A, which is in front of B1, does not have an AVH function or its AVH function is deactivated. When A starts moving at time t1, vehicle A may inadvertently move backward, at least briefly. If the distance between vehicles A and B1 is too small, then vehicle A may accidentally roll backwards and collide with vehicle B1. To avoid this rear-end collision, the driver of B1 would have had to either deactivate the AVH function using a button or engage reverse gear and drive backwards. However, this is often not possible given the short time available.

[0027] In Fig. 2, the same scenario is considered, but vehicle B2 is equipped with an AVH function modified according to the invention, which additionally uses distance sensors to detect and take into account the distance to the preceding and following vehicles. This AVH function is active at time t0, at which vehicles A, B2, and C are standing on an uphill road gradient. Vehicle A again has no AVH function, or it is deactivated. When A starts moving, it can again happen that A rolls backward unintentionally and in the opposite direction of travel. If the distance between A and B2 is small, it can even happen that A reverses into B2.

[0028] However, the distance to the preceding vehicle A and the following vehicle C is continuously recorded in vehicle B2. If it is now detected that the distance between A and B2 is becoming too small, then B2 rolls back independently of the driver due to driver-independent brake pressure reduction, as long as the driver does not want to start moving and the distance to C allows this. This is shown for the time t1 in the middle column of Fig. 2. However, just in time before contact with C, brake pressure is again built up independently of the driver in order to avoid a collision between B2 and C. Due to this driver-independently controlled rollback movement, which is made possible by coupling the AVH function with the distance sensor system, the driver of A has a little more time to stop the rollback movement of his vehicle and bring his vehicle back to a standstill or to move forward.

[0029] However, if a pedestrian, a cyclist, or an interfering object D1 appears between vehicles A and B2, the braking force reduction of B2 is prevented. However, if an interfering object D2 appears between vehicles B2 and C at time t1, the rolling back of B2 is prevented, and B2 is brought to a standstill by a driver-independent braking intervention to prevent a collision between B2 and D2.

[0030] The sequence of an embodiment of the method according to the invention is shown in Fig.3. After the method has started in block 100 with the driver-independent maintenance of the braking force in a vehicle B2 equipped with the system according to the invention, a query is made in block 101 as to whether a predetermined release condition for reducing the braking force has been met. This can be, for example, the expiration of a time interval of a predetermined length or an actuation of the accelerator pedal by the driver. If this is the case, the braking force is reduced and the method ends in block 102. If this is not the case, however, the uphill distance, which corresponds to the distance to the neighboring other vehicle A in the uphill direction, is determined in block 103 using a first distance sensor. This is the spatial distance to the neighboring other vehicle A in the longitudinal direction, which would move towards the vehicle B2 if it rolled away. Furthermore, in block 103 the presence of an interfering object between A and B2 is determined using the same sensor.Then, in block 104, it is determined whether the determined spatial distance to the vehicle in front A exceeds a limit value or whether an interfering object is detected between vehicles A and B2. If one of the two queries is met, i.e. the distance exceeds a limit value or an interfering object is present between vehicles A and B2, then the system returns to block 103. However, if the limit value is not reached and there is no interfering object, i.e. other vehicle A has come sufficiently close to vehicle B2, then in block 105 the braking force holding vehicle B2 is reduced so that it also starts rolling and the distance to other vehicle A ideally either remains constant or even increases again. However, it must now be monitored whether the distance to the also adjacent other vehicle C is decreasing.This is followed by block 106, in which the downhill distance, which corresponds to the distance to the neighboring vehicle C in the downhill direction, is determined using a second distance sensor. This is the spatial distance to the longitudinally adjacent other vehicle C, towards which the vehicle B2 would move if it were to roll away. In block 106, the same sensor system also determines the presence of an interfering object between B2 and C. In block 107, it is therefore then determined whether the downhill distance falls below a predetermined limit or whether an interfering object has appeared between B2 and C. If neither is the case, then the process returns to block 106. However, if one of the two conditions in block 106 is met, then the reduced braking force is increased again in block 108 and the motor vehicle B2 is brought to a standstill in order to avoid a collision with C or the interfering object. The process then returns to block 101.This procedure is designed to reduce the probability of a collision with an interfering object, in particular a pedestrian, or another vehicle during the brake force holding phase of a brake force holding function.

[0031] Furthermore, it is conceivable to deactivate the status "pedestrian detected in downhill direction" or the detection of an interfering object with a time delay. This would take into account the fact that in many cases, not just a single pedestrian, but many pedestrians walk between the vehicles. In this case, a hysteresis would be provided regarding the activation and deactivation of this function.

[0032] The limits applicable to a typical rollback movement of a vehicle can be estimated using a simple calculation.

[0033] The vehicle is accelerated to its maximum with the slope force acting on the vehicle. The slope force is calculated with Fdownhill=9.81ms2⋅mvehicle⋅sin α where α represents the gradient of the vehicle in the current situation.

[0034] The normal force is calculated with Fnormal=9.81ms2⋅mvehicle⋅cos α

[0035] The acceleration of the vehicle results from the ratio of the downhill force to the normal force with avehicle=FdownhillFnormal.

[0036] Example: For example, with a gradient of 10%, acceleration values ​​of vehicle=0.1⋅9.81ms2 vehicle≈1ms2

[0037] The roll over s = 0.1m takes place in t=2savehicle=0.45s.

Claims

[1] Method for carrying out a driver-independent brake force holding function in a motor vehicle (B2) when it is stationary on a roadway (100) inclined in the longitudinal direction of the vehicle, wherein the driver-independently maintained brake force is reduced when a release condition is fulfilled, in which - the uphill distance, which corresponds to the distance to the adjacent vehicle (A) in the uphill direction, is determined by means of a first distance sensor (103), - if the uphill distance (104) falls below a predetermined limit value, the braking force is reduced (105) before the release condition is met, so that the motor vehicle (B2) moves and - wherein the braking force is not reduced if the presence of an interfering object (D1) is detected between the motor vehicle (B2) and the adjacent vehicle (A) in the uphill direction. [2] Method according to claim 1, characterized bythat an interfering object is detected as being present when the uphill distance determined by means of the first distance sensor decreases, whereby its rate of decrease exceeds a predetermined threshold value. [3] Method according to claim 1, characterized by that an interfering object is detected as being present if several spatially parallel distance values ​​for the uphill distance are determined simultaneously by means of the first distance sensor and their fluctuation range exceeds a predetermined threshold value. [4] Method according to claim 1, characterized bythat furthermore, by means of a second distance sensor system, the downhill distance, which corresponds to the distance to the adjacent vehicle (C) in the downhill direction, is determined (106) and if the downhill distance (107) falls below a predetermined limit value, the reduced braking force is increased again and the motor vehicle (B2) is brought to a standstill (108), wherein the braking force is immediately increased again and the motor vehicle is brought to a standstill again if the presence of an interfering object (D2) between the motor vehicle (B2) and the adjacent vehicle (C) in the downhill direction is determined. [5] Method according to claim 1, characterized by that an interfering object is detected as being present when the downhill distance determined by means of the first distance sensor decreases, whereby its decreasing speed exceeds a predetermined threshold value. [6] Method according to claim 1, characterized bythat an interfering object is detected as being present if several spatially parallel distance values ​​for the downhill distance are determined simultaneously by means of the first distance sensor and their fluctuation range exceeds a predetermined threshold value. [7] Method according to claim 1, characterized by that the first and second distance sensors are ultrasonic sensors, video sensors or radar sensors. [8] Method according to claim 1, characterized by that the first and second distance sensors are distance sensors used in a parking assistance system or a parking system. [9] Method according to claim 1, characterized bythat the brake force holding function maintains a braking force that keeps the motor vehicle (B2) stationary when there is a longitudinal inclination of the road and the vehicle is stationary, independently of the driver, and the release condition is a drive-off request by the driver, in particular an actuation of the accelerator pedal by the driver. [10] Method according to claim 5, characterized by that the longitudinal inclination of the road continues to be determined when the motor vehicle is stationary (B2) and that the braking force maintained independently of the driver depends on the determined longitudinal inclination of the road. [11] Method according to claim 5, characterized by that the longitudinal inclination of the road is determined by means of a longitudinal acceleration sensor or by means of GPS information. [12] Method according to claim 1, characterized bythat the brake force holding function maintains the brake pressure prevailing at the time the vehicle is stationary and that the release condition is the expiry of a time interval of a predetermined length after the driver has stopped operating the brake pedal. [13] Device containing means designed to carry out the methods according to the invention.

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