Method for operating an autonomous vehicle

Abstract

Method for operating an autonomous vehicle (10) which has a service brake, an emergency braking device (24) and a monitoring unit (20), wherein a first braking request is formed in order to actuate the service brake when the monitoring unit (20) receives an emergency stop signal, wherein a second braking request is formed in order to actuate the emergency braking device (24) when an effect of the first braking request does not correspond to a predeterminable braking effect, characterized in that the second braking request is formed when a speed or a rotational speed of the autonomous vehicle (10) is above a predeterminable threshold value after the expiry of a predeterminable diagnostic time period after the formation of the first braking request.

Description

[0001] The invention relates to a method for operating an autonomous vehicle according to the preamble of claim 1 as well as a device, a computer program product and a storage medium. State of the art

[0002] Autonomous vehicles, especially autonomous industrial trucks, must comply with technical standards such as EN 1525 regarding their operation. This standard stipulates that the braking function of an autonomous vehicle must meet a safety standard PLr d according to ISO 13849.

[0003] For safety reasons, the area in front of a moving autonomous vehicle must be monitored. A protection zone is typically defined as a subset of the monitored area, so that the detection of an obstacle within the protection zone immediately triggers emergency braking of the autonomous vehicle. The protection zone can also coincide with the monitored area.

[0004] It is known to decelerate vehicles, for example, by driving an electric motor as a generator and thus using it as a brake. Mechanical safety brakes are also known, which, when de-energized, decelerate or block a rotating part of a vehicle using mechanical force. Since these mechanical safety brakes are subjected to considerable mechanical stress when activated, they must be sufficiently large to withstand the mechanical stress of repeated activation, even after repeated activation.

[0005] The published patent application DE 10 2004 014 358 A1 discloses a driverless vehicle having a service brake device, a parking brake device and an emergency brake device and discloses that both a service brake and a parking brake are used during emergency braking.

[0006] The published patent application DE 10 2013 217 973 A1 describes an arrangement and method for detecting the wear of a braking system. During an emergency braking of an industrial truck, the parking brake or handbrake takes over the deceleration at least partially or completely.

[0007] Published patent application EP 3 118 071 A1 describes a safety braking device and a method for safety braking of an autonomous vehicle, comprising a hydraulic braking system with hydraulic wheel brakes, an electrical power supply, and a signaling system for activating autonomous driving. The wheel brakes are activated when a failure of the electrical power supply or signals is detected.

[0008] There is therefore a need to provide a safe method for operating an autonomous vehicle, in particular a safe method for braking an autonomous vehicle, which can be applied to an autonomous vehicle with a smaller mechanical safety brake.

[0009] The object is achieved by a method for operating an autonomous vehicle having the features of independent claim 1. Disclosure of the invention

[0010] The method according to the invention for operating an autonomous vehicle, in particular an autonomous industrial truck, which has a service brake, an emergency braking device and a monitoring unit, wherein a first braking request is formed in order to actuate the service brake when the monitoring unit receives an emergency stop signal, has the advantage that a second braking request is formed in order to actuate the emergency braking device if an effect of the first braking request does not correspond to a predeterminable braking effect.

[0011] This method has the particular advantage that the emergency braking system can be designed with reduced mechanical stress, since the emergency braking system is activated less frequently than with a method that activates the emergency braking system upon receipt of each emergency stop signal. At the same time, the service brake can be used as a safety-relevant component within the scope of the method according to the invention without itself being designed according to safety-relevant standards, since the effectiveness of the service brake is safeguarded by a second fallback level, namely the emergency braking system. Therefore, the service brake does not have to meet the PLr d safety standard.

[0012] According to the invention, the second braking request is generated if a speed or rotational speed of the autonomous vehicle is above a predeterminable threshold value after the expiration of a predeterminable diagnostic period following the generation of the first braking request. After the first braking request has been generated, the system waits for the duration of the diagnostic period and then measures the speed or rotational speed of the autonomous vehicle and compares it with a threshold value. If this comparison reveals that the speed or rotational speed is above the threshold value and thus too high, it can be assumed that the effect of the first braking requests does not correspond to the predeterminable braking effect. The second braking request is generated in response to this.

[0013] It is advantageous that the service brake comprises an electric motor that operates as a generator to brake the autonomous vehicle. Autonomous vehicles, especially autonomous industrial trucks, typically have an electric motor used as a drive, eliminating the need for a separate component used as a service brake.

[0014] It is advantageous that the emergency braking device comprises a mechanical brake configured to decelerate the autonomous vehicle when it is not subjected to an opening signal. The mechanical brake can, in particular, be a brake that is moved into a closed, i.e., braking, position by means of a mechanical force, provided the mechanical force is not overcome by a magnetic counterforce, for example. The magnetic counterforce can be provided, for example, by an electromagnet through which current only flows when it is subjected to an opening signal.

[0015] It is advantageous that the emergency stop signal is generated by an emergency stop actuation unit. This can, in particular, be a control element mounted on the autonomous vehicle, the actuation of which triggers the generation of the emergency stop signal.

[0016] It is advantageous that the emergency stop signal is generated by a collision warning unit when an object is detected within a protection zone in front of the autonomous vehicle. The collision warning unit can, in particular, be a unit comprising a radar sensor, a camera, and / or a lidar sensor.

[0017] It is advantageous that a longitudinal extent of the protection zone is selected such that the longitudinal extent of the protection zone corresponds to at least a stopping distance of the autonomous vehicle. The stopping distance is preferably composed of a braking distance upon actuation of the emergency braking device plus a distance traveled by the autonomous vehicle during the diagnostic period. The longitudinal extent of the protection zone is therefore a function of the speed of the autonomous vehicle and, in other words, is dimensioned such that a safe stopping of the autonomous vehicle is possible within the longitudinal extent of the protection zone if the autonomous vehicle continues to travel at its current speed during the diagnostic period and initiates braking using the emergency braking device after the diagnostic period has elapsed.

[0018] In a particularly advantageous further development, the stopping distance additionally includes an additive term that takes into account tolerances and / or wear of components of the autonomous vehicle.

[0019] The lateral extent of the protection zone advantageously corresponds at least to the width of the autonomous vehicle. In a particularly advantageous embodiment, the lateral extent of the protection zone corresponds to the width of the autonomous vehicle plus a tolerance value.

[0020] Advantageous is a device which is configured to carry out each step of the method according to the invention.

[0021] Advantageously, a computer program product is configured or is configured by compilation to carry out each step of the method according to the invention.

[0022] A storage medium on which the computer program according to the invention is stored is advantageous.

[0023] An exemplary embodiment of the method according to the invention is described in more detail below. It shows: Fig. 1 a schematic representation of an autonomous vehicle to which the embodiment of the method according to the invention is applied; Fig. 2 a schematic sequence of the embodiment of the method according to the invention.

[0024] Fig. 1 shows a schematic representation of an autonomous vehicle (10), which is in particular an autonomous industrial truck. The autonomous vehicle (10) comprises a control unit (12), which in turn comprises a storage medium (14). The autonomous vehicle (10) further comprises a drive axle (16) which connects a wheel of the autonomous vehicle (10) to an electric motor (18) in such a way that the drive axle (16) can be set in rotation by the electric motor (18). The autonomous vehicle (10) also comprises a monitoring unit (20), a rotational speed sensor (22), and an emergency braking device (24). The rotational speed sensor (22) is configured to detect the rotational speed of the drive axle (16). The rotational speed sensor (22) is connected via a signal line to the monitoring unit (20), where the speed of the autonomous vehicle (10) is determined based on the rotational speed signal of the rotational speed sensor (22).The emergency braking device (24), which in particular comprises a mechanical brake, is configured to brake the drive axle (16) when the emergency braking device (24) is not subjected to an opening signal. The emergency braking device (24) is subjected to the opening signal via a signal line, via which the emergency braking device (24) is connected to the monitoring unit (20).

[0025] Both the control unit (12) and the monitoring unit (20) are connected to the electric motor (18) via signal lines, whereby it is ensured that a signal applied by the monitoring unit (20) overwrites a signal applied by the control unit (12), so that the electric motor (18) reacts with priority to the signal applied by the monitoring unit (20).

[0026] The signal lines of the autonomous vehicle (10) are designed to ensure secure transmission of signals, for example by using redundant signal lines (in Fig. 1 (not shown for clarity). In an advantageous embodiment, the signal lines can be signal lines of a bus system, whereby the security of signal transmission is ensured, for example, by the use of checksums. Redundant signal lines are not required when using a bus system.

[0027] The autonomous vehicle (10) further comprises a collision warning unit (26), which may be, for example, a radar sensor, a camera, or a lidar sensor. The collision warning unit (26) is configured to monitor an area in front of the autonomous vehicle (10) for the presence of an object (30). A portion of the area in front of the autonomous vehicle (10), which is monitored by the collision warning unit (26), forms a protection zone (32). The longitudinal extent (34) of the protection zone (32) is dimensioned such that the autonomous vehicle (10) can come to a standstill before a collision with the object (30) if the object (30) enters the protection zone (32) from the front.The longitudinal extent (34) of the protection zone (32) is therefore selected such that it corresponds at least to the sum of a distance traveled by the autonomous vehicle (10) at a given speed during a predeterminable diagnostic period and a braking distance of the autonomous vehicle (10) corresponding to an emergency braking by the emergency braking device (24) from a given speed of the autonomous vehicle (10).

[0028] Fig. Figure 2 shows a schematic flow of the exemplary embodiment of the method according to the invention. The exemplary embodiment of the method according to the invention starts in step 100. The longitudinal extent (34) of the protection zone (32) is determined as a function of the speed of the autonomous vehicle (10). Step 110 is then performed.

[0029] In step 110, the monitoring unit (20) evaluates the signals from the collision warning unit (26) to determine whether an object (30) is located within the protection zone (32). If this is not the case, step 115 is then performed. If this is the case, step 120 follows.

[0030] In step 115, it is determined that no braking action is required. Following step 115, step 100 occurs again.

[0031] In step 120, the monitoring unit (20) generates a first braking request, which is transmitted to the electric motor (18) via the corresponding signal line. The first braking request causes the electric motor (18) to switch to generator mode, thus braking the drive axle (16) or the wheel connected to the drive axle (16). After the first braking request is generated, a delay occurs for a predeterminable diagnostic period. Step 130 then follows.

[0032] In step 130, the signal from the speed sensor (22) is used to check whether the speed of the autonomous vehicle (10) is below a predeterminable threshold. The predeterminable threshold can in turn be a function of the speed of the autonomous vehicle (10). The comparison of the speed of the autonomous vehicle (10) with the predeterminable threshold serves to check the effect of the first braking request. If the speed of the autonomous vehicle (10) does not decrease as expected, it is determined that the first braking request does not achieve an effect that corresponds to a desired, predeterminable braking effect. In an alternative embodiment, a comparison of an actual speed with a predeterminable threshold can be carried out within the scope of step 130.If the comparison in step 130 shows that the speed of the autonomous vehicle (10) is not below the predeterminable threshold value, step 135 is then carried out. If the comparison shows that the speed of the autonomous vehicle (10) is below the predeterminable threshold value, step 140 is then carried out.

[0033] In step 135, the monitoring unit (20) generates a second braking request, which is transmitted to the emergency braking device (24) via the corresponding signal line. The second braking request causes the emergency braking device (24) to brake the drive axle (16).

[0034] In step 140, the braking process triggered by the first braking signal is continued, i.e., the electric motor (18) continues to operate as a generator until the speed of the autonomous vehicle (10) is zero. Following this, step 100 is performed again. Method steps 100 to 140 thus form a cyclical process that is performed throughout the entire operation of the autonomous vehicle (10).

[0035] Braking of the drive axle (16) by the emergency braking device (24) occurs by suppressing an opening signal, which is typically applied to the emergency braking device (24) during operation of the autonomous vehicle (10). Due to the absence of the opening signal, a mechanical force within the emergency braking device (24) causes a mechanical brake, which is part of the emergency braking device (24), to close, thus braking the drive axle (16).

Claims

[1] Method for operating an autonomous vehicle (10) having a service brake, an emergency braking device (24) and a monitoring unit (20), wherein a first braking request is formed to actuate the service brake when the monitoring unit (20) receives an emergency stop signal, wherein a second braking request is formed to actuate the emergency braking device (24) when an effect of the first braking request does not correspond to a predeterminable braking effect characterized by that the second braking request is formed when a speed or a rotational speed of the autonomous vehicle (10) is above a predeterminable threshold value after the expiry of a predeterminable diagnostic time period after the formation of the first braking request. [2] Method according to claim 1, characterized by that the service brake comprises an electric motor (18) which is operated as a generator for braking the autonomous vehicle (10). [3] Method according to one of claims 1 to 2, characterized by that the emergency braking device (24) comprises a mechanical brake which is designed to brake the autonomous vehicle (10) when it is not subjected to an opening signal. [4] Method according to one of claims 1 to 3, characterized by that the emergency stop signal is generated by an emergency stop actuation unit. [5] Method according to one of claims 1 to 3, characterized by that the emergency stop signal is formed by a collision warning unit (26) when an object (30) is detected within a protection area (32) in front of the autonomous vehicle (10). [6] Method according to claim 5 with reference to claim 2, characterized bythat a longitudinal extent (34) of the protection area (32) is selected such that the longitudinal extent (34) corresponds to at least a braking distance of the autonomous vehicle (10) upon actuation of the emergency braking device plus a distance that the autonomous vehicle (10) travels during the diagnostic period. [7] Apparatus arranged to carry out each step of the method according to any one of claims 1 to 6. [8] A computer program product which is arranged or is arranged by compiling to carry out each step of the method according to any one of claims 1 to 6. [9] Storage medium on which the computer program according to claim 8 is stored.

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