Methods for improved collision avoidance

Abstract

The invention relates to a mobile work machine (1) which is configured to pick up loads, wherein the mobile work machine (1) comprises a hydrostatic drive which is responsible for the movement of the mobile work machine (1), wherein the hydrostatic drive comprises a hydraulic pump which can be coupled to a drive machine and which is configured to supply a second hydraulic machine (61) which can be coupled to an output with pressure medium, wherein the mobile work machine (1) comprises at least one environmental sensor (S1) which is configured to detect environmental data, wherein the mobile work machine (1) comprises a first and a second braking function which are each configured to decelerate the mobile work machine (1) by means of a change in a pivot angle of the hydraulic pump and a pivot angle of the hydraulic motor, wherein the second braking function is configured to be activated after it has been determined in the mobile work machine (1),that the mobile work machine (1) is to be decelerated in order to avoid a collision, wherein the first braking function has a first braking behavior and wherein the second braking function has a second braking behavior, wherein the first braking behavior differs from the second braking behavior.,

Description

Collisions between mobile work machines pose a serious risk both to the people they are serving and to the machines themselves. Particularly in situations with limited visibility, for example when a wheel loader with a loaded bucket or a dumper with a filled bucket is in the way, there is the risk of serious accidents. There are already known systems which aim to avoid such collisions or to minimize their effects. These systems include backup cameras, bird eye view cameras for enhanced surround view, and various warning and avoidance systems based on camera, ultrasound, radar, or lidar technology. They act as assistance systems to increase the safety during operation of these machines.If systems are concerned which are based on surroundings sensor systems such as radar, the sensors detect obstacles such as persons, other vehicles or walls. These known systems then calculate a time-to-collision and a critical distance, at which a warning should be issued if undershot--in this case there remains enough time for the driver to brake manually, on the basis of the transmitted data, such as the distance and relative speed of the detected object. Likewise, a distance is determined at which an automatic braking or deceleration intervention is to be triggered when the distance falls below.These systems are an important step in improving safety in the operation of mobile work machines and help avoid accidents or at least reduce their severity.In systems for preventing collisions with active intervention in the traction drive, a targeted deceleration of the vehicle is initiated in order to ensure that the vehicle comes to a standstill in front of the detected obstacle. This delay can be implemented by various mechanisms, such as, for example, by using the hydrostatic travel drive (by pivoting the pump and / or motor) or by using the service brake.When the engine is operated with a conventional traction drive in conjunction with the collision avoidance function, it requires evaluation and monitoring of critical objects over a wide range because a relatively long distance is required until when the mobile engine will come to a standstill. This leads to an increased detection of non-collision-causing objects (false positive rate) which, although on the basis of the current state of the machine are on the predicted path, are actually not on the real path of the machine, since future steering movements or changes in direction cannot be predicted.The use of a higher machine delay could contribute to a reduction in the length of the monitored area and thus a reduction in the probability of reacting to an object that will not be on the actual path of the machine in the future. However, such a higher machine deceleration is very difficult, especially in heavy machines, since high frictions are necessary. Therefore, two partial problems arise which must be solved: I. ensuring a higher engine deceleration in the case of a braking or deceleration intervention even in heavy engines; II. reducing the monitored area in order to minimize non-collision-causing objects.The main object is thus to find a solution to the two described sub-problems.SUMMARYAccording to one specific embodiment of the present invention, a method is provided for preventing a collision of a mobile working machine with an external object (99), the mobile working machine including a hydrostatic drive which is responsible for the movement of the mobile working machine, the hydrostatic drive including a hydraulic pump which can be coupled to a drive machine and is configured to supply a hydraulic motor which can be coupled to an output with pressure medium, the mobile working machine including at least one first environment sensor (S 1) which is configured to acquire environment data, the mobile working machine including a first braking function which is configured to decelerate the mobile working machine by means of a change in a pivot angle of the hydraulic pump and of the hydraulic motor if deceleration of the mobile working machine is required directly or indirectly, wherein the method comprises the following steps: a. determining a relative position between the mobile machine and the object (99) by means of the first environment sensor; b. determining a relative movement between the mobile machine and the object (99); c. determining, on the basis of the determinations from steps a. and b., that the mobile working machine is to be decelerated in order to avoid a collision with the external object (99); d. activating a second braking function, which is configured to decelerate the mobile working machine by means of a change in the pivot angle of the hydraulic pump and of the hydraulic motor, after it has been determined in step c. that the mobile working machine is to be decelerated in order to avoid a collision; e. decelerating the mobile working machine taking into account the second braking function activated in step d; wherein the first braking function has a first braking behavior and wherein the second braking function has a second braking behavior, wherein the first braking behavior differs from the second braking behavior.It will be understood by those skilled in the art that in the present invention, the phrase "changing a swivel angle" means the phrase "changing a swivel angle or a magnitude depending thereon.". Therefore, in order to avoid unnecessary long formulations, the phrase "change of a swivel angle" is simply applied. The variable can be, for example, a displacement volume of the hydraulic motor or of the hydraulic pump (=Schwenkwinkel*maximal stroke volume).BRIEF DESCRIPTION OF THE FIGURESThe present invention will be described with reference to the accompanying figures, wherein like reference numerals refer to like parts and / or to like parts and / or to corresponding parts of the system. Regarding the figures: FIG. 1 shows a wheel loader as an example of a mobile machine; FIG. 2 shows a schematic illustration of a mobile machine with environment sensors; FIG. 3 shows a hydraulic circuit diagram of a hydrostatic travel drive according to the prior art; FIG. 4 shows a field of view of a surroundings sensor according to the prior art (left) and according to the present invention (right); FIG. 5 is a block diagram for a collision avoidance function of a mobile machine according to an embodiment of the present invention; FIG. 6 shows a first braking function (left) and a second braking function (right) according to an embodiment of the present invention.DETAILED DESCRIPTIONThe present invention will now be described with reference to specific embodiments as shown in the accompanying figures. Nevertheless, the present invention is not limited to the particular embodiments described in the following detailed description and shown in the figures, but the described embodiments are merely illustrative of some aspects of the present invention, the scope of which is defined by the claims.Other modifications and variations of the present invention will be apparent to those skilled in the art. The present description thus includes all modifications and / or variations of the present invention, the scope of which is defined by the claims.It is noted that in the course of the description of the present invention, the features "hydraulic pump" and "hydraulic motor" are replaced with the feature "hydraulic machine", as it is known to the skilled person that in many cases (e.g. during deceleration) the hydraulic pump functions as a hydraulic motor and the hydraulic motor as a hydraulic pump.FIG. 1 shows a wheel loader 1 as an example of a mobile work machine. Moreover, the wheel loader is only an example of a mobile work machine. It is not necessary for the mobile work machine to comprise a working kinematics, as in the wheel loader. As will become clearer in the course, it is particularly important for the present invention that a hydrostatic traction drive be present. Whether a working hydraulic system is also present is not relevant in principle for the present invention.The wheel loader 1 has a boom which in turn has a plurality of boom elements for receiving loads. The boom elements are here, by way of example, a lifting arm 2 (also known as a "boom arm") and a bucket 4, which are connected to one another or to a boom carrier 5 (e.g. chassis) of the wheel loader 1 by means of axles in a rotatable or pivotable manner. The cantilever elements 2, 4 are movable by means of actuators 8, 10, i.e. the rotational or pivoting movement about the axes is effected by a movement of the actuators.A first actuator 8 is provided for the lifting arm 2, which brings about the movement or rotation of the lifting arm 2 relative to the boom support 5. Likewise, a second actuator 10 is provided for the blade 4, which moves or rotates (tilts) the blade 4. The actuators comprise in particular hydraulic cylinders 12, 14, i.e. a first hydraulic cylinder 12 of the first actuator 8 and a second hydraulic cylinder 14 of the second actuator 10.The actuators 8, 10 can be controlled by a controller 18, wherein in the case of hydraulic cylinders 12, 14 directional valves are provided which control the flow of hydraulic fluid to the hydraulic cylinders.The mobile work machine 1 includes a plurality of wheels that allow movement of the mobile work machine. The movement may result in collisions between the mobile work machine and external objects (such as another mobile work machine or a tree). Such collisions pose a serious risk both to the people they are serving and to the machines themselves. In order to avoid such a risk, collision avoidance functions are generally used.In such a function, environment sensors (radar sensors, ultrasonic sensors, cameras and lidar) will generally detect their environment and recognize obstacles, other vehicles or persons in the vicinity. The acquired data is then analyzed by a control system to detect potential collisions. Once potential collision hazards are detected, the machine may trigger warnings or alarms. These can be done visually via screens or LED displays, acoustically via warning tones or by vibrations in the interior of the vehicle in order to alert the driver or the operators. Advanced systems may activate automatic emergency brakes or reduce speed to avoid collisions. These systems may be capable of acting independently to stop or slow the machine when there is a risk of a collision.Some mobile machines are equipped with driver assistance systems that help the driver avoid collisions. These systems may include steering assist, lane keeping assist, adaptive cruise control, and other functions to ensure that the engine is operated safely and without collisions. By establishing zones or areas in which the machine can operate safely and implementing zone detection systems, the machine can be programmed to perform certain actions or adjust its speed in certain areas.The exact implementation of these measures depends on the type of machine, its intended uses and the safety standards. A combination of different technologies and systems typically provides the most reliable collision avoidance for mobile machines.Detailed description of a collision avoidance function will be omitted in this description because the method of the present invention can be applied to any collision avoidance function.For this reason, the mobile work machine (as shown in FIG. 2 ) comprises a first environment sensor S 1. Known types of environment sensors are, for example, camera-based, radar-based, ultrasonic- or lidar-based sensors. Environment sensor S 1 is configured to acquire environment data, so that external objects 99 within a field of view 21 can be acquired.In order to enable the mobile working machine to move forward, a hydrostatic travel drive is generally used.According to FIG. 3, a hydrostatic travel drive has a first hydrostatic hydraulic machine 62, which is operated primarily as a hydraulic pump and is driven by a drive machine 40, which can be designed as a diesel engine (or alternatively also as an electric motor). Furthermore, the hydrostatic travel drive 1 has a second hydrostatic hydraulic machine 61 which is coupled via a drive shaft to an axle having two wheels 11 and is operated primarily as a hydraulic motor. The displacement volume of both hydraulic machines 61, 62 is adjustable in each case by means of an adjusting unit 66, 88. The first hydraulic machine 62 is fluidically connected to the second hydraulic machine in a closed hydraulic circuit via a first branch line 20, which in the further considerations is the feed line via which pressure medium flows from the hydraulic machine 62 to the hydraulic machine 61, and via a second branch line 22, which in the further considerations is the second branch line via which pressure medium flows from the hydraulic machine 61 to the hydraulic machine 62.The hydrostatic travel drive has a feed pump 26 which is connected to a drive shaft 24 of the first hydraulic machine 2 and can convey pressure medium from a tank T into a feed line 28. The latter branches into three branches, a first branch being capable of being brought into pressure medium connection with the tank T via a pressure limiting valve 30. A second or third branch can be brought into pressure medium connection with the branch line 20 or with the branch line 22 via a pressure limiting valve 32 or a pressure limiting valve 34, each of which has an integrated suction return valve 36 or 38.Both hydraulic machines 61, 62 can be operated in all four quadrants, so that both the flow direction of the pressure medium in the closed hydraulic circuit and the direction of rotation of each of the hydraulic machines can be reversed.The hydrostatic travel drive has a control unit 18 to which an accelerator pedal 44 is connected via a signal line 42. The latter has a sensor 46, by means of which an actuation intensity of the accelerator pedal 44 can be detected and transmitted to the control unit 18 via the signal line 42. This is connected via an electrical signal line 48 to the actuating device 66 of the hydraulic machine 62 and via an electrical signal line 50 to the actuating device 88 of the hydraulic machine 61. A rotational speed detection unit 54, via which the rotational speed of the second hydraulic machine 61 on the drive shaft can be detected, is connected to the control unit 18 via an electrical signal line 52. A rotational speed detection unit 60, by means of which the rotational speed of the first hydraulic machine 62 on its drive shaft can be detected, is connected to the control unit 18 via an electrical signal line. The control unit 18 has a memory unit 56, in which a method according to the invention is stored, and a processor unit 58, in which the method can be executed.FIG. 4 shows a selection 33 of the field of view 21 of the environment sensor S 1 according to the prior art (left) and according to the present invention (right). In particular, as will be more apparent from the flow of the present description, only a portion of the field of view 21 of the environment sensor is selected, such that only external objects 99 located within the selected field of view are considered in collision avoidance. According to an embodiment of the present invention, a length of the selected field of view is determined. A first portion of the length of the field of view is established using this formula: where L 1 is the first portion of the length of the selected field of view caused by the possible desired deceleration of the mobile work machine, where v is the current travel speed of the mobile work machine, and where a is the desired deceleration of the mobile work machine that can be achieved by the deceleration of the hydraulic motor and the hydraulic pump. In order to calculate the complete length of the field of view, a reaction path and a safety distance should preferably also be taken into account. In particular, this formula may be used, where L is the length of the field of view, L 1 is the length of the first portion that has already been explained, v is the current travel speed of the mobile work machine, t is a driver reaction time, and d is a safety margin.The essence of this invention is that a higher deceleration of the mobile working machine is achieved by the hydrostatic travel drive. This higher delay makes it possible to reduce the selected field of view, so that fewer and fewer external objects are taken into account, which are indeed located on the predicted path due to the current state of the machine but are actually not located on the real path of the machine, since future steering movements or changes in direction cannot be predicted.Referring now to Fig. 5, the logic of the present invention will be roughly explained. However, the exact functions will be explained with reference to FIG. 6.In a first step 100, a relative position between mobile machine 1 and external object 99 is ascertained by means of the first surroundings sensor. As already mentioned, the external object 99 should preferably be located within the selected field of view 33 of the field of view 21 of the environment sensor S 1. In the step, a relative movement between mobile working machine 1 and external object 99 is also ascertained, preferably taking into account the own movement of mobile working machine 1 and the ascertained surroundings sensor data.In a further step 101, it is determined on the basis of the determinations from step 100 whether the mobile work machine should be actively decelerated in order to avoid a collision with the external object 99.After it has been determined in step 101 that the mobile working machine is to be decelerated in order to avoid a collision, a (second) braking function of the mobile working machine is activated in a further step 102. The second function has two subfunctions. The first sub-function is configured to decelerate the mobile work machine by means of a change in the pivot angle of the hydraulic pump and of the hydraulic motor. The second sub-function is configured to decelerate the mobile working machine 1 by decreasing the target rotational speed of the prime mover 40.This means that in a sub-step 103, the mobile work machine is decelerated taking account of the first sub-function, while in the second sub-step 104, the mobile work machine is decelerated taking account of the second sub-function.FIG. 6 illustrates a first braking function (left) and the already described second braking function (right).The first braking function is the function normally used to decelerate the mobile work machine, i.e., in the case where it is determined in step 101 that the mobile work machine should not be actively decelerated to avoid collision with the external object 99. The second braking function is the function to be used in the case where it is determined in the step 101 that the mobile work machine is to be actively decelerated to avoid collision with the external object 99.The same quantities are represented both in the first braking function (left) and in the second braking function (right). A time profile of the setpoint pivot angle of the hydraulic motor 61 is represented by the line 105, while a time profile of the setpoint pivot angle of the hydraulic pump 62 is represented by the line 106. This means that lines 105 and 106 represent the first subfunction of step 103. Line 107 represents a time profile of the actual deceleration of mobile work machine 1. By contrast, the line 108 represents a time profile of the already described actual travel speed v of the mobile working machine 1, which changes on the basis of the braking function. Line 109 represents the setpoint rotational speed of the drive engine 40, which changes on the basis of the braking function.As shown in FIG. 6, the deceleration of the mobile work machine starts from the time t 1. From time t 2, the mobile work machine should have reached a travel speed v equal to zero.As is clear from FIG. 6, the first braking function has a first braking behavior, while the second braking function has a second braking behavior, wherein the first braking behavior differs from the second braking behavior. This is because a rate of change of the target swivel angle of the hydraulic motor and the target swivel angle of the hydraulic pump in the first braking function is provided which is smaller than a rate of change of the target swivel angle of the hydraulic motor and the target swivel angle of the hydraulic pump in the second braking function, so that the mobile work machine can be braked more quickly with the second braking function. In particular, from time t 1, a pivot angle of the hydraulic pump 62 is decreased, while the pivot angle of the hydraulic motor is increased.Moreover, as shown in FIG. 6, the second sub-function of the first function (left) will preferably have a different behavior compared to the second sub-function of the second function (right). This is because the rate of change of the target engine speed is different: the rate of change in the second function is higher compared to the first function (see line 109).The first braking function is dependent on the electrohydraulic components and on the parameterization of the traction drive software and corresponds to the deceleration behavior during normal travel operation. For reasons of comfort, the delay is set such that the maximum possible dynamics are not utilized. In contrast, the second braking function will preferably utilize the complete maximum possible dynamics.The first braking function is generally used in the event that the driver requests an active deceleration of the mobile work machine or in the event that the accelerator pedal 44 is no longer being actuated (the release of the accelerator pedal 44). This means that preferably the first braking function is always active and will intervene as soon as one of the described conditions (or even another condition) occurs. However, as soon as it is determined in step 101 that the mobile work machine is to be actively decelerated in order to avoid a collision with the external object 99, the first function is deactivated (or generally set to standby) as long as the second braking function is activated.It should be noted that it is not necessary for the mobile work machine to have to reach the travel speed v equal to zero. In many cases, it may be enough that the risk of collision is no longer up-to-date and the second braking function is automatically put on standby. Moreover, it is also clear to the person skilled in the art that releasing the accelerator pedal 44 is not necessary for activating the first braking function: e.g. the braking request (i.e. the activation of the first braking function) can be created automatically (e.g. by means of an automation function).In a variant, in order to achieve a load-independent solution, the increased deceleration is preferably achieved by the addition of a retarder.While the present invention has been described with reference to the above-described embodiments, it will be apparent to those skilled in the art that it is possible to realize various modifications, variations and improvements of the present invention in the light of the above-described teaching and within the scope of the appended claims without departing from the scope of the invention.Moreover, the areas of skill in the art would not be described herein to unnecessarily obscure the described invention. Accordingly, the invention is not to be limited by the specific illustrative embodiments, but by the scope of the appended claims.

Claims

Method for avoiding a collision of a mobile working machine (1) with an external object (99), wherein the mobile working machine (1) comprises a hydrostatic drive which is responsible for the movement of the mobile working machine (1), wherein the hydrostatic drive comprises a first hydraulic machine (62) which can be coupled to a drive machine (40) and is configured to supply a second hydraulic machine (61) which can be coupled to a drive output with pressure medium, wherein the mobile working machine (1) comprises at least one environment sensor (S1) which is configured to record environment data, wherein the mobile working machine (1) comprises a first braking function which is configured to decelerate the mobile working machine (1) by means of a change in a pivot angle of the first and the second hydraulic machine (62, 61) if deceleration of the mobile working machine (1) is required directly or indirectly, wherein the method comprises the following steps: a. determining a relative position between the mobile working machine (1) and the external object (99) by means of the first environment sensor; b. determining a relative movement between the mobile working machine (1) and the external object (99); c. determining, on the basis of the determinations from step a. and b., that the mobile working machine (1) is to be decelerated in order to avoid a collision with the external object (99); d. activating a second braking function, which is configured to decelerate the mobile working machine (1) by means of a change in the pivot angle of the first and the second hydraulic machine (62, 61), after it has been determined in step c. that the mobile working machine (1) is to be decelerated in order to avoid a collision; Deceleration of the mobile working machine (1) taking into account the second braking function activated in step d.; wherein the first braking function has a first braking behavior and wherein the second braking function has a second braking behavior, wherein the first braking behavior differs from the second braking behavior.Method according to Claim 1, wherein the first braking function is provided with a rate of change of the setpoint pivot angle of the first and of the second hydraulic machine which is smaller than a rate of change of the first and of the second hydraulic machine of the second braking function, with the result that the mobile working machine (1) can be braked more quickly with the second braking function.Method according to one of Claims 1 or 2, wherein the second braking behavior is also taken into account in the determination of step c. that the mobile working machine (1) is to be decelerated in order to avoid a collision with the external object (99).Method according to Claim 3, wherein the second braking behavior is taken into account in such a way that a portion (33) of a field of view (21) of the environment sensor (S1) is selected on the basis of the second braking behavior, and only external objects (99) which are located within the selected field of view (33) of the environment sensor (S1) are taken into account at least in step c.Method according to claim 4, wherein at least a first part (L 1) of the length of said selected field of view (33) of the environment sensor (S1) is proportional to the square of the current speed of the mobile working machine (1) and inversely proportional to the desired deceleration of the mobile working machine (1) achievable with the second braking function.Method according to one of Claims 1 to 5, wherein, in the case of the second braking function, the pivot angle of the second hydraulic machine (61) is increased, while the pivot angle of the first hydraulic machine (62) is decreased.Method according to one of Claims 1 to 6, wherein, in the case of the second braking function, a setpoint rotational speed of the drive machine (40) is furthermore lowered.Method according to one of Claims 1 to 7, wherein, with the activation of the second braking function from step d., the first braking function is switched off or set to standby.A control unit (18) adapted to perform a method according to any of the preceding claims.Mobile working machine (1) configured to receive loads, wherein the mobile working machine (1) comprises a hydrostatic drive which is responsible for the movement of the mobile working machine (1), wherein the hydrostatic drive comprises a hydraulic pump which can be coupled to a drive machine and is configured to supply a second hydraulic machine (61) which can be coupled to a drive output and is part of the hydrostatic drive with pressure medium, wherein the mobile working machine (1) comprises at least one environment sensor (S1) which is configured to acquire environment data, wherein the mobile working machine (1) comprises a first and a second braking function which are each configured to decelerate the mobile working machine (1) by means of a change in a pivot angle of the hydraulic pump and a pivot angle of the hydraulic motor, wherein the second braking function is configured to be activated after it has been determined in the mobile working machine (1), the mobile working machine (1) being intended to be decelerated in order to avoid a collision, wherein the first braking function has a first braking behavior and wherein the second braking function has a second braking behavior, wherein the first braking behavior differs from the second braking behavior.A computer program that causes a computing unit (18) to perform a method according to any one of claims 1 to 9 when executed on the computing unit.A machine readable storage medium (56) having stored thereon a computer program according to claim 11.

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