SE541115C2 - Control system, and method in connection with a control system, for autonomous vehicles - Google Patents

Abstract

A control system (2) for an autonomous vehicle (4) comprising an anti-spin system (6), the control system (2) comprises a processing device (8) adapted to receive a wheel spin signal (10) comprising a spin value S indicating whether at least one driving wheels on the vehicle spin relative to the road surface, and a propulsion force signal (12) comprising a propulsion force value P, the propulsion force value P being determined depending on the propulsion force of at least one driving wheel on the vehicle. The processing device (8) is adapted to determine, with a set of activation rules, one of a plurality of operating modes for said anti-spin system (6) to operate in, said plurality of operating modes comprising: indicates that at least one driving wheel is spinning.

Description

Field of the Invention The present invention relates to a control system, and a method in connection with such a control system, according to the preambles of the independent claims.

More specifically, the invention is directed to a control system, and a method, for improving the passability of autonomous vehicles in connection with driving on slippery surfaces.

Background of the Invention An unmanned ground vehicle (UGV) is a vehicle that can be driven without a driver. There are two types of driverless ground vehicles, those that are remotely controlled and those that are autonomous.

A remote-controlled UGV is a vehicle that is regulated by a human operator via a communication link. All actions are determined by the operator based on either direct visual observation or the use of sensors such as digital video cameras. A simple example of a remote-controlled UGV is a remote-controlled toy car. There is a wide variety of remote controlled vehicles in use today. These vehicles are often used in dangerous situations and environments that are unsuitable for people to live in, for example to disarm bombs and in the event of dangerous chemical emissions. Remotely controlled driverless vehicles are also used in connection with monitoring assignments and the like.

An autonomous vehicle is essentially an autonomous robot that works without the need for human control. The vehicle uses its sensors to obtain a kind of limited understanding of the environment, which is then used by control algorithms to determine what is the next step to take, taking into account the goal of the overall assignment given by the operator to the vehicle.

Autonomous vehicles have, among other things, been developed to be used in dangerous environments, for example in the defense and war industry and in the mining industry, both above ground and underground.

An autonomous vehicle thus refers to a vehicle that is capable of navigating and maneuvering without human control. The vehicle uses information regarding the road, the surroundings and other conditions that affect the travel to automatically regulate the throttle, braking and steering.

A careful assessment and identification of the planned progress is necessary to assess whether a road is passable and is necessary to be able to successfully replace a person's assessment when it comes to driving the vehicle.

Road conditions can be complex and during normal driving of a vehicle, the driver makes hundreds of observations per minute and adjusts the operation of the vehicle based on the perceived road conditions. One aspect of assessing road conditions is to perceive the road and its surroundings and to find a passable road past objects that may be on the road. In order to be able to replace human perception with an autonomous system, this means, among other things, being able to perceive objects in an accurate way in order to be able to effectively regulate the vehicle so that you steer past these objects.

The technical methods used to identify an object in connection with the vehicle include using one or more cameras and radar to create images of the surroundings. Laser technology is also used, both scanning lasers and fixed lasers, to detect objects and measure distances. These are often referred to as LIDAR (Light Detection and Ranging) or LADAR (Laser Detection and Ranging). In addition, various sensors are used in the vehicle, among other things, to sense speed and accelerations in different directions.

The cameras translate visual images captured in the form of light patterns or infrared radiation into manageable data format. Such a format can be pixelated images where a detected image is broken down into series of pixels. Radar image processing uses radio waves generated by a transmitter which are then detected and used to estimate shapes and objects in front of the transmitter. Different patterns of these reflected shapes and objects can then be analyzed to determine the position of these objects. GPS and other wireless technology can also be used to determine if, for example, you are approaching an intersection, a narrowing of the road, and other vehicles.

More specifically, an autonomous vehicle must be able to read the surroundings well enough to be able to carry out the task to which it has been assigned, for example "moving the boulders from place A to place B via the mine passage C". The autonomous vehicle needs to plan and follow a road to the selected destination while detecting and avoiding obstacles on the road. In addition, the autonomous vehicle must carry out its task as quickly as possible without making any mistakes.

In the environments in which autonomous vehicles work, the ground can often be slippery.

In general, there are several cooperating systems that can be used to increase the safety of a vehicle when driving on slippery roads, and below is an overview of the most important ones.

The function of an electronic stability control system for a vehicle is controlled, for example, by a computer that receives information from, among other things, the wheel sensors of the ABS brakes, a sensor in the steering wheel and a gyro. With this information as a basis, the computer can quickly determine if the vehicle is getting a cord or spin and then acts by individually braking one or more wheels and if necessary also reducing the throttle so that the car regains the right course, or individually braking the wheel that has lost its grip. (antispin). Everything happens in fractions of a second and often without the driver noticing that the vehicle was about to end up in a cord or spin. For trucks, the system's intervention means, among other things, that they do not tip over. The goal is for the driver to always have control over his vehicle and for the border to unstable area not to be violated.

To prevent critical driving situations, the system compares the driver's driving requirements with the car's actual driving condition. The system reads the driver's driving requirements from the steering wheel angle measured by a sensor. Wheel speed, gear speed and engine management provide all information about the car's driving condition. Only if the driving condition deviates from the driving desire is the system activated. Override, which means that the car is turned more than the driver wants to do in a curve (the rear trailer releases), is prevented by braking the cornering front wheel. Understeer, which means that the car drives a larger curve than the driver wants (goes straight ahead in a curve), is prevented by braking the cornering rear wheel. Both of these maneuvers also have the advantage that the car is slower, which makes it easier for the tires to transfer power from the car to the road, but most importantly, the car steers in the direction the steering wheel points (rotation around the center of the car).

Anti-spin systems usually only work at low speeds and only aim to prevent the car's wheels from spinning. This is in contrast to the more advanced anti-cord systems that exist today that work even at high speeds to counteract the cord.

Autonomous vehicles are often used in environments where the road surface is slippery. For example, in mines, and in opencast mines. As discussed above, an anti-spin system is often used on slippery roads, which limits the relative speed between the driving wheels and the ground so that the vehicle does not lose grip. This function is of course also useful for autonomous vehicles. Anti-spin systems have the best effect at moderate slipperiness, but there are situations where a greater relative speed between wheel and surface is required to obtain a propulsive force.

An traction control system is thus designed to prevent the driving wheels from losing the bracket, ie. slips against the ground, so that the vehicle does not drop the side grip on the drive shaft (usually the rear axle) and thus skids around. When engaged, the driver's control of the vehicle is improved. The slip is caused by the gas application applied not corresponding, ie. is too large, with the frictional conditions prevailing between the wheels and the ground.

The anti-spin system consists of performing one or more of the following actions: Reduce or suppress the ignition frequency of one or more cylinders in the engine. Reduce fuel injection to one or more cylinders.

Apply braking force to one or more wheels.

Reduce throttle.

The following patent documents describe various aspects of anti-spin systems.

US2006293841 describes an anti-spin control system that limits the release by reducing the driveline torque. If this does not help, the anti-spin system is reduced or deactivated and control is returned to the driver.

US7499787 describes the anti-spin system mentioned above in more detail.

US8140239 describes an anti-spin system for the purpose of limiting wheel releases in autonomous, semi-autonomous or manned work vehicles.

US5459661 describes deactivation of an anti-spin system if there is a risk of engine stalling.

WO2011062481 relates to the control of autonomous agricultural machines and describes the reduction of the speed when a machine loses its grip on, for example, a slippery floor.

In moderately slippery situations, anti-spin systems can help drive a vehicle, but there is a limit as it is no longer possible to drive a vehicle with the anti-spin function activated. In such cases, a larger release on the wheels is required to obtain a propulsive force.

The inventors have found that anti-spin systems would also be useful for autonomous vehicles as they would help the autonomous system to get the vehicle where it wants and avoid the vehicle ending up in undesirable positions and with undesired turning angles. When anti-spin systems are used in vehicles with a driver, there is always the possibility that the driver, in special situations, enters and takes control from the anti-spin system. Since there is no driver in the autonomous vehicle, that possibility is missing.

The object of the invention is to improve the performance of autonomous vehicles on slippery surfaces and surfaces where the tires for other reasons do not have as good grip as gravel roads or driving in sand, and especially for autonomous vehicles equipped with anti-spin systems.

Summary of the Invention The above object is achieved by the invention defined by the independent claims.

Preferred embodiments are defined by the dependent claims.

In order for an autonomous vehicle to have better maneuverability on slippery surfaces, according to the invention, a so-called "maneuverability mode" is used for the anti-spin system, which means that the anti-spin system allows release on the drive wheels and thus increases the propulsion force.

According to one embodiment, the automatic navigation of the vehicle based on measured wheel movements to calculate the position of the vehicle will not be used because the wheel movements do not correctly reflect the position of the vehicle when the wheels slip. Instead, other sensors are used for positioning, such as accelerometers, gyros, relative distance and speed sensors.

Thus, using a control according to the present invention, the autonomous vehicle could travel even where it is very slippery.

Brief Description of the Drawings Figure 1 is a schematic block diagram schematically illustrating the present invention.

Figure 2 is a flow chart illustrating the method of the present invention.

Figure 3 is a schematic block diagram illustrating an embodiment of the present invention.

Detailed Description of Preferred Embodiments of the Invention The invention will now be described in detail with reference to the accompanying figures.

Figure 1 shows a block diagram illustrating the present invention and relating to a control system 2 for an autonomous vehicle 4, which vehicle comprises an anti-spin system 6 which is adapted to operate in one of a number of operating modes, depending on a control signal 16. A number of activation rules are used to determine which mode of operation is currently to be used. Some of these activation rules are in accordance with what is generally used in connection with anti-spin systems, which have been discussed above, and are based, among other things, on measured slip, applied force, etc.

The control system 2 comprises a processing device 8 which is adapted to receive a wheel spin signal 10 comprising a spin value S, which indicates whether at least one driving wheel on the vehicle spins relative to the road surface, and a propulsion force signal 12 comprising a propulsion force value P. The propulsion force value P has determined of the propulsion force of at least one driving wheel on the vehicle. This measurement of the propulsion force value P takes place in a manner known per se, for example by measuring on an output shaft from the gearbox.

The processing device 8 is adapted to determine, using the set of activation rules, one of a plurality of operating modes for the anti-spin system 6 to operate in, said plurality of operating modes including a maneuverability mode which allows the propulsion force value P to increase, although said spin value S indicates at least one driving wheels spin.

According to one embodiment, the activation rules comprise a rule related to the vehicle maintaining a predetermined safety margin as an obstacle along the roadway and that this rule is used to determine whether said mode of accessibility is to be activated.

By using an activation rule that takes into account that a safety margin is prevented, the activation of the accessibility mode is limited at higher speeds. If one e.g. comes at high speed uphill on a slippery road when the tires start to spin then the system will first evaluate if the pass mode is required, if so it will evaluate if the extra margin of obstacles (in this case the ditches) is enough to activate the pass mode and come to the conclusion that it does not, which will lead to the anti-spin system remaining active and reducing the propulsion force so that the speed of the vehicle also decreases. If the speed of the vehicle decreases so much that the required safety margin drops below the available distance to the obstacles, the passability mode will be allowed to be activated, which will increase the available propulsion force, which is hopefully enough to prevent the speed from falling further.

The safety margin needed for obstacles is strongly linked to the speed, at high speed a much larger safety margin is required because a small uncertainty in lateral movement at high speed gives a large uncertainty in lateral position. The safety margin is determined depending on, among other things, the current friction of the road, the vehicle's speed, the road's topology and curve shape.

As mentioned above, according to one embodiment, the set of predefined activation rules may include that the deactivation of the anti-spin system is related to one or more distances between the vehicle and surrounding objects.

In connection with this, the sensors that are arranged on the autonomous vehicle, e.g. radar, lidar and cameras, to assess the distance to other vehicles and surrounding objects, e.g. walls in mines or rocks.

This can be implemented so that the anti-spin system is not deactivated if a measured distance is less than predetermined threshold values, ie. if you get too close to a wall in the mine, leave the anti-spin system activated.

The control system is also responsible for controlling the anti-spin system and is therefore, among other things, adapted to emit control signals to the anti-spin system for activation or deactivation thereof.

The pass mode can be left, for example, when P exceeds a propulsion force threshold (PTR) by a certain margin; when the wheels stop spinning, or when the required safety margin in position exceeds the available one. This means that if the vehicle reaches the desired speed, P will decrease and the wheels will stop spinning.

PTR is thus a limit value with which the limited propulsion force of the anti-spin system must be compared in order to determine whether the passability mode is necessary at the moment or not. PTR can be considered to represent a propulsion force when the vehicle actually moves. When the maneuverability mode is activated, a propulsion force P exceeding the limited propulsion force of the anti-spin system will be allowed. However, the passability mode does not mean that the engine is allowed to accelerate as much as possible, but a higher slip against the ground will be allowed.

Sometimes it can happen that even though the propulsion force increases in the passability mode, the vehicle does not move forward because the available friction is not sufficient. In such cases, one can preferably exit the passability mode after a predetermined time limit has been passed.

In the maneuverability mode, the propulsion force value P is preferably allowed to increase to a level that exceeds the limited propulsion force of the anti-spin system. This thus means that P is allowed to be above this level.

Among the mentioned several operating modes, there is of course a normal operating mode which is activated in a conventional manner when it is found that a driving wheel is spinning and which means that the anti-spin system functions normally.

Normally, the navigation of the vehicle, which is performed by a navigation system 14 for the vehicle, is based on measuring the wheel movements of the vehicle. This navigation is deactivated if the anti-spin system 6 operates in the pass-through mode. The reason, of course, is that navigation will not be correct if the wheels slip. In the figure, the navigation system 14 has been dashed to indicate that this is an embodiment of the invention. Instead, one or more other measurement signals are used for navigating the vehicle, for example GPS is used, or other position and navigation systems.

The invention also relates to a method in connection with a control system for an autonomous vehicle which comprises an anti-spin system, and wherein the control system comprises a processing device. The control system, the anti-spin system and the processing device have been described above.

With reference to the flow chart in Figure 2, the method will now be described. The method comprises: - receiving a wheel spin signal comprising a spin value S indicating whether at least one driving wheel on the vehicle spins relative to the road surface, - determining a propulsion force value P in dependence on the propulsion force of said at least one driving wheel; generating a propulsion force signal comprising the propulsion force value P and applying this signal to the processing device, and - determining, with a set of activation rules, one of a plurality of operating modes for said anti-spin system to operate, said plurality of operating modes comprising: a propulsion mode P is allowed to increase, even though said spin value S indicates that at least one driving wheel spins.

According to one embodiment, said activation rules comprise a rule related to the vehicle maintaining a predetermined safety margin to obstacles along the roadway and that said rule being used to determine whether said mode of accessibility is to be activated. This rule has been discussed in detail in the description above.

In the passability mode, the propulsion force value P is preferably allowed to increase to a level that exceeds the limited propulsion force of the anti-spin system.

If the vehicle's navigation is based on the measurement of the vehicle's wheel movements, and is performed by a vehicle navigation system, it will be deactivated if the anti - spin system operates in passability mode, and one or more other measurement signals are used instead of the vehicle's navigation.

The present invention further comprises a computer program (D) in vehicles, said computer program (D) comprising program code for causing a processing device 8; 500 or another computer 500 connected to the processing device 8; 500 to perform the steps according to the method described above.

Furthermore, the invention also comprises a computer program product comprising a program code stored on a computer-readable medium for performing the method steps described above, when said program code is executed on a processing device 8; 500 or another computer 500 connected to the processing device 8; 500.

Referring to the block diagram of Figure 3, the computer 500 will now be described.

The program D may be stored in an executable manner or in a compressed manner in a memory 560 and / or in a read / write memory 550. When it is described that the data processing unit 510 performs a certain function, it should be understood that the data processing unit 510 performs a certain part of the program which is stored in the memory 560, or a certain part of the program stored in the read / write memory 550. The data processing device 510 can communicate with a data port 599 via a data bus 515. The non-volatile memory 520 is intended for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is intended to communicate with the data processing unit 510 via a data bus 511. The read / write memory 550 is arranged to communicate with the data processing unit 510 via a data bus 514. To the data port 599 the units connected to the processing device 8 (see figure 1 ) be connected.

When data is received on the data port 599, it is temporarily stored in the second memory part 540. Once the received input data has been temporarily stored, the data processing unit 510 is arranged to perform code execution in a manner described above.

Parts of the methods described herein may be performed by the device 500 (corresponding to the processing device 8 in Figure 1) by means of the data processing unit 510 running the program stored in the memory 560 or the read / write memory 550. When the device 500 runs the program, the methods described herein are executed.

An application of the control system according to the invention is to use the release on the rear axle to give the vehicle a turning angle speed, ie. to turn the vehicle. It is generally known that the parking brake can be used to utilize so much of the longitudinal friction of the rear tires that they lose lateral grip, which makes the vehicle more manoeuvrable. Similarly, the control system, knowing that the friction is low, would increase the utilization of the longitudinally available friction by increasing the torque on the drive wheels to reduce the lateral grip of the driving wheels so as to increase the maneuverability of the vehicle. Occasions when this could be used are e.g. if you are going to pass a very narrow curve; then, instead of driving forward and reversing several times, one could increase the vehicle's maneuverability in this way and get through the curve without having to reverse.

The present invention is not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents can be used. The above embodiments are therefore not to be construed as limiting the scope of the invention as defined by the appended claims.

Claims (10)

Patent claims A control system (2) for an autonomous vehicle (4) comprising an anti-spin system (6), the control system (2) comprises a processing device (8) adapted to receive a wheel spin signal (10) comprising a spin value S indicating whether at least one driving wheel on the vehicle spins relative to the road surface, and a propulsion force signal (12) comprising a propulsion force value P, the propulsion force value P being determined depending on the propulsion force of at least one driving wheel on the vehicle, characterized in that the machining device (8) determining, with a set of activation rules, one of a plurality of operating modes for said anti-spin system (6) to operate in, said plurality of operating modes comprising: - a maneuverability mode which allows the propulsion force value P to be increased, spinner, said activation rules comprising a rule related to the vehicle h or a predetermined safety margin to obstacles along the roadway and that said rule is used to determine whether said mode of accessibility is to be activated. The control system (2) according to claim 1, wherein in the passability mode the propulsion force value P is allowed to increase to a level exceeding the limited propulsion force of the anti-spin system. The control system (2) according to any one of claims 1-2, wherein navigation of the vehicle based on measurement of the wheel movements of the vehicle, and performed by a navigation system (14) for the vehicle, is deactivated if the anti-spin system (6) operates in said passability mode, and a or several other measurement signals are used instead of navigating the vehicle. The control system according to any one of claims 1-3, wherein said control system is adapted to output control signals to said anti-spin system to put it in a determined operating mode. A method in connection with a control system for an autonomous vehicle comprising an anti-spin system, and wherein the control system comprises a processing device, the method comprises: - receiving a wheel spin signal comprising a spin value S indicating whether at least one driving wheel on the vehicle spins in relation to the roadway, - determining a propulsion force value P in dependence on the propulsion force of said at least one driving wheel; generating a propulsion force signal comprising the propulsion force value P and applying this signal to the processing device, characterized in that the method further comprises - determining, with a set of activation rules, one of a plurality of operating modes for said anti-spin system to operate in, said plurality of operating modes comprising: - a passability mode which means that the propulsion force value P is allowed to increase, even though said spin value S indicates that at least one driving wheel spins, said activation rules including a rule related to the vehicle maintaining a predetermined safety margin to obstacles along the roadway and that said rule being used to determine accessibility mode must be activated. The method according to claim 5, wherein in the maneuverability mode, the propulsion force value P is allowed to increase to a level exceeding the limited propulsion force of the anti-spin system. The method according to any one of claims 5-6, wherein navigation of the vehicle based on measuring the wheel movements of the vehicle, and performed by a navigation system for the vehicle, is deactivated if the anti-spin system operates in said passability mode, and one or more other measurement signals are used instead of navigating the vehicle. The method according to any one of claims 5-7, wherein said control system is adapted to output control signals to said anti-spin system to put it in a determined operating mode. Computer program (D) for vehicles, wherein said computer program (D) comprises program code for causing a processing device (8; 500) or another computer (500) connected to the processing device (8; 500) to perform the steps according to the method according to any of requirements 5-8. A computer program product comprising a program code stored on a computer readable medium for performing the method steps according to any one of claims 5-8, when said program code is executed on a processing device (8; 500) or another computer (500) connected to the processing device. (8; 500).