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Title:
REGULATING SYSTEM AND METHOD FOR AUTONOMOUS VEHICLES WITH ANTISPIN SYSTEM
Document Type and Number:
WIPO Patent Application WO/2014/148979
Kind Code:
A1
Abstract:
A regulating system (2) for an autonomous vehicle (4) provided with an antispin system (8), which regulating system (2) comprises a processing device (8) adapted to receiving a wheelspin signal (10) comprising a spin value S which indicates whether at least one of the vehicle's tractive wheels is spinning relative to the roadway, and a propulsive force signal (12) comprising a propulsive force value P determined on the basis of the propulsive force for at least one of the vehicle's tractive wheels. The processing device (8) is adapted to using a set of activation rules to determine one of a number of operating modes for said antispin system (6) to operate in, which modes comprise: an operability mode whereby the propulsive force value P is allowed to increase despite said spin value S indicating that at least one tractive wheel is spinning.

Inventors:
ANDERSSON JON (SE)
AH-KING JOSEPH (SE)
NYSTRÖM TOM (SE)
Application Number:
SE2014/050291
Publication Date:
September 25, 2014
Filing Date:
March 11, 2014
Export Citation:
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Assignee:
SCANIA CV AB (SE)
International Classes:
B60T8/175; B60T7/12; B60T8/1755; B60W30/182; B60W60/00; G05D1/02; B66F9/06
Domestic Patent References:
WO2002004242A12002-01-17
WO2011062481A12011-05-26
Foreign References:
EP0574150A11993-12-15
US20090107748A12009-04-30
GB2446419A2008-08-13
US20100049408A12010-02-25
US8140239B22012-03-20
Attorney, Agent or Firm:
YOUSSEF, Maikel (Scania CV AB, Södertälje, SE-151 87, SE)
Download PDF:
Claims:
Claims

1. A regulating system (2) for an autonomous vehicle (4) provided with an antispin system (6), which regulating system (2) comprises

a processing device (8) adapted to receiving a wheelspin signal (10) comprising a spin value S which indicates whether at least one of the vehicle's tractive wheels is spinning relative to the roadway,

and a propulsive force signal (12) comprising a propulsive force value P determined on the basis of the propulsive force for at least one of the vehicle's tractive wheels,

c h a r a c t e r i s e d in that the processing device (8) is adapted to using a set of activation rules to determine one of a number of operating modes for said antispin system (6) to operate in, which modes comprise:

- an operability mode whereby the propulsive force value P is allowed to increase despite said spin value S indicating that at least one tractive wheel is spinning.

2. The regulating system (2) according to claim 1 , in which said activation rules comprise a rule which is related to the vehicle maintaining a predetermined safety margin relative to obstacles along the roadway and is used to determine whether said operability mode should be activated.

3. The regulating system (2) according to claim 1 or 2, in which in the operability mode the propulsive force value P is allowed to increase to a level which exceeds the limited propulsive force of the antispin system. 4. The regulating system (2) according to any one of claims 1-3, in which the vehicle's navigation based on measurement of its wheel movements and conducted by a navigation system (14) for the vehicle is inactivated if the antispin system (6) is operating in said operability mode, and one or more measurement signals are used instead for the vehicle's navigation.

5. The regulating system according to any one of claims 1-4, in which said regulating system is adapted to delivering control signals to said antispin system in order to put it into particular operating modes. 6. A method pertaining to a regulating system for an autonomous vehicle provided with an antispin system, the regulating system comprising a processing device, which method comprises:

- receiving a wheelspin signal comprising a spin value S which indicates whether at least one of the vehicle's tractive wheels is spinning relative to the roadway, - determining a propulsive force value P on the basis of the propulsive force for said at least one tractive wheel,

- generating a propulsive force signal which comprises the propulsive force value P and conveying this signal to the processing device,

c h a r a c t e r i s e d in that the method further comprises

- using a set of activation rules to determine one of a number of operating modes for said antispin system to operate in, which modes comprise:

- an operability mode whereby the propulsive force value P is allowed to increase despite said spin value S indicating that at least one tractive wheel is spinning. 7. The method according to claim 6, in which said activation rules comprise a rule which is related to the vehicle maintaining a predetermined safety margin relative to obstacles along the roadway and is used to determine whether said operability mode should be activated. 8. The method according to claim 6 or 7, in which in the operability mode the propulsive force value P is allowed to increase to a level which exceeds the limited propulsive force of the antispin system.

9. The method according to any one of claims 6-8, in which the vehicle's navigation based on measurement of its wheel movements and conducted by a navigation system for the vehicle is inactivated if the antispin system is operating in said operability mode, and one or more measurement signals are used instead for the vehicle's navigation.

10. A method according to any one of claims 6-9, in which said regulating system is adapted to delivering control signals to said antispin system in order to put it into particular operating modes.

11. A computer program (D) for vehicles, which 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 steps of the method according to any one of claims 6-10.

12. A computer program product comprising a program code stored on a computer-readable medium for performing method steps according to any one of claims 6-10 when said program code is run on a processing device (8; 500) or another computer (500) connected to the processing device (8; 500).

Description:
Regulating system and method for autonomous vehicles with antispin system

Field of the invention

The present invention relates to a regulating system, and a method pertaining to such a regulating system, according to the preambles of the independent claims. More specifically, the invention focuses on a regulating system, and a method, for improving the operability of autonomous vehicles on slippery surfaces. Background to the invention

A driverless vehicle (unmanned ground vehicle, UGV) is a vehicle which can be used without a driver. There are two types of driverless ground vehicles, those which are remote-controlled and those which are autonomous. A remote-controlled UGV is a vehicle which is regulated by a human operator via a communication link. Each control action is determined by the operator either on the basis of direct visual observation or by using sensors such as digital video cameras. A simple example of a remote-controlled UGV is a remote-controlled toy car. A great variety of remote-controlled vehicles are now in use, often in dangerous situations and environments which are inappropriate for humans to be in, e.g. disarming of bombs and dealing with hazardous chemical discharges. Remote-controlled driverless vehicles are also used in surveillance operations and the like. Λ An autonomous vehicle is substantially an autonomous robot which functions without needing to be controlled by a human. Such a vehicle uses its sensors to gain a kind of limited understanding of the surroundings which is then used by regulating algorithms to determine the next control action for the purposes of the superordinate assignment set for the vehicle by an operator. Autonomous vehicles have inter alia been developed for potential use in dangerous environments, e.g. in the military and defence industry and the mining industry, both above and below ground.

Autonomous vehicle thus means here a vehicle capable of navigating and manoeuvring without human control. It uses information about the road, the surroundings and other conditions which affect the route ahead, with a view to automatically regulating the power mobilised, the braking and the steering.

Accurate assessment and identification of the planned route ahead is necessary for assessing whether a road is negotiable and for being able to successfully replace human judgement in operating the vehicle.

Road conditions may be complex and in normal running of a vehicle the driver will make hundreds of observations per minute and adjust the operation of the vehicle on the basis of the road conditions perceived. One aspect of assessing road conditions is perceiving the road and its surroundings and finding a feasible way past any objects which may be on the road. Using an autonomous system to replace human perception entails inter alia being able accurately to perceive objects to make it effectively possible to regulate the vehicle so that it is directed past them. The technical methods used for identifying an object close to a vehicle comprise inter alia using one or more cameras and radar to create images of the

surroundings. Laser techniques are also used, both scanning lasers and fixed lasers, to identify objects and measure distances. These techniques are often called LIDAR (light detection and ranging) or LADAR (laser detection and ranging). In addition, various sensors on board the vehicle are used inter alia to detect its speed and accelerations in different directions.

The cameras convert visual images picked up in the form of light patterns or infrared radiation to a manageable data format. Such a format may comprise pixelled images whereby a detected image is broken down to a series of pixels. Image processing with radar uses radio waves generated by a transmitter which are then detected and used to assess shapes and objects ahead of the transmitter. Different patterns of these reflected shapes and objects may then be analysed to determine their locations. GPS and other wireless technologies may also be used to determine whether the vehicle is for example approaching an intersection, a narrower stretch of road and other vehicles.

More specifically, an autonomous vehicle has to be able to read the surroundings well enough to be able to perform the assignment set for it, e.g. "move blocks of stone from point A to point B via mine adit C". The autonomous vehicle needs to plan and follow a route to the chosen destination while at the same time detecting and avoiding obstacles on the way. It has also to perform its assignment as quickly as possible without making mistakes.

In the environments in which autonomous vehicles operate the running surface may often be slippery. A general review of the most important of the various interacting systems which can be used to improve safety for a vehicle on slippery roads is set out below.

The operation of a system for electronic stability control of a vehicle is for example controlled by a computer which receives information inter alia from the wheel sensors of the ABS brakes, a sensor in the steering and a gyro. On the basis of this information the computer can with lightning speed decide whether the vehicle is about to skid or spin, and can then act by individually braking one or more wheels and also, where necessary, by reducing the power mobilised so that the vehicle reverts to its proper course, or by individually braking a wheel which has lost grip (antispin). All this takes place in fractions of a second and often without the driver having realised that the vehicle was on the way to beginning to skid or spin. In the case of trucks, the scope of the system comprises inter alia

preventing their overturning. The aim is that the driver should always have control of the vehicle and that the borderline to unstable conditions should not be crossed. To prevent critical operating situations, the system compares the driver's wishes with the vehicle's actual operating state. It reads his/her wishes from the steering wheel angle measured by a sensor. Wheel speeds, yaw rate and engine control all provide information about the vehicle's operating state. The system is only activated if the operating state deviates from that desired. Oversteering, i.e. the vehicle turning more than the driver wishes on a bend (rear end slipping), is prevented by braking the forward wheel on the outside of the bend.

Understeering, i.e. the vehicle following a larger curve than the driver wishes (moving straight ahead on a bend), is prevented by braking the rear wheel on the inside of the bend. Both of these manoeuvres afford also the advantage of slowing the vehicle, which it makes it easier for the tyres to transmit forces from the vehicle to the road, but the most important aspect is that the vehicle steers in the direction pointed by the steering wheel (rotation about the centre of the vehicle).

Antispin systems generally work only at low speeds and are only intended to prevent the vehicle's wheels from spinning, unlike current more advanced antiskid systems which also work at high speeds to counteract skidding. Autonomous vehicles are often used in environments where the roadway is slippery, e.g. in mines and quarries. As discussed above, an antispin system is often used on slippery roads, with the effect of limiting the relative speed between the tractive wheels and the running surface so that the vehicle does not lose grip. This function is of course also usable on autonomous vehicles. Antispin systems are most effective in moderately slippery conditions, but there are situations where a greater relative speed between wheels and running surface is required to achieve a propulsive force.

An antispin system (also called a traction control system) is thus configured to prevent the tractive wheels from losing grip, i.e. from sliding on the running surface, so that the vehicle does not lose lateral grip on the powered axle (most commonly the rear axle) and consequently skid round. When the system is connected, the driver's control of the vehicle's propulsion is improved. The sliding is caused by the power mobilised not corresponding to, i.e. being too great for, the friction conditions prevailing between wheels and running surface. The antispin system comprises one or more of the following control actions:

Reducing or suppressing the ignition rate for one or more of the engine's cylinders.

Reducing the fuel injection to one or more cylinders.

Applying braking force to one or more wheels.

Reducing the power mobilised.

The specifications mentioned below describe various aspects of antispin systems.

US2006293841 describes a system for antispin control which limits slippage by reducing the power train torque. If this does not help, the antispin system is reduced or deactivated and control reverts to the driver.

US7499787 describes the abovementioned antispin system in more detail. US8140239 describes an antispin system with the object of limiting wheel slippage in autonomous, semi-autonomous or manned work vehicles.

US5459661 describes deactivation of an antispin system if there is risk of engine stalling.

WO2011062481 refers to control of autonomous agricultural machines and describes lowering of speed when a machine loses grip, e.g. on a slippery floor.

In moderately slippery situations, antispin systems may help the running of a vehicle, but there is a limit beyond which it is not possible to run a vehicle with the antispin function activated. In such cases a larger slippage on the wheels is required to achieve a propulsive force. The inventors have found that antispin systems would also be usable for autonomous vehicles by helping the autonomous system to cause the vehicle to run as desired and prevent its reaching undesirable positions and undesirable yaw angles. When antispin systems are used in a vehicle with a driver, it is always possible, in particular situations, for him/her to intervene and take over control from the antispin system. In an autonomous vehicle this is not possible, since there is no driver. The object of the invention is to improve the running of autonomous vehicles on slippery surfaces and those where the tyres for other reasons do not grip well, as on gravel roads or in sand, particularly in the case of autonomous vehicles equipped with antispin systems. Summary of the invention

The above object is achieved with the invention defined by the independent claims.

Preferred embodiments are defined by the dependent claims.

For better operability of an autonomous vehicle on slippery running surfaces, the invention uses a so-called "operability mode" for the antispin system, which means that the system allows slippage of the tractive wheels and that the propulsive force is thereby increased.

In one embodiment the vehicle's automatic navigation which calculates its location on the basis of measured wheel movements is not used, since they will not correctly represent the vehicle's location when the wheels slide. Instead, other sensors are used for positioning, e.g. accelerometers, gyros and spacing and speed sensors. Using a form of regulation according to the present invention would thus enable the autonomous vehicle to make its way even in very slippery conditions.

Brief description of drawings

Figure 1 is a schematic block diagram schematically illustrating the present invention.

Figure 2 is a flowchart illustrating the method according to 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 attached drawings. Figure 1 is a block diagram illustrating the present invention and relating to a regulating system 2 for an autonomous vehicle 4, which vehicle is provided with an antispin system 6 adapted to working in any of a number of operating modes, depending on a control signal 16. A number of activation rules are applied to determine which operating mode is appropriate at the time. Some of these rules correspond to what is usual in the context of antispin systems described above, and are based inter alia on measured sliding, power mobilised, etc.

The regulating system 2 comprises a processing device 8 adapted to receiving a wheelspin signal 10 comprising a spin value S which indicates whether at least one of the vehicle's tractive wheels is spinning relative to the roadway, and a propulsive force signal 12 comprising a propulsive force value P determined on the basis of the propulsive force on at least one of the vehicle's tractive wheels. This measurement of the propulsive force value P is effected in known ways, e.g by measurement on an output shaft of the gearbox.

The processing device 8 is adapted to using the set of activation rules to determine one of a number of operating modes for the antispin system 6 to work in, which modes comprise an operability mode in which the propulsive force value P is allowed to increase despite said spin value S indicating that at least one tractive wheel is spinning. In one embodiment the activation rules comprise a rule which is related to the vehicle maintaining a predetermined safety margin relative to obstacles along the roadway and is used to determine whether said operability mode should be activated.

Applying an activation rule which caters for maintaining a safety margin relative to obstacles limits the activation of the operability mode at higher speeds. If for example an uphill run on a slippery major road is commenced at high speed and the tyres begin to spin, the system will first assess whether the operability mode is required, in which case it will assess whether the extra margin relative to obstacles (in this case the ditches) is sufficient for activating the operability mode and will come to the conclusion that it is not doing what will lead to the antispin system continuing to be active and reducing the propulsive force so that the vehicle's speed also decreases. If the vehicle's speed decreases so much that the necessary safety margin declines over the available distance to obstacles, the operability mode will be allowed to be activated, thereby increasing the available propulsive force, which will hopefully be sufficient to prevent the speed from declining further. The safety margin needed relative to obstacles is closely related to the vehicle's speed in that high speeds require very much larger safety margins, since a small uncertainty in lateral movement at high speed results in great uncertainty in lateral position. The safety margin is determined on the basis inter alia of the current friction of the road, the speed of the vehicle and the topology and curvature of the road.

As mentioned above, in one embodiment the set of predefined activation rules may mean that the deactivation of the antispin system is related to one or more distances between the vehicle and nearby objects. This context involves using the sensors on board the autonomous vehicle, e.g. radar, lidar and cameras, to assess the distance between it and other vehicles and nearby objects, e.g. rocks or walls in mines.

This may be implemented in such a way that the antispin system is not

deactivated if a measured distance is below predetermined threshold values, i.e. if the vehicle comes too close to a mine wall the antispin system will be allowed to remain activated.

The regulating system is further responsible for controlling the antispin system and is therefore adapted inter alia to delivering control signals to the antispin system for its activation and inactivation.

The operability mode may for example be dropped when P is above a threshold value for the propulsive force (PTR) by a certain margin, when the wheels stop spinning or when the necessary safety margin at a location exceeds what is available. 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 propulsive force of the antispin system has to be compared to decide whether the operability mode is necessary at the time or not. PTR may be regarded as representing a propulsive force at which the vehicle actually makes its way. When the operability mode is activated, a propulsive force P which exceeds the limited propulsive force of the antispin system will be allowed. The operability mode does not mean, however, that the engine is allowed to produce any desired amount of power, but more slippage on the running surface will be allowed.

It may sometimes happen that despite the propulsive force increasing in the operability mode the vehicle makes no progress because the available friction is not sufficient. In such cases it may be preferable to come out of the operability mode after a predetermined time limit has passed. In the operability mode the propulsive force P is preferably allowed to increase to a level which exceeds the limited propulsive force of the antispin system. This means that P is allowed to be above that level. Among said various operating modes there is of course a normal operating mode which is activated in a conventional way when it is found that a tractive wheel is spinning and which means that the antispin system will operate normally.

The vehicle's navigation conducted by a navigation system 14 is normally based on measurement of the vehicle's wheel movements. This navigation is inactivated if the antispin system 6 is operating in the operability mode. The reason is of course that the navigation will not be correct if the wheels slide. In the diagram the navigation system 14 is depicted in broken lines to indicate that this is one embodiment of the invention. Instead, one or more other measurement signals are used for the vehicle's navigation, e.g. GPS or some other location and navigation system.

The invention relates also to a method pertaining to a regulating system for an autonomous vehicle provided with an antispin system, which regulating system comprises a processing device. The regulating system, the antispin system and the processing device were described above.

The method will now be described with reference to the flowchart in Figure 2. It comprises:

- receiving a wheelspin signal comprising a spin value S which indicates whether at least one of the vehicle's tractive wheels is spinning relative to the roadway,

- determining a propulsive force value P on the basis of the propulsive force for said at least one tractive wheel,

- generating a propulsive force signal which comprises the propulsive force value P and conveying this signal to the processing device, and

- using a set of activation rules to determine one of a number of operating modes for said antispin system to operate in, which modes comprise: - an operability mode whereby the propulsive force value P is allowed to increase despite said spin value S indicating that at least one tractive wheel is spinning.

In one embodiment said activation rules comprise a rule which is related to the vehicle maintaining a predetermined safety margin relative to obstacles along the roadway and is applied to determine whether said operability mode should be activated. This rule was discussed in detail in the above description. In the operability mode the propulsive force value P is preferably allowed to increase to a level which exceeds the limited propulsive force of the antispin system.

If the vehicle's navigation is based on measurement of its wheel movements and is conducted by a navigation system for the vehicle, it will be inactivated if the antispin system is operating in the operability mode, and one or more

measurement signals will be used instead for the vehicle's navigation.

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

The invention also further comprises a computer program product comprising a program code stored on a computer-readable medium for performing method steps described above when said program is run on a processing device 8; 500 or another computer 500 connected to the processing device 8; 500. The computer 500 will now be described with reference to the block diagram in Figure 3.

The program D may be stored in an executable form or in compressed form in a memory 560 and/or a read/write memory 550. Where the data processing unit 510 is described as performing a certain function, it means that it conducts a certain part of the program 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 via a data bus 51 1 . The read/write memory 550 is adapted to communicating with the data processing unit via a data bus 514. The units connected to the processing device 8 (see Figure 1 ) may be connected to the data port 599.

When data are received on the data port, they are stored temporarily in the second memory element 540. When input data received have been temporarily stored, the data processing unit 510 is prepared to conduct code execution as described above.

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

One application of the regulating system according to the invention is to use the slippage on the rear axle to give the vehicle a yaw rate, i.e. to pivot the vehicle. It is generally known that it is possible to apply the handbrake in order to utilise so much of the friction of the rear tyres in the longitudinal direction that they lose grip sideways, thereby rendering the vehicle more manoeuvrable. In the same way the regulating system, when knowing that the friction is low, would increase the utilisation of the longitudinally available friction by increasing the torque on the tractive wheels in order to reduce their lateral grip so that the vehicle's

manoeuvrability increases. The occasions when this might be useful comprise for example negotiating a very tight bend, where it would be possible, instead of running forwards and back several times, to increase the vehicle's

manoeuvrability in this way and negotiate the bend without having to reverse.

The present invention is not restricted to the preferred embodiments described above. Various alternatives, modifications and equivalents may be used. The above embodiments are therefore not to be regarded as limiting the invention's protective scope which is defined by the attached claims.