DE102018219283A1 - Speed determination for a motor vehicle - Google Patents

Abstract

A method for controlling a motor vehicle comprises steps of scanning an area lying in the direction of travel of the motor vehicle by means of a distance sensor; determining a distance to an object that is within the scanned area; and determining a speed of the motor vehicle such that a predetermined minimum distance from the object is maintained. A maximum distance is determined within which the distance sensor can detect the object, and the determined speed is limited in such a way that a speed-dependent braking distance of the motor vehicle is smaller than the maximum distance.

Description

The present invention relates to the control of a motor vehicle. In particular, the invention relates to the determination of a speed at which the motor vehicle is to drive.

A motor vehicle is equipped with a driving assistant that supports longitudinal guidance of the motor vehicle. A speed of the motor vehicle is controlled to a predetermined value, a distance to a possibly preceding motor vehicle being determined simultaneously by means of a radar sensor. If a distance between the motor vehicle and the preceding motor vehicle falls below a predetermined distance, the speed of the motor vehicle is reduced. The reduction in speed can reach zero, for example when the motor vehicle approaches a vehicle standing at the end of a traffic jam.

The radar sensor can only perform optimal scans under predetermined conditions. Unfavorable circumstances, such as fog, can impair the scanning security of the radar sensor. The radar sensor may then still be able to recognize a nearby object well, but only to a limited extent an object further away. If there is an object in front of the motor vehicle that is not recognized by the radar sensor, a rear-end collision may occur.

An object of the invention is to provide an improved technique for determining a speed for a motor vehicle. The invention solves this problem by means of the subject matter of the independent claims. Sub-claims reflect preferred embodiments.

A method for controlling a motor vehicle comprises steps of scanning an area lying in the direction of travel of the motor vehicle by means of a distance sensor; determining a distance to an object that is within the scanned area; and determining a speed of the motor vehicle such that a predetermined minimum distance from the object is maintained. A maximum distance is determined within which the distance sensor can detect the object, and the determined speed is limited in such a way that a speed-dependent braking distance of the motor vehicle is smaller than the maximum distance.

This can ensure that the motor vehicle only drives so fast that it can brake safely when an object is detected in the scanned area. An area lying in front of the motor vehicle that is too far away to be reliably scanned by the distance sensor cannot be taken into account when determining an object. If the motor vehicle does not drive faster than the specific speed, vehicle safety can be increased. Controlling the speed of the motor vehicle can be part of the method.

A maximum distance is preferably determined within which a scanning reliability of the distance sensor exceeds a predetermined value. The scanning security can indicate the probability with which an object that is within the maximum distance is also recognized. The predetermined scanning certainty can be close to 100%. The maximum distance can be predetermined by the design of the scanning device, but is usually subject to certain influences, on the basis of which the maximum distance can be determined. In one embodiment, the scanning device can determine a scanning reliability, for example on the basis of a signal-to-noise ratio or a consistency of several successive scans.

Usually, based on measurements by the distance sensor alone, it is not possible to determine exactly how long the maximum distance is. It is proposed to determine the maximum distance dynamically on the basis of information that is known or can be obtained on board the motor vehicle. This information can e.g. B. concern the existence, quantity or density of particles in the ambient air that can reflect or deflect radar waves. Such particles or objects can comprise, for example, precipitation, that is to say a natural form of solid or liquid water in the air, for example in the form of rain, fog, hail, snow or frost. Other particles such as water in the form of spray, for example if water standing on a road surface is whirled up by rolling tires, or if the water in the air is mixed with dirt particles can reduce the maximum distance.

The information can come from one or more sources. Information from different sources can be correlated with one another or checked against each other for plausibility; one also speaks of a fusion of information. The information can e.g. B. come from another sensor for scanning an environment, such as a camera or a LiDAR system. Furthermore, the information can come from another system on board the motor vehicle, for example a rain sensor which is set up to control a windshield wiper on a windshield of the motor vehicle. It can also include information from an attitude or action of a driver. If the driver switches on a fog lamp, for example, it can be concluded that there is poor visibility and in particular fog, preferably with a visibility of less than approx. 50 m.

The maximum distance can be determined based on local weather. Local weather can include temperature, precipitation, solar radiation, and / or wind. A weather in which the scanning cannot be carried out optimally can be determined and the determined maximum distance can be reduced depending on the determined weather.

A significant restriction of the scanning security can be caused by solid or liquid particles in the air in the scanned area. Such particles can be found in the air, for example in rain, fog or snowfall. In a preferred embodiment, it is therefore determined whether the relative air humidity is approximately 100%, the maximum distance being determined as a function of the determination result. A relative humidity of 100% is a prerequisite for natural precipitation, so that the maximum distance can be adjusted in good time.

The maximum distance can be set to a predetermined value if the relative humidity has reached approximately 100%. This value can represent a preferably conservative estimate for the safely scannable area.

A precipitation can also be determined by means of a precipitation sensor, the maximum distance being determined on the basis of the determined precipitation. A relationship between the type and / or strength of the precipitation and the impairment of the scanning reliability by the precipitation can be modeled by means of a maximum distance that is reduced as a function of the precipitation.

The braking distance may depend on other factors besides the speed of the motor vehicle. For example, the braking distance can be determined on the basis of a local weather, a load on the motor vehicle, a condition, an incline and / or a slope of the ground. It is preferred that the braking distance is determined on the basis of a coefficient of friction that applies between the wheels of the motor vehicle and a surface. An estimate of the coefficient of friction can be provided, for example, by an electronic stability assistant on board the motor vehicle.

According to a further aspect of the invention, a sensor device for a motor vehicle comprises a distance sensor which is set up to scan an area lying in the direction of travel of the motor vehicle; and a processing device that is configured to determine a distance to an object in the scanned area and a maximum distance within which a scanning reliability of the distance sensor exceeds a predetermined value.

The sensor device can be used to provide values on the basis of which a method described herein works. In one embodiment, such a method can also run entirely or partially on the processing device. For this purpose, the processing device can comprise a programmable microcomputer or microcontroller and the method can be in the form of a computer program product with program code means. The computer program product can also be stored on a computer-readable data carrier. Features or advantages of the method can be transferred to the device or vice versa.

The distance sensor preferably comprises a radar sensor. In other embodiments, the distance sensor can also comprise another, preferably non-contact sensor, for example a LiDAR sensor or a camera. The distance sensor can also comprise several sensors, the scans of which can be suitably overlaid, supplemented, validated or fused.

According to a further aspect of the invention, a control system for a motor vehicle comprises a distance sensor described here and a processing device. The processing device is set up to determine a speed of the motor vehicle in such a way that a predetermined minimum distance from the object is maintained, while the speed of the motor vehicle is determined as a function of the maximum distance. The processing device can be set up to carry out a method described here in whole or in part, as is explained in more detail above. Features or advantages of the method can be transferred to the control system or vice versa.

It is particularly preferred that the control system is set up to control the speed of the motor vehicle. Alternatively, the determined speed can be output, for example to inform a driver of the motor vehicle or to be evaluated by another control device.

• 1 ein beispielhaftes System;
• 2 ein Ablaufdiagramm eines exemplarischen Verfahrens; und
• 3 beispielhafte Darstellungen von Abtastsicherheiten eines Abstandssensors

darstellt. The invention will now be described in more detail with reference to the accompanying figures, in which:

• 1 an exemplary system;
• 2nd a flow diagram of an exemplary method; and
• 3rd exemplary representations of scanning security of a distance sensor

represents.

1 shows a system 100 that a motor vehicle 105 and an object 110 includes, which is shown here as a further motor vehicle and in the direction of travel of the motor vehicle 105 located. The object 110 may also include another vehicle, another road user, or any other thing that is moving or stationary.

On board the motor vehicle 105 is a tax system 115 attached that a sensor device 120 with a distance sensor 125 and a processing device 130 includes. The sensor device 120 preferably comprises a radar sensor or another non-contact sensor for scanning one in the direction of travel of the motor vehicle 105 lying area. The sensor device 120 can the processing facility 130 or comprise a separate processing device. The processing facility 130 is preferred with a first interface 135 and a second interface 140 connected. You can also use a precipitation sensor 145 or an interface for connection to a precipitation sensor 145 be provided. The precipitation sensor 145 can e.g. B. include a disk sensor on a window of the motor vehicle 105 attached and set up to control a wiper depending on a precipitation on the window. The disc can e.g. B. include a front windshield. The determination can be carried out, for example, optically or acoustically.

The first interface 135 is for connection to another source of information on board the motor vehicle 105 set up the z. B. may include a sensor, a control device or a communication device. The communication device can be used to connect to an external location 150 be set up, for example using a cellular network. The external body 150 is preferably set up to provide information relating to a position of the motor vehicle 105 refer, e.g. B. Weather information such as a temperature, a precipitation, a humidity, a sun exposure or a wind. A forecast of the weather can also be provided. Such information can be obtained on the basis of an inquiry, which can contain the position of the motor vehicle. The position can be determined using a navigation system or a position sensor e.g. B. can be determined on the basis of a satellite-based navigation system.

The second interface 140 is to be provided by the processing facility 130 certain speed set up. The second interface 140 can be connected to an actuator via which the speed of the motor vehicle 105 can be controlled, for example a drive motor, a transmission for transmitting torque between the drive motor and a drive wheel, or a braking system of the motor vehicle 105 . The second interface 140 can also with an output device on board the motor vehicle 105 connected, for example to inform a person on board about the certain speed or another certain size.

The car 105 is preferably equipped with a speed assistant, which is set up to control a speed of the motor vehicle 105 to control to a predetermined value. At the same time it should be determined whether there is a vehicle 105 an object 110 and in this case what distance 155 the car 105 from the object 110 Has. If this distance falls below a predetermined distance, which is a function of a speed of the motor vehicle 105 can be determined, so the motor vehicle 105 to be slowed down. The deceleration can take place to zero, so that the motor vehicle 105 can be braked to a standstill.

A maximum distance 160 in which the object 110 can be reliably recorded can depend on external factors such as precipitation. It is therefore suggested that the maximum distance 160 determines and the speed of the motor vehicle 105 is limited so that the motor vehicle 105 can be braked within the maximum distance. This can be the length of a speed-dependent braking distance of the motor vehicle 105 be determined and the speed of the motor vehicle 105 can be limited so that the maximum distance 160 is not less than the braking distance. Determinations required for this can be made using the sensor device 120 , the tax system 115 or another system on board the motor vehicle 105 be carried out in whole or in part.

2nd shows a flowchart of an exemplary method 200 . In one step 205 can be the maximum distance 160 of the distance sensor 125 be determined on the basis of currently applicable conditions. The conditions can for example a weather and more preferably a precipitation. To determine an impending precipitation, it can be determined whether there is air humidity in the area of the motor vehicle 105 exceeds a predetermined threshold, which may be close to 100%. Alternatively, precipitation can take place, for example, using the precipitation sensor 145 be recorded. In yet another embodiment, it can be determined whether local conditions exceed a dew point curve, so that precipitation is taking place. The dew point curve usually reflects a relationship between temperature and water vapor partial pressure of water vapor in the air, in which condensation and evaporation are precisely balanced. If the dew point curve is exceeded, the condensation prevails, so that water in the form of rain, fog, hail or snow can be separated from the air.

In one step 210 can calculate the maximum speed of the motor vehicle based on the maximum distance 105 be determined. This can result in a maximum deceleration of the motor vehicle 105 be determined, which may depend on a coefficient of friction between the motor vehicle and a surface. The coefficient of friction can be present, for example, as an estimate of a system that provides driving stability or traction slip of the motor vehicle 105 can control. Factors such as a slope or an incline of the subsoil, a loading of the motor vehicle can also be optionally 105 or a time required to reach the maximum delay.

In one step 215 the speed of the motor vehicle can be limited to the specific maximum speed.

Parallel, concurrent or integrated with the steps 205-215 can in one step 220 a distance to an object lying in the direction of travel 110 be determined. In one embodiment, the distance can only be determined in a range that corresponds to that in the step 205 Maximum distance does not exceed. In one step 225 can be a default for the speed of the motor vehicle depending on the distance 105 be determined. The default can e.g. B. be relative, so control an acceleration or deceleration of the motor vehicle. A predetermined distance can be determined absolutely or based on the speed of the motor vehicle 105 be determined. If the step exceeds 220 determined distance the predetermined distance, the speed can be left the same or increased, otherwise, a reduction in the speed of the motor vehicle 105 be determined.

In one step 230 can see the results of the steps 205-215 and 220-225 be linked together. This can be done in one step 235 a predetermined speed for the motor vehicle 105 be determined. The speed of the motor vehicle 105 is to be controlled to the predetermined speed as far as possible, the predetermined distance being maintained. The linking is preferably carried out in such a way that the speed of the motor vehicle 105 , regardless of the presence or distance of an object 110 in front of the motor vehicle 105 , is limited to the maximum speed in step 215 was determined. Linking in step 230 can be done by means of a controller, for example a PID controller. Undesired effects such as a control oscillation or a “wind-up” can be avoided in a suitable way.

In one step 240 can determine the specific speed for the motor vehicle 105 spent or the motor vehicle 105 can be controlled to the specific speed.

3rd shows exemplary, schematic representations of scanning security of a distance sensor. 3a shows a situation with a clear view and 3b a situation with fog. There is a distance in the horizontal direction s between the object 110 and the sensor device 120 or the motor vehicle 105 , and a scanning certainty in the vertical direction P proposed. The bars shown symbolize measurements that have been carried out.

The scanning reliability of the sensor device decreases regardless of the ambient conditions 120 with increasing distance of the object 110 . Usually a predetermined threshold value is set, which must be exceeded by the scanning security, around the sensor device 120 to control the motor vehicle 105 to use. In a purely illustrative manner, the threshold value is assumed to be 98%.

With a clear view (cf. 3a) If the first two measurements are safe, the scanning certainties are still above the threshold value, so that a first maximum distance 305 can be determined. If visibility is impaired (cf. 3b) the scanning reliability is only above the threshold value for the first measurement, so that a second maximum distance 310 can be determined which is less than the first maximum distance 305 is.

The maximum distance 160 can based on the prevailing conditions in the field of motor vehicles 105 be determined in advance so that the speed of the motor vehicle 105 can be controlled in such a way that it is possible to stop within a braking distance that is not longer than the distance in which a predetermined scanning certainty with the sensor device 120 can be achieved.

Reference symbol list

100

system

105

Motor vehicle

110

object

115

Tax system

120

Sensor device

125

Distance sensor

130

Processing device

135

first interface

140

second interface

145

Precipitation sensor

150

external body

155

Distance between motor vehicle and object

160

Maximum distance

200

method

205

Determine maximum distance

210

Determine maximum speed

215

Limit speed to maximum speed

220

Determine distance

225

Determine speed

230

Link

235

Determine predetermined speed

240

Control speed

305

first maximum distance

310

second maximum distance

s

Distance sensor device to object

P

Safe to scan

Claims (11)

Method (200) for controlling a motor vehicle (105), comprising the following steps: - scanning (220) an area lying in the direction of travel of the motor vehicle (105) by means of a distance sensor (125); - determining (220) a distance to an object (110) which lies in the scanned area; and - determining (230) a speed of the motor vehicle (105) such that a predetermined minimum distance from the object (110) is maintained, characterized in that a maximum distance (160) is determined within which the distance sensor (125) the object (110 ) can capture; wherein the determined speed is limited (215) such that a speed-dependent braking distance of the motor vehicle (105) is less than the maximum distance (160). Method (200) according to Claim 1 , a maximum distance (160) being determined (205) within which a scanning certainty (P) of the distance sensor (125) exceeds a predetermined value. Method (200) according to Claim 1 or 2nd , wherein the maximum distance (160) is determined (205) based on local weather. Method (200) according to one of the preceding claims, it being determined (205) whether a relative atmospheric humidity is approximately 100% and the maximum distance (160) is determined as a function of the determination result. Method (200) according to Claim 4 , the maximum distance (160) being set to a predetermined value if the relative air humidity has reached approximately 100%. Method (200) according to one of the preceding claims, wherein a precipitation is determined by means of a precipitation sensor (145) (205) and the maximum distance (160) is determined on the basis of the determined precipitation. Method (200) according to one of the preceding claims, wherein the braking distance is determined (210) on the basis of a local weather, a load on the motor vehicle (105), a nature, an upward gradient and / or a downward gradient. Sensor device (120) for a motor vehicle (105), comprising a distance sensor (125) which is set up to scan an area lying in the direction of travel of the motor vehicle (105); a processing device which is set up to determine a distance to an object (110) in the scanned area and a maximum distance (160) within which a scanning reliability of the distance sensor (125) exceeds a predetermined value. Sensor device (120) after Claim 8 wherein the distance sensor (125) comprises a radar sensor. Control system (115) for a motor vehicle (105), comprising a distance sensor (125) Claim 8 or 9 and a processing device (130) which is set up to process a To determine the speed of the motor vehicle (105) in such a way that a predetermined minimum distance from the object (110) is maintained, while the speed of the motor vehicle (105) is determined as a function of the maximum distance (160). Control system (115) Claim 10 , the speed of the motor vehicle (105) being controlled.

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