WO1997039918A1

WO1997039918A1 - Process and device for determining skidding conditions on roadways and the like

Info

Publication number: WO1997039918A1
Application number: PCT/EP1996/001653
Authority: WO
Inventors: Werner Schwartz; Christoph Hofmann; Fabian Holzwarth
Original assignee: Hea Hamburger Elektro-Apparate Gmbh
Priority date: 1994-10-20
Filing date: 1996-04-19
Publication date: 1997-10-30
Also published as: DE4437577A1

Abstract

The process for predicting and determining skidding conditions due to ice, frost and snow on roadways and other travelled surfaces, wherein spectral analysis with reflected or diffuse radiation is used to determine whether the roadway is dry, wet or slick, is characterized in that measurable variables, including at least the roadway temperature, are measured, their change over time is extrapolated and, based thereon, the point in time at which a skidding condition will occur is calculated in advance and signalled.

Description

Method and device for determining smoothness on road surfaces and the like.

The invention relates to a method for determining ice, frost and snow on roads and other traffic areas, in which it is determined with the aid of reflected radiation whether the road is dry, wet or smooth. The invention also relates to an apparatus for performing the method.

The smoothness of a roadway can be determined by mechanical means which are attached to a vehicle, for example. Methods of the type mentioned do not use such mechanical sensors, but instead use reflected radiation to determine whether the roadway is dry, wet or smooth (DE-PS 30 23 444, DE-PS 29 12 645, DE-OS 36 40 539, DE-OS 41 33 359). With such methods it can be ascertained in a more or less reliable manner whether the roadway is smooth at the moment or not. However, it cannot be determined with these methods whether the roadway may become smooth after a very short time. Appropriate warning would be highly desirable. Thus, on the one hand, the motorists could be warned that slippery is expected soon, so that they can adjust their driving style to the changing road conditions in good time. But it is even more essential that the road and spreader service could be warned. On the one hand, this could ensure that the road service was alerted in good time and countermeasures against slippery, in particular spreading, in good time can perform. If such a prediction is possible, it is not only costs that are saved by the personnel not being unnecessarily occupied with spreading activities. It is even more important that under certain conditions there is no need to scatter at all. On the one hand, this prevents unnecessary environmental damage from salt. The costs for the spreading material and spreading personnel and the possible damage to motor vehicles and / or roads, bridges, etc. can also be greatly reduced if the spreading only takes place when this is actually necessary.

The object of the invention is therefore to create a method of the type mentioned at the outset with which the time of future smoothness conditions can be predicted.

The solution according to the invention consists in that measured variables, below which the roadway temperature is at least, are measured, their change over time is extrapolated and from this the time of occurrence of a future smoothness condition is calculated and displayed.

The freezing of surfaces is a very complex process, which depends on a large number of parameters, for example the temperature of the road, the air humidity, the dew point of the air, the condition and surface properties of the road, the presence of salts in water, the is on the road, etc. One should therefore think that a prediction is not possible due to the fact that so many parameters are significant. This prejudice was overcome by the invention. In fact, it is possible with the invention to make a reliable prediction in almost all cases, which can be carried out over a period of up to approximately 2 hours. The method works very reliably and cannot predict only when rain or snow falls suddenly. On the other hand, sudden smoothness is recognized.

In a simple method, when the roadway is wet, only the roadway temperature is measured and smoothness is predicted for the point in time at which it reaches the freezing temperature of the roadway. The invention is based on the knowledge that the road temperature is constantly changing changes. In a simple embodiment, the freezing temperature will simply be 0 ° C., ie the freezing temperature of water.

This freezing temperature can, however, have a different value, depending on the surface of the road and in particular if the water on the road is saline, namely lower. In order to enable an even more reliable prediction here, it can be provided in an advantageous embodiment that the freezing temperature is determined with the aid of a coolable measuring point in the roadway. For this purpose, the measuring point will be cooled from time to time until the water freezes. The corresponding temperature is then measured and used as the freezing temperature of the water on the road for the predictions. Then the cooling can then be switched off so that the measuring point returns to normal temperature after some time and this normal temperature can then be measured at this measuring point. The heating of the measuring point following the cooling can also take place by heating elements, so that the measuring point reaches its original temperature again more quickly.

The cooling is expediently effected with one or more Peltier elements which are particularly simple and completely maintenance-free.

The temperature measurement is expediently carried out digitally with a resolution of ± 0.005 degrees in order to reliably represent the naturally very flat temperature gradient.

In a further advantageous method, one measuring point is not used for measuring the freezing temperature and the measuring of the road temperature, but two separate measuring points, so that the road temperature can also be measured during the times during which the freezing temperature is determined.

In the case of a dry roadway, the procedure is expediently such that the roadway temperature and the dew point temperature are measured and smoothness is predicted for the point in time at which the roadway temperature reaches or falls below both the dew point temperature and the freezing temperature. An advantageous embodiment is characterized in that the method is only started when the air temperature, which is continuously measured, falls below a predetermined value, which can be in particular at + 5 ° C. The measurement is advantageously set again after the predetermined value of the air temperature has been exceeded in order not to use up unnecessary energy; however, this only happens when the road condition is no longer smooth. This is to prevent the smoothness warning from being given when the air temperature rises above the freezing point but the road is still smooth. The method is not only intended to predict the time of the smoothness, but also to display the current smoothness.

The air humidity is also advantageously measured, the dew point then being able to be determined, for example, from temperature and air humidity.

If the measuring point at which the smoothness is measured is provided not only with a cooling device but also with a heater, not only the freezing temperature but also the thawing temperature can be measured, which in the case of hypothermia, of course, from the freezer before freezing temperature is different. In this way, an actual freezing temperature can be determined at which freezing can occur if no hypothermia occurs.

The freezing temperature determined in this way is also advantageously used to determine the amount of residual salt on the road.

A device for carrying out the method is characterized in that the measuring point for the state of the road has a lighting device with a broadband infrared light source and two sensors for the light scattered back from the road, one of which is essentially in the range of the absorption maximum of liquid water and the other is essentially sensitive to the area of maximum absorption of ice.

A device with a light source and two sensors for the light scattered back from the road is known (DE-PS 30 23 444), in which on the one hand directly reflected and on the other hand scattered infrared light is received. With this device, however, predictions are no more possible than with a device that has two light sources and a detector (DE-AS 27 12 199). In the latter device, the two light sources, which emit light of different wavelengths, illuminate the detector one after the other, so that the detector or the evaluation electronics must be switched over and over again in a complicated manner, which becomes even more cumbersome when the infrared radiation is used is pulsed or amplitude modulated in order to eliminate influences by extraneous light.

The device of the invention makes particularly advantageous use of the fact that the absorption maxima of water and ice for infrared light are at different wavelengths. Smoothness occurs when the infrared light with a wavelength that corresponds to higher absorption of ice is more strongly absorbed.

The infrared light source is expediently a halogen lamp. The light is expediently modulated, in particular amplitude-modulated or pulse-modulated, in order to avoid falsifying influences from outside light or heat radiation from the outside.

The sensors have to respond to certain wavelength ranges and have optical bandpass filters for this purpose.

The measuring point expediently has a sensor in the road surface with which the adjustment of the infrared light source can be checked. If infrared light no longer falls on the sensor, the measuring point is not illuminated, so that a fault can be indicated.

In order to minimize the effects of weather and to reduce the susceptibility to faults, the lighting device and the sensors are expediently combined into one unit.

The invention is described below using an advantageous embodiment with reference to the accompanying drawings. Show it: 1 shows a graphical representation of the spectral transmission behavior of water and ice in the near infrared range;

2 shows a basic illustration of the device for detecting the physical state of a water layer;

3 shows a block diagram of the device for predicting the state of the road;

4 schematically shows in section a measuring point for determining the freezing temperature and the condition of the road;

5 shows a measuring point for measuring the roadway temperature in a representation similar to that in FIG. 4;

6 to 8 are three diagrams which illustrate the thermal processes during ice and frost formation;

9 shows another embodiment of a measuring point with light guides;

10 shows a further embodiment of the measuring point with the light guide ends arranged parallel to one another;

11 shows a further embodiment of the measuring point with arrangement of the light guide ends at an angle;

Fig. 12 shows another embodiment of the measuring point with the arrangement of

Optical fiber ends flush with the surface of the active carriageway measuring point; and

13 shows the basic structure of the sensor with illumination from above and evaluation in a further embodiment of the active road surface measuring point.

1 is a diagram of the transmission behavior in the wavelength range of the near infrared light of a liquid water layer 1 is compared to the transmission behavior of a frozen layer 2 of the same thickness.

It can be seen that the entire transmission spectrum when water freezes is shifted towards longer wavelengths by a certain amount due to the stronger binding of the water molecules in the crystal lattice of the ice. In particular, an absorption maximum λ ^,, ^r f1.maxi of the liquid water, which is caused by combination vibrations of the water molecules and occurs at a wavelength of 1450 nm, appears in ice

1500 nm wavelength highly absorbing wave

A similar shift of approximately 50 nm occurs in the length ranges. The effect is largely independent of the type and content of dissolved salts.

Fig. 2 shows the principle of the smoothing sensor for contactless detection of the physical state of a water layer.

According to the method for determining the physical state of a water layer 23 on the surface of an active roadway measuring point 4 let into the roadway surface 3, the latter is detected by a suitable illumination device 5 with infrared light with a broad spectrum, ie all wavelengths are present in a larger spectral range ¬ the, illuminated. In order to maintain the spectral influence exclusively of the layer on the surface, the light scattered from the bottom of the layer, which has thus passed through the layer, is received by two or more light receivers 6, 7, each with a suitable spectral sensitivity. A first receiver 6 is for a wavelength range around an absorption maximum of liquid water λr, _{1 (} a

^{3 r 3} fI. Maxi 'second receiver 7 is sensitive to wavelengths in the range of an absorption maximum λr * i of ice. If neither water nor ice is present, two of the receivers 6, 7 each deliver the same signals. The quotient of the two signals is 1.

If a dry surface is scanned, the following applies to the signals of the receivers:

S _j = S ₂ (la) and for the quotient of the signals

^S l

- = 1 (lb) s ₂

In the presence of liquid water, the first receiver 6 delivers a smaller signal S1 and the second receiver 7 a larger signal S2. The quotient of the signals is less than 1.

It follows

^S l S _j <S ₂ and - <1 (2)

^S 2

If frozen water is present, the first receiver 6 delivers a larger signal S1 and the second receiver 7 a smaller signal S2. The quotient of the two signals is greater than 1.

The following applies:

^S l S,> S ₂ and -> 1 (3)

^S 2

A halogen incandescent lamp 8 is used to irradiate the surface of the active road measuring point 4 with broadband light in the infrared wavelength range between 1 and 2 μm, the light of which is focused on the surface of an active road measuring point 4 by suitable optics 9. In order to eliminate interference from the ambient light, the light emitted by the lamp 8 is varied in amplitude by a modulator 10. These components are combined in a lighting unit 5.

The light 11 scattered back from the surface of the active road measuring point 4 is collected by two or more receivers 6, 7, which are preferably located in the vicinity of the lighting unit 5. These receivers each consist of an optical system 12, which covers the illuminated surface image an active roadway measuring point 4 onto an infrared-sensitive detector 13. In the beam path in front of each detector 13, 13 'there is an optical bandpass filter 14, 14', which is only permeable to light in the desired wavelength range. Each filter 14, 14 'can be tuned in order to be able to compensate for manufacturing-related variations in the filter characteristics. The signal S1.S2 of the detector 13, 13 'is amplified by a preamplifier 15 and, in a signal preprocessing unit 16, is rectified in phase synchronization with the modulation of the transmitted light 17 by a synchronous rectifier. For this purpose, the lighting unit 5 supplies a carrier signal 18 with the frequency of the lighting modulation. The respective spectral signal S1 ', S2' is present at the output of a low-pass filter 20 connected in phase-synchronism to the synchronous rectifier 19 for further processing. The evaluation is preferably carried out by forming the ratio of signals in different wavelength ranges, as a result of which fluctuations in the brightness of the lighting and changes in the absorption behavior of the surface of the active roadway measuring point 4 are largely eliminated. This calculation can take place in a separate analog arithmetic unit or in the central evaluation unit 21.

The irradiation and observation of the surface 22 of the active carriageway measuring point 4 takes place at such an angle that direct reflections from the surface into the receiver 6, 7 are excluded, since light which has not passed through an existing layer 23 affects the measuring result would falsify.

Illumination unit 5 and the light receivers 6, 7 can be combined in one unit as a smoothness sensor 24.

Fig. 3 shows the block diagram of the entire device for detecting the road condition and the prediction of slippery roads.

The signals S1 'and S2' generated by the smoothing sensor 24 are linked to one another in a central evaluation unit 21 after processing in a signal preprocessing unit 16.

The ratio of the two signals S1 ', S2' undergoes a change from values <1 to values> 1 when a water layer 23 freezes. This Change can be recorded and used as a characteristic value for the current physical state of layer 23.

In order to maintain the freezing temperature T, a very precise first temperature measuring device 25 is built into the surface of the active road surface measuring point 4, which surface is covered by the two receivers 6, 7. The surface 22 of the active road surface measuring point 4 can be cooled in relation to the surroundings by a built-in cooling device 26. The temperature T of the surface 22 of the active road surface measuring point is fed to the central evaluation unit 21. During the cooling process of the active road surface measuring point 4, the state of aggregate is continuously monitored by the smoothness sensor 24. As soon as ice formation on the surface 22 of the active road measuring point 4 is detected, the current surface temperature T1 is stored in the central evaluation unit 21 and the cooling is switched off, so that the surface of the active road measuring point slowly warms up again. At a certain temperature, the ice layer thaws again, which is recognized by the smoothness sensor. The thawing temperature T2 is also recorded.

Since the water layer 23 may have been supercooled before freezing, the thawing temperature T2 can be different from the freezing temperature T1.

The actual freezing temperature is determined in the central evaluation unit 21 from both temperatures T1, T2.

By considering both a cooling and a heating cycle, a possible temperature gradient in the surface 22 of the active roadway measuring point 4 is largely eliminated.

In order to maintain the actual surface temperature of the road surface 3, there is a passive road measuring point 27 at a location near the active road measuring point 4, which has the same surface properties as the active road measuring point 4. However, only their surface temperature To2 is determined by a second 28 that is the same as the first temperature measuring device 25. This temperature is also fed to the central evaluation unit 21. The central evaluation unit 21 is preferably designed as a digital computer which, in addition to the calculations, also takes on all the control tasks for the system.

If the active measuring point 4 is not cooled, it takes on the temperature of the surrounding roadway 29 after a short time, so that the continuous monitoring of the physical state of a water layer 23 by the smoothness sensor 24 also makes it possible to detect actual occurrence of smoothness.

A sensor for the air humidity 30 serves to detect this parameter, which is also fed to the evaluation unit 21. In addition, the air temperature is detected by a further temperature measuring device 31 and passed on to the central evaluation unit 21. The central evaluation unit 21 is connected, for example, to an output unit 33 in a monitoring center via a data bus 32. The following are displayed: the prediction of the time of smoothness 34, the smoothness 35 actually present, the road temperature 36, the air temperature 37, the air humidity 38 and the dew point 39.

FIG. 4 shows the active measuring point. The active measuring point 4 serves to freeze an existing surface layer 23 or to generate frost from the atmospheric humidity, and to determine the respective surface temperature precisely.

This measuring point consists of a cover plate 40, the surface 22 of which is partially provided with a coating 41 with suitable optical properties (high reflectance, reflection of the incident light 17 in almost the same direction as the irradiation). This cover plate 40 can be cooled far below the ambient temperature by a cooler 26 mounted below it, which preferably works thermoelectrically according to the Peltier principle, in order to safely come below the freezing temperature of a moisture layer 23. The heat generated during the cooling process is released into the surrounding roadway 29. The active carriageway measuring point 4 is designed in two parts, the components of the active measuring point 4 being built into a basic module 42 firmly installed in the carriageway surface 3 for the purpose of easy interchangeability. The current temperature of the cover plate 40 is detected by a very precise temperature sensor 25, which is installed just below the surface 22. A vibration quartz thermometer, for example, which provides very good temperature resolution with good long-term constancy, can be used as the temperature sensor.

The active road measuring point 4 is mounted flush with the road surface 3.

To ensure that the smoothness sensor 24 is aligned precisely with the active road measuring point 4 and thus actually detects the state of the active road measuring point 4, a light sensor 43 is installed in the cover plate 40, the signal 44 of which is also monitored by the central evaluation unit 21. This receiver 43 delivers a signal 44 as long as the system is functioning properly, which provides a self-control function.

5 shows the passive roadway measuring point. The passive measuring point 27 has the same surface structure and consists of the same material as the active roadway measuring point 4. Only the surface temperature is recorded in order to obtain the actual roadway temperature. The temperature is recorded in the same way as for the active measuring point.

6 shows the course of the roadway temperature T _{f over a} wet road using a diagram. If the roadway temperature T _f falls below the freezing temperature T determined under 1, ice forms on the roadway.

FIG. 7 shows a diagram of the time profile of the road temperature T _f on a dry road. If the road temperature T _f falls below the dew point temperature T. of the air, water condenses on the road. If the road temperature T _x falls below the smoothing temperature T determined as under 1, the condensate freezes to frosty smoothness.

8 shows the course of the dew point temperature T over a dry, supercooled roadway using a diagram. Warms up The ambient air is above the temperature of the road and at the same time absorbs moisture, so water vapor sublimes on the road and creates frostiness.

9 to 13 alternative embodiments are shown.

Instead of illuminating and detecting the infrared radiation scattered by the active measuring point by the sensor described above the roadway, the modulated transmission light can also be guided from below to the active measuring point via a light guide. Likewise, light from the active measuring point can be fed to the spectral evaluation via an optical fiber.

The advantage of this method is that there are no superstructures above the carriageway, which is of great advantage particularly in the case of taxiways. Likewise, there is no longer a risk of misalignment of the lighting and reception optics and the problem of contamination of the optical surfaces together with the influences of the air gap between the sensor and the roadway.

By means of an illumination unit 101, similar to that described in the method for detecting the physical state of a water layer, light is fed through suitable optics 102 into a first light guide 103, which can be designed as a single fiber or fiber bundle.

From the end 104 of this first light guide (illuminating light guide) 103, which is expediently located in the cooled area of the active carriageway measuring point 4, light emerges into a possibly existing water or ice layer 23. Part of the light emerging from the first light guide enters a second light guide (receiving light guide) 105, the end 106 of which is preferably located at a short distance from the end 104 of the first light guide 103 on the surface of the active measuring point 4 and becomes a spectral evaluation unit 106 fed. There, the light that has passed through the second fiber is brought through suitable optics 107 to two wavelength-selective receivers 108, 109 and evaluated in accordance with the method for detecting the state of aggregation. The cooling and detection of the temperature of the active road measuring point 4 is carried out as described above. The ends 104, 106 of the light guides can be attached in different angular positions to one another in the surface of the active measuring point.

If the ends 104, 106 of the two light guides 103, 105 are arranged in parallel, the light passes directly through a gap 110 between the ends of the light guide, which can be filled by air, partly by water or ice.

If the two light guide ends are not arranged parallel to one another, part of the light from the transmission light guide 103 can enter the receiving light guide 105 through the intermediate space 110 between the light guide ends. Another part of the light is directed to the surface of a possibly existing water or ice layer 23 by total reflection in the receiving light guide. Light that is scattered inside a layer of water or ice can also enter the receiving light guide 105.

If the two light guide ends 104, 106 are arranged in one plane, specifically in the plane of the surface of the active measuring point 4, light from the transmitting light guide 103 into the receiving light guide 105 cannot be directly, but only by scattering in a water or ice layer 23 and reach the layer surface by total reflection.

In all arrangements, at least part of the light passes through a layer of water or ice 23 and thus receives the spectral information about the physical state of the layer.

It is also possible to illuminate the active measuring point 4 by means of a lighting unit 5, which is located above the carriageway and which is described in the method for detecting the physical state, and the light which has passed through a layer of water or ice with a light guide of the spectral range Supply evaluation. Instead of transmitting the light from the active measuring point through a light guide 105, the spectral evaluation can also take place below the active measuring point 4. The light enters through a window 111, which has the same temperature as the surface of the active measuring point 4, into a spectral evaluation unit 112 inside the active measuring point. For reasons of ease of maintenance, the use of light guides is preferable.

Illumination by a light guide in the active measuring point and reception of the light that has passed through a layer of water or ice by receivers above the roadway are also possible.

Claims

claims

1. A method for determining ice, frost and snow on carriageways and other traffic areas, in which it is determined with the aid of reflected radiation whether the carriageway is dry, wet or smooth, characterized in that measured variables, among which at least the Roadway temperature is, measured, its temporal change extrapolated and from this the time of a future smoothness is calculated and displayed.

2. The method according to claim 1, characterized in that when the roadway is wet only the roadway temperature is measured and smoothness is predicted for the point in time at which it reaches the freezing temperature.

3. The method according to claim 2, characterized in that the Gefrierter¬ temperature is determined with the help of a coolable measuring point in the road.

4. The method according to claim 3, characterized in that the Gefrierter¬ temperature is determined from the temperatures at which the water freezes on the road when cooling and thaws when heated.

5. The method according to claim 3 or 4, characterized in that the cooling is effected with one or more Peltier elements.

6. The method according to any one of claims 1 to 5, characterized in that separate measuring points are used for measuring the state of the road (dry, wet, smooth) and the temperature thereof.

7. The method according to any one of claims 1, 3, 4, 5 or 6, characterized gekenn¬ characterized in that the road surface temperature and the dew point temperature are measured in a dry road surface and smoothness is predicted for the time when the road surface temperature both the dew point temperature the temperature as well as the freezing temperature is reached or fallen below.

8. The method according to any one of claims 1 to 7, characterized in that the air temperature is measured and the remaining measurements are only carried out when the air temperature falls below a predetermined value.

9. The method according to claim 8, characterized in that the predetermined value is approximately 5 ° C.

10. The method according to claim 8 or 9, characterized in that the measurements are only set after exceeding the predetermined value of Lufttempera¬ tur when the road condition is no longer smooth.

11. The method according to any one of claims 1 to 10, characterized in that the air humidity is also measured.

12. The method according to any one of claims 3 to 11, characterized in that a measuring point is provided with a heater.

13. The method according to any one of claims 3, 4 or 5, characterized gekennzeich¬ net that the freezing temperature determined in this way is a measure of the amount of residual salt on the road and this can thus be determined and displayed.

14. The method according to any one of claims 1 to 7, characterized in that only the dew point temperature is measured in a dry, supercooled roadway and smooth is predicted for the time at which this exceeds the roadway temperature.

15. A device for performing the method according to any one of claims 1 to 12, characterized in that the measuring point (4) for the Fahr¬ state of the road an illumination device (5) with a broadband infrared light source and two sensors (6,7,108,109) for that of Has backscattered light, of which one (6,7,108, 109) is essentially sensitive in the area of the absorption maximum of liquid water and the other (7,6,108,109) is essentially sensitive in the area of the absorption maximum of ice.

16. The apparatus according to claim 15, characterized in that the Infra¬ red light source (5) is a halogen lamp.

17. The apparatus of claim 15 or 16, characterized in that the light is modulated.

18. Device according to one of claims 15 to 17, characterized gekennzeich¬ net that the sensors (6,7,108,109) have optical bandpass filters (13,13 ').

19. Device according to one of claims 15 to 18, characterized gekennzeich¬ net that the measuring point (4) has a sensor (43) in the road surface with which the adjustment of the infrared light source (5) can be checked.

20. Device according to one of claims 15 to 19, characterized gekennzeich¬ net that infrared light source (5) and sensors (6,7,108,109) are combined into one unit.

21. Device according to one of claims 15 to 20, characterized gekennzeich¬ net that the lighting device (101) is connected to a light guide (103).

22. Device according to one of claims 15 to 21, characterized gekennzeich¬ net that the sensors (108, 109) are connected to an optical fiber.