APPARATUS FOR SENSING VEHICLES

Abstract: An underground vehicle sensing system (20) extends below a vehicle travel surface to detect the presence of a vehicle. A conduit (24) extends substantially horizontally underground from an access hole placed at the side of the vehicle travel surface. A plurality of sensors (50) are spaced apart in the conduit to detect localized changes in the magnetic field. A plurality of sections house the probes and wiring to orient and position the probes. Sections detachably clip together to form a lightweight support structure and may be added one by one through the access hole. Lightweight extension members are utilized in some configurations between the support sections for positioning and supporting the probes.

Description: APPARATUS FOR SENSING VEHICLES Background of the Invention 1. Field of the Invention The present invention is directed to an underground apparatus and method for sensing vehicles and to a method for installing the apparatus. 2. Prior Art Methods and devices for detecting the presence of vehicles on a street or road are well known. Detecting the presence of a vehicle is done for a variety of reasons. Vehicles may be detected to monitor the traffic flow and determine road usage. This information may be utilized for transportation planning and traffic light control. Pairs of the sensing devices may also be utilized to monitor vehicle speeds. When installed after the road has been constructed, prior art vehicle detection devices generally require boring through the pavement and cutting the surface of the pavement, thereby interrupting traffic flow for extended periods of time. This work creates substantial delays and inconveniences for drivers. A system that detects the change in presence of a vehicle that utilizes inductive loops six feet in diameter or larger is shown in U.S. Patent Number 3,984,764. The '764 patent shows the prior art wherein complex loops require a substantially rectangular cut in the surface of the pavement to accommodate the multiple turn wire loops. A system that utilizes repeated loops for multiple sensors is shown in U.S. Patent number 3,943,399. Separate rectangular cuts must be made into the pavement for each sensor loop. The deeper the loops are buried in the pavement, the more turns of wire that are required to achieve a desired sensitivity for the system. In addition, these systems require a cut to the edge of the pavement to accommodate wiring leading to the system controller. A system that detects the presence of a vehicle by a change in resistance is shown in U.S. Patent number 5,491,475. The '475 patent requires that the conduit is installed when building the roadway or that a wide slot is made through the surface following road creation. Further, an access box must be installed at each side of the roadway to provide access to the conduit for installing the sensors through the conduit and for wiring the system. Installation of this detection system may require cutting through the reinforcing bars used in concrete roadway construction which further complicates the installation. In addition, the accuracy of the change in resistance may be adversely affected by magnetism in the reinforcing grid and reduction in the earth's magnetic field concentration by the grid. Another device shown in U.S. Patent number 4,449,115, requires a bore drilled through the pavement with sensing devices inserted into the bore to sense the change in impedance when a vehicle is present. These devices typically also require cutting a slot in the pavement surface for wiring from the sensor to the side of the pavement. Although this system provides an accurate sensing system, it is also destructive to the pavement and requires extended lane closures for installation and repair. Cuts made in the pavement surface allow water to seep into cracks so that expansion and contraction from freeze and thaw cycles cause the road to deteriorate faster. Pavement expansion and contraction may also damage the vehicle detection system wiring, requiring repair and/or replacement. Sealing compounds to fill the cuts often attack asphalt and accelerate deterioration and seepage. It can be seen then, that a new and improved underground system for detecting vehicles is needed. Such a system should accurately and precisely detect all vehicles passing over a predetermined location. Such a system should eliminate cutting the pavement surface to decrease the number and length of time for lane closures. Such a system should insert below the pavement through a single access point. Such a system should provide for easy and accurate placement and alignment of sensor probes which are placed below the pavement, rather than through or into the pavement. Underground installations are desirable as they cannot be run into by vehicles, are less affected and have lower rates of change due to temperature changes, and are not affected by common pavement restoration methods or maintenance equipment such as plows or street cleaners. The probe support structure should be separable into a plurality of sections for angular alignment, easy insertion and removal. The present invention addresses these, as well as other problems associated with underground vehicle sensing systems. Summary of the Invention The present invention relates to an underground vehicle sensing system, and in particular to a vehicle sensing system which is placed beneath a vehicle travel surface, typically pavement. A vehicle passing over the pavement causes a change in impedance in one or more of a plurality of probes placed beneath the pavement. The probes must be fixed in orientation and stable to reliably detect the presence of a vehicle. The sensor probes are placed in an extended support structure which extends below the surface of the pavement from one side of the pavement. A surface access hole or hand hole connects with the structure and allows for insertion of the support structure and array of sensors. The support structure typically includes a plurality of support sections which clip together to form the extended structure. The system may also utilize members or other connecting material that does not support probes to connect probe supporting sections. These non- supporting sections may be made from a shaft or other structure that maintains relative distance and rotational alignment between supporting sections. In a first embodiment, each support section is connected in an end-to-end manner with a clip that provides for retaining adjacent sections and preventing relative angular displacement. The sections may be substantially rounded to be self-centering and be weighted to maintain the probes in a substantially vertically oriented position. The present invention may use various wiring configurations extending through the sections and connecting the probes to a processor or other controller, placed either at the side of the road or in a remote location. Each probe supporting section includes a frame portion with mounting holes placed therein which receive the sensor probes. The sections fit within the orifice or conduit extending substantially parallel to the pavement surface, typically at a depth of 16 to 24 inches below the surface. Assembly of the system is easily performed as a first section is placed into the surface access hole with a sensor probe mounted therein. The first section may include a rounded nose portion and a retrieval line to assist in pulling the structure out, should removal for maintenance or repair be required. Once the sensor probe is in place, the first section may be slid along the conduit until there is sufficient room in the hand hole for the next section. The second section is then inserted and clipped onto the first section, with this step being repeated for a predetermined spacing. Probes are mounted in predetermined sections to achieve the desired detection coverage area. This process is repeated until an extended structure is assembled with the sections aligned in an end-to-end configuration with the sensor probes positioned along the structure. When sufficient sections have been inserted to place the sensors in their desired pre-determined positions, the last section is clipped in place at the surface access hole so that the sensor probes are retained at their correct spacing and substantially vertical orientation. These features of novelty and various other advantages which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention. Brief Description of the Drawings Referring now to the drawings, wherein like reference letters and numerals indicate corresponding structure throughout the several views: Figure 1 shows a partially broken away side sectional view of a first embodiment of a vehicle sensing system according to the principles of the present invention; Figure 2 shows a partially broken away perspective view of a portion of the vehicle sensing system shown in Figure 1 ; Figure 3 shows a partially broken away perspective view of a first embodiment of a probe carrier support section for the vehicle sensing system shown in Figure 1; Figure 4 shows a perspective view of a connector clip for the support section shown in Figure 3; Figure 5 shows an end perspective view of the support section shown in Figure 3; Figure 6 shows an end perspective view of the a support section shown in Figure 3 and the cradle for the vehicle sensing system shown in Figure 1 ; Figure 7 shows a partially broken away perspective view of a sensor probe and housing for the vehicle sensing system shown in Figure 1 ; Figure 8 shows a perspective view of a second embodiment of a probe carrier support section according to the principles of the present invention; Figure 9 shows a perspective view of a third embodiment of a probe carrier support section according to the principles of the present invention; Figure 10 shows a perspective view of a fourth embodiment of a probe carrier support section with a mounting clip attached according to the principles of the present invention; Figure 11 shows a partially broken away side sectional of a second embodiment of a vehicle sensing system according to the principles of the present invention; and, Figure 12 shows a partially broken away side sectional of a third embodiment of a vehicle sensing system according to the principles of the present invention. Detailed Description of the Preferred Embodiment Referring now to the drawings, and in particular to Figure 1, there is shown a below ground vehicle sensing system, generally designated 20. The vehicle sensing system 20 generally is positioned below a vehicle travel surface 22, normally pavement such as concrete or asphalt, and typically at a depth of 16 to 24 inches below the upper surface of the vehicle travel surface 22. In a preferred embodiment, a bore or conduit 24 extends horizontally under the vehicle 22 from a surface access hole 26, commonly referred to as a hand hole, at the side of the vehicle travel surface 22. The surface access hole 26 typically includes a cover 28 to protect the wiring, electronics and other elements of the vehicle sensing system 20. A cradle 70 having an open upper portion 74 attaches to the conduit 24 with a sleeve member 72 in the access hole 26. As shown in Figure 2, the sensing system 20 includes a plurality of sensor probes 50 in spaced apart relationship. As shown in Figure 7, each of the probes 50 includes a housing 52 having a top portion 54 and bottom portion 56 with an electronic sensor 58 extending substantially vertically in the housing. The probes are connected by cable 60, as shown in Figure 2 or each probe 50 may have a separate cable leading to a processor or controller. As shown in Figure 7, the sensor 58 includes a microloop coil 62 mounted on a planar strip 64 and circuitry box 66 for sensing the change in impedance when a vehicle passes over the probe's position. Rebar or other ferro-magnetic material already present in the road does not normally affect the sensitivity or accuracy of the sensor 58. It can be appreciated that other types of below ground vehicle sensing devices that accurately detect the presence of a vehicle and that do not need to be placed into or through pavement may be utilized with the present invention. When the probe 50 senses the presence of a vehicle, a signal is sent to a microprocessor or other control system for processing, such as traffic light control or other traffic analysis. To function properly, the probes 50 should be aligned in a substantially vertical orientation, as the efficiency is decreased when tilted substantially away from vertical or the preferred design position. The probe housing 52 may include flanges or other structure to aid in stabilizing the sensor 58 in proper orientation. It has been found that the performance of the sensors 58 is substantially unaffected when the sensor 58 is within 10° of vertical. In addition, satisfactory performance has been achieved when the sensor 58 is within 45° of vertical. In a first embodiment shown in Figure 2, the probes 50 are housed in probe carrier support sections 32 forming extended protective supporting structure 30 which protects, spaces and aligns the probes 50. Each of the sections 32 includes a rounded outer wall 34 which preferably inserts into the conduit 24. As shown in Figures 3 and 5, the sections 32 each have a rounded outer wall 34 with an open top portion 36. A frame portion 38 includes probe mounting holes 40 for receiving and aligning the probes 50, as shown on Figure 2. The frame 38 also includes a clip 44 which mounts at one end of the section 32. The frame 38 or lower portion of the support section 32 may be weighted to stabilize the section and hold the probe 50 in a substantially vertical stable position. As shown in Figure 4, the clip 44 attaches to the next adjacent section 32 to hold the sections in a connected arrangement and angularly aligned. The clip 44 includes a retaining section 46 which engages a clip slot 42 formed in the opposite end of the adjacent section frame 38 and resists removal once inserted. In a preferred embodiment, the clip 44 is a corrosion resistant material, such as 300 series stainless steel or plastic. It can be appreciated that a plurality of the sections 32 may be connected to form an extended support 30 housing a plurality of probes 50 in spaced apart relationship. It can be appreciated that the frame 38 includes two or more probe mounting holes 40 in spaced apart relationship so that the spacing of the probes may be varied to accommodate probe spacing specifications. It can be appreciated that to ease insertion of the extended support section 30, a conical rounded nose piece 78 may be affixed to the first support section 32 to aid in clearing any irregularities in the conduit 24, such as joints or bends or to displace debris collected within the bore of conduit 24. To ease removal, a retrieval cord or line 76 is attached to the first section 32 so that the sections may be pulled back for retrieval and removal. Referring to Figure 8, there is shown a second embodiment of a probe carrier support section 90. The support section 90 includes a planar bottom portion and sides extending upward therefrom. Probe mounting orifices 92 are formed in the bottom portion and spaced apart for receiving sensor probes 58. Slots 94 are formed near the end of the support section 90. It can be appreciated that the sections 90 accommodate a clip member 44, shown in Figure 4, to attach to sections in an end-to-end relationship. It can be appreciated that the sections 90 insert within the conduit and support the probes 50 in a spaced apart relationship and substantially vertically aligning the sensors 58. Referring to Figure 9, there is shown a third embodiment of a probe carrier support section 100. The support section 100 includes an outer portion 102 and a mounting potion 104. As shown in Figure 9, the outer portion 102 and mounting portion 104 are integrally formed of a single element but may be attached in other ways as well. The outer portion 102 forms an open top for receiving probes 58 mounting in orifices 106 in the upper portion of the mounting portion 104. It can be appreciated that the mounting portion 104 accommodates a clip 44, shown in Figure 4, for connecting the sections 100 in an end-to-end relationship. The clips 44 attach to the slots 108 in adjacent sections. Referring now to Figure 10, there is shown a fourth embodiment of a probe carrier support section 140. The support section 140 includes an arcing outer portion 142 and a mounting potion 144 having slots 148 formed therein. The outer portion 142 forms an open top for receiving probes 58 mounting in orifices 146 in the upper portion of the mounting portion 144. It can be appreciated that the mounting portion 144 accommodates the clip 44 shown in Figure 4, for connecting the sections 140 in an end-to-end relationship. The clips 44 attach to the slots 148 in adjacent sections with the clips 44 being inverted from the position shown in Figure 4. Referring now to Figures 1 and 2, it can be appreciated that with the present invention, assembly and placement of the probes and the vehicle sensing system 20 is simplified and easily accomplished. Once the bore is formed and a conduit 24, if used, is inserted, the support structure 30 and the probes 50 may be placed. To begin insertion, the first section 32 is placed into the access hole 26 and placed into the opening 74 of the cradle member 70. The cradle member 70 is connected via the sleeve member 72 to the remainder of the conduit 24. The first sensor probe 50 is placed into a mounting hole 40 in the frame 38 and the associated wiring is fed backward toward the open end. In addition, the retrieval line 76 is connected to the first section and extended backward. When this step has been completed, the section 32 is pushed forward into the conduit until sufficient room is made in the opening 74 of the cradle 70 with the second section 32 placed so that the clip member 44 engages the slot 42 in the frame 38 of the first section 32. The string of sensors is placed through the open top 36 of the second section 32 and the retrieval line 76 is also placed over the openings in the section 32. If spacing dictates that a probe 50 should be placed in a section 32, the probe 50 is inserted into one of the mounting holes 40. When this step has been completed, the connected sections 32 are pushed forward into the conduit 24. This process is repeated until sufficient sections 32 have been placed into the conduit 24 so that the sensor probes 50 are aligned with their predetermined sensing positions beneath the vehicle travel surface 22. As shown in Figure 6, a cradle clip 80 is placed onto the opening 74 of the cradle member 70 and over the last section 32. The cradle clip 80 includes a support section frame engaging portion 82 which fits over the frame 38 of the support section 32. The cradle clip 80 also includes a support section wall engaging portion 84 which extends over the opening 36 and the curved wall 34. A cradle engaging portion 86 attaches to the edge of the cradle opening 74. The clip 80 secures the last section 32 into place and retains the entire support structure 30 in proper alignment and positioned at the proper distance into the conduit 24. The wiring 60 is then fed to the proper processors for data analysis, which may either be placed at the hand hole 26 or placed remotely therefrom. Referring now to Figure 11, there is shown a second embodiment of vehicle sensing system 120 similar to the system 20 shown in Figure 1. The system 120 includes sensor probes 50 mounted in support sections 32 within a conduit 24. However, intermediate connector sections 122 may be inserted in place of the selected support sections 32. The connector sections 120 may be solidly attached to the sections 32 or may include a hinge 124 for connecting the connector sections 122 to the support sections 32. It can be appreciated that connector sections 122 may be reduced weight and low cost shafts or struts. The connector sections 122 are typically clipped or otherwise detachably connected to the support sections 32 in such a manner that the distance between the sections 32 and the relative alignment of the sections 32 is maintained. In this manner, the connector sections 122 may be utilized in conjunction with the support sections to provide a low cost, light weight and simple to install and remove system 120. Referring now to Figure 12, there is shown another embodiment of the vehicle sensing system 130. The vehicle sensing system 130 includes support sections 32 inserted into conduit 24. A single access hole 26 may be utilized for installation of the system 130. However, similar to the system 120 shown in Figure 10, along lengths wherein sensors 50 are not supported, connector material 132 may be utilized. The system 130 utilizes the connector material 132 which clips or otherwise attaches to the support sections 32. The connector material 132 may be substantially stiff material which possesses some flexibility such that it may be coiled or rolled. However, when inserted into the conduit 24, the connector material 132 maintains the distance between the support sections 32 and the relative angular alignment. In this manner, support sections 32 may be clipped or otherwise attached to the connector material 132 at predetermined locations along the material 132 or supporting sensors 50. Although the embodiments shown in Figures 1, 11 and 12 make reference to utilization of support sections 32, it can be appreciated that the support sections 90, 100 and 140, as shown in Figures 8, 9 and 10 may also be utilized. It can be appreciated that with the present invention, the method for installation requires placement of only a single support section 32, 90, 100 or 140 at a time. The support structure 30 does not need to be pulled through and requires only a single opening 26 at one side of the vehicle travel surface 22 rather than openings at each end for pulling electronics and other structures through the hole. Moreover, it can be appreciated that the structure provides a light weight support structure 30 which can be easily inserted. Each of the sections provide for no relative angular movement between adjacent sections 32 so that all of the probes 50 may be substantially vertically aligned for improved performance. Should maintenance be required, it can be appreciated that the structure can be pulled outward through the access hole 26 by removing one section 32 at a time and pulling the sections back with the retrieval line 76 or by taking the end most section 32 and pulling it into the opening and unclipping the end most section 32 from the next adjacent section 32. It can also be appreciated that the distance to the endmost sensor may be measured from the access hole 26 and that sufficient support sections 32 may be inserted until the end probe 50 is placed at the proper position beneath the pavement. The distance back from which a sensor probe 50 needs to be placed from the first section may be marked on the retrieval line 76 or on the wiring and a probe inserted into the sections 32 proximate the predetermined position. In this manner, easy installation is provided for following placement of the first endmost probe 50. It can also be appreciated that the present structure provides for magneto- inductive sensing which reduces the number of false readings and provides for a more accurate reading of even smaller vehicles. In addition, since the system is substantially lightweight and low cost, the probes may be placed at different positions within each lane under the pavement for covering substantially the entire width of the pavement, if so desired. It can also be appreciated that since the system senses vehicle induced localized changes in the Earth's magnetic field, the probes 50 may be placed at a lower depth so that the pavement may be left intact, thereby reducing the number of lanes which must be closed, as well as the length of time that traffic flows is interrupted during initial installation of the system 20. Moreover, service or maintenance typically does not require any lane closures. This provides for substantial labor savings and decreased traffic interruption through the location where the presence of vehicles is being sensed. The present invention also provides for easy installation or repair of the vehicle sensing system 20 after the pavement has been laid without loss of efficiency. It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims: What is claimed is: 1. A system for detecting vehicles, comprising: a conduit extending under a vehicle travel surface; one or more sensor probes in spaced apart relation within the conduit; and, one or more support sections supporting the sensor probes in the conduits. 2. A system according to claim 1, further comprising an insertion portion including an access hole connecting to the conduit. 3. A system according to claim 1, wherein the sections are separable and removable from adjacent sections. 4. A system according to claim 3, wherein adjacent sections connect in an end to end manner. 5. A system according to claim 4, further comprising clips for detachably connecting the adjacent sections. 6. A system according to claim 1, wherein the support sections comprise an elliptical cross section. 7. A system according to claim 4, wherein the adjacent sections connect with clips that prevent rotation between adjacent sections. 8. A system according to claim 1, further comprising a cradle connecting to a first end of the conduit, the cradle having an open top portion for accepting the support sections. 9. A system according to claim 1, wherein an endmost support section includes a cord extending back through the conduit. 10. A system according to claim 1, wherein the endmost support section includes a frustro-conical end portion. 11. A system according to claim 1, wherein at least one of the plurality of sections is weighted to stabilize the support section. 12. A system according to claim 1, further comprising an outer member providing a barrier at a periphery of the conduit. 13. A system according to claim 1, wherein the vehicle travel surface comprises pavement, and wherein the conduit is located below the pavement. 14. A system according to claim 1, wherein the conduit is placed between 16 inches and 24 inches below the vehicle travel surface. 15. A system according to claim 1, further comprising spacing means inserting intermediate selected support sections for connecting the support sections at a predetermined spacing. 16. A system according to claim 15, wherein the spacing means comprises a continuous material attaching to the sections. 17. A support system according to claim 1, wherein the system extends under the vehicle travel surface substantially transversely to a prevailing direction of vehicle travel. 18. A system according to claim 1, further comprising a single access hole connecting to the conduit. 19. A support device for a probe, comprising: an outer substantially cylindrical section, defining an open top portion and open end portions; a mounting portion located within the outer section, the mounting portion including receiving means for receiving a probe; and means for attaching the support device to adjacent support devices in an aligned end to end configuration. 20. A support device according to claim 19, wherein the receiving means is configured for aligning the probes toward the open top portion. 21. A support device according to claim 19, wherein the mounting portion defines a slot formed therein, and wherein the attaching means comprises a clip detachably engaging the slot. 22. A support device according to claim 19, wherein the mounting portion comprises a housing including side portions attaching to an inner portion of the outer sections and an upper section attached to the side portions and spaced apart from the outer section. 23. A support device according to claim 22, wherein the mounting means comprises an orifice formed in the upper section of the housing configured for receiving a probe. 24. A method for making an underground vehicle sensing system for sensing the presence of a vehicle on a vehicle travel surface, comprising the steps of: forming an access hole and a bore extending from the access hole substantially horizontally below the vehicle travel surface; inserting a support section into the access hole and mounting a sensor to the support section; directing the support section and sensor into the bore so that the access hole may receive another support section; inserting another support section into the access hole and attaching to the previously inserted support section; selectively mounting a sensor to another support section at a predetermined position; and, continuing to insert the attached support sections into the bore with mounted sensors to the support sections at predetermined locations until the sensors are inserted to align with predetermined locations below the vehicle travel surface. 25. A method according to claim 24, wherein the access hole is formed remote from the vehicle travel surface. 26. An apparatus for sensing the presence of a vehicle, comprising: a conduit extending under a vehicle travel surface; one or more sensors for sensing a vehicle on the vehicle travel surface; one or more support sections for supporting the sensors in spaced apart relationship in the conduit; and, means for connecting the support sections providing for maintaining a predetermined spacing among the support sections and for maintaining a rotational alignment among the support sections. 27. A vehicle sensor support device, comprising: means for supporting a sensor in a predetermined orientation; means for connecting the support sections in an aligned end-to-end configuration maintaining the relative spacing among the sections and maintaining rotational alignment among the sections. 28. A system according to claim 1, further comprising wiring extending from the sensor probes within the support sections to a controller.

Inventors: CYBULSKI CLAUD E, HOEKMAN EARL B, TURK FREDERICK J, CYBULSKI, CLAUD, E., HOEKMAN, EARL, B., TURK, FREDERICK, J.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1997
Main classification: G01V3
IPC codes: G01P3, G01V3, G08G1