METHOD AND DEVICE FOR WHEEL ALIGNMENT

Abstract: The invention relates to a measuring system for measuring wheel angles and projected width of a vehicle (1) having at least two wheel pairs and a connection, such as a vehicle frame (4), between the respective wheel pairs, and that each wheel (5) of each wheel pair has a side facing away from the vehicle (1) and a rotational axis for each wheel (5). The measurement system comprises at least two measuring units (9, 10), each comprising a means (11), arranged to detect the orientation of the wheel side in space through repeated determination of the distance between the measurement unit (9, 10) and at least one point on the rotating wheel side of the wheels (5) of the vehicle (1), which rool on a substrate (U) when the vehicle (1) travels in a certain direction (F) between the measuring units (9, 10), and a processor (15), which, based on the reflected measurement signals (12) calculates the direction of the rotational axis of each wheel (5), the distance of each wheel (5) to the respective measurement unit (9, 10), the distance between each wheel (5) on each side of the vehicle (1) and the longitudinal geometric center line [C] of the vehicle (1).

Description: Method and device for wheel alignment The present invention relates to a method for wheel alignment for a vehicle having at least two wheel pairs and a connection, such as a vehicle frame, therebetween. The invention also relates to a measuring system for measuring wheel angles and projected width of a vehicle. A device for determining the angles of the wheels of a vehicle is described in WO-A1-94/05969. According to this document, the vehicle is placed on a test bed, which has two parallel metal strips on which the wheels of the vehicle rest. A target in the form of a disc is applied to the outside of each wheel, and each disc is provided with a pattern. A camera which is coupled to a computer reads, via a lens and mirror system, the pattern on each target. Depending on how the camera registers the appearance of the pattern, the angle of each wheel relative to a defined system of coordinates can be determined by a calculating algorithm in the computer. In order to carry out the measurement with the device according to the document above, the vehicle must be stationary on the two parallel metal strips. This means that during measurement it is presupposed that the direction of travel of the vehicle coincides with the longitudinal geometric centerline of the vehicle. The frame of a vehicle can, however, be crooked and the axles or wheels can be set so that the longitudinal geometric centerline of the vehicle does not coincide with the direction of travel of the vehicle, and this in turn means that the projected width of the vehicle will be greater than the actual width of the vehicle. Furthermore, the wheel angles of a stationary vehicle differ from the wheel angles when the vehicle is in motion, and therefore the wheel angles obtained from the above known measuring method do not provide the actual wheel angles when the vehicle is in motion. One purpose of the present invention is to reduce tyre wear occurring as a result of deviations in vehicle wheel angles from ideal values and/or because a towing hitch has been mismounted on the vehicle. An additional purpose of the present invention is to achieve the smallest possible projected width of a vehicle as seen in the direction of travel of the vehicle, in order to thereby reduce the air drag and fuel consumption. Another purpose of the present invention is to achieve an accurate measuring system for rapidly checking wheel angles and the projected width of a vehicle. This is achieved according to the invention by virtue of a measuring system comprising at least two measuring units, each comprising a means, arranged to detect the orientation in space of the wheel side by repeated determination of the distance between the measuring unit and at least one point on the rotating wheel side of the vehicle wheels, which rolls on a subsurface when the vehicle is driven in a given direction of travel between the measuring units, and a processor connected to the means, which processor, based on information detected by the means, computes the alignment of the rotational axis of each wheel, the distance of each wheel to the respective measuring point, the distance between the respective wheel on each side of the vehicle and the longitudinal geometric center- line of the vehicle. The process for achieving these objectives is characterized in that the vehicle in a given direction of travel is driven with the wheels rolling on a subsurface between at least two measuring units free from the vehicle, that each measuring unit detects the orientation of the wheel side in space by repeated determination of the distance between the measuring unit and at least one point on the rotating wheel side, that each measuring unit sends the detected information on to a processor, which processes the information and which, after said processing, gives the alignment of rotational axis of each wheel, the distance of each wheel to the respective measuring unit, the distance between the respective wheels on each side of the vehicle and the longitudinal geometric centerline of the vehicle, that the wheels are set so that the difference between the measured values for the alignment of the rotational axis of each wheel and the ideal values for the alignment of the rotational axis of each wheel will be as small as possible and so that said geometric centerline coincides with the given direction of travel. This measuring system and method provides precise measurement rapidly carried out as the vehicle passes with the wheels rolling on a surface past the measuring units. The measurement provides values for vehicle wheel angles, direction of travel and the longitudinal geometric centerline. Based on these values, the vehicle can be adjusted to reduce the projected width and to reduce tyre wear as a result of misaligned wheels. Furthermore, measurement values for the placement of the towing hitch are obtained. An incorrectly placed towing hitch can result in non-symmetrical loading of the vehicle, which must be absorbed by the vehicle wheels which are thus subjected to increased wear. The invention will be described in more detail below with reference to examples shown in the accompanying drawings, where Fig. 1 shows a schematic view from above of a vehicle, Fig. 2 shows a schematic view from above of a vehicle which is provided with a towing hitch, Fig. 3 shows a schematic view from above of a vehicle which is passing between two measuring units, and Fig. 4 shows a schematic view of a vehicle as seen from behind, passing between three measuring units. Fig. 1 shows a schematic view from above of a vehicle, such as a truck, comprising two rear axles 2, a front axle 3 and a vehicle frame 4. Wheels 5 are mounted at each main axle end 6. Two wheels 5 are arranged on an axle forming a wheel pair. The angles of the axles 2, 3 and the wheels 5 are exaggeratedly misaligned in Fig. 1. The dashed rectangles on the vehicle 1 symbolize a cab and a superstructure 7 arranged on the vehicle 1, such as a van or flatbed. The distance between the parallel, solid lines L along the longitudinal sides of the vehicle 1 represents the minimum projected width of the vehicle 1. The distance between the parallel, dash-dot lines S along the longitudinal sides of the vehicle 1 represents the projected width of the vehicle 1 as seen in the direction of travel F of the vehicle. Depending on the angular alignments of the wheels 5 and the axles 2, 3 and on the condition of the vehicle frame 4, the projected width as seen in the direction of travel F of the vehicle 1 can differ from the minimum projected width of the vehicle 1. There are a number of different ways of defining the longitudinal geometric center- line C of a vehicle 1. One definition of the longitudinal geometric centerline C of the vehicle 1 is a line extending between the midpoint of the front edge of the vehicle frame 4 and the midpoint of the rear edge of the vehicle frame 4. Another definition of the longitudinal geometric centerline C of the vehicle 1 is a line extending between the midpoint of the front wheel axle 3 and the midpoint of the rear wheel axle 2. If the vehicle has a number of wheel axles, the longitudinal geometric center- line C coincides with a mean line passing at each midpoint of each axle at a distance which is so determined that the sum of the distances to the midpoints will be as small as possible. This distance is obtained, for example, by the least square method. Since the vehicle frame 4 can be bent and the wheel axles 2, 3 be laterally displaced relative to the vehicle frame 4, the position of the longitudinal geometric centerline C can differ between two vehicles 1 of the same type and make. Fig. 2 shows a schematic view from above of a vehicle 1, which is provided with a towing hitch 8. According to the Figure, the towing hitch 8 of the vehicle 1 is not placed on the longitudinal geometric centerline C. At the same time, the longitudinal geometric centerline C of the vehicle 1 does not coincide with the direction of travel F of the vehicle 1, and this results in asymmetric loading when the vehicle 1 is pulling a trailer (not shown) coupled to the towing hitch 8. Fig. 3 shows schematically from above a vehicle 1, which is travelling with the wheels 5 rolling on a surface U in a given direction of travel F, between at least two measuring units 9, 10 spaced from the vehicle 1. Each measuring unit 9, 10 comprises a radiation source 11, which provides a measuring signal 12 which, as the vehicle 1 passes the measuring units 9, 10, strikes the outside of each wheel 5, i.e. the wheel side facing away from the vehicle 1. In Fig. 3, a reflecting means 13 has been mounted on the outside of each wheel 5, and this reflecting means 13 reflects the measuring signal 12 emitted from the respective radiation source 11. This signal is received by a detector 14. The measuring signal 12 received by the detector 14 is processed in a processor 15, which provides values for the alignment of the rotation axis of each wheel 5, the distance of each wheel 5 to the respective measuring unit 9, 10, the distance between each wheel 5 on each side of the vehicle 1 and the longitudinal geometric centerline C of the vehicle. The measured values for the alignment of the rotational axis of each wheel 5 are compared with predetermined ideal values for the alignments of the rotational axes of the wheels 5. Finally, the wheels 5 are adjusted so that the difference between the measured values for the alignment of the rotation axis of each wheel 5 and the ideal values for the alignment of the rotational axis of each wheel 5 will be as small as possible. When the wheels 5 pass the respective measuring unit 9, 10, the time it takes for the wheels 5 to pass the respective measuring unit 9, 10 can be measured. If the speed of the vehicle is known, the distance between each wheel 5 on each side of the vehicle 1 can be calculated. In order to determine the speed of the vehicle 1, a speedometer (not shown), in the form of a laser for example, can be arranged in front of or above the vehicle 1. The laser emits a measuring ray against the vehicle 1 when it passes the measuring units 9, 10 and the speed of the vehicle 1 can be measured. The speedometer can be coupled to the processor 15 which computes the distance between each wheel 5 on each side of the vehicle 1, based on the known speed and the time it takes for the wheels 5 to pass the measuring units 9, 10. When the alignment of the rotational axes of the wheels 5 agrees with the ideal values for the alignment of the rotational axis of each wheel 5 and when the alignment of each axle 2, 3 has been adjusted in relation to the longitudinal geometric centerline C of the vehicle 1, the longitudinal geometric centerline C of the vehicle 1 will coincide with the direction of travel F of the vehicle 1. This also achieves the smallest possible projected width of the vehicle 1, as seen in the direction of travel F of the vehicle 1. Fig. 4 shows a schematic view of a vehicle 1 as seen from behind, which passes three measuring units 9, 10, 16. One measuring unit 16 is arranged above the vehicle 1 and comprises a radiation source 17, which emits a measuring signal 18 which strikes the towing hitch 8 of the vehicle 1. A reflecting means 19 is mounted on the towing hitch 8 and reflects the measuring signal 12 emitted from the radiation source 17 which is then received by a detector 20. The measuring signal 18 received by the detector 20 is processed in the processor 17, which discloses how far the towing hitch 8 is located from the longitudinal geometric centerline C of the vehicle 1 and how high above the surface U the towing hitch is located. The result of the measurement can be presented on a monitor 21, for example. Finally, the towing hitch 8 is moved or the vehicle frame 4 is adjusted so that the towing hitch 8 is on the geometric longitudinal centerline C of the vehicle 1. The reflecting means 13,19 can be a flat disc which is mounted on the outside of each wheel 5 and on the towing hitch 8. Alternatively, the measuring signals 12, 18 can be reflected directly against the tyre side or rim (not shown) of each wheel 5 and directly against the towing hitch 8. When a disc is mounted on the outside of a wheel 5, an angular error can arise if the disc is placed in such a manner that the rotational axis of the wheel 5 is not normal to the disc. When processing the measuring data, a compensation for this angular error can be made in the processor 15, however. Preferably, the radiation source 11, 17 is a laser line projector, which projects two lines in a cross on each wheel side. By placing the detector 14, 20 at a given distance and at a given angle relative to the laser line projector, the angular variations of the cross projected on the wheel side can be measured. Based on the measured angular variations, the alignment of the rotational axis of each wheel 5 is obtained. Theoretically, it is sufficient to have one detector 11, 17 for two lines, but it is preferable to use two detectors 11, 17, one for each line, for measuring unit 9, 10, 16 to obtain good precision. The laser line projector, which is included in each measuring unit 9, 10, 16 thus emits measuring signals against the respective wheel side, said measuring signals being detected at a number of occasions by means of the detectors 11, 17. The detected information provides values concerning the orientation of the wheels 5, the towing hitch 8 and the longitudinal geometric centerline C of the vehicle 1. In order to measure the projected width of the vehicle 1, additional measuring units (not shown) can be arranged above the vehicle 1, said measuring units detecting the sides of the cab and the rear superstructure 7 and how these relate to the direction of travel F of the vehicle 1. Alternatively, the measuring unit 16 above the vehicle 1 can detect the position of the cab and the rear superstructure 7. In order to acquire more information and thus additionally increase the precision of the measuring system, in addition two measuring units (not shown) can be disposed on either side of the surface U which the vehicle 1 is to pass. A predetermined coordinate system can be defined in the processor 15. One axis of the coordinate system can coincide with a straight line in the plane of the surface U midway between the measuring units 9, 16 placed on either side of the surface. The measuring values which each measuring unit 9, 10, 16 obtains can thus refer to the common coordinate system. The ideal values for the alignment of the rotational axes of the wheels 5 are given for each vehicle type and are preferably preprogrammed in the processor 15. Instead of using a radiation source in the form of a laser line projector, the orientation of the wheel side in space can be determined by stereo matching, which means that two cameras are arranged at a certain distance from each other. A point which is to be detected will appear in different parts of the picture for the two cameras. The difference between the positions perceived by the cameras is a measure of the distance to the point in question. By measuring a number of points located in a plane, the angle of the plane relative to a reference plane can be computed.

Claims: Claims 1. Method for wheel alignment of a vehicle (1), comprising at least two wheel pairs and a connection, such as a vehicle frame (4) between the respective wheel pairs, each wheel (5) of each wheel pair having a wheel side facing away from the vehicle (1) and a rotational axis for each wheel (5), characterized in that the vehicle (1) in a given direction of travel (F) is driven with the wheels (5) rolling on a surface (U) between at least two measuring units (9,10) free from the vehicle (1), that each measuring unit (9,10) detects the orientation of the wheel side in space by repeated determination of the distance between the measuring unit and at least one point on the rotating wheel side, that each measuring unit (9,10) sends the detected information on to a processor (15), which processes the information and which, after said processing, gives the alignment of the rotational axis of each wheel (5), the distance of each wheel (5) to the respective measuring unit (9,10), the distance between the respective wheel (5) on each side of the vehicle (1) and the longitudinal geometric centerline C of (6) the vehicle, that the measured values for the alignment of the rotational axis of each wheel (5) are compared with predetermined ideal values for the alignments of the rotational axes of the wheels (5), and that the wheels (5) are set so that the difference between the measured values for the alignment of the rotational axis of each wheel (5) and the ideal values for the alignment of the rotational axis of each wheel (5) will be as small as possible and so that said geometric centerline coincides with the given direction of travel (F). 2. Method according to Claim 1, characterized in that the measuring unit (9,10) comprises a camera which reads the point on the wheel side. 3. Method according to Claim 1, characterized in that each measuring unit comprises a radiation source (11), which emits a measuring signal (12) which, as the vehicle (1) passes the measuring units (9,10) sequentially strikes the outside of each wheel (5), and that the measuring signal (12) is reflected by the outside of the wheel (5) and is received by a detector (14). 4. Method according to Claim 3, characterized in that a reflecting means (13) is mounted on the outside of each wheel (5), said reflecting means (13) reflecting the measuring signal (12) emitted from the respective radiation source (11). 5. Method according to one or more of the preceding claims, characterized in that the measuring unit (16) above the vehicle (1) detects the orientation of a towing hitch (8) mounted on the vehicle (1) in a plane parallel to the surface (U), by repeated determination of the distance between a reference point in the plane and at least one point on the towing hitch (8), that the information detected by the measuring unit (16) is processed in the processor (15), which discloses how far the towing hitch (8) is situated from the longitudinal geometric centerline C of the vehicle (1), and that the towing hitch (8) is moved or the vehicle frame (4) is adjusted so that the towing hitch (8) ends up on the geometric longitudinal centerline (C) of the vehicle (1). 6. Method according to Claim 5, characterized in that the measuring unit (16) above the vehicle (1) comprises a camera which reads the point on the towing hitch (8). 7. Method according to Claim 5, characterized in that the measuring unit (16) above the vehicle (1) comprises a radiation source (17), which is caused to emit a measuring signal (18) which strikes the towing hitch (8) of the vehicle (1), and that the measuring signal (18) is reflected by the towing hitch (8) and is received by a detector (20). 8. Method according to Claim 7, characterized in that a reflecting means (19) is mounted on the towing hitch (8) of the vehicle (1), said reflecting means (19) reflecting the measuring signal (12) emitted from the radiation source (17). 9. Method according to Claim 5, characterized in that the measuring unit (16) above the vehicle (1) also detects the position of a cab and rear superstructure (7) mounted on the vehicle (1), relative to the direction of travel (F) of the vehicle (1). 10. Measuring system for measuring wheel angles and the projected width of a vehicle (1), which comprises at least two wheel pairs and a connection, such as a vehicle frame (4), between the respective wheel pairs, each wheel (5) of the respective wheel pairs having a wheel side facing away from the vehicle (1) and a rotational axis for each wheel (5), characterized in that the measuring system comprises: at least two measuring units (9,10), each comprising a means (11), arranged to detect the orientation in space of the wheel side by repeated determination of the distance between the measuring unit (9,10) and at least one point on the rotating wheel side of the vehicle wheels (5), which rolls on a surface (U) when the vehicle (1) is driven in a given direction of travel (F) between the measuring units (9,10), and a processor (15) connected to the means (11), which processor, based on information detected by the means (11), computes the alignment of the rotational axis of each wheel (5), the distance of each wheel (5) to the respective measuring point (9,10), the distance between the respective wheel (5) on each side of the vehicle (1) and the longitudinal geometric centerline (C) of the vehicle (1). 11. Measuring system according to Claim 10, characterized in that the means (11) comprises a camera, which reads the point on the wheel side. 12. Measuring system according to Claim 10, characterized in that the means (11) comprises a radiation source (11), which is intended to emit a measuring signal (12) in the direction towards each wheel side and that a detector (14) is arranged to sense the reflected measuring signals (12) against each wheel side. 13. Measuring system according to Claim 12, characterized in that a reflecting means (13) is mounted on each wheel side and reflects the measuring signal (12) emitted from each radiation source (11). 14. Measuring means according to one or more of Claims 10-13, characterized in that an additional measuring unit (16) is arranged above the vehicle (1) and comprises a means (17) arranged to detect the orientation of a vehicle towing hitch (8) in a plane parallel to the surface (U) through repeated determination of the distance between a reference point in the plane and at least one point on the towing hitch (8), the measuring unit (16) being connected to the processor (15), which, based on the information detected, calculates the distance between the towing hitch (8) and the longitudinal geometric centerline (C) of the vehicle (1). 15. Measuring system according to Claim 14, characterized in that the measuring unit (16) above the vehicle (1) comprises a camera, which reads the point on the towing hitch (8). 16. Measuring system according to Claim 14, characterized in that the measuring unit (16) above the vehicle (1) comprises a radiation source (17) intended to emit a measuring signal (18) towards the towing hitch (8) of the vehicle (1), and a detector (20), which senses a measuring signal (12) reflected from the towing hitch (8). 17. Measuring system according to Claim 16, characterized in that a reflecting means (19) is mounted on the towing hitch (8) and reflects the measuring signal (18) emitted from the radiation source (17). 18. Measuring system according to one or more of Claims 13 or 17, characterized in that the reflecting means (13,19) is a flat disc. 19. Measuring system according to one or more of Claims 12, 13, 16-17, characterized in that the radiation source (11,17) is a laser line projector which projects at least one laser line against the reflecting means (13,19). 20 Measuring system according to one or more of Claims 12, 13, 16-19, characterized in that the detector (14,20) consists of at least one camera which is arranged in the measuring unit (9,10,16).

Inventors: INGVARSSON HENRIK, NILSSON MARTIN, INGVARSSON, HENRIK, NILSSON, MARTIN
Applicants: INGVARSSON HENRIK, NILSSON MARTIN, VOLVO LASTVAGNAR AB, INGVARSSON, HENRIK, NILSSON, MARTIN
Application year: 1997
Main classification: G01B11
IPC codes: G01B11