Wheel alignment measuring apparatus

Abstract: The present invention relates to a wheel alignment measuring apparatus which measures the toe-in length or angle and camber angle of each tire (17) of a car. The wheel alignment measuring apparatus can be used to measure the distances to various points on the surface of the tire (17) by means of the light of a predetermined wavelength emitted from the light-emitting means (4) and to determine the toe-in angle or length and camber angle of the tire (17) based on the measured distances. In other words, such measurement can be done without any contact with the tire (17) under inspection, thus it is possible to prevent any trouble which would occur when such measurement is done in contact with the tire, such as error caused by the oscillation or the like of the tire 17). Also, with the wheel alignment measuring apparatus according to the present invention, it is possible to effectively correct any error of measurement caused by any irregularities on the tire (17), thereby attaining a higher accuracy of measurement since the calculating means (6) incorporated appropriately calculates the distances to various points on the tire surface from the data obtained based on the time taken for the light emitted toward various points on the entire circumference of each tire (17) at many short time intervals to return, as reflected, to the light-emitting means (photo-detecting means).

Description: The present invention relates to a wheel alignment measuring apparatus for measurement of the toe-in length or angle and the camber angle of vehicle tires in accordance with the pre-characterizing portion of claim 1. Such an apparatus is known from DE-A-37 29 946. Description of the Prior Art: The tires running while supporting a car body are installed at a predetermined angle, that is, at a predetermined camber angle and toe-in angle, to the right and left ends of an axle by means of their associated wheels. These angles are required to be within respective predetermined ranges. The camber angle is necessary to prevent the tire from being disengaged from the wheel installed on the axis when the weight of the car body is applied. With the camber angle, the tires are positioned on the ground surface as inclined divergently from the ground surface, namely, their tops are projected slightly outward from the bottoms in contact with the ground surface. The toe-in angle is required for securing the linear running of the car and is such that the distance between the front portions of the right and left tires is smaller than that between the rear portions. In other words, when viewed from above, the right and left tires are converged frontally of the car. That is, the camber and toe-in angles are very important factors in safe driving of the car. Thus, it is legally required that these angles should be accurately measured and readjusted after the tires are installed or during car inspection, etc. In these circumstances, a variety of apparatuses and methods have been proposed for such a measurement. For example, an apparatus for measuring the toe-in length or angle and camber angle is known which has a plate or the like to be put in contact with a tire immovably positioned in place to measure the camber and toe-in angles by means of a measuring means such as manometer or the like. With such measuring apparatus, however, the relieved markings of a manufacturer's name, standard, etc. provided on the tire surface with which the plate is placed in contact cause an error in the measurement and thus make it impossible to accurately measure the tire angles. Also in this measuring apparatus, since the plate is put in direct contact with the tire, any slight move of the tire during measurement will possibly cause an error in measurement and the elaborated measuring apparatus to be damaged. DE-A-37 29 946 discloses a wheel alignment measuring apparatus using, in agreement with the present invention, photo-sensors. The photo-sensors of this prior art document are mounted at a linear support which is moved horizontally back and forth in order to measure the toe-in length of a vehicle wheel or tire. In order to measure the camber angle, said support is erected vertically and held at rest during measurement. The wheel is rotated during measurement. The prior art document Patent Abstracts of Japan, JP-A-62 175 607, discloses a similar arrangement using photo-sensors which are mounted at a linear support. The photo-sensors scan a wheel in horizontal direction from the front end to the rear end in order to measure the side face of the wheel at a plurality of different points. The wheel surface is not scanned circumferentially. Therefore, the toe-in length and camber angle have to be measured separately. The technical problem underlying the present invention is to provide an apparatus for measuring wheel alignment with high accuracy in a short time. The apparatus for solving this technical problem in accordance with the present invention is described in claim 1. Preferred embodiments of the apparatus are described in the dependent claims. The wheel alignment measuring apparatus according to the present invention can measure the distances to various points on the outer surface of each tire by means of a light of a predetermined wavelength emitted from a light-emitting means, and determine the toe-in angle or length and camber angle based on the measured distances. Since the apparatus can effect this measurement without any contact with the tire under inspection, no trouble takes place which is caused by the oscillation or the like of the tire. Also the apparatus according to the present invention emits light at many times toward various points on the entire circumferential surface of each tire, appropriately calculates, by means of the calculating means, the toe-in length or angle and camber angle from the data obtained based on the time taken for the light reflected from such points to be received by the photo-detecting means. That is to say, the apparatus can effectively correct any error caused by the irregularities on the tire surface, thereby measuring the toe-in length or angle and camber angle with a high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic illustration of the wheel alignment measuring apparatus according to the present invention; Fig. 2 is a plan view showing the positioning means included in the present invention; Fig. 3 is a perspective view showing the essential parts of the present invention; Fig. 4 is a side elevation showing the apparatus when a tire is mounted on the tire support of the positioning means shown in Fig. 1; Fig. 5 is an explanatory drawing showing the method of measuring using the apparatus according to the present invention; Fig. 6 is a graph showing the method for processing data measured with the apparatus of the present invention; Fig. 7 is a plan view showing an variant of the positioning means in the present invention; Fig. 8 is a front view showing the positioning means shown in Fig. 7; Fig. 9 is an explanatory drawing showing the method for calculating the center of rotation of the tire in the positioning means in the present invention; and Fig. 10 is an explanatory drawing showing the method for calculating the center of rotation of the tire in the positioning means in the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, one embodiment of the wheel alignment measuring apparatus according to the present invention will be described below. Fig. 1 shows the wheel alignment measuring apparatus according to the present invention. The wheel alignment measuring apparatus is used one with each tire 17 under inspection, and it consists of a main unit 1 in which an X-directional move member and Y-directional moving member are housed, a rotary disk 3 projected from the lateral side 2a of a housing 2 of the main unit 1, a positioning means 30 (also see Fig. 2), a light-emitting means 4, a photo-detecting means 5, a calculating means 6 and a displaying means 7. The main unit 1 is accommodated in the box-like housing 2 as shown in Fig. 3, and composed of the X-directional move member 8, a motor 9 for driving the X-directional move member 8, the Y-directional move member 10, a motor 11 for driving the Y-directional move member 10, a -directional move drive motor 12 which rotates the rotary disk 3, and a R-directional move drive motor 13 which moves the light-emitting means 4 and photo-detecting means 5 radially of the rotary disk 3. The X-directional move member 8 has passed therethrough a feed screw 15 driven by the X-directional move drive motor 9 and also a guide shaft 16. Thus the member 8 is made to slide in the X-direction on a base 14 provided on the bottom of the housing 2 as guided on the guide shaft 16. On the other hand, the Y-directional move member 10 has passed therethrough a feed screw 18 driven by the Y-directional move drive motor 11 and also a guide shaft 19. Thus the member 10 is made to slide in the Y-direction, namely, in a direction perpendicular to the X-directional move member 8 as guided on the guide shaft 19, thereby making the center of the rotary disk 3 coincide with that of the tire 17 under inspection according to the diameter of the tire. The -directional move drive motor 12 is fixed on the X-directional move member 8 to rotate a hollow rotary shaft 20 fixed to the center of the rotary disk 3 by means of gears 21 and 22 in this embodiment, thereby rotating the rotary disk 3 in facing the outer surface of the tire 17 in order to measure the toe-in and camber angles of the tire 17. The rotary shaft 20 is rotatably supported on the Y-directional move member 10 and has passed therethrough an elongated hole 2b open at the lateral side 2a of the housing 2. The R-directional move drive motor 13 is provided to freely move the light-emitting means 4 and photo-detecting means 5 radially of the rotary disk 3 according to the diameter of the tire 17 under inspection, thereby positioning the light-emitting means 4 and photo-detecting means 5 so as to face the appropriate positions on the outer surface of the tire 17. In this embodiment, a drive shaft 23 is disposed inside the hollow rotary shaft 20. It is rotated to drive an R-directional move mechanism 24 which will be explained below to move the light-emitting means 4 and photo-detecting means 5. The R-directional move mechanism 24 comprises a bevel gear 26 in mesh with a bevel gear 25 fixed to the end of the drive shaft 23, a feed screw 27 fixed to the bevel gear 26, an R-directional move member 28 screwed on the feed screw 27 and having the light-emitting means 4 and photo-detecting means 5 mounted together thereon, and a guide shaft 29 which guides the R-directional move member 28 moving thereon. There is provided a positioning means 30 for making the rotary shaft 20, being the center of rotation of the rotary disk 3 shown in Fig. 2 coincide with the center of rotation 170 of each tire 17 under inspection shown in Fig. 4. In this embodiment, the positioning means 30 comprises an input button (not shown) used to supply data such as the type of a car having the tires to be measured, the size of the tire, etc., a pair of tire supports 31 movable a predetermined distance in the direction of the wheel space by means of a predetermined driving means (not shown), and a follower 32 which is coupled to the tire supports 31 and moved a same distance in a same direction as the supports 31. Each of the tire supports 31 comprises a support base 33 slidably provided on guide rails 35 as shown in Fig. 4, and a pair of rollers 34A and 34B provided on the support base 33 for each tire and on which the tire 17 can be freely rotated. Note that each of the tire supports 31 is provided with a fine-adjustment means (not shown) which moves the support base 33 in a direction in which a difference in wheel space from one vehicle to another is absorbed, thus permitting to support each tire correctly for the purpose of measurement. The follower 32 is slidably provided on the guide rails 36, and has a support base 37 on which the main unit 1 is mounted. The rotary shaft 20 provided in the main unit 1 is so positioned as to always be horizontally aligned with the center of rotation 170 of each tire 17. Moreover, the rotary shaft 20 is vertically moved a predetermined distance by the Y-directional move member 10 appropriately moved vertically with respect to the tire 17 correspondingly to a preset tire size and thus correctly aligned with the center of rotation of the tire 17. The light-emitting means 4 emits a light of a predetermined wavelength intermittently (at predetermined very short time intervals). In this embodiment, the means 14 uses laser diodes (LD) which can emit laser light of 780 nm in wavelength toward 1,500 points on the entire circumference of the tire 17. A pair of such laser diodes (LD) being the light-emitting means 4 is provided along with the photo-detecting means 5 point-symmetrically with each other as displaced π (rad) out of phase from each other. One of the laser diodes in pair is used to measure the toe-in length or angle and camber angle. If the toe-in length or angle is not found within a predetermined range of permissible value, both the laser diodes are used simultaneously for quick adjustment while watching the display screen 7a of the displaying means, which will be explained later, for the toe-in length or angle to be within the predetermined range. The photo-detecting means 5 is provided to receive the light emitted from the light-emitting means 4 and reflected from the tire surface and deliver a predetermined electrical signal to the calculating means 6. The means 5 uses photo-sensors. Using the electrical signal, namely, the data on the time t taken for the light emitted from the light-emitting means 4 to reach the photo-detecting means 5, supplied from the photo-detecting means 5, the calculating means 6 calculates distances d to various points on the surface of the tire 17 and a toe-in length or angle and camber angle from the data on the calculated distances d . More particularly, the calculating means 6 is adapted to calculate the distance d from each of the points on the outer surface 17a of the tire 17 to the photo-detecting means 5 (or the light-emitting means 4) as shown in Fig. 5 by using the following formula: d = ct/2 (where c : light velocity) The calculation is done of the distances d from the points in, for example, a counterclockwise sequence from the initial point of 0°. The distances from various points, calculated by the calculating means 6, are sequentially plotted like the graph A on the screen 7a of the displaying means 7 as shown in Fig. 6. The calculating means 6 calculates a toe-in length (D) from a difference D between the distance D 0 at the angle of 0° and the distance d 2 at the angle of 180°, among the data in the graph A, and also calculates a camber angle (α) by using the following formula using a distance d 1 at the angle of 90°, distance d 3 at the angle of 270° and a radius of rotation r of the photo-detecting means 5: α = tan -1 [2r/(d 3 - d 1 )] For the camber angle (α), the calculation uses as data an intermediate value between the distances at the angles of 180° and 360° taking in consideration the swelling of the tire portion having an angle of 270° and treading on the ground surface. The displaying means 7 is provided for a positive and rapid adjustment of the toe-in length or angle that should be done as necessary at the same time as the measurement of toe-in length or angle. It sequentially displays on the screen 17a thereof the data on the distances from various points on the tire 17 that are delivered from the calculating means 6. It should be noted that the positioning means in this embodiment uses the follower 32 coupled to the tire supports 31 and which is moved following the supports 31. This movement may be attained as follows. For example, the tire supports are not coupled to the follower, a truck 40 may be inched horizontally (in the Z-direction) near the tire 17 as shown in Fig. 7 and vertically (in the Y-direction) as shown in Fig. 8 to measure the shape of tire side-lace and calculate the center of the tire. Thus the rotary disk 3' is moved so at to be centered with the tire. Also in the positioning means of the present invention, the center of the tire may be calculated by putting a touch-sensor 42 into contact with the outer circumferential surface of the tire at a constant torque, moving the touch-sensor 42 along the outer circumference of the tire 17 with the torque kept constant as it is, and determine the center 170 of the tire based on the moving locus of the touch-sensor 42. Also, the center of the tire may be otherwise determined. That is, a size (diameter) of the tire 17 is previously supplied, three positions on the outer circumferential surface of the tire 17 are measured by the touch-sensor 42, and the center of the tire 17 is calculated from the measured positions. As having been discussed in the foregoing, the wheel alignment measuring apparatus can be used to measure the distances to various points on the tire surface by means of the light of a predetermined wavelength emitted from the light-emitting means and to determine the toe-in angle or length and camber angle of the tire based on the measured distances. In other words, the toe-in length or angle and camber angle can be measured without any contact with the tire under inspection, so it is possible to effectively prevent any trouble which would occur when such measurement is done in contact with the tire, such as damage of the measuring apparatus, error caused by the oscillation or the like of the tire. Also, with the wheel alignment measuring apparatus according to the present invention, it is possible to effectively correct any error of measurement caused by any partial irregularities on the tire, namely, to attain a higher accuracy of measurement since the calculating means incorporated sequentially calculates the distances to various points on the tire surface from the time taken from the light emitted from the light-emitting means at many short time intervals to return, as reflected, to the light-emitting means (photo-detecting means). Furthermore, the present invention provides a wheel alignment measuring apparatus in which the positioning means makes the center of rotation of the tire accurately coincide with that of the rotary disk.

Claims: A wheel alignment measuring apparatus for measurement of the toe-in length or angle and the camber angle of vehicle tires (17), said apparatus comprising: means (3) to be positioned vis-à-vis the outer surface (17a) of each tire (17) and carrying light-emitting means (4) for emitting light in infinitesimal time intervals which is reflected by said outer surface (17a) of the tire (17), and light-detecting means (5) for receiving said reflected light, means (6) for receiving output signals from said light-detecting means (5) and for calculating the toe-in length or angle and the camber angle of each tire (17) on the basis of the time which the light needs to travel from the light-emitting means (4) to the light-detecting means (5), means (8) for moving said means (3) carrying the light-emitting means (4) along an X-direction which is the direction of an axle at which left and right tire-wheels are mounted, means (10) for moving said means (3) carrying the light-emitting means (4) along an Y-direction which is perpendicular to said X-direction, and means (7) for displaying the toe-in length or angle and the camber angle as calculated by the calculating means (6), characterized in that, said means (3) carrying the light-emitting means (4) and the light-detecting means (5) is a rotary disk, a rotary shaft (20) rotates said rotary disk by a drive motor (12), positioning means (30) are provided for making the center of rotation of the tire (17)coincide with that of the rotary disk, and that the tire (17) under inspection is immovable positioned in place. Apparatus according to claim 1, characterized in that said rotary shaft (20) is supported by said Y-direction move means (10). Apparatus according to anyone of the claims 1 or 2, characterized in that light-emitting means (4) are mounted at said rotary disk (3) at locations which are spaced from each other circumferentially by 180°. Apparatus according to anyone of the preceding claims, characterized in that said light-emitting means (4) and said light-detecting means (5) are positioned at the same locations on the rotary disk (3). Apparatus according to anyone of the preceding claims, characterized in that means (24) are provided for moving said light-emitting means (4) and said light-detecting means (5) radially with respect to said rotary shaft (20). Apparatus according to claim 2, characterized in that said rotary shaft (20) is pivotably supported by said Y-direction move means (10).

Inventors: FUCHIWAKI MOTOAKI, KAYA TOSHIYUKI, FUCHIWAKI, MOTOAKI, KAYA, TOSHIYUKI
Applicants: CHUO ELECTRONIC MEASUREMENT CO, CHUO ELECTRONIC MEASUREMENT CO., LTD.
Application year: 1992
Main classification: G01B11
IPC codes: G01B11