Vehicle stress detecting and measuring method

Abstract: The present invention is intended to provide a stress detecting and measuring method wherein in order to measure a shearing strain alone associated with a stress acting in an intended direction, the stress being one of the stresses acting on an axle of a vehicle or a structure having a fixed support point adjacent the axle, the conditions for the optimum position where a stress sensor is to be mounted are indicated. Further, the invention is intended to provide a stress detecting device which accurately measures a shearing strain alone associated with a stress acting in an intended direction by further separating a plurality of stresses acting on a stress sensor. For example, in the case where stresses are applied in two directions to a structure having a fixed support point, in order to measure a shearing strain alone associated with a stress acting in an intended direction, a stress sensor should be mounted in a position which is a transformation knot zone for the other stress strain, i.e., a zone where shearing stress strain is minimum, and which is suitable for measurement of the intended stress.

Description: BACKGROUND OF THE INVENTION The present invention relates to a stress detecting and measuring method, wherein in order to measure a strain alone resulting from a stress acting in an intended direction, said stress being one of the stresses which occur in an axle of a vehicle such as a transporting machine, e.g., an automobile, airplane or railroad vehicle, and in a structure having a fixed support point adjacent the axle, the conditions for the optimum position (neutral spot) where a stress sensor is to be mounted are indicated, and it also relates to a stress detecting method and a stress detecting device, adapted to accurately measure only a strain resulting from a stress acting in an aimed direction by further separating a plurality of stresses acting on the stress sensor. As for methods for measuring stresses, strains or the like acting on or adjacent to an axle of a transporting machine, such as an automobile, airplane or railroad vehicle, mention may be made of the photoelasticity method, brittle coating method, caustic method, holographic method and strain gauge method, of which generally the strain gauge method has been used most frequently. The strain gauge method is convenient to use since a variety of strain gauges are available. In this method, a strain gauge is used for stress measurement by being built in a transducer to serve as a stress sensor. If necessary, a plurality of strain gauges are attached to an axle of a vehicle or a structure adjacent an axle. In this method, however, the sensor is subjected to the stresses acting on the strain gauge in every direction; therefore, analysis is necessary, and it is difficult to measure only a strain resulting from a stress acting in an aimed direction. Few of the stress sensors using strain gauges are capable of cancelling all but one strain acting in an aimed direction, and there is no perfect one. US 5,186,042 and EP-A-0 611 958 describe a wheel-acting force measuring device, wherein a stress sensor is embedded in a hole situated at the centre axis of the device. These publications also provide a calculation method for eliminating crosstalks, such as axle-torque. SUMMARY OF THE INVENTION A conventional stress sensor will detect stresses acting thereon in a plurality of directions; therefore, even if it is desired to detect only a strain resulting from a stress acting in an aimed direction, it has only been possible to detect a stress containing crosstalk acting in other directions. Alternatively, it has been necessary to attach stress sensors in a plurality of positions so as to measure and remove unnecessary stresses With the above in mind, the present invention provides a stress detecting and measuring method and a stress detecting device wherein in order to detect only a stress acting in an aimed direction, said stress being one of a plurality of stresses acting on a stress sensor in a plurality of directions, the position where the stress sensor is to be mounted on a structure is selected such that it is the position where crosstalks are minimized (said position being referred to as the neutral spot). A stress measurement method according this idea is described in claim 1. The arrangement effectively decreases the noises such as crosstalks, making it possible to measure the necessary stress. According to the invention as described in Claim 2 an axle of a vehicle or a structure having a fixed support point adjacent the axle is three-dimensionally represented to perform simulations using the FEM, so as to find the respective transformation knot zones (zones where shearing stress is minimum, hereinafter the same) of the different directions. Then, the obtained data on the transformation knot zones are superposed to find a neutral spot, in which only a shearing stress acting in the aimed direction is measured. In the case where external forces are applied in two directions to an axle of a vehicle or a structure having a fixed support point adjacent the axle, when a shearing strain resulting from a stress acting in one direction is to be measured, a stress sensor is mounted in a position which is the transformation knot zone of the unnecessary stress and which is suitable for measuring the necessary stress, i.e., a position which is not the transformation knot zone of the necessary stress, with the result that stresses acting in the unaimed directions are not detected because of the positioning in the transformation knot zone but a shearing strain alone resulting from a stress acting in the aimed direction is measured. Thereby, a shearing strain alone resulting from a stress acting in the aimed direction can be measured. Concretely, two shearing stress distributions are investigated by means of FEM to find a neutral spot, and a stress sensor will be mounted at the neutral spot. In the case where external forces are applied in three or more directions to an axle of a vehicle or a structure having a fixed support point adjacent the axle, when a shearing strain alone resulting from a stress acting in an aimed direction is to be measured, a stress sensor is mounted in a zone (line or plane) where the transformation knot zones of the unnecessary stresses cross each other, i.e., in a position which is a neutral spot and which is suitable for measuring the necessary stress. If the transformation knot zones of stresses in two or more directions do not cross each other, a stress sensor is mounted at a neutral spot adjacent the tranformation knot zone capable of detecting the stress acting in the aimed direction. The stress distributions of the respective stresses change in a continuous zone resembling a contour line. Therefore, much mixing-in of stresses does not take place even in the vicinity of the transformation knot zone, and only a shearing strain resulting from a stress acting in the aimed direction is measured. According to the aspect of the invention as described above, in the case where a plurality of external forces are applied to an axle of a vehicle or a structure having a fixed support point adjacent the axle, when the transformation knot zones of stresses in two or more directions do not cross each other, stresses acting in unaimed directions are not detected since they lie in or adjacent the transformation knot spot or even if they are detected, crosstalks are very few, so that only a shearing strain resulting from a stress acting in an aimed direction can be measured. Concretely, the required steps are to investigate the stress distribution to find the transformation knot zone for the stress component using FEM, to find a neutral spot where as many transformation knot zones as possible are superposed, and to mount a stress sensor at the neutral spot . In order to completely remove crosstalks applied to the stress sensor, the stress sensor employed in the pressent invention is preferably one of the one-segment type in which four pressure resistance strain gauges.are disposed on the upper and lower surfaces of the sensor board such that they are divided in pairs with the two in each pair crossing each other, so as to selectively measure a stress alone acting in a certain direction or a plurality of stresses. The employment of a stress sensor of the one-segment type makes it possible to obtain a stress acting in an aimed direction since crosstalks can be cancelled by the bridge circuit of the stress sensor even if stresses acting in unaimed directions are in the vicinity of the transformation knot spot. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view showing a compressive region, a tensile region and a transformation knot zone in a structure having a fixed support point; and Fig. 2 is a flowchart for a stress detecting and measuring method. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described as to a stress detecting method as an example with reference to an illustrated embodiment. In addition, what is shown herein is an example of a preferred embodiment, and Claims are not limited thereto. Fig. 1 is a view in which an axle of a vehicle or a structure adjacent the axle ( A ) is considered to be a structure having a simple fixed support point (line or plane). When a stress is applied to this structure A in a direction of arrow P , in a stress distribution, a region where a tensile stress is produced with respect to the fixed support point (line or plane) is named b , and a region where a compressive stress is produced is named a . Disposed between these two regions is a region where neither tensile stress nor compressive stress is produced, i.e., a transformation knot zone c , said region being referred to as the shearing stress zone. In this transformation knot zone, strain resulting from shearing stress can be detected with little influences of tensile stress, compressive stress, bending stress, torsion and the like. Fig. 2 shows in the form of a flowchart the processing according to a vehicle stress detecting and measuring method and a stress detecting device. As for the contents of the operation, at the step 10 a vehicle axle structure on which a stress sensor is to be mounted is selected and then the processing goes to a three-dimensional modeling at the step 11 and step 12. Then the processing goes to the step 13, where a FEM analysis is made as to the necessary stress. Then at the step 14, the analysis data is printed out, and then it goes to the step 15, where an analysis of transformation knot zone is made on the basis of the analysis data. Then at the step 16, the position in which the stress sensor is to be inserted is determined on the basis of the transformation knot zone analysis and a drawing for machining the structure is prepared. Then it goes to the step 17, where an inspection of the machining drawing is made and if it is found faulty, the processing goes back to the step 13, where an FEM analysis is made again, followed by a transformation knot zone analysis on the basis of the analysis data. If the machining drawing is found faultless, the processing goes to the step 18, where the structure is drilled on the basis of the machining drawing. Then at the step 19, the stress sensor is inserted in the hole in the structure on the basis of the machining drawing. And at the step 20, if appropriate data is obtained from the stress sensor, this routine ends here. In addition, the stress sensor used is of a one-segment type, disclosed in the present applicant's Japanese Patent Application No. 130840/91 (Japanese Patent Kokai No. 331336/92), in which four strain gauges are disposed on the opposed upper and lower surfaces of a board such that they are divided in pairs with the two in each pair crossing each other, said stress sensor being mounted in a hole formed in a structure, the strain gauges being built in a bridge circuit, whose output is arithmetically processed. The stress produced in the structure is transmitted to the strain gauges of pressure resistances through the stress sensor board, so that the strain gauges change in resistance. The resistance change of strain gauges has a regularity depending upon the direction of stress, and logical operations are made by making use of this regularity, so as to find the shearing stress acting in the aimed direction. EFFECTS OF THE INVENTION According to the present invention, even in an axle of a vehicle or a complicated structure, such as one disposed adjacent the axle, only a shearing strain resulting from a external force acting in an aimed direction can be detected and measured by making an FEM analysis of stresses acting in a plurality of directions and detecting the neutral spot Therefore, it is possible to accurately measure stresses acting on an axle of a vehicle or a structure adjacent the axle, such as road surface friction forces, transverse forces, vertical loads, brake torques, driving torques, road surface friction coefficients and the like, which will not be influenced by crosstalks. Thus, the invention, if applied to control for anti-lock brake devices or traction control devices for vehicles, remarkably improves the reliability of necessary input signals and enables a quick and accurate control decision to be made under any road condition,- thereby bringing about a remarkable improvement in the performance of anti-lock brake devices and traction control devices. Further, even if the neutral spot is not detected in a perfect form, the present stress sensor can be satisfactorily used even in the vicinity of the transformation knot zone. Further, the employment of a one-segment type stress sensor makes it possible to detect only a shearing strain resulting from a stress acting in an aimed direction without including crosstalks.

Claims: A method of detecting and measuring stress resulting from external forces acting on a vehicle structure (e) using a stress sensor (g), including the following steps: defining the directions of all external forces acting on the structure (e), investigating a first shearing stress distribution resulting from the external force that acts in one direction, investigating at least one second shearing stress distribution resulting from the external force that acts in at least one direction other than the one to be measured, finding the position where the shearing stress in the first distribution is detectable and the shearing stress(es) in the at least one second distribution is/are minimum, mounting the stress sensor (g) at the position thus found, and delivering the shearing stress value measured. A method of detecting and measuring stress resulting from external forces acting on a vehicle structure (e) having an axle or a fixed support point adjacent to the axle, using a stress sensor (g), including the following steps: representing the structure (e) in a three-dimensional graphical form, performing simulations to produce a situation where a plurality of external forces are simultaneously acting on the structure (e) at one point or at a plurality of points, using the finite element method, investigating shearing stress distributions resulting from the respective external forces, finding in the shearing stress distributions a transformation knot zone (c) of each stress resulting from each external force not to be measured, in which transformation knot zone (c) the shearing stress is at the minimum, finding a neutral spot at which the stress to be measured is detectable and crosstalks are minimum, by using the transformation knot zone(s) obtained, and mounting the stress sensor (g) at said neutral spot. The method of claim 2 wherein, when external forces are acting on the vehicle structure (e) in two directions simultaneously, the stress sensor (g) is mounted at the neutral spot situated in the transformation knot zone found (c). The method of claim 2 wherein, when external forces are acting on the vehicle structure (e) in three or more directions simultaneously, the neutral spot is situated in a zone where the transformation knot zones found (c) cross each other, or in one of the transformation knot zones found (c) and adjacent to the other transformation knot zone(s) found, if said transformation knot zones (c) do not cross each other. The method of any preceding claim, wherein a stress sensor (g) of the one-segment type is used in which four pressure resistance strain gauges are disposed on the upper and lower surfaces of a sensor board such that they are divided in pairs, wherein the two in each pair are crossing each other.

Inventors: MIYAZAKI NAGAO, MIYAZAKI, NAGAO, Miyazaki, Nagao, c/o Japan Elecronics Ind. Ltd.
Applicants: JAPAN ELECTRONICS IND LTD, JAPAN ELECTRONICS INDUSTRY, LTD.
Application year: 1995
Main classification: G01L5
IPC codes: G01L1, G01L5