JP6231898B2 - Method for determining the ground cable connection point of a vehicle - Google Patents

Description

  The present invention relates to a method for determining a ground point for connecting a power system ground cable and a ground point for connecting a signal system ground cable from a plurality of ground points provided in a vehicle.

  Some electrical components mounted on the vehicle require grounding. Such an electrical component is connected to any one of ground points provided at a plurality of locations in the vehicle via a ground cable. High-frequency switching noise may be superimposed on the current flowing through the ground cable due to on / off of power supply to the electrical component.

  When the electrical component is connected to the ground point by the ground cable, a feedback current flows through the metal structure provided with the ground point from the ground point to the ground point to which the negative electrode of the power source of the electrical component is connected. This feedback current is the same direct current as the power supply, but if high-frequency switching noise is superimposed on the current flowing through the ground cable, a high-frequency alternating current component is also superimposed on the feedback current.

  Here, the feedback path of the alternating current (high frequency) component of the feedback current concentrates on the path directly below the ground cable when the frequency is high, but when the frequency is low, the ground point to which the electrical components are connected and the ground point to which the power supply is connected The property of trying to return through the shortest path connecting the two, that is, the feedback path of the direct current component, becomes stronger.

  Therefore, the AC component due to switching noise superimposed on the current flowing through the ground cable passes through the feedback path of the DC component of the feedback current at the ground point where the power source is connected from the ground point where the electrical components are connected by the ground cable. It flows with strength according to the nature of the return.

  For this reason, if the impedance between the ground point where the electrical component is connected by the ground cable and the other ground point serving as the feedback path for the DC component of the feedback current is small, high-frequency switching noise superimposed on the current flowing through the ground cable However, there is a possibility of propagation to other earth points due to the AC component of the feedback current flowing between the two earth points.

  By the way, not only the earth cable from an electrical component but the shield line of the communication cable which transmits the control signal in a vehicle is connected to an earth point. Therefore, if the impedance between the earth point to which the shielded cable of the communication cable is connected and the earth point to which the earth cable is connected is small, the switching noise of the earth cable propagates through both earth points and the current flowing through the shielded cable is also noisy. May appear.

  When noise propagates to the current flowing through the shielded wire, noise also appears in the current of the signal line that is capacitively coupled and inductively coupled to the shielded cable of the communication cable, and malfunction due to noise occurs at the signal transmission destination of the signal line. A possibility arises.

  To prevent or suppress the propagation of noise from the ground cable to the shield wire of the communication cable, it is effective to connect the shield wire of the communication cable to a ground point having a large impedance between the ground point and the ground point to which the ground cable is connected. It is.

  For impedance measurement between two earth points, for example, it has been proposed to create a ground resistance network model for each of an engine room ground system and a body ground system (for example, non-patent). Reference 1).

H. Lim, D. Lee, S.S.Ok and J. Park, Analysis of an Automotive Ground System Based on its Steady-State Model, International Journal of Automotive Technology Vol.11, No.6, pp.865-871 (2010)

  By the way, the impedance between two earth points measured by the ground resistance network model of Non-Patent Document 1 is not the impedance of only the shortest path directly connecting the two earth points. What is measured here is a composite impedance obtained by synthesizing impedances of other paths that are circuit-parallel to the shortest path via another ground point on the same metal structure.

  For this reason, even if the connection destination of the shield wire of the ground cable or the communication cable is determined based on the impedance between the two ground points measured by the ground resistance network model of Non-Patent Document 1, the communication cable from the ground cable It is difficult to prevent or suppress the propagation of noise to the shield wire.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a shielded cable (signal system ground) for a communication cable even if high-frequency noise is superimposed on the current flowing through the power system ground cable from the electrical component. An object of the present invention is to provide a vehicle ground cable connection point determination method capable of preventing or suppressing high-frequency noise from propagating to a cable.

In order to achieve the above object, a vehicle ground cable connection point determination method according to the present invention as set forth in claim 1 comprises:
A method for determining an earth point for connecting a power system ground cable and a ground point for connecting a signal system ground cable from a plurality of ground points provided in a vehicle,
A measurement step of sequentially measuring the impedance between the ground point at which the high-frequency current is injected at the reference point to which the vehicle is grounded, while switching the ground point to which the high-frequency current is injected,
A specific step of specifying an inductance between two ground points for each of two arbitrary points from the measured impedance between each ground point and a reference point;
A classification step for converting each inductance between the two specified earth points into a spatial distance, and classifying each ground point by cluster analysis according to the magnitude of the converted spatial distance;
Connection destinations for determining the ground point for connecting the power system ground cable and the ground point for connecting the signal system ground cable as ground points of different coupling levels on the dendrogram showing the classification result by the cluster analysis. A decision step;
It is characterized by including.

  According to the vehicle ground cable connection point determination method of the present invention as set forth in claim 1, the impedance Z between the ground potential reference point and each ground point measured in the measurement step is the resistance (resistance) of the real part. When the component) is R and the reactance of the imaginary part is X, it is expressed by the equation Z = R + jX.

  Among these, the reactance X of the imaginary part represents an alternating current component of the impedance Z, and the larger the reactance X, the more difficult the alternating current component of the current flows between the ground points of the impedance Z.

  However, the impedance Z measured in the measurement step is a combination of the impedance of the shortest path that connects the reference point and the earth point with a straight line and the impedance of the path that passes through another earth point that is circuit-parallel to the shortest path. Impedance. Therefore, it is impossible to directly grasp the difficulty of the flow of the alternating current component of the current in the shortest path connecting the ground points with a straight line from the impedance Z measured in the measurement step.

  In other words, when high-frequency switching noise is superimposed on the current flowing through the power system ground cable, the ease of transmission of high frequency noise from the ground point connected to the power system ground cable to other ground points (difficulty of transmission) Is difficult to directly evaluate by the value of the impedance Z of the earth point.

  By the way, when the high-frequency switching noise is superimposed on the current flowing through the power system ground cable, the resistance R is sufficiently smaller than the reactance X at the ground point to which the ground cable is connected (R << X). For this reason, the impedance Z of the ground point to which the power system ground cable is connected can be considered as Z≈jX.

  When the angular frequency of the feedback current from the ground point connected to the power system ground cable is ω and the inductance of the ground point connected to the power system ground cable is L, the reactance X is expressed by the equation X = ωL. Can be represented. When the frequency of the high frequency component of the feedback current is f, the angular frequency ω can be expressed as ω = 2πf.

  For this reason, the scalar quantity | Z | of the impedance Z of the ground point connected to the power system ground cable can be expressed as | Z | ≈2πfL using the inductance L of the ground point connected to the power system ground cable. it can.

  Here, the inductance L of the earth point is a ratio of the induced electromotive force generated by the change of the current flowing through the earth point to the current change rate. Unlike the impedance Z, this ratio is a value independent of the path between the reference point and the ground point. This ratio can be considered to be a value representing the difficulty (easy to transmit) of the high frequency noise included in the current flowing through the earth point to the reference point.

  An inductance exists between two ground points having a difference in inductance L between the reference point and the higher the inductance, the more difficult high-frequency noise is transmitted between the two ground points. In this way, a set of ground points having inductance between each other can be obtained by selecting two ground points having different inductances converted to a spatial distance from the ground points classified in the classification step.

  Therefore, in the connection destination determining step, one of the two ground points existing at different coupling levels on the dendrogram is set as a connection destination of the power system ground cable, and the other is set as a connection destination of the signal system ground cable. As a result, when high-frequency switching noise is superimposed on the current flowing through the power system ground cable, the high frequency noise is transmitted from the ground point connected to the power system ground cable to the ground point connected to the signal system ground cable. It can be difficult.

  The reference point for measuring the impedance may be another earth point excluding the earth point to which the high-frequency current is injected, or may be any point on the frame (chassis) other than the earth point. Good.

  The vehicle earth cable connection point determination method according to the present invention described in claim 2 is the vehicle earth cable connection point determination method according to the present invention described in claim 1, wherein the measurement step is performed at the reference point, The resistance between the earth point where DC current is injected is sequentially measured while switching the earth point to which the DC current is injected, and the resistance between each earth point and the reference point is measured. The resistance measurement step is obtained for each of two arbitrary points, and the classification step converts each obtained resistance between the two earth points into a spatial distance, and according to the magnitude of the converted spatial distance. , Including a resistance classification step of classifying each earth point by cluster analysis, Determine the ground point for connecting each ground cable of the power system as one of the ground points with the closest resistance in terms of the spatial distance, and set the ground point for connecting each ground cable for the signal system to the spatial distance. The converted resistance is determined to be one of the earth points that are close.

  According to the vehicle earth cable connection point determining method of the present invention described in claim 2, in the vehicle earth cable connection point determining method of the present invention described in claim 1, the power system ground cables are connected to each other. Are connected to ground points where the voltage drop due to resistance is small or does not occur, and the signal system ground cables are also connected to ground points where the voltage drop due to resistance is small or does not occur.

  Therefore, the potential difference is prevented or suppressed from occurring between the ground points connected to the power system ground cables, and the potential difference is also prevented or suppressed from occurring between the ground points connected to the signal system ground cables. can do.

  In addition, when high-frequency switching noise is superimposed on the current flowing through the power system ground cable, high-frequency noise is generated from the ground point connected to the power system ground cable to the ground point connected to the signal system ground cable. It can be made difficult to communicate.

  According to the present invention, even when high-frequency noise is superimposed on the current flowing through the power system ground cable from the electrical component, the ground point connected to the power system ground cable is connected to the ground point via another ground point. It is possible to prevent or suppress high-frequency noise from propagating to the signal system ground cable.

It is explanatory drawing which shows the earth point of the vehicle by which the connection destination of an earth cable is determined by applying this invention. It is explanatory drawing which shows the equivalent circuit formed through a body and a frame (chassis) between each earth | ground point of FIG. It is a flowchart which shows the procedure which determines the ground point which connects the ground cable of the signal system | strain of FIG. It is a flowchart which shows the specific procedure of the measurement step of FIG. It is a flowchart which shows the specific procedure of the classification | category step of FIG. It is explanatory drawing which shows the procedure which converts the resistance value between each earth point into a spatial distance in the resistance classification step of FIG. It is explanatory drawing of the dendrogram showing the classification result of the spatial distance converted from the resistance value in the procedure of FIG.

  The present invention will be described below with reference to the drawings. First, with reference to the explanatory diagram of FIG. 1, a description will be given of a ground point of a vehicle in which a ground cable connection point is determined by the ground cable connection point determination method of the present invention. The body or frame (chassis) which is a metal structure of the vehicle 1 shown in FIG. 1 is provided with 16 earth points AA to AF, C1, E2, EK to EM, L0, LN, MP, NQ, and QR. ing.

  These earth points AA to AF, C1, E2, EK to EM, L0, LN, MP, NQ, and QR are electrically connected to each other via the body and frame (chassis) of the vehicle 1, Therefore, an equivalent circuit shown in FIG. 2 is formed between the ground points.

  A battery (not shown) or a negative electrode of an alternator is connected to one of the ground points shown in FIG. 1 for grounding (grounding). In addition, a power system ground cable P from an electrical component (not shown) of the vehicle 1 to which power is supplied from a battery, and a shield wire (signal system ground cable) S for a signal transmission cable using a coaxial cable, Connected to any earth point for grounding.

  As described in the section of the background art, there may be a case where a current containing high-frequency switching noise flows through the ground point to which the power system ground cable P is connected as the power supply is turned on / off for an electrical component (not shown). Then, switching noise may propagate to another earth point due to an alternating current (high frequency) component of the feedback current from the earth point to which the power system earth cable P is connected.

  Therefore, in the present embodiment, in order to prevent or suppress the switching noise from propagating to the signal ground cable S connected to another ground point, the ground point to which the power ground cable P is connected; An earth point having an inductance between them is a connection destination of the signal system earth cable S.

  The procedure for determining the ground point to which the power ground cable P and the signal ground cable S satisfying such conditions will be described with reference to FIGS.

  As shown in the flowchart of FIG. 3, in this embodiment, the measurement step (step S1), the identification step (step S3), the classification step (step S5), and the connection destination determination step (step S7) are sequentially performed.

  In the measurement step of step S1, as shown in the flowchart of FIG. 4, a resistance measurement step (step S11) and an impedance measurement step (step S13) are performed.

  In the resistance measurement step of step S11, any one of the 16 ground points AA to AF, C1, E2, EK to EM, L0, LN, MP, NQ, QR is grounded as a reference point, and each of the remaining 15 locations Measure the resistance between the earth point and the reference point.

  Specifically, the ground point for passing a DC current Id of a known magnitude to the body or frame (chassis) of the vehicle 1 is sequentially replaced among the 15 ground points other than the reference point so that the DC current Id flows. The voltage Vd (potential difference between the ground point through which a direct current is passed) and the reference point is measured.

  Then, the measured voltage Vd of each earth point is applied to each earth point of the equivalent circuit of FIG. 2 to determine the resistance R between the earth point as the reference point and the other 15 earth points. This procedure is performed by sequentially replacing the ground point as a reference point among the 16 ground points, thereby obtaining the resistance R between the ground points of the equivalent circuit of FIG.

  In the impedance measurement step of step S13, any of the 16 earth points AA to AF, C1, E2, EK to EM, L0, LN, MP, NQ, QR is grounded as a reference point, and the remaining 15 points Measure the impedance between each earth point and the reference point.

  Specifically, the ground point for passing an AC current Ia of a known magnitude to the body or frame (chassis) of the vehicle 1 is sequentially replaced among the 15 ground points other than the reference point, thereby passing the AC current Ia. The voltage drop ΔVa and the alternating current Ia between the measured earth point and the reference point are measured with an oscilloscope or the like. Then, from the measured voltage drop ΔVa and the alternating current Ia, an impedance Z (| Z | = ΔVa / Ia) between the ground point through which the alternating current Ia flows and the reference point is obtained.

  At this time, the frequency of the alternating current Ia is changed to at least two different frequencies, and the impedance Z described above is obtained for each frequency.

  This procedure is performed by sequentially replacing the ground point as a reference point among the 16 ground points, thereby obtaining the impedance Z between the ground points of the equivalent circuit of FIG.

  Note that the resistance measurement step in step S11 and the impedance measurement step in step S13 may be performed in a reversed order.

  In the specifying step of step S3 in FIG. 3, the inductance between the ground points is specified from the impedance Z between the ground points measured in the impedance measurement step of step S13.

  The impedance Z between the ground points measured in step S13 is expressed by the equation Z = R + jX where R is the resistance (resistance component) of the real part and X is the reactance of the imaginary part.

  Among these, the reactance X of the imaginary part represents an alternating current component of the impedance Z, and the larger the reactance X, the more difficult the alternating current component of the current flows between the ground points of the impedance Z.

  However, the impedance Z between the ground points measured in step S13 is the impedance of the shortest path connecting the ground points with a straight line and the impedance of the path via another ground point that is in circuit parallel to the shortest path. Is the combined impedance. Therefore, it is impossible to directly grasp the difficulty of the flow of the alternating current component of the current in the shortest path connecting each earth point with a straight line from the impedance Z measured in step S13.

  That is, when an alternating current Ia flows through a certain ground point, the ease of transmission (difficulty of transmission) of the alternating current component of the alternating current Ia to other ground points is measured between the ground points measured in step S13. It is difficult to evaluate directly by the value of impedance Z.

  By the way, in the impedance measurement step of step S13, since the AC current Ia having a known magnitude is passed through the ground point, the resistance R component in the impedance Z between the ground points is sufficiently smaller than the reactance X component. (R << X). For this reason, the impedance Z measured in step S13 can be considered to be almost a component of reactance X (Z≈jX).

  The inductance of the ground point through which the alternating current Ia having a known magnitude is passed is L, and the angular frequency of the feedback current that returns from the ground point to the ground point of the reference point through the body or frame (chassis) of the vehicle 1 is ω. In this case, the reactance X between the two ground points can be expressed by the equation X = ωL. When the frequency of the alternating current Ia is f, the angular frequency ω can be expressed by ω = 2πf.

  For this reason, the scalar quantity | Z | of the impedance Z of the earth point through which the alternating current Ia is passed can be expressed as | Z | ≈2πfL using the inductance L of the earth point.

  Here, the inductance L of the ground point through which the alternating current Ia flows is a ratio of the induced electromotive force generated at the ground point to the current change rate of the alternating current Ia. Unlike the impedance Z, this ratio is a value irrelevant to the feedback path of the AC component of the feedback current flowing between the two ground points. This ratio can be considered to be a value representing the difficulty (easy to transmit) of the high frequency component (noise) of the alternating current Ia flowing through the earth point to the other earth point.

  Therefore, in the specifying step of step S3, the inductance L between the ground points is calculated and specified from the slope of the change with respect to the frequency of the impedance Z measured in step S13 using the expression | Z | ≈2πfL.

  In the classification step of step S5 in FIG. 3, a resistance classification step (step S51) and an inductance classification step (step S53) are performed.

  In the resistance classification step of step S51, as shown in the flowchart of FIG. 5, the resistance R between the earth points measured in the resistance measurement step of step S11 is classified according to the magnitude of the resistance value by cluster analysis.

  When classifying the resistance R between each earth point by cluster analysis, first, as shown in the explanatory diagram of FIG. 6, the resistance value between each earth point in the upper table is changed to the spatial distance in the lower table. Convert each. The spatial distance converted from the resistance value can be expressed by Euclidean distance, Manhattan distance, or the like.

  Next, the spatial distance regarding the resistance R between each earth point converted from the resistance value is classified (clustered) by cluster analysis (hierarchical clustering). As the algorithm used for hierarchical clustering, known algorithms such as the WARD method, the shortest distance method, the median method, and the centroid method can be used. In this embodiment, a case where the WARD method is used will be described as a representative.

  In the classification of the spatial distance by the WARD method, two earth points having the smallest spatial distance are combined into one cluster. Next, two ground points having the smallest spatial distance other than the combination of the two ground points already joined are joined. At this time, if one or both of the two earth points are already combined with another earth point or cluster to form a cluster, the entire cluster is combined with the other earth point or cluster to create a new 1 One cluster.

  By repeating this operation until all the earth points and clusters are combined into one cluster, each earth point is classified according to the spatial distance. The result can be represented by a dendrogram shown in the explanatory diagram of FIG. In the dendrogram of FIG. 7, the horizontal axis indicates the classification position of each earth point, and the vertical axis indicates the coupling level of two earth points or clusters. The coupling level is higher as it goes up, and the height of the coupling level indicates the low similarity of the spatial distance between two earth points or clusters.

  In the inductance classification step of step S53 in FIG. 5, the inductance L between the ground points specified in the specific step of step S3 is classified according to the magnitude of the inductance value by cluster analysis.

  When classifying the inductance L between each earth point by cluster analysis, the inductance value between each earth point is a space such as Euclidean distance or Manhattan distance, as in the case of classifying the resistance R between each earth point by cluster analysis. Convert to distance. Then, the converted spatial distance is clustered by cluster analysis using, for example, the WARD method.

  Note that the resistance classification step in step S51 and the inductance measurement step in step S53 may be performed in a reversed order.

  In the connection destination determination step of step S7 in FIG. 3, the shield wire of the power system ground cable P or signal transmission cable based on the classification result of the resistance classification step of step S51 of FIG. 5 or the inductance classification step of step S53. (Signal system ground cable) The ground point of the connection destination of S is determined.

  First, a potential difference is generated between the ground points having a large resistance value due to a voltage drop caused by a feedback current flowing. For this reason, it is not preferable that a plurality of power system ground cables P or a plurality of signal system ground cables S be distributed and connected to a plurality of ground points having a large resistance value.

  For this reason, when a plurality of power system ground cables P are distributed and connected to a plurality of ground points, the ground points having a resistance value as small as possible are selected and the power system ground cables P are connected. preferable. Similarly, when a plurality of signal system ground cables S are distributed and connected to a plurality of ground points, ground points having a resistance value as small as possible are selected and the power system ground cables P are connected. preferable.

  An earth point having a small resistance value can be selected by identifying an earth point having a resistance R converted to a spatial distance from the earth points classified in the resistance classification step of step S51 in FIG. .

  Next, when a current containing high-frequency switching noise caused by turning on / off a power supply for an electrical component (not shown) flows to the ground point to which the power system ground cable P is connected, the power system ground cable P is connected. Switching noise may propagate to a signal ground cable S connected to another ground point due to the alternating current (high frequency) component of the feedback current from the ground point.

  Therefore, in order to prevent or suppress the switching noise of the power system ground cable P from propagating to the signal system ground cable S, the ground point for connecting the power system ground cable P and the signal system ground cable S are provided. An inductance L is preferably present between the ground point to be connected.

  An earth point having an inductance L between them is selected by identifying two earth points having different inductances L converted to a spatial distance from the earth points classified in the inductance classification step of step S53 in FIG. be able to.

  As described above, in the connection destination determination step of step S7 in FIG. 3, each ground point to which each power system ground cable P is connected is set to one of the ground points at which the resistance value between the ground points is minimized. decide. In addition, the ground point to which each ground cable S of the signal system is connected is determined to be one of the ground points at which the resistance value between the ground points is minimized.

  Then, the ground point of each connection destination is determined so that an inductance L exists between the ground point to which the power system ground cable P is connected and the ground point to which the signal system ground cable S is connected. .

  As described above, according to the ground cable connection point determination method of the present embodiment, between the ground point to which the power system ground cable P is connected and the ground point to which the signal system ground cable S is connected. The ground point of each connection destination is determined using the result of clustering the ground points by cluster analysis according to the size of the spatial distance converted from the inductance L so that the inductance L exists.

  For this reason, when high-frequency switching noise is superimposed on the current flowing through the power system ground cable P due to the on / off of the power supply to the electrical components, the signal system from the ground point to which the power system ground cable P is connected. It is possible to prevent high-frequency noise from being easily transmitted to the ground point to which the ground cable S is connected.

  As a result, high-frequency noise appears in the signal system ground cable S, that is, the shield line of the signal transmission cable using the coaxial cable, and noise also occurs in the signal line of the coaxial cable that is capacitively and inductively coupled with the shield line. It is possible to prevent or suppress the occurrence of a possibility that a malfunction occurs at the signal transmission destination due to the noise.

  In addition, the ground point that connects each power system ground cable P is a ground point that causes little or no voltage drop due to resistance between them, and the ground point that connects each signal system ground cable S also includes: In order to make a ground point where the voltage drop due to resistance is small or not between each other, the ground point is clustered by cluster analysis according to the size of the spatial distance converted from the resistance between the ground points. Whether or not to determine the earth point is arbitrary.

  In the present embodiment, the case where the signal-system ground cable S is a shielded wire of a coaxial cable for signal transmission has been described. However, for example, a wiring pattern for signal transmission on a grounded wiring board can also be an object to which the present invention is applied as a signal ground cable.

  INDUSTRIAL APPLICABILITY The present invention is extremely useful when determining a ground point for connecting a power system ground cable and a ground point for connecting a signal system ground cable from a plurality of ground points provided in a vehicle. .

1 Vehicle AA to AF, C1, E2, EK to EM, L0, LN, MP, NQ, QR Earth point P Power system ground cable S Signal system ground cable

Claims (2)

A method for determining an earth point for connecting a power system ground cable and a ground point for connecting a signal system ground cable from a plurality of ground points provided in a vehicle,
A measurement step of sequentially measuring the impedance between the ground point at which the high-frequency current is injected at the reference point to which the vehicle is grounded, while switching the ground point to which the high-frequency current is injected,
A specific step of specifying an inductance between two ground points for each of two arbitrary points from the measured impedance between each ground point and a reference point;
A classification step for converting each inductance between the two specified earth points into a spatial distance, and classifying each ground point by cluster analysis according to the magnitude of the converted spatial distance;
Connection destinations for determining the ground point for connecting the power system ground cable and the ground point for connecting the signal system ground cable as ground points of different coupling levels on the dendrogram showing the classification result by the cluster analysis. A decision step;
A method for determining a ground cable connection point of a vehicle.   In the measurement step, the resistance between the reference point and the earth point into which the direct current is injected is sequentially measured while switching the earth point to which the direct current is injected, and the measurement point between the measured earth point and the reference point is measured. A resistance measuring step for obtaining a resistance between two ground points from any two points, respectively, and the classification step converts each obtained resistance between the two ground points into a spatial distance, A resistance classification step of classifying each ground point by cluster analysis in accordance with the converted spatial distance, and in the connection destination determination step, the ground point for connecting each ground cable of the power system, Each earth cable of the signal system is determined to be one of the earth points with the closest resistance in terms of clearance. The ground points respectively connecting the vehicle ground cable attachment point determination method according to claim 1, wherein a resistance in terms of the spatial distance is determined to either the near earth point.

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