JP2012177652A - Electronic control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic control device capable of preventing malfunction of a passenger protection device, by detecting exactly acceleration which acts on a vehicle even if having a resin case.SOLUTION: An electronic control device comprises: a print circuit board mounted by an acceleration sensor; and a case for housing the print circuit board. The case is a resin case, and the acceleration sensor is arranged near a fixing part between the resin case and the print circuit board on the print circuit board.

Description

 The present invention relates to an electronic control device.

In recent years, in order to improve vehicle safety performance, an electronic control unit (ECU) called an SRS (Supplemental Restraint System) unit that controls activation of an occupant protection device such as an air bag at the time of a vehicle collision is installed in the vehicle. It is installed.
The SRS unit includes a printed circuit board on which an acceleration sensor and other electronic components are mounted, and a metal (aluminum die-cast) case that houses the printed circuit board. The printed circuit board has a plurality of screw holes, and is fixed to the inside of the case by being screwed to pins provided in the case (see Patent Document 1 below).

Japanese Patent Laid-Open No. 9-207706

  In the conventional SRS unit, since the case is made of metal (made of aluminum die cast), vibration transmission is good, so there is no particular standard for the position of the acceleration sensor on the printed circuit board. In many cases, it is arranged in the upper dead space (an area that is not utilized) or near the center of the printed circuit board. In recent years, there has been a case where the case is changed from metal to resin due to the low price system of the SRS unit or the cost reduction of the SRS unit. In this case, changing the material of the case from metal to resin changes the vibration transmission due to a decrease in the rigidity of the housing.Therefore, depending on the position of the acceleration sensor, the vibration may occur on the printed circuit board. When a resonance phenomenon occurs, the resonance phenomenon is detected as a large acceleration change, which may cause a malfunction of the occupant protection device.

   The present invention has been made in view of the above-described circumstances, and an electronic control device provided with a resin case accurately detects acceleration acting on a vehicle, thereby preventing malfunction of the occupant protection device. It is an object of the present invention to provide an electronic control device capable of the following.

 In order to achieve the above object, an electronic control device according to the present invention is an electronic control device including a printed circuit board on which an acceleration sensor is mounted, and a resin case that houses the printed circuit board, and the acceleration sensor includes: It is arrange | positioned in the vicinity of the fixed location of the said resin case and the said printed circuit board on the said printed circuit board.

The applicant conducted a vibration test with the printed circuit board fixed to the resin case, and analyzed the acceleration level frequency response characteristics of each acceleration sensor mounting candidate position on the printed circuit board. It has been found that the closer the position is to the fixing position between the resin case and the printed board on the printed board, the lower the sensitivity of the acceleration sensor with respect to the resonance phenomenon of the printed board, and the present invention has been filed.
In other words, according to the present invention, the acceleration sensor is disposed in the vicinity of the fixing portion between the resin case and the printed circuit board on the printed circuit board, so that the acceleration acting on the vehicle can be detected accurately, and thus the occupant protection device is erroneously detected. It becomes possible to prevent the operation.

It is a disassembled perspective view of SRS unit 1 (electronic control device) concerning this embodiment. It is a figure which shows the result of the vibration test implemented in the state in which the printed circuit board 2 was fixed to the resin case 3.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following drawings, the scale of each member is appropriately changed in order to make each member a recognizable size.
FIG. 1 is an exploded perspective view of the SRS unit 1 according to the present embodiment. The SRS unit 1 is an electronic control unit (ECU) that is mounted on a vehicle and controls activation of an occupant protection device such as an air bag in the event of a vehicle collision. 3 is provided.

 The printed circuit board 2 is a rectangular multilayer board having an acceleration sensor 2a, a connector 2b, and other electronic components (not shown) necessary for starting control of other occupant protection devices mounted on the surface thereof. Screw holes 2c for screwing and fixing the printed circuit board 2 to a resin case 3 to be described later are formed at four corners of the printed circuit board 2. In the present embodiment, the acceleration sensor 2a is disposed in the vicinity of the screw hole 2c formed on one side of the side opposite to the side where the connector 2b is disposed among the four screw holes 2c on the printed circuit board 2. .

 As shown in FIG. 2A, assuming that the X-axis direction is the vehicle length direction, the Y-axis direction is the vehicle width direction, and the Z-axis direction is the vehicle height direction, the acceleration sensor 2a When detecting the acceleration acting in the length direction, the acceleration sensor 2a may be arranged in such a posture that the sensitivity axis is parallel to the X axis. When the acceleration sensor 2a is a two-axis acceleration sensor having two sensitivity axes orthogonal to each other, acceleration is performed in such a posture that one sensitivity axis is parallel to the X axis and the other sensitivity axis is parallel to the Y axis. If the sensor 2a is arranged, acceleration acting in the longitudinal direction and the width direction of the vehicle can be detected simultaneously.

The resin case 3 is for accommodating and protecting the printed circuit board 2 inside, and is configured to be divided into two parts, a lower resin case 31 and an upper resin case 32.
The printed circuit board 2 passes through the screw hole 31a of the lower resin case 31 and the screw hole 2c of the printed circuit board 2 from the bottom to the top, and is screwed into a screw hole (not shown) of the upper resin case 32. Thus, both the cases 31 and 32 are fastened together while being sandwiched between the lower resin case 31 and the upper resin case 32.

 In the SRS unit 1 configured as described above, the mounting position of the acceleration sensor 2a on the printed circuit board 2 is based on the result of a vibration test performed in a state where the printed circuit board 2 is fixed to the resin case 3 with screws in advance. Has been determined. The applicant conducts a vibration test in a state where the printed circuit board 2 is fixed to the resin case 3, and frequency response characteristics of acceleration levels in the XYZ-axis directions for each of the mounting positions of the acceleration sensor 2 a on the printed circuit board 2. Was analyzed.

 FIG. 2A is a diagram showing mounting candidate positions of the acceleration sensor 2 a set on the printed circuit board 2. As shown in this figure, the vicinity of the screw hole 2c formed on one side of the side opposite to the side where the connector 2b is disposed is defined as a first mounting candidate position L1, and the first mounting candidate position L1 is extended in the Y-axis direction. A position shifted to the vicinity of the center of the printed circuit board 2 is set as a second mounting candidate position L2, and from these first and second mounting candidate positions L1 and L2, the positions are shifted to the vicinity of the center of the printed circuit board 2 along the X-axis direction. These positions are designated as third and fourth mounting candidate positions L3 and L4.

 FIG. 2B is an analysis result of frequency response characteristics of acceleration levels in the XYZ axis directions obtained for the first mounting candidate position L1 by performing the vibration test. FIG. 2C shows the analysis result of the frequency response characteristics of the acceleration level in the XYZ axis directions obtained for the second mounting candidate position L2 by performing the test. FIG. 2D shows the analysis result of the frequency response characteristic of the acceleration level in the XYZ-axis directions obtained for the third mounting candidate position L3 by performing the test. FIG. 2E shows the analysis result of the frequency response characteristics of the acceleration level in the XYZ-axis directions obtained for the fourth mounting candidate position L4 by performing the test.

 As shown in FIGS. 2B to 2E, the acceleration level at the time of the primary resonance is the first mounting candidate position L1 → third mounting candidate position L3 → second mounting candidate position L2 → second with respect to the upper limit level. It turns out that it becomes high in order of 4 mounting candidate positions L4. That is, there is a mounting candidate position where the sensitivity of the acceleration sensor 2a is low with respect to the resonance phenomenon of the printed circuit board 2 at a position near the board fixing position by screwing or the like.

 From the result of the vibration test described above, it can be seen that the mounting candidate position having the lowest sensitivity of the acceleration sensor 2a with respect to the resonance phenomenon of the printed circuit board 2 is the first mounting candidate position L1. Therefore, as shown in FIG. 1, by mounting the acceleration sensor 2a at the first mounting candidate position L1 on the printed circuit board 2, it can be accurately performed without being affected by the resonance phenomenon of the printed circuit board 2 due to vibration during traveling. The acceleration acting on the vehicle can be detected.

 As described above, according to the present embodiment, the acceleration sensor 2a is arranged in the vicinity of the fixing portion between the resin case 3 and the printed circuit board 2 on the printed circuit board 2, thereby accurately detecting the acceleration acting on the vehicle. Therefore, it is possible to prevent malfunction of an occupant protection device such as an airbag.

 In the above embodiment, the case where the first mounting candidate position L1 is determined as the mounting position of the acceleration sensor 2a from the result of the vibration test in advance is illustrated, but this is only an example, and the optimal mounting of the acceleration sensor 2a is illustrated. Since the position differs depending on the shape and material of the printed circuit board 2 and the structure fixed to the resin case 3, a vibration test is performed in advance for each model (structure) of the SRS unit 1, and based on the result, the acceleration sensor 2 a What is necessary is just to determine a mounting position.

 Further, as can be seen from the result of the vibration test, if the acceleration sensor 2a is disposed in the vicinity of the fixed portion between the resin case 3 and the printed circuit board 2 on the printed circuit board 2, the resonance of the printed circuit board 2 due to vibration during traveling is obtained. Since there is a tendency that acceleration acting on the vehicle can be accurately detected without being affected by the phenomenon, the acceleration sensor 2a can be used for the model without performing a vibration test in advance for each model (structure) of the SRS unit 1. If the resin case 3 and the printed circuit board 2 are disposed in the vicinity of the fixed portion on the printed circuit board 2, certain effects can be obtained. Of course, in order to increase detection accuracy, it is desirable to perform a vibration test.

  Moreover, in the said embodiment, although SRS unit 1 was illustrated as an electronic controller which concerns on this invention, this invention is not limited to SRS unit 1, The printed circuit board with which the acceleration sensor was mounted, and this printed circuit board are accommodated. The present invention can be widely applied to electronic control devices including a resin case. Furthermore, the present invention can be applied to an electronic control device including a plurality of acceleration sensors.

  DESCRIPTION OF SYMBOLS 1 ... SRS unit (electronic control apparatus), 2 ... Printed circuit board, 2a ... Acceleration sensor, 3 ... Resin case, 31 ... Lower resin case, 32 ... Upper resin case

Claims (1)

An electronic control device comprising a printed circuit board on which an acceleration sensor is mounted, and a case for housing the printed circuit board,
The electronic control device according to claim 1, wherein the case is a resin case, and the acceleration sensor is disposed in the vicinity of a fixed portion between the resin case and the printed board on the printed board.

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