Patent Publication Number: US-2021168950-A1

Title: Electronic device and electric power steering apparatus having electronic device mounted thereto

Description:
TECHNICAL FIELD 
     The present disclosure relates to an electronic device having an electronic circuit substrate and an electric power steering apparatus. 
     BACKGROUND ART 
     In a conventional electronic device, a substrate ground, a connector ground line, and a frame ground (controller holding member) are electrically connected directly to each other, to reduce a common mode noise and reduce leakage of the common mode noise to outside (for example, see Patent Document 1). In general, a housing of the electronic device (electric power steering apparatus in Patent Document 1) is electrically connected to a body of a vehicle in many cases. In these cases, power supply current supplied from a battery of an automobile is returned through the body to the battery. In a case where a connector has a ground harness returning to a battery ground, return current is divided so as to flow in the body and the harness, and the ratio in the division is determined by their wiring resistances. 
     In another conventional electronic device, a shield pattern is disposed in an inner layer of a substrate in order to inhibit noise flowing into an electronic component (first electronic component) to which a connector directly connects and which is mounted on a surface or a back face of a multilayer substrate from being transmitted to a built-in electronic component (for example, see Patent Document 2). In this case, the shield pattern is connected to a ground layer, thereby enhancing a shielding effect. 
     CITATION LIST 
     Patent Document 
     
         
         Patent Document 1: Japanese Patent No. 6123848 
         Patent Document 2: Japanese Patent No. 5034453 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the configuration disclosed in Patent Document 1, there is an inconvenience that, if a current division ratio is not determined, wiring cannot be designed. Therefore, the wiring resistance needs to be designed to have a predetermined value, that is, the current division ratio needs to be designed to have a fixed value. 
     Particularly, for example, using, as a bolt for fixing members, a specific bolt for assuring electric connection separately from mechanical fixing needs to be considered for designing a configuration of a body system, thereby increasing cost. The same applies to a case where current is returned to the body only. 
     Total current can be designed to be returned to a harness ground without dividing the flow of the current. However, in this case, an insulating process needs to be performed to electrically insulate the electronic device from the body. Therefore, cost is increased as in the above-described case. 
     Furthermore, in the configuration disclosed in Patent Document 2, a ground layer of the substrate may not necessarily provide a ground that is stable with respect to a common mode noise. Particularly in an inverter circuit in which switching of large current is performed, the ground layer may become a noise source. In this case, use of the ground layer for the shield pattern may cause a problem that a path for transmitting a noise to an electronic component (second electronic component) mounted in the multilayer substrate is generated, and, further, noise is transmitted to outside of the device through the first electronic component and the connector. 
     The present disclosure has been made in view of the aforementioned problems, and an object of the present disclosure is to provide an electronic device capable of effectively reducing a common mode noise which leaks from the electronic device and effectively preventing a noise from coming from outside, at low cost. 
     Solution to the Problems 
     An electronic device according to the present disclosure includes: 
     a substrate having an electronic circuit formed therein; 
     a housing for housing the substrate; and 
     a connector disposed on the substrate and serving as an interface between outside and inside of the housing, in which 
     the substrate has a main circuit pattern portion that forms a main circuit and a frame ground pattern portion that forms a frame ground, 
     the main circuit pattern portion and the frame ground pattern portion are disposed so as not to overlap each other on the substrate and in the substrate, and 
     a terminal of the connector is disposed in the frame ground pattern portion. 
     Effect of the Invention 
     In the electronic device according to the present disclosure, electrostatic coupling between the main circuit pattern portion and the frame ground pattern portion is made sparse, thereby reducing leakage of a common mode noise generated in the main circuit to outside through the electrostatic coupling. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the entire configuration of an electronic device according to embodiment 1, and  FIG. 1A  is a plan view thereof and  FIG. 1B  is an A-A′ cross-sectional view of the electronic device shown in  FIG. 1A . 
         FIG. 2  illustrates the entire configuration of another electronic device according to embodiment 1, and  FIG. 2A  is a plan view thereof and  FIG. 2B  is an A-A′ cross-sectional view of the electronic device shown in  FIG. 2A . 
         FIG. 3  is circuit block diagrams illustrating embodiments 1 and 2,  FIG. 3A  is a circuit block diagram illustrating electrostatic coupling in a dense state,  FIG. 3B  illustrates a noise transmission route in the circuit block diagram shown in  FIG. 3A , and  FIG. 3C  illustrates a noise transmission route in the circuit block diagram illustrating electrostatic coupling in a sparse state. 
         FIG. 4  illustrates the entire configuration of the electronic device in the circuit block diagram shown in  FIG. 3A ,  FIG. 4A  is a plan view thereof,  FIG. 4B  is an A-A′ cross-sectional view of the electronic device shown in  FIG. 3A , and  FIG. 4C  is an enlarged cross-sectional view of a portion B indicated by a broken line in  FIG. 4B . 
         FIG. 5  illustrates the entire configuration of an electronic device according to embodiment 2, and  FIG. 5A  is a plan view thereof and  FIG. 5B  is an A-A′ cross-sectional view of the electronic device shown in  FIG. 5A . 
         FIG. 6  illustrates the entire configuration of an electronic device according to embodiment 3,  FIG. 6A  is a plan view thereof and  FIG. 6B  is an A-A′ cross-sectional view of the electronic device shown in  FIG. 6A . 
         FIG. 7  illustrates a schematic configuration of an electric power steering apparatus according to embodiment 4. 
         FIG. 8  illustrates a cross-section of the electric power steering apparatus as viewed from a motor  1  side at a position where a substrate  100  of an ECU  2  can be seen. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
     Embodiment 1 will be described below with reference to  FIG. 1  to  FIG. 4 . Hereinafter, throughout the drawings, the same or corresponding members and portions are denoted and described by using the same reference characters.  FIG. 1  illustrates the entire configuration of an electronic device according to embodiment 1, and  FIG. 1A  is a plan view of the electronic device and  FIG. 1B  is an A-A′ cross-sectional view of the electronic device shown in  FIG. 1A . The electronic device includes a substrate  100  in which an electronic circuit is configured, a module  200  disposed as appropriate, a connector  300  that serves as an interface to the outside, wiring  400  that electrically connects between the substrate  100  and the module  200 , and a housing  500  that is made of metal and that houses these components. 
     The substrate  100  is divided into a main circuit pattern portion  101  that forms a main circuit and a frame ground pattern portion  102  that forms a frame ground. The main circuit pattern portion  101  and the frame ground pattern portion  102  are wired such that electrostatic coupling is sparse. The frame ground pattern portion  102  is connected to the housing  500  by a frame ground terminal  401  at a low impedance. A noise filter  600  is inserted in a line connected from the main circuit pattern portion  101  to the connector  300 . Components of the noise filter  600  are disposed near a boundary between the main circuit pattern portion  101  and the frame ground pattern portion  102 , or disposed on the frame ground pattern portion  102  side. Among the components of the noise filter  600 , a ground is connected to the frame ground pattern portion  102 , and a connector terminal  301  that connects between the connector  300  and the noise filter  600  is disposed on the frame ground pattern portion  102  side. Wiring  105  represents a pattern connected from the main circuit pattern portion  101  to the connector  300  (the wiring  105  is not shown in  FIG. 1B ). 
     As shown in the A-A′ cross-sectional view in  FIG. 1B , the main circuit pattern portion  101  and the frame ground pattern portion  102  are separated without overlapping each other, and the internal layer patterns thereof are also separated without overlapping each other. Therefore, the electrostatic coupling becomes sparse. 
       FIG. 2  illustrates the entire configuration of another electronic device according to embodiment 1, and  FIG. 2A  is a plan view of the electronic device and  FIG. 2B  is an A-A′ cross-sectional view of the electronic device shown in  FIG. 2A . In the electronic device having such a configuration, the frame ground terminal  401  is configured such that a wall stands from the bottom surface of the housing  500  without soldering the terminal to the substrate as shown in  FIG. 1B , and the frame ground terminal  401  contacts and electrically connects with the back face of the substrate at a wider area. In such a configuration, the housing  500  and the frame ground can be connected at a lower impedance as compared with the configuration in  FIG. 1 . 
     Next, the behavior of a common mode noise in the electronic device shown in  FIG. 1  or  FIG. 2  will be described for a case where electrostatic coupling between the main circuit pattern portion  101  and the frame ground pattern portion  102  is dense and for a case where electrostatic coupling therebetween is sparse. 
       FIG. 3A  is a circuit block diagram of the electronic device. The main circuit pattern portion  101  has a switching power supply  700  and a microcomputer  800  mounted thereto. An oscillator  801  as a clock source is connected to the microcomputer  800 . Meanwhile, the noise filter  600  that includes a coil  601  and a capacitor  602  is connected to the frame ground pattern portion  102 . The main circuit pattern portion  101  and the frame ground pattern portion  102  partially overlap each other. 
     The switching power supply  700  has a several ten KHz to several hundred KHz clock source for operating the circuit. The clock source becomes a noise source, and high-frequency noise is superimposed into a power supply line, a ground line, and a peripheral pattern. Similarly, several MHz to several ten MHz of high-frequency noise is superimposed also into the oscillator  801  of the microcomputer  800 . The high-frequency noise including harmonic components generally increases up to several hundred KHz to several hundred MHz (up to several GHz in some cases). If the noise leaks through the connector  300  to a harness, the noise may interfere with an external device. In an on-vehicle state, the noise mainly becomes interfering radio waves to a radio receiver. 
     Noise generated between the power supply and the ground is a normal mode noise, and noise generated between the circuit and the housing is a common mode noise. 
     It is generally known that the normal mode noise can be removed by a low pass filter that includes a coil  601 - a  and a capacitor  603  in  FIG. 3A , and the description thereof is omitted. 
     A capacitor (stray capacitance)  901  indicated by a broken line is a stray capacitance between the main circuit pattern portion  101  and the housing  500 , and is not provided as a component. Similarly, a capacitor (stray capacitance)  902  is a stray capacitance between the main circuit pattern portion  101  and the frame ground pattern portion  102 , and is not provided as a component. In a case where the stray capacitance is large, electrostatic coupling is dense. In a case where the stray capacitance is small, electrostatic coupling is sparse. In the circuit block diagram shown in  FIG. 3A , as described above, the main circuit pattern portion  101  and the frame ground pattern portion  102  partially overlap each other, so that electrostatic coupling is dense. 
       FIG. 4  illustrates the entire configuration of the electronic device in the circuit block diagram shown in  FIG. 3A ,  FIG. 4A  is a plan view thereof,  FIG. 4B  is an A-A′ cross-sectional view of the electronic device shown in  FIG. 4A , and  FIG. 4C  is an enlarged cross-sectional view of a portion B indicated by a broken line in  FIG. 4B . As shown in  FIG. 4A  and  FIG. 4B , the main circuit pattern portion  101  and the frame ground pattern portion  102  partially overlap each other at inner layer patterns  103 ,  104 . Therefore, even in a case where a point C in  FIG. 3A  is on the main circuit pattern portion  101  side of the inner layer patterns  103 ,  104 , when the pattern that extends from the point C is wired to a portion that overlaps the frame ground pattern portion  102 , electrostatic coupling to a pattern disposed above or below the inner layer patterns  103 ,  104  or the connector terminal  301  occurs through the stray capacitance  902  shown in  FIG. 4C . Thus, noise is easily transmitted from the main circuit pattern portion  101  to the frame ground pattern portion  102 . The noise transmitted to the frame ground pattern portion  102  may leak through the connector terminal  301  to the outside of the electronic device, to interfere with an external device. 
     A specific value of the stray capacitance indicated by the capacitor (stray capacitance)  902  in the case of the electrostatic coupling being dense is considered by using an example of a four layer FR4 printed board which is often used. In a case where a 10 mm square pattern on the inner layer opposes that on the surface layer, the stray capacitance (coupling capacitance) is about 20 pF since the relative permittivity is about 4.7, and a distance between the layers is about 0.21 mm. This indicates that the capacitance is enough for transmitting a high-frequency noise signal. 
     Next, a noise transmission route will be described with reference to the circuit block diagrams shown in  FIG. 3A  and  FIG. 3B . In the drawings, in a case where a clock noise of the switching power supply is superimposed at the point C on the circuit, the noise is suppressed by the noise filter  600  (see  FIG. 1 ) that includes the coil  601 - a  and the capacitor  602 - a , and is not transmitted to a B line of the connector  300  (see  FIG. 3A ). However, as described with reference to  FIG. 4C , in a case where the electrostatic coupling is dense, the stray capacitance  902 - a  occurs, so that the noise filter is bypassed and leakage from the B line to an external harness occurs, to generate a loop L (alternate long and short dash line in  FIG. 3B ) that returns to the point C that is a noise source via a battery  10 , the housing  500 , and a capacitor (stray capacitance)  901 - a  that is a stray capacitance. Strictly speaking, a route for returning a noise signal transmitted through the stray capacitance  902 - a , via the capacitor  602 - a , to the housing is also present, and, thus, the effect of the noise filter may be exerted. However, the coil  601 - a  does not function and the filtering performance is thus substantially degraded. 
     Meanwhile, in the configuration of the electronic device according to embodiment 1 of the present disclosure shown in  FIG. 1  and  FIG. 2 , as described above, the patterns of the areas of the main circuit pattern portion  101  and the frame grand pattern portion  102  are completely separated from each other and wired without overlapping each other, and the electrostatic coupling is thus made sparse, in order to intentionally reduce the coupling capacitance between the main circuit pattern portion  101  and the frame ground pattern portion  102 . Thus, the stray capacitance  902 - a  shown in  FIG. 3A  is absent or very small, and the route for bypassing the noise filter that includes the coil  601 - a  and the capacitor  602 - a  is disconnected (see  FIG. 3C ). The loop L of the noise transmission route described above is disconnected by the noise filter that includes the coil  601 - a  and the capacitor  602 - a , so that the noise does not leak to the outside of the electronic device. 
     The example of the B line of the connector terminal has been described above. Similarly, the electrostatic coupling is made sparse for another line such as a G line and an S line, whereby leakage of noise can be prevented. The line connected from a G terminal shown in  FIG. 3C  into the housing  500  is grounded at the frame ground by the capacitor  602 , and then wired to the main circuit pattern portion  101 . This is for a case where the noise superimposed in the line is assumed to be relatively small. In a case where a large noise is superimposed, a coil similar to the coil  601 - a  of a B terminal is inserted, thereby enhancing the effect of the noise filter to effectively address the noise. 
     As described above, in a case where the coupling capacitance between the main circuit pattern portion  101  and the frame ground pattern portion  102  is made sparse, the noise filter effectively acts, and noise generated in the electronic device can be prevented from leaking to the outside of the device. 
     The example where noise is superimposed in the line connecting to the connector has been described. In a case where noise is not superimposed in the line itself which connects to the connector, the noise filter need not be inserted in the line since the electrostatic coupling between the main circuit pattern portion  101  and the frame ground pattern portion  102  is made sparse and influence of a line in which another noise is superimposed is not exerted. 
     Furthermore, in the present embodiment, the description has been made according to electrostatic coupling between the main circuit pattern portion  101  and the frame ground pattern portion  102  being dense or sparse. However, the electronic device can be configured by applying a similar idea to magnetic coupling. 
     In the present embodiment, the number of the substrates of the electronic circuit is one. However, also in a case where the number of the substrates is plural, the electronic device can be configured in a similar manner. 
     Embodiment 2 
     In embodiment 1, the example where the bypass route for noise is disconnected, that is, the coupling capacitance between the main circuit pattern portion  101  and the frame ground pattern portion  102  is made sparse, has been described. Another important measure for addressing noise is, for example, to enhance performance of the noise filter. The technique therefor will be described below. 
     As described with reference to  FIG. 3B , a noise transmission route in the case of the bypass route being disconnected is a loop that returns to a line of the point C via the line on which the point C is located, the coil  601 - a , the capacitor  602 - a , the frame ground pattern portion  102 , the frame ground terminal  401 , the housing  500 , and the stray capacitance  901 - a  as indicated by a loop M as an alternate long and short dash line in  FIG. 3C . At this time, an impedance at the capacitor  602 - a  as viewed from the right-side terminal of the coil  601 - a  needs to be sufficiently less than an impedance at the B terminal of the connector  300  in order to prevent noise from leaking to the connector B line. In other words, an impedance of the noise transmission route shown in  FIG. 3C  needs to be sufficiently less than an impedance of the noise transmission route shown in  FIG. 3B  (in a case where coupling capacitance is absent). 
     Furthermore, the configurations of an LC, an LCL, a CLC, and the like which include coils and capacitors are known as a noise filter. Each of them is selected and used according to a position at which the filter is inserted, or the required performance. In the case of a low pass filter, one of the terminals of each capacitor is grounded. It is well known that, at this time, the performance of the filter is degraded in a case where an inductance component that enters the capacitor in series increases due to wiring and a component lead. The coil may be any element that electrically has an inductance component. Therefore, ferrite beads may substitute for the coil. 
     In order to address this, the frame ground pattern portion  102  is widely disposed on the substrate, a chip capacitor is used, and the components are connected by the shortest wire, whereby lead inductance can be easily reduced. Furthermore, the frame ground pattern portion  102  and the housing  500  may be connected at a low impedance as described in embodiment 1. 
     An example where the frame ground and the housing  500  are connected by a substantially 0.6 mm square terminal is represented by the frame ground terminal  401  shown in  FIG. 1 . Increase of the length of the terminal leads to increase of an inductance, and the impedance thus increases entirely, so that degradation of the performance may be caused. The performance can be enhanced by making the terminal as short and as thick as possible and maximizing the number of the terminals. 
     An example where the wall stands from each of the bottom surface and the top surface of the housing  500 , and is electrically connected to the upper and lower faces of the frame ground pattern portion  102  of the substrate  100  is represented by the frame ground terminal  401  shown in  FIG. 5 . The diagonal line portion in the drawings represents the contact portion, on the upper face, at which the substrate  100  and the frame ground terminal  401  are in contact with each other. In such a configuration, the connection impedance between the housing  500  and the frame ground can be reduced, and the main circuit pattern portion  101  and the frame ground pattern portion  102  can be shielded by the housing  500 . 
     Embodiment 3 
     In embodiments 1 and 2, the entirety of the housing is made of metal. An example where noise performance is not degraded even when only a part of the housing is made of metal, will be described with reference to  FIG. 6 . 
     In  FIG. 6 , for example, in a case where a noise source is mainly the module  200 , only a diagonal line portion  501  of the housing  500  may be allowed to be made of metal. Generation of stray capacitance between the module  200  and the diagonal line portion  501  is promoted, to generate a noise transmission route in the housing. The configuration in which the noise source and the noise transmission route are generated in the electronic device and impedance is made low has been described in embodiment 2. This configuration is effective in a case where the noise source can be specified. Description has been made by using the module  200  as an example. However, even in a case where the noise source is at another place or the number of the noise sources is plural, the designing can be similarly performed. A portion, of the housing, other than a metal portion (the diagonal line portion  501 ) can be made of resin or the like, whereby freedom of designing increases, and the weight and cost can be reduced. 
     Embodiment 4 
     Application of the electronic device described in each of embodiments 1 to 3 to an electric power steering apparatus will be described. 
       FIG. 7  illustrates a schematic configuration of an electric power steering apparatus. A motor  1  and an ECU (electric control unit)  2  are coaxially disposed, and an output shape of the motor  1  is connected to a gear  3  through the ECU  2 . Power is supplied from a battery (not shown) to the connector  300  of the ECU  2 . A torque signal from a not-illustrated torque sensor mounted to a steering wheel shaft is inputted to the ECU  2 , and the ECU  2  calculates an appropriate steering wheel assist amount according to the magnitude of the torque signal, to drive the motor  1  based on the calculation result. The output from the motor  1  is connected to the steering wheel shaft via the gear  3  to provide a proper assist. 
       FIG. 8  illustrates a cross-section as viewed from the motor  1  side at a position where the substrate  100  of the ECU  2  can be seen. The module  200  where the substrate  100  is housed in the housing  500  produced by aluminum die casting is a power circuit for driving the motor  1  in the present embodiment. The module  200  and the substrate  100  are electrically connected by the wiring  400 . Meanwhile, a plurality of the connector terminals  301  are disposed on the end face of the substrate  100  and soldered. 
     In the drawings, the diagonal line portion represents the frame ground terminal  401 , and is a wall that stands from the case and is in electrical surface contact with the back face of the substrate. A screw  402  has a function to press the substrate  100  against the frame ground terminal  401  to assure the electrical connection. 
     A portion on the connector terminals  301  side from the frame ground terminal  401  indicated by the diagonal lines is the frame ground pattern portion  102 . A portion on the lower side from a line indicated by an alternate long and short dash line is the main circuit pattern portion  101 . The main circuit pattern portion  101  and the frame ground pattern portion  102  are designed such that wiring patterns including the inner layers do not overlap each other, and electrostatic coupling and magnetic coupling are made sparse as described in embodiments 1 to 3. 
     An appropriate noise filter  600  is disposed on a line connected from the main circuit pattern portion  101  to the connector terminals  301  in a boundary portion between the main circuit pattern portion  101  and the frame ground pattern portion  102 , or on the frame ground pattern portion  102  side, which are not shown, thereby preventing noise from leaking to outside. 
     Thus, the main circuit pattern portion and the frame ground pattern portion on the substrate are designed without using specific components so as not to overlap each other, whereby an ECU having excellent noise performance can be provided. 
     As described above, electrostatic coupling between the main circuit pattern portion  101  and the frame ground pattern portion  102  is made sparse, whereby a bypass route for noise can be disconnected to reduce a common mode noise. The frame ground pattern portion  102  and the housing  500  made of metal are connected to each other at a low impedance, whereby the performance of the noise filter can be effectively exhibited to reduce a common mode noise. The metal portion of the housing  500  is disposed at a necessary place relative to the noise source of the electronic device, thereby enhancing cost performance. 
     A common mode noise that leaks from the electronic device to outside has been described above. In the configuration of the present disclosure, impedance to the housing  500  is clearly reduced in the electronic device as viewed from an external harness. Therefore, a noise coming from the outside flows via the connector  300  and the capacitor  602  to the housing  500  made of metal and does not flow into the main circuit. This means that external noise resistance of the electronic device has been improved. 
     Various electronic devices generally have specifications that are required based on an official standard for noise. For example, for on-vehicle devices, five classes of class 1 to class 5 are defined in CISPR 25 of the IEC in many cases. In a case where high performance is required for connection between a housing and a frame ground, configuration designing is restricted, and the size and the cost of the device tend to increase. The technique according to any of embodiments 1 to 3 can be adopted according to the required specifications to optimize the designing, thereby achieving an electronic device which has high performance and good cost performance. 
     The technique of the present disclosure is adopted for a controller of an on-vehicle electric power steering apparatus which has such characteristics and principle as to generate multiple noises based on the circuit mode and which typifies an inverter circuit for driving an inductance load such as a motor, as described in embodiment 4, thereby effectively improving EMC. 
     Although the disclosure is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects, and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead can be applied, alone or in various combinations to one or more of the embodiments of the disclosure. 
     It is therefore understood that numerous modifications which have not been exemplified can be devised without departing from the scope of the present disclosure. For example, at least one of the constituent components may be modified, added, or eliminated. At least one of the constituent components mentioned in at least one of the preferred embodiments may be selected and combined with the constituent components mentioned in another preferred embodiment. 
     DESCRIPTION OF THE REFERENCE CHARACTERS 
     
         
         
           
               100  substrate 
               101  main circuit pattern portion 
               102  frame ground pattern portion 
               200  module 
               300  connector 
               301  connector terminal 
               400  wiring 
               401  frame ground terminal 
               500  housing 
               600  noise filter