JP4019408B2 - control unit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control unit for an electric power steering apparatus in a vehicle.
[0002]
[Prior art]
In general, an electric power steering device (EPS) detects a steering torque generated in a steering shaft by a steering operation using a torque sensor, and in response to an assist motor (hereinafter simply referred to as a motor in some cases) attached to the steering shaft or the like. A steering assist torque is generated by supplying a current from a vehicle battery. Since this electric power steering device is difficult to generate a large steering assist torque as compared with a hydraulic type, it has been conventionally used mainly in light vehicles, but it is easy to electronically control or a hydraulic pump. There are various advantages such as no need for oil pipes and simplified structure, and in recent years, application to a small vehicle with a displacement of 1800 CC level has been studied, and there is a possibility that it will be applied to larger vehicles in the future. There is.
In addition, for the current control of the assist motor in this electric power steering apparatus, a drive circuit consisting of an H bridge circuit, which is normally composed of four (or four) FETs (field effect transistors), is used. Under the control of a control circuit including a microcomputer), the assist motor is driven by a PWM (pulse width modulation) system via this drive circuit.
In general, in this type of device, a power backup capacitor (usually an electrolytic capacitor) and a choke coil are connected to a high potential power line that supplies power to the drive circuit from a vehicle battery, and ripple current is reduced. The problem, the problem of temporary power supply voltage drop due to wiring resistance at a large current, or the problem of noise are solved. In order to detect the motor current, for example, a shunt resistor is connected to the low potential power supply line. In some cases, a power relay for opening and closing the power supply line or the energization line of the motor is also provided.
A large current circuit component such as the drive circuit, the control circuit, or the power backup capacitor is mounted on a circuit board in a single unit called a control unit, and this control unit (hereinafter, depending on the case) For example, the unit is simply disposed in a gap that is not visible to the passenger in the passenger compartment.
[0003]
By the way, the control unit of the conventional electric power steering apparatus has a structure in which one circuit board is housed in a metal case, and the circuit board has a structure as shown in FIG. 9, for example. . In other words, the basic structure is the same as that of a so-called printed circuit board, and circuit conductors, passive elements, etc. are formed on a resin-made substrate having insulating properties by a conductive pattern made of printed wiring technology. A capacitor or the like, or a component such as an IC chip or a power relay constituting the control circuit described above is mounted.
Incidentally, in the circuit board 1 shown in FIG. 9, the reference numeral 2 is a resin-molded FET chip, the reference numeral 3 is a power backup capacitor, and the reference numeral 4 is the above-described one. It is an IC chip (hereinafter referred to as a microcomputer chip) of a microcomputer that constitutes a control circuit. Reference numeral 5 denotes a bus bar (conductive plate) constituting a circuit conductor through which a large current flows, such as a motor energization line, and reference numeral 6 denotes a radiator that mainly dissipates heat generated by the FET 2. What is denoted by reference numeral 7 is a power relay that opens and closes the energization line of the motor under the control of the microcomputer chip 4.
[0004]
In addition, since a current of about 35 A at the maximum flows through the assist motor even in the case of a light vehicle, a conductive pattern on the circuit board 1 having a limited thickness constitutes an assist motor energization line, etc. It was practically impossible from the viewpoint of the upper space. For this reason, the above-mentioned bus bar 5 having a width and thickness that are remarkably larger than the conductor pattern on the circuit board 1 is mounted on the circuit board 1, thereby configuring the energization line and the like. Further, the amount of heat generated in the FET 2 is very large depending on the operating state, and if it is left unattended, the temperature rises to about several hundred degrees Celsius in a short time. Therefore, the radiator 6 is made of aluminum having high thermal conductivity, and is installed in parallel with each FET 2 at the end of the circuit board 1 while being joined to the back surface of the FET 2.
[0005]
[Problems to be solved by the invention]
The control unit of the above-described conventional electric power steering apparatus has the following problems with respect to applicability and mountability particularly to a relatively large vehicle (the assist motor needs to have a current of 60 to 80 A, for example). Had.
(I) That is, in the conventional configuration, when the motor current increases due to application to a relatively large vehicle, in addition to the temperature rise of the printed circuit board due to self-heating, the solder of self-heating components such as switching elements, shunt resistors, power relays, etc. Thermal stress on the connection is large, and sufficient resistance cannot be obtained in terms of thermal shock due to self-heating. Further, in continuous energization with a large current, the solder may melt and cause a connection failure of a component (for example, the shunt resistor described above).
(B) Further, since the components are arranged in a plane on a single printed board, the size in the surface direction of the circuit board is particularly large and the weight is also heavy. In particular, in the case of a relatively large vehicle such as a small automobile, the current of the assist motor is, for example, 80 A at the maximum, so that the radiator and the above-mentioned bus bar become extremely large, and the corresponding amount is the size and weight of the entire unit. As a result, the entire unit becomes extremely large and heavy. In the case of small cars, the problem of voltage drop due to wiring resistance between the unit and the motor cannot be ignored due to the increase in the current of the assist motor. Must be placed near the assist motor (that is, in the engine room). However, as described above, when the unit is enlarged, it is very difficult to place the unit in the gap in the engine room. Application itself becomes difficult in terms of cost and space.
[0006]
Note that the control unit shown in FIG. 8 has been proposed by the applicant in order to cope with the large current described above. In this unit 10, a metal substrate 12 is attached to the lower surface of a base substrate 11, and then this intermediate assembly is assembled to a resin case 13 to which a heat sink 15 (heat sink) is previously attached, and then an insulating substrate 14 (printed substrate). Is attached to the resin case 13 so as to cover the upper surfaces of the base substrate 11 and the insulating substrate 14.
The base substrate 11 is a support member to which the metal substrate 12 and the insulating substrate 14 are attached in an overlapping manner, and for mounting circuit components (large current components) through which a large current flows, such as the power backup capacitor and the power relay described above. It is also a circuit board. The base substrate 11 is formed by integrating a circuit conductor constituting member made of a plurality of metal fittings with a resin base material by insert molding.
[0007]
The metal substrate 12 is an aluminum substrate on which an H bridge circuit including an FET and a shunt resistor are mounted. The metal substrate 12 is attached to the lower surface side of the base substrate 11 by bonding or the like, and circuit connection with the base substrate 11 is realized by wire bonding. The The back surface (lower surface) of the metal substrate 12 is joined to the heat radiating plate 15 so that heat generated by the H bridge circuit or the like is efficiently radiated.
The resin case 13 has a frame-like shape as a whole so that the base substrate 11 and the like can be accommodated. The resin case 13 is a member constituting the outer wall of the side surface of the unit 10 and includes connectors 17, 18, Reference numeral 19 denotes a member provided integrally.
The insulating substrate 14 (printed substrate) is mounted with a small current component such as a microcomputer chip.
The circuit connection between the insulating substrate 14 and the base substrate 11 or the resin case 13 is achieved by connecting the lead terminals 20 and 21 (press-fit terminals) provided on the base substrate 11 or the resin case 13 through the insulating substrate 14 during assembly. This is realized by press-fitting into the holes 22 and 23.
[0008]
With the configuration of the control unit shown in FIG. 8, each circuit component is mounted on an optimal board for each function, and each board is laminated with the base board 11 as the center. In addition to eliminating this problem, the unit can be miniaturized, and mounting on a vehicle is improved.
However, in this case, since the inside of the unit has a three-piece structure in which three substrates are stacked and arranged, a problem arises that a considerable increase in cost cannot be avoided due to an increase in the number of assembly steps and the number of parts.
Accordingly, the present invention solves the above-described problems, and particularly improves the applicability and mountability of a large vehicle in which the motor current increases, and provides a control unit for an electric power steering device that is excellent in cost. It is intended to provide.
[0009]
[Means for Solving the Problems]
  The control unit of the electric power steering apparatus according to each invention of the present application (the first invention and the second invention) has the following configuration as a common feature. That is,A control unit of an electric power steering device that generates a steering assist torque by an assist motor connected to a steering system of a vehicle,
  A drive circuit including a switching element that connects each coil terminal of the assist motor to a high-potential power line or a low-potential power line in a switchable manner;
  A control circuit for controlling the current of the assist motor to a predetermined target current value by operating the switching element according to the steering torque of the steering system so that the steering assist torque becomes a value corresponding to the steering torque. When,
  The base material is made of metal, a metal substrate on which the driving circuit, a shunt resistor for detecting a current flowing through the assist motor through the driving circuit, and a thermistor for temperature detection are mounted,
  An insulating substrate on which the base material is made of an insulating material and the control circuit is mounted;
  The metal substrate and the insulating substrate are attached so as to overlap each other, and comprise a metal heat dissipation case constituting the outer wall of the unit,
  The control circuit includes:
  In order to keep the temperature of the circuit element (mainly the switching element) of the metal substrate below the allowable temperature, the current of the assist motor is made to be below a predetermined current limit value based on the temperature detected by the thermistor. A first current limiting function for lowering the target current value as necessary;
  In order to keep the temperature of the circuit element of the assist motor and the insulating substrate below an allowable temperature, the current of the assist motor is required to be below a predetermined current limit value based on the current detected by the shunt resistor. Accordingly, it has a second current limiting function for lowering the target current value.
[0010]
Here, as the “drive circuit” mounted on the metal substrate, there may be a circuit including a bridge circuit when the assist motor is PWM-driven. Further, the “switching element” includes an FET that forms a bridge circuit when the assist motor is PWM-driven. The “control circuit” mounted on the insulating substrate is a circuit including, for example, a microcomputer and its peripheral circuit (peripheral circuit through which a large current does not flow). The external connection connector may be mounted on an insulating substrate, for example. Large current components such as power backup capacitors (usually electrolytic capacitors), choke coils for noise countermeasures, power relays that open and close motor energization lines, and shunt resistors for current detection are insulated substrates or metal substrates. It may be mounted on either. However, if heat dissipation is taken into consideration, a component (for example, shunt resistor) in which heat generation is particularly problematic among these large current components should be mounted on a metal substrate.
[0011]
  Configuration of the control unit of the present application described aboveTherefore, the internal structure of the unit is a two-piece structure in which two substrates (metal substrate and insulating substrate) are stacked and arranged, reducing the number of assembly steps and the number of parts, improving productivity and increasing costs. Avoided.
  In addition, each circuit component is mounted on an optimum substrate for each function, and the respective substrates are stacked. For this reason, the unit can be significantly reduced in size, and the mounting property on the vehicle is remarkably improved.
  That is, first, a drive circuit that includes a switching element that switches the energization state of the assist motor and generates a large amount of heat is mounted on a metal substrate having good thermal conductivity, and high heat dissipation is ensured. As a result, the width and interval of the conductor pattern on the metal substrate constituting the circuit conductor of the drive circuit can be set narrower than before, and the area of the drive circuit mounting portion and hence the entire area of the metal substrate can be reduced.
  In addition, a control circuit with a small amount of flowing current can be mounted on a normal insulating substrate and disposed within a minimum necessary area. For this reason, it is possible to avoid interference between the mounting parts on the metal board and the mounting parts on the insulating board, reduce the distance between the two boards, and reduce the placement space between each board and its mounting parts in the thickness direction. It becomes.
  In addition, since the metal substrate and the insulating substrate are stacked, the overall size in the plane direction is greatly reduced.
  Therefore, the size in the surface direction of the unit is greatly reduced, and the size in the thickness direction of the unit can be made comparable to the conventional one, and the weight can be reduced accordingly.
[0012]
  furtherAccording to the control unit of the present application described above,The first current limiting function based on the temperature detected by the thermistor mounted on the metal substrate and the second current limiting function based on the current detected by the shunt resistance allow the motor current to be adjusted as necessary from the target current value corresponding to the steering torque. The motor current is controlled to be forcibly lowered (that is, the motor current is limited to a predetermined current limit value or less based on the detected temperature or the like), whereby the temperature of the circuit element (mainly the switching element) of the metal substrate is reduced. In addition, the temperatures of the circuit elements of the assist motor and the insulating substrate are surely held below the allowable temperature.
  For this reason, the problem of thermal shock due to an increase in current (including poor connection due to solder melting) can be solved more reliably, and, for example, the conductor pattern of each board can be compared with the case without such an overheat prevention function. The width and interval can be set narrower, the capacity of the mounted component can be made relatively small, and further downsizing can be achieved as compared with the case of simply using the two-piece structure.
  ThereforeThe large applicability and mountability of the unit can be obtained even for a large vehicle having a large amount of current of the assist motor.
[0013]
In addition, the structure by which the back surface of the said metal substrate is joined to the inner surface of the said heat radiating case is preferable.
With such a configuration, it is possible to ensure high heat dissipation of heat generated in the metal substrate while avoiding an increase in the number of components. This is because the heat radiating case, which is a heat radiating member, has a structure that constitutes the outer wall, so that a member (cover member) that constitutes the outer wall of the portion where the heat radiating member is provided becomes unnecessary, and further, the heat radiating member bonded to the metal substrate Since the outer surface is exposed to the outside air, high heat dissipation is obtained.
[0014]
  In addition to the common features described above, the first invention of the present application has the following features. That is,On the metal substrate, a signal terminal for connection of a signal line between the metal substrate and the insulating substrate is provided outside a mounting region of the switching element or the shunt resistor, and the thermistor It is mounted at a further outer position of the signal terminal away from the switching element and the shunt resistor which are heat generating components on the substrate.
  For this reason,The metal substrate temperature that is optimal for overheating protection of circuit elements on the metal substrate, that is, the weakest switching to overheating, without being affected by transient temperature changes of heat-generating components (switching elements and shunt resistors) on the metal substrate The base temperature of a connection part (junction) such as an element can be measured with high accuracy as the detected temperature. As a result, it is possible to avoid the adverse effect that the steering current torque is unnecessarily lowered due to the first current limiting function unnecessarily operating due to a transient temperature rise.
[0015]
  On the other hand, the second invention of the present application has the following features in addition to the common features described above. That is,When the temperature detected by the thermistor exceeds a first threshold value, the current limit value in the first current limiting function decreases stepwise or continuously in accordance with the increase in the temperature detected by the thermistor, and the temperature detected by the thermistor When the value reaches the second threshold value, the current limit value in the first current limit function becomes zero or a value in the vicinity thereof.
  With such a configuration, for example, when the level of the high temperature state of the metal substrate is at a relatively low level that is not so urgent, the degree of limiting the current is reduced and a steering assist torque as large as possible is obtained. Flexible control such as securing is possible. In particular, when the current limit value is continuously reduced, it is possible to finely control the current according to the degree of the high temperature state of the metal substrate, and overheating of the metal substrate (especially switching) It is possible to precisely avoid the high temperature state that causes melting of the connection portion of the element) and to generate the steering assist torque as much as possible.
[0016]
  The second invention of the present application further has the following characteristics. That is,The first threshold value and the second threshold value in the first current limiting function increase or decrease stepwise or continuously according to the detected value of the power supply voltage (voltage corresponding to the battery voltage of the vehicle). That is, if the power supply voltage is high, the temperature rise is relatively difficult to occur. Therefore, the first threshold value and the second threshold value are changed to relatively large values (step change or continuous change), and conversely the power supply When the voltage is low, the loss of the switching element (eg, FET) etc. increases and the temperature rises relatively easily. Therefore, the first threshold value and the second threshold value are changed to relatively small values. Is.
  With such a configuration, the current limitation by the first current limiting function (in other words, steering assist torque limitation) is executed to the minimum necessary level according to the fluctuation of the power supply voltage. It is no longer necessary to unnecessarily reduce the steering assist torque with a margin corresponding to the fluctuation margin, and it is possible to generate the steering assist torque as much as possible while avoiding a harmful high temperature state.
[0017]
  In addition, the second invention described aboveIn a more preferred configuration, the control circuit calculates a temperature rise due to Joule heat from the current detected by the shunt resistor, and adds an initial temperature to the temperature rise, thereby estimating the estimated temperature of the assist motor or the insulating substrate. When the estimated temperature exceeds the first threshold value, the current limit value in the second current limiting function decreases stepwise or continuously as the estimated temperature increases, and the estimated When the temperature reaches the second threshold value, the current limit value in the second current limit function becomes zero or a value in the vicinity thereof.
  Here, the “initial temperature” is a basic temperature for obtaining the estimated temperature of the assist motor or the insulating substrate, for example, the initial value of the temperature detected by the thermistor can be used as this initial temperature, Alternatively, external temperature data obtained from some sensor may be used as the initial temperature.
  With such a configuration, for example, when the degree of the high temperature state of the assist motor or the insulating substrate is at a relatively low level that is not so urgent, the degree of limiting the current is reduced and the steering is as large as possible. Flexible control such as securing auxiliary torque becomes possible. In particular, when the current limit value is continuously reduced, a fine current limit according to the degree of the high temperature state becomes possible, and the assist motor and the insulating substrate are overheated (particularly, with the minimum necessary current limit). It is possible to precisely avoid the high temperature state that causes melting or the like of the connection portion of the high-current circuit component on the insulating substrate, and to generate the steering assist torque as much as possible.
The features of the second invention described above may be combined with the first invention described above, and such aspects are also included in the present application.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, an example of the circuit configuration of the electric power steering apparatus will be described with reference to FIG. The apparatus controls an assist motor 31 (hereinafter, simply referred to as a motor 31 in some cases) that is connected to a steering system of a vehicle and generates a steering assist torque, and the motor 31 via a drive circuit 32 (H bridge circuit). A control circuit 33, a power supply circuit 35 that supplies predetermined power to the control circuit 33 based on the output of a power supply (battery) 34 of the vehicle, and a torque sensor 36 that detects the steering torque of the steering system are provided. In FIG. 6, what is indicated by reference numeral 30 is a control unit of the electric power steering apparatus (hereinafter, simply referred to as unit 30 in some cases).
[0019]
In FIG. 4, what is indicated by reference numeral 37 is an ignition switch of the vehicle, and functions as a start switch of the control circuit 33 in this apparatus.
What is indicated by reference numeral 38 is an electrolytic capacitor that backs up the power supply when the current of the motor 31 (hereinafter, simply referred to as “motor current” in some cases) increases.
Reference numerals 38a and 38b denote electromagnetic relays (more precisely, contacts of the electromagnetic relays), and the coils of these electromagnetic relays (power relays) are driven and controlled by the control circuit 33 through a circuit not shown. It has a configuration.
The electromagnetic relay 38a is a power supply relay that opens and closes the energization line L1 (high potential power supply line) of the unit 30 and the positive electrode of the power supply, and the electromagnetic relay 38b is a motor that opens and closes the energization line L3 between the drive circuit 32 and the motor 31. It is a relay.
These electromagnetic relays are maintained in an open state when the apparatus is not in operation, and avoid, for example, generation of a large current due to reverse battery connection (connecting a vehicle battery with the opposite polarity). Also, if a ground fault occurs during the operation of the device, the relay is also switched to the open state in order to avoid the occurrence of a large current due to this failure, malfunction of the motor, or regenerative lock. The power line is cut off.
Here, the regenerative lock is a state in which both terminals of the motor coil are connected by a short circuit failure (ON failure) of an FET, which will be described later, constituting the drive circuit 32 (H bridge circuit), and so-called in the motor. This is a phenomenon in which a regenerative braking force is generated and the handle connected to the motor becomes difficult or impossible to rotate. And if it is going to solve such a problem of regenerative lock with a relay, it is necessary to provide a relay in the energization line between an H bridge circuit and a motor like the above-mentioned electromagnetic relay 38b.
[0020]
Reference numeral 39 denotes a shunt resistor connected to the ground side of the drive circuit 32, and a voltage corresponding to the voltage drop of the resistor 39 is input to the control circuit 33 through the input line 40. Since the voltage value input from the input line 40 is naturally proportional to the motor current, the control circuit 33 can detect the motor current value from the voltage value. The resistor 39 and the input line 40 are connected to the motor current. The current detection means is substantially constituted.
Reference numeral 41 denotes a choke coil for suppressing noise generation, and is connected in series to the energization line L1. What is indicated by reference numeral 42 is a thermistor for detecting a temperature related to a heat generating part such as the drive circuit 32 or the shunt resistor 39.
The drive circuit 32, the control circuit 33, the power supply circuit 35, the electrolytic capacitor 38, the electromagnetic relay 38 b, the shunt resistor 39, the choke coil 41, the thermistor 42, etc. are unit parts provided in the unit 30. In this case, the electromagnetic relay 38 a is provided outside the unit 30 (that is, on the vehicle side), but may be provided inside the unit 30.
[0021]
In this case, the drive circuit 32 includes an H bridge circuit in which four field effect transistors SW1 to SW4 (hereinafter referred to as FET SW1 to SW4) are connected to the motor 31 in an H bridge form. The FETs SW <b> 1 to SW <b> 4 that are switching elements constituting the circuit operate according to the PWM drive signal output from the control circuit 33. By this operation of each FET SW1 to SW4, each coil terminal of the motor 31 is intermittently connected to the energization line L1 (high potential power supply line) or the energization line L2 (low potential power supply line) at a duty ratio according to the PWM drive signal. Connected to.
In this case, each of the FETs SW1 to SW4 is an N-channel enhancement type MOSFET, and diodes D1 to D4 (parasitic diodes) are formed between the drain and the source due to their structure.
[0022]
The control circuit 33 is configured by a circuit including a microcomputer, and a motor current target corresponding to the steering torque is generated in order to generate a steering assist torque corresponding to the value of the steering torque detected from the detection signal of the torque sensor 36. In addition to a control function in a normal state (a normal operation state that is not an abnormal state) that generates a PWM drive signal having a duty ratio that realizes a value (target current value) and controls the drive circuit 32, for example, a ground fault is detected. Thus, a fail-safe function is also realized in which failure handling control (processing for turning off all of the FETSW1 to SW4 or opening the electromagnetic relays 38a or 38b) is performed to avoid burning of the FET due to overcurrent.
The control circuit 33 reads the signal from the thermistor 42 and the input line 40 to monitor the temperature state in the unit 30 and forcibly lowers the motor current below the target current value as necessary (predetermined) The overheat preventing function (first current limiting function and second current limiting function) for preventing overheating in the unit 30 is also realized. The details of this overheat prevention function will be described later.
Further, the control circuit 33 can recognize the value of the power supply voltage Vb (in this case, the output voltage of the battery 34) in real time by reading a signal from a power supply voltage detection circuit (not shown) provided separately as necessary. ing.
Here, the power supply voltage detection circuit can be configured by, for example, a voltage dividing resistor (not shown) connected to the energization line L1. Alternatively, the power supply circuit 35 may have a function of outputting a signal proportional to the power supply voltage Vb to the control circuit 33 and function as the power supply voltage detection circuit.
Note that the target current value is a motor current value for generating a target steering assist torque corresponding to (for example, proportional to) the steering torque, but this parameter is also considered in consideration of parameters other than the steering torque (for example, vehicle speed). A target current value may be obtained. For example, even when the steering torque is the same, a configuration in which the target current value is made different depending on the vehicle speed and the steering assist torque is made slightly different depending on the vehicle speed is common.
[0023]
The power supply circuit 35 converts the voltage of the battery 34 (for example, about 12V at a rating) into a predetermined voltage (for example, 5V) and supplies it to the control circuit 33.
The electromagnetic relay 38 a may be provided in the energization line L <b> 2 between the drive circuit 12 and the negative electrode (that is, the ground) of the power supply 34, and the electromagnetic relay 38 b is provided between the drive circuit 12 and the motor 31. You may be provided in the other electricity supply line L4.
Although not shown in the figure, in the control circuit 33 or in the vicinity thereof, an FET drive comprising transistors for driving the switching elements (FETSW1 to SW4) of the drive circuit 32 in accordance with a command from the CPU in the control circuit 33. A circuit, a filter circuit that smoothes a signal input from the input line 40, or an A / D converter (not shown) that digitizes an input signal (analog signal) from the input line 40, the thermistor 42, or the like. Provided as needed. Normally, a vehicle speed detection signal used for setting the PWM drive signal is input to the control circuit 33 from a vehicle speed sensor provided in the vehicle.
Further, the electromagnetic relay 38b is not necessarily required, and the above-described regenerative lock is not a problem (for example, a clutch is provided between the motor 31 and the steering system, and the connection between the motor 31 and the steering system can be appropriately released). ) Is not required.
[0024]
Next, an example of the structure of the unit 30 will be described.
FIG. 1 is an exploded perspective view of the main part of the unit 30. 2A is a perspective view of the unit 30 (with a cover removed), and FIG. 2B is a perspective view of the unit 30 (completed state). As shown in FIGS. 1 and 2A, the unit 30 of this embodiment is roughly divided into a heat dissipation case 50, a metal substrate 60, an insulating substrate 70, and a cover 80 (shown in FIG. 2A). ). The assembly procedure is extremely simple as follows. That is, first, as shown in FIG. 1, the metal substrate 60 and the insulating substrate 70 are sequentially attached to the heat radiating case 50 with screws 91 and 92, and then the cover 80 is attached to the heat radiating case 50 with screws 93 as shown in FIG. Completion.
[0025]
Hereinafter, each component will be described.
First, the heat radiating case 50 has a box shape with an open top surface, and is made of, for example, aluminum (including an aluminum alloy) die-cast, and is a support member to which the metal substrate 60 and the insulating substrate 70 are attached in an overlapping manner. It is a member that also functions as a cover member that covers one surface side, and also as a heat sink for heat dissipation. As shown in FIG. 1, the heat radiating case 50 is provided with a joint surface 51 to which the lower surface (back surface) of the metal substrate 60 is joined, and the aforementioned screw 91 is screwed into a predetermined position of the joint surface 51. The screw hole 52 is formed. Further, support portions 53 that support the insulating substrate 70 are formed at the four corner positions in the heat radiating case 50 so as to contact the four corners of the insulating substrate 70, and the aforementioned screws 92 are screwed into the upper surface of the support portion 53. A screw hole 54 is formed. Further, a notch portion 55 for arranging connectors 71 to 74 to be described later in an exposed state outside the unit is formed at one end portion of the heat radiating case 50.
[0026]
Next, the metal substrate 60 will be described. In the metal substrate 60, an insulating layer is formed on the surface (mounting surface side) of an aluminum plate as a base material, and a conductor pattern as a circuit conductor is further formed thereon by a printed wiring technique, and a predetermined portion of the conductor pattern is formed. On the other hand, components such as switching elements constituting the drive circuit 32 are mounted. In FIG. 1, the upper surface side is a mounting surface of the metal substrate 60. Further, in this case, circuit elements mounted on the metal substrate 60 include those surrounded by an alternate long and short dash line in FIG. 6, that is, switching elements (FETSW1 to SW4), a shunt resistor 39, and a thermistor.
In FIG. 1, what is indicated by reference numeral 61 is an FET chip corresponding to the switching elements (FETSW1 to SW4). In this case, two each are mounted side by side. The shunt resistor 39 and the thermistor 42 are not shown in FIG. 1 to avoid complexity.
As shown in FIG. 1, power terminals 62 and signal terminals 63 (so-called loose terminals) are attached to the upper surface of the metal substrate 60 in a line by surface mounting using cream solder.
[0027]
Among these, the power terminal 62 constitutes a power connection portion that realizes connection of four power lines (the power supply lines L1 and L2 and the energization lines L3 and L4 described above) between the metal substrate 60 and the insulating substrate 70. is there.
The signal terminal 63 includes a plurality of signal lines between the metal substrate 60 and the insulating substrate 70 (the drive lines for the FETs SW1 to SW4, the current detection signal input line 40 and the temperature signal input line from the thermistor 42). Etc.) is formed.
FIG. 3B is a diagram showing the arrangement of circuit elements on the metal substrate 60. As shown in FIG. 3B, on the metal substrate 60, the mounting region for the signal terminal 63 is provided outside the mounting region for the FET chip 61 and the shunt resistor 39. It is mounted on the outer side of the signal terminal 63 away from the FET chip 61 (switching element) and the shunt resistor 39 which are heat generating components on the metal substrate 60.
[0028]
Next, the insulating substrate 70 will be described.
The insulating substrate 70 is formed of a predetermined conductor pattern on a synthetic resin substrate by a printed wiring technique, for example, and circuit components constituting the control circuit 33 (for example, a microcomputer chip or a transistor constituting the input / output circuit thereof) Other circuit elements that are not mounted on the metal substrate 60 (for example, the power supply circuit 35, the electrolytic capacitor 38, the electromagnetic relay 38b, and the choke coil 41 shown in FIG. 4), and connectors 71, 72, 73, 74 for external wiring (Shown in FIG. 1 and FIG. 2) is mounted, and basically has the same configuration as a general printed circuit board.
The connectors 71, 72, 73, and 74 are formed by screwing a connector member, which is a separate component from the substrate, to one end edge of the insulating substrate 70. Here, the connector 71 is a connector to which the wiring of the energization line connected to each coil terminal of the motor 31 is connected, and the connector 72 is the connector to which the power supply wiring connected to the positive electrode or the ground of the battery 34 is connected. The connectors 73 and 74 are connectors to which various signal lines (signal lines for input / output signals to the outside of the unit of the control circuit 33) such as an ignition switch (start switch 37) and a torque sensor 36 are connected.
[0029]
In the insulating substrate 70, through holes 75 and 76 into which the loose terminals are fitted, as shown in FIG. 1, at positions facing the loose terminals (power terminal 62 and signal terminal 63) of the metal substrate 60 described above. As shown in FIG. 1, the tip ends of the loose terminals are formed in the through holes by parallel movement when the insulating substrate 70 is attached to the heat radiating case 50 (with the metal substrate 60 attached). It has a configuration that fits together. That is, the operation of inserting the loose terminal into the through hole is a normal operation when the insulating substrate 70 is attached (in FIG. 1, the insulating substrate 70 is positioned and kept horizontal to be lowered with respect to the heat radiating case 50). All the operations can be realized by this operation, and the attachment of the insulating substrate 70 (excluding the screwing operation of the screw 92) and the terminal joining for electrical connection are completed by this operation.
Here, the number of through holes 76 corresponding to the signal terminals 63 (seven in this case) is provided, and the end of each signal terminal 63 has a shape and dimension that can be easily inserted at the time of mounting.
Further, the through holes 75 are provided in a number corresponding to the power terminals 62 (that is, four), and the end portions of the power terminals 62 have a shape and dimension that can be easily inserted at the time of mounting.
[0030]
In the assembled state, the mounting surface of the circuit component on the insulating substrate 70 is the surface inside the unit (the lower surface in FIG. 1), and the circuit component on the insulating substrate 70 is the same as the circuit component on the metal substrate 60. They are arranged on substantially the same plane. For this reason, all the circuit components mounted on either the metal substrate 60 or the insulating substrate 70 are eventually in the minimum necessary space in the thickness direction of the unit 30 (the same thickness as in the case of a single substrate). All of them are within the range. Furthermore, the size of the entire unit 30 in the thickness direction (vertical direction in FIGS. 1 and 2) is equal to the thickness dimension of a large component (for example, electrolytic capacitor 38) mounted on each substrate. The thickness is such that a relatively small thickness of 50 and a slight thickness of the cover 80 are added.
[0031]
Next, the cover 80 will be described.
The cover 80 is formed by, for example, pressing a steel plate material. As shown in FIG. 2, the cover 80 has a cover main body 81 that covers the opening side of the heat radiating case 50 (the back side of the insulating substrate 70). The fixing leg members 82 and 83 are fixed by, for example, spot welding. The peripheral edge of the cover body 81 is joined to the peripheral edge on the opening side of the heat radiating case 50 (excluding the portion where the connectors 71 to 74 are disposed) in an attached state, and an adhesive is attached to the joint as necessary. It is applied and a so-called adhesive seal is applied.
[0032]
Next, details of the overheat prevention function (first current limiting function and second current limiting function) of the control circuit 33 described above will be described.
The control circuit 33 performs, for example, the processes shown in FIGS. 5A and 5B every time the PWM drive signal is updated, thereby realizing the first current limiting function and the second current limiting function, respectively.
Here, the first current limiting function is based on the detected temperature TA by the thermistor 42 in order to keep the temperature of the circuit element of the metal substrate 60 (particularly, the soldered connection portion of the surface-mounted FET chip 61) below the allowable temperature. Thus, the motor current is reduced below the target current value as necessary so as to be equal to or less than the current limit value ImaxA.
The second current limiting function reduces the motor current to a current limit value ImaxB or less based on the detected current Im by the shunt resistor 39 in order to keep the temperature of the circuit elements of the motor 31 and the insulating substrate 70 below the allowable temperature. Thus, it is a function to lower the target current value as necessary.
[0033]
When the processing of the first current limiting function is started, first, in step S1 of FIG. 5A, data of the detected temperature TA (the output voltage value itself) from the output voltage value (A / D conversion value) of the thermistor 42. The current value of the power supply voltage Vb detected by the power supply voltage detection circuit described above is read. In order to prevent hunting and to avoid adverse effects on steering performance, it is desirable to reduce the resolution of the measured values of the detected temperature TA and power supply voltage Vb by the thermistor 42 as much as possible.
Next, in step S2, the current limit value ImaxA is determined from the relationship between the temperature and the maximum current shown in FIG. 6A based on the latest detected temperature TA and power supply voltage Vb data read in step S1. .
Here, the current limit value ImaxA in the first current limit function is the maximum value (in this case, as shown in FIG. 6A) until the detected temperature TA exceeds the detection threshold KA1 (first threshold). 60A), and when the detection temperature TA exceeds the detection threshold value KA1, the detection temperature TA decreases continuously and linearly as the detection temperature TA increases, and the detection temperature TA becomes the 0A threshold value KA2 (second threshold). The value is set to zero when the value is reached. Further, the detection threshold value KA1 and the 0A threshold value KA2 are 55 to 85 ° C. or 90 to 90 ° C. considering that the temperature of the soldering connection portion (junction portion) of the FET chip 61 does not exceed the allowable temperature, for example. Within a range of 120 ° C., it increases or decreases stepwise according to the power supply voltage Vb (each threshold value decreases if the power supply voltage Vb decreases, for example).
[0034]
Specifically, for example, when the power supply voltage Vb is 9.0 V or less, the detection threshold KA1 is 55 ° C., the 0A threshold KA2 is 90 ° C., and the power supply voltage Vb exceeds 9.0 V to 9.1 V. In the following cases, when the detection threshold KA1 is 59 ° C. and the 0A threshold KA2 is 94 ° C., the middle is omitted and the power supply voltage Vb is 11.5V or more, the detection threshold KA1 is 85 ° C. The values of the detection threshold value KA1 and the 0A threshold value KA2 for each range of the power supply voltage Vb are registered in the memory of the control circuit 33 as table data, for example, so that the 0A threshold value KA2 is 120 ° C. . Then, the control circuit 33 reads the data of the corresponding detection threshold value KA1 and 0A threshold value KA2 from the table data based on the latest data of the power supply voltage Vb read in step S1, and the control circuit 33 shown in FIG. The characteristic shown in FIG. 6A is determined by performing linear interpolation between the detection threshold value KA1 point and the 0A threshold value KA2 point in the characteristic, and the characteristic of the current limit value thus determined and step S1. The value of the current limit value ImaxA is determined based on the latest detected temperature TA data read in (1).
[0035]
Next, in step S3, it is determined whether or not the latest target current value (current command) set by the steering torque and the vehicle speed is equal to or greater than the current limit value ImaxA determined in step S2, and the value of the current limit value ImaxA is determined. If it is above, the process proceeds to step S4 to limit the current. Otherwise, it is less than the current limit value, and it is not necessary to limit the current.
In step S4, the target current value is updated to the current limit value ImaxA and corrected downward, or the gain in the output signal transmission system that outputs the PWM drive signal is reduced according to the target current value, so that the motor current is reduced. The current limit value ImaxA is adjusted (that is, as a result, the motor current is limited to a value equal to or smaller than the current limit value ImaxA).
Note that after step S4, the processing of one sequence is completed.
[0036]
Next, when the processing of the second current limiting function is started, first, in step S21 of FIG. 5B, the detected current Im is determined from the output voltage value (A / D conversion value) of the input line 40 of the shunt resistor 39. (Or the output voltage value itself) is sampled a plurality of times, and the estimated temperature TB of the motor 31 and the insulating substrate 70 is obtained from the data of the detected current Im by, for example, the arithmetic processing shown in FIG.
Specifically, by calculating the square of the detection current Im and multiplying the calculation result by the resistance value R of the monitoring target (for example, the resistance value of the motor 31), the heating value RIm of Joule heat generated in the monitoring target.²Are obtained sequentially. Further, the calorific value RIm thus determined.²Low-pass filter processing (processing that integrates the data string and removes high-frequency noise components) that takes into account the temperature characteristics of the monitoring target (characteristics obtained in advance through experiments or calculations) Thus, a temperature rise value ΔT (for example, TX + TY shown in FIG. 3A) due to the heat generation amount is obtained. Then, the estimated temperature TB (= TZ + ΔT) to be monitored at that time is obtained by adding the latest temperature rise value ΔT thus obtained and the initial temperature TZ measured in advance.
[0037]
FIG. 3A shows an example in which the temperature of the motor 31 is obtained as the estimated temperature TB. In this case, the calorific value RIm²On the other hand, a low-pass filter process (LPF1) in consideration of the brush temperature characteristics of the motor 31 is executed to obtain a temperature rise TX due to heat generated by the brush of the motor 31, and the motor rises with respect to this temperature rise TX. The temperature increase TY due to heat generation in the case of the motor 31 is obtained by executing low-pass filter processing (LPF2) in consideration of the case temperature characteristics of 31. Then, the temperature increase value ΔT of the entire motor 31 is obtained by adding these temperature increases TX and TY.
The initial temperature TZ is the initial temperature to be monitored (the temperature before the operation of the apparatus and is substantially the same as the outside air temperature). As the initial temperature TZ, for example, in a process (not shown) when the control circuit 33 is activated. The temperature detected by the thermistor 42 that has been sampled and stored can be used.
Needless to say, the estimation method of the estimated temperature TB is not limited to the above-described mode, and various preferable modes can be adopted according to the characteristics of the monitoring target.
[0038]
Next, in step S22, the current limit value ImaxB is determined from the relationship between the temperature and the maximum current shown in FIG. 6B based on the latest estimated temperature TB data calculated in step S21.
Here, the current limit value ImaxB in the second current limit function is a maximum value (in this case, as shown in FIG. 6B) until the estimated temperature TB exceeds the detection threshold KB1 (first threshold). 60A), and when the estimated temperature TB exceeds the detection threshold value KB1, the estimated temperature TB decreases continuously and linearly as the estimated temperature TB increases, and the estimated temperature TB decreases to the 0A threshold value KB2 (second threshold). The value is set to zero when the value is reached. However, in this case, when the estimated temperature TB increases from the normal state (state less than KB1) and when the estimated temperature TB once reaches the 0A threshold KB2 and decreases to less than KB1, A difference is provided between the values of the threshold values KB1 and KB2, so that a good hysteresis can be obtained.
[0039]
Specifically, when the estimated temperature TB increases from the normal state, the detection threshold KB1 is set to 160 ° C., for example, and the 0A threshold KB2 is set to 190 ° C. Further, until the estimated temperature TB once reaches the 0A threshold KB2 (190 ° C.) and then returns to less than KB1 (less than 140 ° C.), the detection threshold KB1 is 140 ° C. and the 0A threshold is 170. The detection threshold value KB1 and the 0A threshold value KB2 at the time of increase and recovery are registered in the memory of the control circuit 33. Then, the control circuit 33 determines whether it is increasing or returning based on the fluctuation state of the past estimated temperature TB calculated in step S21, and the corresponding detection threshold value KB1 and 0A threshold value KB2 are stored from the memory. By reading the data and performing a linear interpolation between the detection threshold KB1 point and the 0A threshold KB2 point in the characteristic of FIG. 6B, the characteristic of FIG. The current limit value ImaxB is determined based on the determined current limit value characteristics and the latest estimated temperature TB data obtained in step S21.
[0040]
Next, in step S23, it is determined whether or not the latest target current value (current command) set by the steering torque and the vehicle speed is equal to or greater than the current limit value ImaxB determined in step S22, and the value of the current limit value ImaxB. If so, the process proceeds to step S24 to limit the current. Otherwise, it is less than the current limit value, and it is not necessary to limit the current.
In step S24, the target current value is updated to the current limit value ImaxB and corrected downward, or the gain in the output signal transmission system that outputs the PWM drive signal is reduced in accordance with the target current value, so that the motor Adjustment is made so that the current becomes the current limit value ImaxB (that is, the motor current is limited to the current limit value ImaxB or less as a result).
Note that after step S24, the processing of one sequence is completed.
[0041]
According to the process of FIG. 5 described above, when the temperature of the monitoring target (circuit elements and motors of each board) rises near the allowable temperature and the above-described temperature TA or TB exceeds the detection threshold value, the motor current is maximized. It is limited to each current limit value smaller than the current 60A (that is, limited so as not to exceed the smaller one of ImaxA and ImaxB). For this reason, although the steering assist torque is reduced correspondingly and the steering wheel operation is increased correspondingly, it is possible to positively and reliably avoid the deterioration or damage of the circuit elements and motors of each board due to overheating. Furthermore, since the current that is the source of heat generation is limited, the entire unit and the motor can be reliably protected from overheating without increasing the capacity of the heat radiating case 50 and circuit elements, thereby increasing the size of the device. High reliability can be ensured while avoiding.
[0042]
With the unit 30 described above, the following practically excellent effects can be obtained.
(1) That is, since the unit 30 has a two-piece structure in which two substrates (metal substrate 60 and insulating substrate 70) are stacked and arranged, the number of assembly steps and the number of parts are reduced, and the productivity is increased. As a result, the increase in cost is avoided (compared with the configuration shown in FIG. 8, the cost can be significantly reduced).
In addition, each circuit component is mounted on an optimum substrate for each function, and the respective substrates are stacked. For this reason, the unit can be significantly reduced in size, and the mounting property on the vehicle is remarkably improved.
[0043]
That is, first, the drive circuit 32 and the shunt resistor 39, which generate a large amount of heat, are mounted on the metal substrate 60 having good thermal conductivity to ensure high heat dissipation. As a result, the width and interval of the conductor pattern on the metal substrate 60 constituting the circuit conductor of the drive circuit 32 can be set narrower than before, and the area of the drive circuit mounting portion and hence the entire area of the metal substrate 60 can be reduced. .
In addition, the control circuit 33 with a small amount of flowing current is mounted on the insulating substrate 70 which is a normal printed circuit board and can be disposed within the minimum necessary area. For this reason, interference between the mounting components on the metal substrate 60 and the mounting components on the insulating substrate 70 is avoided, the distance between the two substrates (stacking distance) is reduced, and the arrangement space for each of the substrates 60 and 70 and the mounting components is reduced. It is possible to reduce the thickness in the thickness direction (in this case, the thickness dimension is about the same as that of a single substrate).
In addition, by arranging the metal substrate 60 and the insulating substrate 70 in a stacked manner, the overall size in the surface direction is greatly reduced.
Therefore, the size in the surface direction of the unit is greatly reduced, and the size in the thickness direction of the unit can be made comparable to the conventional one, and the weight can be reduced accordingly.
[0044]
Furthermore, according to the present invention, the steering current and the vehicle speed can be reduced by the first current limiting function based on the detected temperature TA by the thermistor 42 mounted on the metal substrate 60 and the second current limiting function based on the detected current Im by the shunt resistor 39. Control is performed such that the motor current is forcibly reduced as needed from the corresponding target current value (that is, the motor current is limited to a value less than the current limit value based on the detected temperature TA and the estimated temperature TB described above). Thus, the temperatures of the circuit elements of the metal substrate 60 (mainly the switching elements, particularly the solder connection portions of the FET chip 61) and the temperatures of the circuit elements of the motor 31 and the insulating substrate 70 are reliably maintained below the allowable temperature. .
For this reason, the problem of thermal shock due to an increase in current (including poor connection due to solder melting) can be solved more reliably, and, for example, the conductor pattern of each board can be compared with the case without such an overheat prevention function. The width and interval can be set narrower, the capacity of the mounted component can be made relatively small, and further downsizing can be achieved as compared with the case of simply using the two-piece structure.
Therefore, according to this example, high applicability and mountability of the unit can be obtained even for a large vehicle with a large motor current.
[0045]
(2) In this case, the unit 30 includes a heat radiating case 50 arranged to constitute the outer wall on the lower surface side in FIG. 1, and the back surface of the metal substrate 60 is joined to the inner surface of the heat radiating case 50.
For this reason, it is possible to ensure high heat dissipation of heat generated in the drive circuit 32 and the like while avoiding an increase in the number of components. This is because the heat radiating case 50 which is a heat radiating member has a structure constituting the outer wall, so that a member (cover member) constituting the outer wall of the portion where the heat radiating member is provided becomes unnecessary, and heat radiated bonded to the metal substrate 60. Since the outer surface of the member is exposed to the outside air, high heat dissipation is obtained.
[0046]
(3) In the unit 30, the thermistor 42 is mounted at a position further outside the switching element (FET chip 61) that is a heat generating component on the metal substrate 60 and the signal terminal 63 away from the shunt resistor 39 (FIG. 3). (See (b)). For this reason, the temperature of the metal substrate 60 optimum for overheating protection of the circuit elements on the metal substrate 60 without being affected by the transient temperature change of the heat generating components (switching element and shunt resistor 39) on the metal substrate 60, That is, the base temperature of the connection part (junction part) such as the switching element that is most susceptible to overheating can be measured with high accuracy as the detection temperature TA. As a result, it is possible to avoid the adverse effect that the steering current torque is unnecessarily lowered due to the first current limiting function unnecessarily acting due to the transient temperature rise.
[0047]
(4) In the unit 30, when the detected temperature TA exceeds the detection threshold value KB1 (first threshold value), the current limit value ImaxA in the first current limiting function is set to the maximum current 60A according to the increase in the detected temperature TA. When the detected temperature TA reaches the 0A threshold KB2 (second threshold), the current limit value ImaxA becomes zero. For this reason, for example, when the degree of the high temperature state of the metal substrate 60 is a relatively low level that is not so urgent, the degree of limiting the current is reduced, and a flexible steering assist torque is ensured as much as possible. Control is possible. Particularly in this case, since the current limit value ImaxA is continuously reduced, a fine current limit according to the degree of the high temperature state of the metal substrate 60 is possible, and the metal substrate 60 can be controlled with the minimum necessary current limit. It is possible to precisely avoid overheating (particularly, a high temperature state that causes melting or the like of the connection portion of the switching element) while generating as much steering assist torque as possible.
[0048]
(5) In the unit 30, if the power supply voltage Vb is high, the temperature rise is relatively difficult to occur. Therefore, the detection threshold value KA1 and the 0A threshold value KA2 in the first current limiting function are changed to relatively large values, On the other hand, when the power supply voltage is low, the loss of the switching element increases and the temperature rises relatively easily. Therefore, the detection threshold value KA1 and the 0A threshold value KA2 are changed to relatively small values.
For this reason, the current limitation by the first current limiting function (in other words, the steering assist torque limitation) is executed to the minimum necessary level according to the fluctuation of the power supply voltage Vb, and the fluctuation margin of the power supply voltage Vb. It is not necessary to reduce the steering assist torque unnecessarily with sufficient margin, and it becomes possible to generate the steering assist torque as much as possible while avoiding a harmful high temperature state.
[0049]
(6) In the unit 30, when the estimated temperature TB exceeds the detection threshold value KB1 (first threshold value), the current limit value ImaxB in the second current limiting function is set to the maximum current 60A in accordance with the increase of the estimated temperature TB. When the estimated temperature TB reaches the 0A threshold KB2 (second threshold), the current limit value ImaxB becomes zero.
For this reason, for example, when the degree of the high temperature state of the motor 31 or the insulating substrate 70 is a relatively low level that is not so urgent, the degree of current limiting is reduced to ensure as much steering assist torque as possible. Flexible control is possible. Particularly in this case, since the current limit value ImaxB is continuously decreased, a fine current limit according to the degree of the high temperature state is possible, and the motor 31 and the insulating substrate 70 can be controlled with the minimum necessary current limit. It is possible to precisely avoid overheating (particularly, a high temperature state that causes melting or the like of the connection portion of the high-current circuit component on the insulating substrate 70) while generating as much steering assist torque as possible. .
[0050]
Summarizing the above, the unit 30 of the present embodiment can cope with a large current, is small and lightweight, has high mountability on a vehicle, has a simple configuration, has high productivity, and is relatively inexpensive. In addition, the inventors can use the structure of the unit 30 as described above for a large vehicle having a motor current of, for example, about 60A to 80A at the maximum by implementing the above-described overheat prevention function. It has been confirmed by trials of prototypes and the like that there is a significant advantage over the conventional configuration shown in FIG. 9 (or the configuration shown in FIG. 8) in terms of downsizing and the like.
[0051]
Needless to say, the present invention is not limited to the embodiments described above. For example, in the above-described embodiment, as shown in FIG. 3A, the motor temperature is calculated as the estimated temperature TB in the second current limiting function, and the motor temperature is used as an index to activate the second current limiting function. The overheating prevention of the circuit element on the board | substrate 70 is also implement | achieved. This is because the motor temperature and the temperature of the insulating substrate 70 can be handled in substantially the same manner. However, the temperature of the insulating substrate 70 may be estimated instead of the motor temperature, or the motor temperature and the temperature of the insulating substrate 70 are estimated separately, and the processing of the second current limiting function is performed on the motor temperature and the insulating substrate 70. It is also possible to execute the temperature separately.
In the above-described embodiment, the current limit value is linearly decreased in response to the temperature increase exceeding the first threshold value. However, the current limit value may be changed in a curvilinear (non-linear) manner or stepwise (step-like). To). Further, the change of the current limit value with respect to the power supply voltage may be continuously performed by performing proportional calculation, for example.
[0052]
In the above embodiment, when the temperature TA or TB exceeds the first threshold, the current limiting function is immediately activated and the maximum current is reduced from the normal value (for example, 60 A). It may be configured that the maximum current is reduced only when the time during which TA or TB exceeds the first threshold becomes a specified time (for example, 1 second to several seconds) or more, and the current limiting function is activated.
Further, in the above embodiment, the first current limiting function and the second current limiting function are realized by separate processing shown in FIG. 5, but both current limiting functions are performed by a series of processing as shown in FIG. Can also be realized. Here, steps S31 and S32 in FIG. 7 are the same processes as steps S1 and S2 in FIG. 5, and steps S33 and S34 in FIG. 7 are the same processes as steps S21 and S22 in FIG. Step S35 in FIG. 7 is a process for determining the smaller one of the current limit values ImaxA and ImaxB determined in steps S32 and S34 as the current limit value Imax. Steps S36 and S37 in FIG. 7 are processes for limiting the motor current to be equal to or less than the current limit value Imax, similarly to steps S3 and S4 or S23 and S24 in FIG.
[0053]
【The invention's effect】
According to the present invention, since the internal structure of the unit is a two-piece structure in which two substrates (metal substrate and insulating substrate) are stacked, the number of assembly steps and the number of parts are reduced, productivity is improved, and cost is increased. Up is avoided.
In addition, each circuit component is mounted on an optimum substrate for each function, and the respective substrates are stacked. For this reason, the unit can be significantly reduced in size, and the mounting property on the vehicle is remarkably improved.
That is, first, a drive circuit that includes a switching element that switches the energization state of the assist motor and generates a large amount of heat is mounted on a metal substrate having good thermal conductivity, and high heat dissipation is ensured. As a result, the width and interval of the conductor pattern on the metal substrate constituting the circuit conductor of the drive circuit can be set narrower than before, and the area of the drive circuit mounting portion and hence the entire area of the metal substrate can be reduced.
In addition, a control circuit with a small amount of flowing current can be mounted on a normal insulating substrate and disposed within a minimum necessary area. For this reason, it is possible to avoid interference between the mounting parts on the metal board and the mounting parts on the insulating board, reduce the distance between the two boards, and reduce the placement space between each board and its mounting parts in the thickness direction. It becomes.
In addition, since the metal substrate and the insulating substrate are stacked, the overall size in the plane direction is greatly reduced.
Therefore, the size in the surface direction of the unit is greatly reduced, and the size in the thickness direction of the unit can be made comparable to the conventional one, and the weight can be reduced accordingly.
[0054]
Furthermore, according to the present invention, the first current limiting function based on the temperature detected by the thermistor mounted on the metal substrate and the second current limiting function based on the current detected by the shunt resistor are used to achieve a target current value corresponding to the steering torque. The motor current is controlled to be forcibly reduced as necessary (that is, the motor current is limited to a predetermined current limit value or less based on the detected temperature or the like). The temperature of the switching element) and the temperature of the circuit elements of the assist motor and the insulating substrate are surely kept below the allowable temperature.
For this reason, the problem of thermal shock due to an increase in current (including poor connection due to solder melting) can be solved more reliably, and, for example, the conductor pattern of each board can be compared with the case without such an overheat prevention function. The width and interval can be set narrower, the capacity of the mounted component can be made relatively small, and further downsizing can be achieved as compared with the case of simply using the two-piece structure.
Therefore, according to the present invention, high applicability and mountability of the unit can be obtained even for a large vehicle with a large amount of current of the assist motor.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of a main part of a control unit.
FIG. 2 is a perspective view of a control unit (a cover removed state and a completed state).
FIG. 3 is a diagram showing an estimated temperature calculation process and an arrangement of elements on a metal substrate.
FIG. 4 is a diagram showing a circuit configuration of a control unit.
FIG. 5 is a flowchart showing processing of a current limiting function.
FIG. 6 is a diagram illustrating a characteristic of a current limit value.
FIG. 7 is a flowchart showing a current limiting function process (another example).
FIG. 8 is a diagram showing a comparative example of a control unit.
FIG. 9 is a diagram illustrating a conventional example of a control unit.
[Explanation of symbols]
30 Control unit
31 Assist motor
32 Drive circuit
33 Control circuit
39 Shunt resistance
50 Heat dissipation case
60 Metal substrate
63 Signal terminal
70 Insulating substrate
71-74 connector
Temperature detected by TA thermistor
Estimated temperature of TB assist motor or insulating substrate
ImaxA, ImaxB Current limit value
KA1, KB1 detection threshold (first threshold)
KA2, KB2 0A threshold (second threshold)
Vb Power supply voltage

Claims (4)

A control unit of an electric power steering device that generates a steering assist torque by an assist motor connected to a steering system of a vehicle,
A drive circuit including a switching element that connects each coil terminal of the assist motor to a high-potential power line or a low-potential power line in a switchable manner;
A control circuit for controlling the current of the assist motor to a predetermined target current value by operating the switching element according to the steering torque of the steering system so that the steering assist torque becomes a value corresponding to the steering torque. When,
The base material is made of metal, a metal substrate on which the driving circuit, a shunt resistor for detecting a current flowing through the assist motor through the driving circuit, and a thermistor for temperature detection are mounted,
An insulating substrate on which the base material is made of an insulating material and the control circuit is mounted;
The metal substrate and the insulating substrate are attached so as to overlap each other, and comprise a metal heat dissipation case constituting the outer wall of the unit,
The control circuit includes:
Based on the temperature detected by the thermistor, the current of the assist motor is set to the target current as necessary so that the current of the assist motor is not more than a predetermined current limit value in order to keep the temperature of the circuit element of the metal substrate below the allowable temperature. A first current limiting function for lowering than the value;
In order to keep the temperature of the circuit element of the assist motor and the insulating substrate below an allowable temperature, the current of the assist motor is required to be below a predetermined current limit value based on the current detected by the shunt resistor. Correspondingly have a second current limit function to lower than the target current value,
On the metal substrate, a signal terminal for connection of a signal line between the metal substrate and the insulating substrate is provided outside the mounting region of the switching element and the shunt resistor,
The control unit, wherein the thermistor is mounted at a further outer position of the signal terminal away from the switching element and the shunt resistor, which are heat generating components on the metal substrate . The current limit value in the first current limit function is:
When the temperature detected by the thermistor exceeds the first threshold value, it decreases stepwise or continuously as the temperature detected by the thermistor increases, and when the temperature detected by the thermistor reaches the second threshold value, zero. Or its neighborhood value,
2. The control unit according to claim 1, wherein the first threshold value and the second threshold value increase or decrease stepwise or continuously according to a detected value of the power supply voltage . A control unit of an electric power steering device that generates a steering assist torque by an assist motor connected to a steering system of a vehicle,
  A drive circuit including a switching element that connects each coil terminal of the assist motor to a high-potential power line or a low-potential power line in a switchable manner;
  A control circuit for controlling the current of the assist motor to a predetermined target current value by operating the switching element according to the steering torque of the steering system so that the steering assist torque becomes a value corresponding to the steering torque. When,
  The base material is made of metal, a metal substrate on which the driving circuit, a shunt resistor for detecting a current flowing through the assist motor through the driving circuit, and a thermistor for temperature detection are mounted,
  An insulating substrate on which the base material is made of an insulating material and the control circuit is mounted;
  The metal substrate and the insulating substrate are attached so as to overlap each other, and comprise a metal heat dissipation case constituting the outer wall of the unit,
  The control circuit includes:
  Based on the temperature detected by the thermistor, the current of the assist motor is set to the target current as necessary so that the current of the assist motor is not more than a predetermined current limit value in order to keep the temperature of the circuit element of the metal substrate below the allowable temperature. A first current limiting function for lowering than the value;
  In order to keep the temperature of the circuit element of the assist motor and the insulating substrate below an allowable temperature, the current of the assist motor is required to be below a predetermined current limit value based on the current detected by the shunt resistor. And a second current limiting function to reduce the target current value below the target current value,
  The current limit value in the first current limit function is:
  When the temperature detected by the thermistor exceeds the first threshold value, it decreases stepwise or continuously as the temperature detected by the thermistor increases, and when the temperature detected by the thermistor reaches the second threshold value, zero. Or its neighborhood value,
  The control unit according to claim 1, wherein the first threshold value and the second threshold value are increased or decreased stepwise or continuously according to a detected value of the power supply voltage. The control circuit includes:
A function of calculating an estimated temperature of the assist motor or the insulating substrate by calculating a temperature increase due to Joule heat from a detected current due to the shunt resistance and adding an initial temperature to the temperature increase,
The current limit value in the second current limit function is:
When the estimated temperature exceeds the first threshold value, it decreases stepwise or continuously as the estimated temperature increases, and when the estimated temperature reaches the second threshold value, it becomes zero or a value near it. The control unit according to claim 2 or 3, wherein

Images