JP2017096694A - Current value calculation device and on-vehicle system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current value calculation device capable of calculating a current flowing in a pattern wiring in consideration of the temperature change of a resistance value, without requiring a hardware configuration for absorbing the change of the resistance value of the pattern wiring.SOLUTION: An arithmetic processing part executes a first process (ST3) for calculating a current value on the basis of the voltage of the pattern wiring and the resistance value of the pattern wiring, a second process (ST4) for calculating power consumption in the pattern wiring on the basis of the resistance value and the current value, a third process (ST5) for calculating a second temperature which is the temperature of the pattern wiring by adding a product between heat resistance from the pattern wiring to a temperature detection part and the power consumption to the first temperature of the periphery of the pattern wiring and for updating the resistance value on the basis of the second temperature, and a fourth process (ST3) for calculating the current value on the basis of the voltage and the resistance value updated in the third process in this order.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a current value calculation device and an in-vehicle system.

  Patent Document 1 describes a current detection circuit. This current detection circuit employs a diode connected in series with a resistor on one side of a resistor bridge having four sides. The technique disclosed in Patent Document 1 absorbs the temperature characteristic of a resistance for current measurement provided on a side opposite to the one side by using the temperature characteristic of the diode.

JP-A 63-128267

  However, when a large current flows through the current detection circuit of Patent Document 1, it is necessary to employ a diode having a large current rating. The size of such a diode is large and undesirable.

  Therefore, the present invention provides a current value calculation device capable of calculating the current flowing through the pattern wiring in consideration of the temperature change of the resistance value without requiring a hardware configuration for absorbing the temperature change of the resistance value of the pattern wiring. The purpose is to provide.

  The current value calculation device is a device for obtaining a current value of a current flowing in a pattern wiring provided in a vehicle. The current value calculation device includes a temperature detection unit that detects a first temperature that is a temperature around the pattern wiring, a voltage detection unit that detects a voltage applied to the pattern wiring, and an arithmetic processing unit that calculates the current value. Is provided. The arithmetic processing unit calculates a current value based on the voltage and a resistance value of the pattern wiring, and calculates power consumption in the pattern wiring based on the resistance value and the current value. Adding a product of the second step, the thermal resistance from the pattern wiring to the temperature detection unit, and the power consumption to the first temperature to calculate a second temperature as the temperature of the pattern wiring; A third step of updating the resistance value based on the second temperature and a fourth step of calculating the current value based on the voltage and the resistance value updated in the third step are executed in this order. .

  According to this current value calculation device, the current flowing through the pattern wiring can be calculated in consideration of the temperature change of the resistance value without requiring a hardware configuration for absorbing the change in the resistance value of the pattern wiring.

It is a figure which shows roughly an example of a structure of an electric current detection apparatus. It is a figure which shows an example of an internal structure of a voltage detection part roughly. It is a figure which shows an example of an internal structure of an arithmetic processing part roughly. It is a figure which shows an example of a thermal model schematically. It is a flowchart which shows an example of operation | movement of an electric current value calculation apparatus. It is a flowchart which shows an example of operation | movement of an electric current value calculation apparatus. It is a figure which shows roughly an example of a structure of a vehicle-mounted system.

First embodiment.
FIG. 1 is a diagram schematically illustrating an example of the configuration of the current value calculation apparatus 100. This current value calculation device 100 is mounted on a vehicle. For example, a power source such as a generator and a battery is mounted on the vehicle, and the power source supplies power to a load. For example, the current value calculation device 100 calculates the current value of the load current flowing from the power source to the load.

  The current value calculation device 100 includes a pattern wiring 2, an arithmetic processing unit 3, a temperature detection unit 4, and a voltage detection unit 5. In the illustration of FIG. 1, each of these components is provided on the substrate 1. The substrate 1 is a printed circuit board, for example, and has an insulating property. The pattern wiring 2 is used to detect current and functions as a so-called shunt resistor. That is, the pattern wiring 2 is provided on the path through which the load current flows. The pattern wiring 2 is made of a metal such as copper or silver. In the above example, the pattern wiring 2 may be formed as a part of wiring that connects the power source and the load.

  The temperature detection unit 4 detects the temperature Tatm around the pattern wiring 2 and outputs it to the arithmetic processing unit 3. In the illustration of FIG. 1, the temperature detection part 4 is provided on the board | substrate 1 with which the pattern wiring 2 is formed. As a method of temperature detection by the temperature detection unit 4, an appropriate method may be employed. For example, the temperature detection unit 4 may have a thermistor. The resistance value of this thermistor changes depending on the temperature. Then, the voltage and current of the thermistor may be detected, the resistance value of the thermistor may be calculated based on these, and the temperature of the thermistor may be detected based on the resistance value.

  The voltage detection unit 5 detects a voltage applied to the pattern wiring 2, specifically, a voltage V between both ends of the pattern wiring 2, and outputs this to the arithmetic processing unit 3. In the illustration of FIG. 1, the voltage detection unit 5 is also provided on the substrate 1. The voltage detection unit 5 is normally provided in order to obtain the current value of the current flowing through the shunt resistor.

  FIG. 2 shows an example of the internal configuration of the voltage detection unit 5. The voltage detection unit 5 includes resistors R1 to R3, a differential amplifier 52, and a transistor 51, for example. One end of the resistor R 1 is connected to one end 2 a of the pattern wiring 2, and the other end is connected to one end of the transistor 51 and the first input end of the differential amplifier 52. One end of the resistor R2 is connected to the other end 2b of the pattern wiring 2, and the other end is connected to the other end of the transistor 51, the second input end of the differential amplifier 52, and one end of the resistor R3. The other end of the resistor R3 is grounded. In the voltage detector 5, the voltage V of the pattern wiring 2 is amplified and detected as the voltage of the resistor R3.

  The arithmetic processing unit 3 calculates the current value of the current flowing through the pattern wiring 2 based on the temperature Tatm detected by the temperature detection unit 4 and the voltage V detected by the voltage detection unit 5. In the illustration of FIG. 1, the arithmetic processing unit 3 is also provided on the substrate 1. FIG. 3 is a diagram illustrating an example of a connection relationship among the arithmetic processing unit 3, the temperature detection unit 4, and the voltage detection unit 5. The temperature detection unit 4 and the voltage detection unit 5 output the temperature Tatm and the voltage V to the arithmetic processing unit 3, respectively. The arithmetic processing unit 3 includes, for example, AD conversion units 31 and 32 and a current value calculation unit 33. In the example of FIG. 3, the AD conversion units 31 and 32 are represented as “ADC”. An analog signal indicating the temperature Tatm is input to the AD conversion unit 31. The AD conversion unit 31 converts this into a digital signal and outputs it to the current value calculation unit 33. An analog signal indicating the voltage V is input to the AD conversion unit 32. The AD conversion unit 32 converts this into a digital signal and outputs it to the current value calculation unit 33.

  Here, the arithmetic processing unit 3 includes, for example, a microcomputer and a storage device. The microcomputer executes each processing step (in other words, a procedure) described in the program. The storage device is composed of one or more of various storage devices such as a ROM (Read Only Memory), a RAM (Random Access Memory), a rewritable nonvolatile memory (EPROM (Erasable Programmable ROM), etc.), and a hard disk device, for example. Is possible. The storage device stores various information, data, and the like, stores a program executed by the microcomputer, and provides a work area for executing the program. It can be understood that the microcomputer functions as various means corresponding to each processing step described in the program, or can realize that various functions corresponding to each processing step are realized. The arithmetic processing unit 3 is not limited to this, and various procedures executed by the arithmetic processing unit 3 or various means or various functions implemented may be realized by hardware.

  The arithmetic processing unit 3 (more specifically, the current value calculating unit 33) updates the resistance value Rs of the pattern wiring 2 based on the voltage V and the temperature Tatm, and calculates the current value I of the current flowing through the pattern wiring 2 as a voltage. Calculation is based on V and the resistance value Rs. This will be specifically described below.

  It is known that the resistance value Rs of the pattern wiring 2 changes depending on the temperature Ts of the pattern wiring 2 as shown by the following equation.

  Rs = Rs0 · {1 + α (Ts−T0)} (1)

  Here, T0 is a reference temperature, and for example, 25 degrees Celsius can be adopted. Rs0 is the resistance value of the pattern wiring 2 when the temperature is the reference temperature T0, and is obtained in advance by experiment or simulation. α is a change rate of the resistance value of the pattern wiring 2 per unit temperature, and is obtained in advance by experiment or simulation. The resistance value Rs0, the reference temperature T0, and the change rate α are stored in, for example, the storage unit of the arithmetic processing unit 3 or the like.

  By the way, when a current flows through the pattern wiring 2, the pattern wiring 2 generates heat with Joule heat W equal to its power consumption according to the so-called Joule's law. As a result, the temperature Ts of the pattern wiring 2 rises. FIG. 4 is a diagram schematically showing an example of a thermal model. In this thermal model, the pattern wiring 2 functions as the heating element Hth, and a capacitor Cth indicating the amount of heat that can be stored in the pattern wiring 2 is connected in parallel to the heating element Hth. In FIG. 4, the thermal resistance Rth from the pattern wiring 2 to the temperature detection unit 4 is shown, and the thermal resistance R from the temperature detection unit 4 to the outside is also shown. The temperature Ts of the pattern wiring 2 is expressed by the following equation. The thermal resistance Rth can be set in advance, for example, by simulation or experiment. The thermal resistance Rth is stored in, for example, the storage unit of the arithmetic processing unit 3. In order to take into account the time constant due to the thermal resistance Rth and the capacitance Cth, the thermal resistance Rth can be changed over time. For example, it can be realized by performing weighted filter processing calculation. If this is done, an error due to a change in time can be corrected.

  Ts = Tatm + W · Rth (2)

  According to the equations (1) and (2), when the Joule heat W is calculated and the temperature Tatm is detected, the product of the thermal resistance Rth and the Joule heat W is added to the temperature Tatm to calculate the temperature Ts. It can be seen that the resistance value Rs can be calculated based on the temperature Ts. FIG. 5 is a flowchart showing an example of the operation of the current value calculation apparatus 100. This operation is started, for example, when a current starts to flow through the pattern wiring 2. For example, when the pattern wiring 2 is provided between the power source and the load, the current value calculation device 100 starts the operation of FIG. 5 when a current starts flowing from the power source to the load and the load starts the operation.

  In the illustration of FIG. 5, a set of steps ST1 to ST5 is repeatedly executed. An integer n is adopted as the number of repetitions. The integer n is an integer greater than or equal to 1, and increases by one whenever the number of repetitions increases by one. In the following, [n] is added to each value so as to consider each value as a temporal discrete value as necessary. For example, the resistance value Rs used in the (n + 1) th process is also expressed as a resistance value Rs [n].

  First, in step ST <b> 1, the temperature detection unit 4 detects the temperature Tatm and outputs it to the arithmetic processing unit 3. Note that the temperature Tatm detected by the temperature detector 4 may be substantially constant during the operation of the load. That is, the temperature detection unit 4 may be provided at a position that is not easily affected by the heat generated by the pattern wiring 2. As such a position, a position away from the pattern wiring 2 in the substrate 1 can be adopted.

  Next, in step ST <b> 2, the voltage detection unit 5 detects the voltage V [n] and outputs it to the arithmetic processing unit 3. Next, in step ST3, the arithmetic processing unit 3 calculates a current value I [n] based on the voltage V [n] and the resistance value Rs [n]. Specifically, the current value I [n] is calculated based on the following equation.

  I [n] = V [n] / Rs [n] (3)

  The resistance value Rs [n] can be calculated as follows when n = 1, that is, in the first operation. That is, in the first operation, since the load current has just flowed, it can be considered that the temperature Ts of the pattern wiring 2 is approximately the same as the temperature Tatm. Therefore, the resistance value Rs [1] is calculated as Ts = Tatm. Specifically, the resistance value Rs [1] is calculated based on the following equation.

  Rs [1] = Rs0 · {1 + α (Tatm−T0)} (4)

  On the other hand, when n is 2 or more, that is, in the second and subsequent operations, the resistance value Rs [n + 1] calculated (updated) in the previous step ST5 is adopted as the resistance value Rs [n]. To do. Step ST5 will be described in detail later.

  Next, in step ST4, the arithmetic processing unit 3 calculates Joule heat W [n]. For example, the Joule heat W [n] is calculated using the following equation.

W [n] = Rs [n] · I [n] ² (5)

  Next, in step ST5, the arithmetic processing unit 3 calculates a resistance value Rs [n + 1] based on the detected temperature Tatm and the calculated Joule heat W [n]. For example, first, the temperature Ts [n] of the pattern wiring 2 is calculated based on the temperature Tatm and the Joule heat W [n]. Specifically, the temperature Ts [n] is calculated by the following equation with Ts = Ts [n] and W = W [n] in the equation (2).

  Ts [n] = Tatm + W [n] · Rth (6)

  Then, the resistance value Rs [n + 1] is calculated by the following equation with Ts = Ts [n] in the equation (1). That is, the resistance value Rs is updated.

  Rs [n + 1] = Rs0 · {1 + α (Ts [n] −T0)} (7)

  As a result, a value closer to the actual resistance value Rs is calculated as the resistance value Rs [n + 1]. The resistance value Rs [n + 1] is adopted as the resistance value R in the next step ST1. Therefore, in step ST3, the current value I close to the actual value is calculated.

  As described above, according to the present embodiment, the current value I is calculated by the arithmetic processing of the arithmetic processing unit 3. Therefore, the diode for temperature compensation described in Patent Document 1 is unnecessary. In the present embodiment, although the temperature detection unit 4 is provided, a current dependent on the current of the pattern wiring 2 does not flow through the temperature detection unit 4. The diode described in Patent Document 1 is not necessary, and the current of the pattern wiring 2 does not flow through the temperature detection unit 4. Therefore, the current value detection unit 100 can be easily applied to a configuration in which a large current flows through the pattern wiring 2.

  Moreover, the calculation accuracy of the current value I can be improved as compared with the case where the current value I is calculated by always considering the temperature Tatm detected by the temperature detection unit 4 as the temperature Ts of the pattern wiring 2. That is, the value of the current flowing through the pattern wiring 2 is considered in consideration of the temperature change of the resistance value Rs without requiring a hardware configuration (the diode) for absorbing the temperature change of the resistance value Rs of the pattern wiring 2. It can be calculated.

  Note that the execution timing of steps ST1 and ST2 is not limited to the above example. Step ST1 may be performed before step ST5, and step ST2 may be performed before step ST3. When the temperature Tatm is substantially constant, step ST1 may be executed only for the first operation. That is, after the second time, a set of steps ST2 to ST5 may be repeatedly executed.

  Further, the temperature detector 4 is not necessarily provided on the substrate 1. For example, when a package that accommodates the substrate 1 is provided, it may be provided inside the package, or may be provided on the surface of the package.

Modified example.
In the above example, one set of steps ST1 to ST5 is repeatedly executed. However, although the calculation accuracy of the current value is reduced, it is not necessary to perform the repeated operation. FIG. 6 is a flowchart showing an example of the operation of the current value calculation apparatus 100. In the example of FIG. 6, steps ST1 to ST6 are executed in this order. In step ST6, the current value I [n] is calculated using the resistance value Rs [n + 1] calculated in step ST5. That is, the current value I [n] is calculated using the voltage V [n] detected in step ST2 and the resistance value Rs [n + 1] calculated in step ST5. This also makes it possible to calculate a current value I [n] that is closer to the actual value than the current value I [n] calculated in step ST3. However, as shown in FIG. 5, the calculation accuracy of the current value I [n] can be further improved by repeated execution.

Second embodiment.
FIG. 7 is a diagram schematically showing an example of the configuration of the in-vehicle system 110. This in-vehicle system 110 is mounted on a vehicle. The in-vehicle system 110 includes a power supply 10, a current limiting unit 20, a load 30, and a current value calculation device 100. In the illustration of FIG. 7, the power supply 10 is connected to the load 30 via the current limiting unit 20 and the pattern wiring 2. The power source 10 is a battery or a generator (for example, an alternator). The power supply 10 starts to supply power to the load 30 via the current limiting unit 20. The load 30 may be an arbitrary load mounted on the vehicle, for example, a steering motor.

  The current limiting unit 20 limits the load current flowing to the load 30 when the current value calculated by the current value calculating unit 33 exceeds the threshold value. In the illustration of FIG. 7, the current limiting unit 20 includes a switch 21, a driver circuit 22, a determination unit 34, and a logical product unit 35. The switch 21 is, for example, a transistor, and is provided between the power supply 10 and the load 30 (in the illustration of FIG. 7, between the power supply 10 and the pattern wiring 2). The control electrode of the switch 21 is connected to the output of the AND unit 35 via the driver circuit 22.

  In the example of FIG. 7, the determination unit 34 and the logical product unit 35 are also included in the arithmetic processing unit 3. A voltage indicating the current value I calculated by the current value calculation unit 33 is input to the determination unit 34. The determination unit 34 determines whether or not the current value I is larger than a threshold value. When the current value I is larger than the threshold value, the switch 21 is turned off. For example, the determination unit 34 outputs a voltage corresponding to the logic level “L” when the current value I is larger than the threshold value, and outputs a voltage corresponding to the logic level “H” when the current value I is smaller than the threshold value. To do.

  The output of the determination unit 34 is input to the logical product unit 35. An external load drive signal G is also input to the AND unit 35. The load drive signal G takes a logic level “H” when driving the load 30 and takes a logic level “L” when not driving the load 30. The logical product unit 35 outputs the logical product of the output from the determination unit 34 and the load drive signal to the driver circuit 22. Therefore, the signal input to the driver circuit 22 has the same logic level as the output of the load drive signal G when the current value I is smaller than the threshold value. On the other hand, when the current value I is smaller than the threshold value, the signal input to the driver circuit 22 takes the logic level “L” regardless of the output of the load drive signal G.

  The driver circuit 22 outputs the input signal to the switch 21 as a switch signal. When the current value I is smaller than the threshold value, the switch 21 is turned off / on in accordance with the logic level “L” / “H” taken by the load drive signal. However, when the current value I is larger than the threshold value, the switch 21 is turned off regardless of the logic level taken by the load drive signal G. Therefore, it is possible to suppress the load current exceeding the threshold value from flowing through the load 30.

  Moreover, since the current value I is calculated in the same manner as in the first embodiment, the current value I considering the temperature is calculated. Therefore, even if the temperature fluctuates, the switch 21 can be turned off based on the appropriate current value I. Therefore, it can suppress more appropriately that the load current exceeding a threshold value flows into the load 30.

  Each structure demonstrated by each said embodiment and each modification can be suitably combined unless it mutually contradicts.

  As described above, the present invention has been described in detail. However, the above description is illustrative in all aspects, and the present invention is not limited thereto. It is understood that countless variations that are not illustrated can be envisaged without departing from the scope of the present invention.

2 pattern wiring 3 arithmetic processing unit 4 temperature detection unit 5 voltage detection unit 20 current limiting unit 100 current value calculation device 110 in-vehicle system

Claims (2)

An apparatus for obtaining a current value of a current flowing in a pattern wiring provided in a vehicle,
A temperature detection unit for detecting a first temperature as a temperature around the pattern wiring;
A voltage detector for detecting a voltage applied to the pattern wiring;
An arithmetic processing unit for obtaining the current value,
The arithmetic processing unit includes:
A first step of calculating the current value based on the voltage and the resistance value of the pattern wiring;
A second step of calculating power consumption in the pattern wiring based on the resistance value and the current value;
A product of a thermal resistance from the pattern wiring to the temperature detection unit and the power consumption is added to the first temperature to calculate a second temperature as a temperature of the pattern wiring, and based on the second temperature. A third step of updating the resistance value,
A fourth step of calculating the current value based on the voltage and the resistance value updated in the third step;
A current value calculation device that executes the above in this order. A load provided on the vehicle;
The current value calculation device according to claim 1, and a current limiting unit that limits a load current flowing through the load when the current value exceeds a threshold value,
The pattern wiring is an in-vehicle system provided on a path through which the load current flows.

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