JP5407902B2 - PM detector - Google Patents

Description

  The present invention relates to a DPF that collects PM in exhaust gas of an internal combustion engine and burns and removes the accumulated PM with high-temperature exhaust gas, and can accurately detect the amount of accumulated PM with a simple configuration. The present invention relates to a PM detection device.

  In a vehicle equipped with an internal combustion engine such as a diesel engine, a diesel particulate filter (DPF) is installed in the exhaust gas exhaust passage from the internal combustion engine to the atmosphere. That is, particulate matter (Particurate Matter; hereinafter referred to as PM) is collected. The DPF is a filter mainly made of ceramic and having a large number of honeycomb pores (or square pores). In the DPF, PM is collected by adhering to the surface of the honeycomb pores serving as exhaust gas passages.

  If an excessive amount of PM collected in the DPF accumulates, the exhaust pressure of the internal combustion engine increases and the characteristics of the internal combustion engine deteriorate. Therefore, in the internal combustion engine, if necessary, additional fuel injection control is performed to perform additional fuel injection after the main injection, thereby raising the exhaust gas temperature, thereby raising the DPF and burning and removing the PM accumulated in the DPF. To do. This operation is called DPF forced regeneration.

  If the amount of accumulated PM is large at the time of forced regeneration of the DPF, a large amount of PM is burned, the temperature rises excessively, and the DPF is melted. In order to avoid this, it is desirable to detect the amount of PM deposited and start the DPF forced regeneration based on the detected amount of deposition. However, conventionally, since the amount of deposition cannot be accurately detected, a relatively large safety factor is taken, and the DPF is forcibly regenerated before the detected amount of deposition becomes too large. As a result, DPF forced regeneration is executed at an interval shorter than necessary.

  However, if the DPF forced regeneration is executed at an interval shorter than necessary, extra fuel is consumed, resulting in a deterioration in fuel consumption. Therefore, it is desirable to accurately detect the amount of accumulated PM and perform DPF forced regeneration at the most appropriate time.

JP 2008-139294 A JP 2009-97410 A

  Previously, the present inventors obtained the knowledge that when a plurality of electrodes are installed in the DPF, the capacitance between the electrodes varies depending on the amount of PM deposited, and filed a PM sensor using this. However, since the electrostatic capacity of the PM sensor having electrodes installed on the DPF is very small, it is difficult to measure with a conventional apparatus using an inexpensive apparatus.

  In the prior art, a fixed capacitor or a fixed resistor is connected in series to a capacitance measurement target, and a voltage is generated between both ends of the capacitance measurement target by flowing a high-frequency alternating current. Is then input to the AD converter through a low-pass filter, and the capacitance is calculated from the voltage read by the AD converter.

  However, the capacitance of the PM sensor is very small, for example, several pF to several hundred pF. When the frequency of the alternating current to be applied is several hundred KHz or less, the impedance is very high. Therefore, the detection circuit also needs to have a correspondingly high impedance. However, it is difficult to ensure a high impedance from the viewpoint of the distributed capacitance of the elements and wirings, and it is impossible to accurately measure the capacitance.

  On the other hand, if the frequency of the alternating current is increased in order to reduce the impedance, the frequency band used for communication is generated, causing problems of unnecessary radiation and the influence of standing waves generated in the wiring between the PM sensor and the detection circuit. Therefore, the characteristics of the PM sensor greatly change depending on the length of the wiring and the characteristic impedance. Furthermore, in order to calculate the capacitance from the read voltage, the AC current voltage must be accurate, but in order to obtain an AC power supply with an accurate amplitude, a complicated control circuit is required, which stabilizes the operation. It is disadvantageous in terms of sex and cost.

  As described above, in the PM sensor in which the capacitance between the electrodes varies depending on the PM deposition amount, the capacitance cannot be accurately measured by the conventional technique, so the PM deposition amount is accurately detected. Is difficult.

  Accordingly, an object of the present invention is to provide a PM detection apparatus that can solve the above-described problems and can accurately detect the amount of accumulated PM with a simple configuration.

  To achieve the above object, the present invention detects the amount of particulate matter (hereinafter referred to as PM) accumulated in a diesel particulate filter (hereinafter referred to as DPF) inserted in an exhaust gas exhaust passage from an internal combustion engine to the atmosphere. A PM sensor in which the capacitance between two electrodes arranged in the DPF varies according to the amount of PM deposited, an electrically controlled variable resistor, and three fixed resistors. A bridge circuit in which the PM sensor is connected in parallel to the variable resistor, and the electrically controlled variable capacitor is connected in parallel to one of the fixed resistors adjacent to the variable resistor; Of the four connection points of the bridge circuit, the connection point where the variable capacitor and the fixed resistor, the variable resistor and the PM sensor are connected, and the connection point located at the diagonal are the voltage. A DC power source and an AC power source for selectively applying a DC voltage and an AC voltage between the voltage application points, and a DC voltage applied between the voltage application points to balance the bridge circuit. Adjusting the variable resistor, and then adjusting the variable capacitor so that the bridge circuit is balanced by applying an AC voltage between the voltage application points. And a detector for detecting the amount of deposition.

  Among the four connection points of the bridge circuit, two connection points sandwiched between the voltage application points are measurement points, and a differential in which a positive input terminal and a negative input terminal are connected to each of the measurement points. An amplifier, and the detection unit adjusts the variable resistor so that an output of the differential amplifier becomes 0 when a DC voltage is applied between the voltage application points, and an AC voltage is applied between the voltage application points. The variable capacitor may be adjusted so that the output of the differential amplifier becomes zero when is applied.

  The present invention exhibits the following excellent effects.

  (1) The configuration is simple.

  (2) The amount of PM deposition can be accurately detected.

It is a circuit block diagram of PM detection apparatus which shows one Embodiment of this invention. It is a characteristic view of PM sensor used for PM detection device of the present invention. (A)-(d) is a schematic block diagram of PM sensor used for PM detection apparatus of this invention. It is a schematic block diagram of the vehicle carrying the PM detection apparatus of this invention.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, a PM detection device 1 according to the present invention is electrically controlled with a PM sensor 3 in which the capacitance between two electrodes arranged in a DPF 2 changes depending on the amount of PM deposited. Variable resistor 4 and three fixed resistors 5, 6, 7 are sequentially connected, PM sensor 3 is connected in parallel to variable resistor 4, and electrically controlled to fixed resistor 5 adjacent to variable resistor 4. Of the four connection points of the bridge circuit 9 and the variable capacitor 8, the fixed resistor 5, the variable resistor 4, and the PM sensor 3 among the four connection points of the bridge circuit 9. A point a and a connection point b located diagonally there are voltage application points a and b, and a DC power source 10 and an AC for selectively applying a DC voltage and an AC voltage between the voltage application points a and b. DC power between the power supply 11 and the voltage application points a and b And the variable resistor 4 is adjusted so that the bridge circuit 9 is balanced, and then the variable capacitor 8 is adjusted so that the bridge circuit 9 is balanced by applying an AC voltage between the voltage application points a and b. And a detector 12 for detecting the amount of PM deposited from the capacitance of the variable capacitor 8 at the time.

  Furthermore, in this embodiment, the PM detection apparatus 1 has two connection points c and d sandwiched between voltage application points a and b among the four connection points of the bridge circuit 9 as measurement points. Each of the points c and d is provided with a differential amplifier 13 having a positive input terminal and a negative input terminal connected thereto, and the detection unit 12 is connected to the differential amplifier 13 when a DC voltage is applied between the voltage application points a and b. The variable resistor 4 is adjusted so that the output becomes 0, and the variable capacitor 8 is adjusted so that the output of the differential amplifier 13 becomes 0 when an AC voltage is applied between the voltage application points a and b. It has become.

  The DPF 2 is a conventionally known one and is made of a ceramic having a large number of honeycomb pores.

  As shown in FIG. 2, the PM sensor 3 has a characteristic that the capacitance increases in proportion to an increase in the amount of PM trapped in the DPF 2.

  The PM sensor 3a shown in FIG. 3A is provided with one cylindrical piece-like electrode 31 along one half of the outer periphery of the columnar DPF 2, and another one with a cylindrical piece along the opposite half. Two electrodes 32 are provided. As a result, when the two electrodes 31 and 32 face each other with the DPF 2 sandwiched from both sides and PM is collected in the DPF 2, the capacitance changes due to the influence of the PM existing between the electrodes 31 and 32.

  In the PM sensor 3b shown in FIG. 3B, one cylindrical electrode 33 is provided so as to cover the entire outer periphery of the columnar DPF 2, and another cylindrical electrode 34 is provided at the center of the DPF 2. Is. As a result, when the two electrodes 33 and 34 are arranged concentrically inside and outside of the DPF 2 and PM is collected in the DPF 2, the capacitance changes due to the influence of the PM existing between the electrodes 33 and 34.

  The PM sensor 3c shown in FIG. 3C is provided with one cylindrical electrode 35 so as to cover the entire outer periphery of the columnar DPF 2, and a plurality of lines are arranged in the center of the DPF 2 in a cylindrical shape. Another electrode 36 is provided.

  The PM sensor 3d shown in FIG. 3D is provided with two mesh-shaped electrodes 37 and 38 upstream and downstream of a cylindrical DPF 2, respectively.

  Returning to the description of FIG.

  The variable resistor 4 is electrically controlled by the detection unit 12 and changes its resistance value. For example, rotating a potentiometer with a stepping motor, rotating a rotary potentiometer with a DC motor and controlling the rotation angle with a rotation angle sensor, switching a tap of a ladder circuit made up of multiple resistors, etc. Thus, the resistance value changes stepwise between appropriate upper limit resistance values and lower limit resistance values steplessly or in appropriate steps.

  As the fixed resistors 5, 6 and 7, conventionally known resistors are used. The resistance values of the fixed resistors 5, 6 and 7 may be different from each other or may be equal to each other.

  The variable capacitor 8 includes a rotary air variable condenser that is rotated by a stepping motor, a rotary air variable condenser that is rotated by a DC motor and a rotation angle sensor that controls the rotation angle, and a plurality of fixed capacitors having different electrostatic capacities. It is possible to obtain a plurality of composite capacitances with different values by changing the connection between the appropriate upper limit capacitance and the lower limit capacitance in a stepless manner or in an appropriate stepwise manner. The electric capacity changes.

  The bridge circuit 9 constitutes a so-called Wheatstone bridge having voltage application points a and b and measurement points c and d. The bridge circuit 9 is a resistance bridge composed of four resistors at the time of direct current and an alternating current impedance composed of four alternating currents at the time of alternating current. Become a bridge.

  As the DC power source 10, an in-vehicle battery power source or a secondary DC power source using a battery power source as a primary power source can be used. The DC power supply 10 can control whether or not to apply a DC voltage between the voltage application points a and b from the detection unit 12.

  The AC power supply 11 is for operating the PM sensor 3 and the variable capacitor 8 in the bridge circuit 9 as AC impedance, and is constituted by an oscillator, for example. The frequency is preferably a low frequency that does not cause the problem of unnecessary radiation, for example, several hundred KHz or less. The AC power supply 11 can control whether or not an AC voltage is applied between the voltage application points a and b from the detection unit 12.

  The detection unit 12 is a program-type digital circuit that controls the DC power supply 10, the AC power supply 11, the variable resistor 4, and the variable capacitor 8, reads the output voltage of the differential amplifier 13, and balances the bridge circuit 9. Can be detected. The detector 12 is preferably incorporated in an electronic control unit (ECU) that controls fuel injection and the like of the vehicle.

  The differential amplifier 13 is an operational amplifier that amplifies and outputs the voltage difference between the positive input terminal and the negative input terminal.

  As shown in FIG. 4, the PM detection device 1 of the present invention detects the amount of accumulated PM in the DPF 2 inserted into the exhaust gas discharge passage 42 from the internal combustion engine 41 of the vehicle to the atmosphere. A PM sensor 3 is installed in the DPF 2. The bridge circuit 9, the DC power supply 10 (in the case of a secondary DC power supply), the AC power supply 11, and the differential amplifier 13 are mounted on the circuit board 43. The circuit board 43 and the detection unit 12 can be installed in appropriate places such as a vehicle interior, an engine room, and a vehicle body lower surface.

  Hereinafter, the operation of the PM detection apparatus 1 of the present invention will be described.

  In the PM sensor 3, the capacitance between the two electrodes changes substantially linearly as shown in FIG. 2 according to the amount of accumulated PM. Therefore, the amount of accumulated PM can be detected based on the capacitance of the PM sensor 3. This is because the PM, which is a conductor, is inserted between the electrodes, so that the distance between the electrodes is apparently reduced and the capacitance is increased. In addition, the PM increases in the medium between the electrodes and the dielectric constant increases and the static is increased. This is thought to be because the electric capacity increases.

  In the present invention, when the AC impedance bridge is in an equilibrium state in the bridge circuit 9 of FIG. 1, the capacitance of the variable capacitor 8 and the capacitance of the PM sensor 3 are equal, and therefore, based on the capacitance of the variable capacitor 8. To detect the amount of PM deposited. However, prior to this, it is necessary to obtain the balance of the resistance bridge in the bridge circuit 9. This is because there are a plurality of combinations of resistance values and capacitances that give balance when attempting to balance only with an AC impedance bridge, and the capacitance is not fixed to one.

  The detection unit 12 controls the DC power supply 10 to apply a DC voltage between the voltage application points a and b. In this state, the variable resistor 4 is adjusted so that the bridge circuit 9 is balanced. Specifically, the detection unit 12 reads the output of the differential amplifier 13 while controlling the variable resistor 4 so as to sweep the resistance value between the upper limit resistance value and the lower limit resistance value of the variable resistor 4. When the bridge circuit 9 is balanced, the voltage difference between the measurement points c and d does not occur, so the output of the differential amplifier 13 becomes 0 or very small. The detection unit 12 fixes the variable resistor 4 to a resistance value at which the output of the differential amplifier 13 is 0 or very small.

  Thereafter, the detection unit 12 stops applying the DC voltage, controls the AC power supply 11, and applies the AC voltage between the voltage application points a and b. In this state, the variable capacitor 8 is adjusted so that the bridge circuit 9 is balanced. Specifically, the detection unit 12 controls the variable capacitor 8 so as to sweep the capacitance between the upper limit capacitance and the lower limit capacitance of the variable capacitor 8 and outputs the output of the differential amplifier 13. Read. When the bridge circuit 9 is balanced, the voltage difference between the measurement points c and d does not occur, so the output of the differential amplifier 13 becomes 0 or very small.

  When the bridge circuit 9 is balanced in direct current and alternating current in this way, the detection unit 12 detects the amount of PM deposited based on the capacitance of the variable capacitor 8. Since the electrostatic capacitance of the variable capacitor 8 is a value given by the control unit 12, if the comparison table of this value and the amount of PM deposited is set in the detection unit 12 in advance, the detection unit 12 The amount of PM deposition can be read from the table and used as the detection result.

  The bridge circuit 9 is not limited to the balance at the direct current and the balance at the alternating current once, but preferably the balance at the direct current and the balance at the alternating current are alternately repeated a plurality of times.

  According to the PM detection device 1 of the present invention, the capacitance of the PM sensor 3 can be known by searching for the capacitance of the variable capacitor 8 at which the bridge circuit 9 is balanced. The capacitance of the variable capacitor 8 is accurate because it is a value given by the detection unit 12 under control. Therefore, the detected PM accumulation amount is accurate.

  According to the PM detection device 1 of the present invention, the bridge circuit 9 can be balanced regardless of the amplitude value of the AC voltage applied by the AC power supply 11, and therefore the AC voltage amplitude value does not need to be accurate. . For this reason, the oscillator circuit which comprises AC power supply 11 can be made into a simple structure. As a result, the AC power supply 11 can be made highly reliable while being inexpensive.

1 PM detector 2 DPF (diesel particulate filter)
DESCRIPTION OF SYMBOLS 3 PM sensor 4 Variable resistor 5, 6, 7 Fixed resistor 8 Variable capacitor 9 Bridge circuit 10 DC power supply 11 AC power supply 12 Detection part 13 Differential amplifier

Claims (2)

A PM detection device for detecting the amount of particulate matter (hereinafter referred to as PM) deposited in a diesel particulate filter (hereinafter referred to as DPF) inserted in an exhaust gas exhaust passage from an internal combustion engine to the atmosphere,
A PM sensor in which the capacitance between two electrodes arranged in the DPF varies with the amount of PM deposited;
An electrically controlled variable resistor and three fixed resistors are sequentially connected, the PM sensor is connected in parallel to the variable resistor, and one of the fixed resistors adjacent to the variable resistor is electrically connected A bridge circuit in which variable capacitors to be controlled are connected in parallel;
Of the four connection points of the bridge circuit, the connection point where the variable capacitor and the fixed resistor, the variable resistor and the PM sensor are connected, and the connection point located on the diagonal are the voltage application points. A DC power source and an AC power source for selectively applying a DC voltage and an AC voltage between the voltage application points;
The variable resistor is adjusted so that the bridge circuit is balanced by applying a DC voltage between the voltage application points, and then the variable resistor is adjusted so that the bridge circuit is balanced by applying an AC voltage between the voltage application points. A PM detection apparatus comprising: a detection unit that adjusts a capacitor and detects a PM deposition amount from the capacitance of the variable capacitor at this time. Among the four connection points of the bridge circuit, two connection points sandwiched between the voltage application points are measurement points, and a differential in which a positive input terminal and a negative input terminal are connected to each of the measurement points. With an amplifier,
The detection unit adjusts the variable resistor so that the output of the differential amplifier becomes 0 when a DC voltage is applied between the voltage application points, and an AC voltage is applied between the voltage application points. 2. The PM detecting apparatus according to claim 1, wherein the variable capacitor is adjusted so that the output of the differential amplifier is sometimes zero.

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