JP4432624B2 - Actuator drive circuit - Google Patents

Description

  The present invention relates to an actuator drive circuit, and more particularly to improvement of operation stability of an actuator.

  The common rail type fuel injection device is provided with a common rail for storing pressurized fuel in common to an injector provided in each cylinder of a diesel engine, and supplies fuel for injection from the common rail to the injector. As an actuator drive circuit attached to such a fuel injection device, there is an actuator that drives a pressure reducing valve for adjusting the fuel pressure in the common rail, in addition to an injector.

  The pressure reducing valve generates an operating force by, for example, an electromagnetic force of a solenoid, but a particularly large operating force is required when the valve is opened. Therefore, there are some which have two voltage sources having different output voltages. The first voltage source having a high output voltage is terminated when the drive current flowing through the solenoid of the actuator gradually increases during the energization period and the drive current reaches a predetermined peak current value. On the other hand, the second voltage source having a low output voltage maintains the drive current at a current value lower than the peak current value by switching control. The switching control is executed at the end of energization of the first voltage source so that a peak waveform is given to the drive current at the start of driving, so that sufficient magnetic energy is accumulated in the solenoid, The operating force is secured (hereinafter, the drive current corresponding to the peak waveform is referred to as the charge current as appropriate). In the following Patent Document 1 or the like, a capacitor charged by a DC-DC converter that boosts the output voltage of an in-vehicle battery is used as a first voltage source, and the battery is used as a second voltage source. Things are listed.

By the way, an injector having a configuration in which an operating force is generated by a piezo stack using a piezoelectric action such as PZT has been studied today. Piezo stacks require a higher drive voltage than for solenoids. From the viewpoint of cost, it is desirable to use a common voltage source for the injector and the pressure reducing valve, so that the capacitor has a charging voltage that is high enough to be compatible with the piezo stack, and this is the peak waveform. It is desirable to also serve as the first voltage source for applying the voltage.
Japanese Unexamined Patent Publication No. 07-71639

  However, there is the following problem in driving the solenoid due to the high charging voltage of the capacitor. FIG. 5 shows a state when the drive voltage of the solenoid is increased approximately twice. In the figure, the state before the drive voltage is increased is also shown. As the voltage increases, the charge current becomes steeper, and the time until the charge current reaches the threshold for turning off the drive voltage is shortened, so the time during which the charge current is output is shortened. As a result, the valve opening force of the pressure reducing valve on which the solenoid is mounted becomes insufficient and the valve opening operation becomes unstable, which may cause malfunction.

  On the other hand, as shown in FIG. 6, the current value of the second voltage source is lowered in two stages, and a valve opening force is secured by providing a relatively large current value period at the beginning of the constant current period. It is possible. However, since the control method in which the drive current is a constant current is usually based on switching control of voltage application from the battery to the solenoid, the output voltage of the battery (hereinafter referred to as the battery voltage as appropriate) when starting the engine or the like. ) Decreases, the drive current decreases as the battery voltage decreases, as shown in FIG. 7, and eventually there is a possibility that the operating force at the time of valve opening cannot be secured.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an actuator drive circuit capable of improving the operational reliability of an actuator.

According to the first aspect of the present invention, as a voltage source for driving the solenoid that generates the actuation force of the actuator as a load, the drive current flowing through the solenoid gradually increases during the energization period, and the drive current is set at a predetermined peak current value. A first voltage source that is de-energized upon reaching the first voltage source, and a first voltage source for maintaining the drive current at a current value lower than the peak current value by switching control with an output voltage lower than that of the first voltage source. An actuator drive circuit having a peak waveform for a drive current at the start of driving, wherein the switching control is performed at the end of energization of the first voltage source.
Wherein as the peak of the second voltage source output voltage is low enough the drive starting peak waveform becomes higher, the first off time setting means for setting the peak current value to determine the off time of the voltage source Is provided.
The off time setting means determines whether the output voltage of the second voltage source is lower than a preset reference voltage,
If an affirmative determination is made, the peak current value is set to be higher than that at the reference voltage, the energization period by the first voltage source is lengthened, and the energy required to generate the operating force of the actuator Can be stored.

  When the output voltage of the second voltage source decreases, the peak of the peak waveform of the drive current at the start of driving increases, and the magnetic energy accumulated in the solenoid also increases. Thereby, the gradual decrease period of the drive current after reaching the peak becomes longer, and the operating force of the actuator can be ensured.

  According to a second aspect of the present invention, in the configuration of the first aspect of the present invention, the second voltage source is configured to reduce the drive current stepwise.

  Although the current value in the constant current period decreases due to the decrease in the output voltage of the second voltage source, the period in which the first voltage source is energized is reduced by providing a relatively large driving current period at the beginning of the constant current period. Less solenoidal magnetic energy should be reached from time to time. Therefore, the required specification for the current capacity of the parts can be reduced correspondingly, and the cost can be reduced.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a common rail type fuel injection apparatus to which an actuator drive circuit of the present invention is attached. An injector 11 for injecting fuel is provided in a one-to-one correspondence with each cylinder, and a common rail 24 is connected to the injector 11 in common. The common rail 24 stores pressurized fuel supplied to the injector 11. The injector 11 switches the displacement of the needle inserted in the nozzle by the piezoelectric action of the piezo stack between the valve opening side and the valve closing side, and at the time of valve opening, fuel is injected at an injection pressure substantially equal to the fuel pressure in the common rail 24. Spray.

  The common rail 24 is connected to the pump 23, and the pump 23 sucks up the fuel stored in the fuel tank 21 through the fuel filter 22 and pumps it to the common rail 24. The fuel pressure in the common rail 24 rises due to the pumping of fuel by the pump 23. On the other hand, when the pressure reducing valve 25 is connected to the common rail 24 and the pressure reducing valve 25 is opened, the fuel in the common rail 24 returns to the fuel tank 21 and the fuel pressure in the common rail 24 decreases. The pressure reducing valve 25 is opened by the valve body (valve) being lifted by the electromagnetic force of the solenoid 251 (see FIG. 2).

  The injector 11 and the pressure reducing valve 25 are electrically driven by the EDU 32, and the EDU 32 electrically drives the injector 11 and the pressure reducing valve 25 at a predetermined time in accordance with an operation command from the ECU 31. ECU31 controls each part of an engine based on the driving | running state known from the output signal from various sensors, for example, is comprised centering on a microcomputer. As the sensors, the common rail 24 is provided with a pressure sensor 33 for detecting the fuel pressure in the common rail 24, and the ECU 31 is configured so that the fuel pressure in the common rail 24 becomes a target pressure calculated from the operating state by the ECU 31. Controls the pump 23 and the pressure reducing valve 25.

  These electric devices are operated by power feeding from the vehicle-mounted battery 41.

  FIG. 2A shows an actuator drive circuit, and FIG. In the EDU 32, the DC-DC converter 322 is supplied with power from the battery 41 via the filter 321, and the first voltage value is higher than the output voltage of the battery 41 as the second voltage source (hereinafter referred to as battery voltage as appropriate). The capacitor 323, which is a voltage source of, is charged. As the DC-DC converter 322, for example, a general boost chopper type circuit can be used.

  A piezo drive circuit 323 and a solenoid drive circuit 324 are provided using the capacitor 323 as a common voltage source. A battery 41 is connected to the solenoid drive circuit 324 as a voltage source.

  The piezo drive circuit 323 switches between charging and discharging of the piezo stack 111. The piezo stack 111 is extended by charging, and the injector 11 is switched to the valve opening side. As the configuration of the piezo drive circuit 323, for example, a configuration in which an energization path for connecting the capacitor 323 and the piezo stack 111 via an inductor is provided. That is, by closing the energization path, a current that gradually increases flows through the energization path, the piezo stack 111 is charged, energy corresponding to the current value is accumulated in the inductor, and when it is opened, a counter electromotive force is generated in the inductor. In the opening period, a current that gradually decreases flows from the inductor to the piezo stack 111 by another energization path that bypasses the capacitor 323. By repeating this, a predetermined operating force is generated in the piezo stack 111.

  The solenoid drive circuit 324 is provided with two types of the energization path 5 a using the capacitor 323 as a voltage source and the energization path 5 b using the battery 41 as a voltage source with respect to the solenoid 251 of the pressure reducing valve 25. Diodes 51 and 52 are provided with the solenoid 251 side as a cathode in the front part that reaches the line part, and current inflow to the energization paths 5b and 5a is prohibited. Each energization path 5a, 5b is provided with transistors 53, 54 in a one-to-one correspondence to open and close the corresponding energization paths 5a, 5b.

  The transistors 53 and 54 are controlled by the controller 56. As the controller 56, one constituted by a logical operation circuit or one constituted by a microcomputer is used. When an energization command as a command for reducing the fuel pressure in the common rail 24 is input from the ECU 31, the solenoid 251 is energized. The energization command is an on ("H" level) signal for a certain period, and its length defines the energization period for the solenoid 251, and the fuel pressure is reduced according to the length.

  A resistor 55 having a relatively small resistance value is connected in series with the solenoid 251, and the drive current of the solenoid 251 is known by the controller 56 by detecting a voltage drop there.

  FIG. 3 shows the control contents in the controller 56 when the energization command is issued. Steps S101 and S102 are processing as an off time setting means of the controller 56. In step S101, it is determined whether or not the battery voltage is low. This is determined based on whether or not the battery voltage is lower than a preset reference voltage. If a positive determination is made, the charge current threshold is increased in step S102, and the process proceeds to step S103. Therefore, two types of charge current threshold values are prepared. If a negative determination is made in step S101, step S102 is skipped and the process proceeds to step S103.

  In step S103, the capacitor 323 is used as a voltage source to charge the solenoid 251 with magnetic energy that can be opened. This charge gives a peak waveform to the drive current as will be described later. As described above, the current corresponding to the peak waveform is called a charge current.

  In step S104, it is determined whether or not the charge current is greater than or equal to a charge current off threshold that is a peak current value. If step S102 is executed, the charge current off threshold at this time is set higher.

  If a negative determination is made in step S104, the process returns to step S103, and charging of the pressure reducing valve 25 is continued until a positive determination is made in step S104.

  When the charge current reaches the charge current off threshold value and an affirmative determination is made in step S104, the process proceeds to step S105, where the transistor 53 is turned off to stop charging the pressure reducing valve 25 and constant current control is executed. That is, the switching control of the transistor 54 is performed so that the ON ratio becomes a predetermined value. Note that, for a while, a current that gradually decreases while consuming energy having a magnitude corresponding to the peak current, accumulated in the solenoid 251, flows as a drive current. After the drive current reaches a current value corresponding to the ON ratio, the drive current becomes a constant value.

  In step S106, it is determined whether the energization command is off ("L" level). If a negative determination is made, the process returns to step S105, and constant current control is executed. When a predetermined time elapses from the start of constant current control, the ON ratio of the transistor 54 is reduced, and the current value decreases stepwise. When the energization command is turned off and an affirmative determination is made in step S106, the transistor 54 is fixed to be off and this flow ends.

  FIG. 4 shows the operation of this actuator drive circuit. When the battery voltage is low, the charge current off threshold increases, and the magnetic energy accumulated in the solenoid 251 at the time of stopping the charge increases. For this reason, the gradual decrease period of the drive current becomes longer, and the entire charging period becomes longer. Thereby, even if the drive current at the time of constant current control falls by the fall of battery voltage, the valve opening force of the pressure reducing valve 251 is securable.

 In constant current control, a relatively large period is set at the beginning of the drive current, and this acts in the direction of securing the charge period. Therefore, the large charge current off threshold can be suppressed accordingly. Depending on the required specifications, the constant current control may be constant until the energization command is turned off, instead of the drive current being reduced in two steps.

  The present invention can be applied not only to an actuator drive circuit of a common rail type fuel injection device but also to other actuator drive circuits. The type of actuator is not limited to a valve.

It is a figure which shows the structure of the common rail type fuel-injection apparatus which attached the actuator drive circuit to which this invention is applied. (A) is a block diagram showing a configuration of the actuator drive circuit, and (B) is a circuit diagram showing a configuration of a main part thereof. It is a flowchart explaining the control in ECU which comprises the said actuator drive circuit. It is a timing chart which shows the operating state of the actuator drive circuit. It is a 1st timing chart explaining the subject of the prior art. It is a 2nd timing chart explaining the subject of the prior art. It is a 3rd timing chart explaining the subject of the prior art.

Explanation of symbols

11 Injector (actuator)
111 Piezo stack 25 Pressure reducing valve (actuator)
31 ECU
32 EDU
251 Solenoid 322 DC-DC converter 323 Capacitor ( first voltage source)
324 Piezo driving circuit 325 Solenoid driving circuit 41 Battery (second voltage source)
56 Controller (off time setting means)

Claims (2)

As a voltage source for driving the solenoid that generates the actuation force of the actuator as a load, the energization is terminated when the drive current flowing through the solenoid gradually increases during the energization period and the drive current reaches a predetermined peak current value. A first voltage source, and a second voltage source for maintaining the drive current at a current value lower than the peak current value by switching control, the output voltage being lower than that of the first voltage source. In the actuator drive circuit in which the switching control of the second voltage source is performed at the end of energization of the first voltage source, and a peak waveform is given to the drive current at the start of driving,
Wherein as the peak of the second voltage source output voltage is low enough the drive starting peak waveform becomes higher, the first off time setting means for setting the peak current value to determine the off time of the voltage source Equipped with ,
The off time setting means determines whether the output voltage of the second voltage source is lower than a preset reference voltage,
If an affirmative determination is made, the peak current value is set to be higher than that at the reference voltage, the energization period by the first voltage source is lengthened, and the energy required to generate the operating force of the actuator Actuator drive circuit characterized in that can be stored .   2. The actuator driving circuit according to claim 1, wherein the second voltage source reduces the driving current in a stepwise manner.

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