JPH0614077Y2 - Driving circuit for electrostrictive actuator for fuel injection valve - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention [Field of Industrial Application] The present invention relates to a drive circuit for driving an electrostrictive actuator of a fuel injection valve.

[Prior Art] As a drive circuit of this type, the applicant of the present invention has previously disclosed in Japanese Patent Laid-Open No. 62-62.
The one described in Japanese Patent No. -17338 is proposed. The proposed drive circuit includes a charging coil and a charging switching element commonly connected to each electrostrictive actuator incorporated in each injection valve of an internal combustion engine, and a charging coil when the charging switching element is turned on. One of a DC power supply for applying a DC voltage to each electrostrictive actuator, a discharge switching element independently provided for each electrostrictive actuator, and a discharge switching element commonly connected to each electrostrictive actuator And a discharge coil that promotes discharge of the corresponding electrostrictive actuator when the switch is turned on. When the charging switching element is turned on in accordance with the injection timing signal, this drive circuit rapidly charges all the electrostrictive actuators by self-induction of the charging coil and extends the length thereof. As a result, the injection port of the injection valve is closed and the fuel injection is completed. Then, in order to start the injection, the switching element for discharge is turned on and the corresponding electrostrictive actuator is discharged through the discharge coil to shorten its length. As a result,
The injection port of the injection valve is opened.

[Problems to be Solved by the Invention] However, further improvement has been demanded in the following points. That is, the injection valve incorporating the electrostrictive actuator is attached to the engine, and when the temperature of the engine rises, the capacitance of the electrostrictive actuator may change due to the difference in the mounting location of the electrostrictive actuator or the difference in the temperature characteristic coefficient. May change significantly. For this reason, even if a constant DC voltage is applied to each electrostrictive actuator via the charging coil, the energy (1/2 CV ² , C: electrostatic capacity of the electrostrictive actuator, stored in the electrostrictive actuator, V: applied voltage) varies depending on the electrostrictive actuator. As a result, even if a constant voltage is applied for a certain period of time, the amount of expansion / contraction displacement of the electrostrictive actuator is not constant, and there is a problem in that the amount of injected fuel and the injection timing deviate.

The drive circuit of the electrostrictive actuator for a fuel injection valve of the present invention aims to keep the amount of expansion and contraction displacement of the electrostrictive actuator constant.

Configuration of the Invention [Means for Solving the Problems] In order to achieve the above object, a drive circuit of an electrostrictive actuator for a fuel injection valve of the present invention is provided with a plurality of fuel injection valves for injecting fuel into an internal combustion engine. A drive circuit for an electrostrictive actuator for a fuel injection valve that expands and contracts each electrostrictive actuator by charging and discharging each of the provided electrostrictive actuators, which is composed of a primary coil and a secondary coil. A step-up transformer, a constant current circuit that supplies a constant current to the primary coil of the transformer, and a constant current circuit that is operated in advance before fuel injection to indicate the end of fuel injection input from the outside. A constant current control circuit that reduces the current flowing through the primary side coil by a fixed amount by stopping the constant current circuit according to a control signal; A common diode that charges each electrostrictive actuator by the electric power induced in the secondary coil when the current flowing in the primary coil is reduced by a certain amount by the operation of the flow connection circuit; An individual diode, which is connected to each actuator and blocks discharge of electric charges accumulated in each electrostrictive actuator, and a common diode provided in each electrostrictive actuator, which discharges electric charges accumulated in each electrostrictive actuator Discharge coil for, and is provided for each of the electrostrictive actuator, one end is connected between the electrostrictive actuator and the individual diode, the other end is connected to the discharge coil, from the outside A switching element that is temporarily turned on in accordance with a control signal indicating the start of fuel injection that is input.

The electrostrictive actuator may be made of a crystal having a property of generating mechanical strain by applying a voltage, such as lead zirconium titanate-based ceramics and BaTiO ₃ (barium titanate) ceramics. It may be constituted by a piezoelectric element formed by stacking, a polymer-based piezoelectric electrode material, crystal, or the like. Such an electrostrictive actuator may have a configuration of directly driving the valve element of the fuel injection valve or a configuration of indirectly driving the valve element using a lever or the like.

[Operation] According to the electrostrictive actuator drive circuit for fuel injection of the present invention, the constant current control circuit operates the constant current circuit in advance before fuel injection to supply a constant current to the primary coil of the transformer. By stopping the constant current circuit according to the control signal indicating the end of fuel injection to stop the current supply to the primary coil, the current flowing through the primary coil changes by a constant value.

At this time, in the transformer, a constant boosted electric power is induced in the secondary coil according to the change in the current value in the primary coil.

The common diode connected in series to the secondary coil charges the electrostrictive actuator with constant power induced in the secondary coil only when the current flowing in the primary coil decreases. .

In this way, when the electrostrictive actuator is in a charged state, when the switching element is temporarily turned on in accordance with the control signal indicating the start of fuel injection, the charge accumulated in the electrostrictive actuator is transferred via the discharge coil. Is discharged.

At this time, the discharge coil functions to promote discharge, so that the charge potential of the electrostrictive actuator becomes a negative potential.

In addition, the individual diodes prevent the electric charge accumulated in the non-discharged electrostrictive actuator from flowing toward the discharged electrostrictive actuator.

That is, in a state where all the electrostrictive actuators are charged, when a specific switching element is operated by a control signal indicating the start of fuel injection, the electrostrictive actuator to which the operated switching element is connected is The stored charge is discharged and contracts, and the fuel injection valve is opened to start fuel injection. Then, when the constant current control circuit changes the constant current circuit from the operating state to the stop state according to the control signal indicating the end of fuel injection, the current flowing through the primary coil changes from a constant value to zero, and this current value changes. A corresponding amount of electric power is induced in the secondary coil to charge the discharged electrostrictive actuator. The electrostrictive actuator extends by being charged, closes the fuel injection valve, and stops fuel injection.

[Embodiment] An embodiment of the present invention will be described with reference to the drawings in order to further clarify the configuration of the present invention described above. The electrostrictive actuator of this embodiment is constituted by using a piezoelectric element made of lead zirconium titanate-based ceramics. FIG. 1 shows the configuration of a piezoelectric element actuator drive circuit for driving the piezoelectric element actuator. FIG. 2 schematically shows a configuration of a 4-cylinder diesel engine to which a piezoelectric element actuator drive circuit is applied and its peripheral equipment. FIG. 3 shows the structure of a fuel injection valve incorporating a piezoelectric element actuator.

First, the overall configuration of the diesel engine 1 will be described with reference to FIG. The diesel engine 1 has fuel injection valves 8a, 8a for direct injection into the combustion chamber for each cylinder.
b, 8c, 8d are provided. The intake of the diesel engine 1 is performed by the supercharger T via the intake manifold 9.

The fuel injection valves 8a, 8b, 8c, 8d are connected via a fuel supply pipe 10 to a fuel pressure accumulation pipe 11 common to each cylinder. The fuel pressure accumulator 11 has a pressure accumulation chamber 12 having a constant volume therein, and the fuel in the pressure accumulation chamber 12 is supplied to the fuel injection valves 8a, 8b, 8c, 8d via the fuel supply pipe 10. On the other hand, the pressure accumulating chamber 12 is connected via a fuel supply pipe 13 to a projecting port of a fuel supply pump 14 whose discharge pressure can be controlled. The suction port of the fuel supply pump 14 is connected to the discharge port of the fuel pump 15, and the suction port of the fuel pump 15 is connected to the fuel reservoir tank 16. In addition, each fuel injection valve 8a, 8b,
8c and 8d are connected to a fuel reservoir tank 16 via a fuel return conduit 17. The fuel pump 15 is provided to feed the fuel in the fuel reservoir tank 16 into the fuel supply pump 14, and if the fuel can be sucked into the fuel supply pump 14 without the fuel pump 15, the fuel pump 15 It is not necessary to provide 15 in particular. On the other hand, the fuel supply pump 14 is provided for discharging high-pressure fuel, and the high-pressure fuel discharged from the fuel supply pump 14 is accumulated in the pressure accumulating chamber 12. This pressure is also called rail pressure.

Further, the diesel engine 1 has two crank angle sensors 21, 2 for detecting the operating state of the engine 1.
2, a cooling water temperature sensor 24, a supercharging pressure sensor 26, a fuel pressure sensor 28 and the like are provided. Electronic control unit (hereinafter E
A CU) 30 is composed of a well-known arithmetic logic operation circuit centering on a CPU, and based on the outputs of the above sensors and the output of the accelerator pedal 32, a piezoelectric element actuator drive circuit 40 and a pump drive device 45. To control the fuel injection amount and the injection timing to make the output of the diesel engine 1 suitable.

Next, the cylinder head 51 of the diesel engine 1
The fuel injection valves 8a, 8b, 8c, 8d mounted on the fuel injection valve 8a will be described. However, since all the fuel injection valves have the same structure, only the fuel injection valve 8a will be described. The fuel injection valve 8a includes a piezoelectric element 72a, a housing 55 that houses the hydraulic piston 53, and a nozzle hole 5 of the cylinder head 51.
8, a nozzle body 60 that is inserted through the housing 8, a housing 55 for these, a nozzle holder 63 that supports the nozzle body 60,
And a needle 65 and the like housed in the nozzle body 60. The needle 65 is formed in a small diameter portion, a tapered portion, and a large diameter portion from the tip, and moves in the axial direction to open and close the injection port 67 formed at the tip of the nozzle body 60. An oil sump 70 is formed around the tapered portion of the needle 65.

A cylindrical protrusion 71 is formed on a side portion of the nozzle holder 63, and the protrusion 71 is inserted into a pair of holes provided in the radial direction of the pressure accumulating pipe 11 to interpose an O-ring 73. Fixed in the state. The passage 75 formed inside the protruding portion 71 is provided with an oil reservoir 70 for the pressure accumulating chamber 12 and the nozzle body 60.
Communicate with. Therefore, the high-pressure fuel in the pressure accumulating chamber 12 is guided to the oil sump 70, and exerts an upward force (valve opening direction) on the tapered portion of the needle 65. Further, the pressurizing chamber 76 in the housing 55 is filled with fuel, and the fuel pressure in the pressurizing chamber 76 is applied to the end surface of the large diameter portion of the needle 65 via the passage 77 formed in the nozzle holder 63. .
The pressure of this fuel increases or decreases as the piezoelectric element 72a expands or contracts.

Therefore, while the voltage is applied to the piezoelectric element 72a, the piezoelectric element 72a expands to overcome the fuel pressure in the oil sump 70 and press the needle 65 downward to close the injection port 67,
When the voltage applied to the piezoelectric element 72a is removed, the voltage element 72
The force of pressing the needle 65 downward is lost due to the contraction of a. As a result, the fuel pressure in the oil sump 70 causes the needle 6
5 is lifted, the injection port 67 is opened, and injection is performed.

Next, the configuration and function of the piezoelectric element actuator drive circuit 40 in this embodiment will be described in detail.

As shown in FIG. 1, the piezoelectric element actuator drive circuit 40 is connected to a transformer 42, a current limiting unit that controls a current flowing through a primary coil of the transformer 42, and a secondary coil of the transformer 42. Four piezoelectric elements 72a, 72
b, 72c, and 72d.

The current limiting unit is a closed-circuit switching transistor Tr including a battery 82, a primary coil of the transformer 42, a switching transistor Tr1, and a current detection resistor R2.
1 is a circuit that controls ON / OFF of 1 to accurately change the current flowing through the primary side of the transformer 42 by a predetermined amount, and is output to a vehicle-mounted battery 82 in order to output a stabilized voltage of 12 [V] for control. It has a voltage regulator 84 connected to it.
A P-channel FET 86 and an N-channel FET that perform a switching operation according to a charge signal from the ECU 30
88 is connected to the capacitor C1 to charge from the voltage regulator 84 via the resistor R1 when the P-channel FET 86 turns on, and to discharge when the N-channel FET turns on. One end of the capacitor C1 that is charged and discharged in this way is connected to the positive input terminal of the operational amplifier 90, and
The voltage across the resistor R2 that detects the current flowing through the primary coil of the transformer 42 is input to the negative input terminal of the. The output of the operational amplifier 90 is connected to the base of the switching transistor Tr1 via the resistor R3.

The drive unit is composed of the piezoelectric elements 72a, 72b, 72c, 72d.
99 for limiting charging to one direction, thyristors 91a, 91b, 91c, 91d for discharge provided in each piezoelectric element 72a, 72b, 72c, 72d, EC
Differentiating circuit 93 that generates an injection signal from U30 as a trigger signal for driving a thyristor, each piezoelectric element 72a, 72
b, 72c, 72d, discharge coil 95 for promoting the discharge of energy stored in piezoelectric elements 72a, 72b, 72
diodes 98a, 98b, 98c, which prevent discharge from other piezoelectric elements when one of c and 72d discharges.
With 98d.

Next, the operation of the piezoelectric element actuator drive circuit 40 will be described with reference to the timing chart of FIG.
When a high-level voltage charging signal (see FIG. 4) is input from the ECU 30 to the gate terminals of the FETs 86 and 88, N
The channel FET 88 turns off and the P channel FET 8
6 turns on. When the P-channel FET 86 becomes conductive,
The terminal voltage of the capacitor C1 gradually increases to the stabilized output voltage V _{0 of the} voltage regulator 84 at the rising time of the time constant C1R1. The comparator 90 controls the current flowing through the primary coil so that the voltage of the resistor R2 matches the terminal voltage of the capacitor C1, and the current flowing through the primary coil when the terminal voltage of the capacitor C1 reaches the stabilized voltage V _0. Is feedback-controlled to a constant current value I ₀ . When the injection signal A (see FIG. 4) having a constant pulse width is input from the ECU 30 to the terminal A of the differentiating circuit 93 while the constant current I ₀ is flowing through the primary coil, the differentiating circuit 9
3 generates a pulse signal having a narrow pulse width, and this pulse signal acts as a trigger signal for the thyristor 91a and turns on the thyristor 91a. The piezoelectric element 72a is precharged and has a terminal voltage of plus 500 [V],
When the thyristor 91a is turned on, the self-dielectric of the discharge coil 95 causes a rapid discharge, and the voltage drops to a terminal voltage of −200 [V]. At this time, the thyristor 91 turned on
Since a and the other piezoelectric elements 72b, 72c, 72d are blocked from conduction by the diodes 98b, 98c, 98d, only the piezoelectric element 72a is discharged. When the discharge of the piezoelectric element 72a is completed, the thyristor 91a is turned off again. As a result, the length of the piezoelectric element 72a is shortened and the injection hole 67 of the fuel injection valve 8a is opened to inject fuel. Subsequently, the ECU 30 lowers the charge signal from the high level voltage to the low level voltage in synchronization with the fall of the injection signal A. The state at this time will be described in detail. FE
When the voltage of the gate terminal of T86 and FET88 becomes a low level voltage, the P-channel FET86 is turned off and N
The channel FET 88 turns on. The electric charge stored in the capacitor C1 is instantaneously discharged through the turned-on N-channel FET 88, and the terminal voltage of the capacitor C1 falls to the ground potential. Therefore, the operational amplifier 90 makes the constant current I ₀ flowing through the primary coil _zero at once. As a result, due to mutual induction, an electromotive force of constant energy corresponding to the change amount of the primary side current (current I ₀ → zero) is generated in the secondary side coil, and this energy is totally accumulated in the piezoelectric element 72a just discharged. Supplied. When the energy is supplied, the terminal voltage of the piezoelectric element 72a becomes 500 [V] again, and the voltage is maintained until the next injection timing.

As described above, the piezoelectric element actuator drive circuit 40 supplies the constant energy induced in the secondary coil of the transformer 42 to all the piezoelectric elements 72a, 72b, 72c, 72d immediately after being discharged. Then, each piezoelectric element 72
Injection is performed with the amount of expansion / contraction of a, 72b, 72c, and 72d always kept constant.

Therefore, according to the piezoelectric element actuator drive circuit 40 of the present embodiment, the fuel injection valve 8 provided in the engine 1
The temperature of a, 8b, 8c, 8d rises and the piezoelectric elements 72a,
Even if the electrostatic capacities of 72b, 72c, and 72d individually change, the displacement amount of the piezoelectric element is determined by the applied energy, so that the displacement amount can be kept constant. As a result, it is possible to eliminate variations in the injection timing and the fuel injection amount and realize suitable fuel injection. In addition, it is possible to save electric power without supplying excessive energy, and it is possible to easily set the power consumption.

Further, since the transformer 42 isolates the drive unit in which a high voltage of 500 [V] is applied to the piezoelectric elements 72a, 72b, 72c, 72d and the current limiting unit for controlling the current to the primary side coil, respectively. Can be easily controlled and handled.

Further, the current limiting unit as the power supply unit, the secondary coil, and the discharge coil 95 are provided in the piezoelectric elements 72a, 72b, 72c,
Since it is shared with 72d, the number of parts can be reduced and the configuration can be simplified. Therefore, conventionally, there is no variation in the characteristics of the coil or the like provided for each piezoelectric element.

Effect of the Invention As described in detail above, in the electrostrictive actuator for a fuel injection valve of the present invention, when the discharged electrostrictive actuator is recharged, the current value flowing in the primary coil of the transformer is kept constant. By changing only this, constant electric power is always induced in the secondary coil of the transformer, and the electrostrictive actuator is charged by the constant electric power thus induced. The amount of expansion / contraction displacement of the electrostrictive actuator is determined by the energy stored in the electrostrictive actuator.

Therefore, according to the present invention, even when the temperature of the fuel injection valve rises and the capacitance of the electrostrictive actuator changes, a constant energy is always applied when the electrostrictive actuator is charged. Is supplied to the electrostrictive actuator, the advantageous effect that the amount of expansion / contraction of the electrostrictive actuator can be maintained constant. And thereby, it can avoid that the injection timing and the amount of fuel injection produce an error for every fuel injection valve, and can realize suitable fuel injection.

Further, in the present invention, when charging the electrostrictive actuator, after supplying a constant current to the primary coil of the transformer, the constant current circuit is stopped to supply power to the secondary coil. The current is configured to flow only during this minimum required time.

Therefore, according to the present invention, an excessive amount of energy is not supplied to the electrostrictive actuator, power can be saved, and power consumption can be easily designed.

Further, in the present invention, when the electrostrictive actuator is discharged, a negative voltage is applied to the electrostrictive actuator by the operation of the discharge coil, and the electrostrictive actuator is also displaced in the contraction direction, so only a positive voltage is applied. Compared with the case where the electrostrictive actuator is displaced only in the extension direction, the same displacement amount can be obtained at a low voltage, which is advantageous in terms of withstand voltage of the electrostrictive actuator.

Furthermore, the transformer can isolate the primary side circuit that generates a constant current from the secondary side circuit that requires a high voltage, so that they can be easily controlled and handled.

In addition, since the coil and the current limiting circuit are configured in common for a plurality of electrostrictive actuators, the number of parts can be significantly reduced, and in addition, the characteristic of the case where a coil or the like is provided for each electrostrictive actuator is improved. There is no variation.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a piezoelectric element actuator drive circuit of an embodiment, FIG. 2 is a configuration diagram schematically showing a diesel engine and peripheral equipment, and FIG. 3 is a sectional view showing a structure around a fuel injection valve. FIG. 4 is a timing chart showing changes in voltage or current in each part of the piezoelectric element actuator drive circuit. 1 ... Deal engine 8a, 8b, 8c, 8d ... Fuel injection valve 40 ... Piezoelectric element actuator drive circuit 42 ... Transformer 72a, 72b, 72c, 72d ... Piezoelectric element

Claims (1)

[Scope of utility model registration request] 1. An electrostrictive valve for a fuel injection valve, which expands and contracts each electrostrictive actuator by charging and discharging a plurality of electrostrictive actuators respectively provided in a plurality of fuel injection valves for injecting fuel into an internal combustion engine. A drive circuit for a linear actuator, the boosting transformer including a primary coil and a secondary coil, a constant current circuit for supplying a constant current to the primary coil of the transformer, and a constant current circuit for fueling the constant current circuit. A constant current control circuit that is operated in advance before injection and that stops the constant current circuit according to a control signal that is input from the outside and that indicates the end of fuel injection, and that reduces the current flowing through the primary coil by a certain amount. , An electric power which is connected to the secondary side coil and is induced in the secondary side coil when the current flowing through the primary side coil is reduced by a certain amount by the operation of the constant current control circuit. A common diode that charges each of the electrostrictive actuators, an individual diode that is connected to each of the electrostrictive actuators, and that blocks discharge of charges accumulated in each of the electrostrictive actuators, and each of the electrostrictive actuators A discharge coil that is provided in common for the actuators and discharges the electric charge accumulated in each electrostrictive actuator, and is provided for each of the electrostrictive actuators, and one end thereof is the electrostrictive actuator and the individual diode. And a switching element that is connected to the discharge coil and has the other end connected to the discharge coil and that is temporarily conducted in accordance with a control signal that is input from the outside and that indicates the start of fuel injection. Drive circuit for electrostrictive actuator for valves.