JPS6275035A - Fuel injection rate control device - Google Patents

Abstract

PURPOSE:To simplify the structure of a fuel injection rate control device, by connecting a capacitor and an inductor to a piezo-actuator which is installed for the high pressure chamber of an injection pump. CONSTITUTION:The high pressure chamber 12 of an injection pump 1 is installed with a piezo-actuator 3. The piezo-actuator 3 is connected with a capacitor 43 which stores the electric charge generated in the piezo-actuator 3, and with one inductor 44 which carries out the transfer of the electric charge between the piezo-actuator 3 and the capacitor 43. High voltage which is generated at a piezo element with receiving the pressure in the high pressure chamber 12 is stored in the capacitor 43 via the inductor 44 so as to utilize effectively. Thereby, the circuits can be constructed without using a high voltage electric source, so that the structure of a fuel injection rate control device can be simplified.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a fuel injection system having a mechanism for performing pilot injection prior to main injection of fuel in order to reduce noise and vibration of a diesel engine, for example, when idling. Relating to a rate control device.

[Conventional technology]

Conventional pilot injection methods include two plungers for pumping fuel that are driven separately, two fuel injection nozzles that perform pilot injection and main injection with each nozzle, and even fuel injection. There is one that has two levels of nozzle opening pressure.

Among the above-mentioned conventional techniques, the method using two plungers or nozzles has the disadvantage that the drive means becomes complicated and the device becomes large. Further, in the case where the valve opening pressure is set in two stages and pilot injection and main injection are performed separately, the nozzle becomes large and difficult to attach to the engine.

Also, as shown in Japanese Patent Application Laid-Open No. 59-18239,
A pump has been proposed in which injection rate control including pilot injection is performed by applying a voltage to a piezo stack installed in a high pressure chamber of a pump to expand and contract the piezo stack.

[Problem that the invention seeks to solve]

Among the conventional technologies mentioned above, those using piezo elements have a simple piezo actuator structure, are small and lightweight, but because they operate under the high pressure of the pump pressure chamber, they need to be driven at high voltage and require a battery. There was a problem in that it could not be driven directly by voltage and required a direct pressure power source with a large circuit scale.

Therefore, the present invention operates a piezo actuator without using a high voltage power supply and with a simplified circuit configuration.
The purpose is to realize pilot injection using an injection pump.

[Means for solving problems]

In order to achieve the above object, the present invention uses a piezo actuator that applies a piezo element, and instead of driving this piezo actuator unilaterally by a power supply circuit,
The high voltage generated by the piezo element itself in response to the high pressure in the pump pressure chamber is effectively used to perform pilot injection using a switching means, a capacitor, and a single inductor.

〔Example〕

The apparatus according to the present invention will be explained below with reference to embodiments shown in the drawings. FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention. ■ is a Bosch type distribution type fuel injection pump, 11 is a plunger, which is pushed to the left in the figure by a face cam (not shown), makes the fuel in the high pressure chamber 12 high pressure, and sends it from the nozzle 2 to the combustion chamber of a diesel engine (not shown). It injects fuel into the A piezo actuator 3 is mounted facing the high pressure chamber 12 and utilizes a piezo voltage effect. This piezo actuator 3 is, for example, disclosed in Japanese Patent Application Laid-Open No. 59-18249.
The structure is as shown in the publication.

Reference numeral 4 denotes a drive circuit which is the gist of the present invention, which causes a pilot injection to be performed by passing a current through the piezo actuator 3 to cause the piezo element to expand and contract, thereby changing the pressure in the high pressure chamber 12.

This drive circuit 4 includes a transistor 41 that receives a timing signal TMGI from a timing circuit 5 and sets the potential at point a to 0 in the figure, and a transistor that receives a timing signal TMG2 and sets the potential at point b to 0. 42. Electrical energy generated in the piezo actuator 3 due to high pressure (
A capacitor (condenser) 43 for storing charge), an inductor (coil) 44 for efficiently transferring energy between the piezo actuator 3 and the capacitor 43, and reducing the peak value of current flowing through the circuit, and transistors 41 and 42. Varistor 45 absorbs the voltage applied to
, 46, and a diode 47°48.49.

The timing circuit 5 includes projections 51 and 52 provided around the face cam 13 in the injection pump, as shown in FIG. TMG1
, TM01 is obtained. Incidentally, Figure 2 shows the case of a 4-cylinder engine.

Next, the operation of the piezo actuator drive circuit will be explained with reference to the timing chart shown in FIG.

FIG. 3(a) shows the plunger in a lifted state.

As the plunger lifts, the high-pressure chamber pressure increases as shown in if) in the same figure, and when it reaches or exceeds the nozzle opening pressure, injection starts as shown in the injection rate waveform in gl in the same figure. As the pressure in the high-pressure chamber increases, a charge is generated in the vinyl actuator unique 3 due to the piezo effect as shown in the same figure (b), and the voltage increases.Then, when the rotation of the face cam reaches a predetermined angle, the timing circuit Same figure tc+ from 5
The timing signal TMG 1 is generated as shown in FIG. 1, the transistor 41 in FIG.
A loop is formed from the transistor 41 to the diode 48, and the charge generated in the piezo element is discharged, and a current flows as shown in FIG. Even if the voltage across the pump becomes larger, it is possible to further discharge the piezo actuator 3. Due to this discharge, the piezo actuator 3 contracts, the high pressure chamber pressure decreases, the fuel injection is temporarily stopped, and a pilot injection is performed. By lifting, injection (main injection) is started again.

Next, when the fuel is spilled by the governor mechanism, the pressure in the high pressure chamber decreases, and the - injection is completed.

Furthermore, as the pressure decreases, the piezo actuator generates an electric charge in the opposite direction to that during compression, and the voltage across the piezo actuator decreases. When the voltage finally reaches OV, the loop from the piezo actuator negative terminal to the diode 49 to the piezo actuator positive terminal becomes conductive, and current continues to flow until the pressure decreases, and the piezo actuator extends.

Next, at a place where the high pressure chamber pressure is low and unrelated to fuel injection, the timing signal TM is sent from the timing circuit 5 as shown in FIG.
G2 occurs, the transistor 42 in FIG. 1 turns "ON", and the diode 47 - capacitor 43 → inductor 44
→A loop between the piezo actuator 3 and the transistor 42 is generated, and a current flows as shown in FIG. 3 (fe), the charge stored in the capacitor 43 is discharged, and the piezo actuator is charged with the corresponding charge. At this time as well, even if the voltage across the piezo actuator becomes higher than the voltage across the capacitor 43 due to the current inertia of the inductor 44, further charging is possible. As a result, the vinyl crotch unique stretches further and returns to its initial state, completing one cycle.

Charging of the actuator at the timing signal TM02 increases the width of change in the voltage across the piezo actuator (PZTV in FIG. 3) at the time of 7M01, and serves to prevent polarization deterioration of the piezo element. Also 1
The inductors 44 function to efficiently exchange energy between the piezo actuator 3 and the capacitor 43, reduce the peak value of current flowing through the circuit, and enable the use of inexpensive transistors.

Note that although a transistor is used as the switching means in the above embodiment, it is also possible to use a transistor or a relay.

Furthermore, when using a highly sensitive piezo actuator whose element expands and contracts at a large rate with respect to voltage, the inductor 44
By inserting a resistor in series with the circuit, it is possible to lower the current flowing through the circuit and the voltage level applied to the circuit elements, allowing the use of cheaper circuit components.

〔Effect of the invention〕

As described in detail above, the present invention is capable of driving a piezo actuator with a simple configuration by using switching means, a capacitor, and only one inductor without using a high voltage power supply that is expensive and has a large circuit scale as in the past. A circuit can be formed and pilot injection of fuel can be performed accurately.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing one embodiment of the present invention, FIG. 2 is a detailed configuration diagram of the timing circuit in FIG. 1, and FIG. 3 is a timing chart for explaining the operation of the present invention. ■...Injection pump, 3...Piezo actuator. 4... Drive circuit, 5... Timing circuit, 11...
- Plunger, 12... High pressure chamber, 41.42... 1st. A transistor serving as a second switching means, 43
...Capacitor, 44...Inductor. Representative Patent Attorney Takashi Okabe (g) Akebono 1 Base □ Figure 3

Claims (2)

[Claims] 1. A fuel injection pump for a diesel engine that pumps high-pressure fuel by reciprocating a plunger, comprising: a piezo actuator mounted facing a high pressure chamber of the injection pump; a capacitor for storing electric charge generated in the piezo actuator; a first switching means that transfers the electric charge generated in the piezo actuator to the capacitor at a predetermined timing to form a pilot injection preceding the main injection; and a first switching means that transfers the electric charge accumulated in the capacitor to the piezo actuator at a predetermined timing. 1. A fuel injection rate control device comprising: two switching means; and only one inductor for efficiently transferring electric charge between the piezo actuator and the capacitor. 2. 2. The fuel injection rate control device according to claim 1, wherein the first and second switching means are transistors.