JPH0868372A - Superposed discharge type ignition device - Google Patents

Abstract

PURPOSE: To prevent the occurrence of a fear of the circuit constituting element of a DC-DC converter being burnt or damaged occasioned by the occurrence of spark blow-off phenomenon. CONSTITUTION: The intensity of a superposed discharge current i2 to continue a discharge spark at an ignition plug 15 is detected by a current detecting circuit 41. When a detecting current value is reduced to a given current value at which restoration of superposed discharge is considered to be impracticable, to prevent the abnormal increase of the output voltage Vo of a DC-DC converter 21, operation of the DC-DC converter 21 is forcibly stopped by an operation stop circuit 42.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ignition device for an internal combustion engine mounted on a motor vehicle, and more particularly to an improvement of an overlap discharge type ignition device.

[0002]

2. Description of the Related Art Recently, as a vehicle-mounted internal combustion engine, a so-called lean burn engine (lean burn engine) having an extremely low air-fuel ratio has been adopted. However, because this type of engine does not have very good ignition efficiency,
A high energy type ignition device is required. Therefore, a stacked discharge ignition device has been proposed in which the high voltage output of the DC-DC converter is superimposed on the secondary output of the ignition coil generated by the classical current cutoff principle.

FIG. 3 shows a typical example or a principle configuration example of such a conventional overdischarge type ignition device. To explain, the ignition control circuit unit 12 sets the ignition signal Sf to a high level slightly before the ignition timing based on a signal from an ignition timing sensor 11 that notifies the ignition timing of the cylinder, such as a crank angle sensor.
The built-in power switching element (only a single bipolar transistor Q1 is shown in the figure) is turned on to connect the battery (voltage B ⁺
(Implicitly indicated by the above), a primary current i1 is caused to flow, and energy is accumulated in the primary winding of the ignition coil 14.

When the ignition control circuit 12 determines that it is the cylinder ignition timing based on the output from the ignition timing sensor 11, the ignition control circuit 12 lowers the ignition signal Sf to a low level. This is a significant timing as the ignition signal Sf, whereby the power switching element Q1, which is an output stage built in the current interruption unit 13, is turned off, and the primary current of the ignition coil is rapidly interrupted, so that High voltage occurs. In the case of a classic ignition device based only on the current interruption principle, the secondary high voltage of the ignition coil 14 breaks the discharge gap of the ignition plug 15, and thereafter, the gradually decreasing discharge current becomes a spark and the spark plug 15 is discharged. Flowing through.

On the other hand, in the case of the overlap discharge type ignition device shown in the figure, the current based on the high voltage output voltage from the DC-DC converter unit 21 is also superimposed, and the overlap discharge current i2
Is obtained. That is, although not shown in detail, for example, based on the timing obtained by using the ignition signal Sf from the ignition control circuit unit 12, the overlap discharge control circuit (not shown) (generally includes a microcomputer. Generates an overlap discharge time control signal St at a predetermined time point and keeps this signal St for a predetermined time period to cause the oscillation circuit 22 to oscillate for a predetermined time period.
Therefore, in the illustrated case, the oscillator circuit 22 choppers the switching element Q2, which is shown as a MOSFET, in a predetermined cycle, and the primary current flowing through the primary winding of the step-up transformer 23 whose one end is connected to the battery voltage B ^+. By interrupting the current at a predetermined cycle, a high voltage output is generated on the secondary side of the step-up transformer 23.

The current based on the high voltage generated by the DC-DC converter unit 21 is added with the same polarity to the discharge current generated by the current cutoff principle via the diode DL,
As a result, the discharge current flowing through both ends of the spark plug 15
i2 is the stack discharge current i2, and the DC-DC converter unit
Compared to the case where 21 is not used, the size is extended for a predetermined time without being gradually reduced. In addition, the spark plug voltage Vp generally rises to an absolute value of 2 to 3 KV at the beginning of the initial discharge according to the current interruption principle.
Absolute value of 400-
It stabilizes at around 600V, typically around 500V. On the contrary, in order to satisfy this, the output voltage V _O at the output terminal of the DC-DC converter 21 is generally set to 1.5 KV or more under a load in which the discharge current i2 of a predetermined value flows. To be done.

A capacitor C that bypasses the series circuit of the diode DL and the secondary winding of the step-up transformer 23 for adding and superposing the high-voltage output current of the DC-DC converter unit 21 to the current interruption discharge current with the same polarity. Is also a rectifying capacitor, but it can also quickly pass the transient rising component of the discharge current caused by current interruption, and the discharge current i2
Is about 50 to 60 mA, the DC component of this discharge current does not pass through the capacitor C, and the secondary winding of the ignition coil 14, the diode DL, the secondary winding of the step-up transformer 23, It flows through the path of grounding and spark plug 15. In addition, a diode capable of bypassing the current may be intentionally added to the capacitor C. Further, although the DC-DC converter unit 21 which is generally made into a single unit or a single module as a component may be grounded through a dedicated grounding cable, it is usually a metal part of the case of the unit. Often grounded in. These points are the same in the ignition device to which the present invention is applied, which will be described later.

[0008]

However, the combustion in each cylinder combustion chamber of the internal combustion engine sequentially shifts from initial combustion, middle-term combustion, and main combustion from the time when discharge sparks fly to the spark plug 15, When transitioning to medium-term combustion, a rapid change in air flow occurs in the combustion chamber due to flame propagation, and it occurs between the discharge gaps of the spark plug 15 even though the DC-DC converter supplies the overlapping discharge current i2. The so-called "blown out phenomenon" may occur in which the discharge spark is blown out. When such a blow-out phenomenon occurs, not only the desired combustion energy cannot be obtained, but also the circuit elements that compose the DC-DC converter may be burned out or damaged due to overvoltage.

In other words, the output voltage of the DC-DC converter described above is a value when a predetermined discharge current i2 is flowing. Conversely speaking, the output power of the DC-DC converter is set to be considerably high in itself. For example, the magnitude of the overlapping discharge current i2 is determined by the output voltage V _O of the DC-DC converter 21.
Voltage value obtained by subtracting spark plug voltage Vp from (V _O −Vp)
Is a value obtained by dividing by the impedance Rt of the discharge path through which the discharge current i2 flows. This can be expressed by the following equation (1). i2 = (V _O −Vp) / Rt ・ ・ ・ ・ ・ ・ (1) In this impedance Rt, as shown in FIG. This value is also included when Rp is connected.

On the other hand, the output power P of the DC-DC converter 21
_O is defined by the product of the output voltage V _O and the overlapping discharge current i2. In other words, P _O = i2 · V _O・ ・ ・ ・ ・ ・ (2).

Therefore, as described above, under normal operation, the DC-DC converter output voltage V _O is about
In all cases, the expected design value is maintained, from 1.5KV to a level higher than that. However, when the above-mentioned blow-off phenomenon occurs, the overlapping discharge current i2 becomes zero or almost zero, and when this happens, the load of the DC-DC converter 21 becomes extremely light. The output power V _O of the DC-DC converter may become an abnormally high voltage, as is apparent when the output power P _O is considered as the power supply capability and viewed as being almost constant. As a result, the circuit components constituting the DC-DC converter 21 itself, such as a rectifying diode or a rectifying capacitor, do not have a withstand voltage, and may be burned or damaged.

[0012] Therefore also Conventionally, as併示in FIG voltage detection circuit 31 for detecting the output voltage V _O itself of the DC-DC converter is provided, the abnormally high output voltage V _O of this detected It has been proposed to provide an operation stop circuit 32 for forcibly stopping the operation of the DC-DC converter 21 when the voltage is reached.
The deactivation circuit 32 generally acts on the oscillation circuit 22 in the DC-DC converter to stop it.

However, in such monitoring of the DC-DC converter output voltage V _O , it is difficult to accurately correlate with how many volts it actually rises to when the spark is extinguished. , It could not be put to practical use.
The output voltage V _O of the DC-DC converter varies from 0V to 5KV.
It is extremely wide ranging to more than that value, and it is not easy to read an accurate voltage value within such a wide variation range.

[0014]

SUMMARY OF THE INVENTION Therefore, the present invention provides an overlapping discharge type ignition device having a built-in practical structure for protecting the constituent circuit elements of a DC-DC converter against the phenomenon of extinguishing sparks. A current detection circuit for detecting a discharge current; and (b) an operation stop circuit for forcibly stopping the operation of the DC-DC converter when the detected current value of the current detection circuit drops to a predetermined value at which recovery is unlikely. Is proposed. Such a configuration is based on the findings obtained from the experimental results shown in FIG. 2, which will be described in detail in the section of Examples later. The internal circuit configuration of the current detection circuit is not particularly specified,
According to a known existing electric circuit technology, it may be configured to be capable of detecting a current, but it has a current detection resistor inserted in series in the discharge path of the lap discharge current and appears at both ends of the current detection resistor. It is easy to configure so that the overlap discharge current value at each time is detected based on the voltage.

[0015]

1 shows a schematic circuit diagram of an embodiment of a lap discharge type ignition device constructed in accordance with the present invention. In order to clarify the comparison with the conventional example shown in FIG. 3, the same reference numerals as those in FIG. Is attached. Therefore, as for the description of each of these components, the parts already described can also be incorporated unless otherwise specified.

A characteristic improvement in the present invention is that the current detection circuit 41 for detecting the overlap discharge current i2 and the operation for forcibly stopping the operation of the DC-DC converter 21 based on the command of the overlap discharge current detection circuit 41. The circuit 42 is provided. The operating circuit 42 only needs to be able to stop the operation of the DC-DC converter 21, and a person skilled in the art can very easily construct a specific circuit configuration therefor based on ordinary electric circuit technology. For example, a signal of a specific form is sent to the oscillation circuit 22, whereby the power supply to the oscillation circuit 22 is cut off, or both ends of a resistor or a capacitor involved in oscillation are short-circuited or forcibly grounded. Or
Further, it is possible to form various circuits such that the switching element Q2 is turned off by grounding the output terminal of the oscillation circuit 22 through a switching circuit (not shown) with an appropriate low resistance.

However, in detecting the value of the overlapping discharge current i2 flowing through the ignition plug 15, it is troublesome to make magnetic detection in a non-contact manner with respect to the line through which the overlapping discharge current flows. As illustrated, the current detection resistor 43 having a low resistance value is inserted in series in the discharge path of the overlapping discharge current i2,
It is convenient to detect the overlap discharge current value i2 by detecting the voltage across both ends. However, in the case of the present invention, even if it is said that the overlap discharge current value i2 is detected, it is sufficient to judge whether or not the value exceeds a predetermined value, so this is set corresponding to the predetermined current value. This can be realized by comparing the reference voltage value and the voltage value across the current detection resistor 43 with a comparator. Further, in principle, the current detection resistor 43 may be located anywhere in the discharge path of the overlapping discharge current i2 including the spark plug 15, but in the case shown, the step-up transformer 23 which is the DC-DC converter output stage. Is in series between the secondary winding and the ground, and this position is relatively safe in terms of potential. The DC-DC converter is literally unitized or modularized as a single component.
It is a good position to be installed in advance.

Now, the background of the above-described structure in the present invention will be described with reference to the experimental results shown in FIG. First, a lap discharge type ignition device in which the current detection circuit 41 and the operation stop circuit 42 added according to the present invention are omitted from the device configuration shown in FIG. 1, that is, a conventional ignition device is prepared as an experimental device. However, for the purpose of experiment, in order to detect the value of the discharge current that actually flows, the current detection resistor 43 is inserted, and the voltage across the resistor 43 is monitored by a voltmeter device (which can be constructed using a microcomputer). I tried to detect the current value. Also, the voltage Vp across the spark plug 15
The output voltage V _{O of the} DC-DC converter 21 at each time can also be monitored by the voltmeter device.

However, when the operation of the ignition device is followed in the order of operation over time, the ignition control circuit unit 12 determines the ignition timing based on a signal from the ignition timing sensor 11 that notifies the ignition timing of the cylinder, such as a crank angle sensor. Shortly before, the ignition signal Sf is set to a high level, which causes the primary current to flow through the primary winding of the ignition coil 14 via the current interruption unit 13. In the illustrated case, the current cutoff unit 13 is simply shown by a single bipolar transistor Q1, but in reality, it is often a combinational circuit including a plurality of transistor groups. An effect type power switching element may be used. Of course, this is not directly related to the present invention and is an arbitrary problem.

When the ignition control circuit 12 determines the cylinder ignition timing based on the output from the ignition timing sensor 11 while the primary current is flowing through the ignition coil 14, the ignition control circuit 12 outputs the ignition signal Sf. Fall to a low level. This is a significant timing as the ignition signal Sf, by which the current interruption unit 13 suddenly interrupts the primary current of the ignition coil 14 (in the case shown, turns off the power switching element Q1), whereby the ignition coil secondary side A high voltage occurs in the discharge plug, a discharge current flows in the discharge path including the spark plug 15, and a discharge spark is generated in the discharge gap of the spark plug 15. This discharge start time point is indicated by "time point t _O " in FIG.

On the other hand, the lap discharge control circuit (not shown) generates the lap discharge time control signal St for a predetermined time from the discharge start time t _O , and the oscillating circuit in the DC-DC converter 21.
22 is operated for the fixed time, and the DC-DC converter is operated. In the experiment described here, the overlap discharge time (duration of the signal St) is 4.
The DC-DC converter 21 was designed so that the overlap discharge current i2 was about 60 mA for 5 ms. It should be noted that the above-described overlapped discharge control circuit can be assembled by a person skilled in the art as a dedicated circuit by hardware, or can be assembled by software processing by a microcomputer, as described above. Further, in order to determine the generation timing of the signal St, the ignition signal Sf provided from the ignition control circuit unit 12 is used, or a resistor corresponding to a current detection resistor as found in the device of the present embodiment is used. Provided,
It is also possible to use that the voltage across the terminal changes depending on the generation of the initial discharge spark according to the current interruption principle. This point also has no direct relation to the present invention, and may follow the existing technology. However, like the latter, when the current detection resistor is used to obtain the operation start timing of the DC-DC converter, the current detection resistor is also used as the current detection resistor 43 to be provided for the present invention. be able to.

However, in this way, the overlapping discharge current i2
After the occurrence of the current value i2, voltage across spark plug Vp, DC-
When the DC converter output voltage V _O was monitored, as shown in FIG. 2, the lap discharge current value of about 60 mA, which was close to the design expected value, was measured for a while from the discharge start time t _O , but the discharge start time t _O As observed at time ta about 2.4 ms after _O, the phenomenon that the lap discharge current value i2 suddenly decreased to about 15 mA was observed. At this time, the spark plug voltage Vp also rapidly increased. Perhaps this is, as mentioned above,
It is considered that this is the result of a large turbulence in the air flow in the combustion chamber due to the transition from the initial combustion to the mid-term combustion. It is considered that the discharge spark generated between the discharge gaps of the spark plug 15 forms an arc due to the violent air flow, the flying distance becomes longer, the discharge voltage becomes higher, and the discharge current decreases. But,
At this time ta, the overlap discharge current recovered without disappearing. Therefore, the output voltage of the DC-DC converter 21
Although V _O has also started to rise, it has picked up and the spark plug voltage Vp has decreased.

However, after that, the overlapping discharge current i2 again tends to decrease, and as seen at the time point tb when 3.2 ms has passed from the ignition start time point t _O , it does not recover again when the current is cut below 15 mA, and almost disappears. It has fallen to zero. This can be fully inferred to be the result of extinguishing the sparks, but at the same time, the output voltage V _O of the DC-DC converter 21 rises to about 5 KV as shown by the phantom line in FIG. Oops. This is a value that far exceeds the expected DC-DC converter output voltage value (about 1.5KV as described above), and is a value that exceeds the withstand voltage of circuit components or the withstand voltage of many things. Is.

After all, such experimental results show that in the case of the above experimental apparatus, 15 mA is the recoverable lower limit of the stack discharge current. Therefore, in such a case, the value of the overlapping discharge current i2 is a value preset as the predetermined current value.
If the DC-DC converter 21 is forcibly stopped when the current drops to 15 mA, the circuit components of the DC-DC converter can be effectively protected. Moreover, as compared with the case where the output voltage V _O of the DC-DC converter 21 is detected, the overlap discharge current value can be detected with sufficient accuracy and without difficulty, as can be seen from the above experimental example. Based on these findings,
The present invention has provided the structure as described above.

Of course, depending on the device, the minimum current value at which the lap discharge current can be recovered will vary from device to device, but the minimum recoverable current value can be determined by at least the above preliminary experiment for each device. Since it can be verified, the present invention is applied with this value as a predetermined current value for each device, and when the detection current of the current detection circuit 41 drops to the predetermined current value, the operation stop circuit 42 causes the DC- DC converter
When the operation of 21 is stopped, the DC-DC converter 21 can be protected from damage.

Although the embodiment of the present invention has been described above, various modifications can be made without departing from the scope of the present invention. The illustrated DC-DC converter unit 21
However, only a concrete circuit example is schematically shown.

[0027]

According to the present invention, not the output voltage of the DC-DC converter but the lap discharge current itself actually flowing in the discharge path including the spark plug in series is detected. Therefore, the detection is not difficult. Moreover, it can be performed with a certain degree of accuracy or more. As a result, it is possible to forcibly stop the operation of the DC-DC converter when the lap discharge current value drops to a current value that is considered to lead to the extinguishment of sparks, and the output voltage of the DC-DC converter is abnormally high. Become DC
-The possibility of burning or damaging the internal circuit components of the DC converter itself can be prevented.

In other words, the withstand voltage of the circuit elements for constructing the DC-DC converter may be a withstand voltage that is required when the overlapping discharge is normally performed without considering a large margin. Therefore, it is possible to use a device having a necessary and sufficient size and a price, and eventually it is possible to realize the downsizing and cost reduction of the circuit.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of a lap discharge type ignition device configured according to the present invention.

FIG. 2 is an explanatory diagram of an experimental result for verifying a spark blowout phenomenon performed in the process of reaching the present invention.

FIG. 3 is a circuit configuration diagram of a typical example of a conventional overlapped discharge ignition device.

[Explanation of symbols]

 11 Ignition timing sensor, 12 Ignition control circuit unit, 13 Current interruption unit, 14 Ignition coil, 15 Spark plug, 21 DC-DC converter unit, 22 Oscillation circuit, 23 Step-up transformer, 41 Current detection circuit, 42 Operation stop circuit, 43 Current detection resistor.

Claims (2)

[Claims] 1. A high voltage generated on the secondary side of the ignition coil by interrupting the primary current of the ignition coil causes discharge sparks to occur in a spark plug, and a high voltage generated by a DC-DC converter against the discharge spark current. A discharge current based on the above to be a lap discharge current, over the duration of the lap discharge current,
A lap discharge type ignition device for continuing discharge sparks generated in the spark plug; a current detection circuit for detecting the lap discharge current; and a detection current value of the current detection circuit reduced to a predetermined value. And an operation stop circuit for forcibly stopping the operation of the DC-DC converter. 2. The device according to claim 1, wherein the current detection circuit has a current detection resistor inserted in series in a discharge path of the lap discharge current, and a voltage appearing at both ends of the current detection resistor is detected. Detecting the above-mentioned overlap discharge current value based on the above;