JP2811791B2 - Self-excited oscillation contactless ignition device for internal combustion engines - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a capacitor discharge type non-contact ignition device for an internal combustion engine, and more particularly to a transformer of a DC-DC converter.
A self-excited oscillation type non-contact ignition device that charges the capacitor by repeatedly turning on and off the secondary current, cuts off the primary current at a constant current, thereby improving the energy conversion efficiency of the converter and increasing the design flexibility. It relates to an ignition device.

2. Description of the Related Art A non-contact for an internal combustion engine using a DC-DC converter that generates a boosted voltage in a secondary coil by intermitting a current flowing through a primary coil of a transformer, boosts a DC power supply, and charges a main discharge capacitor for ignition. For example, Japanese Patent Application Laid-Open No. 61-85577 discloses an ignition device.
There is a configuration disclosed in Japanese Unexamined Patent Publication (Kokai) No. H10-26095. FIG. 6 shows a configuration according to this Japanese Patent Application Laid-Open Publication No. HEI 9-120, in which a primary coil of a predetermined size is added to a primary coil of a transformer of a DC-DC converter in response to an output of each cycle of an electromagnetic pickup MPU for detecting an engine rotation speed. By supplying current, the main discharge capacitor 12 is charged with the boost voltage generated on the secondary side, and the primary coil 10a of the ignition coil 10 and the thyristor 11 are connected in series and parallel with the capacitor to respond to each output of the MPU. Then, the thyristor gate is driven to conduct the thyristor, thereby discharging the charge voltage of the capacitor and driving the ignition coil. In the configuration in which the main discharge capacitor is charged / discharged for each output of each cycle of the MPU, if the ignition coil connector is disconnected or thyristor conduction failure occurs, the next cycle of charging is performed without discharging the discharge capacitor. Therefore, there is a problem that an overcharge state exceeding an allowable voltage is caused to cause a destruction of circuit elements.
20 is provided to monitor the charging voltage of the main discharge capacitor 12, thereby controlling the conduction and interruption of the primary current of the transformer 2 so that the charging voltage is not charged to a predetermined voltage _VA or more.
That is, during normal operation, the primary current I ₁ flowing through the transistor 3 connected in series to the primary coil of the transformer 2 is detected by the resistor 7 and the comparator 8 and the primary current I ₁ of a predetermined magnitude flows. R (set by MPU output)
The S flip-flop 5 is reset and the transistor 3 is turned off. This main discharge capacitor 12 by a predetermined magnitude of the primary current is designed to the rated voltage V _C is charged. When the allowable voltage that can avoid the destruction of the main discharge capacitor and a thyristor with the other and ^{_{V D, V A 2 <V}} D 2 -V C 2
When the overvoltage protection circuit 20 detects the predetermined voltage _VA given by the above, the base of the transistor 3 is grounded to shut off the transistor, thereby preventing charging of the main discharge capacitor. In other words, by detecting the primary current I ₁ in order to prevent overcharging and pressing into a predetermined size.

According to the above-mentioned conventional system disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2002-287, the power transistor 3 is turned on and off only once in response to a signal generated once per revolution of the engine, and the main discharge capacitor is also charged and discharged only once. This is a one-shot operation. On the other hand, there are a self-oscillation method and a separately-excited oscillation method in the continuous oscillation method in which the power transistor is turned on and off a plurality of times for one charge / discharge cycle of the main discharge capacitor. The excitation oscillation method uses an external oscillation circuit, which makes the circuit complicated and expensive. Further, in the single-shot type, the transformer becomes large in order to obtain a necessary boosted charging voltage by one interruption of the primary current. Further, the self-excited oscillation method can reduce the size of the transformer, but has the problems that the energy conversion efficiency of the DC-DC converter is low and the degree of freedom in design is reduced as described below. In the present specification, the small degree of design freedom means that the variation of the cutoff value of the primary current of the transformer is large, so that it is necessary to adjust the factor of each circuit, and that the setting of the cutoff value is not easy due to the large variation. Means. The following table compares the features of these methods.

In other words, the method of Japanese Patent Application Laid-Open No. 61-85577 (No. 1 in the above table) has a serious problem that the size of the transformer cannot be reduced. In order to reduce the size of the transformer,
o.3 will be used. No. 2 requires an external oscillation circuit, which complicates the circuit. No. 3 has a problem in that the degree of freedom in design is small and the efficiency is low in principle.

Therefore, the above-mentioned problems of the conventional self-excited oscillation system will be discussed with reference to FIG.

FIG. 5 shows a related part of the conventional circuit, in which 13 is a DC-DC converter, 14 is a CDI ignition circuit, 2 is a step-up transformer, 3 is a power transistor for controlling conduction and interruption of a primary current, 4 is a main discharge capacitor and 5 is a thyristor.
Base From what attention of the present inventors, as described in detail below, repetition of on-off power transistor 3 is caused by the positive feedback action of the tertiary winding 2c for the primary current I ₁ transformer 2 since the driving current I ₃ is the transistor 3 is carried out by repeating the course of being driven from the saturation region to the active region, DC-DC, including losses caused power transistor
The energy conversion efficiency of the converter is poor (about 50%).
In addition, variations occur in the shutoff timing of the power transistor, and the degree of freedom in design is reduced.

SUMMARY OF THE INVENTION Problems to be Solved by the Invention The self-excited oscillating type that can reduce the size of the transformer by avoiding the large size of the transformer, which is a drawback of the single-shot type DC-DC converter as described in the above-mentioned Japanese Unexamined Patent Publication, and that does not require an external oscillation circuit. DC
The present invention provides a capacitor discharge type non-contact ignition device in which the problems of increasing the energy conversion efficiency of the DC converter and increasing the degree of freedom in design are solved, and these are improved. Here, an improvement in energy conversion efficiency means a reduction in heat loss generated in power transistors and the like, and an increase in the temporal use efficiency of the circuit described below.

Means for Solving the Problems A capacitor discharge type non-contact ignition for an internal combustion engine that discharges the charge of a main discharge capacitor for ignition by conducting a switching element for ignition based on an ignition signal and thereby ignites an ignition plug. In a device, a current flowing from a DC power supply to a primary winding of a transformer is turned on and off by a switching transistor to charge a main discharge capacitor for ignition by a secondary winding, and a tertiary transformer of the transformer responding to the primary current DC self-oscillating due to positive feedback of winding
A DC converter that detects a collector current or an emitter current of a predetermined value in a saturation region of the switching transistor and turns off the transistor, thereby turning off the primary winding current and repeating oscillation. DC
A self-oscillating contactless ignition device for an internal combustion engine, comprising: a converter; and an oscillation stop circuit that stops self-oscillation of the DC-DC converter in response to an ignition signal. .

Function Switching transistor (power transistor)
When the transistor is turned on when the base current from the DC power supply flows in the initial state of turning off, the primary current of the transformer flows and the base current is supplied by the positive feedback action by the tertiary winding, and the primary current further increases. However, when a predetermined value in the saturation region is reached, the base current is forcibly turned off, the switching transistor is turned off, and the primary current is turned off. This result is the secondary winding of the transformer I ₂ is charging flow main discharge capacitor. Switching transistor Although the base by the positive feedback action of the turned off 3 winding a reverse bias voltage is applied, the I ₂ is completed flows, performs a substantially continuous oscillation operation returns to its initial state . When the ignition switching element (SCR) is turned on based on the ignition signal, the oscillation stop circuit temporarily stops the self-excited oscillation of the DC-DC converter to facilitate turning off the switching element.

Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which an output 13 of a DC-DC converter 13 with a battery 1 as an input voltage.
In a, a voltage boosted to about 200 V appears. This is CDI
(Capacitor discharge type) Used as an ignition power supply for the ignition circuit 14. The DC-DC converter 13 includes a transformer 2 and a shut-off power transistor (hereinafter referred to as a power supply) connected in series with the primary winding 2a for interrupting a current flowing through the primary winding 2a of the transformer 2.
Tr, a diode 12 for rectifying the output of the secondary winding 2b of the transformer, and power from the tertiary winding of the transformer.
Element 11 for applying feedback to the base of Tr3,
It comprises a constant current detection cutoff circuit 9 for cutting off the current flowing through the transformer primary winding 2a at a predetermined value.

Constant current detection blocking circuit 9 is composed of a comparator 9a for comparing and resistors 9b for converting the transformer primary current into a voltage, a voltage generated in the resistor with a predetermined voltage V _R.

The CDI ignition circuit 14 includes an ignition main discharge capacitor 4 charged by the output of the DC-DC converter, an ignition SCR 5 gate-triggered by an ignition signal generated by the timing sensor 8,
It comprises an ignition coil 6 serving as a load when discharging the electric charge of the capacitor 4 when the SCR 5 conducts, and an ignition plug 7 connected to the secondary side of the ignition coil.

In order to explain the improvement of the energy conversion efficiency in the DC-DC converter of this embodiment, the operation of the self-oscillation type DC-DC converter having the conventional configuration shown in FIG. The operation will be described below in comparison with the operation of the configuration shown in FIG.

Fifth embodiment having no constant current detection cutoff circuit 9 according to the present invention.
In the conventional circuit of FIG. (A), first, when the current flows to the base of the power Tr3 by Batsuteri voltage V _B through a resistor 10, power Tr3 moves in the direction of one. That is, 1 of the transformer 2
The primary current I ₁ begins to flow through the primary winding 2a. I ₁ is the fifth
An attempt is made to increase linearly as shown in FIG. Transformer 2
When current flows through the I ₁ to the primary winding 2a of the tertiary winding 2c I ₃
Current flows in the direction of. Through fed back element 11, I ₃ becomes the base current of the transistor 3, more power
Tr3 moves in the ON direction. That is, the power Tr3 operates once the positive feedback from the tertiary winding 2c.

The current I ₁₀ flowing through the resistor 10, since the size relationship between I ₃ are summer and I ₁₀ «I _3, the base current of the power Tr3 may be considered substantially only I _3. Here, since I ₃ is given by the following equation, it can be regarded as a constant value.

On the other hand, I ₁ rising linearly with time cannot be further increased when it reaches (h _{FE of} power Tr3) × I ₃ ... * 2. Then, at the next moment, the operation of the power Tr3 enters the active area and V _CE
Moves in the direction in which the power Tr becomes large (until then, the power Tr is in the ON state in the saturation state and V _CE ≒ 0). Since the voltage V _2a generated at both ends of the primary winding 2a is V _2a = V _B −V _CE , as V _CE increases, V _2a decreases. V _2a
Is smaller, the voltage generated in the tertiary winding 2c which is magnetically coupled also becomes smaller. When that happens,
I ₃ also decreases. Reduction of the base current I ₃ in the active region are increasingly V _CE
And this positive feedback, power Tr3
Moves in the off direction (= blocks). At this timing, the polarity of each winding of the transformer is reversed at a stretch. (Of course, 3
A negative voltage is generated in the next winding to turn off the transistor. ) When the polarity is reversed, the secondary current I ₂ flows through the secondary winding 2b which has failed flowing until then. I ₂ becomes linearly descending characteristics as of FIG. 5 (B). The I _2, main discharge capacitor 4 is charged. If I ₂ is 0, the circuit state is the initial state, power Tr3 by the current I ₁₀ from again resistor 10
The cycle that moves in the ON direction starts.

By repeating the above operation, the oscillation of the power Tr continues, and the capacitor 4 is charged with the voltage. When the ignition timing comes, the gate of the SCR 5 is triggered by a signal generated by the timing sensor 8. As a result, the electric charge of the capacitor 4 is discharged to the ignition coil 6, and a high voltage is generated in the ignition plug 7 to ignite.

In the circuit shown in FIG. 1, when the charged voltage of the capacitor 4 becomes too high during the operation, the transistor 3 is turned off by the overvoltage detection circuit 16 and the oscillation stop circuit 15 to temporarily stop the operation. The self-oscillation operation by the power Tr3-transformer 2 is stopped. Also, immediately after the ignition signal is input, the power Tr3 is turned off by the oscillation stop circuit 15 to temporarily stop the self-excited oscillation, thereby making it easier to turn off the ignition SCR5.

Operation of the oscillation stop circuit 15: When the output of the overvoltage detection circuit 16 or the ignition signal is input to the timing sensor 8 from the timing sensor 8, the transistor 15a is turned on, the base voltage of the power Tr3 is set to 0, and the oscillation is stopped. .

For the conventional circuit, breaking current I ₅ of I ₁ is * 1 set, * 2
From the formula, It can be expressed as.

Next, in the circuit of the present invention of FIG. 1, was set to the primary current I ₁ reaches a predetermined value, interrupting. That is, the constant current cutoff detecting circuit 9, the primary current is cut off Tara summer to the following formula I _C.
In However V _R is the comparator reference voltage, so that the operation of the transistor 3 from entering the active region from the saturation region by I _C Appropriately setting the V _R as I _C is made to an appropriate value in the saturation region. The sub connexion primary current, the voltage generated across the resistor 9, Tara summer to the reference voltage V _R of the comparator 9a, blocking (power Tr3 is turned on → off) will be. The operation is the same as that of the conventional method except that the method of determining the timing of the cutoff is different.

The feature of the oscillation system of the present invention having the above configuration is that it has the following effects.

 Energy conversion efficiency of DC-DC converter.

When the power Tr3 turns on → off, the power Tr3
The operation region of the device shifts from the saturation region to the active region, and power loss occurs at the power Tr (collector current × V _CE saturation voltage)
Is generated. However, in the present invention, since the power transistor is always used in the saturation region, V _CE V
0, the power loss of the power transistor can be reduced, which greatly contributes to the improvement of the energy conversion efficiency of the DC-DC converter of the transformer self-oscillation type. Can be improved to about 60%).

Cutoff current I _C design and ease of production (design freedom improvement in).

The cutoff value I _C of the primary current is set by the formula * 3 in the conventional method and by the formula * 4 in the present method. As is clear from the comparison between the two methods, the conventional method is affected by the transistor h _FE (h _FE
Variation, _hFE temperature change). Accordance connexion, to suppress the I _C within a predetermined range, it is necessary to adjust and screening, such as a transistor circuit components, causing an increase in production costs.

However, in this method, * 4 set of I _C as the formula is easy
It is not necessary to consider variations in _hFE .

As described above, the characteristics of the oscillation system according to the present invention are considered in the range of the transformer self-excited oscillation system, but the significance and effect of the present invention can be pointed out as follows in comparison with the separately excited oscillation system.

(1) In the separately-excited oscillation method, since the power Tr3 is repeatedly turned on and off by an independent oscillation circuit, the transistor 3 can operate in the saturation region even when the transistor 3 shifts from on to off. Low power loss and good energy conversion efficiency. Setting interruption current I _C is also easy. However, an independent oscillation circuit is required, and the circuit scale increases.

Therefore, when compared with the separately excited oscillation method, this method improves the energy conversion efficiency and the easiness of setting I _C to the same degree, but produces an excellent effect that a complicated oscillation circuit is not required. I have.

(2) It has been described above that the power loss when the power transistor goes from ON to OFF is reduced by the present invention.
The energy conversion efficiency can be improved by effectively utilizing the characteristics of the self-excited oscillation system, which has a high temporal use efficiency of the DC-DC converter, without causing a circuit downtime that can occur with the separately excited oscillation system when transitioning from F to ON. Contribute to improvement.

In FIG. 2 (A), which shows the main part of the circuit of FIG. 1, the voltage is charged to the ignition capacitor C (V _C ≠ 0) and the voltage is not charged (V _C = 0).

FIG. 2 (B) When V _C ≠ 0: That is, for one ignition,
The power Tr oscillates several tens to about 100 times and charges C with the same number of small pulses, but this is the case where C is charged to some extent.

FIG. 2 (C) Case of V _C = 0: That is, the case of the first oscillation of several tens to 100 times.

For · I _1, FIG. 2 (B) The second diagram (C) is the same waveform.

For · I _2, the peak value and the second view (B) The second diagram (C) is also the _{same, I 2P (a) = I} 2p (b). However, the flow time is shorter when V _C ≠ 0, T _{OFF (a)} <T _{OFF (b)} .

The upper figure shows the case of transformer type self-excited oscillation. However, if this is performed by separately-excited oscillation (that is, if the oscillation cycle is determined irrespective of the state of the secondary load of the transformer), the following problem occurs.

This is how to set the time for turning off the power Tr in the oscillation cycle. Otherwise excited oscillation, as in the vibration above transformer type self-excited, depending on the value of V _C, power Tr
The OFF time T _OFF cannot be automatically followed and is constant. Therefore, if T _OFF = T _{OFF (b)} is set, if V _C is charged and V _C > ₀ , T _{OFF (a)} becomes T _{OFF (b)} ｛T
Although the period of _{OFF (b) -T OFF (a} )} is power Tr is OFF, I ₁ also I ₂ also does not flow, nothing time that does not work is generated that.

Therefore, if the OFF time is set to be T _OFF <T _{OFF (a),} the power Tr is initially O only for I _on when V _C ≒ 0.
If N is set, the energy that can be charged at one time during the period of T _{OFF (b)} is stored in the transformer as magnetic energy, but is turned off for a shorter time than T _{OFF (b)} .
Therefore, the process proceeds to the next oscillation cycle before transferring all the energy from the transformer to C.

This is a problem when the separately excited oscillation method is applied to the CDI ignition device. When the load on the secondary side of the transformer greatly changes from 0 V to 300 V, as in the case of CDI, it is considered that the transformer self-oscillation system that can automatically follow the OFF time according to the load state is matched.

As described above, the present invention is focused on the advantages of the separately-excited oscillation circuit and the self-excited oscillation circuit, and effectively combines these advantages to eliminate the disadvantage.

 FIG. 3 shows another embodiment. Constant current detection cutoff circuit 9
Is composed of a resistor 9b and two diodes 9c and 9d. Tran
Base potential V of transistor 3 Is I₁Increases, V
= I₁× (resistance of 9b) + V_BEGiven by This value
Is the sum of the forward voltage drops of the diodes 9c and 9d = 2 x V_FTo
Beyond that, the base current will flow to 9c, 9d
And the breaking current value I_CIsIs determined by (V_BE≒ V_FThink. FIG. 4 shows still another embodiment. Constant current detection cutoff circuit
9 comprises a resistor 9b and an SCR 9e as shown in FIG.
You. Breaking current value I_CIsCan be determined by Also, as shown in FIG.
In addition to e, the transistor 9f may be used.

Although not shown, a temperature compensating circuit may be added to necessary elements.

Effect of the Invention In the capacitor discharge type non-contact ignition device, the primary winding current of the transformer is turned on by the switching transistor,
When turning off and charging the main discharge capacitor connected to the secondary winding, the transistor that self-oscillates by the positive feedback of the tertiary winding responding to the primary current is cut off at a constant current within the saturation region. Thus, the base current can be designed to flow sufficiently even when the transistor is turned on, so that the saturation voltage can be reduced. When the ignition switching element (SCR) is turned on based on the ignition signal, the oscillation stop circuit is a DC-DC
The self-excited oscillation of the switching transistor of the converter is temporarily stopped to easily turn off the switching element. Therefore, with a simple configuration, the power loss of the transistor is reduced, the energy conversion efficiency is improved, and the size of the transformer can be reduced. Furthermore, in order to detect a predetermined value of the collector current or the emitter current in the saturation region of the switching transistor and turn off the transistor, the switching transistor is switched between the saturation region and the cut-off region regardless of the level of the power supply voltage. Since it can be operated, the degree of freedom in design is improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of an ignition device according to the present invention, FIG. 2 is a principle diagram for explaining features of the device of FIG. 1, and FIGS. 3 and 4 show the present invention. FIG. 5 and FIG. 6 are circuit diagrams showing a conventional example of another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... Battery 2 ... Transformer for DC-DC converter 3 ... Power Tr for cutting off 4 ... Main discharge capacitor for CDI 5 ... SCR 6 ... Ignition coil 7 ... Spark plug 8 ... Timing sensor 9 ... … Constant current detection cut-off circuit 9a… Comparator 10… Resistance 11… Element for tertiary winding feedback 12… Diode 13… DC-DC converter 14… CDI ignition circuit 15… Oscillation stop circuit 16… Overvoltage detection circuit

Continuation of front page (56) References JP-A-60-204261 (JP, A) JP-A-59-58159 (JP, A) JP-A-57-95081 (JP, U) JP-A-1-71172 (JP) U.S. Pat. No. 3,599,616 (US, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02P 3/08 H02M 3/338

Claims (1)

(57) [Claims] 1. A capacitor discharge type non-contact ignition device for an internal combustion engine which discharges a charge of a main discharge capacitor for ignition by turning on a switching element for ignition based on an ignition signal and thereby ignites an ignition plug. The switching transistor turns on and off the current flowing from the DC power supply to the primary winding of the transformer, charges the main discharge capacitor for ignition with the secondary winding, and responds to the primary current with the tertiary winding of the transformer. DC- that self-oscillates due to the positive feedback of
A DC-DC converter that detects a collector current or an emitter current of a predetermined value in a saturation region of the switching transistor and turns off the transistor to turn off the primary winding current and repeat oscillation. A self-excited oscillation non-contact ignition device for an internal combustion engine, comprising: a converter; and an oscillation stop circuit that stops self-oscillation of the DC-DC converter in response to an ignition signal.