Ignition system for an internal combustion engine

Abstract

 An improved ignition system for an internal combustion engine comprises: (a) an ignition coil (4) having a primary winding (4a) and secondary winding (4b), one end of the primary winding being connected to a battery (1) (low DC voltage supply) via an ignition switch (2) and current limiting resistor (R1) and the other end of the primary winding being grounded via a transistorized ignition switching unit (5) which receives an ignition signal generated at an electromagnetic pick-up (7) at an ignition timing, i.e., when a pick-up rotor (6) adjacent thereto rotates through an angle determined in accordance with the number of engine cylinders; (b) a distributor (9) having a rotor electrode at a center thereof connected to one end of the secondary winding of the ignition coil via a central cable (5) and having a plurality of fixed electrodes spaced radially symmetrically around the rotor electrode; (c) a plurality of spark plugs (11) each located within a corresponding engine cylinder and connected to one of the fixed electrodes of the distributor via a high-tension cable (10) according to an ignition order for the cylinders; (d) a DC-DC converter (20) which receives a low DC voltage from the battery via the ignition switch (2) inverts the low DC voltage into a corresponding AC voltage, boosts the AC voltage into a high AC voltage, rectifies the AC voltage into a high DC voltage and stores the rectified high DC voltage within a capacitor (5) so that the charged high DC voltage within the capacitor is applied to one of the spark plugs (11) via the secondary winding (4b) of the ignition coil and distributor (9) when the spark plug starts a spark discharge by means of the transistorized switching (5) unit and ignition coil (4) to break down the electrical resistance within the gap between electrodes of the spark plug; and (e) an output voltage control means (25) which controls the output voltage of the DC-DC converter (26) so as to provide an appropriate amount of ignition energy for each spark plug according to an engine operating condition.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates generally to an internal combustion engine ignition system, and more specifically to an improved ignition system for an internal. combustion engine, wherein a voltage control means is provided for changing the output voltage of a DC-DC converter according to engine operating conditions so that an appropriate amount of ignition energy in accordance with engine operating conditions is applied across the spark gap of each spark plug.

Description of the Prior Art.

[0002] A conventional ignition system comprises: (a) a DC-DC converter which receives a low DC voltage from a storage battery via an ignition switch, converts the low DC voltage into a corresponding AC voltage, and boosts and rectifies the AC voltage into a high DC voltage; (b) an ignition coil having a primary winding and secondary winding, one end of the primary winding thereof being connected to the ignition switch via a current limiting resistor; the other end of the primary winding being grounded via a transistorized switching unit, the transistorized switching unit receiving an ignition signal outputted from a electromagnetic pick-up, the ignition signal being generated according to a predetermined angular rotation of a rotor in synchronization with the engine revolutional speed, so that the current flowing through the primary winding of the ignition coil is interrupted at each ignition timing of the engine cylinders; and (c) a distributor having a rotor electrode connected to one end of the secondary winding of the ignition coil via a central cable (the other end of the secondary winding thereof being connected to an output terminal of the DC-DC converter) and a plurality of outer electrodes each connected to a spark plug located within a corresponding cylinder via a high-tension cable. The DC-DC converter is a voltage boosting circuit which generates a DC high voltage of approximately 2 kilovolts and applies the DC high voltage to the secondary winding of the ignition coil. The DC-DC converter comprises a voltage boosting transformer having a primary winding, an intermediate tap thereof being connected to the battery via the ignition switch and both ends thereof being grounded via respective transistors, the bases of which are connected to opposite ends of a third winding so as to energize the primary winding to cause a primary current to flow in opposite directions, a secondary winding, at either end of which high voltage alternatingly appears, and double voltage rectifying circuit which converts the alternating voltage into the doubled high DC voltage. It should be noted that a filter circuit is provided between the input terminal of the DC-DC converter and intermediate tap of the primary winding of the voltage boosting transformer for suppressing noise and serial resistors are provided at the output terminal of the DC-_DC converter in parallel with two capacitors of the double voltage rectifying circuit for gradually discharging the electrical charge within the two capacitors when the ignition switch is turned off.

[0003] When the primary current flowing through the primary winding of the ignition coil is interrupted according to an ignition timing by means of the transistorized ignition switching unit, the high voltage generated at the secondary winding thereof causes a spark discharge across the gap between the electrodes of one of the spark plugs connected via the distributor so as to break down the gap thereof.

[0004] When the spark discharge is started, the high DC voltage of approximately 2 kilovolts charged within the two capacitors of the double voltage rectifying circuit of the DC-DC converter is applied across the gap of the spark plug via the secondary winding of the ignition coil and distributor so as to sustain a subsequent arc discharge. If the gap resistance between the electrodes of the spark plug remains low, the discharge continues to ensure fuel ignition.

[0005] On the other hand, in general, combustion conditions change according to engine operating conditions. A large ignition energy is required when the engine load is light or the engine speed is low, while the ignition energy may be reduced as the engine load and engine speed increase.

[0006] However, since the conventional ignition system as described hereinbefore keeps the output voltage of the DC-DC converter constant, the available ignition energy is reduced as the engine speed increases due to the charging response characteristics of the two capacitors of the double voltage rectifying circuit. In this case, if the output voltage of the DC-DC converter is set to a DC voltage high enough to provide sufficient ignition energy when the engine load is light or engine speed is low, more ignition energy than necessary will be generated when the engine load and engine speed are high. Consequently, power consumption becomes inefficient. Conversely, if the output voltage of he DC-DC converter is set to a lower DC voltage, insufficient ignition energy may be generated at low engine load and speed. Consequently, misfire may occur.

SUMMARY OF THE INVENTION

[0007] With the above-described problem in mind, it is an object of the present invention to provide an improved ignition system for an internal combustion engine, wherein a voltage control means is provided for adjusting the output voltage of the DC-DC converter according to engine operating conditions so that the charge voltage of the two capacitors in the double voltage rectifying circuit of the DC-DC converter increases as the engine speed or engine load decreases and decreases as the engine speed or engine load increases. Consequently, efficient electrical power consumption and fuel consumption can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] A more complete understanding of the present invention may be obtained from the attached drawing in which like reference numerals designate corresponding elements and in which:

Fig. 1 shows a conventional ignition system applied to a four-cylinder internal combustion engine;

Fig. 2(A) is a circuit wiring diagram of a DC-_DC converter shown in Fig. 1;

Fig. 2(B) is a circuit block diagram of an example of the transistorized ignition switching unit shown in Fig. 1;

Fig. 3 is a graph of the relationship between ignition energy and engine speed or engine load;

Fig. 4 is a graph of the relationship between engine speed, engine load and ignition energy;

Fig. 5(A) is a circuit diagram of a preferred embodiment of the ignition system applicable to a four-cylinder internal combustion engine;

Fig. 5(B) is a circuit diagram of an alternative high DC voltage control circuit;

Fig. 5(C) is a circuit diagram of another alternative high DC voltage control circuit;

Fig. 6 is a graph showing the relationship between ignition energy and engine load as outputted by the -DC-DC converter shown in Fig. 5; and

Figs. 7 and 8 are graphs each showing the discharge characteristics of the spark plug shown in Fig. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0009] Reference will be made to the drawings in order to facilitate understanding of the present invention.

[0010] First, Fig. 1 shows a conventional ignition system applied to a four-cylinder internal combustion engine.

[0011] In Fig. 1, numeral 1 denotes a battery (low DC voltage supply), numeral 2 denotes an ignition switch 2, numeral 3 denotes a DC-DC converter, numeral 4 denotes an ignition coil having a primary winding 4a and secondary winding 4b, numeral 5 denotes a transistorized ignition switching unit, numeral 6 denotes a pick-up rotor, numeral 7 denotes an electromagnetic pick-up, numeral 8 denotes a central cable, numeral 9 denotes a distributor having a rotor electrode 9a and a plurality of fixed electrodes 9b spaced symmetrically around the rotor electrode 9b, numeral 10 denotes a high-tension cables designed for suppressing high-frequency ignition noise, and numeral 11 denotes a plurality of spark plugs, each located within a corresponding cylinder. An input terminal A of the DC-DC converter 3 is connected to the battery 1 via the ignition switch 2 and output terminal B thereof is connected to one end of the secondary winding 4b of the ignition coil 4. The other end of the secondary winding thereof 4b is connected to the rotor electrode 9a of the distributor 9 via the central cable 8. One end of the primary winding 4a of the ignition coil 4 is connected to the battery 1 via a current limiting resistor R1 and the ignition switch 2 and the other end of the primary winding 4a is connected to the ground via the transistorized ignition switching unit 5. The transistorized ignition switching unit 5 receives an ignition signal from the electromagnetic pick-up 7, generated as the pick-up rotor 6 rotates in synchronization with the engine revolution, and interrupts the current flowing through the primary winding 4a of the ignition coil 4.

[0012] Fig. 2(A) shows the internal configuration of the DC-DC converter 3. In Fig. 2(A), the low DC voltage from the battery 1 via the input terminal A is sent into a primary winding 12a of a voltage boosting transformer 12 via the intermediate tap of the primary winding 12a. Two transistors Q₁ and Q₂ are provided between the ends of the primary winding 12a and ground. A third winding 12b is provided at the primary winding side between the two transistors Q 1 and Q₂ so that the primary winding 12a is excited to generate a current directed alternatingly from the intermediate tap of either end thereof as shown by arrows. Consequently, both ends of the secondary winding 12c of the voltage boosting transformer 12 experience a boosted alternating voltage determined by the winding ratio between the primary and secondary windings 12a and 12c. The boosted AC voltage is rectified by means of two diodes D₁ and _D2 and the rectified voltage is used to charge two capacitors C₁ and C₂. The anode of the first diode D₁ is connected to one end of the first capacitor C₁. The cathode of the first diode D_l is connected to one end of the secondary winding 12c and to the anode of the second diode D₂. The cathode of the second diode D₂ is grounded. The other end of the secondary winding 12c is connected to the other end of the first capacitor C₁ and to one end of the second capacitor C₂. The other end of the second capacitor C₂ is grounded. These diodes and capacitors D₁, D₂, C₁, and C₂ constitute a double voltage rectifying circuit. The one end of the first capacitor C₁ and the anode of the first diode D₁ constitute an output terminal B of the DC-DC converter 3. It will be seen that serial resistors R₂ through R₄ are provided between the output terminal B and ground as a means for discharging the electrical charge within the two capacitors C₁ and C₂ gradually after the ignition switch 2 is turned off in order to prevent an electrical shock. A filter circuit comprising two capacitors C₃ and C₄ and inductor L is provided between the input terminal A and ground for suppressing ignition noise generated by the internal DC-DC converter 3.

[0013] Each time the primary current flowing in the primary winding 4a is interrupted by means of the transistorized ignition switching unit 5, a high surge voltage generated at the secondary winding 4b starts a spark discharge at the one of the spark plugs 11 currently in contact with the rotor electrode of the distributor 9. At this time, the rectified high DC voltage of approximately 2 kilovolts in the first and second capacitors C₁ and C₂ of the DC-DC converter 3 is sent to the spark plug via the secondary winding 4b so as to sustain the arc discharge after the gap between electrodes of the spark plug breaks down.

[0014] An example of the transistorized ignition switching unit is shown by Fig. 2(B).

Fig. 3 shows a relationship between ignition energy and engine load or engine speed. As shown in Fig. 3, as the engine load or engine speed decreases, the ignition energy required increases.

Fig. 4 shows the relationship between engine load and engine speed with the ignition energy held constant. As appreciated from Fig. 4, the engine speed and engine load have a symmetrical relationship if the ignition energy is maintained constant.

Fig. 5(A) shows a preferred embodiment of the ignition system according to the present invention applicable to a four-cylinder internal combustion engine.

[0015] Another type of the DC-DC converter 20 comprises:

(a) a modified voltage boosting transformer 21 having a primary winding 21a and secondary winding 21b, an intermediate tap of the primary winding 21a is connected to the battery 1 via the ignition switch 2 and input terrminal A of the DC-DC converter 20. Each end of the priimary winding 21a is groounded via a corresponding transistor Q₄ and Q₆. The transistor Q₄ is connected to ancother transistor Q₃ in a Darlington configuration. The transistor Q₆ is connected to another transistor Q₅ in the Dirlington configuration. The base of each transistor Q₃ and Q₅ is connected to an emitter follower 22 and 23 via a resistor R₀ and R_O'. The base of the transistor Q₃ is comnected to that of the opposite transistor Q₅ via two opposite connected diodes D₇ and D₈ and is also connected to the ground via another transistor Q₇. An oscillator 24 is provided between the input terminal A and the two emitter followers 22 and 23. The output voltage of the oscillator 24 controls both pairs of transistors Q₃ and Q₄, and Q₅ and Q₆ via the corresponding emitter follower 22 and ₂₃ so as to turn each pair of transistors Q₃ and Q₄, and Q₅ and Q₆ on alternatingly so that a high-amplitude alternating voltage is generated at the secondary winding 21b of the voltage boosting transformer 21. The generated alternating voltage is rectified by means of a diode bridge full-wave rectifier comprising four diodes D₃ through D6. The rectified high DC voltage is used to charge a capacitor C₅. The charged voltage is applied to the secondary winding 4b of the ignition coil 4 via a first output terminal B_I. The base of the transistor Q₇ is connected to the junction between two resistors R₅ and R₆ connected in series between the emitters of transistors Q₄ and Q₆ and ground. Therefore, the voltage divided by the two emitter resistors R₅ and R₆ is applied to the base of the transistor R₇ so as to control the switching duration of both pairs of transistors Q₃ and Q₄, Q₅, and Q₆.

[0016] In this embodiment, the base voltage of the transistor Q₇ in the DC-DC converter is controlled by means of a high DC voltage control circuit 25 so that the output voltage of the DC-DC converter 20 is adjusted according to engine operating conditions, as explained below. The high DC voltage control circuitry 25 comprises: (a) a comparator 26 whose output terminal is connected to the base of the transistor Q₇ in the DC-DC converter 20 via a diode D₉; (b) a voltage regulator 27 whose input terminal is connected to the input terminal A of the DC-DC converter 20 which transforms the input voltage, e.g., 12 volts from the battery 1 via the ignition switch 2 to provide a constant DC voltage, e.g., 8 volts; and (c) a rotary switch 29 which connects the non-inverting input terminal of the comparator 26 to one of four terminals a through d according to an opening angle of a throttle valve 28 within an intake manifold of the engine. The noninverting input terminal of the comparator 26 is also connected to a second input terminal B₂ of the DC-DC converter 20. The end of the capacitor C₅ is connected to the second output terminal B₂ of the DC-DC converter 20 via a resistor R₇. The contacts a through d of the rotary switch 29 are grounded via respective resistors Ra through Rd for changing the divided voltage applied to the noninverting input terminal of the comparator 26 according to the opening angle of the throttle valve 28. The rotary switch 29 and the resitors Ra through Rd constitute a variable voltage dividing circuit. The inverting input terminal of the comparator 26 receives a reference voltage V_ref from the voltage regulator 27 and dividing resistors R₈ and ^R₉.

[0017] When a divided voltage V_e applied via the resistor R₇ and the variable voltage dividing circuit 30 to the noninverting input terminal of the comparator 26 exceeds the reference voltage V_ref, the output voltage of the comparator 26 goes high so that the transistor Q₇ is rendered conductive. Consequently, all transistors Q₃, Q₄, _Q5, and _Q6 are forcibly turned off and the voltage boosting operation of the DC-DC converter 20 is halted so that the output voltage V_H of the DC-DC converter 20 becomes equal to the reference voltage V_ref. In this way, the change in the voltage dividing ratio by means of the variable voltage dividing circuit 30 enables control of the output voltage V_H of the DC-DC converter 20, i.e., charge voltage across the capacitor C₅.

[0018] In this embodiment, when the opening angle of the throttle valve 28 is small, i.e., in cases of low engine load, the resistor R_d with the lowest resistance value of all the parallel voltage dividing resistors is connected to the rotor e of the rotary switch 29. As the opening angle of the throttle valve 28 increases, i.e., as the engine load increases, the rotor e of the rotary switch 29 comes into contact with the contacts c, b, and a sequentially so as to increase the dividing ratio of the output voltage of the DC-DC converter 20, i.e., increase the resistance value of the applied resistors R , R_b, and R. Since the divided voltage V_e increases as the engine load increases, the output voltage V_H of the DC-DC converter 20 decreases.

[0019] If at three values I, II, and III of engine load as shown in Fig. 6, the rotor e of the rotary switch 29 switches from the contact a to the subsequent contact b and vice versa, from the contact b to the subsequent contact c and vice versa, from the contact c to the subsequent contact d and vice versa, a load vs ignition energy characteristic curve as shown by solid line of Fig. 6 can be selected.

[0020] In this way, a sufficiently large ignition energy can be supplied to each spark plug 11 even in cases of low engine load.

[0021] Fig. 7 shows ignition energy, denoted by the hatched portion, at constant engine load in the case of the conventional ignition system. In Fig. 7, symbol V_s denotes the breakdown voltage of the gap between the electrodes of the spark plug 11, symbol _VAl denotes the sustained arc discharge voltage, and symbol D_S1 denotes the interval of time for which the sustained arc discharge continues.

[0022] Fig. 8 shows the ignition energy at the same load as in Fig. 7 in the case of the ignition system shown in Fig. 5 according to the present invention.

[0023] As appreciated from Fig. 8, the sustained arc discharge voltage is increased slightly as indicated by V_A2 (V_A2>V_A1) and the interval of discharge is significantly longer so that the overall ignition energy is increased. Consequently, misfire will not occur. In addition, since the ignition energy is decreased as the engine load increases, a wasteful power consumption can be prevented.

[0024] In this embodiment, the voltage dividing ratio of the output voltage V of the DC-DC converter 20 is changed incrementally by means of the voltage dividing resistors R a through R_d and rotary switch 29. Alternatively, a potentiometer interlocked with the throttle valve 28 which changes the voltage dividing ratio continuously as the throttle valve 28 opens may be used as shown by Fig. 5(C). The reference voltage V_ref may alternatively be adjusted according to the opening angle of the throttle valve 28 while the divided voltage V remains constant as shown in Fig. 5(B).

[0025] Furthermore, in this embodiment the opening angle of the throttle valve 28 is representative of engine operating conditions. Alternatively, engine operating conditions may be detected by means of an engine speed detector, negative pressure detector within the intake manifold of the engine, air flow meter for detecting intake air flow rate, etc. Therefore, the voltage dividing ratio or reference voltage described hereinabove may be changed according to any of these detected results.

[0026] As described hereinbefore, the ignition system according to the present invention controls the output voltage of the DC-DC converter according to the current engine operating conditions so that the voltage across the capacitor, i.e., output voltage of the DC-DC converter increases when the engine load or engine speed is low. Consequently, sufficient ignition energy for complete combustion of air-fuel mixture can be supplied to the spark plugs. As a result, flame propagation can be enhanced and fuel economy can be improved.

[0027] Since the ignition energy is reduced to a minimum when the engine load or engine speed is high, electrical power consumption for the ignition operation can be minimized and fuel efficiency of the automotive vehicle in which the ignition system according to the present invention is incorporated can be improved.

[0028] It will be clearly understood by those skilled in the art that modifications may be made in the preferred embodiment described hereinbefore without departing from the spirit and scope of the present invention, which is to be defined by the appended claims.

Claims

1. An ignition system for an internal combustion engine, comprising:

(a) a voltage transforming coil having a primary winding and secondary winding, said primary winding receiving a periodically interrupted current and said secondary winding having a first end connected to common ground via a spark gap across which a spark discharge starts when the current flowing through said primary winding is periodically interrupted at controlled times;

(b) means for periodically interrupting the current flowing through the primary winding of said coil;

(c) a high DC voltage boosting means, connected to a second end of the secondary winding of -said coil, which converts low DC voltage into a corresponding AC voltage, boosts the AC voltage into a high-amplitude AC voltage, rectifies the high-amplitude AC voltage into a corresponding high DC voltage, and stores the high DC voltage so that the stored high DC voltage is applied to the spark gap via the secondary winding of said coil so as to sustain the subsequent arc discharge across the spark gap when the spark discharge occurs thereacross; and

(d) an output voltage control means which controls the output voltage of said high DC voltage boosting means according to engine operating conditions so as to provide an engine condition-dependent amount of ignition energy to the spark gap.

_'2. An ignition system for an internal combustion engine as set forth in claim 1, wherein said high _DC voltage boosting means comprises:

(a) a voltage boosting transformer having a primary winding and secondary winding, said primary winding thereof having an intermediate tap receiving the low _DC voltage;

(b) an oscillating means which produces two alternating voltage signals having opposite phases with respect to each other in response to the low DC voltage;

(c) a pair of switching means each connected between one end of the primary winding of said voltage boosting transformer and ground for generating an intermittent current from the intermediate tap to ground through the primary winding thereof when one of the two alternating voltage signals is received from said oscillating means;

(d) a rectifying means connected between the ends of the secondary winding of said voltage boosting means for rectifying a boosted high AC voltage across the secondary winding of said voltage boosting transformer;

(e) a capacitor connected to said rectifying means and to the second end of the secondary winding of said coil so as to be charged by the rectified high _DC voltage; and

(f) another switching means which turns off said pair of switching means so as to halt the generation _'of the intermittent current when an input signal is received.

3. An ignition system for an internal combustion engine as set forth in claim 2, wherein said output voltage control means comprises:

(a) an engine operating condition detecting means which detects engine operating conditions and outputs a signal according to the detected engine operating conditions;

(b) a divided voltage level changing means connected to said capacitor of said high DC voltage boosting means which changes a voltage dividing ratio of the voltage across said capacitor according to the signal from,said engine operating detecting means; and

(c) a comparing means which compares the divided voltage level of said capacitor with a reference voltage level and outputs the signal to said other switching means when the divided voltage level of said capacitor exceeds the reference voltage level.

4. An ignition system for an internal combustion engine as set forth in claim 2, wherein said output voltage control means comprises:

(a) an engine operating condition detecting means which detects engine operating conditions and outputs a signal according to the detected engine operating conditions;

(b) a reference voltage level changing means which changes the reference voltage level according to the signal from said engine operating condition detecting means; and

(c) a comparing means which compares a divided voltage level of the voltage across the capacitor of said high DC voltage boosting means with the changed reference voltage level and outputs the signal to said other switching means of said high DC voltage boosting means when the changed reference voltage level exceeds the divided voltage level.

5. An ignition system for an internal combustion engine as set forth in claim 3, wherein said engine operating condition detecting means is a throttle valve located within an intake manifold of the engine and wherein said divided voltage level changing means comprises a rotary switch having a rotor terminal connected electrically to said comparing means and interlocked for rotation with said throttle valve and a plurality of fixed terminals, each individually contactable by said rotor terminal according to the opening angle of said throttle valve and a plurality of resistors, each connected between a corresponding fixed terminal and ground such that as the opening angle of said throttle valve increases, the resistance of the contacted resistor decreases,
whereby the divided voltage level to be compared by said comparing means with the reference voltage level increases incrementally as the opening angle of said throttle valve increases.

6. An ignition system as set forth in claim 4, wherein said engine operating condition detecting means is a throttle valve located within an intake manifold of the engine and wherein said reference voltage level changing means comprises a rotary switch having a rotor terminal electrically connected to said comparing means and interlocked for rotation with'said throttle valve and a plurality of fixed terminals, each individually contactable by said rotor terminal according to the opening angle of said throttle valve and a plurality of resistors, each connected between a corresponding fixed terminal and ground and arranged so that as the opening angle of said throttle valve increases, the resistance valu of the contacted resistor decreases,
whereby the reference voltage level to be compared by said comparing means with the divided voltage level of said high DC voltage boosting means decreases incrementally as the opening angle of said throttle valve increases.

7. An ignition system for an internal combustion engine as set forth in claim 3, wherein said engine operating condition detecting means is a throttle valve located within an intake manifold of the engine and wherein said divided voltage level changing means comprises a potentiometer connected between said comparing means and ground and interlocked with said throttle value such that its resistance value increases as the opening angle of said throttle valve increases,
whereby the divided voltage level to be compared by said comparing means with the reference voltage level increases continuously as the opening angle of said throttle valve increases.

Drawing