Ignition circuit for spark ignition internal combustion engines

Abstract

 An ignition circuit (1) for use in a spark ignition internal combustions engine comprises a high voltage source (2), a spark gap (5), and two diodes (4, 4') connected in series between the high voltage source (2) and the spark gap (5), both diodes (4, 4') having an inherent junction capacitance (7).

Description

Technical Field

[0001] The present invention relates to ignition circuits for spark ignition internal combustions engines, to electric components for such ignition circuits, and spark ignition internal combustions engines comprising such ignition circuits, according to the preamble of the independent claims.

State of the Art

[0002] There has been a lot of effort so far to improve and optimize the ignition systems in spark ignition internal combustion engines. One aspect of improvement are the characteristics of the spark itself, produced in the spark plug to ignite the compressed fuel air mixture in the cylinder.
WO 94/17302 describes an electrical circuit for connection between the high voltage source of an ignition system, namely the secondary coil of the ignition coil system, and the spark plug. Such an electrical circuit primarily comprises a capacitor, having a voltage dependant capacitance between 300 to 1000 pF, which may be connected in parallel with a resistor. In addition the capacitor may be connected in series with a diode, or a diode and another resistor in parallel. The purpose of the disclosed electrical circuit is to change the current waveform of the spark, by improving or even repeating the bright line part of a spark event. The bright line part constitutes the short period following the ionisation of the gas in the gap of the spark plug, equivalent with the ignition of the spark. At the same time the flaring part, following the bright line part of the spark event, is reduced in length. The optional diode has only the purpose to avoid repetitive re-ionisation with changing polarity, which may else disturb some control systems of the engine. Since meanwhile it was found that the flare part of the spark is important for the combustion process, the shown ignition circuit is actually counterproductive.
GB 2330878 discloses an ignition circuit with a single diode connected between the high voltage source and the spark plug. The purpose of the shown ignition circuit is to extend the effective length of the flare part of the spark, which is believed being important for the combustion process. Moulding it in a suitable dielectric material additionally insulates the diode. Nevertheless the reverse breakdown voltage of the diode is limited, and thus also the maximum reverse voltage. The achievable voltage over the electrode gap during the flare part of the diode is between 1 and 2 kV.

Summary of the Invention

[0003] It is an object of the present invention to provide an ignition circuit for spark ignition internal combustions engines, which allows higher voltages during the flare part of the spark. It is another object of the present invention to provide an ignition circuit that allows a more efficient oxidation process of the air/fuel mixture, thereby reducing fuel consumption and carbon dioxide production, and reducing the emission of pollutants such as nitrogen oxides NO_x, carbon monoxide, particulate matter, and remaining hydrocarbons.

[0004] These and other problems are solved by an ignition circuit according to the present invention as defined in claim 1, an electric component according to the present invention as defined in claim 5, and a spark ignition internal combustions engine according to the present invention as defined in claim 11. Advantageous embodiments are given in the dependent claims.

[0005] An ignition circuit according to the invention contains an electric component between the high voltage source and the spark plug. Said electric component comprises two high voltage, ultra fast, soft recovery diodes with inherent junction capacitance, which are connected in series. To increase the insulation above the maximum rating of the diodes, and to prevent the current arcing back over the length of the electric component, the diodes are moulded in an additional dielectric insulation material. The achievable reverse bias voltage with such electric components according to the inventions can be well above 100 kV.

[0006] The ignition circuit according to the invention will convert the positive / alternating current after the end of the initial flare part of the spark to an extended flare part, by suppressing the oscillations, and using the charged junction capacitors of the diodes to reignite the flare part, thus producing a strong and sustained negative current secondary discharge. Since the achievable reverse bias voltage and capacitance are higher than known from the prior art, the achievable voltage during the extended flare part can be 4 to 30 kV instead of the known 1 to 2 kV. The increased energy transfer to the fuel/air mixture resulting from the larger current during the extended flare part leads to much stronger ionisation of the gas mixture. This process is assisted by the electrons being able to move more freely through the air to fuel mixture due to the atomic dissociation of the molecules.
The increased ionisation leads to a principal change of the combustion process. After the initial ignition of the exothermic oxidation reaction by the initial bright line part of the spark, an avalanche of free electrons produced by the ionisation process during the secondary discharge will flow away from the spark gap. The molecules outside the spark area are effectively excited, ionised, and dissociated by these free electrons, and the oxidation process is maintained until complete oxidation.
Since at the same time the gas translation temperature is not essentially changed, NO_x production is not increased, or is even reduced, even under lean conditions. This removes the well-known dilemma between lean air/fuel mixtures and NO_x emission. The catalytic function of the electrons thus allows the more efficient oxidation of lean fuel/air mixtures than with conventional spark ignition. A complete oxidation of fuel/air mixtures with a value of lambda > 2 becomes possible.
An additional advantage of the excited atomic oxygen concentration resulting from the extended flare part of the spark is the scrubbing of contaminants in the combustion chamber.

[0007] The ignition circuit according to the invention can be used both for four stroke and two spark ignition engines, and also for rotary spark ignition engines. An engine according to the invention equipped with such an ignition circuit may be run with leaded or unleaded petrol, having high or low octane ratings, two-stroke fuel, competition fuel, methane, hydrogen, LPG, SNG, Diesel, paraffin grades, kerosene, JP 1-10 jet engine fuels, naphthalene, biomass derived fuel, methanol, ethanol, and any other fuel suitable for spark ignition internal combustion engines.
A four stroke engine can be run for example at lambda = 2, which represents an air to fuel ratio of 29.4, based on unleaded petrol with 96 RON rating. An internal combustion engine according to the invention at lambda = 2 is more efficient than a standard engine at lambda = 2 equipped with a catalytic converter, since all the fuel is burned within the combustion chamber, and thus is used to run the engine. The achievable reduction in fuel consumption of an internal combustion engine equipped with an ignition circuit according to the invention is 50% or more, and therefore in parallel the carbon dioxide reduction is also 50% or more.
As a further consequence of the improved oxidation efficiency the amount of emission of pollutants, such as carbon monoxide, unburned hydrocarbons/volatile organic compounds, and particulate matter, is drastically reduced, even while an engine is idle on 750 to 1000 rpm.
Another advantage of an ignition circuit according to the invention is the reduced degradation of the spark plugs, as a consequence of the reduction of the reverse polarity oscillations.

Ways to implement the Invention

[0008] Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings.

Figure 1 schematically shows an ignition circuit according to the present invention, comprising an electric component according to the invention.

Figures 2(a) and (b) schematically describe an electric component according to the invention, and its equivalent circuit diagram.

Figure 2(c) shows another embodiment of an electric component according to the invention.

Figure 3 shows a cross section along the longitudinal axis of a unit comprising an electric component moulded in an insulation body.

Figure 4 shows schematically the voltage on the electrode gap with a prior art ignition circuit and an ignition circuit according to the invention.

[0009] Figure 1 schematically describes an ignition circuit 1 according to the invention, consisting of a primary circuit 11, which is shown in a very simplified manner, and a secondary, high voltage circuit 12. There exist several variants of primary circuits 11. They all have in common that in order to create a spark the primary circuit 11 is opened. The drop in the current through the primary coil 61 induces a magnetic field, which is transformed to a high voltage spike in the secondary coil 62. This high voltage spike then ignites the spark in the spark gap 5.
The electric component 3 according to the invention is mounted between the high voltage source in the form of the secondary coil 62, and the spark gap 5. The ignition distributor, which is not shown, can be arranged between the electric component 3 and the spark gap 5. Alternatively the ignition distributor may be arranged between the secondary coil 62 and the electric component 3. In the first variant only one electric component 3 according to the invention is necessary, whereas in the latter case there has be a separate component 3 for each spark plug. The electric component may be a separate unit, or may be integrated into the ignition coil housing or the spark plug housing. A separate unit can be used to modify existing ignition circuits to ignition circuits according to the invention. For equipping new vehicles it is more advantageous to integrate the electric component according to the invention into the housing of the ignition coil device or the spark plug device.

[0010] Figure 2(a) schematically shows an embodiment of an electric component 3 according to the invention, and its equivalent circuit diagram. Two diodes 4, 4' are connected in series. The two diodes are high voltage, ultra fast, soft recovery diodes, with an inherent junction capacitance C_j of maximum 0.25pF (C_j at 50 V DC and 1 kHz). Typically components would rate at between 300 and 1000 pF.
Possible diode types which may be used for the purpose are unique to this device. These diode types are specifically designed and are unique in as much as they provide a strong reverse polarity voltage discharge at the spark plug across the electrode of 40 kV to 120 kV unlike all other rectifier diodes, where the current remains positive. These diode types have a reverse recovery time in the range of 30 to 100 ns. Figure 2(b) shows an equivalent circuit diagram of the electric component of Figure 2(a), consisting of the two diodes 4, 4', a capacitor 7 representing the combined inherent junction capacitance of the diodes, and a resistor 8 representing the Ohmic resistance. Figure 2(c) shows another possible embodiment of an electric component according to the invention, with three diodes connected in series.

[0011] As can be seen in Figure 1 the electric component 3 is mounted in such an orientation that the diodes 4, 4' are reversely biased when the high voltage source 62 is positive. The high voltage peak induced by the primary coil 61 is positive, and the electric component 3 has high impedance. The diodes 4, 4' of the electric component 3 according to the invention are now reversely biased, and the junction capacitor 7 gets charged. After ignition, flare part, and break down of the spark, the damped LC oscillator in the primary circuit induces an oscillation in the secondary circuit, leading to a change in polarity of the applied voltage. The charged capacitor of the diodes then leads to a reignition of the spark, with an negative current flare part.

[0012] This is in contrast to the prior art in GB 2330878, where a component was disclosed that changed its reversed biased polarity while still retaining oscillations via an inherent intermittent leakage from positive to negative causing the reversed bias voltages to vary. This variance limited the spark plug gap across the electrode to 0.04 inch for petrol fuels and 0.035 inch for natural gas combustion, in both instances restricting the optimum burn performance of the air to fuel mixtures. Said electrical component had a recovery time of 200 ns.

[0013] In the case of the electric component according to the invention the combined voltage for the two diodes linked in series is 40 kV, with the additional capacity to treble if necessary the power through the components, by concentrating the power through the exit of the device, by holding a strong dielectric in excess of 28 kV/mm³, thereby making the device four times more powerful than the known systems. The voltage is higher due to the rectifier diodes' inherent capacitance being higher, up to that of 40 kV, which provides the greater combined voltage. The ultra fast soft recovery speed of the device also concentrates the electrical discharge into a smaller initial discharge length of time, maintaining maximum power through the dwell time.
The electric component according to the invention provides a recovery of 50 ns, which is four times faster than the known systems. This provides an ultra fast recovery time and additional power, allowing the spark plug electrode gap to be extended to 1.1 mm or 0.044 inch, totally consuming both the petroleum fuels and also natural gas. It is this improved performance at a Lambda=2 that will allow the ignition circuit according to the invention to reduce the carbon dioxide exhaust emissions by over to 50%, due to the creation of a concentrated plasma burning process of the fuel/air mixture.

[0014] Figure 3 shows a cross section along the longitudinal axis of a unit 20 comprising an electric component 3 according to the invention, moulded in an insulation body 9. The axial leads 22 are connected to end caps 21 for the attachment of the high-tension leads. The insulation body 9 fully covers the electric component 3 and the axial leads 22. The end caps 21 are arranged in recesses of the insulation body 9, to avoid arcing between these two non-insulated parts. The insulating body 9 preferably consists of an organically filled, glass fibre reinforced polyester moulding compound with high dimensional stability and low flammability. The breakdown voltage of said compound is preferably 28 kV / mm or above. As an additional protective measure, after connection of the high-tension leads to the end caps 21, the unit 20 may be enclosed in an additional plastic casing in the form of a lockable hinged tube. This provides electrical resistance from outside influences and acts to prevent damage from water ingression.

[0015] Figure 4 schematically shows the voltage across the electrode gap of the spark plug, with a prior art ignition circuit (dotted line) and an ignition circuit according to the invention (full line). After ignition of the spark at top-dead-centre position of the piston, a first bright-line part of the spark with positive voltage ignites the exothermic oxidation reaction of the air/fuel mixture. After the bright-line part the voltage in the prior art ignition circuit oscillates, due to the oscillating damped LC-circuit formed by the primary coil circuit. In the case of the ignition circuit according to the invention, the electric component reignites the spark, resulting in an extended flare part with high negative voltage. This flare part then results in the sustained plasma ionization/oxidation process.

Examples

[0016] Tests of the ignition circuit according to the invention were carried out with a number of vehicles, with different types of spark ignition internal combustion engines. During all tests a considerable reduction in fuel consumption and exhaust emission was achieved.

Example 1

[0017] Vehicle: BMW 318i Saloon, 1999, 50875 miles; Engine: 1900cc four cylinder, fuel injected, catalytic converter; Fuel: Unleaded Petrol 96 RON.
A four-gas analysis was carried out whilst in standard trim using a Probike Microgas analyser. The gases tested for were Carbon Monoxide (CO), Carbon Dioxide (CO2), Oxygen (02), and Hydrocarbons (HC). Once a base-line measurement had been established, one electric component according to the invention was fitted to each high-tension lead from the electronic distributor direct to the spark plug. Using a software program supplied by the company Superchips the vehicle's fuelling was reduced by 40%. Using the same software, the vehicle's ignition management system was disarmed, including the oxygen sensor, and again a gas analysis test was carried out and the figures recorded. Finally the vehicle's fuelling was returned to standard from - 40%, a gas test was carried out and the figures were recorded. The results of the analysis are shown in Table 1.
A road test was carried out with the weight of approx. 4 adults. The vehicle started perfectly and was able to pull smoothly without hesitation from 1000 rpm in fourth gear.

Table 1

CO	CO2	HC	O2	Lambda	Air-fuel-ratio AFR
Base-line measurement before installation of ignition circuit according to the invention
0.01 %Vol	114.90 %vol	94 ppm	0.26 %vol	1.01	14.847
After installation of ignition circuit according to the invention (% of baseline value)
0.005 %vol	9.20 %vol	11 ppm	10.12 %vol	1.70	25.000
50 %	62 %	12 %	3892 %	168 %	168 %
Fuelling returned to standard and ignition circuit according to the invention disconnected
2.17 %vol	13.00 %vol	41 ppm	0.11 %vol	0.93	13.671

Example 2

Vehicle: Toyota MR2 2.0L

[0018] This car had no management system installed, and did not have a three way regulated catalytic converter. Normally the car was operating on Lambda 1 (14.7 parts of air to 1 of fuel). With the ignition circuit according to the invention installed, fuel savings were estimated at 45%, which was in line with the reduction of the CO₂ on idle, and corresponds to a Lambda = 1.71. The results of the gas analysis are shown in Table 2.

Table 2

CO	CO2	HC	O2	Lambda
Base-line measurement before installation of ignition circuit according to the invention
1.01 %vol	13.8 %vol	261 ppm	1.10%vol	1.01
After installation of ignition circuit according to the invention (% to baseline)
0.13 %vol	7.6 %vol	126 ppm	13.00 %vol	1.71
13 %	55 %	48 %	1287 %	169 %

Example 3

Vehicle: Honda Pan European Motorcycle 1100cc

[0019] Without the ignition circuit according to the invention the bike completed 251 miles with one tank-full. With the ignition circuit according to the invention installed, the engine leaned off, and spark plugs adjusted from 35/1000 inch to 40/1000 inch electrode gap, the bike then travelled on the track for 362 miles with one tank-full. This represents a fuel saving of 43% on the road, corresponding to a Lambda reading of 1.81, or AFR 26.548 air to 1 of fuel.

Example 4

Vehicle: Jet Ski, Kawasaki STX R1200; Engine: 3 cylinder 2 stroke engine

[0020] During a 2 month trial, improved throttle response and smoother power were found. Fuel savings in the order of 30 - 40% were achieved, equivalent to a 40% drop in CO₂ emissions, respectively a Lambda=1.71 and AFR 25.137 air to 1 of fuel. Other emissions could not be measured while the craft was in the water.

Reference numerals

[0021] 

1

ignition circuit

11

primary circuit

12

secondary circuit

2

high voltage source

3

electric component

4, 4', 4"

diode

5

spark gap

6

ignition coil

61

primary coil

62

secondary coil

7

junction capacitor

8

resistor

9

insulation body

20

unit

21

axial lead

22

end cap

30

contact breaker

Claims

1. An ignition circuit (1) for use in a spark ignition internal combustions engine, comprising a high voltage source (2), a spark gap (5), and a first diode (4) between the high voltage source (2) and the spark gap (5), characterized in that
a second diode (4') is connected in series with the first diode (4) between the high voltage source (2) and the spark gap (5), both diodes (4, 4') having an inherent junction capacitance (7).

2. The ignition circuit according to claim 1, characterised in that all diodes are reversely biased in relation to a first high voltage peak of a spark event.

3. The ignition circuit according to claim 1 or 2, characterised in that the diodes have a junction capacitance of maximum 0.25 pF.

4. The ignition circuit according to any of claims 1 to 3, characterised in that the diodes have a reverse recovery time in the range of 30 ns to 100 ns

5. An electric component (3) for use in an ignition circuit (1) of a spark ignition internal combustions engine, comprising two diodes (4, 4') connected in series, both diodes (4, 4') having an inherent junction capacitance (7).

6. The electric component according to claim 5, characterised in that the diodes have a junction capacitance of maximum 0.25 pF.

7. The electric component according to claim 5 or 6, characterised in that the diodes have a reverse recovery time in the range of 30 ns to 100 ns

8. The electric component according to any of claims 5 to 7, characterised in that the electric component (3) is moulded into an insulation body (9).

9. The electric component according to claim 9, characterised in that the insulation body (9) consists of an organically filled, glass fibre reinforced polyester moulding compound.

10. Spark ignition internal combustions engine, comprising an ignition circuit (1) according to any of claims 1 to 4.

11. Spark ignition internal combustions engine, comprising one or more electric components (3) according to any of claims 5 to 9.

12. Ignition coil device for a spark ignition internal combustions engine, comprising one or more electric components (3) according to any of claims 5 to 9.

13. Spark plug device, comprising an electric component (3) according to any of claims 5 to 9.

Drawing