NZ203530A - Dual fuel i.c. engine ignition timing:advance angle varied with engine speed - Google Patents

Description

2 035 3 0 Priority Date(s): JJ.. .3.'.$P- Complete Specification Filed: Class: /T.Q.3.P5 )Q^i.

Publication Dote: . .. M P. J9BB P.O. Journal, No: v-> Patents Form No. 5 NEW ZEALAND PATENTS ACT 195 3 COMPLETE SPECIFICATION "IGNITION TIMING DEVICE" "T",WE REPCO LIMITED, a company incorporated under the K*(b ^^1 in laws of the State of Victoria ,^of 6 30 St. Kilda Road, ;Melbourne, 3004, Victoria, Australia, ;hereby declare the invention, for which-f/we pray that a patent may be granted to-me-AJs, and the method by which it is to be performed, to be particularly described in and by the following statement ;-1- ;- 2 - ;? All T r\ ;This invention relates to an ignition timing device and has been devised particularly though not solely for use in dual fuel engines capable of running on both liquid and gaseous fuels. ;5 It is a well known fact than an internal combustion engine burning gaseous fuels performs better if its spark timing is modified in respect to the timing used for the same engine running on liquid fuels such as petrol. To achieve spark timing advance, switchable 10 devices have been constructed in the past which allow selection of ignition advance characteristics depending on the fuel used in the engine. The ignition advance required for gaseous fuels has been achieved in the past by initially advancing the distributor or other spark 15 impulse generating means to a position representing the maximum advance required and then electronically delaying the actual ignition point to that required. ;When liquid petrol fuel is in use a delay equal to the initial distributor advancement is introduced, that 20 restores original spark timing. This approach has several disadvantages. The prior art method requires an accurate ignition advance meter to be used at installation and every time the distributor timing components are attended to during maintenance and does not allow the 25 deletion of the retarding apparatus in case of failure of the system. If the retard system fails considerable damage may be done to the engine when running on petrol in an over advanced situation. Designs of this kind also tend to over advance the ignition at cranking 30 speed and thus cause unsatisfactory starting on either or both modes of fueling. ;It is therefore an object of the present invention to provide a method of and apparatus for generating spark actuating pulses in the ignition system of an internal 35 combustion engine which will obviate or minimize the foregoing disadvantages in a simple yet effective manner ;- 3 - ;2 03530 ;or which will at least provide the public with a useful choice. ;Accordingly, in one aspect the invention consists in a method of controlling the timing of the supply of spark ignition pulses to the cylinders of an internal combustion engine characterized in that the trigger pulses from the ignition system of the engine for actuating spark ignition pulses are electronically delayed by an amount not less than one half of the time interval between successive trigger pulses to create corresponding delayed pulses, and in that spark ignition pulses actuated by the delayed pulses are supplied in the same fitting order as the spark ignition pulses actuated by the undelayed trigger pulses would normally be supplied, but delayed by one cylinder in the firing order, to the cylinder of the engine. ;In a further aspect the invention consists in apparatus for controlling the timing of the supply spark ignition pulses to the cylinders of an internal ocmbustion engine, comprising an electronic circuit arranged to delay the trigger pulses fran the ignition systan of the engine for actuation of spark ignition pulses by a predetermined time, ;such time being in excess of one half the time interval between successive trigger pulses, and means to supply the cylinders of the engine with spark ignition pulses actuated by said delayed trigger pulses, said spark ignition pulses being delayed one cylinder in the firing order to what spark ignition pulses actuated by the undelayed trigger pulses would normally be supplied. ;Preferably said delay is produced by a ironostable oscillator triggered by said trigger pulses which in turn initiates said delayed trigger pulses at the carpletion of its timing cycle. ;Preferably one of the elements controlling the timing period of said monostable is a tachometer circuit producing an output substantially proportional to engine speed. ;Notwithstanding any other forms that may fall within its scope one preferred form of the invention will now be described by way of exanple only with reference to the acocnparxing drawings in which: ;Fig. 1 is a block circuit diagram of a conventional analogue method of solving the problem of generating a pulse wave form with a duty cycle which is a function of a command voltage but is relatively independent of speed, ;Fig. 2 is a block circuit diagram of an improved pulse wave ^ form generating circuit according to the invention; and ;- 4 - ;2 035 3 ;Fig. 3 is a circuit diagram of one practical embodiment of the invention. ;In the preferred form of the invention advancing of the spark for use with gaseous type fuels such as liquid petroleum gas without interfering with the original setting of the distributor or other spark initiating means applicable to a liquid fuel such as petrol is achieved by initiating a spark not from the particular trigger pulse related to the cylinder about to be fired but by using a delayed pulse generated by the previous trigger pulse. Thus an increase in spark advance is generated by reducing the delay of the pulse in the system described. This concept although simple in principle is difficult to achieve in practice given the requirements of a practical system for use in a motor vehicle. The range of engine speeds may vary from 100 rpm at cranking to over 6,000 rpm at top speed. A range of 10 to 1 in delay time has to be maintained within close limits. of the order of 1% and under dynamic conditions of rapid changes of speed inherent in automotive engine applications. ;A conventional analogue method of solving the problem of generating a pulse wave form with a duty cycle which is a function of a command voltage that is relatively independent of speed is shown in Fig. 1. In this system conditioned pulses are used to trigger a monostable circuit with variable "on" time. The output is averaged into an R-C network which develops a potential proportional to the duty cycle. This potential is compared with the command voltage Vc, and differences between the two are amplified and used to control the "on" time of the multivibrator which will thus adjust to keep the duty cycle close to that selected by the command voltage over a range of operating frequencies. ;It will be appreciated by those skilled in the art that in order to satisfy stability criteria in such ;2 035 3 ;- 5 - ;a system loop gain has to be limited and time constants have to be long compared to the pulse period. This system is both slow and inaccurate and regardless of how complex the feed back circuit is made the criteria necessary to fulfil the function cannot be met. ;These problems are overcome in the preferred form of the invention as shown in Fig. 2 which resembles the circuit of Fig. 1 but adds a feed-forward circuit. This circuit includes a tachometer which develops a voltage propoz-tional to frequency. Such circuits can be made to respond quickly as long as the accuracy required is not high. The monostable "on" period is of a length which is inversely proportional to the tachometer voltage and consequently the duty ratio of the monostable will remain substantially if not accurately constant when pulse frequency is varied. The command voltage in this circuit is compared with the actual duty ratio in an integrating comparator with very high D.C. loop gain and the resulting control voltage summed with the tachometer voltage controlling the rronostable period. It will be seen that due to feed-forward control this circuit can be made to respond quickly if initially only with moderate accuracy to conditions of rapid engine speed changes. After reaching steady engine speed conditionsV, delay time is controlled with great accuracy by means of the feedback circuit. ;It can be seen that for running on liquid fuels such as petrol the control circuit is not required and is switched out of operation. This not only ensures fail-safe action but also allows normal ignition timing procedures to be used in maintenance. ;It can further be seen that of time of cranking where advanced ignition is not desired the control circuit may be disabled to restore normal static timing thus achieving improved starting characteristics. ;The command voltage required for controlling the advance unit can be generated in various known ways from the tachometer voltage. As a tachometer circuit ;I ;£» \J — W,' «J ;- 6 - ;is an essential part of any such control system regardless of whether or not it uses the circuits according to the invention it will be apparent that the circuit according to the invention is no more costly to manufacture than 5 the prior art circuits which suffer from the drawbacks referred to above. ;One particular practical embodiment of the invention will now be described in detail with particular reference to Fig. 3 which shows a circuit comprising the following 10 features; ;1. Power Supply ;The power supply is of conventional design and consists of transistor Q3, diodes D2 to D4 and associated passive components. Its primary function is to remove 15 fluctuations and high voltage transients from the incoming electrical supply source. In this particular application (motor vehicle using 12V negative ground system) it provides a +12 volt unregulated supply for the operational amplifiers and other supply tolerant circuitry, and an 20 additional +6V regulated supply to the tachometer, ;advance timing, advance control and dwell control circui try. ;2. Trigger Signal Input Conditioning ;The incoming trigger signal at the "C/B input" 25 terminal is a square wave signal generated by conventional cam driven contact breakers or other electronic means such as an existing electronic ignition system. This signal is conditioned by the circuitry associated with transistors Ql and Q2 so that multiple edges and/or 30 impulse interference are not interpreted as eroneous input signals. This circuitry is connected as a mono-stable multivibrator with low-pass filters on both its input and output. The mono-stable oscillator when triggered by a long duration positive going trigger 35 pulse undergoes an output transition in the negative direction that is coupled into the tachometer ..integrated ;. 2 035 3 ;- 7 - ;circuit ICl by the R.C. differentiator circuit (R8,C4). ;3. Tachometer ;The tachometer circuitry is of conventional design comprising a monostable multivibrator of fixed period 5 followed by low-pass output filtering that produces an output voltage change proportional to trigger pulse rate (or engine speed). ;In this application a proprietary integrated circuit timer ICl (type LM555) is connected as a 10 monostable oscillator. This monostable is followed by a two section low-pass filter comprising R12, R13, C9 and CIO that achieves a high degree of smoothing action simultaneously with rapid response to changes in engine speed. The high output impedance 15 of this filter is buffered and D.C. level shifted by IC2 to produce the control signal for the advance and dwell control circuitry. ;4. Timing Control Circuitry ;The timing control circuitry is important to the 20 operation of the invention and as previously stated relates to the combined use of feed-forward and feedback techniques around a timing circuit to achieve both accuracy and fast dynamic response. ;Spark timing advance is achieved by introducing 25 a delay between the input trigger pulse and spark initiating pulse of such time duration that the spark initiating pulse and thus ignition occurs earlier in the next engine ignition cycle. ;The timing element in this practical embodiment is 30 a variable analog delay circuit comprising a charge integrator, level comparator and reset circuit. The integrator comprises level shift transistor Q5 current mirror Q6 and integrating capacitor C16. It produces a positive going voltage ramp on C6 the rise rate of 35 which is proportional to the potential across R20. ;During normal circuit operation the potential across ;- 8 - ;2 035 3 0 ;R20 is related to the potential on the base of transistor Q5 by this transistor's forward base emitter voltage characteristic (approx. 62V for silicon transistor). ;The voltage on the base of 05 thus determines the 5 changing rate of the integrator capacitor C16 and this node is the summing node where the feed forward compensation signal from the tachometer circuit, and the feedback signal from the advance angle error detector are summed by resistor R18 and R19 respectively. 10 The integrator is reset at the commencement of a timing cycle by transistor Q7 which is turned on momentarily at each tacho monostable operation by capacitor Cll. Integrator output level is monitored by a high gain transistor amplifier consisting of transistors Q8 and 15 Q9. In this circuit the amplifier performs a comparator function that results in a positive output transistion (collector transistor Q9) when the transistor Q8 commences conduction. ;The time delay produced by this circuit is the time 20 required for the integrating capacitor C16 to rise to the comparator threshold. ;Circuit component values are proportional so that the feedforward tacho voltage signal produces a time delay inversely proportional to speed, that is of such 25 a magnitude that a mean value of advance is achieved and little feedback error correction is required. ;Feedback error correction is performed by operational amplifier IC3 which is connected as a differencial integrator. This integrator compares the average D.C. 30 value of the comparator output (which is proportional to advance cycle) with advance angle command voltage on the integrator non-inverting input (IC3 + input). The integrating components are C14 and R2 5, passive components R26, C13 and C12 are required for interference suppression 35 and to improve high-frequency stability. The feedback integrated advance angle error is to the ramp-control summing node by R19. ;2 0 3 1 ;Mmm \u#; '*«<•' Vr'" vfJ/ • The advanced timing signal present at the comparator output is gated by transistor Q10 and feed into Qll by R46. A direct undelayed timing signal is also applied to Qll via R48 so that in the absence of the advanced 5 timing signal normal ignition operation continues. Gate transistor Q10 is open during the petrol mode of operation or during cranking when no advance is required. Transistor Qll performs inversion and amplification necessary for triggering of the ignition coil dwell control monostable 10 oscillator IC6 (type LM555).

. Timing Command Circuitry The circuitry associated with IC4, IC5, vacuum switch IC7, CNG/LPG and cylinder switching generates an advance angle command signal appropriate to application 15 engine speed and load. This signal is averaged by R49 and C25 and applied to the non-inverting terminal of the differential integrator. 6. Additional Circuitry Circuitry associated with Q13, Q14 and IC6 provide 20 a speed dependent dwell characteristic.

Transistors Q15, Q16, Q17, Q18, Q19, Q20 and associated components provide conditioning and amplication for drive to the ignition coil and other peripheral control functions.

Whilst the invention has been described initially as consisting of proportional feed-forward control to maintain the duty cycle with changes in speed, in a further embodiment of the invention the amount of feedforward may be deliberately used to tailor the system 30 response curve under transient conditions. For instance by undercompensating for speed in the feed-forward circuit the pulse delay under acceleration conditions may be made longer by a low value of proportional feed-forward thereby producing ignition retardation. 35 Under static conditions the integral feedback will produce the amount of delay time determined by the 203 command voltage.

In this manner apparatus for generating spark actuating pulses in the ignition systems of dual fuel internal combustion engines is provided which will work in a fail safe manner which will not damage the engine on failure of the apparatus and which is much simpler to install and maintain and on average is more accurate in controlling the spark actuating pulses in the ignition. 203530

Claims (9)

WHAT WE CLAIM IS:

1. A method of controlling the timing of the supply of spark ignition pulses to the cylinders of an internal combustion engine characterised in that the trigger pulses from the ignition system of the engine for actuating spark ignition pulses are electronically delayed by an amount not less than one half of the time interval between successive trigger pulses to create corresponding delayed pulses, and in that spark ignition pulses actuated by the delayed pulses are supplied in the same firing order as the spark ignition pulses actuated by the undelayed trigger pulses would normally be supplied, but delayed by one cylinder in the firing order, to the cylindersof the engine. of

2. Apparatus for controlling the timing of the supply/spark ignition pulses to the cylinders of an internal combustion engine, comprising an electronic circuit arranged to delay the trigger pulses from the ignition system of the engine for actuation of spark ignition pulses by a predetermined time, such time being in excess of one half the time interval between successive trigger pulses, and tneans to supply the cylinders of the engine with spark ignition pulses actuated by said delayed trigger pulses, said spark ignition pulses being delayed one cylinder in the firing order to what spark ignition pulses actuated by the undelayed trigger pulses would normally be supplied.

3. Apparatus as claimed in Claim 2 wherein said delay is produced by a monostable oscillator triggered by said trigger pulses which in turn initiates said delayed trigger pulses at the completion of its timing cycle.

4. Apparatus as claimed in Claim 3 wherein one of the elements controlling the timing period of said monostable is a tachometer circuit producing an output substantially proportional to engine speed.

5. Apparatus as claimed in Claim A wherein a further element controlling the timing period of said monostable is a feedback circuit from an advance angle error detector.

6. Apparatus as claimed in Claim 5 wherein said feedback circuit comprises arr^operational amplifier connected as a differential integrator. ■ / 203530 »

7. Apparatus for generating spark actuating pulses in the ignition system of an internal combustion engine, according to Claim 2 using a combination of feed-forward and feedback electronic circuits arranged to delay each said trigger pulse by a predetermined time.

8. Apparatus for controlling the timing of spark actuating pulses in the ignition system of an internal combustion engine when constructed, arranged and operable substantially as described heroin with reference to Fig. 2 of the accompanying drawings.

9. Apparatus for controllirjg the timing of spark actuating pulses in the ignition system of an internal combustion engine when constructed, arranged and operable substantially as described herein with reference to Fig. 3 of the accompanying drawings. REPCO LIMITED by their Attorne£y^ BALDWIN, SON & CAREY .2 27FEBI986™